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

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.

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)

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)

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

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

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.)

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

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

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

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.

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

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

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

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.

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.

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

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.

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.)

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)

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

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)

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)

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).

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

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

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.

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

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)

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

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)

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)

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)

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)

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)

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)

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.

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.

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)

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)

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)

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)

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)

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

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)

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

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

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)

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)

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)

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

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.

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)

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)

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)

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)

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)

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.

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

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)

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)

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

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

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).

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)

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

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.

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

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

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)

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

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)

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

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

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

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

Partial Oxidation of High-Boiling Hydrocarbon Mixtures in the Pilot Unit

Czech Academy of Sciences Publication Activity Database

Hanika, Jiří; Lederer, J.; Nečesaný, F.; Poslední, W.; Tukač, V.; Veselý, Václav

2014-01-01

Roč. 68, č. 12 (2014), s. 1701-1706 ISSN 0366-6352 Institutional support: RVO:67985858 Keywords : partial oxidation * high-boiling hydrocarbons * pilot plant Subject RIV: CI - Industrial Chemistry , Chemical Engineering Impact factor: 1.468, year: 2014

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

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)

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)

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.

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)

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

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)

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)

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

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)

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

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.

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

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)

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

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.

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.

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

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.

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)

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)

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.

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

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

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

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

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

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

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)

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

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

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)

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.

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.

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)

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.

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.

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

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

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...

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

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.

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

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.

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.

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...

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)

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

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

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)

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)

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.

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

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

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

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

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)

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)

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)

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

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.

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

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

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.

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)

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.

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.

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

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

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)

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)

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)

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)

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

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

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.

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)

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.

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)

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

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.

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

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)

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)

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)

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.

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.

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

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.

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.

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.

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.)

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.)

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)

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

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

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)

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

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...

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.

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)

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

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.

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.

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.

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)

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)

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

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

Nucleation barrier reconstruction via the seeding method in a lattice model with competing nucleation pathways.

Science.gov (United States)

Lifanov, Yuri; Vorselaars, Bart; Quigley, David

2016-12-07

We study a three-species analogue of the Potts lattice gas model of nucleation from solution in a regime where partially disordered solute is a viable thermodynamic phase. Using a multicanonical sampling protocol, we compute phase diagrams for the system, from which we determine a parameter regime where the partially disordered phase is metastable almost everywhere in the temperature-fugacity plane. The resulting model shows non-trivial nucleation and growth behaviour, which we examine via multidimensional free energy calculations. We consider the applicability of the model in capturing the multi-stage nucleation mechanisms of polymorphic biominerals (e.g., CaCO 3 ). We then quantitatively explore the kinetics of nucleation in our model using the increasingly popular "seeding" method. We compare the resulting free energy barrier heights to those obtained via explicit free energy calculations over a wide range of temperatures and fugacities, carefully considering the propagation of statistical error. We find that the ability of the "seeding" method to reproduce accurate free energy barriers is dependent on the degree of supersaturation, and severely limited by the use of a nucleation driving force Δμ computed for bulk phases. We discuss possible reasons for this in terms of underlying kinetic assumptions, and those of classical nucleation theory.

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

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.)

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

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

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

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

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.

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

accurately predict the heat transfer. In order to evaluate the wall law implemented in the CFD tool, computations have been compared with KALLA experimental results obtained in the case of a rod heated with a constant heat flux which is concentrically embedded in a pipe liquid metal flow (single-phase flow). Secondly, the incipient boiling superheat of sodium is quite different from that of conventional fluids. As a consequence, the nucleate boiling model has been improved and validated against the Charlety’s experiment where a rod heated with a constant heat flux is concentrically embedded in a pipe sodium flow. For different values of the heat flux, the pressure is measured at different locations as function of the mass flow rate. A reasonable agreement has been reached which is very encouraging for further applications. Finally, preliminary computations have been carried out in an assembly constituted of 19 pins equipped with a wrapped wire where partial experimental results are available. Computations have shown a pressure drop at the end of the heated length due to the sudden increase of the hydraulic diameter. Thus, the pressure can drop below the vapour pressure leading to liquid vaporization. This first result supports the assumption of boiling in the upper subassembly zone which could possibly lead to a sodium boiling stabilization.

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

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

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.

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)

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)

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.

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.

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.

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

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

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.

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

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)

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.

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)

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

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)

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.

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)

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)

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)

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.

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

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)

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)

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.

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)

Nucleation in As2Se3 glass studied by DSC

International Nuclear Information System (INIS)

Svoboda, Roman; Málek, Jiří

2014-01-01

Highlights: • Nucleation behavior of As 2 Se 3 glass was studied by DSC in dependence on particle size. • Correlation between the enthalpies of fusion and crystallization were confirmed. • Apart from classical heterogeneous nucleation a second nucleation mechanism was found. • Rapid formation of crystallization centers from a damaged glassy structure occurs. • Mechanical defects seem to partially suppress the CNT nucleation process. - Abstract: Differential scanning calorimetry was used to study nucleation behavior in As 2 Se 3 glass, dependent on particle size. The nucleation process was examined for a series of different coarse powders; the nucleation rate was estimated from the proportion of the crystalline material fraction. The enthalpy of fusion was utilized in this respect, and a correlation between ΔH m and ΔH c was confirmed. Two mechanisms of nucleus formation were found: classical heterogeneous nucleation (following CNT) and so-called “activation” of mechanically-induced defects. The latter appears to represent rapid formation of crystallization centers from a damaged glassy structure, where complete saturation occurs for fine powders in the range of 195–235 °C. A high amount of mechanical defects, on the other hand, was found to partially suppress the CNT nucleation process

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

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.

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)

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

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.

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 ...

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.

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

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)

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

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.)

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.

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

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

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).

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%.

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.

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.

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)

Chlorine-containing salts as water ice nucleating particles on Mars

Science.gov (United States)

Santiago-Materese, D. L.; Iraci, L. T.; Clapham, M. E.; Chuang, P. Y.

2018-03-01

Water ice cloud formation on Mars largely is expected to occur on the most efficient ice nucleating particle available. Salts have been observed on the Martian surface and have been known to facilitate water cloud formation on Earth. We examined heterogeneous ice nucleation onto sodium chloride and sodium perchlorate substrates under Martian atmospheric conditions, in the range of 150 to 180 K and 10-7 to 10-5 Torr water partial pressure. Sub-155 K data for the critical saturation ratio (Scrit) suggests an exponential model best describes the temperature-dependence of nucleation onset of water ice for all substrates tested. While sodium chloride does not facilitate water ice nucleation more easily than bare silicon, sodium perchlorate does support depositional nucleation at lower saturation levels than other substrates shown and is comparable to smectite-rich clay in its ability to support cloud initiation. Perchlorates could nucleate water ice at partial pressures up to 40% lower than other substrates examined to date under Martian atmospheric conditions. These findings suggest air masses on Mars containing uplifted salts such as perchlorates could form water ice clouds at lower saturation ratios than in air masses absent similar particles.

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

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)

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.

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

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.)

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)

Freezing nucleation apparatus puts new slant on study of biological ice nucleators in precipitation

Science.gov (United States)

Stopelli, E.; Conen, F.; Zimmermann, L.; Alewell, C.; Morris, C. E.

2014-01-01

For decades, drop-freezing instruments have contributed to a better understanding of biological ice nucleation and its likely implications for cloud and precipitation development. Yet, current instruments have limitations. Drops analysed on a cold stage are subject to evaporation and potential contamination. The use of closed tubes provides a partial solution to these problems, but freezing events are still difficult to be clearly detected. Here, we present a new apparatus where freezing in closed tubes is detected automatically by a change in light transmission upon ice development, caused by the formation of air bubbles and crystal facets that scatter light. Risks of contamination and introduction of biases linked to detecting the freezing temperature of a sample are then minimized. To illustrate the performance of the new apparatus we show initial results of two assays with snow samples. In one, we repeatedly analysed the sample (208 tubes) over the course of a month with storage at +4 °C, during which evidence for biological ice nucleation activity emerged through an increase in the number of ice nucleators active around -4 °C. In the second assay, we indicate the possibility of increasingly isolating a single ice nucleator from a precipitation sample, potentially determining the nature of a particle responsible for a nucleation activity measured directly in the sample. These two seminal approaches highlight the relevance of this handy apparatus for providing new points of view in biological ice nucleation research.

