WorldWideScience

Sample records for boiling heat transfer

  1. Nucleate boiling heat transfer

    Energy Technology Data Exchange (ETDEWEB)

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

    2009-07-01

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

  2. Enhanced heat transfer in confined pool boiling

    NARCIS (Netherlands)

    Rops, C.M.; Lindken, R.; Velthuis, J.F.M.; Westerweel, J.

    2009-01-01

    We report the results of an experimental investigation of the heat transfer during nucleate boiling on a spatially confined boiling surface. The heat flux as a function of the boiling surface temperature was measured in pool boiling pots with diameters ranging from 15 mm down to 4.5 mm. It was found

  3. Boiling Heat Transfer to Halogenated Hydrocarbon Refrigerants

    Science.gov (United States)

    Yoshida, Suguru; Fujita, Yasunobu

    The current state of knowledge on heat transfer to boiling refrigerants (halogenated hydrocarbons) in a pool and flowing inside a horizontal tube is reviewed with an emphasis on information relevant to the design of refrigerant evaporators, and some recommendations are made for future research. The review covers two-phase flow pattern, heat transfer characteristics, correlation of heat transfer coefficient, influence of oil, heat transfer augmentation, boiling from tube-bundle, influence of return bend, burnout heat flux, film boiling, dryout and post-dryout heat transfer.

  4. Heat transfer coefficient for boiling carbon dioxide

    DEFF Research Database (Denmark)

    Knudsen, Hans Jørgen Høgaard; Jensen, Per Henrik

    1998-01-01

    Heat transfer coefficient and pressure drop for boiling carbon dioxide (R744) flowing in a horizontal pipe has been measured. The calculated heat transfer coeeficient has been compared with the Chart correlation of Shah. The Chart Correlation predits too low heat transfer coefficient but the ratio...

  5. Heat transfer coeffcient for boiling carbon dioxide

    DEFF Research Database (Denmark)

    Knudsen, Hans Jørgen Høgaard; Jensen, Per Henrik

    1997-01-01

    Heat transfer coefficient and pressure drop for boiling carbon dioxide (R744) flowing in a horizontal pipe has been measured. The pipe is heated by condensing R22 outside the pipe. The heat input is supplied by an electrical heater wich evaporates the R22. With the heat flux assumed constant over...

  6. Thermodynamics of Flow Boiling Heat Transfer

    Science.gov (United States)

    Collado, F. J.

    2003-05-01

    Convective boiling in sub-cooled water flowing through a heated channel is essential in many engineering applications where high heat flux needs to be accommodated. It has been customary to represent the heat transfer by the boiling curve, which shows the heat flux versus the wall-minus-saturation temperature difference. However it is a rather complicated problem, and recent revisions of two-phase flow and heat transfer note that calculated values of boiling heat transfer coefficients present many uncertainties. Quite recently, the author has shown that the average thermal gap in the heated channel (the wall temperature minus the average temperature of the coolant) was tightly connected with the thermodynamic efficiency of a theoretical reversible engine placed in this thermal gap. In this work, whereas this correlation is checked again with data taken by General Electric (task III) for water at high pressure, a possible connection between this wall efficiency and the reversible-work theorem is explored.

  7. Boiling Heat Transfer in Circulating Fluidized Beds

    Institute of Scientific and Technical Information of China (English)

    张利斌; 李修伦

    2001-01-01

    A model is proposed to predict boiling heat transfer coefficient in a three-phase circulating fluidized bed (CFB), which is a new type of evaporation boiling means for enhancing heat transfer and preventing fouling. To verify the model, experiments are conducted in a stainless steel column with 39 mm ID and 2.0 m height, in which the heat transfer coefficient is measured for different superficial velocities, steam pressures, particle concentrations and materials of particle. As the steam pressure and particle concentrations increase, the heat transfer coefficient in the bed increases. The heat transfer coefficient increases with the liquid velocity but it exhibits a local minimum.The heat transfer coefficient is correlated with cluster renewed model and two-mechanism method. The prediction of the model is in good agreement with experimental data.

  8. Boiling Heat Transfer in Circulating Fluidized Beds

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    A model is proposed to predict boiling heat transfer coefficient in a three-phase circulating fluidized bed (CFB), which is a new type of evaporation boiling means for enhancing heat transfer and preventing fouling. To verify the model, experiments are conducted in a stainless steel column with 39mm ID and 2.0m height, in which the heat transfer coefficient is measured for different superficial velocities, steam pressures, particle concentrations and materials of particle. As the steam pressure and particle concentrations increase, the heat transfer coefficient in the bed increases. The heat transfer coefficient increases with the liquid velocity but it exhibits a local minimum. The heat transfer coefficient is correlated with cluster renewed model and two-mechanism method. The prediction of the model is in good agreement with experimental data.

  9. Pool Boiling Heat Transfer on structured Surfaces

    Science.gov (United States)

    Addy, J.; Olbricht, M.; Müller, B.; Luke, A.

    2016-09-01

    The development in the process and energy sector shows the importance of efficient utilization of available resources to improve thermal devices. To achieve this goal, all thermal components have to be optimized continuously. Various applications of multi-phase heat and mass transfer have to be improved. Therefore, the heat transfer and the influence of surface roughness in nucleate boiling with the working fluid propane is experimentally investigated on structured mild steel tubes, because only few data are available in the literature. The mild steel tube is sandblasted to obtain different surface roughness. The measurements are carried out over wide ranges of heat flux and pressure. The experimental results are compared with correlations from literature and the effect of surface roughness on the heat transfer is discussed. It is shown that the heat transfer coefficient increases with increasing surface roughness, heat flux and reduced pressure at nucleate pool boiling.

  10. Boiling heat transfer modern developments and advances

    CERN Document Server

    Lahey, Jr, RT

    2013-01-01

    This volume covers the modern developments in boiling heat transfer and two-phase flow, and is intended to provide industrial, government and academic researchers with state-of-the-art research findings in the area of multiphase flow and heat transfer technology. Special attention is given to technology transfer, indicating how recent significant results may be used for practical applications. The chapters give detailed technical material that will be useful to engineers and scientists who work in the field of multiphase flow and heat transfer. The authors of all chapters are members of the

  11. Flow boiling heat transfer in circulating fluidized bed

    Institute of Scientific and Technical Information of China (English)

    Xiaoguang REN; Jiangdong ZHENG; Sefiane KHELLII; Arumemi-Ikhide MICHAEL

    2009-01-01

    In order to enhance heat transfer and mitigate contamination in the boiling processes, a new type of vapor-liquid-solid (3-phase) circulating fluidized bed boil-ing system has been designed, combining a circulating fluidized bed with boiling heat transfer. Experimental results show an enhancement of the boiling curve. Flow visualization studies concerning flow hydrodynamics within the riser column are also conducted whose results are presented and discussed.

  12. Unsteady heat transfer during subcooled film boiling

    Science.gov (United States)

    Yagov, V. V.; Zabirov, A. R.; Lexin, M. A.

    2015-11-01

    Cooling of high-temperature bodies in subcooled liquid is of importance for quenching technologies and also for understanding the processes initiating vapor explosion. An analysis of the available experimental information shows that the mechanisms governing heat transfer in these processes are interpreted ambiguously; a more clear-cut definition of the Leidenfrost temperature notion is required. The results of experimental observations (Hewitt, Kenning, and previous investigations performed by the authors of this article) allow us to draw a conclusion that there exists a special mode of intense heat transfer during film boil- ing of highly subcooled liquid. For revealing regularities and mechanisms governing intense transfer of energy in this process, specialists of Moscow Power Engineering Institute's (MPEI) Department of Engineering Thermal Physics conduct systematic works aimed at investigating the cooling of high-temperature balls made of different metals in water with a temperature ranging from 20 to 100°C. It has been determined that the field of temperatures that takes place in balls with a diameter of more than 30 mm in intense cooling modes loses its spherical symmetry. An approximate procedure for solving the inverse thermal conductivity problem for calculating the heat flux density on the ball surface is developed. During film boiling, in which the ball surface temperature is well above the critical level for water, and in which liquid cannot come in direct contact with the wall, the calculated heat fluxes reach 3-7 MW/m2.

  13. Heat transfer mechanisms in microgravity flow boiling.

    Science.gov (United States)

    Ohta, Haruhiko

    2002-10-01

    The objective of this paper is to clarify the mechanisms of heat transfer and dryout phenomena in flow boiling under microgravity conditions. Liquid-vapor behavior in annular flow, encountered in the moderate quality region, has extreme significance for practical application in space. To clarify the gravity effect on the heat transfer observed for an upward flow in a tube, the research described here started from the measurement of pressure drop for binary gas-liquid mixture under various gravity conditions. The shear stress acting on the surface of the annular liquid film was correlated by an empirical method. Gravity effects on the heat transfer due to two-phase forced convection were investigated by the analysis of velocity and temperature profiles in the film. The results reproduce well the trends of heat transfer coefficients varying with the gravity level, quality, and mass velocity. Dryout phenomena in the moderate quality region were observed in detail by the introduction of a transparent heated tube. At heat fluxes just lower and higher than CHF value, a transition of the heat transfer coefficient was calculated from oscillating wall temperature, where a series of opposing heat transfer trends--the enhancement due to the quenching of dried areas or evaporation from thin liquid films and the deterioration due to the extension of dry patches--were observed between the passage of disturbance waves. The CHF condition that resulted from the insufficient decrease of wall temperature in the period of enhanced heat transfer was overcome by a temperature increase in the deterioration period. No clear effect of gravity on the mechanisms of dryout was observed within the range of experiments.

  14. Low-Flow Film Boiling Heat Transfer on Vertical Surfaces

    DEFF Research Database (Denmark)

    Munthe Andersen, J. G.; Dix, G. E.; Leonard, J. E.

    1976-01-01

    The phenomenon of film boiling heat transfer for high wall temperatures has been investigated. Based on the assumption of laminar flow for the film, the continuity, momentum, and energy equations for the vapor film are solved and a Bromley-type analytical expression for the heat transfer...... length, an average film boiling heat transfer coefficient is obtained....

  15. Pool boiling heat transfer performance of Newtonian nanofluids

    Energy Technology Data Exchange (ETDEWEB)

    Soltani, Saide; Etemad, Seyed Gholamreza [Isfahan University of Technology, Department of Chemical Engineering, Isfahan (Iran); Thibault, Jules [University of Ottawa, Department of Chemical and Biological Engineering, Ottawa, ON (Canada)

    2009-10-15

    Experimental measurements were carried out on the boiling heat transfer characteristics of {gamma}-Al{sub 2}O{sub 3}/water and SnO{sub 2}/water Newtonian nanofluids. Nanofluids are liquid suspensions containing nanoparticles with sizes smaller than 100 nm. In this research, suspensions with different concentrations of {gamma}-Al{sub 2}O{sub 3} and SnO{sub 2} nanoparticles in water were studied under nucleate pool boiling heat transfer conditions. Results show that nanofluids possess noticeably higher boiling heat transfer coefficients than the base fluid. The boiling heat transfer coefficients depend on the type and concentration of nanoparticles. (orig.)

  16. Boiling Heat Transfer on Porous Surfaces with Vapor Channels

    Institute of Scientific and Technical Information of China (English)

    吴伟; 杜建华; 王补宣

    2002-01-01

    Boiling heat transfer on porous coated surfaces with vapor channels was investigated experimentally to determine the effects of the size and density of the vapor channels on the boiling heat transfer. Observations showed that bubbles escaping from the channels enhanced the heat transfer. Three regimes were identified: liquid flooding, bubbles in the channel and the bottom drying out region. The maximum heat transfer occurred for an optimum vapor channel density and the boiling heat transfer performance was increased if the channels were open to the bottom of the porous coating.

  17. Experimental study about ONB and subcooled boiling heat transfer

    Energy Technology Data Exchange (ETDEWEB)

    Changhong, P.; Myint, A.; Yun, G.; Dounan, J. [State Key Laboratory of Multiphase Flow in power engineering, Department of Nuclear and Thermal Power Engineering, Xian (China)

    2004-07-01

    Water subcooled boiling heat transfer were experimentally investigated in the vertical annuli with narrow gap. Subcooled flow boiling covers the region from the location where the bubbles forms on the wall to the location where the bulk temperature reaches saturated temperature. Three locations in the subcooled flow boiling have been identified by earlier researchers as the onset of nucleate boiling (ONB), the beginning of fully developed boiling, and the location where the thermodynamic quality is zero that is inferred from the enthalpy balance equation. The heat transfer regions are identified as single-phase heat transfer prior to ONB, partial boiling (PB) and fully developed boiling (FDB). In this study, the available models for predicting heat transfer in the different regions and the modified correlation can predict our experimental data: -) the heat flux of ONB can be predicted by the Unal correlation, nevertheless the h{sub FC} is calculated by the modified Dittus-Boelter correlations in the narrow annuli, -) Griffith's method can be modified to identify the beginning of fully develop boiling, -) in the partial boiling region, the heat transfer coefficient can be calculated by h{sub PB} equals (1-a)*h{sub L} + a*h{sub FDB}, and -) in the fully developed region, the correlation for saturated flow boiling can be employed to describe the heat transfer.

  18. A review on boiling heat transfer enhancement with nanofluids.

    Science.gov (United States)

    Barber, Jacqueline; Brutin, David; Tadrist, Lounes

    2011-04-04

    There has been increasing interest of late in nanofluid boiling and its use in heat transfer enhancement. This article covers recent advances in the last decade by researchers in both pool boiling and convective boiling applications, with nanofluids as the working fluid. The available data in the literature is reviewed in terms of enhancements, and degradations in the nucleate boiling heat transfer and critical heat flux. Conflicting data have been presented in the literature on the effect that nanofluids have on the boiling heat-transfer coefficient; however, almost all researchers have noted an enhancement in the critical heat flux during nanofluid boiling. Several researchers have observed nanoparticle deposition at the heater surface, which they have related back to the critical heat flux enhancement.

  19. Investigation of Enhanced Boiling Heat Transfer from Porous Surfaces

    Institute of Scientific and Technical Information of China (English)

    LinZhiping; MaTongze; 等

    1994-01-01

    Experimental investigations of boiling heat transfer from porous surfaces at atmospheric pressure were performne.The porous surfaces are plain tubes coverd with metal screens.V-shaped groove tubes covered with screens,plain tubes sintered with screens.and V-shaped groove tubes sintered with screens,The experimental results show that sintering metal screens around spiral V-shaped groove tubes can greatly improve the boiling heat transfer,The boiling hystesis was observed in the experiment.This paper discusses the mechanism of the boiling heat transfer from those kinds of porous surfaces stated above.

  20. Boiling local heat transfer enhancement in minichannels using nanofluids.

    Science.gov (United States)

    Chehade, Ali Ahmad; Gualous, Hasna Louahlia; Le Masson, Stephane; Fardoun, Farouk; Besq, Anthony

    2013-03-18

    This paper reports an experimental study on nanofluid convective boiling heat transfer in parallel rectangular minichannels of 800 μm hydraulic diameter. Experiments are conducted with pure water and silver nanoparticles suspended in water base fluid. Two small volume fractions of silver nanoparticles suspended in water are tested: 0.000237% and 0.000475%. The experimental results show that the local heat transfer coefficient, local heat flux, and local wall temperature are affected by silver nanoparticle concentration in water base fluid. In addition, different correlations established for boiling flow heat transfer in minichannels or macrochannels are evaluated. It is found that the correlation of Kandlikar and Balasubramanian is the closest to the water boiling heat transfer results. The boiling local heat transfer enhancement by adding silver nanoparticles in base fluid is not uniform along the channel flow. Better performances and highest effect of nanoparticle concentration on the heat transfer are obtained at the minichannels entrance.

  1. Bubble Coalescence Heat Transfer During Subcooled Nucleate Pool Boiling

    Institute of Scientific and Technical Information of China (English)

    Abdoulaye Coulibaly; LIN Xipeng; Bi Jingliang; David M Christopher

    2012-01-01

    Bubble coalescence during subcooled nucleate pool boiling was investigated experimentally using constant wall temperature boundary conditions while the wall heat flux was measured at a various locations to understand the effects of coalescence on the heat transfer. The observations showed that the coalesced bubble moved and oscillated on the heater surface with significant heat transfer variations prior to departure. Some observations also showed coalescence with no increase in the heat transfer rate. The heat flux for boiling with coalescence fluctuated much more than for single bubble boiling due to the vaporization of the liquid layer trapped between the bubbles.

  2. Contact Angle Effects in Boiling Heat Transfer

    OpenAIRE

    Urquiola, Erwin; Fujita, Yasunobu

    2002-01-01

    This paper reports boiling experiments with pure water and surfactant solutions of SDS on horizontal heating surface. The static contact angle, rather than the surface tension value, was found to be the leading factor for the results and probably its prev

  3. Heat transfer and pressure drop in flow boiling in microchannels

    CERN Document Server

    Saha, Sujoy Kumar

    2016-01-01

    This Brief addresses the phenomena of heat transfer and pressure drop in flow boiling in micro channels occurring in high heat flux electronic cooling. A companion edition in the Springer Brief Subseries on Thermal Engineering and Applied Science to “Critical Heat Flux in Flow Boiling in Micro channels,” by the same author team, this volume is idea for professionals, researchers and graduate students concerned with electronic cooling.

  4. 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.

  5. Marangoni heat transfer in subcooled nucleate pool boiling

    Energy Technology Data Exchange (ETDEWEB)

    Petrovic, S.; Robinson, T.; Judd, R.L. [McMaster University, Hamilton, ON (Canada). Dept. of Mechanical Engineering

    2004-11-01

    The liquid motion induced by surface tension variation, termed the Marangoni effect, and its contribution to boiling heat transfer has been an issue of much controversy. Boiling heat transfer theory, although acknowledging its existence, considers its contribution to heat transfer to be insignificant in comparison with buoyancy induced convection. However, recent microgravity experiments have shown that although the boiling mechanism in a reduced gravity environment is different, the corresponding heat transfer rates are similar to those obtained under normal gravity conditions, raising questions about the validity of the assumption. An experimental investigation was performed in which distilled water was gradually heated to boiling conditions on a copper heater surface at four different levels of subcooling. Photographic investigation of the bubbles appearing on the surface was carried out in support of the measurements. The results obtained indicate that Marangoni convection associated with the bubbles formed by the air dissolved in the water which emerged from solution when the water was heated sufficiently, significantly influenced the heat transfer rate in subcooled nucleate pool boiling. A heat transfer model was developed in order to explain the phenomena observed. (author)

  6. Boiling Experiment Facility for Heat Transfer Studies in Microgravity

    Science.gov (United States)

    Delombard, Richard; McQuillen, John; Chao, David

    2008-01-01

    Pool boiling in microgravity is an area of both scientific and practical interest. By conducting tests in microgravity, it is possible to assess the effect of buoyancy on the overall boiling process and assess the relative magnitude of effects with regards to other "forces" and phenomena such as Marangoni forces, liquid momentum forces, and microlayer evaporation. The Boiling eXperiment Facility is now being built for the Microgravity Science Glovebox that will use normal perfluorohexane as a test fluid to extend the range of test conditions to include longer test durations and less liquid subcooling. Two experiments, the Microheater Array Boiling Experiment and the Nucleate Pool Boiling eXperiment will use the Boiling eXperiment Facility. The objectives of these studies are to determine the differences in local boiling heat transfer mechanisms in microgravity and normal gravity from nucleate boiling, through critical heat flux and into the transition boiling regime and to examine the bubble nucleation, growth, departure and coalescence processes. Custom-designed heaters will be utilized to achieve these objectives.

  7. Gravity and Heater Size Effects on Pool Boiling Heat Transfer

    Science.gov (United States)

    Kim, Jungho; Raj, Rishi

    2014-01-01

    The current work is based on observations of boiling heat transfer over a continuous range of gravity levels between 0g to 1.8g and varying heater sizes with a fluorinert as the test liquid (FC-72/n-perfluorohexane). Variable gravity pool boiling heat transfer measurements over a wide range of gravity levels were made during parabolic flight campaigns as well as onboard the International Space Station. For large heaters and-or higher gravity conditions, buoyancy dominated boiling and heat transfer results were heater size independent. The power law coefficient for gravity in the heat transfer equation was found to be a function of wall temperature under these conditions. Under low gravity conditions and-or for smaller heaters, surface tension forces dominated and heat transfer results were heater size dependent. A pool boiling regime map differentiating buoyancy and surface tension dominated regimes was developed along with a unified framework that allowed for scaling of pool boiling over a wide range of gravity levels and heater sizes. The scaling laws developed in this study are expected to allow performance quantification of phase change based technologies under variable gravity environments eventually leading to their implementation in space based applications.

  8. Boiling heat transfer and droplet spreading of nanofluids.

    Science.gov (United States)

    Murshed, S M Sohel; de Castro, C A Nieto

    2013-11-01

    Nanofluids- a new class of heat transfer fluids have recently been a very attractive area of research due to their fascinating thermophysical properties and numerous potential benefits and applications in many important fields. However, there are many controversies and inconsistencies in reported arguments and experimental results on various thermal characteristics such as effective thermal conductivity, convective heat transfer coefficient and boiling heat transfer rate of nanofluids. As of today, researchers have mostly focused on anomalous thermal conductivity of nanofluids. Although investigations on boiling and droplet spreading are very important for practical application of nanofluids as advanced coolants, considerably fewer efforts have been made on these thermal features of nanofluids. In this paper, recent research and development in boiling heat transfer and droplet spreading of nanofluids are reviewed together with summarizing most related patents on nanofluids published in literature. Review reveals that despite some inconsistent results nanofluids exhibit significantly higher boiling heat transfer performance compared to their base fluids and show great promises to be used as advanced heat transfer fluids in numerous applications. However, there is a clear lack of in-depth understanding of heat transport mechanisms during phase change of nanofluids. It is also found that the nanofluids related patents are limited and among them most of the patents are based on thermal conductivity enhancement and synthesising processes of specific type of nanofluids.

  9. Lattice Boltzmann modeling of boiling heat transfer: The boiling curve and the effects of wettability

    CERN Document Server

    Li, Q; Francois, M M; He, Y L; Luo, K H

    2015-01-01

    A hybrid thermal lattice Boltzmann (LB) model is presented to simulate thermal multiphase flows with phase change based on an improved pseudopotential LB approach [Q. Li, K. H. Luo, and X. J. Li, Phys. Rev. E 87, 053301 (2013)]. The present model does not suffer from the spurious term caused by the forcing-term effect, which was encountered in some previous thermal LB models for liquid-vapor phase change. Using the model, the liquid-vapor boiling process is simulated. The boiling curve together with the three boiling stages (nucleate boiling, transition boiling, and film boiling) is numerically reproduced in the LB community for the first time. The numerical results show that the basic features and the fundamental characteristics of boiling heat transfer are well captured, such as the severe fluctuation of transient heat flux in the transition boiling and the feature that the maximum heat transfer coefficient lies at a lower wall superheat than that of the maximum heat flux. Furthermore, the effects of the he...

  10. Heat Transfer in Boiling Dilute Emulsion with Strong Buoyancy

    Science.gov (United States)

    Freeburg, Eric Thomas

    Little attention has been given to the boiling of emulsions compared to that of boiling in pure liquids. The advantages of using emulsions as a heat transfer agent were first discovered in the 1970s and several interesting features have since been studied by few researchers. Early research focuses primarily on pool and flow boiling and looks to determine a mechanism by which the boiling process occurs. This thesis looks at the boiling of dilute emulsions in fluids with strong buoyant forces. The boiling of dilute emulsions presents many favorable characteristics that make it an ideal agent for heat transfer. High heat flux electronics, such as those seen in avionics equipment, produce high heat fluxes of 100 W/cm2 or more, but must be maintained at low temperatures. So far, research on single phase convection and flow boiling in small diameter channels have yet to provide an adequate solution. Emulsions allow the engineer to tailor the solution to the specific problem. The fluid can be customized to retain the high thermal conductivity and specific heat capacity of the continuous phase while enhancing the heat transfer coefficient through boiling of the dispersed phase component. Heat transfer experiments were carried out with FC-72 in water emulsions. FC-72 has a saturation temperature of 56 °C, far below that of water. The parameters were varied as follows: 0% ≤ epsilon ≤ 1% and 1.82 x 1012 ≤ RaH ≤ 4.42 x 1012. Surface temperatures along the heated surface reached temperature that were 20 °C in excess of the dispersed phase saturation temperature. An increase of ˜20% was seen in the average Nusselt numbers at the highest Rayleigh numbers. Holography was used to obtain images of individual and multiple FC-72 droplets in the boundary layer next to the heated surface. The droplet diameters ranged from 0.5 mm to 1.3 mm. The Magnus effect was observed when larger individual droplets were injected into the boundary layer, causing the droplets to be pushed

  11. Boiling heat transfer on fins – experimental and numerical procedure

    Directory of Open Access Journals (Sweden)

    Orzechowski T.

    2014-03-01

    Full Text Available The paper presents the research methodology, the test facility and the results of investigations into non-isothermal surfaces in water boiling at atmospheric pressure, together with a discussion of errors. The investigations were conducted for two aluminium samples with technically smooth surfaces and thickness of 4 mm and 10 mm, respectively. For the sample of lower thickness, on the basis of the surface temperature distribution measured with an infrared camera, the local heat flux and the heat transfer coefficient were determined and shown in the form of a boiling curve. For the thicker sample, for which 1-D model cannot be used, numerical calculations were conducted. They resulted in obtaining the values of the local heat flux on the surface the invisible to the infrared, camera i.e. on the side on which the boiling of the medium proceeds.

  12. Early-Evaporation of Microlayer for Boiling Heat Transfer Enhancement.

    Science.gov (United States)

    Zou, An; Singh, Dhirendra P; Maroo, Shalabh C

    2016-10-06

    For over five decades, enhancement in pool boiling heat transfer has been achieved by altering the surface wetting, wickability, roughness, nucleation site density and providing separate liquid/vapor pathways. In this work, a new enhancement mechanism based on the early-evaporation of the microlayer is discovered and validated. The microlayer is a thin liquid film present at the base of a vapor bubble. Presence of micro-ridges on the silicon-dioxide surface partitions the microlayer and disconnects it from bulk liquid causing it to evaporate sooner, thus leading to increase in bubble growth rate, heat transfer, departure frequency and critical heat flux (CHF). Compared to a plain surface, ~120% enhancement in CHF is obtained with only ~18% increase in surface area. A CHF enhancement map is developed based on ridge height and spacing, resulting in three regions of full, partial and no enhancement. The new mechanism is validated by comparing the growth rate of a laser created vapor bubble on ridge-structured surface and plain surface, and the corresponding prediction of CHF enhancement is found to be in good agreement with experimental boiling data. This discovery opens up a new field of CHF enhancement and can be coupled with existing techniques to further push the limits of boiling heat transfer.

  13. Numerical prediction of nucleate pool boiling heat transfer coefficient under high heat fluxes

    OpenAIRE

    Pezo Milada L.; Stevanović Vladimir D.

    2016-01-01

    This paper presents CFD (Computational Fluid Dynamics) approach to prediction of the heat transfer coefficient for nucleate pool boiling under high heat fluxes. Three-dimensional numerical simulations of the atmospheric saturated pool boiling are performed. Mathematical modelling of pool boiling requires a treatment of vapor-liquid two-phase mixture on the macro level, as well as on the micro level, such as bubble growth and departure from the heating surfa...

  14. Boiling heat transfer in horizontal and inclined rectangular channels

    Energy Technology Data Exchange (ETDEWEB)

    Morcos, S.M.; Mobarak, A.; Hilal, M.; Mohareb, M.R. (Cairo Univ. (Egypt))

    1987-05-01

    The present experimental investigation is concerned with boiling heat transfer of water inside both horizontal and inclined rectangular channels under a relatively low heat flux. These configurations simulate the absorber channel of line-focus solar concentrations under boiling conditions. The experimental facility includes electrically heated aluminum rectangular channels with aspect ratios of 2.67 and 0.37. The experimental results of the two-phase Nusselt number for the two aspect ratios and for the inclination angles 0, 15, 30, and 45 deg were correlated in terms of a ratio of the two-phase to the liquid-phase Reynolds number for the forced-convection vaporization region. The proposed correlations agree well with previous investigations. In the present work, classifications of the various flow patterns were made by direct observation through a glass window at the end of the test section.

  15. Prediction of film boiling heat transfer coefficients for binary mixtures

    Science.gov (United States)

    Liu, Ming-Huei; Yang, Yu-Min; Maa, Jer-Ru

    Film boiling of binary liquid mixtures may be significantly different from that of single-component liquids due to the mass diffusion effect. A theoretical analysis is performed to outline the effects of mass diffusion phenomena on film boiling heat transfer process from a horizontal cylinder heating surface to the binary liquid mixtures of ethylene oxide/water and ethanol/benzene over whole range of compositions. These two binary systems are chosen for illustrating the strong and weak mass diffusion effects, respectively, on film boiling. Furthermore, a simple correlation for predicting heat transfer coefficient is proposed to demonstrate the idea that the dimensionless F factor can satisfactorily account for the mass diffusion effect on film boiling heat transfer of binary mixtures. Zusammenfassung Infolge des Stoffdiffusionseffektes kann sich das Filmsiedeverhalten binärer Flüssigkeitsgemische ganz wesentlich von dem der Einzelkomponentenfluide unterscheiden. In einer theoretischen Studie sollen die Einflüsse der Stoffdiffusionsphänomene auf den Wärmeübergang beim Filmsieden untersucht werden, und zwar bezüglich einer horizontalen zylindrischen Heizfläche, die Wärme an die Binärgemische Ethylenoxid/Wasser und Ethanol/Benzol bei beliebigen Konzentrationsverhältnissen abgibt. Die beiden Binärsysteme wurden ausgewählt, um einmal starken und dann schwachen Einfluß des Stoffdiffusionseffektes auf das Filmsieden zu zeigen. Schließlich wird eine einfache Korrelationsbeziehung zur Berechnung von Wärmeübergangskoeffizienten vorgeschlagen, die darlegen soll, daß der dimensionslose F-Faktor geeignet ist, den Einfluß des Stoffdiffusionseffektes auf das Filmsieden binärer Gemische befriedigend zu berücksichtigen.

  16. A heat transfer model for slug flow boiling within microchannels

    Science.gov (United States)

    Magnini, Mirco; Thome, John

    2016-11-01

    We propose a novel physics-based model for the fluid mechanics and heat transfer associated with slug flow boiling in horizontal circular microchannels, to update the widely used three-zone model for the design of multi-microchannel evaporators. The flow is modelled as the cyclic passage of a liquid slug, an elongated bubble which traps a thin liquid film against the channel wall, and a dry vapor plug. The capillary flow theory, extended to incorporate evaporation effects, is applied to estimate the bubble velocity along the channel. A liquid film thickness prediction method considering bubble proximity effects, which may limit the radial extension of the film, is included. Theoretical heat transfer models accounting for the thermal inertia of the liquid film and for the recirculating flow within the liquid slug are utilized. The heat transfer model is compared to experimental data taken from three independent studies: 833 slug flow boiling data points covering R134a, R245fa and R236fa and channel diameters from 0.4 mm to 1 mm. The new model predicts more than 80% of the database to within +/- 30 % and it represents an important step toward a complete physics-based modelling of bubble dynamics and heat transfer within microchannels under evaporating flow conditions.

  17. Boiling heat transfer in a small horizontal rectangular channel

    Energy Technology Data Exchange (ETDEWEB)

    Tran, T.N.; Wambsganss, M.W.; Jendrzejczyk, J.A. [Argonne National Lab., IL (United States); France, D.M. [Illinois Univ., Chicago, IL (United States). Dept. of Mechanical Engineering

    1993-08-01

    Compact heat exchangers have traditionally found wide application in the transportation industry, where they are used as evaporators and condensers in vapor compression cycles for air conditioning and refrigeration. Such heat exchangers possess numerous attractive features including high thermal effectiveness, small size, low weight, design flexibility, and pure counterflow, and they can accommodate multiple streams. Today, there is a widespread interest in expanding the range of application of compact heat exchangers to include phase-change heat transfer in the process industries, among others. An overall objective of this effort is to provide the basis for establishing design technology in this area. In the present study, small channel flow boiling heat transfer was extended to a rectangular channel (4.06 {times} 1.70 mm) using refrigerant 12 (R-12). As with the circular tube studies, the flow channel wall was electrically heated providing a constant heat flux. Tests were performed over a quality range of 0.15 to 0.80, and large ranges of mass fluxes (50 to 400 kg/m{sup 2}s) and heat flux (4 to 34 kW/m{sup 2}). Heat transfer was measured and results are compared with correlation predictions.

  18. Film Boiling Heat Transfer Properties of Liquid Hydrogen in Natural Convection

    Science.gov (United States)

    Horie, Y.; Shirai, Y.; Shiotsu, M.; Matsuzawa, T.; Yoneda, K.; Shigeta, H.; Tatsumoto, H.; Hata, K.; Naruo, Y.; Kobayashi, H.; Inatani, Y.

    Film boiling heat transfer properties of LH2 for various pressures and subcooling conditions were measured by applying electric current to give an exponential heat input to a PtCo wire with a diameter of 1.2 mm submerged in LH2. The heated wire was set to be horizontal to the ground. The heat transfer coefficient in the film boiling region was higher for higher pressure and higher subcooling. The experimental results are compared with the equation of pool film boiling heat transfer. It is confirmed that the pool film boiling heat transfer coefficients in LH2 can be expressed by this equation.

  19. Measurement of boiling heat transfer coefficient in liquid nitrogen bath by inverse heat conduction method

    Institute of Scientific and Technical Information of China (English)

    Tao JIN; Jian-ping HONG; Hao ZHENG; Ke TANG; Zhi-hua GAN

    2009-01-01

    Inverse heat conduction method (IHCM)is one of the most effective approaches to obtaining the boiling heat transfer coefficient from measured results.This paper focuses on its application in cryogenic boiling heat transfer.Experiments were conducted on the heattransfer of a stainless steel block in a liquid nitrogen bath.with the assumption of a ID conduction condition to realize fast acquisition of the temperature of the test points inside the block.With the inverse-heat conduction theory and the explicit finite difference model,a solving program was developed to calculate the heat flux and the boiling heat transfer coefficient of a stainless steel block in liquid nitrogen bath based on the temperature acquisition data.Considering the oscillating data and some unsmooth transition points in the inverse-heat-conduction calculation result of the heat-transfer coefficient,a two-step data-fitting procedure was proposed to obtain the expression for the boiling heat transfer coefficients.The coefficient was then verified for accuracy by a comparison between the simulation results using this expression and the verifying experimental results of a stainless steel block.The maximum error with a revised segment fitting iS around 6%.which verifies the feasibility of using IHCM to measure the boiling heat transfer coefficient in liquid nitrogen bath.

  20. Boiling heat transfer of nanofluids--special emphasis on critical heat flux.

    Science.gov (United States)

    Kim, Sung Joong; Kim, Hyungdae

    2013-11-01

    As innovative nanotechnology-based heat-transfer media, nanofluids have evoked considerable interest among researchers owing to their improved thermal properties as well as their extendable applications to various high-power thermal systems. This paper presents a comprehensive review of recent research developments and patents pertaining to nanofluid boiling heat transfer. Nanofluids definitely offer a wide range of potential improvements in boiling heat-transfer performance. However, experimental data available from different studies are currently beset by numerous contradictions, suggesting that the fundamental mechanisms of nanofluid boiling heat transfer are not yet well understood. Consequently application of these technologies has been limited in some aspects. Only a small number of patents related to nanofluid boiling heat transfer have thus far been reported in the literature. Based on the present review, future technological development and research requirements in this area are outlined in line with technical challenges. To utilize nanofluid boiling heat-transfer technologies for practical applications, more systematic and fundamental studies are required to understand the physical mechanisms involved.

  1. Evaluation of correlations of flow boiling heat transfer of R22 in horizontal channels.

    Science.gov (United States)

    Zhou, Zhanru; Fang, Xiande; Li, Dingkun

    2013-01-01

    The calculation of two-phase flow boiling heat transfer of R22 in channels is required in a variety of applications, such as chemical process cooling systems, refrigeration, and air conditioning. A number of correlations for flow boiling heat transfer in channels have been proposed. This work evaluates the existing correlations for flow boiling heat transfer coefficient with 1669 experimental data points of flow boiling heat transfer of R22 collected from 18 published papers. The top two correlations for R22 are those of Liu and Winterton (1991) and Fang (2013), with the mean absolute deviation of 32.7% and 32.8%, respectively. More studies should be carried out to develop better ones. Effects of channel dimension and vapor quality on heat transfer are analyzed, and the results provide valuable information for further research in the correlation of two-phase flow boiling heat transfer of R22 in channels.

  2. Transition boiling heat transfer and the film transition regime

    Science.gov (United States)

    Ramilison, J. M.; Lienhard, J. H.

    1987-01-01

    The Berenson (1960) flat-plate transition-boiling experiment has been recreated with a reduced thermal resistance in the heater, and an improved access to those portions of the transition boiling regime that have a steep negative slope. Tests have been made in Freon-113, acetone, benzene, and n-pentane boiling on horizontal flat copper heaters that have been mirror-polished, 'roughened', or teflon-coated. The resulting data reproduce and clarify certain features observed by Berenson: the modest surface finish dependence of boiling burnout, and the influence of surface chemistry on both the minimum heat flux and the mode of transition boiling, for example. A rational scheme of correlation yields a prediction of the heat flux in what Witte and Lienhard (1982) previously identified as the 'film-transition boiling' region. It is also shown how to calculate the heat flux at the boundary between the pure-film, and the film-transition, boiling regimes, as a function of the advancing contact angle.

  3. Boiling heat transfer in a hydrofoil-based micro pin fin heat sink

    Energy Technology Data Exchange (ETDEWEB)

    Kosar, Ali; Peles, Yoav [Department of Mechanical, Aerospace and Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, NY 12180 (United States)

    2007-03-15

    Flow boiling of R-123 in a hydrofoil-based micro pin fin heat sink was investigated. Average two-phase heat transfer coefficients were obtained over effective heat fluxes ranging from 19 to 312 W/cm{sup 2} and mass fluxes from 976 to 2349 kg/m{sup 2} s. The paper presents a flow map, which divides the data into three flow pattern regions: bubbly, wavy intermittent and spray-annular flows. Heat transfer coefficient trends and flow morphologies were used to infer boiling heat transfer mechanisms. Existing conventional scale correlations for circular tubes resulted in large scatter and were not able to predict the heat transfer coefficients accurately. (author)

  4. Enhanced convective and film boiling heat transfer by surface gas injection

    Energy Technology Data Exchange (ETDEWEB)

    Duignan, M.R.; Greene, G.A. (Brookhaven National Lab., Upton, NY (United States)); Irvine, T.F., Jr. (State Univ. of New York, Stony Brook, NY (United States). Dept. of Mechanical Engineering)

    1992-04-01

    Heat transfer measurements were made for stable film boiling of water over a horizontal, flat stainless steel plate from the minimum film boiling point temperature, T{sub SURFACE} {approximately}500K, to T{sub SURFACE} {approximately}950K. The pressure at the plate was approximately 1 atmosphere and the temperature of the water pool was maintained at saturation. The data were compared to the Berenson film-boiling model, which was developed for minimum film-boiling-point conditions. The model accurately represented the data near the minimum film-boiling point and at the highest temperatures measured, as long it was corrected for the heat transferred by radiation. On the average, the experimental data lay within {plus minus}7% of the model. Measurements of heat transfer were made without film boiling for nitrogen jetting into an overlying pool of water from nine 1-mm- diameter holes, drilled in the heat transfer plate. The heat flux was maintained constant at approximately 26.4 kW/m{sup 2}. For water-pool heights of less than 6cm the heat transfer coefficient deceased linearly with a decrease in heights. Above 6cm the heat transfer coefficient was unaffected. For the entire range of gas velocities measured (0 to 8.5 cm/s), the magnitude of the magnitude of the heat transfer coefficient only changed by approximately 20%. The heat transfer data bound the Konsetov model for turbulent pool heat transfer which was developed for vertical heat transfer surfaces. This agreement suggests that surface orientation may not be important when the gas jets do not locally affect the surface heat transfer. Finally, a database was developed for heat transfer from the plate with both film boiling and gas jetting occurring simultaneously, in a pool of water maintained at its saturation temperature. The effect of passing nitrogen through established film boiling is to increase the heat transfer from that surface. 60 refs.

  5. Enhanced convective and film boiling heat transfer by surface gas injection

    Energy Technology Data Exchange (ETDEWEB)

    Duignan, M.R.; Greene, G.A. [Brookhaven National Lab., Upton, NY (United States); Irvine, T.F., Jr. [State Univ. of New York, Stony Brook, NY (United States). Dept. of Mechanical Engineering

    1992-04-01

    Heat transfer measurements were made for stable film boiling of water over a horizontal, flat stainless steel plate from the minimum film boiling point temperature, T{sub SURFACE} {approximately}500K, to T{sub SURFACE} {approximately}950K. The pressure at the plate was approximately 1 atmosphere and the temperature of the water pool was maintained at saturation. The data were compared to the Berenson film-boiling model, which was developed for minimum film-boiling-point conditions. The model accurately represented the data near the minimum film-boiling point and at the highest temperatures measured, as long it was corrected for the heat transferred by radiation. On the average, the experimental data lay within {plus_minus}7% of the model. Measurements of heat transfer were made without film boiling for nitrogen jetting into an overlying pool of water from nine 1-mm- diameter holes, drilled in the heat transfer plate. The heat flux was maintained constant at approximately 26.4 kW/m{sup 2}. For water-pool heights of less than 6cm the heat transfer coefficient deceased linearly with a decrease in heights. Above 6cm the heat transfer coefficient was unaffected. For the entire range of gas velocities measured [0 to 8.5 cm/s], the magnitude of the magnitude of the heat transfer coefficient only changed by approximately 20%. The heat transfer data bound the Konsetov model for turbulent pool heat transfer which was developed for vertical heat transfer surfaces. This agreement suggests that surface orientation may not be important when the gas jets do not locally affect the surface heat transfer. Finally, a database was developed for heat transfer from the plate with both film boiling and gas jetting occurring simultaneously, in a pool of water maintained at its saturation temperature. The effect of passing nitrogen through established film boiling is to increase the heat transfer from that surface. 60 refs.

  6. Boiling heat transfer of refrigerant R-21 in upward flow in plate-fin heat exchanger

    Science.gov (United States)

    Kuznetsov, V. V.; Shamirzaev, A. S.

    2015-11-01

    The article presents the results of experimental investigation of boiling heat transfer of refrigerant R-21 in upward flow in a vertical plate-fin heat exchanger with transverse size of the channels that is smaller than the capillary constant. The heat transfer coefficients obtained in ranges of small mass velocities and low heat fluxes, which are typical of the industry, have been poorly studied yet. The characteristic patterns of the upward liquid-vapor flow in the heat exchanger channels and the regions of their existence are detected. The obtained data show a weak dependence of heat transfer coefficient on equilibrium vapor quality, mass flow rate, and heat flux density and do not correspond to calculations by the known heat transfer models. A possible reason for this behavior is a decisive influence of evaporation of thin liquid films on the heat transfer at low heat flux.

  7. An analytical model for annular flow boiling heat transfer in microchannel heat sinks

    Energy Technology Data Exchange (ETDEWEB)

    Megahed, A.; Hassan, I. [Concordia University, Montreal, QC (Canada). Dept. of Mechanical and Industrial Engineering

    2009-07-01

    An analytical model has been developed to predict flow boiling heat transfer coefficient in microchannel heat sinks. The new analytical model is proposed to predict the two-phase heat transfer coefficient during annular flow regime based on the separated model. Opposing to the majority of annular flow heat transfer models, the model is based on fundamental conservation principles. The model considers the characteristics of microchannel heat sink during annular flow and eliminates using any empirical closure relations. Comparison with limited experimental data was found to validate the usefulness of this analytical model. The model predicts the experimental data with a mean absolute error 8%. (author)

  8. A fractal study for nucleate pool boiling heat transfer of nanofluids

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    In this paper, a fractal model for nucleate pool boiling heat transfer of nanofluids is developed based on the fractal distribution of nanoparticles and nucleation sites on boiling surfaces. The model shows the dependences of the heat flux on nanoparticle size and the nanoparticle volume fraction of the suspension, the fractal dimension of the nanoparticle and nucleation site, temperature of nanofluids and properties of fluids. The fractal model predictions show that the natural convection stage continues relatively longer in the case of nanofluids. The addition of nanoparticles causes a decrease of the pool nucleate boiling heat transfer. The nucleate pool boiling heat transfer coefficient is decreased by increasing particle concentration. An excellent agreement between the proposed model predictions and experimental data is found. The validity of the fractal model for nucleate pool boiling heat transfer is thus verified.

  9. Numerical prediction of nucleate pool boiling heat transfer coefficient under high heat fluxes

    Directory of Open Access Journals (Sweden)

    Pezo Milada L.

    2016-01-01

    Full Text Available This paper presents CFD (Computational Fluid Dynamics approach to prediction of the heat transfer coefficient for nucleate pool boiling under high heat fluxes. Three-dimensional numerical simulations of the atmospheric saturated pool boiling are performed. Mathematical modelling of pool boiling requires a treatment of vapor-liquid two-phase mixture on the macro level, as well as on the micro level, such as bubble growth and departure from the heating surface. Two-phase flow is modelled by the two-fluid model, which consists of the mass, momentum and energy conservation equations for each phase. Interface transfer processes are calculated by the closure laws. Micro level phenomena on the heating surface are modelled with the bubble nucleation site density, the bubble resistance time on the heating wall and with the certain level of randomness in the location of bubble nucleation sites. The developed model was used to determine the heat transfer coefficient and results of numerical simulations are compared with available experimental results and several empirical correlations. A considerable scattering of the predictions of the pool boiling heat transfer coefficient by experimental correlations is observed, while the numerically predicted values are within the range of results calculated by well-known Kutateladze, Mostinski, Kruzhilin and Rohsenow correlations. The presented numerical modeling approach is original regarding both the application of the two-fluid two-phase model for the determination of heat transfer coefficient in pool boiling and the defined boundary conditions at the heated wall surface. [Projekat Ministarstva nauke Republike Srbije, br. 174014

  10. Flow impinging effect of critical heat flux and nucleation boiling heat transfer on a downward facing heating surface

    Energy Technology Data Exchange (ETDEWEB)

    Hsieh, Huai-En; Chen, Mei-Shiue; Chen, Jyun-Wei; Lin, Wei-Keng; Pei, Bau-Shei [National Tsing Hua Univ., Taiwan (China). Inst. of Nuclear Engineering and Science

    2015-05-15

    Boiling heat transfer has a high heat removal capability in convective cooling. However, the heat removal capability of downward-facing boiling is significantly worse than that of upward-facing cases because of the confined buoyancy effect. This study was inspired by the conception of external reactor vessel cooling (ERVC) condition relevant to the in-vessel retention (IVR) design of Westinghouse AP1000 plant. In the present study, a small-scale test facility had been established to investigate the local phenomena of boiling heat transfer under a downward-facing horizontal heated surface with impinging coolant flow. In this study, the surface temperature, heat flux information and several specific scenes of bubbles are taken down throughout the boiling processes for detailed investigation. It is observed that bubbles are confined under the downward-facing heated surface, which causes a worse heat transfer rate and a lower critical heat flux (CHF) limit than upward-facing boiling. Nevertheless, the impinging coolant flow is found to disturb the thermal boundary layer formed by the heated surface, so the CHF increases with an increase of coolant flow rate. In addition, during nucleate boiling, it is discovered that the growth, combination and dissipation of bubbles induce turbulent wakes and therefore enhance the heat transfer capability.

  11. 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)

  12. Comprehensive Evaluation and Prediction of Enhancement of Boiling Heat Transfer with Additives

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    A model of evaluation and prediction of enhancement of boiling heat transfer with additives has been propoeed according to fuzzy fundamentals. Correlative appraisement of boiling heat transfer augmentation was done with the model based on 39 additives which were tested by the authors and other researchers. The results show that the evaluation of 35 additives is consistent with experiments, which means that the accuracy of the model is 89.7 percent. In addition, the prediction of the ability of boiling heat transfer enhancement with sodium oleate,polyethylene glycol and Tween-40 is also in good agreement with correspondent experiments.

  13. Experimental analysis of nanofluid pool boiling heat transfer in copper bead packed porous layers

    Science.gov (United States)

    Chen, Wei; Wang, Ji

    2017-03-01

    Coupling the nanofluid as working fluid and the copper beads packed porous structure on heating surface were employed to enhance the pool boiling heat transfer by changing the fluid properties with the adjunction of nanoparticles in liquid and altering the heating surface with a bead porous layer. Due to the higher thermal conductivity, the copper beads served as an extended heating surface and the boiling nucleation sites rose, but the flow resistance increased. The CuO-water and SiO2-water nanofluids as well as the pure water were respectively employed as working fluids in the pool boiling experiments. Comparing with the base fluid of water, the higher thermal conductivity and lower surface tension occur in the nanofluids and those favor the boiling heat transfer, but the higher viscosity and density of nanofluids serve as deteriorative factors. So, the concentration region of the nanofluids should be chosen properly. The maximum relative error between the collected experimental data of the pure water on a flat surface and the theoretical prediction of pool boiling using the Rohsenow correlation was less than 12 %. The comparisons of the pool boiling heat transfer characteristics were also conducted between the pure water and the nanofluids respectively on the horizontal flat surface and on the heating surface packed with a copper bead porous layer. Besides, the boiling bubble generation, integration and departure have a great affect on the pool boiling and were recorded with a camera in the bead stacked porous structures at different heat flux.

  14. Experimental investigation on partial pool boiling heat transfer in pure liquids

    Directory of Open Access Journals (Sweden)

    Fazel Seyed Ali Alavi

    2016-01-01

    Full Text Available Saturated partial pool boiling heat transfer has been experimentally investigated on a horizontal rod heater. The boiling liquids are including water and ethanol. The heating section is made by various materials including SS316, copper, aluminum and brass. Experiments have been performed at several degrees of surface roughness ranging between 30 and 360 micrometer average vertical deviation. The measurements are including boiling heat transfer coefficient, bubble departing diameter and frequency and also nucleation site density. The data have been compared to major existing correlations. It is shown that experimental data do not match with major correlations at the entire range of experiments with acceptable accuracy. In this article, the boiling heat transfer area has been divided in two complementary areas, the induced forced convection area and the boiling affected area. Based on two dimensionless groups, including Eötvös and Roshko numbers, a semi-empirical model have been proposed to predict the boiling heat transfer coefficient. It is shown that the proposed model provides improved performance in prediction of the boiling heat transfer coefficient in comparison with to existing correlations.

  15. Numerical investigation of boiling heat transfer on the shell-side of spiral wound heat exchanger

    Science.gov (United States)

    Wu, Zhi-Yong; Wang, He; Cai, Wei-Hua; Jiang, Yi-Qiang

    2016-09-01

    The aim of this paper is to numerically study boiling heat transfer on the shell-side of spiral wound heat exchanger (SWHE). The physical model for the shell-side of SWHE is established and the volume of fluid (VOF) method is used in the calculation. For propane and ethane, there are thirty cases to be simulated . Through the comparison with experimental data, the cause which leads to the simulation distortion is found, and the satisfied results of calculation are finally achieved. The simulation results show that the VOF model can be adopted well to those calculations whose inlet quality are lower than 0.1 kg/kg, and the calculation deviations are generally within ±20 %. In falling film flow, the heat transfer performance for the shell-side of SWHE is primarily influenced by Reynolds number. The visualization of simulation results displays that the boiling bubbles have three flow directions, besides flowing down with liquid phase, one portion of bubbles flows reversely up, and another portion is blocked at axial gaps of coils where the heat transfer is reduced. The studies of boiling on the shell-side of SWHE not only reveal the characteristics of heat transfer, but also point out the improvement direction of SWHE.

  16. Boiling heat transfer region with independence of the wall temperature

    Science.gov (United States)

    Mühlenbruch, G. H. D.; Schmidt, J.

    Extensive measurements of the intensive cooling of hot-rolled wires with temperatures between 1000 °C and 1100 °C are analysed. The analysis proves the existence of a convection-controlled boiling region, which has been previously observed by few authors in the case of high mass fluxes and high liquid subcooling. This region is characterised by an independence of the heat flux of the surface temperature. The heat flux depends essentially on the Reynolds number, the main influence parameter of the single phase convection, and on the liquid subcooling.

  17. Experimental Investigation on Pool Boiling Heat Transfer With Ammonium Dodecyl Sulfate

    Directory of Open Access Journals (Sweden)

    Mr.P. Atcha Rao

    2015-11-01

    Full Text Available We have so many applications related to Pool Boiling. The Pool Boiling is mostly useful in arid areas to produce drinking water from impure water like sea water by distillation process. It is very difficult to distill the only water which having high surface tension. The surface tension is important factor to affect heat transfer enhancement in pool boiling. By reducing the surface tension we can increase the heat transfer rate in pool boiling. From so many years we are using surfactants domestically. It is proven previously by experiments that the addition of little amount of surfactant reduces the surface tension and increase the rate of heat transfer. There are different groups of surfactants. From those I‟m conducting experimentation with anionic surfactant Ammonium Dodecyl Sulfate (ADS, which is most human friendly and three times best soluble than Sodium Dodecyl Sulfate, to test the heat transfer enhancement.

  18. The influence of three-dimensional capillary-porous coatings on heat transfer at liquid boiling

    Science.gov (United States)

    Surtaev, A. S.; Pavlenko, A. N.; Kalita, V. I.; Kuznetsov, D. V.; Komlev, D. I.; Radyuk, A. A.; Ivannikov, A. Yu.

    2016-04-01

    The process of heat transfer at pool boiling of liquid (Freon R21) on tubes with three-dimensional plasma-deposited capillary-porous coatings of various thicknesses has been experimentally studied. Comparative analysis of experimental data showed that the heat transfer coefficient for a heater tube with a 500-μm-thick porous coating is more than twice as large as that in liquid boiling on an otherwise similar uncoated tube. At the same time, no intensification of heat exchange in the regime of bubble boiling is observed on a tube with a 100-μm-thick porous coating.

  19. A molecular dynamics study of phobic/philic nano-patterning on pool boiling heat transfer

    Science.gov (United States)

    Diaz, Ricardo; Guo, Zhixiong

    2017-03-01

    Molecular dynamics (MD) simulations were employed to investigate the pool boiling heat transfer of a liquid argon thin film on a flat, horizontal copper wall structured with vertical nanoscale pillars. The efficacy of phobic/philic nano-patterning for enhancing boiling heat transfer was scrutinized. Both nucleate and explosive boiling modes were considered. An error analysis demonstrated that the typical 2.5σ cutoff in MD simulations could under-predict heat flux by about 8.7 %, and 6σ cutoff was chosen here in order to maintain high accuracy. A new coordination number criterion was also introduced to better quantify evaporation characteristics. Results indicate that the argon-phobic/philic patterning tends to either have no effect, or decrease overall boiling heat flux, while the argon-philic nano-pillar/argon-philic wall shows the best heat transfer performance.

  20. A molecular dynamics study of phobic/philic nano-patterning on pool boiling heat transfer

    Science.gov (United States)

    Diaz, Ricardo; Guo, Zhixiong

    2016-07-01

    Molecular dynamics (MD) simulations were employed to investigate the pool boiling heat transfer of a liquid argon thin film on a flat, horizontal copper wall structured with vertical nanoscale pillars. The efficacy of phobic/philic nano-patterning for enhancing boiling heat transfer was scrutinized. Both nucleate and explosive boiling modes were considered. An error analysis demonstrated that the typical 2.5σ cutoff in MD simulations could under-predict heat flux by about 8.7 %, and 6σ cutoff was chosen here in order to maintain high accuracy. A new coordination number criterion was also introduced to better quantify evaporation characteristics. Results indicate that the argon-phobic/philic patterning tends to either have no effect, or decrease overall boiling heat flux, while the argon-philic nano-pillar/argon-philic wall shows the best heat transfer performance.

  1. Heat Transfer in Nucleate Pool Boiling of Binary and Ternary Refrigerant Mixtures

    Institute of Scientific and Technical Information of China (English)

    赵耀华; 刁彦华; 鹤田隆治; 西川日出男

    2004-01-01

    Heat transfer coefficients in nucleate pool boiling were measured on a horizontal copper surface for refrigerants, HFC-134a, HFC-32, and HFC-125, their binary and ternary mixtures under saturated conditions at 0.9MPa. Compared to pure components, both binary and ternary mixtures showed lower heat transfer coefficients.This deterioration was more pronounced as heat flux was increased. Experimental data were compared with some empirical and semi-empirical correlations available in literature. For binary mixture, the accuracy of the correlations varied considerably with mixtures and the heat flux. Experimental data for HFC-32/134a/125 were also compared with available correlated equation obtained by Thome. For ternary mixture, the boiling range of binary mixture composed by the pure fluids with the lowest and the medium boiling points, and their concentration difference had important effects on boiling heat transfer coefficients.

  2. Introduction of image analysis for the quantification of the boiling flow heat transfer

    NARCIS (Netherlands)

    Ferret, C.; Falk, L.; d'Ortona, U.; Chenu, A.; Veenstra, T.T.

