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Sample records for sub-cooled nucleate boiling

  1. Radiolysis effects in sub-cooled nucleate boiling

    International Nuclear Information System (INIS)

    Dickinson, S.; Henshaw, J.; Tuson, A.; Sims, H.E.

    2002-01-01

    A hydrogen depleted region may form in the water during bubble formation when boiling occurs in a PWR. This would arise from stripping of gases into the steam phase. The depleted water may then become oxidising due to radiolysis forming H 2 O 2 . The presence of radiolytic oxidising conditions is one of the mechanisms proposed to explain deposits formed in Axial Offset Anomalies. This work describes a model that has been developed to examine this behaviour. The model deals with bubble growth and material transport as well as the radiolysis chemistry. The model simulates diffusion of species through the gas/liquid boundary layer. The appropriate mass conservation equations for this problem are described and the results of their numerical solution discussed. This model indicates the importance of the assumed boundary conditions on the results of the calculations. These boundary conditions are discussed in detail and the most appropriate ones for the actual reactor situation are outlined. The conclusion of this modelling study is that at normal PWR operating conditions of 40 cc H 2 (STP) kg -1 it is unlikely that radiolysis in a subcooled boiling region would be important. The situation is more ambiguous at the 1 to 5 cc H 2 (STP) kg -1 range. (author)

  2. Radiolysis effects in sub-cooled nucleate boiling

    Energy Technology Data Exchange (ETDEWEB)

    Dickinson, S.; Henshaw, J.; Tuson, A.; Sims, H.E. [AEA Technology (United Kingdom)

    2002-07-01

    A hydrogen depleted region may form in the water during bubble formation when boiling occurs in a PWR. This would arise from stripping of gases into the steam phase. The depleted water may then become oxidising due to radiolysis forming H{sub 2}O{sub 2}. The presence of radiolytic oxidising conditions is one of the mechanisms proposed to explain deposits formed in Axial Offset Anomalies. This work describes a model that has been developed to examine this behaviour. The model deals with bubble growth and material transport as well as the radiolysis chemistry. The model simulates diffusion of species through the gas/liquid boundary layer. The appropriate mass conservation equations for this problem are described and the results of their numerical solution discussed. This model indicates the importance of the assumed boundary conditions on the results of the calculations. These boundary conditions are discussed in detail and the most appropriate ones for the actual reactor situation are outlined. The conclusion of this modelling study is that at normal PWR operating conditions of 40 cc H{sub 2} (STP) kg{sup -1} it is unlikely that radiolysis in a subcooled boiling region would be important. The situation is more ambiguous at the 1 to 5 cc H{sub 2} (STP) kg{sup -1} range. (author)

  3. Modeling and Thermal Performance Evaluation of Porous Curd Layers in Sub-Cooled Boiling Region of PWRs and Effects of Sub-Cooled Nucleate Boiling on Anomalous Porous Crud Deposition on Fuel Pin Surfaces

    International Nuclear Information System (INIS)

    Barclay Jones

    2005-01-01

    A significant number of current PWRs around the world are experiencing anomalous crud deposition in the sub-cooled region of the core, resulting in an axial power shift or Axial Offset Anomaly (AOA), a condition that continues to elude prediction of occurrence and thermal/neutronic performance. This creates an operational difficulty of not being able to accurately determine power safety margin. In some cases this condition has required power ''down rating'' by as much as thirty percent and the concomitant considerable loss of revenue for the utility. This study examines two aspects of the issue: thermal performance of crud layer and effect of sub-cooled nucleate boiling on the solute concentration and its influence on initiation of crud deposition/formation on fuel pin surface

  4. In-situ Monitoring of Sub-cooled Nucleate Boiling on Fuel Cladding Surface in Water at 1 bar and 130 bars using Acoustic Emission Method

    Energy Technology Data Exchange (ETDEWEB)

    Baek, Seung Heon; Wu, Kaige; Shim, Hee-Sang; Lee, Deok Hyun; Hur, Do Haeng [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

    2016-10-15

    Crud deposition increases through a sufficient corrosion product supply around the steam-liquid interface of a boiling bubble. Therefore, the understanding of this SNB phenomenon is important for effective and safe operation of nuclear plants. The experimental SNB studies have been performed in visible conditions at a low pressure using a high speed video camera. Meanwhile, an acoustic emission (AE) method is an on-line non-destructive evaluation method to sense transient elastic wave resulting from a rapid release of energy within a dynamic process. Some researchers have investigated boiling phenomena using the AE method. However, their works were performed at atmospheric pressure conditions. Therefore, the objective of this work is for the first time to detect and monitor SNB on fuel cladding surface in simulated PWR primary water at 325 .deg. C and 130 bars using an AE technique. We successfully observed the boiling AE signals in primary water at 1 bar and 130 bars using AE technique. Visualization test was performed effectively to identify a correlation between water boiling phenomenon and AE signals in a transparent glass cell at 1 bar, and the boiling AE signals were in good agreement with the boiling behavior. Based on the obtained correlations at 1 bar, the AE signals obtained at 130 bars were analyzed. The boiling density and size of the AE signals at 130 bars were decreased by the flow parameters. However, overall AE signals showed characteristics and a trend similar to the AE signals at 1 bar. This indicates that boiling AE signals are detected successfully at 130 bars, and the AE technique can be effectively implemented in non-visualized condition at high pressures.

  5. Application of Sub-cooled Boiling Model to Thermal-hydraulic Analysis Inside a CANDU-6 Fuel Channel

    International Nuclear Information System (INIS)

    Kim, Man Woong; Lee, Sang Kyu; Kim, Hyun Koon; Yoo, Kun Joong; Kang, Hyoung Chul; Yoo, Seong Yeon

    2007-01-01

    Forced convection nucleate boiling is encountered in heat exchangers during normal and non-nominal modes of operation in pressurized water or boiling water reactors (PWRs or BWRs). If the wall temperature of the piping is higher than the saturation temperature of the nearby liquid, nucleate boiling occurs. In this regime, bubbles are formed at the wall. Their growth is promoted by the wall superheat (the difference between the wall and saturation temperatures), and they depart from the wall as a result of gravitational and liquid inertia forces. If the bulk liquid is subcooled, condensation at the bubble-liquid interface takes place and the bubble may collapse. This convection nucleate boiling is called as a sub-cooled nucleate boiling. As for the fuel channel of a CANDU 6 reactor, forced convection nucleate boiling models for flows along fuel elements enclosed inside typical CANDU-6 fuel channel has encountered difficulties due to the modeling of local effects along the horizontal channel. Therefore, the subcooled nucleate boiling has been modeled through temperature driven boiling heat and mass transfer, using a model developed at Rensselaer Polytechnic Institute. The objectives of this study are: (i) to investigate a proposed sub-cooled boiling model developed at Rensselaer Polytechnic Institute and (ii) to apply against a experiment and (iii) to predict local distributions of flow fields for the actual fuel channel geometries of CANDU-6 reactors. The numerical implementation is conducted using by the FLUENT 6.2 CFD computer code

  6. Use of ultrasonic waves in sub-cooled boiling

    International Nuclear Information System (INIS)

    Bartoli, Carlo; Baffigi, Federica

    2012-01-01

    %. - Highlights: ► We investigated experimentally the heat transfer from a circular cylinder to distilled water in presence of ultrasounds. ► The cylinder was heated up to reach particular temperatures, which are critical for last generation electronic components. ► All tests are carried on in sub-cooled boiling conditions, at atmospheric pressure. ► The tests reported an increase in the heat transfer up to 57%, in the optimal conditions. ► The sub-cooling degree is the only parameter that has the most significant influence on the heat transfer enhancement.

  7. Return to nucleate boiling

    International Nuclear Information System (INIS)

    Shumway, R.W.

    1985-01-01

    This paper presents a collection of TMIN (temperature of return to nucleate boiling) correlations, evaluates them under several conditions, and compares them with a wide range of data. Purpose is to obtain the best one for use in a water reactor safety computer simulator known as TRAC-B. Return to nucleate boiling can occur in a reactor accident at either high or low pressure and flow rates. Most of the correlations yield unrealistic results under some conditions. A new correlation is proposed which overcomes many of the deficiencies

  8. Nucleate boiling heat transfer

    Energy Technology Data Exchange (ETDEWEB)

    Saiz Jabardo, J.M. [Universidade da Coruna (Spain). Escola Politecnica Superior], e-mail: mjabardo@cdf.udc.es

    2009-07-01

    Nucleate boiling heat transfer has been intensely studied during the last 70 years. However boiling remains a science to be understood and equated. In other words, using the definition given by Boulding, it is an 'insecure science'. It would be pretentious of the part of the author to explore all the nuances that the title of the paper suggests in a single conference paper. Instead the paper will focus on one interesting aspect such as the effect of the surface microstructure on nucleate boiling heat transfer. A summary of a chronological literature survey is done followed by an analysis of the results of an experimental investigation of boiling on tubes of different materials and surface roughness. The effect of the surface roughness is performed through data from the boiling of refrigerants R-134a and R-123, medium and low pressure refrigerants, respectively. In order to investigate the extent to which the surface roughness affects boiling heat transfer, very rough surfaces (4.6 {mu}m and 10.5 {mu}m ) have been tested. Though most of the data confirm previous literature trends, the very rough surfaces present a peculiar behaviour with respect to that of the smoother surfaces (Ra<3.0 {mu}m). (author)

  9. Nucleate boiling heat transfer

    International Nuclear Information System (INIS)

    Saiz Jabardo, J.M.

    2009-01-01

    Nucleate boiling heat transfer has been intensely studied during the last 70 years. However boiling remains a science to be understood and equated. In other words, using the definition given by Boulding, it is an 'insecure science'. It would be pretentious of the part of the author to explore all the nuances that the title of the paper suggests in a single conference paper. Instead the paper will focus on one interesting aspect such as the effect of the surface microstructure on nucleate boiling heat transfer. A summary of a chronological literature survey is done followed by an analysis of the results of an experimental investigation of boiling on tubes of different materials and surface roughness. The effect of the surface roughness is performed through data from the boiling of refrigerants R-134a and R-123, medium and low pressure refrigerants, respectively. In order to investigate the extent to which the surface roughness affects boiling heat transfer, very rough surfaces (4.6 μm and 10.5 μm ) have been tested. Though most of the data confirm previous literature trends, the very rough surfaces present a peculiar behaviour with respect to that of the smoother surfaces (Ra<3.0 μm). (author)

  10. Characteristic of onset of nucleate boiling in natural circulation

    International Nuclear Information System (INIS)

    Zhou Tao; Yang Ruichang; Liu Ruolei

    2006-01-01

    Two kinds of thermodynamics quality at onset of nucleate boiling with sub-cooled boiling were calculated for force circulation by using Bergles and Rohesenow method or Davis and Anderson method, and natural circulation by using Tsinghua University project group's empirical equations suggested in our natural circulation experiment at same condition. The characteristic of onset of nucleate boiling with subcooled boiling in natural circulation were pointed out. The research result indicates that the thermodynamics quality at onset of nucleate boiling with subcooled boiling in natural circulation is more sensitive for heat and inlet temperature and system pressure. Producing of onset of nucleate boiling with subcooled boiling is early at same condition. The research result also indicates more from microcosmic angle of statistical physics that the phenomena are caused by the effects of characteristic of dissipative structure of natural circulation in self organization, fluctuation force and momentum force of dynamics on thermodynamics equilibrium. these can lay good basis for study and application on sub-cooled boiling in natural circulation in future. (authors)

  11. Revision of nucleated boiling mechanisms

    International Nuclear Information System (INIS)

    Converti, J.; Balino, J.L.

    1987-01-01

    The boiling occurrence plays an important role in the power reactors energy transfer. But still, there is not a final theory on the boiling mechanisms. This paper presents a critical analysis of the most important nucleated boiling models that appear in literature. The conflicting points are identified and experiments are proposed to clear them up. Some of these experiments have been performed at the Thermohydraulics laboratory (Bariloche Atomic Center). (Author)

  12. Experiment study of the onset of nucleate boiling in narrow annular channel

    International Nuclear Information System (INIS)

    Wang Jiaqiang; Jia Dounan; Guo Yun

    2004-01-01

    The onset of nucleate boiling (ONB) was investigated for water flowing in the annular duct which clearance is 1.2 mm at the pressure range from 1.0 to 4.5 MPa. The effect on ONB of some thermodynamics parameters was also analyzed. The available data dealing with sub-cooled boiling initial point of water in narrow annular clearance duct are analyzed by using regression method. The new developed correlation was obtained by considering the bilateral heating factor

  13. Heat transfer enhancement on nucleate boiling

    International Nuclear Information System (INIS)

    Zhuang, M.; Guibai, L.

    1990-01-01

    This paper reports on enhancement of nucleate boiling heat transfer with additives that was investigated experimentally. More than fifteen kinds of additives were chosen and tested. Eight kinds of effective additives which can enhance nucleate boiling heat transfer were selected. Experimental results showed that boiling heat transfer coefficient of water was increased by 1 to 5 times and that of R-113 was increased by 1 to 4 times when trace amount additives were put in the two boiling liquids. There exist optimum concentrations for the additives, respectively, which can enhance nucleate boiling heat transfer rate best. In order to analyze the mechanism of the enhancement of boiling heat transfer with additives, the surface tension and the bubble departure diameter were measured. The nucleation sites were investigated by use of high-speed photograph. Experimental results showed that nucleation sites increase with additive amount increasing and get maximum. Increasing nucleation sites is one of the most important reason why nucleate boiling heat transfer can be enhanced with additives

  14. Superheating in nucleate boiling calculated by the heterogeneous nucleation theory

    International Nuclear Information System (INIS)

    Gerum, E.; Straub, J.; Grigull, U.

    1979-01-01

    With the heterogeneous nucleation theory the superheating of the liquid boundary layer in nucleate boiling is described not only for the onset of nuclear boiling but also for the boiling crisis. The rate of superheat depends on the thermodynamic stability of the metastable liquid, which is influenced by the statistical fluctuations in the liquid and the nucleation at the solid surface. Because of the fact that the cavities acting as nuclei are too small for microscopic observation, the size and distribution function of the nuclei on the surface necessary for the determination of the probability of bubble formation cannot be detected by measuring techniques. The work of bubble formation reduced by the nuclei can be represented by a simple empirical function whose coefficients are determined from boiling experiments. Using this the heterogeneous nucleation theory describes the superheating of the liquid. Several fluids including refrigerants, liquid gases, organic liquids and water were used to check the theory. (author)

  15. Surface wettability and subcooling on nucleate pool boiling heat transfer

    Science.gov (United States)

    Suroto, Bambang Joko; Kohno, Masamichi; Takata, Yasuyuki

    2018-02-01

    The effect of varying surface wettabilities and subcooling on nucleate pool boiling heat transfer at intermediate heat flux has been examined and investigated. The experiments were performed using pure water as the working fluid and subcooling ranging from 0, 5 and 10 K, respectively. The three types of heat transfer block were used that are bare surface/hydrophilic (polished copper), superhydrophilic/TiO2-coated on copper and hydrophobic/PTFE surface. The experimental results will be examined by the existing model. The results show that the heat transfer performance of surfaces with PTFE coating is better at low heat flux. While for an intermediate heat flux, superhydrophilic surface (TiO2) is superior compared to hydrophilic and hydrophobic surfaces. It is observed that the heat transfer performance is decreasing when the sub cooling degree is increased.

  16. Experimental investigation of nucleate boiling on heated surfaces under subcooled conditions

    International Nuclear Information System (INIS)

    Schneider, C.; Hampel, R.; Traichel, A.; Hurtado, A.; Meissner, S.; Koch, E.

    2011-01-01

    In case of an accident at pressurized water reactors (PWR), critical boiling conditions can appear at the transition from bubble- to film boiling. During full power operation, heat transfer phenomena of sub cooled nucleate boiling occur on the surface of the fuel rods. To investigate the microscopic processes in nucleate boiling, a test facility with optical measuring methods was constructed. This allows analyzing the effects on a single bubble system at different parameters. For the generation of nucleate boiling, an optically transparent, electrically conductive coating was applied as a heating surface on a borosilicate substrate. The so-called ITO (Indium-Tin-Oxide) coating with a sheet resistance of 20 ohms enables an electrical heating at an optical transparent surface. These properties are prerequisites for the study of microscopic phenomena in the bubble formation with optical coherence tomography (OCT). OCT, generally used in medical diagnostics, is an imaging modality providing cross sectional and volumetric high resolution images. To make sure that the bubble formation takes place at a specific site, artificial nucleation sites in form of micro cavity will be inserted into the surface. Furthermore a small test facility was constructed to dedicate the wall temperature of a heated metal foil during subcooled boiling in non degassed water, which is the content of this paper. (author)

  17. Void Measurements in the Regions of Sub-Cooled and Low-Quality Boiling. Part 1. Low Mass Velocities

    Energy Technology Data Exchange (ETDEWEB)

    Rouhani, S Z

    1966-07-15

    By the application of the ({gamma}, n) reaction to boiling heavy water, void volume fractions have been measured in a vertical annular channel with 25 mm O.D. and 12 mm I.D. at a heated length of 1090 mm. The experiments covered pressures from 10 to 50 bars, mass velocities from 50 to 1450 kg/m-sec, heat fluxes from 30 to 90 W/cm{sup 2}, sub coolings from 30 to 0 C, and steam qualities from 0 to 15 %. The results indicate noticeable effects of pressure, heat flux and even mass velocity upon the variations of void with subcooling and steam quality. A novel explanation of the mechanism of their effects has been found and proved by qualitative analysis.

  18. Evaluation of onset of nucleate boiling models

    Energy Technology Data Exchange (ETDEWEB)

    Huang, LiDong [Heat Transfer Research, Inc., College Station, TX (United States)], e-mail: lh@htri.net

    2009-07-01

    This article discusses available models and correlations for predicting the required heat flux or wall superheat for the Onset of Nucleate Boiling (ONB) on plain surfaces. It reviews ONB data in the open literature and discusses the continuing efforts of Heat Transfer Research, Inc. in this area. Our ONB database contains ten individual sources for ten test fluids and a wide range of operating conditions for different geometries, e.g., tube side and shell side flow boiling and falling film evaporation. The article also evaluates literature models and correlations based on the data: no single model in the open literature predicts all data well. The prediction uncertainty is especially higher in vacuum conditions. Surface roughness is another critical criterion in determining which model should be used. However, most models do not directly account for surface roughness, and most investigators do not provide surface roughness information in their published findings. Additional experimental research is needed to improve confidence in predicting the required wall superheats for nucleation boiling for engineering design purposes. (author)

  19. Evaluation of onset of nucleate boiling models

    International Nuclear Information System (INIS)

    Huang, LiDong

    2009-01-01

    This article discusses available models and correlations for predicting the required heat flux or wall superheat for the Onset of Nucleate Boiling (ONB) on plain surfaces. It reviews ONB data in the open literature and discusses the continuing efforts of Heat Transfer Research, Inc. in this area. Our ONB database contains ten individual sources for ten test fluids and a wide range of operating conditions for different geometries, e.g., tube side and shell side flow boiling and falling film evaporation. The article also evaluates literature models and correlations based on the data: no single model in the open literature predicts all data well. The prediction uncertainty is especially higher in vacuum conditions. Surface roughness is another critical criterion in determining which model should be used. However, most models do not directly account for surface roughness, and most investigators do not provide surface roughness information in their published findings. Additional experimental research is needed to improve confidence in predicting the required wall superheats for nucleation boiling for engineering design purposes. (author)

  20. The mechanisms of transitions from natural convection and nucleate boiling to nucleate boiling or film boiling caused by rapid depressurization in highly subcooled water

    International Nuclear Information System (INIS)

    Sakurai, Akira; Shiotsu, Masahiro; Hata, Koichi; Fukuda, Katsuya

    1999-01-01

    The mechanisms of transient boiling process including the transitions to nucleate boiling or film boiling from initial heat fluxes, q in , in natural convection and nucleate boiling regimes caused by exponentially decreasing system pressure with various decreasing periods, τ p on a horizontal cylinder in a pool of highly subcooled water were clarified. The transient boiling processes with different characteristics were divided into three groups for low and intermediate q in in natural convection regime, and for high q in in nucleate boiling regime. The transitions at maximum heat fluxes from low q in in natural convection regime to stable nucleate boiling regime occurred independently of the τ p values. The transitions from intermediate and high q in values in natural convection and nucleate boiling to stable film boiling occurred for short τ p values, although those to stable nucleate boiling occurred for tong τ p values. The CHF and corresponding surface superheat values at which the transition to film boiling occurred were considerably lower and higher than the steady-state values at the corresponding pressure during the depressurization respectively. It was suggested that the transitions to stable film boiling at transient critical heat fluxes from intermediate q in in natural convection and from high q in in nucleate boiling for short τ p occur due to explosive-like heterogeneous spontaneous nucleation (HSN). The photographs of typical vapor behavior due to the HSN during depressurization from natural convection regime for short τ p were shown. (author)

  1. An improved nucleate boiling design equation

    International Nuclear Information System (INIS)

    Basu, D.K.; Pinder, K.L.

    1976-01-01

    The effect of varying ΔT, the primary variable, on the value of heat transfer coefficient (h) in nucleate boiling is discussed. The three-parameter quadratic equation, h=P 1 + P 2 (ΔT) + P 3 (ΔT) 2 (where the constants, P 1 ,P 2 ,P 3 are functions of pressure, liquid properties and surface properties of the heater) is suggested. Ten sets of data at atmospheric pressure from six different workers and two more sets for pressure variation have been tested. The above quadratic equation fits the experimental data better than the existing two-parameter power relation, h=C(ΔT)sup(n) (where C is constant). The values of the three coeffcients in the quadratic equations are dependent on pressure, liquid properties and surface properties. A generalized empirical equation has been derived, which fits the selected pressure data well. (author)

  2. Suppression of saturated nucleate boiling by forced convective flow

    International Nuclear Information System (INIS)

    Bennett, D.L.; Davis, M.W.; Hertzler, B.L.

    1980-01-01

    Tube-side forced convective boiling nitrogen and oxygen and thin film shell-side forced convective boiling R-11 data demonstrate a reduction in the heat transfer coefficient associated with nucleate boiling as the two-phase friction pressure drop increases. Techniques proposed in the literature to account for nucleate boiling during forced convective boiling are discussed. The observed suppression of nucleate boiling for the tube-side data is compared against the Chen correlation. Although general agreement is exhibited, supporting the interactive heat transfer mechanism theory, better agreement is obtained by defining a bubble growth region within the thermal boundary layer. The data suggests that the size of the bubble growth region is independent of the friction drop, but is only a function of the physical properties of the boiling liquid. 15 refs

  3. Delays due to gas diffusion in flash boiling nucleation

    International Nuclear Information System (INIS)

    Hanbury, W.T.; McCartney, W.S.

    1976-01-01

    A theoretical model to account for the time delay between decompression and nucleation in flash boiling is presented and analyzed. It shows that gas diffusion can be responsible for delayed nucleation when the critical radius for nucleation and the suspended particle size are of the same order of magnitude

  4. Development of an experimental apparatus for nucleate boiling analysis

    International Nuclear Information System (INIS)

    Castro, A.J.A. de.

    1984-01-01

    An experimental apparatus is developed for the study of the parameters that affect nucleate boiling. The experimental set up is tested for nucleate boiling in an annular test section with subcooled water flow. The following parameters are analysed: pressure, fluid velocity and the fluid temperature at the test section entrance. The performance of the experimental apparatus is analysed by the results and by the problems raised by the operation of the setup. (Author) [pt

  5. Numerical investigation of nucleate pool boiling heat transfer

    Directory of Open Access Journals (Sweden)

    Stojanović Andrijana D.

    2016-01-01

    Full Text Available Multidimensional numerical simulation of the atmospheric saturated pool boiling is performed. The applied modelling and numerical methods enable a full representation of the liquid and vapour two-phase mixture behaviour on the heated surface, with included prediction of the swell level and heated wall temperature field. In this way the integral behaviour of nucleate pool boiling is simulated. The micro conditions of bubble generation at the heated wall surface are modelled by the bubble nucleation site density, the liquid wetting contact angle and the bubble grow time. The bubble nucleation sites are randomly located within zones of equal size, where the number of zones equals the nucleation site density. The conjugate heat transfer from the heated wall to the liquid is taken into account in wetted heated wall areas around bubble nucleation sites. The boiling curve relation between the heat flux and the heated wall surface temperature in excess of the saturation temperature is predicted for the pool boiling conditions reported in the literature and a good agreement is achieved with experimentally measured data. The influence of the nucleation site density on the boiling curve characteristic is confirmed. In addition, the influence of the heat flux intensity on the spatial effects of vapour generation and two-phase flow are shown, such as the increase of the swell level position and the reduced wetting of the heated wall surface by the heat flux increase. [Projekat Ministarstva nauke Republike Srbije, br. TR-33018 i br. OI-174014

  6. Molecular dynamics simulation of bubble nucleation in explosive boiling

    International Nuclear Information System (INIS)

    Zou Yu; Chinese Academy of Sciences, Beijing; Huai Xiulan; Liang Shiqiang

    2009-01-01

    Molecular dynamics (MD) simulation is carried out for the bubble nucleation of liquid nitrogen in explosive boiling. The heat is transferred into the simulation system by rescaling the velocity of the molecules. The results indicate that the initial equilibrium temperature of liquid and molecular cluster size affect the energy conversion in the process of bubble nucleation. The potential energy of the system violently varies at the beginning of the bubble nucleation, and then varies around a fixed value. At the end of bubble nucleation, the potential energy of the system slowly increases. In the bubble nucleation of explosive boiling, the lower the initial equilibrium temperature, the larger the size of the molecular cluster, and the more the heat transferred into the system of the simulation cell, causing the increase potential energy in a larger range. (authors)

  7. Nucleate pool-boiling heat transfer - I. Review of parametric effects of boiling surface

    International Nuclear Information System (INIS)

    Pioro, I.L.; Rohsenow, W.; Doerffer, S.S.

    2004-01-01

    The objective of this paper is to assess the state-of-the-art of heat transfer in nucleate pool-boiling. Therefore, the paper consists of two parts: part I reviews and examines the effects of major boiling surface parameters affecting nucleate-boiling heat transfer, and part II reviews and examines the existing prediction methods to calculate the nucleate pool-boiling heat transfer coefficient (HTC). A literature review of the parametric trends points out that the major parameters affecting the HTC under nucleate pool-boiling conditions are heat flux, saturation pressure, and thermophysical properties of a working fluid. Therefore, these effects on the HTC under nucleate pool-boiling conditions have been the most investigated and are quite well established. On the other hand, the effects of surface characteristics such as thermophysical properties of the material, dimensions, thickness, surface finish, microstructure, etc., still cannot be quantified, and further investigations are needed. Particular attention has to be paid to the characteristics of boiling surfaces. (author)

  8. Thermal interaction effect on nucleation site distribution in subcooled boiling

    International Nuclear Information System (INIS)

    Zou, Ling; Jones, Barclay

    2012-01-01

    An experimental work on subcooled boiling of refrigerant, R134a, to examine nucleation site distributions on both copper and stainless steel heating surfaces was performed. In order to obtain high fidelity active nucleation site density and distribution data, a high-speed digital camera was utilized to record bubble emission images from a view normal to heating surfaces. Statistical analyses on nucleation site data were done and their statistical distributions were obtained. Those experimentally observed nucleation site distributions were compared to the random spatial Poisson distribution. The comparisons showed that, rather than purely random, active nucleation site distributions on boiling surfaces are relatively more uniform. Experimental results also showed that on the copper heating surface, nucleation site distributions are slightly more uniform than on the stainless steel surface. This was concluded as the results of thermal interactions between nucleation sites with different solid thermal conductivities. A two dimensional thermal interaction model was then developed to quantitatively examine the thermal interactions between nucleation sites. The results give a reasonable explanation to the experimental observation on nucleation site distributions.

  9. Direct numerical simulations of nucleate boiling flows of binary mixtures

    International Nuclear Information System (INIS)

    Didier Jamet; Celia Fouillet

    2005-01-01

    Full text of publication follows: Better understand the origin and characteristics of boiling crisis is still a scientific challenge despite many years of valuable studies. One of the reasons why boiling crisis is so difficult to understand is that local and coupled physical phenomena are believed to play a key role in the trigger of instabilities which lead to the dry out of large portions of the heated solid phase. Nucleate boiling of a single bubble is fairly well understood compared to boiling crisis. Therefore, the numerical simulation of a single bubble growth during nucleate boiling is a good candidate to evaluate the capabilities of a numerical method to deal with complex liquid-vapor phenomena with phase-change and eventually to tackle the boiling crisis problem. In this paper, we present results of direct numerical simulations of nucleate boiling. The numerical method used is the second gradient method, which is a diffuse interface method dedicated to liquid vapor flows with phase-change. This study is not intended to provide quantitative results, partly because all the simulations are two-dimensional. However, particular attention is paid to the influence of some parameters on the main features of nucleate boiling, i.e. the radius of departure and the frequency of detachment of bubbles. In particular, we show that, as the contact angle increases, the radius of departure increases whereas the frequency of detachment decreases. Moreover, the influence of the existence of quasi non-condensable gas is studied. Numerical results show an important decrease of the heat exchange coefficient when a small amount of a quasi non-condensable gas is added to the pure liquid-vapor water system. This result is in agreement with experimental observations. Beyond these qualitative results, this numerical study allows to get insight into some important physical phenomena and to confirm that during nucleate boiling, large scale quantities are influenced by small scale

  10. Experimental Investigation on the Effects of Coolant Concentration on Sub-Cooled Boiling and Crud Deposition on Reactor Cladding at Prototypical PWR Operating Conditions

    Energy Technology Data Exchange (ETDEWEB)

    Schultis, J., Kenneth; Fenton, Donald, L.

    2006-10-20

    Increasing demand for energy necessitates nuclear power units to increase power limits. This implies significant changes in the design of the core of the nuclear power units, therefore providing better performance and safety in operations. A major hindrance to the increase of nuclear reactor performance especially in Pressurized Deionized water Reactors (PWR) is Axial Offset Anomaly (AOA)--the unexpected change in the core axial power distribution during operation from the predicted distribution. This problem is thought to be occur because of precipitation and deposition of lithiated compounds like boric acid (H{sub 2}BO{sub 3}) and lithium metaborate (LiBO{sub 2}) on the fuel rod cladding. Deposited boron absorbs neutrons thereby affecting the total power distribution inside the reactor. AOA is thought to occur when there is sufficient build-up of crud deposits on the cladding during subcooled nucleate boiling. Predicting AOA is difficult as there is very little information regarding the heat and mass transfer during subcooled nucleate boiling. An experimental investigation was conducted to study the heat transfer characteristics during subcooled nucleate boiling at prototypical PWR conditions. Pool boiling tests were conducted with varying concentrations of lithium metaborate (LiBO{sub 2}) and boric acid (H{sub 2}BO{sub 3}) solutions in deionized water. The experimental data collected includes the effect of coolant concentration, subcooling, system pressure and heat flux on pool the boiling heat transfer coefficient. The analysis of particulate deposits formed on the fuel cladding surface during subcooled nucleate boiling was also performed. The results indicate that the pool boiling heat transfer coefficient degrades in the presence of boric acid and lithium metaborate compared to pure deionized water due to lesser nucleation. The pool boiling heat transfer coefficients decreased by about 24% for 5000 ppm concentrated boric acid solution and by 27% for 5000 ppm

  11. Spray structure as generated under homogeneous flash boiling nucleation regime

    International Nuclear Information System (INIS)

    Levy, M.; Levy, Y.; Sher, E.

    2014-01-01

    We show the effect of the initial pressure and temperature on the spatial distribution of droplets size and their velocity profile inside a spray cloud that is generated by a flash boiling mechanism under homogeneous nucleation regime. We used TSI's Phase Doppler Particle Analyzer (PDPA) to characterize the spray. We conclude that the homogeneous nucleation process is strongly affected by the initial liquid temperature while the initial pressure has only a minor effect. The spray shape is not affected by temperature or pressure under homogeneous nucleation regime. We noted that the only visible effect is in the spray opacity. Finally, homogeneous nucleation may be easily achieved by using a simple atomizer construction, and thus is potentially suitable for fuel injection systems in combustors and engines. - Highlights: • We study the characteristics of a spray that is generated by a flash boiling process. • In this study, the flash boiling process occurs under homogeneous nucleation regime. • We used Phase Doppler Particle Analyzer (PDPA) to characterize the spray. • The SMD has been found to be strongly affected by the initial liquid temperature. • Homogeneous nucleation may be easily achieved by using a simple atomizer unit

  12. Direct numerical simulation of bubble dynamics in subcooled and near-saturated convective nucleate boiling

    International Nuclear Information System (INIS)

    Lal, Sreeyuth; Sato, Yohei; Niceno, Bojan

    2015-01-01

    Highlights: • We simulate convective nucleate pool boiling with a novel phase-change model. • We simulate four cases at different sub-cooling and wall superheat levels. • We investigate the flow structures around the growing bubble and analyze the accompanying physics. • We accurately simulate bubble shape elongation and enhanced wall cooling due to the sliding and slanting motions of bubbles. • Bubble cycle durations show good agreement with experimental observations. - Abstract: With the long-term objective of Critical Heat Flux (CHF) prediction, bubble dynamics in convective nucleate boiling flows has been studied using a Direct Numerical Simulation (DNS). A sharp-interface phase change model which was originally developed for pool boiling flows is extended to convective boiling flows. For physical scales smaller than the smallest flow scales (smaller than the grid size), a micro-scale model was used. After a grid dependency study and a parametric study for the contact angle, four cases of simulation were carried out with different wall superheat and degree of subcooling. The flow structures around the growing bubble were investigated together with the accompanying physics. The relation between the heat flux evolution and the bubble growth was studied, along with investigations of bubble diameter and bubble base diameter evolutions across the four cases. As a validation, the evolutions of bubble diameter and bubble base diameter were compared to experimental observations. The bubble departure period and the bubble shapes show good agreement between the experiment and the simulation, although the Reynolds number of the simulation cases is relatively low

  13. Void Measurements in the Regions of Sub-Cooled and Low-Quality Boiling. Part 2. Higher Mass Velocities

    Energy Technology Data Exchange (ETDEWEB)

    Rouhani, S Z

    1966-07-15

    This report consists mostly of tables of experimental data obtained in void measurements. It is a continuation and the completing part of a previous report with the same title. The data are from the measurements in a vertical annular channel with 25 mm O.D. and 12 mm I.D. at a heated length of 1090 mm. These experiments covered pressures from 10 to 50 bars, mass velocities from 650 to 1450 kg/m -sec., heat fluxes from 60 to 120 W/cm{sup 2}, sub-coolings from 30 to 0 C, and steam qualities from 0 to 12 %. The tables include the inlet temperatures and measured wall super-heat.

  14. THE PREDICTION OF VOID VOLUME IN SUBCOOLED NUCLEATE POOL BOILING

    Energy Technology Data Exchange (ETDEWEB)

    Duke, E. E. [General Dynamics, San Diego, CA (United States)

    1963-11-15

    A three- step equation was developed that adequately describes the average volume of vapor occurring on a horizontal surface due to nucleate pool boiling of subcooled water. Since extensive bubble frequency data are lacking, the data of others were combined with experimental observations to make predictions of void volume at ambient pressure with various degrees of subcooling. (auth)

  15. Interface tracking computations of bubble dynamics in nucleate flow boiling

    International Nuclear Information System (INIS)

    Giustini, G.

    2015-01-01

    The boiling process is of utter importance for the design and operation of water-cooled nuclear reactors. Despite continuous effort over the past decades, a fully mechanistic model of boiling in the presence of a solid surface has not yet been achieved. Uncertainties exist at fundamental level, since the microscopic phenomena governing nucleate boiling are still not understood, and as regards 'component scale' modelling, which relies heavily on empirical representations of wall boiling. Accurate models of these phenomena at sub-milli-metric scale are capable of elucidating the various processes and to produce quantitative data needed for up-scaling. Within this context, Direct Numerical Simulation (DNS) represents a powerful tool for CFD analysis of boiling flows. In this contribution, DNS coupled with an Interface Tracking method (Y. Sato, B. Niceno, Journal of Computational Physics, Volume 249, 15 September 2013, Pages 127-161) are used to analyse the hydrodynamics and heat transfer associated with heat diffusion controlled bubble growth at a solid substrate during nucleate flow boiling. The growth of successive bubbles from a single nucleation site is simulated with a computational model that includes heat conduction in the solid substrate and evaporation from the liquid film (micro-layer) present beneath the bubble. Bubble evolution is investigated and the additional (with respect to single phase convection) heat transfer mechanisms due to the ebullition cycle are quantified. The simulations show that latent heat exchange due to evaporation in the micro-layer and sensible heat exchange during the waiting time after bubble departure are the main heat transfer mechanisms. It is found that the presence of an imposed flow normal to the bubble rising path determines a complex velocity and temperature distribution near the nucleation site. This conditions can result in bubble sliding, and influence bubble shape, departure diameter and departure frequency

  16. Interaction of centres on nucleate boiling

    International Nuclear Information System (INIS)

    Chekanov, V.V.

    1977-01-01

    An experimental set-up is described which enables to analyse the growth of a bubble on a heater, the frequency of succession of the bubbles, etc., by the change in the electric signal from a photomultiplier, onto whose photocathode the bubble is projected. The change in the first moments of the statistical distribution of the corresponding parameters (growth time, frequency of succession, and so on) is adopted as the measure of the external effect on the vapour formation centre. It is shown that for single-bubble boiling the greatest effect is exerted by the acoustic waves produced by the bubble in the growth period; during developed boiling one observes mutual suppression of centres spaced at a distance of the order of the detachment diameter. As the heat flux increases, the correlation of the motion of the interface over the heater surface increases as well. When the correlation radius becomes equal to the centre-to-centre distance, the first crisis sets in. It is suggested that heaters with a variable coefficient of temperature conductance along the heat-releasing surface must withstand high subcritical heat fluxes

  17. Nucleate Boiling Heat Transfer Studied Under Reduced-Gravity Conditions

    Science.gov (United States)

    Chao, David F.; Hasan, Mohammad M.

    2000-01-01

    Boiling is known to be a very efficient mode of heat transfer, and as such, it is employed in component cooling and in various energy-conversion systems. In space, boiling heat transfer may be used in thermal management, fluid handling and control, power systems, and on-orbit storage and supply systems for cryogenic propellants and life-support fluids. Recent interest in the exploration of Mars and other planets and in the concept of in situ resource utilization on the Martian and Lunar surfaces highlights the need to understand how gravity levels varying from the Earth's gravity to microgravity (1g = or > g/g(sub e) = or > 10(exp -6)g) affect boiling heat transfer. Because of the complex nature of the boiling process, no generalized prediction or procedure has been developed to describe the boiling heat transfer coefficient, particularly at reduced gravity levels. Recently, Professor Vijay K. Dhir of the University of California at Los Angeles proposed a novel building-block approach to investigate the boiling phenomena in low-gravity to microgravity environments. This approach experimentally investigates the complete process of bubble inception, growth, and departure for single bubbles formed at a well-defined and controllable nucleation site. Principal investigator Professor Vijay K. Dhir, with support from researchers from the NASA Glenn Research Center at Lewis Field, is performing a series of pool boiling experiments in the low-gravity environments of the KC 135 microgravity aircraft s parabolic flight to investigate the inception, growth, departure, and merger of bubbles from single- and multiple-nucleation sites as a function of the wall superheat and the liquid subcooling. Silicon wafers with single and multiple cavities of known characteristics are being used as test surfaces. Water and PF5060 (an inert liquid) were chosen as test liquids so that the role of surface wettability and the magnitude of the effect of interfacial tension on boiling in reduced

  18. A new correlation for nucleate pool boiling of aqueous mixtures

    International Nuclear Information System (INIS)

    Thome, J.R.; Shakir, S.

    1987-01-01

    A new mixture boiling correlation was developed for nucleate pool boiling of aqueous mixtures on plain, smooth tubes. The semi-empirical correlation models the rise in the local bubble point temperature in a mixture caused by the preferential evaporation of the more volatile component during bubble growth. This rise varies from zero at low heat fluxes (where only single-phase natural convection is present) up to nearly the entire boiling range at the peak heat flux (where latent heat transport is dominant). The boiling range, which is the temperature difference between the dew point and bubble point of a mixture, is used to characterize phase equilibrium effects. An exponential term models the rise in the local bubble point temperature as a function of heat flux. The correlation was compared against binary mixture boiling data for ethanol-water, methanol-water, n-propanol-water, and acetone-water. The majority of the data was predicted to within 20%. Further experimental research is currently underway to obtain multicomponent boiling data for aqueous mixtures with up to five components and for wider boiling ranges

  19. Study on onset of nucleate boiling and net vapor generation point in subcooled flow boiling

    International Nuclear Information System (INIS)

    Ohtake, Hiroyasu; Wada, Noriyoshi; Koizumi, Yasuo

    2002-01-01

    The onset of nucleate boiling (ONB) and the point of net vapor generation on subcooled flow boiling, focusing on liquid subcooling and liquid velocity were investigated experimentally and analytically. Experiments were conducted using a copper thin-film (35μm) and subcooled water in a range of the liquid velocity from 0.27 to 4.6 m/s at 0.10MPa. The liquid subcoolings were 20, 30 and 40K, respectively. Temperatures at the onset of nucleate boiling obtained in the experiments increased with the liquid subcoolings and the liquid velocities. The increases in the temperature of ONB were represented with the classical stability theory of preexisting nuclei. The measured results of the net vapor generation agreed well with the results of correlation by Saha and Zuber in the range of the present experiments. (J.P.N.)

  20. Visualization of nucleate pool boiling of freon 113

    International Nuclear Information System (INIS)

    Afify, M.A.; Fruman, D.H.

    1987-01-01

    The purpose of this investigation is to give a fine description of the behaviour of vapour bubbles in nucleate pool boiling at sites of known sizes using high speed photography. The shapes and growth history of isolated bubbles were determined for a variety of experimental conditions. Coalescence effects between two adjacent or consecutive bubbles were also visualized and the occurrence of vapour patches and continuous vapour columns was demonstrated. Quantitative analysis of the films allows to determine the history and nucleation characteristics of bubbles as a function of various parameters such as heat flux, liquid subcooling and size and nature of nucleation sites. These results are in good agreement with those found in the literature

  1. Interaction of the nucleation phenomena at adjacent sites in nucleate boiling

    International Nuclear Information System (INIS)

    Sultan, M.; Judd, R.L.

    1983-01-01

    The present investigation is an original study in nucleate pool boiling heat transfer combining theory and experiment in which water boiling at atmospheric pressure on a single copper surface at two different levels of heat and different levels of subcooling was studied. Cross spectral analysis of the signals generated by the emission of bubbles at adjacent nucleation sites was used to determine the relationship of the time elapsed between the start of bubble growth at the two neighbouring active sites with the distance separating them. The experimental results obtained indicated that for the lower level of heat flux at three different levels of subcooling, the elapsed time and distance were directly related. Theoretical predictions of a temperature disturbance propagating through the heating surface in the radial direction gave good agreement with the experimental findings, suggesting that this is the mechanism responsible for the activation of the surrounding nucleation sites

  2. Experiments on nucleate boiling heat transfer with a highly-wetting dielectric fluid

    International Nuclear Information System (INIS)

    You, S.M.; Simon, T.W.; Bar-Cohen, A.

    1990-01-01

    This paper reports on experiments on pool boiling heat transfer in an electronic cooling fluid (Fluorinert, FC-72) that were conducted using a 0.51 mm diameter cylindrical heater. The effects of pressure, subcooling and dissolved gas content on nucleate boiling heat transfer are investigated. When boiling with dissolved gas in the bulk fluid, the fluid in the vicinity of the heating element appears to be liberated of dissolved gas by boiling. Thus, boiling under these conditions appears to be similar to subcooled boiling without dissolved gas. Nucleate boiling hysteresis is observed for subcooled and gassy-subcooled situations

  3. Nucleate boiling heat transfer on horizontal tubes in bundles

    International Nuclear Information System (INIS)

    Fujital, Y.; Ohta, H.; Hidaka, S.; Nishikawa, K.

    1986-01-01

    In order to clarify the heat transfer mechanisms of the flooded type horizontal tube bundle evaporator, heat transfer characteristics of tube bundles of experimental scale which consist both of smooth and enhanced tubes were investigated in detail. The experiments of saturated nucleate boiling were performed by using Freon 113 under pressures 0.1 to 1 MPa, and the effects of various parameters, for example, bundle arrangement, heat flux, pressure on the characteristics of an individual tube are clarified. Experimental data is reproduced well by a proposed heat transfer model in which convective heat transfer coefficients due to rising bubbles are estimated as a function of their volumetric flow rate

  4. Interactions between bubble formation and heating surface in nucleate boiling

    International Nuclear Information System (INIS)

    Luke, Andrea

    2009-01-01

    The heat transfer and bubble formation is investigated in pool boiling of propane. Size distributions of active nucleation sites on single horizontal copper and steel tubes with different diameter and surface finishes have been calculated from heat transfer measurements over wide ranges of heat flux and selected pressure. The model assumptions of Luke and Gorenflo for the heat transfer near growing and departing bubbles, which were applied in the calculations, have been slightly modified and the calculated results have been compared to experimental investigations by high speed video techniques. The calculated number of active sites shows a good coincidence for the tube with smaller diameter, while the results for the tube with larger diameter describe the same relative increase of the active sites. The comparison of the cumulative size distribution of the active and potential nucleation sites demonstrates the same slope of the curve and that the critical radius of a stable bubble nuclei is smaller than the average cavity size. (author)

  5. Interactions between bubble formation and heating surface in nucleate boiling

    Energy Technology Data Exchange (ETDEWEB)

    Luke, Andrea [Leibniz University, Hannover (Denmark). Inst. of Thermodynamics], e-mail: ift@ift.uni-hannover.de

    2009-07-01

    The heat transfer and bubble formation is investigated in pool boiling of propane. Size distributions of active nucleation sites on single horizontal copper and steel tubes with different diameter and surface finishes have been calculated from heat transfer measurements over wide ranges of heat flux and selected pressure. The model assumptions of Luke and Gorenflo for the heat transfer near growing and departing bubbles, which were applied in the calculations, have been slightly modified and the calculated results have been compared to experimental investigations by high speed video techniques. The calculated number of active sites shows a good coincidence for the tube with smaller diameter, while the results for the tube with larger diameter describe the same relative increase of the active sites. The comparison of the cumulative size distribution of the active and potential nucleation sites demonstrates the same slope of the curve and that the critical radius of a stable bubble nuclei is smaller than the average cavity size. (author)

  6. Microlayer Topology And Bubble Growth In Nucleate Boiling

    Science.gov (United States)

    Jawurek, H. H.; Macgregor, H. G.; Bodenheimer, J. S.

    1987-09-01

    During nucleate boiling thin liquid films (nicrolayers) form beneath the base of bubbles and evaporate into the bubble interiors. A technique is presented which permits the simultaneous determination of microlayer topology and the contribution of microlayer evaporation to bubble growth. Isolated-bubble boiling takes place on an electrically heated, transparent tin-oxide coating deposited on a glass plate, the latter forming the floor of a vessel. With coherent Claser) illumination from beneath, the microlayers reflect fringe patterns similar to Newton's rings. Owing to the rapid evaporation of the layers (the process is completed within milliseconds) the fringes are in rapid motion and are recorded by eine photography at some 4 000 frames per second and exposure times of 50 μs. The resulting interferograms provide details of microlayer shape and thickness versus time, and thus evaporation rate. Simultaneously, and on the same film, bubble profiles (and thus volumes) are obtained under white light illumination. The two bubble images are manipulated by mirrors and lenses so as to appear side by side on the same frame of film, the fringes magnified and the profiles reduced. Sample results for methanol boiling at a pressure of 58.5 kPa and with the liquid bulk at saturation temperature, are presented. Under such conditions microlayer evaporation accounts for 37 per cent of the total bubble volume at detachment.

  7. Void fraction and incipient point of boiling during the subcooled nucleate flow boiling of water

    International Nuclear Information System (INIS)

    Unal, H.C.

    1977-01-01

    Void fraction has been determined with high-speed photography for subcooled nucleate flow boiling of water. The data obtained and the data of various investigators for adiabatic flow of stream-water mixtures and saturated bulk boiling of water have yielded a correlation which covers the following conditions: geometry: vertically orientated circular tubes, rectangular channels and annuli; pressure: 2 to 15.9 MN/m 2 ; mass velocity: 388 to 3500 kg/m 2 s; void fraction: 0 to 99%; hydraulic diameter: 0.0047 to 0.0343 m; heat flux: adiabatic and 0.01 to 2.0 MW/m 2 . The accuracy of the correlation is estimated to be 12.5%. The value of the so-called distribution (or flow) parameter has been experimentally determined and found to be equal to 1 for a vertical small-diameter circular tube. The incipient point of boiling for subcooled nucleate flow boiling of water has been determined with high-speed photography. The data obtained and the data available in the literature have yielded a correlation which covers the following conditions: geometry: plate, circular tube and inner tube-heated, outer tube-heated and inner - and outer tube heated annulus; pressure: 0.15 to 15.9 MN/m 2 ; mass velocity: 470 to 17355 kg/m 2 s; hydraulic diameter: 0.00239 to 0.032 m; heat flux: 0.13 to 9.8 MW/m 2 ; subcooling: 2.6 to 108 K; material of heating surface: stainless steel and nickel. The accuracy of the correlation is estimated to be 27.5%. Maximum bubble diameters have been measured at the incipient point of boiling. These data and the data from literature have been correlated for the pressure range of 0.1 to 15.9 MN/m 2 . (author)

  8. New Departure from Nucleate Boiling model relying on first principle energy balance at the boiling surface

    Science.gov (United States)

    Demarly, Etienne; Baglietto, Emilio

    2017-11-01

    Predictions of Departure from Nucleate Boiling have been a longstanding challenge when designing heat exchangers such as boilers or nuclear reactors. Many mechanistic models have been postulated over more than 50 years in order to explain this phenomenon but none is able to predict accurately the conditions which trigger the sudden change of heat transfer mode. This work aims at demonstrating the pertinence of a new approach for detecting DNB by leveraging recent experimental insights. The new model proposed departs from all the previous models by making the DNB inception come from an energy balance instability at the heating surface rather than a hydrodynamic instability of the bubbly layer above the surface (Zuber, 1959). The main idea is to modulate the amount of heat flux being exchanged via the nucleate boiling mechanism by the wetted area fraction on the surface, thus allowing a completely automatic trigger of DNB that doesn't require any parameter prescription. This approach is implemented as a surrogate model in MATLAB in order to validate the principles of the model in a simple and controlled geometry. Good agreement is found with the experimental data leveraged from the MIT Flow Boiling at various flow regimes. Consortium for Advanced Simulation of Light Water Reactors (CASL).

  9. Nucleate boiling at the forced flow of binary non-azeotropic mixtures in horizontal tubes

    Directory of Open Access Journals (Sweden)

    Mezentseva N.N.

    2015-01-01

    Full Text Available Analysis of experimental values of heat transfer coefficients obtained through investigation of nucleate boiling of the two-component non-azeotropic mixtures inside the horizontal smooth tubes by various authors is presented. In the zone of nucleate boiling, the experimental data are in good agreement with the calculation dependence.

  10. Latent heat transport and microlayer evaporation in nucleate boiling

    International Nuclear Information System (INIS)

    Jawurek, H.H.

    1977-08-01

    Part 1 of this work provides a broad overview and, where possible, a quantitative assessment of the complex physical processes which together constitute the mechanism of nucleate boiling heat transfer. It is shown that under a wide range of conditions the primary surface-to-liquid heat flows within an area of bubble influence are so redistributed as to manifest themselves predominantly as latent heat transport, that is, as vaporisation into attached bubbles. Part 2 deals in greater detail with one of the component processes of latent heat transport, namely microlayer evaporation. A literature review reveals the need for synchronised records of microlayer geometry versus time and of normal bubble growth and departure. An apparatus developed to provide such records is described. High-speed cine interference photography from beneath and through a transparent heating surface provided details of microlayer geometry and an image reflection system synchronised these records with the bubble profile views. Results are given for methanol and ethanol boiling at sub-atmospheric pressures and at various heat fluxes and bulk subcoolings. In all cases it is found that microlayers were of sub-micron thickness, that microlayer thinning was restricted to the inner layer edge (with the thickness elsewhere remaining constant or increasing with time) and that the contribution of this visible evaporation to the total vapour flow into bubbles was negligible. The observation of thickening towards the outer microlayer edge, however, demonstrates that a liquid replenishment flow occurred simultaneously with the evaporation process

  11. Basic Study for Active Nucleation Site Density Evaluation in Subcooled Flow Boiling

    International Nuclear Information System (INIS)

    Chu, In Cheol; Song, Chul Hwa

    2008-01-01

    Numerous studies have been performed on a active nucleation site density (ANSD) due to its governing influence on a heat transfer. However, most of the studies were focused on pool boiling conditions. Kocamustafaogullari and Ishii developed an ANSD correlation from a parametric study of the existing pool boiling data. Also, they extended the correlation to a convective flow boiling condition by adopting the nucleation suppression factor of Chen's heat transfer correlation. However, the appropriateness of applying the Chen's suppression factor to an ANSD correlation was not fully validated because there was not enough experimental data on ANSD in the forced convective flow boiling. Basu et al. performed forced convective boiling experiments and proposed a correlation of ANSD which is the only correlation based on experimental data for a forced convective boiling. They concluded that the ANSD is only dependent on the static contact angle and the wall superheat, and is independent of the flow rate and the subcooling, which contradict the general acceptance of the nucleation suppression in the forced convective boiling. It seems that no reliable ANSD correlation or model is available for a forced convective boiling. In the present study, the effect of the flow velocity on the suppression of the nucleation site was examined, and the effectiveness of a Brewster reflection technique for the identification of the nucleation site was also examined

  12. A correlation to the heat transfer coefficient in nucleate boiling

    International Nuclear Information System (INIS)

    Ribatski, Gherhardt; Jabardo, Jose M. Saiz

    1999-01-01

    Nucleate boiling heat transfer is a complex phenomenon, making the development of a correlation for the heat transfer coefficient rather cumbersome due to the number of physical parameters involved in it. Some authors have followed a pragmatic approach to the problem by correlating the heat transfer coefficient in terms of reduced primitive properties. Two of the most knowledgeable authors who have followed this approach are Gorenflo and Cooper. Comparisons have been performed among results from the correlations proposed by these researchers and experimental results obtained elsewhere for refrigerants R-11, R-113 and R-114. These comparisons have shown that Cooper's correlation is best fitted for halocarbon refrigerants. The correlation proposed by Gorenflo ads the difficulty of including a numerical factor specific for each fluid. Leiner modified Gorenflo's correlation to determine the numerical factor as a function of known physical parameters of the fluid. In present study, the form of this function has been investigated for halocarbon refrigerants. The obtained correlation is written in terms of the following parameters: reduced pressure, eccentric and compressibility factors at the critical state, and a dimensionless specific heat of the vapor phase. The correlation compares well with experimental results. (author)

  13. Investigation of bubble flow regimes in nucleate boiling of highly-wetting liquids

    International Nuclear Information System (INIS)

    Tong, W.; Bar-Cohen, A.; Simon, T.W.

    1991-01-01

    This paper describes an investigation of the bubble flow regimes in nucleate boiling of FC-72, a highly-wetting liquid. Theoretically analysis of vapor bubble generation and departure from the heated surface reveals that the heat fluxes required for the merging of consecutive bubbles, for highly-wetting liquids, lie in the upper range of the nucleate boiling heat flux. A visual and photographic study of nucleate boiling from sputtered platinum surfaces has supported the theoretical results and shown that the isolated bubble behavior extends to at least 50-80% of the critical heat flux, considerably higher than observed by others with water. Lateral coalescence of adjacent bubbles has been found to be a more likely cause of the termination of the isolated bubble regime. These findings suggest that thermal transport models which are based on isolated bubble behavior may be applicable to nearly the entire range of nucleate boiling of electronic cooling fluids

  14. Influence of surface conditions in nucleate boiling--the concept of bubble flux density

    International Nuclear Information System (INIS)

    Shoukri, M.; Judd, R.L.

    1978-01-01

    A study of the influence of surface conditions in nucleate pool boiling is presented. The surface conditions are represented by the number and distribution of the active nucleation sites as well as the size and size distribution of the cavities that constitute the nucleation sites. The heat transfer rate during nucleate boiling is shown to be influenced by the surface condition through its effect on the number and distribution of the active nucleation sites as well as the frequency of bubble departure from each of these different size cavities. The concept of bubble flux density, which is a function of both the active site density and frequency of bubble departure, is introduced. A method of evaluating the bubble flux density is proposed and a uniform correlation between the boiling heat flux and the bubble flux density is found to exist for a particular solid-liquid combination irrespective of the surface finish within the region of isolated bubbles

  15. Assessment of Nucleation Site Density Models for CFD Simulations of Subcooled Flow Boiling

    International Nuclear Information System (INIS)

    Hoang, N. H.; Chu, I. C.; Euh, D. J.; Song, C. H.

    2015-01-01

    The framework of a CFD simulation of subcooled flow boiling basically includes a block of wall boiling models communicating with governing equations of a two-phase flow via parameters like temperature, rate of phasic change, etc. In the block of wall boiling models, a heat flux partitioning model, which describes how the heat is taken away from a heated surface, is combined with models quantifying boiling parameters, i.e. nucleation site density, and bubble departure diameter and frequency. It is realized that the nucleation site density is an important parameter for predicting the subcooled flow boiling. The number of nucleation sites per unit area decides the influence region of each heat transfer mechanism. The variation of the nucleation site density will mutually change the dynamics of vapor bubbles formed at these sites. In addition, the nucleation site density is needed as one initial and boundary condition to solve the interfacial area transport equation. A lot of effort has been devoted to mathematically formulate the nucleation site density. As a consequence, numerous correlations of the nucleation site density are available in the literature. These correlations are commonly quite different in their mathematical form as well as application range. Some correlations of the nucleation site density have been applied successfully to CFD simulations of several specific subcooled boiling flows, but in combination with different correlations of the bubble departure diameter and frequency. In addition, the values of the nucleation site density, and bubble departure diameter and frequency obtained from simulations for a same problem are relatively different, depending on which models are used, even when global characteristics, e.g., void fraction and mean bubble diameter, agree well with experimental values. It is realized that having a good CFD simulations of the subcooled flow boiling requires a detailed validations of all the models used. Owing to the importance

  16. The analogy between the bubbling of air into water and nucleate boiling at saturation temperature

    International Nuclear Information System (INIS)

    Wallis, G.B.

    1960-01-01

    This paper presents a case for the separate consideration of the hydrodynamic and thermal aspects of nucleate boiling. It is shown how boiling phenomena may be simulated in detail by the use of porous media to introduce air bubbles into water. Points of similarity and equivalence are described and analysed. (author)

  17. Evaluation of forced-convection nucleate boiling detection by acoustic emission

    International Nuclear Information System (INIS)

    Wells, R.P.; Paterson, J.A.

    1981-10-01

    Acoustic Emission techniques are being investigated for use as protection systems in neutral beam accelerators and water cooled beam dumps. For this purpose, the characteristics of the boiling curve for forced-convection surface boiling have been compared to the Acoustic Emission (AE) produced. Results indicate that AE, in the form of count-rate, is a sensitive indicator of nucleate boiling incipience and is relatively insensitive to flow velocity in the 0 to 12 m/s range

  18. Study on Enhancement of Sub-Cooled Flow Boiling Heat Transfer and Critical Heat Flux of Solid-Water Two-Phase Mixture

    International Nuclear Information System (INIS)

    Yasuo Koizumi; Hiroyasu Ohtake; Tomoyuki Suzuki

    2002-01-01

    The influence of particle introduction into a subcooled water flow on boiling heat transfer and critical heat flux (CHF) was examined. When the water velocity was low, the particles crowded on the bottom wall of the flow channel and flowed just like sliding on the wall. When the water velocity was high, the particles were well dispersed in the water flow. In the non-boiling region, the heat transfer was augmented by the introduction of the particles into the water flow. As the introduction of the particles were increased, the augmentation was also increased in the high water flow rate region. However, it was independent upon the particle introduction rate in the low water flow rate region. The onset of boiling was delayed by the particle inclusion. The boiling heat transfer was enhanced by the particles. However, it was rather decreased in the high heat flux fully-developed-boiling region. The CHF was decreased by the particle inclusion in the low water flow region and was not affected in the high water flow region. (authors)

  19. Steady-state nucleate pool boiling mechanism at low heat fluxes

    International Nuclear Information System (INIS)

    Bastos, L.E.G.

    1979-01-01

    Heat is transfered in the steady state to a horizontal cooper disc inmersed in water at saturation temperature. Levels of heat flux are controlled so that convection and the nucleate boiling can be observed. The value of heat flux is determined experimentally and high speed film is used to record bubble growth. In order to explain the phenomenon the oretical model is proposed in which part of the heat is transfered by free convection during nucleate boiling regime. Agreement between the experiments and the theoretical model is good. (Author) [pt

  20. Onset of nucleate boiling and onset of fully developed subcooled boiling detection using pressure transducers signals spectral analysis

    International Nuclear Information System (INIS)

    Maprelian, Eduardo; Castro, Alvaro Alvim de; Ting, Daniel Kao Sun

    1999-01-01

    The experimental technique used for detection of subcooled boiling through analysis of the fluctuation contained in pressure transducers signals is presented. The experimental part of this work was conducted at the Institut fuer Kerntechnik und zertoerungsfreie Pruefverfahren von Hannover (IKPH, Germany) in a thermal-hydraulic circuit with one electrically heated rod with annular geometry test section. Piezo resistive pressure sensors are used for onset of nucleate boiling (ONB) and onset of fully developed boiling (OFDB) detection using spectral analysis/signal correlation techniques. Experimental results are interpreted by phenomenological analysis of these two points and compared with existing correlation. The results allows us to conclude that this technique is adequate for the detection and monitoring of the ONB and OFDB. (author)

  1. Surface roughness effects on onset of nucleate boiling and net vapor generation point in subcooled flow boiling

    International Nuclear Information System (INIS)

    Ohtake, Hiroyasu; Wada, Noriyoshi; Koizumi, Yasuo

    2003-01-01

    The ability to predict void formation and void fraction in subcooled flow boiling is of importance to the nuclear reactor technology because the presence of voids affects the steady state and transient response of a reactor. The onset of nucleate boiling and the point of net vapor generation on subcooled flow boiling, focusing on surface roughness, liquid subcooling and liquid velocity were investigated experimentally and analytically. Experiments were conducted using a copper thin-film and subcooled water in a range of the liquid velocity from 0.27 to 4.6 m/s at 0.10MPa; the liquid subcoolings were 20, 30 and 40K, respectively. The surface roughness on the test heater was observed by SEM. Experimental results showed that temperatures at the onset nucleate boiling increased with increasing the liquid subcoolings or the liquid velocities. The trend of increase in the temperature at the ONB was in good agreement with the present analytical result based on the stability theory of preexisting nuclei. The measured results for the net vapor generation point agreed well with the results of correlation by Saha and Zuber in the range of the present experiments. The temperature at the ONB decreased with an increasing size of surface roughness, while the NVG-point was independent on the surface roughness. The dependence on the ONB temperature of the roughness size was also represented well by the present analytical model

  2. Steady-state subcooled nucleate boiling on a downward facing hemispherical surface

    International Nuclear Information System (INIS)

    Haddad, K.H.; Cheung, F.B.

    1996-01-01

    Steady-state nucleate boiling heat transfer experiments in saturated and subcooled water were conducted. The heating surface was a 0.305 m hemispherical aluminum vessel heated from the inside with water boiling on the outside. It was found that subcooling had very little effect on the nucleate boiling curve in the high heat flux regime where latent heat transport dominated. On the other hand, a relatively large effect of subcooling was observed in the low heat flux regime where sensible heat transport was important. Photographic records of the boiling phenomenon and the bubble dynamics indicated that in the high heat flux regime, boiling in the bottom center region of the vessel was cyclic in nature with a liquid heating phase, a bubble nucleation and growth phase, a bubble coalescence phase, and a large vapor mass ejection phase. At the same heat flux level, the size of the vapor masses was found to decrease from the bottom center toward the upper edge of the vessel, which was consistent with the observed increase in the critical heat flux in the flow direction along the curved heating surface

  3. Effects of carbon nanotube arrays on nucleate pool boiling

    OpenAIRE

    Ujereh, Sebastine; Fisher, Timothy; Mudawar, Issam

    2007-01-01

    Experiments were performed to assess the impact coating silicon and copper substrates with nanotubes (CNTs) have on pool boiling performance. Different CNT array densities and area coverages were tested on 1.27 1.27 mm2 samples in FC-72. The CNT preparation techniques used provided strong adherence of CNTs to both substrate materials. Very small contact angle enabled deep penetration of FC-72 liquid inside surface cavities of smooth uncoated silicon surfaces, requiring unusually high surface...

  4. Study on calculation model of onset of nucleate boiling in narrow channels

    International Nuclear Information System (INIS)

    Zhang Ming; Zhou Tao; Sheng Cheng; Fu Tao; Xiao Zejun

    2011-01-01

    In the reactor engineering, narrow channels was used widely for its high power density, exceptional heat transfer and actual engineering requirements. The point of Onset of Nucleate Boiling (ONB) is the key point of boiling heat transfer in narrow channels. The point of ONB can directly influence the following flow and heat transfer characteristics in the reactor. Due to the special structure and complexity flow, the point of ONB in narrow channels are effected by many factors, which characteristics are not understood completely yet. Using B and R model, Su Shun-yu model, Pan Liang-ming model and Yang Rui-chang model, the heat flux of onset of nucleate boiling is compared and analyzed by taking water as the medium . And then the relationships of the heat flux with pressure, mass flow and wall temperature are obtained. Based on the differences of each model, the mechanisms for the main influence factors are suggested. (authors)

  5. Prediction of flow boiling curves based on artificial neural network

    International Nuclear Information System (INIS)

    Wu Junmei; Xi'an Jiaotong Univ., Xi'an; Su Guanghui

    2007-01-01

    The effects of the main system parameters on flow boiling curves were analyzed by using an artificial neural network (ANN) based on the database selected from the 1960s. The input parameters of the ANN are system pressure, mass flow rate, inlet subcooling, wall superheat and steady/transition boiling, and the output parameter is heat flux. The results obtained by the ANN show that the heat flux increases with increasing inlet sub cooling for all heat transfer modes. Mass flow rate has no significant effects on nucleate boiling curves. The transition boiling and film boiling heat fluxes will increase with an increase of mass flow rate. The pressure plays a predominant role and improves heat transfer in whole boiling regions except film boiling. There are slight differences between the steady and the transient boiling curves in all boiling regions except the nucleate one. (authors)

  6. Study on model of onset of nucleate boiling in natural circulation with subcooled boiling using unascertained mathematics

    Energy Technology Data Exchange (ETDEWEB)

    Zhou Tao [Department of Thermal Engineering, Tsinghua University, Beijing 100084 (China)]. E-mail: zhoutao@mail.tsinghua.edu.cn; Wang Zenghui [Department of Engineering Mechanics, Tsinghua University, Beijing 100084 (China); Yang Ruichang [Department of Thermal Engineering, Tsinghua University, Beijing 100084 (China)

    2005-10-01

    Experiment data got from onset of nucleate boiling (ONB) in natural circulation is analyzed using unascertained mathematics. Unitary mathematics model of the relation between the temperature and onset of nucleate boiling is built up to analysis ONB. Multiple unascertained mathematics models are also built up with the onset of natural circulation boiling equation based on the experiment. Unascertained mathematics makes that affirmative results are a range of numbers that reflect the fluctuation of experiment data more truly. The fluctuating value with the distribution function F(x) is the feature of unascertained mathematics model and can express fluctuating experimental data. Real status can be actually described through using unascertained mathematics. Thus, for calculation of ONB point, the description of unascertained mathematics model is more precise than common mathematics model. Based on the unascertained mathematics, a new ONB model is developed, which is important for advanced reactor safety analysis. It is conceivable that the unascertained mathematics could be applied to many other two-phase measurements as well.