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)

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.

Cooling Performance of a Partially-Confined FC-72 Spray: The Effect of Dissolved Air (Postprint)

Science.gov (United States)

2007-01-01

plate FC = FC-72 fluid htr = heater conductive layer int = interface between heater substrate and insulating support post m = measured s = heater... microporous enhanced surface and a plain reference surface, and developed correlations for nucleate boiling and CHF. The results of the experiment...8Rainey, K. N., You, S. M., and Lee, S., “Effect of Pressure, Subcooling, and Dissolved Gas on Pool Boiling Heat Transfer from Microporous Surfaces

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.

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

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�

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)

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)

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)

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)

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.

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

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)

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.

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

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

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

DYNAM, Once Through Boiling Flow with Steam Superheat, Laplace Transformation

International Nuclear Information System (INIS)

Schlueter, G.; Efferding, L.E.

1973-01-01

1 - Description of problem or function: DYNAM performs a dynamic analysis of once-through boiling flow oscillations with steam superheat. The model describing the superheat regime (single- phase, variable density fluid) for subcritical pressure operation is also applicable to the study of once-through operation using supercritical pressure water. 2 - Method of solution: Linearized partial differential conservation equations are solved using Laplace transformation of the temporal terms and integration of the spatial variations. DYNAM is written in complex variable notation. 3 - Restrictions on the complexity of the problem - Maxima of: 30 intervals used to describe the power distribution in the non-boiling and boiling regions, 29 boiling nodes, 7 intervals and corresponding friction multipliers read in per case, 14 exit qualities read in per case, 40 superheat nodes, 10 coefficients read in for the phi 2 vs, x-polynomial fit, 48 frequencies at which open-loop frequency response is desired, 48 frequencies at which signal output is desired

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.

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)

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

On the Application of Image Processing Methods for Bubble Recognition to the Study of Subcooled Flow Boiling of Water in Rectangular Channels

Directory of Open Access Journals (Sweden)

Concepción Paz

2017-06-01

Full Text Available This work introduces the use of machine vision in the massive bubble recognition process, which supports the validation of boiling models involving bubble dynamics, as well as nucleation frequency, active site density and size of the bubbles. The two algorithms presented are meant to be run employing quite standard images of the bubbling process, recorded in general-purpose boiling facilities. The recognition routines are easily adaptable to other facilities if a minimum number of precautions are taken in the setup and in the treatment of the information. Both the side and front projections of subcooled flow-boiling phenomenon over a plain plate are covered. Once all of the intended bubbles have been located in space and time, the proper post-process of the recorded data become capable of tracking each of the recognized bubbles, sketching their trajectories and size evolution, locating the nucleation sites, computing their diameters, and so on. After validating the algorithm’s output against the human eye and data from other researchers, machine vision systems have been demonstrated to be a very valuable option to successfully perform the recognition process, even though the optical analysis of bubbles has not been set as the main goal of the experimental facility.

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

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)

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

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

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

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)

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)

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)

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.

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.

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.

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.)

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

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.

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

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

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

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

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)

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)

Sulfur driven nucleation mode formation in diesel exhaust under transient driving conditions.

Science.gov (United States)

Karjalainen, Panu; Rönkkö, Topi; Pirjola, Liisa; Heikkilä, Juha; Happonen, Matti; Arnold, Frank; Rothe, Dieter; Bielaczyc, Piotr; Keskinen, Jorma

2014-02-18

Sulfur driven diesel exhaust nucleation particle formation processes were studied in an aerosol laboratory, on engine dynamometers, and on the road. All test engines were equipped with a combination of a diesel oxidation catalyst (DOC) and a partial diesel particulate filter (pDPF). At steady operating conditions, the formation of semivolatile nucleation particles directly depended on SO2 conversion in the catalyst. The nucleation particle emission was most significant after a rapid increase in engine load and exhaust gas temperature. Results indicate that the nucleation particle formation at transient driving conditions does not require compounds such as hydrocarbons or sulfated hydrocarbons, however, it cannot be explained only by the nucleation of sulfuric acid. A real-world exhaust study with a heavy duty diesel truck showed that the nucleation particle formation occurs even with ultralow sulfur diesel fuel, even at downhill driving conditions, and that nucleation particles can contribute 60% of total particle number emissions. In general, due to sulfur storage and release within the exhaust aftertreatment systems and transients in driving, emissions of nucleation particles can even be the dominant part of modern diesel vehicle exhaust particulate number emissions.

Minimum heat flux (MHF) point in pool and external-flow boiling

International Nuclear Information System (INIS)

Nishio, Shigefumi

1983-01-01

As for the boiling phenomena near a minimum heat flux (MHF) point to which attention has been paid recently concerning the safety analysis of LWR cores, the results of research have not been put in order sufficiently. Therefore in this explanation, the object is limited to pool boiling and external flow boiling, and it is attempted to rearrange the present knowledge on the phenomena near a MHF point from the viewpoint of the relation to the state of solid-liquid contact, the effect of various factors on a MHF point and the modeling of a MHF point. The heat transfer characteristics in boiling phenomena are represented by a curve with one maximum and one minimum points. The MHF point is called also minimum film boiling point. In a heat flux-controlled heating surface, temperature jump arises when heat flux is decreased at a MHF point. The phenomena near a MHF point and the technological background when a MHF point becomes a problem are explained. Near a MHF point, only partial, intermittent solid-liquid contact is maintained. The effects of solid-liquid contact mode, the geometry of a heating surface, pressure and others on a MHF point are discussed. (Kako, I.)

FILM-30: A Heat Transfer Properties Code for Water Coolant

International Nuclear Information System (INIS)

MARSHALL, THERON D.

2001-01-01

A FORTRAN computer code has been written to calculate the heat transfer properties at the wetted perimeter of a coolant channel when provided the bulk water conditions. This computer code is titled FILM-30 and the code calculates its heat transfer properties by using the following correlations: (1) Sieder-Tate: forced convection, (2) Bergles-Rohsenow: onset to nucleate boiling, (3) Bergles-Rohsenow: partially developed nucleate boiling, (4) Araki: fully developed nucleate boiling, (5) Tong-75: critical heat flux (CHF), and (6) Marshall-98: transition boiling. FILM-30 produces output files that provide the heat flux and heat transfer coefficient at the wetted perimeter as a function of temperature. To validate FILM-30, the calculated heat transfer properties were used in finite element analyses to predict internal temperatures for a water-cooled copper mockup under one-sided heating from a rastered electron beam. These predicted temperatures were compared with the measured temperatures from the author's 1994 and 1998 heat transfer experiments. There was excellent agreement between the predicted and experimentally measured temperatures, which confirmed the accuracy of FILM-30 within the experimental range of the tests. FILM-30 can accurately predict the CHF and transition boiling regimes, which is an important advantage over current heat transfer codes. Consequently, FILM-30 is ideal for predicting heat transfer properties for applications that feature high heat fluxes produced by one-sided heating

Electrostatic interactions govern both nucleation and elongation during phage P22 procapsid assembly

International Nuclear Information System (INIS)

Parent, Kristin N.; Doyle, Shannon M.; Anderson, Eric; Teschke, Carolyn M.

2005-01-01

Icosahedral capsid assembly is an example of a reaction controlled solely by the interactions of the proteins involved. Bacteriophage P22 procapsids can be assembled in vitro by mixing coat and scaffolding proteins in a nucleation-limited reaction, where scaffolding protein directs the proper assembly of coat protein. Here, we investigated the effect of the buffer composition on the interactions necessary for capsid assembly. Different concentrations of various salts, chosen to follow the electroselectivity series for anions, were added to the assembly reaction. The concentration and type of salt was found to be crucial for proper nucleation of procapsids. Nucleation in low salt concentrations readily occurred but led to bowl-like partial procapsids, as visualized by negative stain electron microscopy. The edge of the partial capsids remained assembly-competent since coat protein addition triggered procapsid completion. The addition of salt to the partial capsids also caused procapsid completion. In addition, each salt affected both assembly rates and the extent of procapsid formation. We hypothesize that low salt conditions increase the coat protein:scaffolding protein affinity, causing excessive nuclei to form, which decreases coat protein levels leading to incomplete assembly

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

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.

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

Identification of flow patterns by neutron noise analysis during actual coolant boiling in thin rectangular channels

International Nuclear Information System (INIS)

Kozma, R.; van Dam, H.; Hoogenboom, J.E.