    2004-01-01

    Heat transfer performances for non-boiling and boiling flow of a micro-vaporizer have been measured by standard methods (temperatures, flow rates, effective power input). The study was carried out for laminar flow (Re<25) in silicon micro-channels (5 mm×3 cm×200 μm) filled with ordered obstacles to

  3. Experimental study on convective boiling heat transfer in narrow-gap annulus tubes

    Institute of Scientific and Technical Information of China (English)

    LI Bin; ZHAO Jian-Fu; ZHOU Fang-De; TANG Ze-Mei; HU Wen-Rui

    2004-01-01

    Since convective boiling or highly subcooled single-phase forced convection in micro-channels is an effective cooling mechanism with a wide range of applications, more experimental and theoretical studies are required to explain and verify the forced convection heat transfer phenomenon in narrow channels. In this experimental study, we model the convective boiling behavior of water with low latent heat substance Freon 113 (R-113), with the purpose of saving power consumption and visualizing experiments. Both heat transfer and pressure drop characteristics were measured in subcooled and saturated concentric narrow gap forced convection boiling. Data were obtained to qualitatively identify the effects of gap size, pressure, flow rate and wall superheat on boiling regimes and the transition between various regimes. Some significant differences from unconfined forced convection boiling were found,and also, the flow patterns in narrow vertical annulus tubes have been studied quantitatively.

  4. Critical Heat Flux of Boiling Heat Transfer in a Moderate Narrow Space

    Institute of Scientific and Technical Information of China (English)

    Yao-HuaZhan; TakashiMasuoka; 等

    1998-01-01

    Boiling heat transfer process is analyzed in a moderate narrow space consisted of two horizontal plates,The main difference between this process and the conventional unconfined pool boiling is the liquid supply mechanism which is absolutely prevented by the growth of coalescence bubble along with the heated surface in the narrow space.As a result,the macrolayer becomes thinner due to the evaporation of the individual bubbles within the macrolayer during the period of bubble coalescence,with or without dryout that depends on both the gap size of narrow space and the size of heated surface.For a specified size of the heated surface,the initial thickness of the liquid layer has a critical value which approaches a constant while the space height is larger than a critical value.The individual bubble behaviors and the heat transfer can be considered as the same as that in the unconfined pool boiling,if the space gap is large,However,the individual bubbles do not generate in the last period of the bubble coalescence and a lower maximum heat flux will be resulted if the space gap is reduced.In such a case,the macrolayer is dryout.

  5. Numerical Analysis of Lead-Bismuth-Water Direct Contact Boiling Heat Transfer

    Science.gov (United States)

    Yamada, Yumi; Takahashi, Minoru

    Direct contact boiling heat transfer of sub-cooled water with lead-bismuth eutectic (Pb-Bi) was investigated for the evaluation of the performance of steam generation in direct contact of feed water with primary Pb-Bi coolant in upper plenum above the core in Pb-Bi-cooled direct contact boiling water fast reactor. An analytical two-fluid model was developed to estimate the heat transfer numerically. Numerical results were compared with experimental ones for verification of the model. The overall volumetric heat transfer coefficient was calculated from heat exchange rate in the chimney. It was confirmed that the calculated results agreed well with the experimental result.

  6. Pool Boiling of FC 770 on Graphene Oxide Coatings: A Study of Critical Heat Flux and Boiling Heat Transfer Enhancement Mechanisms

    OpenAIRE

    Sayee Mohan, Kaushik

    2016-01-01

    This thesis investigates pool boiling heat transfer from bare and graphene-coated NiCr wires in a saturated liquid of FC 770, a fluorocarbon fluid. Of particular interest was the effect of graphene-oxide platelets, dip-coated onto the heater surface, in enhancing the nucleate boiling heat transfer (BHT) rates and the critical heat flux (CHF) value. In the course of the pool boiling experiment, the primary focus was on the reduction mechanism of graphene oxide. The transition from hydrophilic ...

  7. Heat Transfer From Electrically Heated Nichrome Wires to Boiling Water at Different Pressures

    Directory of Open Access Journals (Sweden)

    Devi Dayal

    1968-01-01

    Full Text Available Boiling curves for nucleate and film boiling have been drawn for nichrome of three sizes in distilled and degasified water at saturation temperatures under five different sub-atmospheric vapour pressure. It has been observed that (i for the same Q/A (heat transfer, Delta Theta (excess of wire temperature over saturation point of water decreases with pressure in both nucleate and film boiling ranges, (ii Both Q/A max. and Delta Theta/SubC show a rapid decrease with pressure but these variations become more gradual at higher pressures, and (iii Q/A max. and Delta Theta/SubC increase with wire size at all pressures; increase in Delta Theta/SubC however, becomes less conspicuous at higher pressures approaching one atmosphere.

  8. Heat transfer enhancement and surface thermostabilization for pool boiling on porous structures

    Directory of Open Access Journals (Sweden)

    Wojcik Tadeusz Michal

    2012-04-01

    Full Text Available The scope of the article includes the description of the experimental setup, methodology of the experimental studies, the study results for pool boiling heat transfer coefficient encountered on sintered capillary porous coverings. The results of own studies presented here refer to the boiling in a large volume on copper fibrous coverings. Hysteresis type I, II and III were described. Several examples of capillary porous surface coverings applications in purposely chosen complex boiling heat transfer processes have been presented based on Wojcik and Poniewski patents.

  9. Experimental Study on Convective Boiling Heat Transfer in Vertical Narrow Gap Annular Tube

    Institute of Scientific and Technical Information of China (English)

    Li Bin; He Anding; Wang Yueshe; Zhou Fangde

    2001-01-01

    Experiments are conducted to investigate the characteristics of single-phase forced-flow convection and boiling heat transfer of R113 flowing through annular tube with gap of 1, 1.5 and 2.5 mm, and also the visualization test are carried out to get two-phase flow regime. The data show that the Nusselt numbers for the narrow-gap are higher than those predicted by traditional large channel correlation and boiling heat transfer is enhanced. Based on the data obtained in this investigation, correlations for single-phase, forced convection and flow boiling in annular tube of different gap size has been developed.

  10. 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.

  11. 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.

  12. Design, Construction, and Qualification of a Microscale Heater Array for Use in Boiling Heat Transfer

    Science.gov (United States)

    Rule, T. D.; Kim, J.; Kalkur, T. S.

    1998-01-01

    Boiling heat transfer is an efficient means of heat transfer because a large amount of heat can be removed from a surface using a relatively small temperature difference between the surface and the bulk liquid. However, the mechanisms that govern boiling heat transfer are not well understood. Measurements of 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 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.

  13. Nucleate boiling heat transfer from a structured surface - Effect of liquid intake

    Energy Technology Data Exchange (ETDEWEB)

    Das, A.K.; Das, P.K.; Bhattacharyya, S.; Saha, P. [Department of Mechanical Engineering, Indian Institute of Technology, Kharagpur 721 302 (India)

    2007-04-15

    A model of the suction evaporation mode in nucleate boiling from tunnel and pore structures is presented. The model is based on the analysis by Nakayama et al. [W. Nakayama, T. Daikoku, H. Kuwahara, T. Nakajima, Dynamic model of enhanced boiling heat transfer on porous surfaces - Part II. Analytical model, ASME J. Heat Transfer 102 (3) (1980) 451-456] and L.H. Chein and R.L. Webb [A nucleate boiling model for structured enhanced surfaces, Int. J. Heat Mass Transfer 41 (14) (1998) 2183-2195]. Additionally, a detailed phenomenological model of liquid refill has been developed. It has been shown that the process of liquid refill and the time needed for it is strongly dependent on pool height. Effect of liquid pool height on bubble frequency has also been discussed. Finally, a generalized methodology is given for the prediction of boiling data from a structured surface. (author)

  14. Boiling heat transfer on single phosphor bronze and copper mesh microstructures

    Directory of Open Access Journals (Sweden)

    Orman Łukasz J.

    2014-03-01

    Full Text Available The paper presents experimental results of boiling heat transfer of distilled water and ethyl alcohol on surfaces covered with single layers of wire mesh structures made of phosphor bronze and copper. For each material two kinds of structures have been considered (higher and lower in order to determine the impact of the height of the structure on boiling heat transfer. The wire diameter of the copper meshes was 0,25 mm and 0,32 mm, while of the bronze meshes: 0,20 mm and 0,25 mm. The structures had the same mesh aperture (distance between the wires – 0,50 mm for copper and 0,40 for bronze but different wire diameter and, consequently, different height of the layers. The tests have been performed under ambient pressure in the pool boiling mode. The obtained results indicate a visible impact of the layer height on the boiling heat transfer performance of the analysed microstructures.

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

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Sung Joong; McKrell, Tom [Nuclear Science and Engineering Department, Massachusetts Institute of Technology (United States); Buongiorno, Jacopo, E-mail: jacopo@mit.ed [Nuclear Science and Engineering Department, Massachusetts Institute of Technology (United States); Hu Linwen [Nuclear Reactor Laboratory, Massachusetts Institute of Technology (United States)

    2010-05-15

    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 (approx40-50%) at the highest mass flux (G = 2500 kg/m{sup 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.

  16. Surface wettability effects on critical heat flux of boiling heat transfer using nanoparticle coatings

    KAUST Repository

    Hsu, Chin-Chi

    2012-06-01

    This study investigates the effects of surface wettability on pool boiling heat transfer. Nano-silica particle coatings were used to vary the wettability of the copper surface from superhydrophilic to superhydrophobic by modifying surface topography and chemistry. Experimental results show that critical heat flux (CHF) values are higher in the hydrophilic region. Conversely, CHF values are lower in the hydrophobic region. The experimental CHF data of the modified surface do not fit the classical models. Therefore, this study proposes a simple model to build the nexus between the surface wettability and the growth of bubbles on the heating surface. © 2012 Elsevier Ltd. All rights reserved.

  17. Mathematical and experimental modeling of nucleate boiling heat transfer in liquid nitrogen

    Science.gov (United States)

    Fusco, Ciro

    The investigation of nucleate boiling heat transfer, because of its complexity, is usually carried out experimentally and by using phenomenological approximations. The purpose of this work is to capture the essential features of nucleate boiling heat transfer in liquid nitrogen and to formulate a theoretical description useful for the prediction of the temperature fluctuations and beat flux. Experimental analysis was coupled with mathematical modeling to elucidate nucleate boiling heat transfer. The experimental setting consists of a platinum wire immersed in liquid nitrogen. A current is passed through the wire while the resistance is measured. The orientation of the wire can be changed from horizontal to vertical. The fluctuations of the wire temperature are measured. Using high-speed analysis, we characterized nucleate boiling heat transfer from the wire as occurring in two distinct phases or regimes: discrete nucleate boiling and transition boiling. We defined discrete nucleate boiling as the phase during which the active nucleation sites are clearly distinguishable from one another with no bubble coalescence occurring between adjacent sites. The high-speed analysis helped also to compute the frequencies, diameters, and nucleation density of departing bubbles as well as the energy loss by a single bubble during the discrete nucleate boiling regime. These parameters were subsequently used to formulate a mathematical model to simulate by discrete time steps the discrete nucleate boiling heat transfer from the platinum wire. The average temperature of the wire can be adequately modeled with only one variable, the power input. In addition to predicting the average temperature of the wire in the discrete nucleate boiling regime the model predicts well the average temperature of the wire in the conduction and convection regime and the transition regime. The model also reproduces the fluctuation of temperature in the discrete nucleate boiling regime. The mathematical

  18. Enhancing flow boiling heat transfer in microchannels for thermal management with monolithically-integrated silicon nanowires.

    Science.gov (United States)

    Li, D; Wu, G S; Wang, W; Wang, Y D; Liu, Dong; Zhang, D C; Chen, Y F; Peterson, G P; Yang, Ronggui

    2012-07-11

    Thermal management has become a critical issue for high heat flux electronics and energy systems. Integrated two-phase microchannel liquid-cooling technology has been envisioned as a promising solution, but with great challenges in flow instability. In this work, silicon nanowires were synthesized in situ in parallel silicon microchannel arrays for the first time to suppress the flow instability and to augment flow boiling heat transfer. Significant enhancement in flow boiling heat transfer performance was demonstrated for the nanowire-coated microchannel heat sink, such as an early onset of nucleate boiling, a delayed onset of flow oscillation, suppressed oscillating amplitudes of temperature and pressure drop, and an increased heat transfer coefficient.

  19. Boiling Heat Transfer in High Temperature Generator of Absorption Chiller/Heater

    Science.gov (United States)

    Furukawa, Masahiro; Enomoto, Eiichi; Sekoguchi, Kotohiko

    The heat transfer performance of forced convective boiling was tested using a high temperature generator of absorption chiller/heater, the rear furnace wall of which was composed of two different surfaces; i. e., plain and sprayed heated surfaces. These two surfaces were bisymmetrically set. Wall surface temperatures of both the fire and fluid sides were measured at three locations along the upward flow direction in each heated surface for determining the heat flux and heat transfer coefficient. Nickel-chromium and alumina were employed as the spray materials. The test results show that the sprayed surface can yield a marked elevation in the heat transfer performance due to boiling on the plain surface. Therefore the level of heated surface temperature is largely reduced by means of the spraying surface treatment. This implies that the spraying would much improve a corrosive condition of the heated surface.

  20. Experimental research on heat transfer to liquid sodium and its incipient boiling wall superheat in an annulus

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    Liquid sodium is mainly used as a cooling fluid in the liquid metal fast breeder reactor (LMFBR), whose heat transfer, whether convective heat transfer or boiling heat transfer, is different from that of water. So it is important for both normal and accidental operations of LMFBR to perform experimental research on heat transfer to liquid sodium and its boiling heat transfer. This study deals with heat transfer with high temperature (300-700℃) and low Pe number (20~70) and heat transfer with low temperature (250~270℃) and high Pe number (125~860), and its incipient boiling wall superheat in an annulus. Research on heat transfer involves theoretical research and experiments on heat transfer to liquid sodium. It also focuses on the theoretical analysis and experimental research on its incipient boiling wall superheat at positive pressure in an annulus. Semiempirical correlations were obtained and they were well coincident with the experimental data.

  1. Pool boiling heat transfer of deionized and degassed water in packed-perforated copper beads

    Science.gov (United States)

    Wen, Mao-Yu; Jang, Kuang-Jang; Ho, Ching-Yen

    2016-11-01

    Nucleate pool boiling with porous media made of perforated copper beads as the enhanced structure is conducted in saturated, deionized and degassed water. Data are taken at an atmospheric pressure (saturation temperature of 100 °C) and at heat fluxes from 4500 to 72,300 W/m2 while increasing the heat flux. The bead-packed structure is heated on the bottom. The layer of loose particles on the heated surface is free to move under the action of bulk liquid convection and vapor nucleation. The effects of the weight (number), size and layers of the free particles are experimentally explored using copper particles for different copper bead diameters which were 2, 3, 4 and 5 mm. The boiling enhancement is closely related to the particle weight, size and layers, and the heat flux applied. The results show that free particles are presented to have a distinct advantage in boiling heat transfer, resulting in an average increase in the heat transfer coefficient of 126 % relative to the flat plate without particles. In order to obtain insight into the fluid boiling phenomena, flow visualization is also made to observe the detailed fluid boiling characteristics of the copper particles present. The visualizations show that bubble nucleation preferentially occurs at the narrow corner cavities formed between the free particles and the heated surface.

  2. Studying heat transfer enhancement for water boiling on a surface with micro- and nanorelief

    Science.gov (United States)

    Kuzma-Kichta, Yu. A.; Lavrikov, A. V.; Shustov, M. V.; Chursin, P. S.; Chistyakova, A. V.; Zvonarev, Yu. A.; Zhukov, V. M.; Vasil'eva, L. T.

    2014-03-01

    We present the results from a study of heat transfer enhancement for bulk water boiling at atmospheric pressure on a surface with micro- and nanorelief, including a relief formed from silicon carbide and aluminum oxide nanoparticles. Horizontally oriented steel tube 1.2 mm in diameter and copper plate 15 × 3 mm in size were selected as test sections. The process was recorded by means of a video camera, and the values of heat transfer, critical heat fluxes, and contact angles were measured. The use of surface with micro- and nanorelief makes it possible to obtain a significantly higher critical heat flux and boiling heat transfer coefficient owing to a change of surface wettability. The results of investigations can find use in compact heat exchangers, refrigerating plants, heat pipes, in the mirrors of high-capacity lasers, in the targets and resonators of charged particle accelerators and for external cooling of reactor vessels under emergency conditions.

  3. Heat Transfer of Single and Binary Systems inPool Boiling

    Directory of Open Access Journals (Sweden)

    Abbas J. Sultan

    2010-01-01

    Full Text Available The present research focuses on the study of the effect of mass transfer resistance on the rate of heat transfer in pool boiling. The nucleate pool boiling heat transfer coefficients for binary mixtures (ethanol-n-butanol, acetone-n-butanol, acetone-ethanol, hexane-benzene, hexane-heptane, and methanol-water were measured at different concentrations of the more volatile components. The systems chosen covered a wide range of mixture behaviors.The experimental set up for the present investigation includes electric heating element submerged in the test liquid mounted vertically. Thermocouple and a digital indictor measured the temperature of the heater surface. The actual heat transfer rate being obtained by multiplying the voltmeter and ammeter readings. A water cooled coil condenses the vapor produced by the heat input and the liquid formed returns to the cylinder for re-evaporation.The boiling results show that the nucleate pool boiling heat transfer coefficients of binary mixtures were always lower than the pure components nucleate pool boiling heat transfer coefficients. This confirmed that the mass transfer resistance to the movement of the more volatile component was responsible for decrease in heat transfer and that the maximum deterioration that was observed at a point was the absolute concentration differences between vapor and liquid phases at their maximum. All the data points were tested with the most widely known correlations namely those of Calus-Leonidopoulos, Fujita and Thome. It was found that Thome's correlation is the more representative form, for it gave the least mean and standard deviations

  4. Development of Empirical Correlation to Calculate Pool Boiling Heat Transfer of Tandem Tubes

    Energy Technology Data Exchange (ETDEWEB)

    Kang, Myeong-Gie [Andong National University, Andong (Korea, Republic of)

    2015-10-15

    The heat exchanging tubes are in vertical alignment. For the cases, the upper tube is affected by the lower tube. Since heat transfer is closely related to the conditions of tube surface, bundle geometry, and liquid, lots of studies have been carried out for the several decades to investigate the combined effects of those factors on pool boiling heat transfer. One of the most important parameters in the analysis of a tube array is the pitch ( P ) between tubes. Many researchers have been investigated its effect on heat transfer enhancement for the tube bundles and the tandem tubes. The effect of a tube array on heat transfer enhancement was also studied for application to the flooded evaporators. Cornwell and Schuller studied the sliding bubbles by high speed photography to account the enhancement of heat transfer observed at the upper tubes of a bundle. The study by Memory et al. shows the effects of the enhanced surface and oil adds to the heat transfer of tube bundles. They identified that, for the structured and porous bundles, oil addition leads to a steady decrease in performance. The flow boiling of n-pentane across a horizontal tube bundle was investigated experimentally by Roser et al. They identified that convective evaporation played a significant part of the total heat transfer. The fouling of the tube bundle under pool boiling was also studied by Malayeri et al. They identified that the mechanisms of fouling on the middle and top heater substantially differ from those at the bottom heater.

  5. Boiling heat transfer enhancement of nanofluids on a smooth surface with agitation

    Science.gov (United States)

    Kong, Xin; Qi, Baojin; Wei, Jinjia; Li, Wei; Ding, Jie; Zhang, Yonghai

    2016-12-01

    The pool boiling heat transfer performance on a smooth silicon chip surface with agitation was experimentally investigated in this study. The nanofluids (Ag/alcohol) of 0.02 % volume concentration and ethyl alcohol with purification over 99.9 % were the two contrast working fluids. For each group, subcoolings of 40, 50 and 60 K were conducted under atmospheric pressure. To enhance the heat transfer performance, an agitating device was fixed above the top of the chip. The experimental results indicated that nanofluids could enhance the heat transfer performance especially in the nucleate boiling region. The heat transfer coefficient was significantly increased with nanofluids, while the critical heat flux (CHF) was nearly not changed. In the agitation Reynolds number of 20,300, the heat transfer performance of nanofluids was significantly enhanced in the convection region, and the CHF was increased by more than 25 % for all groups. This boiling phenomenon was observed for both nanofluids and alcohol groups. Meanwhile, the boiling curves of different liquid subcoolings in the nucleate region were quite similar to each other under agitation.

  6. A study on the correlations development for film boiling heat transfer on spheres

    Energy Technology Data Exchange (ETDEWEB)

    Jeong, Yong Hoon; Baek, Won Pil; Chang, Soon Heung [Korea Advanced Institute of Science and Technology, Taejon (Korea, Republic of)

    1998-12-31

    Film boiling is the heat transfer mechanism that can occurs when large temperature differences exist between a cold liquid and hot material. In the nuclear reactor safety analysis, film boiling has become an important issue in recent years. During severe accident, hot molten corium fall into relatively cool water, and fragment into spheres or sphere-like particles. If the steam explosion is triggered, the thermal energy of corlium is converted into the mechanical energy that can threaten the integrity of reactor vessel or reactor cavity. One of the important concerns in the heat transfer analysis during pre-mixing stage is the film boiling heat transfer between the corium and water/steam two-phase flow. Until now, considerable works on film boiling have been performed. However, there is no available correlation adequate for severe accident analysis. In this study, film boiling heat transfer correlations have been developed, and their applicable ranges have been enlarged and their prediction accuracy has been enhanced. 7 refs., 5 figs., 5 tabs. (Author)

  7. Bubble Dynamics, Two-Phase Flow, and Boiling Heat Transfer in Microgravity

    Science.gov (United States)

    Chung, Jacob N.

    1998-01-01

    This report contains two independent sections. Part one is titled "Terrestrial and Microgravity Pool Boiling Heat Transfer and Critical heat flux phenomenon in an acoustic standing wave." Terrestrial and microgravity pool boiling heat transfer experiments were performed in the presence of a standing acoustic wave from a platinum wire resistance heater using degassed FC-72 Fluorinert liquid. The sound wave was created by driving a half wavelength resonator at a frequency of 10.15 kHz. Microgravity conditions were created using the 2.1 second drop tower on the campus of Washington State University. Burnout of the heater wire, often encountered with heat flux controlled systems, was avoided by using a constant temperature controller to regulate the heater wire temperature. The amplitude of the acoustic standing wave was increased from 28 kPa to over 70 kPa and these pressure measurements were made using a hydrophone fabricated with a small piezoelectric ceramic. Cavitation incurred during experiments at higher acoustic amplitudes contributed to the vapor bubble dynamics and heat transfer. The heater wire was positioned at three different locations within the acoustic field: the acoustic node, antinode, and halfway between these locations. Complete boiling curves are presented to show how the applied acoustic field enhanced boiling heat transfer and increased critical heat flux in microgravity and terrestrial environments. Video images provide information on the interaction between the vapor bubbles and the acoustic field. Part two is titled, "Design and qualification of a microscale heater array for use in boiling heat transfer." This part is summarized herein. Boiling heat transfer is an efficient means of heat transfer because a large amount of heat can be removed from a surface using a relatively small temperature difference between the surface and the bulk liquid. However, the mechanisms that govern boiling heat transfer are not well understood. Measurements of

  8. Flow Boiling Heat Transfer in Two-Phase Micro Channel Heat Sink at Low Water Mass Flux

    Science.gov (United States)

    Kuznetsov, Vladimir V.; Shamirzaev, Alisher S.

    2009-08-01

    Boiling heat transfer at water flow with low mass flux in heat sink which contained rectangular microchannels was studied. The stainless steel heat sink contained ten parallel microchannels with a size of 640 × 2050 μm in cross-section with typical wall roughness of 10-15 μm. The local flow boiling heat transfer coefficients were measured at mass velocity of 17 and 51 kg/m2s, heat flux on 30 to 150 kW/m2 and vapor quality of up to 0.8 at pressure in the channels closed to atmospheric one. It was observed that Kandlikar nucleate boiling correlation is in good agreement with the experimental data at mass flow velocity of 85 kg/m2s. At smaller mass flux the Kandlikar model and Zhang, Hibiki and Mishima model demonstrate incorrect trend of heat transfer coefficients variation with vapor quality.

  9. Natural convection heat transfer characteristics of the molten metal pool with solidification by boiling coolant

    Energy Technology Data Exchange (ETDEWEB)

    Cho, Jae Seon; Suh, Kune Yull; Chung, Chang Hyun [Seoul National University, Seoul (Korea, Republic of); Paark, Rae Joon; Kim, Sang Baik [Korea Atomic Energy Research Institute, Taejon (Korea, Republic of)

    1997-12-31

    This paper presents results of experimental studies on the heat transfer and solidification of the molten metal pool with overlying coolant with boiling. The metal pool is heated from the bottom surface and coolant is injected onto the molten metal pool. Ad a result, the crust, which is a solidified layer, may form at the top of the molten metal pool. Heat transfer is accomplished by a conjugate mechanism, which consists of the natural convection of the molten metal pool, the conduction in the crust layer and the convective boiling heat transfer in the coolant. This work examines the crust formation and the heat transfer rate on the molten metal pool with boiling coolant. The simulant molten pool material is tin (Sn) with the melting temperature of 232 deg C. Demineralized water is used as the working coolant. The crust layer thickness was ostensibly varied by the heated bottom surface temperature of the test section, but not much affected by the coolant injection rate. The correlation between the Nusselt number and the Rayleigh number in the molten metal pool region of this study is compared against the crust formation experiment without coolant boiling and the literature correlations. The present experimental results are higher than those from the experiment without coolant boiling, but show general agreement with the Eckert correlation, with some deviations in the high and low ends of the Rayleigh number. This discrepancy is currently attributed to concurrent rapid boiling of the coolant on top of the metal layer. 10 refs., 4 figs., 1 tab. (Author)

  10. Heat Transfer Enhancement Due to Marangoni Flow Around Moving Bubbles During Nucleate Boiling

    Institute of Scientific and Technical Information of China (English)

    David M. Christopher; WANG Hao; PENG Xiaofeng

    2006-01-01

    Nucleate boiling is a very efficient method for generating high heat transfer rates from solid surfaces; however, the fundamental physical mechanisms governing nucleate boiling heat transfer are not well understood. The heat transfer mechanisms around stationary and moving bubbles on very thin microwires were analyzed numerically to evaluate the effect of the bubble motion on the heat transfer from the wire surface. The numerical analysis accurately models the experimentally observed bubble movement and fluid velocities. The analytical model includes the effects of the Marangoni flow around the bubble and the evaporation and condensation within the bubble. The analysis shows that the heat transfer was significantly enhanced by the Marangoni flow around the outside of the bubble which transfers at least twice as much energy from the wire as the heat transfer directly from the wire to the bubble. The enhanced heat transfer due to the Marangoni flow was evident for both stationary and moving bubbles. The moving bubbles also created a wake that further enhanced the heat transfer from the wire. Since the Marangoni number for water is greater than for ethanol for the same conditions, the Marangoni flow and, hence, the bubble velocities are predicted to be greater in water than in ethanol.

  11. Enhancement of Pool Boiling Heat Transfer to Lithium Bromide Aqueous Solution

    Science.gov (United States)

    Furukawa, Masahiro; Kaji, Masuo; Suyama, Takayuki; Sekoguchi, Kotohiko

    An experimental study on enhancement of nucleate pool boiling heat tranfer by placing a sponge metal close to a plain heated surface was conducted in order to improve the heat transfer performance of the high temperature generator of absorption chiller/heater. The sponge metal has three dimensional porous mesh framework like sponge. Boiling curves of water under the atmospheric pressure were compared with those of lithium bromide aqueous solution of mass concentration 55 to 58%. Heat transfer characteristics were improved by 2 to3 times both for water and lithium bromide aqueous solution when the sponge metal was placed on the heated surface with and without cleareance. Three kinds of sponge metals were used for lithium bromide aqueous solution under the reduced pressure (24 kPa). At lower heat fluxes,#6 sponge metal which has the finest mesh and the lowest porosity shows excellent results. At high heat fluxes, however,it causes deterioration of heat transfer. Over the wide range of heat fluxes,# 4 sponge metal was found to be most suitable and the optimal clearence was determined as 0.5 mm. The sponge metal is of good practical use as a device to enhance the boiling, since no special manufacturing is required for placing it on the heated surface.

  12. Two-phase flow and boiling heat transfer in two vertical narrow annuli

    Energy Technology Data Exchange (ETDEWEB)

    Peng Changhong [Department of Nuclear and Thermal Power Engineering, Xi' an Jiaotong University, Xian 710049 (China)]. E-mail: pxm321@163.com; Guo Yun [Department of Nuclear and Thermal Power Engineering, Xi' an Jiaotong University, Xian 710049 (China); Qiu Suizheng [Department of Nuclear and Thermal Power Engineering, Xi' an Jiaotong University, Xian 710049 (China); Jia Dounan [Department of Nuclear and Thermal Power Engineering, Xi' an Jiaotong University, Xian 710049 (China); Nie Changhua [Nuclear Power Institute of China, Chengdu 610041 (China)

    2005-07-01

    Experimental study associated with two-phase flow and heat transfer during flow boiling in two vertical narrow annuli has been conducted. The parameters examined were: mass flux from 38.8 to 163.1 kg/m{sup 2} s; heat flux from 4.9 to 50.7 kW/m{sup 2} for inside tube and from 4.2 to 78.8 kW/m{sup 2} for outside tube; equilibrium mass quality from 0.02 to 0.88; system pressure from 1.5 to 6.0 MPa. It was found that the boiling heat transfer was strongly influenced by heat flux, while the effect of mass velocity and mass quality were not very significant. This suggested that the boiling heat transfer was mainly via nucleate boiling. The data were used to develop a new correlation for boiling heat transfer in the narrow annuli. In the two-phase flow study, the comparison with the correlation of Chisholm [Chisholm, D., 1967. A theoretical basis for the Lockhart-Martinelli correlation for two-phase flow. Int. J. Heat Mass Transfer 10, 1767-1778] and Mishima and Hibiki [Mishima, K., Hibiki, T., 1996. Some characteristics of air-water two-phase flow in small diameter vertical tubes. Int. J. Multiphase Flow 22, 703-712] indicated that the existing correlations could not predict the two-phase multiplier in the narrow annuli well. Based on the experimental data, a new correlation was developed.

  13. Analysis of flow boiling heat transfer in narrow annular gaps applying the design of experiments method

    Directory of Open Access Journals (Sweden)

    Gunar Boye

    2015-06-01

    Full Text Available The axial heat transfer coefficient during flow boiling of n-hexane was measured using infrared thermography to determine the axial wall temperature in three geometrically similar annular gaps with different widths (s = 1.5 mm, s = 1 mm, s = 0.5 mm. During the design and evaluation process, the methods of statistical experimental design were applied. The following factors/parameters were varied: the heat flux q · = 30 − 190 kW / m 2 , the mass flux m · = 30 − 700 kg / m 2 s , the vapor quality x · = 0 . 2 − 0 . 7 , and the subcooled inlet temperature T U = 20 − 60 K . The test sections with gap widths of s = 1.5 mm and s = 1 mm had very similar heat transfer characteristics. The heat transfer coefficient increases significantly in the range of subcooled boiling, and after reaching a maximum at the transition to the saturated flow boiling, it drops almost monotonically with increasing vapor quality. With a gap width of 0.5 mm, however, the heat transfer coefficient in the range of saturated flow boiling first has a downward trend and then increases at higher vapor qualities. For each test section, two correlations between the heat transfer coefficient and the operating parameters have been created. The comparison also shows a clear trend of an increasing heat transfer coefficient with increasing heat flux for test sections s = 1.5 mm and s = 1.0 mm, but with increasing vapor quality, this trend is reversed for test section 0.5 mm.

  14. Heat and momentum transfer model studies applicable to once-through, forced convection potassium boiling

    Science.gov (United States)

    Sabin, C. M.; Poppendiek, H. F.

    1971-01-01

    A number of heat transfer and fluid flow mechanisms that control once-through, forced convection potassium boiling are studied analytically. The topics discussed are: (1) flow through tubes containing helical wire inserts, (2) motion of droplets entrained in vapor flow, (3) liquid phase distribution in boilers, (4) temperature distributions in boiler tube walls, (5) mechanisms of heat transfer regime change, and (6) heat transfer in boiler tubes. Whenever possible, comparisons of predicted and actual performances are made. The model work presented aids in the prediction of operating characteristics of actual boilers.

  15. Heat transfer coefficient determination for flow boiling in vertical and horizontal minichannels

    Directory of Open Access Journals (Sweden)

    Piasecka Magdalena

    2014-03-01

    Full Text Available The paper presents the results of boiling heat transfer research during FC-72 laminar flow along a minichannel of 1 mm depth, positioned vertically and horizontally, with an enhanced heating surface. One glass pane allows to determine the temperature of the heating wall by liquid crystal thermography. Calculations are aimed at the evaluation of one- and two-dimensional heat transfer approaches to determine the local heat transfer coefficient. In the one-dimensional approach only the direction of the flow in the channel is considered. In the two-dimensional approach the inverse problem in the heating wall and the direct problem in the glass barrier were solved by the finite element method with Trefftz functions as shape functions (FEMT. The developed flow boiling area was studied. Heat transfer coefficient values obtained for the horizontal minichannel were higher than those obtained for the vertical one. When the heat flux supplied to heating wall grows, the share of gas-phase increases leading to the heat transfer coefficient decreases. The same courses of the experiment were observed for the two applied methods, but the results obtained in the one-dimensional approach are considerably higher than in the two-dimensional one. One-dimensional approach seems to be less sensitive to measurement errors.

  16. Physics of microstructures enhancement of thin film evaporation heat transfer in microchannels flow boiling

    Science.gov (United States)

    Bigham, Sajjad; Fazeli, Abdolreza; Moghaddam, Saeed

    2017-03-01

    Performance enhancement of the two-phase flow boiling heat transfer process in microchannels through implementation of surface micro- and nanostructures has gained substantial interest in recent years. However, the reported results range widely from a decline to improvements in performance depending on the test conditions and fluid properties, without a consensus on the physical mechanisms responsible for the observed behavior. This gap in knowledge stems from a lack of understanding of the physics of surface structures interactions with microscale heat and mass transfer events involved in the microchannel flow boiling process. Here, using a novel measurement technique, the heat and mass transfer process is analyzed within surface structures with unprecedented detail. The local heat flux and dryout time scale are measured as the liquid wicks through surface structures and evaporates. The physics governing heat transfer enhancement on textured surfaces is explained by a deterministic model that involves three key parameters: the drying time scale of the liquid film wicking into the surface structures (τd), the heating length scale of the liquid film (δH) and the area fraction of the evaporating liquid film (Ar). It is shown that the model accurately predicts the optimum spacing between surface structures (i.e. pillars fabricated on the microchannel wall) in boiling of two fluids FC-72 and water with fundamentally different wicking characteristics.

  17. Physics of microstructures enhancement of thin film evaporation heat transfer in microchannels flow boiling

    Science.gov (United States)

    Bigham, Sajjad; Fazeli, Abdolreza; Moghaddam, Saeed

    2017-01-01

    Performance enhancement of the two-phase flow boiling heat transfer process in microchannels through implementation of surface micro- and nanostructures has gained substantial interest in recent years. However, the reported results range widely from a decline to improvements in performance depending on the test conditions and fluid properties, without a consensus on the physical mechanisms responsible for the observed behavior. This gap in knowledge stems from a lack of understanding of the physics of surface structures interactions with microscale heat and mass transfer events involved in the microchannel flow boiling process. Here, using a novel measurement technique, the heat and mass transfer process is analyzed within surface structures with unprecedented detail. The local heat flux and dryout time scale are measured as the liquid wicks through surface structures and evaporates. The physics governing heat transfer enhancement on textured surfaces is explained by a deterministic model that involves three key parameters: the drying time scale of the liquid film wicking into the surface structures (τd), the heating length scale of the liquid film (δH) and the area fraction of the evaporating liquid film (Ar). It is shown that the model accurately predicts the optimum spacing between surface structures (i.e. pillars fabricated on the microchannel wall) in boiling of two fluids FC-72 and water with fundamentally different wicking characteristics. PMID:28303952

  18. Physics of microstructures enhancement of thin film evaporation heat transfer in microchannels flow boiling.

    Science.gov (United States)

    Bigham, Sajjad; Fazeli, Abdolreza; Moghaddam, Saeed

    2017-03-17

    Performance enhancement of the two-phase flow boiling heat transfer process in microchannels through implementation of surface micro- and nanostructures has gained substantial interest in recent years. However, the reported results range widely from a decline to improvements in performance depending on the test conditions and fluid properties, without a consensus on the physical mechanisms responsible for the observed behavior. This gap in knowledge stems from a lack of understanding of the physics of surface structures interactions with microscale heat and mass transfer events involved in the microchannel flow boiling process. Here, using a novel measurement technique, the heat and mass transfer process is analyzed within surface structures with unprecedented detail. The local heat flux and dryout time scale are measured as the liquid wicks through surface structures and evaporates. The physics governing heat transfer enhancement on textured surfaces is explained by a deterministic model that involves three key parameters: the drying time scale of the liquid film wicking into the surface structures (τd), the heating length scale of the liquid film (δH) and the area fraction of the evaporating liquid film (Ar). It is shown that the model accurately predicts the optimum spacing between surface structures (i.e. pillars fabricated on the microchannel wall) in boiling of two fluids FC-72 and water with fundamentally different wicking characteristics.

  19. Experimental Study and Heat Transfer Analysis on the Boiling of Saturated Liquid Nitrogen under Transient Pulsed Laser Irradiation

    Institute of Scientific and Technical Information of China (English)

    Zhaoyi DONG; Xiulan HUAI

    2005-01-01

    The boiling behavior of the liquid nitrogen (LN2) under the transient high heat flux urgently needs to be researched systematically. In this paper, the high power short pulse duration laser was used to heat the saturated LN2 rapidly, and the high-speed photography aided by the spark light system was employed to take series of photos which displayed the process of LN2's boiling behavior under such conditions. Also, a special temperature measuring system was applied to record the temperature variation of the heating surface. The experiments indicated that an explosive boiling happened within LN2 by the laser heating, and a conventional boiling followed up after the newly-defined changeover time. By analyzing the temperature variation of the heating surface, it is found that the latent heat released by the crack of the bubbles in the bubble cluster induced by the explosive boiling is an important factor that greatly influences the boiling heat transfer mechanism.

  20. Pool boiling heat transfer on vertical fins with wire mesh structures

    Directory of Open Access Journals (Sweden)

    Pastuszko Robert

    2012-04-01

    Full Text Available Experimental investigations into pool boiling heat transfer on finned arrays with internal tunnels limited by copper wire mesh were conducted. The experiments were carried out for water, ethanol and fluorinert FC-72 at atmospheric pressure. The wire net with mesh aperture of 0.3 and 0.5 mm, sintered with the vertical side of the 10 mm high rectangular fins and horizontal inter-fin surface formed a system of connected tunnels. Tunnel width was 0.6 and 1.0 mm. Substantial enhancement of heat transfer coefficient was observed for the investigated surfaces. In water, ethanol and FC-72 boiling the highest increase in the heat transfer coefficient was obtained for the surface with mesh aperture of 0.5 mm and tunnel width of 0.6 mm. The ratio of boiling heat transfer coefficients for the investigated fins with mesh covering and smooth fins (10 mm height, at the heat flux 100 kW/m2, was about 3 for water and ethanol as working fluids.

  1. Film boiling heat transfer from a wire to upward flow of liquid hydrogen and liquid nitrogen

    Science.gov (United States)

    Shiotsu, M.; Shirai, Y.; Horie, Y.; Shigeta, H.; Higa, D.; Tatsumoto, H.; Hata, K.; Kobayashi, H.; Nonaka, S.; Naruo, Y.; Inatani, Y.

    2015-11-01

    Film boiling heat transfer coefficients in liquid hydrogen were measured for the heater surface superheats to 300 K under pressures from 0.4 to 1.1 MPa, liquid subcoolings to 11 K and flow velocities to 8 m/s. Two test wires were both 1.2 mm in diameter, 120 mm and 200 mm in lengths and were made of PtCo alloy. The test wires were located on the center of 8 mm and 5 mm diameter conduits of FRP (Fiber Reinforced Plastics). Furthermore film boiling heat transfer coefficients in liquid nitrogen were measured only for the 200 mm long wire. The film boiling heat transfer coefficients are higher for higher pressure, higher subcooling, and higher flow velocity. The experimental data were compared with a conventional equation for forced flow film boiling in a wide channel. The data for the 8 mm diameter conduit were about 1.7 times and those for the 5 mm conduit were about 1.9 times higher than the predicted values by the equation. A new equation was presented modifying the conventional equation based on the liquid hydrogen and liquid nitrogen data. The experimental data were expressed well by the equation.

  2. Investigation on the heat transfer characteristics during flow boiling of liquefied natural gas in a vertical micro-fin tube

    Science.gov (United States)

    Xu, Bin; Shi, Yumei; Chen, Dongsheng

    2014-03-01

    This paper presents an experimental investigation on the heat transfer characteristics of liquefied natural gas flow boiling in a vertical micro-fin tube. The effect of heat flux, mass flux and inlet pressure on the flow boiling heat transfer coefficients was analyzed. The Kim, Koyama, and two kinds of Wellsandt correlations with different Ftp coefficients were used to predict the flow boiling heat transfer coefficients. The predicted results showed that the Koyama correlation was the most accurate over the range of experimental conditions.

  3. Heat transfer effect of an extended surface in downward-facing subcooled flow boiling

    Energy Technology Data Exchange (ETDEWEB)

    Khan, Abdul R., E-mail: khan@vis.t.u-tokyo.ac.jp [Department of Nuclear Engineering and Management, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan); Erkan, Nejdet, E-mail: erkan@vis.t.u-tokyo.ac.jp [Nuclear Professional School, School of Engineering, The University of Tokyo, 2-22 Shirakata, Tokai-mura, Ibaraki, 319-1188 (Japan); Okamoto, Koji, E-mail: okamoto@n.t.u-tokyo.ac.jp [Nuclear Professional School, School of Engineering, The University of Tokyo, 2-22 Shirakata, Tokai-mura, Ibaraki, 319-1188 (Japan)

    2015-12-15

    Highlights: • Compare downward-facing flow boiling results from bare and extended surfaces. • Upstream and downstream temperatures were measured on the extended surface. • Downstream temperatures exceed upstream temperatures for all flow rates. • Bubble accumulation occurs downstream on extended surface. • Extended surface heat transfer lower than bare surface as flow rate reduced. - Abstract: New BWR containment designs are considering cavity flooding as an accident management strategy. Unlike the PWR, the BWR has many Control Rod Guide Tube (CRGT) penetrations in the lower head. During a severe accident scenario with core melt in the lower plenum along with cavity flooding, the penetrations may affect the heat transfer on the ex-vessel surface and disrupt fluid flow during the boiling process. A small-scale experiment was performed to investigate the issues existing in downward-facing boiling phenomenon with an extended surface. The results were compared with a bare (flat) surface. The mass flux of 244 kg/m{sup 2} s, 215 kg/m{sup 2} s, and 177 kg/m{sup 2} s were applied in this study. CHF conditions were observed only for the 177 kg/m{sup 2} s case. The boiling curves for both types of surfaces and all flow rates were obtained. The boiling curves for the highest flow rate showed lower surface temperatures for the extended surface experiments when compared to the bare surface. The downstream location on the extended surface yielded the highest surface temperatures as the flow rate was reduced. The bubble accumulation and low velocity in the wake produced by flow around the extended surface was believed to have caused the elevated temperatures in the downstream location. Although an extended surface may enhance the overall heat transfer, a reduction in the local heat transfer was observed in the current experiments.

  4. Bubble dynamics and heat transfer for pool boiling on hydrophilic, superhydrophobic and biphilic surfaces

    Science.gov (United States)

    Teodori, E.; Palma, T.; Valente, T.; Moita, A. S.; Moreira, A. L. N.

    2016-09-01

    This paper proposes a detailed analysis of bubble dynamics to describe pool boiling heat transfer in extreme wetting scenarios (superhydrophobic vs hydrophilic). A mechanistic approach, based on extensive post-processing allows quantifying the relative advantage of the superhydrophobic surfaces to endorse the onset of boiling at very low superheats (1-2K) vs their worse heat transfer performance associated to the swift formation of an insulating vapour film. Based on this analysis, a simple biphilic surface is created. The results suggest that for high heat fluxes, bubble dynamics is dominated by the emission of very small bubbles, which seems to affect the interaction mechanisms, precluding the emission of the large bubbles from the surface, thus compromising the good performance of the biphilic surfaces.

  5. Nano-inspired fluidic interactivity for boiling heat transfer: impact and criteria

    Science.gov (United States)

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

    2016-01-01

    The enhancement of boiling heat transfer, the most powerful energy-transferring technology, will lead to milestones in the development of high-efficiency, next-generation energy systems. Perceiving nano-inspired interface functionalities from their rough morphologies, we demonstrate interface-induced liquid refreshing is essential to improve heat transfer by intrinsically avoiding Leidenfrost phenomenon. High liquid accessibility of hemi-wicking and catalytic nucleation, triggered by the morphological and hydrodynamic peculiarities of nano-inspired interfaces, contribute to the critical heat flux (CHF) and the heat transfer coefficient (HTC). Our experiments show CHF is a function of universal hydrodynamic characteristics involving interfacial liquid accessibility and HTC is improved with a higher probability of smaller nuclei with less superheat. Considering the interface-induced and bulk liquid accessibility at boiling, we discuss functionalizing the interactivity between an interface and a counteracting fluid seeking to create a novel interface, a so-called smart interface, for a breakthrough in boiling and its pragmatic application in energy systems. PMID:27708341

  6. Nano-inspired fluidic interactivity for boiling heat transfer: impact and criteria

    Science.gov (United States)

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

    2016-10-01

    The enhancement of boiling heat transfer, the most powerful energy-transferring technology, will lead to milestones in the development of high-efficiency, next-generation energy systems. Perceiving nano-inspired interface functionalities from their rough morphologies, we demonstrate interface-induced liquid refreshing is essential to improve heat transfer by intrinsically avoiding Leidenfrost phenomenon. High liquid accessibility of hemi-wicking and catalytic nucleation, triggered by the morphological and hydrodynamic peculiarities of nano-inspired interfaces, contribute to the critical heat flux (CHF) and the heat transfer coefficient (HTC). Our experiments show CHF is a function of universal hydrodynamic characteristics involving interfacial liquid accessibility and HTC is improved with a higher probability of smaller nuclei with less superheat. Considering the interface-induced and bulk liquid accessibility at boiling, we discuss functionalizing the interactivity between an interface and a counteracting fluid seeking to create a novel interface, a so-called smart interface, for a breakthrough in boiling and its pragmatic application in energy systems.

  7. Lattice Boltzmann modeling of boiling heat transfer: The boiling curve and the effects of wettability

    OpenAIRE

    Li, Q; Kang, Q. J.; Francois, M. M.; He, Y. L.; Luo, K. H.

    2015-01-01

    A hybrid thermal lattice Boltzmann (LB) model is presented to simulate thermal multiphase flows with phase change based on an improved pseudopotential LB approach [Q. Li, K. H. Luo, and X. J. Li, Phys. Rev. E 87, 053301 (2013)]. The present model does not suffer from the spurious term caused by the forcing-term effect, which was encountered in some previous thermal LB models for liquid-vapor phase change. Using the model, the liquid-vapor boiling process is simulated. The boiling curve togeth...

  8. Heat Transfer in Film Boiling from Electrically Heated Nichrome Wire to Boiling Water at Different Pressure-II

    Directory of Open Access Journals (Sweden)

    Devi Dayal

    1969-01-01

    Full Text Available Values of film thickness in film boiling have been computed for three different sizes of nichrome wires at five different sub-atmospheric pressures. The values of alpha , total heat transmission co-efficient, ac heat transmission co-efficient due to conduction through the vapour film and alpha R, heat transmission co-efficient due to radiation, have been calculated. The values of film thickness were found to decrease with external pressure, but were found to increase slightly with the radius of the wire. alpha & alpha c both increase with rise of pressure but decrease with the radius of the radius of the heated wire. Alpha R shows a minimum value at a pressure of 15 cm. of Hg. in the case of all the wire sizes. The radiation loss alpha R is much smaller than conduction loss alpha. "

  9. An experimental study on micro-scale flow boiling heat transfer

    Energy Technology Data Exchange (ETDEWEB)

    Tibirica, Cristiano Bigonha; Ribatski, Gherhardt [Universidade de Sao Paulo (USP), Sao Carlos, SP (Brazil). Escola de Engenharia. Dept. de Engenharia Mecanica

    2009-07-01

    In this paper, new experimental flow boiling heat transfer results in micro-scale tubes are presented. The experimental data were obtained in a horizontal 2.32 mm I.D. stainless steel tube with heating length of 464 mm, R134a as working fluid, mass velocities ranging from 50 to 600 kg/m{sup 2}s, heat flux from 5 to 55 kW/m{sup 2}, exit saturation temperatures of 22, 31 and 41 deg C, and vapor qualities from 0.05 to 0.98. Flow pattern characterization was also performed from images obtained by high speed filming. Heat transfer coefficient results from 2 to 14 kW/m{sup 2}K were measured. It was found that the heat transfer coefficient is a strong function of the saturation pressure, heat flux, mass velocity and vapor quality. The experimental data were compared against the following micro-scale flow boiling predictive methods from the literature: Saitoh et al., Kandlikar, Zhang et al. and Thome et al. Comparisons against these methods based on the data segregated according to flow patterns were also performed. Though not satisfactory, Saitoh et al. worked the best and was able of capturing most of the experimental heat transfer trends. (author)

  10. Two dimensional heat transfer problem in flow boiling in a rectangular minichannel

    Directory of Open Access Journals (Sweden)

    Hożejowska Sylwia

    2015-01-01

    Full Text Available The paper presents mathematical modelling of flow boiling heat transfer in a rectangular minichannel asymmetrically heated by a thin and one-sided enhanced foil. Both surfaces are available for observations due to the openings covered with glass sheets. Thus, changes in the colour of the plain foil surface can be registered and then processed. Plain side of the heating foil is covered with a base coat and liquid crystal paint. Observation of the opposite, enhanced surface of the minichannel allows for identification of the gas-liquid two-phase flow patterns and vapour quality. A two-dimensional mathematical model of heat transfer in three subsequent layers (sheet glass, heating foil, liquid was proposed. Heat transfer in all these layers was described with the respective equations: Laplace equation, Poisson equation and energy equation, subject to boundary conditions corresponding to the observed physical process. The solutions (temperature distributions in all three layers were obtained by Trefftz method. Additionally, the temperature of the boiling liquid was obtained by homotopy perturbation method (HPM combined with Trefftz method. The heat transfer coefficient, derived from Robin boundary condition, was estimated in both approaches. In comparison, the results by both methods show very good agreement especially when restricted to the thermal sublayer.

  11. Flow film boiling heat transfer for subcooled liquids flowing upward perpendicular to single horizontal cylinders

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Q.S. [Kobe Univ. of Mercantile Marine, Dept. of Nuclear Engineering (Japan); Shiotsu, M. [Kyoto Univ., Dept. of Energy Sci. and Tech. (Japan); Sakurai, A. [Kyoto Univ. (Japan)

    2001-07-01

    The knowledge of flow film boiling heat transfer on a horizontal cylinder in various liquids flowing upward perpendicular to the cylinder is important as the database for the safety evaluation of the accidents such as rapid power burst and pressure reduction in the nuclear power plants. Flow film boiling heat transfer from single horizontal cylinders in water and Freon-113 flowing upward perpendicular to the cylinder under subcooled conditions was measured under wide experimental conditions. The flow velocities ranged from 0 to 1 m/s, the system pressures ranged from 100 to 500 kPa, and the surface superheats were raised up to 800 K for water and 400 K for Freon-113, respectively. Platinum horizontal cylinders with diameters ranging from 0.7 to 5 mm were used as the test heaters. The test heater was heated by direct electric current. The experimental data of film boiling heat transfer coefficients show that they increase with the increase of flow velocity, liquid subcooling, system pressure and with the decrease of cylinder diameter. Based on the experimental data, a correlation for subcooled flow film boiling heat transfer including the effects of liquid subcooling and radiation was presented, which can describe the experimental data obtained within 20% for the flow velocities below 0.7 m/s, and within -30% to +20% for the higher flow velocities. The correlation also predicted well the data by Shigechi (1983), Motte and Bromley (1957), and Sankaran and Witte (1990) obtained for the larger diameter cylinders and higher flow velocities in various liquids at the pressures of near atmospheric. The Shigechi's data were in the range from about -20% to +15%, the data of Motte and Bromley were about 30%,and the data of Sankaran and Witte were within +20 % of the curves given by the corresponding predicted values. (authors)

  12. Experimental study on flow boiling heat transfer of LNG in a vertical smooth tube

    Science.gov (United States)

    Chen, Dongsheng; Shi, Yumei

    2013-10-01

    An experimental apparatus is set up in this work to study the upward flow boiling heat transfer characteristics of LNG (liquefied natural gas) in vertical smooth tubes with inner diameters of 8 mm and 14 mm. The experiments were performed at various inlet pressures from 0.3 to 0.7 MPa. The results were obtained over the mass flux range from 16 to 200 kg m-2 s-1 and heat fluxes ranging from 8.0 to 32 kW m-2. The influences of quality, heat flux and mass flux, tube diameter on the heat transfer characteristic are examined and discussed. The comparisons of the experimental heat transfer coefficients with the predicted values from the existing correlations are analyzed. The correlation by Zou et al. [16] shows the best accuracy with the RMS deviation of 31.7% in comparison with the experimental data.

  13. Experimental study of multi-scale heat transfer characteristics at pool boiling

    Science.gov (United States)

    Serdyukov, V.; Surtaev, A.

    2017-01-01

    This study presents the results of the experimental investigation of local and integral characteristics of heat transfer at liquid pool boiling. Saturated ethanol and water were used as the working fluids. Thin, resistively heated indium-tin oxide films deposited onto the sapphire substrates were used as the heaters. The synchronized measurements of the heater surface temperature field and dynamics of vapor bubbles were performed by high-speed infrared thermography with the frame rate of 1000 fps and resolution of up to 0.13 μm/px and high-speed video recording. In this paper new data on major local boiling characteristics, such as nucleation site density, dynamics of vapor bubbles, temporal characteristics and nucleation frequency at different heat fluxes and superheating and their comparison with correlations are presented.

  14. Numerical thermal analysis of water's boiling heat transfer based on a turbulent jet impingement on heated surface

    Science.gov (United States)

    Toghraie, D.

    2016-10-01

    In this study, a numerical method for simulation of flow boiling through subcooled jet on a hot surface with 800 °C has been presented. Volume fraction (VOF) has been used to simulate boiling heat transfer and investigation of the quench phenomena through fluid jet on a hot horizontal surface. Simulation has been done in a fixed Tsub=55 °C, Re=5000 to Re=50,000 and also in different Tsub =Tsat -Tf between 10 °C and 95 °C. The effect of fluid jet velocity and subcooled temperature on the rewetting temperature, wet zone propagation, cooling rate and maximum heat flux has been investigated. The results of this study show that by increasing the velocity of fluid jet of water, convective heat transfer coefficient at stagnation point increases. More ever, by decreasing the temperature of the fluid jet, convective heat transfer coefficient increases.

  15. Flow Pattern and Heat Transfer Behavior of Boiling Two—Phase flow in Inclined Pipes

    Institute of Scientific and Technical Information of China (English)

    LiuDezhang; OuyangNing

    1992-01-01

    Movable Electrical Conducting Probe (MECP),a kind of simple and reliable measuring transducer,used for predicting full-flow-path flow pattern in a boiling vapor/liquid two-phase flow is introduced in this paper when the test pipe is set at different inclination angles,several kinds of flow patterns,such as bubble,slug,churn,intermittent,and annular flows,may be observed in accordance with the locations of MECP.By means of flow pattern analysis,flow fleld numerical calculations have been carried out,and heat transfer coeffcient correlations along full-flow-path derived.The results show that heat transfer performance of boiling two-phase flow could be significanfly augmanted as expected in some flow pattern zones.The results of the investigation,measuring techniques and conclusions contained in this paper would be a useful reference in foundational research for prediction of flow pattern and heat transfer behavior in boiling two-phase flow,as well as for turbine vane liquid-cooling design.

  16. Saturated flow boiling heat transfer correlation for carbon dioxide for horizontal smooth tubes

    Science.gov (United States)

    Turgut, Oguz Emrah; Asker, Mustafa

    2017-01-01

    Literature comprises fewer studies about flow boiling modelling of refrigerants for in tube flows. In addition, researches on two phase flow heat transfer are based on the mathematical models which were derived in a very limited operational condition and correlated for their own measurements. In this study, a new flow boiling model including the superposed effects of nucleate and convective boiling mechanisms is proposed through the minimization of the cumulative error between the proposed mathematical model and actual data by means of artificial cooperative search algorithm and applied to the database of R-744 (carbon dioxide), available from different studies in the literature. Predictions obtained from the proposed model have been compared with those of retained from the literature correlations developed for flow boiling in tubes. The comparison results indicate that the new model outperforms the literature correlations in terms of prediction accuracy. Results of the comparisons reveal that the proposed flow boiling mathematical model has a mean absolute relative error of 14.6% and predicts 76.7% of the experimental data within ±20.0%.