  7. Study on model of onset of nucleate boiling in natural circulation with subcooled boiling using unascertained mathematics

    International Nuclear Information System (INIS)

    Zhou Tao; Wang Zenghui; Yang Ruichang

    2005-01-01

    Experiment data got from onset of nucleate boiling (ONB) in natural circulation is analyzed using unascertained mathematics. Unitary mathematics model of the relation between the temperature and onset of nucleate boiling is built up to analysis ONB. Multiple unascertained mathematics models are also built up with the onset of natural circulation boiling equation based on the experiment. Unascertained mathematics makes that affirmative results are a range of numbers that reflect the fluctuation of experiment data more truly. The fluctuating value with the distribution function F(x) is the feature of unascertained mathematics model and can express fluctuating experimental data. Real status can be actually described through using unascertained mathematics. Thus, for calculation of ONB point, the description of unascertained mathematics model is more precise than common mathematics model. Based on the unascertained mathematics, a new ONB model is developed, which is important for advanced reactor safety analysis. It is conceivable that the unascertained mathematics could be applied to many other two-phase measurements as well

  8. Numerical modeling of the effect of surface topology on the saturated pool nucleate boiling curve

    International Nuclear Information System (INIS)

    Unal, C.; Pasamehmetoglu, K.O.

    1993-01-01

    A numerical study of saturated pool nucleate boiling with an emphasis on the effect of surface topography is presented. The numerical model consisted of solving the three-dimensional transient heat conduction equation within the heater subjected to nucleate boiling over its upper surface. The surface topography model considered the distribution of the cavity and cavity angles based on exponential and normal probability functions. Parametric results showed that the saturated nucleate boiling curve shifted left and became steeper with an increase in the mean cavity radius. The boiling curve was found to be sensitive to the selection of how many cavities were selected for each octagonal cell. A small variation in the statistical parameters, especially cavity radii for smooth surfaces, resulted in noticeable differences in wall superheat for a given heat flux. This result indicated that while the heat transfer coefficient increased with cavity radii, the cavity radii or height alone was not sufficient to characterize the boiling curve. It also suggested that statistical experimental data should consider large samples to characterize the surface topology. The boiling curve shifted to the right when the cavity angle was obtained using a normal distribution. This effect became less important when the number of cavities for each cell was increasing because the probability of the potential cavity with a larger radius in each cell was increased. When the contact angle of the fluid decreased for a given mean cavity radii, the boiling curve shifted to the right. This shift was more pronounced at smaller mean cavity radii and decreased with increasing mean cavity radii

  9. Nucleate boiling pressure drop in an annulus: Book 5

    International Nuclear Information System (INIS)

    1992-11-01

    The application of the work described in this report is the production reactors at the Savannah River Site, and the context is nuclear reactor safety. The Loss of Coolant Accident (LOCA) scenario considered involves a double-ended break of a primary coolant pipe in the reactor. During a LOCA, the flow through portions of the reactor may reverse direction or be greatly reduced, depending upon the location of the break. The reduced flow rate of coolant (D 2 O) through the fuel assembly channels of the reactor -- downflow in this situation -- can lead to boiling and to the potential for flow instabilities which may cause some of the fuel assembly channels to overheat and melt. That situation is to be avoided. The experimental approach is to provide a test annulus which simulates geometry, materials, and flow conditions in a Mark-22 fuel assembly (Coolant Channel 3) to the extent possible. The key analysis approaches are: To compare the minima in the measured demand curves with analytical criteria, in particular the Saha-Zuber (1974) model; and to compare the pressure and temperature as a function of length in the annulus with an integral model for flow boiling in a heated channel. Nineteen test series and a total of 178 tests were performed. Testing addressed the effects of: Heat flux; pressure; helium gas; power tilt; ribs; asymmetric heat flux. This document consists solely of the plato file index from 11/87 to 11/90

  10. Heat transfer in nucleate pool boiling of aqueous SDS and triton X-100 solutions

    Energy Technology Data Exchange (ETDEWEB)

    Wasekar, Vivek M. [Tata Steel Limited, Department of Research and Development, Jamshedpur (India)

    2009-09-15

    Variation in degree of surface wettability is presented through the application of Cooper's correlative approach (h{proportional_to}M{sup -0.5}q{sub w}''0.67) for computing enhancement ({phi}) in nucleate pool boiling of aqueous solutions of SDS and Triton X-100 and its presentation with Marangoni parameter ({chi}) that represents the dynamic convection effects due to surface tension gradients. Dynamic spreading coefficient defined as {sigma} {sub dyn}N{sub a}, which relates spreading and wetting characteristics with the active nucleation site density on the heated surface and bubble evolution process, represents cavity filling and activation process and eliminates the concentration dependence of nucleate pool boiling heat transfer in boiling of aqueous surfactant solutions. Using the dynamic spreading coefficient ({sigma}{sub dyn}N{sub a}=0.09q{sub w}''0.71), correlation predictions within {+-}15% for both SDS and triton X-100 solutions for low heat flux boiling condition (q{sub w}''{<=} 100 kW/m {sup 2}) characterised primarily by isolated bubble regime are presented. (orig.)

  11. Spreaders for immersion nucleate boiling cooling of a computer chip with a central hot spot

    International Nuclear Information System (INIS)

    Ali, Amir F.; El-Genk, Mohamed S.

    2012-01-01

    Highlights: ► The paper introduces a spreader concept for cooling high power chip with a hot spot. ► Spreader is comprised of a Cu substrate and copper micro-porous surface. ► Spreaders surface is cooled by nucleate boiling of PF-5060 dielectric liquid. ► Analysis demonstrated spreader effectiveness for mitigating hot spot effect. - Abstract: This paper numerically investigates the performance of composite spreaders comprised of Cu substrates and Cu micro-porous surfaces of different thicknesses for immersion cooling of 10 × 10 mm underlying computer chip with a 2 × 2 mm central hot spot. The local heat flux at the hot spot is three times the chip’s surface average outside the hot spot. The thickness of the Cu substrate changes from 1.6 to 3.2 mm and that of the Cu micro-porous surface changes from 80 to 197 μm. The spreaders are cooled by saturation nucleate boiling of PF-5060 dielectric liquid. The local values of the nucleate boiling heat transfer coefficients on the various Cu micro-porous surfaces are based on pool boiling experimental measurements. Results demonstrated the effectiveness of immersion cooling nucleate boiling for mitigating the effect of the hot spot. The spreaders decrease the maximum surface temperature and the temperature gradient on the chip surface and increase the dissipated thermal power by the chip and removed from the spreader surface. Increasing the thickness of the Cu substrate and/or decreasing the thickness of the Cu micro-porous surface increases the total thermal power removed, the chip surface temperature and the spreader’s footprint area.

  12. Nucleate boiling pressure drop in an annulus: Book 3

    International Nuclear Information System (INIS)

    Block, J.A.; Crowley, C.; Dolan, F.X.; Sam, R.G.; Stoedefalke, B.H.

    1992-11-01

    The application of the work described in this report is the production reactors at the Savannah River Site, and the context is nuclear reactor safety. The Loss of Coolant Accident (LOCA) scenario considered involves a double-ended break of a primary coolant pipe in the reactor. During a LOCA, the flow through portions of the reactor may reverse direction or be greatly reduced, depending upon the location of the break. The reduced flow rate of coolant (D 2 O) through the fuel assembly channels of the reactor -- downflow in this situation -- can lead to boiling and to the potential for flow instabilities which may cause some of the fuel assembly channels to overheat and melt. That situation is to be avoided. The experimental approach is to provide a test annulus which simulates geometry, materials, and flow conditions in a Mark-22 fuel assembly (Coolant Channel 3) to the extent possible. The annulus has a full-scale geometry, and in fat uses SRL dummy hardware for the inner annulus wall in the ribbed geometry. The materials aluminum. The annulus is uniformly heated in the axial direction, but the circumferential heat flux can be varied to provide ''power tilt'' or asymmetric heating of the inner and outer annulus walls. The test facility uses H 2 O rather than D 2 O, but it includes the effects of dissolved helium gas present in the reactor. The key analysis approaches are: To compare the minima in the measured demand curves with analytical criteria, in particular the Saha-Zuber (1974) model; and to compare the pressure and temperature as a function of length in the annulus with an integral model for flow boiling in a heated channel. This document consists of data plots and summary files of temperature measurements

  13. Nucleate boiling pressure drop in an annulus: Book 6

    International Nuclear Information System (INIS)

    1992-11-01

    The application of the work described in this report is the production reactors at the Savannah River Site, and the context is nuclear reactor safety. The Loss of Coolant Accident (LOCA) scenario considered involves a double-ended break of a primary coolant pipe in the reactor. During a LOCA, the flow through portions of the reactor may reverse direction or be greatly reduced, depending upon the location of the break. The reduced flow rate of coolant (D 2 O) through the fuel assembly channels of the reactor -- downflow in this situation -- can lead to boiling and to the potential for flow instabilities which may cause some of the fuel assembly channels to overheat and melt. That situation is to be avoided. The experimental approach is to provide a test annulus which simulates geometry, materials, and flow conditions in a Mark-22 fuel assembly (Coolant Channel 3) to the extent possible. The annulus has a full-scale geometry, and in fat uses SRL dummy hardware for the inner annulus wall in the ribbed geometry. The materials aluminum. The annulus is uniformly heated in the axial direction, but the circumferential heat flux can be varied to provide ''power tilt'' or asymmetric heating of the inner and outer annulus walls. The test facility uses H 2 O rather than D 2 O, but it includes the effects of dissolved helium gas present in the reactor. The key analysis approaches are: To compare the minima in the measured demand curves with analytical criteria, in particular the Saha-Zuber (1974) model; and to compare the pressure and temperature as a function of length in the annulus with an integral model for flow boiling in a heated channel. This document consists of a summary of temperature measurements to include recorded minima, maxima, averages and standard deviations

  14. Nucleate boiling pressure drop in an annulus: Book 6

    Energy Technology Data Exchange (ETDEWEB)

    1992-11-01

    The application of the work described in this report is the production reactors at the Savannah River Site, and the context is nuclear reactor safety. The Loss of Coolant Accident (LOCA) scenario considered involves a double-ended break of a primary coolant pipe in the reactor. During a LOCA, the flow through portions of the reactor may reverse direction or be greatly reduced, depending upon the location of the break. The reduced flow rate of coolant (D{sub 2}O) through the fuel assembly channels of the reactor -- downflow in this situation -- can lead to boiling and to the potential for flow instabilities which may cause some of the fuel assembly channels to overheat and melt. That situation is to be avoided. The experimental approach is to provide a test annulus which simulates geometry, materials, and flow conditions in a Mark-22 fuel assembly (Coolant Channel 3) to the extent possible. The annulus has a full-scale geometry, and in fat uses SRL dummy hardware for the inner annulus wall in the ribbed geometry. The materials aluminum. The annulus is uniformly heated in the axial direction, but the circumferential heat flux can be varied to provide ``power tilt`` or asymmetric heating of the inner and outer annulus walls. The test facility uses H{sub 2}O rather than D{sub 2}O, but it includes the effects of dissolved helium gas present in the reactor. The key analysis approaches are: To compare the minima in the measured demand curves with analytical criteria, in particular the Saha-Zuber (1974) model; and to compare the pressure and temperature as a function of length in the annulus with an integral model for flow boiling in a heated channel. This document consists of a summary of temperature measurements to include recorded minima, maxima, averages and standard deviations.

  15. Development and validation of a new solver based on the interfacial area transport equation for the numerical simulation of sub-cooled boiling with OpenFOAM CFD code for nuclear safety applications

    Energy Technology Data Exchange (ETDEWEB)

    Alali, Abdullah

    2014-02-21

    The one-group interfacial area transport equation has been coupled to a wall heat flux partitioning model in the framework of two-phase Eulerian approach using the OpenFOAM CFD code for better prediction of subcooled boiling phenomena which is essential for safety analysis of nuclear reactors. The interfacial area transport equation has been modified to include the effect of bubble nucleation at the wall and condensation by subcooled liquid in the bulk that governs the non-uniform bubble size distribution.

  16. Development and validation of a new solver based on the interfacial area transport equation for the numerical simulation of sub-cooled boiling with OpenFOAM CFD code for nuclear safety applications

    International Nuclear Information System (INIS)

    Alali, Abdullah

    2014-01-01

    The one-group interfacial area transport equation has been coupled to a wall heat flux partitioning model in the framework of two-phase Eulerian approach using the OpenFOAM CFD code for better prediction of subcooled boiling phenomena which is essential for safety analysis of nuclear reactors. The interfacial area transport equation has been modified to include the effect of bubble nucleation at the wall and condensation by subcooled liquid in the bulk that governs the non-uniform bubble size distribution.

  17. An electrical simulator of a nuclear fuel rod cooled by nucleate boiling

    International Nuclear Information System (INIS)

    Costa, Antonio Carlos Lopes da; Machado, Luiz; Koury, Ricardo Nicolau Nassar; Passos, Julio Cesar

    2009-01-01

    This study investigates an electrical heated test section designed to simulate a nuclear fuel rod. This simulator comprises a stainless steel vertical tube, with length and outside diameter of 600 mm and 10 mm, respectively, inside which there is a high power electrical resistor. The heat generated is removed by means of enhanced confined subcooled nucleate boiling of water in an annular space containing 153 small metal inclined discs. The tests were performed under electrical power and pressure up to 48 kW and 40 bar, respectively. The results show that the experimental boiling heat transfer coefficients are in good agreement with those calculated using the Jens-Lottes correlation. (author)

  18. An electrical simulator of a nuclear fuel rod cooled by nucleate boiling

    Energy Technology Data Exchange (ETDEWEB)

    Costa, Antonio Carlos Lopes da [Centro de Desenvolvimento da Tecnologia Nuclear (CDTN/CNEN-MG), Belo Horizonte, MG (Brazil)], e-mail: aclc@cdtn.br; Machado, Luiz; Koury, Ricardo Nicolau Nassar [Universidade Federal de Minas Gerais (UFMG), Belo Horizonte, MG (Brazil). Dept. de Engenharia Mecanica], e-mail: luizm@demec.ufmg.br; Bonjour, Jocelyn [CETHIL, UMR5008, CNRS, INSA-Lyon (France)], e-mail: jocelyn.bonjour@insa-lyon.fr; Passos, Julio Cesar [Universidade Federal de Santa Catarina (UFSC), Florianopolis, SC (Brazil). Dept. de Engenharia Mecanica. LEPTEN/Boiling], e-mail: jpassos@emc.ufsc.br

    2009-07-01

    This study investigates an electrical heated test section designed to simulate a nuclear fuel rod. This simulator comprises a stainless steel vertical tube, with length and outside diameter of 600 mm and 10 mm, respectively, inside which there is a high power electrical resistor. The heat generated is removed by means of enhanced confined subcooled nucleate boiling of water in an annular space containing 153 small metal inclined discs. The tests were performed under electrical power and pressure up to 48 kW and 40 bar, respectively. The results show that the experimental boiling heat transfer coefficients are in good agreement with those calculated using the Jens-Lottes correlation. (author)

  19. A study of the rates of heat transfer and bubble site density for nucleate boiling on an inclined heating surface

    International Nuclear Information System (INIS)

    Bonamy, S.E.; Symons, J.G.

    1974-08-01

    Nucleate pool boiling of distilled water from an electrically heated surface at atmospheric pressure is studied for varying heating surface inclinations. The constants of the accepted boiling equation phi = K Tsup(B) and the Rohsenow Correlation Coefficient are found to be dependent on surface orientation. Convection cooling is observed to play a major role in pool boiling phenomena and causes large changes in the heat transfer rates for a given excess of temperature of the heated surface. Active nucleation site density is studied and found to be independent of surface inclination. Empirical relations are presented to provide an understanding of the effects of inclination on other boiling parameters. (author)

  20. Experimental investigation on the phenomena around the onset nucleate boiling during the impacting of a droplet on the hot surface

    Energy Technology Data Exchange (ETDEWEB)

    Mitrakusuma, Windy H., E-mail: windyhm@polban.ac.id [Graduate Program at Mechanical Engineering, Engineering Faculty, Gadjah Mada University, Jl. Grafika No. 2 Yogyakarta 55281 (Indonesia); Refrigeration and Airconditioning Department, Politeknik Negeri Bandung, Jl. Gegerkalong Hilir, Ds. Ciwaruga Kotak Pos 1234 Bandung (Indonesia); Deendarlianto,; Kamal, Samsul; Indarto [Mechanical and Industrial Department, Engineering Faculty, Gadjah Mada University, Jl. Grafika No. 2 Yogyakarta 55281 (Indonesia); Centre for Energy Studies, Gadjah Mada University, Sekip K-1A Kampus UGM, Yogyakarta 55281 (Indonesia); Nuriyadi, M. [Refrigeration and Airconditioning Department, Politeknik Negeri Bandung, Jl. Gegerkalong Hilir, Ds. Ciwaruga Kotak Pos 1234 Bandung (Indonesia)

    2016-06-03

    Onset of nucleate boiling of a droplet when impacted onto hot surface was investigated. Three kinds of surfaces, normal stainless steel (NSS), stainless steel with TiO{sub 2} coating (UVN), and stainless steel with TiO{sub 2} coating and radiated by ultraviolet ray were employed to examine the effect of wettability. The droplet size was 2.4 mm diameter, and dropped under different We number. The image is generated by high speed camera with the frame speed of 1000 fps. The boiling conditions are identified as natural convection, nucleate boiling, critical heat flux, transition, and film boiling. In the present report, the discussion will be focused on the beginning of nucleate boiling on the droplet. Nucleate boiling occurs when bubbles are generated. These bubbles are probably caused by nucleation on the impurities within the liquid rather than at nucleation sites on the heated surface because the bubbles appear to be in the bulk of the liquid instead of at the liquid-solid interface. In addition, the smaller the contact angle, the fastest the boiling.

  1. Nucleate boiling of halogenated coolants - correlation analysis; Ebulicao nucleada de refrigerantes halogenados: analise de correlacoes

    Energy Technology Data Exchange (ETDEWEB)

    Ribatski, Gherhardt; Jabardo, Jose M. Saiz [Sao Paulo Univ., Sao Carlos, SP (Brazil). Escola de Engenharia. Dept. de Engenharia Mecanica

    1998-07-01

    Present study has been focused on a literature of heat transfer under nucleate boiling conditions of halocarbon refrigerants and their mixtures with lubricating oil. Two kind of correlations regarding the heat transfer mechanism have been found: strictly empirical, based on a straight curve fitting of experimental data, and semi-empirical, based on the particular point of view of the author regarding the physical mechanism but still fitted with experimental data. As a general rule, it has been noted that correlations present significant discrepancies among each other, a result which mostly reflects the wide range of experimental conditions used as a reference. A similar trend has been observed with refrigerant/oil mixtures. Given the current status of halocarbon refrigerants for refrigeration applications, there is clearly a need for further research regarding the nucleate boiling phenomenon related to those compounds. (author)

  2. A numerical investigation of electrohydrodynamic (EHD) effects on bubble deformation under pseudo-nucleate boiling conditions

    International Nuclear Information System (INIS)

    Zu, Y.Q.; Yan, Y.Y.

    2009-01-01

    In this article, the electrohydrodynamic (EHD) effects on nucleate boiling are studied by developing a numerical modelling of EHD effect on bubble deformation in pseudo-nucleate boiling conditions. The volume of fluid (VOF) method is employed to track the interface between the gas-liquid two phases; the user-defined code is written and added to the commercial software FLUENT to solve the electric field and the corresponding electric body force. On this basis, the model is applied to study the EHD effects on heat transfer and fluid flows. An initial air bubble surrounded by liquid CCl 4 and attached to a horizontal superheated wall under the action of electric field is studied. The results of the EHD effect on bubble shape evolution are compared with those of available experiments showing good agreement. The mechanism of EHD enhancement of heat transfer and the EHD induced phenomena including bubble elongation and detachment are analyzed in detail.

  3. Numerical analysis of the bubble detachment diameter in nucleate boiling

    International Nuclear Information System (INIS)

    Lamas, M I; Sáiz Jabardo, J M; Arce, A; Fariñas, P

    2012-01-01

    The present paper presents a tri-dimensional CFD (Computational Fluid Dynamics) model to investigate the fluid flow around bubbles attached to heated walls. Transient solutions of the governing field equations in a domain containing the bubbles and the surrounding liquid have been obtained. The nucleation, growing and detachment processes have been analyzed. Concerning the software, the open source OpenFOAM has been used. Special attention has been given to the bubble detachment diameter. Two mechanisms have been considered as physically related to the detachment: surface tension and buoyancy. As expected, it has been verified that the bubble detachment diameter depends on the contact angle, operating pressure and properties of the fluid. Several fluids have been considered (water, R134a, ammonia and R123), as well as several operating pressures (between 0.1 and 10 bar) and contact angles (between 10 and 80°). It has been concluded that the detachment diameter depends strongly on the contact angle and fluid properties and slightly on the pressure. A correlation for the bubble detachment diameter has been developed based on the obtained numerical results. Data from this expression compare reasonably well with those from other correlations from the literature.

  4. Non-isothermal desorption and nucleate boiling in a water-salt droplet LiBr

    Directory of Open Access Journals (Sweden)

    Misyura Sergey Ya.

    2018-01-01

    Full Text Available Experimental data on desorption and nucleate boiling in a droplet of LiBr-water solution were obtained. An increase in salt concentration in a liquid-layer leads to a considerable decrease in the rate of desorption. The significant decrease in desorption intensity with a rise of initial mass concentration of salt has been observed. Evaporation rate of distillate droplet is constant for a long time period. At nucleate boiling of a water-salt solution of droplet several characteristic regimes occur: heating, nucleate boiling, desorption without bubble formation, formation of the solid, thin crystalline-hydrate film on the upper droplet surface, and formation of the ordered crystalline-hydrate structures during the longer time periods. For the final stage of desorption there is a big difference in desorption rate for initial salt concentration, C0, 11% and 51%. This great difference in the rate of desorption is associated with significantly more thin solution film for C0 = 11% and higher heat flux.

  5. A study on the effects of heated surface wettability on nucleation characteristics in subcooled flow boiling

    International Nuclear Information System (INIS)

    Kajihara, Tomoyuki; Kaiho, Kazuhiro; Okawa, Tomio

    2014-01-01

    Subcooled flow boiling plays an important role in boiling water reactors because it influences the heat transfer performance from fuel rods, two-phase flow stabilities, and neutron moderation characteristics. In the present study, flow visualization of water subcooled flow boiling in a vertical heated channel was carried out to investigate the mechanisms of void fraction development. The two surfaces of distinctly different contact angles were used as the heated surface to investigate the effect of the surface wettability. It was observed that with an increase in the wall heat flux, more nucleation sites were activated and larger bubbles were produced at low-frequency. It was considered that formation of these large bubbles primarily contributed to the void fraction development. (author)

  6. Computational fluid dynamics and population balance modelling of nucleate boiling of cryogenic liquids: Theoretical developments

    Directory of Open Access Journals (Sweden)

    Guan Heng Yeoh

    2016-12-01

    Full Text Available The main focus in the analysis of pool or flow boiling in saturated or subcooled conditions is the basic understanding of the phase change process through the heat transfer and wall heat flux partitioning at the heated wall and the two-phase bubble behaviours in the bulk liquid as they migrate away from the heated wall. This paper reviews the work in this rapid developing area with special reference to modelling nucleate boiling of cryogenic liquids in the context of computational fluid dynamics and associated theoretical developments. The partitioning of the wall heat flux at the heated wall into three components – single-phase convection, transient conduction and evaporation – remains the most popular mechanistic approach in predicting the heat transfer process during boiling. Nevertheless, the respective wall heat flux components generally require the determination of the active nucleation site density, bubble departure diameter and nucleation frequency, which are crucial to the proper prediction of the heat transfer process. Numerous empirical correlations presented in this paper have been developed to ascertain these three important parameters with some degree of success. Albeit the simplicity of empirical correlations, they remain applicable to only a narrow range of flow conditions. In order to extend the wall heat flux partitioning approach to a wider range of flow conditions, the fractal model proposed for the active nucleation site density, force balance model for bubble departing from the cavity and bubble lifting off from the heated wall and evaluation of nucleation frequency based on fundamental theory depict the many enhancements that can improve the mechanistic model predictions. The macroscopic consideration of the two-phase boiling in the bulk liquid via the two-fluid model represents the most effective continuum approach in predicting the volume fraction and velocity distributions of each phase. Nevertheless, the

  7. Detection of the departure from nucleate boiling (DNB) in nuclear fuel rod simulators

    Energy Technology Data Exchange (ETDEWEB)

    Mesquita, Amir Z.; Rezende, Hugo C.; Santos, Andre Augusto C.; Silva, Vitor Vasconcelos A.; Campolina, Daniel de Almeida M., E-mail: amir@cdtn.br, E-mail: hcr@cdtn.br, E-mail: aacs@cdtn.br, E-mail: vitors@cdtn.br, E-mail: campolina@cdtn.br [Centro de Desenvolvimento da Tecnologia Nuclear (CDTN/UFMG), Belo Horizonte, MG (Brazil). Servico de Tecnologia de Reatores; Palma, Daniel Artur P., E-mail: dapalma@cnen.gov.br [Comissao Nacional de Energia Nuclear (CNEN), Rio de Janeiro, RJ (Brazil)

    2013-07-01

    In the thermal hydraulic experiments to determinate parameters of heat transfer, where fuel rod simulators are heated by electric current, the preservation of the simulators are essential when the heat flux goes to the critical point. One of the most important limits in the design of cooling water reactors is the condition in which the heat transfer coefficient by boiling in the core deteriorates itself. The departure from nucleate boiling (DNB) happens in the area of low steam quality when there is nucleus formation of bubbles. This result in a departure from nucleate boiling in which steam bubbles no longer break away from the solid surface of the channel, bubbles dominate the channel or surface, and the heat flux dramatically decreases. Vapor essentially insulates the bulk liquid from the hot surface. At this time, the small increase in the heat flux or in the inlet temperature of the cooler in the core, or the small decrease in the inlet flux of cooling, results in changes in the heat transfer mechanism. This causes increases in the surface temperature of the fuel elements causing failures at the fuel (burnout). This paper describes the experiments conducted to detection of critical heat flux in nuclear fuel element simulators carried out in the thermal-hydraulic laboratory of Nuclear Technology Development Centre (CDTN). It is concluded that the use of displacement transducer is the most efficient technique for detecting of critical heat flux in nuclear simulators heated by electric current in open pool. (author)

  8. Detection of the departure from nucleate boiling (DNB) in nuclear fuel rod simulators

    International Nuclear Information System (INIS)

    Mesquita, Amir Z.; Rezende, Hugo C.; Santos, Andre Augusto C.; Silva, Vitor Vasconcelos A.; Campolina, Daniel de Almeida M.

    2013-01-01

    In the thermal hydraulic experiments to determinate parameters of heat transfer, where fuel rod simulators are heated by electric current, the preservation of the simulators are essential when the heat flux goes to the critical point. One of the most important limits in the design of cooling water reactors is the condition in which the heat transfer coefficient by boiling in the core deteriorates itself. The departure from nucleate boiling (DNB) happens in the area of low steam quality when there is nucleus formation of bubbles. This result in a departure from nucleate boiling in which steam bubbles no longer break away from the solid surface of the channel, bubbles dominate the channel or surface, and the heat flux dramatically decreases. Vapor essentially insulates the bulk liquid from the hot surface. At this time, the small increase in the heat flux or in the inlet temperature of the cooler in the core, or the small decrease in the inlet flux of cooling, results in changes in the heat transfer mechanism. This causes increases in the surface temperature of the fuel elements causing failures at the fuel (burnout). This paper describes the experiments conducted to detection of critical heat flux in nuclear fuel element simulators carried out in the thermal-hydraulic laboratory of Nuclear Technology Development Centre (CDTN). It is concluded that the use of displacement transducer is the most efficient technique for detecting of critical heat flux in nuclear simulators heated by electric current in open pool. (author)

  9. Boiling nucleation

    International Nuclear Information System (INIS)

    Cole, R.

    1974-01-01

    Experimental results of flash evaporation of a pool of water subjected to sudden pressure drop are reported. The experiments were conducted with pure water at equilibrium temperatures between 40 to 80 0 C and with superheat in the range of about 3 to 5 0 C. Two distinct exponential decaying processes were identified for flash evaporation and the flashing time was found to decrease with an increase of equilibrium temperature and with the decrease of superheat. Basic experiments on flash evaporation of distilled water were conducted. However, the results may not be quantitatively applicable to seawater flash evaporators as the presence of salts in the seawater will considerably change the surface tension and in turn affect the nonequilibrium fraction

  10. Onset of a nucleate boiling and incipient point of net vapor generation in narrow channel

    International Nuclear Information System (INIS)

    Hong, G.

    2014-01-01

    An experimental study on onset of nucleate boiling (ONB) and incipient point of net vapor generation (IPNVG) in narrow rectangular channel was presented. Flow direction in the channel was vertical upward. The experimental results indicate that the classical correlations of ONB for conventional channels were not suitable for the present narrow rectangular channel. The wall superheat needed to initiate boiling is found to be higher for the same given values of heat and mass flux. The experimental results of IPNVG indicate that the heat flux, triggering net vapor generation in narrow rectangular channel, is litter lower than that calculated by correlations for conventional channels. The relative prediction error of qIPNVG by Griffith model, Saha model and Sun model ranges from -17.9% to +9.6%. A new correlation was developed to predict the ONB in narrow rectangular channel. The proposed correlation predictions agreed well with the experimental data. (author)

  11. Experiments on the effects of nanoparticles on subcooled nucleate pool boiling

    Science.gov (United States)

    Kangude, Prasad; Bhatt, Dhairya; Srivastava, Atul

    2018-05-01

    The effect of nanoparticles on a single bubble-based nucleate pool boiling phenomenon under subcooled conditions has been studied. Water (as the base fluid) and two different concentrations of water-silica nanofluids (0.005% and 0.01% V/V) have been employed as the working fluids. The boiling experiments have been conducted in a specially designed chamber, wherein an ITO-coated heater substrate has been used to induce single bubble nucleation. Measurements have been performed in a completely non-intrusive manner using one of the refractive index-based diagnostics techniques, namely, rainbow schlieren deflectometry. Thus, the thermal gradients prevailing in the boiling chamber have directly been mapped as a two-dimensional distribution of hue values that are recorded in the form of rainbow schlieren images. The schlieren-based measurements clearly revealed the plausible influence of nanoparticles on the strength of temperature gradients prevailing in the boiling chamber. As compared to the base fluid, the experiments with dilute nanofluids showed that the suspended nanoparticles tend to diffuse (homogenize) the strength of temperature gradients, both in the vicinity of the heated substrate and in the thermal boundary layer enveloping the vapor bubble. An overall reduction in the bubble volume and dynamic contact angle was seen with increasing concentrations of dilute nanofluids. In addition, the vapor bubble was found to assume a more spherical shape at higher concentrations of dilute nanofluids in comparison to its shape with water-based experiments. Clear oscillations of the vapor bubble in the subcooled pool of liquids (water and/or nanofluids) were observed, the frequency of which was found to be significantly reduced as the nanoparticle concentration was increased from 0% (water) to 0.01% (V/V). A force balance analysis has been performed to elucidate the plausible mechanisms explaining the observed trends of the oscillation frequencies of the vapor bubble.

  12. Nucleate and film pool boiling in R11: the effects of orientation

    International Nuclear Information System (INIS)

    Venart, J.E.S.; Sousa, A.C.M.; Jung, D.S.

    1985-01-01

    In order to understand and model the behaviour of LPG tanks in fires [1] it is necessary to characterize the internal flow and specify its boundary conditions. Tank storage and transport normally utilize horizontal cylinders or spheres and hence the interior fluid sees a variety of surfaces inclinations and heat fluxes. The purpose of this paper is to present results obtained in R11 as a function of heat flux (1-180 kW/m 2 ) and angle (0-80 o ) at pressures from 1 to 2 bars in the free convective, nucleate and film boiling regions. (author)

  13. Nucleate pool boiling investigation on a silicon test section with micro-fabricated cavities

    International Nuclear Information System (INIS)

    Sanna, A.; Kenning, D.B.R.; Karayiannis, T.G.; Hutter, C.; Sefiane, K.; Nelson, R.A.

    2009-01-01

    The basic mechanisms of nucleate boiling are still not completely understood, in spite of the many numerical and experimental studies dedicated to the topic. The use of a hybrid code allows reasonable computational times for simulations of a solid plate with a large population of artificial micro-cavities with fixed distribution. This paper analyses the guidelines for the design, through numerical simulations, of the location and sizes of micro-fabricated cavities on a new silicon test section immersed in FC-72 at the saturation temperature for different pressures with an imposed heat flux applied at the back of the plate. Particular focus is on variations of wall temperature around nucleation sites. (author)

  14. Boiling transition and the possibility of spontaneous nucleation under high subcooling and high mass flux density flow in a tube

    International Nuclear Information System (INIS)

    Fukuyama, Y.; Kuriyama, T.; Hirata, M.

    1986-01-01

    Boiling transition and inverted annular heat transfer for R-113 have been investigated experimentally in a horizontal tube of 1.2 X 10/sup -3/ meter inner diameter with heating length over inner diameter ratio of 50. Experiments cover a high mass flux density range, a high local subcooling range and a wide local pressure range. Heat transfer characteristics were obtained by using heat flux control steady-state apparatus. Film boiling treated here is limited to the case of inverted annular heat transfer with very thin vapor film, on the order of 10/sup -6/ meter. Moreover, film boiling region is always limited to a certain downstream part, since the system has a pressure gradient along the flow direction. Discussions are presented on the parametric trends of boiling heat transfer characteristic curves and characteristic points. The possible existence is suggested of a spontaneous nucleation control surface boiling phenomena. And boiling transition heat flux and inverted annular heat transfer were correlated

  15. Bubble nucleation of R134A refrigerant in a pressurized flow boiling system

    Energy Technology Data Exchange (ETDEWEB)

    Murshed, S.M. Sohel; Vereen, Keon; Kumar, Ranganathan [University of Central Florida, Orlando, FL (United States). Dept. of Mechanical, Materials and Aerospace Engineering], e-mail: rnkumar@mail.ucf.edu

    2009-07-01

    The effect of heat flux and pressure on bubble nucleation of R134a refrigerant in a flow boiling system is experimentally studied. An experimental facility was built and an innovative concept of thermochromic liquid crystal (TLC) technique was introduced for the high resolution and accurate measurement of the overall heater surface temperature. The visualization and image recording process is performed by employing two synchronized high resolution and high speed cameras which simultaneously capture colored TLC images as well as bubble nucleation activities at high frame rates. Experiments were conducted at different high pressures ranging from 690 to 830 kPa and at different heat flux conditions in order to identify their influence on flow boiling performance specially bubbling event. Present results demonstrate that both the heat flux and pressure influence the bubble generation rate and size. For example, bubble generation frequency and size are found to increase with heat flux. An increase in pressure of 137 kPa (from 690 to 827 kPa) increased the bubble frequency and size about 32 Hz and 20 {mu}m, respectively. (author)

  16. Bubble nucleation of R134A refrigerant in a pressurized flow boiling system

    International Nuclear Information System (INIS)

    Murshed, S.M. Sohel; Vereen, Keon; Kumar, Ranganathan

    2009-01-01

    The effect of heat flux and pressure on bubble nucleation of R134a refrigerant in a flow boiling system is experimentally studied. An experimental facility was built and an innovative concept of thermochromic liquid crystal (TLC) technique was introduced for the high resolution and accurate measurement of the overall heater surface temperature. The visualization and image recording process is performed by employing two synchronized high resolution and high speed cameras which simultaneously capture colored TLC images as well as bubble nucleation activities at high frame rates. Experiments were conducted at different high pressures ranging from 690 to 830 kPa and at different heat flux conditions in order to identify their influence on flow boiling performance specially bubbling event. Present results demonstrate that both the heat flux and pressure influence the bubble generation rate and size. For example, bubble generation frequency and size are found to increase with heat flux. An increase in pressure of 137 kPa (from 690 to 827 kPa) increased the bubble frequency and size about 32 Hz and 20 μm, respectively. (author)

  17. Generalisation to binary mixtures of the second gradient method and application to direct numerical simulation of nucleate boiling

    International Nuclear Information System (INIS)

    Fouillet, C.

    2003-01-01

    In this work, we simulate a nucleate boiling problem using direct numerical simulation. The numerical method used is the second gradient method based on a diffuse interface model which represents interfaces as volumetric regions of finite thickness across which the physical properties of the fluid vary continuously. First, this method is successfully applied to nucleate boiling of a pure fluid. Then, the model is extended to dilute binary mixtures. After studying its validity and its limits in simple configurations, it is then applied to nucleate boiling of a dilute mixture. These simulations show a strong decrease of the heat transfer coefficient as the concentration increases, in agreement with the numerous experimental studies published in this domain. (author) [fr

  18. Spatial distribution of nanoparticles in PWR nanofluid coolant subjected to local nucleate boiling

    Energy Technology Data Exchange (ETDEWEB)

    Mirghaffari, Reza; Jahanfarnia, Gholamreza [Islamic Azad Univ., Tehran (Iran, Islamic Republic of). Dept. of Nuclear Engineering

    2016-12-15

    Nanofluids have shown to be promising as an alternative for a PWR reactor coolant or as a safety system coolant to cover the core in the event of a loss of coolant accident. The nanoparticles distribution and neutronic parameters are intensively affected by the local boiling of nanofluid coolant. The main goal of this study was the physical-mathematical modeling of the nanoparticles distribution in the nucleate boiling of nanofluids within the viscous sublayer. Nanoparticles concentration, especially near the heat transfer surfaces, plays a significant role in the enhancement of thermal conductivity of nanofluids and prediction of CHF, Hide Out and Return phenomena. By solving the equation of convection-diffusion for the liquid phase near the heating surface and the bulk stream, the effect of heat flux on the distribution of nanoparticles was studied. The steady state mass conservation equations for liquids, vapors and nanoparticles were written for the flow boiling within the viscous sublayer adjacent the fuel cladding surface. The derived differential equations were discretized by the finite difference method and were solved numerically. It was found out that by increasing the surface heat flux, the concentration of nanoparticles increased.

  19. Convective boiling in a parallel microchannel heat sink with a diverging cross-section design and artificial nucleation sites

    International Nuclear Information System (INIS)

    Lu, Chun Ting; Pan, Chin

    2009-01-01

    To develop a highly stable boiling heat transfer microchannel heat sink, the three types of diverging microchannels, namely Type-1, Type-2 and Type-3, were designed to explore experimentally the effect of different distribution of artificial nucleation sites on enhancing boiling heat transfer in 10 parallel diverging microchannels with a mean hydraulic diameter of 120 μm. The Type-1 system is with no cavities, Type-2 is with cavities distributed uniformly along the downstream half of the channel, while Type-3 is with cavities distributed uniformly along the whole channel. The artificial nucleation sites are laser-etched pits on the channel bottom wall with a mouth diameter of about 20-22 μm based on the heterogeneous nucleation theory. The results of the present study reveal the presence of the artificial nucleation sites for flow boiling in parallel diverging microchannel significantly reduces the wall superheat and enhances the boiling heat transfer performance. Additionally, the Type-3 design demonstrates the best boiling heat transfer performance. (author)

  20. Nucleate pool boiling, film boiling and single-phase free convection at pressures up to the critical state. Part I: Integral heat transfer for horizontal copper cylinders

    Energy Technology Data Exchange (ETDEWEB)

    Gorenflo, Dieter; Baumhoegger, Elmar; Windmann, Thorsten; Herres, Gerhard [Institut fuer Energie- und Verfahrenstechnik, Universitaet Paderborn, Warburger Str. 100, D-33098 Paderborn (Germany)

    2010-11-15

    Transcritical working cycles for refrigerants have led to increased interest in heat transfer near the Critical State. In general, experimental results for this region differ significantly from those far from it because some fluid properties vary much more there than at a greater distance. In this paper, measurements for two-phase and single-phase free convective heat transfer from an electrically heated copper tube with 25 mm O.D. to refrigerant R125 are discussed for fluid states very close to the Critical Point and far from it. It is shown that heat transfer for film boiling slightly below and for free convection slightly above the critical pressure is very similar. The new - and also previous - experimental data for nucleate boiling, film boiling, and single-phase free convection are compared with calculated results between atmospheric and critical pressure. It can be concluded that the Principle of Corresponding States in its simplest form is very well suited to transfer the results to other refrigerants. In Part II, particular attention will be given to a minimum superheat for nucleate boiling and a maximum superheat for film boiling and single-phase free convection within the circumferential variation of the isobaric wall superheat on the lower parts of the tube. (author)

  1. Experimental investigation of onset of nucleate boiling in this rectangular channels

    International Nuclear Information System (INIS)

    Belhadj, M.; Christensen, R.N.; Aldemir, T.

    1988-01-01

    The 10 kW, HEU fueled Ohio State University Research Reactor (OSURR) will be upgraded to operate with plate type LEU U 3 Si 2 , fuel elements in the power range 250-500 kW. The core will be cooled by natural convection and an onset of nucleate boiling (ONB) margin of 1.2 will be maintained in the hot channel under steady-state operation. The validity of the correlations used for predicting ONB in plate type research reactors is not known for low heat flux-low velocity flows. An experiment has been set up at The Ohio State University to investigate ONB for laminar flow in this rectangular channels. The results show that: The Bergles-Rohsenow correlation and the correlation proposed by Ricque and Siboul predict higher and lower ONB fluxes than actual, respectively. The ONB heat flux is flow velocity dependent

  2. Effect of coolant flow rate on the power at onset of nucleate boiling in a swimming pool type research reactor

    International Nuclear Information System (INIS)

    Khan, L.A.; Ahmad, N.; Ahmad, S.

    1998-01-01

    The effect of flow rate of coolant on power of Onset Nucleate Boiling (ONB) in a reference core of a swimming pool type research reactor has been studied using a as standard computer code PARET. It has been found that the decrease in the coolant flow rate results in a corresponding decrease in power at ONB. (author)

  3. Numerical simulation of nucleate boiling and heat transfer using MPL-MAFL

    Energy Technology Data Exchange (ETDEWEB)

    Han Young Yoon, Hee Cheol Kim [Korea Atomic Energy Research Inst., Taejon (Korea, Republic of); Koshizuka, Seiichi; Oka, Yoshiaki [Tokyo Univ., Tokai, Ibaraki (Japan). Nuclear Engineering Research Lab

    2000-10-01

    A mesh-free numerical method is presented for direct calculation of bubble growth. It is a combination of particle and gridless methods where the terms, 'particle' and 'gridless', refer to Lagrangian and Eulerian schemes respectively. Thus, an arbitrary-Lagrangian-Eulerian calculation is possible, in this method, with a cloud of computing points that are equivalent to the computing cells in mesh-based methods. The moving interface is traced through the Lagrangian motion of the computing points using a particle method and, at the fixed computing points, convection is calculated using a gridless method. The particle interaction model of the moving-particle semi-implicit (MPS) method is applied to the differential operators and the meshless-advection using a flow-directional local-grid (MAFL) scheme is utilized for the gridless method. A complex moving interface problems can be effectively analyzed by MPS-MAFL since the mesh is no longer used. The present method is applied to the calculation of gas-liquid two-phase flow with and without the phase change in two dimensions. The pressure and temperature gradients are ignored for the vapor region and the phase interface is treated as a free boundary. As an isothermal flow, a gas bubble rising in viscous liquids is simulated numerically and the results are compared with the empirical correlation. The energy equation is coupled with the equation of motion for the calculation of nucleate pool boiling. The numerical results are provided for the bubble growth rate, departure radius, and the heat transfer rate, which show good agreement with the experimental observations. The heat transfer mechanism associated with nucleate pool boiling is quantitatively evaluated and discussed with previous empirical studies. (author)

  4. Predicting the onset of nucleate boiling in wavy free-falling turbulent liquid films

    Energy Technology Data Exchange (ETDEWEB)

    Marsh, W J; Mudawar, I [Purdue Univ., Lafayette, IN (USA). School of Mechanical Engineering

    1989-02-01

    Experiments are performed to develop a fundamental understanding of boiling incipience in wavy free-falling turbulent liquid films. Incipience conditions are measured and correlated for water and a fluorocarbon (FC-72) liquid. Incipience in water films is influenced by turbulent eddies and, to a larger extent, by interfacial waves. A new approach to predicting incipience in water and other non-wetting fluids is presented. This approach utilizes physical parameters of commonly accepted incipience models and provides a means of correcting these models for the effects of turbulent eddies and roll waves. This study also demonstrates some unique incipience characteristics of fluorocarbon films. The weak surface tension forces of FC-72 allow droplets and liquid streams to break of the crests of incoming roll waves prior to, and during nucleate boiling. The low contact angle of FC-72 allows the liquid to penetrate deep inside wall cavities. Thus incipience from these flooded cavities requires much higher wall superheat than predicted from incipience models. (author).

  5. Predicting the onset of nucleate boiling in wavy free-falling turbulent liquid films

    International Nuclear Information System (INIS)

    Marsh, W.J.; Mudawar, I.

    1989-01-01

    Experiments are performed to develop a fundamental understanding of boiling incipience in wavy free-falling turbulent liquid films. Incipience conditions are measured and correlated for water and a fluorocarbon (FC-72) liquid. Incipience in water films is influenced by turbulent eddies and, to a larger extent, by interfacial waves. A new approach to predicting incipience in water and other non-wetting fluids is presented. This approach utilizes physical parameters of commonly accepted incipience models and provides a means of correcting these models for the effects of turbulent eddies and roll waves. This study also demonstrates some unique incipience characteristics of fluorocarbon films. The weak surface tension forces of FC-72 allow droplets and liquid streams to break of the crests of incoming roll waves prior to, and during nucleate boiling. The low contact angle of FC-72 allows the liquid to penetrate deep inside wall cavities. Thus incipience from these flooded cavities requires much higher wall superheat than predicted from incipience models. (author)

  6. Correlations of Nucleate Boiling Heat Transfer and Critical Heat Flux for External Reactor Vessel Cooling

    International Nuclear Information System (INIS)

    J. Yang; F. B. Cheung; J. L. Rempe; K. Y. Suh; S. B. Kim

    2005-01-01

    Four types of steady-state boiling experiments were conducted to investigate the efficacy of two distinctly different heat transfer enhancement methods for external reactor vessel cooling under severe accident conditions. One method involved the use of a thin vessel coating and the other involved the use of an enhanced insulation structure. By comparing the results obtained in the four types of experiments, the separate and integral effect of vessel coating and insulation structure were determined. Correlation equations were obtained for the nucleate boiling heat transfer and the critical heat flux. It was found that both enhancement methods were quite effective. Depending on the angular location, the local critical heat flux could be enhanced by 1.4 to 2.5 times using vessel coating alone whereas it could be enhanced by 1.8 to 3.0 times using an enhanced insulation structure alone. When both vessel coating and insulation structure were used simultaneously, the integral effect on the enhancement was found much less than the product of the two separate effects, indicating possible competing mechanisms (i.e., interference) between the two enhancement methods

  7. Study of heat transfer in the heating wall during nucleate pool boiling

    International Nuclear Information System (INIS)

    Bergez, W.

    1991-12-01

    The subject of this these is to show the role of heat transfer in the wall during saturated pool boiling. This effect, usually neglected in the modelizations of boiling, can explain some behaviours of the ebullition cycle and of the activities of nucleation sites. Il has been found that the ebullition cycle can be described by two steps: (1) during bubble growth, the wall temperature decreases due to the evaporation of the micro-layer at the base of the bubble; (2) initial superheat is re-established mainly by radial heat conduction in the wall. It is then possible to account for the variations of the wall temperature displayed by liquid crystals put a the bottom of the heating surface, and for the influence of the contact angle on the heat transfer. In the case of the infinitely thick wall the main results are that the thermal transfer during the growth of the bubble depends on the thermal properties of both wall and liquid and that the time separating the detachment of a bubble and its replacement by a new one is proportional to the cross-section of the bubble and to the thermal diffusivity of the wall

  8. Power distribution changes caused by subcooled nucleate boiling at Callaway Nuclear Power Plant

    International Nuclear Information System (INIS)

    Konya, M.J.; Bryant, K.R.; Hopkins, D.L.

    1993-01-01

    This paper reports the results of an evaluation undertaken by Union Electric (UE) and Westinghouse to explain anomalous behavior of the core axial power distribution at the Callaway Nuclear Power Plant. The behavior was characterized by a gradual unexpected power shift toward the bottom of the core and was first detected during cycle 4 at a core average burnup of approximately 7,000 MWD/MTU. Once started, the power shift continued until burnup effects became dominant and caused power to shift back to the top of the core at the end of the cycle. In addition to the anomalous power distribution, UE observed that estimated critical control rod position (ECP) deviations increased to over 500 pcm (0.5%Δk/k) during Cycles 4 and 5. ECPs for plant restarts that occurred early in each cycle agreed well with measured critical conditions. However, this agreement disappeared for restarts that occurred later in core life. After analyzing relevant data, performing scoping calculations and reviewing industry experience, the authors concluded that the power distribution anomaly was most likely caused by subcooled nucleate boiling. Crud deposition on the fuel was believed to enhance the subcooled boiling. The ECP deviations were a secondary effect of the power shift, since void fraction, axial burnup and xenon distributions departed design predictions during a substantial portion of the fuel cycles. Significant evidence supporting these conclusions include incore detector indications of flux depressions between intermediate flow mixing (IFM) and structural grids. In addition, visual exam results show the presence of crud deposits on fuel pins

  9. Experimental investigation of tube length effect on nucleate pool boiling heat transfer

    International Nuclear Information System (INIS)

    Kang, Myeong-Gie

    1998-01-01

    The effect of a vertically installed tube length on the nucleate pool boiling heat transfer coefficient under atmospheric pressure has been empirically obtained using various combination of major parameters for application to advanced light water reactor design. The experimental data for q'' versus ΔT test are counted as 1,063 points and can cover the extent of D = 9.7 ∼ 25.4 mm, ε = 15.1 ∼ 60.9 nm, H = 5.25 ∼ 30.93, and q'' ≤ 160 kW/m 2 . The experimental results show that a shorter tube is more efficient to increase heat transfer rate due to smaller bubble slug formation on the tube surface. The effect of tube length is greatly observed before H(= L/D) gets 50. After that, the heat flux decreases linearly with H increase. To quantify tube length effect, a new empirical correlation has been developed based on the experimental data bank for pool boiling heat transfer and some parametric studies have been done using the newly developed empirical correlation to broaden its applicability. The newly developed empirical correlation has the form of q'' 0.019ε 0.570 ΔT 4.676 /(D 1.238 H 0.072 ) and can predict the experimental data within ± 20% bound. Heat transfer characteristics can be changed with tube length variation and the transition point is H ∼ 50. Before the transition point, bubble coalescence is active and heat transfer rate gets rapidly decreased with increasing tube length. After that, heat transfer gets somewhat slowly decreased since bubble coalescence effect gets nearly equilibrium with liquid agitation effect

  10. Measurement of nucleation site density, bubble departure diameter and frequency in pool boiling of water using high-speed infrared and optical cameras

    Energy Technology Data Exchange (ETDEWEB)

    Gerardi, Craig; Buongiorno, Jacopo; Hu, Lin-wen; McKrell, Thomas [Massachusetts Institute of Technology, Cambridge, MA (United States)], e-mail: jacopo@mit.edu

    2009-07-01

    A high-speed video and IR thermometry based technique has been used to obtain time and space resolved information on bubble nucleation and boiling heat transfer. This approach provides a fundamental and systematic method for investigating nucleate boiling in a very detailed fashion. Data on bubble departure diameter and frequency, growth and wait times, and nucleation site density are measured with relative ease. The data have been compared to the traditional decades-old and poorly-validated nucleate-boiling models and correlations. The agreement between the data and the models is relatively good. This study also shows that new insights into boiling heat transfer mechanisms can be obtained with the present technique. For example, our data and analysis suggest that a large contribution to bubble growth comes from heat transfer through the superheated liquid layer in addition to micro layer evaporation. (author)

  11. Measurement of nucleation site density, bubble departure diameter and frequency in pool boiling of water using high-speed infrared and optical cameras

    International Nuclear Information System (INIS)

    Gerardi, Craig; Buongiorno, Jacopo; Hu, Lin-wen; McKrell, Thomas

    2009-01-01

    A high-speed video and IR thermometry based technique has been used to obtain time and space resolved information on bubble nucleation and boiling heat transfer. This approach provides a fundamental and systematic method for investigating nucleate boiling in a very detailed fashion. Data on bubble departure diameter and frequency, growth and wait times, and nucleation site density are measured with relative ease. The data have been compared to the traditional decades-old and poorly-validated nucleate-boiling models and correlations. The agreement between the data and the models is relatively good. This study also shows that new insights into boiling heat transfer mechanisms can be obtained with the present technique. For example, our data and analysis suggest that a large contribution to bubble growth comes from heat transfer through the superheated liquid layer in addition to micro layer evaporation. (author)

  12. Experimental study of nucleate pool boiling heat transfer of water on silicon oxide nanoparticle coated copper heating surface

    International Nuclear Information System (INIS)

    Das, Sudev; Kumar, D.S.; Bhaumik, Swapan

    2016-01-01

    Highlights: • EBPVD approach was employed for fabrication of well-ordered nanoparticle coated micro/nanostructure on metal surface. • Nucleate boiling heat transfer performance on nanoparticle coated micro/nanostructure surface was experimentally studied. • Stability of nanoparticle coated surface under boiling environment was systematically studied. • 58% enhancement of boiling heat transfer coefficient was found. • Present experimental results are validated with well known boiling correlations. - Abstract: Electron beam physical vapor deposition (EBPVD) coating approach was employed for fabrication of well-ordered of nanoparticle coated micronanostructures on metal surfaces. This paper reports the experimental study of augmentation of pool boiling heat transfer performance and stabilities of silicon oxide nanoparticle coated surfaces with water at atmospheric pressure. The surfaces were characterized with respect to dynamic contact angle, surface roughness, topography, and morphology. The results were found that there is a reduction of about 36% in the incipience superheat and 58% enhancement in heat transfer coefficient for silicon oxide coated surface over the untreated surface. This enhancement might be the reason of enhanced wettability, enhanced surface roughness and increased number of a small artificial cavity on a heating surface. The performance and stability of nanoparticle coated micro/nanostructure surfaces were examined and found that after three runs of experiment the heat transfer coefficient with heat flux almost remain constant.

  13. Thermal behavior in the transition region between nucleate and film boiling

    International Nuclear Information System (INIS)

    Adiutori, E.F.

    1991-01-01

    The prediction of post Critical Heat Flux (CHF) behavior is complicated by the highly nonlinear thermal behavior of boiling interfaces--ie by the nonlinear nature of the boiling curve. Nonlinearity in the boiling curve can and does cause thermal instability, resulting in temperature discontinuities. Thus the prediction of post CHF behavior requires the analysis of thermal stability. This in turn requires an accurate description of thermal behavior in transition boiling. This paper determines thermal behavior in transition boiling by analysis of literature data. It also describes design features which improve post CHF performance and are reported in the literature

  14. An Experimental Study on the Onset of Nucleate Boiling in Narrow Rectangular Channels for Downward Flow

    International Nuclear Information System (INIS)

    Song, Jung-Hyun; Lee, Juhyung; Jeong, Yong Hoon; Chang, Soon Heung

    2014-01-01

    As the research reactors operates with downward flow, they have some advantages; downward flow can reduce the radioisotopes in the upper part of research reactor and simplify the locking mechanism as countervailing the buoyancy force on the nuclear fuel. However, as the research reactor operates under the low pressure condition, the premature critical heat flux (CHF) can occur during the onset of flow instability (OFI) according to circumstances as the pressure fluctuates significantly. For that reason, it is important to know and set the margin for the onset of nucleate boiling (ONB) which is the preceding phenomena of OFI and CHF to predict and handle with OFI. In addition, research reactor is the nuclear reactor serves neutron source for many research fields such as neutron scattering, non-destructive testing, radioisotope treatment and so on, it is important to avoid ONB to get stable neutron source. IAEA also recommends for research reactors to have enough ONB margin to maintain the normal operation state in 'IAEA-TECDOC-233' (1980). Though the ONB in research reactor is emphasized for these reasons, there isn't sufficient ONB data under downward flow condition and no ONB prediction correlation for downward flow as well. In addition, in many researches; Mosyak et al., Hapke et al., Wu et al. and Hong et al., the existing ONB correlations are not suitable for narrow rectangular channel. In the present work, not only a new ONB prediction correlation would be developed, but also comparison between new correlation with several ONB correlations would be shown. In this paper, ONB data would be analyzed to develop new ONB prediction correlation

  15. Measurement and analysis of bubble behavior in subcooled nucleate boiling flow field with high fidelity imaging system

    International Nuclear Information System (INIS)

    Wu, W.; Jones, B.G.; Newell, T.A.

    2004-01-01

    Axial offset anomaly (AOA) is an unexpected deviation in the core axial power distribution from the predicted curve. AOA is a current major consideration for reactors operating at increased power levels and is becoming immediate threat to nuclear power's competitiveness in the market. Despite much effort focusing on this topic, a comprehensive understanding is far from being developed. However, previous research indicates first, that a close connection exists between subcooled nucleate boiling occurring in core region and the formation of crud, which directly results in AOA phenomena, secondly, that deposition is greater, and sometimes much greater, on heated than on unheated surfaces. A number of researchers have suggested that boiling promotes deposition, and several observed increased deposition in the subcooled boiling region. Limited detailed information is available on the interaction between heat and mass transfer in subcooled nucleate boiling (SNB) flow. Bubbles formed in SNB region play an important role in helping the formation of crud. This research examines bubble behavior under SNB condition from the dynamic point of view, using a high fidelity digital imaging apparatus. Freon R-134a is chosen as a simulant fluid due to its merit of having smaller surface tension and lower boiling temperature. The apparatus is operated at reduced pressure. Series of images at frame rates up to 4000 frames/s were obtained, showing different characteristics of bubble behavior with varying experimental parameters e.g. flow velocity, fluid subcooled level, etc. Analyses that combine the experimental results with analytical result on flow field in velocity boundary layer are considered. A tentative suggestion is that a rolling movement of a bubble accompanies its sliding along the heating surface in the flow channel. Numerical computations using FLUENT v5.5 have been performed to support this conclusion

  16. Experimental Investigation of the Combined Effects of Heat Exchanger Geometries on Nucleate Pool Boiling Heat Transfer in a Scaled IRWST

    International Nuclear Information System (INIS)

    Kang, Myeong Gie; Chun, Moon Hyun

    1996-01-01

    In an effort to determine the combined effects of major parameters of heat exchanger tubes on the nucleate pool boiling heat transfer in the scaled in-containment refueling water storage tank (IRWST), a total of 1,966 data for q v ersus ΔT has been obtained using various combinations of tube diameters, surface roughness, and tube orientations. The experimental results show that (1) increased surface roughness enhances heat transfer for both horizontal and vertical tubes, (2) the two heat transfer mechanisms, i.e.,enhanced heat transfer for both horizontal and vertical tubes, (2) the two heat transfer mechanisms, i.e., enhanced heat transfer due to liquid agitation by bubbles generated and reduced heat transfer by the formation of large vapor slugs and bubble coalescence are different in two regions of low heat fluxes (q ≤ 50kW/m 2 ) and high heat fluxes (q > 50kW/m 2 ) depending on the orientation of tubes and the degree of surface roughness, and (3) the heat transfer rate decreases as the tube diameter is increased for both horizontal and vertical tubes, but the effect of tube diameter on the nucleate pool boiling heat transfer for vertical tubes is greater than that for horizontal tubes. Two empirical heat transfer correlations for q , one for horizontal tubes and the other for vertical tubes, are obtained in terms of surface roughness (ε) and tube diameter (D). In addition, a simple empirical correlation for nucleate pool boiling heat transfer coefficient (h b ) is obtained as a function of heat flux (q ) only. 9 figs., 4 tabs., 15 refs. (Author)

  17. Early detection of nucleate boiling and spectral analysis of acoustical noise

    International Nuclear Information System (INIS)

    Bouneder, M.

    1987-01-01

    The development of a reliable detection technique for the onset of boiling has been further pursued. Besides the already studied tube geometry, a more realistic annular set up has been used where a fuel pin model, electrically heated, is placed. Using accelerometers on the pin, on the structure and on specific instrumentation cables the onset of boiling was clearly monitored by the emergence of a typical resonance frequency. The influence of pressure and heat power was analysed in detail. Furthermore, a glass model has been constructed in order to better correlate the observed measurement with the boiling parameters, as bubble radius, frequency and collapse mode

  18. A study on bubble detachment and the impact of heated surface structure in subcooled nucleate boiling flows

    International Nuclear Information System (INIS)

    Wu Wen; Chen Peipei; Jones, Barclay G.; Newell, Ty A.

    2008-01-01

    This study examines the bubble detachment phenomena under subcooled nucleate boiling conditions, in order to obtain a better understanding of the bubble dynamics on horizontal flat heat exchangers. Refrigerant R134a is chosen as a simulant fluid due to its merits of having smaller surface tension, reduced latent heat, and lower boiling temperature than water. Experiments are run with varying experimental parameters, e.g. pressure, inlet subcooled level, flow rate, etc. Digital images are obtained at frame rates up to 4000 frames/s, showing the characteristics of bubble movements. Bubble departure and bubble lift-off, which are described as bubbles detaching from the original nucleation sites and bubbles detaching from the horizontal heated surface respectively, are both considered and measured. Results are compared against the model proposed by Klausner et al. for the prediction of bubble detachment sizes. While good overall agreement is shown, it is suggested that finite rather than zero bubble contact area should be assumed, which improves the model prediction at the pressure range of 300-500 kPa while playing no significant role at a lower pressure of 150 kPa where the model was originally benchmarked. The impact of heated surface structure is studied whose results provide support to the above assumption

  19. Nucleate pool boiling: High gravity to reduced gravity; liquid metals to cryogens

    Science.gov (United States)

    Merte, Herman, Jr.

    1988-01-01

    Requirements for the proper functioning of equipment and personnel in reduced gravity associated with space platforms and future space station modules introduce unique problems in temperature control; power generation; energy dissipation; the storage, transfer, control and conditioning of fluids; and liquid-vapor separation. The phase change of boiling is significant in all of these. Although both pool and flow boiling would be involved, research results to date include only pool boiling because buoyancy effects are maximized for this case. The effective application of forced convection boiling heat transfer in the microgravity of space will require a well grounded and cogent understanding of the mechanisms involved. Experimental results are presented for pool boiling from a single geometrical configuration, a flat surface, covering a wide range of body forces from a/g = 20 to 1 to a/g = 0 to -1 for a cryogenic liquid, and from a/g = 20 to 1 for water and a liquid metal. Similarities in behavior are noted for these three fluids at the higher gravity levels, and may reasonably be expected to continue at reduced gravity levels.

  20. Semi-transparent gold film as simultaneous surface heater and resistance thermometer for nucleate boiling studies

    International Nuclear Information System (INIS)

    Oker, E.; Merte, H. Jr.

    1981-01-01

    A large (22 x 25 mm) semi-transparent thin film of gold, approximately 400 A in thickness, is deposited on a glass substrate for simultaneous use as a heat source and resistance thermometer. Construction techniques and calibration procedures are described, and a sample application to a transient boiling process is included with simultaneous high speed photographs taken through the thin film from beneath

  1. Local-Scale Simulations of Nucleate Boiling on Micrometer Featured Surfaces: Preprint

    Energy Technology Data Exchange (ETDEWEB)

    Sitaraman, Hariswaran [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Moreno, Gilberto [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Narumanchi, Sreekant V [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Dede, Ercan M. [Toyota Research Institute of North America; Joshi, Shailesh N. [Toyota Research Institute of North America; Zhou, Feng [Toyota Research Institute of North America

    2017-08-03

    A high-fidelity computational fluid dynamics (CFD)-based model for bubble nucleation of the refrigerant HFE7100 on micrometer-featured surfaces is presented in this work. The single-fluid incompressible Navier-Stokes equations, along with energy transport and natural convection effects are solved on a featured surface resolved grid. An a priori cavity detection method is employed to convert raw profilometer data of a surface into well-defined cavities. The cavity information and surface morphology are represented in the CFD model by geometric mesh deformations. Surface morphology is observed to initiate buoyancy-driven convection in the liquid phase, which in turn results in faster nucleation of cavities. Simulations pertaining to a generic rough surface show a trend where smaller size cavities nucleate with higher wall superheat. This local-scale model will serve as a self-consistent connection to larger device scale continuum models where local feature representation is not possible.

  2. Local-Scale Simulations of Nucleate Boiling on Micrometer-Featured Surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Sitaraman, Hariswaran [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Moreno, Gilberto [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Narumanchi, Sreekant V [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Dede, Ercan M. [Toyota Research Institute of North America; Joshi, Shailesh N. [Toyota Research Institute of North America; Zhou, Feng [Toyota Research Institute of North America

    2017-07-12

    A high-fidelity computational fluid dynamics (CFD)-based model for bubble nucleation of the refrigerant HFE7100 on micrometer-featured surfaces is presented in this work. The single-fluid incompressible Navier-Stokes equations, along with energy transport and natural convection effects are solved on a featured surface resolved grid. An a priori cavity detection method is employed to convert raw profilometer data of a surface into well-defined cavities. The cavity information and surface morphology are represented in the CFD model by geometric mesh deformations. Surface morphology is observed to initiate buoyancy-driven convection in the liquid phase, which in turn results in faster nucleation of cavities. Simulations pertaining to a generic rough surface show a trend where smaller size cavities nucleate with higher wall superheat. This local-scale model will serve as a self-consistent connection to larger device scale continuum models where local feature representation is not possible.

  3. International Benchmark based on Pressurised Water Reactor Sub-channel and Bundle Tests. Volume III: Departure from Nucleate Boiling

    International Nuclear Information System (INIS)

    Rubin, Adam; Avramova, Maria; Velazquez-Lozada, Alexander

    2016-03-01

    This report summarised the second phase of the Nuclear Energy Agency (NEA) and the Nuclear Regulatory Commission (NRC) Benchmark Based on NUPEC PWR Sub-channel and Bundle Tests (PSBT), which was intended to provide data for the verification of Departure from Nucleate Boiling (DNB) prediction in existing thermal-hydraulics codes and provide direction in the development of future methods. This phase was composed of three exercises; Exercise 1: fluid temperature benchmark, Exercise 2: steady-state rod bundle benchmark and Exercise 3: transient rod bundle benchmark. The experimental data provided to the participants of this benchmark is from a series of void measurement tests using full-size mock-up tests for both BWRs and PWRs. These tests were performed from 1987 to 1995 by the Nuclear Power Engineering Corporation (NUPEC) in Japan and made available by the Japan Nuclear Energy Safety Organisation (JNES) for the purposes of this benchmark, which was organised by Pennsylvania State University. Nine institutions from seven countries participated in this benchmark. Nine different computer codes were used in Exercise 1, 2 and 3. Among the computer codes were porous media, sub-channel and systems thermal-hydraulic code. The improvement between FLICA-OVAP (sub-channel) and FLICA (sub-channel) was noticeable. The main difference between the two was that FLICA-OVAP implicitly assigned flow regime based on drift flux, while FLICA assumes single phase flows. In Exercises 2 and 3, the codes were generally able to predict the Departure from Nucleate Boiling (DNB) power as well as the axial location of the onset of DNB (for the steady-state cases) and the time of DNB (for the transient cases). It was noted that the codes that used the Electric-Power-Research- Institute (EPRI) Critical-Heat-Flux (CHF) correlation had the lowest mean error in Exercise 2 for the predicted DNB power

  4. CFD investigation of nucleate boiling in non-circular geometries at high pressure

    Energy Technology Data Exchange (ETDEWEB)

    Thakrar, R., E-mail: rkt08@imperial.ac.uk; Murallidharan, J.; Walker, S.P.