1992-01-01

The primary objective of this paper is to introduce results of coolant boiling experiments in a simulated materials test reactor-type fuel assembly with plate fuel in an actual reactor environment. The experiments have been performed in the Hoger Onderwijs Reactor (HOR) research reactor at the Interfaculty Reactor Institute, Delft, The Netherlands. In the analysis, noise signals of self-powered neutron detectors located in the neighborhood of the boiling region and thermocouple in the channel wall and in the coolant are used. Flow patterns in the boiling coolant have been identified by means of analysis of probability density functions and power spectral densities of neutron noise. It is shown that boiling has an oscillating character due to partial channel blockage caused by steam slugs generated periodically between the plates. The observed phenomenon can serve as a basis for a boiling detection method in reactors with plate-type fuels

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.

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.)

Fundamental study of FC-72 pool boiling surface temperature fluctuations and bubble behavior

Science.gov (United States)

Griffin, Alison R.

a bubble growing over the TFTC junction on both the sapphire and fused silica heater surfaces. When the fused silica heater produced a temperature drop of 1.4°C, the sapphire heater produced a drop of only 0.04°C under the same conditions. These results verified that the lack of temperature drops present in the sapphire data was due to the thermal properties of the sapphire layer. By observing the bubble departure frequency and site density on the heater, as well as the bubble departure diameter, the contribution of nucleate boiling to the overall heat removal from the surface could be calculated. These results showed that bubble vapor generation contributed to approximately 10% at 1 W/cm2, 23% at 1.75 W/cm2, and 35% at 2.9 W/cm 2 of the heat removed from a fused silica heater. Bubble growth and contact ring growth were observed and measured from images obtained with the high-speed camera. Bubble data recorded on a fused silica heater at 3 W/cm2, 4 W/cm2, and 5 W/cm 2 showed that bubble departure diameter and lifetime were negligibly affected by the increase in heat flux. Bubble and contact ring growth rates demonstrated significant differences when compared on the fused silica and sapphire heaters at 3 W/cm2. The bubble departure diameters were smaller, the bubble lifetimes were longer, and the bubble departure frequency was larger on the sapphire heater, while microlayer evaporation was faster on the fused silica heater. Additional considerations revealed that these differences may be due to surface conditions as well as differing thermal properties. Nucleate boiling curves were recorded on the fused silica and sapphire heaters by adjusting the heat flux input and monitoring the local surface temperature with the TFTCs. The resulting curves showed a temperature drop at the onset of nucleate boiling due to the increase in heat transfer coefficient associated with bubble nucleation. One of the TFTC locations on the sapphire heater frequently experienced a second

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

Dependence of calculated void reactivity on film-boiling representation

International Nuclear Information System (INIS)

Whitlock, J.; Garland, W.

1992-01-01

Partial voiding of a fuel channel can lead to complicated neutronic analysis, because of highly nonuniform spatial distributions. An investigation of the distribution dependence of void reactivity in a Canada deuterium uranium (CANDU) lattice, specifically in the regime of film boiling, was done. Although the core is not expected to be critical at the time of sheath dryout, this study augments current knowledge of void reactivity in this type of lattice

An experimental study on pool boiling characteristics of carbon nano tube (CNT) and fullerene (C-60) nanofluids

International Nuclear Information System (INIS)

Ai, Melani

2009-02-01

In recent years, it was found that pool boiling critical heat flux (CHF) increases in nanofluids. The CHF conditions are important for safe and economic design of many heat transfer units including nuclear reactor. In this study, our objective is to evaluate the impact of Carbone Nano Tubes (Singlewalled CNTs and Multiwalled CNTs) and Fullerene (C-60) nanofluids at different particle concentration on pool boiling critical heat flux experimentally at saturated conditions. Multiwalled CNT and fullerene (C-60) added in the pure water at three volume concentrations (0.01%, 0.001%, and 0.0001%). Singlewalled CNT nanoparticles added in the pure water at two volume concentrations (0.0005%, and 0.0001%). For the dispersion of nanoparticles in pure water, several treatments were performed. Multiwalled CNTs and Fullerene (C-60) prepared using acid treatment, meanwhile two treatment are using for Singlewalled CNTs: (1)Singlewalled CNTs prepared using polymer treatment, (2)Singlewalled CNTs prepared using pre polymerization of micelle treatment. The zeta potential of CNTs and Fullerene nanofluids were in the range of 13-71 mV. The zeta potential of nanofluids was constant for more than one month. It concludes that the treatment has been succeeded produces water dispersible CNTs and Fullerene nanofluids with good stability. The critical heat flux (CHFs) of the solution is enhanced greatly for all nanofluids. Enhanced (∼167.9%) CHF was observed for solutions with Multiwalled CNT nanoparticles with concentration 0.01 vol%. Enhanced (∼109.4%) CHF was observed for solutions with Singlewalled CNT nanoparticles with concentration 0.0005 vol%. Enhanced (∼108.9%) CHF was observed for solutions with Fullerene nanoparticles with concentration 0.01 vol%. The pool boiling Heat Transfer Coefficient (HTCs) of the CNTs nanofluids are lower than those of pure water in the entire nucleate boiling regime. On the other hand, the pool boiling HTCs of Fullerene nanofluids are higher than

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.

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

Nucleation of dislocations from [0 0 1] bicrystal interfaces in aluminum

International Nuclear Information System (INIS)

Spearot, Douglas E.; Jacob, Karl I.; McDowell, David L.

2005-01-01

It is well established from molecular dynamics simulations that grain boundaries in nanocrystalline samples serve as sources of dislocations. In this work, we use molecular dynamics simulations to study the mechanisms associated with dislocation nucleation from bicrystal [0 0 1] interfaces in aluminum. Three interface misorientations are studied, including the Σ5 (3 1 0) boundary, which has a high density of coincident atomic sites. Molecular dynamics simulations show that full dislocation loops are nucleated from each interface during uniaxial tension. After the second partial dislocation is emitted, a ledge remains within the interface at the intersection of the slip plane and the bicrystal boundary. A disclination dipole model is proposed for the structure of the distorted interface accounting for local lattice rotations and the ledge at the nucleation site

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...

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.)

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

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

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)

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

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

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.

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)

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.

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

Cork boiling wastewater treatment and reuse through combination of advanced oxidation technologies.

Science.gov (United States)

Ponce-Robles, L; Miralles-Cuevas, S; Oller, I; Agüera, A; Trinidad-Lozano, M J; Yuste, F J; Malato, S

2017-03-01

Industrial preparation of cork consists of its immersion for approximately 1 hour in boiling water. The use of herbicides and pesticides in oak tree forests leads to absorption of these compounds by cork; thus, after boiling process, they are present in wastewater. Cork boiling wastewater shows low biodegradability and high acute toxicity involving partial inhibition of their biodegradation when conventional biological treatment is applied. In this work, a treatment line strategy based on the combination of advanced physicochemical technologies is proposed. The final objective is the reuse of wastewater in the cork boiling process; thus, reducing consumption of fresh water in the industrial process itself. Coagulation pre-treatment with 0.5 g/L of FeCl 3 attained the highest turbidity elimination (86 %) and 29 % of DOC elimination. Similar DOC removal was attained when using 1 g/L of ECOTAN BIO (selected for ozonation tests), accompanied of 64 % of turbidity removal. Ozonation treatments showed less efficiency in the complete oxidation of cork boiling wastewater, compared to solar photo-Fenton process, under the studied conditions. Nanofiltration system was successfully employed as a final purification step with the aim of obtaining a high-quality reusable permeate stream. Monitoring of unknown compounds by LC-QTOF-MS allowed the qualitative evaluation of the whole process. Acute and chronic toxicity as well as biodegradability assays were performed throughout the whole proposed treatment line.

1995 national heat transfer conference: Proceedings. Volume 12: Falling films; Fundamentals of subcooled flow boiling; Compact heat exchanger technology for the process industry; HTD-Volume 314

International Nuclear Information System (INIS)

Sernas, V.; Boyd, R.D.; Jensen, M.K.