  17. Experimental investigation and mechanism of critical heat flux enhancement in pool boiling heat transfer with nanofluids

    Science.gov (United States)

    Kamatchi, R.; Venkatachalapathy, S.; Nithya, C.

    2016-11-01

    In the present study, reduced graphene oxide (rGO) is synthesized from graphite using modified Hummer and chemical reduction methods. Various characterizations techniques are carried out to study the in-plane crystallite size, number of layers, presence of functional groups and surface morphology. Different concentrations of 0.01, 0.1, and 0.3 g/l of rGO/water nanofluids are prepared by dispersing the flakes in DI water. The colloidal stability of 0.3 g/l concentration is measured after 5 days using Zetasizer and found to be stable. The rGO/water nanofluids are then used to study the effect on the enhancement of critical heat flux (CHF) in pool boiling heat transfer. Results indicate an enhancement in CHF ranging from 145 to 245 % for the tested concentrations. The mechanisms of CHF enhancement are analyzed based on surface wettability, surface roughness, and porous layer thickness. The macrolayer dryout model sufficiently supports the mechanism of CHF enhancement of thin wire with rGO deposits, which is not reported yet.

  18. Interfacial energies of aqueous mixtures and porous coverings for enhancing pool boiling heat transfer

    Energy Technology Data Exchange (ETDEWEB)

    Melendez, Elva [CIICAp, Universidad Autonoma del Estado de Morelos, 62210 (Mexico); Reyes, Rene [Departamento de Ingenieria Quimica y Alimentos, Universidad de las Americas Puebla, Santa Catarina Martir Cholula, Puebla 72820 (Mexico)

    2006-08-15

    The interfacial energies effects on pool boiling were measured for combinations of aqueous ethanol mixtures and cationic surfactants. The mixture with 16% ethanol by weight had the lowest contact angle (associated to the highest wettability) and produced the highest convective heat transfer coefficient, h, among the aqueous ethanol mixtures. The surfactant sodium-lauryl-sulfate added at 100 ppm (its calculated critical micelle concentration CMC) to the 16% ethanol aqueous mixture produced an additional increment of the wettability of the mixture and of the h values; other concentrations of the surfactant reduced de contact angle and h values. The effect of these interfacial energies represents a mass-transfer contribution to pool boiling and the proposal of mixture effects both as increased spreadability and as micelle states. Several randomly constructed porous coverings, contributing to the breakage of vapor slugs around the heater, were tested; produced the highest h values for average pore diameters of 0.5 mm, and covering thickness of 0.972 mm. The synergistic effect on h of the interfacial energies of mixtures at their critical micelle concentration, and porous coverings was measured. Therefore, the independent driving forces combined in this study for increasing pool boiling heat transfer are (a) spreadability of the liquid on the solid; (b) the bubble's size reduction, achieved by micelle states; and (c) the bubble's breakage, induced by the porous coverings, for vapor flow not under pressure drop control. (author)

  19. Bubble Departure from Metal-Graphite Composite Surfaces and Its Effects on Pool Boiling Heat Transfer

    Science.gov (United States)

    Chao, David F.; Sankovic, John M.; Motil, Brian J.; Yang, W-J.; Zhang, Nengli

    2010-01-01

    The formation and growth processes of a bubble in the vicinity of graphite micro-fiber tips on metal-graphite composite boiling surfaces and their effects on boiling behavior are investigated. It is discovered that a large number of micro bubbles are formed first at the micro scratches and cavities on the metal matrix in pool boiling. By virtue of the non-wetting property of graphite, once the growing micro bubbles touch the graphite tips, the micro bubbles are sucked by the tips and merged into larger micro bubbles sitting on the end of the tips. The micro bubbles grow rapidly and coalesce to form macro bubbles, each spanning several tips. The necking process of a detaching macro bubble is analyzed. It is revealed that a liquid jet is produced by sudden break-off of the bubble throat. The composite surfaces not only have higher temperatures in micro- and macrolayers but also make higher frequency of the bubble departure, which increase the average heat fluxes in both the bubble growth stage and in the bubble departure period. Based on these analyses, the enhancement mechanism of pool boiling heat transfer on composite surfaces is clearly revealed.

  20. Experimental investigation on the boiling heat transfer of nanofluids on a flat plate in the presence of a magnetic field

    Science.gov (United States)

    Abdollahi, Ali; Reza Salimpour, Mohammad

    2016-11-01

    In this paper, the pool boiling heat transfer of Fe3O4 -deionized (DI) water as a magnetic nanofluid has been experimentally analyzed in the atmospheric pressure. The applied nanofluid within this research has been synthesized through a single step to retain a high stability. The repeatability and precision of the testing device with deionized water show a good agreement with the equations introduced in previous studies. Parametric studies on magnetic field, surface roughness, and magnetic nanofluid concentration are performed to reveal various aspects of the boiling heat transfer. In order to study the surface roughness, two surfaces with high average roughness (480nm) and low average roughness (7.3nm) were used. The obtained results indicate that the boiling heat transfer on the rough surface increases when raising the nanofluid concentration up to 0.1% volume concentration. In addition, it is observed that there is an optimum 0.1% volume concentration for the nanofluid which makes the boiling heat transfer coefficient increase up to 43%. Moreover, the heat transfer of a nanofluid with volume concentration of 0.1% is greater for the rough surface compared with the smooth one. The results of the experiments indicate that adding nanoparticles would not necessarily increase the boiling heat transfer coefficient. In fact, the surface roughness and the magnetic field gradient on the boiling surface were the main factors that could affect the boiling heat transfer coefficient significantly. The simultaneous analysis of magnetic field, surface roughness, and nanofluid concentration reveals that the boiling heat transfer coefficient of the magnetic nanofluid with 0.1% volume concentration in the presence of a magnetic field on the rough surface is higher than on the smooth surface. Our findings show that this increase is associated to the increase of nucleation sites concentration and bubble formation sites for the rough surface.

  1. 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.

  2. Heat transfer coefficient for flow boiling in an annular mini gap

    Directory of Open Access Journals (Sweden)

    Hożejowska Sylwia

    2016-01-01

    Full Text Available The aim of this paper was to present the concept of mathematical models of heat transfer in flow boiling in an annular mini gap between the metal pipe with enhanced exterior surface and the external glass pipe. The one- and two-dimensional mathematical models were proposed to describe stationary heat transfer in the gap. A set of experimental data governed both the form of energy equations in cylindrical coordinates and the boundary conditions. The models were formulated to minimize the number of experimentally determined constants. Known temperature distributions in the enhanced surface and in the fluid helped to determine, from the Robin condition, the local heat transfer coefficients at the enhanced surface – fluid contact. The Trefftz method was used to find two-dimensional temperature distributions for the thermal conductive filler layer, enhanced surface and flowing fluid. The method of temperature calculation depended on whether the area of single-phase convection ended with boiling incipience in the gap or the two-phase flow region prevailed, with either fully developed bubbly flow or bubbly-slug flow. In the two–phase flow, the fluid temperature was calculated by Trefftz method. Trefftz functions for the Laplace equation and for the energy equation were used in the calculations.

  3. Heat transfer coefficient for flow boiling in an annular mini gap

    Science.gov (United States)

    Hożejowska, Sylwia; Musiał, Tomasz; Piasecka, Magdalena

    2016-03-01

    The aim of this paper was to present the concept of mathematical models of heat transfer in flow boiling in an annular mini gap between the metal pipe with enhanced exterior surface and the external glass pipe. The one- and two-dimensional mathematical models were proposed to describe stationary heat transfer in the gap. A set of experimental data governed both the form of energy equations in cylindrical coordinates and the boundary conditions. The models were formulated to minimize the number of experimentally determined constants. Known temperature distributions in the enhanced surface and in the fluid helped to determine, from the Robin condition, the local heat transfer coefficients at the enhanced surface - fluid contact. The Trefftz method was used to find two-dimensional temperature distributions for the thermal conductive filler layer, enhanced surface and flowing fluid. The method of temperature calculation depended on whether the area of single-phase convection ended with boiling incipience in the gap or the two-phase flow region prevailed, with either fully developed bubbly flow or bubbly-slug flow. In the two-phase flow, the fluid temperature was calculated by Trefftz method. Trefftz functions for the Laplace equation and for the energy equation were used in the calculations.

  4. Boiling heat transfer correlations for refrigerant mixtures flowing inside micro-fin tubes

    Institute of Scientific and Technical Information of China (English)

    Xiaoyan ZHANG; Xingqun ZHANG; Yunguang CHEN; Xiuling YUAN

    2008-01-01

    Based on experimental results of ternary non-azeotropic refrigerant mixture R417A flowing and boiling in one smooth and two internally grooved horizontal tubes with different geometrical parameters, a boiling heat transfer correlations was developed for refrigerant mix-tures flowing inside micro-fin tubes by applying the enhancement factor in the present modified-Kattan model which was modified by the experimental data of R417A in a smooth tube. The comparison between the calculation and the experimental results indicates that the prediction by the present correlations is in good agreement with the experiment of refrigerant mixtures inside different micro-fin tubes with a standard deviation of ± 30% for vapor qualities below 80%.

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

    Science.gov (United States)

    Herman, Cila

    1999-01-01

    In boiling high heat fluxes are possible driven by relatively small temperature differences, which make its use increasingly attractive in aerospace applications. The objective of the research is to develop ways to overcome specific problems associated with boiling in the low gravity environment by substituting the buoyancy force with the electric force to enhance bubble removal from the heated surface. Previous studies indicate that in terrestrial applications nucleate boiling heat transfer can be increased by a factor of 50, as compared to values obtained for the same system without electric fields. The goal of our research is to experimentally explore the mechanisms responsible for EHD heat transfer enhancement in boiling in low gravity conditions, by visualizing the temperature distributions in the vicinity of the heated surface and around the bubble during boiling using real-time holographic interferometry (HI) combined with high-speed cinematography. In the first phase of the project the influence of the electric field on a single bubble is investigated. Pool boiling is simulated by injecting a single bubble through a nozzle into the subcooled liquid or into the thermal boundary layer developed along the flat heater surface. Since the exact location of bubble formation is known, the optical equipment can be aligned and focused accurately, which is an essential requirement for precision measurements of bubble shape, size and deformation, as well as the visualization of temperature fields by HI. The size of the bubble and the frequency of bubble departure can be controlled by suitable selection of nozzle diameter and mass flow rate of vapor. In this approach effects due to the presence of the electric field can be separated from effects caused by the temperature gradients in the thermal boundary layer. The influence of the thermal boundary layer can be investigated after activating the heater at a later stage of the research. For the visualization experiments a

  6. Technical support to the Nuclear Regulatory Commission for the boiling water reactor blowdown heat transfer program

    Energy Technology Data Exchange (ETDEWEB)

    Rice, R.E.

    1976-09-01

    Results are presented of studies conducted by Aerojet Nuclear Company (ANC) in FY 1975 to support the Nuclear Regulatory Commission (NRC) on the boiling water reactor blowdown heat transfer (BWR-BDHT) program. The support provided by ANC is that of an independent assessor of the program to ensure that the data obtained are adequate for verification of analytical models used for predicting reactor response to a postulated loss-of-coolant accident. The support included reviews of program plans, objectives, measurements, and actual data. Additional activity included analysis of experimental system performance and evaluation of the RELAP4 computer code as applied to the experiments.

  7. A genetic algorithm-based optimization model for pool boiling heat transfer on horizontal rod heaters at isolated bubble regime

    Science.gov (United States)

    Alavi Fazel, S. Ali

    2017-03-01

    A new optimized model which can predict the heat transfer in the nucleate boiling at isolated bubble regime is proposed for pool boiling on a horizontal rod heater. This model is developed based on the results of direct observations of the physical boiling phenomena. Boiling heat flux, wall temperature, bubble departing diameter, bubble generation frequency and bubble nucleation site density have been experimentally measured. Water and ethanol have been used as two different boiling fluids. Heating surface was made by several metals and various degrees of roughness. The mentioned model considers various mechanisms such as latent heat transfer due to micro-layer evaporation, transient conduction due to thermal boundary layer reformation, natural convection, heat transfer due to the sliding bubbles and bubble super-heating. The fractional contributions of individual mentioned heat transfer mechanisms have been calculated by genetic algorithm. The results show that at wall temperature difference more that about 3 K, bubble sliding transient conduction, non-sliding transient conduction, micro-layer evaporation, natural convection, radial forced convection and bubble super-heating have higher to lower fractional contributions respectively. The performance of the new optimized model has been verified by comparison of the existing experimental data.

  8. Vertically oriented TiO2 nanotube arrays with different anodization times for enhanced boiling heat transfer

    Institute of Scientific and Technical Information of China (English)

    XU Jia; YANG MingJie; XU JinLiang; JI XianBing

    2012-01-01

    Pool boiling of saturated water on a plain Ti surface and surfaces covered with vertically-oriented TiO2 nanotube arrays NTAs) has been studied.The technique of potentiostatic anodization using non-aqueous electrolytes was adopted to fabricate three types of TiO2 NTAs distinguished by their anodization time.Compared to the bare Ti surface,the incipient boiling wall superheat on the TiO2 NTAs was decreased by 11 K.Both the critical heat flux and heat transfer coefficient of pool boiling on the TiO2 NTAs were higher than those from boiling on a bare Ti surface.The measured maximum critical heat flux and heat transfer coefficient values were 186.7 W/cm2 and 6.22 W/cm2K,respectively.Different performances for the enhancement of heat transfer by the three types of TiO2 NTAs were attributed to the different degrees of deformation in the nanostructure during boiling.Long-term performance of the nanomaterial-coated surfaces for enhanced pool boiling showed degradation of the TiO2 NTAs prepared with an anodization time of 3 hours.

  9. Experimental Research on Water Boiling Heat Transfer on Horizontal Copper Rod Surface at Sub-Atmospheric Pressure

    Directory of Open Access Journals (Sweden)

    Li-Hua Yu

    2015-09-01

    Full Text Available In recent years, water (R718 as a kind of natural refrigerant—which is environmentally-friendly, safe and cheap—has been reconsidered by scholars. The systems of using water as the refrigerant, such as water vapor compression refrigeration and heat pump systems run at sub-atmospheric pressure. So, the research on water boiling heat transfer at sub-atmospheric pressure has been an important issue. There are many research papers on the evaporation of water, but there is a lack of data on the characteristics at sub-atmospheric pressures, especially lower than 3 kPa (the saturation temperature is 24 °C. In this paper, the experimental research on water boiling heat transfer on a horizontal copper rod surface at 1.8–3.3 kPa is presented. Regression equations of the boiling heat transfer coefficient are obtained based on the experimental data, which are convenient for practical application.

  10. Comparison of pool boiling heat transfer for different tunnel-pore surfaces

    Directory of Open Access Journals (Sweden)

    Pastuszko Robert

    2014-03-01

    Full Text Available Complex experimental investigations of boiling heat transfer on structured surfaces covered with perforated foil were performed. Experimental data were discussed for three kinds of enhanced surfaces: tunnel structures (TS, narrow tunnel structures (NTS and mini-fins with the copper wire net (NTS-L. The experiments were carried out with water, ethanol, R-123 and FC-72 at atmospheric pressure. The TS and NTS surfaces were manufactured out of perforated copper foil (hole diameters: 0.3, 0.4, 0.5 mm sintered with the mini-fins, formed on the vertical side of the 5 and 10 mm high rectangular main fins and horizontal inter-fin surface. The NTS-L surfaces were formed by mini-fins of 0.5 and 1 mm height uniformly spaced on the base surface. The wire mesh with an aperture of 0.32, 0.4 and 0.5 mm sintered with the fin tips formed a system of connected perpendicular horizontal tunnels. The tunnel width was 0.6 – 1.0 – 1.5 mm and the depth was 0.5 or 1.0 mm. The effects of the Bond number and dimensionless parameters for three kinds of enhanced structures on heat transfer ratio at nucleate pool boiling were examined.

  11. Comparison of pool boiling heat transfer for different tunnel-pore surfaces

    Science.gov (United States)

    Pastuszko, Robert

    2014-03-01

    Complex experimental investigations of boiling heat transfer on structured surfaces covered with perforated foil were performed. Experimental data were discussed for three kinds of enhanced surfaces: tunnel structures (TS), narrow tunnel structures (NTS) and mini-fins with the copper wire net (NTS-L). The experiments were carried out with water, ethanol, R-123 and FC-72 at atmospheric pressure. The TS and NTS surfaces were manufactured out of perforated copper foil (hole diameters: 0.3, 0.4, 0.5 mm) sintered with the mini-fins, formed on the vertical side of the 5 and 10 mm high rectangular main fins and horizontal inter-fin surface. The NTS-L surfaces were formed by mini-fins of 0.5 and 1 mm height uniformly spaced on the base surface. The wire mesh with an aperture of 0.32, 0.4 and 0.5 mm sintered with the fin tips formed a system of connected perpendicular horizontal tunnels. The tunnel width was 0.6 - 1.0 - 1.5 mm and the depth was 0.5 or 1.0 mm. The effects of the Bond number and dimensionless parameters for three kinds of enhanced structures on heat transfer ratio at nucleate pool boiling were examined.

  12. 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.

  13. Prediction of nucleate boiling heat transfer on horizontal U-shaped heat exchanger submerged in a pool of water using MARS code

    Energy Technology Data Exchange (ETDEWEB)

    Jeon, Seong-Su [Department of Nuclear Thermal-hydraulic Research, FNC Technology Co., Ltd., 46, Tapsil-ro, Giheung-gu, Yongin-si 446-902, Gyeonggi-do (Korea, Republic of); Department of Nuclear Engineering, Seoul National University, Gwanak-gu, Seoul 151-744 (Korea, Republic of); Hong, Soon-Joon [Department of Nuclear Thermal-hydraulic Research, FNC Technology Co., Ltd., 46, Tapsil-ro, Giheung-gu, Yongin-si 446-902, Gyeonggi-do (Korea, Republic of); Cho, Hyoung-Kyu, E-mail: chohk@snu.ac.kr [Department of Nuclear Engineering, Seoul National University, Gwanak-gu, Seoul 151-744 (Korea, Republic of); Park, Goon-Cherl [Department of Nuclear Engineering, Seoul National University, Gwanak-gu, Seoul 151-744 (Korea, Republic of)

    2015-12-15

    Highlights: • PAFS has a horizontal U-shaped heat exchanger submerged in a pool. • PASCAL and ATLAS-PAFS experiments were simulated using MARS code. • This study assessed the predictive capability of 15 nucleate boiling correlations on horizontal tubes. • This study investigated heat transfer mechanisms of the heat exchanger and proposed new boiling model. • The proposed boiling model predicted the experimental heat transfer coefficients well. - Abstract: In advanced nuclear power plants, a horizontal U-shaped heat exchanger submerged in a pool is under development as a key equipment of a passive safety system. For the successful design of the heat exchanger and the safety analysis of the nuclear power plant incorporating this passive safety system, the reliable prediction of the nucleate boiling heat transfer on the horizontal parts of the U-shaped tubes is one of the important factors. At present, the best estimate thermal hydraulic analysis codes such as RELAP5 and MARS are used to analyze the nucleate boiling heat transfer on the horizontal U-shaped heat exchanger submerged in a pool; however, it is still not known how to physically model the heat exchanger pool, and which correlations are suitable among the pool boiling and forced convective boiling correlations. To secure the applicable correlation for the heat exchanger, this study assessed 15 nucleate boiling correlations using MARS. To improve the prediction capability of the best estimate code, this study investigated the main heat transfer mechanisms on the horizontal U-shaped heat exchanger submerged in a pool, then proposed a prediction method, and finally developed a nucleate boiling model. From the validation of the proposed model against PAFS (passive auxiliary feedwater system)-related experimental data of PASCAL and ATLAS-PAFS, the proposed boiling model predicted the experimental heat transfer coefficients much better than the default nucleate boiling model by Chen (1966, Ind. Eng. Chem

  14. Prediction of flow boiling heat transfer coefficient for carbon dioxide in minichannels and conventional channels

    Directory of Open Access Journals (Sweden)

    Mikielewicz Dariusz

    2016-06-01

    Full Text Available In the paper presented are the results of calculations using authors own model to predict heat transfer coefficient during flow boiling of carbon dioxide. The experimental data from various researches were collected. Calculations were conducted for a full range of quality variation and a wide range of mass velocity. The aim of the study was to test the sensitivity of the in-house model. The results show the importance of taking into account the surface tension as the parameter exhibiting its importance in case of the flow in minichannels as well as the influence of reduced pressure. The calculations were accomplished to test the sensitivity of the heat transfer model with respect to selection of the appropriate two-phase flow multiplier, which is one of the elements of the heat transfer model. For that purpose correlations due to Müller-Steinhagen and Heck as well as the one due to Friedel were considered. Obtained results show a good consistency with experimental results, however the selection of two-phase flow multiplier does not significantly influence the consistency of calculations.

  15. A Review of Boiling Heat Transfer Processes at High Heat Flux

    Science.gov (United States)

    1991-04-01

    liquid metals) which can lead to explosive boiling (known as bumping) that can lead to structural damage to hardware. 3 Transition boiling occurs between...to initiate boiling, in some cases having an explosive transition that can cause structural damage to hardware. A thorough understanding of boiling...graphical correlations for the pressure drops encountered in their experiments. About the same time, Staub and Walmet (Ref. 173) identified the two regions

  16. Latent Heat storage characteristics of solid-liquid phase change Heat Storage Microcapsule Slurry by Boiling Heat Transfer under a Vacuum Condition

    Science.gov (United States)

    Inaba, Hideo; Horibe, Akihiko; Haruki, Naoto; Katayama, Masatoshi; Manabe, Ken

    Recently, the new heat transfer medium, which fulfills both functions of heat storage and heat transportation, has been developed in ah eat storage field. Solid-liquid latent heat microcapsule slurry would correspond to the topical medium, so-called functionally thermal fluid. The preset study has clarified the latent heat storage characteristics of microcapsule slurry by making heat transfer enlargement with the help of slurry water pool boiling phenomenon. The paraffin wax at a melting point of 62°C was used as a phase change material which was packed into the microcapsule. The heating surface temperature and concentration of paraffin in the microcapsule slurry was selected as experimental parameters. As a result, the non-dimensional correlation equations of heat storage completion time and heat transfer were derived in terms of non-dimensional parameters.

  17. Pressure drop, heat transfer, critical heat flux, and flow stability of two-phase flow boiling of water and ethylene glycol/water mixtures - final report for project "Efficent cooling in engines with nucleate boiling."

    Energy Technology Data Exchange (ETDEWEB)

    Yu, W.; France, D. M.; Routbort, J. L. (Energy Systems)

    2011-01-19

    Because of its order-of-magnitude higher heat transfer rates, there is interest in using controllable two-phase nucleate boiling instead of conventional single-phase forced convection in vehicular cooling systems to remove ever increasing heat loads and to eliminate potential hot spots in engines. However, the fundamental understanding of flow boiling mechanisms of a 50/50 ethylene glycol/water mixture under engineering application conditions is still limited. In addition, it is impractical to precisely maintain the volume concentration ratio of the ethylene glycol/water mixture coolant at 50/50. Therefore, any investigation into engine coolant characteristics should include a range of volume concentration ratios around the nominal 50/50 mark. In this study, the forced convective boiling heat transfer of distilled water and ethylene glycol/water mixtures with volume concentration ratios of 40/60, 50/50, and 60/40 in a 2.98-mm-inner-diameter circular tube has been investigated in both the horizontal flow and the vertical flow. The two-phase pressure drop, the forced convective boiling heat transfer coefficient, and the critical heat flux of the test fluids were determined experimentally over a range of the mass flux, the vapor mass quality, and the inlet subcooling through a new boiling data reduction procedure that allowed the analytical calculation of the fluid boiling temperatures along the experimental test section by applying the ideal mixture assumption and the equilibrium assumption along with Raoult's law. Based on the experimental data, predictive methods for the two-phase pressure drop, the forced convective boiling heat transfer coefficient, and the critical heat flux under engine application conditions were developed. The results summarized in this final project report provide the necessary information for designing and implementing nucleate-boiling vehicular cooling systems.

  18. Film Boiling Heat Transfer from a Round Wire to Liquid Hydrogen Flowing Upward in a Concentric Annulus

    Science.gov (United States)

    Shiotsu, M.; Shirai, Y.; Oura, Y.; Horie, Y.; Yoneda, K.; Tatsumoto, H.; Hata, K.; Kobayashi, H.; Naruo, Y.; Inatani, Y.

    Hydrogen film boiling heat transfer coefficients were measured for the heater surface superheats up to 400 K under pressures from 400 to 1100 kPa, liquid subcoolings from 0 to 11 K and flow velocities up to 7 m/s. The test wire used was 1.2 mm in diameter and 120 mm in length made of PtCo (0.5 wt.%) alloy, which was located at the center of 8 mm diameter conduit made of FRP (Fiber Reinforced Plastics). The heat transfer coefficients were higher for higher pressure, higher subcooling and higher flow velocity. The heat transfer coefficients were about 1.6 times higher than those predicted by Shiotsu-Hama equation for forced flow film boiling in a wide channel. Discussions were made on the mechanism of difference between them.

  19. Boiling Heat-Transfer Processes and Their Application in the Cooling of High Heat Flux Devices

    Science.gov (United States)

    1993-06-01

    large for very smooth surfaces or highly wettable fluids (e.g., refrigerants or liquid metals) which can lead to explosive boiling (known as bumping) that...of the high wettability of liquid metals, high superheats are normally required to initiate boiling, in some cases having an explosive transition that...About the same time, Staub and Walmet (Ref. 175) identified the two regions before and after the point of significant vapor generation (SNVG) where the

  20. Heat transfer 1982; Proceedings of the Seventh International Conference, Technische Universitaet Muenchen, Munich, West Germany, September 6-10, 1982. Volume 4 - General papers: Pool boiling, flow boiling, measuring techniques

    Science.gov (United States)

    Grigull, U.; Straub, J.; Hahne, E.; Stephan, K.

    Papers are presented on nucleate pool boiling in a microgravity environment; the influence of diameter on nucleate boiling outside tubes; burnout during flow across a small cylinder influenced by parallel cylinders; and the application of the swollen polymer technique to the study of heat transfer on film-cooled surfaces. Other topics include homogeneous nucleation in transient boiling; the heat transfer characteristics of the two-phase closed thermosyphon (wickless heat pipe); boiling heat transfer in annular flow; and the effect of rod bundle geometry (even-odd) on burnout. Attention is also given to wall temperature fluctuation of the evaporating tube at the dryout region, to the flow boiling of ethanol/cyclohexane mixtures, and to capillary flows around hemispherical bubbles. For individual items see A83-42758 to A83-42781

  1. Varmeovergang og trykfald ved fordampning af kuldioxid (Heat Transfer and Pressure Drop for Boiling Carbon Dioxide)

    DEFF Research Database (Denmark)

    Knudsen, Hans Jørgen Høgaard

    1999-01-01

    Heat transfer and pressure drop for carbon dioxide, pure and mixed with oil, has the been measured for flow in pipe. The measured heat transfer coefficient for pure carbon dioxide is much higher than the value calculated with the Shah correlation. With oil even higher heat transfer coefficient ha...

  2. Laminar Film Boiling Heat Transfer on a Horizontal Cylinder Submerged in an Upward Crossflow of Saturated Liquids

    OpenAIRE

    茂地, 徹; 川江, 信治; 金丸, 邦康; 山田, 岹

    1988-01-01

    An analysis was made of the steady-state, forced convection film boiling heat transfer on an isothermal horizontal cylinder submerged in an upward crossflow of saturated liquids in the gravitational field. The boundary-layer equations of momentum and of energy for the laminar vapor film, including both the inertia force in the former and the convection term in the latter, were solved using an integral method. The analytical solution was obtained for the integrated boundary-layer equations. A ...

  3. 混合制冷工质核态沸腾的传热研究%Heat transfer in nucleate pool boiling of binary and ternary refrigerant mixtures

    Institute of Scientific and Technical Information of China (English)

    赵耀华; 刁彦华; 鹤田隆治; 西川日出男

    2004-01-01

    Heat transfer coefficients in nucleate pool boiling were measured on a horizontal copper surface for refrigerants,HFC-134a,HFC-32,and HFC-125,their binary and ternary mixtures under saturated conditions at 0.9MPa.Compared to pure components,both binary and ternary mixtures showed lower heat transfer coefficients.This deterioration was more pronounced as heat flux was increased.Experimental data were compared with some empirical and semi-empirical correlations available in literature.For binary mixture,the accuracy of the correlations varied considerably with mixtures and the heat flux.Experimental data for HFC-32/134a/125 were also compared with available correlated equation obtained by Thome.For ternary mixture,the boiling range of binary mixture composed by the pure fluids with the lowest and the medium boiling points,and their concentration difference had important effects on boiling heat transfer coefficients.

  4. Heat transfer partitioning model of film boiling of particle cluster in a liquid pool: implementation in a CFD code

    Science.gov (United States)

    Mahapatra, Pallab S.; Ghosh, Koushik; Manna, Nirmal K.

    2015-08-01

    In the present work an effective heat transfer partitioning model of three phase (particles, liquid and vapour) flow and thermal interaction have been developed by a multi-fluid approach under film boiling condition. The in-house multiphase flow code is based on finite volume method of discretization and SIMPLE-based pressure correction algorithm. From consideration of mass, momentum and energy balance across the liquid-vapour interface, the vapour bubble generated from the vapour film have been modeled and incorporated in the code. Different interaction terms between each phase are incorporated depending upon the flow regime. The code is validated with in-house and available experimental results. Finally the effect of relevant parameters on void generation under film boiling condition of particles is estimated.

  5. Enhancemet of flow boiling heat transfer in pHEMA/pPFDA coated microtubes with longitudinal variations in wettability

    Directory of Open Access Journals (Sweden)

    Masoumeh Nedaei

    2016-03-01

    Full Text Available Flow boiling heat transfer was investigated in stainless steel hypodermic microtubes, whose surfaces were enhanced by gradient crosslinked polyhydroxyethylmethacrylate (pHEMA/polyperfluorodecylacrylate (pPFDA coatings thereby offering variations in wettability along the surface as well as high porosity. The initiated chemical vapor deposition (iCVD method was implemented for coating the inner walls of the microtubes with an inner diameter of 502 μm, and deionized water was used as the working fluid. Experimental results were obtained from the coated microtubes, where one end corresponded to the pHEMA (hydrophilic coated part and the other end was the most hydrophobic location with the pPFDA (hydrophobic coating so that wettability varied along the length of the microtube. The results of both the hydrophobic and hydrophilic inlet cases were compared to their plain surface counterparts at the mass flux of 9500 kg/m2s. The experimental results showed a remarkable increase in boiling heat transfer with the coatings. The highest heat transfer coefficients were attained for the pHEMA coated (hydrophobic inlet and hydrophilic outlet outlet case with a maximum heat transfer enhancement ratio of ∼64%. The reason for the enhanced heat transfer with the coated microtubes can be attributed to the increased nucleation site density and bubble release as well as enhanced convection and bubble motion near the surface due to the variation in wettability along the length. The results proved that gradient pHEMA/pPFDA coatings can be utilized as a viable surface enhancement method in microscale cooling applications.

  6. Dynamical Behavior of Discrete Bubble and Heat Transfer of Nucleate Pool Boiling in Short-Term Microgravity

    Science.gov (United States)

    Zhao, Jian-Fu

    2012-07-01

    Boiling in microgravity is an increasing significant subject of investigation. Motivation for the study comes not only from many potential space applications due to its high efficiency to transfer high heat flux with liquid-vapor phase change, but also from powerful platform of microgravity to reveal the mechanism of heat transfer underneath the phenomenon of boiling. In the present paper, the growth of a discrete bubble during nucleate pool boiling and heat transfer in short-term microgravity is studied experimentally utilizing the drop tower Beijing. A P-doped N-type square silicon chip with the dimensions of 10x10x0.5 mm ^{3} was used as the heater. Two 0.25-mm diameters copper wires for power supply was soldered to the side surfaces of the chip at the opposite ends. The normal resistant of the chip is 75 Ω. The chip was heated by using Joule effect. A D.C. power supply of constant current was used to input energy to the heater element. A 0.12-mm diameter, T-type thermocouple adhered on the centre of the backside of the chip was used for the measurement of wall temperature, while two other T-type thermocouples were used for the bulk liquid temperature. FC-72 was used as working fluid. The concentration of air was determined by using Henry law as 0.0046 moles gas/mole liquid. The pressure and the bulk liquid temperature in the boiling chamber were nominally 102.0 kPa and 12.0 °C, respectively. The shapes of the bubbles were recorded using a high speed camera at a speed of 250 fps with a shutter speed of 1/2000 s. Based on the image manipulation, the effective diameter of the discrete bubble is obtained. The experiments were conducted utilizing the drop tower Beijing, which can provide a short-term microgravity condition. The residual gravity of 10 ^{-2 ... -3} g _{0} can be maintained throughout the short duration of 3.6 s. To avoid the influence of natural convection in normal gravity environment, the heating switched on at the release of the drop capsule

  7. Two phase convective heat transfer augmentation in swirl flow with non-boiling

    Energy Technology Data Exchange (ETDEWEB)

    Cha, K.O. [Myong Ji University, Kyonggi-do (Korea, Republic of); Kim, J.G. [Myongji University Graduate School, Kyonggi-do (Korea, Republic of)

    1995-10-01

    Two phase flow phenomena are observed in many industrial facilities and make much importance of optimum design for nuclear power plant and various heat exchangers. This experimental study has been investigated the classification of the flow pattern, the local void distribution and convective heat transfer in swirl and non-swirl two phase flow under the isothermal and nonisothermal conditions. The convective heat transfer coefficients in the single phase water flow were measured and compared with the calculated results from the Sieder-Tate correlation. These coefficients were used for comparisons with the two-phase heat transfer coefficients in the flow orientations. The experimental results indicate, that the void probe signal and probability density function of void distribution can used into classify the flow patterns, no significant difference in voidage distribution was observed between isothermal and non-isothermal condition in non-swirl flow, the values of two phase heat transfer coefficients increase when superficial air velocities increase, and the enhancement of the values is observed to be most pronounced at the highest superficial water velocity in non-swirl flow. Also two phase heat transfer coefficients in swirl flow are increased when the twist ratios are decreased. (author). 13 refs., 15 figs.

  8. Three dimensional simulation of nucleate boiling heat and mass transfer in cooling passages of internal combustion engines

    Science.gov (United States)

    Mehdipour, R.; Baniamerian, Z.; Delauré, Y.

    2016-05-01

    An accurate knowledge of heat transfer and temperature distribution in vehicle engines is essential to have a good management of heat transfer performance in combustion engines. This may be achieved by numerical simulation of flow through the engine cooling passages; but the task becomes particularly challenging when boiling occurs. Neglecting two phase flow processes in the simulation would however result in significant inaccuracy in the predictions. In this study a three dimensional numerical model is proposed using Fluent 6.3 to simulate heat transfer of fluid flowing through channels of conventional size. Results of the present theoretical and numerical model are then compared with some empirical results. For high fluid flow velocities, departure between experimental and numerical results is about 9 %, while for lower velocity conditions, the model inaccuracy increases to 18 %. One of the outstanding capabilities of the present model, beside its ability to simulate two phase fluid flow and heat transfer in three dimensions, is the prediction of the location of bubble formation and condensation which can be a key issue in the evaluation of the engine performance and thermal stresses.

  9. Boiling heat-transfer coefficient variation for R407C inside horizontal tubes of a refrigerating vapour-compression plant's shell-and-tube evaporator

    Energy Technology Data Exchange (ETDEWEB)

    Torrella, Enrique [Department of Applied Thermodynamics, Camino de Vera, 14, Polytechnic University of Valencia, E-46022 Valencia (Spain); Navarro-Esbri, Joaquin; Cabello, Ramon [Department of Technology, Campus de Riu Sec,University Jaume I, E-12071 Castellon (Spain)

    2006-03-01

    The present paper presents experimental results obtained from a refrigerating vapour-compression plant's shell-and-tube (1-2) evaporator working with R407C. Several tests have been carried out to study the influence of the evaporating pressure and the refrigerant's mass flow rate on the refrigerant's boiling heat-transfer coefficient inside horizontal tubes. This work has been performed by analyzing the variations of the evaporator's overall thermal-resistance, computed using the effectiveness-NTU method, considering the influence of pressure drops and glide at the evaporator, and finally transferring the results and conclusions to the boiling heat-transfer coefficient. It has been observed that the variations of the boiling heat-transfer coefficient show a dependence on the evaporating temperature and the refrigerant's mass-flow rate, which has been analyzed in the test range. [Author].

  10. R1234yf vs. R134a Flow Boiling Heat Transfer Inside a 3.4 mm ID Microfin Tube

    Science.gov (United States)

    Diani, A.; Mancin, S.; Rossetto, L.

    2014-11-01

    The refrigerant charge minimization as well as the use of eco-friendly fluids can be considered two of the most important targets for these applications to cope with the new environmental challenges. This paper compares the R1234yf and R134a flow boiling heat transfer and pressure drop measurements inside a small microfin tube with internal diameter at the fin tip of 3.4 mm. This study is carried out in an experimental facility built at the Dipartimento di Ingegneria Industriale of the University of Padova especially designed to study both single and two phase heat transfer processes. The microfin tube is brazed inside a copper plate and electrically heated from the bottom. Several T -type thermocouples are inserted in the wall to measure the temperature distribution during the phase change process. In particular, the experimental measurements were carried out at constant saturation temperature of 30 °C, by varying the refrigerant mass velocity between 190 kg m-2 s-1 and 940 kg m-2 s-1, the vapour quality from 0.2 to 0.99, at different imposed heat fluxes. The two refrigerants are compared considering the values of the two-phase heat transfer coefficient and pressure drop.

  11. Influence of tube's diameter on boiling heat transfer performance in small diameter tubes

    Science.gov (United States)

    Gan, Chengjun; Wang, Weicheng; Zhang, Lining

    1998-03-01

    This paper reports the experiments of evaporation study in 6 mm inner copper diameter tubes using HFC-134a, HCFC-22 and CFC-12 as working fluid. The results show that the evaporation heat transfer coefficient increases with the decreasing of inner diameter of tubes. A new concept of non-dimensional tube diameter U is proposed in this paper for correction of the influence of the tube diameter on the evaporation heat transfer coefficient. And further, a convenient empirical correction method is presented.

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

    Science.gov (United States)

    Zupančič, Matevž; Može, Matic; Gregorčič, Peter; Golobič, Iztok

    2017-03-01

    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.

  13. A 2D inverse problem of predicting boiling heat transfer in a long fin

    Science.gov (United States)

    Orzechowski, Tadeusz

    2016-10-01

    A method for the determination of local values of the heat transfer coefficient on non-isothermal surfaces was analyzed on the example of a long smooth-surfaced fin made of aluminium. On the basis of the experimental data, two cases were taken into consideration: one-dimensional model for Bi 0.1, the problem was modelled using a 2-D heat conduction equation, for which the boundary conditions were posed on the surface observed with a thermovision camera. The ill-conditioned inverse problem was solved using a method of heat polynomials, which required validation.

  14. Quantification of the water boiling heat transfer in micro-structures by image analysis

    NARCIS (Netherlands)

    Ferret, C.; Falk, L.; Chenu, A.; d'Ortona, U.; Veenstra, T.T.

    2004-01-01

    The heat transfer performance of a micro-vaporizer has been measured by conventional methods (using temperatures, flow rates, effective power input). The study was carried out for laminar flow in channels (5 mm×3 cm×200 μm) micro-structured with square obstacles to increase the specific area. The re

  15. An Enhanced VOF Method Coupled with Heat Transfer and Phase Change to Characterise Bubble Detachment in Saturated Pool Boiling

    Directory of Open Access Journals (Sweden)

    Anastasios Georgoulas

    2017-02-01

    Full Text Available The present numerical investigation identifies quantitative effects of fundamental controlling parameters on the detachment characteristics of isolated bubbles in cases of pool boiling in the nucleate boiling regime. For this purpose, an improved Volume of Fluid (VOF approach, developed previously in the general framework of OpenFOAM Computational Fluid Dynamics (CFD Toolbox, is further coupled with heat transfer and phase change. The predictions of the model are quantitatively verified against an existing analytical solution and experimental data in the literature. Following the model validation, four different series of parametric numerical experiments are performed, exploring the effect of the initial thermal boundary layer (ITBL thickness for the case of saturated pool boiling of R113 as well as the effects of the surface wettability, wall superheat and gravity level for the cases of R113, R22 and R134a refrigerants. It is confirmed that the ITBL is a very important parameter in the bubble growth and detachment process. Furthermore, for all of the examined working fluids the bubble detachment characteristics seem to be significantly affected by the triple-line contact angle (i.e., the wettability of the heated plate for equilibrium contact angles higher than 45°. As expected, the simulations revealed that the heated wall superheat is very influential on the bubble growth and detachment process. Finally, besides the novelty of the numerical approach, a last finding is the fact that the effect of the gravity level variation in the bubble detachment time and the volume diminishes with the increase of the ambient pressure.

  16. On the Effect of Lubricant on Pool Boiling Heat Transfer Performance

    OpenAIRE

    2016-01-01

    Â Â Â For typical vapor compression processes, lubricant oil is very essential for lubricating and sealing the sliding parts and the lubricant also takes part in cushioning cylinder valves. However lubricants may migrate to the evaporator to alter the heat transfer characteristics. This is can be made clear from the viscosity and surface tension of lubricant since the viscosity of lubricant oil is about two to three orders higher than that of refrigerant whereas the corresponding surface t...

  17. Effects of Adding Nanoparticles on Boiling and Condensing Heat Transfer inside a horizontal round tube

    Science.gov (United States)

    Sheikholeslami, Mohsen; Sadoughi, Mohammadkazem; Shariatmadar, Hamed; Akhavan-Behabadi, Mohammad Ali

    2015-11-01

    An experimental investigation is performed on heat transfer evaluation of a nano-refrigerant flow during condensation and evaporation inside a horizontal round tube. Experiments are carried out for three working fluid types including: i) pure refrigerant (R600a); ii) refrigerant/lubricant (R600a/oil); and iii) nano-refrigerant: refrigerant/lubricant/nanoparticles (R600a/oil/CuO). Nanoparticles are added to the lubricant and their mixture is mixed with pure refrigerant. Therefore, nano-refrigerants (R600a/oil/CuO) are prepared by dispersing CuO nanoparticles with different fractions of 0.5%, 1% and 1.5% in the baseline mixture (R600a/oil). Effects of different factors including vapor quality, mass flux, and nanoparticles on the heat transfer coefficient are examined for both of condensation and evaporation flows, separately. The results shows that maximum heat transfer augmentation of 79% and 83% are achieved by using the refrigerant/lubricant/nanoparticles mixture, in comparison with the pure refrigerant case in condensation and evaporation, respectively which are occurred for nano-refrigerant with 1.5% mass fraction in both of them.

  18. The Effect of Coating Thickness and Roughness of Nucleate Pool Boiling Heat Transfer on Nanoparticle Coated Surface

    Science.gov (United States)

    Das, Sudev; Bhaumik, Swapan

    2016-04-01

    The influence of coating thickness and surface roughness on pool boiling heat transfer is experimentally studied over a range of surface roughness values with varied coating thickness with water at atmospheric pressure. Test surfaces used in this experiment are namely, untreated surface (Ra = 0.0899 µm), polished surface (Ra = 0.0493 µm), TiO2 nanoparticle coated surface with a roughness (Ra) ranging from 0.0338 to 0.289 µm. The surfaces were characterized with respect to contact angle, surface roughness and coating thickness. The contact angle, surface roughness and coating thickness were measured by sessile drop method, optical surface profiler and instrument thickness monitor respectively. Heat fluxes observed ranged from 52.63 to 144.73 W/cm2. Different trends were observed in the Heat Transfer Coefficient (HTC) with respect to the surface roughness and coating thickness values on the same set of heat flux. The HTC was found to increase with increasing the roughness values for untreated and polish surface but nanoparticle coated surfaces displayed different trend in HTCs. The HTC was found to increase with increasing coating thickness with all wall superheat.

  19. Flow Boiling Heat Transfer Enhancement by Using ZnO-Water Nanofluids

    Directory of Open Access Journals (Sweden)

    Om Shankar Prajapati

    2014-01-01

    Full Text Available Nanofluids are liquid suspensions containing nanoparticles that are smaller than 100 nm. There is an increased interest in nanofluids as thermal conductivity of nanofluids is significantly higher than that of the base liquids. ZnO-water nanofluids with volume concentration of ZnO particles varying from 0.0001 to 0.1% were prepared using ultrasonic vibration mixer. Thermal conductivity of the ZnO-water fluids was investigated for different sonication time using thermal property analyzer (KD2 Pro. Thermal conductivity of nanofluids for a given concentration of nanoparticle varies with sonication time. Heat transfer coefficient and pressure drop in an annular test section with variable pressure (1–2.5 bar and heat flux (0–400 kW/m2 at constant mass flux of 400 kg/m2s were studied for samples having maximum thermal conductivity. Surface roughness of the heating rod was also measured before and after the experimentation. The study shows that heat transfer coefficient increases beyond the base fluid with pressure and concentration of ZnO.

  20. Investigation of Boiling Heat Transfer of Binary Mixture from Vertical Tube Embedded in porous Media

    Institute of Scientific and Technical Information of China (English)

    HailongMo; TongzeMa; 等

    1996-01-01

    Ethanol-water binary mixtures with 7 different mole fractions of ethanol ranging from 0 to 1 were adopted as testing liquids in the experiment.The vertical heating tube was inserted in porous matrix composed of five well sorted glass beads whise diameters range from 0.5 to 4.3mm.Due to the effect of composition,the trend of combination of vapor bubbles was reduced.resulting in the increase of peak heat flux of binary mixture,With the increase of ethanol mole fraction,0.5mm diameter bead of peak heat flux of binary mixture.with the increase of ethanol mole fraction.0.5mm diameter bead had lower value of peak heat flux,while for pure liquid the critical state is difficult to appear,with given diameter of glass bead,there existed an optimum value of mole fraction of ethanol,which was decreased with the increase of bead diameter,A dimensionless heat transfer coefficient was predicted through the introduction of a dimensionless parameter of porous matrix which agreed with the experimental results satisfactorily.

  1. An application of the non-continuous Trefftz method to the determination of heat transfer coefficient for flow boiling in a minichannel

    Science.gov (United States)

    Maciejewska, Beata; Piasecka, Magdalena

    2016-08-01

    The paper presents an application of the semi-analytical method, called the non-continuous Trefftz method, to the calculation of the heat transfer coefficients. It is very effective method for solving direct and inverse problems. The results obtained by this method are consistent with the results obtained by using complicated methods: the FEM and Beck method. Sought local heat transfer coefficients between the heating surface and the boiling liquid flowing through 1 mm deep minichannel were calculated from the Robin boundary condition. The temperature of the heating surface and the derivative of the temperature were was found from solving the inverse problem. The study is limited to the identification of the heat transfer coefficient in the subcooled and the saturated nucleate boiling regions. The article presents also the measurement stand and methodology of conducting the experiment. Presented issues allows verification of state-of-the-art methods of solving the inverse problem by using the authors' empirical data from the experiment.

  2. Forced Convection Film Boiling Heat Transfer from a Horizontal Cylinder to Liquid Cross-flowing Upward : 1st Report, Saturated Liquid

    OpenAIRE

    Ito, Takehiro; Nishikawa, Kaneyasu; Shigechi, Tooru

    1981-01-01

    Forced convection film boiling heat transfer from a horizontal cylinder to saturated liquid cross-flowing upward is analyzed based on the two-phase boundary-layer theory. Numerical solution of the conservation equations is determined by means of the integral method of boundary-layer for water, ethanol and hexane under the atmospheric pressure. The velocity profile, separation point of the boundary-layer, thickness of the boundary-layer, distribution of the heat transfer coefficients and avera...

  3. Enhanced pool boiling heat transfer on mini- and micro- structured surfaces

    Science.gov (United States)

    Pastuszko, Robert

    2016-03-01

    The surfaces used for investigating nucleate pool boiling for four working fluids had mini- and micro-fins of variable configurations, cross-sections and pitches, restrained by perforated foil or mesh cloth with various pore/opening diameters. Unique enhanced structures on these surfaces formed a system of interconnected horizontal and vertical tunnels. Four structured surfaces were proposed, each being a system of subsurface tunnels connected to 10 and 5 mm fins or 1 and 0.5 mm mini-fins. Measurement results for boiling water, ethanol, Fluorinert FC-72 and R-123 from more than 60 samples constituted the database used to verify the proposed theoretical models. These models were based on the results from the visualization studies, including internal visualization allowing observation of bubble nucleation, growth and displacement inside the tunnels, and on the analysis of existing boiling models for mini- and micro-structures.

  4. Refrigeration. Heat Transfer. Part I: Evaporators and Condensers

    DEFF Research Database (Denmark)

    Knudsen, Hans-Jørgen Høgaard

    2002-01-01

    The note gives an introduction to heat transfer with phase shift. Pool Boiling, Flow Boiling, Condensation.......The note gives an introduction to heat transfer with phase shift. Pool Boiling, Flow Boiling, Condensation....

  5. CO 2池沸腾换热关联式理论分析%Theoretical Analysis on Correlation of CO2 Pool Boiling Heat Transfer

    Institute of Scientific and Technical Information of China (English)

    刘圣春; 刘江彬; 宁静红

    2013-01-01

    The common heat transfer correlations of pool boiling is summarized,and a correlation of CO2 heat transfer is at-tained after analyzing heat transfer performance.The deviation within 16% of CO2 fitting formula value compared to prediction values of theoretical pool boiling correlation of conventional refrigerants and experimental fitting correlation of CO2 is obtained, which shows that it is of universal.The effects on pool boiling heat transfer and the variation law are pointed out by analyzing the process of CO2 pool boiling heat transfer,and the common methods,using to enhance pool boiling heat transfer,are summarized in the paper.%总结了常见的池沸腾换热关联式。通过对池沸腾换热过程分析得出CO2在小热流密度和大热流密度范围下的一种分段的换热关联式。将新的拟合公式值和预测关联式值进行比较,得出CO2的拟合公式值与理论关联式及实验拟合关联式的预测值的偏差在±16%之内,具有一定的通用性。通过对CO2池沸腾换热过程的分析,得出池沸腾换热的影响因素及其变化规律,并总结了常用的强化池沸腾换热方法。

  6. Prediction of Mass Transfer Time Relaxation Parameter for Boiling Simulation on the Shell-Side of LNG Spiral Wound Heat Exchanger

    Directory of Open Access Journals (Sweden)

    Zhi-Yong Wu

    2014-07-01

    Full Text Available The objective of this present study is to propose an approach to predict mass transfer time relaxation parameter for boiling simulation on the shell-side of LNG spiral wound heat exchanger (SWHE. The numerical model for the shell-side of LNG SWHE was established. For propane and ethane, a predicted value of mass transfer time relaxation parameter was presented through the equivalent evaporation simulations and was validated by the Chisholm void fraction correlation recommended under various testing conditions. In addition, heat transfer deviations between simulations using the predicted value of mass transfer time relaxation parameter and experiments from Aunan were investigated. The boiling characteristics of SWHE shell-side were also visualized based on the simulations with VOF model. The method of predicting mass transfer time relaxation parameter may be well applicable to various phase change simulations.

  7. Flow boiling heat transfer enhancement on copper surface using Fe doped Al{sub 2}O{sub 3}–TiO{sub 2} composite coatings

    Energy Technology Data Exchange (ETDEWEB)

    Sujith Kumar, C.S., E-mail: sujithdeepam@gmail.com [Department of Mechanical Engineering, National Institute of Technology, Tiruchirappalli 620015, Tamil Nadu (India); Suresh, S., E-mail: ssuresh@nitt.edu [Department of Mechanical Engineering, National Institute of Technology, Tiruchirappalli 620015, Tamil Nadu (India); Aneesh, C.R., E-mail: aneeshcr87@gmail.com [Department of Mechanical Engineering, National Institute of Technology, Tiruchirappalli 620015, Tamil Nadu (India); Santhosh Kumar, M.C., E-mail: santhoshmc@nitt.edu [Department of Physics, National Institute of Technology, Tiruchirappalli 620015, Tamil Nadu (India); Praveen, A.S., E-mail: praveen_as_1215@yahoo.co.in [Department of Mechanical Engineering, National Institute of Technology, Tiruchirappalli 620015, Tamil Nadu (India); Raji, K., E-mail: raji.kochandra@gmail.com [School of Nano Science and Technology, National Institute of Technology, Calicut 673601, Kerala (India)

    2015-04-15

    Graphical abstract: - Highlights: • Fe–Al{sub 2}O{sub 3}–TiO{sub 2} composite coatings were coated on the copper using spray pyrolysis. • Effect of Fe doping on porosity was determined using AFM. • Effect of Fe doping on hydrophilicity was determined. • Higher enhancement in CHF was obtained for 7.2 at% Fe doped coated sample. - Abstract: In the present work, flow boiling experiments were conducted to study the effect of spray pyrolyzed Fe doped Al{sub 2}O{sub 3}–TiO{sub 2} composite coatings over the copper heater blocks on critical heat flux (CHF) and boiling heat transfer coefficient. Heat transfer studies were conducted in a mini-channel of overall dimension 30 mm × 20 mm × 0.4 mm using de-mineralized water as the working fluid. Each coated sample was tested for two mass fluxes to explore the heat transfer performance. The effect of Fe addition on wettability and porosity of the coated surfaces were measured using the static contact angle metre and the atomic force microscope (AFM), and their effect on flow boiling heat transfer were investigated. A significant enhancement in CHF and boiling heat transfer coefficient were observed on all coated samples compared to sand blasted copper surface. A maximum enhancement of 52.39% and 44.11% in the CHF and heat transfer coefficient were observed for 7.2% Fe doped TiO{sub 2}–Al{sub 2}O{sub 3} for a mass flux of 88 kg/m{sup 2} s.

  8. Experimental boiling heat transfer coefficients in the high temperature generator of a double effect absorption machine for the lithium bromide/water mixture

    Energy Technology Data Exchange (ETDEWEB)

    Marcos, J.D. [Escuela Tecnica Superior Ingenieria Industrial, UNED, c/Juan del Rosal 12, 28040 Madrid (Spain); Izquierdo, M. [Instituto de Ciencias de la Construccion Eduardo Torroja (CSIC), c/Serrano Galvache 4, 28033 Madrid (Spain); Escuela Politecnica Superior, Universidad Carlos III de Madrid, Avenida de la Universidad 30, 28911 Leganes, Madrid (Spain); Lizarte, R. [Escuela Politecnica Superior, Universidad Carlos III de Madrid, Avenida de la Universidad 30, 28911 Leganes, Madrid (Spain); Palacios, E. [Escuela Universitaria Ingenieria Tecnica Industrial, Universidad Politecnica de Madrid, C/ Ronda de Valencia 3, 28012 Madrid (Spain); Infante Ferreira, C.A. [Delft University of Technology, Engineering Thermodynamics, Leeghwaterstraat 44, 2628 CA Delft (Netherlands)

    2009-06-15

    The aim of this work is to determine the boiling heat transfer coefficients in the high temperature desorber (HTD) of an air-cooled double effect lithium bromide/water absorption prototype. The HTD is a plate heat exchanger (PHE) with thermal oil on one side, and a lithium bromide solution on the other side. Several experiments were performed with this PHE while the prototype was working with an outdoor dry bulb temperature around 42 C and condensation temperature around 55 C. The registered data allowed to calculate the global heat transfer coefficient and the heat transfer coefficient for the LiBr/water mixture in forced convective boiling. The pressure drop produced by the boiling of the refrigerant has been calculated as well. It has been verified that the largest part of the heat supplied in the generator is required for desorbing the refrigerant (except for the maximum solution mass flow), while the sensible heat varies from 10% to 50% of the total heat supplied. (author)

  9. Critical heat flux in flow boiling in microchannels

    CERN Document Server

    Saha, Sujoy Kumar

    2015-01-01

    This Brief concerns the important problem of critical heat flux in flow boiling in microchannels. A companion edition in the SpringerBrief Subseries on Thermal Engineering and Applied Science to “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.