    2017-02-15

    Highlights: • Blind CFD benchmark of high-pressure boiling test case in rectangular geometry. • Influence of turbulence, wall boiling, interfacial area transport and lift force modelling examined. • Good agreement of the area-averaged void with the most mechanistic approaches. • Transition from wall to core void peaking due to regime transition captured only in part. - Abstract: Boiling flows are commonplace in the nuclear industry. Computational Fluid Dynamics (CFD) is slowly beginning to be used to deliver the relevant two-phase thermal hydraulic analyses required for nuclear applications. This paper presents a blind assessment of the capabilities of the commercial CFD code STAR-CCM+ against measurements for a vertically upward mildly subcooled boiling flow approaching saturation in a rectangular channel at a pressure of 41 bar. The available measurements comprised transverse distributions and cross-sectional area averages of void fraction at numerous axial positions along the channel. The predictive ability of several combinations of turbulence, wall heat flux partitioning, interfacial area transport and lift force models was tested. In general, good agreement was obtained for the area-averaged void, with the most mechanistic modelling combination reproducing the measurements accurately. Reasonable agreement was also observed for the distributions of transverse void, however this agreement could not be maintained beyond the channel entrance. The transition from near-wall to core void peaking exhibited in the experiments, attributable presumably to a bubbly to churn-turbulent flow regime transition, could not be reproduced accurately with any of the modelling combinations used, and the basic qualitative trend was captured only in part. Suggestions for future investigation are outlined subsequently.

  5. Analysis of heat transfer under high heat flux nucleate boiling conditions

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Y.; Dinh, N. [3145 Burlington Laboratories, Raleigh, NC (United States)

    2016-07-15

    Analysis was performed for a heater infrared thermometric imaging temperature data obtained from high heat flux pool boiling and liquid film boiling experiments BETA. With the OpenFOAM solver, heat flux distribution towards the coolant was obtained by solving transient heat conduction of heater substrate given the heater surface temperature data as boundary condition. The so-obtained heat flux data was used to validate them against the state-of-art wall boiling model developed by D. R. Shaver (2015) with the assumption of micro-layer hydrodynamics. Good agreement was found between the model prediction and data for conditions away from the critical heat flux (CHF). However, the data indicate a different heat transfer pattern under CHF, which is not captured by the current model. Experimental data strengthen the notion of burnout caused by the irreversible hot spot due to failure of rewetting. The observation forms a basis for a detailed modeling of micro-layer hydrodynamics under high heat flux.

  6. Analysis of heat transfer under high heat flux nucleate boiling conditions

    International Nuclear Information System (INIS)

    Liu, Y.; Dinh, N.

    2016-01-01

    Analysis was performed for a heater infrared thermometric imaging temperature data obtained from high heat flux pool boiling and liquid film boiling experiments BETA. With the OpenFOAM solver, heat flux distribution towards the coolant was obtained by solving transient heat conduction of heater substrate given the heater surface temperature data as boundary condition. The so-obtained heat flux data was used to validate them against the state-of-art wall boiling model developed by D. R. Shaver (2015) with the assumption of micro-layer hydrodynamics. Good agreement was found between the model prediction and data for conditions away from the critical heat flux (CHF). However, the data indicate a different heat transfer pattern under CHF, which is not captured by the current model. Experimental data strengthen the notion of burnout caused by the irreversible hot spot due to failure of rewetting. The observation forms a basis for a detailed modeling of micro-layer hydrodynamics under high heat flux.

  7. A New Correlation to Predict Nucleate Pool Boiling Heat Transfer in Vertical Annuli with Closed Bottoms

    International Nuclear Information System (INIS)

    Kang, Myeong Gie

    2012-01-01

    It is important to find a way of enhancing heat transfer coefficients if the space for heat exchanger installation is limited, as it is in advanced light water reactors. One of the effective methods to increase heat transfer coefficients ( h b ) of pool boiling is to consider a confined space. It is well known from the literature that the confined boiling is an effective technique to enhance heat transfer. Once the flow inlet at the tube bottom is closed, a very rapid increase in heat transfer coefficient is observed at low heat fluxes ( q ' ). The similar tendency is observed regardless of the geometric shape. Yao and Chang and Kang investigated a vertical annulus while Rops et al. investigated a confined plate. Fujita et al., in other wise, used parallel plates with side and bottom inflow is restricted. Around the upper region of the annulus with closed bottoms the downward liquid interrupts the upward movement of the bubble slugs. Thereafter, bubbles are coalescing into much bigger bubbles while fluctuating up and down in the annular space. As the heat flux increases (1) the isolate bubble region, (2) the coalesced big size bubble region, and (3) the dryout region is observed in series. The major causes of the heat transfer enhancement are related with the liquid film evaporation and active liquid agitation. Literature review on the previous studies about crevice effects on pool boiling denotes that heat transfer is highly dependent on the geometric parameters. Therefore, it is necessary to quantify the effect of each geometric parameter to estimate heat transfer coefficients accurately. Although some correlations were developed to predict pool boiling heat transfer in confined spaces based on open bottoms, the application of them to a confined space with closed bottoms could result in much error. To overcome the limits of the published correlations, Kang developed a correlation to predict pool boiling heat transfer in annuli with closed bottoms. However, the

  8. A study of vapor bubble departure in subcooled flow boiling at low pressure

    International Nuclear Information System (INIS)

    Donevski, Bozin; Saga, Tetsuo; Kobayashi, Toshio; Segawa, Shigeki

    1999-01-01

    An experimental study of vapor bubble dynamics in sub-cooled flow boiling was conducted using the flow visualization and digital image processing methods. Vapor bubble departure departure in subcooled flow boiling have been experimentally investigated over a range of mass flux G=0.384 (kg/m 2 s), and heat flux q w = 27.2 x 10 4 (W/m 2 ), for the subcooled flow boiling region. It has been observed that once a vapor bubble departs from a nucleation site, it typically slides along the heating surface at sonic finite distance down-stream of nucleation site. The image processing method proposed in this study is based on the detachment and tracing of the edges of the bubbles and their background. The proposed method can be used in various fields of engineering applications. (Original)

  9. Heat transfer correlation development and assessment: a summary and assessment of return to nucleate boiling phenomena during blowdown tests conducted at the Idaho National Engineering Laboratory (INEL)

    International Nuclear Information System (INIS)

    Eaton, A.M.; Tolman, E.L.

    1979-04-01

    The data are presented which were obtained in Loss-of-Coolant Experiments (LOCE) at Idaho National Engineering Laboratory (INEL) which demonstrate the presence of cladding rewetting after the critical heat flux has been exceeded as a viable cooling mechanism during the blowdown phase of a LOCE. A brief review of the mechanisms associated with the boiling crisis and rewetting is also provided. The relevance of INEL LOCE rewetting data to nuclear reactor licensing Evaluation Model Requirements is considered, and the conclusion is made that the elimination of rewetting and return to nucleate boiling (RNB) in Evaluation Models represents a definite conservatism

  10. Reference Computational Meshing Strategy for Computational Fluid Dynamics Simulation of Departure from Nucleate BoilingReference Computational Meshing Strategy for Computational Fluid Dynamics Simulation of Departure from Nucleate Boiling

    Energy Technology Data Exchange (ETDEWEB)

    Pointer, William David [ORNL

    2017-08-01

    The objective of this effort is to establish a strategy and process for generation of suitable computational mesh for computational fluid dynamics simulations of departure from nucleate boiling in a 5 by 5 fuel rod assembly held in place by PWR mixing vane spacer grids. This mesh generation process will support ongoing efforts to develop, demonstrate and validate advanced multi-phase computational fluid dynamics methods that enable more robust identification of dryout conditions and DNB occurrence.Building upon prior efforts and experience, multiple computational meshes were developed using the native mesh generation capabilities of the commercial CFD code STAR-CCM+. These meshes were used to simulate two test cases from the Westinghouse 5 by 5 rod bundle facility. The sensitivity of predicted quantities of interest to the mesh resolution was then established using two evaluation methods, the Grid Convergence Index method and the Least Squares method. This evaluation suggests that the Least Squares method can reliably establish the uncertainty associated with local parameters such as vector velocity components at a point in the domain or surface averaged quantities such as outlet velocity magnitude. However, neither method is suitable for characterization of uncertainty in global extrema such as peak fuel surface temperature, primarily because such parameters are not necessarily associated with a fixed point in space. This shortcoming is significant because the current generation algorithm for identification of DNB event conditions relies on identification of such global extrema. Ongoing efforts to identify DNB based on local surface conditions will address this challenge

  11. Studies in boiling heat transfer in two phase flow through tube arrays: nucleate boiling heat transfer coefficient and maximum heat flux as a function of velocity and quality of Freon-113

    International Nuclear Information System (INIS)

    Rahmani, R.

    1983-01-01

    The nucleate boiling heat-transfer coefficient and the maximum heat flux were studied experimentally as functions of velocity, quality and heater diameter for single-phase flow, and two-phase flow of Freon-113 (trichlorotrifluorethane). Results show: (1) peak heat flux: over 300 measured peak heat flux data from two 0.875-in. and four 0.625-in.-diameter heaters indicated that: (a) for pool boiling, single-phase and two-phase forced convection boiling the only parameter (among hysteresis, rate of power increase, aging, presence and proximity of unheated rods) that has a statistically significant effect on the peak heat flux is the velocity. (b) In the velocity range (0 0 position or the point of impact of the incident fluid) and the top (180 0 position) of the test element, respectively

  12. Feedwater line break accident analysis for SMART in the view point of minimum departure from nucleate boiling ratio

    International Nuclear Information System (INIS)

    Kim Soo Hyoung; Bae, Kyoo Hwan; Chung, Young Jong; Kim, Keung Koo

    2012-01-01

    KAERI and KEPCO consortium had performed standard design of SMART(System integrated Modular Advanced ReacTor) from 2009 to 2011 and obtained standard design approval in July 2012. To confirm the safety of SMART design, all of the safety related design basis events were analyzed. A feedwater line break (FLB) is a postulated accident and is a limiting accident for a decrease in the heat removal by the secondary system in the view point of the peak RCS pressure. It is well known that departure from nucleate boiling ratio (DNBR) increases with the increase of the system pressure for conventional nuclear power plants. But SMART has comparatively lower RCS flow rate, and there is a possibility to show different DNBR behavior depending on the system pressure. To confirm that SMART is safe in case of FLB accident, the Korean nuclear regulatory body required to perform the safety analysis in the view point of minimum DNBR (MDNBR) during the licensing review process for standard design approval (SDA) of SMART design. In this paper, the safety analysis results of the FLB accident for SMART in the view point of MDNBR is described

  13. Feedwater line break accident analysis for SMART in the view point of minimum departure from nucleate boiling ratio

    Energy Technology Data Exchange (ETDEWEB)

    Kim Soo Hyoung; Bae, Kyoo Hwan; Chung, Young Jong; Kim, Keung Koo [KAERI, Daejeon (Korea, Republic of)

    2012-10-15

    KAERI and KEPCO consortium had performed standard design of SMART(System integrated Modular Advanced ReacTor) from 2009 to 2011 and obtained standard design approval in July 2012. To confirm the safety of SMART design, all of the safety related design basis events were analyzed. A feedwater line break (FLB) is a postulated accident and is a limiting accident for a decrease in the heat removal by the secondary system in the view point of the peak RCS pressure. It is well known that departure from nucleate boiling ratio (DNBR) increases with the increase of the system pressure for conventional nuclear power plants. But SMART has comparatively lower RCS flow rate, and there is a possibility to show different DNBR behavior depending on the system pressure. To confirm that SMART is safe in case of FLB accident, the Korean nuclear regulatory body required to perform the safety analysis in the view point of minimum DNBR (MDNBR) during the licensing review process for standard design approval (SDA) of SMART design. In this paper, the safety analysis results of the FLB accident for SMART in the view point of MDNBR is described.

  14. Study of the hovering period and bubble size in fully developed pool nucleate boiling of saturated liquid with a time-dependent heat source

    International Nuclear Information System (INIS)

    Pasamehmetoglu, K.O.; Nelson, R.A.

    1987-01-01

    In this paper, the bubble behavior in saturated pool boiling with a time-dependent heat source is analyzed. The study is restricted to the period from fully developed nucleate boiling until critical heat flux occurs. The hovering period and the departure volume of the bubble are selected as the characteristic parameters for bubble behavior. These parameters are quantified by solving the equation of motion for an idealized bubble. This equation is solved for cases in which the surface heat flux changes linearly and exponentially as a function of time. After nondimensionalization, the results are compared directly with the results of the steady-state problem. The comparison shows that the transient heat input has practically no effect on the hovering period. However, the transient heat flux causes a decreased volume at bubble departure. The volume decrease is dependent on the severity of the transient. These results are in qualitative agreement with the experimental observation quoted in the literature

  15. Preliminary Study of the Onset of Nucleate Boiling (ONB) for the Thermal-hydraulic Design of HANARO Irradiation non-instrumented Capsule during the Natural Convection

    Energy Technology Data Exchange (ETDEWEB)

    Nam, Kyungho [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

    2016-10-15

    The HANARO reactor is an open-tank-in-pool type for easy access, and the capsules are being utilized for the irradiation test of materials and nuclear fuel in HANARO. The concept of the capsule is the direct contact with the coolant to cool the temperature of specimen down. To successfully accomplish the irradiation test, it is essential that the capsule should be designed considering the thermal margin such as the margin to Onset of Nucleate Boiling (ONB), the margin to Departure from Nucleate Boiling (DNB). In this paper, the preliminary study was performed by focusing on the ONB and the capsule design will be performed using the heat flux and temperature at ONB condition calculated in this paper. In this paper, the temperature and heat flux under ONB condition are simply calculated for the thermal design of fuel capsule for irradiation test. These values will be considered to design the non-instrumented capsule for natural circulation. To confirm the calculated value, detailed calculation will be performed using the one dimensional and multi-dimensional codes.

  16. Study of the internal heat transfer of the water flow in nucleate boiling; Estudio de la transferencia de calor del flujo interno de agua en ebullicion nucleada

    Energy Technology Data Exchange (ETDEWEB)

    Payan Rodriguez, Luis Alfredo

    2003-09-01

    In this paper the development of a research project oriented to the analysis of the heat transfer of the water flow in nucleate boiling is presented. Here a mathematical model is described to characterize the water flow in boiling condition in vertical tubes by means of which the temperature distributions in the tube wall and in the water flow are obtained, including the calculation of the pressure drop throughout the tube. In addition, a mechanistic model focused to the prediction of the critical heat flow in vertical tubes uniformly heated was modified to be applied in non-uniform heat flow conditions. The proposed mathematical models were used in a case study derived from a real problem in a thermoelectric power plant, where it was required to simulate the process of boiling in fireplace tubes of the steam generator to determine the causes of the faults that happened in a considerable number of tubes. With the obtained results it was possible to establish that the faults in the tubes of the analyzed steam generator were originated because the heat transfer rate in the fireplace reached critical values that caused the deviation of the nucleate boiling to film boiling, causing the diminution of the heat transfer coefficient with the consequent sudden increase in the tube wall temperature. [Spanish] En este trabajo se presenta el desarrollo de un proyecto de investigacion orientado al analisis de la transferencia de calor en flujo de agua en ebullicion nucleada. Aqui se describe un modelo matematico para caracterizar el flujo de agua en ebullicion en tubos verticales mediante el cual se obtienen las distribuciones de temperatura en la pared del tubo y en el flujo de agua, incluyendo el calculo de la caida de presion a lo largo del tubo. Ademas, un modelo mecanistico enfocado a la prediccion del flujo de calor critico en tubos verticales uniformemente calentados fue modificado para aplicarlo en condiciones de flujo de calor no uniforme. Los modelos matematicos

  17. Analysis of Void Fraction Distribution and Departure from Nucleate Boiling in Single Subchannel and Bundle Geometries Using Subchannel, System, and Computational Fluid Dynamics Codes

    Directory of Open Access Journals (Sweden)

    Taewan Kim

    2012-01-01

    Full Text Available In order to assess the accuracy and validity of subchannel, system, and computational fluid dynamics codes, the Paul Scherrer Institut has participated in the OECD/NRC PSBT benchmark with the thermal-hydraulic system code TRACE5.0 developed by US NRC, the subchannel code FLICA4 developed by CEA, and the computational fluid dynamic code STAR-CD developed by CD-adapco. The PSBT benchmark consists of a series of void distribution exercises and departure from nucleate boiling exercises. The results reveal that the prediction by the subchannel code FLICA4 agrees with the experimental data reasonably well in both steady-state and transient conditions. The analyses of single-subchannel experiments by means of the computational fluid dynamic code STAR-CD with the CD-adapco boiling model indicate that the prediction of the void fraction has no significant discrepancy from the experiments. The analyses with TRACE point out the necessity to perform additional assessment of the subcooled boiling model and bulk condensation model of TRACE.

  18. Experimental study of the effect of the reduced graphene oxide films on nucleate boiling performances of inclined surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Ji Hoon; Kong, Byeong Tak [Incheon National University, Incheon (Korea, Republic of); Kim, Ji Min [POSTECH, Pohang (Korea, Republic of); and others

    2016-05-15

    For the enhancing the CHF, surface coating techniques are available. Yang et al. performed small scale boiling experiments for the vessel lower head, which was coated by aluminum/copper micro particles. Recently, graphene has received much attention for applications in thermal engineering due to its large thermal conductivity. Ahn et al. used a silicon dioxide substrate, which was coated graphene films, as a heating surface during pool boiling experiments. The graphene films inhibited the formation of hot spots, increasing the CHF. For applying novel material 'Graphene' in nuclear industry, here we investigated the effects of graphene film coatings on boiling performances. The experimental pool boiling facility, copying the geometry of lower head of reactor, was designed for verifying orientation effects. The effects of graphene films coating on varied inclined heater surfaces were investigated. The CHF values were increased at every case, but the increased amounts were decreased for downward heater surfaces. At the downward-facing region, however, coating the RGO films would change the CHF mechanisms and boiling heat transfer performances. Generally, RGO films, made by colloidal fabrication, has defects on each flakes.

  19. Experimental study of the effect of the reduced graphene oxide films on nucleate boiling performances of inclined surfaces

    International Nuclear Information System (INIS)

    Kim, Ji Hoon; Kong, Byeong Tak; Kim, Ji Min

    2016-01-01

    For the enhancing the CHF, surface coating techniques are available. Yang et al. performed small scale boiling experiments for the vessel lower head, which was coated by aluminum/copper micro particles. Recently, graphene has received much attention for applications in thermal engineering due to its large thermal conductivity. Ahn et al. used a silicon dioxide substrate, which was coated graphene films, as a heating surface during pool boiling experiments. The graphene films inhibited the formation of hot spots, increasing the CHF. For applying novel material 'Graphene' in nuclear industry, here we investigated the effects of graphene film coatings on boiling performances. The experimental pool boiling facility, copying the geometry of lower head of reactor, was designed for verifying orientation effects. The effects of graphene films coating on varied inclined heater surfaces were investigated. The CHF values were increased at every case, but the increased amounts were decreased for downward heater surfaces. At the downward-facing region, however, coating the RGO films would change the CHF mechanisms and boiling heat transfer performances. Generally, RGO films, made by colloidal fabrication, has defects on each flakes.

  20. Studies on boiling heat transfer on a hemispherical downward heating surface supposing IVR-AM

    International Nuclear Information System (INIS)

    Yoshida, Kenji; Matsumoto, Hiroyuki; Matsumoto, Tadayoshi; Kataoka, Isao

    2006-01-01

    The scale-down experiments supposing the IVR-AM were made on the pool boiling heat transfer from hemispherical downward facing heating surface. The boiling phenomena were realized by flooding the heated hemispherical vessel into the sub-cooled water or saturated water under the atmospheric pressure. The hemispherical vessel supposing the scale-down pressure vessel was made of SUS304 stainless steel. Molten lead, which was preheated up to about 500 degrees Celsius, was put into the vessel and used as the heat source. The vessel was cooled down by flooding into the water to realize the quenching process. The direct observation by using the digital video camera was performed and made clear the special characteristics of boiling phenomena such as the film boiling, the transition boiling and the nucleate boiling taking place in order during the cooling process. The measurement for the wall superheat and heat flux by using thermocouples was also carried out to make clear the boiling heat transfer characteristics during the cooling process. Fifteen thermocouples are inserted in the wall of the hemispherical bowl to measure the temperature distributions and heat flux in the hemispherical bowl. (author)

  1. An Experimental Study on the Convective Heat Transfer in Narrow Rectangular Channels for Downward Flow to Predict Onset of Nucleate Boiling

    International Nuclear Information System (INIS)

    Song, Junghyun; Jeong, Yong Hoon; Lee, Juhyung; Chang, Soon Heung

    2014-01-01

    Research reactor is the nuclear reactor serves neutron source for many research fields such as neutron scattering, non-destructive testing, radioisotope treatment and so on. Due to that characteristic of research reactor, as many people work around the research reactor, research reactor should be designed to have much more conservative margin for normal operation. Boiling heat transfer is the one of the most efficient type in heat transfer modes, however, research reactor needs to avoid onset of nucleate boiling (ONB) in normal operation as IAEA recommend for research reactors to have enough ONB margin to maintain the normal operation state in 'IAEA-TECDOC-233' (1980) for the same reason explained above. Jordan Research and Training Reactor (JRTR) operates under downward flow in narrow rectangular channel in fuel assembly. There isn't sufficient heat transfer data under downward flow condition and only few ONB prediction correlation as well. In the present work, not only a new ONB prediction model would be developed, but also comparison between heat transfer data with several heat transfer correlations could be shown. In addition, as Sudo and Omar S. proposed differently about the Nusselt number behaviors in upward and downward convective heat transfer, the study of convective heat transfer should be conducted continuously to determine it exactly. In this paper, single-phase heat transfer data is analyzed by several heat transfer correlations before developing ONB prediction correlation. In this study, an experiment on the single-phase heat transfer was conducted. As shown in Fig. 5, comparison between experimental data and existing correlations shows quite huge difference as about 40%. Additional experiments on single-phase heat transfer at low heat flux are necessary to clarify the tendency of Nusselt number among heat flux and to develop new correlation for single-phase heat transfer

  2. Dry patch formed boiling and burnout in potassium pool boiling

    International Nuclear Information System (INIS)

    Michiyoshi, I.; Takenaka, N.; Takahashi, O.

    1986-01-01

    Experimental results are presented on dry patch formed boiling and burnout in saturated potassium pool boiling on a horizontal plane heater for system pressures from 30 to 760 torr and liquid levels from 5 to 50 mm. The dry patch formation occurs in the intermittent boiling which is often encountered when liquid alkali metals are used under relatively low pressure conditions. Burnout is caused from both continuous nucleate and dry patch formed boiling. The burnout heat flux together with nucleate boiling heat transfer coefficients are empirically correlated with system pressures. A model is also proposed to predict the minimum heat flux to form the dry patch. (author)

  3. influence of sub-cooling on the energy performance of two eco

    African Journals Online (AJOL)

    PUBLICATIONS1

    frigerants, consistently exhibited better performance than R22 in sub-cooling heat ... 2014 Kwame Nkrumah University of Science and Technology (KNUST) ... sales volume among all refrigerants. .... The sub-cooling heat exchanger affects the.

  4. Downward transfer of a sub-cooled cryoliquid

    CERN Document Server

    Wertelaers, P

    2016-01-01

    An alternative is proposed to the traditional transfer of a cryo fluid in gaseous -- and warm -- form, a method of low productivity and high energy cost. In order to prevent the much-feared geysering, focus is on sub-cooling of the liquid, and the safe maintaining of such state all along the journey. A cryogenic transfer line of simplest construction is proposed, and the difficulties with such line extending over a transfer depth of the order of the kilometre, are discussed.

  5. Best estimate plus uncertainty analysis of departure from nucleate boiling limiting case with CASL core simulator VERA-CS in response to PWR main steam line break event

    Energy Technology Data Exchange (ETDEWEB)

    Brown, C.S., E-mail: csbrown3@ncsu.edu [Department of Nuclear Engineering, North Carolina State University, 2500 Stinson Drive, Raleigh, NC 27695-7909 (United States); Zhang, H., E-mail: Hongbin.Zhang@inl.gov [Idaho National Laboratory, P.O. Box 1625, Idaho Falls, ID 83415-3870 (United States); Kucukboyaci, V., E-mail: kucukbvn@westinghouse.com [Westinghouse Electric Company, 1000 Westinghouse Drive, Cranberry Township, PA 16066 (United States); Sung, Y., E-mail: sungy@westinghouse.com [Westinghouse Electric Company, 1000 Westinghouse Drive, Cranberry Township, PA 16066 (United States)

    2016-12-01

    Highlights: • Best estimate plus uncertainty (BEPU) analyses of PWR core responses under main steam line break (MSLB) accident. • CASL’s coupled neutron transport/subchannel code VERA-CS. • Wilks’ nonparametric statistical method. • MDNBR 95/95 tolerance limit. - Abstract: VERA-CS (Virtual Environment for Reactor Applications, Core Simulator) is a coupled neutron transport and thermal-hydraulics subchannel code under development by the Consortium for Advanced Simulation of Light Water Reactors (CASL). VERA-CS was applied to simulate core behavior of a typical Westinghouse-designed 4-loop pressurized water reactor (PWR) with 17 × 17 fuel assemblies in response to two main steam line break (MSLB) accident scenarios initiated at hot zero power (HZP) at the end of the first fuel cycle with the most reactive rod cluster control assembly stuck out of the core. The reactor core boundary conditions at the most DNB limiting time step were determined by a system analysis code. The core inlet flow and temperature distributions were obtained from computational fluid dynamics (CFD) simulations. The two MSLB scenarios consisted of the high and low flow situations, where reactor coolant pumps either continue to operate with offsite power or do not continue to operate since offsite power is unavailable. The best estimate plus uncertainty (BEPU) analysis method was applied using Wilks’ nonparametric statistical approach. In this demonstration of BEPU application, 59 full core simulations were performed for each accident scenario to provide the minimum departure from nucleate boiling ratio (MDNBR) at the 95/95 (95% probability with 95% confidence level) tolerance limit. A parametric goodness-of-fit approach was also applied to the results to obtain the MDNBR value at the 95/95 tolerance limit. Initial sensitivity analysis was performed with the 59 cases per accident scenario by use of Pearson correlation coefficients. The results show that this typical PWR core

  6. Best estimate plus uncertainty analysis of departure from nucleate boiling limiting case with CASL core simulator VERA-CS in response to PWR main steam line break event

    International Nuclear Information System (INIS)

    Brown, C.S.; Zhang, H.; Kucukboyaci, V.; Sung, Y.

    2016-01-01

    Highlights: • Best estimate plus uncertainty (BEPU) analyses of PWR core responses under main steam line break (MSLB) accident. • CASL’s coupled neutron transport/subchannel code VERA-CS. • Wilks’ nonparametric statistical method. • MDNBR 95/95 tolerance limit. - Abstract: VERA-CS (Virtual Environment for Reactor Applications, Core Simulator) is a coupled neutron transport and thermal-hydraulics subchannel code under development by the Consortium for Advanced Simulation of Light Water Reactors (CASL). VERA-CS was applied to simulate core behavior of a typical Westinghouse-designed 4-loop pressurized water reactor (PWR) with 17 × 17 fuel assemblies in response to two main steam line break (MSLB) accident scenarios initiated at hot zero power (HZP) at the end of the first fuel cycle with the most reactive rod cluster control assembly stuck out of the core. The reactor core boundary conditions at the most DNB limiting time step were determined by a system analysis code. The core inlet flow and temperature distributions were obtained from computational fluid dynamics (CFD) simulations. The two MSLB scenarios consisted of the high and low flow situations, where reactor coolant pumps either continue to operate with offsite power or do not continue to operate since offsite power is unavailable. The best estimate plus uncertainty (BEPU) analysis method was applied using Wilks’ nonparametric statistical approach. In this demonstration of BEPU application, 59 full core simulations were performed for each accident scenario to provide the minimum departure from nucleate boiling ratio (MDNBR) at the 95/95 (95% probability with 95% confidence level) tolerance limit. A parametric goodness-of-fit approach was also applied to the results to obtain the MDNBR value at the 95/95 tolerance limit. Initial sensitivity analysis was performed with the 59 cases per accident scenario by use of Pearson correlation coefficients. The results show that this typical PWR core

  7. Prediction model for initial point of net vapor generation for low-flow boiling

    International Nuclear Information System (INIS)

    Sun Qi; Zhao Hua; Yang Ruichang

    2003-01-01

    The prediction of the initial point of net vapor generation is significant for the calculation of phase distribution in sub-cooled boiling. However, most of the investigations were developed in high-flow boiling, and there is no common model that could be successfully applied for the low-flow boiling. A predictive model for the initial point of net vapor generation for low-flow forced convection and natural circulation is established here, by the analysis of evaporation and condensation heat transfer. The comparison between experimental data and calculated results shows that this model can predict the net vapor generation point successfully in low-flow sub-cooled boiling

  8. Numerical simulation on the explosive boiling phenomena on the surface of molten metal

    International Nuclear Information System (INIS)

    Chen Deqi; Peng Cheng; Wang Qinghua; Pan Liangming

    2014-01-01

    In this paper, numerical simulation was carried out to investigate the explosive boiling phenomenon on high temperature surface also the influence of vapor growth rate during explosive boiling, vapor condensation in sub-cooled water and the subsequent effect on flowing and heat transfer. The simulation result indicates that the steam on the molten metal surface grows with very high speed, and it pushes away the sub-cooled water around and causes severe flowing. The steam clusters which block the sub-cooled water to rewet the molten metal surface are appearing at the same time. During the growth, lifting off as well as condensation of the steam clusters, the sub-cooled water around is strongly disturbed, and obvious vortexes appear. Conversely, the vortex will influence the steam cluster detachment and cub-cooled water rewetting the metal surface. This simulation visually displays the complex explosive boiling phenomena on the molten metal surface with high temperature. (authors)

  9. Experimental investigation of time and repeated cycles in nucleate pool boiling of alumina/water nanofluid on polished and machined surfaces

    Science.gov (United States)

    Rajabzadeh Dareh, F.; Haghshenasfard, M.; Nasr Esfahany, M.; Salimi Jazi, H.

    2018-06-01

    Pool boiling heat transfer of pure water and nanofluids on a copper block has been studied experimentally. Nanofluids with various concentrations of 0.0025, 0.005 and 0.01 vol.% are employed and two simple surfaces (polished and machined copper surface) are used as the heating surfaces. The results indicated that the critical heat flux (CHF) in boiling of fluids on the polished surface is 7% higher than CHF on the machined surface. In the case of machined surface, the heat transfer coefficient (HTC) of 0.01 vol.% nanofluid is about 37% higher than HTC of base fluid, while in the polished surface the average HTC of 0.01% nanofluid is about 19% lower than HTC of the pure water. The results also showed that the boiling time and boiling cycles on the polished surface changes the heat transfer performance. By increasing the boiling time from 5 to 10 min, the roughness enhances about 150%, but by increasing the boiling time to 15 min, the roughness enhancement is only 8%.

  10. A Review of Wettability Effect on Boiling Heat Transfer Enhancement

    International Nuclear Information System (INIS)

    Seo, Gwang Hyeok; Jeun, Gyoo Dong; Kim, Sung Joong

    2012-01-01

    Critical heat flux (CHF) and nucleate boiling heat transfer coefficient (NBHTC) are the key parameters characterizing pool boiling heat transfer. These variables are complicatedly related to thermal-hydraulic parameters of surface wettability, nucleation site density, bubble departure diameter and frequency, to mention a few. In essence, wettability effect on pool boiling heat transfer has been a major fuel to enhance the CHF. Often, however, the improved wettability effect hinders the nucleate boiling. Thus a comprehensive review of such wettability effect may enlighten a further study in this boiling heat transfer area. Phan et al. described surface wettability effects on boiling heat transfer

  11. Dual-zone boiling process

    International Nuclear Information System (INIS)

    Bennett, D.L.; Schwarz, A.; Thorogood, R.M.

    1987-01-01

    This patent describes a process for boiling flowing liquids in a heat exchanger wherein the flowing liquids is heated in a single heat exchanger to vaporize the liquid. The improvement described here comprises: (a) passing the boiling flowing liquid through a first heat transfer zone of the heat exchanger comprising a surface with a high-convective-heat-transfer characteristic and a higher pressure drop characteristic; and then (b) passing the boiling flowing liquid through a second heat transfer zone of the heat exchanger comprising an essentially open channel with only minor obstructions by secondary surfaces, with an enhanced nucleate boiling heat transfer surface and a lower pressure drop characteristic

  12. A study on boiling heat transfer with mixture boiling from vertical rod fin

    International Nuclear Information System (INIS)

    Kim, M.C.

    1981-01-01

    The purpose of the present study is concerned with the boiling characteristic of variations of the length-diameter ratio on the heat transfer rate where the nucleate boiling and natural convection occurred simultaneously. Circular fins were made with copper rod 32 mm in diameter, and those surfaces were mirror finished. The length-diameter ratio was varied 1 to 6. As a boiling liquid, the distilled water was used in this experiment. The results of this experiment were obtained as below. 1) From the observations, it was confirmed that nucleate boiling and natural convection occurred simultaneously. 2) As the length-diameter ratio increased, the boiling heat transfer rate also augmented. (author)

  13. High-Speed Detection of Onset of Nucleate Boiling of DI Water at Stainless Steel Heated Confined in Narrow Rectangular Vertical Channel

    Energy Technology Data Exchange (ETDEWEB)

    Han, Junkyu; Lee, Yongjae; Kim, Sung Joong [Hanyang Univ., Seoul (Korea, Republic of)

    2014-05-15

    In operational conditions at Section of Safety of Research Reactor in IAEA Safety Standards, there are five items: Safety limits, Safety system settings, Limiting conditions for safe operation, Surveillance requirements and Administrative requirements. ONB is included in Safety System Settings (SSS). Limiting Safety System Settings (LSSS) are some range parameters in SSS. Major findings from this study can be summarized as followings: The ONB heat flux was predicted using B-R, D-B and P-G correlation. It is observed that the ONB heat flux increases with mass flux. In addition to the prediction, the ONB heat flux was measured experimentally. The experimental results are higher heat flux and temperature compared by two predictions at the bubble departure frequency of 450ms. Visualization of the ONB heat flux suggests that incipience of boiling appears earlier. Need to make sure the visual criteria of determination about ONB. Although the heat flux condition of 900kW/m{sup 2} sec have ONB occurrence, the bubbles are nearly no affect to waterway and blocking.

  14. Analysis of boiling

    International Nuclear Information System (INIS)

    Kolev, N.I.

    2011-01-01

    This paper summarizes the author's results in boiling analysis obtained in the last 17 years. It demonstrates that more information can be extracted from the analysis by incorporating even of gross turbulence characteristics consistently in the analysis and appropriate local volume and time averaging. The main findings are: Even in large scale analysis (no direct numerical simulation) the steady and transient averaged turbulence characteristics are necessary to increase the quality of predicting heat and mass transfer. It allows simulating the heat transfer change behind spacer grids analytically which is not the practice up to now. This allows also to simulate the change of the deposition behind the spacer grid and therefore this bring us closer to the mechanistic prediction of dry out. Accurate boiling heat transfer predictions require knowledge on the nucleation characteristics of each particular surface. The pulsation characteristics at the wall controlling the heat transfer are associated with the bubble departure frequencies but not identical with them. Considering the mutual interactions of the bubbles leads to the surprising analytical prediction of the departure from nucleate boiling just by using the mechanisms acting during flow boiling only. The performance of the author's analytical two-phase convection model combined with its analytical nuclide boiling model is proven to have the accuracy of the empirical Chen's model by having the advantage of predicting analytically the internal characteristics of the flow each of it validated by experiment. This is also important for the future use in multiphase CFD where details about the flow field generation have to be also predicted by constitutive relation as summarized in this paper. (author)

  15. Analysis of boiling

    International Nuclear Information System (INIS)

    Kolev, Nikolay Ivanov

    2011-01-01

    This paper summarizes the author's results in boiling analysis obtained in the last 17 years. It demonstrates that more information can be extracted from the analysis by incorporating even of gross turbulence characteristics consistently in the analysis and appropriate local volume and time averaging. The main findings are: Even in large scale analysis (no direct numerical simulation) the steady and transient averaged turbulence characteristics are necessary to increase the quality of predicting heat and mass transfer. It allows to simulate the heat transfer change behind spacer grids analytically which is not the practice up to now. This allows also to simulate the change of the deposition behind the spacer grid and therefore this bring us closer to the mechanistic prediction of dry out. Accurate boiling heat transfer predictions require knowledge on the nucleation characteristics of each particular surface. The pulsation characteristics at the wall controlling the heat transfer are associated with the bubble departure frequencies but not identical with them. Considering the mutual interactions of the bubbles leads to the surprising analytical prediction of the departure from nucleate boiling just by using the mechanisms acting during flow boiling only. The performance of the author's analytical two-phase convection model combined with its analytical nuclide boiling model is proven to have the accuracy of the empirical Chen's model by having the advantage of predicting analytically the internal characteristics of the flow each of it validated by experiment. This is also important for the future use in multiphase CFD where details about the flow field generation have to be also predicted by constitutive relation as summarized in this paper. (author)

  16. Development of an experimental apparatus for boiling analysis

    International Nuclear Information System (INIS)

    Castro, A.J.A. de.

    1984-04-01

    The nucleate boiling is the most interesting boiling regime for practical appliccations, including nuclear reactor engineering. such regime is characterized by very high heat transfer rates with only small surface superheating. An experimental apparatus is developed for studying parameters which affect nucleate boiling. The following parameters are analysed: pressure, fluid velocity and the fluid temperature at the test section entrance. The performance of experimental apparatus is analysed by results and by problems raised by the oeration of setup. (Author) [pt

  17. Measurement of partial discharge inception characteristics in sub-cooled liquid nitrogen

    International Nuclear Information System (INIS)

    Koo, J.Y.; Lee, S.H.; Shin, W.J.; Khan, Umer A.; Oh, S.H.; Seong, J.K.; Lee, B.W.

    2011-01-01

    We measured partial discharge and partial discharge initiation voltage of subcooled liquid nitrogen. Various kinds of test samples have been prepared. Sub-cooled temperature in liquid nitrogen were changed. The number of PD pluses were decreased when 68 K liquid nitrogen was used. Sub-cooled liquid nitrogen has positive effects to suppress PD activities. Partial discharge (PD) measurement is one of the effective diagnostic techniques to predict abnormal high voltage dielectric insulation conditions of the electric equipments. PD diagnostic techniques were also could be utilized to evaluate the conditions of cryogenic dielectric insulation media of high temperature superconducting electric equipment in liquid nitrogen. Generally, liquid nitrogen at 77 K is used as cryogenic and dielectric media for high temperature superconducting devices for high voltage electric power systems. But due to generation of bubbles during quench conditions which cause harmful effect on the properties of liquid nitrogen insulation, sub-cooled nitrogen under 77 K was also employed to suppress bubble formation. In this work, investigation of PD characteristics of sub-cooled liquid nitrogen was conducted in order to clarify the relation between PD inception and the temperature of liquid nitrogen. It was observed that measured PDIV (PD inception voltage) shows little differences according to the sub-cooled temperature of liquid nitrogen, but the magnitude and total numbers of PD has been slightly decreased according the decrease of cooled temperature of liquid nitrogen. From experimental results, it was deduced that the sub-cooled liquid nitrogen from 68 K to 77 K, could be applicable without any considerations of the variation of PDIV.

  18. Enabling Highly Effective Boiling from Superhydrophobic Surfaces

    Science.gov (United States)

    Allred, Taylor P.; Weibel, Justin A.; Garimella, Suresh V.

    2018-04-01

    A variety of industrial applications such as power generation, water distillation, and high-density cooling rely on heat transfer processes involving boiling. Enhancements to the boiling process can improve the energy efficiency and performance across multiple industries. Highly wetting textured surfaces have shown promise in boiling applications since capillary wicking increases the maximum heat flux that can be dissipated. Conversely, highly nonwetting textured (superhydrophobic) surfaces have been largely dismissed for these applications as they have been shown to promote formation of an insulating vapor film that greatly diminishes heat transfer efficiency. The current Letter shows that boiling from a superhydrophobic surface in an initial Wenzel state, in which the surface texture is infiltrated with liquid, results in remarkably low surface superheat with nucleate boiling sustained up to a critical heat flux typical of hydrophilic wetting surfaces, and thus upends this conventional wisdom. Two distinct boiling behaviors are demonstrated on both micro- and nanostructured superhydrophobic surfaces based on the initial wetting state. For an initial surface condition in which vapor occupies the interstices of the surface texture (Cassie-Baxter state), premature film boiling occurs, as has been commonly observed in the literature. However, if the surface texture is infiltrated with liquid (Wenzel state) prior to boiling, drastically improved thermal performance is observed; in this wetting state, the three-phase contact line is pinned during vapor bubble growth, which prevents the development of a vapor film over the surface and maintains efficient nucleate boiling behavior.

  19. Experimental study and modelling of transient boiling

    International Nuclear Information System (INIS)

    Baudin, Nicolas

    2015-01-01

    A failure in the control system of the power of a nuclear reactor can lead to a Reactivity Initiated Accident in a nuclear power plant. Then, a power peak occurs in some fuel rods, high enough to lead to the coolant film boiling. It leads to an important increase of the temperature of the rod. The possible risk of the clad failure is a matter of interest for the Institut de Radioprotection et de Securite Nucleaire. The transient boiling heat transfer is not yet understood and modelled. An experimental set-up has been built at the Institut de Mecanique des Fluides de Toulouse (IMFT). Subcooled HFE-7000 flows vertically upward in a semi annulus test section. The inner half cylinder simulates the clad and is made of a stainless steel foil, heated by Joule effect. Its temperature is measured by an infrared camera, coupled with a high speed camera for the visualization of the flow topology. The whole boiling curve is studied in steady state and transient regimes: convection, onset of boiling, nucleate boiling, critical heat flux, film boiling and rewetting. The steady state heat transfers are well modelled by literature correlations. Models are suggested for the transient heat flux: the convection and nucleate boiling evolutions are self-similar during a power step. This observation allows to model more complex evolutions, as temperature ramps. The transient Hsu model well represents the onset of nucleate boiling. When the intensity of the power step increases, the film boiling begins at the same temperature but with an increasing heat flux. For power ramps, the critical heat flux decreases while the corresponding temperature increases with the heating rate. When the wall is heated, the film boiling heat transfer is higher than in steady state but it is not understood. A two-fluid model well simulates the cooling film boiling and the rewetting. (author)

  20. Some observations on boiling heat transfer with surface oscillation

    International Nuclear Information System (INIS)

    Miyashita, H.

    1992-01-01

    The effects of surface oscillation on pool boiling heat transfer are experimentally studied. Experiments were performed in saturated ethanol and distilled water, covering the range from nucleate to film boiling except in the transition region. Two different geometries were employed as the heating surface with the same wetting area, stainless steel pipe and molybdenum ribbon. The results confirm earlier work on the effect of surface oscillation especially in lower heat flux region of nucleate boiling. Interesting boiling behavior during surface oscillation is observed, which was not referred to in previous work. (2 figures) (Author)

  1. Contribution to the boiling curve of sodium

    International Nuclear Information System (INIS)

    Schins, H.E.J.

    1975-01-01

    Sodium in a pool was preheated to saturation temperatures at system pressures of 200, 350 and 500 torr. A test section of normal stainless steel was then extra heated by means of the conical fitting condenser zone of a heat pipe. Measurements were made of heat transfer fluxes, q in W/cm 2 , as a function of wall excess temperature above saturation, THETA = Tsub(w) - Tsub(s) in 0 C, both, in natural convection and in boiling regimes. These measurements make it possible to select the Subbotin natural convection and nucleate boiling curves among other variants proposed in literature. Further it is empirically demonstrated on water that the minimum film boiling point corresponds to the homogeneous nucleation temperature calculated by the Doering formula. Assuming that the minimum film boiling point of sodium can be obtained in the same manner, it is then possible to give an appoximate boiling curve of sodium for the use in thermal interaction studies. At 1 atm the heat transfer fluxes q versus wall temperatures THETA are for a point on the natural convection curve 0.3 W/cm 2 and 2 0 C; for start of boiling 1.6 W/cm 2 and 6 0 C; for peak heat flux 360 W/cm 2 and 37 0 C; for minimum film boiling 30 W/cm 2 and 905 0 C and for a point on the film boiling curve 160 W/cm 2 and 2,000 0 C. (orig.) [de

  2. Cryogenic system with the sub-cooled liquid nitrogen for cooling HTS power cable

    Energy Technology Data Exchange (ETDEWEB)

    Fan, Y.F. [Chinese Academy of Sciences, Beijing (China). Technical Institute of Physics and Chemistry; Graduate School of Chinese Academy of Sciences, Beijing (China); Gong, L.H.; Xu, X.D.; Li, L.F.; Zhang, L. [Chinese Academy of Sciences, Beijing (China). Technical Institute of Physics and Chemistry; Xiao, L.Y. [Chinese Academy of Sciences, Beijing (China). Institute of Electrical Engineering

    2005-04-01

    A 10 m long, three-phase AC high-temperature superconducting (HTS) power cable had been fabricated and tested in China August 2003. The sub-cooled liquid nitrogen (LN{sub 2}) was used to cool the HTS cable. The sub-cooled LN{sub 2} circulation was built by means of a centrifugal pump through a heat exchanger in the sub-cooler, the three-phase HTS cable cryostats and a LN{sub 2} gas-liquid separator. The LN{sub 2} was cooled down to 65 K by means of decompressing, and the maximum cooling capacity was about 3.3 kW and the amount of consumed LN{sub 2} was about 72 L/h at 1500 A. Cryogenic system design, test and some experimental results would be presented in this paper. (author)

  3. GreenChill Store Certification Protocol for Sub-Cooling Contained on Racks Separate from Refrigeration Equipment

    Science.gov (United States)

    Document describes the protocol used to determine the total load and refrigerant charge of stores that have placed all sub-cooling on a rack separate from all other commercial refrigeration equipment.

  4. Research progresses and future directions on pool boiling heat transfer

    OpenAIRE

    M. Kumar; V. Bhutani; P. Khatak

    2015-01-01

    This paper reviews the previous work carried on pool boiling heat transfer during heating of various liquids and commodities categorized as refrigerants and dielectric fluids, pure liquids, nanofluids, hydrocarbons and additive mixtures, as well as natural and synthetic colloidal solutions. Nucleate pool boiling is an efficient and effective method of boiling because high heat fluxes are possible with moderate temperature differences. It is characterized by the growth of bubbles on a heated s...

  5. Experimental Study on Boiling Crisis in Pool Boiling

    Energy Technology Data Exchange (ETDEWEB)

    Jung, Satbyoul; Kim, Hyungdae [Kyung Hee University, Yongin (Korea, Republic of)

    2016-10-15

    They postulated that failure in re-wetting of a dry patch by a cooling liquid is governed by microhydrodynamics near the wall. Chu et al. commonly observed that active coalescence of newly generated bubbles with preexisting bubbles results in a residual dry patch and prevents the complete rewetting of the dry patch, leading to CHF. In this work, to reveal the key physical mechanism of CHF during the rewetting process of a dry patch, dynamics of dry patches and thermal pattern of a boiling surface are simultaneously observed using TR and IR thermometry techniques. Local dynamics of dry patch and thermal pattern on a boiling surface in synchronized manner for both space and time using TR and IR thermometry were measured during pool boiling of water. Observation and quantitative examination of CHF was performed. - The hydrodynamic and thermal behaviors of irreversible dry patch were observed. The dry patches coalesce into a large dry patch and it locally dried out. Due to the failure of liquid rewetting, the dry patch is not completely rewetted, resulting in the burn out at which temperature is -140°C. - When temperature of a dry patch rises beyond the instantaneous nucleation temperature, several bubbles nucleate at the head of the advancing liquid meniscus and prevents the liquid front, and eventually the overheated dry patch remains alive after the departure of the massive bubble.

  6. An investigation of transition boiling mechanisms of subcooled water under forced convective conditions

    Energy Technology Data Exchange (ETDEWEB)

    Kwang-Won, Lee; Sang-Yong, Lee

    1995-09-01

    A mechanistic model for forced convective transition boiling has been developed to investigate transition boiling mechanisms and to predict transition boiling heat flux realistically. This model is based on a postulated multi-stage boiling process occurring during the passage time of the elongated vapor blanket specified at a critical heat flux (CHF) condition. Between the departure from nucleate boiling (DNB) and the departure from film boiling (DFB) points, the boiling heat transfer is established through three boiling stages, namely, the macrolayer evaporation and dryout governed by nucleate boiling in a thin liquid film and the unstable film boiling characterized by the frequent touches of the interface and the heated wall. The total heat transfer rates after the DNB is weighted by the time fractions of each stage, which are defined as the ratio of each stage duration to the vapor blanket passage time. The model predictions are compared with some available experimental transition boiling data. The parametric effects of pressure, mass flux, inlet subcooling on the transition boiling heat transfer are also investigated. From these comparisons, it can be seen that this model can identify the crucial mechanisms of forced convective transition boiling, and that the transition boiling heat fluxes including the maximum heat flux and the minimum film boiling heat flux are well predicted at low qualities/high pressures near 10 bar. In future, this model will be improved in the unstable film boiling stage and generalized for high quality and low pressure situations.

  7. A dry-spot model of critical heat flux and transition boiling in pool and subcooled forced convection boiling

    International Nuclear Information System (INIS)

    Ha, Sang Jun

    1998-02-01

    A new dry-spot model for critical heat flux (CHF) is proposed. The new concept for dry area formation based on Poisson distribution of active nucleation sites and the critical active site number is introduced. The model is based on the boiling phenomena observed in nucleate boiling such as Poisson distribution of active nucleation sites and formation of dry spots on the heating surface. It is hypothesized that when the number of bubbles surrounding one bubble exceeds a critical number, the surrounding bubbles restrict the feed of liquid to the microlayer under the bubble. Then a dry spot of vapor will form on the heated surface. As the surface temperature is raised, more and more bubbles will have a population of surrounding active sites over the critical number. Consequently, the number of the spots will increase and the size of dry areas will increase due to merger of several dry spots. If this trend continues, the number of effective sites for heat transport through the wall will diminish, and CHF and transition boiling occur. The model is applicable to pool and subcooled forced convection boiling conditions, based on the common mechanism that CHF and transition boiling are caused by the accumulation and coalescences of dry spots. It is shown that CHF and heat flux in transition boiling can be determined without any empirical parameter based on information on the boiling parameters such as active site density and bubble diameter, etc., in nucleate boiling. It is also shown that the present model well represents actual phenomena on CHF and transition boiling and explains the mechanism on how parameters such as flow modes (pool or flow) and surface wettability influence CHF and transition boiling. Validation of the present model for CHF and transition boiling is achieved without any tuning parameter always present in earlier models. It is achieved by comparing the predictions of CHF and heat flux in transition boiling using measured boiling parameters in nucleate

  8. Some specific features of subcooled boiling heat transfer and crisis at extremely high heat flux densities

    International Nuclear Information System (INIS)

    Gotovsky, M.A.

    2001-01-01

    Forced convection boiling is the process used widely in a lot of industry branches including NPP. Heat transfer intensity under forced convection boiling is considered in different way in dependence on conditions. One of main problems for the process considered is an influence of interaction between forced flow and boiling on heat transfer character. For saturated water case a transition from ''pure'' forced convection to nucleate boiling can be realized in smooth form. (author)

  9. Determination of heat transfer coefficient for an interaction of sub-cooled gas and metal

    International Nuclear Information System (INIS)

    Sidek, Mohd Zaidi; Kamarudin, Muhammad Syahidan

    2016-01-01

    Heat transfer coefficient (HTC) for a hot metal surface and their surrounding is one of the need be defined parameter in hot forming process. This study has been conducted to determine the HTC for an interaction between sub-cooled gas sprayed on a hot metal surface. Both experiments and finite element have been adopted in this work. Initially, the designated experiment was conducted to obtain temperature history of spray cooling process. Then, an inverse method was adopted to calculate the HTC value before we validate in a finite element simulation model. The result shows that the heat transfer coefficient for interaction of subcooled gas and hot metal surface is 1000 W/m 2 K. (paper)

  10. High-speed infrared thermography for the measurement of microscopic boiling parameters on micro- and nano-structured surfaces

    International Nuclear Information System (INIS)

    Park, Youngjae; Kim, Hyungdae; Kim, Hyungmo; Kim, Joonwon

    2014-01-01

    Micro- and nano-scale structures on boiling surfaces can enhance nucleate boiling heat transfer coefficient (HTC) and critical heat flux (CHF). A few studies were conducted to explain the enhancements of HTC and CHF using the microscopic boiling parameters. Quantitative measurements of microscopic boiling parameters are needed to understand the physical mechanism of the boiling heat transfer augmentation on structured surfaces. However, there is no existing experimental techniques to conveniently measure the boiling parameters on the structured surfaces because of the small (nucleate pool boiling on micro- and nano-structured surfaces. The visualization results are analyzed to obtain the microscopic boiling parameters. Finally, quantitative microscopic boiling parameters are used to interpret the enhancement of HTC and CHF. In this study, liquid-vapor phase distributions of each surface were clearly visualized by IR thermography during the nucleate boiling phenomena. From the visualization results, following microscopic boiling parameters were quantitatively measured by image processing. - Number density of dry patch, NDP IR thermography technique was demonstrated by nucleate pool boiling experiments with M- and N surfaces. The enhancement of HTC and CHF could be explained by microscopic boiling parameters

  11. Numerical simulation of pool boiling of a Lennard-Jones liquid

    KAUST Repository

    Inaoka, Hajime

    2013-09-01

    We performed a numerical simulation of pool boiling by a molecular dynamics model. In the simulation, a liquid composed of Lennard-Jones particles in a uniform gravitational field is heated by a heat source at the bottom of the system. The model successfully reproduces the change in regimes of boiling from nucleate boiling to film boiling with the increase of the heat source temperature. We present the pool boiling curve by the model, whose general behavior is consistent with those observed in experiments of pool boiling. © 2013 Elsevier B.V. All rights reserved.

  12. Numerical simulation of pool boiling of a Lennard-Jones liquid

    KAUST Repository

    Inaoka, Hajime; Ito, Nobuyasu

    2013-01-01

    We performed a numerical simulation of pool boiling by a molecular dynamics model. In the simulation, a liquid composed of Lennard-Jones particles in a uniform gravitational field is heated by a heat source at the bottom of the system. The model successfully reproduces the change in regimes of boiling from nucleate boiling to film boiling with the increase of the heat source temperature. We present the pool boiling curve by the model, whose general behavior is consistent with those observed in experiments of pool boiling. © 2013 Elsevier B.V. All rights reserved.

  13. Effects of entrained gas on the acoustic detection of sodium boiling in a simulated LMFBR fuel bundle

    International Nuclear Information System (INIS)

    Leavell, W.H.; Sides, W.H.

    1975-01-01

    The relationship between acoustic intensity of nucleate boiling and void fraction was studied in a simulated LMFBR fuel bundle. Results indicate that as the void fraction increases the detected intensity of nucleate boiling decreased until it was indistinguishable from background noise. (JWR)

  14. Flow boiling heat transfer at low liquid Reynolds number

    International Nuclear Information System (INIS)

    Weizhong Zhang; Takashi Hibiki; Kaichiro Mishima

    2005-01-01

    Full text of publication follows: In view of the significance of a heat transfer correlation of flow boiling at conditions of low liquid Reynolds number or liquid laminar flow, and very few existing correlations in principle suitable for such flow conditions, this study is aiming at developing a heat transfer correlation of flow boiling at low liquid Reynolds number conditions. The obtained results are as follows: 1. A new heat transfer correlation has been developed for saturated flow boiling at low liquid Reynolds number conditions based on superimposition of two boiling mechanisms, namely convective boiling and nucleate boiling. In the new correlation, two terms corresponding to the mechanisms of nucleate boiling and convective boiling are obtained from the pool boiling correlation by Forster and Zuber and the analytical annular flow model by Hewitt and Hall-Taylor, respectively. 2. An extensive database was collected for saturated flow boiling heat transfer at low liquid Reynolds number conditions, including data for different channels geometries (circular and rectangular), flow orientations (vertical and horizontal), and working fluids (water, R11, R12, R113). 3. An extensive comparison of the new correlation with the collected database shows that the new correlation works satisfactorily with the mean deviation of 16.6% for saturated flow boiling at low liquid Reynolds number conditions. 4. The detailed discussion reveals the similarity of the newly developed correlation for flow boiling at low liquid Reynolds number to the Chen correlation for flow boiling at high liquid Reynolds number. The Reynolds number factor F can be analytically deduced in this study. (authors)

  15. Pool film boiling heat transfer, 5

    International Nuclear Information System (INIS)

    Sakurai, A.; Shiotsu, M.; Hata, K.

    1981-01-01

    Steady minimum film boiling heat flux and temperature were experimentally studied for a horizontal cylinder test heater in a pool of saturated water under pressures ranging from 0.1 to 2 MPa. Minimum temperature of film boiling may be determined by hydrodynamic Taylor instability for the pressures lower than around 1.0 MPa and by homogeneous nucleation temperature for the higher pressures. However, conventional correlations of minimum heat flux based on the hydrodynamic Taylor instability cannot at all predict the pressure dependency of the experimental data in the lower pressure region. Semi-empirical equation of the minimum heat flux based on the hydrodynamic Taylor instability was given. (author)

  16. Experimental and theoretical studies on subcooled flow boiling of pure liquids and multicomponent mixtures

    Energy Technology Data Exchange (ETDEWEB)

    Jamialahmadi, M.; Abdollahi, H.; Shariati, A. [The University of Petroleum Industry, Ahwaz (Iran); Mueller-Steinhagen, H. [Institute of Technical Thermodynamics, German Aerospace Center (Germany); Institute of Thermodynamics and Thermal Engineering, University of Stuttgart (Germany)

    2008-05-15

    To improve the design of modern industrial reboilers, accurate knowledge of boiling heat transfer coefficients is essential. In this study flow boiling heat transfer coefficients for binary and ternary mixtures of acetone, isopropanol and water were measured over a wide range of heat flux, subcooling, flow velocity and composition. The measurements cover the regimes of convective heat transfer, transitional boiling and fully developed subcooled flow boiling. Two models are presented for the prediction of flow boiling heat transfer coefficients. The first model is the combination of the Chen model with the Gorenflo correlation and the Schluender model for single and multicomponent boiling, respectively. This model predicts flow boiling heat transfer coefficients with acceptable accuracy, but fails to predict the nucleate boiling fraction NBF reasonably well. The second model is based on the asymptotic addition of forced convective and nucleate boiling heat transfer coefficients. The benefit of this model is a further improvement in the accuracy of flow boiling heat transfer coefficient over the Chen type model, simplicity and the more realistic prediction of the nucleate boiling fraction NBF. (author)

  17. Numerical simulation of flow boiling for organic fluid with high saturation temperature in vertical porous coated tube

    Energy Technology Data Exchange (ETDEWEB)

    Yang Dong, E-mail: dyang@mail.xjtu.edu.cn [State Key Laboratory of Multiphase Flow in Power Engineering, Xi' an Jiaotong University, Xi' an, Shaanxi Province 710049 (China); Pan Jie; Wu Yanhua; Chen Tingkuan [State Key Laboratory of Multiphase Flow in Power Engineering, Xi' an Jiaotong University, Xi' an, Shaanxi Province 710049 (China); Zhou, Chenn Q. [Department of Mechanical Engineering, Purdue University Calumet, Hammond, IN 46323 (United States)

    2011-08-15

    Highlights: > A model is developed for the prediction of flow boiling in vertical porous tubes. > The model assumes that the nucleate boiling plays an important role. > The present model can predict most of the experimental values within {+-}20%. > The results indicate the nucleate boiling contribution decreases from 50% to 15%. - Abstract: A semi-analytical model is developed for the prediction of flow boiling heat transfer inside vertical porous coated tubes. The model assumes that the forced convection and nucleate boiling coexist together in the annular flow regime. Conservations of mass, momentum, and energy are used to solve for the liquid film thickness and temperature. The heat flux due to nucleate boiling consists of those inside and outside micro-tunnels. To close the equations, a detailed analysis of various forces acting on the bubble is presented to predict its mean departure diameter. The active nucleation site density of porous layer is determined from the pool boiling correlation by introducing suppression factor. The flow boiling heat transfer coefficients of organic fluid (cumene) with high saturation temperature in a vertical flame-spraying porous coated tube are studied numerically. It is shown that the present model can predict most of the experimental values within {+-}20%. The numerical results also indicate that the nucleate boiling contribution to the overall heat transfer coefficient decreases from 50% to 15% with vapor quality increasing from 0.1 to 0.5.

  18. Comparative analysis of heat transfer correlations for forced convection boiling

    International Nuclear Information System (INIS)

    Guglielmini, G.; Nannei, E.; Pisoni, C.

    1978-01-01

    A critical survey was conducted of the most relevant correlations of boiling heat transfer in forced convection flow. Most of the investigations carried out on partial nucleate boiling and fully developed nucleate boiling have led to the formulation of correlations that are not able to cover a wide range of operating conditions, due to the empirical approach of the problem. A comparative analysis is therefore required in order to delineate the relative accuracy of the proposed correlations, on the basis of the experimental data presently available. The survey performed allows the evaluation of the accuracy of the different calculating procedure; the results obtained, moreover, indicate the most reliable heat transfer correlations for the different operating conditions investigated. This survey was developed for five pressure range (up to 180bar) and for both saturation and subcooled boiling condition

  19. Thermodynamic analysis of hydrocarbon refrigerants in a sub-cooling refrigeration system

    Directory of Open Access Journals (Sweden)

    BUKOLA O. BOLAJI

    2013-06-01

    Full Text Available In this study, the performance simulation of some hydrocarbon refrigerants (R290, R600 and R600a as alternatives to R134a in refrigeration system with sub-cooling is conducted by thermodynamic calculation of performance parameters using the REFPROP software. The results obtained showed that the saturated vapour pressure and temperature characteristic profiles for R600 and R600a are very close to that of R134a. The three hydrocarbon refrigerants exhibited very high refrigerating effect and condenser duty than R134a. The best of these parameters was obtained using R600. The discharge temperatures obtained using R600 and R600a were low, while that of R290 was very much higher. The highest coefficient of performance (COP and relative capacity index were obtained using R600. Average COPs of R600 and R600a are 4.6 and 2.2% higher than that of R134a, respectively. The performances of R600 and R600a in system were better than those of R134a and R290. The best performance was obtained using R600 in the system.

  20. Experimental study on transient boiling heat transfer

    International Nuclear Information System (INIS)

    Visentini, R.

    2012-01-01

    well. A flexible power supply that can generate a free-shape signal, allows to get to a wall-temperature increase rate up to 2500 K/s but also to obtain lower rates, which permits to study weaker transients and steady state conditions. The thermal measurements are realised by means of an infra-red camera and a high-speed camera is employed in order to see the boiling phenomena at the same time. From the voltage and current measurements the heat flux that is passed to the fluid is known. It is possible to underline some of the main results of this work. We found that, even when the boiling onset occurs soon because of the high power, transient conduction is always coupled with transient convection. The boiling onset occurs when the wall superheat is between 10 K et 30 K. This value corresponds to the activation of the smallest nucleation sites at the wall. The literature correlations well fit the nucleate boiling data in steady-state conditions. When the wall-temperature increase rate leads to transient boiling, the heat flux is higher than in steady state. This is consistent with what was found in previous studies. The nucleate boiling phase may last only a few milliseconds when the power is really high and the wall temperature increases really rapidly (500-2000 K/s). The experiments in transient boiling also point out that the heat flux is larger than in steady state conditions for the other regimes: Critical heat flux and also film boiling. The experimental set-up allows to investigate a large range of parameters (wall-temperature increase rate, flow rate, fluid temperature) by means of accurate temperature measurements and visualisations. Some modeling of the heat transfer are also proposed. (author)

  1. A highly stable microchannel heat sink for convective boiling

    International Nuclear Information System (INIS)

    Lu, Chun Ting; Pan Chin

    2009-01-01

    To develop a highly stable two-phase microchannel heat sink, we experimented with convective boiling in diverging, parallel microchannels with different distributions of laser-etched artificial nucleation sites. Each microchannel had a mean hydraulic diameter of 120 µm. The two-phase flow visualization and the magnitudes of pressure drop and inlet temperature oscillations under boiling conditions demonstrated clearly the merits of using artificial nucleation sites to further stabilize the flow boiling in diverging, parallel microchannels. The stability map showed the plane of subcooling number versus phase change number. It illustrated that diverging, parallel microchannels with artificial nucleation cavities have a much wider stable region than parallel microchannels with uniform cross-sections or diverging, parallel microchannels without artificial nucleation cavities. In addition, the results revealed that the design with cavities distributed uniformly along the downstream half of the channel presented the best stability performance among the three distributions of nucleation sites. This particular design can be regarded as a highly stable microchannel heat sink for convective boiling

  2. Applications of artificial neutral network for the prediction of flow boiling curves

    International Nuclear Information System (INIS)

    Su Guanghui; Jia Dounan; Fukuda, Kenji; Morita, Koji; Pidduck, Mark; Matsumoto, Tatsuya; Akasaka, Ryo

    2002-01-01

    An artificial neural network (ANN) was applied successfully to predict flow boiling curves. The databases used in the analysis are from the 1960's, including 1,305 data points which cover these parameter ranges: pressure P=100-1,000 kPa, mass flow rate G=40-500 kg/m 2 ·s, inlet subcooling ΔT sub =0-35degC, wall superheat ΔT w =10-300degC and heat flux Q=20-8,000 kW/m 2 . The proposed methodology allows us to achieve accurate results, thus it is suitable for the processing of the boiling curve data. The effects of the main parameters on flow boiling curves were analyzed using the ANN. The heat flux increases with increasing inlet subcooling for all heat transfer modes. Mass flow rate has no significant effects on nucleate boiling curves. The transition boiling and film boiling heat fluxes will increase with an increase in the mass flow rate. Pressure plays a predominant role and improves heat transfer in all boiling regions except the film boiling region. There are slight differences between the steady and the transient boiling curves in all boiling regions except the nucleate region. The transient boiling curve lies below the corresponding steady boiling curve. (author)

  3. Boiling in microchannels: a review of experiment and theory

    International Nuclear Information System (INIS)

    Thome, John R.