1995-01-01

The papers in the first section cover falling films and heat transfer. Papers in the second section address issues associated with heat exchangers, such as: plate-and-frame heat exchanger technology; thermal design issues; condensation; and single-phase flows. The papers in the third section deal with studies related to: the turbulent velocity field in a vertical annulus; the effects of curvature and a dissolved noncondensable gas on nucleate boiling heat transfer; the effects of flow obstruction on the onset of a Ledinegg-type flow instability; pool boiling from a large-diameter tube; and two-dimensional wall temperature distributions and convection in a single-sided heated vertical tube. Separate abstracts were prepared for most papers in this volume

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

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...

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

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.

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

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.

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.

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

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

Size-exclusion chromatography for the determination of the boiling point distribution of high-boiling petroleum fractions.

Science.gov (United States)

Boczkaj, Grzegorz; Przyjazny, Andrzej; Kamiński, Marian

2015-03-01

The paper describes a new procedure for the determination of boiling point distribution of high-boiling petroleum fractions using size-exclusion chromatography with refractive index detection. Thus far, the determination of boiling range distribution by chromatography has been accomplished using simulated distillation with gas chromatography with flame ionization detection. This study revealed that in spite of substantial differences in the separation mechanism and the detection mode, the size-exclusion chromatography technique yields similar results for the determination of boiling point distribution compared with simulated distillation and novel empty column gas chromatography. The developed procedure using size-exclusion chromatography has a substantial applicability, especially for the determination of exact final boiling point values for high-boiling mixtures, for which a standard high-temperature simulated distillation would have to be used. In this case, the precision of final boiling point determination is low due to the high final temperatures of the gas chromatograph oven and an insufficient thermal stability of both the gas chromatography stationary phase and the sample. Additionally, the use of high-performance liquid chromatography detectors more sensitive than refractive index detection allows a lower detection limit for high-molar-mass aromatic compounds, and thus increases the sensitivity of final boiling point determination. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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

A simpler, safer, higher performance cooling system arrangement for water cooled divertors

International Nuclear Information System (INIS)

Carelli, M.D.; Kothmann, R.E.; Green, L.; Zhan, N.J.; Stefani, F.; Roidt, R.M.

1994-01-01

A cooling system arrangement is presented which is specifically designed for high heat flux water cooled divertors. The motivation behind the proposed open-quotes unichannelclose quotes configuration is to provide maximum safety; this design eliminates flow instabilities liable to occur in parallel channel designs, it eliminates total blockage, it promotes cross flow to counteract the effects of partial blockage and/or local hot spots, and it is much more tolerant to the effects of debonding between the beryllium armor and the copper substrate. Added degrees of freedom allow optimization of the design, including the possibility of operating at very high heat transfer coefficients associated with nucleate boiling, while at the same time providing ample margin against departure from nucleate boiling. Projected pressure drop, pumping power, and maximum operating temperatures are lower than for conventional parallel channel designs

Homogeneous nucleation limit on the bulk formation of metallic glasses

International Nuclear Information System (INIS)

Drehman, A.J.

1983-01-01

Glassy Pd 82 Si 18 spheres, of up to 1 mm diameter, were formed in a drop tube filled with He gas. The largest spheres were successfully cooled to a glass using a cooling rate of less than 800 K/sec. Even at this low cooling rate, crystallization (complete or partial) was the result of heterogeneous nucleation at a high temperature, relative to the temperature at which copious homogeneous nucleation would commence. Bulk underscoring experiments demonstrated that this alloy could be cooled to 385 K below its eutectic melting temperature (1083 K) without the occurrence of crystallization. If heterogeneous nucleation can be avoided, it is estimated that a cooling rate of at most 100 K/sec would be required to form this alloy in the glassy state. Ingots of glassy Pd 40 Ni 40 P 20 were formed from the liquid by cooling at a rate of only 1 K/sec. It was found that glassy samples of this alloy could be heated well above the glass transition temperature without the occurrence of rapid divitrification. This is a result due, in part of the low density of pre-existing nuclei, but, more importantly, due to the low homogeneous nucleation rate and the slow crystal growth kinetics. Based on the observed devitrification kinetics, the steady-state homogeneous nucleation rate is approximately 1 nuclei/cm 3 sec at 590 K (the temperature at which the homogeneous nucleation rate is estimated to be a maximum). Two iron-nickel based glass-forming alloys (Fe 40 Ni 40 P 14 B 6 and Fe 40 Ni 40 B 20 , were not successfully formed into glassy spheres, however, microstructural examination indicates that crystallization was not the result of copious homogeneous nucleation. In contrast, glass forming iron based alloys (Fe 80 B 20 and Fe/sub 79.3/B/sub 16.4/Si/sub 4.0/C/sub 0.3/) exhibit copious homogeneous nucleation when cooled at approximately the same rate

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...

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.

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.

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.)

Characterization of Single Phase and Two Phase Heat and Momentum Transport in a Spiraling Radial Inow Microchannel Heat Sink

Science.gov (United States)

Ruiz, Maritza

as enhancements due to increased buoyant forces on vapor bubbles resulting from centripetal acceleration in the flow which will tend to draw the vapor towards the outlet. This can also aid in the reduction of vapor obstruction of the flow. The flow was identified as transitioning through three regimes as the heat rate was increased: partial subcooled flow boiling, oscillating boiling and fully developed flow boiling. During partial subcooled flow boiling, both forced convective and nucleate boiling effects are important. During oscillating boiling, the system fluctuated between partial subcooled flow boiling and fully developed nucleate boiling. Temperature and pressure oscillations were significant in this regime and are likely due to bubble constriction of flow in the microchannel. This regime of boiling is generally undesirable due to the large oscillations in temperatures and pressure and design constraints should be established to avoid large oscillations from occurring. During fully developed flow boiling, water vapor rapidly leaves the surface and the flow does not sustain large oscillations. Reducing inlet subcooling levels was found to reduce the magnitude of oscillations in the oscillating boiling regime. Additionally, reduced inlet subcooling levels reduced the average surface temperature at the highest heat flux levels tested when heat transfer was dominated by nucleate boiling, yet increased the average surface temperatures at low heat flux levels when heat transfer was dominated by forced convection. Experiments demonstrated heat fluxes up to 301 W/cm. 2at an average surface temperature of 134 deg C under partial subcooled flow boiling conditions. At this peak heat flux, the system required a pumping power to heat rate ratio of 0.01%. This heat flux is 2.4 times the typical values for critical heat flux in pool boiling under similar conditions.

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.

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…

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)

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.

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.

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

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

A Study on the Violent Interactions of an Immiscible Drop impacting on a Superheated Pool

KAUST Repository

Alchalabi, Mohamad

2014-01-01

turning into strong nucleate boiling. The strong nucleate boiling usually starts right upon impact, and when the temperature of the oil at one impact velocity is increased, it starts turning into film boiling, in which the liquid Perfluorohexane is covered by a vapor layer of its own vapor.

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

Dislocation creation and void nucleation in FCC ductile metals under tensile loading: a general microscopic picture.

Science.gov (United States)

Pang, Wei-Wei; Zhang, Ping; Zhang, Guang-Cai; Xu, Ai-Guo; Zhao, Xian-Geng

2014-11-10

Numerous theoretical and experimental efforts have been paid to describe and understand the dislocation and void nucleation processes that are fundamental for dynamic fracture modeling of strained metals. To date an essential physical picture on the self-organized atomic collective motions during dislocation creation, as well as the essential mechanisms for the void nucleation obscured by the extreme diversity in structural configurations around the void nucleation core, is still severely lacking in literature. Here, we depict the origin of dislocation creation and void nucleation during uniaxial high strain rate tensile processes in face-centered-cubic (FCC) ductile metals. We find that the dislocations are created through three distinguished stages: (i) Flattened octahedral structures (FOSs) are randomly activated by thermal fluctuations; (ii) The double-layer defect clusters are formed by self-organized stacking of FOSs on the close-packed plane; (iii) The stacking faults are formed and the Shockley partial dislocations are created from the double-layer defect clusters. Whereas, the void nucleation is shown to follow a two-stage description. We demonstrate that our findings on the origin of dislocation creation and void nucleation are universal for a variety of FCC ductile metals with low stacking fault energies.

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

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

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.

Experimental investigation of heat transfer of R134a in pool boiling on stainless steel and aluminum tubes

Science.gov (United States)

Wengler, C.; Addy, J.; Luke, A.