  10. Basic research and industrialization of CANDU advanced fuel - Effect of transverse convex curvature on boiling heat transfer and ONB point of nucleate fuel rods

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Kyung Chun; Lee, Young; Lee, Sung Hong [Pusan National University, Pusan (Korea)

    2000-04-01

    Recently, the effect of convex curvature on heat transfer should not be ignored when the radius of curvature tends to be small and/or associated with high heat transfer rate cases. Both analytical and experimental studies were performed to prove the effect of transverse convex curvature on the boiling heat transfer in concentric annuli flows. The effect of the transverse convex surface curvature on ONB are studied analytically in the case of reactor and evaporator. It is seen that the inner wall heat flux depends on R/sub i/, Rc, Re, Pr, {alpha}, and the {theta} of working fluid. An experimental study on the incipience of nucleate boiling is performed as a verification ad extension of previous analyses. Through flow visualization, the results show that the most dominant parameter to affect the heat flux at ONB is found to be the surface curvature. The heat flux data at ONB increases with the Re and the subcooling, and the effect of subcooling on ONB becomes smaller with decreasing Re. The heat flux at ONB increases rapidly as increase in {alpha} due to higher convective motion of bulk flow. Comparison between both results are accomplished with respect to the relative enhancement due to the convex curvature. The relative heat transfer enhancement ratio shows a good agreement between theory and experiment qualitatively and quantitatively. In conclusion, the obtained results suggest that the effect transverse convex curvature appears significantly in the boiling heat transfer. Therefore, it can be clearly expected that the effect should be more strong at the case of critical heat flux condition which is the most important design goal of the advanced nuclear fuel rods. 30 refs., 78 figs. (Author)

  11. Experimental Study on Fundamental Phenomena of Nucleate-Boiling by Using Heat Transfer Surface with Artificial Cavities Created by MEMS Technology

    Science.gov (United States)

    Sato, Takato; Koizumi, Yasuo; Ohtake, Hiroyasu

    Pool nucleate boiling heat transfer experiments were performed for water by using a well-controlled and -defined heat transfer surfaces in the range of the surface heat flux of ˜ 4.54×104 W⁄m2. One or three cavities were created on a mirror-finished silicon plate of 0.525 mm thickness by utilizing the Micro-Electro Mechanical Systems (MEMS) technology. In present experiments, the cavities were arranged in a straight line. The silicon plate was placed facing up at the bottom of the test container filled with distilled water. The back side of the silicon plate was irradiated by a laser beam to heat up the test heat transfer surface. The back side temperature was measured with a radiation thermometer. A boiling state was recorded with a high speed video camera. Thermal interaction between neighboring cavities became weak as the cavity spacing became wide and it disappeared when S⁄Lc = 1.6 in present experimental range. Four bubble coalescence patterns; vertical, horizontal and declining coalescence and vertical lift (no coalescence), were confirmed. When S⁄Lc ≥ 1.6, horizontal and declining coalescence disappeared. When the cavity spacing was narrow, hydraulic interaction between neighboring cavities played an important role in heat transfer. It became less important as the cavity spacing became wide. When S⁄Lc ≥ 1.2, the hydraulic interaction between neighboring cavities became negligible and phase change heat transfer took a main part.

  12. Nucleate Pool Boiling of Pure Liquids and Binary Mixtures:part II—Analytical Model for Boiling Heat Transfer of Binary Mixtures on Smooth Tubes and Comparison of Analytical Models for both Pure Liqu

    Institute of Scientific and Technical Information of China (English)

    GuoqingWang; YingkeTan

    1996-01-01

    A combined physical model of bubbel growth is propsed along with a corresponding bubble growth model for binary mixtures on smooth tubes.Using the general model of Wang et al.[1].and the bubble growth model for binary mixtures,an analytical model for nucleate pool boiling heat transfer of binary mixtures on smooth tubes is developed.In addition,nucleate pool boiling heat transfer of pure liquids and binary mixtrues on a horizontal smooth tube was studied experimentally.The pure liquids and binary mixtures included water methanol,ehanol,and their binary mixtures.The analytical models for both pure liquids and binary mixtures are in good agreement with the experimental data.

  13. Experimental investigation of certain internal condensing and boiling flows: Their sensitivity to pressure fluctuations and heat transfer enhancements

    Science.gov (United States)

    Kivisalu, Michael Toomas

    Space-based (satellite, scientific probe, space station, etc.) and millimeter -- to -- micro-scale (such as are used in high power electronics cooling, weapons cooling in aircraft, etc.) condensers and boilers are shear/pressure driven. They are of increasing interest to system engineers for thermal management because flow boilers and flow condensers offer both high fluid flow-rate-specific heat transfer capacity and very low thermal resistance between the fluid and the heat exchange surface, so large amounts of heat may be removed using reasonably-sized devices without the need for excessive temperature differences. However, flow stability issues and degredation of performance of shear/pressure driven condensers and boilers due to non-desireable flow morphology over large portions of their lengths have mostly prevented their use in these applications. This research is part of an ongoing investigation seeking to close the gap between science and engineering by analyzing two key innovations which could help address these problems. First, it is recommended that the condenser and boiler be operated in an innovative flow configuration which provides a non-participating core vapor stream to stabilize the annular flow regime throughout the device length, accomplished in an energy-efficient manner by means of ducted vapor re-circulation. This is demonstrated experimentally.. Second, suitable pulsations applied to the vapor entering the condenser or boiler (from the re-circulating vapor stream) greatly reduce the thermal resistance of the already effective annular flow regime. For experiments reported here, application of pulsations increased time-averaged heat-flux up to 900 % at a location within the flow condenser and up to 200 % at a location within the flow boiler, measured at the heat-exchange surface. Traditional fully condensing flows, reported here for comparison purposes, show similar heat-flux enhancements due to imposed pulsations over a range of frequencies

  14. Measurement of Nucleate Pool Boiling Heat Transfer Limit using Fuel Cladding Material

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Chi Young; Shin, Chang Hwan; Oh, Dong Seok; Chun, Tae Hyun; In, Wang Kee [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

    2013-10-15

    Zircaloy has been widely used as a fuel cladding material of light water reactor for more than three decades because it has a lower neutron absorption cross section and cracking rate. Recently, HANA-6 has been developed in KAERI (Korea Atomic Energy Research Institute) as the advanced fuel cladding for high burn-up fuel. Generally, under the normal and accident operating conditions of a nuclear reactor, the nuclear fuel cladding of zirconium based alloys undergoes the surface change, and the oxide layer can be formed. In such a case, the previous CHF correlations should be assessed and examined using the experimental results for not a fresh zircaloy surface but an oxidized one, to predict and examine the thermal margin and safety of a nuclear reactor core. Therefore, the experimental data using the oxidized zircaloy surface need to be provided quantitatively. In this paper, the CHF in saturated water pool boiling is measured and discussed using the specimens of zircaloy-4, HANA-6, and oxidized zircaloy-4 in high temperature air environment. The CHF of zircaloy-4, HANA-6, and oxidized surface was tested. Zircaloy-4 and HANA-6 had a similar CHF performance. This is because both are the zirconium based alloys, and appear the almost same water contact angle. On the other hands, the oxidized specimen became to be higher CHF than plain zircaloy-4 and HANA-6 specimens, due to smaller water contact angle (i. e., good hydrophilicity of specimen). The Kandlikar's (2001) correlation reasonably predicted the present experimental data.

  15. Boiling Heat Transfer Enhancement in a Vertical Annulus by Introduction of Air in Liquid Flow%内加热垂直环隙中引入惰性气体时的沸腾传热

    Institute of Scientific and Technical Information of China (English)

    王军; 苗君; 刘芸; 沈自求

    2004-01-01

    In this paper, boiling heat transfer in a vertical annulus with inner side heated with and without air introduction is experimentally studied. Results show that boiling heat transfer is significantly enhanced by the introduction of air. When air is introduced into the liquid with a temperature below boiling point, the enhancement of heat transfer is also detected. It is concluded from the study that the heat transfer enhanced by introduction of inert gas is due to the liquid vaporization at the gas-liquid interface near the wall, which removes a large amount of latent heat and lowers the interfacial temperature considerably. Thus the gas-liquid interface acts as a "heat sink"and the heat transfer is augmented significantly.

  16. On the heat transfer in the pool boiling at tightly finned steel tubes; Zum Waermeuebergang beim Behaeltersieden an eng berippten Stahlrohren

    Energy Technology Data Exchange (ETDEWEB)

    Bujok, Patrick; Wang, Yabai; Luke, Andrea [Kassel Univ. (Germany). Lehrstuhl fuer Technische Thermodynamik

    2012-07-01

    from the laboratory scale (single tube, mini-bundle) to the technical scales. On this occasion, the authors investigate the impact of tightly finned steel tubes with trapezoidal cross-sectional ribs on the heat transfer during the boiling in case of free convection over a wide range of pressures from the beginning up to the fully developed nucleate boiling. Hydrocarbons such as n-pentane and i-octane as a natural refrigerant in the process industry are used as a boiling fluid. The results of the investigations at an electrically heated and horizontally placed test tube consisting of structural steel are compared with correlations from the literature. First results from a mixture of both hydrocarbons show that the heat transfer deteriorates if only a little amount of the heavier boiling component is added.

  17. Dynamics of single and multiple bubbles and associated heat transfer in nucleate boiling under low gravity conditions.

    Science.gov (United States)

    Qiu, D; Son, G; Dhir, V K; Chao, D; Logsdon, K

    2002-10-01

    Experimental studies and numerical simulation of growth and lift-off processes of single bubbles formed on designed nucleation sites have been conducted under low-gravity conditions. Merging of multiple bubbles and lift-off processes during boiling of water in the parabola flights of KC-135 aircraft were also experimentally studied. The heating area of the flat heater surface was discretized and equipped with a number of small heating elements that were separately powered in the temperature-control mode. As such, the wall superheat remained nearly constant during the growth and departure of the bubbles, whereas the local heat flux varied during the boiling process. From numerical calculation it is found that peak of heat flux occurs locally at the contact line of bubble and heater surface. Dry conditions exist inside the bubble base area, which is characterized through a zero heat flux region in the numerical calculation and a lower heat flux period in the experimental results. During the merger of multiple bubbles, dry-out continues. In both the numerical calculations and experimental results, the bubble lift-off is associated with an apparent increase in heat flux. Wall heat flux variation with time and spatial distribution during the growth of a single bubble from numerical simulations are compared with experimental data.

  18. Forced Convection Film Boiling Heat Transfer from a Horizontal Cylinder to Liquid Cross-flowing Upward : 2nd Report, Subcooled Liquid

    OpenAIRE

    Shigechi, Tooru; Ito, Takehiro; Nishikawa, Kaneyasu

    1983-01-01

    Forced convection film boiling heat transfer from a horizontal cylinder to a subcooled liquid cross-flowing upward is analysed based on the two-phase boundary-layer theory. Numerical solution of the conservation equations is determined for subcooled water, ethanol and hexane under the atmospheric pressure by the method similar to that of the first report for saturated liquid. The velocity profile, the separation point in the vapor film, the thickness of the boundary-layer and the average Nuss...

  19. Flow boiling heat transfer and pressure drop characteristics of R134a, R1234yf and R1234ze in a plate heat exchanger for organic Rankine cycle units

    DEFF Research Database (Denmark)

    Zhang, Ji; Desideri, Adriano; Kærn, Martin Ryhl

    2017-01-01

    . This paper is aimed at obtaining flow boiling heat transfer and pressure drop characteristics in a plate heat exchanger under the working conditions prevailing in the evaporator of organic Rankine cycle units. Two hydrofluoroolefins R1234yf and R1234ze, and one hydrofluorocarbon R134a, were selected...

  20. 气泡微细化沸腾传热特性%Heat transfer property of micro-bubble emission boiling

    Institute of Scientific and Technical Information of China (English)

    朱光昱; 高力; 于方小稚; 田齐伟

    2015-01-01

    Background:Micro-bubble Emission Boiling (MEB) is a special subcooling boiling phenomenon that the heat flux increases more highly than critical heat flux (CHF). Due to its extremely high heat transfer capability, many researchers have shown interest in it.Purpose: In this paper, we fit the heat transfer correlation of experimental data collected in visualized boiling experiments after deeply analyzing the heat transfer mechanism of MEB. Methods:Four Si-C heaters were employed for heating the copper block, which has a round heating surface with diameter of 10mm on its upper. Temperature data were measured by T-type sheathed thermocouples. The temperature of the heating surface was obtained by extrapolating the temperature distribution. Based on the heating surface temperature date in different subcoolings, least square method was used to fit Rohsenow relation to MEB. Bubble behaviors were captured by high-speed video camera with light system. Results: The experimental results showed that, when the subcooling exceeded 40 K, disturbance emerged at the liquid-vapor interface and the micro-bubble emission boiling occurred after the CHF was attained, thereafter the heat flux increased rapidly with the superheat increasing like that in typical nucleate boiling region. Based on Rohsenow relation, MEB heat transfer correlation is fitted according to the measured temperature data for heating surface of 10-mm copper in different subcoolings. The error of the relation is less than ±15%, which meets the requirement of general engineering. Conclusion:The efficient convective heat transfer of vapor-liquid replacement caused by periodic damage of the unsteady vapor film on the heating surface is the heat transfer mechanism of MEB.%气泡微细化沸腾(Micro-bubble Emission Boiling, MEB)是一种特殊的过冷沸腾现象,当其发生时加热面的热流密度会远高于临界热流密度(Critical Heat Flux, CHF).根据采集到的可视化沸腾资料,对MEB的传热机理

  1. Survey of Thermal-Fluids Evaluation and Confirmatory Experimental Validation Requirements of Accident Tolerant Cladding Concepts with Focus on Boiling Heat Transfer Characteristics

    Energy Technology Data Exchange (ETDEWEB)

    Brown, Nicholas R. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Wysocki, Aaron J. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Terrani, Kurt A. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Ali, Amir [Univ. of New Mexico, Albuquerque, NM (United States); Liu, Maolong [Univ. of New Mexico, Albuquerque, NM (United States); Blandford, Edward [Univ. of New Mexico, Albuquerque, NM (United States)

    2016-06-01

    The U.S. Department of Energy Office of Nuclear Energy (DOE-NE) Advanced Fuels Campaign (AFC) is working closely with the nuclear industry to develop fuel and cladding candidates with potentially enhanced accident tolerance, also known as accident tolerant fuel (ATF). Thermal-fluids characteristics are a vital element of a holistic engineering evaluation of ATF concepts. One vital characteristic related to boiling heat transfer is the critical heat flux (CHF). CHF plays a vital role in determining safety margins during normal operation and also in the progression of potential transient or accident scenarios. This deliverable is a scoping survey of thermal-fluids evaluation and confirmatory experimental validation requirements of accident tolerant cladding concepts with a focus on boiling heat transfer characteristics. The key takeaway messages of this report are: 1. CHF prediction accuracy is important and the correlations may have significant uncertainty. 2. Surface conditions are important factors for CHF, primarily the wettability that is characterized by contact angle. Smaller contact angle indicates greater wettability, which increases the CHF. Surface roughness also impacts wettability. Results in the literature for pool boiling experiments indicate changes in CHF by up to 60% for several ATF cladding candidates. 3. The measured wettability of FeCrAl (i.e., contact angle and roughness) indicates that CHF should be investigated further through pool boiling and flow boiling experiments. 4. Initial measurements of static advancing contact angle and surface roughness indicate that FeCrAl is expected to have a higher CHF than Zircaloy. The measured contact angle of different FeCrAl alloy samples depends on oxide layer thickness and composition. The static advancing contact angle tends to decrease as the oxide layer thickness increases.

  2. Modeling of Heat Exchange with Developed Nucleate Boiling on Tenons

    Directory of Open Access Journals (Sweden)

    A. V. Оvsiannik

    2007-01-01

    Full Text Available The paper proposes a thermal and physical model for heat exchange processes with developed nucleate boiling on the developed surfaces (tenons with various contours of heat transfer surface. Dependences for calculating convective heat exchange factor have been obtained on the basis of modeling representation. Investigations have shown that an intensity of convective heat exchange does not depend on tenon profile when boiling takes place on the tenons. The intensity is determined by operating conditions, thermal and physical properties of liquid, internal characteristics of boiling processes and geometrical characteristics of a tenon.

  3. 加入惰性固体粒子的二元物系的流动沸腾传热特性%HEAT TRANSFER ON VAPOR-LIQUID-SOLID THREE-PHASE FLOW BOILING OF BINARY MIXTURES

    Institute of Scientific and Technical Information of China (English)

    王春雨; 李修伦

    2000-01-01

    Experimental study on vapor-liquid-solid three-phase flow boiling heat transfer of ethanol-water binary mixtures in a vertical tube was carried out. The results showed that with the presence of inert solid particles in binary mixtures, the heat transfer coefficients were 1.5—2.0 times of those with the vapor-liquid two-phase flow. The effects of several parameters on heat transfer were also discussed. The results showed that the three-phase flow boiling heat transfer coefficients of binary mixtures decreased with the increase of the composition of ethanol in binary mixtures when the composition were within 3%—18% and the heat transfer coefficients increased with the increase of the heat flux and the flow rate. The three-phase flow boiling heat transfer coefficients of binary mixtures increased with the increase of the volume fractions of solid particles and this tendency was the same for different particles. But the enhancement by particles with dissimilar physical properties are not the same.It was due to their different density, specific heat and thermal conductivity. The heat transfer coefficients increased with the increase of these three properties. Surface wettability had great effects on the enhancement of boiling heat transfer. Heat transfer coefficients increased with the decrease of the surface wettability, which was shown by the polyacrylamide particles.

  4. Heat transfer measurements on smooth and finned tubes in a standard apparatus for boiling experiments. Waermeuebergangsmessungen an Glatt- und Rippenrohren in einer Standardapparatur fuer Siedeversuche

    Energy Technology Data Exchange (ETDEWEB)

    Fath, W.

    1986-07-28

    The use of Rankine cycles with refrigerants or other organic working fluids for waste heat recovery has been a matter of discussion lately. The evaporating pressure is higher in these systems than in conventional application of finned tubes, so the problems of heat transfer in nucleate boiling on finned tubes are investigated here. Measurements were made on smooth and finned tubes and on surface-treated smooth and finned tubes. Refrigerant R-22 was used for the experiments; the measurements cover a wide range of pressures. (HAG).

  5. 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

  6. Effect of External Forced Flow and Boiling Film on Heat Transfer of AISI 4140 Steel Horizontal Rod During Direct Quenching%Effect of External Forced Flow and Boiling Film on Heat Transfer of AISI 4140 Steel Horizontal Rod During Direct Quenching

    Institute of Scientific and Technical Information of China (English)

    A H Meysami; R Ghasemzadeh; S H Seyedein; M R Aboutalebi

    2011-01-01

    The effects of rod falling and moving, external flow field, boiling film and radiation were investigated on fluid flow and heat transfer of AISI 4140 steel horizontal rod during direct quenching by mathematical modeling. The flow field and heat transfer in quenching tank were simulated by computational fluid dynamics (CFD) method considering falling and moving of rods during process. Therefore, modeling of flow field was done by a fixed-mesh method for general moving objects equations, and then, energy equation was solved with a numerical approach so that effeet of boiling film heat flux was considered as a source term in energy equation for solid-liquid boundary. Simulated results were verified by comparing with published and experimental data and there was a good agreement between them. Also, the effects of external forced flow and film boiling were investigated on heat flux output, temperature distribution and heat transfer coefficient of rod. Also simulated results determined optimum quenching time for this process.

  7. 干涸后膜态沸腾传热计算模型%Numerical model of post-dryout film boiling heat transfer

    Institute of Scientific and Technical Information of China (English)

    李虹波; 陈炳德; 熊万玉

    2011-01-01

    提出了膜态沸腾传热的物理模型,建立相应的数学模型,对干涸后膜态沸腾传热特性进行分析.通过矩形通道试验数据确定关系式系数,得到了适用于矩形通道的干涸后膜态沸腾传热计算模型,并对计算偏差进行了统计计算.文中提出的理论计算模型与现有不同工况范围内取得的试验数据和已有计算模型进行了比较分析.结果表明:模型计算值与现有试验数据符合良好,且相对于已有计算模型,本模型具有良好的适用性.%A physical model was proposed for the film boiling heat transfer, and the corresponding mathematical descriptions were given.The heat transfer characteristics of post-dryout film boiling were analyzed.The numerical model of post-d~out film boiling heat transfer in rectangular channel was obtained as the empirical value of the coefficient was determined by the experimental data from rectangular channel, and the statistical deviations were calculated.The numerical model was compared with the experimental data of different parameters and other numerical models.The calculated results of the numerical model show a good agreement with the experimental data, and the numerical model has good applicability, compared with other numerical models.

  8. Numerical model of post-DNB film boiling heat transfer%DNB后膜态沸腾传热计算模型

    Institute of Scientific and Technical Information of China (English)

    李虹波; 陈炳德; 赵华; 熊万玉

    2011-01-01

    It is proposed in this paper a physical model for the film boiling heat transfer. The corresponding mathematical descriptions are given in details and the heat transfer characteristic of post-DNB film boiling is analyzed. The numerical model of post-DNB film boiling heat transfer is obtained as the empirical value of the coefficient is determined by the experimental data. The numerical model is compared with the experimental data of different parameters and other numerical models, and the statistical deviations are calculated. The calculating results of the numerical model in this paper show good agreement with the experimental data, and the numerical model in this paper has comprehensive applicability compared with other numerical models. The effects of thermal-hydraulic parameters on the post-DNB film boiling heat transfer have been numerically researched using the numerical model in this paper. The calculating results are as same as the experimental results.%提出膜态沸腾传热的物理模型,建立相应的数学模型,对DNB后膜态沸腾传热特性进行分析,通过实验数据确定关系式系数,得到了DNB后膜态沸腾传热计算模型.本文提出的理论计算模型与现有不同工况范围内取得的实验数据和已有计算模型进行了比较分析,并对计算偏差进行了统计计算.比较结果表明,本文的计算结果与实验数据符合较好,且相对于已有计算模型,本文模型具有较广的适用性.针对各系统参数对DNB后膜态沸腾传热的影响,对所提出的理论计算模型进行了研究,所得结果的规律与已有实验研究结果符合.

  9. A novel 1D/2D model for simulating conjugate heat transfer applied to flow boiling in tubes with external fins

    Science.gov (United States)

    Ocłoń, Paweł; Łopata, Stanisław; Nowak, Marzena

    2015-04-01

    This study presents a novel, simplified model for the time-efficient simulation of transient conjugate heat transfer in round tubes. The flow domain and the tube wall are modeled in 1D and 2D, respectively and empirical correlations are used to model the flow domain in 1D. The model is particularly useful when dealing with complex physics, such as flow boiling, which is the main focus of this study. The tube wall is assumed to have external fins. The flow is vertical upwards. Note that straightforward computational fluid dynamics (CFD) analysis of conjugate heat transfer in a system of tubes, leads to 3D modeling of fluid and solid domains. Because correlation is used and dimensionality reduced, the model is numerically more stable and computationally more time-efficient compared to the CFD approach. The benefit of the proposed approach is that it can be applied to large systems of tubes as encountered in many practical applications. The modeled equations are discretized in space using the finite volume method, with central differencing for the heat conduction equation in the solid domain, and upwind differencing of the convective term of the enthalpy transport equation in the flow domain. An explicit time discretization with forward differencing was applied to the enthalpy transport equation in the fluid domain. The conduction equation in the solid domain was time discretized using the Crank-Nicholson scheme. The model is applied in different boundary conditions and the predicted boiling patterns and temperature fields are discussed.

  10. Nucleate boiling heat transfer in vertical rectangular mini-channel%竖直矩形细通道内的水沸腾换热特性

    Institute of Scientific and Technical Information of China (English)

    常威; 张树生; 程林; 郭雷

    2012-01-01

    以宽度为1.0mm和0.1mm的竖直矩形细通道内的沸腾换热特性为研究对象,运用数值模拟的方法探索气泡生成、长大和脱离的过程,通过几何重构和界面追踪的方法获取相界面移动和变化对系统内压差以及平均表面换热系数的影响.计算中考虑重力、表面张力和壁面黏性的作用.研究结果表明:通道宽度的不同对气泡生长方式和气泡形态产生很大影响,且核态沸腾换热系数随着细通道宽度的减小而增大;表面张力在细通道沸腾换热过程中所起的作用明显增大,证明细通道有强化换热的作用;由于数值计算中进行了理想化假设,导致数值模拟的沸腾传热系数比现有细通道沸腾传热实验传热系数普遍偏高.%In order to study the characteristics of boiling two-phase heat transfer in vertical rectangular mini-channels with width of 1.0 mm and 0.1 mm, a numerical simulation was conducted to explore the course of bubble generation, growing up and departure from the wall. Gravity, surface tension and the wall adhesion were taken into consideration, the effect caused by the interface movement on the system pressure difference and the average surface heat transfer coefficient was also discussed by using the geometry reconstruction and interface tracking method. The results show that the variation of channel width has great influence on the course of bubble growth and motion. As the channel size decreases, the nucleate boiling heat transfer coefficient increases obviously, proving that the mini-channel can enhance the heat transfer. However, due to some idealized assumptions, the boiling heat transfer coefficient of the numerical simulation is higher than the existing experimental value.

  11. Pool boiling heat transfer of water in porous copper foam%水在开孔泡沫铜中的池沸腾传热特性

    Institute of Scientific and Technical Information of China (English)

    程云; 李菊香; 莫光东

    2013-01-01

    对常温、大气压下水在开孔泡沫铜中池沸腾的传热特性进行了试验研究,观察了开孔泡沫铜中汽泡的生长特性及其变化规律,并与水在光管加热面的池沸腾特性进行了对比.试验结果表明:水在泡沫铜中池沸腾时,汽泡脱离直径和汽泡脱离频率随热通量的增加而不断增大,泡沫铜对水的池沸腾传热具有很好的强化效果.根据试验结果,得到了水在开孔泡沫铜中池沸腾传热的传热系数拟合关联式,为进一步的研究提供了依据.%The pool boiling heat transfer performance of water in porous copper foam was investigated experimentally at room temperature and atmospheric pressure. The growth characteristics of bubble in copper foam with open cells were obtained by visual observation. The results showed that the bubble escape diameters and bubble escape frequency increased with the increase of heat flux, and the enhancement effect of copper foam for pool boiling was obtained by comparing with plain tube. A correlation for water pool boiling heat transfer coefficient in copper foam was obtained, providing a basis to further study.

  12. Two-phase heat transfer and pressure drop of LNG during saturated flow boiling in a horizontal tube

    Science.gov (United States)

    Chen, Dongsheng; Shi, Yumei

    2013-12-01

    Two-phase heat transfer and pressure drop of LNG (liquefied natural gas) have been measured in a horizontal smooth tube with an inner diameter of 8 mm. The experiments were conducted at inlet pressures from 0.3 to 0.7 MPa with a heat flux of 8-36 kW m-2, and mass flux of 49.2-201.8 kg m-2 s-1. The effect of vapor quality, inlet pressure, heat flux and mass flux on the heat transfer characteristic are discussed. The comparisons of the experimental data with the predicted value by existing correlations are analyzed. Zou et al. (2010) correlation shows the best accuracy with 24.1% RMS deviation among them. Moreover four frictional pressure drop methods are also chosen to compare with the experimental database.

  13. Experimental Investigation on Microbubble Emission Boiling Heat Transfer%微细化沸腾传热实验研究

    Institute of Scientific and Technical Information of China (English)

    朱光昱; 唐继国; 孙立成

    2013-01-01

    气泡微细化沸腾是沸腾到达某个临界热负荷后,加热面温度升高不大,与该临界热负荷相比,热流密度大幅提高的沸腾现象。本文在设计完成一可视化实验装置的基础上,通过高速摄影仪观察并结合采集的壁温数据,对常压下直径为10 m m铜加热面上的池式气泡微细化沸腾现象进行了研究,并讨论了液体过冷度对其的影响。实验发现,气泡微细化沸腾状态下,加热面上生成1层极其不稳定的气膜,气液交界面上不停地有大量微小气泡生成并以极高速度射入过冷液体中。随加热面热流密度的增大,气膜厚度波动周期缩短,气膜最大厚度减小,所生成微小气泡的直径也明显减小。实验中获得的最高热流密度达9 M W/m2。%Microbubble emission boiling (MEB) is a phenomenon that the heat flux increases more rapidly compared to the critical heat flux (CHF) with a little increase of the heating surface superheat .A subcooled pool boiling experimental setup was built up to investigate the bubble behaviors of M EB under the atmospheric condition at different liquid subcoolings with the help of high-speed video camera .The heating element of the experimental setup is a copper block with its upper part of a 10 mm diameter cylinder . T he experimental results show that ,in M EB regime ,an unsteady vapor film spreads on the heating surface . Numerous microbubbles are emitted into subcooled liquid continuously with an extremely high speed from the interface .Along with the rise of heat flux ,the oscillation period of vapor film along its thickness gets shorter and the maximum thickness also becomes smaller . T he microbubble diameter under higher power heating is much smaller than that under low heating flux .The maximum heat flux in the experiment is about 9 M W/m2 at 60 K subcooling .

  14. Augmentation of boiling heat transfer by utilizing the EHD effect. 1st report. ; Basic study on the enhancement of nucleate boiling heat transfer by applying electric field. EHD koka wo katsuyosuru futto dennetsu sokushin ni kansuru kenkyu. 1. ; Futto sokushin no kisoteki kenkyu

    Energy Technology Data Exchange (ETDEWEB)

    Ogata, J. (Mitsubishi Heavy Industries, Ltd., Tokyo (Japan)); Yabe, A. (Mechanical Engineering Lab., Tsukuba (Japan)); Yamazaki, T. (The Tokyo Electric Power Co. Inc., Tokyo (Japan)); Hirao, Y. (Mitsubishi Heavy Industries, Ltd., Tokyo (Japan))

    1990-07-25

    What utilizes the effect of electrohydrodynamical technique (EHD), as one of heat transfer augmentation methods, is methodically frequented and partially prepared to be put to practical use. Then, the heat transfer augmentation effect on nucleate boiling, utilizing the EHD effect, was both experimentally and theoretically studied from both the applicative and basic viewpoints. By adding fleon with 2wt% ethyl alcohol, higher in electric conductivity, in order to have the mitigation time of electric charge correspond to the bubbling frequency of bubble, the heat transfer augmentation was enabled to be about 8.5 times as high as that without impressing the electric field. As a result of observing the behavior of bubble in the electric field, was observed a phenomenon of bubble, moving from place to place, without ascending, on the plane electrode plate, by which could be found one of causes of the heat transfer augmentation. From analyzing the electric field around the bubble, it was clear that the static electric field force of vertical component generates force to push the bubble down on the heat transfer surface, and that the horizontal component of static electric field force is more than four times as large as its vertical component, and gives force to have the bubble move and rotate easily on the heat transfer surface. 8 refs., 9 figs.

  15. Heat transfer during boiling at finned tubes and finned tube bundles; Der Waermeuebergang beim Sieden an Rippenrohren und Rippenrohrbuendeln

    Energy Technology Data Exchange (ETDEWEB)

    Chen Qiurong

    1991-06-10

    Based on bubble dynamics at single tubes and hydrodynamics at multi-tube arrangements (a vertical tube row, tube bundle), a theory for calculation of heat transfer at single tubes, at a vertical tube row and at tube bundles was developed. The theory applies both to finned tubes and plain tubes. To verify the presented theory, measured heat transfer coefficients taken from literature are recalculated. A comparison between heat transfer coefficients for single tubes and two-tube arrangements, calculated according to the theory and determined by measurements shows good agreement. Measuring results for plain tube bundles and bundles of finned tubes also agree well with the theory. (orig./MM) [Deutsch] Aufbauend auf der Blasendynamik an Einzelrohren und der Hydrodynamik in Mehrrohranordnungen (eine senkrechte Rohrreihe, Rohrbuendel) wurde eine Theorie zur Berechnung des Waermeuebergangs an Einzelrohren, an einer senkrechten Rohrreihe und an Rohrbuendeln entwickelt. Die Theorie gilt sowohl fuer Rippenrohre als auch fuer Glattrohre. Zur Ueberpruefung der vorgestellten Theorie werden gemessene Waermeuebergangskoeffizienten aus der Literatur nachgerechnet. Ein Vergleich zwischen den nach der Theorie berechneten und den aus Messungen ermittelten Waermeuebergangskoeffizienten fuer Einzelrohre und Zweirohranordnungen zeigt gute Uebereinstimmung. Auch die Messergebnisse von Glattrohrbuendeln und von Buendeln mit den Rippenrohren lassen sich durch die Theorie gut wiedergeben. (orig./MM)

  16. Interferometric and numerical study of the temperature field in the boundary layer and heat transfer in subcooled flow boiling

    Energy Technology Data Exchange (ETDEWEB)

    Lucic, Anita; Emans, Maximilian; Mayinger, Franz; Zenger, Christoph

    2004-04-01

    An interferometric study and a numerical simulation are presented of the combined process of the bulk turbulent convection and the dynamic of a vapor bubble which is formed in the superheated boundary layer of a subcooled flowing liquid, in order to determine the heat transfer to the flowing subcooled liquid. In this investigation focus has been given on a single vapor bubble at a defined cavity site to provide reproducible conditions. In the experimental study single bubbles were generated at a single artificial cavity by means of a CO{sub 2}-laser as a spot heater at a uniformly heated wall of a vertical rectangular channel with water as the test fluid. The experiments were performed at various degrees of subcooling and mass flow rates. The bubble growth and the temporal decrease of the bubble volume were captured by means of the high-speed cinematography. The thermal boundary layer and the temperature field at the phase-interface between fluid and bubble were visualized by means of the optical measurement method holographic interferometry with a high temporal and spatial resolution, and thus the local and temporal heat transfer could be quantified. The experimental results form a significant data basis for the description of the mean as well as the local heat transfer as a function of the flow conditions. According to the experimental configuration and the obtained data the numerical simulations were performed. A numerical method has been developed to simulate the influence of single bubbles on the surrounding fluid which is based on a Lagrangian approach to describe the motion of the bubbles. The method is coupled to a large-eddy simulations by the body force term which is locally evaluated based on the density field. The obtained experimental data correspond well with the numerical predictions, both of which demonstrate the thermo- and fluiddynamic characteristics of the interaction between the vapor bubble and the subcooled liquid.

  17. Effect of Bubble Size on Cylinder Head Boiling Heat Transfer%气泡尺寸对气缸盖沸腾换热的影响

    Institute of Scientific and Technical Information of China (English)

    何联格; 左正兴; 向建华

    2013-01-01

    In Eulerian multiphase flow model to simulate the gas-liquid two-phase flow boiling heat transfer, the bubble size of discrete phase is often treated as the constant. However, bubbles exist in different shapes and sizes, and bubble size is vital important to the simulation results. Using ANSYS Workbench as the simulation platform, and by considering the effects of different bubble sizes in the computational fluid dynamics module CFX, the gas-liquid two-phase flow boiling heat transfer model was applied in the fluid-solid coupling heat transfer system, which consists of cylinder head and cooling water jacket. Gas-liquid two-phase flow field distribution in cooling water jacket and cylinder head temperature distribution was obtained and validated by the experimental data. Results show that, in the case of bubble size=l mm, simulation results agree well with the experimental data. Gas-liquid two-phase flow boiling heat transfer can effectively reduce the peak temperature of cylinder head flame-face in the nose region of exhaust port and decreases heat load at this position.%在应用欧拉多相流模型仿真计算气液两相流沸腾换热时,离散相的气泡尺寸常常被看作常数,而实际上往往气泡具有不同的形状和尺寸,因此研究气泡尺寸大小对仿真计算结果的影响显得至关重要.以ANSYS Workbench为仿真计算平台,在计算流体动力学模块CFX中,用气液两相流沸腾换热计算模型,对不同气泡尺寸下柴油机气缸盖与冷却水腔所组成的流固耦合传热系统进行了整场离散、整场求解,得到了冷却水腔中气液两相流流场分布特性和气缸盖温度场分布,通过与试验结果的对比分析证明了计算模型的有效性.结果表明,在气泡尺寸大小为1 mm的情况下,仿真结果更接近试验结果,并且考虑气液两相流沸腾换热能够有效地降低气缸盖火力面排气道鼻梁区的最高温度,以此降低此处的热负荷.

  18. Appliance & Analysis of Enhanced Pool Boiling Heat Transfer for Horizontal Tube in Water Jacket Heater%水平管强化池沸腾传热在水套炉中的应用分析

    Institute of Scientific and Technical Information of China (English)

    苏海鹏

    2011-01-01

    油气集输换热设备中,更多关注的是强化对流传热的研究和应用,而对于管外强化沸腾换热关注较少。在介绍池沸腾传热相关理论一般性原理的基础上,分析了影响池沸腾传热的主要因素。通过改良换热管外表面结构型式,在换热管表面形成凹凸或多孔的结构,这种结构下沸腾传热提高了一个数量级。选择合适的外界压力能够强化管外沸腾传热,提高了管外换热系数。最后讨论了池沸腾传热计算的有关问题。%The convection heat transfer enhancement were researched and applied widely on heat exchange equipment in oil - gas gathering and transportation. Based on the general principles of pool boiling heat transfer theory, the main influenced factors to pool boiling were analyzed. The outside wall of tube was changed to make it concave - convex or porous surface, the pool boiling heat transfer was enhanced by an order of magnitude. Correct design pressure could make the pool boiling enhancing and improving the heat transfer coefficient outside horizontal tube. Finally, the pool boiling heat transfer calculation was discussed.

  19. Coupling effect between film boiling heat transfer and evaporation drag around a hot-particle in cold liquid

    Institute of Scientific and Technical Information of China (English)

    LI Xiao-Yan; YANG Yan-Hua; XU Ji-Jun

    2003-01-01

    Extremely rapid evaporation could occur when high-temperature particles contact withlow-temperature liquid. This kind of phenomenon is associated with the engineering safety and the problems inhigh-transient multi-phase fluid and heat transfer. The aim of our study was to design and build an observable ex-periment facility. The first series of experiments were performed by pouring one or six high-temperature particles intoa low saturated temperature liquid pool. The particle's falling-down speed was recorded by a high-speed camera, thuswe can find the special resistant feature of the moving high-temperature particles, which is induced by the high-speedevaporation surrounding the particles. The study has experimentally verified the theory of evaporation drag model.

  20. Heat transfer characteristics of boiling R134a in forced supercooled flows; Waermeuebergang beim Sieden von R134a in erzwungener unterkuehlter Stroemung

    Energy Technology Data Exchange (ETDEWEB)

    Spindler, K.; Hahne, E. [Stuttgart Univ. (Germany). Inst. fuer Thermodynamik und Waermetechnik

    2000-07-01

    Supercooled boiling is characterized by evaporation at the heating surface although the average temperature of the fluid is still below saturation temperature. There is a superheated metastable boundary layer at the wall in which steam bubbles nucleate and grow. They recondense when they enter the turbulent supercooled flow because of volume increase or detachment from the wall. This phenomenon results in a significant improvement of heat transfer as compared with single-phase forced convection. The contribution presents experimental findings on the heat transfer characteristics of R134a in forced supercooled flow. [German] Das unterkuehlte Sieden ist dadurch gekennzeichnet, dass an der Heizflaeche Verdampfung auftritt, obwohl die Fluessigkeit im Mittel noch nicht die zum Druck gehoerende Saettigungstemperatur erreicht hat. In unmittelbarer Wandnaehe ist eine ueberhitzte metastabile Grenzschicht vorhanden, in der die Dampfblasen an Blasenkeimstellen entstehen und wachsen. Sobald sie wegen ihrer Volumenzunahme oder Abloesung aus der ueberhitzten Grenzschicht in die turbulente, unterkuehlte Kernstroemung gelangen, kondensieren sie wieder. Dieser Vorgang fuehrt zu einer deutlichen Verbesserung des Waermeuebergangs gegenueber der einphasigen erzwungenen Konvektion. Es werden experimentelle Ergebnisse zum Waermeuebergang beim Sieden von R134a in erzwungener unterkuehlter Stroemung vorgestellt. Die Messstrecke ist ein senkrecht angeordnetes, gezogenes Kupferrohr mit einer Laenge von 550 mm und einem Innendurchmesser von 20 mm. Die Messstrecke wird mit Miniatur-Mantelheizleitern beheizt, die in spiralfoermig aussen umlaufende Nuten eingestemmt und zusaetzlich mit Waermeleitzement fixiert sind. Die Versuchsparameter wurden in folgenden Bereichen variiert: Massenstromdichte von 1000 bis 2000 kg/(m{sup 2}s), Waermestromdichte bis 100000 W/m{sup 2}, Unterkuehlung von 2 bis 11 K, Druck zwischen 8 und 10 bar. Die Waermeuebergangskoeffizienten werden mit Nusseltkorrelationen der

  1. 矩形通道干涸后过渡沸腾传热试验研究%Experimental Study on Post-Dryout Transition Boiling Heat Transfer ( ) Rectangular Channel

    Institute of Scientific and Technical Information of China (English)

    李虹波; 陈炳德; 熊万玉

    2011-01-01

    在流动传热基础试验平台上进行了矩形通道干涸后过渡沸腾传热试验.对过渡沸腾的传热特性进行分析;对进口含汽率、质量流速、系统压力等各热工水力参数对过渡沸腾传热的影响进行试验研究.结果表明:干涸后过渡沸腾是一个不稳定的传热过程,壁面温度发生明显的脉动,过渡沸腾会引起质量流速和流道进出口压降等流动参数的脉动;进口含汽率的增加会导致过渡沸腾热流密度减小,壁面温度升高,传热系数减小;质量流速的增大或者系统压力的升高均会导致过渡沸腾热流密度增大,壁面温度降低,传热系数增大.%The experiment of post-dryout transition boiling heat transfer in rectangular channel has been carried out on the basic experimental loop of flow and heat transfer. The characteristics of the transition boiling heat transfer is analyzed. The effects of thermal-hydraulic parameters such as inlet quality,mass flow velocity,and system pressure on the characteristics of post-dryout transition boiling heat transfer are experimentally researched. The results show that the post-dryout transition boiling is unstable,wall temperature oscillates fiercely,and the mass flow velocity and pressure drop oscillate as also; the post-dryout transition boiling heat flux and heat transfer coefficient are decreased,but the wall temperature is increased with the increasing of inlet quality; and the post-dryout transition boiling heat flux and heat transfer coefficient are increased,but the wall temperature is decreased with the increasing of mass flow velocity or system press.

  2. Taking a fresh Look at boiling heat transfer on the road to improved nuclear economics and efficiency

    Energy Technology Data Exchange (ETDEWEB)

    Baglietto, E.; Pointer, W. D.

    2016-08-01

    In the effort to reinvigorate innovation in the way we design, build, and operate the nuclear power generating stations of today and tomorrow, nothing can be taken for granted. Not even the seemingly familiar physics of boiling water. The Consortium for the Advanced Simulation of Light Water Reactors, or CASL, is focused on the deployment of advanced modeling and simulation capabilities to enable the nuclear industry to reduce uncertainties in the prediction of multi-physics phenomena and continue to improve the performance of todays light water reactors and their fuel. An important part of the CASL mission is the development of a next generation thermal hydraulics simulation capability, integrating the history of engineering models based on based on experimental experience with the computing technology of the future. (Author)

  3. Applicability of Correlations of Flow Boiling Heat Transfer to R410A%管内流动沸腾传热关系式对 R410A 的适应性研究

    Institute of Scientific and Technical Information of China (English)

    李定坤; 方贤德

    2015-01-01

    As an alternative refrigerant,R410A has been widely used in industries.The determination of R410A flow boiling heat transfer in channels is needed in the design and development of a refrigeration system using R410A as the refrigerant.There are a lot of correlations for predicting the coefficient of flow boiling heat transfer.However,their applicability to R410A needs to be assessed.This paper has compiled a database of R410A flow boiling heat transfer containing 1268 experimental data points from 10 open papers,based on which 27 correlations of flow boiling heat transfer are evaluated.The work provides a guide for choosing a proper correlation for calculating R410A flow boiling heat transfer and for developing more accurate correlations of R410A flow boiling heat transfer.%R410A 作为一种替代制冷剂,已经大量用在工业生产中。R410A 制冷系统的设计和研发需要进行 R410A 管内流动沸腾换热计算。目前有很多公式预测两相流流动沸腾换热系数,它们对 R410A 的适应性需要判断。本文从10篇论文中收集了1268组 R410A 流动沸腾传热实验数据,用这些数据对27个两相流流动沸腾换热关系式进行了评价,选出了较为精确的 R410A 管内流动沸腾换热关系式,为 R410A 管内流动沸腾换热计算的公式选择提供了依据,为提出精确度更高的 R410A 管内流动沸腾公式提供了参考。

  4. CHF Phenomena by Photographic Study of Boiling Behavior due to Transient Heat Inputs

    Directory of Open Access Journals (Sweden)

    Jongdoc Park

    2012-01-01

    Full Text Available The transient boiling heat transfer characteristics in a pool of water and highly wetting liquids such as ethanol and FC-72 due to an exponentially increasing heat input of various rates were investigated using the 1.0 mm diameter experimental heater shaped in a horizontal cylinder for wide ranges of pressure and subcooling. The trend of critical heat flux (CHF values in relation to the periods was divided into three groups. The CHF belonging to the 1st group with a longer period occurs with a fully developed nucleate boiling (FDNB heat transfer process. For the 2nd group with shorter periods, the direct transition to film boiling from non boiling occurs as an explosive boiling. The direct boiling transition at the CHF from non-boiling regime to film boiling occurred without a heat flux increase. It was confirmed that the initial boiling behavior is significantly affected by the property and the wettability of the liquid. The photographic observations on the vapor bubble behavior during transitions to film boiling were performed using a high-speed video camera system.

  5. Pool boiling of distilled water over tube bundle with variable heat flux

    Science.gov (United States)

    Swain, Abhilas; Mohanty, Rajiva Lochan; Das, Mihir Kumar

    2017-02-01

    The experimental investigation of saturated pool boiling heat transfer of distilled water over plain tube bundle, under uniform and varying heat flux condition along the height are presented in this article. Experiments are carried out under various heat flux configurations applied to rows of tube bundles and pitch distance to diameter ratios of 1.25, 1.6 and 1.95. The wall superheats and pool boiling heat transfer coefficients over individual rows are determined. The pool boiling heat transfer coefficients for variable heat flux and uniform heat flux conditions are compared. The results indicate that the bundle effect is found to exist for uniform as well as variable heat flux under all operating conditions in the present investigation. The variable heat flux resulted in range of wall superheat being highest for decreasing heat flux from bottom to top and lowest for increasing heat flux from bottom to top.

  6. Experimental investigation into effects of ultrasonic vibration on pool boiling heat transfer performance of horizontal low-finned U-tube in TiO2/R141b nanofluid

    Science.gov (United States)

    Chang, Tong-Bou; Wang, Zi-Long

    2016-11-01

    An experimental investigation was performed into the pool boiling heat transfer performance of a low-finned U-tube immersed in TiO2/R141b nanofluid with four different nanoparticle loadings (0, 0.0001, 0.001, and 0.01 vol%). The energy-dispersive X-ray spectrometry results revealed that some of the TiO2 nanoparticles adhered to the heated surface during boiling, and therefore increased the thermal resistance. The heat transfer performance of the nanofluids with particle loadings of 0.0001, 0.001 and 0.01 vol% was thus found to be reduced by around 10, 20 and 50 %, respectively, compared to that of pure R141b refrigerant. Accordingly, an ultrasonic vibration crusher was used to inhibit the formation of the TiO2 nano-sorption layer on the U-tube surface. The ultrasonic vibration suppressed the deposition of TiO2 nanoparticles and improved the heat transfer performance of the nanofluids as a result. Of the four working fluids, the nanofluid with a particle loading of 0.0001 vol% yielded the optimal heat transfer performance (i.e., a heat transfer coefficient around 30 % higher than that of pure R141b refrigerant.)

  7. Experimental research of flow boiling heat transfer with nanotube arrays surface on titanium%纳米管阵列表面流动沸腾传热特性的实验研究

    Institute of Scientific and Technical Information of China (English)

    王新亮; 杨文刚; 史晓平; 陶金亮; 邢晓康

    2013-01-01

    A nano-film with structure of tube arrays was prepared on the inner surface of titanium tube via anodic oxidization. Taking deionized water as the working fluid,the flow boiling heat transfer properties of the nanoporous surface vertical tube with electrically heated outside surface were studied at constant mass velocity employed by forced circulation. The flow boiling heat transfer coefficient correlation of the tube was obtained. Compared to the smooth tube,the flow boiling heat transfer temperature differences were lowered 30%-55%,and its boiling heat transfer coefficient could be increased 1.5-2.2 times.%  利用阳极氧化法在钛换热管内表面制备出了一层管阵列结构纳米薄膜。以该纳米管阵列表面管为传热元件,蒸馏水为工质,采用管外电加热竖管强制循环工艺,在恒质量流速下考察了纳米管阵列表面管的流动沸腾传热性能。在实验的基础上,得出了纳米管阵列表面管流动沸腾传热系数关联式。实验结果表明,与光滑表面管相比,流动沸腾传热温差降低了30%~55%,在没有增加阻力的情况下,沸腾传热系数提高了1.5~2.2倍。

  8. Studies on Water Flow Boiling Heat Transfer Characteristics in Vertical Narrow Rectangular Channel%竖直矩形窄通道内水流动沸腾换热特性的研究

    Institute of Scientific and Technical Information of China (English)

    郑志皋; 陶乐仁; 黄理浩

    2014-01-01

    A single-side heating apparatus is set up to study the flow boiling and heat transfer in vertical narrow rectangular channel,experiment research on flow boiling and heat transfer characteristics in a vertical narrow rectangular channel with the section of 250mm ×5 mm is carried out.According to the experimental analysis:(1 )With the increase of dryness,the local heat transfer coefficient firstly increases then decreases ,there is a maximum,which is saturated nucleate boiling region ,the steam quality is close to zero,also it is close to the onset of boiling.Accordingly flow mode of fluid is from single phase,bubble,slug, churn to annular flow.(2)For flow boiling heat transfer,nuclear boiling heat transfer is significantly affected by heat flux,but liquid film evaporation is nearly not.So it is assumed that heat transfer is caused by the change of heat flux.(3 )The change of inlet temperature has influence on single-phase flow heat transfer coefficient,but flow boiling heat transfer coefficient has great re-lationship with flow pattern and generated bubbles,and not inlet temperature.%建立单面加热垂直矩形窄通道流动沸腾换热试验装置,针对截面250mm ×3.5mm的窄缝通道,对水流动沸腾换热特性进行试验研究。通过试验分析可知:(1)随着干度的增加,局部换热系数先增加后减小,有一个最大值,此时处于饱和核沸腾区域,其蒸汽干度也接近于0,同时也接近于沸腾起始点。相应地流体从单相流-泡状-块状流-搅拌-环状流转变。(2)在流动沸腾换热中,热流密度对核态沸腾换热有明显影响,而对流动沸腾液膜蒸发的影响甚小,所以可以认为由热流密度的变化而引起的换热变化,主要表现在核态沸腾。(3)入口温度的变化对单相流动的换热系数有影响,而沸腾换热系数与流型及汽泡的产生及扰动有极大关系,入口温度对流动沸腾局部换热系数基本没有影响。

  9. Study of rapid transient explosive boiling under short-pulsed laser heating

    Institute of Scientific and Technical Information of China (English)

    JIN Renxi; HUAI Xiulan; LIU Dengying

    2004-01-01

    Using acetone, ethanol, water and acetone-water mixture as test liquids, the rapid transient explosive boiling (RTEB) taking place under short-pulsed laser heating is observed in experiment. The behaviors of temperature variation are investigated via transient temperature measurement. The vapor bubble behaviors of RTEB are captured by high-speed photography, and the difference between RTEB and normal boiling is analyzed. The boiling heat transfer of RTEB is also discussed. It shows that the character of RTEB is far different from normal boiling.

  10. Experimental Investigation of Coolant Boiling in a Half-Heated Circular Tube - Final CRADA Report

    Energy Technology Data Exchange (ETDEWEB)

    Yu, Wenhua [Argonne National Lab. (ANL), Argonne, IL (United States); Singh, Dileep [Argonne National Lab. (ANL), Argonne, IL (United States); France, David M. [Argonne National Lab. (ANL), Argonne, IL (United States)

    2016-11-01

    Coolant subcooled boiling in the cylinder head regions of heavy-duty vehicle engines is unavoidable at high thermal loads due to high metal temperatures. However, theoretical, numerical, and experimental studies of coolant subcooled flow boiling under these specific application conditions are generally lacking in the engineering literature. The objective of this project was to provide such much-needed information, including the coolant subcooled flow boiling characteristics and the corresponding heat transfer coefficients, through experimental investigations.

  11. Heat transfer behavior in non-uniform electric field. 1st Report. Observation of boiling phenomena by Schlieren method; Fukin`itsu denbanai no netsudentatsu kyodo. 1. Schlieren ho ni yoru futto gensho no kansatsu

    Energy Technology Data Exchange (ETDEWEB)

    Nei, H.; Kagawa, T. [Toshiba Corp., Tokyo (Japan)

    1994-08-25

    This paper reports the result of observation using the Schlieren method on how temperature boundary layer changes when an electric field is applied in boiling heat transfer. The experiment used a fine nichrome wire in water as a heat generator. The electric field was built by placing a nickel rod as an electrode placed obliquely above and parallel with the heat generator, and applying electric potential to the electrode. The temperature boundary layer produced near the heat transfer face is disturbed by the electric field. The stronger the electric field, the more vigorous the disturbance. The turbulence in this boundary layer is relatively regular, and observed as stripes of temperatures. The stronger the electric field, the more the number of the stripes in the temperature boundary layer, and the higher the stripe density in the axial direction of the heat generator where the temperature difference appears. Boiling bubbles, occurring when the electric field is applied, are kicked out of the temperature boundary layer that varies due to the electric field force, and the bubbles grow thereat. The turbulence is caused by the low-temperature high-density liquid impinging the heat transfer face perpendicularly as a result of the electric field force, and changing its place vigorously with low-density liquid in the boundary layer. 6 refs., 16 figs.

  12. Numerical simulation of boiling heat and mass transfer in the tube for MVR evaporator%MVR蒸发器管内沸腾传热传质数值模拟

    Institute of Scientific and Technical Information of China (English)

    张琳; 高丽丽; 崔磊; 赵庆良

    2013-01-01

    建立了MVR升膜循环蒸发器管内沸腾蒸发传热传质三维物理模型,采用标准k-ε湍流模型、多相流混合模型和C语言编写气液两相之间质量传递和能量传递的自定义函数,对光管和波纹管内氨基酸废水溶液的沸腾蒸发传热传质特性进行了数值模拟研究,得到了光管和波纹管内湍流强度、温度场、相变含气率和平均沸腾传热系数的分布规律,比较了光管和波纹管内流体的流动和传热传质特性,分析了不同管壁加热温度和进口流速对沸腾传热性能的影响.结果表明,采用MVR升膜循环蒸发器可以实现氨基酸废水溶液的低温负压沸腾蒸发操作,传热管的结构对流体的流动和传热传质有影响,波纹管与光管相比可使平均沸腾传热系数提高2.2倍.%A three-dimensional physical model of boiling heat and mass transfer in the tube for MVR rising film circulation evaporator was built by CFD software. Standard k-s turbulent model, multiphase mixture model and user-defined function (UFD) of the mass transfer and energy transfer between vapor phase and liquid phase compiled by C language were used in the simulation of the performances of boiling evaporation heat and mass transfer of amino acid waste water in the smooth tube and corrugated tube. The distribution laws of the turbulent characteristic field, temperature field, phase change volume fraction and average boiling heat transfer coefficient of smooth tube and corrugated tube were obtained. The flow and the heat and mass transfer characteristic of smooth tube and corrugated tube were compared. The influences of different wall heating temperature and inlet velocity on boiling heat transfer performance were analyzed. The results showed that the boiling evaporation operation of amino acid waste water in low temperature and negative pressure conditions can be realized by MVR rising film circulating evaporator, the different structures of heat transfer tube

  13. Advances in heat transfer enhancement

    CERN Document Server

    Saha, Sujoy Kumar; Sundén, Bengt; Wu, Zan

    2016-01-01

    This Brief addresses the phenomena of heat transfer enhancement. A companion edition in the SpringerBrief Subseries on Thermal Engineering and Applied Science to three other monographs including “Critical Heat Flux in Flow Boiling in Microchannels,” this volume is idea for professionals, researchers, and graduate students concerned with electronic cooling.

  14. Heat transfer

    CERN Document Server

    Holman, J P

    2010-01-01

    As one of the most popular heat transfer texts, Jack Holman's "Heat Transfer" is noted for its clarity, accessible approach, and inclusion of many examples and problem sets. The new tenth edition retains the straight-forward, to-the-point writing style while covering both analytical and empirical approaches to the subject. Throughout the book, emphasis is placed on physical understanding while, at the same time, relying on meaningful experimental data in those situations that do not permit a simple analytical solution. New examples and templates provide students with updated resources for computer-numerical solutions.