    2004-01-01

    A summary of recent research on boiling in microchannels is presented. The review addresses the topics of macroscale versus microscale heat transfer, two-phase flow regimes, flow boiling heat transfer results for microchannels, heat transfer mechanisms in microchannels and flow boiling models for microchannels. In microchannels, the most dominant flow regime appears to be the elongated bubble mode that can persist up to vapor qualities as high as 60-70% in microchannels, followed by annular flow. Flow boiling heat transfer coefficients have been shown experimentally to be dependent on heat flux and saturation pressure while only slightly dependent on mass velocity and vapor quality. Hence, these studies have concluded that nucleate boiling controls evaporation in microchannels. Instead, a recent analytical study has shown that transient evaporation of the thin liquid films surrounding elongated bubbles is the dominant heat transfer mechanism as opposed to nucleate boiling and is able to predict these trends in the experimental data. Newer experimental studies have further shown that there is in fact a significant effect of mass velocity and vapor quality on heat transfer when covering a broader range of conditions, including a sharp peak at low vapor qualities at high heat fluxes. Furthermore, it is concluded that macroscale models are not realistic for predicting flowing boiling coefficients in microchannels as the controlling mechanism is not nucleate boiling nor turbulent convection but is transient thin film evaporation (also, microchannel flows are typically laminar and not turbulent as assumed by macroscopic models). A more advanced three-zone flow boiling model for evaporation of elongated bubbles in microchannels is currently under development that so far qualitatively describes all these trends. Numerous fundamental aspects of two-phase flow and evaporation remain to be better understood and some of these aspects are also discussed

  4. Cavitational boiling of liquids

    International Nuclear Information System (INIS)

    Kostyuk, V.V.; Berlin, I.I.; Borisov, N.N.; Karpyshev, A.V.

    1986-01-01

    Transition boiling is a term usually denoting the segment of boiling curve 1-2, where the heat flux, q, decreases as the temperature head, ΔT/sub w/=T/sub w/-T/sub s/, increases. Transition boiling is the subject of numerous papers. Whereas most researchers have studied transition boiling of saturated liquids the authors studied for many years transition boiling of liquids subcooled to the saturation temperature. At high values of subcooling, ΔT/sub sub/=T/sub s/-T/sub 1/, an anomalous dependence of the heat flux density on the temperature head was detected. Unlike a conventional boiling curve, where a single heat flux maximum occurs, another maximum is seen in the transition boiling segment, the boiling being accompanied by strong noise. The authors refer to this kind of boiling as cavitational. This process is largely similar to noisy boiling of helium-II. This article reports experimental findings for cavitational boiling of water, ethanol, freon-113 and noisy boiling of helium-II

  5. CARR-CNS with crescent-shape moderator cell and sub-cooling helium jacket around cell

    International Nuclear Information System (INIS)

    Yu, Qingfeng; Feng, Quanke; Kawai, Takeshi; Cheng, Liang; Shen, Feng; Yuan, Luzheng

    2005-01-01

    The new type of the moderator cell was developed for the Cold Neutron Source (CNS) of the China Advanced Research Reactor (CARR) which is now constructing at the China Institute of Atomic Energy in Beijing. A crescent-shape moderator cell covered by the sub-cooling helium jacket is adopted. A crescent-shape would help to increase the volume of the moderator cell for corresponding it to the 4 cold neutron guide tubes, even if liquid hydrogen not liquid deuterium were used as a cold moderator. The sub-cooling helium jacket covering the moderator cell removes the nuclear heating of the outer shell wall of the cell. It contributes to reduce the void fraction of liquid hydrogen in the inner shell. Such a type of a moderator cell is suitable for the CNS with higher nuclear heating. The cold helium gas flows down firstly into the sub-cooling helium jacket and then flows up to the condenser. Therefore, the theory of the self-regulation for the thermo-siphon type of the CNS is also applicable

  6. Strength analysis of CARR-CNS with crescent-shape moderator cell and helium sub-cooling jacket covering cell

    International Nuclear Information System (INIS)

    Yu Qingfeng; Feng Quanke; Kawai Takeshi; Shen Feng; Yuan Luzheng; Cheng Liang

    2005-01-01

    The new type of the moderator cell was developed for the cold neutron source (CNS) of the China Advanced Research Reactor (CARR) which is now being constructed at the China Institute of Atomic Energy in Beijing. A crescent-shape moderator cell covered by the helium sub-cooling jacket is adopted. The structure of the moderator cell is optimized by the stress FEM analysis. A crescent-shape would help to increase the volume of the moderator cell for fitting it to the four cold neutron guide tubes, even if liquid hydrogen, not liquid deuterium, was used as a cold moderator. The helium sub-cooling jacket covering the moderator cell removes the nuclear heating of the outer shell wall of the cell. It contributes to reduce the void fraction of liquid hydrogen in the outer shell of the moderator cell. Such a type of a moderator cell is suitable for the CNS with higher nuclear heating. The cold helium gas flows down first into the helium sub-cooling jacket and then flows up to the condenser. The theory of the self-regulation suitable to the thermo-siphon type of the CNS is also applicable and validated

  7. CARR-CNS with crescent-shape moderator cell and sub-cooling helium jacket surrounding cell

    International Nuclear Information System (INIS)

    Yu, Qingfeng; Feng, Quanke; Kawai, Takeshi; Shen, Feng; Yuan, Luzheng

    2005-01-01

    The new type of the moderator cell was developed for the Cold Neutron Source (CNS) of the China Advanced Research Reactor (CARR) which is now constructing at the China Institute of Atomic Energy in Beijing. A crescent-shape moderator cell covered by the sub-cooling helium jacket is adopted. A crescent-shape would help to increase the volume of the moderator cell for corresponding it to the 4 cold neutron guide tubes, even if liquid hydrogen not liquid deuterium were used as a cold moderator. The sub-cooling helium jacket covering the moderator cell removes the nuclear heating of the outer shell wall of the cell. It contributes to reduce the void fraction of liquid hydrogen in the inner shell. Such a type of a moderator cell is suitable for the CNS with higher nuclear heating. The cold helium gas flows down firstly into the sub-cooling helium jacket and then flows up to the condenser. Therefore, the theory of the self-regulation for the thermo-siphon type of the CNS is also applicable

  8. A high-fidelity approach towards simulation of pool boiling

    Energy Technology Data Exchange (ETDEWEB)

    Yazdani, Miad; Radcliff, Thomas; Soteriou, Marios; Alahyari, Abbas A. [United Technologies Research Center, East Hartford, Connecticut 06108 (United States)

    2016-01-15

    A novel numerical approach is developed to simulate the multiscale problem of pool-boiling phase change. The particular focus is to develop a simulation technique that is capable of predicting the heat transfer and hydrodynamic characteristics of nucleate boiling and the transition to critical heat flux on surfaces of arbitrary shape and roughness distribution addressing a critical need to design enhanced boiling heat transfer surfaces. The macro-scale of the phase change and bubble dynamics is addressed through employing off-the-shelf Computational Fluid Dynamics (CFD) methods for interface tracking and interphase mass and energy transfer. The micro-scale of the microlayer, which forms at early stage of bubble nucleation near the wall, is resolved through asymptotic approximation of the thin-film theory which provides a closed-form solution for the distribution of the micro-layer and its influence on the evaporation process. In addition, the sub-grid surface roughness is represented stochastically through probabilistic density functions and its role in bubble nucleation and growth is then represented based on the thermodynamics of nucleation process. This combination of deterministic CFD, local approximation, and stochastic representation allows the simulation of pool boiling on any surface with known roughness and enhancement characteristics. The numerical model is validated for dynamics and hydrothermal characteristics of a single nucleated bubble on a flat surface against available literature data. In addition, the prediction of pool-boiling heat transfer coefficient is verified against experimental measurements as well as reputable correlations for various roughness distributions and different surface orientations. Finally, the model is employed to demonstrate pool-boiling phenomenon on enhanced structures with reentrance cavities and to explore the effect of enhancement feature design on thermal and hydrodynamic characteristics of these surfaces.

  9. A high-fidelity approach towards simulation of pool boiling

    International Nuclear Information System (INIS)

    Yazdani, Miad; Radcliff, Thomas; Soteriou, Marios; Alahyari, Abbas A.

    2016-01-01

    A novel numerical approach is developed to simulate the multiscale problem of pool-boiling phase change. The particular focus is to develop a simulation technique that is capable of predicting the heat transfer and hydrodynamic characteristics of nucleate boiling and the transition to critical heat flux on surfaces of arbitrary shape and roughness distribution addressing a critical need to design enhanced boiling heat transfer surfaces. The macro-scale of the phase change and bubble dynamics is addressed through employing off-the-shelf Computational Fluid Dynamics (CFD) methods for interface tracking and interphase mass and energy transfer. The micro-scale of the microlayer, which forms at early stage of bubble nucleation near the wall, is resolved through asymptotic approximation of the thin-film theory which provides a closed-form solution for the distribution of the micro-layer and its influence on the evaporation process. In addition, the sub-grid surface roughness is represented stochastically through probabilistic density functions and its role in bubble nucleation and growth is then represented based on the thermodynamics of nucleation process. This combination of deterministic CFD, local approximation, and stochastic representation allows the simulation of pool boiling on any surface with known roughness and enhancement characteristics. The numerical model is validated for dynamics and hydrothermal characteristics of a single nucleated bubble on a flat surface against available literature data. In addition, the prediction of pool-boiling heat transfer coefficient is verified against experimental measurements as well as reputable correlations for various roughness distributions and different surface orientations. Finally, the model is employed to demonstrate pool-boiling phenomenon on enhanced structures with reentrance cavities and to explore the effect of enhancement feature design on thermal and hydrodynamic characteristics of these surfaces

  10. An analytical and experimental study of pool boiling with particular reference to additives

    International Nuclear Information System (INIS)

    Owens, W.L. Jr.

    1963-05-01

    An experimental investigation of nucleate boiling heat transfer and critical heat flux is presented for water and various aqueous solutions boiling from horizontal stainless steel tubes and flat strips at atmospheric pressure. An integral method solution for film boiling is given and compared with existing experimental data. Analytical solutions are also obtained for the temperature profiles with periodic internal heating of a flat plate and a cylinder. (author)

  11. Availability analysis for heterogeneous nucleation in a uniform electric field

    CERN Document Server

    Saidi, M H

    2003-01-01

    Industrial demands for more compact heat exchangers are a motivation to find new technology features. Electrohydrodynamics (EHD) is introduced as a promising phenomenon for heat transfer enhancement mechanisms. Similar to any new technology, EHD has not been understood completely yet and require more fundamental studies. In boiling phase change phenomena, nucleation is the dominant mechanism in heat transfer. Because of higher performance in heat transfer, nucleate boiling is considered as the main regime in thermal components. Hence, bubble dynamic investigation is a means to evaluate heat transfer. This study investigate bubble formation, including homogeneous and heterogeneous nucleation, from a thermodynamic point of view. Change in availability due to bubble embryo nucleation is discussed. Stability criteria for these systems are theoretically studied and results are discussed considering experimental data. In addition, a conceptual discussion on entropy generation in a thermodynamic system under electri...

  12. Boiling of superheated liquids near the spinodal: II. Application

    Energy Technology Data Exchange (ETDEWEB)

    Aus der Wiesche, S.; Rembe, C.; Hofer, E.P. [Ulm Univ. (Germany). Dept. of Measurement, Control and Microtechnology

    1999-07-01

    The general theory of boiling near the spinodal as critical phenomenon will be used on the nucleation process of explosive evaporating liquids. In experiments with thermal micro heater the occurrence of the critical opalescence can be demonstrated which is characteristic for phase transitions of second order. In case of water the experiments permit the determination of the gradient energy coefficient {kappa} for nonuniform systems. The homogeneous nucleation rate for extremely superheated water at normal pressure is discussed. It is found that the explosive evaporation starts very closed to the spinodal and leads to spatial extended nuclei in contrast to the conventional nucleation mode. (orig.) With 5 figs., 16 refs.

  13. Boiling of superheated liquids near the spinodal: II Application

    Science.gov (United States)

    aus der Wiesche, S.; Rembe, C.; Hofer, E. P.

    The general theory of boiling near the spinodal as critical phenomenon will be used on the nucleation process of explosive evaporating liquids. In experiments with thermal micro heater the occurrence of the critical opalescence can be demonstrated which is characteristic for phase transitions of second order. In case of water the experiments permit the determination of the gradient energy coefficient κ for nonuniform systems. The homogeneous nucleation rate for extremely superheated water at normal pressure is discussed. It is found that the explosive evaporation starts very closed to the spinodal and leads to spatial extended nuclei in contrast to the conventional nucleation mode.

  14. New flow boiling heat transfer model for hydrocarbons evaporating inside horizontal tubes

    International Nuclear Information System (INIS)

    Chen, G. F.; Gong, M. Q.; Wu, J. F.; Zou, X.; Wang, S.

    2014-01-01

    Hydrocarbons have high thermodynamic performances, belong to the group of natural refrigerants, and they are the main components in mixture Joule-Thomson low temperature refrigerators (MJTR). New evaluations of nucleate boiling contribution and nucleate boiling suppression factor in flow boiling heat transfer have been proposed for hydrocarbons. A forced convection heat transfer enhancement factor correlation incorporating liquid velocity has also been proposed. In addition, the comparisons of the new model and other classic models were made to evaluate its accuracy in heat transfer prediction

  15. Prediction of incipient flow boiling from a uniformly heated surface

    International Nuclear Information System (INIS)

    Yin, S.T.; Abdelmessih, A.H.

    1977-01-01

    This study was undertaken to investigate the phenomenon of liquid superheat during incipient boiling in a uniformly heated forced convection channel. Experimental data were obtained using Freon 11 as the test medium. Based on existing theories, an analytical method was developed for predicting the point of termination of nucleate boiling, observed during a decreasing heat flux process with a nucleation activated surface. The method may also be used to predict the point of boiling incipience, observed during an increasing heat flux process with a non-activated surface; this point does not appear to have been treated analytically in previous work. It can be shown that some of the existing models are special cases of the present formulation

  16. Dynamics of homogeneous nucleation

    DEFF Research Database (Denmark)

    Toxværd, Søren

    2015-01-01

    The classical nucleation theory for homogeneous nucleation is formulated as a theory for a density fluctuation in a supersaturated gas at a given temperature. But molecular dynamics simulations reveal that it is small cold clusters which initiates the nucleation. The temperature in the nucleating...

  17. Converting high boiling hydrocarbons

    Energy Technology Data Exchange (ETDEWEB)

    Terrisse, H; DuFour, L

    1929-02-12

    A process is given for converting high boiling hydrocarbons into low boiling hydrocarbons, characterized in that the high boiling hydrocarbons are heated to 200 to 500/sup 0/C in the presence of ferrous chloride and of such gases as hydrogen, water gas, and the like gases under a pressure of from 5 to 40 kilograms per square centimeter. The desulfurization of the hydrocarbons occurs simultaneously.

  18. Surface boiling of superheated liquid

    Energy Technology Data Exchange (ETDEWEB)

    Reinke, P. [Paul Scherrer Inst. (PSI), Villigen (Switzerland)

    1997-01-01

    A basic vaporization mechanism that possibly affects the qualitative and quantitative prediction of the consequences of accidental releases of hazardous superheated liquids was experimentally and analytically investigated. The studies are of relevance for the instantaneous failure of a containment vessel filled with liquefied gas. Even though catastrophical vessel failure is a rare event, it is considered to be a major technological hazard. Modeling the initial phase of depressurisation and vaporization of the contents is an essential step for the subsequent analysis of the spread and dispersion of the materials liberated. There is only limited understanding of this inertial expansion stage of the superheated liquid, before gravity and atmospheric turbulence begin to dominate the expansion. This work aims at a better understanding of the vaporization process and to supply more precise source-term data. It is also intended to provide knowledge for the prediction of the behavior of large-scale releases by the investigation of boiling on a small scale. Release experiments with butane, propane, R-134a and water were conducted. The vaporization of liquids that became superheated by sudden depressurisation was studied in nucleation-site-free glass receptacles. Several novel techniques for preventing undesired nucleation and for opening the test-section were developed. Releases from pipes and from a cylindrical geometry allowed both linear one-dimensional, and radial-front two-dimensional propagation to be investigated. Releases were made to atmospheric pressure over a range of superheats. It was found that, above a certain superheat temperature, the free surface of the metastable liquid rapidly broke up and ejected a high-velocity vapor/liquid stream. The zone of intense vaporization and liquid fragmentation proceeded as a front that advanced into the test fluids. No nucleation of bubbles in the bulk of the superheated liquid was observed. (author) figs., tabs., refs.

  19. Surface boiling of superheated liquid

    International Nuclear Information System (INIS)

    Reinke, P.

    1997-01-01

    A basic vaporization mechanism that possibly affects the qualitative and quantitative prediction of the consequences of accidental releases of hazardous superheated liquids was experimentally and analytically investigated. The studies are of relevance for the instantaneous failure of a containment vessel filled with liquefied gas. Even though catastrophical vessel failure is a rare event, it is considered to be a major technological hazard. Modeling the initial phase of depressurisation and vaporization of the contents is an essential step for the subsequent analysis of the spread and dispersion of the materials liberated. There is only limited understanding of this inertial expansion stage of the superheated liquid, before gravity and atmospheric turbulence begin to dominate the expansion. This work aims at a better understanding of the vaporization process and to supply more precise source-term data. It is also intended to provide knowledge for the prediction of the behavior of large-scale releases by the investigation of boiling on a small scale. Release experiments with butane, propane, R-134a and water were conducted. The vaporization of liquids that became superheated by sudden depressurisation was studied in nucleation-site-free glass receptacles. Several novel techniques for preventing undesired nucleation and for opening the test-section were developed. Releases from pipes and from a cylindrical geometry allowed both linear one-dimensional, and radial-front two-dimensional propagation to be investigated. Releases were made to atmospheric pressure over a range of superheats. It was found that, above a certain superheat temperature, the free surface of the metastable liquid rapidly broke up and ejected a high-velocity vapor/liquid stream. The zone of intense vaporization and liquid fragmentation proceeded as a front that advanced into the test fluids. No nucleation of bubbles in the bulk of the superheated liquid was observed. (author) figs., tabs., refs

  20. Thermal-hydraulic performance of convective boiling jet array impingement

    International Nuclear Information System (INIS)

    Jenkins, R; De Brún, C; Kempers, R; Lupoi, R; Robinson, A J

    2016-01-01

    Jet impingement boiling is investigated with regard to heat transfer and pressure drop performance using a novel laser sintered 3D printed jet impingement manifold design. Water was the working fluid at atmospheric pressure with inlet subcooling of 7 o C. The convective boiling performance of the impinging jet system was investigated for a flat copper target surface for 2700≤Re≤5400. The results indicate that the heat transfer performance of the impinging jet is independent of Reynolds number for fully developed boiling. Also, the investigation of nozzle to plate spacing shows that low spacing delays the onset of nucleate boiling causing a superheat overshoot that is not observed with larger gaps. However, no sensitivity to the gap spacing was measured once boiling was fully developed. The assessment of the pressure drop performance showed that the design effectively transfers heat with low pumping power requirements. In particular, owing to the insensitivity of the heat transfer to flow rate during fully developed boiling, the coefficient of performance of jet impingement boiling in the fully developed boiling regime deteriorates with increased flow rate due to the increase in pumping power flux. (paper)

  1. Two-phase flow boiling pressure drop in small channels

    International Nuclear Information System (INIS)

    Sardeshpande, Madhavi V.; Shastri, Parikshit; Ranade, Vivek V.

    2016-01-01

    Highlights: • Study of typical 19 mm steam generator tube has been undertaken in detail. • Study of two phase flow boiling pressure drop, flow instability and identification of flow regimes using pressure fluctuations is the main focus of present work. • Effect of heat and mass flux on pressure drop and void fraction was studied. • Flow regimes identified from pressure fluctuations data using FFT plots. • Homogeneous model predicted pressure drop well in agreement. - Abstract: Two-phase flow boiling in small channels finds a variety of applications in power and process industries. Heat transfer, boiling flow regimes, flow instabilities, pressure drop and dry out are some of the key issues related to two-phase flow boiling in channels. In this work, the focus is on pressure drop in two-phase flow boiling in tubes of 19 mm diameter. These tubes are typically used in steam generators. Relatively limited experimental database is available on 19 mm ID tube. Therefore, in the present work, the experimental set-up is designed for studying flow boiling in 19 mm ID tube in such a way that any of the different flow regimes occurring in a steam generator tube (from pre-heating of sub-cooled water to dry-out) can be investigated by varying inlet conditions. The reported results cover a reasonable range of heat and mass flux conditions such as 9–27 kW/m 2 and 2.9–5.9 kg/m 2 s respectively. In this paper, various existing correlations are assessed against experimental data for the pressure drop in a single, vertical channel during flow boiling of water at near-atmospheric pressure. A special feature of these experiments is that time-dependent pressures are measured at four locations along the channel. The steady-state pressure drop is estimated and the identification of boiling flow regimes is done with transient characteristics using time series analysis. Experimental data and corresponding results are compared with the reported correlations. The results will be

  2. Contribution to the development of a Local Predictive Approach of the boiling crisis

    International Nuclear Information System (INIS)

    Montout, M.

    2009-01-01

    EDF aims at developing a 'Local Predictive Approach' of the boiling crisis for PWR core configurations, i.e. an approach resulting in (empirical) critical heat flux predictors based on local parameters provided by NEPTUNE-CFD code (for boiling bubbly flows, only in a first stage). Within this general framework, this PhD work consisted in assess one modelling of NEPTUNE-CFD code selected to simulate boiling bubble flows, then improve it. The latter objective led us to focus on the mechanistic modelling of subcooled nucleate boiling in forced convection. After a literature review, we identified physical improvements to be accounted for, especially with respect to bubble sliding phenomenon along the heated wall. Subsequently, we developed a force balance model in order to provide needed closure laws related to bubble detachment diameter from the nucleation site and lift-off bubble diameter from the wall. A new boiling model including such developments was eventually proposed, and preliminary assessed. (author)

  3. Boiling curve in high quality flow boiling

    International Nuclear Information System (INIS)

    Shiralkar, B.S.; Hein, R.A.; Yadigaroglu, G.

    1980-01-01

    The post dry-out heat transfer regime of the flow boiling curve was investigated experimentally for high pressure water at high qualities. The test section was a short round tube located downstream of a hot patch created by a temperature controlled segment of tubing. Results from the experiment showed that the distance from the dryout point has a significant effect on the downstream temperatures and there was no unique boiling curve. The heat transfer coefficients measured sufficiently downstream of the dryout point could be correlated using the Heineman correlation for superheated steam, indicating that the droplet deposition effects could be neglected in this region

  4. Evaporation, Boiling and Bubbles

    Science.gov (United States)

    Goodwin, Alan

    2012-01-01

    Evaporation and boiling are both terms applied to the change of a liquid to the vapour/gaseous state. This article argues that it is the formation of bubbles of vapour within the liquid that most clearly differentiates boiling from evaporation although only a minority of chemistry textbooks seems to mention bubble formation in this context. The…

  5. Nucleation Characteristics in Physical Experiments/explosions

    International Nuclear Information System (INIS)

    Henry, R.E.; Fauske, Hans K.

    1976-01-01

    Large-scale vapor explosion experiments have shown that intimate contact between hot and cold liquids, and a temperature upon contact that is greater than the spontaneous nucleation temperature of the system, are two necessary conditions for the onset of large scale vapor explosions. A model, based on spontaneous nucleation of the homogeneous type, has been proposed to describe the relevant processes and the resulting energetics for explosive boiling systems. The model considers that spontaneous nucleation cannot occur either during the relief time for constant volume heating or until the thermal boundary layer is sufficiently thick to support a vapor cavity of the critical size. After nucleation, bubble growth does not occur until an acoustic wave establishes a pressure gradient in the cold liquid. These considerations lead to the prediction that, for a given temperature, drops greater than a critical size will remain in film boiling due to coalescence of vapor nuclei and drops smaller than this value will wet and be captured by the hot liquid surface. These results are compared to small drop data for well-wetted systems and excellent agreement is obtained between the observed behavior and the model predictions. In conclusion: A model, based on spontaneous nucleation, has been proposed to describe vaporization potential and behavior upon contact in a liquid/liquid system. This behavior is determined by the size of the liquid mass, single-phase pressurization and acoustic relief, nucleation frequency due to random density fluctuations, the initiation of unstable growth and acoustic relief, and the development of the thermal boundary layer in the cold liquid. The proposed model predicts that the stability of a given size drop upon intimate contact with another liquid is extremely dependent upon the interface temperature. For low interface temperatures, large masses will be captured by the hot liquid and the resulting vaporization rates will be extremely low because

  6. Optical studies of boiling heat transfer: insights and limitations

    International Nuclear Information System (INIS)

    Kenning, David B.R.

    2004-01-01

    Optical studies provide valuable insights into the complex mechanisms of boiling heat transfer but the large gradients of temperature (and therefore of refractive index) deflect light and multiple reflections at interfaces limit the distance over which observations can be made. Optical measurements are thought of as non-intrusive but this is rarely true. Because they are difficult and time consuming, they constrain the design of boiling experiments and are applied to limited ranges of conditions. There is a risk that deductions from the observations will be applied (not necessarily by the authors) more generally than is justified. These characteristics of optical studies are illustrated by examples from forced convective film boiling on spheres and pool nucleate boiling

  7. Boiling and burnout phenomena under transient heat input, 1

    International Nuclear Information System (INIS)

    Aoki, Shigebumi; Kozawa, Yoshiyuki; Iwasaki, Hideaki.

    1976-01-01

    In order to simulate the thermo-hydrodynamic conditions at reactor power excursions, a test piece was placed in a forced convective channel and heated with exponential power inputs. The boiling heat transfer and the burnout heat flux under the transient heat input were measured, and pressure and water temperature changes in the test section were recorded at the same time. Following experimental results were obtained; (1) Transient boiling heat transfer characteristics at high heat flux stayed on the stationary nucleate boiling curve of each flow condition, or extrapolated line of the curves. (2) Transient burnout heat flux increased remarkably with decreasing heating-time-constant, when the flow rate was lower and the subcooling was higher. (3) Transient burnout phenomena were expressed with the relation of (q sub(max) - q sub(sBO)) tau = constant at several flow conditions. This relation was derived from the stationary burnout mechanism of pool boiling. (auth.)

  8. Transition from boiling to two-phase forced convection

    International Nuclear Information System (INIS)

    Maroti, L.

    1985-01-01

    The paper presents a method for the prediction of the boundary points of the transition region between fully developed boiling and two-phase forced convection. It is shown that the concept for the determination of the onset of fully developed boiling can also be applied for the calculation of the point where the heat transfer is effected again by the forced convection. Similarly, the criterion for the onset of nucleate boiling can be used for the definition of the point where boiling is completely suppressed and pure two-phase forced convection starts. To calculate the heat transfer coefficient for the transition region, an equation is proposed that applies the boundary points and a relaxation function ensuring the smooth transition of the heat transfer coefficient at the boundaries

  9. Boiling in porous media

    International Nuclear Information System (INIS)

    1998-01-01

    This conference day of the French society of thermal engineers was devoted to the analysis of heat transfers and fluid flows during boiling phenomena in porous media. This book of proceedings comprises 8 communications entitled: 'boiling in porous medium: effect of natural convection in the liquid zone'; 'numerical modeling of boiling in porous media using a 'dual-fluid' approach: asymmetrical characteristic of the phenomenon'; 'boiling during fluid flow in an induction heated porous column'; 'cooling of corium fragment beds during a severe accident. State of the art and the SILFIDE experimental project'; 'state of knowledge about the cooling of a particulates bed during a reactor accident'; 'mass transfer analysis inside a concrete slab during fire resistance tests'; 'heat transfers and boiling in porous media. Experimental analysis and modeling'; 'concrete in accidental situation - influence of boundary conditions (thermal, hydric) - case studies'. (J.S.)

  10. Development of surface wettability characteristics for enhancing pool boiling heat transfer

    International Nuclear Information System (INIS)

    Kim, Moo Hwan; Jo, Hang Jin

    2010-05-01

    For several centuries, many boiling experiments have been conducted. Based on literature survey, the characteristic of heating surface in boiling condition played as an important role which mainly influenced to boiling performance. Among many surface factor, the fact that wettability effect is significant to not only the enhancement of critical heat flux(CHF) but also the nucleate boiling heat transfer is also supported by other kinds of boiling experiments. In this regard, the excellent boiling performance (a high CHF and heat transfer performance) in pool boiling could be achieved through some favorable surface modification which satisfies the optimized wettability condition. To find the optimized boiling condition, we design the special heaters to examine how two materials, which have different wettability (e.g. hydrophilic and hydrophobic), affect the boiling phenomena. The special heaters have hydrophobic dots on hydrophilic surface. The contact angle of hydrophobic surface is 120 .deg. to water at the room temperature. The contact angle of hydrophilic surface is 60 .deg. at same conditions. To conduct the experiment with new surface condition, we developed new fabrication method and design the pool boiling experimental apparatus. Through this facility, we can the higher CHF on pattern surface than that on hydrophobic surface, and the higher boiling heat transfer performance on pattern surface than that on hydrophilic surface. Based on this experimental results, we concluded that we proposed new heating surface condition and surface fabrication method to realize the best boiling condition by modified heating surface condition

  11. Flow with boiling in four-cusp channels simulating damaged core in PWR type reactors

    International Nuclear Information System (INIS)

    Esteves, M.M.

    1985-01-01

    The study of subcooled nucleate flow boiling in non-circular channels is of great importance to engineering applications in particular to Nuclear Engineering. In the present work, an experimental apparatus, consisting basically of a refrigeration system, running on refrigerant-12, has been developed. Preliminary tests were made with a circular tube. The main objective has been to analyse subcooled flow boiling in four-cusp channels simulating the flow conditions in a PWR core degraded by accident. Correlations were developed for the forced convection film coefficient for both single-phase and subcooled flow boiling. The incipience of boiling in such geometry has also been studied. (author) [pt

  12. Burnout in a high heat-flux boiling system with an impinging jet

    International Nuclear Information System (INIS)

    Monde, M.; Katto, Y.

    1978-01-01

    An experimental study has been made on the fully-developed nucleate boiling at atmospheric pressure in a simple forced-convection boiling system, which consists of a heated flat surface and a small, high-speed jet of water or of freon-113 impinging on the heated surface. A generalized correlation for burnout heat flux data, that is applied to either water or freon-113 is successfully evolved, and it is shown that surface tension has an important role for the onset of burnout phenomenon, not only in the ordinary pool boiling, but also in the present boiling system with a forced flow. (author)

  13. Pool boiling visualization on open microchannel surfaces

    Directory of Open Access Journals (Sweden)

    Kaniowski Robert

    2017-01-01

    Full Text Available The paper presents visualization investigations into pool boiling heat transfer for open minichannel surfaces. The experiments were carried out wih saturated water at atmospheric pressure. Parallel microchannels fabricated by machining were about 0.3 mm wide and 0.2 to 0.4 mm deep. High-speed videos were used as an aid to understanding the heat transfer mechanism. The visualization study aimed at identifying nucleation sites of the departing bubbles and determining their diameters and frequency at various superheats.

  14. Explosive Boiling of Superheated Cryogenic Liquids

    CERN Document Server

    Baidakov, V G

    2007-01-01

    The monograph is devoted to the description of the kinetics of spontaneous boiling of superheated liquefied gases and their solutions. Experimental results are given on the temperature of accessible superheating, the limits of tensile strength of liquids due to processes of cavitation and the rates of nucleation of classical and quantum liquids. The kinetics of evolution of the gas phase is studied in detail for solutions of cryogenic liquids and gas-saturated fluids. The properties of the critical clusters (bubbles of critical sizes) of the newly evolving gas phase are analyzed for initial st

  15. Measurements of Burnout Conditions for Flow of Boiling Water in Vertical Round Ducts (Part 2)

    Energy Technology Data Exchange (ETDEWEB)

    Becker, Kurt M; Mathisen, R P; Eklind, O; Norman, B

    1964-01-15

    The hydrodynamic stability and the burnout conditions for flow of boiling water have been studied in a natural circulation loop in the pressure range from 10 to 70 atg. The test section was a round, duct of 20 mm inner diameter and 4890 mm heated length. The experimental results showed that within the ranges tested the stability of the flow increases with increasing pressure, increasing throttling before the test section, but decreases with increasing inlet sub-cooling and increasing throttling after the test section. The measured thresholds of instability compared well with the analytical results by Jahnberg. For an inlet sub-cooling temperature of about 2 deg C the measured burnout steam qualities were low by a factor of about 1.3 compared to forced circulation data obtained with the same test section. At higher sub-cooling temperatures the discrepancy between forced and natural circulation data increased, so that at {delta}t{sub sub} = 16 deg C, the natural circulation data were low by a factor of about 2.5. However, by applying inlet throttling of the flow the burnout values approached and finally coincided with the forced circulation data.

  16. Advanced Wall Boiling Model with Wide Range Applicability for the Subcooled Boiling Flow and its Application into the CFD Code

    International Nuclear Information System (INIS)

    Yun, B. J.; Song, C. H.; Splawski, A.; Lo, S.

    2010-01-01

    Subcooled boiling is one of the crucial phenomena for the design, operation and safety analysis of a nuclear power plant. It occurs due to the thermally nonequilibrium state in the two-phase heat transfer system. Many complicated phenomena such as a bubble generation, a bubble departure, a bubble growth, and a bubble condensation are created by this thermally nonequilibrium condition in the subcooled boiling flow. However, it has been revealed that most of the existing best estimate safety analysis codes have a weakness in the prediction of the subcooled boiling phenomena in which multi-dimensional flow behavior is dominant. In recent years, many investigators are trying to apply CFD (Computational Fluid Dynamics) codes for an accurate prediction of the subcooled boiling flow. In the CFD codes, evaporation heat flux from heated wall is one of the key parameters to be modeled for an accurate prediction of the subcooled boiling flow. The evaporate heat flux for the CFD codes is expressed typically as follows, q' e = πD 3 d /6 ρ g h fg fN' where, D d , f ,N' are bubble departure size, bubble departure frequency and active nucleation site density, respectively. In the most of the commercial CFD codes, Tolubinsky bubble departure size model, Kurul and Podowski active nucleation site density model and Ceumem-Lindenstjerna bubble departure frequency model are adopted as a basic wall boiling model. However, these models do not consider their dependency on the flow, pressure and fluid type. In this paper, an advanced wall boiling model was proposed in order to improve subcooled boiling model for the CFD codes

  17. Study on boiling heat transfer of high temperature liquid sodium

    International Nuclear Information System (INIS)

    Sakurai, Akira

    1978-01-01

    In the Intitute of Atomic Energy, Kyoto University, fundamental studies on steady state and non-steady state heat flow are underway in connection with reactor design and the safety in a critical accident in a sodium-cooled fast breeder reactor. First, the experimental apparatus for sodium heat transfer and the testing system are described in detail. The apparatus is composed of sodium-purifying section including the plugging meter for measuring purity and cold trap, the pool boiling test section for experimenting natural convection boiling heat transfer, the forced convection boiling test section for experimenting forced convection boiling heat transfer, and gas system. Next, the experimental results by the author and the data obtained so far are compared regarding heat transfer in sodium natural convection and stable nucleating boiling and critical heat flux. The effect of liquid head on a heater on boiling heat transfer coefficient and critical heat flux under the condition of low system pressure in most fundamental pool boiling was elucidated quantitatively, which has been overlooked in previous studies. It was clarified that this is the essentially important problem that can not be overlooked. From this point of view, expressions on heat transfer were also re-investigated. (Wakatsuki, Y.)

  18. Research progresses and future directions on pool boiling heat transfer

    Directory of Open Access Journals (Sweden)

    M. Kumar

    2015-12-01

    Full Text Available This paper reviews the previous work carried on pool boiling heat transfer during heating of various liquids and commodities categorized as refrigerants and dielectric fluids, pure liquids, nanofluids, hydrocarbons and additive mixtures, as well as natural and synthetic colloidal solutions. Nucleate pool boiling is an efficient and effective method of boiling because high heat fluxes are possible with moderate temperature differences. It is characterized by the growth of bubbles on a heated surface. It occurs during boiling of liquids for excess temperature ranging from 5 to 30 °C in various processes related to high vaporization of liquid for specific purposes like sugarcane juice heating for jaggery making, milk heating for khoa making, steam generation, cooling of electronic equipments, refrigeration and etcetera. In this review paper, pool boiling method during heating of liquids for specific purpose is depicted. It is inferred that enhancement in pool boiling heat transfer is a challenging and complex task. Also, recent research and use of various correlations for natural convection pool boiling is reviewed.

  19. Acoustic phenomena during boiling

    International Nuclear Information System (INIS)

    Dorofeev, B.M.

    1985-01-01

    Applied and theoretical significance of investigation into acoustic phenomena on boiling is discussed. Effect of spatial and time conditions on pressure vapour bubble has been elucidated. Collective effects were considered: acoustic interaction of bubbles, noise formation ion developed boiling, resonance and hydrodynamic autooscillations. Different methods for predicting heat transfer crisis using changes of accompanying noise characteristics were analysed. Principle peculiarities of generation mechanism of thermoacoustic autooscillations were analysed as well: formation of standing waves; change of two-phase medium contraction in a channel; relation of alternating pressure with boiling process as well as with instantaneous and local temperatures of heat transfer surface and liquid in a boundary layer

  20. Nucleation in ZBLAN glasses

    NARCIS (Netherlands)

    de Leede, G.L.A.; Waal, de H.

    1989-01-01

    Nucleation rates were detd. in a ZrF4-BaF2-NaF-LaF3-AlF3 glass (ZBLAN) using an optical method. The results were compared with a similar glass having a slightly different compn. The difference in the nucleation rate is explained by classical nucleation theory using calcd. free-energy differences

  1. Nuclear boiling heat transfer and critical heat flux in titanium dioxide-water nanofluids

    International Nuclear Information System (INIS)

    Okawa, Tomio; Takamura, Masahiro; Kamiya, Takahito

    2011-01-01

    Nucleate boiling heat transfer was experimentally studied for saturated pool boiling of water-based nanofluids. Since significant nanoparticle deposition on the heated surface was observed after the nucleate boiling in nanofluids, measurement of CHF was also carried out using the nanoparticle deposited heated surface; pure water was used in the CHF measurement. In the present work, the heated surface was a 20 mm diameter cupper surface, and titanium-dioxide was selected as the material of nanoparticles. Experiments were performed for upward- and downward-facing surfaces. Although the CHFs for the downward-facing surface were generally lower than those for the upward-facing surface, the CHFs for the nanoparticle deposited surface were about 1.9 times greater than those for the bare surface in both the configurations. The CHF improvement corresponded well to the reduction of the surface contact angle. During the nucleate boiling in nanofluids, the boiling heat transfer showed peculiar behavior; it was first deteriorated, then improved, and finally approached to an equilibrium state. This observation indicated that the present nanofluid had competing effects to deteriorate and improve the nucleate boiling heat transfer. It was assumed that the wettability and the roughness of the heated surface were influenced by the deposited nanoparticles to cause complex variation of the number of active nucleation sites. During the nucleate boiling of pure water using the downward-facing surface, a sudden increase in the wall temperature was observed stochastically probably due to the accumulation of bubbles beneath the heated surface. Such behavior was not observed when the pure water was replaced by the nanofluid. (author)

  2. The sudden coalescene model of the boiling crisis

    International Nuclear Information System (INIS)

    Carrica, P.M.; Clausse, A.

    1995-01-01

    A local two-phase flow integral model of nucleate boiling and crisis is presented. The model is based on average balances on a control volume, yielding to a set of three nonlinear differential equations for the local void fraction, bubble number density and velocity. Boiling crisis as critical heat flux is interpreted as a dynamic transition caused by the coalescence of bubbles near the heater. The theoretical dynamic model is compared with experimental results obtained for linear power ramps in a horizontal plate heater in R-113, showing an excellent qualitative agreement

  3. The sudden coalescene model of the boiling crisis

    Energy Technology Data Exchange (ETDEWEB)

    Carrica, P.M.; Clausse, A. [Centro Atomico Bariloche and Instituto Balseiro, Bariloche (Argentina)

    1995-09-01

    A local two-phase flow integral model of nucleate boiling and crisis is presented. The model is based on average balances on a control volume, yielding to a set of three nonlinear differential equations for the local void fraction, bubble number density and velocity. Boiling crisis as critical heat flux is interpreted as a dynamic transition caused by the coalescence of bubbles near the heater. The theoretical dynamic model is compared with experimental results obtained for linear power ramps in a horizontal plate heater in R-113, showing an excellent qualitative agreement.

  4. Pool Boiling CHF in Inclined Narrow Annuli

    International Nuclear Information System (INIS)

    Kang, Myeong Gie

    2010-01-01

    by Kang to identify the combined effects of the surface orientation and a confined space on pool boiling heat transfer in annuli. The gap size was 15 mm and the annuli with both open and closed bottoms were considered. At a given heat flux, the heat transfer coefficient was increased with the inclination angle increase. However, no occurrence of the CHF was observed regardless of the flow inlet condition for the given gap size and heat fluxes tested. Summarizing the published results, it can be said that the narrow gap size, restriction of the bottom inlet flow into the confined space, and the inclination angle not only changes nucleate boiling heat transfer but also initiates the CHF. Therefore, the present study is aimed at the investigation of the effects of a narrow gap size (5 mm) on pool boiling heat transfer in inclined annuli to improve Kang's previous results

  5. Odd-Boiled Eggs

    Science.gov (United States)

    Kaminsky, Kenneth; Scheman, Naomi

    2010-01-01

    At a Shabbat lunch in Madrid not long ago, the conversation turned to the question of boiling eggs. One of the guests mentioned that a Dutch rabbi he knew had heard that in order to make it more likely that boiled eggs be kosher, you should add an egg to the pot if the number you began with was even. According to the laws of Kashruth, Jews may not…

  6. Nucleation in the atmosphere

    International Nuclear Information System (INIS)

    Hegg, D A; Baker, M B

    2009-01-01

    Small particles play major roles in modulating radiative and hydrological fluxes in the atmosphere and thus they impact both climate (IPCC 2007) and weather. Most atmospheric particles outside clouds are created in situ through nucleation from gas phase precursors and most ice particles within clouds are formed by nucleation, usually from the liquid. Thus, the nucleation process is of great significance in the Earth's atmosphere. The theoretical examination of nucleation in the atmosphere has been based mostly on classical nucleation theory. While diagnostically very useful, the prognostic skill demonstrated by this approach has been marginal. Microscopic approaches such as molecular dynamics and density functional theory have also proven useful in elucidating various aspects of the process but are not yet sufficiently refined to offer a significant prognostic advantage to the classical approach, due primarily to the heteromolecular nature of atmospheric nucleation. An important aspect of the nucleation process in the atmosphere is that the degree of metastability of the parent phase for the nucleation is modulated by a number of atmospheric processes such as condensation onto pre-existing particles, updraft velocities that are the main driving force for supersaturation of water (a major factor in all atmospheric nucleation), and photochemical production rates of nucleation precursors. Hence, atmospheric nucleation is both temporally and spatially inhomogeneous

  7. Pool Boiling Characteristics on the Microstructure surfaces with Both Rectangular Cavities and Channels

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Dong Eok; Myung, Byung-Soo [Kyungpook Nat’l Univ., Daegu (Korea, Republic of); Park, Su Cheong; Yu, Dong In [POSTECH, Pohang (Korea, Republic of); Kim, Moo Hwan [Korea Institute of Nuclear Safety (KINS), Daejeon (Korea, Republic of); Ahn, Ho Seon [Incheon Nat’l Univ., Incheon (Korea, Republic of)

    2016-06-15

    Based on a surface design with rectangular cavities and channels, we investigated the effects of gravity and capillary pressure on pool-boiling Critical Heat Flux (CHF). The microcavity structures could prevent liquid flow by the capillary pressure effect. In addition, the microchannel structures contributed to induce one-dimensional liquid flow on the boiling surface. The relationship between the CHF and capillary flow was clearly established. The driving potentials for the liquid supply into a boiling surface can be generated by the gravitational head and capillary pressure. Through an analysis of pool boiling and visualization data, we reveal that the liquid supplement to maintain the nucleate boiling condition on a boiling surface is closely related to the gravitational pressure head and capillary pressure effect.

  8. Boiling heat transfer on horizontal tube bundles

    International Nuclear Information System (INIS)

    Anon.

    1987-01-01

    Nucleate boiling heat transfer characteristics for a tube in a bundle differ from that for a single tube in a pool and this difference is known as 'tube bundle effect.' There exist two bundle effects, positive and negative. The positive bundle effect enhances heat transfer due to convective flow induced by rising bubbles generated from the lower tubes, while the negative bundle effect deteriorates heat transfer due to vapor blanketing caused by accumulation of bubbles. Staggered tube bundles tested and found that the upper tubes in bundles have higher heat transfer coefficients than the lower tubes. The effects of various parameters such as pressure, tube geometry and oil contamination on heat transfer have been examined. Some workers attempted to clarify the mechanism of occurrence of 'bundle effect' by testing tube arrangements of small scale. All reported only enhancement in heat transfer but results showed the symptom of heat transfer deterioration at higher heat fluxes. As mentioned above, it has not been clarified so far even whether the 'tube bundle effect' should serve as enhancement or deterioration of heat transfer in nucleate boiling. In this study, experiments are performed in detail by using bundles of small scale, and effects of heat flux distribution, pressure and tube location are clarified. Furthermore, some consideration on the mechanisms of occurrence of 'tube bundle effect' is made and a method for prediction of heat transfer rate is proposed

  9. Experimental Investigation of Pool Boiling for Single and Double Heaters Using Printed Circuit Board

    International Nuclear Information System (INIS)

    Han, Won Seok; Lee, Jae Young

    2012-01-01

    Over the past several decades, a considerable number of studies have been conducted on boiling heat transfer in pool boiling. Boiling heat transfer is used in a variety of cooling applications, such as heat exchangers, high powered electronics, and nuclear reactors. Nucleate boiling is one of the most efficient heat transfer mechanisms in boiling regime, but it is imperative that the critical heat flux(CHF) should not be exceeded. CHF phenomenon leads to a dramatic rise in wall temperature, decreased heat transfer, and material failure. Although numerous attempts have been made by researchers to demonstrate the CHF, there is little agreement with the CHF mechanism. In recent years, many researchers have been focusing on surface condition using nanoparticles and surface enhancements, such as a micro structure and artificial cavities, due to enhancement of the CHF point. Cooke and Kandlikar used chips etched with microchannels to prove that these structure has the most enhancement effect. They found that the most efficient boiling surface is with a larger channel size and deep etch. The purpose of this paper is to evaluate the heat transfer and CHF of double heaters on printed circuit board(PCB) in pool boiling. In addition, bubble dynamics of nucleate boiling were observed with high speed observation on single and double heaters using PCB heater

  10. Correlations for developing film boiling effect in tubes

    International Nuclear Information System (INIS)

    Guo, Y.; Leung, L.K.H.

    2005-01-01

    look-up table, h NB is the nucleate boiling heat transfer coefficient, T W is the film-boiling surface temperature, T sat is the saturation temperature, and TCHF is the surface temperature at the local critical heat flux, q CHF , calculated as: T CHF = T sat + q CHF /h NB The modification factor for the developing film-boiling effect was correlated with an extensive database of film-boiling heat transfer coefficients in tubes. In conjunction with the fully developed film-boiling look-up table, the correlation predicts the experimental values of the film-boiling heat transfer coefficient with an average error of -2.37% and a root-mean-square (RMS) error of 13.03% for 11,163 data points. A separate correlation has been derived to improve the prediction accuracy at low-pressure conditions, which are anticipated to be of interest in the analysis of postulated large break loss-of-coolant accident. It provides improved prediction accuracy with an average prediction error of the film-boiling heat transfer coefficient of -0.07% and an RMS error of 5.98% for 554 data points. (authors)

  11. Modelling of boiling bubbly flows using a polydisperse approach

    International Nuclear Information System (INIS)

    Zaepffel, D.

    2011-01-01

    The objective of this work was to improve the modelling of boiling bubbly flows.We focused on the modelling of the polydisperse aspect of a bubble population, i.e. the fact that bubbles have different sizes and different velocities. The multi-size aspect of a bubble population can originate from various mechanisms. For the bubbly flows we are interested in, bubble coalescence, bubble break-up, phase change kinematics and/or gas compressibility inside the bubbles can be mentioned. Since, bubble velocity depends on bubble size, the bubble size spectrum also leads to a bubble velocity spectrum. An averaged model especially dedicated to dispersed flows is introduced in this thesis. Closure of averaged interphase transfer terms are written in a polydisperse framework, i.e. using a distribution function of the bubble sizes and velocities. A quadratic law and a cubic law are here proposed for the modelling of the size distribution function, whose evolution in space and time is then obtained with the use of the moment method. Our averaged model has been implemented in the NEPTUNE-CFD computation code in order to simulate the DEBORA experiment. The ability of our model to deal with sub-cooled boiling flows has therefore been evaluated. (author) [fr

  12. Principles of nucleation theory

    International Nuclear Information System (INIS)

    Clement, C.F.; Wood, M.H.

    1980-01-01

    The nucleation of small stable species is described in the problem of void growth by discrete rate equations. When gas is being produced the problem reduces to one of calculating the incubation dose for the gas bubble to void transition. A general expression for the steady state nucleation rate is derived for the case when voids are formed by vacancy fluctuations which enable an effective nucleation barrier to be crossed. (author)

  13. On void nucleation

    International Nuclear Information System (INIS)

    Subbotin, A.V.

    1978-01-01

    Nucleation of viable voids in irradiated materials is considered. The mechanism of evaporation and absorption of interstitials and vacancies disregarding the possibility of void merging is laid down into the basis of the discussion. The effect of irradiated material structure on void nucleation is separated from the effect of the properties of supersaturated solutions of vacancies and interstitials. An analytical expression for the nucleation rate is obtained and analyzed in different cases. The interstitials are concluded to effect severely the nucleation rate of viable voids

  14. Enhancement of pool boiling heat transfer coefficients using carbon nanotubes

    International Nuclear Information System (INIS)

    Park, Ki Jung; Jung, Dong Soo

    2007-01-01

    In this study, the effect of carbon nanotubes (CNTs) on nucleate boiling heat transfer is investigated. Three refrigerants of R22, R123, R134a, and water were used as working fluids and 1.0 vol.% of CNTs was added to the working fluids to examine the effect of CNTs. Experimental apparatus was composed of a stainless steel vessel and a plain horizontal tube heated by a cartridge heater. All data were obtained at the pool temperature of 7 .deg. C for all refrigerants and 100 .deg. C for water in the heat flux range of 10∼80 kW/m 2 . Test results showed that CNTs increase nucleate boiling heat transfer coefficients for all fluids. Especially, large enhancement was observed at low heat fluxes of less than 30 kW/m 2 . With increasing heat flux, however, the enhancement was suppressed due to vigorous bubble generation. Fouling on the heat transfer surface was not observed during the course of this study. Optimum quantity and type of CNTs and their dispersion should be examined for their commercial application to enhance nucleate boiling heat transfer in many applications

  15. Heat transfer coefficient correlation for convective boiling inside plain and micro fin tubes using genetic algorithms

    International Nuclear Information System (INIS)

    Picanco, Marco Antonio Silva; Bandarra Filho, Enio Pedone; Passos, Julio Cesar

    2006-01-01

    Two-phase flow heat transfer has been exhaustively studied over recent years. However, in this field several questions remain unanswered. Heat transfer coefficient prediction related to nucleate and convective boiling have been studied using different approaches, numerical, analytical and experimental. In this work, an experimental analysis, data representation and heat transfer coefficient prediction on two-phase heat transfer on nucleate and convective boiling are presented. An empirical correlation is obtained based on genetic algorithms search engine over a dimensional analysis of the two-phase flow heat transfer problem. (author)

  16. Hydrodynamic instability induced liquid--solid contacts in film boiling

    International Nuclear Information System (INIS)

    Yao, S.; Henry, R.E.

    1976-01-01

    The film boiling liquid-solid contacts of saturated ethanol and water to horizontal flat gold plated copper are examined by using electric conductance probe. It is observed that the liquid-solid contacts occur over a wide temperature range, and generally, induced by hydrodynamic instabilities. The area of contact decreases exponentially with interface temperature and is liquid depth dependent. The averaged duration of contacts is strongly influenced by the dominant nucleation process, and thus, depends on the interface temperature and the wettability of the solid during the contact. The frequency of major contacts is about 1.5 times the bubble detaching frequency. It is found that the liquid-solid contacts may account for a large percentage of the film boiling heat transfer near the low temperature end of film boiling and decreases as the interface temperature increases

  17. Characteristics of phenomenon and sound in microbubble emission boiling

    International Nuclear Information System (INIS)

    Zhu Guangyu; Sun Licheng; Tang Jiguo

    2014-01-01

    Background: Nowadays, the efficient heat transfer technology is required in nuclear energy. Therefore, micro-bubble emission boiling (MEB) is getting more attentions from many researchers due to its extremely high heat-transfer dissipation capability. Purpose: An experimental setup was built up to study the correspondences between the characteristics on the amplitude spectrum of boiling sound in different boiling modes. Methods: The heat element was a copper block heated by four Si-C heaters. The upper of the copper block was a cylinder with the diameter of 10 mm and height of 10 mm. Temperature data were measured by three T-type sheathed thermocouples fitted on the upper of the copper block and recorded by NI acquisition system. The temperature of the heating surface was estimated by extrapolating the temperature distribution. Boiling sound data were acquired by hydrophone and processed by Fourier transform. Bubble behaviors were captured by high-speed video camera with light system. Results: In nucleate boiling region, the boiling was not intensive and as a result, the spectra didn't present any peak. While the MEB fully developed on the heating surface, an obvious peak came into being around the frequency of 300 Hz. This could be explained by analyzing the video data. The periodic expansion and collapse into many extremely small bubbles of the vapor film lead to MEB presenting an obvious characteristic peak in its amplitude spectrum. Conclusion: The boiling mode can be distinguished by its amplitude spectrum. When the MEB fully developed, it presented a characteristic peak in its amplitude spectrum around the frequency between 300-400 Hz. This proved that boiling sound of MEB has a close relation with the behavior of vapor film. (authors)

  18. Saturated Pool Boiling in Vertical Annulus with Reduced Outflow Area

    International Nuclear Information System (INIS)

    Kang, Myeong Gie

    2012-01-01

    The mechanisms of pool boiling heat transfer have been studied extensively to design efficient heat transfer devices or to assure the integrity of safety related systems. However, knowledge on pool boiling heat transfer in a confined space is still quite limited. The confined nucleate boiling is an effective technique to enhance heat transfer. Improved heat transfer might be attributed to an increase in the heat transfer coefficient due to vaporization from the thin liquid film on the heating surface or increased bubble activity. According to Cornwell and Houston, the bubbles sliding on the heated surface agitate environmental liquid. In a confined space a kind of pulsating flow due to the bubbles is created and, as a result very active liquid agitation is generated. The increase in the intensity of liquid agitation results in heat transfer enhancement. Sometimes a deterioration of heat transfer appears at high heat fluxes for confined boiling. The cause of the deterioration is suggested as active bubble coalescence. Recently, Kang published inflow effects on pool boiling heat transfer in a vertical annulus with closed bottoms. Kang regulated the gap size at the upper regions of the annulus and identified that effects of the reduced gaps on heat transfer become evident as the heat flux increases. This kind of geometry is found in an in-pile test section. Since more detailed analysis is necessary, effects of the outflow area on nucleate pool boiling heat transfer are investigated in this study. Up to the author's knowledge, no previous results concerning to this effect have been published yet

  19. Diamond Nucleation Using Polyethene

    Science.gov (United States)

    Morell, Gerardo (Inventor); Makarov, Vladimir (Inventor); Varshney, Deepak (Inventor); Weiner, Brad (Inventor)

    2013-01-01

    The invention presents a simple, non-destructive and non-abrasive method of diamond nucleation using polyethene. It particularly describes the nucleation of diamond on an electrically viable substrate surface using polyethene via chemical vapor deposition (CVD) technique in a gaseous environment.

  20. Void nucleation at heterogeneities

    International Nuclear Information System (INIS)

    Seyyedi, S.A.; Hadji-Mirzai, M.; Russell, K.C.

    The energetics and kinetics of void nucleation at dislocations and interfaces are analyzed. These are potential void nucleation sites only when they are not point defect sinks. Both kinds of site are found to be excellent catalysts in the presence of inert gas

  1. Subcooled flow boiling heat transfer from microporous surfaces in a small channel

    International Nuclear Information System (INIS)

    Yan, Sun; Li, Zhang; Hong, Xu; Xiaocheng, Zhong

    2011-01-01

    The continuously increasing requirement for high heat transfer rate in a compact space can be met by combining the small channel/microchannel and heat transfer enhancement methods during fluid subcooled flow boiling. In this paper, the sintered microporous coating, as an efficient means of enhancing nucleate boiling, was applied to a horizontal, rectangular small channel. Water flow boiling heat transfer characteristics from the small channel with/without the microporous coating were experimentally investigated. The small channel, even without the coating, presented flow boiling heat transfer enhancement at low vapor quality due to size effects of the channel. This enhancement was also verified by under-predictions from macro-scale correlations. In addition to the enhancement from the channel size, all six microporous coatings with various structural parameters were found to further enhance nucleate boiling significantly. Effects of the coating structural parameters, fluid mass flux and inlet subcooling were also investigated to identify the optimum condition for heat transfer enhancement. Under the optimum condition, the microporous coating could produce the heat transfer coefficients 2.7 times the smooth surface value in subcooled flow boiling and 3 times in saturated flow boiling. The combination of the microporous coating and small channel led to excellent heat transfer performance, and therefore was deemed to have promising application prospects in many areas such as air conditioning, chip cooling, refrigeration systems, and many others involving compact heat exchangers. (authors)

  2. MTD-MFC: unified framework for investigation of diversity of boiling heat transfer curves

    Energy Technology Data Exchange (ETDEWEB)

    Shekriladze, I.G. [Georgian Technical University, Tbilisi (Georgia)], e-mail: shekri@geo.net.ge

    2009-07-01

    A keynote paper presents just the next attempt to promote a discussion of modern state of art in the field of boiling heat transfer research. It is shown how longstanding disregard of internal contradictions of applicable approaches has resulted theoretical deadlock. Alternatively, it also is shown how resolution of these contradictions opens the ways to breakthrough in boiling heat transfer theory. Basic experimental facts, physical models and correlations are reconsidered. Principal contradictions between experimental knowledge and traditional model of 'the theatre of actors' (MTA) are discussed. Crucial role of pumping effect of growing bubble (PEGB) in boiling heat transfer and hydrodynamics is shown. Basic role of control of HTC by thermodynamic conditions on nucleation sites is demonstrated and consequent model of 'the theatre of director' (MTD) is discussed. Universal MTD-based correlation of boiling HTC of all types of liquids is considered. Unified consistent research framework for developed boiling heat transfer and diverse specific boiling heat transfer regimes is outlined through supplementing MTD by so-called multifactoring concept (MFC). The latter links transition from developed boiling mode to diverse boiling curves to a phenomenon of multiplication of factors influencing HTC. The ways of further research of the boiling problem are discussed. (author)

  3. MTD-MFC: unified framework for investigation of diversity of boiling heat transfer curves

    International Nuclear Information System (INIS)

    Shekriladze, I.G.

    2009-01-01

    A keynote paper presents just the next attempt to promote a discussion of modern state of art in the field of boiling heat transfer research. It is shown how longstanding disregard of internal contradictions of applicable approaches has resulted theoretical deadlock. Alternatively, it also is shown how resolution of these contradictions opens the ways to breakthrough in boiling heat transfer theory. Basic experimental facts, physical models and correlations are reconsidered. Principal contradictions between experimental knowledge and traditional model of 'the theatre of actors' (MTA) are discussed. Crucial role of pumping effect of growing bubble (PEGB) in boiling heat transfer and hydrodynamics is shown. Basic role of control of HTC by thermodynamic conditions on nucleation sites is demonstrated and consequent model of 'the theatre of director' (MTD) is discussed. Universal MTD-based correlation of boiling HTC of all types of liquids is considered. Unified consistent research framework for developed boiling heat transfer and diverse specific boiling heat transfer regimes is outlined through supplementing MTD by so-called multifactoring concept (MFC). The latter links transition from developed boiling mode to diverse boiling curves to a phenomenon of multiplication of factors influencing HTC. The ways of further research of the boiling problem are discussed. (author)

  4. Geysering in boiling channels

    Energy Technology Data Exchange (ETDEWEB)

    Aritomi, Masanori; Takemoto, Takatoshi [Tokyo Institute of Technology, Tokyo (Japan); Chiang, Jing-Hsien [Japan NUS Corp. Ltd., Toyko (Japan)] [and others

    1995-09-01

    A concept of natural circulation BWRs such as the SBWR has been proposed and seems to be promising in that the primary cooling system can be simplified. The authors have been investigating thermo-hydraulic instabilities which may appear during the start-up in natural circulation BWRs. In our previous works, geysering was investigated in parallel boiling channels for both natural and forced circulations, and its driving mechanism and the effect of system pressure on geysering occurrence were made clear. In this paper, geysering is investigated in a vertical column and a U-shaped vertical column heated in the lower parts. It is clarified from the results that the occurrence mechanism of geysering and the dependence of system pressure on geysering occurrence coincide between parallel boiling channels in circulation systems and vertical columns in non-circulation systems.

  5. Recent developments in the modeling of boiling heat transfer mechanisms

    International Nuclear Information System (INIS)

    Podowski, M.Z.

    2009-01-01

    Due to the importance of boiling for the analysis of operation and safety of nuclear reactors, extensive efforts have been made in the past to develop a variety of methods and tools to study boiling heat transfer for various geometries and operating conditions. Recent progress in the computational multiphase fluid dynamics (CMFD) methods of two- and multiphase flows has already started opening up new exciting possibilities for using complete multidimensional models to predict the operation of boiling systems under both steady-state and transient conditions. However, such models still require closure laws and boundary conditions, the accuracy of which determines the predictive capabilities of the overall models and the associated CMFD simulations. Because of the complexity of the underlying physical phenomena, boiling heat transfer has traditionally been quantified using phenomenological models and correlations obtained by curve-fitting extensive experimental data. Since simple heuristic formulae are not capable of capturing the effect of various specific experimental conditions and the associated wide scattering of data points, most existing correlations are characterized by large uncertainties which are typically hidden behind the 'logarithmic scale' format of plots. Furthermore, such an approach provides only limited insight into the local phenomena of: nucleation, heated surface material properties, temperature fluctuations, and others. The objectives of this paper are two-fold. First, the state of the art is reviewed in the area of modeling concepts for both pool boiling and forced-convection (bulk and subcooled) boiling. Then, new results are shown concerning the development of new mechanistic models and their validation against experimental data. It is shown that a combination of the proposed theoretical approach with advanced computational methods leads to a dramatic improvement in both our understanding of the physics of boiling and the predictive

  6. High boiling point hydrocarbons

    Energy Technology Data Exchange (ETDEWEB)

    Pier, M

    1929-04-29

    A process is given for the production of hydrocarbons of high boiling point, such as lubricating oils, from bituminous substances, such as varieties of coal, shale, or other solid distillable carbonaceous materials. The process consists of treating the initial materials with organic solvents and then subjecting the products extracted from the initial materials, preferably directly, to a reducing treatment in respect to temperature, pressure, and time. The reduction treatment is performed by means of hydrogen under pressure.

  7. Natural Circulation with Boiling

    Energy Technology Data Exchange (ETDEWEB)

    Mathisen, R P

    1967-09-15

    A number of parameters with dominant influence on the power level at hydrodynamic instability in natural circulation, two-phase flow, have been studied experimentally. The geometrical dependent quantities were: the system driving head, the boiling channel and riser dimensions, the single-phase as well as the two phase flow restrictions. The parameters influencing the liquid properties were the system pressure and the test section inlet subcooling. The threshold of instability was determined by plotting the noise characteristics in the mass flow records against power. The flow responses to artificially obtained power disturbances at instability conditions were also measured in order to study the nature of hydrodynamic instability. The results presented give a review over relatively wide ranges of the main parameters, mainly concerning the coolant performance in both single and parallel boiling channel flow. With regard to the power limits the experimental results verified that the single boiling channel performance was intimately related to that of the parallel channels. In the latter case the additional inter-channel factors with attenuating effects were studied. Some optimum values of the parameters were observed.

  8. Boiling induced mixed convection in cooling loops

    International Nuclear Information System (INIS)

    Knebel, J.U.; Janssens-Maenhout, G.; Mueller, U.

    2000-01-01

    This article describes the SUCO program performed at the Forschungszentrum Karlsruhe. The SUCO program is a three-step series of scaled model experiments investigating the possibility of a sump cooling concept for future light water reactors. In case of a core melt accident, the sump cooling concept realises a decay heat removal system that is based on passive safety features within the containment. The article gives, first, results of the experiments in the 1:20 linearly scaled SUCOS-2D test facility. The experimental results are scaled-up to the conditions in the prototype, allowing a statement with regard to the feasibility of the sump cooling concept. Second, the real height SUCOT test facility with a volume and power scale of 1:356 that is aimed at investigating the mixed single-phase and two-phase natural circulation flow in the reactor sump, together with first measurement results, are discussed. Finally, a numerical approach to model the subcooled nucleate boiling phenomena in the test facility SUCOT is presented. Physical models describing interfacial mass, momentum and-heat transfer are developed and implemented in the commercial software package CFX4.1. The models are validated for an isothermal air-water bubbly flow experiment and a subcooled boiling experiment in vertical annular water flow. (author)

  9. Boiling and quenching heat transfer advancement by nanoscale surface modification.

    Science.gov (United States)

    Hu, Hong; Xu, Cheng; Zhao, Yang; Ziegler, Kirk J; Chung, J N

    2017-07-21

    All power production, refrigeration, and advanced electronic systems depend on efficient heat transfer mechanisms for achieving high power density and best system efficiency. Breakthrough advancement in boiling and quenching phase-change heat transfer processes by nanoscale surface texturing can lead to higher energy transfer efficiencies, substantial energy savings, and global reduction in greenhouse gas emissions. This paper reports breakthrough advancements on both fronts of boiling and quenching. The critical heat flux (CHF) in boiling and the Leidenfrost point temperature (LPT) in quenching are the bottlenecks to the heat transfer advancements. As compared to a conventional aluminum surface, the current research reports a substantial enhancement of the CHF by 112% and an increase of the LPT by 40 K using an aluminum surface with anodized aluminum oxide (AAO) nanoporous texture finish. These heat transfer enhancements imply that the power density would increase by more than 100% and the quenching efficiency would be raised by 33%. A theory that links the nucleation potential of the surface to heat transfer rates has been developed and it successfully explains the current finding by revealing that the heat transfer modification and enhancement are mainly attributed to the superhydrophilic surface property and excessive nanoscale nucleation sites created by the nanoporous surface.

  10. Subcooled boiling heat transfer to R 12 in an annular vertical channel

    Energy Technology Data Exchange (ETDEWEB)

    Braeuer, H.; Mayinger, F.

    1988-10-01

    Detailed knowledge of the physical phenomena involved in subcooled boiling is of great importance for the design of liquid-cooled heat generating systems with high heat fluxes. Experimental heat transfer data were obtained for forced convective boiling of dichloro-difluoroethane (R 12). The flow is circulated upwards through a concentric annular vertical channel. The inner and outer diameters of the annulus are 0.016 m and 0.03 m respectively. The reduced pressures studied were 0.24 less than or equal to p/p/sub crit/ less than or equal to 0.8, inlet subcooling varied from 10 to 75 K and mass fluxes from 500 to 3000 kg/m/sup 2/s, which corresponds to Re numbers from 30 000 to 300 000. The experiments, described in this study, demonstrate that liquid fluorocarbons show certain unusual boiling characteristics in the subcooled flow, such as hysteresis of the boiling curve. These characteristics are attributed to the properties of the fluid, mainly the Pr number and the very low surface tension. The pronounced boiling curve hysteresis can be explained by the fact that large nucleation sites may have been flooded prior to incipient boiling. A dimensionless regression formula is presented which predicts the onset of subcooled boiling as a function of reduced pressure (p/p/sub crit/), Boiling-(Bo), Reynolds-(Re), and a modified Jacob Number (Ja), over the whole range of parameters studied, with a good accuracy, including water data from literature.