2018-03-01

Due to high energy demand required for chemical processes, refrigeration and process industries the increase of efficiency and performance of thermal systems especially evaporators is indispensable. One of the possibilities to meet this purpose are investigations in enhancement of the heat transfer in nucleate boiling where high heat fluxes at low superheat are transferred. In the present work, the heat transfer in pool boiling is investigated with pure R134a over wide ranges of reduced pressures and heat fluxes. The heating materials of the test tubes are aluminum and stainless steel. The influence of the thermal conductivity on the heat transfer coefficients is analysed by the surface roughness of sandblasted surfaces. The heat transfer coefficient increases with increasing thermal conductivity, surface roughness and reduced pressures. The experimental results show a small degradation of the heat transfer coefficients between the two heating materials aluminum and stainless steel. In correlation with the VDI Heat Atlas, the experimental results are matching well with the predictions but do not accurately consider the stainless steel material reference properties.

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.)

Letter Report: Progress in developing EQ3/6 for modeling boiling processes

Energy Technology Data Exchange (ETDEWEB)

Wolery, T. J., LLNL

1995-08-28

EQ3/6 is a software package for geochemical modeling of aqueous systems, such as water/rock or waste/water rock. It is being developed for a variety of applications in geochemical studies for the Yucca Mountain Site Characterization Project. The present focus is on development of capabilities to be used in studies of geochemical processes which will take place in the near-field environment and the altered zone of the potential repository. We have completed the first year of a planned two-year effort to develop capabilities for modeling boiling processes. These capabilities will interface with other existing and future modeling capabilities to provide a means of integrating the effects of various kinds of geochemical processes in complex systems. This year, the software has been modified to allow the formation of a generalized gas phase in a closed system for which the temperature and pressure are known (but not necessarily constant). The gas phase forms when its formation is thermodynamically favored; that is, when the system pressure is equal to the sum of the partial pressures of the gas species as computed from their equilibrium fugacities. It disappears when this sum falls below that pressure. `Boiling` is the special case in which the gas phase which forms consists mostly of water vapor. The reverse process is then `condensation.` To support calculations of boiling and condensation, we have added a capability to calculate the fugacity coefficients of gas species in the system H{sub 2}O-CO{sub 2}-CH{sub 4}-H{sub 2},-Awe{sub 2}-N{sub 2},-H{sub 2}S-NH3. This capability at present is accurate only at relatively low pressures, but is adequate for all likely repository boiling conditions. We have also modified the software to calculate changes in enthalpy (heat) and volume functions. Next year we will be extending the boiling capability to calculate the pressure or the temperature at known enthalpy. We will also add an option for open system boiling.

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)

Phospholipid analysis and fractional reconstitution of the ice nucleation protein activity purified from Escherichia coli overexpressing the inaZ gene of Pseudomonas syringae.

Science.gov (United States)

Palaiomylitou, M A; Kalimanis, A; Koukkou, A I; Drainas, C; Anastassopoulos, E; Panopoulos, N J; Ekateriniadou, L V; Kyriakidis, D A

1998-08-01

Ice nucleation protein was partially purified from the membrane fraction of E. coli carrying inaZ from Pseudomonas syringae. The ice nucleation protein was totally localized in the bacterial envelope and was extracted by either salt (0.25 M NH4Cl) or the nonionic detergent Tween 20. The extracted protein was partially purified by sequential passage through DEAE-52 cellulose and Sephacryl-S400 columns. The activity of the purified protein was lost after treatment with phospholipase C, and its activity was subsequently restored by addition of the naturally occurring lipid phosphatidylethanolamine. These results suggest that ice nucleation proteins have a requirement for lipids that reconstitute a physiological hydrophobic environment similar to the one existing in vivo, to attain and maintain a structure that enables ice catalysis. Copyright 1998 Academic Press.

Influence of a flow obstacle on the occurrence of burnout in boiling two-phase upward flow within a vertical annular channel

Energy Technology Data Exchange (ETDEWEB)

Mori, S.; Fukano, T. E-mail: fukanot@mech.kyushu-u.ac.jp

2003-10-01

When a flow obstruction such as a cylindrical spacer is set in a boiling two-phase flow within an annular channel, the inner tube of which is used as a heater, the temperature on the surface of the heating tube is severely affected by its existence. In some cases, the cylindrical spacer has a cooling effect, and in the other cases it causes the dryout of the cooling water film on the heating surface resulting in the burnout of the heating tube. In the present paper, we have focused our attention on the influence of a flow obstacle on the occurrence of burnout of the heating tube in boiling two-phase flow. The results are summarized as follows: - When the heat flux approaches the burnout condition, the wall temperature on the heating tube fluctuates with a large amplitude. And once the wall temperature exceeds the Leidenfrost temperature, the burnout occurs without exception. - The trigger of dryout of the water film which causes the burnout is not the nucleate boiling but the evaporation of the base film between disturbance waves. - The burnout never occurs at the downstream side of the spacer. This is because the dryout area downstream of the spacer is rewetted easily by the disturbance waves.

Phase field model for the study of boiling; Modele de champ de phase pour l'etude de l'ebullition

Energy Technology Data Exchange (ETDEWEB)

Ruyer, P

2006-07-15

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)

Influence of a flow obstacle on the occurrence of burnout in boiling two-phase upward flow within a vertical annular channel

International Nuclear Information System (INIS)

Mori, S.; Fukano, T.

2003-01-01

When a flow obstruction such as a cylindrical spacer is set in a boiling two-phase flow within an annular channel, the inner tube of which is used as a heater, the temperature on the surface of the heating tube is severely affected by its existence. In some cases, the cylindrical spacer has a cooling effect, and in the other cases it causes the dryout of the cooling water film on the heating surface resulting in the burnout of the heating tube. In the present paper, we have focused our attention on the influence of a flow obstacle on the occurrence of burnout of the heating tube in boiling two-phase flow. The results are summarized as follows: - When the heat flux approaches the burnout condition, the wall temperature on the heating tube fluctuates with a large amplitude. And once the wall temperature exceeds the Leidenfrost temperature, the burnout occurs without exception. - The trigger of dryout of the water film which causes the burnout is not the nucleate boiling but the evaporation of the base film between disturbance waves. - The burnout never occurs at the downstream side of the spacer. This is because the dryout area downstream of the spacer is rewetted easily by the disturbance waves

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

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…

Experiments of Pool Boiling Performance (Boiling Heat Transfer and Critical Heat Flux) on Designed Micro-Structures

International Nuclear Information System (INIS)

Kim, Seol Ha; Kang, Jun Young; Lee, Gi Chol; Kiyofumia, Moriyama; Kim, Moo Hwan; Park, Hyun Sun

2015-01-01

In general, the evaluation of the boiling performance mainly focuses on two physical parameters: boiling heat transfer (BHT) and critical heat flux (CHF). In the nuclear power plants, both BHT and CHF contribute the nuclear system efficiency and safety, respectively. In this study, BHT and CHF of the pool boiling on well-organized fabricated structured (micro scaled) surface has been evaluated. As a results, BHT change on microstructured surface shows strongly dependent on Pin-fin effect analysis. In terms of CHF, critical size of micro structure for CHF enhancement has been observed and analyzed based on the capillary wicking effect. In this study, BHT and CHF of the pool boiling on well-organized fabricated structured (micro scaled) surface has been evaluated. As a results, BHT change on microstructured surface shows strongly dependent on the roughness ratio. The extended heat transfer area contributes the boiling heat transfer increase on the structured surface, and its quantitative analysis has been performed. In terms of CHF, the critical size of micro structure for CHF enhancement has been observed and analyzed based on the capillary wicking effect. We suggested a capillary limit to CHF delay for modeling capillary induced liquid inflow through microstructured surfaces. The critical size of the capillary limit on the prepared structured surface, determined by a model, could be reasonable explanation points for the experimental results (optimal size for CHF delay). The present experimental results also showed clearly the critical size (10 - 20 μm) for CHF delay, predicted by capillary limit analysis. This study provides fundamental insight into BHT and CHF enhancement of structured surfaces, and an optimal design guide for the required CHF and boiling heat-transfer performance. Finally, this study can contribute the basic understanding of the boiling on designed microstructure surface, and it also suggest the optimal micro scaled structured surface of boiling

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

Droplet and bubble nucleation modeled by density gradient theory – cubic equation of state versus saft model

Directory of Open Access Journals (Sweden)

Hrubý Jan

2012-04-01

Full Text Available The study presents some preliminary results of the density gradient theory (GT combined with two different equations of state (EoS: the classical cubic equation by van der Waals and a recent approach based on the statistical associating fluid theory (SAFT, namely its perturbed-chain (PC modification. The results showed that the cubic EoS predicted for a given surface tension the density profile with a noticeable defect. Bulk densities predicted by the cubic EoS differed as much as by 100 % from the reference data. On the other hand, the PC-SAFT EoS provided accurate results for density profile and both bulk densities in the large range of temperatures. It has been shown that PC-SAFT is a promising tool for accurate modeling of nucleation using the GT. Besides the basic case of a planar phase interface, the spherical interface was analyzed to model a critical cluster occurring either for nucleation of droplets (condensation or bubbles (boiling, cavitation. However, the general solution for the spherical interface will require some more attention due to its numerical difficulty.