  15. 制冷系统不同表面能微通道的流动沸腾传热特性试验%Flowing boiling heat transfer characteristics test for microchannels with different surface energy in refrigeration system

    Institute of Scientific and Technical Information of China (English)

    罗小平; 邓聪; 冯振飞; 周建阳

    2016-01-01

    With the development of many applications in modern industrial system and equipment, the ability to dissipate a large amount of heat from small surface area has been becoming increasingly urgent. Flow boiling in microchannels provides unique advantages when applied in micro-module equipment. Therefore, the microchannel heat exchangers have a broad industrial and market prospects for their high heat transfer coefficients and appreciable reduction in weight and volume. Flow boiling heat transfer in microchannels becomes one of popular researching hot spots. But the researches about flow boiling in microchannels with different surface energy are still lacked and further researches are needed. In this study, the current experiments fabricated 3 different modules with the identical sizes of 240 mm × 400 mm × 7.5 mm and with the different surface energy. Flow boiling experiments were conducted with the refrigerant R141b in a test module containing 22 microchannels which were 2 mm wide and 1 mm deep. During the experiments, the heat flux imposed on the aluminum substrate varied from 9 to 26 kW/m2 and the mass flux flowing into the channel varied from 50 to 583 kg/(m2·s). The effects of the microchannels with different energy on boiling heat transfer under a certain pressure were experimentally investigated with different heat flux and mass flux. The results showed that the thermodynamic equilibrium quality increased fairly linearly with axial variation, with the slope inversely proportional to mass flow rate. The two-phase boiling heat transfer came earlier when mass flow rate was smaller and the increase of mass flow rate was beneficial to boiling heat transfer, but leading to the increasing of the length of the subcooled region. Heat transfer coefficient was relatively stable in the saturated boiling region of the microchannels and had a tendency to decrease along the flow direction due to the rise of gas phase proportion. Compared to the microchannels with the

  16. Visualization Study on High Heat Flux Boiling and Critical Heat Flux

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-10-15

    In this study, an integrated visible and infrared-based experimental method is introduced to simultaneously measure the details of high-resolution liquid-vapor phase and heat transfer distributions on a heated wall. The dynamics and heat transfer at high heat flux boiling and critical heat flux were observed. The experiment was conducted in pool of saturated water under atmospheric pressure. There have been many studies to examine the physical mechanisms of nucleation boiling and critical heat flux over several decades. Several visible and infrared-based optical techniques for time-resolved high resolution measurements for liquid-vapor phase and heater surface temperature during boiling have been introduced to understand the characteristics and mechanisms of them. Liquid-vapor phase, temperature, and heat flux distributions on the heated surface were measured during pool boiling of water using the integrated total reflection and infrared thermometry technique. Qualitative examination of the data for high heat flux boiling and CHF was performed. The main contributions of this work are summarized below. The existence and behavior of dry patches lead the way toward CHF condition. Therefore, the mechanistic modeling of the CHF phenomenon necessarily needs to include the physical parameters related to dynamics of the large dry patch such as life time and size. In addition to the dynamic behavior of the dry patch, the thermal behavior of the hot patch is also important. Even though the dry area was rewetted, the stored thermal energy in the hot patch can be remained if the rewetting time is short and the subsequent dry patch is regenerated quickly.

  17. Explosive Boiling at Very Low Heat Fluxes: A Microgravity Phenomenon

    Science.gov (United States)

    Hasan, M. M.; Lin, C. S.; Knoll, R. H.; Bentz, M. D.

    1993-01-01

    The paper presents experimental observations of explosive boiling from a large (relative to bubble sizes) flat heating surface at very low heat fluxes in microgravity. The explosive boiling is characterized as either a rapid growth of vapor mass over the entire heating surface due to the flashing of superheated liquid or a violent boiling spread following the appearance of single bubbles on the heating surface. Pool boiling data with saturated Freon 113 was obtained in the microgravity environment of the space shuttle. The unique features of the experimental results are the sustainability of high liquid superheat for long periods and the occurrence of explosive boiling at low heat fluxes (0.2 to 1.2 kW/sq m). For a heat flux of 1.0 kW/sq m a wall superheat of 17.9 degrees C was attained in ten minutes of heating. This was followed by an explosive boiling accompanied with a pressure spike and a violent bulk liquid motion. However, at this heat flux the vapor blanketing the heating surface could not be sustained. Stable nucleate boiling continued following the explosive boiling.

  18. Study on LXe system for particle detector (2). Boiling heat transfer characteristics of LXe; Ryushi kenshutsu yo ekitai Xenon shisutemu no kenkyu (2). Ekitai Xenon no futto netsudentatsu tokusei

    Energy Technology Data Exchange (ETDEWEB)

    Haruyama, T. [High Energy Accelerator Research Organization, Tsukuba (Japan)

    2000-05-29

    In the experiments using a large quantity of liquid xenon as caloric meter, in order to catch the scintillation light generated by collision of the injected high-energy particles with the liquid Xenon, a plurality of photomultiplier cells is arranged in the liquid. At this time, density variation of the liquid is caused as the chip resistance for signal processing generates heat in the liquid Xenon, and makes influence on the scintillation light. Therefore, the basic data concerning heat transfer characteristics such as convection and boiling of the liquid Xenon are necessary. In this study, the heat transfer characteristics of the liquid Xenon is investigated using a Xenon liquefier including a pulse tube-refrigerating machine. Platinum fine wire horizontally placed and a copper round plate are used as a heating element. The system for the experiment is an installation of installing the small pulse tube refrigerating machine for 80K to a glass Dewar. Experimental values of natural convection region and the nucleate boiling region agree comparatively well with the calculation results according to empirical formula. (NEDO)

  19. Revisión del cálculo del coeficiente de traspaso de calor en ebullición en minicanales y microcanales//Review of heat transfer coefficient calculation in boiling in minichannels and microchannels

    Directory of Open Access Journals (Sweden)

    César Arnaldo Cisneros‐Ramírez

    2014-05-01

    Full Text Available La necesidad de disipar altas densidades de flujo de calor ha llevado a los investigadores y diseñadores a emplear el cambio de fase como mecanismo para lograr tal objetivo y con ello lograr equipos intercambiadores de calor más compactos. En el presente trabajo se realizó un estudio de la bibliográfica sobre la ebullición en minicanales y microcanales. Para ello se consultaron bibliografíasque datan desde los años 90 hasta la actualidad, con lo cual se revelaron los principales parámetros o tópicos que caracterizan a este proceso en minicanales y microcanales. Es así que se abordan los términos minicanales y microcanales, ebullición en flujo forzado y regímenes (mapa de flujo.Además se presenta un resumen de las ecuaciones para la determinación del coeficiente de traspaso de calor en régimen bifásico (hdf.Palabras claves: ebullición, microcanales, minicanales, coeficiente de traspaso de calor.____________________________________________________________________________AbstractThe necessity of transfer high heat flux had led to researchers and designers to use the change of phase in order to get this objective. In this work was made a review in more of seventy sources of information dating since 90´s up to the present, where were revealed the main parameters that characterize the boiling process in minichanels-microchannels. It deals with terms minimicrochannels,flow boiling and flow pattern map. Also, it is presented a summary of equations used for calculate the two-phase heat transfer coefficient.Key words: boiling, minichannels, microchannels, heat transfer coefficient.

  20. BOILING OF WATER AND ORGANIC LIQUIDS ON LOW-TEMPERATURE POROUS SURFACES OF HEAT PIPES

    OpenAIRE

    Шаповал, Андрій Андрійович; Панов, Євген Миколайович; Сауліна, Юлія Валеріївна; Романчук, Борис Васильович; Трубійчук, Р. П.

    2015-01-01

    The experimental study results of the influence of porous metal fiber structures on the intensity of two-phase heat transfer of water and acetone boiling on porous surfaces in conditions of free movement and capillary transport of liquids are presented in the article. The experiments were realized using specially designed experimental installation simulated the operating conditions of heat pipes and thermosyphons. Such conditions are typical for two-phase heat transfer devices – heat pipes an...

  1. 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.

  2. Heat transfer

    CERN Document Server

    Jorge, Kubie; Thomas, Grassie

    2012-01-01

    A core task of engineers is to analyse energy related problems. The analytical treatment is usually based on principles of thermodynamics, fluid mechanics and heat transfer, but is increasingly being handled computationally.This unique resource presents a practical textbook, written for both undergraduates and professionals, with a series of over 60 computer workbooks on an accompanying CD.The book emphasizes how complex problems can be deconstructed into a series of simple steps. All thermophysical property computations are illustrated using diagrams within text and on the compani

  3. Partial Nucleate Pool Boiling at Low Heat Flux: Preliminary Ground Test for SOBER-SJ10

    Science.gov (United States)

    Wu, Ke; Li, Zhen-Dong; Zhao, Jian-Fu; Li, Hui-Xiong; Li, Kai

    2016-05-01

    Focusing on partial nucleate pool boiling at low heat flux, SOBER-SJ10, one of 27 experiments of the program SJ-10, has been proposed to study local convection and heat transfer around an isolated growing vapor bubble during nucleate pool boiling on a well characterized flat surface in microgravity. An integrated micro heater has been developed. By using a local pulse overheating method in the experimental mode of single bubble boiling, a bubble nucleus can be excited with accurate spatial and temporal positioning on the top-side of a quartz glass substrate with a thickness of 2 mm and an effective heating area of 4.5 mm in diameter, and then grows under an approximate constant heat input provided by the main heater on the back-side of the substrate. Ten thin film micro-RTDs are used for local temperature measurements on the heating surface underneath the growing bubble. Normal pool boiling experiments can also be carried out with step-by-step increase of heating voltage. A series of ground test of the flight module of SOBER-SJ10 have been conducted. Good agreement of the measured data of single phase natural convection with the common-used empirical correlation warrants reasonable confidence in the data. It is found that the values of the incipience superheat of pool boiling at different subcooling are consistent with each others, verifying that the influence of subcooling on boiling incipience can be neglected. Pool boiling curves are also obtained, which shows great influence of subcooling on heat transfer of partial nucleate pool boiling, particularly in lower heat flux.

  4. Sorption and agglutination phenomenon of nanofluids on a plain heating surface during pool boiling

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Zhen-hua; Liao, Liang [School of Mechanical and Power Engineering, Shanghai Jiaotong University, 200030 Shanghai (China)

    2008-05-15

    The pool nucleate boiling heat transfer experiments of water (H{sub 2}O) based and alcohol (C{sub 2}H{sub 5}OH) based nanofluids and nanoparticles-suspensions on the plain heated copper surface were carried out. The study was focused on the sorption and agglutination phenomenon of nanofluids on a heated surface. The nanofluids consisted of the base liquid, the nanoparticles and the surfactant. The nanoparticles-suspensions consisted of the base liquid and nanoparticles. The both liquids of water and alcohol and both nanoparticles of CuO and SiO{sub 2} were used. The surfactant was sodium dodecyl benzene sulphate (SDBS). The experimental results show that for nanofluids, the agglutination phenomenon occurred on the heated surface when the wall temperature was over 112{sup o}C and steady nucleated boiling experiment could not be carried out. The reason was that an unsteady porous agglutination layer was formed on the heated surface. However, for nanoparticles-suspensions, no agglutination phenomenon occurred on the heating surface and the steady boiling could be carried out in the whole nucleate boiling region. For the both of alcohol based nanofluids and nano-suspensions, no agglutination phenomenon occurred on the heating surface and steady nucleate boiling experiment could be carried out in the whole nucleate boiling region whose wall temperature did not exceed 112{sup o}C. The boiling heat transfer characteristics of the nanofluids and nanoparticles-suspensions are somewhat poor compared with that of the base fluids, since the decrease of the active nucleate cavities on the heating surface with a very thin nanoparticles sorption layer. The very thin nanoparticles sorption layer also caused a decrease in the solid-liquid contact angle on the heating surface which leaded to an increase of the critical heat flux (CHF). (author)

  5. Analysis of heat transfer correlation for CO2 in-tube flow boiling%二氧化碳管内沸腾换热系数关联式的分析

    Institute of Scientific and Technical Information of China (English)

    杨建超; 柳建华; 张良; 葛琪林; 张海江; 朱立伟

    2011-01-01

    了解管内流动沸腾特性并准确地预测出其换热系数,对设计紧凑、高效的CO2蒸发换热器有着至关重要的作用.文中分析了几个国内外已公开发表的换热关联式,并将预测结果与实验数据进行对比和误差分析,比较后发现Yoon2004、Jung关联式的预测精度相对较高,但各关联式对干涸后的换热系数预测普遍有较大偏差,有待进一步的改进.%Understanding intube flow boiling heat transfer character and precisely predicting of its heat transfer are essential in the design of a compact and efficient evaporator for CO2. Several heat transfer correlations of C02 published in abroad were analysed in this article. It is found that precisions of Yoon2004 and Jung correlation are relatively higher, however correlations need to be improved for their predictive values have large deviation between the experimental values in the prediction of post - dryout heat transfer.

  6. Time and Space Resolved Heat Flux Measurements During Nucleate Boiling with Constant Heat Flux Boundary Conditions

    Science.gov (United States)

    Yerramilli, Vamsee K.; Myers, Jerry G.; Hussey, Sam W.; Yee, Glenda F.; Kim, Jungho

    2005-01-01

    The lack of temporally and spatially resolved measurements under nucleate bubbles has complicated efforts to fully explain pool-boiling phenomena. The objective of this current work was to acquire time and space resolved temperature distributions under nucleating bubbles on a constant heat flux surface using a microheater array with 100x 100 square microns resolution, then numerically determine the wall to liquid heat flux. This data was then correlated with high speed (greater than l000Hz) visual recordings of The bubble growth and departure from the heater surface acquired from below and from the side of the heater. The data indicate that microlayer evaporation and contact line heat transfer are not major heat transfer mechanisms for bubble growth. The dominant heat transfer mechanism appears to be transient conduction into the liquid as the liquid rewets the wall during the bubble departure process.

  7. Investigation Status of Heat Exchange while Boiling Hydrocarbon Fuel

    Directory of Open Access Journals (Sweden)

    D. S. Obukhov

    2006-01-01

    Full Text Available The paper contains analysis of heat exchange investigations while boiling hydrocarbon fuel. The obtained data are within the limits of the S.S. Kutateladze dependence proposed in 1939. Heat exchange at non-stationary heat release has not been investigated. The data for hydrocarbon fuel with respect to critical density of heat flow are not available even for stationary conditions.

  8. High Heat Flux Burnout in Subcooled Flow Boiling

    Institute of Scientific and Technical Information of China (English)

    G.P.Celata; M.Cumo; 等

    1995-01-01

    The paper reports the results of an experimental research carried out at the Heat transfer divison of the Energy Department,C.R.Casaccia,on the thermal hydraulic characterization of subcooled flow boiling CHF under typical conditions of thermonuclear fusion reactors.I.e.high liquid velocity and subcooling.The experiment was carried out exploring the following parameters:channel diameter(from 2.5to 8.0 mm),heated length(10 and 15cm) ,liquid velocity (from 2 to 40m/s),exit pressure(from atmospheric to 5.0 MPa),inlet temperature(from 30 to 80℃),channel orientation (vertical and horizontal),A maximum CHF value of 60.6MW/m2 has been obtained under the following conditions:Tin-30°,p=2.5MPa,u=40m/s,D=2.5mm(smooth channel) Turbulence promoters(helically coiled wires)have been employed to further enhance the CHF attainable with subcooled flow boiling.Helically coiled wires allow an increase of 50% of the maximum CHF obtained with smooth channels.

  9. Heat Transfer of Boiling R134a and R142b on a Twisted Tube with Machine Processed Porous Surface%R134a和R142b在表面多孔螺旋扁管外的沸腾传热

    Institute of Scientific and Technical Information of China (English)

    高学农; 尹辉斌; 黄玉优; 凌双梅; 张正国; 方玉堂

    2008-01-01

    The objective of this work was to investigate nucleate pool boiling heat transfer performance and mechanism of R134a and R142b on a twisted tube with machine processed porous surface (T-MPPS tube) as well as to determine its potential application to flooded refrigerant evaporators. In the experimental range, the boiling heat transfer coefficients of R134a on a T-MPPS tube were 1.8-2.0 times larger than those of R134a on a plain tube. In addition, the developed experimental correlations verified that the predictions of the heat transfer coefficients of boiling R134a and R142b on a T-MPPS tube at the experimental conditions were considerably accurate.

  10. High heat flux transport by microbubble emission boiling

    Science.gov (United States)

    Suzuki, Koichi

    2007-10-01

    In highly subcooled flow boiling, coalescing bubbles on the heating surface collapse to many microbubbles in the beginning of transition boiling and the heat flux increases higher than the ordinary critical heat flux. This phenomenon is called Microbubble Emission Boiling, MEB. It is generated in subcooled flow boiling and the maximum heat flux reaches about 1 kW/cm2(10 MW/m2) at liquid subcooling of 40 K and liquid velocity of 0.5 m/s for a small heating surface of 10 mm×10 mm which is placed at the bottom surface of horizontal rectangular channel. The high pressure in the channel is observed at collapse of the coalescing bubbles and it is closely related the size of coalescing bubbles. Periodic pressure waves are observed in MEB and the heat flux increases linearly in proportion to the pressure frequency. The frequency is considered the frequency of liquid-solid exchange on the heating surface. For the large sized heating surface of 50 mm length×20 mm width, the maximum heat flux obtained is 500 W/cm2 (5 MW/m2) at liquid subcooling of 40 K and liquid velocity of 0.5 m/s. This is considerably higher heat flux than the conventional cooling limit in power electronics. It is difficult to remove the high heat flux by MEB for a longer heating surface than 50 mm by single channel type. A model of advanced cooling device is introduced for power electronics by subcooled flow boiling with impinging jets. Themaxumum cooling heat flux is 500 W/cm2 (5 MW/m2). Microbubble emission boiling is useful for a high heat flux transport technology in future power electronics used in a fuel-cell power plant and a space facility.

  11. Heat Transfer Basics and Practice

    CERN Document Server

    Böckh, Peter

    2012-01-01

    The book provides an easy way to understand the fundamentals of heat transfer. The reader will acquire the ability to design and analyze heat exchangers. Without extensive derivation of the fundamentals, the latest correlations for heat transfer coefficients and their application are discussed. The following topics are presented - Steady state and transient heat conduction - Free and forced convection - Finned surfaces - Condensation and boiling - Radiation - Heat exchanger design - Problem-solving After introducing the basic terminology, the reader is made familiar with the different mechanisms of heat transfer. Their practical application is demonstrated in examples, which are available in the Internet as MathCad files for further use. Tables of material properties and formulas for their use in programs are included in the appendix. This book will serve as a valuable resource for both students and engineers in the industry. The author’s experience indicates that students, after 40 lectures and exercises ...

  12. Flow boiling critical heat flux enhancement by using magnetic nanofluids and external magnetic fields

    Energy Technology Data Exchange (ETDEWEB)

    Lee, T.; Jeong, Y.H. [Korea Advanced Inst. of Science and Tech., Daejeon (Korea, Republic of)

    2011-07-01

    By using the nanofluid as a working fluid, we can expect the enhancement in the flow boiling critical heat flux mainly due to the deposition of nanoparticles on the heat transfer surface. In this study, we suggest the magnetic nanofluid, or magnetite-water nanofluid, as a working fluid which is regarded as a controllable nanofluid, that is, nanoparticles or magnetite nanoparticles in a nanofluid can be controlled by an external magnetic field. Therefore, we can expect the advantages of magnetic nanofluid such as, i) control of nanofluid concentration to maintain nanoparticle suspension and to localize nanofluid concentration, and ii) removal of nanoparticle from nanofluid when we want. In this study, we focused on the investigation of flow boiling critical heat flux characteristics for the magnetic nanofluid. Series of experiments were performed under the low pressure and low flow conditions, and based on the experimental results; we can conclude that the use of magnetic nanofluid improves the flow boiling critical heat flux characteristics. This is mainly due to the deposition of magnetite nanoparticles on the heat transfer surface, which results in the improvement of wettability and re-wetting characteristics of heat transfer surface. Preliminary results of the magnetic field effects on the flow boiling critical heat flux would be presented also. (author)

  13. 微通道内非共沸混合制冷剂的流动沸腾特性%Investigation on flow boiling heat transfer of non-azeotropic refrigerant mixture in microchannel

    Institute of Scientific and Technical Information of China (English)

    吕凤勇; 马虎根; 何红萍; 齐鲁山

    2012-01-01

    采用了3种不同组分比例的R32/R134a工质在0.86 mm的微通道中进行了传热特性和阻力特性的实验研究,考察了非共沸工质不同组分比例对微通道换热特性的影响。实验结果表明:在组分质量分数比为35%/65%时,核态沸腾在小干度下换热效果最好;干度较大时,组分比例对换热的影响效果降低。在大质量流量下传热阻力效应的影响不再明显。在压降方面,组分比为15%/85%的相对压降最大,其它两种组分的压降较小。%The heat transfer characteristics in microchannel 0.86 mm in diameter for refrigerant mixture R32/R134a with three different mass proportions were studied and the effect of non-azeotropic working media with different mass proportions on heart transfer in the microchannel was investigated.The experiment result showed that when mass proportion was 35%/65%,flow boiling heat transfer was the best at low dryness fraction,while the effect of mass proportion on heat transfer was not obvious at high dryness fraction.Heat transfer resistance effect was not obvious at a high mass flux.Pressure drop was the largest when mass proportion was 15%/85%,and for the other two mass proportions,25%/75% and 35%/65%,pressure drop was relatively smaller.

  14. 羟基化多壁碳纳米管/R141b纳米流体核沸腾%Nucleate boiling heat transfer of hydroxylated carbon nano-tubes/R141b nanofluids on smooth plate

    Institute of Scientific and Technical Information of China (English)

    许世民; 郎中敏; 王亚雄; 赫文秀; 梁倩卿

    2015-01-01

    A refrigerant R141b-based nanofluid was made by hydroxylated carbon nano-tube particles in 0.01%, 0.03%, 0.05%, 0.07% and 0.10% mass fractions. An experimental study was carried out to investigate the nucleate boiling heat transfer characteristics of nanofluid on a smooth copper surface at pressure of 90.3 kPa. The surface roughness was made by sandpaper of grade 5000#. The result illustrates that the boiling heat transfer is enhanced by increasing nanoparticles. The improvement is related to the coefficient of thermal conductivity, deposition of nanoparticles and their disturbances to flow. The heat transfer coefficient increases with nanoparticle mass added except in later boiling period. The coefficient of thermal conductivity of 0.10% nanofluid is 1.18 times that of pure fluid R141b. The heat transfer coefficient is increased by 168% for 0.05% mass fraction at the heat flux of 87.4 kW·m−2. The boiling process of 0.03% mass fraction was recorded by the high-speed CCD.%向多壁碳纳米管引入羟基基团,改善了其在制冷剂R141b中的分散性和稳定性。同时研究了不同质量分数纳米流体热导率、表面颗粒沉积、接触角变化对核沸腾传热性能的影响。结果表明:羟基化碳纳米流体强化沸腾传热,强化率随质量分数的增加而增加,沸腾后期有所下降。在测试浓度范围内,质量分数为0.05%,热通量为87.4 kW·m−2时,强化率达到最大168%。流体的热导率随着质量分数的增加而增大,质量分数为0.10%时其热导率是纯R141b的1.18倍。分析认为:纳米流体热导率的增加、表面沉积颗粒及纳米颗粒扰动是强化传热的主要影响因素,接触角变化的影响可忽略不计。结论由质量分数为0.03%纳米流体沸腾过程高速成像得到验证。

  15. Boiling heat transfer characteristics of fatty acid methyl ester(FAME)in falling film evaporator%脂肪酸甲酯降膜蒸发器沸腾传热性能

    Institute of Scientific and Technical Information of China (English)

    徐委托; 马晓建; 马力; 陈俊英; 杨闪; 张芬芬

    2016-01-01

    利用传统的多管排列式蒸发器对高黏度、易结垢的混合物进行蒸发,容易造成布液器堵塞,且结垢后的传热管难以清理。因此根据物料特性,本文设计了一种新型的降膜蒸发器,采用大降液孔加倾斜环板进行布膜,利用内径较大的锥筒作为传热壁面,并以粗甲酯作为试验工质对蒸发器的降膜蒸发传热系数随蒸发器筒体半锥度角、液膜流动雷诺数以及输入热通量之间的关系进行了试验研究。结果表明:该型蒸发器对于上述工质具有较好的适用性,蒸发系统能够在保持较高的传热系数的条件下,连续运行而不发生堵塞;蒸发器筒体锥度角有效地强化了降膜蒸发传热过程,而较大的热通量及进料流量在一定程度上却不利于蒸发传热。最后建立了降膜蒸发传热系数随蒸发器筒体半锥角和流动准数之间的经验关联式。%Using conventional line-tube heat exchanger for evaporation of high viscosity and easy-to-scaling mixture can easily block liquid distributor and make the cleaning of foul tube impossible. Therefore,a new type of falling film evaporator was designed,which used large liquid orifice plus tilt ring plate for liquid distribution and took larger diameter of conical shell as heat transfer wall. The variation of boiling heat transfer coefficients with shell’s taper angle,Reynolds number and heat fluxes were determined by a pilot scale falling film evaporation system,using the FAME mixture as liquid model. Result showed that this type of evaporator worked well for FAME,the system could work smoothly with high heat transfer efficiency for a long time and without the occurrence of clogging. The evaporator shell’s taper angle can intensify heat transfer process. The increase of heat flux and feed flow had a negative influence on heat transfer coefficient. Experimental correlation for boiling heat transfer coefficients with consideration of

  16. Computational multi-fluid dynamics predictions of critical heat flux in boiling flow

    Energy Technology Data Exchange (ETDEWEB)

    Mimouni, S., E-mail: stephane.mimouni@edf.fr; Baudry, C.; Guingo, M.; Lavieville, J.; Merigoux, N.; Mechitoua, N.

    2016-04-01

    Highlights: • A new mechanistic model dedicated to DNB has been implemented in the Neptune-CFD code. • The model has been validated against 150 tests. • Neptune-CFD code is a CFD tool dedicated to boiling flows. - Abstract: Extensive efforts have been made in the last five decades to evaluate the boiling heat transfer coefficient and the critical heat flux in particular. Boiling crisis remains a major limiting phenomenon for the analysis of operation and safety of both nuclear reactors and conventional thermal power systems. As a consequence, models dedicated to boiling flows have being improved. For example, Reynolds Stress Transport Model, polydispersion and two-phase flow wall law have been recently implemented. In a previous work, we have evaluated computational fluid dynamics results against single-phase liquid water tests equipped with a mixing vane and against two-phase boiling cases. The objective of this paper is to propose a new mechanistic model in a computational multi-fluid dynamics tool leading to wall temperature excursion and onset of boiling crisis. Critical heat flux is calculated against 150 tests and the mean relative error between calculations and experimental values is equal to 8.3%. The model tested covers a large physics scope in terms of mass flux, pressure, quality and channel diameter. Water and R12 refrigerant fluid are considered. Furthermore, it was found that the sensitivity to the grid refinement was acceptable.

  17. Cryogenic heat transfer

    CERN Document Server

    Barron, Randall F

    2016-01-01

    Cryogenic Heat Transfer, Second Edition continues to address specific heat transfer problems that occur in the cryogenic temperature range where there are distinct differences from conventional heat transfer problems. This updated version examines the use of computer-aided design in cryogenic engineering and emphasizes commonly used computer programs to address modern cryogenic heat transfer problems. It introduces additional topics in cryogenic heat transfer that include latent heat expressions; lumped-capacity transient heat transfer; thermal stresses; Laplace transform solutions; oscillating flow heat transfer, and computer-aided heat exchanger design. It also includes new examples and homework problems throughout the book, and provides ample references for further study.

  18. An experimental investigation of critical heat flux performance of hypervapotron in subcooled boiling

    Science.gov (United States)

    Chen, Peipei

    The successful use of subcooled flow boiling for high heat flux components requires that the critical heat flux (CHF), i.e., a fast reduction in the boiling heat transfer, must be avoided. Among the many techniques available to enhance CHF, particular attention has been focused on the hypervapotron concept. In this study, the CHF characteristics of the hypervapotron were experimentally investigated using a simulant fluid, R134a, which has been found to be an effective modeling fluid to simulate CHF in water-cooled environments. An experimental and modeling study of the subcooled boiling heat transfer on plain surface and hypervapotron has been conduced. A test facility was designed and constructed to perform required boiling heat transfer experiments. A high speed visualization system was utilized to give details of bubble formation and departure and of nucleation site density. Surface measurements of various specimens were performed to investigate the relationship between nucleation sites and surface microstructure. Full characterization of the hypervapotron effect as a function of fluid thermal hydraulic conditions was accomplished. A non-dimensional CHF correlation for smooth rectangular channels and the hypervapotron channel was developed and compared with experimental data in this work. In addition, a hot-spot model was developed to give predictions of critical heat flux on both plain and hypervapotron surfaces. It was developed on observations of bubble formation, departure and coalescence, and on the confirmation of nucleation structure on the heating surface. Finally, a numerical code was successfully developed to give CHF predictions for hypervapotron configurations. The simulation indicates that the better performance of CHF in hypervapotron configurations is a result of high conductivity material with augmented heating surfaces in subcooled boiling environment. Different fin dimensions were also tested numerically to compare the experimental results, and

  19. Research on the Characters of Boiling Heat Transfer from High Temperature Sphere to Water%高温球体与水的沸腾传热特性研究

    Institute of Scientific and Technical Information of China (English)

    沈正祥; 李金柱; 吕中杰; 黄风雷

    2013-01-01

    With the purpose of investigating the characteristics of heat transfer between high temperature liquid and water,the film boiling process from hot sphere surface was analyzed by an improved boiling model and free surface tracking method.The results show that,when the temperature of sphere is constant,the film thickness increases from stagnation point of particle,the temperature contribution decreases with non-linear posture and the velocity contribution is parabolic in film.With the increase of initial temperature of sphere,both the film thickness and peak value of vapor velocity raise,while the overall heat transfer coefficient decreases.Meanwhile,the numerical technique captures the evolution of instability at interface and the process of bubble growing,which reveal the dynamic process of boiling clearly.%为研究高温流体与水的传热特性,采用理论分析与自由界面追踪数值技术对高温球体表面的沸腾传热过程进行研究,得到球体表面传热特性的变化规律.分析结果表明,当球体温度不变时,蒸气膜层厚度自前滞点往后逐渐增大,膜层内温度呈非线性分布降低,速率呈抛物型分布.当球体温度提高时蒸气膜层厚度变大,相应的蒸气速率峰值也变大,球面传热系数却变小.数值仿真结果显示了气-液界面上不稳定性波动发展和气泡成长过程,较为真实地反映出沸腾传热的动态过程.

  20. Transition process leading to microbubble emission boiling on horizontal circular heated surface in subcooled pool

    Science.gov (United States)

    Ueno, Ichiro; Ando, Jun; Horiuchi, Kazuna; Saiki, Takahito; Kaneko, Toshihiro

    2016-11-01

    Microbubble emission boiling (MEB) produces a higher heat flux than critical heat flux (CHF) and therefore has been investigated in terms of its heat transfer characteristics as well as the conditions under which MEB occurs. Its physical mechanism, however, is not yet clearly understood. We carried out a series of experiments to examine boiling on horizontal circular heated surfaces of 5 mm and of 10 mm in diameter, in a subcooled pool, paying close attention to the transition process to MEB. High-speed observation results show that, in the MEB regime, the growth, condensation, and collapse of the vapor bubbles occur within a very short time. In addition, a number of fine bubbles are emitted from the collapse of the vapor bubbles. By tracking these tiny bubbles, we clearly visualize that the collapse of the vapor bubbles drives the liquid near the bubbles towards the heated surface, such that the convection field around the vapor bubbles under MEB significantly differs from that under nucleate boiling. Moreover, the axial temperature gradient in a heated block (quasi-heat flux) indicates a clear difference between nucleate boiling and MEB. A combination of quasi-heat flux and the measurement of the behavior of the vapor bubbles allows us to discuss the transition to MEB. This work was financially supported by the 45th Research Grant in Natural Sciences from The Mitsubishi Foundation (2014 - 2015), and by Research Grant for Boiler and Pressurized Vessels from The Japan Boiler Association (2016).

  1. Boiling phenomenon due to quasi-steadily and rapidly increasing heat inputs in LN 2 and LHe I

    Science.gov (United States)

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

    Dynamic boiling processes, including the transition from a single-phase non-boiling regime to film boiling caused by exponentially increasing heat inputs, Q 0e t/τ for a wide range of periods and pressures on horizontal wires in LN 2 and LHe I were investigated. The main problem is that there are no active cavities on the wire surfaces for initial boiling in the liquids. The heat transfer processes due to increasing heat inputs with increasing rates ranging from quasi-steady to rapidly increasing ones in LN 2 were classified into three types for the pressures. The dynamic boiling processes in LHe I due to rapidly increasing heat inputs at the pressures tested here correspond to Type 3 processes including semi-direct transitions in LN 2 at pressures higher than about 1 MPa. The lower limit temperatures of boiling initiation on the wire surfaces for initial boiling in liquids at pressures due to quasi-steadily increasing heat inputs are clearly lower than the homogeneous spontaneous nucleation temperatures corresponding to these pressures. Liquid superheat close to the solid surface in LHe I was evaluated from the value of the wire surface temperature, taking off the temperature drop due to Kapitza resistance. The initial boiling temperatures due to quasi-steady heat inputs at pressures in saturated LN 2 and LHe I agreed with the values derived from the theoretical model based on the heterogeneous spontaneous nucleation in flooded cavities on the solid surface.

  2. Review of the influence of nanoparticles on thermal conductivity, nucleate pool boiling and critical heat flux

    Science.gov (United States)

    Kshirsagar, Jagdeep M.; Shrivastava, Ramakant

    2015-03-01

    Nanofluids, the fluid suspensions of nonmaterials, have shown many interesting properties and the unique features offer unprecedented potential for many applications. Research on nanofluids has progressed rapidly since its enhanced thermal conductivity was first noted, about a decade ago, though much debate and inconsistency have been reported. Insufficient understanding of the formulation, mechanism of nanofluids further limits their applications [1-34]. Inconsistent data have been presented in the literature on the effect that nanofluids have on the boiling heat-transfer coefficient; however, almost all researchers [35-43] have noted an enhancement in the critical heat flux during nanofluid boiling. Some researchers have observed nanoparticle deposition at the heater surface, which they have related back to the critical heat flux augmentation. In the review, the future developments of these technologies are discussed. In order to be able to put the nanofluid heat transfer technologies into practice, fundamental of these studies are greatly needed to comprehend the physical mechanisms.

  3. Thermal performance of a prototype plate heat exchanger with minichannels under boiling conditions

    Science.gov (United States)

    Wajs, J.; Mikielewicz, D.; Fornalik-Wajs, E.

    2016-09-01

    To solve the problem and to meet the requirements of customers in the field of high heat fluxes transfer in compact units, a new design of plate heat exchanger with minichannels (minichannels PHE) was proposed. The aim was to construct a compact heat exchanger of high effectiveness for the purpose of household cogeneration ORC system. In this paper the experimental analysis of an assembled prototype of such compact heat exchanger was described. The attention was paid to its thermal performance and the heat transfer coefficients under the boiling conditions. Water and ethanol were chosen as working fluids. The maximal value of transferred heat flux was about 84 kW/m2, while of the overall heat transfer coefficient was about 4000 W/(m2K). Estimated values of heat transfer coefficient on the ethanol (boiling) side reached the level of 7500 W/(m2K). The results are promising in the light of future applications, for example in cogeneration ORC systems, however further systematic investigations are necessary.

  4. Nucleate Pool Boiling Heat Transfer Characteristics of Refrigerant/Oil Mixture with Diamond Nanoparticles%含油金刚石纳米制冷剂的核态池沸腾换热特性

    Institute of Scientific and Technical Information of China (English)

    庄大伟; 彭浩; 胡海涛; 丁国良; 朱禹

    2011-01-01

    研究了含油金刚石纳米制冷剂(即由制冷剂R113、润滑油VG68和金刚石纳米颗粒组成的纳米流体)的核态池沸腾换热特性,分析了金刚石纳米颗粒对含油制冷剂核态池沸腾换热的影响.实验中饱和压力为101.3 kPa;热流密度为10~80 kW/m2;纳米油(纳米颗粒和润滑油的混合物)的质量分数为0~5%;在纳米油中金刚石纳米颗粒的质量分数为0~15%.实验结果表明:金刚石纳米颗粒增强了含油制冷剂的池沸腾换热,在测试工况下换热系数最大可增加63.4%,并且增加幅度随纳米油中纳米颗粒质量分数的增加而增加,随纳米油质量分数的降低而增加.开发了含油纳米制冷剂池沸腾换热关联式,关联式预测值与94%的实验数据偏差在±20%以内.%Nucleate pool boiling heat transfer characteristics of refrigerant/oil mixture with diamond nanop-articles were investigated experimentally. The refrigerant is R113 and the oil is VG68. The experimental conditions include a saturation pressure of 101. 3 kPa, heat fluxes from 10 to 80 kW · m-2, nanoparticles concentrations in the nanoparticles/oil suspension from 0 to 15 %, and nanoparticles/oil suspension concentrations from 0 to 5 %. The experimental results indicate that the nucleate pool boiling heat transfer coefficient of R113/oil mixture with diamond nanoparticles is larger than that of R113/oil mixture by maximum of 63. 4% under the present experimental conditions, and the enhancement increases with the increase of nanoparticles concentration in the nanoparticles/oil suspension and decreases with the increase of nanoparticles/oil suspension concentration. A correlation for predicting the nucleate pool boiling heat transfer coefficient of refrigerant/oil mixture with nanoparticles was proposed. The predicted values of the new correlation can agree with 94% of the experimental data of R113/oil mixture with diamond nanoparticles in the present study within the

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

    Energy Technology Data Exchange (ETDEWEB)

    MARSHALL, THERON D.

    2001-02-01

    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.

  6. Introduction to heat transfer

    CERN Document Server

    SUNDÉN, B

    2012-01-01

    Presenting the basic mechanisms for transfer of heat, Introduction to Heat Transfer gives a deeper and more comprehensive view than existing titles on the subject. Derivation and presentation of analytical and empirical methods are provided for calculation of heat transfer rates and temperature fields as well as pressure drop. The book covers thermal conduction, forced and natural laminar and turbulent convective heat transfer, thermal radiation including participating media, condensation, evaporation and heat exchangers.

  7. 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). [PWR; BWR

    Energy Technology Data Exchange (ETDEWEB)

    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.

  8. Convective heat transfer

    CERN Document Server

    Kakac, Sadik; Pramuanjaroenkij, Anchasa

    2014-01-01

    Intended for readers who have taken a basic heat transfer course and have a basic knowledge of thermodynamics, heat transfer, fluid mechanics, and differential equations, Convective Heat Transfer, Third Edition provides an overview of phenomenological convective heat transfer. This book combines applications of engineering with the basic concepts of convection. It offers a clear and balanced presentation of essential topics using both traditional and numerical methods. The text addresses emerging science and technology matters, and highlights biomedical applications and energy technologies. What’s New in the Third Edition: Includes updated chapters and two new chapters on heat transfer in microchannels and heat transfer with nanofluids Expands problem sets and introduces new correlations and solved examples Provides more coverage of numerical/computer methods The third edition details the new research areas of heat transfer in microchannels and the enhancement of convective heat transfer with nanofluids....

  9. Fiscal 1999 research result report. Research on improvement of boiling heat transfer characteristics by photocatalyst wall; 1999 nendo hikari shokubai hekimen ni yoru futto netsu dentatsu tokusei kaizen ni kansuru kenkyu chosa hokokusho

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    2000-03-01

    Research was made on improvement of the wettability and boiling heat transfer characteristics of a photocatalyst wall. Measurement experiment of the wettability was made for anatase type titan oxide-coated Al, SUS and Pb plates, rutil type titan oxide-flame coated SUS plate, raw plate, and oxide-plasma coated titan plate. In the ground experiment, the contact angles of distilled water and oil on specimen surfaces were measured. In the microgravity experiment, falling droplet images were recorded by using the facility of Japan Microgravity Center (JAMIC). For obtaining the effect of radioactive emission, UV irradiation, {gamma} ray and neutron beam irradiation by nuclear reactor, and {gamma} ray irradiation by Co-60 were carried out. As the experiment result, the rutil type titan oxide-flame coated SUS plate, nonconductor-coated titan plate, and zircaloy plate showed large improvement of the wettability by {gamma} ray irradiation with Co-60. It was also confirmed that in particular, titan shows the large effect of radioactive emission, and the wettability deteriorates rapidly after {gamma} ray irradiation. (NEDO)

  10. 基于Fluent螺旋槽管沸腾换热的数值模拟%Numerically Simulate Based on FLUENT for the Heat Transfer of Boiling of Outside Spiral Tube

    Institute of Scientific and Technical Information of China (English)

    陈志静

    2011-01-01

    基于FLUENT软件对制冷剂R134a在水平螺旋槽管管外沸腾换热进行了三维数值模拟,得到了其饱和泡状沸腾过程中体积含汽率的分布规律和换热系数,并和光管进行了比较。结果表明螺旋槽管外侧能够很好地强化沸腾传热。此外,还通过改变边界条件分析了质量流量、热流密度的变化对螺旋管管外沸腾换热系数的影响。%Numerically simulate based on FLUENT software for boiling heat transfer of refrigerant R134a which flowed outside borizontal spiral tube is carried out in this article to obtain regularities of volumetric steam quality distribution during saturation proce

  11. Free convection film flows and heat transfer

    CERN Document Server

    Shang, Deyi

    2010-01-01

    Presents development of systematic studies for hydrodynamics and heat and mass transfer in laminar free convection, accelerating film boiling and condensation of Newtonian fluids, and accelerating film flow of non-Newtonian power-law fluids. This book provides a system of analysis models with a developed velocity component method.

  12. Effect of size sprinkled heat exchange surface on developing boiling

    Directory of Open Access Journals (Sweden)

    Petr Kracík

    2016-06-01

    Full Text Available This article presents research of sprinkled heat exchangers. This type of research has become rather topical in relation to sea water desalination. This process uses sprinkling of exchangers which rapidly separates vapour phase from a liquid phase. Applications help better utilize low-potential heat which is commonly wasted in utility systems. Low-potential heat may increase utilization of primary materials. Our ambition is to analyse and describe the whole sprinkled exchanger. Two heat exchangers were tested with a similar tube pitch: heat exchanger no. 1 had a four-tube bundle and heat exchanger no. 2 had eight-tube bundle. Efforts were made to maintain similar physical characteristics. They were tested at two flow rates (ca 0.07 and 0.11 kg s−1 m−1 and progress of boiling on the bundle was observed. Initial pressure was ca 10 kPa (abs at which no liquid was boiling at any part of the exchanger; the pressure was then lowered. Other input parameters were roughly similar for both flow rates. Temperature of heating water was ca 50°C at a constant flow rate of ca 7.2 L min−1. Results of our experiments provide optimum parameters for the given conditions for both tube bundles.

  13. CHF Phenomena by Photographic Study of Boiling Behavior due to Transient Heat Inputs

    OpenAIRE

    Jongdoc Park; Katsuya Fukuda; Qiusheng Liu

    2012-01-01

    The transient boiling heat transfer characteristics in a pool of water and highly wetting liquids such as ethanol and FC-72 due to an exponentially increasing heat input of various rates were investigated using the 1.0 mm diameter experimental heater shaped in a horizontal cylinder for wide ranges of pressure and subcooling. The trend of critical heat flux (CHF) values in relation to the periods was divided into three groups. The CHF belonging to the 1st group with a longer period occurs with...

  14. CaSO4溶液中表面处理对流动沸腾传热系数的影响%Effect of Surface Treatment on Flow Boiling Heat Transfer Coefficient in CaSO4 Containing Water

    Institute of Scientific and Technical Information of China (English)

    任晓光; 李铁凤; 赵起

    2006-01-01

    This paper reports the influence of heat transfer surface treatment on the formation of calcium sulphate deposit during flow boiling heat transfer. The surface of several test heaters was treated by surface modification techniques,such as dynamic mixing magnetron sputtering [DLC (diamond-like carbon), DLC-F (diamond-like carbon-fluorine) and AC (amorphous carbon)] and polishing to reduce surface energy. The results showed that heat transfer surface with low surface energy experienced significant reduction of formation of CaSO4 deposit. (1) Magnetron sputtering stainless steel heat transfer surface with DLC, DLC-F and plasma arc sputtering with AC did not change the surface roughness, but they reduced surface energy and improved heat transfer coefficient, so hindered CaSO4 deposit formation significantly. The DLC-F surface performed better than the DLC surface. (2) Surface energy played an important pole in improving heat transfer coefficient. The less the surface energy the more significant the heat transfer coefficient improved with other experimental conditions identical. (3) The polished surface improved the roughness of the heater, but owing to the high surface energy it was not better than the DLC-F surface for a long-term consideration on improving the heat transfer coefficient.

  15. Basic heat transfer

    CERN Document Server

    Bacon, D H

    2013-01-01

    Basic Heat Transfer aims to help readers use a computer to solve heat transfer problems and to promote greater understanding by changing data values and observing the effects, which are necessary in design and optimization calculations.The book is concerned with applications including insulation and heating in buildings and pipes, temperature distributions in solids for steady state and transient conditions, the determination of surface heat transfer coefficients for convection in various situations, radiation heat transfer in grey body problems, the use of finned surfaces, and simple heat exc

  16. 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.

  17. Thermal radiation heat transfer

    CERN Document Server

    Howell, John R; Siegel, Robert

    2016-01-01

    Further expanding on the changes made to the fifth edition, Thermal Radiation Heat Transfer, 6th Edition continues to highlight the relevance of thermal radiative transfer and focus on concepts that develop the radiative transfer equation (RTE). The book explains the fundamentals of radiative transfer, introduces the energy and radiative transfer equations, covers a variety of approaches used to gauge radiative heat exchange between different surfaces and structures, and provides solution techniques for solving the RTE.

  18. Evaporative heat transfer in beds of sensible heat pellets

    Energy Technology Data Exchange (ETDEWEB)

    Arimilli, R.V.; Moy, C.A. [Univ. of Tennessee, Knoxville, TN (United States)

    1989-03-01

    An experimental study of boiling/evaporative heat transfer from heated spheres in vertical packed beds with downward liquid-vapor flow of Refrigerant-113 was conducted. Surface superheats of 1 to 50{degrees}C, mass flow rates of 1.7 to 5.6 Kg/min, sphere diameters of 1.59 and 2.54 cm, quality (i.e., mass fraction of vapor) of the inlet flow of 0.02 to 1.0, and two surface conditions were considered. Instrumented smooth and rough aluminum spheres were used to measure the heat transfer coefficients under steady state conditions. Heat transfer coefficients were independently determined for each sphere at three values three values of surface superheat. The quantitative results of this extensive experimental study are successfully correlated. The correlation equation for the boiling heat transfer coefficients is presented in terms of a homogeneous model. The correlation may be used in the development of numerical models to simulate the transient thermal performance of packed bed thermal energy storage unit while operating as an evaporator. The boiling of the liquid-vapor flow around the spheres in the packed bed was visually observed with a fiber-optic baroscope and recorded on a videotape. The visualization results showed qualitatively the presence of four distinct flow regimes. One of these occurs under saturated inlet conditions and are referred to as the Low-quality, Medium-quality, and High-quality Regimes. The regimes are discussed in detail in this paper.

  19. Visualization of the boiling phenomena and counter-current flow limit of annular heat pipe

    Energy Technology Data Exchange (ETDEWEB)

    Kim, In Guk; Kim, Kyung Mo; Jeong, Yeong Shin; Bang, In Cheol [UNIST, Ulsan (Korea, Republic of)

    2015-10-15

    The thermal resistance of conventional heat pipes increases over the capillary limit because of the insufficient supplement of the working fluid. Due to the shortage of the liquid supplement, thermosyphon is widely used for vertically oriented heat transport and high heat load conditions. Thermosyphons are two-phase heat transfer devices that have the highly efficient heat transport from evaporation to condensation section that makes an upward driving force for vapor. In the condenser section, the vapor condenses and releases the latent heat. Due to the gravitation force acting on the liquid in the tube, working fluid back to the evaporator section, normally this process operate at the vertical and inclination position. The use of two-phase closed thermosyphon (TPCT) for the cooling devices has the limitation due to the phase change of the working fluid assisted by gravity force. Due to the complex phenomenon of two-phase flow, it is required to understand what happened in TPCT. The visualization of the thermosyphon and heat pipe is investigated for the decrease of thermal resistance and enhancement of operation limit. Weibel et al. investigated capillary-fed boiling of water with porous sintered powder wick structure using high speed camera. At the high heat flux condition, dry-out phenomenon and a thin liquid film are observed at the porous wick structure. Wong and Kao investigated the evaporation and boiling process of mesh wicked heat pipe using optical camera. At the high heat flux condition, the water filing became thin and partial dry-out was observed in the evaporator section. Our group suggested the concept of a hybrid heat pipe with control rod as Passive IN-core Cooling System (PINCs) for decay heat removal for advanced nuclear power plant. The hybrid heat pipe is the combination of the heat pipe and control rod. It is necessary for PINCs to contain a neutron absorber (B{sub 4}C) to have the ability of reactivity control. It has annular vapor space and

  20. 蒸汽发生器传热管一、二次侧耦合换热及管外过冷沸腾数值研究%Numerical Investigation of Coupled Heat Transfer Between Primary and Secondary Side of SG Tube and Subcooled Flow Boiling on Secondary Side

    Institute of Scientific and Technical Information of China (English)

    王成龙; 丛腾龙; 王泽勇; 田文喜; 秋穗正; 苏光辉; 安洪振

    2014-01-01

    Two fluid model combing with inter-phase heat and mass transfer model , inter-phase momentum transfer model ,and RPI wall boiling model was applied to solve the local flow and heat transfer of subcooled flow boiling in the secondary side of SG tubes by using commercial CFD code ANSYS CFX 12.0 . The numerical calculation results were validated by experimental data and calculation results .The results show that adopting RPI wall boiling model can predict the onset of subcooled flow boiling accurately ,meanw hile the existence of orifice plate has a great effect on the flow and heat transfer characteristics of the secondary side .%采用两流体欧拉数学模型,结合气相和液相之间的界面传热、传质和动量交换封闭模型以及 RPI壁面沸腾模型,利用ANSYS CFX 12.0对蒸汽发生器局部传热管束二次侧的过冷沸腾进行数值研究。数值研究结果与单管内过冷沸腾实验数据对比验证符合良好。结果表明,采用壁面沸腾模型能准确预测沸腾起始点的位置,同时梅花孔板的存在对二次侧流动换热特性影响显著。

  1. Heat Transfer Enhancement by Fluidized Solid Particles in Gas Carrying Evaporation

    Institute of Scientific and Technical Information of China (English)

    于志家; 孙成新; 孙相彧; 刘展红

    2001-01-01

    Heat transfer characteristics are studied for gas carrying evaporation with fluidized solid particles in a vertical rectangular conduit. Experimental results show that heat transfer of gas carrying evaporation is enhanced and the superheat of liquid in contact with heating surface lowers remarkably by introducing solid particles. Nucleate boiling on the heating surface is suppressed to a considerable degree. The mechanism of heat transfer enhancement by fluidized solid particles is analyzed with the consideration of collisions of solid particles with the boiling vapor bubbles.

  2. Interface oscillation of subcooled flow boiling in locally heated microchannels

    Science.gov (United States)

    Liu, J. T.; Peng, X. F.

    2009-02-01

    An investigation was conducted to understand flow boiling of subcooled de-ionized water in locally heated parallel microchannels. High-speed visualization technology was employed to visually observe the transient phase change process in an individual microchannel. Signal analysis method was employed in studying the interface movement and phase change process. The phase change at locally heated condition was different from those at entirely heated condition where elongated bubble(s) stayed quasi-stable for a long time without venting out. Diversified and intensive interface oscillation was observed occurring on both of the upstream and downstream bubble caps. Evaporation and condensation modes were characterized with distinguished oscillation frequencies. The film-driven oscillations of both evaporating and condensing interfaces generally operated at higher frequencies than the oscillations driven by nucleation or dropwise condensation.

  3. Development of a high-performance boiling heat exchanger by improved liquid supply to narrow channels.

    Science.gov (United States)

    Ohta, Haruhiko; Ohno, Toshiyuki; Hioki, Fumiaki; Shinmoto, Yasuhisa

    2004-11-01

    A two-phase flow loop is a promising method for application to thermal management systems for large-scale space platforms handling large amounts of energy. Boiling heat transfer reduces the size and weight of cold plates. The transportation of latent heat reduces the mass flow rate of working fluid and pump power. To develop compact heat exchangers for the removal of waste heat from electronic devices with high heat generation density, experiments on a method to increase the critical heat flux for a narrow heated channel between parallel heated and unheated plates were conducted. Fine grooves are machined on the heating surface in a transverse direction to the flow and liquid is supplied underneath flattened bubbles by the capillary pressure difference from auxiliary liquid channels separated by porous metal plates from the main heated channel. The critical heat flux values for the present heated channel structure are more than twice those for a flat surface at gap sizes 2 mm and 0.7 mm. The validity of the present structure with auxiliary liquid channels is confirmed by experiments in which the liquid supply to the grooves is interrupted. The increment in the critical heat flux compared to those for a flat surface takes a maximum value at a certain flow rate of liquid supply to the heated channel. The increment is expected to become larger when the length of the heated channel is increased and/or the gravity level is reduced.

  4. Microgravity experiments on boiling and applications: research activity of advanced high heat flux cooling technology for electronic devices in Japan.

    Science.gov (United States)

    Suzuki, Koichi; Kawamura, Hiroshi

    2004-11-01

    Research and development on advanced high heat flux cooling technology for electronic devices has been carried out as the Project of Fundamental Technology Development for Energy Conservation, promoted by the New Energy and Industrial Technology Development Organization of Japan (NEDO). Based on the microgravity experiments on boiling heat transfer, the following useful results have obtained for the cooling of electronic devices. In subcooled flow boiling in a small channel, heat flux increases considerably more than the ordinary critical heat flux with microbubble emission in transition boiling, and dry out of the heating surface is disturbed. Successful enhancement of heat transfer is achieved by a capillary effect from grooved surface dual subchannels on the liquid supply. The critical heat flux increases 30-40 percent more than for ordinary subchannels. A self-wetting mechanism has been proposed, following investigation of bubble behavior in pool boiling of binary mixtures under microgravity. Ideas and a new concept have been proposed for the design of future cooling system in power electronics.

  5. Critical heat flux and dynamics of boiling in nanofluids at stepwise heat release

    Science.gov (United States)

    Moiseev, M. I.; Kuznetsov, D. V.

    2016-10-01

    In this paper results of an experimental study on critical heat flux and dynamics of boiling crisis onset in nanofluids at stepwise heat generation are presented. Freon R21 with three types of nanoparticles - SiO2, Cu and Al2O3 was used as test fluid. Critical heat fluxes and temperatures of boiling initiation were obtained. It was shown that the addition of nanoparticles increased CHF at stepwise heat generation by up to 21%. Under conditions of the experiment transition to film boiling occurred via evaporation fronts. Data on propagation velocity and structure of evaporation fronts were obtained; the spectral analysis of fluctuations of the evaporation front interface was carried out. The characteristic frequencies and amplitudes of interface fluctuations were determined depending on the velocity of evaporation front propagation. It was shown that the addition of nano-sized particles significantly affects development of interface instability and increases the front velocity.

  6. High flux film and transition boiling

    Energy Technology Data Exchange (ETDEWEB)

    Witte, L.C.

    1990-01-01

    This report is a bench-scale experiment on transition boiling. The author gives a detailed description on experimental apparatus and conditions. The visual observed boiling phenomena; nucleate boiling and film boiling, and the effect of heat transfer are also elucidated. 10 refs., 11 figs., 1 tab.

  7. Heat transport in boiling turbulent Rayleigh-B\\'{e}nard convection

    CERN Document Server

    Lakkaraju, Rajaram; Oresta, Paolo; Verzicco, Roberto; Lohse, Detlef; Prosperetti, Andrea

    2014-01-01

    Boiling is an extremely effective way to promote heat transfer from a hot surface to a liquid due to several mechanisms many of which are not understood in quantitative detail. An important component of the overall process is that the buoyancy of the bubbles compounds with that of the liquid to give rise to a much enhanced natural convection. In this paper we focus specifically on this enhancement and present a numerical study of the resulting two-phase Rayleigh-B\\'enard convection process. We make no attempt to model other aspects of the boiling process such as bubble nucleation and detachment. We consider a cylindrical cell with a diameter equal to its height. The cell base and top are held at temperatures above and below the boiling point of the liquid, respectively. By keeping the temperature difference constant and changing the liquid pressure we study the effect of the liquid superheat in a Rayleigh number range that, in the absence of boiling, would be between $2\\times10^6$ and $5\\times10^9$. We find a...

  8. Convection heat transfer

    CERN Document Server

    Bejan, Adrian

    2013-01-01

    Written by an internationally recognized authority on heat transfer and thermodynamics, this second edition of Convection Heat Transfer contains new and updated problems and examples reflecting real-world research and applications, including heat exchanger design. Teaching not only structure but also technique, the book begins with the simplest problem solving method (scale analysis), and moves on to progressively more advanced and exact methods (integral method, self similarity, asymptotic behavior). A solutions manual is available for all problems and exercises.

  9. Radiative heat transfer

    CERN Document Server

    Modest, Michael F

    2013-01-01

    The third edition of Radiative Heat Transfer describes the basic physics of radiation heat transfer. The book provides models, methodologies, and calculations essential in solving research problems in a variety of industries, including solar and nuclear energy, nanotechnology, biomedical, and environmental. Every chapter of Radiative Heat Transfer offers uncluttered nomenclature, numerous worked examples, and a large number of problems-many based on real world situations-making it ideal for classroom use as well as for self-study. The book's 24 chapters cover the four major areas in the field: surface properties; surface transport; properties of participating media; and transfer through participating media. Within each chapter, all analytical methods are developed in substantial detail, and a number of examples show how the developed relations may be applied to practical problems. It is an extensive solution manual for adopting instructors. Features: most complete text in the field of radiative heat transfer;...

  10. Microwave super-heated boiling of organic liquids: Origin, effect and application

    NARCIS (Netherlands)

    Chemat, F.; Esveld, E.