  11. Numerical investigation of boiling heat transfer on hydrocarbon mixture refrigerant in vertical rectangular minichannel

    Directory of Open Access Journals (Sweden)

    Huixing Li

    2016-05-01

    Full Text Available In order to investigate the characteristics of boiling heat transfer for hydrocarbon mixture refrigerant in plate-fin heat exchanger which is used in the petrochemical industry field, a model was established on boiling heat transfer in vertical rectangular channel. The simulated results were compared with the experimental data from literature. The results show that the deviation between the simulated results and experimental data is within ±15%. Meanwhile, the characteristic of boiling heat transfer was investigated in vertical rectangular minichannel of plate-fin heat exchanger. The results show that the boiling heat transfer coefficient increases with the increase in quality and mass flux and is slightly impacted by the heat flux. This is because that the main boiling mechanism is forced convective boiling while the contribution of nucleate boiling is slight. The correlation of Liu and Winterton is in good agreement with the simulation results. The deviation between correlation calculations and simulation results is mostly less than ±15%. These results will provide some constructive instructions for the understanding of saturated boiling mechanism in a vertical rectangular minichannel and the prediction of heat transfer performance in plate-fin heat exchanger.

  12. Subcooled flow boiling heat transfer of dilute alumina, zinc oxide, and diamond nanofluids at atmospheric pressure

    International Nuclear Information System (INIS)

    Kim, Sung Joong; McKrell, Tom; Buongiorno, Jacopo; Hu Linwen

    2010-01-01

    A nanofluid is a colloidal suspension of nano-scale particles in water, or other base fluids. Previous pool boiling studies have shown that nanofluids can improve the critical heat flux (CHF) by as much as 200%. In a previous paper, we reported on subcooled flow boiling CHF experiments with low concentrations of alumina, zinc oxide, and diamond nanoparticles in water (≤0.1% by volume) at atmospheric pressure, which revealed a substantial CHF enhancement (∼40-50%) at the highest mass flux (G = 2500 kg/m 2 s) and concentration (0.1 vol.%) for all nanoparticle materials (). In this paper, we focus on the flow boiling heat transfer coefficient data collected in the same tests. It was found that for comparable test conditions the values of the nanofluid and water heat transfer coefficient are similar (within ±20%). The heat transfer coefficient increased with mass flux and heat flux for water and nanofluids alike, as expected in flow boiling. A confocal microscopy-based examination of the test section revealed that nanoparticle deposition on the boiling surface occurred during nanofluid boiling. Such deposition changes the number of micro-cavities on the surface, but also changes the surface wettability. A simple model was used to estimate the ensuing nucleation site density changes, but no definitive correlation between the nucleation site density and the heat transfer coefficient data could be found.

  13. Specific features of hydrogen boiling heat transfer on the AMg-6 alloy massive heater

    International Nuclear Information System (INIS)

    Kirichenko, Yu.A.; Kozlov, S.M.; Rusanov, K.V.; Tyurina, E.G.

    1989-01-01

    Heat transfer and nucleate burns-out saturated with hydrogen at a plate heater (thickness-13 mm, diameter of heat-transferring surface - 30 mm) made of an aluminium alloy with the low value of a heat assimilation coefficient in the pressure range from 7.2x10 3 to 6x10 5 Pa is experimentally investigated. Value of start of boiling characteristics and heat transfer coefficients during nucleate burn-out, as well as the first critical densities of a heat flux and temperature heads are obtained. Existence of certain differrences of heat exchange during boiling is shown using a massive heater made of low-heat-conductive material in comparison with other cases of hydrogen boiling. Hypothesis concerning the existence of so-called mixed boiling on the heat transfer surface, which has been detected earlier only in helium boiling, as well as concerning possible reasons of stability of film boiling ficii in preburn-out region of heat duty is discussed

  14. Predictions of void fraction in convective subcooled boiling channels using a one-dimensional two-fluid model

    International Nuclear Information System (INIS)

    Hu, Lin-Wen; Pan, Chin

    1995-01-01

    Subcooled nucleate boiling under forced convective conditions is of considerable interest for many disciplines, such as nuclear reactor technology and other energy conversion systems, due to its high heat transfer capability. For such applications, the liquid entering the heating channel is usually in a subcooled state and nucleate boiling is initiated at some distance from the entrance. Further downstream from the boiling incipient point, the bubbles may depart from the heating wall. The point of first bubble departure is called the net vapor generation (NVG) point, because after this point, significant void is present in the subcooled liquid and the void fraction rises very rapidly even though the bulk liquid may still be in a highly subcooled state. The presence of vapor bubbles, which are at a temperature near the saturation temperature, in a subcooled liquid shows the existence of thermal nonequilibrium, which complicates the analysis of this boiling regime. 13 refs., 4 figs

  15. Dimers in nucleating vapors

    Science.gov (United States)

    Lushnikov, A. A.; Kulmala, M.

    1998-09-01

    The dimer stage of nucleation may affect considerably the rate of the nucleation process at high supersaturation of the nucleating vapor. Assuming that the dimer formation limits the nucleation rate, the kinetics of the particle formation-growth process is studied starting with the definition of dimers as bound states of two associating molecules. The partition function of dimer states is calculated by summing the Boltzmann factor over all classical bound states, and the equilibrium population of dimers is found for two types of intermolecular forces: the Lennard-Jones (LJ) and rectangular well+hard core (RW) potentials. The principle of detailed balance is used for calculating the evaporation rate of dimers. The kinetics of the particle formation-growth process is then investigated under the assumption that the trimers are stable with respect to evaporation and that the condensation rate is a power function of the particle mass. If the power exponent λ=n/(n+1) (n is a non-negative integer), the kinetics of the process is described by a finite set of moments of particle mass distribution. When the characteristic time of the particle formation by nucleation is much shorter than that of the condensational growth, n+2 universal functions of a nondimensional time define the kinetic process. These functions are calculated for λ=2/3 (gas-to-particle conversion in the free molecular regime) and λ=1/2 (formation of islands on surfaces).

  16. Boiling heat transfer to LN2 and LH2 - Influence of surface orientation and reduced body forces

    Science.gov (United States)

    Merte, H., Jr.; Oker, E.; Littles, J. W.

    1973-01-01

    The quantitative determination of the influence of heater surface orientation and gravity on nucleate pool boiling of liquid nitrogen and liquid hydrogen is described. A transient calorimeter technique, well suited for obtaining pool boiling data under reduced gravity and used earlier by Clark and Merte (1963), was employed after being adapted to flat a surface whose orientation could be varied. The obtained determination results are reviewed.

  17. Boiling on fins with wire screen of variable effective conductivity

    Directory of Open Access Journals (Sweden)

    Orzechowski Tadeusz

    2017-01-01

    Full Text Available The high scale of integration of modern equipment used for medical, military and other purposes puts heavy demands as regards the removal of great heat fluxes. This can be achieved only in exchangers that apply the phase change phenomena. Among many methods to improve boiling heat transfer, the wire mesh covering demonstrates some advantages due to the possibilities of designing the desired microstructure parameters, availability on the market, and low cost. The wire mesh microstucture with specified geometrical parameters produces anisotropy in conductivity. The different arrangement of the mesh layers relative to the direction of the heat flux is a cause of the change of temperature distribution within the layer. The consequence is a respective change in the discharge conditions of the gas phase and liquid feed. The experiments were conducted on fins covered with a single layer of copper mesh with lumen of 38 % and boiling FC-72 at ambient pressure. Compared with the smooth surface, the wire mesh structures yield an increase in the heat transfer rate at boiling. It is also shown that nucleate boiling is initiated at lower wall superheat. Formulas for longitudinal and perpendicular thermal conductivity are given for different mesh structure arrangements.

  18. Numerical analysis on pool boiling using user defined function

    Energy Technology Data Exchange (ETDEWEB)

    Ryu, Sung Uk; Jeon, Byong Guk; Kim, Seok; Euh, Dong-Jin [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

    2015-10-15

    PAFS (passive auxiliary feedwater system) adopted in the APR+ (Advanced Power Reactor Plus) of Korea is one such application. When PAFS is activated with an actuation signal, steam from the steam generator passes through heat exchanger tubes submerged in a water tank of the PAFS. Outside these heat exchanger tubes, nucleate boiling phenomena appears. In the present work, a numerical study is reported on three-dimensional transient state pool boiling of water having an immersed heat source. The velocity vector fields during the decrease in the water level are numerically investigated in a pool, and the accuracy of the results is checked by comparing the experimental results conducted using the PIV techniques by Kim et al. These numerical results can be used as basic research data for an analysis and prediction of the natural circulation phenomena in the cooling tank of the passive safety system in a nuclear power plant.

  19. Assessment of interfacial heat transfer models under subcooled flow boiling

    Energy Technology Data Exchange (ETDEWEB)

    Ribeiro, Guilherme B.; Braz Filho, Francisco A., E-mail: gbribeiro@ieav.cta.br, E-mail: fbraz@ieav.cta.br [Instituto de Estudos Avançados (DCTA/IEAv), São José dos Campos, SP (Brazil). Div. de Energia Nuclear

    2017-07-01

    The present study concerns a detailed analysis of subcooled flow boiling characteristics under high pressure systems using a two-fluid Eulerian approach provided by a Computational Fluid Dynamics (CFD) solver. For this purpose, a vertical heated pipe made of stainless steel with an internal diameter of 15.4 mm was considered as the modeled domain. An uniform heat flux of 570 kW/m2 and saturation pressure of 4.5 MPa were applied to the channel wall, whereas water mass flux of 900 kg/m2s was considered for all simulation cases. The model was validated against a set of experimental data and results have indicated a promising use of CFD technique for the estimation of wall temperature, the liquid bulk temperature and the location of the departure of nucleate boiling. Different sub-models of interfacial heat transfer coefficient were applied and compared, allowing a better prediction of void fraction along the heated channel. (author)

  20. Boiling crisis as inhibition of bubble detachment by the vapor recoil force

    International Nuclear Information System (INIS)

    Nikolayev, V.S.; Beysens, D.; Garrabos, Y.

    2004-01-01

    Boiling crisis is a transition between nucleate and film boiling. In this communication we present a physical model of the boiling crisis based on the vapor recoil effect. Our numerical simulations of the thermally controlled bubble growth at high heat fluxes show how the bubble begins to spread over the heater thus forming a germ for the vapor film. The vapor recoil force not only causes the vapor spreading, it also creates a strong adhesion to the heater that prevents the bubble departure, thus favoring the further bubble spreading. Near the liquid-gas critical point, the bubble growth is very slow and allows the kinetics of the bubble spreading to be observed. Since the surface tension is very small in this regime, only microgravity conditions can preserve a convex bubble shape. Under such conditions, we observed an increase of the apparent contact angle and spreading of the dry spot under the bubble, thus confirming our model of the boiling crisis. (authors)

  1. Research on boiling and two-phase flow

    International Nuclear Information System (INIS)

    Marinsek, Z.; Gaspersic, B.; Pavselj, D.; Tomsic, M.

    1977-01-01

    Report consists of three contributions. Experimental apparatus with pressure chamber (up to 25 bar and 250 deg C) was constructed including optical bubble detection device, and test measurements of mutual influence of boiling bubbles from two adjacent nucleation sites were performed; for analyses, a computer programme package for coincidence analyses of events was made, including data acquisition hardware. Two-phase pressure drop in subcooled Vertical annular water flow was measured, for pressures up to 10 bar, mass velocity 500 to 760 kg/m 2 s and vapour quality 0 to .01. Results agree fairly well with Martinelli-Nelson model

  2. Nonequilibrium thermodynamics of nucleation

    NARCIS (Netherlands)

    Schweizer, M.; Sagis, L.M.C.

    2014-01-01

    We present a novel approach to nucleation processes based on the GENERIC framework (general equation for the nonequilibrium reversible-irreversible coupling). Solely based on the GENERIC structure of time-evolution equations and thermodynamic consistency arguments of exchange processes between a

  3. Dispersed flow film boiling

    International Nuclear Information System (INIS)

    Andreani, M.; Yadigaroglu, G.

    1989-12-01

    Dispersed flow film boiling is the heat transfer regime that occurs at high void fractions in a heated channel. The way this transfer mode is modelled in the NRC computer codes (RELAP5 and TRAC) and the validity of the assumption and empirical correlations used is discussed. An extensive review of the theoretical and experimental work related with heat transfer to highly dispersed mixtures reveals the basic deficiencies of these models: the investigation refers mostly to the typical conditions of low rate bottom reflooding, since the simulation of this physical situation by the computer codes has often showed poor results. The alternative models that are available in the literature are reviewed, and their merits and limits are highlighted. The modification that could improve the physics of the models implemented in the codes are identified. (author) 13 figs., 123 refs

  4. Advanced boiling water reactor

    International Nuclear Information System (INIS)

    Nishimura, N.; Nakai, H.; Ross, M.A.

    1999-01-01

    In the Boiling Water Reactor (BWR) system, steam generated within the nuclear boiler is sent directly to the main turbine. This direct cycle steam delivery system enables the BWR to have a compact power generation building design. Another feature of the BWR is the inherent safety that results from the negative reactivity coefficient of the steam void in the core. Based on the significant construction and operation experience accumulated on the BWR throughout the world, the ABWR was developed to further improve the BWR characteristics and to achieve higher performance goals. The ABWR adopted 'First of a Kind' type technologies to achieve the desired performance improvements. The Reactor Internal Pump (RIP), Fine Motion Control Rod Drive (FMCRD), Reinforced Concrete Containment Vessel (RCCV), three full divisions of Emergency Core Cooling System (ECCS), integrated digital Instrumentation and Control (I and C), and a high thermal efficiency main steam turbine system were developed and introduced into the ABWR. (author)

  5. When water does not boil at the boiling point.

    Science.gov (United States)

    Chang, Hasok

    2007-03-01

    Every schoolchild learns that, under standard pressure, pure water always boils at 100 degrees C. Except that it does not. By the late 18th century, pioneering scientists had already discovered great variations in the boiling temperature of water under fixed pressure. So, why have most of us been taught that the boiling point of water is constant? And, if it is not constant, how can it be used as a 'fixed point' for the calibration of thermometers? History of science has the answers.

  6. Single-bubble dynamics in pool boiling of one-component fluids

    KAUST Repository

    Xu, Xinpeng; Qian, Tiezheng

    2014-01-01

    We numerically investigate the pool boiling of one-component fluids with a focus on the effects of surface wettability on the single-bubble dynamics. We employed the dynamic van der Waals theory [Phys. Rev. E 75, 036304 (2007)], a diffuse-interface model for liquid-vapor flows involving liquid-vapor transition in nonuniform temperature fields. We first perform simulations for bubbles on homogeneous surfaces. We find that an increase in either the contact angle or the surface superheating can enhance the bubble spreading over the heating surface and increase the bubble departure diameter as well and therefore facilitate the transition into film boiling. We then examine the dynamics of bubbles on patterned surfaces, which incorporate the advantages of both hydrophobic and hydrophilic surfaces. The central hydrophobic region increases the thermodynamic probability of bubble nucleation while the surrounding hydrophilic region hinders the continuous bubble spreading by pinning the contact line at the hydrophobic-hydrophilic intersection. This leads to a small bubble departure diameter and therefore prevents the transition from nucleate boiling into film boiling. With the bubble nucleation probability increased and the bubble departure facilitated, the efficiency of heat transfer on such patterned surfaces is highly enhanced, as observed experimentally [Int. J. Heat Mass Transfer 57, 733 (2013)]. In addition, the stick-slip motion of contact line on patterned surfaces is demonstrated in one-component fluids, with the effect weakened by surface superheating.

  7. Boiling Heat Transfer Coefficients of Nanofluids Containing Carbon Nanotubes up to Critical Heat Fluxes

    International Nuclear Information System (INIS)

    Park, Ki Jung; Lee, Yohan; Jung, Dong Soo; Shim, Sang Eun

    2011-01-01

    In this study, the nucleate pool boiling heat transfer coefficients (HTCs) and critical heat flux (CHF) for a smooth and square flat heater in a pool of pure water with and without carbon nanotubes (CNTs) dispersed at 60 .deg. C were measured. Tested aqueous nanofluids were prepared using CNTs with volume concentrations of 0.0001%, 0.001%, and 0.01%. The CNTs were dispersed by chemically treating them with an acid in the absence of any polymers. The results showed that the pool boiling HTCs of the nanofluids are higher than those of pure water in the entire nucleate boiling regime. The acid-treated CNTs led to the deposition of a small amount of CNTs on the surface, and the CNTs themselves acted as heat-transfer-enhancing particles, owing to their very high thermal conductivity. There was a significant increase in the CHF- up to 150%-when compared to that of pure water containing CNTs with a volume concentration of 0.001%. This is attributed to the change in surface characteristics due to the deposition of a very thin layer of CNTs on the surface. This layer delays nucleate boiling and causes a reduction in the size of the large vapor canopy around the CHF. This results in a significant increase in the CHF

  8. Single-bubble dynamics in pool boiling of one-component fluids

    KAUST Repository

    Xu, Xinpeng

    2014-06-04

    We numerically investigate the pool boiling of one-component fluids with a focus on the effects of surface wettability on the single-bubble dynamics. We employed the dynamic van der Waals theory [Phys. Rev. E 75, 036304 (2007)], a diffuse-interface model for liquid-vapor flows involving liquid-vapor transition in nonuniform temperature fields. We first perform simulations for bubbles on homogeneous surfaces. We find that an increase in either the contact angle or the surface superheating can enhance the bubble spreading over the heating surface and increase the bubble departure diameter as well and therefore facilitate the transition into film boiling. We then examine the dynamics of bubbles on patterned surfaces, which incorporate the advantages of both hydrophobic and hydrophilic surfaces. The central hydrophobic region increases the thermodynamic probability of bubble nucleation while the surrounding hydrophilic region hinders the continuous bubble spreading by pinning the contact line at the hydrophobic-hydrophilic intersection. This leads to a small bubble departure diameter and therefore prevents the transition from nucleate boiling into film boiling. With the bubble nucleation probability increased and the bubble departure facilitated, the efficiency of heat transfer on such patterned surfaces is highly enhanced, as observed experimentally [Int. J. Heat Mass Transfer 57, 733 (2013)]. In addition, the stick-slip motion of contact line on patterned surfaces is demonstrated in one-component fluids, with the effect weakened by surface superheating.

  9. Homogeneous crystal nucleation in polymers.

    Science.gov (United States)

    Schick, C; Androsch, R; Schmelzer, J W P

    2017-11-15

    The pathway of crystal nucleation significantly influences the structure and properties of semi-crystalline polymers. Crystal nucleation is normally heterogeneous at low supercooling, and homogeneous at high supercooling, of the polymer melt. Homogeneous nucleation in bulk polymers has been, so far, hardly accessible experimentally, and was even doubted to occur at all. This topical review summarizes experimental findings on homogeneous crystal nucleation in polymers. Recently developed fast scanning calorimetry, with cooling and heating rates up to 10 6 K s -1 , allows for detailed investigations of nucleation near and even below the glass transition temperature, including analysis of nuclei stability. As for other materials, the maximum homogeneous nucleation rate for polymers is located close to the glass transition temperature. In the experiments discussed here, it is shown that polymer nucleation is homogeneous at such temperatures. Homogeneous nucleation in polymers is discussed in the framework of the classical nucleation theory. The majority of our observations are consistent with the theory. The discrepancies may guide further research, particularly experiments to progress theoretical development. Progress in the understanding of homogeneous nucleation is much needed, since most of the modelling approaches dealing with polymer crystallization exclusively consider homogeneous nucleation. This is also the basis for advancing theoretical approaches to the much more complex phenomena governing heterogeneous nucleation.

  10. Interfacial area transport of subcooled boiling flow in a vertical annulus

    Energy Technology Data Exchange (ETDEWEB)

    Brooks, Caleb S.; Ozar, Basar; Hibiki, Takashi; Ishii, Mamoru, E-mail: ishii@purdue.edu

    2014-03-15

    Highlights: • Discussion of boiling and wall nucleation dataset obtained in a vertical annulus. • Overview of the interfacial area transport equation modeling in boiling flow. • Comparison of bubble departure diameter and frequency with existing models. • Evaluation of the interfacial area transport equation prediction in boiling flow. - Abstract: In an effort to improve the prediction of void fraction and heat transfer characteristics in two-phase systems, the two-group interfacial area transport equation has been developed for use with the two-group two-fluid model. The two-group approach treats spherical/distorted bubbles as Group-1 and cap/slug/churn-turbulent bubbles as Group-2. Therefore, the interfacial area transport of steam-water two-phase flow in a vertical annulus has been investigated experimentally, including bulk flow parameters and wall nucleation characteristics. The theoretical modeling of interfacial area transport equation with phase change terms is introduced and discussed along with the experimental results. Benchmark of the interfacial area transport equation is performed considering the effects of bubble interaction mechanisms such as bubble break-up and coalescence, as well as, effects of phase change mechanisms such as wall nucleation and condensation for subcooled boiling. From the benchmark, sensitivity in the constitutive relations for Group-1 phase change mechanisms, such as wall nucleation and condensation is clear. The Group-2 interfacial area transport is shown to be dominated by the interfacial heat transfer mechanism causing expansion of Group-1 bubbles into Group-2 bubbles in the boiling flow.

  11. Enhanced Boiling on Micro-Configured Composite Surfaces Under Microgravity Conditions

    Science.gov (United States)

    Zhang, Nengli; Chai, An-Ti

    1999-01-01

    In order to accommodate the growing thermal management needs of future space platforms, several two-phase active thermal control systems (ATCSs) have evolved and were included in the designs of space stations. Compared to the pumped single-phase liquid loops used in the conventional Space Transportation System and Spacelab, ATCSs offer significant benefits that may be realized by adopting a two-phase fluid-loop system. Alternately, dynamic power systems (DPSs), based on the Rankine cycle, seem inevitably to be required to supply the electrical power requirements of expanding space activities. Boiling heat transfer is one of the key technologies for both ATCSs and DPSs. Nucleate boiling near critical heat flux (CHF) can transport very large thermal loads with much smaller device size and much lower pumping power. However, boiling performance deteriorates in a reduced gravity environment and operation in the CHF regime is precarious because any slight overload will cause the heat transfer to suddenly move to the film boiling regime, which in turn, will result in burnout of the heat transfer surfaces. New materials, such as micro-configured metal-graphite composites, can provide a solution for boiling enhancement. It has been shown experimentally that this type of material manifests outstanding boiling heat transfer performance and their CHF is also extended to higher values. Due to the high thermal conductivity of graphite fiber (up to 1,200 W/m-K in the fiber direction), the composite surfaces are non-isothermal during the boiling process. The composite surfaces are believed to have a much wider safe operating region (a more uniform boiling curve in the CHF regime) because non-isothermal surfaces have been found to be less sensitive to variations of wall superheat in the CHF regime. The thermocapillary forces formed by the temperature difference between the fiber tips and the metal matrix play a more important role than the buoyancy in the bubble detachment, for the

  12. Large-scale boiling experiments of the flooded cavity concept for in-vessel core retention

    International Nuclear Information System (INIS)

    Chu, T.Y.; Slezak, S.E.; Bentz, J.H.; Pasedag, W.F.

    1994-01-01

    This paper presents results of ex-vessel boiling experiments performed in the CYBL (CYlindrical BoiLing) facility. CYBL is a reactor-scale facility for confirmatory research of the flooded cavity concept for accident management. CYBL has a tank-within-a-tank design; the inner tank simulates the reactor vessel and the outer tank simulates the reactor cavity. Experiments with uniform and edge-peaked heat flux distributions up to 20 W/cm 2 across the vessel bottom were performed. Boiling outside the reactor vessel was found to be subcooled nucleate boiling. The subcooling is mainly due to the gravity head which results from flooding the sides of the reactor vessel. The boiling process exhibits a cyclic pattern with four distinct phases: direct liquid/solid contact, bubble nucleation and growth, coalescence, and vapor mass dispersion (ejection). The results suggest that under prototypic heat load and heat flux distributions, the flooded cavity in a passive pressurized water reactor like the AP-600 should be capable of cooling the reactor pressure vessel in the central region of the lower head that is addressed by these tests

  13. Computational Fluid Dynamic Simulation of Single Bubble Growth under High-Pressure Pool Boiling Conditions

    Directory of Open Access Journals (Sweden)

    Janani Murallidharan

    2016-08-01

    Full Text Available Component-scale modeling of boiling is predominantly based on the Eulerian–Eulerian two-fluid approach. Within this framework, wall boiling is accounted for via the Rensselaer Polytechnic Institute (RPI model and, within this model, the bubble is characterized using three main parameters: departure diameter (D, nucleation site density (N, and departure frequency (f. Typically, the magnitudes of these three parameters are obtained from empirical correlations. However, in recent years, efforts have been directed toward mechanistic modeling of the boiling process. Of the three parameters mentioned above, the departure diameter (D is least affected by the intrinsic uncertainties of the nucleate boiling process. This feature, along with its prominence within the RPI boiling model, has made it the primary candidate for mechanistic modeling ventures. Mechanistic modeling of D is mostly carried out through solving of force balance equations on the bubble. Forces incorporated in these equations are formulated as functions of the radius of the bubble and have been developed for, and applied to, low-pressure conditions only. Conversely, for high-pressure conditions, no mechanistic information is available regarding the growth rates of bubbles and the forces acting on them. In this study, we use direct numerical simulation coupled with an interface tracking method to simulate bubble growth under high (up to 45 bar pressure, to obtain the kind of mechanistic information required for an RPI-type approach. In this study, we compare the resulting bubble growth rate curves with predictions made with existing experimental data.

  14. Flow boiling heat transfer on nanowire-coated surfaces with highly wetting liquid

    International Nuclear Information System (INIS)

    Shin, Sangwoo; Choi, Geehong; Kim, Beom Seok; Cho, Hyung Hee

    2014-01-01

    Owing to the recent advances in nanotechnology, one significant progress in energy technology is increased cooling ability. It has recently been shown that nanowires can improve pool boiling heat transfer due to the unique features such as enhanced wetting and enlarged nucleation sites. Applying such nanowires on a flow boiling, which is another major class of boiling phenomenon that is associated with forced convection, is yet immature and scarce despite its importance in various applications such as liquid cooling of energy, electronics and refrigeration systems. Here, we investigate flow boiling heat transfer on surfaces that are coated with SiNWs (silicon nanowires). Also, we use highly-wetting dielectric liquid, FC-72, as a working fluid. An interesting wetting behavior is observed where the presence of SiNWs reduces wetting and wicking that in turn leads to significant decrease of CHF (critical heat flux) compared to the plain surface, which opposes the current consensus. Also, the effects of nanowire length and Reynolds number on the boiling heat transfer are shown to be highly nonmonotonic. We attempt to explain such an unusual behavior on the basis of wetting, nucleation and forced convection, and we show that such factors are highly coupled in a way that lead to unusual behavior. - Highlights: • Observation of suppressed wettability in the presence of surface roughness (nanowires). • Significant reduction of critical heat flux in the presence of nanowires. • Nonmonotonic behavior of heat transfer coefficient vs. nanowire length and Reynolds number

  15. Prediction of subcooled flow boiling characteristics using two-fluid Eulerian CFD model

    Energy Technology Data Exchange (ETDEWEB)

    Braz Filho, Francisco A.; Ribeiro, Guilherme B., E-mail: gbribeiro@ieav.cta.br; Caldeira, Alexandre D.

    2016-11-15

    Highlights: • CFD multiphase model is used to predict subcooled flow boiling characteristics. • Better agreement is achieved for higher saturation pressures. • Onset of nucleate boiling and saturated boiling are well predicted. • CFD multiphase model tends to underestimate the void fraction. • Factors were adjusted in order to improve the void fraction results. - Abstract: The present study concerns a detailed analysis of flow boiling phenomena under high pressure systems using a two-fluid Eulerian approach provided by a Computational Fluid Dynamics (CFD) solver. For this purpose, a vertical heated pipe made of stainless steel with an internal diameter of 15.4 mm was considered as the modeled domain. Two different uniform heat fluxes and three saturation pressures were applied to the channel wall, whereas water mass flux of 900 kg/m{sup 2} s was considered for all simulation cases. The model was validated against a set of experimental data and results have indicated a promising use of the CFD technique for estimation of the wall temperature, the liquid bulk temperature and the location of the departure of nucleate boiling. Changes in factors applied in the modeling of the interfacial heat transfer coefficient and bubble departure frequency were suggested, allowing a better prediction of the void fraction along the heated channel. The commercial CFD solver FLUENT 14.5 was used for the model implementation.

  16. Prediction of subcooled flow boiling characteristics using two-fluid Eulerian CFD model

    International Nuclear Information System (INIS)

    Braz Filho, Francisco A.; Ribeiro, Guilherme B.; Caldeira, Alexandre D.

    2016-01-01

    Highlights: • CFD multiphase model is used to predict subcooled flow boiling characteristics. • Better agreement is achieved for higher saturation pressures. • Onset of nucleate boiling and saturated boiling are well predicted. • CFD multiphase model tends to underestimate the void fraction. • Factors were adjusted in order to improve the void fraction results. - Abstract: The present study concerns a detailed analysis of flow boiling phenomena under high pressure systems using a two-fluid Eulerian approach provided by a Computational Fluid Dynamics (CFD) solver. For this purpose, a vertical heated pipe made of stainless steel with an internal diameter of 15.4 mm was considered as the modeled domain. Two different uniform heat fluxes and three saturation pressures were applied to the channel wall, whereas water mass flux of 900 kg/m"2 s was considered for all simulation cases. The model was validated against a set of experimental data and results have indicated a promising use of the CFD technique for estimation of the wall temperature, the liquid bulk temperature and the location of the departure of nucleate boiling. Changes in factors applied in the modeling of the interfacial heat transfer coefficient and bubble departure frequency were suggested, allowing a better prediction of the void fraction along the heated channel. The commercial CFD solver FLUENT 14.5 was used for the model implementation.

  17. Subcooled boiling heat transfer and dryout on a constant temperature microheater

    International Nuclear Information System (INIS)

    Chen Tailian; Klausner, James F.; Chung, Jacob N.

    2004-01-01

    An experimental study of single-bubble subcooled boiling heat transfer (ΔT sub =31.5 K) on a small heater with constant wall temperature has been performed to better understand the boiling heat transfer associated with this unique configuration. The heater of 0.27 mm x 0.27 mm is set at different superheats to generate vapor bubbles on the microheater surface. For each superheat, the heater temperature is maintained constant by an electronic feedback control circuit while its power dissipation is measured at a frequency of 4.5 kHz. The single-bubble boiling is characterized by a transient bubble nucleation-departure period and a slow growth period. For the superheat range of 34-114 K in this study, at wall superheats below 84 K, the heater remains partially wetted following bubble departure and subsequent nucleation, and this period is characterized by a heat flux spike. At wall superheats above 90 K, the heater is blanketed with vapor following bubble departure and the heat flux experiences a dip during this period. At all superheats, the slow growth period is characterized by an almost uniform heat flux, and it has been observed that the heater surface is mostly covered by vapor. The unique heat transfer processes associated with boiling on this microheater are considerably different than those typically observed during boiling on a large heater

  18. Tube micro-fouling, boiling and steam pressure after chemical cleaning

    International Nuclear Information System (INIS)

    Hu, M.H.

    1998-01-01

    This paper presents steam pressure trends after chemical cleaning of steam generator tubes at four plants. The paper also presents tube fouling factor that serves as an objective parameter to assess tubing boiling conditions for understanding the steam pressure trend. Available water chemistry data helps substantiate the concept of tube micro-fouling, its effect on tubing boiling, and its impact on steam pressure. All four plants experienced a first mode of decreasing steam pressure in the post-cleaning operation. After 3 to 4 months of operation, the decreasing trend stopped for three plants and then restored to a pre-cleaning value or better. The fourth plant is soil in decreasing trend after 12 months of operation. Dissolved chemicals, such as silica, titanium can precipitate on tube surface. The precipitate micro-fouling can deactivate or eliminate boiling nucleation sites. Therefore, the first phase of the post-cleaning operation suffered a decrease in steam pressure or an increase in fouling factor. It appears that micro fouling by magnetite deposit can activate or create more bubble nucleation sites. Therefore, the magnetite deposit micro-fouling results in a decrease in fouling factor, and a recovery in steam pressure. Fully understanding the boiling characteristics of the tubing at brand new, fouled and cleaned conditions requires further study of tubing surface conditions. Such study should include boiling heat transfer tests and scanning electronic microscope examination. (author)

  19. Overview: Nucleation of clathrate hydrates.

    Science.gov (United States)

    Warrier, Pramod; Khan, M Naveed; Srivastava, Vishal; Maupin, C Mark; Koh, Carolyn A

    2016-12-07

    Molecular level knowledge of nucleation and growth of clathrate hydrates is of importance for advancing fundamental understanding on the nature of water and hydrophobic hydrate formers, and their interactions that result in the formation of ice-like solids at temperatures higher than the ice-point. The stochastic nature and the inability to probe the small length and time scales associated with the nucleation process make it very difficult to experimentally determine the molecular level changes that lead to the nucleation event. Conversely, for this reason, there have been increasing efforts to obtain this information using molecular simulations. Accurate knowledge of how and when hydrate structures nucleate will be tremendously beneficial for the development of sustainable hydrate management strategies in oil and gas flowlines, as well as for their application in energy storage and recovery, gas separation, carbon sequestration, seawater desalination, and refrigeration. This article reviews various aspects of hydrate nucleation. First, properties of supercooled water and ice nucleation are reviewed briefly due to their apparent similarity to hydrates. Hydrate nucleation is then reviewed starting from macroscopic observations as obtained from experiments in laboratories and operations in industries, followed by various hydrate nucleation hypotheses and hydrate nucleation driving force calculations based on the classical nucleation theory. Finally, molecular simulations on hydrate nucleation are discussed in detail followed by potential future research directions.

  20. Overview: Nucleation of clathrate hydrates

    Science.gov (United States)

    Warrier, Pramod; Khan, M. Naveed; Srivastava, Vishal; Maupin, C. Mark; Koh, Carolyn A.

    2016-12-01

    Molecular level knowledge of nucleation and growth of clathrate hydrates is of importance for advancing fundamental understanding on the nature of water and hydrophobic hydrate formers, and their interactions that result in the formation of ice-like solids at temperatures higher than the ice-point. The stochastic nature and the inability to probe the small length and time scales associated with the nucleation process make it very difficult to experimentally determine the molecular level changes that lead to the nucleation event. Conversely, for this reason, there have been increasing efforts to obtain this information using molecular simulations. Accurate knowledge of how and when hydrate structures nucleate will be tremendously beneficial for the development of sustainable hydrate management strategies in oil and gas flowlines, as well as for their application in energy storage and recovery, gas separation, carbon sequestration, seawater desalination, and refrigeration. This article reviews various aspects of hydrate nucleation. First, properties of supercooled water and ice nucleation are reviewed briefly due to their apparent similarity to hydrates. Hydrate nucleation is then reviewed starting from macroscopic observations as obtained from experiments in laboratories and operations in industries, followed by various hydrate nucleation hypotheses and hydrate nucleation driving force calculations based on the classical nucleation theory. Finally, molecular simulations on hydrate nucleation are discussed in detail followed by potential future research directions.

  1. Bubble and boundary layer behaviour in subcooled flow boiling

    Energy Technology Data Exchange (ETDEWEB)

    Maurus, Reinhold; Sattelmayer, Thomas [Lehrstuhl fuer Thermodynamik, Technische Universitaet Muenchen, 85747 Garching (Germany)

    2006-03-15

    Subcooled flow boiling is a commonly applied technique for achieving efficient heat transfer. In the study, an experimental investigation in the nucleate boiling regime was performed for water circulating in a closed loop at atmospheric pressure. The horizontal orientated test-section consists of a rectangular channel with a one side heated copper strip and good optical access. Various optical observation techniques were applied to study the bubble behaviour and the characteristics of the fluid phase. The bubble behaviour was recorded by the high-speed cinematography and by a digital high resolution camera. Automated image processing and analysis algorithms developed by the authors were applied for a wide range of mass flow rates and heat fluxes in order to extract characteristic length and time scales of the bubbly layer during the boiling process. Using this methodology, the bubbles were automatically analysed and the bubble size, bubble lifetime, waiting time between two cycles were evaluated. Due to the huge number of observed bubbles a statistical analysis was performed and distribution functions were derived. Using a two-dimensional cross-correlation algorithm, the averaged axial phase boundary velocity profile could be extracted. In addition, the fluid phase velocity profile was characterised by means of the particle image velocimetry (PIV) for the single phase flow as well as under subcooled flow boiling conditions. The results indicate that the bubbles increase the flow resistance. The impact on the flow exceeds by far the bubbly region and it depends on the magnitude of the boiling activity. Finally, the ratio of the averaged phase boundary velocity and of the averaged fluid velocity was evaluated for the bubbly region. (authors)

  2. Heterogeneous ice nucleation

    Energy Technology Data Exchange (ETDEWEB)

    Bogdan, A. [Helsinki Univ. (Finland). Dept. of Physics

    1994-12-31

    The classical theory of heterogenous ice nucleation is reviewed in detail. The modelling of ice nucleation in the adsorbed water films on natural particles by analogous ice nucleation in adsorbed water films on the walls of porous media is discussed. Ice nucleation in adsorbed films of purewater and the HNO{sub 3}/H{sub 2}0 binary system on the surface of porous aerosol (SiO{sub 2}) was investigated using the method of NMR spectroscopy. The median freezing temperature and freezing temperature region were shown to be highly sensitive both to the average thickness of the adsorbed films and to the amount of adsorbed nitric acid. The character of the ice phase formation tends to approach that of bulk liquid with increasing adsorbed film thickness. Under the given conditions the thickness of the adsorbed films decreases with an increasing amount of adsorbed nitric acid molecules The molar concentration of nitric acid in the adsorbed films is very small (of the order of 10{sup -}3 10{sup -}2 (M/l)). Nitric acid molecules tend to adsorb on the surface of aerosol to a greater extent than in subsequent layers. The concentration is greatest in layers situated close to the surface and sharply decreases with the distance from the surface. The difference between the median freezing temperatures for adsorbed pure water and for the binary system was found to be about 9 K for films of equal thickness. This is about 150 times greater than the difference between the median freezing temperatures of bulk pure water and a solution with the same concentration of nitric acid. (orig.)

  3. Two-phase flow in the localized boiling field adjacent to a heated wall

    International Nuclear Information System (INIS)

    Bonetto, F.J.; Clausse, A.; Converti, J.

    1991-01-01

    An experiment performed in a small horizontal heater immersed in refrigerant FC-72 is presented. The spatial distribution of the vapor is measured using a hot wire anemometer located over the heater, for different heat power inputs. The experimental data is analyzed using a probabilistic model to obtain information about the void fraction, bubble size and vapor velocity. A theoretical model based in conservation equations is derived which accounts for a comprehensive description of the experimental results. Moreover, a unified explanation of the interrelation between the mechanisms of nucleate boiling and boiling crisis is concluded. (Author)

  4. Relationships between boiling regimes and chemical concentration processes in tube support plate crevices

    International Nuclear Information System (INIS)

    Baum, A.

    2002-01-01

    The results of a test inter-relating crevice boiling regimes and chemical concentration in tube support plate crevices are presented. Testing of highly soluble, non-volatile autoclave chemistries produced characteristic crevice pH and impedance distributions during nucleate boiling, initiation of dryout, steady-state operation, and following shutdown. However, the patterns changed as a function of the solubility and volatility of the autoclave chemistry, the solute concentration, and the presence of residual solutes from previous testing. The changes were related to variations in the rates of concentrated solution formation, transport, volatilization, and precipitation. (authors)

  5. Micro transport phenomena during boiling

    CERN Document Server

    Peng, Xiaofeng

    2011-01-01

    "Micro Transport Phenomena During Boiling" reviews the new achievements and contributions in recent investigations at microscale. It presents some original research results and discusses topics at the frontier of thermal and fluid sciences.

  6. Nucleation in Synoptically Forced Cirrostratus

    Science.gov (United States)

    Lin, R.-F.; Starr, D. OC.; Reichardt, J.; DeMott, P. J.

    2004-01-01

    Formation and evolution of cirrostratus in response to weak, uniform and constant synoptic forcing is simulated using a one-dimensional numerical model with explicit microphysics, in which the particle size distribution in each grid box is fully resolved. A series of tests of the model response to nucleation modes (homogeneous-freezing-only/heterogeneous nucleation) and heterogeneous nucleation parameters are performed. In the case studied here, nucleation is first activated in the prescribed moist layer. A continuous cloud-top nucleation zone with a depth depending on the vertical humidity gradient and one of the nucleation parameters is developed afterward. For the heterogeneous nucleation cases, intermittent nucleation zones in the mid-upper portion of the cloud form where the relative humidity is on the rise, because existent ice crystals do not uptake excess water vapor efficiently, and ice nuclei (IN) are available. Vertical resolution as fine as 1 m is required for realistic simulation of the homogeneous-freezing-only scenario, while the model resolution requirement is more relaxed in the cases where heterogeneous nucleation dominates. Bulk microphysical and optical properties are evaluated and compared. Ice particle number flux divergence, which is due to the vertical gradient of the gravity-induced particle sedimentation, is constantly and rapidly changing the local ice number concentration, even in the nucleation zone. When the depth of the nucleation zone is shallow, particle number concentration decreases rapidly as ice particles grow and sediment away from the nucleation zone. When the depth of the nucleation zone is large, a region of high ice number concentration can be sustained. The depth of nucleation zone is an important parameter to be considered in parametric treatments of ice cloud generation.

  7. Boiling Suppression in Convective Flow

    International Nuclear Information System (INIS)

    Aounallah, Y.

    2004-01-01

    The development of convective boiling heat transfer correlations and analytical models has almost exclusively been based on measurements of the total heat flux, and therefore on the overall two-phase heat transfer coefficient, when the well-known heat transfer correlations have often assumed additive mechanisms, one for each mode of heat transfer, convection and boiling. While the global performance of such correlations can readily be assessed, the predictive capability of the individual components of the correlation has usually remained elusive. This becomes important when, for example, developing mechanistic models for subcooled void formation based on the partitioning of the wall heat flux into a boiling and a convective component, or when extending a correlation beyond its original range of applications where the preponderance of the heat transfer mechanisms involved can be significantly different. A new examination of existing experimental heat transfer data obtained under fixed hydrodynamic conditions, whereby the local flow conditions are decoupled from the local heat flux, has allowed the unequivocal isolation of the boiling contribution over a broad range of thermodynamic qualities (0 to 0.8) for water at 7 MPa. Boiling suppression, as the quality increases, has consequently been quantified, thus providing valuable new insights on the functionality and contribution of boiling in convective flows. (author)

  8. Pool boiling of water on nano-structured micro wires at sub-atmospheric conditions

    Science.gov (United States)

    Arya, Mahendra; Khandekar, Sameer; Pratap, Dheeraj; Ramakrishna, S. Anantha

    2016-09-01

    Past decades have seen active research in enhancement of boiling heat transfer by surface modifications. Favorable surface modifications are expected to enhance boiling efficiency. Several interrelated mechanisms such as capillarity, surface energy alteration, wettability, cavity geometry, wetting transitions, geometrical features of surface morphology, etc., are responsible for change in the boiling behavior of modified surfaces. Not much work is available on pool boiling at low pressures on microscale/nanoscale geometries; low pressure boiling is attractive in many applications wherein low operating temperatures are desired for a particular working fluid. In this background, an experimental setup was designed and developed to investigate the pool boiling performance of water on (a) plain aluminum micro wire (99.999 % pure) and, (b) nano-porous alumina structured aluminum micro wire, both having diameter of 250 µm, under sub-atmospheric pressure. Nano-structuring on the plain wire surface was achieved via anodization. Two samples, A and B of anodized wires, differing by the degree of anodization were tested. The heater length scale (wire diameter) was much smaller than the capillary length scale. Pool boiling characteristics of water were investigated at three different sub-atmospheric pressures of 73, 123 and 199 mbar (corresponding to T sat = 40, 50 and 60 °C). First, the boiling characteristics of plain wire were measured. It was noticed that at sub-atmospheric pressures, boiling heat transfer performance for plain wire was quite low due to the increased bubble sizes and low nucleation site density. Subsequently, boiling performance of nano-structured wires (both Sample A and Sample B) was compared with plain wire and it was noted that boiling heat transfer for the former was considerably enhanced as compared to the plain wire. This enhancement is attributed to increased nucleation site density, change in wettability and possibly due to enhanced pore scale

  9. A study of forced convective subcooled flow boiling

    International Nuclear Information System (INIS)

    Serizawa, Akimi; Kenning, D.B.R.

    1979-01-01

    Based on a simple nucleation model, parameter survey technique is used to derive a predictive correlation for boiling initiation under forced convection. Results are expressed by a semi-empirical equation which considers effects of the flow turbulence on interfacial heat transfer coefficient for evaporation and condensation of vapour bubbles during their growth. This correlation agrees within +-25% with a variety of experimental water data presently available. The bubble departure diameter and the subcooling-dependence of active nucleation sites were examined, using experimental data available. Results are expressed by empirical equations. Finally, an analytical model is presented to predict conditions for the point of net vapour generation. The model is based on the formation and growth of a bubble boundary layer adjacent to the heated wall. It is shown that the point of net vapour generation is determined by the liquid subcooling at the boiling initiation and the subcooling-dependences of bubble departure diameter and bubble flux. The result implies that the bubble ejection from bubble layer is a possible mechanism for the significant void increase even at high velocities. (author)

  10. Simulation of heat and mass transfer in boiling water with the Melodif code

    International Nuclear Information System (INIS)

    Freydier, P.; Chen, O.; Olive, J.; Simonin, O.

    1991-04-01

    The Melodif code is developed at Electricite de France, Research and Development Division. It is an eulerian two dimensional code for the simulation of turbulent two phase flows (a three dimensional code derived from Melodif, ASTRID, is currently being prepared). Melodif is based on the two fluid model, solving the equations of conservation for mass, momentum and energy, for both phases. In such a two fluid model, the description of interfacial transfers between phases is a crucial issue. The model used applies to a dominant continuous phase, and a dispersed phase. A good description of interfacial momentum transfer exists in the standard MELODIF code: the drag force, the apparent mass force... are taken into account. An important factor for interfacial transfers is the interfacial area per volume unit. With the assumption of spherical gas bubbles, an equation has been written for this variable. In the present wok, a model has been tested for interfacial heat and mass transfer in the case of boiling water: it is assumed that mass transfer is controlled by heat transfer through the latent massic energy taken in the phase that vaporizes (or condenses). This heat and mass transfer model has been tested in various configurations: - a cylinder with water flowing inside, is being heated. Boiling takes place near the wall, while bubbles migrating to the core of the flow recondense. This roughly simulates a sub-cooled boiling phenomenon. - a box containing liquid water is depressurized. Boiling takes place in the whole volume of the fluid. The Melodif code can simulate this configuration due to the implicitation of the relation between interphase mass transfer and the pressure variable

  11. An Experimental Study on the Pool Boiling Heat Transfer on a Square Surface

    International Nuclear Information System (INIS)

    Kim, Jae Kwang

    2000-02-01

    An experimental study was carried out to identify the various regimes of natural convective boiling and to determine the Critical Heat Flux (CHF) on a square surface. The basic knowledge on the boiling heat transfer and CHF on the square surface is necessary for various engineering problems, such as the design of compact heat exchangers, cooling of CPU chips, and design of the external cooling mechanism for the reactor during the severe accidents in the nuclear power plants. The heater block made of copper with cartridge heaters in it is submerged in a water tank with windows for visualization. The heater surface has dimension of 70mm x 70mm and the maximum heat flux capacity is about 1.8MW/m 2 . The boiling heat transfer coefficient for the various flow regimes up to CHF has been measured for upward facing surface, vertical surface, and nearly horizontal downward facing surfaces. The temperatures of the heater block are measured by the thermocouples imbedded in the heater block. As the heat flux increases from 100kW/m 2 to 1.0MW/m 2 , the heat-transfer regime changes from the nucleate boiling to the CHF. Near 1.0MW/m 2 , the heat transfer regime suddenly changed from nucleate boiling to film boiling and it resulted in a rapid heat up of the heater block. The various boiling patterns on the vertical surface, upward facing surface, and downward facing surface are observed by a high speed video camera whose frame rate is 1000fps. An explosive vapor generation on the heated surface, whose size and frequency are characterized by the heat flux and inclination angle, is observed

  12. On the Ice Nucleation Spectrum

    Science.gov (United States)

    Barahona, D.

    2012-01-01

    This work presents a novel formulation of the ice nucleation spectrum, i.e. the function relating the ice crystal concentration to cloud formation conditions and aerosol properties. The new formulation is physically-based and explicitly accounts for the dependency of the ice crystal concentration on temperature, supersaturation, cooling rate, and particle size, surface area and composition. This is achieved by introducing the concepts of ice nucleation coefficient (the number of ice germs present in a particle) and nucleation probability dispersion function (the distribution of ice nucleation coefficients within the aerosol population). The new formulation is used to generate ice nucleation parameterizations for the homogeneous freezing of cloud droplets and the heterogeneous deposition ice nucleation on dust and soot ice nuclei. For homogeneous freezing, it was found that by increasing the dispersion in the droplet volume distribution the fraction of supercooled droplets in the population increases. For heterogeneous ice nucleation the new formulation consistently describes singular and stochastic behavior within a single framework. Using a fundamentally stochastic approach, both cooling rate independence and constancy of the ice nucleation fraction over time, features typically associated with singular behavior, were reproduced. Analysis of the temporal dependency of the ice nucleation spectrum suggested that experimental methods that measure the ice nucleation fraction over few seconds would tend to underestimate the ice nuclei concentration. It is shown that inferring the aerosol heterogeneous ice nucleation properties from measurements of the onset supersaturation and temperature may carry significant error as the variability in ice nucleation properties within the aerosol population is not accounted for. This work provides a simple and rigorous ice nucleation framework where theoretical predictions, laboratory measurements and field campaign data can be

  13. Study on subcooled-forced flow boiling heat transfer and critical heat flux of solid particle-water two-phase mixture

    International Nuclear Information System (INIS)

    Koizumi, Yasuo; Mochizuki, Manabu; Ohtake, Hiroyasu

    1999-01-01

    The effect of solid particle introduction on forced flow boiling and the critical heat flux was examined for the mixture of subcooled-water and 0.6 mm glass beads. When the particles were introduced, the growth on of a superheated layer near a wall seemed to be suppressed and the onset of nucleate boiling was delayed. The particles tempted for bubbles to condense at nucleation sites, and then the initiation of net vapor generation was also delayed and sifted to a high wall-superheat region. The nucleate boiling heat transfer was augmented by the particles, which considered to be caused by the combination of the suppression of the superheated layer growth and the promotion of the condensation and dissipation of the bubbles. The wall superheat at the critical heat flux condition was sifted to a high wall superheat region and the critical heat flux itself was also elevated a little. (author)

  14. Phase field model for the study of boiling

    International Nuclear Information System (INIS)

    Ruyer, P.

    2006-07-01

    This study concerns both the modeling and the numerical simulation of boiling flows. First we propose a review concerning nucleate boiling at high wall heat flux and focus more particularly on the current understanding of the boiling crisis. From this analysis we deduce a motivation for the numerical simulation of bubble growth dynamics. The main and remaining part of this study is then devoted to the development and analyze of a phase field model for the liquid-vapor flows with phase change. We propose a thermodynamic quasi-compressible formulation whose properties match the one required for the numerical study envisaged. The system of governing equations is a thermodynamically consistent regularization of the sharp interface model, that is the advantage of the di use interface models. We show that the thickness of the interface transition layer can be defined independently from the thermodynamic description of the bulk phases, a property that is numerically attractive. We derive the kinetic relation that allows to analyze the consequences of the phase field formulation on the model of the dissipative mechanisms. Finally we study the numerical resolution of the model with the help of simulations of phase transition in simple configurations as well as of isothermal bubble dynamics. (author)

  15. Nucleation phenomena at Suzuki phases

    International Nuclear Information System (INIS)

    Acosta-Najarro, D.; Jose Y, M.

    1982-01-01

    Crystal of NaCl doped with Mn present regions with an increase in nucleation densities when observed by surface gold decoration; this increase is related to the nucleation of the Suzuki phases which are induced by cooling of the crystal matrix. Calculations based on atomistic nucleation theory are developed to explain the increased nucleation density. Experiments were made to compare with the theoretical results. In particular the density of nuclei was measured as a function of the rate or arrival of atoms to the surface. Therefore, the changes in the nucleation densities are explained in terms of change in migration energies between the Suzuki phase and the NaCl matrix excluding the possibility of nucleation induced by point defects. (author)

  16. Thermal hydraulic test for reactor safety system; a visualization study on flow boiling and bubble behavior

    Energy Technology Data Exchange (ETDEWEB)

    Chang, Soon Heung; Baek, Won Pil; Ban, In Cheol [Korea Advanced Institute of Science and Technology, Taejeon (Korea)

    2002-03-01

    The project contribute to understand and to clarify the physical mechanism of flow nucleate boiling and CHF phenomena through the visualization experiments. the results are useful in the development of the enhancement device of heat transfer and to enhance nuclear fuel safety 1. Visual experimental facility 2. Application method of visualization Technique 3. Visualization results of flow nucleate boiling regime - Overall Bubble Behavior on the Heated Surface - Bubble Behavior near CHF Condition - Identification of Flow Structure - Three-layer flow structure 4. Quantifying of bubble parameter through a digital image processing - Image Processing Techniques - Classification of objects and measurements of the size - Three dimensional surface plot with using the luminance 5. Development and estimation of a correlation between bubble diameter and flow parameter - The effect of system parameter on bubble diameter - The development of a bubble diameter correlation . 49 refs., 42 figs., 7 tabs. (Author)

  17. Burnout in subcooled flow boiling of water. A visual experimental study

    Energy Technology Data Exchange (ETDEWEB)

    Celata, G.P.; Mariani, A.; Zummo, G. [ENEA, Engineering Div., National Institute of Thermal Fluid-Dynamics, Rome (Italy); Cumo, M. [University of Rome la Sapienza, Rome (Italy)

    2000-12-01

    The objective of the present work is to perform a photographic study of the burnout in highly subcooled flow boiling, in order to provide a qualitative description of the flow pattern under different conditions of boiling regime: ONB (onset of nucleate boiling), subcooled flow boiling and thermal crisis. In particular, the flow visualisation is focused on the phenomena occurring on the heated wall during the thermal crisis up to the physical burnout of the heater. Vapour bubble parameters are measured from flow images recorded, while the wall temperature is measured with an indirect method, by recording the heater elongation during all flow regimes studied. The combination of bubble parameters and wall temperature measurements as well as direct observations of the flow pattern, for all flow regimes, are collected in graphs which provide a useful global point of view of boiling phenomena, especially during boiling crisis. Under these conditions, a detailed analysis of the mechanisms leading to the critical heat flux is reported, and the so called events sequence, from thermal crisis occurrence up to heater burnout, is illustrated. (authors)

  18. Burnout in subcooled flow boiling of water. A visual experimental study

    International Nuclear Information System (INIS)

    Celata, G.P.; Mariani, A.; Zummo, G.; Cumo, M.

    2000-01-01

    The objective of the present work is to perform a photographic study of the burnout in highly subcooled flow boiling, in order to provide a qualitative description of the flow pattern under different conditions of boiling regime: ONB (onset of nucleate boiling), subcooled flow boiling and thermal crisis. In particular, the flow visualisation is focused on the phenomena occurring on the heated wall during the thermal crisis up to the physical burnout of the heater. Vapour bubble parameters are measured from flow images recorded, while the wall temperature is measured with an indirect method, by recording the heater elongation during all flow regimes studied. The combination of bubble parameters and wall temperature measurements as well as direct observations of the flow pattern, for all flow regimes, are collected in graphs which provide a useful global point of view of boiling phenomena, especially during boiling crisis. Under these conditions, a detailed analysis of the mechanisms leading to the critical heat flux is reported, and the so called events sequence, from thermal crisis occurrence up to heater burnout, is illustrated. (authors)

  19. The influence of surface roughness and solution concentration on pool boiling process in Diethanolamine aqueous solution

    Science.gov (United States)

    Khoshechin, Mohsen; Salimi, Farhad; Jahangiri, Alireza

    2018-04-01

    In this research, the effect of surface roughness and concentration of solution on bubble departing frequency and nucleation site density for pool boiling of water/diethanolamine (DEA) binary solution were investigated experimentally. In this investigation, boiling heat transfer coefficient, bubble departing frequency and nucleation site density have been experimentally investigated in various concentrations and heat fluxes. Microstructured surfaces with a wide range of well-defined surface roughness were fabricated, and a heat flux between 1.5-86 kW/m2 was achieved under atmospheric conditions. The Results indicated that surface roughness and concentration of solution increase the bubble departing frequency and nucleation site density with increasing heat flux. The boiling heat transfer coefficient in mixtures of water/DEA increases with increasing concentration of DEA in water. The experimental results were compared with predictions of several used correlations in the literatures. Results showed that the boiling heat transfer coefficients of this case study are much higher than the predicted values by major existing correlations and models. The excellent agreement for bubble departing frequency found between the models of Jackob and Fritz (1966) and experimental data and also the nucleation site density were in close agreement with the model of Paul (1983) data. f bubble departure frequency, 1/s or Hz N Number of nucleation sites per area per time R c Minimum cavity size, m D c critical diameter, m g gravitational acceleration, m/s2 ρ density, kg/m3 T temperature, °c ΔT temperature difference, °c d d vapor bubble diameter, m h fg enthalpy of vaporization, J/kg R Roughness, μm Ja Jakob number cp specific heat, J/kg °c Pr Prandtl number Ar Archimedes number h Heat transfer coefficient, J/(m2 °c) tg time it takes to grow a bubble, s q/A heat flux (kW/m2) tw time required to heat the layer, s gc Correction coefficient of incompatible units R a Surface

  20. Study of two-phase boundary layer phenomena in boiling water by means of photographic techniques

    International Nuclear Information System (INIS)

    Molen, S.B. van der

    1976-01-01

    The behaviour of bubbles in the boundary layer of a two-phase flow is important for the heat exchange between the heat production unit and the cooling medium. Theoretical knowledge of the forces on a bubble and the interaction between molecules of different kind are essential for understanding the phenomena. The photographic techniques are needed for the investigation of the bubble pattern which exists where we find Departure from Nucleate Boiling. (orig.) [de

  1. Flow Boiling in a Micro-Channel Coated With Carbon Nanotubes

    OpenAIRE

    Khanikar, Vikash; Mudawar, Issam; Fisher, Timothy

    2009-01-01

    This study examines the heat transfer enhancement attributes of carbon nanotubes (CNTs) applied to the bottom wall of a shallow rectangular micro-channel. Using deionized water as working fluid, experiments were performed with both a bare copper bottom wall and a CNT-coated copper wall. Boiling curves were generated for both walls, aided by high-speed video analysis of interfacial features. CNT arrays promoted earlier, abundant and intense bubble nucleation at low mass velocities, consistent ...

  2. Confined boiling of the n-pentane in a horizontal space

    Energy Technology Data Exchange (ETDEWEB)

    Cardoso, E.M.; Passos, J.C. [Universidade Federal de Santa Catarina (UFSC), Florianopolis, SC (Brazil). Dept. de Engenharia Mecanica. LABSOLAR; Stutz, B. [CNRS, Villeurbanne (France). Institut National des Sciences Appliquees de Lyon. Centre Thermique

    2009-07-01

    This paper presents experimental results for saturated nucleated boiling of n-Pentane on a heating surface facing upward, at atmospheric pressure, for different degrees of confinement, s = 0.2, 0.5, 0.7 and s = 13 mm, corresponding to Bond numbers 0.13, 0.32, 0.45 and 8.35. Comparative studies with results from literature, together with analysis of the experimental data allowing the improvement of the experimental apparatus. The results show the enhancement of boiling heat transfer with a decreasing distance s between the heating surface and an unheated surface. The experimental heat transfer coefficients for unconfined boiling, s=13 mm, are compared with three empirical correlations. (author)

  3. Confined boiling of the n-pentane in a horizontal space

    International Nuclear Information System (INIS)

    Cardoso, E.M.; Passos, J.C.; Stutz, B.

    2009-01-01

    This paper presents experimental results for saturated nucleated boiling of n-Pentane on a heating surface facing upward, at atmospheric pressure, for different degrees of confinement, s = 0.2, 0.5, 0.7 and s = 13 mm, corresponding to Bond numbers 0.13, 0.32, 0.45 and 8.35. Comparative studies with results from literature, together with analysis of the experimental data allowing the improvement of the experimental apparatus. The results show the enhancement of boiling heat transfer with a decreasing distance s between the heating surface and an unheated surface. The experimental heat transfer coefficients for unconfined boiling, s=13 mm, are compared with three empirical correlations. (author)

  4. Flow boiling in expanding microchannels

    CERN Document Server

    Alam, Tamanna

    2017-01-01

    This Brief presents an up to date summary of details of the flow boiling heat transfer, pressure drop and instability characteristics; two phase flow patterns of expanding microchannels. Results obtained from the different expanding microscale geometries are presented for comparison and addition to that, comparison with literatures is also performed. Finally, parametric studies are performed and presented in the brief. The findings from this study could help in understanding the complex microscale flow boiling behavior and aid in the design and implementation of reliable compact heat sinks for practical applications.

  5. LMFBR safety and sodium boiling

    Energy Technology Data Exchange (ETDEWEB)

    Hinkle, W.D.; Tschamper, P.M.; Fontana, M.H.; Henry, R.E.; Padilla, A. Jr.

    1978-01-01

    Within the U.S. Fast Breeder Reactor Safety R and D Work Breakdown Structure for Line of Assurance 2, Limit Core Damage, the influence of sodium boiling upon the progression and termination of accidents is being studied in loss of flow, transient overpower, loss of piping integrity, loss of shutdown heat removal system and local fault situations. The pertinent analytical and experimental results of this research to date are surveyed and compared with the requirements for demonstrating the effectiveness of this line of assurance. A discussion of specific technical issues concerned with sodium boiling and the need for future development work is also presented.

  6. Simulation of boiling flow in evaporator of separate type heat pipe with low heat flux

    International Nuclear Information System (INIS)

    Kuang, Y.W.; Wang, Wen; Zhuan, Rui; Yi, C.C.

    2015-01-01

    Highlights: • A boiling flow model in a separate type heat pipe with 65 mm diameter tube. • Nucleate boiling is the dominant mechanism in large pipes at low mass and heat flux. • The two-phase heat transfer coefficient is less sensitive to the total mass flux. - Abstract: The separate type heat pipe heat exchanger is considered to be a potential selection for developing passive cooling spent fuel pool – for the passive pressurized water reactor. This paper simulates the boiling flow behavior in the evaporator of separate type heat pipe, consisting of a bundle of tubes of inner diameter 65 mm. It displays two-phase characteristic in the evaporation section of the heat pipe working in low heat flux. In this study, the two-phase flow model in the evaporation section of the separate type heat pipe is presented. The volume of fluid (VOF) model is used to consider the interaction between the ammonia gas and liquid. The flow patterns and flow behaviors are studied and the agitated bubbly flow, churn bubbly flow are obtained, the slug bubble is likely to break into churn slug or churn froth flow. In addition, study on the heat transfer coefficients indicates that the nucleate boiling is the dominant mechanism in large pipes at low mass and heat flux, with the heat transfer coefficient being less sensitive to the total mass flux

  7. Subcooled flow boiling heat transfer of ethanol aqueous solutions in vertical annulus space

    Directory of Open Access Journals (Sweden)

    Sarafraz M.M.

    2012-01-01

    Full Text Available The subcooled flow boiling heat-transfer characteristics of water and ethanol solutions in a vertical annulus have been investigated up to heat flux 132kW/m2. The variations in the effects of heat flux and fluid velocity, and concentration of ethanol on the observed heat-transfer coefficients over a range of ethanol concentrations implied an enhanced contribution of nucleate boiling heat transfer in flow boiling, where both forced convection and nucleate boiling heat transfer occurred. Increasing the ethanol concentration led to a significant deterioration in the observed heat-transfer coefficient because of a mixture effect, that resulted in a local rise in the saturation temperature of ethanol/water solution at the vapor-liquid interface. The reduction in the heat-transfer coefficient with increasing ethanol concentration is also attributed to changes in the fluid properties (for example, viscosity and heat capacity of tested solutions with different ethanol content. The experimental data were compared with some well-established existing correlations. Results of comparisons indicate existing correlations are unable to obtain the acceptable values. Therefore a modified correlation based on Gnielinski correlation has been proposed that predicts the heat transfer coefficient for ethanol/water solution with uncertainty about 8% that is the least in comparison to other well-known existing correlations.

  8. Homogeneous versus heterogeneous zeolite nucleation

    NARCIS (Netherlands)

    Dokter, W.H.; Garderen, van H.F.; Beelen, T.P.M.; Santen, van R.A.; Bras, W.

    1995-01-01

    Aggregates of fractal dimension were found in the intermediate gel phases that organize prior to nucleation and crystallization (shown right) of silicalite from a homogeneous reaction mixture. Small- and wide-angle X-ray scattering studies prove that for zeolites nucleation may be homogeneous or

  9. On Capillary Rise and Nucleation

    Science.gov (United States)

    Prasad, R.

    2008-01-01

    A comparison of capillary rise and nucleation is presented. It is shown that both phenomena result from a balance between two competing energy factors: a volume energy and a surface energy. Such a comparison may help to introduce nucleation with a topic familiar to the students, capillary rise. (Contains 1 table and 3 figures.)

  10. Theory and Simulation of Nucleation

    NARCIS (Netherlands)

    Kuipers, J.|info:eu-repo/dai/nl/304832049

    2009-01-01

    Nucleation is the process where a stable nucleus spontaneously emerges in a metastable environment. Examples of nucleation abound, for instance the formation of droplets in undercooled gasses and of crystals in undercooled liquids. The process is thermally activated and is key to understanding

  11. A dynamical theory of nucleation

    Science.gov (United States)

    Lutsko, James F.

    2013-05-01

    A dynamical theory of nucleation based on fluctuating hydrodynamics is described. It is developed in detail for the case of diffusion-limited nucleation appropriate to colloids and macro-molecules in solution. By incorporating fluctuations, realistic fluid-transport and realistic free energy models the theory is able to give a unified treatment of both the pre-critical development of fluctuations leading to a critical cluster as well as of post-critical growth. Standard results from classical nucleation theory are shown to follow in the weak noise limit while the generality of the theory allows for many extensions including the description of very high supersaturations (small clusters), multiple order parameters and strong-noise effects to name a few. The theory is applied to homogeneous and heterogeneous nucleation of a model globular protein in a confined volume and it is found that nucleation depends critically on the existence of long-wavelength, small-amplitude density fluctuations.

  12. Research progress on microgravity boiling heat transfer

    International Nuclear Information System (INIS)

    Xiao Zejun; Chen Bingde

    2003-01-01

    Microgravity boiling heat transfer is one of the most basic research topics in aerospace technology, which is important for both scientific research and engineering application. Research progress on microgravity boiling heat transfer is presented, including terrestrial simulation technique, terrestrial simulation experiment, microgravity experiment, and flow boiling heat transfer

  13. Protein crystal nucleation in pores.

    Science.gov (United States)

    Nanev, Christo N; Saridakis, Emmanuel; Chayen, Naomi E

    2017-01-16

    The most powerful method for protein structure determination is X-ray crystallography which relies on the availability of high quality crystals. Obtaining protein crystals is a major bottleneck, and inducing their nucleation is of crucial importance in this field. An effective method to form crystals is to introduce nucleation-inducing heterologous materials into the crystallization solution. Porous materials are exceptionally effective at inducing nucleation. It is shown here that a combined diffusion-adsorption effect can increase protein concentration inside pores, which enables crystal nucleation even under conditions where heterogeneous nucleation on flat surfaces is absent. Provided the pore is sufficiently narrow, protein molecules approach its walls and adsorb more frequently than they can escape. The decrease in the nucleation energy barrier is calculated, exhibiting its quantitative dependence on the confinement space and the energy of interaction with the pore walls. These results provide a detailed explanation of the effectiveness of porous materials for nucleation of protein crystals, and will be useful for optimal design of such materials.