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

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)

Hydrogen or Soot?: Partial Oxidation of High-boiling Hydrocarbon Wastes

Czech Academy of Sciences Publication Activity Database

Lederer, J.; Hanika, Jiří; Nečesaný, F.; Poslední, W.; Tukač, V.; Veselý, Václav

2015-01-01

Roč. 29, č. 1 (2015), s. 5-11 ISSN 0352-9568 Institutional support: RVO:67985858 Keywords : partial oxidation * waste * hydrocarbon Subject RIV: CI - Industrial Chemistry, Chemical Engineering Impact factor: 0.675, year: 2015

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)

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.

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.

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.

Using the thermal diffusion cloud chamber to study the ion-induced nucleation by radon decay

International Nuclear Information System (INIS)

Wu, Yefei.

1991-01-01

Thermal diffusion cloud chamber is steady-state device and has been extensively used for nucleation research. In order to study the ion-induced nucleation by radon decay, a new chamber was designed with improved both upper and bottom plates, the system of circulating fluid, the gasketting, the temperature measurement and the insulation. An alternative method of using oxygen as carrier gas was examined. Therefore, the heavy carrier gas including nitrogen, oxygen, neon, argon and air can be used to study radon radiolysis-induced nucleation for the water or organic compounds in the TDCC. The effects of the pressure and temperature ranges on the density, supersaturation, temperature and partial pressure profile for the water-oxygen-helium in the TDCC have been examined. Based on the classical theory, the rate profile of ion-induced nucleation by radon decays was calculated and compared with the homogeneous nucleation. From measured indoor concentrations of Volatile Organic Compounds (VOC), thermodynamic theory models were used to assess the possibility that these compounds will form ultrafine particles in indoor air by ion-induced nucleation. The energy, number of molecules and equilibrium radius of clusters have been calculated based on Such and Thomson theories. These two sets of values have been compared. Ion cluster radii corresponding to 1--3 VOC molecules are in range of 3--5 x 10 -8 cm. 43 refs., 18 figs., 5 tabs

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

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

A one-dimensional semi-empirical model considering transition boiling effect for dispersed flow film boiling

Energy Technology Data Exchange (ETDEWEB)

Wang, Yu-Jou [Institute of Nuclear Engineering and Science, National Tsing Hua University, Hsinchu 30013, Taiwan, ROC (China); Pan, Chin, E-mail: cpan@ess.nthu.edu.tw [Institute of Nuclear Engineering and Science, National Tsing Hua University, Hsinchu 30013, Taiwan, ROC (China); Department of Engineering and System Science, National Tsing Hua University, Hsinchu 30013, Taiwan, ROC (China); Low Carbon Energy Research Center, National Tsing Hua University, Hsinchu 30013, Taiwan, ROC (China)

2017-05-15

Highlights: • Seven heat transfer mechanisms are studied numerically by the model. • A semi-empirical method is proposed to account for the transition boiling effect. • The parametric effects on the heat transfer mechanisms are investigated. • The thermal non-equilibrium phenomenon between vapor and droplets is investigated. - Abstract: The objective of this paper is to develop a one-dimensional semi-empirical model for the dispersed flow film boiling considering transition boiling effects. The proposed model consists of conservation equations, i.e., vapor mass, vapor energy, droplet mass and droplet momentum conservation, and a set of closure relations to address the interactions among wall, vapor and droplets. The results show that the transition boiling effect is of vital importance in the dispersed flow film boiling regime, since the flowing situation in the downstream would be influenced by the conditions in the upstream. In addition, the present paper, through evaluating the vapor temperature and the amount of heat transferred to droplets, investigates the thermal non-equilibrium phenomenon under different flowing conditions. Comparison of the wall temperature predictions with the 1394 experimental data in the literature, the present model ranging from system pressure of 30–140 bar, heat flux of 204–1837 kW/m{sup 2} and mass flux of 380–5180 kg/m{sup 2} s, shows very good agreement with RMS of 8.80% and standard deviation of 8.81%. Moreover, the model well depicts the thermal non-equilibrium phenomenon for the dispersed flow film boiling.

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.

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)

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).

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.

Measurement of key pool boiling parameters in nanofluids for nuclear applications

International Nuclear Information System (INIS)

Bang, In Cheol; Buongiorno, Jacopo; Hu, Lin-Wen; Wang, Hsin

2008-01-01

Nanofluids, colloidal dispersions of nanoparticles in a base fluid such as water, can afford very significant Critical Heat Flux (CHF) enhancement. Such engineered fluids potentially could be employed in reactors as advanced coolants in safety systems with significant safety and economic advantages. However, a satisfactory explanation of the CHF enhancement mechanism in nanofluids is lacking. To close this gap, we have identified the important boiling parameters to be measured. These are the properties (e.g., density, viscosity, thermal conductivity, specific heat, vaporization enthalpy, surface tension), hydrodynamic parameters (i.e., bubble size, bubble velocity, departure frequency, hot/dry spot dynamics) and surface conditions (i.e., contact angle, nucleation site density). We have also deployed a pool boiling facility in which many such parameters can be measured. The facility is equipped with a thin indium-tin-oxide heater deposited over a sapphire substrate. An infra-red high-speed camera and an optical probe are used to measure the temperature distribution on the heater and the hydrodynamics above the heater, respectively. The first data generated with this facility already provide some clue on the CHF enhancement mechanism in nanofluids. Specifically, the progression to burnout in a pure fluid (ethanol in this case) is characterized by a smoothly-shaped and steadily-expanding hot spot. By contrast, in the ethanol-based nanofluid the hot spot pulsates and the progression to burnout lasts longer, although the nanofluid CHF is higher than the pure fluid CHF. The presence of a nanoparticle deposition layer on the heater surface seems to enhance wettability and aid hot spot dissipation, thus delaying burnout. (author)

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

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.

PSI-BOIL, a building block towards the multi-scale modeling of flow boiling phenomena

International Nuclear Information System (INIS)

Niceno, Bojan; Andreani, Michele; Prasser, Horst-Michael

2008-01-01

Full text of publication follows: In these work we report the current status of the Swiss project Multi-scale Modeling Analysis (MSMA), jointly financed by PSI and Swissnuclear. The project aims at addressing the multi-scale (down to nano-scale) modelling of convective boiling phenomena, and the development of physically-based closure laws for the physical scales appropriate to the problem considered, to be used within Computational Fluid Dynamics (CFD) codes. The final goal is to construct a new computational tool, called Parallel Simulator of Boiling phenomena (PSI-BOIL) for the direct simulation of processes all the way down to the small-scales of interest and an improved CFD code for the mechanistic prediction of two-phase flow and heat transfer in the fuel rod bundle of a nuclear reactor. An improved understanding of the physics of boiling will be gained from the theoretical work as well as from novel small- and medium scale experiments targeted to assist the development of closure laws. PSI-BOIL is a computer program designed for efficient simulation of turbulent fluid flow and heat transfer phenomena in simple geometries. Turbulence is simulated directly (DNS) and its efficiency plays a vital role in a successful simulation. Having high performance as one of the main prerequisites, PSIBOIL is tailored in such a way to be as efficient a tool as possible, relying on well-established numerical techniques and sacrificing all the features which are not essential for the success of this project and which might slow down the solution procedure. The governing equations are discretized in space with orthogonal staggered finite volume method. Time discretization is performed with projection method, the most obvious a the most widely used choice for DNS. Systems of linearized equation, stemming from the discretization of governing equations, are solved with the Additive Correction Multigrid (ACM). methods. Two distinguished features of PSI-BOIL are the possibility to

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.

Determination of heat transfer coefficients in plastic French straws plunged in liquid nitrogen.