    2001-01-01

    This paper reports the state of the art of the microwave super-heated boiling phenomenon. When a liquid is heated by microwaves, the temperature increases rapidly to reach a steady temperature while refluxing. It happens that this steady state temperature can be up to 40 K higher than the boiling po

  11. Effect of evaporation temperature on boiling heat transfer in horizontal ribbed and embossing finned tube pool%蒸发温度对水平正反齿压花齿型肋管池沸腾换热的影响

    Institute of Scientific and Technical Information of China (English)

    张吉礼; 陈敬东; 马志先; 王永辉

    2016-01-01

    随着节能减排的大力推广,管外沸腾强化传热技术得到了广泛的研究和发展。设计建立了水平双侧强化管管外沸腾试验系统,以R134a为循环工质试验研究了不同热通量工况下,蒸发温度对正反齿压花齿型三维肋管池沸腾换热特性影响,并结合试验结果分析探讨了其理论描述方法。结果表明:蒸发传热系数随蒸发温度变化趋势线的斜率随热通量呈现非线性变化;在同一蒸发温度下,管表面传热系数均随热通量单调递增,但增长率随热通量增加而逐步降低;回归分析获得不同热通量下蒸发温度对正反齿压花齿型蒸发管表面传热系数影响的统一表达式;等热通量工况强化传热因子在热通量超过10 kW·m−2后升至2以上,在热通量接近20 kW·m−2时达到极大值2.588,但在热通量接近5 kW·m−2时接近1;蒸发温度及其与热通量合同对正反齿压花齿型蒸发管表面传热系数的作用机理与理论描述方法有待进一步深入研究。%Under a promotion of energy conservation and emission reduction, efforts on research and development of the technologies related to boiling heat transfer enhancement of outer tube have been conducted extensively. In this article, a testing system for boiling heat transfer outside the horizontal double-side enhanced tubes was established. Using R134a as a cyclic working medium, the effect of evaporation temperature on the characteristics of boiling heat transfer in three-dimensional ribbed and embossing finned tube under conditions of varied heat flux was investigated, on basis of which theoretical descriptive method was discussed. It showed that , the curve slope of evaporation heat transfer coefficient as a function of evaporation temperature is non-linearly related to the heat flux. At the same evaporation temperature, it shows a monotonic increase in the heat transfer coefficient on tube surface with the heat flux

  12. Condensation heat transfer

    Science.gov (United States)

    Rose, J. W.

    The paper gives a brief description of some of the better understood aspects of condensation heat transfer and includes discussion of the liquid-vapour interface, natural and forced convection laminar film condensation and dropwise condensation.

  13. Digitized Heat Transfer

    Science.gov (United States)

    Mohseni, Kamran; Young, Patrick

    2007-11-01

    This presentation presents theoretical and numerical results describing digitized heat transfer (DHT), an active thermal management technique for high-power electronics and integrated micro systems. In digitized heat transfer discrete droplets are employed. The internal flow inside a discrete droplet is dominated by internal circulation imposed by the boundaries. This internal circulation imposes a new timescale for recirculating cold liquid from the middle of the droplet to the boundary. This internal circulation produces periodic oscillation in the overall convective heat transfer rate. Numerical simulations are presented for heat transfer in the droplet for both constant temperature and flux boundary conditions. The effectiveness of DHT for managing both localized temperature spikes and steady state cooling is demonstrated, identifying key parameters for optimization of the DHT method.

  14. An assessment of in-tube flow boiling correlations for ammonia-water mixtures and their influence on heat exchanger size

    DEFF Research Database (Denmark)

    Kærn, Martin Ryhl; Modi, Anish; Jensen, Jonas Kjær;

    2016-01-01

    on the required heat exchanger size (surface area)is investigated during numerical design. For this purpose, two case studies related to the use of the Kalina cycle are considered: a flue gas based heat recovery boiler for acombined cycle power plant and a hot oil based boiler for a solar thermal power plant......Heat transfer correlations for pool and flow boiling are indispensable for boiler design. The correlations for predicting in-tube flow boiling heat transfer ofammonia-water mixtures are not well established in the open literature and there is a lack of experimental measurements for the full range...... of composition, vapor qualities, fluid conditions, etc. This paper presents a comparison of several flow boiling heat transfer prediction methods (correlations) for ammonia-water mixtures. Firstly, these methods are reviewed and compared at various fluid conditions. The methods include: (1) the ammonia...

  15. Boiling incipience and convective boiling of neon and nitrogen

    Science.gov (United States)

    Papell, S. S.; Hendricks, R. C.

    1977-01-01

    Forced convection and subcooled boiling heat transfer data for liquid nitrogen and liquid neon were obtained in support of a design study for a 30 tesla cryomagnet cooled by forced convection of liquid neon. This design precludes nucleate boiling in the flow channels as they are too small to handle vapor flow. Consequently, it was necessary to determine boiling incipience under the operating conditions of the magnet system. The cryogen data obtained over a range of system pressures, fluid flow rates, and applied heat fluxes were used to develop correlations for predicting boiling incipience and convective boiling heat transfer coefficients in uniformly heated flow channels. The accuracy of the correlating equations was then evaluated. A technique was also developed to calculate the position of boiling incipience in a uniformly heated flow channel. Comparisons made with the experimental data showed a prediction accuracy of plus or minus 15 percent

  16. Analysis of Continuous Heat Exchangers for Cryogenic Boil-Off Reduction

    Science.gov (United States)

    Feller, J. R.; Kashani, A.; Helvensteign, B. P. M.; Salerno, L. J.; Kittel, P.; Plachta, D.; Christie, R.; Carlberg, E.

    2008-03-01

    Cryogenic boil-off reduction systems (CBRS) employing continuous heat exchangers in pressurized helium distributed cooling networks for active thermal control of large surfaces such as propellant tank walls and light-weight radiation shields have been studied for some time. Usually, very simple and intuitive relations are used to derive such quantities as the pressure drop across the network and the required flow rate for a given heat load. Here, detailed thermal-fluid and heat transfer relations for such systems are formulated and then studied term by term in order to determine the conditions under which various approximations to them may reasonably be made. It is found that in most applications of interest, use of the simplified relations is justifiable.

  17. A heat transfer textbook

    CERN Document Server

    Lienhard, John H

    2011-01-01

    This introduction to heat transfer offers advanced undergraduate and graduate engineering students a solid foundation in the subjects of conduction, convection, radiation, and phase-change, in addition to the related topic of mass transfer. A staple of engineering courses around the world for more than three decades, it has been revised and updated regularly by the authors, a pair of recognized experts in the field. The text addresses the implications, limitations, and meanings of many aspects of heat transfer, connecting the subject to its real-world applications and developing students' ins

  18. Elementary heat transfer analysis

    CERN Document Server

    Whitaker, Stephen; Hartnett, James P

    1976-01-01

    Elementary Heat Transfer Analysis provides information pertinent to the fundamental aspects of the nature of transient heat conduction. This book presents a thorough understanding of the thermal energy equation and its application to boundary layer flows and confined and unconfined turbulent flows. Organized into nine chapters, this book begins with an overview of the use of heat transfer coefficients in formulating the flux condition at phase interface. This text then explains the specification as well as application of flux boundary conditions. Other chapters consider a derivation of the tra

  19. Heat and mass transfer

    CERN Document Server

    Karwa, Rajendra

    2017-01-01

    This textbook presents the classical treatment of the problems of heat transfer in an exhaustive manner with due emphasis on understanding of the physics of the problems. This emphasis is especially visible in the chapters on convective heat transfer. Emphasis is laid on the solution of steady and unsteady two-dimensional heat conduction problems. Another special feature of the book is a chapter on introduction to design of heat exchangers and their illustrative design problems. A simple and understandable treatment of gaseous radiation has been presented. A special chapter on flat plate solar air heater has been incorporated that covers thermo-hydraulic modeling and simulation. The chapter on mass transfer has been written looking specifically at the needs of the students of mechanical engineering. The book includes a large number and variety of solved problems with supporting line diagrams. The author has avoided duplicating similar problems, while incorporating more application-based examples. All the end-...

  20. Enhancement of Nucleate Boiling Heat Flux on Macro/Micro-Structured Surfaces Cooled by Multiple Impinging Jets

    Science.gov (United States)

    Kugler, Scott Lee

    1997-01-01

    An experimental investigation of nucleate boiling heat transfer from modified surfaces cooled by multiple in-line impinging circular jets is reported and found to agree with single jet results. A copper block is heated from the back by two electrical arcs, and cooled on the opposite side by three identical liquid jets of distilled water at subcoolings of 25 C 50 C and 77 C and Freon 113 at 24 C subcooling. Liquid flow rates are held constant at 5, 10, and 15 GPH for each of the three jets with jet velocities ranging from 1.4 m/s to 1 1.2 m/s and jet diameters from 0.95 mm to 2.2 mm. To increase the maximum heat flux (CHF) and heat removal rate, the boiling surface was modified by both macro and micro enhancements. Macro modification consists of machined radial grooves in the boiling surface arranged in an optimally designed pattern to allow better liquid distribution along the surface. These grooves also reduce splashing of liquid droplets, and provide 'channels' to sweep away bubbles. Micro modification was achieved by flame spraying metal powder on the boiling surface, creating a porous, sintered surface. With the addition of both micro and macro structured enhancements, maximum heat flux and nucleate boiling can be enhanced by more than 200%. Examination of each surface modification separately and together indicates that at lower superheats, the micro structure provides the enhanced heat transfer by providing more nucleation sites, while for higher superheats the macro structure allows better liquid distribution and bubble removal. A correlation is presented to account for liquid subcoolings and surface enhancements, in addition to the geometrical and fluid properties previously reported in the literature.

  1. Heat Transfer Mechanism of a Vertical Wall Inside a Two-Phase Closed Thermosiphon Evaporator and Its Estimation

    Science.gov (United States)

    O-Uchi, Masaki; Hirose, Koichi; Saito, Futami

    The inside heat transfer coefficient, overall heat transfer coefficient, and heat flow rate at the heating section of the thermosiphon were determined for each heating method. In order to observe the heat transfer mechanism in the evaporator, a thermosiphon unit made of glass was assembled and conducted separately. The results of these experiments with these two units are summarized as follows. (1) Nucleate boiling due to the internal heat transfer mechanism improves the heat transfer characteristics of the thermosiphon unit. Under the specific heating conditions with dropwise condensation, there are two types of heat transfer mechanism occur in the evaporator accompanying nucleate boiling, i. e. latent heat transfer and sensible heat transfer. (2) In the case of latent heat transfer, the inside heat transfer coefficient has an upper limit which can be used as a criterion to determine the type of internal heat transfer mechanism.

  2. Heat transfer fluids containing nanoparticles

    Science.gov (United States)

    Singh, Dileep; Routbort, Jules; Routbort, A.J.; Yu, Wenhua; Timofeeva, Elena; Smith, David S.; France, David M.

    2016-05-17

    A nanofluid of a base heat transfer fluid and a plurality of ceramic nanoparticles suspended throughout the base heat transfer fluid applicable to commercial and industrial heat transfer applications. The nanofluid is stable, non-reactive and exhibits enhanced heat transfer properties relative to the base heat transfer fluid, with only minimal increases in pumping power required relative to the base heat transfer fluid. In a particular embodiment, the plurality of ceramic nanoparticles comprise silicon carbide and the base heat transfer fluid comprises water and water and ethylene glycol mixtures.

  3. Heat and mass transfer

    CERN Document Server

    Baehr, Hans Dieter

    2011-01-01

    This comprehensive textbook provides a solid foundation of knowledge on the principles of heat and mass transfer and shows how to solve problems by applying modern methods. The basic theory is developed systematically, exploring in detail the solution methods to all important problems.   The thoroughly revised 3rd edition includes an introduction to the numerical solution of Finite Elements. A new section on heat and mass transfer in porous media has also been added.   The book will be useful not only to upper-level and graduate students, but also to practicing scientists and engineers, offering a firm understanding of the principles of heat and mass transfer, and showing how to solve problems by applying modern methods. Many completed examples and numerous exercises with solutions facilitate learning and understanding, and an appendix includes data on key properties of important substances.

  4. Thermal radiation heat transfer

    CERN Document Server

    Howell, John R; Mengüç, M Pinar

    2011-01-01

    Providing a comprehensive overview of the radiative behavior and properties of materials, the fifth edition of this classic textbook describes the physics of radiative heat transfer, development of relevant analysis methods, and associated mathematical and numerical techniques. Retaining the salient features and fundamental coverage that have made it popular, Thermal Radiation Heat Transfer, Fifth Edition has been carefully streamlined to omit superfluous material, yet enhanced to update information with extensive references. Includes four new chapters on Inverse Methods, Electromagnetic Theory, Scattering and Absorption by Particles, and Near-Field Radiative Transfer Keeping pace with significant developments, this book begins by addressing the radiative properties of blackbody and opaque materials, and how they are predicted using electromagnetic theory and obtained through measurements. It discusses radiative exchange in enclosures without any radiating medium between the surfaces-and where heat conduction...

  5. Heat transfer in vapour-liquid flow of carbon dioxide

    Energy Technology Data Exchange (ETDEWEB)

    Yagov, V.V. [Moscow Power Engineering Institute (Technical University), Moscow (Russian Federation)], e-mail: YagovVV@mpei.ru

    2009-07-01

    During the last decade a number of studies of boiling heat transfer in carbon dioxide notably increase. As a field of CO{sub 2} practical using corresponds to high reduced pressures, and a majority of available experimental data on CO{sub 2} flow boiling even in submillimetric channels relate to turbulent liquid flow regimes, a possibility arises to develop sufficiently general method for HTC predicting. Under the above conditions nucleate boiling occurs up to rather high flow quality, even in annular flow regime due to extremely small size of an equilibrium vapour bubble. This conclusion is in agreement with the available experimental data. The predicting equation for nucleate boiling heat transfer developed by the present author in 1988 is valid for any nonmetallic liquid. A contribution of forced convection in heat transfer is calculated according to the Petukhov et al. equation with correction factor, which accounted for an effect of velocity increase due to evaporation. This effect can be essential at relatively small heat fluxes and rather high mass flow rates. The Reynolds analogy and homogeneous model are used in order to account for the convective heat transfer augmentation in two-phase flow. Due to low ratio of liquid and vapour densities at high reduced pressures the homogeneous approximation of two-phase flow seems to be warranted. A total heat transfer coefficient is calculated as an interpolated value of boiling and convective HTCs. The experimental data on CO{sub 2} flow boiling related to regimes before heated wall dryout incipience are in rather good agreement with the calculations. (author)

  6. An introduction to heat transfer principles and calculations

    CERN Document Server

    Ede, A J; Ower, E

    1967-01-01

    An Introduction to Heat Transfer Principles and Calculations is an introductory text to the principles and calculations of heat transfer. The theory underlying heat transfer is described, and the principal results and formulae are presented. Available techniques for obtaining rapid, approximate solutions to complicated problems are also considered. This book is comprised of 12 chapters and begins with a brief account of some of the concepts, methods, nomenclature, and other relevant information about heat transfer. The reader is then introduced to radiation, conduction, convection, and boiling

  7. Solar Energy: Heat Transfer.

    Science.gov (United States)

    Knapp, Henry H., III

    This module on heat transfer is one of six in a series intended for use as supplements to currently available materials on solar energy and energy conservation. Together with the recommended texts and references (sources are identified), these modules provide an effective introduction to energy conservation and solar energy technologies. The…

  8. 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)

  9. Experimental investigation of saturated and supercooled boiling on miniature heating surfaces under microgravitation; Experimentelle Untersuchung des gesaettigten und unterkuehlten Siedens an Miniaturheizflaechen unter Mikrogravitation

    Energy Technology Data Exchange (ETDEWEB)

    Steinbichler, M.

    2000-07-01

    In many empirical and theoretical models of nucleate boiling the gravity level and the gravity induced natural convection play an important role on the heat transfer process. Usually a decrease in the heat transfer coefficients of nucleate boiling with decreasing system acceleration is predicted. The results of nucleate boiling measurements under microgravity during two space shuttle flights (IML-2, LMS) demonstrate, that no decrease of the heat transfer coefficients during saturated and subcooled nucleate boiling takes place. As a main result it can be stated, that the acceleration level itself cannot be regarded as a primary influence parameter on the heat transfer process during nucleate boiling. (orig.) [German] Bei der Formulierung von den Siedevorgang beschreibenden Modellvorstellungen, spielt in gaengigen theoretischen Ansaetzen die Systemgravitation und die damit verbundene Auftriebskonvention eine entscheidende Rolle. Bei einer Reduktion der Systemgravitation wird eine Abnahme der Waermeuebergangszahlen prognostiziert. Die Messungen, die im Rahmen von zwei Space Shuttle Missionen (IML-2, LMS) durchgefuehrt wurden, zeigen, dass weder beim gesaettigten, noch beim unterkuehlten Sieden diese prognostizierte Abnahme eintritt. Es ergibt sich, dass die Systemgravitation nicht als primaerer Einflussparameter fuer den Waermeuebergang beim Sieden aufgefasst werden kann. (orig.)

  10. 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

  11. Geothermal Heat Transfer

    Energy Technology Data Exchange (ETDEWEB)

    Basmajian, V.V.

    1986-01-28

    This patent describes a heat transfer apparatus which consists of: heat exchanging means for orientation in the earth below ground substantially vertically, having a hollow conduit of length from top to bottom much greater than the span across the hollow conduit orthogonal to its length with a top, bottom and an intermediate portion contiguous and communicating with the top and bottom portions for allowing thermally conductive fluid to flow freely between the top, intermediate and bottom portions for immersion in thermally conductive fluid in the region around the heat exchanging means for increasing the heat flow between the latter and earth when inserted into a substantially vertical borehole in the earth with the top portion above the bottom portion. The heat exchanger consists of heat exchanging conduit means in the intermediate portion for carrying refrigerant. The heat exchanging conduit consisting of tubes of thermally conductive material for carrying the refrigerant and extending along the length of the hollow conduit for a tube length that is less than the length of the hollow conduit. The hollow conduit is formed with port means between the top and the plurality of tubes for allowing the thermally conductive fluid to pass in a flow path embracing the tubes, the bottom portion, an outer channel around the hollow conduit and the port means.

  12. Elements of heat transfer

    CERN Document Server

    Rathakrishnan, Ethirajan

    2012-01-01

    1 Basic Concepts and Definitions1.1 Introduction1.1.1 Driving Potential1.2 Dimensions and Units1.2.1 Dimensional Homogeneity1.3 Closed and Open Systems1.3.1 Closed System (ControlMass)1.3.2 Isolated System1.3.3 Open System (ControlVolume)1.4 Forms of Energy1.4.1 Internal Energy1.5 Properties of a System1.5.1 Intensive and Extensive Properties1.6 State and Equilibrium1.7 Thermal and Calorical Properties1.7.1 Specific Heat of an Incompressible Substance1.7.2 Thermally Perfect Gas 1.8 The Perfect Gas1.9 Summary1.10 Exercise ProblemsConduction Heat Transfer2.1 Introduction2.2 Conduction Heat Trans

  13. Heat transfer mechanisms in bubbly Rayleigh-Bénard convection

    NARCIS (Netherlands)

    Oresta, Paolo; Verzicco, Roberto; Lohse, Detlef; Presperetti, Andrea

    2009-01-01

    The heat transfer mechanism in Rayleigh-Bénard convection in a liquid with a mean temperature close to its boiling point is studied through numerical simulations with pointlike vapor bubbles, which are allowed to grow or shrink through evaporation and condensation and which act back on the flow both

  14. Oscillate Boiling

    CERN Document Server

    Li, Fenfang; Nguyen, Dang Minh; Ohl, Claus-Dieter

    2016-01-01

    We report about an intriguing boiling regime occurring for small heaters embedded on the boundary in subcooled water. The microheater is realized by focusing a continuous wave laser beam to about $10\\,\\mu$m in diameter onto a 165\\,nm-thick layer of gold, which is submerged in water. After an initial vaporous explosion a single bubble oscillates continuously and repeatably at several $100\\,$kHz. The microbubble's oscillations are accompanied with bubble pinch-off leading to a stream of gaseous bubbles into the subcooled water. The self-driven bubble oscillation is explained with a thermally kicked oscillator caused by the non-spherical collapses and by surface pinning. Additionally, Marangoni stresses induce a recirculating streaming flow which transports cold liquid towards the microheater reducing diffusion of heat along the substrate and therefore stabilizing the phenomenon to many million cycles. We speculate that this oscillate boiling regime may allow to overcome the heat transfer thresholds observed dur...

  15. 烧结型多孔管管内流动沸腾传热数值模拟%Numerical Simulation of Flow Boiling Heat Transfer in Sintered Surface Porous Tubing

    Institute of Scientific and Technical Information of China (English)

    韩坤; 刘阿龙; 彭东辉; 孙定芳; 王经

    2011-01-01

    A theoretical model for the porous layer of sintered porous surface tubing(SPST) was established to simulate the flow boiling performances of cooling water in SPST and smooth tube based on Fluent software; and the cloud figures of gas volume distribution and pressure were got under different fluid velocities, including analysis of the velocity and the temperature by field synergy principle. The results show that SPST can enhance the heat flux and influence the pressure drop not too much. Analyzing different pipe flow influences on the vaporization proves the smaller the pipe flow, the greater the vaporization.%建立了烧结型表面多孔管多孔层的理论模型,应用Fluent软件对去离子水在烧结型表面多孔管和光滑管竖直管内的流动沸腾进行数值模拟,得到了不同流速下的气相体积分布云图和压力场云图,并利用场协同原理分析了管内的速度、温度场.结果表明,烧结型表面多孔管具有良好的强化沸腾传热性能.同时并未大幅度增加管内压力降.此外还分析了不同体积流速对沸腾汽化量的影响,研究表明,对于同一管型,管内流速越小,汽化量越大.

  16. Experimental verification of the horizontal steam generator boil-off transfer degradation at natural circulation

    Energy Technology Data Exchange (ETDEWEB)

    Hyvaerinen, J. [Finnish Centre for Radiation and Nuclear Safety, Helsinki (Finland); Kouhia, J. [VTT Energy, Lappeenranta (Finland)

    1997-12-31

    The presentation summarises the highlights of experimental results obtained for VVER type horizontal steam generator heat transfer, primary side flow pattern, and mixing in the hot collector during secondary side boil-off with primary at single-phase natural circulation. The experiments were performed using the PACTEL facility with Large Diameter (LD) steam generator models, with collector instrumentation designed specifically for these tests. The key findings are as follows: (1) the primary to secondary heat transfer degrades as the secondary water inventory is depleted, following closely the wetted tube area; (2) a circulatory flow pattern exists in the tube bundle, resulting in reversed flow (from cold to the hot collector) in the lower part of the tube bundle, and continuous flow through the upper part, including the tubes that have already dried out; and (3) mixing of the hot leg flow entering the hot collector and reversed, cold, tube flow remains confined within the collector itself, extending only a row or two above the elevation at which tube flow reversal has taken place. 6 refs.

  17. Measuring of heat transfer coefficient

    DEFF Research Database (Denmark)

    Henningsen, Poul; Lindegren, Maria

    Subtask 3.4 Measuring of heat transfer coefficient Subtask 3.4.1 Design and setting up of tests to measure heat transfer coefficient Objective: Complementary testing methods together with the relevant experimental equipment are to be designed by the two partners involved in order to measure...... the heat transfer coefficient for a wide range of interface conditions in hot and warm forging processes. Subtask 3.4.2 Measurement of heat transfer coefficient The objective of subtask 3.4.2 is to determine heat transfer values for different interface conditions reflecting those typically operating in hot...

  18. Heat Transfer and Cooling Techniques at Low Temperature

    CERN Document Server

    Baudouy, B

    2014-01-01

    The first part of this chapter gives an introduction to heat transfer and cooling techniques at low temperature. We review the fundamental laws of heat transfer (conduction, convection and radiation) and give useful data specific to cryogenic conditions (thermal contact resistance, total emissivity of materials and heat transfer correlation in forced or boiling flow for example) used in the design of cooling systems. In the second part, we review the main cooling techniques at low temperature, with or without cryogen, from the simplest ones (bath cooling) to the ones involving the use of cryocoolers without forgetting the cooling flow techniques.

  19. 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.

  20. Forced Convection Boiling and Critical Heat Flux of Ethanol in Electrically Heated Tube Tests

    Science.gov (United States)

    Meyer, Michael L.; Linne, Diane L.; Rousar, Donald C.

    1998-01-01

    Electrically heated tube tests were conducted to characterize the critical heat flux (transition from nucleate to film boiling) of subcritical ethanol flowing at conditions relevant to the design of a regeneratively cooled rocket engine thrust chamber. The coolant was SDA-3C alcohol (95% ethyl alcohol, 5% isopropyl alcohol by weight), and tests were conducted over the following ranges of conditions: pressure from 144 to 703 psia, flow velocities from 9.7 to 77 ft/s, coolant subcooling from 33 to 362 F, and critical heat fluxes up to 8.7 BTU/in(exp 2)/sec. For the data taken near 200 psia, critical heat flux was correlated as a function of the product of velocity and fluid subcooling to within +/- 20%. For data taken at higher pressures, an additional pressure term is needed to correlate the critical heat flux. It was also shown that at the higher test pressures and/or flow rates, exceeding the critical heat flux did not result in wall burnout. This result may significantly increase the engine heat flux design envelope for higher pressure conditions.

  1. The heat-pipe resembling action of boiling bubbles in endovenous laser ablation

    NARCIS (Netherlands)

    C.W.M. van der Geld (Cees); R.R. van den Bos (Renate); P.W.M. van Ruijven (Peter); T.E.C. Nijsten (Tamar); H.A.M. Neumann (Martino); M.J.C. van Gemert (Martin)

    2010-01-01

    textabstractEndovenous laser ablation (EVLA) produces boiling bubbles emerging from pores within the hot fiber tip and traveling over a distal length of about 20 mm before condensing. This evaporation-condensation mechanism makes the vein act like a heat pipe, where very efficient heat transport mai

  2. The heat-pipe resembling action of boiling bubbles in endovenous laser ablation

    NARCIS (Netherlands)

    van der Geld, C.W.M.; van den Bos, R.R.; van Ruijven, P.W.M.; Nijsten, T.; Neumann, H.A.M.; van Gemert, M.J.C.

    2010-01-01

    Endovenous laser ablation (EVLA) produces boiling bubbles emerging from pores within the hot fiber tip and traveling over a distal length of about 20 mm before condensing. This evaporation-condensation mechanism makes the vein act like a heat pipe, where very efficient heat transport maintains a con

  3. Time and Space Resolved Wall Temperature Measurements during Nucleate Boiling with Constant Heat Flux Boundary Conditions

    Science.gov (United States)

    Myers, Jerry G.; Hussey, Sam W.; Yee, Glenda F.; Yerramilli, Vamsee K.; Kim, Jungho

    2005-01-01

    The lack of temporally and spatially resolved measurements under nucleate bubbles has complicated efforts to fully explain pool-boiling phenomena. The objective of this current work is to acquire time and space resolved temperature distributions under nucleate bubbles on a constant heat flux surface. This was performed using a microheater array with 100 micron resolution that allowed effectively simultaneous measurements of surface temperature while supplying a constant dissipative heat flux. This data is then correlated with high speed (> 1000Hz) visual recordings of the bubble growth and departure from the heater surface acquired from below and from the side of the heater. The data indicate that a significant source of energy during bubble nucleation and initial growth is the superheated layer around the bubble. Bubble coalescence was not observed to decrease surface temperature as significantly as bubble departure from the surface. Since bubble departure is typically followed by a sharp increase in the heater surface temperature, it is surmised that the departing bubble effectively removes the superheated layer, allowing a high local heat transfer rate with the bulk fluid through transient conduction/micro-convection during rewetting.

  4. Numerical study of heat transfer characteristics in BOG heat exchanger

    Science.gov (United States)

    Yan, Yan; Pfotenhauer, John M.; Miller, Franklin; Ni, Zhonghua; Zhi, Xiaoqin

    2016-12-01

    In this study, a numerical study of turbulent flow and the heat transfer process in a boil-off liquefied natural gas (BOG) heat exchanger was performed. Finite volume computational fluid dynamics and the k - ω based shear stress transport model were applied to simulate thermal flow of BOG and ethylene glycol in a full-sized 3D tubular heat exchanger. The simulation model has been validated and compared with the engineering specification data from its supplier. In order to investigate thermal characteristics of the heat exchanger, velocity, temperature, heat flux and thermal response were studied under different mass flowrates in the shell-side. The shell-side flow pattern is mostly determined by viscous forces, which lead to a small velocity and low temperature buffer area in the bottom-right corner of the heat exchanger. Changing the shell-side mass flowrate could result in different distributions of the shell-side flow. However, the distribution in the BOG will remain in a relatively stable pattern. Heat flux increases along with the shell-side mass flowrate, but the increase is not linear. The ratio of increased heat flux to the mass flow interval is superior at lower mass flow conditions, and the threshold mass flow for stable working conditions is defined as greater than 0.41 kg/s.

  5. An improved mechanistic critical heat flux model for subcooled flow boiling

    Energy Technology Data Exchange (ETDEWEB)

    Kwon, Young Min [Korea Atomic Energy Research Institute, Taejon (Korea, Republic of); Chang, Soon Heung [Korea Advanced Institute of Science and Technology, Taejon (Korea, Republic of)

    1997-12-31

    Based on the bubble coalescence adjacent to the heated wall as a flow structure for CHF condition, Chang and Lee developed a mechanistic critical heat flux (CHF) model for subcooled flow boiling. In this paper, improvements of Chang-Lee model are implemented with more solid theoretical bases for subcooled and low-quality flow boiling in tubes. Nedderman-Shearer`s equations for the skin friction factor and universal velocity profile models are employed. Slip effect of movable bubbly layer is implemented to improve the predictability of low mass flow. Also, mechanistic subcooled flow boiling model is used to predict the flow quality and void fraction. The performance of the present model is verified using the KAIST CHF database of water in uniformly heated tubes. It is found that the present model can give a satisfactory agreement with experimental data within less than 9% RMS error. 9 refs., 5 figs. (Author)

  6. Investigation of change in surface morphology of heated surfaces upon pool boiling of magnetic fluids under magnetic actuation

    Science.gov (United States)

    Shojaeian, Mostafa; Yildizhan, Melike-Mercan; Coşkun, Ömer; Ozkalay, Ebrar; Tekşen, Yiğit; Gulgun, Mehmet Ali; Funda Yagci Acar, Havva; Koşar, Ali

    2016-09-01

    Nanofluids are becoming a significant candidate for new generation coolants to be used in industrial applications. In order to reduce clustering and sedimentation of nanoparticles and improve the heat transfer performance simultaneously, magnetic fluids prepared with magnetic Fe3O4 nanoparticles dispersed in water, which were placed in a pool and were exposed to varying magnetic fields to actuate nanoparticles in the system. The effect of magnetic actuation on boiling heat transfer characteristics and on the surface morphology of the pool was examined. An average enhancement of 29% in boiling heat transfer was achieved via magnetic actuation with rather low magnetic field (magnetic flux densities up to 11 mT) densities. Furthermore, it was observed that magnetic actuation significantly prevented the deposition and sedimentation of the nanoparticles in the pool. Otherwise, significant destabilization of nanoparticles causing aggregation and heavy sedimentation was present as a result of the performed surface analysis. Even though magnetic actuation reduced the sedimentation on the macroscale, the deposition of a thick and porous film occurred onto the pool floor, increasing the surface roughness.

  7. Heat transfer physics

    CERN Document Server

    Kaviany, Massoud

    2014-01-01

    This graduate textbook describes atomic-level kinetics (mechanisms and rates) of thermal energy storage, transport (conduction, convection, and radiation), and transformation (various energy conversions) by principal energy carriers. The approach combines the fundamentals of molecular orbitals-potentials, statistical thermodynamics, computational molecular dynamics, quantum energy states, transport theories, solid-state and fluid-state physics, and quantum optics. The textbook presents a unified theory, over fine-structure/molecular-dynamics/Boltzmann/macroscopic length and time scales, of heat transfer kinetics in terms of transition rates and relaxation times, and its modern applications, including nano- and microscale size effects. Numerous examples, illustrations, and homework problems with answers that enhance learning are included. This new edition includes applications in energy conversion (including chemical bond, nuclear, and solar), expanded examples of size effects, inclusion of junction quantum tr...

  8. Physical concept and calculation of boiling point in a pulsating heat pipe

    Directory of Open Access Journals (Sweden)

    Naumova A. N.

    2014-06-01

    Full Text Available LED development is accompanied by the need to ensure a constructive solution for the thermal conditions problem. For this purpose one can use pulsating heat pipes (PHP, that operate more efficiently after the start of heat carrier boiling. This article describes the physical representation and formula that allows determining the boiling point, which is a lower bound of the PHP effective operating range. It is shown that the main factors influencing the required heat flow are driving capillary pressure and velocity of the vapor bubble. The formula was obtained for the closed PHP made of the copper with water as a heat carrier. Information about this heat flux can be used for further design of cooling systems for heat-sensitive elements, such as LED for promising lighting devices.

  9. Tubing for augmented heat transfer

    Energy Technology Data Exchange (ETDEWEB)

    Yampolsky, J.S.; Pavlics, P.

    1983-08-01

    The objectives of the program reported were: to determine the heat transfer and friction characteristics on the outside of spiral fluted tubing in single phase flow of water, and to assess the relative cost of a heat exchanger constructed with spiral fluted tubing with one using conventional smooth tubing. An application is examined where an isolation water/water heat exchanger was used to transfer the heat from a gaseous diffusion plant to an external system for energy recovery. (LEW)

  10. Gas turbine heat transfer and cooling technology

    CERN Document Server

    Han, Je-Chin; Ekkad, Srinath

    2012-01-01

    FundamentalsNeed for Turbine Blade CoolingTurbine-Cooling TechnologyTurbine Heat Transfer and Cooling IssuesStructure of the BookReview Articles and Book Chapters on Turbine Cooling and Heat TransferNew Information from 2000 to 2010ReferencesTurbine Heat TransferIntroductionTurbine-Stage Heat TransferCascade Vane Heat-Transfer ExperimentsCascade Blade Heat TransferAirfoil Endwall Heat TransferTurbine Rotor Blade Tip Heat TransferLeading-Edge Region Heat TransferFlat-Surface Heat TransferNew Information from 2000 to 20102.10 ClosureReferencesTurbine Film CoolingIntroductionFilm Cooling on Rotat

  11. Heat transfer and fluid flow in minichannels and microchannels

    CERN Document Server

    Kandlikar, Satish; Li, Dongqing; Colin, Stephane; King, Michael R

    2013-01-01

    Heat exchangers with minichannel and microchannel flow passages are becoming increasingly popular due to their ability to remove large heat fluxes under single-phase and two-phase applications. Heat Transfer and Fluid Flow in Minichannels and Microchannels methodically covers gas, liquid, and electrokinetic flows, as well as flow boiling and condensation, in minichannel and microchannel applications. Examining biomedical applications as well, the book is an ideal reference for anyone involved in the design processes of microchannel flow passages in a heat exchanger. Each chapter is accompan

  12. Heat transfer, thermal control, and heat pipes

    Science.gov (United States)

    Olstad, W. B.

    1980-01-01

    This volume provides information on recent progress in spacecraft thermal control and the supporting disciplines of conduction, thermal radiation, and heat pipe theory and application. Four problem areas are considered: conduction heat transfer, radiation heat transfer, thermal control, and heat pipes. The topics covered include finite-element methodology for transient conduction/forced-convection thermal analysis; effects of surface finish on thermal contact resistance between different materials; mathematical models for wide-band nongray gas radiation in spherical and cylindrical geometries; thermal design, analysis and testing of the Shuttle remote manipulator arm; porous heat pipe; and transient behavior of liquid trap heat-pipe thermal diodes. Also discussed is the thermal design concept for a high-resolution UV spectrometer.

  13. Hybrid Graphene and Single-Walled Carbon Nanotube Films for Enhanced Phase-Change Heat Transfer.

    Science.gov (United States)

    Seo, Han; Yun, Hyung Duk; Kwon, Soon-Yong; Bang, In Cheol

    2016-02-10

    Nucleate boiling is an effective heat transfer method in power generation systems and cooling devices. In this letter, hybrid graphene/single-walled carbon nanotube (SWCNT), graphene, and SWCNT films deposited on indium tin oxide (ITO) surfaces were fabricated to investigate the enhancement of nucleate boiling phenomena described by the critical heat flux and heat transfer coefficient. The graphene films were grown on Cu foils and transferred to ITO surfaces. Furthermore, SWCNTs were deposited on the graphene layer to fabricate hybrid graphene/SWCNT films. We determined that the hybrid graphene/SWCNT film deposited on an ITO surface is the most effective heat transfer surface in pool boiling because of the interconnected network of carbon structures.

  14. Aspects of subcooled boiling

    Energy Technology Data Exchange (ETDEWEB)

    Bankoff, S.G. [Northwestern Univ., Evanston, IL (United States)

    1997-12-31

    Subcooled boiling boiling refers to boiling from a solid surface where the bulk liquid temperature is below the saturation temperature (subcooled). Two classes are considered: (1) nucleate boiling, where, for large subcoolings, individual bubbles grow and collapse while remaining attached to the solid wall, and (2) film boiling, where a continuous vapor film separates the solid from the bulk liquid. One mechanism by which subcooled nucleate boiling results in very large surface heat transfer coefficient is thought to be latent heat transport within the bubble, resulting from simultaneous evaporation from a thin residual liquid layer at the bubble base, and condensation at the polar bubble cap. Another is the increased liquid microconvection around the oscillating bubble. Two related problems have been attacked. One is the rupture of a thin liquid film subject to attractive and repulsive dispersion forces, leading to the formation of mesoscopic drops, which then coalesce and evaporate. Another is the liquid motion in the vicinity of an oscillating contact line, where the bubble wall is idealized as a wedge of constant angle sliding on the solid wall. The subcooled film boiling problem has been attacked by deriving a general long-range nonlinear evolution equation for the local thickness of the vapor layer. Linear and weakly-nonlinear stability results have been obtained. A number of other related problems have been attacked.

  15. The heat-pipe resembling action of boiling bubbles in endovenous laser ablation.

    Science.gov (United States)

    van der Geld, Cees W M; van den Bos, Renate R; van Ruijven, Peter W M; Nijsten, Tamar; Neumann, H A Martino; van Gemert, Martin J C

    2010-11-01

    Endovenous laser ablation (EVLA) produces boiling bubbles emerging from pores within the hot fiber tip and traveling over a distal length of about 20 mm before condensing. This evaporation-condensation mechanism makes the vein act like a heat pipe, where very efficient heat transport maintains a constant temperature, the saturation temperature of 100 degrees C, over the volume where these non-condensing bubbles exist. During EVLA the above-mentioned observations indicate that a venous cylindrical volume with a length of about 20 mm is kept at 100 degrees C. Pullback velocities of a few mm/s then cause at least the upper part of the treated vein wall to remain close to 100 degrees C for a time sufficient to cause irreversible injury. In conclusion, we propose that the mechanism of action of boiling bubbles during EVLA is an efficient heat-pipe resembling way of heating of the vein wall.

  16. Heat transfer and thermal control

    Science.gov (United States)

    Crosbie, A. L.

    Radiation heat transfer is considered along with conduction heat transfer, heat pipes, and thermal control. Attention is given to the radiative properties of a painted layer containing nonspherical pigment, bidirectional reflectance measurements of specular and diffuse surfaces with a simple spectrometer, the radiative equilibrium in a general plane-parallel environment, and the application of finite-element techniques to the interaction of conduction and radiation in participating medium, a finite-element approach to combined conductive and radiative heat transfer in a planar medium. Heat transfer in irradiated shallow layers of water, an analytical and experimental investigation of temperature distribution in laser heated gases, numerical methods for the analysis of laser annealing of doped semiconductor wafers, and approximate solutions of transient heat conduction in a finite slab are also examined. Consideration is also given to performance testing of a hydrogen heat pipe, heat pipe performance with gravity assist and liquid overfill, vapor chambers for an atmospheric cloud physics laboratory, a prototype heat pipe radiator for the German Direct Broadcasting TV Satellite, free convection in enclosures exposed to compressive heating, and a thermal analysis of a multipurpose furnace for material processing in space.

  17. Enhancement of critical heat flux in nucleate boiling of nanofluids: a state-of-art review.

    Science.gov (United States)

    Kim, Hyungdae

    2011-06-09

    Nanofluids (suspensions of nanometer-sized particles in base fluids) have recently been shown to have nucleate boiling critical heat flux (CHF) far superior to that of the pure base fluid. Over the past decade, numerous experimental and analytical studies on the nucleate boiling CHF of nanofluids have been conducted. The purpose of this article is to provide an exhaustive review of these studies. The characteristics of CHF enhancement in nanofluids are systemically presented according to the effects of the primary boiling parameters. Research efforts to identify the effects of nanoparticles underlying irregular enhancement phenomena of CHF in nanofluids are then presented. Also, attempts to explain the physical mechanism based on available CHF theories are described. Finally, future research needs are identified.

  18. Identification of Heat Transfer Coefficients by Use Conditions of Quenching Oil

    Institute of Scientific and Technical Information of China (English)

    Katsumi Ichitani

    2004-01-01

    Heat transfer coefficients of the quench medium are necessary for heat-treatment simulation. Cooling characteristics of quenching oil vary with kinds and usage greatly. Users are selecting oil solutions that come up to their desired hardness and quenching distortion requirements. In particular cooling performance rises by agitation and decompression. Therefore we identified a heat transfer coefficient by usage and kinds of quenching oil. Cooling characteristics are different greatly by a kind of quenching oil. A difference of a cooling characteristic by a kind of oil depends on a temperature range of a boiling stage and the maximum heat transfer coefficient mainly. On the other hand, in a convection stage, there are few changes in a boiling stage. Even if quenching oil temperature is changed, heat transfer coefficients do not change greatly. When quenching oil stirred, heat transfer coefficients of vapor blanket stage and a convection stage rise, but there are a few changes in a boiling stage. When quenching oil is decompressed a temperature range of a high heat transfer coefficient moves to the low temperature side. In addition, a heat transfer coefficient in a vapor blanket stage comes down. For precision improvement of heat-treatment simulation, it is important that the heat transfer coefficient is calculated in conformity to the on-site use reality.

  19. Advances in industrial heat transfer

    CERN Document Server

    Minea, Alina Adriana

    2012-01-01

    Advances in Industrial Heat Transfer presents the basic principles of industrial heat transfer enhancement. Serving as a reference and guide for future research, this book presents a complete approach, from redesigning equipment to the use of nanofluids in industry. Based on the latest methods of the experiment and their interpretation, this book presents a unified conception of the industrial heat transfer process and procedures which will help decrease global energy consumption. Containing both theoretical and practical results, the book uses text, pictures, graphs, and definitions to illust

  20. Free convection film flows and heat transfer laminar free convection of phase flows and models for heat-transfer analysis

    CERN Document Server

    Shang, De-Yi

    2012-01-01

    This book presents recent developments in our systematic studies of hydrodynamics and heat and mass transfer in laminar free convection, accelerating film boiling and condensation of Newtonian fluids, as well as accelerating film flow of non-Newtonian power-law fluids (FFNF). These new developments provided in this book are (i) novel system of analysis models based on the developed New Similarity Analysis Method; (ii) a system of advanced methods for treatment of gas temperature- dependent physical properties, and liquid temperature- dependent physical properties; (iii) the organically combined models of the governing mathematical models with those on treatment model of variable physical properties; (iv) rigorous approach of overcoming a challenge on accurate solution of three-point boundary value problem related to two-phase film boiling and condensation; and (v) A pseudo-similarity method of dealing with thermal boundary layer of FFNF for greatly simplifies the heat-transfer analysis and numerical calculati...

  1. Sphere Drag and Heat Transfer.

    Science.gov (United States)

    Duan, Zhipeng; He, Boshu; Duan, Yuanyuan

    2015-07-20

    Modelling fluid flows past a body is a general problem in science and engineering. Historical sphere drag and heat transfer data are critically examined. The appropriate drag coefficient is proposed to replace the inertia type definition proposed by Newton. It is found that the appropriate drag coefficient is a desirable dimensionless parameter to describe fluid flow physical behavior so that fluid flow problems can be solved in the simple and intuitive manner. The appropriate drag coefficient is presented graphically, and appears more general and reasonable to reflect the fluid flow physical behavior than the traditional century old drag coefficient diagram. Here we present drag and heat transfer experimental results which indicate that there exists a relationship in nature between the sphere drag and heat transfer. The role played by the heat flux has similar nature as the drag. The appropriate drag coefficient can be related to the Nusselt number. This finding opens new possibilities in predicting heat transfer characteristics by drag data. As heat transfer for flow over a body is inherently complex, the proposed simple means may provide an insight into the mechanism of heat transfer for flow past a body.

  2. Contaminant Mass Transfer During Boiling in Fractured Geologic Media

    Science.gov (United States)

    2011-04-01

    make the dough , i.e. C0, and DCA and bromide mass recovery during heating, normalized to the inside mass, measured by extraction of clay dough ...gradually to the powder. The mixture was manually kneaded into a uniform dough - like material that was divided into three parts. Each part was placed...process took about 15- 20 min to mix and knead the dough , another 15-20 min to pack the dough into the container and seal it. The sample weight was

  3. Heat-transfer thermal switch

    Science.gov (United States)

    Friedell, M. V.; Anderson, A. J.

    1974-01-01

    Thermal switch maintains temperature of planetary lander, within definite range, by transferring heat. Switch produces relatively large stroke and force, uses minimum electrical power, is lightweight, is vapor pressure actuated, and withstands sterilization temperatures without damage.

  4. Heat transfer, diffusion, and evaporation

    Science.gov (United States)

    Nusselt, Wilhelm

    1954-01-01

    Although it has long been known that the differential equations of the heat-transfer and diffusion processes are identical, application to technical problems has only recently been made. In 1916 it was shown that the speed of oxidation of the carbon in iron ore depends upon the speed with which the oxygen of the combustion air diffuses through the core of gas surrounding the carbon surface. The identity previously referred to was then used to calculate the amount of oxygen diffusing to the carbon surface on the basis of the heat transfer between the gas stream and the carbon surface. Then in 1921, H. Thoma reversed that procedure; he used diffusion experiments to determine heat-transfer coefficients. Recently Lohrisch has extended this work by experiment. A technically very important application of the identity of heat transfer and diffusion is that of the cooling tower, since in this case both processes occur simultaneously.

  5. Experimental result of BWR post-CHF tests. Critical heat flux and post-CHF heat transfer coefficient. Contract research

    Energy Technology Data Exchange (ETDEWEB)

    Iguchi, Tadashi; Anoda, Yoshinari [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment; Iwaki, Chikako [Toshiba Corp., Tokyo (Japan)

    2002-02-01

    Authors performed post-CHF experiments under wider pressure ranges of 2 MPa - 18 MPa, wider mass flux ranges of 33 kg/m{sup 2}s - 1651 kg/m{sup 2}s and wider superheat of heaters up to 500 K in comparison to experimental ranges at previous post-CHF experiments. Data on boiling transition, critical heat flux and post-CHF heat transfer coefficient were obtained. Used test section was 4x4-rod bundle with heaters, which diameter and length were the same as those of BWR nuclear fuels. As the result of the experiments, it was found that the boiling transition occurred just below several grid spacers, and that the fronts of the boiling transition region proceeded lower with increase of heated power. Heat transfer was due to nucleate boiling above grid spacers, while it was due to film boiling below grid spacers. Consequently, critical heat flux is affected on the distance from the grid spacers. Critical heat flux above the grid spacers was about 15% higher than that below the grid spacers, by comparing them under the same local condition. Heat transfer by steam turbulent flow was dominant to post-CHF heat transfer, when superheat of heaters was sufficiently high. Then, post-CHF heat transfer coefficient was predicted with heat transfer correlations for single-phase flow. On the other hand, when superhead of heaters was not sufficiently high, post-CHF heat transfer coefficient was higher than the prediction with heat transfer correlations for single-phase flow. Mass flux effect on post-CHF heat transfer coefficient was described by standardization of post-CHF heat transfer coefficient with the prediction for single-phase flow. However, pressure effect, superheat effect and effect of position were not described. Authors clarified that those effects could be described with functions of heater temperature and position. Post-CHF heat transfer coefficient was lowest just blow the grid spacers, and it increased with the lower positions. It increased by about 30% in one span of

  6. Nanofluids for power engineering: Emergency cooling of overheated heat transfer surfaces

    Science.gov (United States)

    Bondarenko, B. I.; Moraru, V. N.; Sidorenko, S. V.; Komysh, D. V.

    2016-07-01

    The possibility of emergency cooling of an overheated heat transfer surface using nanofluids in the case of a boiling crisis is explored by means of synchronous recording of changes of main heat transfer parameters of boiling water over time. Two nanofluids are tested, which are derived from a mixture of natural aluminosilicates (AlSi-7) and titanium dioxide (NF-8). It is found that the introduction of a small portions of nanofluid into a boiling coolant (distilled water) in a state of film boiling ( t heater > 500°C) can dramatically decrease the heat transfer surface temperature to 130-150°C, which corresponds to a transition to a safe nucleate boiling regime without affecting the specific heat flux. The fact that this regime is kept for a long time at a specific heat load exceeding the critical heat flux for water and t heater = 125-130°C is particularly important. This makes it possible to prevent a potential accident emergency (heater burnout and failure of the heat exchanger) and to ensure the smooth operation of the equipment.

  7. An assessment of RELAP5 MOD3.1.1 condensation heat transfer modeling with GIRAFFE heat transfer tests

    Energy Technology Data Exchange (ETDEWEB)

    Boyer, B.D.; Parlatan, Y.; Slovik, G.C. [and others

    1995-09-01

    RELAP5 MOD3.1.1 is being used to simulate Loss of Coolant Accidents (LOCA) for the Simplified Boiling Water Reactor (SBWR) being proposed by General Electric (GE). One of the major components associated with the SBWR is the Passive Containment Cooling System (PCCS) which provides the long-term heat sink to reject decay heat. The RELAP5 MOD3.1.1 code is being assessed for its ability to represent accurately the PCCS. Data from the Phase 1, Step 1 Heat Transfer Tests performed at Toshiba`s Gravity-Driven Integral Full-Height Test for Passive Heat Removal (GIRAFFE) facility will be used for assessing the ability of RELAP5 to model condensation in the presence of noncondensables. The RELAP5 MOD3.1.1 condensation model uses the University of California at Berkeley (UCB) correlation developed by Vierow and Schrock. The RELAP5 code uses this heat transfer coefficient with the gas velocity effect multiplier being limited to 2. This heat transfer option was used to analyze the condensation heat transfer in the GIRAFFE PCCS heat exchanger tubes in the Phase 1, Step 1 Heat Transfer Tests which were at a pressure of 3 bar and had a range of nitrogen partial pressure fractions from 0.0 to 0.10. The results of a set of RELAP5 calculations at these conditions were compared with the GIRAFFE data. The effects of PCCS cell noding on the heat transfer process were also studied. The UCB correlation, as implemented in RELAP5, predicted the heat transfer to {plus_minus}5% of the data with a three--node model. The three-node model has a large cell in the entrance region which smeared out the entrance effects on the heat transfer, which tend to overpredict the condensation. Hence, the UCB correlation predicts condensation heat transfer correlation implemented in the code must be removed to allow for accurate calculations with smaller cell sizes.

  8. Heat Transfer Parametric System Identification

    Science.gov (United States)

    1993-06-01

    Transfer Parametric System Identification 6. AUTHOR(S Parker, Gregory K. 7. PERFORMING ORGANIZATION NAME(S) AND AOORESS(ES) 8. PERFORMING ORGANIZATION...distribution is unlimited. Heat Transfer Parametric System Identification by Gregory K. Parker Lieutenant, United States Navy BS., DeVry Institute of...Modeling Concept ........ ........... 3 2. Lumped Parameter Approach ...... ......... 4 3. Parametric System Identification ....... 4 B. BASIC MODELING

  9. Investigation of Martensite Formation in Fe Based Alloys During Heating From Boiling Nitrogen Temperature

    DEFF Research Database (Denmark)

    Villa, Matteo; Christiansen, Thomas L.; Hansen, Mikkel F.;

    2015-01-01

    he austenite-to-martensite transformation at temperatures below room temperature was investigated in situ by magnetometry in Fe-N, Fe-Cr-C and Fe-Cr-Ni based alloys. After quenching to room temperature, samples were immersed in boiling nitrogen and martensite formation was followed during...... heating was convincingly demonstrated for all investigated materials by showing heating rate dependent transformation kinetics. Moreover, magnetometry showed that the heating rate influences the fraction of martensite formed during the thermal treatment. The activation energy for thermally activated...

  10. Enhanced heat transfer using nanofluids

    Science.gov (United States)

    Choi, Stephen U. S.; Eastman, Jeffrey A.

    2001-01-01

    This invention is directed to a method of and apparatus for enhancing heat transfer in fluids such as deionized water. ethylene glycol, or oil by dispersing nanocrystalline particles of substances such as copper, copper oxide, aluminum oxide, or the like in the fluids. Nanocrystalline particles are produced and dispersed in the fluid by heating the substance to be dispersed in a vacuum while passing a thin film of the fluid near the heated substance. The fluid is cooled to control its vapor pressure.

  11. Fundamental principles of heat transfer

    CERN Document Server

    Whitaker, Stephen

    1977-01-01

    Fundamental Principles of Heat Transfer introduces the fundamental concepts of heat transfer: conduction, convection, and radiation. It presents theoretical developments and example and design problems and illustrates the practical applications of fundamental principles. The chapters in this book cover various topics such as one-dimensional and transient heat conduction, energy and turbulent transport, forced convection, thermal radiation, and radiant energy exchange. There are example problems and solutions at the end of every chapter dealing with design problems. This book is a valuable int

  12. Heat transfer enhancement with nanofluids

    CERN Document Server

    Bianco, Vincenzo; Nardini, Sergio; Vafai, Kambiz

    2015-01-01

    Properties of NanofluidSamuel Paolucci and Gianluca PolitiExact Solutions and Their Implications in Anomalous Heat TransferWenhao Li, Chen Yang and Akira NakayamaMechanisms and Models of Thermal Conductivity in NanofluidsSeung-Hyun Lee and Seok Pil JangExperimental Methods for the Characterization of Thermophysical Properties of NanofluidsSergio Bobbo and Laura FedeleNanofluid Forced ConvectionGilles RoyExperimental Study of Convective Heat Transfer in NanofluidsEhsan B. Haghighi, Adi T. Utomo, Andrzej W. Pacek and Björn E. PalmPerformance of Heat Exchangers Using NanofluidsBengt Sundén and Za

  13. Nanofluid impingement jet heat transfer.

    Science.gov (United States)

    Zeitoun, Obida; Ali, Mohamed

    2012-02-17

    Experimental investigation to study the heat transfer between a vertical round alumina-water nanofluid jet and a horizontal circular round surface is carried out. Different jet flow rates, jet nozzle diameters, various circular disk diameters and three nanoparticles concentrations (0, 6.6 and 10%, respectively) are used. The experimental results indicate that using nanofluid as a heat transfer carrier can enhance the heat transfer process. For the same Reynolds number, the experimental data show an increase in the Nusselt numbers as the nanoparticle concentration increases. Size of heating disk diameters shows reverse effect on heat transfer. It is also found that presenting the data in terms of Reynolds number at impingement jet diameter can take into account on both effects of jet heights and nozzle diameter. Presenting the data in terms of Peclet numbers, at fixed impingement nozzle diameter, makes the data less sensitive to the percentage change of the nanoparticle concentrations. Finally, general heat transfer correlation is obtained verses Peclet numbers using nanoparticle concentrations and the nozzle diameter ratio as parameters.

  14. Tissue Erosion Using Shock Wave Heating and Millisecond Boiling in HIFU Fields

    Science.gov (United States)

    Canney, Michael S.; Khokhlova, Tatiana D.; Khokhlova, Vera A.; Bailey, Michael R.; Ha Hwang, Joo; Crum, Lawrence A.

    2010-03-01

    A wide variety of treatment protocols have been employed in high intensity focused ultrasound (HIFU) treatments, and the resulting bioeffects observed include both mechanical as well as thermal effects. In recent studies, there has been significant interest in generating purely mechanical damage using protocols with short, microsecond pulses. Tissue erosion effects have been attained by operating HIFU sources using short pulses of 10-20 cycles, low duty cycles (<1%), and pulse average intensities of greater than 20 kW/cm2. The goal of this work was to use a modified pulsing protocol, consisting of longer, millisecond-long pulses of ultrasound and to demonstrate that heating and rapid millisecond boiling from shock wave formation can be harnessed to induce controlled mechanical destruction of soft tissue. Experiments were performed in excised bovine liver and heart tissue using a 2-MHz transducer. Boiling activity was monitored during exposures using a high voltage probe in parallel with the HIFU source. In situ acoustic fields and heating rates were determined for exposures using a novel derating approach for nonlinear HIFU fields. Several different exposure protocols were used and included varying the duty cycle, pulse length, and power to the source. After exposures, the tissue was sectioned, and the gross lesion morphology was observed. Different types of lesions were induced in experiments that ranged from purely thermal to purely mechanical depending on the pulsing protocol used. Therefore, shock wave heating and millisecond boiling may be an effective method for reliably generating significant tissue erosion effects.