  14. Numerical simulation in a subcooled water flow boiling for one-sided high heat flux in reactor divertor

    Energy Technology Data Exchange (ETDEWEB)

    Liu, P., E-mail: pinliu@aust.edu.cn [Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031 (China); University of Science and Technology of China, Hefei 230026 (China); School of Mechanical Engineering, Anhui University of Science and Technology, Huainan 232001 (China); Peng, X.B., E-mail: pengxb@ipp.ac.cn [Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031 (China); Song, Y.T. [Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031 (China); University of Science and Technology of China, Hefei 230026 (China); Fang, X.D. [Institute of Air Conditioning and Refrigeration, Nanjing University of Aeronautics and Astronautics, Nanjing 210016 (China); Huang, S.H. [University of Science and Technology of China, Hefei 230026 (China); Mao, X. [Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031 (China)

    2016-11-15

    Highlights: • The Eulerian multiphase models coupled with Non-equilibrium Boiling model can effectively simulate the subcooled water flow boiling. • ONB and FDB appear earlier and earlier with the increase of heat fluxes. • The void fraction increases gradually along the flow direction. • The inner CuCrZr tube deteriorates earlier than the outer tungsten layer and the middle OFHC copper layer. - Abstract: In order to remove high heat fluxes for plasma facing components in International Thermonuclear Experimental Reactor (ITER) divertor, a numerical simulation of subcooled water flow boiling heat transfer in a vertically upward smooth tube was conducted in this paper on the condition of one-sided high heat fluxes. The Eulerian multiphase model coupled with Non-equilibrium Boiling model was adopted in numerical simulation of the subcooled boiling two-phase flow. The heat transfer regions, thermodynamic vapor quality (x{sub th}), void fraction and temperatures of three components on the condition of the different heat fluxes were analyzed. Numerical results indicate that the onset of nucleate boiling (ONB) and fully developed boiling (FDB) appear earlier and earlier with increasing heat flux. With the increase of heat fluxes, the inner CuCrZr tube will deteriorate earlier than the outer tungsten layer and the middle oxygen-free high-conductivity (OFHC) copper layer. These results provide a valuable reference for the thermal-hydraulic design of a water-cooled W/Cu divertor.

  15. Climate Impacts of Ice Nucleation

    Science.gov (United States)

    Gettelman, Andrew; Liu, Xiaohong; Barahona, Donifan; Lohmann, Ulrike; Chen, Celia

    2012-01-01

    Several different ice nucleation parameterizations in two different General Circulation Models (GCMs) are used to understand the effects of ice nucleation on the mean climate state, and the Aerosol Indirect Effects (AIE) of cirrus clouds on climate. Simulations have a range of ice microphysical states that are consistent with the spread of observations, but many simulations have higher present-day ice crystal number concentrations than in-situ observations. These different states result from different parameterizations of ice cloud nucleation processes, and feature different balances of homogeneous and heterogeneous nucleation. Black carbon aerosols have a small (0.06 Wm(exp-2) and not statistically significant AIE when included as ice nuclei, for nucleation efficiencies within the range of laboratory measurements. Indirect effects of anthropogenic aerosols on cirrus clouds occur as a consequence of increasing anthropogenic sulfur emissions with different mechanisms important in different models. In one model this is due to increases in homogeneous nucleation fraction, and in the other due to increases in heterogeneous nucleation with coated dust. The magnitude of the effect is the same however. The resulting ice AIE does not seem strongly dependent on the balance between homogeneous and heterogeneous ice nucleation. Regional effects can reach several Wm2. Indirect effects are slightly larger for those states with less homogeneous nucleation and lower ice number concentration in the base state. The total ice AIE is estimated at 0.27 +/- 0.10 Wm(exp-2) (1 sigma uncertainty). This represents a 20% offset of the simulated total shortwave AIE for ice and liquid clouds of 1.6 Wm(sup-2).

  16. Metadynamics studies of crystal nucleation

    Science.gov (United States)

    Giberti, Federico; Salvalaglio, Matteo; Parrinello, Michele

    2015-01-01

    Crystallization processes are characterized by activated events and long timescales. These characteristics prevent standard molecular dynamics techniques from being efficiently used for the direct investigation of processes such as nucleation. This short review provides an overview on the use of metadynamics, a state-of-the-art enhanced sampling technique, for the simulation of phase transitions involving the production of a crystalline solid. In particular the principles of metadynamics are outlined, several order parameters are described that have been or could be used in conjunction with metadynamics to sample nucleation events and then an overview is given of recent metadynamics results in the field of crystal nucleation. PMID:25866662

  17. Metadynamics studies of crystal nucleation

    Directory of Open Access Journals (Sweden)

    Federico Giberti

    2015-03-01

    Full Text Available Crystallization processes are characterized by activated events and long timescales. These characteristics prevent standard molecular dynamics techniques from being efficiently used for the direct investigation of processes such as nucleation. This short review provides an overview on the use of metadynamics, a state-of-the-art enhanced sampling technique, for the simulation of phase transitions involving the production of a crystalline solid. In particular the principles of metadynamics are outlined, several order parameters are described that have been or could be used in conjunction with metadynamics to sample nucleation events and then an overview is given of recent metadynamics results in the field of crystal nucleation.

  18. Review: The nucleation of disorder

    International Nuclear Information System (INIS)

    Cahn, R.W.; Johnson, W.L.

    1986-01-01

    Four types of phase transformation that involve the conversion of crystalline phases into more disordered forms are reviewed: melting, disordering of superlattices, amorphization by diffusion between crystalline phases, and irradation amorphization. In the review emphasis is placed on evidence for the heterogeneous nucleation of the product phases; in this connection, the role of surfaces, antiphase domain boundaries, dislocations, vacancies, and grain boundaries is specifically discussed. All of these features have been either observed, or hypothesized, to play a role as heterogeneous nucleation sites in one or more of the four transformations. An attempt is made to draw parallels between nucleation mechanisms in the various processes

  19. The role of graphite foam pore structure on saturated pool boiling enhancement

    International Nuclear Information System (INIS)

    Pranoto, I.; Leong, K.C.; Jin, L.W.

    2012-01-01

    This paper presents an experimental study of the pool boiling phenomena and performance of porous graphite foam evaporators of different structures and thermophysical properties. Two dielectric liquids viz. FC-72 and HFE-7000 were used as working fluids. Block and fin evaporators of different fin-to-block-surface-area ratios (AR) were designed to study the role of the internal pore structure of graphite foams in a compact air-cooled thermosyphon under saturated pool boiling condition for high heat flux electronics cooling applications. The wall temperatures were measured and the boiling heat transfer coefficients were calculated to analyze the boiling performance. It was found that both fin structures with AR = 3.70 and 2.73 result in reduced boiling heat transfer performances and higher wall temperatures. The experimental results show that the boiling heat transfer coefficients of the block structures are about 1.2–1.6 times higher than those of the fin structures. The total internal surface area to volume ratio (β) and the total exposed areas (A T ) of the graphite foams were calculated in this study. The results show that the values of β and A T of the block structures are much higher than the fin structures for both tested “Pocofoam” 61% porosity and “Kfoam” 78% porosity evaporators which resulted in higher boiling heat transfer coefficient and lower wall temperature of the block structures. A visualization study shows that more bubbles were generated from the block structures compared to the fin structures due to the larger number of nucleation sites from the block structures. It was also found that use of FC-72 resulted in better boiling heat transfer performance compared to HFE-7000. - Highlights: ► We studied the pool boiling performance of a thermosyphon with graphite foam evaporators of block and fin structures. ► FC-72 and HFE-7000 were used as the working fluids. ► The boiling heat transfer coefficients of the block structures are 1.2

  20. The myth of the boiling point.

    Science.gov (United States)

    Chang, Hasok

    2008-01-01

    Around 1800, many reputable scientists reported significant variations in the temperature of pure water boiling under normal atmospheric pressure. The reported variations included a difference of over 1 degree C between boiling in metallic and glass vessels (Gay-Lussac), and "superheating" up to 112 degrees C on extracting dissolved air out of water (De Luc). I have confirmed most of these observations in my own experiments, many of which are described in this paper. Water boils at the "boiling point" only under very particular circumstances. Our common-sense intuition about the fixedness of the boiling point is only sustained by our limited experience.

  1. Experimental Investigation of Pool Boiling Heat Transfer Enhancement in Microgravity in the Presence of Electric Fields

    Science.gov (United States)

    Herman, Cila

    1996-01-01

    Boiling is an effective mode of heat transfer since high heat flux levels are possible driven by relatively small temperature differences. The high heat transfer coefficients associated with boiling have made the use of these processes increasingly attractive to aerospace engineering. Applications of this type include compact evaporators in the thermal control of aircraft avionics and spacecraft environments, heat pipes, and use of boiling to cool electronic equipment. In spite of its efficiency, cooling based on liquid-vapor phase change processes has not yet found wide application in aerospace engineering due to specific problems associated with the low gravity environment. After a heated surface has reached the superheat required for the initiation of nucleate boiling, bubbles will start forming at nucleation sites along the solid interface by evaporation of the liquid. Bubbles in contact with the wall will continue growing by this mechanism until they detach. In terrestrial conditions, bubble detachment is determined by the competition between body forces (e.g. buoyancy) and surface tension forces that act to anchor the bubble along the three phase contact line. For a given body force potential and a balance of tensions along the three phase contact line, bubbles must reach a critical size before the body force can cause them to detach from the wall. In a low gravity environment the critical bubble size for detachment is much larger than under terrestrial conditions, since buoyancy is a less effective means of bubble removal. Active techniques of heat transfer enhancement in single phase and phase change processes by utilizing electric fields have been the subject of intensive research during recent years. The field of electrohydrodynamics (EHD) deals with the interactions between electric fields, flow fields and temperature fields. Previous studies indicate that in terrestrial applications nucleate boiling heat transfer can be increased by a factor of 50 as

  2. Burnout in boiling heat transfer. part I: pool boiling systems

    International Nuclear Information System (INIS)

    Bergles, A.E.

    1977-01-01

    Recent experimental and analytical developments in pool-boiling burnout are reviewed, and results are summarized that clarify the dependence of critical heat flux on heater geometry and fluid properties. New analytical interpretations of burnout are discussed, and the effects of surface condition, aging, acceleration, and transient heating (or cooling) are described. The relation of sound to burnout and new techniques for stabilizing electric heaters at burnout are also considered

  3. Improvement of boiling heat transfer by radiation induced boiling enhancement

    International Nuclear Information System (INIS)

    Imai, Yasuyuki; Okamoto, Koji; Madarame, Haruki; Takamasa, Tomoji

    2003-01-01

    For nuclear reactor systems, the critical heat flux (CHF) data is very important because it limits reactor efficiency. Improvement of CHF requires that the cooling liquid can contact the heating surface, or a high-wettability, highly hydrophilic heating surface, even if a vapor bubble layer is generated on the surface. In our previous study, we confirmed that the surface wettability changed significantly or that highly hydrophilic conditions were achieved, after irradiation of 60 Co gamma ray, by the Radiation Induced Surface Activation (RISA) phenomenon. To delineate the effect of RISA on boiling phenomena, surface wettability in a high-temperature environment and critical heat flux (CHF) of metal oxides irradiated by gamma rays were investigated. A CHF experiment in the pool boiling condition was carried out under atmospheric pressure. The heating test section made of titanium was 0.2 mm in thickness, 3 mm in height, and 60 mm in length. Oxidation of the surface was carried out by plasma jetting for 40 seconds. The test section was irradiated by 60 Co gamma ray with predetermined radiation intensity and period. The CHF of oxidized titanium was improved up to 100 percent after 800 kGy 60 Co gamma ray irradiation. We call this effect Radiation Induced Boiling Enhancement (RIBE). Before we conducted the CHF experiment, contact angles of the test pieces were measured to show the relationship between wettability and CHF. The CHF in the present experiment increases will surface wettability in the same manner as shown by Liaw and Dhir's results. (author)

  4. Improvement of boiling heat transfer by radiation induced boiling enhancement

    International Nuclear Information System (INIS)

    Imai, Y.; Okamoto, K.; Madarame, H.; Takamasa, T.

    2003-01-01

    For nuclear reactor systems, the Critical Heat Flux (CHF) data is very important because it limits reactor efficiency. Improvement of CHF requires that the cooling liquid can contact the heating surface, or a high-wettability, highly hydrophilic heating surface, even if a vapor bubble layer is generated on the surface. In our previous study, we confirmed that the surface wettability changed significantly or that highly hydrophilic conditions were achieved, after irradiation of 60Co gamma ray, by the Radiation Induced Surface Activation (RISA) phenomenon. To delineate the effect of RISA on boiling phenomena, surface wettability in a high-temperature environment and Critical Heat Flux (CHF) of metal oxides irradiated by gamma rays were investigated. A CHF experiment in the pool boiling condition was carried out under atmospheric pressure. The heating test section made of titanium was 0.2mm in thickness, 3mm in height, and 60mm in length. Oxidation of the surfaces was carried out by plasma jetting for 40 seconds. The test section was irradiated by 60Co gamma ray with predetermined radiation intensity and period. The CHF of oxidized titanium was improved up to 100 percent after 800kGy 60Co gamma ray irradiation. We call this effect Radiation Induced Boiling Enhancement (RIBE). Before we conducted the CHF experiment, contact angles of the test pieces were measured to show the relationship between wettability and CHF. The CHF in the present experiment increases with surface wettability in the same manner as shown by Liaw and Dhir's results

  5. Subcooled boiling heat transfer correlation to calculate the effects of dissolved gas in a liquid

    International Nuclear Information System (INIS)

    Zarkasi, Amin S.; Chao, W.W.; Kunze, Jay F.

    2004-01-01

    The water coolant in most operating power reactor systems is kept free of dissolved gas, so as to minimize corrosion. However, in most research reactors, which operate at temperatures below 70 deg. C, and between 1 and 5 atm. pressure, the dissolved gas remains present in the water coolant system during operation. This dissolved gas can have a significant effect during accident conditions (i.e. a LOCA), when the fluid quickly reaches boiling, coincident with flow stagnation and subsequent flow reversal. A benchmark experiment was conducted, with an electrically heated, closed loop channel, modeling a research reactor fuel coolant channels (2 mm thick). The results showed 'boiling (bubble) noise' occurring before wall temperatures reached saturation, and a significant increase (up to 50%) in the heat transfer coefficient in the subcooled boiling region when in the presence of dissolved gas, compared to degassed water. Since power reactors do not involve dissolved gas, the RELAP safety analysis code does not include any provisions for the effect of dissolved gas on heat transfer. In this work, the effects of the dissolved gas are evaluated for inclusion in the RELAP code, including provision for initiating 'nucleate boiling' at a lower temperature, and a provision for enhancing the heat transfer coefficient during the subcooled boiling region. Instead of relying on Chen's correlation alone, a modification of the superposition method of Bjorge was adopted. (author)

  6. Theory of boiling-up jump

    International Nuclear Information System (INIS)

    Labuntsov, D.A.; Avdeev, A.A.

    1981-01-01

    Concept of boiling-up jump representing a zone of intense volume boiling-up separating overtaking flow of overheated metastable liquid from an area of equilibrium flow located below along the flow is introduced. It is shown that boiling-up jump is a shock wave of rarefaction. It is concluded that entropy increment occurs on the jump. Characteristics of adiabatic shock wave curve of boiling- up in ''pressure-specific volume'' coordinates have been found and its form has been investigated. Stability of boiling-up jump has been analyzed as well. On the basis of approach developed analysis is carried out on the shock adiobatic curve of condensation. Concept of boiling-up jump may be applied to the analysis of boiling-up processes when flowing liquid through packings during emergency pressure drop etc [ru

  7. Computer simulation of chemical nucleation

    International Nuclear Information System (INIS)

    Turner, J.S.

    1979-01-01

    The problem of nucleation at chemical instabilities is investigated by means of microscopic computer simulation. The first-order transition of interest involves a new kind of nucleation arising from chemical transformations rather than physical forces. Here it is the chemical state of matter, and not matter itself, which is spatially localized to form the nucleus for transition between different chemical states. First, the concepts of chemical instability, nonequilibrium phase transition, and dissipative structure are reviewed briefly. Then recently developed methods of reactive molecular dynamics are used to study chemical nucleation in a simple model chemical reactions. Finally, the connection of these studies to nucleation and condensation processes involving physical and chemical interactions is explored. (orig.)

  8. A dry-spot model for the prediction of critical heat flux in water boiling in bubbly flow regime

    International Nuclear Information System (INIS)

    Ha, Sang Jun; No, Hee Cheon

    1997-01-01

    This paper presents a prediction of critical heat flux (CHF) in bubbly flow regime using dry-spot model proposed recently by authors for pool and flow boiling CHF and existing correlations for forced convective heat transfer coefficient, active site density and bubble departure diameter in nucleate boiling region. Without any empirical constants always present in earlier models, comparisons of the model predictions with experimental data for upward flow of water in vertical, uniformly-heated round tubes are performed and show a good agreement. The parametric trends of CHF have been explored with respect to variation in pressure, tube diameter and length, mass flux and inlet subcooling

  9. Development of a novel infrared-based visualization technique to detect liquid-gas phase dynamics on boiling surfaces

    International Nuclear Information System (INIS)

    Kim, Hyung Dae

    2011-01-01

    Complex two-phase heat transfer phenomena such as nucleate boiling, critical heat flux, quenching and condensation govern the thermal performance of Light Water Reactors (LWRs) under normal operation and during transients/accidents. These phenomena are typically characterized by the presence of a liquid vapor- solid contact line on the surface from/to which the heat is transferred. For example, in nucleate boiling, a significant fraction of the energy needed for bubble growth comes from evaporation of a liquid meniscus, or microlayer, underneath the bubble itself. As the liquid vapor- solid line at the edge of the meniscus retreats, a circular dry patch in the middle of the bubble is exposed; the speed of the triple line retreat is a measure of the ability of the surface to transfer heat to the bubble. At very high heat fluxes, near the upper limit of the nucleate boiling regime, also known as Critical Heat Flux (CHF), the situation is characterized by larger dry areas on the surface, dispersed within an interconnected network of liquid menisci. In quenching heat transfer, which refers to the rapid cooling of a very hot object by immersion in a cooler liquid, the process is initially dominated by film boiling. In film boiling a continuous vapor film completely separates the liquid phase from the solid surface: however, as the temperature gets closer to the Leidenfrost point, intermittent and short-lived liquid-solid contacts occur at discrete locations on the surface, thus creating liquid vapor- solid interfaces once again. Ultimately, if bubble nucleation ensues at such contact points, the vapor film is disrupted and the heat transfer regime transitions from film boiling to transition boiling. Finally, in dropwise condensation, the phase transition from vapor to liquid occurs via formation of discrete droplets on the surface, and the resulting liquid-vapor-solid triple line is where heat transfer is most intense. To gain insight into and enable mechanistic

  10. Local Heat Transfer and CHF for Subcooled Flow Boiling - Annual Report 1993

    International Nuclear Information System (INIS)

    Boyd, Ronald D.

    2000-01-01

    Subcooled flow boiling in heated coolant channels is an important heat transfer enhancement technique in the development of fusion reactor components, where high heat fluxes must be accommodated. As energy fluxes increase in magnitude, additional emphasis must be devoted to enhancing techniques such as sub cooling and enhanced surfaces. In addition to subcooling, other high heat flux alternatives such as high velocity helium and liquid metal cooling have been considered as serious contenders. Each technique has its advantages and disadvantages [1], which must be weighed as to reliability and reduced cost of fusion reactor components. Previous studies [2] have set the stage for the present work, which will concentrate on fundamental thermal hydraulic issues associated with the h-international Thermonuclear Experimental Reactor (ITER) and the Engineering Design Activity (EDA). This proposed work is intended to increase our understanding of high heat flux removal alternatives as well as our present capabilities by: (1) including single-side heating effects in models for local predictions of heat transfer and critical heat flux; (2) inspection of the US, Japanese, and other possible data sources for single-side heating, with the aim of exploring possible correlations for both CHF and local heat transfer; and (3) assessing the viability of various high heat flux removal techniques. The latter task includes: (a) sub-cooled water flow boiling with enhancements such as twisted tapes, and hypervapotrons, (b) high velocity helium cooling, and (c) other potential techniques such as liquid metal cooling. This assessment will increase our understanding of: (1) hypervapotron heat transfer via fins, flow recirculation, and flow oscillation, and (2) swirl flow. This progress report contains selective examples of ongoing work. Section II contains an extended abstract, which is part of and evolving technical paper on single-side f heating. Section III describes additional details

  11. Gas hydrate nucleation

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    1997-12-31

    The overall aim of the project was to gain more knowledge about the kinetics of gas hydrate formation especially the early growth phase. Knowledge of kinetics of gas hydrate formation is important and measurements of gas hydrate particle size and concentration can contribute to improve this knowledge. An experimental setup for carrying out experimental studies of the nucleation and growth of gas hydrates has been constructed and tested. Multi wavelength extinction (MWE) was the experimental technique selected for obtaining particle diameter and concentration. The principle behind MWE is described as well as turbidity spectrum analysis that in an initial stage of the project was considered as an alternative experimental technique. Details of the experimental setup and its operation are outlined. The measuring cell consists of a 1 litre horizontal tube sustaining pressures up to 200 bar. Laser light for particle size determination can be applied through sapphire windows. A description of the various auxiliary equipment and of another gas hydrate cell used in the study are given. A computer program for simulation and analysis of gas hydrate experiments is based on the gas hydrate kinetics model proposed by Skovborg and Rasmussen (1993). Initial measurements showed that knowledge of the refractive index of gas hydrates was important in order to use MWE. An experimental determination of the refractive index of methane and natural gas hydrate is described. The test experiments performed with MWE on collectives of gas hydrate particles and experiments with ethane, methane and natural gas hydrate are discussed. Gas hydrate particles initially seem to grow mainly in size and at latter stages in number. (EG) EFP-94; 41 refs.

  12. Gas hydrate nucleation

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    1998-12-31

    The overall aim of the project was to gain more knowledge about the kinetics of gas hydrate formation especially the early growth phase. Knowledge of kinetics of gas hydrate formation is important and measurements of gas hydrate particle size and concentration can contribute to improve this knowledge. An experimental setup for carrying out experimental studies of the nucleation and growth of gas hydrates has been constructed and tested. Multi wavelength extinction (MWE) was the experimental technique selected for obtaining particle diameter and concentration. The principle behind MWE is described as well as turbidity spectrum analysis that in an initial stage of the project was considered as an alternative experimental technique. Details of the experimental setup and its operation are outlined. The measuring cell consists of a 1 litre horizontal tube sustaining pressures up to 200 bar. Laser light for particle size determination can be applied through sapphire windows. A description of the various auxiliary equipment and of another gas hydrate cell used in the study are given. A computer program for simulation and analysis of gas hydrate experiments is based on the gas hydrate kinetics model proposed by Skovborg and Rasmussen (1993). Initial measurements showed that knowledge of the refractive index of gas hydrates was important in order to use MWE. An experimental determination of the refractive index of methane and natural gas hydrate is described. The test experiments performed with MWE on collectives of gas hydrate particles and experiments with ethane, methane and natural gas hydrate are discussed. Gas hydrate particles initially seem to grow mainly in size and at latter stages in number. (EG) EFP-94; 41 refs.

  13. Nanosecond laser texturing of uniformly and non-uniformly wettable micro structured metal surfaces for enhanced boiling heat transfer

    Energy Technology Data Exchange (ETDEWEB)

    Zupančič, Matevž, E-mail: matevz.zupancic@fs.uni-lj.si; Može, Matic; Gregorčič, Peter; Golobič, Iztok

    2017-03-31

    Highlights: • Surfaces with periodically changed wettability were produced by a ns marking laser. • Heat transfer was investigated on uniformly and non-uniformly wettable surfaces. • Microporous surfaces with non-uniform wettability enhance boiling heat transfer. • The most bubble nucleations were observed in the vicinity of the microcavities. • Results agree with the predictions of the nucleation criteria. - Abstract: Microstructured uniformly and non-uniformly wettable surfaces were created on 25-μm-thin stainless steel foils by laser texturing using a marking nanosecond Nd:YAG laser (λ = 1064 nm) and utilizing various laser fluences and scan line separations. High-speed photography and high-speed IR thermography were used to investigate nucleate boiling heat transfer on the microstructured surfaces. The most pronounced results were obtained on a surface with non-uniform microstructure and non-uniform wettability. The obtained results show up to a 110% higher heat transfer coefficients and 20–40 times higher nucleation site densities compared to the untextured surface. We show that the number of active nucleation sites is significantly increased in the vicinity of microcavities that appeared in areas with the smallest (10 μm) scan line separation. Furthermore, this confirms the predictions of nucleation criteria and proves that straightforward, cost-effective nanosecond laser texturing allows the production of cavities with diameters of up to a few micrometers and surfaces with non-uniform wettability. Additionally, this opens up important possibilities for a more deterministic control over the complex boiling process.

  14. Role of nucleation in nanodiamond film growth

    International Nuclear Information System (INIS)

    Lifshitz, Y.; Lee, C.H.; Wu, Y.; Zhang, W.J.; Bello, I.; Lee, S.T.

    2006-01-01

    Nanodiamond films were deposited using different microwave plasma chemical vapor deposition schemes following several nucleation pretreatment methods. The nucleation efficiency and the films structure were investigated using scanning and transmission electron microscopy and Raman spectroscopy. C 2 dimer growth (CH 4 and H 2 in 90% Ar) cannot nucleate diamond and works only on existing diamond surfaces. The methyl radical process (up to 20% CH 4 in H 2 ) allows some nucleation probability on appropriate substrates. Prolonged bias enhanced nucleation initiates both diamond nucleation and growth. C 2 dimer growth results in pure nanodiamond free of amorphous carbon, while prolonged bias enhanced nucleation forms an amorphous carbon/nanodiamond composite

  15. Influence of surface topography in the boiling mechanisms

    International Nuclear Information System (INIS)

    Moita, A.S.; Teodori, E.; Moreira, A.L.N.

    2015-01-01

    Highlights: • Pool boiling heat transfer. • Use of micro-textured surfaces to enhance heat transfer. • Importance of the bubble dynamics and of the interaction mechanisms in the overall heat transfer efficiency. • Effect of the micro-textures on bubble dynamics as a way to enhance pool boiling heat transfer. - Abstract: The present paper addresses the qualitative and quantitative analysis of the pool boiling heat transfer over micro-structured surfaces. The surfaces are made from silicon chips, in the context of pool boiling heat transfer enhancement of immersion liquid cooling schemes for electronic components. The first part of the analysis deals with the effect of the liquid properties. Then the effect of surface micro-structuring is discussed, covering different configurations, from cavities to pillars being the latter used to infer on the potential profit of a fin-like configuration. The use of rough surfaces to enhance pool boiling mainly stands on the arguments that the surface roughness will increase the liquid–solid contact area, thus enhancing the convection heat transfer coefficient and will promote the generation of nucleation sites. However, one should not disregard bubble dynamics. Indeed, the results show a strong effect of bubble dynamics and particularly of the interaction mechanisms in the overall cooling performance of the pair liquid–surface. The inaccurate control of these mechanisms leads to the formation of large bubbles and strong vertical and horizontal coalescence effects promote the very fast formation of a vapor blanket, which causes a steep decrease of the heat transfer coefficient. This effect can be strong enough to prevail over the benefit of increasing the contact area by roughening the surface. For the micro-patterns used in the present work, the results evidence that one can reasonably determine guiding pattern characteristics to evaluate the intensity of the interaction mechanisms and take out the most of the

  16. Pool boiling performance of NovecTM 649 engineered fluid

    International Nuclear Information System (INIS)

    Forrest, Eric; Buongiorno, Jacopo; McKrell, Thomas; Hu, Lin-Wen

    2009-01-01

    A new fluorinated ketone, C 2 F 5 C(O)CF(CF 3 ) 2 , is currently being considered as an environmentally friendly alternative for power electronics cooling applications due to its high dielectric strength and low global warming potential (GWP). Sold commercially by the 3M Company as Novec TM 649 Engineered Fluid, C 2 F 5 C(O)CF(CF 3 ) 2 exhibits very low acute toxicity while maintaining long-term stability. To assess the general two-phase heat transfer performance of Novec TM 649, pool boiling tests were conducted by resistively heating a 0.01 in. diameter nickel wire at the fluid's atmospheric saturation temperature of 49 deg C. The nucleate boiling heat transfer coefficient and critical heat flux (CHF) obtained for the fluorinated ketone compare favorably with results obtained for FC-72, a fluorocarbon widely used for the direct cooling of electronic devices. Initial results indicate that Novec TM 649 may prove to be a viable alternative to FC-72 and other halo alkanes for the cooling of high power density electronic devices. (author)

  17. A Correlation for Forced Convective Boiling Heat Transfer of Refrigerants in a Microfin Tube

    Science.gov (United States)

    Momoki, Satoru; Yu, Jian; Koyama, Shigeru; Fujii, Tetsu; Honda, Hiroshi

    The experimental study is reported on the forced convective boiling of pure refrigerants HCFC22, HFC134a and HCFC123 flowing in a horizontal microfin tube. The local heat transfer coefficient defined based on the actual inside surface area is measured in the ranges of mass velocity of 200 to 400 kg/m2s, heat flux of 5 to 64 kW/m2 and reduced pressure of 0.07 to 0.24. Using the Chen-type model, a new correlation for microfin tubes is proposed considering the enhancement effect of microfins on both the convective heat transfer and the nucleate boiling components. In the convective heat transfer component, the correlation to predict the heat transfer coefficient of liquid-only flow is determined from preliminary experiments on single-phase flow in microfin tubes, and the two-phase flow enhancement factor is determined from the present experimental data. For the nucleate boiling component, the correlation of Takamatsu et al. for smooth tube is modified. The prediction of the present correlation agrees well with present experimental data, and is available for several microfin tubes which were tested by other researchers.

  18. A Photographic study of subcooled flow boiling burnout at high heat flux and velocity

    Energy Technology Data Exchange (ETDEWEB)

    Celata, G.P.; Mariani, A.; Zummo, G. [ENEA, National Institute of Thermal-Fluid Dynamics, Rome (Italy); Cumo, M. [University of Rome (Italy); Gallo, D. [University of Palermo (Italy). Department of Nuclear Engineering

    2007-01-15

    The present paper reports the results of a visualization study of the burnout in subcooled flow boiling of water, with square cross section annular geometry (formed by a central heater rod contained in a duct characterized by a square cross section). The coolant velocity is in the range 3-10m/s. High speed movies of flow pattern in subcooled flow boiling of water from the onset of nucleate boiling up to physical burnout of the heater are recorded. From video images (single frames taken with a stroboscope light and an exposure time of 1{mu}s), the following general behaviour of vapour bubbles was observed: when the rate of bubble generation is increasing, with bubbles growing in the superheated layer close to the heating wall, their coalescence produces a type of elongated bubble called vapour blanket. One of the main features of the vapour blanket is that it is rooted to the nucleation site on the heated surface. Bubble dimensions are given as a function of thermal-hydraulic tested conditions for the whole range of velocity until the burnout region. A qualitative analysis of the behaviour of four stainless steel heater wires with different macroscopic surface finishes is also presented, showing the importance of this parameter on the dynamics of the bubbles and on the critical heat flux. (author)

  19. Neutralized wettability effect of superhydrophilic Cr-layered surface on pool boiling critical heat flux

    International Nuclear Information System (INIS)

    Son, Hong Hyun; Jeong, Ui Ju; Seo, Gwang Hyeok; Jeun, Gyoo Dong; Kim, Sung Joong

    2016-01-01

    The former method is deemed challenging due to longer development period and license issue. In this regard, FeCrAl, Cr, and SiC have been received positive attention as ATF coating materials because they are highly resistant to high temperature steam reaction causing massive hydrogen generation. In this study, Cr was selected as a target deposition material on the metal substrate because we found that Cr-layered surface becomes superhydrophilic, favorable to delaying the triggering of the critical heat flux (CHF). Thus in order to investigate the effect of Cr-layered superhydrophilic surfaces (under explored coating conditions) on pool boiling heat transfer, pool boiling experiment was conducted in the saturated deionized water under atmospheric pressure. As a physical vapor deposition (PVD) method, the DC magnetron sputtering technique was introduced to develop Cr-layered nanostructure. As a control variable of DC sputtering, substrate temperature was selected. Surface wettability and nanostructure were analyzed as major surface parameters on the CHF. We believe that highly dense micro/nano structure without nucleation cavities and inner pores neutralized the wettability effect on the CHF. Moreover, superhydrophilic surface with deficient cavity density rather hinders active nucleation. This emphasizes the importance of micro/nano structure surface for enhanced boiling heat transfer.

  20. Fouling of Structured Surfaces during Pool Boiling of Aqueous Solutions

    International Nuclear Information System (INIS)

    Esawy, M.

    2011-01-01

    Bubble characteristics in terms of density, size, frequency and motion are key factors that contribute to the superiority of nucleate pool boiling over the other modes of heat transfer. Nevertheless, if heat transfer occurs in an environment which is prone to fouling, the very same parameters may lead to accelerated deposit formation due to concentration effects beneath the growing bubbles. This has led heat exchanger designers frequently to maintain the surface temperature below the boiling point if fouling occurs, e.g. in thermal seawater desalination plants. The present study investigates the crystallization fouling of various structured surfaces during nucleate pool boiling of CaSO 4 solutions to shed light into their fouling behaviour compared with that of plain surfaces for the same operating conditions. As for the experimental part, a comprehensive set of clean and fouling experiments was performed rigorously. The structured tubes included low finned tubes of different fin densities, heights and materials and re-entrant cavity Turbo-B tube types.The fouling experiments were carried out at atmospheric pressure for different heat fluxes ranging from 100 to 300 k W/m 2 and CaSO 4 concentrations of 1.2 and 1.6 g/L. For the sake of comparison, similar runs were performed on plain stainless steel and copper tubes.Overall for the finned tubes, the experimental results showed a significant reduction of fouling resistances of up to 95% compared to those of the stainless steel and copper plain tubes. In addition, the scale formation that occurred on finned tubes was primarily a scattered and thin crystalline layer which differs significantly from those of plain tubes which suffered from a thick and homogenous layer of deposit with strong adhesion. Higher fin densities and lower fin heights always led to better antifouling performance for all investigated finned tubes. It was also shown that the surface material strongly affects the scale formation of finned tubes i

  1. Gamma heated subassembly for sodium boiling experiments

    International Nuclear Information System (INIS)

    Artus, S.C.

    1975-01-01

    The design of a system to boil sodium in an LMFBR is examined. This design should be regarded as a first step in a series of boiling experiments. The reactor chosen for the design of the boiling apparatus is the Experimental Breeder Reactor-II (EBR-II), located at the National Reactor Testing Station in Idaho. Criteria broadly classified as design objectives and design requirements are discussed

  2. Gamma heated subassembly for sodium boiling experiments

    Energy Technology Data Exchange (ETDEWEB)

    Artus, S.C.

    1975-01-01

    The design of a system to boil sodium in an LMFBR is examined. This design should be regarded as a first step in a series of boiling experiments. The reactor chosen for the design of the boiling apparatus is the Experimental Breeder Reactor-II (EBR-II), located at the National Reactor Testing Station in Idaho. Criteria broadly classified as design objectives and design requirements are discussed.

  3. Instability in flow boiling in microchannels

    CERN Document Server

    Saha, Sujoy Kumar

    2016-01-01

    This Brief addresses the phenomena of instability in flow boiling in microchannels occurring in high heat flux electronic cooling. A companion edition in the SpringerBrief Subseries on Thermal Engineering and Applied Science to “Critical Heat Flux in Flow Boiling in Microchannels,” and "Heat Transfer and Pressure Drop in Flow Boiling in Microchannels,"by the same author team, this volume is idea for professionals, researchers, and graduate students concerned with electronic cooling.

  4. Preliminary results from film boiling destabilisation experiments

    International Nuclear Information System (INIS)

    Naylor, P.

    1984-05-01

    A series of experiments to investigate the triggered destabilisation of film boiling has been undertaken. Film boiling was established on a polished brass rod immersed in water and the effects of various triggers were investigated. Preliminary results are presented and two thresholds have been observed: an impulse threshold below which triggered destabilisation will not occur and a thermal threshold above which film boiling will re-establish following triggered destabilisation. (author)

  5. Pool Boiling of Hydrocarbon Mixtures on Water

    Energy Technology Data Exchange (ETDEWEB)

    Boee, R.

    1996-09-01

    In maritime transport of liquefied natural gas (LNG) there is a risk of spilling cryogenic liquid onto water. The present doctoral thesis discusses transient boiling experiments in which liquid hydrocarbons were poured onto water and left to boil off. Composition changes during boiling are believed to be connected with the initiation of rapid phase transition in LNG spilled on water. 64 experimental runs were carried out, 14 using pure liquid methane, 36 using methane-ethane, and 14 using methane-propane binary mixtures of different composition. The water surface was open to the atmosphere and covered an area of 200 cm{sup 2} at 25 - 40{sup o}C. The heat flux was obtained by monitoring the change of mass vs time. The void fraction in the boiling layer was measured with a gamma densitometer, and a method for adapting this measurement concept to the case of a boiling cryogenic liquid mixture is suggested. Significant differences in the boil-off characteristics between pure methane and binary mixtures revealed by previous studies are confirmed. Pure methane is in film boiling, whereas the mixtures appear to enter the transitional boiling regime with only small amounts of the second component added. The results indicate that the common assumption that LNG will be in film boiling on water because of the high temperature difference, may be questioned. Comparison with previous work shows that at this small scale the results are influenced by the experimental apparatus and procedures. 66 refs., 76 figs., 28 tabs.

  6. Film boiling heat transfer in liquid helium

    International Nuclear Information System (INIS)

    Inai, Nobuhiko

    1979-01-01

    The experimental data on the film boiling heat transfer in liquid helium are required for investigating the stability of superconducting wires. On the other hand, liquid helium has the extremely different physical properties as compared with the liquids at normal temperature such as water. In this study, the experiments on pool boiling were carried out, using the horizontal top surface of a 20 mm diameter copper cylinder in liquid helium. For observing individual bubbles, the experiments on film boiling from a horizontal platinum wire were performed separately in liquid nitrogen and liquid helium, and photographs of floating-away bubbles were taken. The author pointed out the considerable upward shift of the boiling curve near the least heat flux point in film boiling from the one given by the Berenson's equation which has been said to agree comparatively well with the data on the film boiling of the liquids at normal temperature, and the reason was investigated. Consequently, a model for film boiling heat transfer was presented. Also one equation expressing the film boiling at low heat flux for low temperature liquids was proposed. It represents well the tendency to shift from Berenson's equation of the experimental data on film boiling at the least heat flux point for liquid helium, liquid nitrogen and water having extremely different physical properties. Some discussions are added at the end of the paper. (Wakatsuki, Y.)

  7. Investigation of pool boiling dynamics on a rectangular heater using nano-thermocouples: is it chaotic or stochastic?

    Energy Technology Data Exchange (ETDEWEB)

    Sathyamurthi, Vijaykumar; Banerjee, Debjyoti [Texas A and M University, College Station, TX (United States). Dept. of Mechanical Engineering], e-mail: dbanerjee@tamu.edu

    2009-07-01

    The non-linear dynamical model of pool boiling on a horizontal rectangular heater is assessed from experimental results in this study. Pool boiling experiments are conducted over a horizontal rectangular silicon substrate measuring 63 mm x 35 mm with PF-5060 as the test fluid. Novel nano-thermocouples, micro-machined in-situ on the silicon substrate are used to measure the surface temperature fluctuations for steady state pool boiling. The acquisition frequency for temperature data from the nano-thermocouples is 1 k Hz. The surface temperature fluctuations are analyzed using the TISEAN{sup c} package. A time-delay embedding is employed to generate higher dimensional phase-space vectors from the temperature time series record. The optimal delay is determined from the first minimum of the mutual information function. Techniques such as recurrence plots, and false nearest neighbors tests are employed to assess the presence of deterministic chaotic dynamics. Chaos quantifiers such as correlation dimensions are found for various pool boiling regimes using the raw data as well as noise-reduced data. Additionally, pseudo-phase spaces are used to reconstruct the 'attractors'. The results after non-linear noise reduction shows definitive presence of low-dimensional (d {<=} 7) chaos in fully developed nucleate boiling, at critical heat flux and in film boiling. (author)

  8. Investigation of pool boiling dynamics on a rectangular heater using nano-thermocouples: is it chaotic or stochastic?

    International Nuclear Information System (INIS)

    Sathyamurthi, Vijaykumar; Banerjee, Debjyoti

    2009-01-01

    The non-linear dynamical model of pool boiling on a horizontal rectangular heater is assessed from experimental results in this study. Pool boiling experiments are conducted over a horizontal rectangular silicon substrate measuring 63 mm x 35 mm with PF-5060 as the test fluid. Novel nano-thermocouples, micro-machined in-situ on the silicon substrate are used to measure the surface temperature fluctuations for steady state pool boiling. The acquisition frequency for temperature data from the nano-thermocouples is 1 k Hz. The surface temperature fluctuations are analyzed using the TISEAN c package. A time-delay embedding is employed to generate higher dimensional phase-space vectors from the temperature time series record. The optimal delay is determined from the first minimum of the mutual information function. Techniques such as recurrence plots, and false nearest neighbors tests are employed to assess the presence of deterministic chaotic dynamics. Chaos quantifiers such as correlation dimensions are found for various pool boiling regimes using the raw data as well as noise-reduced data. Additionally, pseudo-phase spaces are used to reconstruct the 'attractors'. The results after non-linear noise reduction shows definitive presence of low-dimensional (d ≤ 7) chaos in fully developed nucleate boiling, at critical heat flux and in film boiling. (author)

  9. A note on the nucleation with multiple steps: Parallel and series nucleation

    OpenAIRE

    Iwamatsu, Masao

    2012-01-01

    Parallel and series nucleation are the basic elements of the complex nucleation process when two saddle points exist on the free-energy landscape. It is pointed out that the nucleation rates follow formulas similar to those of parallel and series connection of resistors or conductors in an electric circuit. Necessary formulas to calculate individual nucleation rates at the saddle points and the total nucleation rate are summarized and the extension to the more complex nucleation process is su...

  10. Boiling of the Interface between Two Immiscible Liquids below the Bulk Boiling Temperatures of Both Components

    OpenAIRE

    Pimenova, Anastasiya V.; Goldobin, Denis S.

    2014-01-01

    We consider the problem of boiling of the direct contact of two immiscible liquids. An intense vapour formation at such a direct contact is possible below the bulk boiling points of both components, meaning an effective decrease of the boiling temperature of the system. Although the phenomenon is known in science and widely employed in technology, the direct contact boiling process was thoroughly studied (both experimentally and theoretically) only for the case where one of liquids is becomin...

  11. Boils

    Science.gov (United States)

    ... of Giving Governance By-Laws Committees Committee Service Conflict of Interest Policy Meeting Minutes Archive History Mission ... the normal, harmless bacteria we all carry. The source may be a family member, a pet or ...

  12. Forced convection flow boiling and two-phase flow phenomena in a microchannel

    Science.gov (United States)

    Na, Yun Whan

    2008-07-01

    ) technique. The effects of different constant heat fluxes and different channel heights on the boiling mechanisms were investigated. The effects of liquid velocity on the bubble departure diameter were analyzed. The obtained results showed that the wall superheats at the position of nucleate boiling are relatively independent of the mass flow rates at the same channel height. The obtained results, however, showed that the heat flux at the onset of nucleate boiling strongly depends on the channel height. With a decrease of the channel height and an increase of the liquid velocity at the channel inlet, the departure diameter of a bubble was smaller. The periodic flow patterns, such as the bubbly flow, elongated slug flow, and churn flow were observed in the microchannel. Flow instabilities of two-phase flow boiling in a trapezoidal microchannel using a three-dimensional model were investigated. Fluctuation behaviors of flow boiling parameters such as wall temperature and inlet pressure caused by periodic flow patterns were studied at different heat fluxes and mass fluxes. The numerical results showed large amplitude and short period oscillations for wall temperature and inlet pressure fluctuations. Stable and unstable flow boiling regime with short period oscillations were investigated. Those flow boiling regimes were not listed in stable and unstable boiling regime map proposed by Wang et al. (2007).

  13. Nucleation and cavitation in parahydrogen

    International Nuclear Information System (INIS)

    Pi, Martí; Barranco, Manuel; Navarro, Jesús; Ancilotto, Francesco

    2012-01-01

    Highlights: ► We have constructed a density functional (DF) for parahydrogen between 14 and 32 K. ► The experimental equation of state and the surface tension are well reproduced. ► We have investigated nucleation and cavitations processes in the metastable phase. ► We have obtained the electron bubble explosion within the capillary model. - Abstract: We have used a density functional approach to investigate thermal homogeneous nucleation and cavitation in parahydrogen. The effect of electrons as seeds of heterogeneous cavitation in liquid parahydrogen is also discussed within the capillary model.

  14. A classical density functional investigation of nucleation

    International Nuclear Information System (INIS)

    Ghosh, Satinath; Ghosh, Swapan K.

    2009-01-01

    Study of nucleation and growth phenomena in condensation is of prime importance in various applications such as crystal growth, nanoparticle synthesis, pattern formation etc. The knowledge of nucleation barrier in condensation is necessary to control the nucleation kinetics, size of the nanoparticles etc. Classical nucleation theory (CNT) assumes the density of the drop as bulk density irrespective of the size of the drop and overestimates the nucleation barrier. Here we are interested in solving the problem analytically using density functional theory (DFT) with square gradient approximation along the lines of Cahn and Hilliard. Nucleation barrier and density profile obtained in this work are consistent with other works based on nonclassical theory. (author)

  15. Ex-vessel boiling experiments: laboratory- and reactor-scale testing of the flooded cavity concept for in-vessel core retention. Pt. II. Reactor-scale boiling experiments of the flooded cavity concept for in-vessel core retention

    International Nuclear Information System (INIS)

    Chu, T.Y.; Bentz, J.H.; Slezak, S.E.; Pasedag, W.F.

    1997-01-01

    For pt.I see ibid., p.77-88 (1997). This paper summarizes the results of a reactor-scale ex-vessel boiling experiment for assessing the flooded cavity design of the heavy water new production reactor. The simulated reactor vessel has a cylindrical diameter of 3.7 m and a torispherical bottom head. Boiling outside the reactor vessel was found to be subcooled nucleate boiling. The subcooling mainly results from the gravity head, which in turn results from flooding the side of the reactor vessel. The boiling process exhibits a cyclic pattern with four distinct phases: direct liquid-solid contact, bubble nucleation and growth, coalescence, and vapor mass dispersion. The results show that, under prototypic heat load and heat flux distributions, the flooded cavity will be effective for in-vessel core retention in the heavy water new production reactor. The results also demonstrate that the heat dissipation requirement for in-vessel core retention, for the central region of the lower head of an AP-600 advanced light water reactor, can be met with the flooded cavity design. (orig.)

  16. On the frontier of boiling curve and beyond design of its origin

    International Nuclear Information System (INIS)

    Stosic, Z.V.

    2005-01-01

    An advanced approach of Extended Design of the Boiling Curve beyond its origin is proposed. It is developed from the fact that both CHF (Critical Heat Flux) and rewetting affect the Boiling Curve on the heating surface through two simultaneous processes taking place on both sides of the heating surface. The first is two-phase flow thermal-hydraulics with resultant heat transferred from the heating surface to the coolant. The second one is the heat conduction through material itself, allied with the balance of generated and accumulated energy. Both of these processes are triggered by the change in HTC (Heat Transfer Coefficient) on the heating surface, which accordingly influences the Boiling Curve. Depending on direction of the Transition - from nucleate to film boiling or vice versa - these processes act differently and direct the Boiling Curve to diverse paths. The proposed physically based concept recognises this fact and introduces HTC as the triggering parameter with instant effect. It is implemented in the subchannel code COBRA 3-CP providing stable rewetting which has been deficient in COBRA since its origin. Results of validation and obtained agreements with transient measured data prove legality of the advanced concept of Boiling Curve. This approach is being used for transient analyses of PWR (Pressurised Water Reactor) gaining benefits from properly predicting the rewetting. The method is well-qualified to be applied also in other thermal-hydraulic codes like COBRA/TRAC, COBRA-TF, TRAC and/or RELAP, where the classical steady-state and poolboiling approach has been originally implemented. (author)

  17. Mechanism of subcooled water flow boiling critical heat flux in a circular tube at high liquid Reynolds number

    International Nuclear Information System (INIS)

    Hata, K.; Fukuda, K.; Masuzaki, S.

    2014-01-01

    The subcooled boiling heat transfer and the steady state critical heat flux (CHF) in a vertical circular tube for the flow velocities (u=3.95 to 30.80 m/s) are systematically measured by the experimental water loop comprised of a multistage canned-type circulation pump with high pump head. The SUS304 test tube of inner diameter (d=6 mm) and heated length (L=59.5 mm) is used in this work. The outer surface temperatures of the SUS304 test tube with heating are observed by an infrared thermal imaging camera and a video camera. The subcooled boiling heat transfers for SUS304 test tube are compared with the values calculated by other workers' correlations for the subcooled boiling heat transfer. The influence of flow velocity on the subcooled boiling heat transfer and the CHF is investigated into details based on the experimental data. Nucleate boiling surface superheats at the CHF are close to the lower limit of the heterogeneous spontaneous nucleation temperature and the homogeneous spontaneous nucleation temperature. The dominant mechanism of the subcooled flow boiling CHF on the SUS304 circular tube is discussed at high liquid Reynolds number. On the other hand, theoretical equations for k-ε turbulence model in a circular tube of a 3 mm in diameter and a 526 mm long are numerically solved for heating of water on heated section of a 3 mm in diameter and a 67 mm long with various thicknesses of conductive sub-layer by using PHOENICS code under the same conditions as the experimental ones previously obtained considering the temperature dependence of thermo-physical properties concerned. The Platinum (Pt) test tube of inner diameter (d=3 mm) and heated length (L=66.5 mm) was used in this experiment. The thicknesses of conductive sub-layer from non-boiling regime to CHF are clarified. The thicknesses of conductive sub-layer at the CHF point are evaluated for various flow velocities. The experimental values of the CHF are also compared with the corresponding

  18. Flow regimes and mechanistic modeling of critical heat flux under subcooled flow boiling conditions

    Science.gov (United States)

    Le Corre, Jean-Marie

    Thermal performance of heat flux controlled boiling heat exchangers are usually limited by the Critical Heat Flux (CHF) above which the heat transfer degrades quickly, possibly leading to heater overheating and destruction. In an effort to better understand the phenomena, a literature review of CHF experimental visualizations under subcooled flow boiling conditions was performed and systematically analyzed. Three major types of CHF flow regimes were identified (bubbly, vapor clot and slug flow regime) and a CHF flow regime map was developed, based on a dimensional analysis of the phenomena and available data. It was found that for similar geometric characteristics and pressure, a Weber number (We)/thermodynamic quality (x) map can be used to predict the CHF flow regime. Based on the experimental observations and the review of the available CHF mechanistic models under subcooled flow boiling conditions, hypothetical CHF mechanisms were selected for each CHF flow regime, all based on a concept of wall dry spot overheating, rewetting prevention and subsequent dry spot spreading. It is postulated that a high local wall superheat occurs locally in a dry area of the heated wall, due to a cyclical event inherent to the considered CHF two-phase flow regime, preventing rewetting (Leidenfrost effect). The selected modeling concept has the potential to span the CHF conditions from highly subcooled bubbly flow to early stage of annular flow. A numerical model using a two-dimensional transient thermal analysis of the heater undergoing nucleation was developed to mechanistically predict CHF in the case of a bubbly flow regime. In this type of CHF two-phase flow regime, the high local wall superheat occurs underneath a nucleating bubble at the time of bubble departure. The model simulates the spatial and temporal heater temperature variations during nucleation at the wall, accounting for the stochastic nature of the boiling phenomena. The model has also the potential to evaluate

  19. The effect of nozzle collar on signle phase and boiling heat transfer by planar impinging jet

    International Nuclear Information System (INIS)

    Shin, Chang Hwan; Yim, Seong Hwan; Cho, Hyung Hee; Wu, Seong Je

    2005-01-01

    The water jet impingement cooling is one of the techniques to remove the heat from high heat flux equipment. Local heat transfer of the confined water impinging jet and the effect of nozzle collar to enhance the heat transfer are investigated in the free surface jet and submerged jet. Boiling is initiated from the farthest downstream and increase of the wall temperature is reduced with developing boiling, forming the flat temperature distributions. The reduction in the nozzle-to-surface distance for H/W≤1 causes significant increases and distribution changes of heat transfer. Developed boiling reduces the differences of heat transfer for various conditions. The nozzle collar is employed at the nozzle exit. The distances from heated surface to nozzle collar, H c are 0.25W, 0.5W and 1.0W. The liquid film thickness is reduced and the velocity of wall jet increases as decreased spacing of collar to heated surface. Heat transfer is enhanced for region from the stagnation to x/W∼8 in the free surface jet and to x/W∼5 in the submerged jet. For nucleate boiling region of further downstream, the heat transfer by the nozzle collar is decreased in submerged jet comparing with higher velocity condition. It is because the increased velocity by collar is de-accelerated downstream

  20. Electric fields effect on the rise of single bubbles during boiling

    International Nuclear Information System (INIS)

    Siedel, Samuel; Cioulachtjian, Serge; Bonjour, Jocelyn

    2009-01-01

    An experimental study of saturated pool boiling on a single artificial nucleation site without and with the application of an electric field on the boiling surface has been conducted. N-pentane is boiling on a copper surface and is recorded with a high speed camera providing high quality pictures and movies. The accuracy of the visualization allowed establishing an experimental bubble growth law from a large number of experiments. This law shows that the evaporation rate is decreasing during the bubble growth, and underlines the importance of liquid motion induced by the preceding bubble. Bubble rise is therefore studied: once detached, bubbles accelerate vertically until reaching a maximum velocity in good agreement with a correlation from literature. The bubbles then turn to another direction. The effect of applying an electric field on the boiling surface in finally studied. In addition to changes of the bubble shape, changes are also shown in the liquid plume and the convective structures above the surface. Lower maximum rising velocities were measured in the presence of electric fields, especially with a negative polarity. (author)

  1. A sensitivity analysis of the mass balance equation terms in subcooled flow boiling

    International Nuclear Information System (INIS)

    Braz Filho, Francisco A.; Caldeira, Alexandre D.; Borges, Eduardo M.

    2013-01-01

    In a heated vertical channel, the subcooled flow boiling occurs when the fluid temperature reaches the saturation point, actually a small overheating, near the channel wall while the bulk fluid temperature is below this point. In this case, vapor bubbles are generated along the channel resulting in a significant increase in the heat flux between the wall and the fluid. This study is particularly important to the thermal-hydraulics analysis of Pressurized Water Reactors (PWRs). The computational fluid dynamics software FLUENT uses the Eulerian multiphase model to analyze the subcooled flow boiling. In a previous paper, the comparison of the FLUENT results with experimental data for the void fraction presented a good agreement, both at the beginning of boiling as in nucleate boiling at the end of the channel. In the region between these two points the comparison with experimental data was not so good. Thus, a sensitivity analysis of the mass balance equation terms, steam production and condensation, was performed. Factors applied to the terms mentioned above can improve the agreement of the FLUENT results to the experimental data. Void fraction calculations show satisfactory results in relation to the experimental data in pressures values of 15, 30 and 45 bars. (author)

  2. Lecture background notes on transient sodium boiling and voiding in fast reactors

    International Nuclear Information System (INIS)

    Okrent, D.; Fauske, H.K.

    1972-01-01

    This set of lecture background notes includes the following: (1) Introductory remarks on fast reactor safety, which are intended to provide some perspective on the role played by sodium boiling. (2) A discussion of superheat which reviews the experimental data and nucleation models with emphasis on the pressure-temperature history effect on radius of active cavity sites, including the role played by inert gas. (3) A discussion of the growth and collapse of spherical bubbles. (4) A historical description of the development of computer codes to describe voiding and a detailed description of the analytical formulation of typical models for calculating voiding due to boiling, fission gas release, and molten fuel-coolant interaction. (U.S.)

  3. Signal processing for boiling noise detection

    International Nuclear Information System (INIS)

    Ledwidge, T.J.; Black, J.L.

    1989-01-01

    The present paper deals with investigations of acoustic signals from a boiling experiment performed on the KNS I loop at KfK Karlsruhe. Signals have been analysed in frequency as well as in time domain. Signal characteristics successfully used to detect the boiling process have been found in time domain. (author). 6 refs, figs

  4. Feedback stabilization of transition boiling states

    NARCIS (Netherlands)

    Gils, van R.W.; Speetjens, M.F.M.; Nijmeijer, H.

    2010-01-01

    A nonlinear one-dimensional heat-transfer model for pool boiling systems is considered. The model involves only the temperature distribution within the heater and models the heat exchange with the boiling medium via a nonlinear boundary condition imposed at the fluid-heater interface. This compact

  5. Nuclear fragmentation by nucleation approach

    International Nuclear Information System (INIS)

    Chung, K.C.

    1992-01-01

    The nucleation model is used to simulate nuclear fragmentation processes. The critical value of the effective interaction radius is shown to vary linearly with the expansion factor α. The calculated mass and charge distributions are compared with some experimental data. (author)

  6. Multi-scale Control and Enhancement of Reactor Boiling Heat Flux by Reagents and Nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Manglik, R M; Athavale, A; Kalaikadal, D S; Deodhar, A; Verma, U

    2011-09-02

    The phenomenological characterization of the use of non-invasive and passive techniques to enhance the boiling heat transfer in water has been carried out in this extended study. It provides fundamental enhanced heat transfer data for nucleate boiling and discusses the associated physics with the aim of addressing future and next-generation reactor thermal-hydraulic management. It essentially addresses the hypothesis that in phase-change processes during boiling, the primary mechanisms can be related to the liquid-vapor interfacial tension and surface wetting at the solidliquid interface. These interfacial characteristics can be significantly altered and decoupled by introducing small quantities of additives in water, such as surface-active polymers, surfactants, and nanoparticles. The changes are fundamentally caused at a molecular-scale by the relative bulk molecular dynamics and adsorption-desorption of the additive at the liquid-vapor interface, and its physisorption and electrokinetics at the liquid-solid interface. At the micro-scale, the transient transport mechanisms at the solid-liquid-vapor interface during nucleation and bubblegrowth can be attributed to thin-film spreading, surface-micro-cavity activation, and micro-layer evaporation. Furthermore at the macro-scale, the heat transport is in turn governed by the bubble growth and distribution, macro-layer heat transfer, bubble dynamics (bubble coalescence, collapse, break-up, and translation), and liquid rheology. Some of these behaviors and processes are measured and characterized in this study, the outcomes of which advance the concomitant fundamental physics, as well as provide insights for developing control strategies for the molecular-scale manipulation of interfacial tension and surface wetting in boiling by means of polymeric reagents, surfactants, and other soluble surface-active additives.

  7. Multi-scale Control and Enhancement of Reactor Boiling Heat Flux by Reagents and Nanoparticles

    International Nuclear Information System (INIS)

    Manglik, R.M.; Athavale, A.; Kalaikadal, D.S.; Deodhar, A.; Verma, U.

    2011-01-01

    The phenomenological characterization of the use of non-invasive and passive techniques to enhance the boiling heat transfer in water has been carried out in this extended study. It provides fundamental enhanced heat transfer data for nucleate boiling and discusses the associated physics with the aim of addressing future and next-generation reactor thermal-hydraulic management. It essentially addresses the hypothesis that in phase-change processes during boiling, the primary mechanisms can be related to the liquid-vapor interfacial tension and surface wetting at the solidliquid interface. These interfacial characteristics can be significantly altered and decoupled by introducing small quantities of additives in water, such as surface-active polymers, surfactants, and nanoparticles. The changes are fundamentally caused at a molecular-scale by the relative bulk molecular dynamics and adsorption-desorption of the additive at the liquid-vapor interface, and its physisorption and electrokinetics at the liquid-solid interface. At the micro-scale, the transient transport mechanisms at the solid-liquid-vapor interface during nucleation and bubblegrowth can be attributed to thin-film spreading, surface-micro-cavity activation, and micro-layer evaporation. Furthermore at the macro-scale, the heat transport is in turn governed by the bubble growth and distribution, macro-layer heat transfer, bubble dynamics (bubble coalescence, collapse, break-up, and translation), and liquid rheology. Some of these behaviors and processes are measured and characterized in this study, the outcomes of which advance the concomitant fundamental physics, as well as provide insights for developing control strategies for the molecular-scale manipulation of interfacial tension and surface wetting in boiling by means of polymeric reagents, surfactants, and other soluble surface-active additives.

  8. Ice nucleation properties of mineral dusts

    OpenAIRE

    Steinke, Isabelle

    2013-01-01

    Ice nucleation in clouds has a significant impact on the global hydrological cycle as well as on the radiative budget of the Earth. The AIDA cloud chamber was used to investigate the ice nucleation efficiency of various atmospherically relevant mineral dusts. From experiments with Arizona Test Dust (ATD) a humidity and temperature dependent ice nucleation active surface site density parameterization was developed to describe deposition nucleation at temperatures above 220 K. Based...

  9. Nucleation in Polymers and Soft Matter

    Science.gov (United States)

    Xu, Xiaofei; Ting, Christina L.; Kusaka, Isamu; Wang, Zhen-Gang

    2014-04-01

    Nucleation is a ubiquitous phenomenon in many physical, chemical, and biological processes. In this review, we describe recent progress on the theoretical study of nucleation in polymeric fluids and soft matter, including binary mixtures (polymer blends, polymers in poor solvents, compressible polymer-small molecule mixtures), block copolymer melts, and lipid membranes. We discuss the methodological development for studying nucleation as well as novel insights and new physics obtained in the study of the nucleation behavior in these systems.

  10. Local pressure gradients due to incipience of boiling in subcooled flows

    Energy Technology Data Exchange (ETDEWEB)

    Ruggles, A.E.; McDuffee, J.L. [Univ. of Tennessee, Knoxville, TN (United States)

    1995-09-01

    Models for vapor bubble behavior and nucleation site density during subcooled boiling are integrated with boundary layer theory in order to predict the local pressure gradient and heat transfer coefficient. Models for bubble growth rate and bubble departure diameter are used to scale the movement of displaced liquid in the laminar sublayer. An added shear stress, analogous to a turbulent shear stress, is derived by considering the liquid movement normal to the heated surface. The resulting mechanistic model has plausible functional dependence on wall superheat, mass flow, and heat flux and agrees well with data available in the literature.

  11. Homogeneous nucleation of water in synthetic air

    NARCIS (Netherlands)

    Fransen, M.A.L.J.; Sachteleben, E.; Hruby, J.; Smeulders, D.M.J.; DeMott, P.J.; O'Dowd, C.D.

    2013-01-01

    Homogeneous nucleation rates for water vapor in synthetic air are measured by means of a Pulse-Expansion Wave Tube (PEWT). A comparison of the experimental nucleation rates with the Classical Nucleation Theory (CNT) shows that a more elaborated model is necessary to describe supercooled water

  12. A classical view on nonclassical nucleation

    NARCIS (Netherlands)

    Smeets, P.J.M.; Finney, A.R.; Habraken, W.J.E.M.; Nudelman, F.; Friedrich, H.; Laven, J.; De Yoreo, J.J.; Rodger, P.M.; Sommerdijk, N.A.J.M.

    2017-01-01

    Understanding and controlling nucleation is important for many crystallization applications. Calcium carbonate (CaCO3) is often used as a model system to investigate nucleation mechanisms. Despite its great importance in geology, biology, and many industrial applications, CaCO3 nucleation is still a

  13. Boiling water reactor fuel bundle

    International Nuclear Information System (INIS)

    Weitzberg, A.

    1986-01-01

    A method is described of compensating, without the use of control rods or burnable poisons for power shaping, for reduced moderation of neutrons in an uppermost section of the active core of a boiling water nuclear reactor containing a plurality of elongated fuel rods vertically oriented therein, the fuel rods having nuclear fuel therein, the fuel rods being cooled by water pressurized such that boiling thereof occurs. The method consists of: replacing all of the nuclear fuel in a portion of only the upper half of first predetermined ones of the fuel rods with a solid moderator material of zirconium hydride so that the fuel and the moderator material are axially distributed in the predetermined ones of the fuel rods in an asymmetrical manner relative to a plane through the axial midpoint of each rod and perpendicular to the axis of the rod; placing the moderator material in the first predetermined ones of the fuel rods in respective sealed internal cladding tubes, which are separate from respective external cladding tubes of the first predetermined ones of the fuel rods, to prevent interaction between the moderator material and the external cladding tube of each of the first predetermined ones of the fuel rods; and wherein the number of the first predetermined ones of the fuel rods is at least thirty, and further comprising the steps of: replacing with the moderator material all of the fuel in the upper quarter of each of the at least thirty rods; and also replacing with the moderator material all of the fuel in the adjacent lower quarter of at least sixteen of the at least thirty rods

  14. Investigation on energetics of ex-vessel vapor explosion based on spontaneous nucleation fragmentation

    International Nuclear Information System (INIS)

    Liu, Jie; Koshizuka, Seiichi; Oka, Yoshiaki

    2002-01-01

    A computer code PROVER-I is developed for propagation phase of vapor explosion. A new thermal fragmentation model is proposed with three kinds of time scale for modeling instant fragmentation, spontaneous nucleation fragmentation and normal boiling fragmentation. The energetics of ex-vessel vapor explosion is investigated based on different fragmentation models. A higher pressure peak and a larger mechanical energy conversion ratio are obtained by spontaneous nucleation fragmentation. A smaller energy conversion ratio results from normal boiling fragmentation. When the delay time in thermal fragmentation model is near 0.0 ms, the pressure propagation behavior tends to be analogous with that in hydrodynamic fragmentation. If the delay time is longer, pressure attenuation occurs at the shock front. The high energy conversion ratio (>4%) is obtained in a small vapor volume fraction together with spontaneous nucleation fragmentation. These results are consistent with fuel-coolant interaction experiments with alumina melt. However, in larger vapor volume fraction conditions (α υ >0.3), the vapor explosion is weak. For corium melt, a coarse mixture with void fraction of more than 30% can be generated in the pre-mixing process because of its physical properties. In the mixture with such a high void fraction the energetic vapor explosion hardly takes place. (author)

  15. Injection of Nucleate-Boiling Slug Flows into a Heat Exchange Chamber in Microgravity

    Science.gov (United States)

    2015-06-01

    colorless, fully- fluorinated liquid. Like other Fluorinert electronic liquids, Fluorinert liquid FC-72 is thermally and chernically stable, compatible...with sensitive materials, nonflammable, practically non- toxic and leaves essentially no residue upon evaporation. Tiris unique combination of

  16. Utilization of the MAT method to analyze the nucleate boiling boundary in rod bundles subchannels

    International Nuclear Information System (INIS)

    Pedron, M.Q.