Science.gov (United States)

Santos, M Victoria; Sansinena, M; Chirife, J; Zaritzky, N

2014-12-01

The knowledge of the thermodynamic process during the cooling of reproductive biological systems is important to assess and optimize the cryopreservation procedures. The time-temperature curve of a sample immersed in liquid nitrogen enables the calculation of cooling rates and helps to determine whether it is vitrified or undergoes phase change transition. When dealing with cryogenic liquids, the temperature difference between the solid and the sample is high enough to cause boiling of the liquid, and the sample can undergo different regimes such as film and/or nucleate pool boiling. In the present work, the surface heat transfer coefficients (h) for plastic French straws plunged in liquid nitrogen were determined using the measurement of time-temperature curves. When straws filled with ice were used the cooling curve showed an abrupt slope change which was attributed to the transition of film into nucleate pool boiling regime. The h value that fitted each stage of the cooling process was calculated using a numerical finite element program that solves the heat transfer partial differential equation under transient conditions. In the cooling process corresponding to film boiling regime, the h that best fitted experimental results was h=148.12±5.4 W/m(2) K and for nucleate-boiling h=1355±51 W/m(2) K. These values were further validated by predicting the time-temperature curve for French straws filled with a biological fluid system (bovine semen-extender) which undergoes freezing. Good agreement was obtained between the experimental and predicted temperature profiles, further confirming the accuracy of the h values previously determined for the ice-filled straw. These coefficients were corroborated using literature correlations. The determination of the boiling regimes that govern the cooling process when plunging straws in liquid nitrogen constitutes an important issue when trying to optimize cryopreservation procedures. Furthermore, this information can lead to

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.

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

Ice nucleation in sulfuric acid/organic aerosols: implications for cirrus cloud formation

Directory of Open Access Journals (Sweden)

M. R. Beaver

2006-01-01

Full Text Available Using an aerosol flow tube apparatus, we have studied the effects of aliphatic aldehydes (C3 to C10 and ketones (C3 and C9 on ice nucleation in sulfuric acid aerosols. Mixed aerosols were prepared by combining an organic vapor flow with a flow of sulfuric acid aerosols over a small mixing time (~60 s at room temperature. No acid-catalyzed reactions were observed under these conditions, and physical uptake was responsible for the organic content of the sulfuric acid aerosols. In these experiments, aerosol organic content, determined by a Mie scattering analysis, was found to vary with the partial pressure of organic, the flow tube temperature, and the identity of the organic compound. The physical properties of the organic compounds (primarily the solubility and melting point were found to play a dominant role in determining the inferred mode of nucleation (homogenous or heterogeneous and the specific freezing temperatures observed. Overall, very soluble, low-melting organics, such as acetone and propanal, caused a decrease in aerosol ice nucleation temperatures when compared with aqueous sulfuric acid aerosol. In contrast, sulfuric acid particles exposed to organic compounds of eight carbons and greater, of much lower solubility and higher melting temperatures, nucleate ice at temperatures above aqueous sulfuric acid aerosols. Organic compounds of intermediate carbon chain length, C4-C7, (of intermediate solubility and melting temperatures nucleated ice at the same temperature as aqueous sulfuric acid aerosols. Interpretations and implications of these results for cirrus cloud formation are discussed.

A nanoscale temperature-dependent heterogeneous nucleation theory

International Nuclear Information System (INIS)

Cao, Y. Y.; Yang, G. W.

2015-01-01

Classical nucleation theory relies on the hypothetical equilibrium of the whole nucleation system, and neglects the thermal fluctuations of the surface; this is because the high entropic gains of the (thermodynamically extensive) surface would lead to multiple stable states. In fact, at the nanometer scale, the entropic gains of the surface are high enough to destroy the stability of the thermal equilibrium during nucleation, comparing with the whole system. We developed a temperature-dependent nucleation theory to elucidate the heterogeneous nucleation process, by considering the thermal fluctuations based on classical nucleation theory. It was found that the temperature not only affected the phase transformation, but also influenced the surface energy of the nuclei. With changes in the Gibbs free energy barrier, nucleation behaviors, such as the nucleation rate and the critical radius of the nuclei, showed temperature-dependent characteristics that were different from those predicted by classical nucleation theory. The temperature-dependent surface energy density of a nucleus was deduced based on our theoretical model. The agreement between the theoretical and experimental results suggested that the developed nucleation theory has the potential to contribute to the understanding and design of heterogeneous nucleation at the nanoscale

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

Little low-power boiling never hurt anybody

International Nuclear Information System (INIS)

Dunn, F.E.

1985-01-01

Failures in the shutdown heat removal system of an LMFBR might lead to flow stagnation and coolant boiling in the reactor core. At normal operating power, the onset of sodium boiling will lead to film dryout and melting of the cladding and fuel within a few seconds. On the other hand, both calculations and currently available experimental data indicate that at heat fluxes corresponding to decay heat power levels, boiling leads to improved heat removal; and it limits the temperature rise in the fuel pins. Therefore, when setting safety criteria for decay heat removal systems, there is no reason to preclude sodium boiling per se because of heat removal considerations. As an example that illustrates the beneficial impact of coolant boiling, a case involving temporary loss of feedwater and staggered pump failures in a hypothetical, 1000-MWe loop-type reactor was run in the SASSYS-1 code

Flow dynamics of volume-heated boiling pools

International Nuclear Information System (INIS)

Ginsberg, T.; Jones, O.C.; Chen, J.C.

1979-01-01

Safety analyses of fast breeder reactors require understanding of the two-phase fluid dynamic and heat transfer characteristics of volume-heated boiling pool systems. Design of direct contact three-phase boilers, of practical interest in the chemical industries also requires understanding of the fundamental two-phase flow and heat transfer behavior of volume boiling systems. Several experiments have been recently reported relevant to the boundary heat-loss mechanisms of boiling pool systems. Considerably less is known about the two-phase fluid dynamic behavior of such systems. This paper describes an experimental investigation of the steady-state flow dynamics of volume-heated boiling pool systems

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

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

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.

Pressurized water reactor fuel performance problems connected with fuel cladding corrosion processes

International Nuclear Information System (INIS)

Dobrevski, I.; Zaharieva, N.

2008-01-01

Generally, Pressurized Water Reactor (WWER, PWR) Fuel Element Performance is connected with fuel cladding corrosion and crud deposition processes. By transient to extended fuel cycles in nuclear power reactors, aiming to achieve higher burnup and better fuel utilization, the role of these processes increases significantly. This evolution modifies the chemical and electrochemical conditions in the reactor primary system, including change of fuel claddings' environment. The higher duty cores are always attended with increased boiling (sub-cooled nucleate boiling) mainly on the feed fuel assemblies. This boiling process on fuel cladding surfaces can cause different consequences on fuel element cladding's environment characteristics. In the case of boiling at the cladding surfaces without or with some cover of corrosion product deposition, the behavior of gases dissolved in water phase is strongly influenced by the vapor generation. The increase of vapor partial pressure will reduce the partial pressures of dissolved gases and will cause their stripping out. By these circumstances the concentrations of dissolved gases in cladding wall water layer can dramatically decrease, including also the case by which all dissolved gases to be stripped out. On the other hand it is known that the hydrogen is added to primary coolant in order to avoid the production of oxidants by radiolysis of water. It is clear that if boiling strips out dissolved hydrogen, the creation of oxidizing conditions at the cladding surfaces will be favored. In this case the local production of oxidants will be a result from local processes of water radiolysis, by which not only both oxygen (O 2 ) and hydrogen (H 2 ) but also hydrogen peroxide (H 2 O 2 ) will be produced. While these hydrogen and oxygen will be stripped out preferentially by boiling, the bigger part of hydrogen peroxide will remain in wall water phase and will act as the most important factor for creation of oxidizing conditions in fuel

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

Two-phase wall function for modeling of turbulent boundary layer in subcooled boiling flow

International Nuclear Information System (INIS)