  15. 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)

  16. Effect of the heating surface enhancement on the heat transfer coefficient for a vertical minichannel

    Directory of Open Access Journals (Sweden)

    Piasecka Magdalena

    2016-01-01

    Full Text Available The aim of the paper is to estimate effect of the heating surface enhancement on FC-72 flow boiling heat transfer for a vertical minichannel 1.7 mm deep, 24 mm wide and 360 mm long. Two types of enhanced heating surfaces were used: one with minicavities distributed unevenly, and the other with capillary metal fibrous structure. It was to measure temperature field on the plain side of the heating surface by means of the infrared thermography and to observe the two-phase flow patterns on the enhanced foil side. The paper analyses mainly the impact of the microstructured heating surface on the heat transfer coefficient. The results are presented as heat transfer coefficient dependences on the distance along the minichannel length. The data obtained using two types of enhanced heating surfaces in experiments was compared with the data when smooth foil as the heating surface was used. The highest local values of heat transfer coefficient were obtained using enhanced foil with minicavities - in comparison to other cases. Local values of heat transfer coefficient received for capillary fibrous structure were the lowest, even compared with data obtained for smooth foil. Probably this porous structure caused local flow disturbances.

  17. Bubble Behavior in Nucleate Boiling Experiment Aboard the Space Shuttle

    OpenAIRE

    Koeln, Justin P.; Boulware, Jeffrey C.; Ban, Heng

    2009-01-01

    Boiling dynamics in microgravity need to be better understood before heat transfer systems based on boiling mechanism can be developed for space applications. This paper presents the results of a nucleate boiling experiment aboard Space Shuttle Endeavor (STS- 108). The experiment utilized nickel-chromium resistance wire to boil water in microgravity, and the data was recorded with a CCD camera and six thermistors. This data was analyzed to determine the behavior of bubble formation, detachmen...

  18. Advances in heat transfer volume 21

    CERN Document Server

    Hartnett †, James P; Cho, Young I

    1991-01-01

    This volume in a series on heat transfer covers the modelling of the dynamics of turbulent transport processes, supercritical pressures, hydrodynamics, mass transfer near rotating surfaces, lost heat in entropy and the mechanics of heat transfer in a multifluid bubbling pool. Other related titles are "Advances in Heat Transfer", volumes 18, 19 and 20.

  19. Fundamental Research on Convective Heat Transfer in Electronic Cooling Technology

    Institute of Scientific and Technical Information of China (English)

    C.F.Ma; Y.P.Gan; 等

    1992-01-01

    During the past six years comprehensive research programs have been conducted at the Beijing Polytechnic University to provide a better understanding of heat transfer characteristics of existing and condidate cooling techniques for electronic and microelestanding of heat transfer characteristics of existing and condidate cooling techniques for electronic and microleectronic devices.This paper provides a review and summary of the programs with emphasis on direct liquid cooling.Included in this review are the heat transfer investigations related to the following cooling modes:liquid free,mixed and forced convection.liquid jet impingement,flowing liquid film cooling,pool boiling,spray cooling,foreign gas jet impingement in liquid pool,and forced convection air-cooling.

  20. Film boiling on vertical surfaces.

    Science.gov (United States)

    Suryanarayana, N. V.; Merte, H., Jr.

    1972-01-01

    Film boiling of a saturated liquid on a vertical surface is analyzed to determine the local heat-transfer rates as a function of height and heater-surface superheat. Experiments show that the laminar-flow model is inadequate. A turbulent-vapor-flow model is used, and the influence of the interfacial oscillations is incorporated on a semiempirical basis. Measurements of local film boiling were obtained with a transient technique using saturated liquid nitrogen.

  1. Engineering heat transfer

    CERN Document Server

    Annaratone, Donatello

    2010-01-01

    This book is a generalist textbook; it is designed for anybody interested in heat transmission, including scholars, designers and students. Two criteria constitute the foundation of Annaratone's books, including the present one. The first one consists of indispensable scientific rigor without theoretical exasperation. The inclusion in the book of some theoretical studies, even if admirable for their scientific rigor, would have strengthened the scientific foundation of this publication, yet without providing the reader with further applicable know-how. The second criterion is to deliver practi

  2. Essentials of radiation heat transfer

    CERN Document Server

    Balaji

    2014-01-01

    Essentials of Radiation Heat Transfer is a textbook presenting the essential, fundamental information required to gain an understanding of radiation heat transfer and equips the reader with enough knowledge to be able to tackle more challenging problems. All concepts are reinforced by carefully chosen and fully worked examples, and exercise problems are provided at the end of every chapter. In a significant departure from other books on this subject, this book completely dispenses with the network method to solve problems of radiation heat transfer in surfaces. It instead presents the powerful radiosity-irradiation method and shows how this technique can be used to solve problems of radiation in enclosures made of one to any number of surfaces. The network method is not easily scalable. Secondly, the book introduces atmospheric radiation, which is now being considered as a potentially important area, in which engineers can contribute to the technology of remote sensing and atmospheric sciences in general, b...

  3. Heat transfer and fluid flow in nuclear systems

    CERN Document Server

    Fenech, Henri

    1982-01-01

    Heat Transfer and Fluid in Flow Nuclear Systems discusses topics that bridge the gap between the fundamental principles and the designed practices. The book is comprised of six chapters that cover analysis of the predicting thermal-hydraulics performance of large nuclear reactors and associated heat-exchangers or steam generators of various nuclear systems. Chapter 1 tackles the general considerations on thermal design and performance requirements of nuclear reactor cores. The second chapter deals with pressurized subcooled light water systems, and the third chapter covers boiling water reacto

  4. Critical Heat Flux in forced Convective Boiling with a Wall Jet

    Institute of Scientific and Technical Information of China (English)

    王迅

    2004-01-01

    The critical heat flux (CHF) in the forced convective boiling with a wall jet has been investigated.The experiments of CHF with a wall jet have been performed over a wide range of ρl/ρg=6.6-1 603 and ΔTsub=0-60 K.The mechanism on CHF is discussed and a CHF model based on heat balance in sublayer can provide a good clue for analyzing and deriving CHF.Finally,a generalized correlation is presented, which can predict CHF for saturated and subcooled conditions.

  5. Boiling Delay phenomenon in a Thermosyphon Heat Sink and Its Effect on Device Performance

    Institute of Scientific and Technical Information of China (English)

    WeilinHu; YihuiZhou; 等

    1994-01-01

    A new kind of thermosyphon heat sink has been studied and developed,its peformance being measured.It was found that a remarkable boiling delay phenomenon occurs during its work.The phenomenon is described and explained and its effects on thermoresistance performance at both steady and transient states are discussed.The thermoresistance of this sink is found to be 0.029℃/W at air velocity 5m/s.THis heat sink will satisfy the needs of cooling rectifier diodes and thyristors of rated currents up to 1000 amperes.

  6. Heat transfer by natural convection into an horizontal cavity; Transferencia de calor por conveccion natural en una cavidad horizontal

    Energy Technology Data Exchange (ETDEWEB)

    Arevalo J, P

    1998-12-31

    At this thesis it is studied the heat transfer by natural convection in an horizontal cavity, it is involved a boiling`s part that is described the regimes and correlations differences for boiling`s curve. It is designed a horizontal cavity for realize the experimental part and it`s mention from equipment or instrumentation to succeed in a experimentation that permits to realize the analysis of heat transfer, handling as water fluid at atmospheric pressure and where it`s present process from natural convection involving part boiling`s subcooled. The system consists of heater zone submerged in a horizontal cavity with water. Once part finished experimental with information to obtained it`s proceeded to obtain a correlation, realized starting from analysis dimensionless such as: Jakob, Bond and Grasoft (Boiling) besides of knows in natural convection: Prandtl and Nusselt. The mathematical model explains the behavior for natural convection continued part boiling`s subcooled. It is realize analysis graphics too where it`s show comparing with Globe Dropkin and Catton equations by natural convection with bottom heating. (Author)

  7. Time and Space Resolved Heat Transfer Measurements Under Nucleate Bubbles with Constant Heat Flux Boundary Conditions

    Science.gov (United States)

    Myers, Jerry G.; Hussey, Sam W.; Yee, Glenda F.; Kim, Jungho

    2003-01-01

    Investigations into single bubble pool boiling phenomena are often complicated by the difficulties in obtaining time and space resolved information in the bubble region. This usually occurs because the heaters and diagnostics used to measure heat transfer data are often on the order of, or larger than, the bubble characteristic length or region of influence. This has contributed to the development of many different and sometimes contradictory models of pool boiling phenomena and dominant heat transfer mechanisms. Recent investigations by Yaddanapyddi and Kim and Demiray and Kim have obtained time and space resolved heat transfer information at the bubble/heater interface under constant temperature conditions using a novel micro-heater array (10x10 array, each heater 100 microns on a side) that is semi-transparent and doubles as a measurement sensor. By using active feedback to maintain a state of constant temperature at the heater surface, they showed that the area of influence of bubbles generated in FC-72 was much smaller than predicted by standard models and that micro-conduction/micro-convection due to re-wetting dominated heat transfer effects. This study seeks to expand on the previous work by making time and space resolved measurements under bubbles nucleating on a micro-heater array operated under constant heat flux conditions. In the planned investigation, wall temperature measurements made under a single bubble nucleation site will be synchronized with high-speed video to allow analysis of the bubble energy removal from the wall.

  8. Literature survey of heat transfer enhancement techniques in refrigeration applications

    Energy Technology Data Exchange (ETDEWEB)

    Jensen, M.K.; Shome, B. [Rensselaer Polytechnic Inst., Troy, NY (United States). Dept. of Mechanical Engineering, Aeronautical Engineering and Mechanics

    1994-05-01

    A survey has been performed of the technical and patent literature on enhanced heat transfer of refrigerants in pool boiling, forced convection evaporation, and condensation. Extensive bibliographies of the technical literature and patents are given. Many passive and active techniques were examined for pure refrigerants, refrigerant-oil mixtures, and refrigerant mixtures. The citations were categorized according to enhancement technique, heat transfer mode, and tube or shell side focus. The effects of the enhancement techniques relative to smooth and/or pure refrigerants were illustrated through the discussion of selected papers. Patented enhancement techniques also are discussed. Enhanced heat transfer has demonstrated significant improvements in performance in many refrigerant applications. However, refrigerant mixtures and refrigerant-oil mixtures have not been studied extensively; no research has been performed with enhanced refrigerant mixtures with oil. Most studies have been of the parametric type; there has been inadequate examination of the fundamental processes governing enhanced refrigerant heat transfer, but some modeling is being done and correlations developed. It is clear that an enhancement technique must be optimized for the refrigerant and operating condition. Fundamental processes governing the heat transfer must be examined if models for enhancement techniques are to be developed; these models could provide the method to optimize a surface. Refrigerant mixtures, with and without oil present, must be studied with enhancement devices; there is too little known to be able to estimate the effects of mixtures (particularly NARMs) with enhanced heat transfer. Other conclusions and recommendations are offered.

  9. High heat transfer oxidizer heat exchanger design and analysis. [RL10-2B engine

    Science.gov (United States)

    Kmiec, Thomas D.; Kanic, Paul G.; Peckham, Richard J.

    1987-01-01

    The RL10-2B engine, a derivative of the RL10, is capable of multimode thrust operation. This engine operates at two low thrust levels: tank head idle (THI), which is approximately 1 to 2% of full thrust, and pumped idle (PI), which is 10% of full thrust. Operation at THI provides vehicle propellant settling thrust and efficient engine thermal conditioning; PI operation provides vehicle tank pre-pressurization and maneuver thrust for low-g deployment. Stable combustion of the RL10-2B engine during the low thrust operating modes can be accomplished by using a heat exchanger to supply gaseous oxygen to the propellant injector. The oxidizer heat exchanger (OHE) vaporizes the liquid oxygen using hydrogen as the energy source. The design, concept verification testing and analysis for such a heat exchanger is discussed. The design presented uses a high efficiency compact core to vaporize the oxygen, and in the self-contained unit, attenuates any pressure and flow oscillations which result from unstable boiling in the core. This approach is referred to as the high heat transfer design. An alternative approach which prevents unstable boiling of the oxygen by limiting the heat transfer is referred to as the low heat transfer design and is reported in Pratt & Whitney report FR-19135-2.

  10. Experimental research on heat transfer of pulsating heat pipe

    Institute of Scientific and Technical Information of China (English)

    LI Jia; Yan Li

    2008-01-01

    Experimental research was conducted to understand heat transfer characteristic of pulsating heat pipe in this paper,and the PHP is made of high quality glass capillary tube. Under different fill ratio, heat transfer rate and many other influence factors, the flow patterns were observed in the start-up, transition and stable stage. The effects of heating position on heat transfer were discussed. The experimental results indicate that no annular flow appears in top heating condition. Under different fill ratios and heat transfer rate, the flow pattern in PHP is transferred from bulk flow to semi-annular flow and annular flow, and the performance of heat transfer is improved for down heating case. The experimental results indicate that the total heat resistant of PHP is increased with fill ratio, and heat transfer rate achieves optimum at filling rate 50%. But for pulsating heat pipe with changing diameters the thermal resistance is higher than that with uniform diameters.

  11. A Mini-channel Heat Exchanger System for Heating, Boiling, and Superheating Water by Radiant Combustion

    Science.gov (United States)

    2007-11-02

    location ( Incropera and DeWitt, 1990; Walas, 1990). Experimental Procedures Experiments were initiated by starting the metering pumps, starting data...0.05*Re* DH ( Incropera and DeWitt, 1990). For the lowest flow rate, the Exh-HX entrance length was xenter = 0.05 * 400 * 0.14 cm = 2.8 cm. For...34 Transactions JSME, Series B, Vol.63, No.6, pp. 871-879, AD 1998. Incropera Frank P. and David P. DeWitt, Fundamentals of Heat and Mass Transfer, 3rd Ed

  12. Heat transfer enhancement accompanying Leidenfrost state suppression at ultrahigh temperatures.

    Science.gov (United States)

    Shahriari, Arjang; Wurz, Jillian; Bahadur, Vaibhav

    2014-10-14

    The well-known Leidenfrost effect is the formation of a vapor layer between a liquid and an underlying hot surface. This insulating vapor layer severely degrades heat transfer and results in surface dryout. We measure the heat transfer enhancement and dryout prevention benefits accompanying electrostatic suppression of the Leidenfrost state. Interfacial electric fields in the vapor layer can attract liquid toward the surface and promote wetting. This principle can suppress dryout even at ultrahigh temperatures exceeding 500 °C, which is more than 8 times the Leidenfrost superheat for organic solvents. Robust Leidenfrost state suppression is observed for a variety of liquids, ranging from low electrical conductivity organic solvents to electrically conducting salt solutions. Elimination of the vapor layer increases heat dissipation capacity by more than 1 order of magnitude. Heat removal capacities exceeding 500 W/cm(2) are measured, which is 5 times the critical heat flux (CHF) of water on common engineering surfaces. Furthermore, the heat transfer rate can be electrically controlled by the applied voltage. The underlying science is explained via a multiphysics analytical model which captures the coupled electrostatic-fluid-thermal transport phenomena underlying electrostatic Leidenfrost state suppression. Overall, this work uncovers the physics underlying dryout prevention and demonstrates electrically tunable boiling heat transfer with ultralow power consumption.

  13. Helium I heat transfer in a small natural circulation loop with self-sustaining recondensation

    Science.gov (United States)

    Song, Yu; Four, Aurélien; Baudouy, Bertrand

    2014-01-01

    Heat transfer of helium I in a natural circulation loop is experimentally studied around atmospheric pressure. The test section of the loop has an inner diameter of 4 mm and a height of 23 cm and can be uniformly heated by wire heater. On top of the loop, a condenser is mounted and thermally connected to the second-stage of a 1.5 W at 4.2 K GM cryocooler. Helium can be recondensed in the condenser, where the pressure is regulated around the atmospheric pressure. While the dissipated heat flux is increased from 0 to 1 W, one encounters the different heat transfer regimes as single phase liquid convection, two phase nucleate boiling and single phase vapor convection. The wall superheat varies up to 11 K in the single phase vapor convection regime. The wall temperature measurement allows obtaining the boiling curve and determining the heat transfer coefficient.

  14. Flow and heat transfer characteristics of magnetic nanofluids: A review

    Energy Technology Data Exchange (ETDEWEB)

    Bahiraei, Mehdi, E-mail: m.bahiraei@kut.ac.ir [Mechanical Engineering Department, School of Energy, Kermanshah University of Technology, Kermanshah (Iran, Islamic Republic of); Hangi, Morteza [School of Mechanical Engineering, Iran University of Science and Technology, Tehran (Iran, Islamic Republic of)

    2015-01-15

    Magnetic nanofluids (MNFs) are suspensions which are comprised of a non-magnetic base fluid and magnetic nanoparticles. In this modern set of suspensions which can be called smart or functional fluids, fluid flow, particles movement and heat transfer process can be controlled by applying magnetic fields. Regarding unique characteristics of MNFs, studies in this field have witnessed a phenomenal growth. This paper reviews and summarizes recent investigations implemented on MNFs including those conducted on thermophysical properties, natural convection, forced convection, boiling as well as their practical applications. Moreover, this review identifies the challenges and opportunities for future research. - Highlights: • A review on recent studies on magnetic nanofluids in the field of thermal engineering. • Different categories such as properties, natural and forced convection, and boiling. • Practical applications of magnetic nanofluids in the field of thermal engineering. • Identifying the challenges and opportunities for future research.

  15. Experimental Study on the Thermal Stratification in a Pool Boiling with a Horizontal Heat Source

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Seok; Ryu, Sung Uk; Euh, Dong-Jin; Song, Chul-Hwa [KAERI, Daejeon (Korea, Republic of)

    2015-05-15

    Thermal stratification is formed in horizontal fluid layers with different temperatures, where the warmer fluid layers are situated above the cooler fluid layers. Thermal stratification phenomena are common in pool type reactor systems, such as the liquid-salt cooled advanced high temperature reactor (AHTR) and liquid-metal cooled fast reactor systems such as the sodium fast reactor (SFR). Thermal stratification is increasingly encountered in large pools that are being used as heat sinks in the new generation of advanced reactors. The small-scale pool test was conducted to investigate the thermal stratification phenomena that occurred during the heat-up of a water in a pool. Because turbulence and boiling models affect the natural convection significantly, it is important to obtain local information regarding the fluid velocity and void distribution to determine the relevant physical models. To understand the flow phenomena inside a pool, a non-intrusive technique is adopted to measure the flow velocity field. In this study, the 2D particle image velocimetry (PIV) measurement technique is used to determine the fluid velocity vector field of single- and/or two-phase natural convection flow and thermal stratification in a pool. Detailed velocity measurements using the 2D PIV measurement technique were conducted to investigate single- and/or two-phase natural convection flow and thermal stratification in a pool boiling. In this study, the two-dimensional velocity vector fields as the water temperature increased were experimentally acquired in a pool that contained a horizontal heater rod. The experimental results indicate a large natural convection flow at the region above the heater rod and thermal stratification at the region below the heater rod. The flow of the opposite direction to each other was shown in the region between the heater rod and the thermal boundary layer. This flow pattern will contribute to maintain the thermal stratification and retard the water

  16. Influence of the heater material on the critical heat load at boiling of liquids on surfaces with different sizes

    Science.gov (United States)

    Anokhina, E. V.

    2010-05-01

    Data on critical heat loads q cr for the saturated and unsaturated pool boiling of water and ethanol under atmospheric pressure are reported. It is found experimentally that the critical heat load does not necessarily coincide with the heat load causing burnout of the heater, which should be taken into account. The absolute values of q cr for the boiling of water and ethanol on copper surfaces 65, 80, 100, 120, and 200 μm in diameter; tungsten surface 100 μm in diameter; and nichrome surface 100 μm in diameter are obtained experimentally.

  17. Enhancement of Boiling Heat Transfer in Di-Electric Fluids

    Science.gov (United States)

    1991-09-01

    solid state thermoelectric cooling devices from the MELCOR corp were employed to cool the cover plate condensor. They w ’re nom- inally operated about...Postgraduate School, Monterey, California, March 1991. 12. Materials Electronic Products Corporation, MELCOR FRIGICHIPS Product Manual, Thermoelectric

  18. Transient Heat Transfer in Cylinpers.

    Directory of Open Access Journals (Sweden)

    M.G. Chopra

    2000-07-01

    Full Text Available A numerical solution has been obtained for transient heat transfer in cylinders by appropriate choice of body ,conforming grid points. The physical domain is transformed to computational domain using elliptic partial differential equation technique, wherein the grid spacing becomes uniform. The advantage of this method is that the discretisation of transformed equations. and accompanying boundary conditipns becdme very simple. The applicability of this method is very broad, as it can beused for carryinI giout study of any comple'x domain in contrast to finite difference methods, which have limited applicability. Detailedcalculations have been carried out to trace the evolution of temperaturedistribution frpm the initiial stages to the steadystate for circular cylinder, elliptical cylinder and square block with circular hole. This paper is aimed for general-shaped bodies and it has been applied to studytransient heat transfer in combustion-driven shock tube.

  19. Influence of Pressure on Stable Film Boiling of Subcooled Liquid

    Science.gov (United States)

    Zabirov, A. R.; Yagov, V. V.; Kaban'kov, O. N.; Leksin, M. A.; Kanin, P. K.

    2016-11-01

    Film boiling of subcooled liquids is an integral part of the hardening process. Understanding of the mechanisms underlying film boiling is important for modeling processes in atomic power engineering and cryogenic technology. Stationary processes of film boiling of subcooled liquids under conditions of their free motion near cylindrical heaters, just as subcooled liquid turbulent flow past high-temperature surfaces, represent quite a different type of process. In cooling metal spheres heated to a high temperature by a subcooled water, a special regime of film boiling is observed (microbubble boiling) distinguished by high intensity of heat transfer. Such a regime has not been revealed up to now for nonaqueous liquids. The paper presents new experimental data on heat transfer regimes in cooling nickel spheres in subcooled isopropanol and perfluorohexane at pressures of up to 1 MPa. It has been established that stable film boiling is the main regime of heat transfer that accounts for the larger part of the total time of cooling. The regimes of highly intensive film boiling heat transfer were not observed in the entire range of operational parameters even in the case of extreme subcoolings of liquid below their saturation temperature (to 170 K). The intensity of heat transfer in stable film boiling increases noticeably with subcooling of a chilling liquid.

  20. Experimental Study on Behavior of Bubbles and Heat transfer by Using Heat Transfer Surface with Artificial Cavities Created by MEMS Technology

    Science.gov (United States)

    Sato, Takato; Koizumi, Yasuo; Ohtake, Hiroyasu

    Pool nucleate boiling heat transfer experiments were performed for water using heat transfer surfaces having unified cavities. Cylindrical holes of 10 μm in diameter and 40 μm in depth were formed on a mirror-finished silicon wafer of 0.2 mm in thickness using Micro-Electro Mechanical Systems (MEMS) technology. This silicon plate was used as the heat transfer surface. The test heat transfer surface was heated by a semiconductor laser beam. Experiments were conducted in the range of up to 1.35 × 105 W⁄m2. When a single cavity was formed, the vertical coalescence of bubbles above the cavity was 60 % and no coalescence was 40 %. The ratios of the convection and the phase change were 80 % and 20 %, respectively. When the number of cavities were increased to three, the coalescence of bubbles on the heat transfer surface became important. When the role of the convection and the phase change in nucleate boiling is considered, it is appropriate to examine the bubble departure from the vapor mass on the heat transfer surface not from cavities.

  1. Heat transfer enhancement by pin elements

    Energy Technology Data Exchange (ETDEWEB)

    Sahiti, N.; Durst, F.; Dewan, A. [LSTM-Erlangen, Institute of Fluid Mechanics, Friedrich-Alexander-Universitaet Erlangen-Nuernberg, Cauerstrasse 4, D-91058 Erlangen (Germany)

    2005-11-01

    Heat transfer enhancement is an active and important field of engineering research since increases in the effectiveness of heat exchangers through suitable heat transfer augmentation techniques can result in considerable technical advantages and savings of costs. Considerable enhancements were demonstrated in the present work by using small cylindrical pins on surfaces of heat exchangers. A partly quantitative theoretical treatment of the proposed method is presented. It uses simple relationships for the conductive and convective heat transfer to derive an equation that shows which parameters permit the achievement of heat transfer enhancements. Experiments are reported that demonstrate the effectiveness of the results of the proposed approach. It is shown that the suggested method of heat transfer enhancements is much more effective than existing methods, since it results in an increase in heat transfer area (like fins) and also an increase in the heat transfer coefficient. (author)

  2. Utilization of heat pipes for transfer heat from the flue gas into the heat transfer medium

    Directory of Open Access Journals (Sweden)

    Lenhard Richard

    2014-03-01

    Full Text Available The contribution is listed possible application of heat pipes in systems for obtaining heat from flue gas of small heat sources. It is also stated in the contribution design an experimental device on which to study the impact of fill (the quantity, type of load at various temperature parameters (temperature heating and cooling thermal power transferred to the heat pipe. Is listed measurement methodology using heat pipes designed experimental facility, measurement results and analysis of the results obtained.

  3. Liquid neon heat transfer as applied to a 30 tesla cryomagnet

    Science.gov (United States)

    Papell, S. S.; Hendricks, R. C.

    1975-01-01

    Since superconducting magnets cooled by liquid helium are limited to magnetic fields of about 18 teslas, the design of a 30 tesla cryomagnet necessitates forced convection liquid neon heat transfer in small coolant channels. As these channels are too small to handle the vapor flow if the coolant were to boil, the design philosophy calls for suppressing boiling by subjecting the fluid to high pressures. Forced convection heat transfer data are obtained by using a blowdown technique to force the fluid vertically through a resistance-heated instrumented tube. The data are obtained at inlet temperatures between 28 and 34 K and system pressures between 28 to 29 bars. Data correlation is limited to a very narrow range of test conditions, since the tests were designed to simulate the heat transfer characteristics in the coolant channels of the 30 tesla cryomagnet concerned. The results can therefore be applied directly to the design of the magnet system.-

  4. NASA Physical Sciences - Presentation to Annual Two Phase Heat Transfer International Topical Team Meeting

    Science.gov (United States)

    Chiaramonte, Francis; Motil, Brian; McQuillen, John

    2014-01-01

    The Two-phase Heat Transfer International Topical Team consists of researchers and members from various space agencies including ESA, JAXA, CSA, and RSA. This presentation included descriptions various fluid experiments either being conducted by or planned by NASA for the International Space Station in the areas of two-phase flow, flow boiling, capillary flow, and crygenic fluid storage.

  5. Design Model for the Heat Transfer in a Short Straight Tube Boiler.

    Science.gov (United States)

    1981-06-01

    in vertical upflow for Re򒾐. Water properties are evaluated at the film tempera- ture; Prw, at the wall temperature. The work done by Sieder and...Boiling and Condensation, McGraw-Hill Book Co., New York, 1972. 16. Sieder , E.N., and Tate, C.E., Heat Transfer and Pressure Drop of Liquids in Tubes, Inc

  6. Prediction of Critical Heat Flux for Saturated Flow Boiling Water in Vertical Narrow Rectangular Channels

    Energy Technology Data Exchange (ETDEWEB)

    Choi, Gil Sik; Jeong, Yong Hun [KAIST, Daejeon (Korea, Republic of); Chang, Soon Heung [Handong Univ., Pohang (Korea, Republic of)

    2015-12-15

    There is an increasing need to understand the thermal-hydraulic phenomena, including the critical heat flux (CHF), in narrow rectangular channels and consider these in system design. The CHF mechanism under a saturated flow boiling condition involves the depletion of the liquid film of an annular flow. To predict this type of CHF, the previous representative liquid film dryout models (LFD models) were studied, and their shortcomings were reviewed, including the assumption that void fraction or quality is constant at the boundary condition for the onset of annular flow (OAF). A new LFD model was proposed based on the recent constitutive correlations for the droplet deposition rate and entrainment rate. In addition, this LFD model was applied to predict the CHF in vertical narrow rectangular channels that were uniformly heated. The predicted CHF showed good agreement with 284 pieces of experimental data, with a mean absolute error of 18. 1 % and root mean square error of 22.9 %.

  7. Heat transfer in the Knudsen layer

    Science.gov (United States)

    Sharipov, Felix

    2004-06-01

    A concept of the surface heat conductivity determining a heat transfer in the Knudsen layer was introduced. It has the same order with respect to the Knudsen number as the bulk heat transfer and must be taken into account in practical calculations. Using the Onsager principle the coefficient of the surface heat conductivity was related to the thermal slip coefficient.

  8. Heat Transfer in a Thermoacoustic Process

    Science.gov (United States)

    Beke, Tamas

    2012-01-01

    Thermoacoustic instability is defined as the excitation of acoustic modes in chambers with heat sources due to the coupling between acoustic perturbations and unsteady heat addition. The major objective of this paper is to achieve accurate theoretical results in a thermoacoustic heat transfer process. We carry out a detailed heat transfer analysis…

  9. Heat transfer and critical heat flux in a asymmetrically heated tube helicoidal flow; Transfert thermique et flux critique dans un ecoulement helicoidal en tube chauffe asymetriquement

    Energy Technology Data Exchange (ETDEWEB)

    Boscary, J.

    1995-10-01

    The design of plasma facing components is crucial for plasma performance in next fusion reactors. These elements will be submitted to very high heat flux. They will be actively water-cooled by swirl tubes in the subcooled boiling regime. High heat flux experiments were conducted in order to analyse the heat transfer and to evaluate the critical heat flux. Water-cooled mock-ups were one-side heated by an electron beam gun for different thermal-hydraulic conditions. The critical heat flux was detected by an original method based on the isotherm modification on the heated surface. The wall heat transfer law including forced convection and subcooled boiling regimes was established. Numerical calculations of the material heat transfer conduction allowed the non-homogeneous distribution of the wall temperature and of the wall heat flux to be evaluated. The critical heat flux value was defined as the wall maximum heat flux. A critical heat flux model based on the liquid sublayer dryout under a vapor blanket was established. A good agreement with test results was found. (author). 198 refs., 126 figs., 21 tabs.

  10. Heat transfer and critical heat flux in a spiral flow in an asymmetrical heated tube; Transfert thermique et flux critique dans un ecoulement helicoidal en tube chauffe asymetriquement

    Energy Technology Data Exchange (ETDEWEB)

    Boscary, J. [CEA Centre d`Etudes de Cadarache, 13 - Saint-Paul-lez-Durance (France). Direction des Sciences de la Matiere]|[Association Euratom-CEA, Centre d`Etudes Nucleaires de Cadarache, 13 - Saint-Paul-lez-Durance (France). Dept. de Recherches sur la Fusion Controlee

    1997-03-01

    The design of plasma facing components is crucial for plasma performance in next fusion reactors. These elements will be submitted to very high heat flux. They will be actively water-cooled by swirl tubes in the subcooled boiling regime. High heat flux experiments were conducted in order to analyse the heat transfer and to evaluate the critical heat flux. Water-cooled mock-ups were one-side heated by an electron beam gun for different thermal-hydraulic conditions. The critical heat flux was detected by an original method based on the isotherm modification on the heated surface. The wall heat transfer law including forced convection and subcooled boiling regimes was established. Numerical calculations of the material heat transfer conduction allowed the non-homogeneous distribution of the wall temperature and of the wall heat flux to be evaluated. The critical heat flux value was defined as the wall maximum heat flux. A critical heat flux model based on the liquid sublayer dryout under a vapor blanket was established. A good agreement with test results was found. (author) 197 refs.

  11. Vaporization heat transfer of dielectric liquids on a wick-covered surface

    Science.gov (United States)

    Gu, C. B.; Chow, L. C.; Baker, K.

    1993-01-01

    Vaporization heat transfer characteristics were measured for the dielectric liquid FC-72 on a horizontal heated surface covered with wire screen wicks with the mesh number for the screens varying from 24 to 100. In such a situation the liquid level can be either higher or lower than the heated surface. When the liquid level was above the heated surface (shallow pool boiling), the height of the liquid level above the surface, h, was varied from 0 to 10 mm. When the liquid level was below the heated surface (evaporation through capillary pumping), the distance from the liquid level to the edge of the surface, L, was adjusted from 0 to 15 mm. Experimental data revealed that the critical heat flux (CHF) decreases as the mesh number is increased from 24 to 100 for both vaporation and shallow pool boiling, showing that the vapor-escaping limit is more important than the capillary limit in flat plate heat pipe application.

  12. Mechanical design and fabrication of a heat exchanger. Report of the design and construction of a heat exchanger which will be used in 'Experimental analysis of heat transfer in the boiling in forced convection; Diseno mecanico y fabricacion de un intercambiador de calor. Reporte del diseno y construccion de un intercambiador de calor que sera usado en 'Analisis experimental de transferencia de calor en la ebullicion en conveccion forzada

    Energy Technology Data Exchange (ETDEWEB)

    Mariano H, E

    1991-08-15

    To continue with the equipment of the thermal hydraulics laboratory, it was designed thermal and mechanically an heat exchanger, to satisfy the requirements to have circuit that allows to carry out heat transfer experiments. The heat exchanger was manufactured and proven in the workshops of the Prototypes and Models Management, and it is expected that to obtain the foreseen results once completely installed the circuit, in the laboratory of thermal hydraulics of the Management of Nuclear Systems. (Author)

  13. Review of thermo-physical properties, wetting and heat transfer characteristics of nanofluids and their applicability in industrial quench heat treatment.

    Science.gov (United States)

    Ramesh, Gopalan; Prabhu, Narayan Kotekar

    2011-04-14

    The success of quenching process during industrial heat treatment mainly depends on the heat transfer characteristics of the quenching medium. In the case of quenching, the scope for redesigning the system or operational parameters for enhancing the heat transfer is very much limited and the emphasis should be on designing quench media with enhanced heat transfer characteristics. Recent studies on nanofluids have shown that these fluids offer improved wetting and heat transfer characteristics. Further water-based nanofluids are environment friendly as compared to mineral oil quench media. These potential advantages have led to the development of nanofluid-based quench media for heat treatment practices. In this article, thermo-physical properties, wetting and boiling heat transfer characteristics of nanofluids are reviewed and discussed. The unique thermal and heat transfer characteristics of nanofluids would be extremely useful for exploiting them as quench media for industrial heat treatment.

  14. Review of thermo-physical properties, wetting and heat transfer characteristics of nanofluids and their applicability in industrial quench heat treatment

    Directory of Open Access Journals (Sweden)

    Ramesh Gopalan

    2011-01-01

    Full Text Available Abstract The success of quenching process during industrial heat treatment mainly depends on the heat transfer characteristics of the quenching medium. In the case of quenching, the scope for redesigning the system or operational parameters for enhancing the heat transfer is very much limited and the emphasis should be on designing quench media with enhanced heat transfer characteristics. Recent studies on nanofluids have shown that these fluids offer improved wetting and heat transfer characteristics. Further water-based nanofluids are environment friendly as compared to mineral oil quench media. These potential advantages have led to the development of nanofluid-based quench media for heat treatment practices. In this article, thermo-physical properties, wetting and boiling heat transfer characteristics of nanofluids are reviewed and discussed. The unique thermal and heat transfer characteristics of nanofluids would be extremely useful for exploiting them as quench media for industrial heat treatment.

  15. Flow and Heat Transfer Characteristics in a Closed-Type Two-Phase Loop Thermosyphon

    Science.gov (United States)

    Imura, Hideaki; Saito, Yuji; Fujimoto, Hiromitsu

    A closed-loop two-phase thermosyphon can transport a large amount of thermal energy with small temperature differences without any external power supply. A fundamental investigation of flow and heat transfer characteristics was performed experimentally and theoretically using water, ethanol and R113 as the working liquids. Heat transfer coefficients in an evaporator and a condenser, and circulation flow rates were measured experimentally. The effects of liquid fill charge, rotation angle, pressure in the loop and heat flux on the heat transfer coefficients were examined. The heat transfer coefficients in the evaporator and the condenser were correlated by the expressions for pool boiling and film condensation respectively. As a result, the heat transfer coefficients in the evaporator were correlated by the Stephan-Abdelsalam equations within a±40% error. Theoretically, the circulation flow rate was predicted by calculating pressure, temperature, quality and void fraction along the loop. And, the comparison between the calculated and experimental results was made.

  16. Experimental investigation on Heat Transfer Performance of Annular Flow Path Heat Pipe

    Energy Technology Data Exchange (ETDEWEB)

    Kim, In Guk; Kim, Kyung Mo; Jeong, Yeong Shin; Bang, In Cheol [UNIST, Ulsan (Korea, Republic of)

    2015-05-15

    Mochizuki et al. was suggested the passive cooling system to spent nuclear fuel pool. Detail analysis of various heat pipe design cases was studied to determine the heat pipes cooling performance. Wang et al. suggested the concept PRHRS of MSR using sodium heat pipes, and the transient performance of high temperature sodium heat pipe was numerically simulated in the case of MSR accident. The meltdown at the Fukushima Daiichi nuclear power plants alarmed to the dangers of station blackout (SBO) accident. After the SBO accident, passive decay heat removal systems have been investigated to prevent the severe accidents. Mochizuki et al. suggested the heat pipes cooling system using loop heat pipes for decay heat removal cooling and analysis of heat pipe thermal resistance for boiling water reactor (BWR). The decay heat removal systems for pressurized water reactor (PWR) were suggested using natural convection mechanisms and modification of PWR design. Our group suggested the concept of a hybrid heat pipe with control rod as Passive IN-core Cooling System (PINCs) for decay heat removal for advanced nuclear power plant. Hybrid heat pipe is the combination of the heat pipe and control rod. In the present research, the main objective is to investigate the effect of the inner structure to the heat transfer performance of heat pipe containing neutron absorber material, B{sub 4}C. The main objective is to investigate the effect of the inner structure in heat pipe to the heat transfer performance with annular flow path. ABS pellet was used instead of B{sub 4}C pellet as cylindrical structures. The thermal performances of each heat pipes were measured experimentally. Among them, concentric heat pipe showed the best performance compared with others. 1. Annular evaporation section heat pipe and annular flow path heat pipe showed heat transfer degradation. 2. AHP also had annular vapor space and contact cooling surface per unit volume of vapor was increased. Heat transfer

  17. Experimental investigation on heat transfer of a single droplet during collision with a heated wall above Leidenfrost temperature

    Energy Technology Data Exchange (ETDEWEB)

    Park, Junseok; Kim, Hyungdae [Kyung Hee University, Seoul (Korea, Republic of)

    2015-10-15

    The correlation was derived based on the mechanistic model of Baumeister4 for film boiling heat transfer coefficient of a Leidenfrost droplet floated on a heated surface. The model was formulated only with the physical parameters of the stationary droplet while the droplet collision heat transfer phenomenon is very dynamic. Therefore, it is needed to improve the existing prediction correlation for droplet-wall collision heat transfer by incorporating dynamic characteristics of collision droplets into heat transfer coefficient model. In this study, effects of droplet velocity on collision dynamics and heat transfer characteristics during droplet-wall collision beyond the Leidenfrost point were examined using the integrated high-speed visible and infrared (IR) imaging technique. The experimental results obtained from the synchronized HSV and IR measurement could provide a better understanding than the previous existing results because various physical parameters associated with droplet-wall collision dynamics and heat transfer phenomena can be simultaneously obtained and the relation between collision dynamics and local heat transfer characteristics can be examined. This study experimentally investigated the dynamic behavior and heat transfer characteristics of droplet. The tests were conducted using a water droplet with diameter of 2 mm at atmospheric pressure. Droplet with velocity in the range from 0.2 to 1.5 collided with heated wall.

  18. Shock-induced heating and millisecond boiling in gels and tissue due to high intensity focused ultrasound.

    Science.gov (United States)

    Canney, Michael S; Khokhlova, Vera A; Bessonova, Olga V; Bailey, Michael R; Crum, Lawrence A

    2010-02-01

    Nonlinear propagation causes high-intensity ultrasound waves to distort and generate higher harmonics, which are more readily absorbed and converted to heat than the fundamental frequency. Although such nonlinear effects have been investigated previously and found to not significantly alter high-intensity focused ultrasound (HIFU) treatments, two results reported here change this paradigm. One is that at clinically relevant intensity levels, HIFU waves not only become distorted but form shock waves in tissue. The other is that the generated shock waves heat the tissue to boiling in much less time than predicted for undistorted or weakly distorted waves. In this study, a 2-MHz HIFU source operating at peak intensities up to 25,000 W/cm(2) was used to heat transparent tissue-mimicking phantoms and ex vivo bovine liver samples. Initiation of boiling was detected using high-speed photography, a 20-MHz passive cavitation detector and fluctuation of the drive voltage at the HIFU source. The time to boil obtained experimentally was used to quantify heating rates and was compared with calculations using weak shock theory and the shock amplitudes obtained from nonlinear modeling and measurements with a fiber optic hydrophone. As observed experimentally and predicted by calculations, shocked focal waveforms produced boiling in as little as 3 ms and the time to initiate boiling was sensitive to small changes in HIFU output. Nonlinear heating as a result of shock waves is therefore important to HIFU, and clinicians should be aware of the potential for very rapid boiling because it alters treatments.

  19. Oscillate boiling from microheaters

    Science.gov (United States)

    Li, Fenfang; Gonzalez-Avila, S. Roberto; Nguyen, Dang Minh; Ohl, Claus-Dieter

    2017-01-01

    We report about an intriguing boiling regime occurring for small heaters embedded on the boundary in subcooled water. The microheater is realized by focusing a continuous wave laser beam to about 10 μ m in diameter onto a 165-nm-thick layer of gold, which is submerged in water. After an initial vaporous explosion a single bubble oscillates continuously and repeatedly at several 100 kHz albeit with constant laser power input. The microbubble's oscillations are accompanied with bubble pinch-off, leading to a stream of gaseous bubbles in the subcooled water. The self-driven bubble oscillation is explained with a thermally kicked oscillator caused by surface attachment and by the nonspherical collapses. Additionally, Marangoni stresses induce a recirculating streaming flow which transports cold liquid towards the microheater, reducing diffusion of heat along the substrate and therefore stabilizing the phenomenon to many million cycles. We speculate that this oscillate boiling regime may overcome the heat transfer thresholds observed during the nucleate boiling crisis and offers a new pathway for heat transfer under microgravity conditions.

  20. Boiling in porous media; Ebullition en milieux poreux

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    1998-03-11

    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.)

  1. Heat Transfer in Complex Fluids

    Energy Technology Data Exchange (ETDEWEB)

    Mehrdad Massoudi

    2012-01-01

    fluids show Newtonian (linear) behavior for a given range of parameters or geometries; there are many empirical or semi-empirical constitutive equations suggested for these fluids. There have also been many non-linear constitutive relations which have been derived based on the techniques of continuum mechanics. The non-linearities oftentimes appear due to higher gradient terms or time derivatives. When thermal and or chemical effects are also important, the (coupled) momentum and energy equations can give rise to a variety of interesting problems, such as instability, for example the phenomenon of double-diffusive convection in a fluid layer. In Conclusion, we have studied the flow of a compressible (density gradient type) non-linear fluid down an inclined plane, subject to radiation boundary condition. The heat transfer is also considered where a source term, similar to the Arrhenius type reaction, is included. The non-dimensional forms of the equations are solved numerically and the competing effects of conduction, dissipation, heat generation and radiation are discussed. It is observed that the velocity increases rapidly in the region near the inclined surface and is slower in the region near the free surface. Since R{sub 7} is a measure of the heat generation due to chemical reaction, when the reaction is frozen (R{sub 7}=0.0) the temperature distributions would depend only on R{sub 1}, and R{sub 2}, representing the effects of the pressure force developed in the material due to the distribution, R{sub 3} and R{sub 4} viscous dissipation, R{sub 5} the normal stress coefficient, R{sub 6} the measure of the emissivity of the particles to the thermal conductivity, etc. When the flow is not frozen (RP{sub 7} > 0) the temperature inside the flow domain is much higher than those at the inclined and free surfaces. As a result, heat is transferred away from the flow toward both the inclined surface and the free surface with a rate that increases as R{sub 7} increases. For a

  2. Engineering calculations in radiative heat transfer

    CERN Document Server

    Gray, W A; Hopkins, D W

    1974-01-01

    Engineering Calculations in Radiative Heat Transfer is a six-chapter book that first explains the basic principles of thermal radiation and direct radiative transfer. Total exchange of radiation within an enclosure containing an absorbing or non-absorbing medium is then described. Subsequent chapters detail the radiative heat transfer applications and measurement of radiation and temperature.

  3. Boiling water reactor in a prestressed reinforced concrete vessel for an atomic central heating-and-power plant

    Energy Technology Data Exchange (ETDEWEB)

    Tokarev, Yu.I.; Sokolov, I.N.; Skvortsov, S.A.; Sidorov, A.M.; Krauze, L.V.

    1978-04-01

    The possibility of using a boiling water reactor in a prestressed reinforced concrete vessel for an atomic central heating-and-power plant (CHPP) was considered, with design features of the reactor intended for a two-purpose plant. A prestressed reinforced concrete vessel and integral arrangement of the primary circuit ensured reliability of the atomic CHPP using various CHPP flowsheets.

  4. Change of heat transfer- and mass transfer-coefficients with simultaneous heat- and mass transfer

    Energy Technology Data Exchange (ETDEWEB)

    Kast, W.

    1981-01-01

    The values of sensible and latent heat and of the resulting energy flow through laminar boundary layer have been developed for the four possible combinations of the directions of heat- and mass flows. When the values of heat- and mass flows are used with the correct sign according to the definitions of Fourier's law and Fick's law, the changes of heat transfer- and mass transfer coefficients can be described by one equation alone for all cases. The equations extended in that way are valid for arbitrary cases of countercurrent diffusing mass flows - not only for the well known case of Stefan diffusion.

  5. Heat transfer performance of a pulsating heat pipe charged with acetone-based mixtures

    Science.gov (United States)

    Wang, Wenqing; Cui, Xiaoyu; Zhu, Yue

    2016-12-01

    Pulsating heat pipes (PHPs) are used as high efficiency heat exchangers, and the selection of working fluids in PHPs has a great impact on the heat transfer performance. This study investigates the thermal resistance characteristics of the PHP charged with acetone-based binary mixtures, where deionized water, methanol and ethanol were added to and mixed with acetone, respectively. The volume mixing ratios were 2:1, 4:1 and 7:1, and the heating power ranged from 10 to 100 W with filling ratios of 45, 55, 62 and 70%. At a low filling ratio (45%), the zeotropic characteristics of the binary mixtures have an influence on the heat transfer performance of the PHP. Adding water, which has a substantially different boiling point compared with that of acetone, can significantly improve the anti-dry-out ability inside the PHP. At a medium filling ratio (55%), the heat transfer performance of the PHP is affected by both phase transition characteristics and physical properties of working fluids. At high heating power, the thermal resistance of the PHP with acetone-water mixture is between that with pure acetone and pure water, whereas the thermal resistance of the PHP with acetone-methanol and acetone-ethanol mixtures at mixing ratios of 2:1 and 4:1 is less than that with the corresponding pure fluids. At high filling ratios (62 and 70%), the heat transfer performance of the PHP is mainly determined by the properties of working fluids that affects the flow resistance. Thus, the PHP with acetone-methanol and acetone-ethanol mixtures that have a lower flow resistance shows better heat transfer performance than that with acetone-water mixture.

  6. Heat and mass transfer in particulate suspensions

    CERN Document Server

    Michaelides, Efstathios E (Stathis)

    2013-01-01

    Heat and Mass Transfer in Particulate Suspensions is a critical review of the subject of heat and mass transfer related to particulate Suspensions, which include both fluid-particles and fluid-droplet Suspensions. Fundamentals, recent advances and industrial applications are examined. The subject of particulate heat and mass transfer is currently driven by two significant applications: energy transformations –primarily combustion – and heat transfer equipment. The first includes particle and droplet combustion processes in engineering Suspensions as diverse as the Fluidized Bed Reactors (FBR’s) and Internal Combustion Engines (ICE’s). On the heat transfer side, cooling with nanofluids, which include nanoparticles, has attracted a great deal of attention in the last decade both from the fundamental and the applied side and has produced several scientific publications. A monograph that combines the fundamentals of heat transfer with particulates as well as the modern applications of the subject would be...

  7. Vaporization heat transfer of dielectric liquids on enhanced surfaces covered with screen wicks

    Science.gov (United States)

    Gu, C. B.; Chow, L. C.; Pais, M. R.; Baker, K.

    1993-01-01

    Experiments were conducted to investigate the vaporization heat transfer characteristics for the dielectric liquid FC-72 on several wicking surfaces which may be used in flat-plate heat pipes. The wicking materials studied included microstructure enhanced surfaces and coarse surfaces covered with screen meshes. Experimental data for q versus deltaT curves and critical heat fluxes were obtained for the two different operating conditions of a heat pipe, evaporation, and shallow pool boiling. When the liquid level was above the heated surface, the height of the liquid level above the surface was varied from 0 to 10 mm. When the liquid level was below the heated surface, the distance from the liquid level to the edge of the surface was adjusted from 0 to 15 mm. Experimental results revealed that for shallow pool boiling when the heated surface was covered with a wire screen mesh, the heat transfer coefficient increased at lower heat fluxes but the critical heat flux (CHF) decreased for all the surfaces tested. In the case of evaporation, both CHF and the heat transfer coefficient increased as the microstructure surfaces were covered with screen meshes.

  8. Heat transfer in porous media

    Directory of Open Access Journals (Sweden)

    N. Amanifard

    2007-06-01

    Full Text Available In this work, the effects of electrical double layer (EDL near the solid/ liquid interface, on three dimensional heat transfer characteristic and pressure drop of water flow through a rectangular microchannel numerically are investigated. An additional body force originating from the existence of EDL is considered to modify the conventional Navier-stokes and energy equations. These modified equations are solved numerically for steady laminar flow on the basis of control volume approaches. Fluid velocity distribution and temperature with presence and absence of EDL effects are presented for various geometric cases and different boundary conditions. The results illustrate that, the liquid flow in rectangular microchannels is influenced significantly by the EDL, particularly in the high electric potentials, and hence deviates from flow characteristics described by classical fluid mechanics.

  9. Heat Transfer in Gas Turbines

    Science.gov (United States)

    Garg, Vijay K.

    2001-01-01

    The turbine gas path is a very complex flow field. This is due to a variety of flow and heat transfer phenomena encountered in turbine passages. This manuscript provides an overview of the current work in this field at the NASA Glenn Research Center. Also, based on the author's preference, more emphasis is on the computational work. There is much more experimental work in progress at GRC than that reported here. While much has been achieved, more needs to be done in terms of validating the predictions against experimental data. More experimental data, especially on film cooled and rough turbine blades, are required for code validation. Also, the combined film cooling and internal cooling flow computation for a real blade is yet to be performed. While most computational work to date has assumed steady state conditions, the flow is clearly unsteady due to the presence of wakes. All this points to a long road ahead. However, we are well on course.

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

    Science.gov (United States)

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

    2016-09-01

    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 7oC. 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.

  11. Thermal Regulation of Heat Transfer Processes

    Science.gov (United States)

    2014-10-02

    be approximately 320 m2g-1, 32 times higher than graphite flakes for more efficient heat transfer to the fluid. The evaporation rates of water...AFRL-OSR-VA-TR-2014-0249 THERMAL REGULATION OF HEAT TRANSFER PROCESSES GANG CHEN MASSACHUSETTS INSTITUTE OF TECHNOLOGY Final Report 10/02/2014...Prescribed by ANSI Std. Z39.18 FINAL REPORT FOR FA9550-11-1-0174 THERMAL REGULATION OF HEAT TRANSFER PROCESSES Principal Investigator: Gang Chen

  12. Radiative heat transfer between metallic nanoparticles

    OpenAIRE

    Chapuis, Pierre-Olivier; Laroche, Marine; Volz, Sebastian; Greffet, Jean-Jacques

    2008-01-01

    International audience; In this letter, we study the radiative heat transfer between two nanoparticles in the near field and in the far field. We find that the heat transfer is dominated by the electric dipole-dipole interaction for dielectric particles and by the magnetic dipole-dipole interaction for metallic nanoparticles. We introduce polarizabilities formulas valid for arbitrary values of the skin depth. While the heat transfer mechanism is different for metallic and dielectric nanoparti...

  13. Finite element simulation of heat transfer

    CERN Document Server

    Bergheau, Jean-Michel

    2010-01-01

    This book introduces the finite element method applied to the resolution of industrial heat transfer problems. Starting from steady conduction, the method is gradually extended to transient regimes, to traditional non-linearities, and to convective phenomena. Coupled problems involving heat transfer are then presented. Three types of couplings are discussed: coupling through boundary conditions (such as radiative heat transfer in cavities), addition of state variables (such as metallurgical phase change), and coupling through partial differential equations (such as electrical phenomena).? A re

  14. Heat-transfer data for hydrogen

    Science.gov (United States)

    Mc Carthy, J. R.; Miller, W. S.; Okuda, A. S.; Seader, J. D.

    1970-01-01

    Information is given regarding experimental heat-transfer data compiled for the turbulent flow of hydrogen within straight, electrically heated, round cross section tubes. Tube materials, test conditions, parameters studied, and generalized conclusions are presented.

  15. The speed of propagation of small vibrations in hydraulic systems with a boiling transfer agent

    Energy Technology Data Exchange (ETDEWEB)

    Proskuryakov, K.N.

    1981-01-01

    Vibration resonance in a steam generation channel is studied. A formula is derived for the calculation of the speed of dispersion of acoustical vibrations in a singular steam generation pipe. Methods are indicated for changing the resonance frequency in the vibrations of the heat transfer agent.

  16. Selection of Rational Heat Transfer Intensifiers in the Heat Exchanger

    Directory of Open Access Journals (Sweden)

    S. A. Burtsev

    2016-01-01

    Full Text Available The paper considers the applicability of different types of heat transfer intensifiers in the heat exchange equipment. A review of the experimental and numerical works devoted to the intensification of the dimpled surface, surfaces with pins and internally ribbed surface were presented and data on the thermal-hydraulic characteristics of these surfaces were given. We obtained variation of thermal-hydraulic efficiency criteria for 4 different objective functions and 15 options for the intensification of heat transfer. This makes it possible to evaluate the advantages of the various heat transfer intensifiers. These equations show influence of thermal and hydraulic characteristics of the heat transfer intensifiers (the values of the relative heat transfer and drag coefficients on the basic parameters of the shell-and-tube heat exchanger: the number and length of the tubes, the volume of the heat exchanger matrix, the coolant velocity in the heat exchanger matrix, coolant flow rate, power to pump coolant (or pressure drop, the amount of heat transferred, as well as the average logarithmic temperature difference. The paper gives an example to compare two promising heat transfer intensifiers in the tubes and shows that choosing the required efficiency criterion to search for optimal heat exchanger geometry is of importance. Analysis is performed to show that a dimpled surface will improve the effectiveness of the heat exchanger despite the relatively small value of the heat transfer intensification, while a significant increase in drag of other heat transfer enhancers negatively affects their thermalhydraulic efficiency. For example, when comparing the target functions of reducing the heat exchanger volume, the data suggest that application of dimpled surfaces in various fields of technology is possible. But there are also certain surfaces that can reduce the parameters of a heat exchanger. It is shown that further work development should be aimed at

  17. Radiative heat transfer in porous uranium dioxide

    Energy Technology Data Exchange (ETDEWEB)

    Hayes, S.L. [Texas A and M Univ., College Station, TX (United States)

    1992-12-01

    Due to low thermal conductivity and high emissivity of UO{sub 2}, it has been suggested that radiative heat transfer may play a significant role in heat transfer through pores of UO{sub 2} fuel. This possibility was computationally investigated and contribution of radiative heat transfer within pores to overall heat transport in porous UO{sub 2} quantified. A repeating unit cell was developed to model approximately a porous UO{sub 2} fuel system, and the heat transfer through unit cells representing a wide variety of fuel conditions was calculated using a finite element computer program. Conduction through solid fuel matrix as wekk as pore gas, and radiative exchange at pore surface was incorporated. A variety of pore compositions were investigated: porosity, pore size, shape and orientation, temperature, and temperature gradient. Calculations were made in which pore surface radiation was both modeled and neglected. The difference between yielding the integral contribution of radiative heat transfer mechanism to overall heat transport. Results indicate that radiative component of heat transfer within pores is small for conditions representative of light water reactor fuel, typically less than 1% of total heat transport. It is much larger, however, for conditions present in liquid metal fast breeder reactor fuel; during restructuring of this fuel type early in life, the radiative heat transfer mode was shown to contribute as much as 10-20% of total heat transport in hottest regions of fuel.

  18. CFD simulation on critical heat flux of flow boiling in IVR-ERVC of a nuclear reactor

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Xiang, E-mail: zhangxiang3@snptc.com.cn [State Nuclear Power Technology Research & Development Center, South Area, Future Science and Technology Park, Chang Ping District, Beijing 102209 (China); Hu, Teng [State Nuclear Power Technology Research & Development Center, South Area, Future Science and Technology Park, Chang Ping District, Beijing 102209 (China); Chen, Deqi, E-mail: chendeqi@cqu.edu.cn [Key Laboratory of Low-grade Energy Utilization Technologies and Systems, Chongqing University, 400044 (China); Zhong, Yunke; Gao, Hong [Key Laboratory of Low-grade Energy Utilization Technologies and Systems, Chongqing University, 400044 (China)

    2016-08-01

    Highlights: • CFD simulation on CHF of boiling two-phase flow in ERVC is proposed. • CFD simulation result of CHF agrees well with that of experimental result. • The characteristics of boiling two-phase flow and boiling crisis are analyzed. - Abstract: The effectiveness of in-vessel retention (IVR) by external reactor vessel cooling (ERVC) strongly depends on the critical heat flux (CHF). As long as the local CHF does not exceed the local heat flux, the lower head of the pressure vessel can be cooled sufficiently to prevent from failure. In this paper, a CFD simulation is carried out to investigate the CHF of ERVC. This simulation is performed by a CFD code fluent couple with a boiling model by UDF (User-Defined Function). The experimental CHF of ERVC obtained by State Nuclear Power Technology Research and Development Center (SNPTRD) is used to validate this CFD simulation, and it is found that the simulation result agrees well with the experimental result. Based on the CFD simulation, detailed analysis focusing on the pressure distribution, velocity distribution, void fraction distribution, heating wall temperature distribution are proposed in this paper.