    1983-01-01

    The digital program PANTERA-1P, a new version of the COBRA-IIIC code, developed at CDTN, is directed to the thermal-hydraulic analysis of water cooled rod bundles and reactor cores, insteady state and transient conditions. Both the new and the old code versions have identical capacities in what concerns evaluation of fluid variables, nevertheless PANTERA-1P has better and faster performance. Improvements introduced in the scheme for solution of the conservation equations have contributed significantly to reduce the computer time, without affecting the accuracy of results. While the momentum equations are solved in COBRA-IIIC for the crossflow distribution, the PANTERA-1P code solves these equations for the pressure distribution by using the MAT method (Modified and Advanced Theta). The calculation of the pressure coefficient matrix has been optimized and simultaneous linear equations are solved optionally by means of the transpose elimination with storage requirements or the successive over-relaxation methods. The program presents others features specially in what concerns the thermal conduction model for fuel rods and the critical heat flux calculations options. A new input/output scheme is provided for optional use of the British or Internacional System of Units. The results of the program are compared to the critical heat flux experimental data and to the results of COBRA-IIIC. Excellent agreement is observed in both cases. (Author) [pt

  17. Heat transfer in nucleate boiling of R134a/R152a mixtures

    Energy Technology Data Exchange (ETDEWEB)

    Shi, Kehong [Hugo Kern und Liebers GmbH and Co. KG, Schramberg (Germany); Spindler, Klaus; Hahne, Erich [Universitaet Stuttgart ITW, Stuttgart (Germany)

    2010-11-15

    Heat transfer coefficients were measured on a horizontal platinum wire and converted to data on horizontal copper tubes. The measurements spanned a large region of pressures p*=p/p{sub crit}=0.05-0.50 and heat fluxes of q=10{sup 3}-1.5 x 10{sup 5} W/m{sup 2}. The preparation of the test equipment is described. The effects of pressure and concentration on the heat transfer coefficients are shown. The mixture behaves very much like an azeotropic mixture; concentration has only a small effect, the heat transfer coefficients can be obtained from the heat transfer coefficients of the pure components according to their molar fractions. The conversion steps from wire- to tube-data are presented. A comparison of wire-data with correlations given in literature is shown. It renders good agreement. (orig.)

  18. On the Partitioning of Wall Heat Flux in Subcooled Flow Boiling

    International Nuclear Information System (INIS)

    Chu, In-Cheol; Hoang, Nhan Hien; Euh, Dong-Jin; Song, Chul-Hwa

    2015-01-01

    This region has been treated successfully by two-fluid model coupled with a population balance model or interfacial area transport equation (IATE). The second region is near-wall heat transfer which has been commonly described by a wall heat flux partitioning model coupled with models of nucleation site density (NSD), bubble departure diameter and bubble release frequency. Since the phase change process in the near-wall heat transfer is really complex, comprising different heat transfer mechanisms, bubble dynamics, bubble nucleation and thermal response of heated surface, the modeling of the second region is still a great challenge despite intensive efforts. Numerous models and correlations have been proposed to aim for computing the near-wall heat transfer. The models of nucleation site density, bubble departure diameter and bubble release frequency are used to quantify these components. The models closely related to each other. The heat flux partitioning model controls the wall and liquid temperatures. Then, it turns to control the boiling parameters, i.e. nucleation site density, bubble departure diameter and bubble release frequency. In this study, the partitioning of wall heat flux is taken into account. The existing issues occurred with previous models of the heat flux partitioning are pointed out and then a new model which considers the heat transfer caused by evaporation of superheated liquid at bubble boundary and the actual period of transient conduction term is formulated. The new model is then validated with a collected experimental database. This paper presented a new heat flux partitioning model in which the heat transfer by evaporation of the superheated liquid at the bubble boundary and the active period of the transient conduction were considered. The new model was validated with the experimental data of the subcooled flow boiling of water obtained by Phillips

  19. Characterization of the parameters at the origin of the chemical species hideout process at the fuel rod surface in boiling conditions

    International Nuclear Information System (INIS)

    Peybernes, J.; March, P.

    1999-01-01

    Current trends in nuclear power generation (and particularly in pressurized water reactors) are toward plant life extension and extended fuel burnup. A higher heat generation rate can induce local boiling regimes at the fuel rod surface in the hottest channels of the core, which can strongly modify the chemical environment of the cladding and influence the oxidation rate of zirconium alloys. Tests performed in out-of-pile loops under severe chemical and thermal-hydraulic conditions (nucleate boiling, higher lithium contents compared to PWRs) reveal two important phenomena: an increase of the oxidation rate of Zircaloy-4 cladding materials in 'high' lithiated environments; an enrichment of the chemical additives in the primary water (boron, lithium) at the surface of the cladding under nucleate boiling conditions. The latter phenomenon, also called 'hideout effect', is mainly controlled by some thermal hydraulic parameters such as bubble diameters and nucleation site density. These parameters strongly depend on the oxide morphology (roughness, porosity). The lack of reliable data in high temperature water environments has led to the development of a specific instrumentation based on visualization. The fitting of windows on the REGGAE out-of-pile loop provides an optical access to the two-phase flow regime under PWR operating conditions, allowing for the characterization of the parameters at the origin of the chemical species hideout process. These direct observations of the cladding surfaces subjected to nucleate boiling conditions provide information about the development of the boiling mechanisms in relation to the morphology of the oxide layers (porosity, thickness, roughness). (author)

  20. Propagation of Local Bubble Parameters of Subcooled Boiling Flow in a Pressurized Vertical Annulus Channel

    International Nuclear Information System (INIS)

    Chu, In-Cheol; Lee, Seung Jun; Youn, Young Jung; Park, Jong Kuk; Choi, Hae Seob; Euh, Dong Jin

    2015-01-01

    CMFD (Computation Multi-Fluid Dynamics) tools have been being developed to simulate two-phase flow safety problems in nuclear reactor, including the precise prediction of local bubble parameters in subcooled boiling flow. However, a lot of complicated phenomena are encountered in the subcooled boiling flow such as bubble nucleation and departure, interfacial drag of bubbles, lateral migration of bubbles, bubble coalescence and break-up, and condensation of bubbles, and the constitutive models for these phenomena are not yet complete. As a result, it is a difficult task to predict the radial profile of bubble parameters and its propagation along the flow direction. Several experiments were performed to measure the local bubble parameters for the validation of the CMFD code analysis and improvement of the constitutive models of the subcooled boiling flow, and to enhance the fundamental understanding on the subcooled boiling flow. The information on the propagation of the local flow parameters along the flow direction was not provided because the measurements were conducted at the fixed elevation. In SUBO experiments, the radial profiles of local bubble parameters, liquid velocity and temperature were obtained for steam-water subcooled boiling flow in a vertical annulus. The local flow parameters were measured at six elevations along the flow direction. The pressure was in the range of 0.15 to 0.2 MPa. We have launched an experimental program to investigate quantify the local subcooled boiling flow structure under elevated pressure condition in order to provide high precision experimental data for thorough validation of up-to-date CMFD codes. In the present study, the first set of experimental data on the propagation of the radial profile of the bubble parameters was obtained for the subcooled boiling flow of R-134a in a pressurized vertical annulus channel. An experimental program was launched for an in-depth investigation of a subcooled boiling flow in an elevated

  1. Flow Boiling on a Downward-Facing Inclined Plane Wall of Core Catcher

    International Nuclear Information System (INIS)

    Kim, Hyoung Tak; Bang, Kwang Hyun; Suh, Jung Soo

    2013-01-01

    In order to investigate boiling behavior on downward-facing inclined heated wall prior to the CHF condition, an experiment was carried out with 1.2 m long rectangular channel, inclined by 10 .deg. from the horizontal plane. High speed video images showed that the bubbles were sliding along the heated wall, continuing to grow and combining with the bubbles growing at their nucleation sites in the downstream. These large bubbles continued to slide along the heated wall and formed elongated slug bubbles. Under this slug bubble thin liquid film layer on the heated wall was observed and this liquid film prevents the wall from dryout. The length, velocity and frequency of slug bubbles sliding on the heated wall were measured as a function of wall heat flux and these parameters were used to develop wall boiling model for inclined, downward-facing heated wall. One approach to achieve coolable state of molten core in a PWR-like reactor cavity during a severe accident is to retain the core melt on a so-called core catcher residing on the reactor cavity floor after its relocation from the reactor pressure vessel. The core melt retained in the core catcher is cooled by water coolant flowing in an inclined cooling channel underneath as well as the water pool overlaid on the melt layer. Two-phase flow boiling with downward-facing heated wall such as this core catcher cooling channel has drawn a special attention because this orientation of heated wall may reach boiling crisis at lower heat flux than that of a vertical or upward-facing heated wall. Nishikawa and Fujita, Howard and Mudawar, Qiu and Dhir have conducted experiments to study the effect of heater orientation on boiling heat transfer and CHF. SULTAN experiment was conducted to study inclined large-scale structure coolability by water in boiling natural convection. In this paper, high-speed visualization of boiling behavior on downward-facing heated wall inclined by 10 .deg. is presented and wall boiling model for the

  2. Boiling Heat Transfer to Halogenated Hydrocarbon Refrigerants

    Science.gov (United States)

    Yoshida, Suguru; Fujita, Yasunobu

    The current state of knowledge on heat transfer to boiling refrigerants (halogenated hydrocarbons) in a pool and flowing inside a horizontal tube is reviewed with an emphasis on information relevant to the design of refrigerant evaporators, and some recommendations are made for future research. The review covers two-phase flow pattern, heat transfer characteristics, correlation of heat transfer coefficient, influence of oil, heat transfer augmentation, boiling from tube-bundle, influence of return bend, burnout heat flux, film boiling, dryout and post-dryout heat transfer.

  3. Ice nucleation activity of polysaccharides

    Science.gov (United States)

    Bichler, Magdalena; Felgitsch, Laura; Haeusler, Thomas; Seidl-Seiboth, Verena; Grothe, Hinrich

    2015-04-01

    Heterogeneous ice nucleation is an important process in the atmosphere. It shows direct impact on our climate by triggering ice cloud formation and therefore it has much influence on the radiation balance of our planet (Lohmann et al. 2002; Mishchenko et al. 1996). The process itself is not completely understood so far and many questions remain open. Different substances have been found to exhibit ice nucleation activity (INA). Due to their vast differences in chemistry and morphology it is difficult to predict what substance will make good ice nuclei and which will not. Hence simple model substances must be found and be tested regarding INA. Our work aims at gaining to a deeper understanding of heterogeneous ice nucleation. We intend to find some reference standards with defined chemistry, which may explain the mechanisms of heterogeneous ice nucleation. A particular focus lies on biological carbohydrates in regards to their INA. Biological carbohydrates are widely distributed in all kingdoms of life. Mostly they are specific for certain organisms and have well defined purposes, e.g. structural polysaccharides like chitin (in fungi and insects) and pectin (in plants), which has also water-binding properties. Since they are widely distributed throughout our biosphere and mostly safe to use for nutrition purposes, they are well studied and easily accessible, rendering them ideal candidates as proxies. In our experiments we examined various carbohydrates, like the already mentioned chitin and pectin, as well as their chemical modifications. Lohmann U.; A Glaciation Indirect Aerosol Effect Caused by Soot Aerosols; J. Geoph. Res.; Vol. 24 No.4; pp 11-1 - 11-4; 2002 Mishchenko M.I., Rossow W.B., Macke A., Lacis A. A.; Sensitivity of Cirrus Cloud Albedo, Bidirectional Reflectance and Optical Thickness Retrieval Accuracy to Ice Particle Shape, J. Geoph. Res.; Vol. 101, No D12; pp. 16,973 - 16,985; 1996

  4. Mechanisms of nucleation in flashing flows

    International Nuclear Information System (INIS)

    Yan, F.; Giot, M.

    1989-01-01

    The mechanisms of nucleation have been analysed. Starting from the assumption that the activation of micro-cavities in the wall surfaces is the most probable nucleation mechanism in practical flashing system, the authors study in detail the nucleation in a micro-cavity. A three step nucleation criterion is proposed, namely: trapping cavity, activable cavity and active cavity. Then, a new nucleation model is presented. The output of the model is the prediction of the bubble departure frequency versus the thermodynamic state of the liquid and the geometry of the cavity. The model can also predict the nucleation site density if the nature of the wall and the surface roughness are know. The prediction have been successfully compared with some preliminary experimental results. By combining the present model with Jones'theory, the flashing inception is correctly predicted. The use of this nucleation model for the complete modelling of a flashing non-equilibrium flow is in progress

  5. Bubble Dynamics, Two-Phase Flow, and Boiling Heat Transfer in Microgravity

    Science.gov (United States)

    Chung, Jacob N.

    1998-01-01

    wall temperature and heat flux near the wall would add to the database of knowledge which is necessary to understand the mechanisms of nucleate boiling. A heater array has been developed which contains 96 heater elements within a 2.5 mm square area. The temperature of each heater element is held constant by an electronic control system similar to a hot-wire anemometer. The voltage that is being applied to each heater element can be measured and digitized using a high-speed Analog to Digital (A/D) converter, and this digital information can be compiled into a series of heat-flux maps. Information for up to 10,000 heat flux maps can be obtained each second. The heater control system, the A/D system and the heater array construction are described in detail. Results are presented which show that this is an effective method of measuring the local heat flux during nucleate and transition boiling. Heat flux maps are obtained for pool boiling in FC-72 on a horizontal surface. Local heat flux variations are shown to be three to six times larger than variations in the spatially averaged heat flux.

  6. IR-thermography-based investigation of critical heat flux in subcooled flow boiling of water at atmospheric and high pressure conditions

    Energy Technology Data Exchange (ETDEWEB)

    Bucci, Matteo [Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States); Seong, Jee H. [Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States); Buongiorno, Jdacopo [Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States); Richenderfer, Andrew [Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States); Kossolapov, A. [Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)

    2017-11-01

    Here we report on MIT’s THM work in Q4 2016 and Q1 2017. The goal of this project is to design, construct and execute tests of flow boiling critical heat flux (CHF) at high-pressure using high-resolution and high-speed video and infrared (IR) thermometry, to generate unique data to inform the development of and validate mechanistic boiling heat transfer and CHF models. In FY2016, a new test section was designed and fabricated. Data was collected at atmospheric conditions at 10, 25 and 50 K subcoolings, and three mass fluxes, i.e. 500, 750 and 1000 kg/m2/s. Starting in Q4 2016 and continuing forward, new post-processing techniques have been developed to analyze the data collected. These new algorithms analyze the time-dependent temperature and heat flux distributions to calculate nucleation site density, nucleation frequency, growth and wait time, dry area fraction, and the complete heat flux partitioning. In Q1 2017 a new flow boiling loop was designed and constructed to support flow boiling tests up 10 bar pressure and 180 °C. Initial shakedown and testing has been completed. The flow loop and test section are now ready to begin high-pressure flow boiling testing.

  7. Technical and QA plan: Boiling behavior during flow instability

    International Nuclear Information System (INIS)

    Coutts, D.A.

    1991-01-01

    The coolant flow in a nuclear reactor core under normal operating conditions is kept as a subcooled liquid. This coolant is evenly distributed throughout the multiple flow channels with a uniform pressure profile across each coolant flow channel. If the coolant flow is reduced, the flow through individual channels will also decrease. A decrease in coolant flow will result in higher coolant temperatures if the heat flux is not reduced. When flow is significantly decreased, localized boiling may occur. This localized boiling can restrict coolant flow and the ability to transfer heat out of the reactor system. The maximum operating power for the reactor may be limited by how the coolant system reacts to a flow instability. One of the methods to assure safe operation during a reducing flow transient, is to operate at a power level below that necessary to initiate a flow excursion. Several correlations have been used to predict the conditions which will proceed a flow excursion. These correlations rely on the steady state behavior of the coolant and are based on steady-state testing. There are two significant points which this project will try to identify. The first is when vapor first forms on the channel surface. This might be designated as the Nucleate Vapor Transition. (Steady state equivalent is ONB). The second is when the vapor formation rate is large enough to lead to flow instability and thermal excursion. This point might be designated as the Significant Vapor Transition. (Steady state equivalent is OSV). A correlation will be developed to relate established steady state relations with the behavior of transient systems

  8. Evaporation rate of nucleating clusters.

    Science.gov (United States)

    Zapadinsky, Evgeni

    2011-11-21

    The Becker-Döring kinetic scheme is the most frequently used approach to vapor liquid nucleation. In the present study it has been extended so that master equations for all cluster configurations are included into consideration. In the Becker-Döring kinetic scheme the nucleation rate is calculated through comparison of the balanced steady state and unbalanced steady state solutions of the set of kinetic equations. It is usually assumed that the balanced steady state produces equilibrium cluster distribution, and the evaporation rates are identical in the balanced and unbalanced steady state cases. In the present study we have shown that the evaporation rates are not identical in the equilibrium and unbalanced steady state cases. The evaporation rate depends on the number of clusters at the limit of the cluster definition. We have shown that the ratio of the number of n-clusters at the limit of the cluster definition to the total number of n-clusters is different in equilibrium and unbalanced steady state cases. This causes difference in evaporation rates for these cases and results in a correction factor to the nucleation rate. According to rough estimation it is 10(-1) by the order of magnitude and can be lower if carrier gas effectively equilibrates the clusters. The developed approach allows one to refine the correction factor with Monte Carlo and molecular dynamic simulations.

  9. An evaluation of analytical heat transfer area with various boiling heat transfer correlations in steam generator thermal sizing

    International Nuclear Information System (INIS)

    Jung, B. R.; Park, H. S.; Chung, D. M.; Baik, S. J.

    1999-01-01

    The computer program SAFE has been used to size and analyze the performance of a steam generator which has two types of heat transfer regions in Korean Standard Nuclear Power Plants (KSNP) and Korean Next Generation Reactor (KNGR) design. The SAFE code calculates the analytical boiling heat transfer area using the modified form of the saturated nucleate pool boiling correlation suggested by Rohsenow. The predicted heat transfer area in the boiling region is multiplied by a constant to obtain a final analytical heat transfer area. The inclusion of the multiplier in the analytical calculation has some disadvantage of loss of complete correlation by the governing heat transfer equation. Several comparative analyses have been performed quantitatively to evaluate the possibility of removing the multiplier in the analytical calculation in the SAFE code. The evaluation shows that the boiling correlation and multiplier used in predicting the boiling region heat transfer area can be replaced with other correlations predicting nearly the same heat transfer area. The removal of multiplier included in the analytical calculation will facilitate a direct use of a set of concerned analytical sizing values that can be exactly correlated by the governing heat transfer equation. In addition this will provide more reasonable basis for the steam generator thermal sizing calculation and enhance the code usability without loss of any validity of the current sizing procedure. (author)

  10. Assessment of RANS at low Prandtl number and simulation of sodium boiling flows with a CMFD code

    Energy Technology Data Exchange (ETDEWEB)

    Mimouni, S., E-mail: stephane.mimouni@edf.fr; Guingo, M.; Lavieville, J.

    2017-02-15

    Highlights: • Modelling of boiling sodium flows in a multiphase flow solver. • Rod heated with a constant heat flux in a pipe liquid metal flow. • Sodium boiling flow around a rod heated with a constant heat. • Computations in progress in an assembly constituted of 19 pins equipped with a wrapped wire. - Abstract: In France, Sodium-cooled Fast Reactors (SFR) have recently received a renewed interest. In 2006, the decision was taken by the French Government to initiate research in order to build a first Generation IV prototype (called ASTRID) by 2020. The improvement in the safety of SFR is one of the key points in their conception. Accidental sequences may lead to a significant increase of reactivity. This is for instance the case when the sodium coolant is boiling within the fissile zone. As a consequence, incipient boiling superheat of sodium is an important parameter, as it can influence boiling process which may appear during some postulated accidents as the unexpected loss of flow (ULOF). The problem is that despite the reduction in core power, when boiling conditions are reached, the flow decreases progressively and vapour expands into the heating zone. A crucial investigating way is to optimize the design of the fissile assemblies of the core in order to lead to stable boiling during a ULOF accident, without voiding of the fissile zone. Moreover, in order to evaluate nuclear plant design and safety, a CFD tool has been developed at EDF in the framework of the nuclear industry. Advanced models dedicated to boiling flows have been implemented and validated against experimental data for ten years now including a wall law for boiling flows, wall transfer for nucleate boiling, turbulence and polydispersion model. This paper aims at evaluating the generalization of these models to SFR. At least two main issues are encountered. Firstly, at low Prandtl numbers such as those of liquid metal, classical approaches derived for unity or close to unity fail to

  11. Characterization and modeling of the thermal hydraulic and chemical environment of fuel claddings of PWR reactors during boiling

    International Nuclear Information System (INIS)

    March, Ph.

    1999-01-01

    In pressurised water reactors (PWR), nucleate boiling can strongly influence the oxidation rate of the fuel cladding. To improve our understanding of the effect of the boiling phenomenon on corrosion kinetics, information about the chemical and thermal hydraulic boundary conditions at the heating rod surface is needed. Moreover, very few data are available in the range of thermal hydraulic parameters of PWR cores (15,5 MPa and 340 deg C) concerning the two-phase flow pattern close to the fuel cladding. A visualization device has been adapted on an out-of-pile loop Reggae to obtain both qualitative and quantitative data. These observations provide a direct access to the geometrical properties of the vapor inclusions, the onset of nucleate boiling and the gas velocity and trajectory. An image processing method has been validated to measure both void fraction and interfacial area concentration in a bubbly two-phase flow. Thus, the visualization device proves to be a suitable and accurate instrumentation to characterize nucleate boiling in PWR conditions. The experimental results analysis indicates that a local approach is needed for the modelling of the fuel rod chemical environment. To simulate the chemical additives enrichment, a new model is proposed where the vapor bubbles are now considered as physical obstacles for the liquid access to the rod surface. The influence of the two-phase flow pattern appears to be of major importance for the enrichment phenomenon. This study clearly demonstrates the existence of strong interactions between the two-phase flow pattern, the rod surface condition, the corrosion process and the water chemistry. (author)

  12. Physical interpretation of geysering phenomena and periodic boiling instability at low flows

    International Nuclear Information System (INIS)

    Duffey, R.B.; Rohatgi, U.S.

    1996-01-01

    Over 30 years ago, Griffith showed that unstable and periodic initial boiling occurred in stagnant liquids in heated pipes coupled to a cooler or condensing plenum volume. This was called ''geysering'', and is a similar phenomenon to the rapid nucleation and voiding observed in tubes filled with superheated liquid. It is also called ''bumping'' when non-uniformly heated water or a chemical suddenly boils in laboratory glassware. In engineering, the stability and predictability has importance to the onset of bulk boiling in a natural and forced circulation loops. The latest available data show the observed stability and periodicity of the onset of boiling flow when there is a plenum, multiple heated channels, and a sustained subcooling in a circulating loop. We examine the available data, both old and new, and develop a new theory to illustrate the simple physics causing the observed periodicity of the flow. We examine the validity of the theory by comparison to all the geysering data, and develop a useful and simple correlation. We illustrate the equivalence of the onset of geysering to the onset of static instability in subcooled boiling. We also derive the stability boundary for geysering, utilizing turbulent transport analysis to determine the effects of pressure and other key parameters. This new result explains the greater stability region observed at higher pressures. The paper builds on the 30 years of quite independent thermal hydraulic work that is still fresh and useful today. We discuss the physical interpretation of geysering onset with a consistent theory, and show where refinements would be useful to the data correlations

  13. Forced convective boiling heat transfer of water in vertical rectangular narrow channel

    International Nuclear Information System (INIS)

    Chen, Chong; Gao, Pu-zhen; Tan, Si-chao; Chen, Han-ying; Chen, Xian-bing

    2015-01-01

    Highlights: • Chen correlation cannot well predict the coefficient of rectangular channel. • Kim and Mudawar correlation is the best one among the Chen type correlations. • Lazarek and Black correlation predicted 7.0% of data within the ±30% error band. • The new correlation can well predict the coefficient with a small MAE of 14.4%. - Abstract: In order to research the characteristics of boiling flows in a vertical rectangular narrow channel, a series of convective boiling heat transfer experiments are performed. The test section is made of stainless steel with an inner diameter of 2 × 40 mm and heated length of 1100 mm. The 3194 experimental data points are obtained for a heat flux range of 10–700 kW/m 2 , a mass flux range of 200–2400 kg/m 2 s, a system pressure range of 0.1–2.5 MPa, and a quality range of 0–0.8. Eighteen prediction models are used to predict the flow boiling heat transfer coefficient of the rectangular narrow channel and the predicted value is compared against the database including 3194 data points, the results show that Chen type correlations and Lazarek and Black type correlations are not suitable for the rectangular channel very much. The Kim and Mudawar correlation is the best one among the 18 models. A new correlation is developed based on the superposition concept of nucleate boiling and convective boiling. the new correlation is shown to provide a good prediction against the database, evidenced by an overall MAE of 14.4%, with 95.2% and 98.6% of the data falling within ±30% and ±35% error bands, respectively

  14. Nuclear fuel performance in boiling water reactors

    International Nuclear Information System (INIS)

    Elkins, R.B.; Baily, W.E.; Proebstle, R.A.; Armijo, J.S.; Klepfer, H.H.

    1981-01-01

    A major development program is described to improve the performance of Boiling Water Reactor fuel. This sustained program is described in four parts: 1) performance monitoring, 2) fuel design changes, 3) plant operating recommendations, and 4) advanced fuel programs

  15. Recovering low-boiling hydrocarbons, etc

    Energy Technology Data Exchange (ETDEWEB)

    Pier, M

    1934-10-03

    A process is described for the recovery of low-boiling hydrocarbons of the nature of benzine through treatment of liquid carbonaceous materials with hydrogen under pressure at raised temperature, suitably in the presence of catalysts. Middle oils (practically saturated with hydrogen) or higher boiling oils at a temperature above 500/sup 0/ (with or without the addition of hydrogen) containing cyclic hydrocarbons not saturated with hydrogen are changed into low boiling hydrocarbons of the nature of benzine. The cracking takes place under strongly hydrogenating conditions (with the use of a strongly active hydrogenating catalyst or high pressure) at temperatures below 500/sup 0/. If necessary, the constituents boiling below 200/sup 0/ can be reconverted into cyclic hydrocarbons partially saturated with hydrogen. (BLM)

  16. Influence of subcooled boiling on out-of-phase oscillations in boiling water reactors

    International Nuclear Information System (INIS)

    Munoz-Cobo, J.L.; Chiva, S.; Escriva, A.

    2005-01-01

    In this paper, we develop a reduced order model with modal kinetics for the study of the dynamic behavior of boiling water reactors. This model includes the subcooled boiling in the lower part of the reactor channels. New additional equations have been obtained for the following dynamics magnitudes: the effective inception length for subcooled boiling, the average void fraction in the subcooled boiling region, the average void fraction in the bulk-boiling region, the mass fluxes at the boiling boundary and the channel exit, respectively, and so on. Each channel has three nodes, one of liquid, one with subcooled boiling, and one with bulk boiling. The reduced order model includes also a modal kinetics with the fundamental mode and the first subcritical one, and two channels representing both halves of the reactor core. Also, in this paper, we perform a detailed study of the way to calculate the feedback reactivity parameters. The model displays out-of-phase oscillations when enough feedback gain is provided. The feedback gain that is necessary to self-sustain these oscillations is approximately one-half the gain that is needed when the subcooled boiling node is not included

  17. Dynamic model for a boiling water reactor

    International Nuclear Information System (INIS)

    Muscettola, M.

    1963-07-01

    A theoretical formulation is derived for the dynamics of a boiling water reactor of the pressure tube and forced circulation type. Attention is concentrated on neutron kinetics, fuel element heat transfer dynamics, and the primary circuit - that is the boiling channel, riser, steam drum, downcomer and recirculating pump of a conventional La Mont loop. Models for the steam and feedwater plant are not derived. (author)

  18. Numerical simulation of single bubble boiling behavior

    Directory of Open Access Journals (Sweden)

    Junjie Liu

    2017-06-01

    Full Text Available The phenomena of a single bubble boiling process are studied with numerical modeling. The mass, momentum, energy and level set equations are solved using COMSOL multi-physics software. The bubble boiling dynamics, the transient pressure field, velocity field and temperature field in time are analyzed, and reasonable results are obtained. The numeral model is validated by the empirical equation of Fritz and could be used for various applications.

  19. Modelling of a DNB mechanism by dry-out of a nucleation site

    International Nuclear Information System (INIS)

    Bricard, P.

    1995-10-01

    This study deals with the modelling of a nucleation site dry-out DNB mechanism which unifies those of Kirby et al. (1967) and Fiori and Bergles (1970). A first model based on a simplified heat balance in the wall at the location of the dry spot is developed and a set of closure relations is proposed. The model is then quantitatively and qualitatively compared to CHF data. In order to support the likelihood of the mechanism, we develop a more elaborated model which couples the unsteady thermal behavior of the wall and the thermal-hydraulics of the fluid described by the different phases of the nucleation cycle. The conditions which enable the boiling crisis to be reached are given

  20. Thermodynamic and Dynamic Aspects of Ice Nucleation

    Science.gov (United States)

    Barahona, Donifan

    2018-01-01

    It is known that ice nucleating particles (INP) immersed within supercooled droplets promote the formation of ice. Common theoretical models used to represent this process assume that the immersed particle lowers the work of ice nucleation without significantly affecting the dynamics of water in the vicinity of the particle. This is contrary to evidence showing that immersed surfaces significantly affect the viscosity and diffusivity of vicinal water. To study how this may affect ice formation this work introduces a model linking the ice nucleation rate to the modification of the dynamics and thermodynamics of vicinal water by immersed particles. It is shown that INP that significantly reduce the work of ice nucleation also pose strong limitations to the growth of the nascent ice germs. This leads to the onset of a new ice nucleation regime, called spinodal ice nucleation, where the dynamics of ice germ growth instead of the ice germ size determines the nucleation rate. Nucleation in this regime is characterized by an enhanced sensitivity to particle area and cooling rate. Comparison of the predicted ice nucleation rate against experimental measurements for a diverse set of species relevant to cloud formation suggests that spinodal ice nucleation may be common in nature.

  1. Boiling of subcooled water in forced convection

    International Nuclear Information System (INIS)

    Ricque, R.; Siboul, R.

    1970-01-01

    As a part of a research about water cooled high magnetic field coils, an experimental study of heat transfer and pressure drop is made with the following conditions: local boiling in tubes of small diameters (2 and 4 mm), high heat fluxes (about 1000 W/cm 2 ), high coolant velocities (up to 25 meters/s), low outlet absolute pressures (below a few atmospheres). Wall temperatures are determined with a good accuracy, because very thin tubes are used and heat losses are prevented. Two regimes of boiling are observed: the establishment regime and the established boiling regime and the inception of each regime is correlated. Important delays on boiling inception are also observed. The pressure drop is measured; provided the axial temperature distribution of the fluid and the axial distributions of the wall temperatures, in other words the axial distribution of the heat transfer coefficients under boiling and non boiling conditions, at the same heat flux or the same wall temperatures, are taken in account, then total pressure drop can be correlated, but probably under certain limits of void fraction only. Using the same parameters, it seems possible to correlate the experimental values on critical heat flux obtained previously, which show very important effect of length and hydraulic diameter of the test sections. (authors) [fr

  2. Boiling experiments in DFR and PFR

    International Nuclear Information System (INIS)

    Judd, A.M.

    1994-01-01

    At the end of its life, in 1975-1977, a series of Special Experiments was conducted in the Dounreay Fast Reactor. Fuel pins were deliberately subjected to overheating, up to the coolant boiling point, for periods of several hours at a time. The boiling was monitored by acoustic sensors and thermocouples, and after the tests the fuel pins were examined to determine the extent of damage. The results of these experiments have been widely reported. The present paper summarises the results as a reminder of their significance. The outstanding conclusion was that coolant boiling had no severe consequences. In some, but not all, cases the pins failed, but little fuel was released, no local blockages were formed, and there was no fuel melting. At around the same time PFR was being commissioned, and for a time the primary coolant circuit was operated with a dummy core, containing no nuclear fuel. An electrically-heated boiling rig was deployed in the dummy core, and observed by acoustic monitors. The data gathered enabled the noise of boiling to be compared with the background noise, and provided valuable support for the design of acoustic boiling noise detection systems. (author)

  3. A note on the nucleation with multiple steps: parallel and series nucleation.

    Science.gov (United States)

    Iwamatsu, Masao

    2012-01-28

    Parallel and series nucleation are the basic elements of the complex nucleation process when two saddle points exist on the free-energy landscape. It is pointed out that the nucleation rates follow formulas similar to those of parallel and series connection of resistors or conductors in an electric circuit. Necessary formulas to calculate individual nucleation rates at the saddle points and the total nucleation rate are summarized, and the extension to the more complex nucleation process is suggested. © 2012 American Institute of Physics

  4. Numerical simulation of bubble growth and departure during flow boiling period by lattice Boltzmann method

    International Nuclear Information System (INIS)

    Sun, Tao; Li, Weizhong; Yang, Shuai

    2013-01-01

    Highlights: • The bubble departure diameter is proportional to g −0.425 in quiescent fluid. • The bubble release frequency is proportional to g 0.678 in quiescent fluid. • The simulation result supports the transient micro-convection model. • The bubble departure diameter has exponential relation with inlet velocity. • The bubble release frequency has linear relation with inlet velocity. -- Abstract: Nucleate boiling flows on a horizontal plate are studied in this paper by a hybrid lattice Boltzmann method, where both quiescent and slowly flowing ambient are concerned. The process of a single bubble growth on and departure from the superheated wall is simulated. The simulation result supports the transient micro-convection model. The bubble departure diameter and the release frequency are investigated from the simulation result. It is found that the bubble departure diameter and the release frequency are proportional to g −0.425 and g 0.678 in quiescent fluid, respectively, where g is the gravitational acceleration. Nucleate boiling in slowly flowing ambient is also calculated in consideration of forced convection. It is presented that the bubble departure diameter and the release frequency have exponential relationship and linear relationship with inlet velocity in slowly flowing fluid, respectively

  5. Thermally activated vapor bubble nucleation: The Landau-Lifshitz-Van der Waals approach

    Science.gov (United States)

    Gallo, Mirko; Magaletti, Francesco; Casciola, Carlo Massimo

    2018-05-01

    Vapor bubbles are formed in liquids by two mechanisms: evaporation (temperature above the boiling threshold) and cavitation (pressure below the vapor pressure). The liquid resists in these metastable (overheating and tensile, respectively) states for a long time since bubble nucleation is an activated process that needs to surmount the free energy barrier separating the liquid and the vapor states. The bubble nucleation rate is difficult to assess and, typically, only for extremely small systems treated at an atomistic level of detail. In this work a powerful approach, based on a continuum diffuse interface modeling of the two-phase fluid embedded with thermal fluctuations (fluctuating hydrodynamics), is exploited to study the nucleation process in homogeneous conditions, evaluating the bubble nucleation rates and following the long-term dynamics of the metastable system, up to the bubble coalescence and expansion stages. In comparison with more classical approaches, this methodology allows us on the one hand to deal with much larger systems observed for a much longer time than possible with even the most advanced atomistic models. On the other, it extends continuum formulations to thermally activated processes, impossible to deal with in a purely determinist setting.

  6. Nucleation in an ultra low ionization environment

    DEFF Research Database (Denmark)

    Pedersen, Jens Olaf Pepke; Enghoff, Martin Andreas Bødker; Paling, Sean

    Atmospheric ions can enhance the nucleation of aerosols, as has been established by experiments, observation, and theory. In the clean marine atmosphere ionization is mainly caused by cosmic rays which in turn are controlled by the activity of the Sun, thus providing a potential link between solar...... activity and climate. In order to understand the effect ions may have on the production of cloud condensation nuclei the overall contribution of ion induced nucleation to the global production of secondary aerosols must be determined. One issue with determining this contribution is that several mechanisms...... for nucleation exist and it can be difficult to determine the relative importance of the various mechanisms in a given nucleation event when both ion induced and electrically neutral nucleation mechanisms are at work at the same time. We have carried out nucleation experiments in the Boulby Underground...

  7. Truncated Dual-Cap Nucleation Site Development

    Science.gov (United States)

    Matson, Douglas M.; Sander, Paul J.

    2012-01-01

    During heterogeneous nucleation within a metastable mushy-zone, several geometries for nucleation site development must be considered. Traditional spherical dual cap and crevice models are compared to a truncated dual cap to determine the activation energy and critical cluster growth kinetics in ternary Fe-Cr-Ni steel alloys. Results of activation energy results indicate that nucleation is more probable at grain boundaries within the solid than at the solid-liquid interface.

  8. Effects of clustered nucleation on recrystallization

    DEFF Research Database (Denmark)

    Storm, Søren; Juul Jensen, Dorte

    2009-01-01

    Computer simulations are used to study effects of an experimentally determined 3D distribution of nucleation sites on the recrystallization kinetics and on the evolution of the recrystallized microstructure as compared to simulations with random nucleation. It is found that although...... the experimentally observed clustering is not very strong, it changes the kinetics and the recrystallized microstructural morphology plus leads to a recrystallized grain size distribution, which is significantly broadened compared to that of random nucleation simulations. (C) 2009 Published by Elsevier Ltd...

  9. Dependence of bubble behavior in subcooled boiling on surface wettability

    International Nuclear Information System (INIS)

    Harada, Takahiro; Nagakura, Hiroshi; Okawa, Tomio

    2010-01-01

    This paper presents the results of visualization experiments that were carried out to investigate the dynamics of vapor bubbles generated in water pool boiling. In the experiments, vapor bubbles were generated on a vertical circular surface of a copper block containing nine cartridge heaters, and the contact angle of the heated surface was used as a main experimental parameter. The experiments were performed under subcooled as well as nearly saturated conditions. To enable clear observation of individual bubbles with a high speed camera, the heat flux was kept low enough to eliminate significant overlapping of bubbles. When the contact angle was small, the bubbles were lifted-off the vertical heated surface within a short period of time after the nucleation. On the other hand, when the contact angle was large, they slid up the vertical surface for a long distance. When bubbles were lifted-off the heated surface in subcooled liquid, bubble life-time was significantly shortened since bubbles collapsed rapidly due to condensation. It was shown that this distinct difference in bubble dynamics could be attributed to the effects of surface tension force.

  10. Ice nucleation triggered by negative pressure.

    Science.gov (United States)

    Marcolli, Claudia

    2017-11-30

    Homogeneous ice nucleation needs supercooling of more than 35 K to become effective. When pressure is applied to water, the melting and the freezing points both decrease. Conversely, melting and freezing temperatures increase under negative pressure, i.e. when water is stretched. This study presents an extrapolation of homogeneous ice nucleation temperatures from positive to negative pressures as a basis for further exploration of ice nucleation under negative pressure. It predicts that increasing negative pressure at temperatures below about 262 K eventually results in homogeneous ice nucleation while at warmer temperature homogeneous cavitation, i. e. bubble nucleation, dominates. Negative pressure occurs locally and briefly when water is stretched due to mechanical shock, sonic waves, or fragmentation. The occurrence of such transient negative pressure should suffice to trigger homogeneous ice nucleation at large supercooling in the absence of ice-nucleating surfaces. In addition, negative pressure can act together with ice-inducing surfaces to enhance their intrinsic ice nucleation efficiency. Dynamic ice nucleation can be used to improve properties and uniformity of frozen products by applying ultrasonic fields and might also be relevant for the freezing of large drops in rainclouds.

  11. Probabilistic approach to lysozyme crystal nucleation kinetics.

    Science.gov (United States)

    Dimitrov, Ivaylo L; Hodzhaoglu, Feyzim V; Koleva, Dobryana P

    2015-09-01

    Nucleation of lysozyme crystals in quiescent solutions at a regime of progressive nucleation is investigated under an optical microscope at conditions of constant supersaturation. A method based on the stochastic nature of crystal nucleation and using discrete time sampling of small solution volumes for the presence or absence of detectable crystals is developed. It allows probabilities for crystal detection to be experimentally estimated. One hundred single samplings were used for each probability determination for 18 time intervals and six lysozyme concentrations. Fitting of a particular probability function to experimentally obtained data made possible the direct evaluation of stationary rates for lysozyme crystal nucleation, the time for growth of supernuclei to a detectable size and probability distribution of nucleation times. Obtained stationary nucleation rates were then used for the calculation of other nucleation parameters, such as the kinetic nucleation factor, nucleus size, work for nucleus formation and effective specific surface energy of the nucleus. The experimental method itself is simple and adaptable and can be used for crystal nucleation studies of arbitrary soluble substances with known solubility at particular solution conditions.

  12. Pool-Boiling Heat-Transfer Enhancement on Cylindrical Surfaces with Hybrid Wettable Patterns.

    Science.gov (United States)

    Kumar C S, Sujith; Chang, Yao Wen; Chen, Ping-Hei

    2017-04-10

    In this study, pool-boiling heat-transfer experiments were performed to investigate the effect of the number of interlines and the orientation of the hybrid wettable pattern. Hybrid wettable patterns were produced by coating superhydrophilic SiO2 on a masked, hydrophobic, cylindrical copper surface. Using de-ionized (DI) water as the working fluid, pool-boiling heat-transfer studies were conducted on the different surface-treated copper cylinders of a 25-mm diameter and a 40-mm length. The experimental results showed that the number of interlines and the orientation of the hybrid wettable pattern influenced the wall superheat and the HTC. By increasing the number of interlines, the HTC was enhanced when compared to the plain surface. Images obtained from the charge-coupled device (CCD) camera indicated that more bubbles formed on the interlines as compared to other parts. The hybrid wettable pattern with the lowermost section being hydrophobic gave the best heat-transfer coefficient (HTC). The experimental results indicated that the bubble dynamics of the surface is an important factor that determines the nucleate boiling.

  13. The influence of film-forming amines on heat transfer during saturated pool boiling

    Energy Technology Data Exchange (ETDEWEB)

    Topp, Holger [Rostock Univ. (Germany). Mechanical Engineering; Steinbrecht, Dieter [Rostock Univ. (Germany). Dept. of Power and Environmental Technologies; Hater, Wolfgang [BK Giulini GmbH, Duesseldorf (Germany); BK Giulini, Ludwigshafen (Germany). Water Solutions; Bache, Andre de [BK Giulini, Ludwigshafen (Germany). Water Solutions

    2010-07-15

    The heat transfer coefficients during pool boiling of water at steel heating surfaces are subject to irreversible temporal changes. The influence of the responsible physicochemical processes on the steel surface was investigated by thermo-technical measurements in a special apparatus using conditioned water. For this purpose an oxide layer, whose surface structure, composition and thickness vary with the respective kind of treatment, was generated on steel tube samples under specified conditions. Due to their surface activity, film-forming amine-based organic corrosion inhibitors feature a theoretical improvement potential regarding the heat transfer in nucleate boiling at steel heating surfaces. The intensifying impact of these filming agents on bubble evaporation during pool boiling compared to a classic water treatment was quantified in long-term tests. The impact of the corresponding conditioning program was examined and characterised by means of analytical methods. Significantly higher heat transmission coefficients were determined for film-forming amine treated tubes as compared to classic conditioning. (orig.)

  14. Preliminary Study on CHF Enhancement of Cellulose Nano Fiber (CNF) Fluid with Wire Pool Boiling Experiment

    Energy Technology Data Exchange (ETDEWEB)

    Hwang, Won Ki; Lee, Yun Seok; Lim, Dong Young; Song, Sub Lee; Lee, Jae Young; Lee, Kwon Yeong [Hanyang Global University, Pohang (Korea, Republic of); Hwang, Dong Soo [POSTECH, Pohang (Korea, Republic of)

    2016-05-15

    Critical heat flux (CHF) is enhancement of a boiling system will make more compact and effective cooling systems, for examples, nuclear reactors, and air conditioning units. For decades, researchers have been trying to develop more efficient working fluid for heat transfer. This is where nano-fluid could play a key role. There have been a lot of researches for CHF enhancements in nucleate boiling by using nano-fluid which are composed of metal such as copper, Al{sub 2}O{sub 3} and ceramic. And a critical factor of the enhancement is deposition of nano-particles on heating surface, although some results of recent studies are contrary. Also, previous nano-fluid are expensive and have a problem in mass production, so they are difficult to apply to practical industries. Therefore we chose a new material, cellulose nano fiber (CNF) as a solution. CNF can be applied to real situation because it has some advantages which are cost-effectiveness, easiness to get and to make it in nano scale. CHF performance of CNF fluid was different from that of distilled water. Compared to CHF of distilled water, CHF of the CNF fluid which had 0.001V%, 0.01V%, and 0.1V% volumetric concentrations were enhanced to 1%, 104%, and 13% respectively. Likewise other nano-fluid, deposition phenomena was observed in this CNF fluid boiling experiment.

  15. A new mechanistic model of critical heat flux in forced-convection subcooled boiling

    International Nuclear Information System (INIS)

    Alajbegovic, A.; Kurul, N.; Podowski, M.Z.; Drew, D.A.; Lahey, R.T. Jr.

    1997-10-01

    Because of its practical importance and various industrial applications, the process of subcooled flow boiling has attracted a lot of attention in the research community in the past. However, the existing models are primarily phenomenological and are based on correlating experimental data rather than on a first-principle analysis of the governing physical phenomena. Even though the mechanisms leading to critical heat flux (CHF) are very complex, the recent progress in the understanding of local phenomena of multiphase flow and heat transfer, combined with the development of mathematical models and advanced Computational Fluid Dynamics (CFD) methods, makes analytical predictions of CHF quite feasible. Various mechanisms leading to CHF in subcooled boiling have been investigated. A new model for the predictions of the onset of CHF has been developed. This new model has been coupled with the overall boiling channel model, numerically implemented in the CFX 4 computer code, tested and validated against the experimental data of Hino and Ueda. The predicted critical heat flux for various channel operating conditions shows good agreement with the measurements using the aforementioned closure laws for the various local phenomena governing nucleation and bubble departure from the wall. The observed differences are consistent with typical uncertainties associated with CHF data

  16. Preliminary Study on CHF Enhancement of Cellulose Nano Fiber (CNF) Fluid with Wire Pool Boiling Experiment

    International Nuclear Information System (INIS)

    Hwang, Won Ki; Lee, Yun Seok; Lim, Dong Young; Song, Sub Lee; Lee, Jae Young; Lee, Kwon Yeong; Hwang, Dong Soo

    2016-01-01

    Critical heat flux (CHF) is enhancement of a boiling system will make more compact and effective cooling systems, for examples, nuclear reactors, and air conditioning units. For decades, researchers have been trying to develop more efficient working fluid for heat transfer. This is where nano-fluid could play a key role. There have been a lot of researches for CHF enhancements in nucleate boiling by using nano-fluid which are composed of metal such as copper, Al_2O_3 and ceramic. And a critical factor of the enhancement is deposition of nano-particles on heating surface, although some results of recent studies are contrary. Also, previous nano-fluid are expensive and have a problem in mass production, so they are difficult to apply to practical industries. Therefore we chose a new material, cellulose nano fiber (CNF) as a solution. CNF can be applied to real situation because it has some advantages which are cost-effectiveness, easiness to get and to make it in nano scale. CHF performance of CNF fluid was different from that of distilled water. Compared to CHF of distilled water, CHF of the CNF fluid which had 0.001V%, 0.01V%, and 0.1V% volumetric concentrations were enhanced to 1%, 104%, and 13% respectively. Likewise other nano-fluid, deposition phenomena was observed in this CNF fluid boiling experiment.

  17. Advanced modeling of the size poly-dispersion of boiling flows

    International Nuclear Information System (INIS)

    Ruyer, Pierre; Seiler, Nathalie

    2008-01-01

    Full text of publication follows: This work has been performed within the Institut de Radioprotection et de Surete Nucleaire that leads research programs concerning safety analysis of nuclear power plants. During a LOCA (Loss Of Coolant Accident), in-vessel pressure decreases and temperature increases, leading to the onset of nucleate boiling. The present study focuses on the numerical simulation of the local topology of the boiling flow. There is experimental evidence of a local and statistical large spectra of possible bubble sizes. The relative importance of the correct description of this poly-dispersion in size is due to the dependency of (i) main hydrodynamic forces, like lift, as well as of (ii) transfer area with respect to the individual bubble size. We study the corresponding CFD model in the framework of an ensemble averaged description of the dispersed two-phase flow. The transport equations of the main statistical moment densities of the population size distribution are derived and models for the mass, momentum and heat transfers at the bubble scale as well as for bubble coalescence are achieved. This model introduced within NEPTUNE-CFD code of the NEPTUNE thermal-hydraulic platform, a joint project of CEA, EDF, IRSN and AREVA, has been tested on boiling flows obtained on the DEBORA facility of the CEA at Grenoble. These numerical simulations provide a validation and attest the impact of the proposed model. (authors) [fr

  18. Forced convective boiling of water inside helically coiled tube. Characteristics of oscillation of dryout point

    International Nuclear Information System (INIS)

    Nagai, Niro; Sugiyama, Kenta; Takeuchi, Masanori; Yoshikawa, Shinji; Yamamoto, Fujio

    2006-01-01

    The helically coiled tube of heat exchanger is used for the evaporator of prototype fast breeder reactor 'Monju'. This paper aims at the grasp of two-phase flow phenomena of forced convective boiling of water inside helical coiled tube, especially focusing on oscillation phenomena of dryout point. A glass-made helically coiled tube was used to observe the inside water boiling behavior flowing upward, which was heated by high temperature oil outside the tube. This oil was also circulated through a glass made tank to provide the heat source for water evaporation. The criterion for oscillation of dryout point was found to be a function of inlet liquid velocity and hot oil temperature. The observation results suggest the mechanism of dryout point oscillation mainly consists of intensive nucleate boiling near the dryout point and evaporation of thin liquid film flowing along the helical tube. In addition, the oscillation characteristics were experimentally confirmed. As inlet liquid velocity increases, oscillation amplitude also increases but oscillation cycle does not change so much. As hot oil temperature increases, oscillation amplitude and cycle gradually decreases. (author)

  19. Study on boiling heat transfer of subcooled flow under oscillatory flow condition

    International Nuclear Information System (INIS)

    Ohtake, Hiroyasu; Yamazaki, Satoshi; Koizumi, Yasuo

    2004-01-01

    The Onset of Nucleate Boiling, the point of Net Vapor Generation and Critical Heat Flux on subcooled flow boiling under oscillatory flow, focusing on liquid velocity, amplitude and frequency of oscillatory flow were investigated experimentally and analytically. Experiments were conducted using a copper thin-film and subcooled water in a range of the liquid velocity from 0.27 to 4.07 m/s at 0.10MPa. The liquid subcooling was 20K. Frequency of oscillatory flow was 2 and 4 Hz, respectively; amplitude of oscillatory flow was 25 and 50% in a ratio of main flow rate, respectively. Temperatures at Onset of Nuclear Boiling and Critical Heat Flux obtained in the experiments decreased with the oscillatory flow. The decrease of liquid velocity by oscillatory flow caused the ONB and the CHF to decrease. On the other hand, heat flux at Net Vapor Generation decreased with oscillatory flow; the increase of liquid velocity by oscillatory flow caused the NVG to decrease. (author)

  20. Comparative study of heat transfer and pressure drop during flow boiling and flow condensation in minichannels

    Directory of Open Access Journals (Sweden)

    Mikielewicz Dariusz

    2014-09-01

    Full Text Available In the paper a method developed earlier by authors is applied to calculations of pressure drop and heat transfer coefficient for flow boiling and also flow condensation for some recent data collected from literature for such fluids as R404a, R600a, R290, R32,R134a, R1234yf and other. The modification of interface shear stresses between flow boiling and flow condensation in annular flow structure are considered through incorporation of the so called blowing parameter. The shear stress between vapor phase and liquid phase is generally a function of nonisothermal effects. The mechanism of modification of shear stresses at the vapor-liquid interface has been presented in detail. In case of annular flow it contributes to thickening and thinning of the liquid film, which corresponds to condensation and boiling respectively. There is also a different influence of heat flux on the modification of shear stress in the bubbly flow structure, where it affects bubble nucleation. In that case the effect of applied heat flux is considered. As a result a modified form of the two-phase flow multiplier is obtained, in which the nonadiabatic effect is clearly pronounced.

  1. Critical heat flux and exit film flow rate in a flow boiling system

    International Nuclear Information System (INIS)

    Ueda, Tatsuhiro; Isayama, Yasushi

    1981-01-01

    The critical heat flux in a flowing boiling system is an important problem in the evaporating tubes with high thermal load such as nuclear reactors and boilers, and gives the practical design limit. When the heat flux in uniformly heated evaporating tubes is gradually raised, the tube exit quality increases, and soon, the critical heat flux condition arises, and the wall temperature near tube exit rises rapidly. In the region of low exit quality, the critical heat flux condition is caused by the transition from nucleating boiling, and in the region of high exit quality, it is caused by dry-out. But the demarcation of both regions is not clear. In this study, for the purpose of obtaining the knowledge concerning the critical heat flux condition in a flowing boiling system, the relation between the critical heat flux and exit liquid film flow rate was examined. For the experiment, a uniformly heated vertical tube supplying R 113 liquid was used, and the measurement in the range of higher heating flux and mass velocity than the experiment by Ueda and Kin was carried out. The experimental setup and experimental method, the critical heat flux and exit quality, the liquid film flow rate at heating zone exit, and the relation between the critical heat flux and the liquid film flow rate at exit are described. (Kako, I.)

  2. Structuring effects in binary nucleation : Molecular dynamics simulatons and coarse-grained nucleation theory

    NARCIS (Netherlands)

    Braun, S.; Kraska, T.; Kalikmanov, V.I.

    2013-01-01

    Binary clusters formed by vapor-liquid nucleation are frequently nonhomogeneous objects in which components are not well mixed. The structure of a cluster plays an important role in nucleation and cluster growth. We demonstrate structuring effects by studying high-pressure nucleation and cluster

  3. New trends in the nucleation research

    Science.gov (United States)

    Anisimov, M. P.; Hopke, P. K.

    2017-09-01

    During the last half of century the most of efforts have been directed towards small molecule system modeling using intermolecular potentials. Summarizing the nucleation theory, it can be concluded that the nowadays theory is far from complete. The vapor-gas nucleation theory can produce values that deviate from the experimental results by several orders of magnitude currently. Experiments on the vapor-gas nucleation rate measurements using different devices show significant inconsistencies in the measured rates as well. Theoretical results generally are quite reasonable for sufficiently low vapor nucleation rates where the capillary approximation is applicable. In the present research the advantages and current problems of the vapor-gas nucleation experiments are discussed briefly and a view of the future studies is presented. Using the brake points of the first derivative for the nucleation rate surface as markers of the critical embryos phase change is fresh idea to show the gas-pressure effect for the nucleating vapor-gas systems. To test the accuracy of experimental techniques, it is important to have a standard system that can be measured over a range of nucleation conditions. Several results illustrate that high-pressure techniques are needed to study multi-channel nucleation. In practical applications, parametric theories can be used for the systems of interest. However, experimental measurements are still the best source of information on nucleation rates. Experiments are labor intensive and costly, and thus, it is useful to extend the value of limited experimental measurements to a broader range of nucleation conditions. Only limited experimental data one needs for use in normalizing the slopes of the linearized nucleation rate surfaces. The nucleation rate surface is described in terms of steady-state nucleation rates. It is supposed that several new measuring systems, such as High Pressure Flow Diffusion Chamber for pressure limit up to 150 bar will be

  4. Steady-state pool boiling heat transfer on nicr wire surface submerged in Al2O3 nano-fluids

    International Nuclear Information System (INIS)

    Dereje Shiferaw; Hyun Sun Park; Bal Raj Sehgal

    2005-01-01

    Full text of publication follows: nano-fluids, or conventional liquids, e.g., water, with small concentration of nano-particles uniformly suspended, have attracted attention as a new heat transport medium with enhanced thermo-physical properties. Up to the present, only exploratory experiments on nano-fluids have been reported. Das et al (Int. J. Heat Mass Transfer 43, pp 3701-3707, 2003) conducted boiling experiments with water containing 38 nm Al 2 O 3 nano-particles. They observed deterioration in the nucleate boiling heat transfer due to the deposition of nano-particles. Boiling experiments conducted by Vassallo et al (Int. J. Heat Mass Transfer 47, pp 407-411, 2004) using silica nano-fluid using 0.4 mm diameter NiCr wire showed three times higher critical heat flux (CHF) and the wire traversed the film boiling region before it failed. Another independent experiment performed on 1 cm 2 square plate with a very low concentration of nano-particles ranging from 0.01 to 0.05 g/liter and at under pressure (2.89 psia), nano-fluids resulted in drastic 2∼3 times enhancement of the CHF (You and Kim, Appl. Phys. Lett. 83. No 16, 2003). However in all the aforementioned studies no appropriate explanation of the CHF enhancement has been advanced. The measured 2-3 times higher critical heat flux for very dilute nano-fluids may have high significance if such nano-fluids could be employed in heat transport systems. Recently, we investigated the effect of nano-particles on film boiling, which governs heat transfer during accident conditions in a reactor plant, e.g., in coolability of a degraded core, or a particulate debris bed or a core melt, and in steam explosions. Our previous experiments performed on film boiling in nano-fluids having larger concentrations of 5, 10, and 20 g/liter than those in You's experiments showed that the nano-fluids lower the film boiling temperature, decrease the film boiling heat transfer and provide a much thicker and more stable film than

  5. A stability analysis of ventilated boiling channels

    International Nuclear Information System (INIS)

    Taleyarkhan, R.P.; Podowski, M.Z.; Lahey, R.T. Jr.

    1986-01-01

    A mathematical model has been developed for the linear stability analysis of a system of ventilated parallel boiling channels. This model accounts for subcooled boiling, an arbitrary heat flux distribution, distributed and local hydraulic losses, heated wall dynamics, slip flow, turbulent mixing and arbitrary flow paths for transverse ventilation. The digital computer program MAZDA-NF was written for numerical evaluation of the mathematical model. Comparison of MAZDA-NF results with those obtained form both a closed form analytical solution and experiment, showed good agreement. A parametric study revealed that such phenomena as subcooled boiling, the transverse coupling between channels (due to cross-flow and mixing) and power skewing can have a significant impact on predicted stability margins. An analysis of an advanced BWR fuel, of the ASEA-ATOM SVEA design, has indicated that transverse ventilation may considerably improve channel stability. (orig.)

  6. Critical superheats upon boiling of dissociating liquids

    International Nuclear Information System (INIS)

    Kolykhan, L.I.; Solov'ev, V.N.

    1985-01-01

    The experimental data on critical superheats of dissociating liquids, i.e. nitrogen tetroxide and nitrine are presented (nitrine is the solution of nitrogen oxide in nitrogen tetroxide). The experiments with boiling N 2 O 4 have been carried out in the pressure range 0.1-3.0 MPa and with boiling nitrine within the pressure range 0.2-9.0 MPa. The experiments have revealed an anomalous dependence of critical superheats on pressure P, thus at P>=2.5 MPa the critical superheat values exceed the limiting ones, and at P=4.5 MPa this excess amounts to more than 16 K, essentially exceeding the errors of the experiments. The results for N 2 O 4 critical superheats agree with experimental data of other authors. Complex phenomena observed upon boiling of dissociating liquids require further theoretical and experimental studies

  7. Nucleation at high pressure I: Theoretical considerations.

    NARCIS (Netherlands)

    Luijten, C.C.M.; Dongen, van M.E.H.

    1999-01-01

    A theoretical approach is presented that accounts for the influence of high pressure background gases on the vapor-to-liquid nucleation process. The key idea is to treat the carrier gas pressure as a perturbation parameter that modifies the properties of the nucleating substance. Two important

  8. Simple improvements to classical bubble nucleation models.

    Science.gov (United States)

    Tanaka, Kyoko K; Tanaka, Hidekazu; Angélil, Raymond; Diemand, Jürg

    2015-08-01

    We revisit classical nucleation theory (CNT) for the homogeneous bubble nucleation rate and improve the classical formula using a correct prefactor in the nucleation rate. Most of the previous theoretical studies have used the constant prefactor determined by the bubble growth due to the evaporation process from the bubble surface. However, the growth of bubbles is also regulated by the thermal conduction, the viscosity, and the inertia of liquid motion. These effects can decrease the prefactor significantly, especially when the liquid pressure is much smaller than the equilibrium one. The deviation in the nucleation rate between the improved formula and the CNT can be as large as several orders of magnitude. Our improved, accurate prefactor and recent advances in molecular dynamics simulations and laboratory experiments for argon bubble nucleation enable us to precisely constrain the free energy barrier for bubble nucleation. Assuming the correction to the CNT free energy is of the functional form suggested by Tolman, the precise evaluations of the free energy barriers suggest the Tolman length is ≃0.3σ independently of the temperature for argon bubble nucleation, where σ is the unit length of the Lennard-Jones potential. With this Tolman correction and our prefactor one gets accurate bubble nucleation rate predictions in the parameter range probed by current experiments and molecular dynamics simulations.

  9. Nucleation in an ultra low ionisation environment

    DEFF Research Database (Denmark)

    Enghoff, Martin Andreas Bødker

    in aerosol nucleation. By exposing a controlled volume of air to varying levels of ionising radiation, and with the minimum ionisation level vastly reduced compared to normal surface laboratory conditions, we have provided both a validation of earlier studies of ion-induced nucleation and extended...

  10. Tuning Ice Nucleation with Supercharged Polypeptides

    NARCIS (Netherlands)

    Yang, Huige; Ma, Chao; Li, Kaiyong; Liu, Kai; Loznik, Mark; Teeuwen, Rosalie; van Hest, Jan C. M.; Zhou, Xin; Herrmann, Andreas; Wang, Jianjun

    2016-01-01

    Supercharged unfolded polypeptides (SUPs) are exploited for controlling ice nucleation via tuning the nature of charge and charge density of SUPs. The results show that positively charged SUPs facilitate ice nucleation, while negatively charged ones suppress it. Moreover, the charge density of the

  11. An Experimental Study of Pressure Gradients for Flow of Boiling Water in a Vertical Round Duct. (Part 2)

    Energy Technology Data Exchange (ETDEWEB)

    Becker, Kurt M; Hernborg, Gunnar; Bode, Manfred

    1962-03-15

    The present report contains the results of the second phase of an experimental investigation concerning frictional pressure gradients for the flow of boiling water in vertical channels. The test section for this phase consisted of an electric heated stainless steel tube of 3120 mm length and 7.76 mm inner diameter. Data were obtained for pressures between 6 and 41 ata, steam qualities between 0 and 70 per cent, flow rates between 0.025 and 0.210 Kg/sec and surface heat flux between 30 and 91 W/cm. The results are in excellent agreement with our earlier data for flow in a 9.93 mm inner diameter ducts which were presented in report AE-69. From the measurements we conclude that in the range investigated the non dimensional pressure gradient ratio, {phi}{sup 2} is independent of mass flow rate, inlet sub-cooling and surface heat flux. On the basis of the measured pressure gradients, the following empirical equation has been established for engineering use, {phi}{sup 2} = 1 + 2400 (x/p){sup 0.96} This equation correlates our data (more than 1000 points) with a discrepancy of less than {+-} 15 per cent.

  12. Damage instability and Earthquake nucleation

    Science.gov (United States)

    Ionescu, I. R.; Gomez, Q.; Campillo, M.; Jia, X.

    2017-12-01

    Earthquake nucleation (initiation) is usually associated to the loss of the stability of the geological structure under a slip-weakening friction acting on the fault. The key parameters involved in the stability of the fault are the stress drop, the critical slip distance but also the elastic stiffness of the surrounding materials (rocks). We want to explore here how the nucleation phenomena are correlated to the material softening during damage accumulation by dynamic and/or quasi-static processes. Since damage models are describing micro-cracks growth, which is generally an unstable phenomenon, it is natural to expect some loss of stability on the associated micro-mechanics based models. If the model accurately captures the material behavior, then this can be due to the unstable nature of the brittle material itself. We obtained stability criteria at the microscopic scale, which are related to a large class of damage models. We show that for a given continuous strain history the quasi-static or dynamic problems are instable or ill-posed (multiplicity of material responses) and whatever the selection rule is adopted, shocks (time discontinuities) will occur. We show that the quasi-static equilibria chosen by the "perfect delay convention" is always stable. These stability criteria are used to analyze how NIC (Non Interacting Crack) effective elasticity associated to "self similar growth" model work in some special configurations (one family of micro-cracks in mode I, II and III and in plane strain or plain stress). In each case we determine a critical crack density parameter and critical micro-crack radius (length) which distinguish between stable and unstable behaviors. This critical crack density depends only on the chosen configuration and on the Poisson ratio.

  13. Chemically assisted crack nucleation in zircaloy

    International Nuclear Information System (INIS)

    Williford, R.E.

    1985-01-01

    Stress corrosion cracking models (proposed to explain fuel rod failures) generally address crack propagation and cladding rupture, but frequently neglect the necessary nucleation stage for microcracks small enough to violate fracture mechanics continuum requirements. Intergranular microcrack nucleation was modeled with diffusion-controlled grain-boundary cavitation concepts, including the effects of metal embrittlement by iodine species. Computed microcrack nucleation times and strains agree with experimental observation, but the predicted grain-boundary cavities are so small that detection may be difficult. Without a protective oxide film intergranular microcracks can nucleate within 30 s at even low stresses when the embrittler concentration exceeds a threshold value. Indications were found that intergranular microcrack nucleation may be caused by combined corrosive and embrittlement phenomena. (orig.)

  14. CONTINUOUS ANALYZER UTILIZING BOILING POINT DETERMINATION

    Science.gov (United States)

    Pappas, W.S.

    1963-03-19

    A device is designed for continuously determining the boiling point of a mixture of liquids. The device comprises a distillation chamber for boiling a liquid; outlet conduit means for maintaining the liquid contents of said chamber at a constant level; a reflux condenser mounted above said distillation chamber; means for continuously introducing an incoming liquid sample into said reflux condenser and into intimate contact with vapors refluxing within said condenser; and means for measuring the temperature of the liquid flowing through said distillation chamber. (AEC)

  15. Boiling point measurements on liquid UO2

    International Nuclear Information System (INIS)

    Bober, M.; Singer, J.; Trapp, M.

    1986-01-01

    In analogy to the classic boiling point method, a quasi-stationary millisecond laser-heating technique was applied to measure the saturated-vapour pressure curve of liquid UO 2 in the temperature range of 3500 to 4500 K. The result is represented by log p(MPa) 5.049 -23042/T(K) according to an average heat of vaporization of 441 kJ/mol and a normal boiling point of 3808 K. Besides, spectral emissivities of liquid UO 2 were measured at the pyrometer wavelengths of 752 and 1064 nm. (author)

  16. The boiling point of stratospheric aerosols.

    Science.gov (United States)

    Rosen, J. M.

    1971-01-01

    A photoelectric particle counter was used for the measurement of aerosol boiling points. The operational principle involves raising the temperature of the aerosol by vigorously heating a portion of the intake tube. At or above the boiling point, the particles disintegrate rather quickly, and a noticeable effect on the size distribution and concentration is observed. Stratospheric aerosols appear to have the same volatility as a solution of 75% sulfuric acid. Chemical analysis of the aerosols indicates that there are other substances present, but that the sulfate radical is apparently the major constituent.