Bostjan Koncar; Borut Mavko; Yassin A Hassan

2005-01-01

Full text of publication follows: The heat transfer and phase-change mechanisms in the subcooled flow boiling are governed mainly by local multidimensional mechanisms near the heated wall, where bubbles are generated. The structure of such 'wall boiling flow' is inherently non-homogeneous and is further influenced by the two-phase flow turbulence, phase-change effects in the bulk, interfacial forces and bubble interactions (collisions, coalescence, break-up). In this work the effect of two-phase flow turbulence on the development of subcooled boiling flow is considered. Recently, the modeling of two-phase flow turbulence has been extensively investigated. A notable progress has been made towards deriving reliable models for description of turbulent behaviour of continuous (liquid) and dispersed phase (bubbles) in the bulk flow. However, there is a lack of investigation considering the modeling of two-phase flow boundary layer. In most Eulerian two-fluid models standard single-phase wall functions are used for description of turbulent boundary layer of continuous phase. That might be a good approximation at adiabatic flows, but their use for boundary layers with high concentration of dispersed phase is questionable. In this work, the turbulent boundary layer near the heated wall will be modeled with the so-called 'two-phase' wall function, which is based on the assumption of additional turbulence due to bubble-induced stirring in the boundary layer. In the two-phase turbulent boundary layer the wall function coefficients strongly depend on the void fraction. Moreover, in the turbulent boundary layer with nucleating bubbles, the bubble size variation also has a significant impact on the liquid phase. As a basis, the wall function of Troshko and Hassan (2001), developed for adiabatic bubbly flows will be used. The simulations will be performed by a general-purpose CFD code CFX-4.4 using additional models provided by authors. The results will be compared to the boiling

Procedures and instrumentation for sodium boiling experiments in EBR-II

International Nuclear Information System (INIS)

Crowe, R.D.

1976-01-01

The development of instrumentation capable of detecting localized coolant boiling in a liquid metal cooled breeder reactor (LMFBR) has a high priority in fast reactor safety. The detection must be rapid enough to allow corrective action to be taken before significant damage occurs to the core. To develop and test a method of boiling detection, it is desirable to produce boiling in a reactor and thereby introduce a condition in the reactor the original design concepts were chosen to preclude. The proposed boiling experiments are designed to safely produce boiling in the subassembly of a fast reactor and provide the information to develop boiling detection instrumentation without core damage or safety compromise. The experiment consists of the operation of two separate subassemblies, first, a gamma heated boiling subassembly which produces non-typical but highly conservative boiling and then a fission heated subassembly which simulates a prototypical boiling event. The two boiling subassemblies are designed to operate in the instrumentation subassembly test facility (INSAT) of Experiment Breeder Reactor II

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

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)

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.

MD simulation of plastic deformation nucleation in stressed crystallites under irradiation

Energy Technology Data Exchange (ETDEWEB)

Korchuganov, A. V., E-mail: avkor@ispms.tsc.ru; Zolnikov, K. P., E-mail: kost@ispms.tsc.ru; Kryzhevich, D. S., E-mail: kryzhev@ispms.tsc.ru [Russian Academy of Sciences, Institute of Strength Physics and Materials Science, Siberian Branch (Russian Federation); Chernov, V. M., E-mail: VMChernov@bochvar.ru [National Research Tomsk State University (Russian Federation); Psakhie, S. G., E-mail: sp@ispms.tsc.ru [Russian Academy of Sciences, Institute of Strength Physics and Materials Science, Siberian Branch (Russian Federation)

2016-12-15

The investigation of plastic deformation nucleation in metals and alloys under irradiation and mechanical loading is one of the topical issues of materials science. Specific features of nucleation and evolution of the defect system in stressed and irradiated iron, vanadium, and copper crystallites were studied by molecular dynamics simulation. Mechanical loading was performed in such a way that the modeled crystallite volume remained unchanged. The energy of the primary knock-on atom initiating a cascade of atomic displacements in a stressed crystallite was varied from 0.05 to 50 keV. It was found that atomic displacement cascades might cause global structural transformations in a region far larger than the radiation-damaged area. These changes are similar to the ones occurring in the process of mechanical loading of samples. They are implemented by twinning (in iron and vanadium) or through the formation of partial dislocation loops (in copper).

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

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.

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

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

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...

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

Boiling points of halogenated aliphatic compounds: a quantitative structure-property relationship for prediction and validation.

Science.gov (United States)

Oberg, Tomas

2004-01-01

Halogenated aliphatic compounds have many technical uses, but substances within this group are also ubiquitous environmental pollutants that can affect the ozone layer and contribute to global warming. The establishment of quantitative structure-property relationships is of interest not only to fill in gaps in the available database but also to validate experimental data already acquired. The three-dimensional structures of 240 compounds were modeled with molecular mechanics prior to the generation of empirical descriptors. Two bilinear projection methods, principal component analysis (PCA) and partial-least-squares regression (PLSR), were used to identify outliers. PLSR was subsequently used to build a multivariate calibration model by extracting the latent variables that describe most of the covariation between the molecular structure and the boiling point. Boiling points were also estimated with an extension of the group contribution method of Stein and Brown.

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.

Homogeneous ice nucleation from aqueous inorganic/organic particles representative of biomass burning: water activity, freezing temperatures, nucleation rates.

Science.gov (United States)

Knopf, Daniel A; Rigg, Yannick J

2011-02-10

Homogeneous ice nucleation plays an important role in the formation of cirrus clouds with subsequent effects on the global radiative budget. Here we report on homogeneous ice nucleation temperatures and corresponding nucleation rate coefficients of aqueous droplets serving as surrogates of biomass burning aerosol. Micrometer-sized (NH(4))(2)SO(4)/levoglucosan droplets with mass ratios of 10:1, 1:1, 1:5, and 1:10 and aqueous multicomponent organic droplets with and without (NH(4))(2)SO(4) under typical tropospheric temperatures and relative humidities are investigated experimentally using a droplet conditioning and ice nucleation apparatus coupled to an optical microscope with image analysis. Homogeneous freezing was determined as a function of temperature and water activity, a(w), which was set at droplet preparation conditions. The ice nucleation data indicate that minor addition of (NH(4))(2)SO(4) to the aqueous organic droplets renders the temperature dependency of water activity negligible in contrast to the case of aqueous organic solution droplets. The mean homogeneous ice nucleation rate coefficient derived from 8 different aqueous droplet compositions with average diameters of ∼60 μm for temperatures as low as 195 K and a(w) of 0.82-1 is 2.18 × 10(6) cm(-3) s(-1). The experimentally derived freezing temperatures and homogeneous ice nucleation rate coefficients are in agreement with predictions of the water activity-based homogeneous ice nucleation theory when taking predictive uncertainties into account. However, the presented ice nucleation data indicate that the water activity-based homogeneous ice nucleation theory overpredicts the freezing temperatures by up to 3 K and corresponding ice nucleation rate coefficients by up to ∼2 orders of magnitude. A shift of 0.01 in a(w), which is well within the uncertainty of typical field and laboratory relative humidity measurements, brings experimental and predicted freezing temperatures and homogeneous ice

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.

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.

Signal processing techniques for sodium boiling noise detection

International Nuclear Information System (INIS)

1989-05-01

At the Specialists' Meeting on Sodium Boiling Detection organized by the International Working Group on Fast Reactors (IWGFR) of the International Atomic Energy Agency at Chester in the United Kingdom in 1981 various methods of detecting sodium boiling were reported. But, it was not possible to make a comparative assessment of these methods because the signal condition in each experiment was different from others. That is why participants of this meeting recommended that a benchmark test should be carried out in order to evaluate and compare signal processing methods for boiling detection. Organization of the Co-ordinated Research Programme (CRP) on signal processing techniques for sodium boiling noise detection was also recommended at the 16th meeting of the IWGFR. The CRP on Signal Processing Techniques for Sodium Boiling Noise Detection was set up in 1984. Eight laboratories from six countries have agreed to participate in this CRP. The overall objective of the programme was the development of reliable on-line signal processing techniques which could be used for the detection of sodium boiling in an LMFBR core. During the first stage of the programme a number of existing processing techniques used by different countries have been compared and evaluated. In the course of further work, an algorithm for implementation of this sodium boiling detection system in the nuclear reactor will be developed. It was also considered that the acoustic signal processing techniques developed for boiling detection could well make a useful contribution to other acoustic applications in the reactor. This publication consists of two parts. Part I is the final report of the co-ordinated research programme on signal processing techniques for sodium boiling noise detection. Part II contains two introductory papers and 20 papers presented at four research co-ordination meetings since 1985. A separate abstract was prepared for each of these 22 papers. Refs, figs and tabs

Physical insight in the burnout region of water-subcooled flow boiling

International Nuclear Information System (INIS)