  17. Boiling Heat Transfer Mechanisms in Earth and Low Gravity: Boundary Condition and Heater Aspect Ratio Effects

    Science.gov (United States)

    Kim, Jungho

    2004-01-01

    Boiling is a complex phenomenon where hydrodynamics, heat transfer, mass transfer, and interfacial phenomena are tightly interwoven. An understanding of boiling and critical heat flux in microgravity environments is of importance to space based hardware and processes such as heat exchange, cryogenic fuel storage and transportation, electronic cooling, and material processing due to the large amounts of heat that can be removed with relatively little increase in temperature. Although research in this area has been performed in the past four decades, the mechanisms by which heat is removed from surfaces in microgravity are still unclear. Recently, time and space resolved heat transfer data were obtained in both earth and low gravity environments using an array of microheaters varying in size between 100 microns to 700 microns. These heaters were operated in both constant temperature as well as constant heat flux mode. Heat transfer under nucleating bubbles in earth gravity were directly measured using a microheater array with 100 m resolution operated in constant temperature mode with low and high subcooled bulk liquid along with images from below and from the side. The individual bubble departure diameter and energy transfer were larger with low subcooling but the departure frequency increased at high subcooling, resulting in higher overall heat transfer. The bubble growth for both subcoolings was primarily due to energy transfer from the superheated liquid layer relatively little was due to wall heat transfer during the bubble growth process. Oscillating bubbles and sliding bubbles were also observed in highly subcooled boiling. Transient conduction and/or microconvection was the dominant heat transfer mechanism in the above cases. A transient conduction model was developed and compared with the experimental data with good agreement. Data was also obtained with the heater array operated in a constant heat flux mode and measuring the temperature distribution across

  18. Automated high-speed video analysis of the bubble dynamics in subcooled flow boiling

    Energy Technology Data Exchange (ETDEWEB)

    Maurus, Reinhold; Ilchenko, Volodymyr; Sattelmayer, Thomas [Technische Univ. Muenchen, Lehrstuhl fuer Thermodynamik, Garching (Germany)

    2004-04-01

    Subcooled flow boiling is a commonly applied technique for achieving efficient heat transfer. In the study, an experimental investigation in the nucleate boiling regime was performed for water circulating in a closed loop at atmospheric pressure. The test-section consists of a rectangular channel with a one side heated copper strip and a very good optical access. For the optical observation of the bubble behaviour the high-speed cinematography is used. Automated image processing and analysis algorithms developed by the authors were applied for a wide range of mass flow rates and heat fluxes in order to extract characteristic length and time scales of the bubbly layer during the boiling process. Using this methodology, a huge number of bubble cycles could be analysed. The structure of the developed algorithms for the detection of the bubble diameter, the bubble lifetime, the lifetime after the detachment process and the waiting time between two bubble cycles is described. Subsequently, the results from using these automated procedures are presented. A remarkable novelty is the presentation of all results as distribution functions. This is of physical importance because the commonly applied spatial and temporal averaging leads to a loss of information and, moreover, to an unjustified deterministic view of the boiling process, which exhibits in reality a very wide spread of bubble sizes and characteristic times. The results show that the mass flux dominates the temporal bubble behaviour. An increase of the liquid mass flux reveals a strong decrease of the bubble life - and waiting time. In contrast, the variation of the heat flux has a much smaller impact. It is shown in addition that the investigation of the bubble history using automated algorithms delivers novel information with respect to the bubble lift-off probability. (Author)

  19. Automated high-speed video analysis of the bubble dynamics in subcooled flow boiling

    International Nuclear Information System (INIS)

    Maurus, Reinhold; Ilchenko, Volodymyr; Sattelmayer, Thomas

    2004-01-01

    Subcooled flow boiling is a commonly applied technique for achieving efficient heat transfer. In the study, an experimental investigation in the nucleate boiling regime was performed for water circulating in a closed loop at atmospheric pressure. The test-section consists of a rectangular channel with a one side heated copper strip and a very good optical access. For the optical observation of the bubble behaviour the high-speed cinematography is used. Automated image processing and analysis algorithms developed by the authors were applied for a wide range of mass flow rates and heat fluxes in order to extract characteristic length and time scales of the bubbly layer during the boiling process. Using this methodology, a huge number of bubble cycles could be analysed. The structure of the developed algorithms for the detection of the bubble diameter, the bubble lifetime, the lifetime after the detachment process and the waiting time between two bubble cycles is described. Subsequently, the results from using these automated procedures are presented. A remarkable novelty is the presentation of all results as distribution functions. This is of physical importance because the commonly applied spatial and temporal averaging leads to a loss of information and, moreover, to an unjustified deterministic view of the boiling process, which exhibits in reality a very wide spread of bubble sizes and characteristic times. The results show that the mass flux dominates the temporal bubble behaviour. An increase of the liquid mass flux reveals a strong decrease of the bubble life- and waiting time. In contrast, the variation of the heat flux has a much smaller impact. It is shown in addition that the investigation of the bubble history using automated algorithms delivers novel information with respect to the bubble lift-off probability

  20. Role of stacking disorder in ice nucleation.

    Science.gov (United States)

    Lupi, Laura; Hudait, Arpa; Peters, Baron; Grünwald, Michael; Gotchy Mullen, Ryan; Nguyen, Andrew H; Molinero, Valeria

    2017-11-08

    The freezing of water affects the processes that determine Earth's climate. Therefore, accurate weather and climate forecasts hinge on good predictions of ice nucleation rates. Such rate predictions are based on extrapolations using classical nucleation theory, which assumes that the structure of nanometre-sized ice crystallites corresponds to that of hexagonal ice, the thermodynamically stable form of bulk ice. However, simulations with various water models find that ice nucleated and grown under atmospheric temperatures is at all sizes stacking-disordered, consisting of random sequences of cubic and hexagonal ice layers. This implies that stacking-disordered ice crystallites either are more stable than hexagonal ice crystallites or form because of non-equilibrium dynamical effects. Both scenarios challenge central tenets of classical nucleation theory. Here we use rare-event sampling and free energy calculations with the mW water model to show that the entropy of mixing cubic and hexagonal layers makes stacking-disordered ice the stable phase for crystallites up to a size of at least 100,000 molecules. We find that stacking-disordered critical crystallites at 230 kelvin are about 14 kilojoules per mole of crystallite more stable than hexagonal crystallites, making their ice nucleation rates more than three orders of magnitude higher than predicted by classical nucleation theory. This effect on nucleation rates is temperature dependent, being the most pronounced at the warmest conditions, and should affect the modelling of cloud formation and ice particle numbers, which are very sensitive to the temperature dependence of ice nucleation rates. We conclude that classical nucleation theory needs to be corrected to include the dependence of the crystallization driving force on the size of the ice crystallite when interpreting and extrapolating ice nucleation rates from experimental laboratory conditions to the temperatures that occur in clouds.

  1. Heat transfer in pool boiling liquid neon, deuterium and hydrogen, and critical heat flux in forced convection of liquid neon

    International Nuclear Information System (INIS)

    Astruc, J.M.

    1967-12-01

    In the first part, free-convection and nucleate pool boiling heat transfer (up to burn-out heat flux) between a platinum wire of 0.15 mm in diameter in neon, deuterium and hydrogen has been studied at atmospheric pressure. These measurements were continued in liquid neon up to 23 bars (Pc ≅ 26.8 b). Film boiling heat transfer coefficients have been measured in pool boiling liquid neon at atmospheric pressure with three heating wires (diameters 0.2, 0.5, 2 mm). All the results have been compared with existing correlations. The second part is devoted to measurements of the critical heat flux limiting heat transfer with small temperature differences between the wall and the liquid neon flowing inside a tube (diameters 3 x 3.5 mm) heated by joule effect on 30 cm of length. Influences of flow stability, nature of electrical current, pressure, mass flow rate and subcooling are shown. In conclusion, the similarity of the heat transfer characteristics in pool boiling as well as in forced convection of liquid neon and hydrogen is emphasized. (author) [fr

  2. Forced convective and subcooled flow boiling heat transfer to pure water and n-heptane in an annular heat exchanger

    International Nuclear Information System (INIS)

    Peyghambarzadeh, S.M.; Sarafraz, M.M.; Vaeli, N.; Ameri, E.; Vatani, A.; Jamialahmadi, M.

    2013-01-01

    Highlights: ► The cooling performance of water and n-heptane is compared during subcooled flow boiling. ► Although n-heptane leaves the heat exchanger warmer it has a lower heat transfer coefficient. ► Flow rate, heat flux and degree of subcooling have direct effect on heat transfer coefficient. ► The predictions of some correlations are evaluated against experimental data. - Abstract: In this research, subcooled flow boiling heat transfer coefficients of pure n-heptane and distilled water at different operating conditions have been experimentally measured and compared. The heat exchanger consisted of vertical annulus which is heated from the inner cylindrical heater with variable heat flux (less than 140 kW/m 2 ). Heat flux is varied so that two different flow regimes from single phase forced convection to nucleate boiling condition are created. Meanwhile, liquid flow rate is changed in the range of 2.5 × 10 −5 –5.8 × 10 −5 m 3 /s to create laminar up to transition flow regimes. Three subcooling levels including 10, 20 and 30 °C are also considered. Experimental results demonstrated that subcooled flow boiling heat transfer coefficient increases when higher heat flux, higher liquid flow rate and greater subcooling level are applied. Furthermore, influence of the operating conditions on the bubbles generation on the heat transfer surface is also discussed. It is also shown that water is better cooling fluid in comparison with n-heptane

  3. Study of mechanism of burnout in a high heat-flux boiling system with an impinging jet

    International Nuclear Information System (INIS)

    Katto, Y.; Monde, M.

    1974-01-01

    Nucleate boiling at very high heat fluxes was created on a heated surface covered with a flowing film of saturated water at atmospheric pressure being maintained by a small circular jet of water held at the center of the heated surface. It was found that increasing the heat flux led to a limiting state of flow where the splashing of droplets from the heated surface was no longer increased being kept constant until burnout appeared; and that there was a close relation between the burnout heat flux and the jet velocity. A flow model, which can explain the characteristics of this boiling system, is proposed. It is suggested that the burnout may be connected with the separation of a liquid flow from the heated surface accompanied with the effusion of vapor. (U.S.)

  4. A dry-spot model for the prediction of critical heat flux in water boiling in bubbly flow regime

    Energy Technology Data Exchange (ETDEWEB)

    Ha, Sang Jun; No, Hee Cheon [Korea Advanced Institute of Science and Technology, Taejon (Korea, Republic of)

    1997-12-31

    This paper presents a prediction of critical heat flux (CHF) in bubbly flow regime using dry-spot model proposed recently by authors for pool and flow boiling CHF and existing correlations for forced convective heat transfer coefficient, active site density and bubble departure diameter in nucleate boiling region. Without any empirical constants always present in earlier models, comparisons of the model predictions with experimental data for upward flow of water in vertical, uniformly-heated round tubes are performed and show a good agreement. The parametric trends of CHF have been explored with respect to variations in pressure, tube diameter and length, mass flux and inlet subcooling. 16 refs., 6 figs., 1 tab. (Author)

  5. A dry-spot model for the prediction of critical heat flux in water boiling in bubbly flow regime

    Energy Technology Data Exchange (ETDEWEB)

    Ha, Sang Jun; No, Hee Cheon [Korea Advanced Institute of Science and Technology, Taejon (Korea, Republic of)

    1998-12-31

    This paper presents a prediction of critical heat flux (CHF) in bubbly flow regime using dry-spot model proposed recently by authors for pool and flow boiling CHF and existing correlations for forced convective heat transfer coefficient, active site density and bubble departure diameter in nucleate boiling region. Without any empirical constants always present in earlier models, comparisons of the model predictions with experimental data for upward flow of water in vertical, uniformly-heated round tubes are performed and show a good agreement. The parametric trends of CHF have been explored with respect to variations in pressure, tube diameter and length, mass flux and inlet subcooling. 16 refs., 6 figs., 1 tab. (Author)

  6. SAS3A analysis of natural convection boiling behavior in the Sodium Boiling Test Facility

    International Nuclear Information System (INIS)

    Klein, G.A.

    1979-01-01

    An analysis of natural convection boiling behavior in the Sodium Boiling Test (SBT) Facility has been performed using the SAS3A computer code. The predictions from this analysis indicate that stable boiling can be achieved for extensive periods of time for channel powers less than 1.4 kW and indicate intermittent dryout at higher powers up to at least 1.7 kW. The results of this anaysis are in reasonable agreement with the SBT Facility test results

  7. Heterogeneous nucleation of calcium oxalate on native oxide surfaces

    International Nuclear Information System (INIS)

    Song, L.; Pattillo, M.J.; Graff, G.L.; Campbell, A.A.; Bunker, B.C.

    1994-04-01

    The aqueous deposition of calcium oxalate onto colloidal oxides has been studied as a model system for understanding heterogeneous nucleation processes of importance in biomimetic synthesis of ceramic thin films. Calcium oxalate nucleation has been monitored by measuring induction times for nucleation using Constant Composition techniques and by measuring nucleation densities on extended oxide surfaces using an atomic force microscope. Results show that the dependence of calcium oxalate nucleation on solution supersaturation fits the functional form predicted by classical nucleation theories. Anionic surfaces appear to promote nucleation better than cationic surfaces, lowering the effective energy barrier to heterogeneous nucleation

  8. Tube temperature rise limits: Boiling considerations

    Energy Technology Data Exchange (ETDEWEB)

    Vanderwater, R.G.

    1952-03-26

    A revision of tube power limits based on boiling considerations was presented earlier. The limits were given on a basis of tube power versus header pressure. However, for convenience of operation, the limits have been converted from tube power to permissible water temperature rise. The permissible {triangle}t`s water are given in this document.

  9. Boiling Heat Transfer in Battery Electric vehicles

    NARCIS (Netherlands)

    Gils, van R.W.; Speetjens, M.F.M.; Nijmeijer, H.

    2011-01-01

    In this paper the feedback stabilisation of a boiling-based cooling scheme is discussed. Application of such cooling schemes in practical setups is greatly limited by the formation of a thermally insulating vapour film on the to-be-cooled device, called burn-out. In this study a first step is made,

  10. The CEA program on boiling noise detection

    International Nuclear Information System (INIS)

    Le Guillou, G.; Brunet, M.; Girard, J.P.; Flory, D.

    1982-01-01

    The research program on the application of noise analysis on boiling detection in a fast subassembly began 10 years ago at the CEA, mainly in the Nuclear Center of Cadarache. Referring exclusively to the aspects of premature detection of the boiling phenomenon it can be said that this program is organized around the following three detection techniques: acoustic noise analysis; neutron noise analysis; temperature noise analysis. Its development is in conjunction with in-pile experiments in Phenix or Rapsodie as well as 'ex-pile' (boiling experiments through electric heating). Three detection techniques were developed independent of each other, but that they were regrouped during the execution of the most important experiments and with the 'Super Phenix' project. The noise analysis system ANABEL with which Superphenix will be equipped with shows the industrial interest in detection methods based on noises. One of the results of the CEA program today is the possibility to evaluate the potential capacity for boiling detection in the subassembly. But in order to obtain the necessary funds from the commercial nuclear plant operators it is mandatory to have successful demonstrations which will be the objective of the future program

  11. Impact of surface nanostructure on ice nucleation.

    Science.gov (United States)

    Zhang, Xiang-Xiong; Chen, Min; Fu, Ming

    2014-09-28

    Nucleation of water on solid surface can be promoted noticeably when the lattice parameter of a surface matches well with the ice structure. However, the characteristic length of the surface lattice reported is generally less than 0.5 nm and is hardly tunable. In this paper, we show that a surface with nanoscale roughness can also remarkably promote ice nucleation if the characteristic length of the surface structure matches well with the ice crystal. A series of surfaces composed of periodic grooves with same depth but different widths are constructed in molecular dynamics simulations. Water cylinders are placed on the constructed surfaces and frozen at constant undercooling. The nucleation rates of the water cylinders are calculated in the simulation using the mean first-passage time method and then used to measure the nucleation promotion ability of the surfaces. Results suggest that the nucleation behavior of the supercooled water is significantly sensitive to the width of the groove. When the width of the groove matches well with the specific lengths of the ice crystal structure, the nucleation can be promoted remarkably. If the width does not match with the ice crystal, this kind of promotion disappears and the nucleation rate is even smaller than that on the smooth surface. Simulations also indicate that even when water molecules are adsorbed onto the surface structure in high-humidity environment, the solid surface can provide promising anti-icing ability as long as the characteristic length of the surface structure is carefully designed to avoid geometric match.

  12. Nucleation behavior of glutathione polymorphs in water

    International Nuclear Information System (INIS)

    Chen, Zhi; Dang, Leping; Li, Shuai; Wei, Hongyuan

    2013-01-01

    Nucleation behavior of glutathione (GSH) polymorphs in water was investigated by experimental method combined with classical nucleation theory. The solubility of α and β forms GSH in water at different temperatures, and the nucleation induction period at various supersaturations and temperatures were determined experimentally. The results show that, in a certain range of supersaturation, the nucleation of β form predominates at relatively higher temperature, while α form will be obtained at lower temperature. The nucleation kinetics parameters of α and β form were then calculated. To understand the crucial role of temperature on crystal forms, “hypothetic” nucleation parameters of β form at 283.15 K were deduced based on extrapolation method. The results show that the interfacial tension, critical free energy, critical nucleus radius and nucleus number of α form are smaller than that of β form in the same condition at 283.15 K, which implies that α form nucleates easier than β form at low temperature. This work may be useful for the control and optimization of GSH crystallization process in industry

  13. Nucleation of voids - the impurity effect

    International Nuclear Information System (INIS)

    Chen, I-W; Taiwo, A.

    1984-01-01

    Nucleation of voids under irradiation in multicomponent alloys remains an unsolved theoretical problem. Of particular interest are the effects of nonequilibrium solute segregation phenomena on the critical nucleus and the nucleation rate. The resolution of the multicomponent nucleation in a dissipative system also has broader implication to the field of irreversible thermodynamics. The present paper describes a recent study of solute segregation effects in void nucleation. We begin with a thermodynamic model for a nonequilibrium void with interfacial segregation. The thermodynamic model is coupled with kinetic considerations of solute/solvent diffusion under a bias, which is itself related to segregation by the coating effect, to assess the stability of void embryos. To determine nucleation rate, we develop a novel technique by extending the most probable path method in statistical mechanics for nonequilibrium steady state to simulate large fluctuation with nonlinear dissipation. The path of nucleation is determined by solving an analogous problem on particle trajectory in classical dynamics. The results of both the stability analysis and the fluctuation analysis establish the paramount significance of the impurity effect via the mechanism of nonequilibrium segregation. We conclude that over-segregation is probably the most general cause for the apparently low nucleation barriers that are responsible for nearly ubiquitous occurrence of void swelling in common metals

  14. Nonclassical nucleation pathways in protein crystallization.

    Science.gov (United States)

    Zhang, Fajun

    2017-11-08

    Classical nucleation theory (CNT), which was established about 90 years ago, has been very successful in many research fields, and continues to be the most commonly used theory in describing the nucleation process. For a fluid-to-solid phase transition, CNT states that the solute molecules in a supersaturated solution reversibly form small clusters. Once the cluster size reaches a critical value, it becomes thermodynamically stable and favored for further growth. One of the most important assumptions of CNT is that the nucleation process is described by one reaction coordinate and all order parameters proceed simultaneously. Recent studies in experiments, computer simulations and theory have revealed nonclassical features in the early stage of nucleation. In particular, the decoupling of order parameters involved during a fluid-to-solid transition leads to the so-called two-step nucleation mechanism, in which a metastable intermediate phase (MIP) exists between the initial supersaturated solution and the final crystals. Depending on the exact free energy landscapes, the MIPs can be a high density liquid phase, mesoscopic clusters, or a pre-ordered state. In this review, we focus on the studies of nonclassical pathways in protein crystallization and discuss the applications of the various scenarios of two-step nucleation theory. In particular, we focus on protein solutions in the presence of multivalent salts, which serve as a model protein system to study the nucleation pathways. We wish to point out the unique features of proteins as model systems for further studies.

  15. Nonclassical nucleation pathways in protein crystallization

    Science.gov (United States)

    Zhang, Fajun

    2017-11-01

    Classical nucleation theory (CNT), which was established about 90 years ago, has been very successful in many research fields, and continues to be the most commonly used theory in describing the nucleation process. For a fluid-to-solid phase transition, CNT states that the solute molecules in a supersaturated solution reversibly form small clusters. Once the cluster size reaches a critical value, it becomes thermodynamically stable and favored for further growth. One of the most important assumptions of CNT is that the nucleation process is described by one reaction coordinate and all order parameters proceed simultaneously. Recent studies in experiments, computer simulations and theory have revealed nonclassical features in the early stage of nucleation. In particular, the decoupling of order parameters involved during a fluid-to-solid transition leads to the so-called two-step nucleation mechanism, in which a metastable intermediate phase (MIP) exists between the initial supersaturated solution and the final crystals. Depending on the exact free energy landscapes, the MIPs can be a high density liquid phase, mesoscopic clusters, or a pre-ordered state. In this review, we focus on the studies of nonclassical pathways in protein crystallization and discuss the applications of the various scenarios of two-step nucleation theory. In particular, we focus on protein solutions in the presence of multivalent salts, which serve as a model protein system to study the nucleation pathways. We wish to point out the unique features of proteins as model systems for further studies.

  16. An experimental investigation of untriggered film boiling collapse

    International Nuclear Information System (INIS)

    Naylor, P.

    1985-03-01

    Film boiling has been investigated in a stagnant pool, using polished brass or anodised aluminium alloy rods in water. Experimental boiling curves were obtained, and pronounced ripples on the vapour/liquid interface were photographed. A criterion for untriggered film boiling collapse is proposed, consistent with experimental results. Application of the results to molten fuel coolant interaction studies is discussed. (U.K.)

  17. Estimation of boiling point of radon by radiogas chromatography

    International Nuclear Information System (INIS)

    Takahashi, N.; Otozai, K.

    1986-01-01

    The retention volume of radon was measured by means of radiogas chromatography. The boiling point of radon was estimated from the retention volume by the use of the semi-empirical formula relating the boiling point to the retention volume. The obtained boiling point (198+-2)K was lower by 13 K than that measured by Gray and Ramsay. (author)

  18. Subcooled boiling heat transfer in a short vertical SUS304-tube at liquid Reynolds number range 5.19 x 104 to 7.43 x 105

    International Nuclear Information System (INIS)

    Hata, Koichi; Masuzaki, Suguru

    2009-01-01

    The subcooled boiling heat transfer and the steady-state critical heat fluxes (CHFs) in a short vertical SUS304-tube for the flow velocities (u = 17.28-40.20 m/s), the inlet liquid temperatures (T in = 293.30-362.49 K), the inlet pressures (P in = 842.90-1467.93 kPa) and the exponentially increasing heat input (Q = Q 0 exp(t/τ), τ = 8.5 s) are systematically measured by the experimental water loop comprised of a multistage canned-type circulation pump with high pump head. The SUS304 test tubes of inner diameters (d = 3 and 6 mm), heated lengths (L = 33 and 59.5 mm), effective lengths (L eff = 23.3 and 49.1 mm), L/d (=11 and 9.92), L eff /d (=7.77 and 8.18), and wall thickness (δ = 0.5 mm) with average surface roughness (Ra = 3.18 μm) are used in this work. The inner surface temperature and the heat flux from non-boiling to CHF are clarified. The subcooled boiling heat transfer for SUS304 test tube is compared with our Platinum test tube data and the values calculated by other workers' correlations for the subcooled boiling heat transfer. The influence of flow velocity on the subcooled boiling heat transfer and the CHF is investigated into details and the widely and precisely predictable correlation of the subcooled boiling heat transfer for turbulent flow of water in a short vertical SUS304-tube is given based on the experimental data. The correlation can describe the subcooled boiling heat transfer obtained in this work within 15% difference. Nucleate boiling surface superheats for the SUS304 test tube become very high. Those at the high flow velocity are close to the lower limit of Heterogeneous Spontaneous Nucleation Temperature. The dominant mechanisms of the flow boiling CHF in a short vertical SUS304-tube are discussed.

  19. A photographic study on flow boiling of R-134a in a vertical channel

    International Nuclear Information System (INIS)

    Bang, In Cheol; Baek, Won Pil; Chang, Soon Heung

    2002-01-01

    The behavior of near-wall bubbles in subcooled flow boiling has been investigated photographically for R134a flow in vertical, one-side heated and rectangular channels at mass fluxes of 0, 190, 1000 and 2000 kg/m 2 s and inlet subcooling condition of 8 .deg. C under 7 bar(Tsat 27 .deg. C). Digital photographic techniques and high-speed camera are used for the visualization, which have significantly advanced for recent decades. Primary attention is given to the bubble coalescence phenomena and the structure of the near-wall bubble layer. At subcooled and low-quality conditions, discrete attached bubbles, sliding bubbles, small coalesced bubbles and large coalesced bubbles or vapor clots are observed on the heated surface as the heat flux is increased from a low value. Particularly in beginning of vapor formation, vapor remnants below discrete bubble on the heating surface are clearly observed. Nucleation site density increases with the increases in heat flux and channel-averaged enthalpy, while discrete bubbles coalesce and form large bubbles, resulting in large vapor clots. Waves formed on the surface of the vapor clots are closely related to Helmholtz instability. At CHF occurrence it is also observed that wall bubble layer beneath large vapor clots is removed and large film boiling occurs. Through the present visual test, it is observed that wall bubble layer begins to develop with the onset of nucleate boiling(ONB) and to extinguish with the occurrence of the CHF. It could be considered that this layer made an important role of CHF mechanism macroscopically. However, there may be another structure beneath wall bubbles which supplies specific information on CHF from viewpoint of microstructure based upon the observation of the liquid sublayer beneath coalesced bubbles. Through this microscopic visualization, it may be suggested that the following flow structures characterize the flow boiling phenomena : (a) vapor remnants as a continuous source of bubbles, (b

  20. Damage nucleation in Si during ion irradiation

    International Nuclear Information System (INIS)

    Holland, O.W.; Fathy, D.; Narayan, J.

    1984-01-01

    Damage nucleation in single crystals of silicon during ion irradiation is investigated. Experimental results and mechanisms for damage nucleation during both room and liquid nitrogen temperature irradiation with different mass ions are discussed. It is shown that the accumulation of damage during room temperature irradiation depends on the rate of implantation. These dose rate effects are found to decrease in magnitude as the mass of the ions is increased. The significance of dose rate effects and their mass dependence on nucleation mechanisms is discussed

  1. Controlled nucleation and crystallization of fluorozirconate glasses

    International Nuclear Information System (INIS)

    Frischat, G.H.

    1993-01-01

    Pt, Se, and Ag, respectively, were used as nucleating agents for a ZrF 4 -BaF 4 -YF 3 -AlF 3 glass. Nucleation and crystal growth rates were determined as a function of experimental conditions. In all cases the bulk crystals mainly consist of β-BaZrF6, leading to a relatively coarse-grained microstructure. However, in the case of Ag used as a nucleating agent, the microstructure is bimodal with an additional fine-grained crystal phase. In the cases of Se and Ag the relative crystal fraction could be developed in a controlled way between 0 and 100%

  2. Viscosity of interfacial water regulates ice nucleation

    International Nuclear Information System (INIS)

    Li, Kaiyong; Chen, Jing; Zhang, Qiaolan; Zhang, Yifan; Xu, Shun; Zhou, Xin; Cui, Dapeng; Wang, Jianjun; Song, Yanlin

    2014-01-01

    Ice formation on solid surfaces is an important phenomenon in many fields, such as cloud formation and atmospheric icing, and a key factor for applications in preventing freezing. Here, we report temperature-dependent nucleation rates of ice for hydrophilic and hydrophobic surfaces. The results show that hydrophilic surface presents a lower ice nucleation rate. We develop a strategy to extract the thermodynamic parameters, J 0 and Γ, in the context of classical nucleation theory. From the extracted J 0 and Γ, we reveal the dominant role played by interfacial water. The results provide an insight into freezing mechanism on solid surfaces

  3. Nanowires and nanoneedles nucleation on vicinal substrate

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Xu, E-mail: zhangxubetter@gmail.com [Henan Key Laboratory of Laser and Opto-electric Information Technology, School of Information Engineering, Zhengzhou University, Zhengzhou 450052 (China); Xie, Dan; Huang, Genling [Zhengzhou Railway Vocational and Technical College, Zhengzhou 450052 (China); Sun, Xiao-Hong [Henan Key Laboratory of Laser and Opto-electric Information Technology, School of Information Engineering, Zhengzhou University, Zhengzhou 450052 (China)

    2015-01-01

    An analytic stress-driven nucleation model of nanowires (NWs) and nanoneedles (NNs) growing on a mismatched vicinal substrate is proposed. It is demonstrated that the formation enthalpy of NWs and NNs is a function of three independent variables, the base radius, aspect ratio and miscut angle of the vicinal surface. Theoretical analysis shows that the minimum nucleation barrier of an island decreases with increment of substrate misorientation, which means the nucleation of islands on a vicinal substrate is more favorable than that on a flat substrate.

  4. Flow boiling in microgap channels experiment, visualization and analysis

    CERN Document Server

    Alam, Tamanna; Jin, Li-Wen

    2013-01-01

    Flow Boiling in Microgap Channels: Experiment, Visualization and Analysis presents an up-to-date summary of the details of the confined to unconfined flow boiling transition criteria, flow boiling heat transfer and pressure drop characteristics, instability characteristics, two phase flow pattern and flow regime map and the parametric study of microgap dimension. Advantages of flow boiling in microgaps over microchannels are also highlighted. The objective of this Brief is to obtain a better fundamental understanding of the flow boiling processes, compare the performance between microgap and c

  5. Energetics of dislocation nucleation under a nanoindenter

    International Nuclear Information System (INIS)

    Zhang Chuanli; Xu Guanshui

    2005-01-01

    We present an analysis of dislocation nucleation under an idealized nanoindenter based on the variational boundary integral formulation of the Peierls-Nabarro dislocation model. By solving the embryonic dislocation profiles, corresponding to the relative displacements between the two adjacent atomic layers along the slip plane, we have determined the critical conditions for athermal dislocation nucleation as well as the activation energies required to thermally activate embryonic dislocations from their stable to unstable saddle point configurations. The effect of the size of the indenter on the energetics of dislocation nucleation is quantitatively characterized. The result is compared with a simplified analysis based on the application of the Rice model for dislocation nucleation at a crack tip

  6. Energetics of dislocation nucleation under a nanoindenter

    Energy Technology Data Exchange (ETDEWEB)

    Zhang Chuanli [College of Mechanical Engineering, Yangtze University, Jingzhou, Hubei 434023 (China); Department of Mechanical Engineering, University of California, Riverside, CA 92521 (United States); Xu Guanshui [Department of Mechanical Engineering, University of California, Riverside, CA 92521 (United States)]. E-mail: guanshui.xu@ucr.edu

    2005-07-25

    We present an analysis of dislocation nucleation under an idealized nanoindenter based on the variational boundary integral formulation of the Peierls-Nabarro dislocation model. By solving the embryonic dislocation profiles, corresponding to the relative displacements between the two adjacent atomic layers along the slip plane, we have determined the critical conditions for athermal dislocation nucleation as well as the activation energies required to thermally activate embryonic dislocations from their stable to unstable saddle point configurations. The effect of the size of the indenter on the energetics of dislocation nucleation is quantitatively characterized. The result is compared with a simplified analysis based on the application of the Rice model for dislocation nucleation at a crack tip.

  7. Stochastic simulation of nucleation in binary alloys

    Science.gov (United States)

    L’vov, P. E.; Svetukhin, V. V.

    2018-06-01

    In this study, we simulate nucleation in binary alloys with respect to thermal fluctuations of the alloy composition. The simulation is based on the Cahn–Hilliard–Cook equation. We have considered the influence of some fluctuation parameters (wave vector cutoff and noise amplitude) on the kinetics of nucleation and growth of minority phase precipitates. The obtained results are validated by the example of iron–chromium alloys.

  8. Grain nucleation and growth during phase transformations

    DEFF Research Database (Denmark)

    Offerman, S.E.; Dijk, N.H. van; Sietsma, J.

    2002-01-01

    of individual grains. Our measurements show that the activation energy for grain nucleation is at least two orders of magnitude smaller than that predicted by thermodynamic models. The observed growth curves of the newly formed grains confirm the parabolic growth model but also show three fundamentally...... different types of growth. Insight into the grain nucleation and growth mechanisms during phase transformations contributes to the development of materials with optimal mechanical properties....

  9. Nucleation versus instability race in strained films

    Science.gov (United States)

    Liu, Kailang; Berbezier, Isabelle; David, Thomas; Favre, Luc; Ronda, Antoine; Abbarchi, Marco; Voorhees, Peter; Aqua, Jean-Noël

    2017-10-01

    Under the generic term "Stranski-Krastanov" are grouped two different growth mechanisms of SiGe quantum dots. They result from the self-organized Asaro-Tiller-Grinfel'd (ATG) instability at low strain, while at high strain, from a stochastic nucleation. While these regimes are well known, we elucidate here the origin of the transition between these two pathways thanks to a joint theoretical and experimental work. Nucleation is described within the master equation framework. By comparing the time scales for ATG instability development and three-dimensional (3D) nucleation onset, we demonstrate that the transition between these two regimes is simply explained by the crossover between their divergent evolutions. Nucleation exhibits a strong exponential deviation at low strain while ATG behaves only algebraically. The associated time scale varies with exp(1 /x4) for nucleation, while it only behaves as 1 /x8 for the ATG instability. Consequently, at high (low) strain, nucleation (instability) occurs faster and inhibits the alternate evolution. It is then this different kinetic evolution which explains the transition from one regime to the other. Such a kinetic view of the transition between these two 3D growth regimes was not provided before. The crossover between nucleation and ATG instability is found to occur both experimentally and theoretically at a Ge composition around 50% in the experimental conditions used here. Varying the experimental conditions and/or the system parameters does not allow us to suppress the transition. This means that the SiGe quantum dots always grow via ATG instability at low strain and nucleation at high strain. This result is important for the self-organization of quantum dots.

  10. New mechanism for bubble nucleation: Classical transitions

    International Nuclear Information System (INIS)

    Easther, Richard; Giblin, John T. Jr; Hui Lam; Lim, Eugene A.

    2009-01-01

    Given a scalar field with metastable minima, bubbles nucleate quantum mechanically. When bubbles collide, energy stored in the bubble walls is converted into kinetic energy of the field. This kinetic energy can facilitate the classical nucleation of new bubbles in minima that lie below those of the 'parent' bubbles. This process is efficient and classical, and changes the dynamics and statistics of bubble formation in models with multiple vacua, relative to that derived from quantum tunneling.

  11. Boiling point of volatile liquids at various pressures

    Directory of Open Access Journals (Sweden)

    Luisa Maria Valencia

    2017-07-01

    Full Text Available Water, under normal conditions, tends to boil at a “normal boiling temperature” at which the atmospheric pressure fixes the average amount of kinetic energy needed to reach its boiling point. Yet, the normal boiling temperature of different substances varies depending on their nature, for which substances like alcohols, known as volatile, boil faster than water under same conditions. In response to this phenomenon, an investigation on the coexistence of both gas and liquid phases of a volatile substance in a closed system was made, establishing vapor pressure as the determining tendency of a substance to vaporize, which increases exponentially with temperature until a critical point is reached. Since atmospheric pressure is fixed, the internal pressure of the system was varied to determine its relationship with vapor pressure and thus with the boiling point of the substance, concluding that the internal pressure and boiling point of a volatile liquid in a closed system are negatively proportional.

  12. The mechanism of heat transfer in transition boiling

    International Nuclear Information System (INIS)

    Chin Pan; Hwang, J.Y.; Lin, T.L.

    1989-01-01

    Liquid-solid contact in transition boiling is modelled by involving transient conduction, boiling incipience, macrolayer evaporation and vapour film boiling. The prediction of liquid contact duration and time fraction agrees reasonably well with experimental data, and the model is able to predict both of the boiling curve transitions - the critical and minimum heat fluxes. The study concludes that the liquid turbulence due to buoyancy forces and bubble agitation is an important parameter for transition boiling. It is found that surface coating (oxidation or deposition) tends to improve the transition boiling heat transfer and elevate the wall superheats at both the critical heat flux and the minimum film boiling points, which agrees with the experimental observations. (author)

  13. A classical view on nonclassical nucleation.

    Science.gov (United States)

    Smeets, Paul J M; Finney, Aaron R; Habraken, Wouter J E M; Nudelman, Fabio; Friedrich, Heiner; Laven, Jozua; De Yoreo, James J; Rodger, P Mark; Sommerdijk, Nico A J M

    2017-09-19

    Understanding and controlling nucleation is important for many crystallization applications. Calcium carbonate (CaCO 3 ) is often used as a model system to investigate nucleation mechanisms. Despite its great importance in geology, biology, and many industrial applications, CaCO 3 nucleation is still a topic of intense discussion, with new pathways for its growth from ions in solution proposed in recent years. These new pathways include the so-called nonclassical nucleation mechanism via the assembly of thermodynamically stable prenucleation clusters, as well as the formation of a dense liquid precursor phase via liquid-liquid phase separation. Here, we present results from a combined experimental and computational investigation on the precipitation of CaCO 3 in dilute aqueous solutions. We propose that a dense liquid phase (containing 4-7 H 2 O per CaCO 3 unit) forms in supersaturated solutions through the association of ions and ion pairs without significant participation of larger ion clusters. This liquid acts as the precursor for the formation of solid CaCO 3 in the form of vaterite, which grows via a net transfer of ions from solution according to z Ca 2+ + z CO 3 2- → z CaCO 3 The results show that all steps in this process can be explained according to classical concepts of crystal nucleation and growth, and that long-standing physical concepts of nucleation can describe multistep, multiphase growth mechanisms.

  14. Axial propagation of free surface boiling into superheated liquids in vertical tubes

    International Nuclear Information System (INIS)

    Grolmes, M.A.; Fauske, H.K.

    1974-01-01

    A unique free surface boiling phenomenon has been observed as a result of rapid depressurization of an initially saturated or slightly subcooled stagnant liquid column in the absence of wall and bulk nucleation sites. Closeup high-speed photographs of water, refrigerant-11, and methyl alcohol in tubes from 0.2 to 15 in. dia reveal that the initiation of violent free surface flashing (vapor plus entrained liquid) follows from the development of Marangoni-type surface waves. The rate of propagation of the flashing surface shows evidence of choked flow limitations and proceeds at a rate which is several orders of magnitude greater than surface evaporation (vapor only) alone. The onset of free surface flashing was found to be dependent upon both the degree of initial liquid superheat and the tube diameter. (U.S.)

  15. Critical heat flux enhancement regarding to the thickness of graphene films under pool boiling

    International Nuclear Information System (INIS)

    Kim, Jin Man; Park, Hyun Sun; Park, Youngjae; Kim, Hyungdae; Kim, Dong Eok; Kim, Moo Hwan; Ahn, Ho Seon

    2014-01-01

    The large thermal conductivity of the graphene films inhibits the formation of hot spots, thereby increasing the CHF. An infrared high-speed visualization showed graphene effect on boiling characteristics during operation. The graphene-coated heater showed an increase in BHT and CHF. As the thickness of the graphene films increased, the CHF also increased up to an asymptotic limit when the graphene layer was approximately 150 nm thick. The increased BHT was explained by the slight decrease in the wettability and the folded edges of the RGO flakes, which led to a decrease in the diameter of the departing bubbles, a larger bubble generation frequency, and an increase in the areal density of the bubble nucleation sites. The increase in the CHF was explained by considering the thermal activity of the graphene films, and the dependence thereof on the thickness and thermal properties of the layer, which was calculated based on high-speed IR visualization data

  16. Fuel-coolant interaction in a shock tube with initially-established film boiling

    International Nuclear Information System (INIS)

    Sharon, A.; Bankoff, S.G.

    1979-01-01

    A new mode of thermal interaction has been employed, in which liquid metal is melted in a crucible within a shock tube; the coolant level is raised to overflow the crucible and establish subcooled film boiling with known bulk metal temperature; and a pressure shock is then initiated. With water and lead-tin alloy an initial splash of metal may be obtained after the vapor film has collapsed, due primarily to thermal interaction, followed by a successive cycle of bubble growth and collapse. To obtain large interactions, the interfacial contact temperature must exceed the spontaneous nucleation temperature of the coolant. Other cutoff behavior is observed with respect to the initial system pressure and temperatures and with the shock pressure and rise time. Experiments with butanol and lead-tin alloy show only relatively mild interactions. Qualitative explanations are proposed for the different behaviors of the two liquids

  17. A phenomenological model of the thermal hydraulics of convective boiling during the quenching of hot rod bundles

    International Nuclear Information System (INIS)

    Nelson, R.A.; Unal, C.

    1991-01-01

    In this paper, a phenomenological model of the thermal hydraulics of convective boiling in the post-critical-heat-flux (post-CHF) regime is developed and discussed. The model was implemented in the TRAC-PF1/MOD2 computer code (an advanced best-estimate computer program written for the analysis of pressurized water reactor systems). The model was built around the determination of flow regimes downstream of the quench front. The regimes were determined from the flow-regime map suggested by Ishii and his coworkers. Heat transfer in the transition boiling region was formulated as a position-dependent model. The propagation of the CHF point was strongly dependent on the length of the transition boiling region. Wall-to-fluid film boiling heat transfer was considered to consist of two components: first, a wall-to-vapor convective heat-transfer portion and, second, a wall-to-liquid heat transfer representing near-wall effects. Each contribution was considered separately in each of the inverted annular flow (IAF) regimes. The interfacial heat transfer was also formulated as flow-regime dependent. The interfacial drag coefficient model upstream of the CHF point was considered to be similar to flow through a roughened pipe. A free-stream contribution was calculated using Ishii's bubbly flow model for either fully developed subcooled or saturated nucleate boiling. For the drag in the smooth IAF region, a simple smooth-tube correlation for the interfacial friction factor was used. The drag coefficient for the rough-wavy IAF was formulated in the same way as for the smooth IAF model except that the roughness parameter was assumed to be proportional to liquid droplet diameter entrained from the wavy interface. The drag coefficient in the highly dispersed flow regime considered the combined effects of the liquid droplets within the channel and a liquid film on wet unheated walls. 431 refs., 6 figs., 4 tabs

  18. Microchannel boiling mechanisms leading to burnout

    International Nuclear Information System (INIS)

    Landram, C.S.; Riddle, R.A.

    1994-01-01

    The authors are analyzing the thermal performance of microchannel heat sinks to extend their applied heat loads beyond coolant single-phase limits. This is the first investigation of boiling in the narrow (50-μm) microchannels having typically high-aspect-ratio (of order 10/1) flow cross-sections. The prescription of local, wall-coolant, interfacial, two-phase correlations first required development of a validated, approximate, thermal-model accounting for conjugate heat transfer. The strongest mechanism for heat transfer in two-phase microchannel flow was found to be saturated boiling in a channel region near the heated base. When this region dried out, burnout occurred, both in the computations and in the experiment

  19. Compatibility of refractory materials with boiling sodium

    International Nuclear Information System (INIS)

    Meacham, S.A.

    1976-01-01

    The program employed to determine the compatibility of commercially available refractories with boiling sodium is described. The effects of impurities contained within the refractory material, and their relations with the refractory's physical stability are discussed. Also, since consideration of refractories for use as an insulating material within Liquid Metal Fast Breeder Reactor Plants (LMFBR's) is currently under investigation; recommendations, based upon this program, are presented

  20. The fluid similarity of the boiling crisis

    International Nuclear Information System (INIS)

    Katsaounis, A.

    1986-01-01

    Most of the measurements related to the boiling crisis have, until now, been undertaken for a wide parameter variation in the water, and were mainly related to the water-cooled reactor. This article investigates, whether or how the measuring results can be transferred to other fluids. Derived dimensionless similarity figures and those taken from literature are verified by measurements from complex geometries in water and freon 12. (orig.) [de

  1. The fluid similarity of the boiling crisis

    International Nuclear Information System (INIS)

    Katsaounis, A.

    1987-01-01

    Most of the measurements related to the boiling crisis have, until now, been undertaken for a wide parameter variation in the water, and were mainly related to the water-cooled reactor. This article investigates, whether or how the measuring results can be transferred to other fluids. Derived dimensionless similarity figures and those taken from literature are verified by measurements from complex geometries in water and freon 12. (orig./GL) [de

  2. Transient pool boiling heat transfer due to increasing heat inputs in subcooled water at high pressures

    Energy Technology Data Exchange (ETDEWEB)

    Fukuda, K. [Kobe Univ. of Mercantile Marine (Japan); Shiotsu, M.; Sakurai, A. [Kyoto Univ. (Japan)

    1995-09-01

    Understanding of transient boiling phenomenon caused by increasing heat inputs in subcooled water at high pressures is necessary to predict correctly a severe accident due to a power burst in a water-cooled nuclear reactor. Transient maximum heat fluxes, q{sub max}, on a 1.2 mm diameter horizontal cylinder in a pool of saturated and subcooled water for exponential heat inputs, q{sub o}e{sup t/T}, with periods, {tau}, ranging from about 2 ms to 20 s at pressures from atmospheric up to 2063 kPa for water subcoolings from 0 to about 80 K were measured to obtain the extended data base to investigate the effect of high subcoolings on steady-state and transient maximum heat fluxes, q{sub max}. Two main mechanisms of q{sub max} exist depending on the exponential periods at low subcoolings. One is due to the time lag of the hydrodynamic instability which starts at steady-state maximum heat flux on fully developed nucleate boiling (FDNB), and the other is due to the heterogenous spontaneous nucleations (HSN) in flooded cavities which coexist with vapor bubbles growing up from active cavities. The shortest period corresponding to the maximum q{sub max} for long period range belonging to the former mechanism becomes longer and the q{sub max}mechanism for long period range shifts to that due the HSN on FDNB with the increase of subcooling and pressure. The longest period corresponding to the minimum q{sub max} for the short period range belonging to the latter mechanism becomes shorter with the increase in saturated pressure. On the contrary, the longest period becomes longer with the increase in subcooling at high pressures. Correlations for steady-state and transient maximum heat fluxes were presented for a wide range of pressure and subcooling.

  3. Transient pool boiling heat transfer due to increasing heat inputs in subcooled water at high pressures

    International Nuclear Information System (INIS)

    Fukuda, K.; Shiotsu, M.; Sakurai, A.

    1995-01-01

    Understanding of transient boiling phenomenon caused by increasing heat inputs in subcooled water at high pressures is necessary to predict correctly a severe accident due to a power burst in a water-cooled nuclear reactor. Transient maximum heat fluxes, q max , on a 1.2 mm diameter horizontal cylinder in a pool of saturated and subcooled water for exponential heat inputs, q o e t/T , with periods, τ, ranging from about 2 ms to 20 s at pressures from atmospheric up to 2063 kPa for water subcoolings from 0 to about 80 K were measured to obtain the extended data base to investigate the effect of high subcoolings on steady-state and transient maximum heat fluxes, q max . Two main mechanisms of q max exist depending on the exponential periods at low subcoolings. One is due to the time lag of the hydrodynamic instability which starts at steady-state maximum heat flux on fully developed nucleate boiling (FDNB), and the other is due to the heterogenous spontaneous nucleations (HSN) in flooded cavities which coexist with vapor bubbles growing up from active cavities. The shortest period corresponding to the maximum q max for long period range belonging to the former mechanism becomes longer and the q max mechanism for long period range shifts to that due the HSN on FDNB with the increase of subcooling and pressure. The longest period corresponding to the minimum q max for the short period range belonging to the latter mechanism becomes shorter with the increase in saturated pressure. On the contrary, the longest period becomes longer with the increase in subcooling at high pressures. Correlations for steady-state and transient maximum heat fluxes were presented for a wide range of pressure and subcooling

  4. Some effects of favorable and adverse electric fields on pool boiling in dielectric fluids

    International Nuclear Information System (INIS)

    Masson, Viviana

    2001-01-01

    The effects of the application of an electric field on pool boiling in dielectric fluids were studied in this work.Two different geometries were used: one which is favorable to the bubble detachment (favorable electric field) and other which attract the bubbles toward the heater (adverse electric field).In the favorable electric field experiments, the void fraction and impact rate were calculated from the measured indicator function.Those parameters were obtained varying the probe-heater distance and the power to the heater.The results show a reduction of the void fraction with increasing applied voltage, probably caused by the combination of the dielectrophoretic force and a smaller bubble size due to the electric field application. Also, the impact rate decreases when a voltage is applied and the heat fluxes are close to the critical heat flux (CHF).On the other hand, the impact rate increases with voltage for moderate heat fluxes.Another interesting result is the approximately exponential decay of the void fraction and impact rate with the distance to the heater. Both the void fraction and the impact rate grow with heat flux if the heat fluxes are moderate, with or without applied voltage.For highest heat fluxes the void fraction still grows with heat flux if there are no applied electric fields while decreases with heat flux when there is an applied voltage. Similar behavior is observed in the impact rate.The boiling regimes was measured with adverse electric fields using two techniques.The heat transfer in the nucleate boiling regime was measured on an electrically powered heater.The results in these experiments show a reduction in the CHF of 10 % for saturation conditions and 10 kV of applied voltage, and a reduction of up to 40 % for 20 oC of liquid subcooling.The boiling curve corresponding to the transition and film boiling was performed with quenching experiments.An increase in the heat flux was achieved when an electric field was applied in spite of the

  5. Flow boiling test of GDP replacement coolants

    International Nuclear Information System (INIS)

    Park, S.H.

    1995-01-01

    The tests were part of the CFC replacement program to identify and test alternate coolants to replace CFC-114 being used in the uranium enrichment plants at Paducah and Portsmouth. The coolants tested, C 4 F 10 and C 4 F 8 , were selected based on their compatibility with the uranium hexafluoride process gas and how well the boiling temperature and vapor pressure matched that of CFC-114. However, the heat of vaporization of both coolants is lower than that of CFC-114 requiring larger coolant mass flow than CFC-114 to remove the same amount of heat. The vapor pressure of these coolants is higher than CFC-114 within the cascade operational range, and each coolant can be used as a replacement coolant with some limitation at 3,300 hp operation. The results of the CFC-114/C 4 F 10 mixture tests show boiling heat transfer coefficient degraded to a minimum value with about 25% C 4 F 10 weight mixture in CFC-114 and the degree of degradation is about 20% from that of CFC-114 boiling heat transfer coefficient. This report consists of the final reports from Cudo Technologies, Ltd

  6. Pressure drops in low pressure local boiling

    International Nuclear Information System (INIS)

    Courtaud, Michel; Schleisiek, Karl

    1969-01-01

    For prediction of flow reduction in nuclear research reactors, it was necessary to establish a correlation giving the pressure drop in subcooled boiling for rectangular channels. Measurements of pressure drop on rectangular channel 60 and 90 cm long and with a coolant gap of 1,8 and 3,6 mm were performed in the following range of parameters. -) 3 < pressure at the outlet < 11 bars abs; -) 25 < inlet temperature < 70 deg. C; -) 200 < heat flux < 700 W/cm 2 . It appeared that the usual parameter, relative length in subcooled boiling, was not sufficient to correlate experimental pressure losses on the subcooled boiling length and that there was a supplementary influence of pressure, heat flux and subcooling. With an a dimensional parameter including these terms a correlation was established with an error band of ±10%. With a computer code it was possible to derive the relation giving the overall pressure drop along the channel and to determine the local gradients of pressure drop. These local gradients were then correlated with the above parameter calculated in local conditions. 95 % of the experimental points were computed with an accuracy of ±10% with this correlation of gradients which can be used for non-uniform heated channels. (authors) [fr

  7. Subcooled boiling effect on dissolved gases behaviour

    International Nuclear Information System (INIS)

    Zmitko, M.; Sinkule, J.; Linek, V.

    1999-01-01

    A model describing dissolved gasses (hydrogen, nitrogen) and ammonia behaviour in subcooled boiling conditions of WWERs was developed. Main objective of the study was to analyse conditions and mechanisms leading to formation of a zone with different concentration of dissolved gases, eg. a zone depleted in dissolved hydrogen in relation to the bulk of coolant. Both, an equilibrium and dynamic approaches were used to describe a depletion of the liquid surrounding a steam bubble in the gas components. The obtained results show that locally different water chemistry conditions can be met in the subcooled boiling conditions, especially, in the developed subcooled boiling regime. For example, a 70% hydrogen depletion in relation to the bulk of coolant takes about 1 ms and concerns a liquid layer of 1 μn surrounding the steam bubble. The locally different concentration of dissolved gases can influence physic-chemical and radiolytic processes in the reactor system, eg. Zr cladding corrosion, radioactivity transport and determination of the critical hydrogen concentration. (author)

  8. Measurement of wetted area fraction in subcooled pool boiling of water using infrared thermography

    International Nuclear Information System (INIS)

    Kim, Hyungdae; Park, Youngjae; Buongiorno, Jacopo

    2013-01-01

    The wetted area fraction in subcooled pool boiling of water at atmospheric pressure is measured using the DEPIcT (DEtection of Phase by Infrared Thermography) technique. DEPIcT exploits the contrast in infrared (IR) light emissions between wet and dry areas on the surface of an IR-transparent heater to visualize the instantaneous distribution of the liquid and gas phases in contact with the heater surface. In this paper time-averaged wetted area fraction data in nucleate boiling are reported as functions of heat flux (from 30% up to 100% of the Critical Heat Flux) and subcooling (ΔT sub = 0, 5, 10, 30 and 50 °C). The results show that the wetted area fraction monotonically decreases with increasing heat flux and increases with increasing subcooling: both trends are expected. The range of time-averaged wetted area fractions is from 90%, at low heat flux and high subcooling, to 50% at high heat flux (right before CHF) and low subcooling. It is also shown that the dry areas are periodically rewetted by liquid sloshing on the surface at any subcooling and heat flux; however, the dry areas expand irreversibly at CHF

  9. Flow boiling heat transfer of carbon dioxide inside a small-sized microfin tube

    Energy Technology Data Exchange (ETDEWEB)

    Dang, Chaobin; Haraguchi, Nobori; Hihara, Eiji [Department of Human and Engineered Environmental Studies, Graduate School of Frontier Sciences, The University of Tokyo, Kashiwanoha, Kashiwa-shi, Chiba 277-8563 (Japan)

    2010-06-15

    This study investigated the flow boiling heat transfer of carbon dioxide inside a small-sized microfin tube (mean inner diameter: 2.0 mm; helix angle: 6.3 ) at a saturation temperature of 15 C, and heat and mass flux ranges of 4.5-18 kW m{sup -2} and 360-720 kg m{sup -2} s{sup -1}, respectively. Although, experimental results indicated that heat flux has a significant effect on the heat transfer coefficient, the coefficient does not always increase with mass flux, as in the case of conventional refrigerants such as HFCs or HCFCs. Under certain conditions, the heat transfer coefficient at a high mass flux was lower than that at a lower mass flux, indicating that convective heat transfer had a suppression effect on nucleate boiling. The heat transfer coefficients in the microfin tubes were 1.9{proportional_to}2.3 times the values in smooth tubes of the same diameter under the same experimental conditions, and the dryout quality was much higher, ranging from 0.9 to 0.95. The experimental results indicated that using microfin tubes may considerably increase the overall heat transfer performance. (author)

  10. Effect of diameter of metal nanowires on pool boiling heat transfer with FC-72

    Science.gov (United States)

    Kumar G., Udaya; S., Suresh; M. R., Thansekhar; Babu P., Dinesh

    2017-11-01

    Effect of varying diameter of metal nanowires on pool boiling heat transfer performance is presented in this study. Copper nanowires (CuNWs) of four different diameters (∼35 nm, ∼70 nm, ∼130 nm and ∼200 nm) were grown directly on copper specimen using template-based electrodeposition technique. Both critical heat flux (CHF) and boiling heat transfer coefficient (h) were found to be improved in surfaces with nanowires as compared to the bare copper surface. Moreover, both the parameters were found to increase with increasing diameter of the nanowires. The percentage increases observed in CHF for the samples with nanowires were 38.37%, 40.16%, 48.48% and 45.57% whereas the percentage increase in the heat transfer coefficient were 86.36%, 95.45%, 184.1% and 131.82% respectively as compared to the bare copper surface. Important reasons believed for this enhancement were improvement in micron scale cavity density and cavity size which arises as a result of the coagulation and grouping of nanowires during the drying process. In addition to this, superhydrophilic nature, capillary effect, and enhanced bubble dynamics parameters (bubble frequency, bubble departure diameter, and nucleation site density) were found to be the concurring mechanisms responsible for this enhancement in heat transfer performance. Qualitative bubble dynamics analysis was done for the surfaces involved and the visual observations are provided to support the results presented and discussed.

  11. Numerical study of the bubbly flow regime in micro-channel flow boiling

    Science.gov (United States)

    Bhuvankar, Pramod; Dabiri, Sadegh

    2017-11-01

    Two-phase flow accompanied by boiling in micro-channel heat sinks is an effective means for heat removal from computer chips. We present a numerical study of flow boiling in micro-channels with conjugate heat transfer with a focus on the bubbly flow regime. The bubbles are assumed to nucleate at a pre-determined location and frequency. The Navier Stokes equations are solved using a single fluid formulation with the Front tracking method. Phase change is implemented using the deficit in heat flux across the bubble interface. The analytical solution for bubble growth in a superheated liquid is used as a benchmark to validate the mentioned numerical method. Water and FC-72 are studied as the operating fluids in a micro-channel made of Copper with a focus on hotspot mitigation. The micro-channel of cross-section 231 μm × 1000 μm , is used to study the effects of vertical up-flow, vertical down-flow and horizontal flow of the mentioned fluids on the heat transfer coefficients. A simple film model accounting for mass and energy conservation is applied wherever the bubble approaches closer than a cell width to the wall. The results of the simulation are compared with existing experimental data for bubble growth rates and heat transfer coefficients.

  12. Pool boiling performance of Novec{sup TM} 649 engineered fluid

    Energy Technology Data Exchange (ETDEWEB)

    Forrest, Eric; Buongiorno, Jacopo; McKrell, Thomas [Massachusetts Institute of Technology, Cambridge (United States). Dept. of Nuclear Science and Engineering; Hu, Lin-Wen [Massachusetts Institute of Technology, Cambridge (United States). Nuclear Reactor Lab.], e-mail: lwhu@mit.edu

    2009-07-01

    A new fluorinated ketone, C{sub 2}F{sub 5}C(O)CF(CF{sub 3}){sub 2}, is currently being considered as an environmentally friendly alternative for power electronics cooling applications due to its high dielectric strength and low global warming potential (GWP). Sold commercially by the 3M Company as Novec{sup TM} 649 Engineered Fluid, C{sub 2}F{sub 5}C(O)CF(CF{sub 3}){sub 2} exhibits very low acute toxicity while maintaining long-term stability. To assess the general two-phase heat transfer performance of Novec{sup TM} 649, pool boiling tests were conducted by resistively heating a 0.01 in. diameter nickel wire at the fluid's atmospheric saturation temperature of 49 deg C. The nucleate boiling heat transfer coefficient and critical heat flux (CHF) obtained for the fluorinated ketone compare favorably with results obtained for FC-72, a fluorocarbon widely used for the direct cooling of electronic devices. Initial results indicate that Novec{sup TM} 649 may prove to be a viable alternative to FC-72 and other halo alkanes for the cooling of high power density electronic devices. (author)

  13. Enhancement of pool boiling heat transfer in water using sintered copper microporous coatings

    Energy Technology Data Exchange (ETDEWEB)

    Jun, Seong Chul; KIm, Jin Sub; You, Seung M. [Dept. of Mechanical Engineering, The University of Texas at Dallas, Richardson (United States); Son, Dong Gun; KIm, Hwan Yeol [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

    2016-08-15

    Pool boiling heat transfer of water saturated at atmospheric pressure was investigated experimentally on Cu surfaces with high-temperature, thermally-conductive, microporous coatings (HTCMC). The coatings were created by sintering Cu powders on Cu surfaces in a nitrogen gas environment. A parametric study of the effects of particle size and coating thickness was conducted using three average particle sizes (APSs) of 10 μm, 25 μm, and 67 μm and various coating thicknesses. It was found that nucleate boiling heat transfer (NBHT) and critical heat flux (CHF) were enhanced significantly for sintered microporous coatings. This is believed to have resulted from the random porous structures that appear to include reentrant type cavities. The maximum NBHT coefficient was measured to be approximately 400 kW/m2k with APS 67 μm and 296 μm coating thicknesses. This value is approximately eight times higher than that of a plain Cu surface. The maximum CHF observed was 2.1 MW/m2 at APS 67 μm and 428 μm coating thicknesses, which is approximately double the CHF of a plain Cu surface. The enhancement of NBHT and CHF appeared to increase as the particle size increased in the tested range. However, two larger particle sizes (25 μm and 67 μm) showed a similar level of enhancement.

  14. Generalized syntheses of nanocrystal-graphene hybrids in high-boiling-point organic solvents.

    Science.gov (United States)

    Pang, Danny Wei-Ping; Yuan, Fang-Wei; Chang, Yan-Cheng; Li, Guo-An; Tuan, Hsing-Yu

    2012-08-07

    Nanocrystal-graphene have been proposed as a new kind of promising hybrid for a wide range of application areas including catalysts, electronics, sensors, biomedicine, and energy storage, etc. Although a variety of methods have been developed for the preparation of hybrids, a facile and general synthetic approach is still highly required. In this study, nanocrystal-graphene hybrids were successfully synthesized in high-boiling-point organic solvents. Graphene oxide (GO) nanosheets were modified by oleylamine (OLA) to form a OLA-GO complex in order to be readily incorporated into hydrophobic synthesis. A rich library of highly crystalline nanocrystals, with types including noble metal, metal oxide, magnetic material and semiconductor were successfully grown on chemically converted graphene (CCG), which is simultaneously reduced from GO during the synthesis. High boiling-point solvents afford sufficient thermal energy to assure the high-quality crystalline nature of NCs, therefore the post-annealing process is obviated. Controlled experiments revealed that OLA-GO triggers heterogeneous nucleation and serves as excellent nuclei anchorage media. The protocol developed here brings one step closer to achieve "unity in diversity" on the preparation of nanocrystal-graphene hybrids.

  15. Nanosecond laser ablation of target Al in a gaseous medium: explosive boiling

    Science.gov (United States)

    Mazhukin, V. I.; Mazhukin, A. V.; Demin, M. M.; Shapranov, A. V.

    2018-03-01

    An approximate mathematical description of the processes of homogeneous nucleation and homogeneous evaporation (explosive boiling) of a metal target (Al) under the influence of ns laser radiation is proposed in the framework of the hydrodynamic model. Within the continuum approach, a multi-phase, multi-front hydrodynamic model and a computational algorithm are designed to simulate nanosecond laser ablation of the metal targets immersed in gaseous media. The proposed approach is intended for modeling and detailed analysis of the mechanisms of heterogeneous and homogeneous evaporation and their interaction with each other. It is shown that the proposed model and computational algorithm allow modeling of interrelated mechanisms of heterogeneous and homogeneous evaporation of metals, manifested in the form of pulsating explosive boiling. Modeling has shown that explosive evaporation in metals is due to the presence of a near-surface temperature maximum. It has been established that in nanosecond pulsed laser ablation, such exposure regimes can be implemented in which phase explosion is the main mechanism of material removal.

  16. Using rheometry for determining nucleation density in colored system containing a nucleation agent

    NARCIS (Netherlands)

    Ma, Z.; Steenbakkers, R.J.A.; Giboz, J.; Peters, G.W.M.

    2011-01-01

    A new suspension-based rheological method was applied to study experimentally the crystallization of a nucleating agent (NA) filled isotactic polypropylene. This method allows for determination of point-nucleation densities where other methods fail. For example, optical microscopy can fail because

  17. Cytoplasmic Nucleation and Atypical Branching Nucleation Generate Endoplasmic Microtubules in Physcomitrella patens[OPEN

    Science.gov (United States)

    Nakaoka, Yuki; Kimura, Akatsuki; Tani, Tomomi; Goshima, Gohta

    2015-01-01

    The mechanism underlying microtubule (MT) generation in plants has been primarily studied using the cortical MT array, in which fixed-angled branching nucleation and katanin-dependent MT severing predominate. However, little is known about MT generation in the endoplasm. Here, we explored the mechanism of endoplasmic MT generation in protonemal cells of Physcomitrella patens. We developed an assay that utilizes flow cell and oblique illumination fluorescence microscopy, which allowed visualization and quantification of individual MT dynamics. MT severing was infrequently observed, and disruption of katanin did not severely affect MT generation. Branching nucleation was observed, but it showed markedly variable branch angles and was occasionally accompanied by the transport of nucleated MTs. Cytoplasmic nucleation at seemingly random locations was most frequently observed and predominated when depolymerized MTs were regrown. The MT nucleator γ-tubulin was detected at the majority of the nucleation sites, at which a single MT was generated in random directions. When γ-tubulin was knocked down, MT generation was significantly delayed in the regrowth assay. However, nucleation occurred at a normal frequency in steady state, suggesting the presence of a γ-tubulin-independent backup mechanism. Thus, endoplasmic MTs in this cell type are generated in a less ordered manner, showing a broader spectrum of nucleation mechanisms in plants. PMID:25616870

  18. Modelling of subcooled boiling and DNB-type boiling crisis in forced convection

    International Nuclear Information System (INIS)

    Bricard, Patrick

    1995-01-01

    This research thesis aims at being a contribution to the modelling of two phenomena occurring during a forced convection: the axial evolution of the vacuum rate, and the boiling crisis. Thus, the first part of this thesis addresses the prediction of the vacuum rate, and reports the development of a modelling of under-saturated convection in forced convection. The author reports the development and assessment of two-fluid one-dimensional model, the development of a finer analysis based on an averaging of local equations of right cross-sections in different areas. The second part of this thesis addresses the prediction of initiation of a boiling crisis. The author presents generalities and motivations for this study, reports a bibliographical study and a detailed analysis of mechanistic models present in this literature. A mechanism of boiling crisis is retained, and then further developed in a numerical modelling which is used to assess some underlying hypotheses [fr

  19. Effect of transverse power distribution on the ONB location in the subcooled boiling flow

    International Nuclear Information System (INIS)

    Al-Yahia, Omar S.; Lee, Yong Joong; Jo, Daeseong

    2017-01-01

    Highlights: • Effect of transverse power distribution on ONB incipient. • Uniform and non-uniform heat distribution is simulated in a narrow rectangular channel. • Simulations are performed using CFX and TMAP codes. • For uniform heating, ONB incipient by CFX occurs between predictions by TMAP analyses. • For non-uniform heating, ONB incipient by CFX occurs at a higher power than that by TMAP analysis. - Abstract: This study investigates the effect of transverse power distribution on the ONB (Onset of Nucleate Boiling) incipient. For this purpose, a subcooled boiling model with uniform and non-uniform heat flux distribution is simulated in a narrow vertical rectangular channel heated from both sides by applying a wide range of thermal power (8–16 kW). The simulations are performed using the CFX and TMAP codes. The CFX code incorporates both a two-fluid model and RPI wall boiling model to investigate coolant and wall temperature distributions along the heated channel. The TMAP code implements two different sets of heat transfer correlations to evaluate the wall temperature. The results obtained from the TMAP analyses show that the wall temperatures predicted by the Jo et al. heat transfer correlation are higher than the ones predicted by the Dittus and Boelter heat transfer correlation. The wall temperatures predicted by the CFX analyses lie between the predicted wall temperatures obtained by the TMAP analyses. Based on the superheated temperature on the heated surface, the ONB incipient is determined. The axial locations of the ONB incipient are predicted differently by the CFX and TMAP analyses. For uniform heating, the ONB incipient predicted by the CFX analysis occurs between the predictions made by the TMAP analyses. For non-uniform heating, the ONB incipient by the CFX analysis occurs at a higher power than the power required by the TMAP analyses.

  20. Vapour–to–liquid nucleation: Nucleation theorems for nonisothermal–nonideal case

    Energy Technology Data Exchange (ETDEWEB)

    Malila, J.; McGraw, R.; Napari, I.; Laaksonen, A.

    2010-08-29

    Homogeneous vapour-to-liquid nucleation, a basic process of aerosol formation, is often considered as a type example of nucleation phenomena, while most treatment of the subject introduce several simplifying assumptions (ideal gas phase, incompressible nucleus, isothermal kinetics, size-independent surface free energy...). During last decades, nucleation theorems have provided new insights into properties of critical nuclei facilitating direct comparison between laboratory experiments and molecular simulations. These theorems are, despite of their generality, often applied in forms where the aforementioned assumptions are made. Here we present forms of nucleation theorems that explicitly take into account these effects and allow direct estimation of their importance. Only assumptions are Arrhenius-type kinetics of nucleation process and exclusion carrier gas molecules from the critical nucleus.