  19. Microlayer during boiling in narrow slot channels

    Science.gov (United States)

    Diev, Mikhail D.; Leontiev, Alexander I.

    1997-01-01

    An international space station Alpha will have a two-phase thermal control system. Boiling of a liquid ammonia will be a process of heat collection in evaporative heat exchangers. Unfortunately, only little data is available for boiling heat transfer in microgravity. Geometries of boiling channels working good in normal gravity are not appropriate in microgravity, and special means should be worked out to avoid some undesired events. From this point of view, the narrow slot channels may be assumed as a promising geometry for microgravity operation. During boiling in narrow slots, the vapor bubbles are flattened between the channel walls. The vapor phase and the channel wall are separated by a thin liquid film which is known as a microlayer. The paper presents the experimental results compared to the theoretical analysis, the paper also shows the narrow slot channels as a perspective configuration for microgravity applications.

  20. Conjugate heat and mass transfer in heat mass exchanger ducts

    CERN Document Server

    Zhang, Li-Zhi

    2013-01-01

    Conjugate Heat and Mass Transfer in Heat Mass Exchanger Ducts bridges the gap between fundamentals and recent discoveries, making it a valuable tool for anyone looking to expand their knowledge of heat exchangers. The first book on the market to cover conjugate heat and mass transfer in heat exchangers, author Li-Zhi Zhang goes beyond the basics to cover recent advancements in equipment for energy use and environmental control (such as heat and moisture recovery ventilators, hollow fiber membrane modules for humidification/dehumidification, membrane modules for air purification, desi

  1. Numerical Investigation of Boiling

    Science.gov (United States)

    Sagan, Michael; Tanguy, Sebastien; Colin, Catherine

    2012-11-01

    In this work, boiling is numerically investigated, using two phase flow direct numerical simulation based on a level set / Ghost Fluid method. Nucleate boiling implies both thermal issue and multiphase dynamics issues at different scales and at different stages of bubble growth. As a result, the different phenomena are investigated separately, considering their nature and the scale at which they occur. First, boiling of a static bubble immersed in an overheated liquid is analysed. Numerical simulations have been performed at different Jakob numbers in the case of strong density discontinuity through the interface. The results show a good agreement on bubble radius evolution between the theoretical evolution and numerical simulation. After the validation of the code for the Scriven test case, interaction of a bubble with a wall is studied. A numerical method taking into account contact angle is evaluated by comparing simulations of the spreading of a liquid droplet impacting on a plate, with experimental data. Then the heat transfer near the contact line is investigated, and simulations of nucleate boiling are performed considering different contact angles values. Finally, the relevance of including a model to take into account the evaporation of the micro layer is discussed.

  2. Natural convection heat transfer for a staggered array of heated, horizontal cylinders within a rectangular enclosure

    Energy Technology Data Exchange (ETDEWEB)

    Triplett, C.E.

    1996-12-01

    This thesis presents the results of an experimental investigation of natural convection heat transfer in a staggered array of heated cylinders, oriented horizontally within a rectangular enclosure. The main purpose of this research was to extend the knowledge of heat transfer within enclosed bundles of spent nuclear fuel rods sealed within a shipping or storage container. This research extends Canaan`s investigation of an aligned array of heated cylinders that thermally simulated a boiling water reactor (BWR) spent fuel assembly sealed within a shipping or storage cask. The results are presented in terms of piecewise Nusselt-Rayleigh number correlations of the form Nu = C(Ra){sup n}, where C and n are constants. Correlations are presented both for individual rods within the array and for the array as a whole. The correlations are based only on the convective component of the heat transfer. The radiative component was calculated with a finite-element code that used measured surface temperatures, rod array geometry, and measured surface emissivities as inputs. The correlation results are compared to Canaan`s aligned array results and to other studies of natural convection in horizontal tube arrays.

  3. Dynamic Heat Transfer Model of Refrigerated Foodstuff

    DEFF Research Database (Denmark)

    Cai, Junping; Risum, Jørgen; Thybo, Claus

    2006-01-01

    their temperature relation. This paper discusses the dynamic heat transfer model of foodstuff inside the display cabinet, one-dimensional dynamic model is developed, and the Explicit Finite Difference Method is applied, to handle the unsteady heat transfer problem with phase change, as well as time varying boundary...

  4. Radiative heat transfer between metallic nanoparticles

    CERN Document Server

    Chapuis, Pierre-Olivier; Volz, Sebastian; Greffet, Jean-Jacques

    2008-01-01

    In this letter, we study the radiative heat transfer between two nanoparticles in the near field and in the far field. We find that the heat transfer is dominated by the electric dipole-dipole interaction for dielectric particles and by the magnetic dipole-dipole interaction for metallic nanoparticles. We introduce polarizabilities formulas valid for arbitrary values of the skin depth. While the heat transfer mechanism is different for metallic and dielectric nanoparticles, we show that the distance dependence is the same. However, the dependence of the heat flux on the particle radius is different.

  5. Heat transfer coefficient of cryotop during freezing.

    Science.gov (United States)

    Li, W J; Zhou, X L; Wang, H S; Liu, B L; Dai, J J

    2013-01-01

    Cryotop is an efficient vitrification method for cryopreservation of oocytes. It has been widely used owing to its simple operation and high freezing rate. Recently, the heat transfer performance of cryotop was studied by numerical simulation in several studies. However, the range of heat transfer coefficient in the simulation is uncertain. In this study, the heat transfer coefficient for cryotop during freezing process was analyzed. The cooling rates of 40 percent ethylene glycol (EG) droplet in cryotop during freezing were measured by ultra-fast measurement system and calculated by numerical simulation at different value of heat transfer coefficient. Compared with the results obtained by two methods, the range of the heat transfer coefficient necessary for the numerical simulation of cryotop was determined, which is between 9000 W/(m(2)·K) and 10000 W/(m (2)·K).

  6. Heat transfer correlations in mantle tanks

    DEFF Research Database (Denmark)

    Furbo, Simon; Knudsen, Søren

    2005-01-01

    Small solar domestic hot water systems are best designed as low flow systems based on vertical mantle tanks. Theoretical investigations of the heat transfer in differently designed vertical mantle tanks during different operation conditions have been carried out. The investigations are based...... of the inner hot water tank and the domestic water in all levels of the tank. The heat transfer analysis showed that the heat transfer near the mantle inlet port between the solar collector fluid in the mantle and the walls surrounding the mantle is in the mixed convection regime, and as the distance from...... the inlet increases, natural convection starts to dominate. The heat transfer between the wall of the inner hot water tank and the domestic water is governed by natural convection. The results of the CFD-calculations are used to determine improved heat transfer correlations based on dimensionless analysis...

  7. "Nanotechnology Enabled Advanced Industrial Heat Transfer Fluids"

    Energy Technology Data Exchange (ETDEWEB)

    Dr. Ganesh Skandan; Dr. Amit Singhal; Mr. Kenneth Eberts; Mr. Damian Sobrevilla; Prof. Jerry Shan; Stephen Tse; Toby Rossmann

    2008-06-12

    ABSTRACT Nanotechnology Enabled Advanced industrial Heat Transfer Fluids” Improving the efficiency of Industrial Heat Exchangers offers a great opportunity to improve overall process efficiencies in diverse industries such as pharmaceutical, materials manufacturing and food processing. The higher efficiencies can come in part from improved heat transfer during both cooling and heating of the material being processed. Additionally, there is great interest in enhancing the performance and reducing the weight of heat exchangers used in automotives in order to increase fuel efficiency. The goal of the Phase I program was to develop nanoparticle containing heat transfer fluids (e.g., antifreeze, water, silicone and hydrocarbon-based oils) that are used in transportation and in the chemical industry for heating, cooling and recovering waste heat. Much work has been done to date at investigating the potential use of nanoparticle-enhanced thermal fluids to improve heat transfer in heat exchangers. In most cases the effect in a commercial heat transfer fluid has been marginal at best. In the Phase I work, we demonstrated that the thermal conductivity, and hence heat transfer, of a fluid containing nanoparticles can be dramatically increased when subjected to an external influence. The increase in thermal conductivity was significantly larger than what is predicted by commonly used thermal models for two-phase materials. Additionally, the surface of the nanoparticles was engineered so as to have a minimal influence on the viscosity of the fluid. As a result, a nanoparticle-laden fluid was successfully developed that can lead to enhanced heat transfer in both industrial and automotive heat exchangers

  8. Forced convective heat transfer in curved diffusers

    Science.gov (United States)

    Rojas, J.; Whitelaw, J. H.; Yianneskis, M.

    1987-01-01

    Measurements of the velocity characteristics of the flows in two curved diffusers of rectangular cross section with C and S-shaped centerlines are presented and related to measurements of wall heat transfer coefficients along the heated flat walls of the ducts. The velocity results were obtained by laser-Doppler anemometry in a water tunnel and the heat transfer results by liquid crystal thermography in a wind tunnel. The thermographic technique allowed the rapid and inexpensive measurement of wall heat transfer coefficients along flat walls of arbitrary boundary shapes with an accuracy of about 5 percent. The results show that an increase in secondary flow velocities near the heated wall causes an increase in the local wall heat transfer coefficient, and quantify the variation for maximum secondary-flow velocities in a range from 1.5 to 17 percent of the bulk flow velocity.

  9. Impact of different wort boiling temperatures on the beer foam stabilizing properties of lipid transfer protein 1.

    Science.gov (United States)

    Van Nierop, Sandra N E; Evans, David E; Axcell, Barry C; Cantrell, Ian C; Rautenbach, Marina

    2004-05-19

    Beer consumers demand satisfactory and consistent foam stability; thus, it is a high priority for brewers. Beer foam is stabilized by the interaction between certain beer proteins, including lipid transfer protein 1 (LTP1), and isomerized hop alpha-acids, but destabilized by lipids. In this study it was shown that the wort boiling temperature during the brewing process was critical in determining the final beer LTP1 content and conformation. LTP1 levels during brewing were measured by an LTP1 ELISA, using antinative barley LTP1 polyclonal antibodies. It was observed that the higher wort boiling temperatures ( approximately 102 degrees C), resulting from low altitude at sea level, reduced the final beer LTP1 level to 2-3 microg/mL, whereas the lower wort boiling temperatures ( approximately 96 degrees C), resulting from higher altitudes (1800 m), produced LTP1 levels between 17 and 35 microg/mL. Low levels of LTP1 in combination with elevated levels of free fatty acids (FFA) resulted in poor foam stability, whereas beer produced with low levels of LTP1 and FFA had satisfactory foam stability. Previous studies indicated the need for LTP1 denaturing to improve its foam stabilizing properties. However, the results presented here show that LTP1 denaturation reduces its ability to act as a binding protein for foam-damaging FFA. These investigations suggest that wort boiling temperature is an important factor in determining the level and conformation of LTP1, thereby favoring satisfactory beer foam stability.

  10. Experimental and theoretical analysis of the local condensation heat transfer in a plate heat exchanger

    Science.gov (United States)

    Grabenstein, V.; Kabelac, S.

    2012-11-01

    Plate heat exchanger (PHE) are today widely used in industrial heat transfer applications due to their good thermal performance, modest space requirement, easy accessibility to all areas and their lower capital and operating costs as compared to shell-and-tube heat exchangers. Although authoritative models for the design of PHE used as condensers are missing, the number of applications where a PHE is operating as a condenser increases. On the way to a reliable model based on physical approaches for the prediction of heat transfer and pressure drop during the condensation process inside a PHE, the flow and heat interactions as well as their dependence on the geometrical parameters of the corrugated plates and the operating conditions must be studied in detail. In this work the stepwise procedure for the fundamental construction of such a model is described. An experimental setup was built to analyze the characteristics of the two-phase-flow in PHE. A single gap, consisting of two transparent corrugated plates, was tested with a two-phase flow of air/water and also with boiling refrigerant R365mfc. Flow pattern maps were constructed for plates with corrugation angles of 27 and 63 degrees relative to the direction of flow. Investigations of the local heat transfer coefficients and the pressure drop were done with the same plates. The measurement of the local heat transfer coefficients was carried out by the use of the "Temperature Oscillation InfraRed Thermography" (TOIRT) method. Based on these results three main flow patterns are defined: film flow, bubbly flow and slug flow. For each of the three flow patterns an own model for the heat transfer and pressure drop mechanism are developed and the heat transfer coefficient and the friction factor is calculated with different equations depending on the actual steam quality, mass flow and geometrical parameters by means of a flow pattern map. The theory of the flow pattern based prediction models is proved with own

  11. Flow visualization and study of CHF enhancement in pool boiling with Al2O3 - Water nano-fluids

    Directory of Open Access Journals (Sweden)

    Hegde Ramakrishna N.

    2012-01-01

    Full Text Available Pool boiling heat transfer characteristics of Al2O3-Water nanofluids is studied experimentally using a NiCr test wire of 36 SWG diameter. The experimental work mainly concentrated on i change of Critical Heat Flux(CHF with different volume concentrations of nanofluid ii flow visualization of pool boiling using a fixed concentration of nanofluid at different heat flux values. The experimental work revealed an increase in CHF value of around 48% and flow visualization helped in studying the pool boiling behaviour of nanofluid. Out of the various reasons which could affect the CHF enhancement, surface roughness plays a major role in pool boiling heat transfer.

  12. Heat Transfer of Nanofluid in a Double Pipe Heat Exchanger.

    Science.gov (United States)

    Aghayari, Reza; Maddah, Heydar; Zarei, Malihe; Dehghani, Mehdi; Kaskari Mahalle, Sahar Ghanbari

    2014-01-01

    This paper investigates the enhancement of heat transfer coefficient and Nusselt number of a nanofluid containing nanoparticles (γ-AL2O3) with a particle size of 20 nm and volume fraction of 0.1%-0.3% (V/V). Effects of temperature and concentration of nanoparticles on Nusselt number changes and heat transfer coefficient in a double pipe heat exchanger with counter turbulent flow are investigated. Comparison of experimental results with valid theoretical data based on semiempirical equations shows an acceptable agreement. Experimental results show a considerable increase in heat transfer coefficient and Nusselt number up to 19%-24%, respectively. Also, it has been observed that the heat transfer coefficient increases with the operating temperature and concentration of nanoparticles.

  13. Van der Waals Force Assisted Heat Transfer

    Science.gov (United States)

    Sasihithlu, K.; Pendry, J. B.; Craster, R. V.

    2017-02-01

    Phonons (collective atomic vibrations in solids) are more effective in transporting heat than photons. This is the reason why the conduction mode of heat transport in nonmetals (mediated by phonons) is dominant compared to the radiation mode of heat transport (mediated by photons). However, since phonons are unable to traverse a vacuum gap (unlike photons), it is commonly believed that two bodies separated by a gap cannot exchange heat via phonons. Recently, a mechanism was proposed [J. B. Pendry, K. Sasihithlu, and R. V. Craster, Phys. Rev. B 94, 075414 (2016)] by which phonons can transport heat across a vacuum gap - through the Van der Waals interaction between two bodies with gap less than the wavelength of light. Such heat transfer mechanisms are highly relevant for heating (and cooling) of nanostructures; the heating of the flying heads in magnetic storage disks is a case in point. Here, the theoretical derivation for modelling phonon transmission is revisited and extended to the case of two bodies made of different materials separated by a vacuum gap. Magnitudes of phonon transmission, and hence the heat transfer, for commonly used materials in the micro- and nano-electromechanical industry are calculated and compared with the calculation of conduction heat transfer through air for small gaps as well as the heat transfer calculation due to photon exchange.

  14. Effect of orientation on heat transfer in pulsating heat pipe

    Directory of Open Access Journals (Sweden)

    Naumova A. M.

    2010-10-01

    Full Text Available The paper presents the results of experimental research of orientation effect on heat transfer characteristics of a pulsating heat pipe (PHP. It is shown that transport of either mass or heat depends on PHP orientation against it`s axis. As a consequence of comparing experimental data with other authors’ results it was concluded that PHP thermal resistance depends not only on orientation but on some other determinal factors such as device construction and thermophysical properties of heat carrier.

  15. Pumped two-phase heat transfer loop

    Science.gov (United States)

    Edelstein, Fred

    1988-01-01

    A pumped loop two-phase heat transfer system, operating at a nearly constant temperature throughout, includes several independently operating grooved capillary heat exchanger plates supplied with working fluid through independent flow modulation valves connected to a liquid supply line, a vapor line for collecting vapor from the heat exchangers, a condenser between the vapor and the liquid lines, and a fluid circulating pump between the condenser and the heat exchangers.

  16. Observation on rapid transient explosive boiling under pulsed-laser heating

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    Using various kinds of liquids (pure acetone, binary mixtures in various volume fractions of ethanol and acetone) as working liquids, the experiments of rapid transient explosive boiling induced by pulsed-laser irradiation are carried out. The temperature field on a microsecond scale is measured, and the behavior of bubbles is observed and captured by a microscopic camera system. The extreme characteristics that differ from those in normal boiling are clearly revealed. The influence of working liquid species, volume fraction of the mixture, nanoparticles added in the working liquid, and the laser irradiation parameters on the boiling behavior are also studied.

  17. Heat Transfer Augmentation for Electronic Cooling

    Directory of Open Access Journals (Sweden)

    Suabsakul Gururatana

    2012-01-01

    Full Text Available Problem statement: The performance of electronic devices has been improving along with the rapid technology development. Cooling of electronic systems is consequently essential in controlling the component temperature and avoiding any hot spot. The study aims to review the present electronic cooling methods which are widely used in electronic devices. Approach: There are several methods to cool down the electronics components such as the pin-fin heat sink, confined jet impingement, heat pipe, micro heat sink and so on. Results: The cooling techniques can obviously increase heat transfer rate. Nonetheless, for active and passive cooling methods the pressure drop could extremely rise, when the heat transfer rate is increased. Conclusion: When the cooling techniques are used, it is clearly seen that the heat transfer increases with pressure drop. To avoid excessive expense due to high pressure drop, optimization method is required to obtain optimum cost and cooling rate.

  18. 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

  19. Temperature Distribution and Heat Saturating Time of Regenerative Heat Transfer

    Institute of Scientific and Technical Information of China (English)

    Li JIA; Ying MAO; Lixin YANG

    2006-01-01

    In this paper, heat transfer of the ceramic honeycomb regenerator was numerically simulated based on the computational fluid dynamics numerical analysis software CFX5. The longitudinal temperature distribution of regenerator and gas were obtained. The variation of temperature with time was discussed. In addition, the effects of some parameters such as switching time, gas temperature at the inlet of regenerator, height of regenerator and specific heat of the regenerative materials on heat saturating time were discussed. It provided primarily theoretic basis for further study of regenerative heat transfer mechanism.

  20. Flow and Heat Flux Behavior of Micro-bubble Jet Flows Observed in Thin, Twisted-Wire, Subcooled Boiling in Microgravity

    Science.gov (United States)

    Munro, Troy R.; Ban, Heng

    2015-02-01

    Thin wire, subcooled boiling experiments were performed onboard an aircraft flying a parabolic trajectory to provide microgravity conditions for improved observation of jet flow phenomena and their behavior in the absence of buoyant forces. A new type of nucleation jet flow was observed in microgravity. This new micro-bubble jet flow is seen at medium to high heat fluxes and is characterized by a region of the wire that forms multiple jet columns which contain micro-bubbles. These columns flow together and penetrate tens of millimeters into the bulk fluid. Bubble behavior on the wire was observed to progress from a dominance of larger isolated bubbles on the wire to a dominance of micro-bubble jet flows on the wire as heat flux was increased. There was also a transient transition from a few large isolated bubbles to micro-bubble jet flow dominance for a set heat flux. A cross correlation calculation provided velocities of micro-bubbles in the flow, which were in the range of 4-14 mm/s. These velocities were used with convection correlations to show that fluid flows induced by jet flows are a significant contributor to the subcooled boiling heat transfer in microgravity, but are not the primary contributor. Additionally, a relative bubble area analysis approximates the direct contribution of these jet flows to the overall heat dissipation. These micro-bubble jet flows, which are only observed on thin wires (not flat surfaces), and the convection currents they induce, have the potential to allow for sustained fluid motion to occur in microgravity.

  1. Study of heat transfer in CI engine using heat transfer correlation based on intake jet velocity

    Energy Technology Data Exchange (ETDEWEB)

    Sharief, A. [Sri Siddharhta Inst. of Technology, Tumkur, Karnataka (India); Samaga, B.S.; Shrinivas Rao, B.R. [Nitte Mahalinga Adyantaya Institute of Technology, Karkala, Karnataka (India); JAntonyc, A. [Sahyadri Inst. of Technology, Mangalore, Karnataka (India)

    2009-07-01

    A reliable heat transfer formulation is needed to simulate reciprocating combustion engines. In order to reduce heat loss and improve thermal efficiency, it is necessary to calculate the rate of heat transfer from the working fluid to the combustion chamber walls. The thermal stresses in the engine components must also be determined. In this study, the author calculated heat transfer coefficient in a diesel engine using a heat transfer correlation based on intake jet velocity instead of mean piston speed. Experiments were conducted in a diesel engine with natural aspiration of hot air at 150 to 300 degrees C. Peak temperature was 1100 degrees C at various loads. The convective heat transfer coefficient and radiative heat transfer coefficient component was also determined separately at various loads. This model based on intake jet velocity instead of mean piston speed was found to be more realistic when considering the influence of gas velocities on the thermal boundary layer thickness. 11 refs., 12 figs.

  2. Effects of Microencapsulated Phase Change Material (MPCM) on Critical Heat Flux in Pool Boiling

    Energy Technology Data Exchange (ETDEWEB)

    Park, Sung Dae; Kim, Seong Man; Kang, Sarah; Lee, Seung Won; Seo, Han; Bang, In Cheol [Ulsan National Institute of Science and Technology, Ulsan (Korea, Republic of)

    2011-10-15

    Thermal power is limited by critical heat flux (CHF) in the nuclear power plant. And the in-vessel retention by external reactor vessel cooling (IVR-ERVC) is applied in some nuclear power plants; AP600, AP1000, Loviisa and APR1400. The heat removal capacity of IVR-ERVC is also restricted by CHF. So, it is essential to get CHF margin to improve an economics and a safety of the plant. There are some typical approaches to enhance CHF: vibrating the heater or fluid, coating with porous media on the heater surface, applying an electric field. The recent study related to the CHF is focus on using the nanofluid. In this paper, the new approach was investigated by using the microencapsulated phase change material (MPCM). MPCM is the particles whose diameter is from 0.1{mu}m to 1000{mu}m. The MPCM consists of the core material and the shell material. The core material can be solid, liquid, gas or even the mixture. The solid paraffin is the best candidate as the core material due to its stable chemical and thermal properties. And the shell material is generally synthesized polymer of about several micrometers in thickness. The most interesting feature of the MPCM is that the latent heat associated with the solid-liquid phase change is related to the heat transfer. When the MPCM is dispersed into the carrier fluid, a kind of suspension named as microencapsulated phase change slurry (MPCS) is formed. The study on the MPCS was conducted in field of both the heat transfer fluids and energy storage media. It is inspired by the fact that the latent heat can serve distribution to the additional CHF margin. The purpose of this work is to confirm whether or not the CHF is enhanced

  3. Anomalous heat transfer modes of nanofluids: a review based on statistical analysis.

    Science.gov (United States)

    Sergis, Antonis; Hardalupas, Yannis

    2011-05-19

    This paper contains the results of a concise statistical review analysis of a large amount of publications regarding the anomalous heat transfer modes of nanofluids. The application of nanofluids as coolants is a novel practise with no established physical foundations explaining the observed anomalous heat transfer. As a consequence, traditional methods of performing a literature review may not be adequate in presenting objectively the results representing the bulk of the available literature. The current literature review analysis aims to resolve the problems faced by researchers in the past by employing an unbiased statistical analysis to present and reveal the current trends and general belief of the scientific community regarding the anomalous heat transfer modes of nanofluids. The thermal performance analysis indicated that statistically there exists a variable enhancement for conduction, convection/mixed heat transfer, pool boiling heat transfer and critical heat flux modes. The most popular proposed mechanisms in the literature to explain heat transfer in nanofluids are revealed, as well as possible trends between nanofluid properties and thermal performance. The review also suggests future experimentation to provide more conclusive answers to the control mechanisms and influential parameters of heat transfer in nanofluids.

  4. Heat transfer behavior of molten nitrate salt

    Science.gov (United States)

    Das, Apurba K.; Clark, Michael M.; Teigen, Bard C.; Fiveland, Woodrow A.; Anderson, Mark H.

    2016-05-01

    The usage of molten nitrate salt as heat transfer fluid and thermal storage medium decouples the generation of electricity from the variable nature of the solar resource, allowing CSP plants to avoid curtailment and match production with demand. This however brings some unique challenges for the design of the molten salt central receiver (MSCR). An aspect critical to the use of molten nitrate (60wt%/40wt% - NaNO3/KNO3) salt as heat transfer fluid in the MSCR is to understand its heat transfer behavior. Alstom collaborated with the University of Wisconsin to conduct a series of experiments and experimentally determined the heat transfer coefficients of molten nitrate salt up to high Reynolds number (Re > 2.0E5) and heat flux (q″ > 1000 kW/m2), conditions heretofore not reported in the literature. A cartridge heater instrumented with thermocouples was installed inside a stainless steel pipe to form an annular test section. The test section was installed in the molten salt flow loop at the University of Wisconsin facility, and operated over a range of test conditions to determine heat transfer data that covered the expected operating regime of a practical molten salt receiver. Heat transfer data were compared to widely accepted correlations found in heat transfer literature, including that of Gnielinski. At lower Reynolds number conditions, the results from this work concurred with the molten salt heat transfer data reported in literature and followed the aforementioned correlations. However, in the region of interest for practical receiver design, the correlations did not accurately model the experimentally determined heat transfer data. Two major effects were observed: (i) all other factors remaining constant, the Nusselt numbers gradually plateaued at higher Reynolds number; and (ii) at higher Reynolds number a positive interaction of heat flux on Nusselt number was noted. These effects are definitely not modeled by the existing correlations. In this paper a new

  5. Characteristics of critical heat flux under rolling condition for flow boiling in vertical tube

    Energy Technology Data Exchange (ETDEWEB)

    Hwang, Jin-Seok, E-mail: hjscd@snu.ac.kr [Seoul National University, 599 Gwanak-Ro, Gwanak-Gu, Seoul 151-742 (Korea, Republic of); Lee, Yeon-Gun, E-mail: yeongun2@snu.ac.kr [Seoul National University, 599 Gwanak-Ro, Gwanak-Gu, Seoul 151-742 (Korea, Republic of); Park, Goon-Cherl, E-mail: parkgc@snu.ac.kr [Seoul National University, 599 Gwanak-Ro, Gwanak-Gu, Seoul 151-742 (Korea, Republic of)

    2012-11-15

    Highlights: Black-Right-Pointing-Pointer Experiment was conducted on CHF under rolling condition in vertical tube. Black-Right-Pointing-Pointer CHF loop was mounted on rolling device to achieve rolling conditions. Black-Right-Pointing-Pointer Trends of CHF ratio as mass flux and pressure were studied. Black-Right-Pointing-Pointer Trends of CHF ratio under rolling motion was suggested using hypothetical CHF mechanism. - Abstract: This paper presents the characteristics of the critical heat flux (CHF) for the boiling of R-134a in vertical tube under rolling motion in a marine reactor. It is important to predict CHF of marine reactor under rolling motion in order to consider the safety margin of the reactor. MArine Reactor Moving Simulator (MARMS) test was conducted to measure the CHF of R-134a flowing upward in a uniformly heated vertical tube under rolling motion. A CHF loop mounted on rolling equipment, which can periodically roll from side to side through rotating by motor and mechanical power transmission gear. The CHF tests were performed in a 9.5 mm I.D. test section with heated length of 1 m. Mass flux ranges from 285 kg/m{sup 2} s to 1300 kg/m{sup 2} s, inlet subcoolings from 3 to 38 Degree-Sign C and outlet pressures from 1.3 to 2.4 bar, respectively. Amplitudes of rolling range from 15 Degree-Sign to 40 Degree-Sign and period from 6 to 12 s. Fluid-to-fluid (FTF) scaling was applied to convert the test matrix of MARMS from water to R-134a equivalent conditions. CHF ratios (ratio of the CHF under rolling condition to the stationary CHF) as mass flux and pressure in rolling motion are quite different from those of other existing transient CHF experiments. For the mass fluxes below 500 kg/m{sup 2} s (region of relative low mass flux) at 13, 16 bar, CHF ratios seem smaller than unit but in region (region of relative high mass flux) where mass fluxes are above 500 kg/m{sup 2} s, it was found that the ratios increased. Moreover, rolling CHFs tend to enhance

  6. Some Aspects Concerning Convective Circulation Mode of Heat Transfer in Furnace to Wood Heat Treatment

    Directory of Open Access Journals (Sweden)

    Nadia Potoceanu

    2007-10-01

    Full Text Available The paper presented the most aspects of convective circulate mode of heat transfer : heat transfer through the boundary layer formed at the surface of the heat generator; heat transfer in the heat carrier and heat transfer through the boundary layer formed at the heated surface

  7. Heat Transfer Phenomena of Supercritical Fluids

    Energy Technology Data Exchange (ETDEWEB)

    Krau, Carmen Isabella; Kuhn, Dietmar; Schulenberg, Thomas [Forschungszentrum Karlsruhe, Institute for Nuclear and Energy Technologies, 76021 Karlsruhe (Germany)

    2008-07-01

    In concepts for supercritical water cooled reactors, the reactor core is cooled and moderated by water at supercritical pressures. The significant temperature dependence of the fluid properties of water requires an exact knowledge of the heat transfer mechanism to avoid fuel pin damages. Near the pseudo-critical point a deterioration of heat transfer might happen. Processes, that take place in this case, are not fully understood and are due to be examined systematically. In this paper a general overview on the properties of supercritical water is given, experimental observations of different authors will be reviewed in order to identify heat transfer phenomena and onset of occurrence. The conceptional design of a test rig to investigate heat transfer in the boundary layer will be discussed. Both, water and carbon dioxide, may serve as operating fluids. The loop, including instrumentation and safety devices, is shown and suitable measuring methods are described. (authors)

  8. Convective Heat Transfer for Ship Propulsion.

    Science.gov (United States)

    1982-04-01

    RD-A124 Wi CONVECTIVE HEAT TRANSFER FOR SHIP PROPULSION (U) ARIZONA 112 UNIV TUCSON ENGINEERING EXPERIMENT STATION PARK ET AL. 01 APR 82 1248-9 N814...395 CONVECTIVE HEAT TRANSFER FOR SHIP PROPULSION Prepared for Office of Naval Research Code 431 Arlington, Virginia Prepared by J. S. Park, M. F...FOR SHIP PROPULSION By J. S. Park, M. F. Taylor and D. M. McEligot Aerospace and Mechanical Engineering Department University of Arizona Tucson

  9. Low-temperature heat transfer in nanowires

    OpenAIRE

    Glavin, B. A.

    2000-01-01

    The new regime of low-temperature heat transfer in suspended nanowires is predicted. It takes place when (i) only ``acoustic'' phonon modes of the wire are thermally populated and (ii) phonons are subject to the effective elastic scattering. Qualitatively, the main peculiarities of heat transfer originate due to appearance of the flexural modes with high density of states in the wire phonon spectrum. They give rise to the $T^{1/2}$ temperature dependence of the wire thermal conductance. The e...

  10. Nanoparticle enhanced ionic liquid heat transfer fluids

    Science.gov (United States)

    Fox, Elise B.; Visser, Ann E.; Bridges, Nicholas J.; Gray, Joshua R.; Garcia-Diaz, Brenda L.

    2014-08-12

    A heat transfer fluid created from nanoparticles that are dispersed into an ionic liquid is provided. Small volumes of nanoparticles are created from e.g., metals or metal oxides and/or alloys of such materials are dispersed into ionic liquids to create a heat transfer fluid. The nanoparticles can be dispersed directly into the ionic liquid during nanoparticle formation or the nanoparticles can be formed and then, in a subsequent step, dispersed into the ionic liquid using e.g., agitation.

  11. Prediction of heat transfer of nanofluid on critical heat flux based on fractal geometry

    Institute of Scientific and Technical Information of China (English)

    Xiao Bo-Qi

    2013-01-01

    Analytical expressions for nucleate pool boiling heat transfer of nanofluid in the critical heat flux (CHF) region are derived taking into account the effect of nanoparticles moving in liquid based on the fractal geometry theory.The proposed fractal model for the CHF of nanofluid is explicitly related to the average diameter of the nanoparticles,the volumetric nanoparticle concentration,the thermal conductivity of nanoparticles,the fractal dimension of nanoparticles,the fractal dimension of active cavities on the heated surfaces,the temperature,and the properties of the fluid.It is found that the CHF of nanofluid decreases with the increase of the average diameter of nanoparticles.Each parameter of the proposed formulas on CHF has a clear physical meaning.The model predictions are compared with the existing experimental data,and a good agreement between the model predictions and experimental data is found.The validity of the present model is thus verified.The proposed fractal model can reveal the mechanism of heat transfer in nanofluid.

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

    Energy Technology Data Exchange (ETDEWEB)

    Park, Youngjae; Kim, Hyungdae [Kyung Hee Univ., Yongin (Korea, Republic of); Kim, Hyungmo [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of); Kim, Joonwon [POSTECH, Pohang (Korea, Republic of)

    2014-10-15

    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 (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.

  13. A Review on Heat Transfer Improvent of Plate Heat Exchanger

    Directory of Open Access Journals (Sweden)

    Abhishek Nandan

    2015-03-01

    Full Text Available Plate heat exchanger has found a wide range of application in various industries like food industries, chemical industries, power plants etc. It reduces the wastage of energy and improves the overall efficiency of the system. Hence, it must be designed to obtain the maximum heat transfer possible. This paper is presented in order to study the various theories and results given over the improvement of heat transfer performance in a plate heat exchanger. However, there is still a lack in data and generalized equations for the calculation of different parameters in the heat exchanger. It requires more attention to find out various possible correlations and generalized solutions for the performance improvement of plate heat exchanger.

  14. Evaluation of complex heat transfer coefficients for passive heating concepts

    Energy Technology Data Exchange (ETDEWEB)

    Bansal, N.K.; Sodha, M.S.; Singh, S.P.; Ram, S.

    1987-01-01

    Passive heating concepts namely Trombe wall, Water wall and Trans wall have been analysed to obtain overall heat transfer coefficients for average values and for time-dependent variations. The numerical values have been obtained and tabulated for various wall thicknesses.

  15. Mass and Heat Transfer Enhancement of Chemical Heat Pumps

    Institute of Scientific and Technical Information of China (English)

    Gui-PingLin; Xiu-GanYuan

    1993-01-01

    An inert additive,expanded graphit(EG),has been prepared and used to enhance the heat and mass transfer process of chemical heat pumps.The effects of mixing ratio and mixing method on the chemical reaction time are investigated.

  16. Capillary-Pumped Heat-Transfer Loop

    Science.gov (United States)

    1989-01-01

    New type of capillary-pumped heat-transfer loop primes itself at startup. Removes substantial quantities of heat like that generated by people and equipment in rooms and vehicles. Creates continuous path for its working fluid; both vapor and liquid move in same direction. Key element in operation of loop is formation of slugs of liquid, condensed from vapor and moved along loop by vapor bubbles before and after it. Both evaporator and condenser contain axial arteries carrying water. Heat entering evaporator from heat source provides energy for transport of fluid and heat. Dimensions in inches.

  17. Heat Flux Sensors for Infrared Thermography in Convective Heat Transfer

    OpenAIRE

    Giovanni Maria Carlomagno; Luigi de Luca; Gennaro Cardone; Tommaso Astarita

    2014-01-01

    This paper reviews the most dependable heat flux sensors, which can be used with InfraRed (IR) thermography to measure convective heat transfer coefficient distributions, and some of their applications performed by the authors’ research group at the University of Naples Federico II. After recalling the basic principles that make IR thermography work, the various heat flux sensors to be used with it are presented and discussed, describing their capability to investigate complex thermo-fluid-dy...

  18. Theory of periodic conjugate heat transfer

    CERN Document Server

    Zudin, Yuri B

    2016-01-01

    This book presents the theory of periodic conjugate heat transfer in detail. It offers a simplified description of the interaction between a solid body and a fluid as a boundary value problem of the heat conduction equation for the solid body.

  19. Topology optimization for transient heat transfer problems

    DEFF Research Database (Denmark)

    Zeidan, Said; Sigmund, Ole; Lazarov, Boyan Stefanov

    The focus of this work is on passive control of transient heat transfer problems using the topology optimization (TopOpt) method [1]. The goal is to find distributions of a limited amount of phase change material (PCM), within a given design domain, which optimizes the heat energy storage [2]. Our...

  20. Interactive Heat Transfer Simulations for Everyone

    Science.gov (United States)

    Xie, Charles

    2012-01-01

    Heat transfer is widely taught in secondary Earth science and physics. Researchers have identified many misconceptions related to heat and temperature. These misconceptions primarily stem from hunches developed in everyday life (though the confusions in terminology often worsen them). Interactive computer simulations that visualize thermal energy,…

  1. Boiling on Microconfigured Composite Surfaces Enhanced

    Science.gov (United States)

    Chao, David F.

    2000-01-01

    Boiling heat transfer is one of the key technologies for the two-phase active thermal-control system used on space platforms, as well as for the dynamic power systems aboard the International Space Station. Because it is an effective heat transfer mode, boiling is integral to many space applications, such as heat exchangers and other cooling devices. Nucleate boiling near the critical heat flux (CHF) can transport very large thermal loads with a much smaller device and much lower pumping power than for single-phase heat exchangers. However, boiling performance sharply deteriorates in a reduced-gravity environment, and operation in the CHF regime is somewhat perilous because of the risk of burnout to the device surface. New materials called microconfigured metal-graphite composites can enhance boiling. The photomicrograph shows the microconfiguration (x3000) of the copper-graphite (Cu-Gr) surface as viewed by scanning electronic microscope. The graphite fiber tips appear as plateaus with rugged surfaces embedded in the copper matrix. It has been experimentally demonstrated that this type of material manifests excellent boiling heat transfer performance characteristics and an increased CHF. Nonisothermal surfaces were less sensitive to variations of wall superheat in the CHF regime. Because of the great difference in conductivity between the copper base and the graphite fiber, the composite surfaces have a nonisothermal surface characteristic and, therefore, will have a much larger "safe" operating region in the CHF regime. In addition, the thermocapillary forces induced by the temperature differences between the fiber tips and the metal matrix play an important role in bubble detachment, and may not be adversely affected in a reduced-gravity environment. All these factors indicate that microconfigured composites may improve the reliability and economy (dominant factors in all space applications) of various thermal components found on spacecraft during future

  2. Experimental studies of heat exchange for sodium boiling in the fuel assembly model: Safety substantiation of a promising fast reactor

    Science.gov (United States)

    Khafizov, R. R.; Poplavskii, V. M.; Rachkov, V. I.; Sorokin, A. P.; Trufanov, A. A.; Ashurko, Yu. M.; Volkov, A. V.; Ivanov, E. F.; Privezentsev, V. V.

    2017-01-01

    Numerical simulation of the ULOF-type accident development in a fast reactor with sodium coolant performed using the COREMELT code indicates that sodium boiling in the active core takes place. The boiling is accompanied by oscillations of the technological parameters of the reactor installation; these oscillations can go on during several tens of seconds. In this case, it is possible that a stable regime of removal of heat from residual energy release is implemented. The model of the two-phase coolant flow applied in the code has an important effect on the numerical results; that is why this model needs experimental verification. For eliminating the development of an accident resulting in destruction of the active core elements, a structural solution is proposed; the essence of it is the application of the sodium void above the reactor active core. The experimental installation was developed and the heat exchange at sodium boiling in the model fuel assembly of the fast reactor in the regimes of natural and forced circulation in the presence of the sodium void and the top end shield was studied. It was demonstrated that, in the presence of the sodium void, it is possible to provide long-term cooling of the fuel assembly for a thermal flux density on the fuel element simulator surface of up to 140 and 170 kW/m2 in the natural and forced circulation modes, respectively. The obtained data are used for more precise determination of the numerical model of sodium boiling in the fuel assembly and verification of the COREMELT code.

  3. Bistable heat transfer in a nanofluid.

    Science.gov (United States)

    Donzelli, Gea; Cerbino, Roberto; Vailati, Alberto

    2009-03-13

    Heat convection in water can be suppressed by adding a small amount of highly thermophilic nanoparticles. We show that such suppression is not effective when a suspension with uniform concentration of nanoparticles is suddenly heated from below. At Rayleigh numbers smaller than a sample dependent threshold Ra;{*} we observe transient oscillatory convection. Unexpectedly, the duration of convection diverges at Ra;{*}. Above Ra;{*} oscillatory convection becomes permanent and the heat transferred exhibits bistability. Our results are explained only partially and qualitatively by existing theories.

  4. Capillary-Condenser-Pumped Heat-Transfer Loop

    Science.gov (United States)

    Silverstein, Calvin C.

    1989-01-01

    Heat being transferred supplies operating power. Capillary-condenser-pumped heat-transfer loop similar to heat pipe and to capillary-evaporator-pumped heat-transfer loop in that heat-transfer fluid pumped by evaporation and condensation of fluid at heat source and sink, respectively. Capillary condenser pump combined with capillary evaporator pump to form heat exchanger circulating heat-transfer fluids in both loops. Transport of heat more nearly isothermal. Thermal stress in loop reduced, and less external surface area needed in condenser section for rejection of heat to heat sink.

  5. Heat transfer with freezing and thawing

    CERN Document Server

    Lunardini, VJ

    1991-01-01

    This volume provides a comprehensive overview on the vast amount of literature on solidification heat transfer. Chapter one develops important basic equations and discusses the validity of considering only conductive heat transfer, while ignoring convection, in the large class of materials which make up the porous media. Chapters 2 to 4 deal with problems that can be expressed in plane (Cartesian) coordinates. These problems are further divided into boundary conditions of temperature, prescribed heat flux, and surface convection. Chapter 5 examines some plane geometries involving three-dime

  6. Heat transfer in a conical porous cylinder with partial heating

    Science.gov (United States)

    Yunus Khan, T. M.; Anjum Badruddin, Irfan; Quadir, G. A.

    2016-09-01

    The current work simulates the heat transfer across a porous medium fixed in an annular conical cylinder. The geometry is such that the lower part is conical annulus supporting a regular annular cylinder. The porous medium is fixed between inner and outer radius of conical annular cylinder. The inner radius until conical section is heated with constant temperature Th whereas the outer radius is cooled to isothermal temperature Tc such that Th>Tc . The heat transfer phenomenon in this case can be described by two coupled partial differential equations which are solved using finite element method by using 3-node triangular elements. The heat transfer characteristics in this case are quite different from other geometries being discussed in the literature. It is observed that the fluid flow is stronger in the conical section as compared to the cylindrical part of porous geometry. A very few isothermal lines penetrate into the cylindrical porous region as compared to that of conical section.

  7. The law of stable equilibrium and the entropy-based boiling curve for flow boiling

    Energy Technology Data Exchange (ETDEWEB)

    Collado, F.J. [Universidad de Zaragoza (Spain). Dpto. Ingenieria Mecanica Motores Termicos

    2005-05-01

    Convective flow boiling in sub-cooled fluids is recognized as one of the few means of accommodating very high heat fluxes. There are many available correlations for predicting the inner wall temperature of the heated duct in the several regimes of the empirical Nukiyama boiling curve, although unfortunately there is no physical fundamentals of such curve. Recently, the author has shown that the classical entropy balance could contain key information about boiling heat transfer. So, it was found that the average thermal gap in the heated channel (the inner wall temperature minus the average temperature of the coolant fluid) was strongly correlated with the efficiency of a theoretical reversible engine placed in this thermal gap. From this new correlation, a new boiling curve plotting the wall temperature versus the average fluid temperature was derived and successfully checked against low- and high-pressure water data. This curve suggested a new and simple definition of the critical heat flux (CHF) namely, the value of the coolant average temperature at the maximum. In this work, after briefly reviewing the entropy balance of a non-equilibrium boiling flow and its relationship with the thermodynamic average temperature and the law of stable equilibrium (LSE), the possibilities of the new approach for the design of flow boiling cooling systems are highlighted. Finally, the strong correlation found between the reversible engine efficiency and the thermal driving force is verified again, now with high-pressure refrigerant 22 (R-22) data. (author)

  8. The Principles of Turbulent Heat Transfer

    Science.gov (United States)

    Reichardt, H.

    1957-01-01

    The literature on turbulent heat transfer has in the course of years attained a considerable volume. Since this very complicated problem has not as yet found a complete solution, further studies in this field may be expected. The heat engineer must therefore accomodate himself to a constantly increasing number of theories and formulas. Since the theories generally start from hypothetical assumptions, and since they contain true and false assertions, verified knowledge and pure suppositions often being intermingled in a manner difficult to tell them apart, the specialist had difficulty in forming a correct evaluation of the individual studies. The need therefore arises for a presentation of the problem of turbulent heat transfer which is not initially bound by hypothetical assumptions and in which uninvestigated can be clearly distinguished form each other. Such a presentation will be given in the present treatment. Brief remarks with regard to the development of the theory of local heat transfer are included.

  9. Heat transfer in rocket combustion chambers

    Science.gov (United States)

    Anderson, P.; Cheng, G.; Farmer, R.

    1993-01-01

    Complexities of liquid rocket engine heat transfer which involve the injector faceplate and film cooled walls are being investigated by computational analysis. A conjugate heat transfer analysis was used to describe localized heating phenomena associated with particular injector configurations and film coolant flows. These components were analyzed, and the analyses verified when appropriate test data were available. The component analyses are being synthesized into an overall flowfield/heat transfer model. A Navier-Stokes flow solver, the FDNS code, was used to make the analyses. Particular attention was given to the representation of the thermodynamic properties of the fluid streams. Unit flow models of specific coaxial injector elements have been developed and are being used to describe the flame structure near the injector faceplate.

  10. Modeling microscale heat transfer using Calore.

    Energy Technology Data Exchange (ETDEWEB)

    Gallis, Michail A.; Rader, Daniel John; Wong, Chung-Nin Channy; Bainbridge, Bruce L.; Torczynski, John Robert; Piekos, Edward Stanley

    2005-09-01

    Modeling microscale heat transfer with the computational-heat-transfer code Calore is discussed. Microscale heat transfer problems differ from their macroscopic counterparts in that conductive heat transfer in both solid and gaseous materials may have important noncontinuum effects. In a solid material, three noncontinuum effects are considered: ballistic transport of phonons across a thin film, scattering of phonons from surface roughness at a gas-solid interface, and scattering of phonons from grain boundaries within the solid material. These processes are modeled for polycrystalline silicon, and the thermal-conductivity values predicted by these models are compared to experimental data. In a gaseous material, two noncontinuum effects are considered: ballistic transport of gas molecules across a thin gap and accommodation of gas molecules to solid conditions when reflecting from a solid surface. These processes are modeled for arbitrary gases by allowing the gas and solid temperatures across a gas-solid interface to differ: a finite heat transfer coefficient (contact conductance) is imposed at the gas-solid interface so that the temperature difference is proportional to the normal heat flux. In this approach, the behavior of gas in the bulk is not changed from behavior observed under macroscopic conditions. These models are implemented in Calore as user subroutines. The user subroutines reside within Sandia's Source Forge server, where they undergo version control and regression testing and are available to analysts needing these capabilities. A Calore simulation is presented that exercises these models for a heated microbeam separated from an ambient-temperature substrate by a thin gas-filled gap. Failure to use the noncontinuum heat transfer models for the solid and the gas causes the maximum temperature of the microbeam to be significantly underpredicted.

  11. Simplified models for heat transfer in rooms

    Science.gov (United States)

    Graca, Guilherme C. C. Carrilho Da

    Buildings protect their occupants from the outside environment. As a semi-enclosed environment, buildings tend to contain the internally generated heat and air pollutants, as well as the solar and conductive heat gains that can occur in the facade. In the warmer months of the year this generally leads to overheating, creating a need for a cooling system. Ventilation air replaces contaminated air in the building and is often used as the dominant medium for heat transfer between indoor and outdoor environments. The goal of the research presented in this thesis is to develop a better understanding of the important parameters in the performance of ventilation systems and to develop simplified convective heat transfer models. The general approach used in this study seeks to capture the dominant physical processes for these problems with first order accuracy, and develop simple models that show the correct system behavior trends. Dimensional analysis, in conjunction with simple momentum and energy conservation, scaled model experiments and numerical simulations, is used to improve airflow and heat transfer rate predictions in both single and multi room ventilation systems. This study includes the three commonly used room ventilation modes: mixing, displacement and cross-ventilation. A new modeling approach to convective heat transfer between the building and the outside is presented: the concept of equivalent room heat transfer coefficient. The new model quantifies the reduction in heat transfer between ventilation air and internal room surfaces caused by limited thermal capacity and temperature variation of the air for the three modes studied. Particular emphasis is placed on cross-ventilation, and on the development of a simple model to characterize the airflow patterns that occur in this case. The implementation of the models in a building thermal simulation software tool is presented as well as comparisons between model predictions, experimental results and complex

  12. A heat transfer model of a horizontal ground heat exchanger

    Science.gov (United States)

    Mironov, R. E.; Shtern, Yu. I.; Shtern, M. Yu.; Rogachev, M. S.

    2016-04-01

    Ground-source heat pumps are gaining popularity in Eastern Europe, especially those which are using the horizontal ground heat exchanger (GHX). Due to the difficulty of accessing GHX after the installation, materials and the quality of the installation must satisfy the very high requirements. An inaccurate calculation of GHX can be the reason of a scarcity of heat power in a crucial moment. So far, there isn't any appropriate mathematical description of the horizontal GHX which takes into account the mutual influence of GHX pipes on each other. To solve this problem we used the temperature wave approach. As a result, a mathematical model which describes the dependence of the heat transfer rate per unit length of the horizontal GHX pipe on the thermal properties of soil, operating time of GHX and the distance between pipes was obtained. Using this model, heat transfer rates per unit length of a horizontal GHX were plotted as functions of the distance between pipes and operating time. The modeling shows that heat transfer rates decreases rapidly with the distance between pipes lower then 2 meters. After the launch of heat pump, heat power of GHX is reduced during the first 20 - 30 days and get steady after that. The obtained results correlate with experimental data. Therefore the proposed mathematical model can be used to design a horizontal GHX with the optimal characteristics, and predict its capability during operation.

  13. Microscale and nanoscale heat transfer fundamentals and engineering applications

    CERN Document Server

    Sobhan, CB

    2008-01-01

    Preface Introduction to Microscale Heat Transfer Microscale Heat Transfer: A Recent Avenue in Energy Transport State of the Art: Some Introductory Remarks Overview of Microscale Transport Phenomena Discussions on Size-Effect Behavior Fundamental Approach for Microscale Heat Transfer Introduction to Engineering Applications of Microscale Heat Transfer Microscale Heat Conduction Review of Conduction Heat Transfer Conduction at the Microscale Space and Timescales Fundamental Approach Thermal Conductivity Boltzmann Equation and Phonon Transport Conduction in Thin Films

  14. The solution of the two-dimensional inverse heat transfer problem with the use of the FEM in combination with Trefftz functions

    Directory of Open Access Journals (Sweden)

    Maciejewska Beata

    2012-04-01

    Full Text Available The aim of this paper is to determine the boiling heat transfer coefficient for the cooling liquid flow in a rectangular minichannel with asymmetric heating. The main part of the test section is made up of a vertical minichannel of 1.0 mm depth. The heating foil on the side of the fluid flowing in the minichannel is singlesided enhanced on the selected area. The experiment is carried out with FC-72. The investigations focus on the transition from single-phase forced convection to nucleate boiling, that is, from the zone of boiling incipience further to developed boiling. Owing to the liquid crystal layer located on the heating surface contacting the glass, it is possible to measure the heating wall temperature distribution while increasing the heat flux transferred to the liquid flowing in the minichannel. The objective of the calculations is to evaluate a heat transfer model and numerical approach to solving the inverse boundary problem, and to calculate the heat transfer coefficient. This problem has been solved by means the finite element method in combination with Trefftz functions (FEMT. Trefftz functions are used to construct base functions in Hermite space of the finite element.

  15. Experimental study on the explosive boiling in saturated liquid nitrogen

    Institute of Scientific and Technical Information of China (English)

    DONG Zhaoyi; HUAI Xiulan; LIU Dengying

    2005-01-01

    Studies on the heat-transfer characteristics of liquid nitrogen (LN2) have received increasing attention. When there is a transient high heatflux input to the LN2, explosive boiling may take place. In this paper, using the high-power short-duration pulsed laser heating method and the high-speed photography technology, the experimental result of explosive boiling in saturated LN2 is illustrated; and the two exclusive characteristics of explosive boiling in LN2: changeover time and the relative long-time adherence of the bubble cluster to the surface, are investigated.

  16. Heat transfer in suspensions of rigid particles

    Science.gov (United States)

    Brandt, Luca; Niazi Ardekani, Mehdi; Abouali, Omid

    2016-11-01

    We study the heat transfer in laminar Couette flow of suspensions of rigid neutrally buoyant particles by means of numerical simulations. An Immersed Boundary Method is coupled with a VOF approach to simulate the heat transfer in the fluid and solid phase, enabling us to fully resolve the heat diffusion. First, we consider spherical particles and show that the proposed algorithm is able to reproduce the correlations between heat flux across the channel, the particle volume fraction and the heat diffusivity obtained in laboratory experiments and recently proposed in the literature, results valid in the limit of vanishing inertia. We then investigate the role of inertia on the heat transfer and show an increase of the suspension diffusivity at finite particle Reynolds numbers. Finally, we vary the relativity diffusivity of the fluid and solid phase and investigate its effect on the effective heat flux across the channel. The data are analyzed by considering the ensemble averaged energy equation and decomposing the heat flux in 4 different contributions, related to diffusion in the solid and fluid phase, and the correlations between wall-normal velocity and temperature fluctuations. Results for non-spherical particles will be examined before the meeting. Supported by the European Research Council Grant No. ERC-2013- CoG-616186, TRITOS. The authors acknowledge computer time provided by SNIC (Swedish National Infrastructure for Computing).

  17. Heat transfer law in leaching dump

    Institute of Scientific and Technical Information of China (English)

    WU Ai-xiang; WANG Hong-jiang; XI Yong; YANG Bao-hua; LI Jian-feng; YIN Sheng-hua; ZHA Ke-bing

    2005-01-01

    Based on the law of temperature changes in the leaching dump and the forming process of heat flux, the basic balance equation of heat flow in dump was established, the dissipated heat flow from dump to the atmosphere was analyzed to estimate the surface temperature of the ore particle in dump and discover the law of forced heat convection of heat flow transfer in dump. And the lixiviate flow formula taking a certain heat flow out of dump was deduced by using the inversion method. Through theoretic analysis, combining Dexing copper mine heap leaching production practice, the results show that the heat flow of chalcopyrite leaching emitted is not so great, but the heat flow of pyrite leaching and sulphur oxidation produced take up a higher proportion of total heat flow; the dissipated heat flow takes up a lower proportion, and most of heat flow is absorbed by itself, thus the inside temperature rises gradually; and the saturation flow form for leaching is adopted, which makes the lixiviate seepage in the transitional flow or even in the turbulent flow, so as to accelerate the heat flow diffusing and keep the leaching dump temperature suitable for bacteria living.

  18. Comparison of heat transfer efficiency between heat pipe and tube bundles heat exchanger

    Directory of Open Access Journals (Sweden)

    Wu Zhao-Chun

    2015-01-01

    Full Text Available A comparison of heat transfer efficiency between the heat pipe and tube bundles heat exchanger is made based on heat transfer principle and the analysis of thermal characteristics. This paper argues that although heat pipe has the feature of high axial thermal conductivity, to those cases where this special function of heat transfer is unnecessary, heat pipe exchanger is not a high efficient heat exchanger when it is just used as a conventional heat exchanger in the industrial fields. In turn, there are some deficiencies for heat pipe exchanger, such as complicated manufacturing process, critical requirements for manufacturing materials, etc. which leads to a higher cost in comparison to a tubular heat exchanger. Nonetheless, due to its diverse structural features and extraordinary properties, heat pipe exchanger still has wide applications on special occasions.

  19. Heat transfer in Rockwool modelling and method of measurement. Modelling radiative heat transfer in fibrous materials

    Energy Technology Data Exchange (ETDEWEB)

    Dyrboel, Susanne

    1998-05-01

    Fibrous materials are some of the most widely used materials for thermal insulation. In this project the focus of interest has been on fibrous materials for building application. Interest in improving the thermal properties of insulation materials is increasing as legislation is being tightened to reduce the overall energy consumption. A knowledge of the individual heat transfer mechanisms - whereby heat is transferred within a particular material is an essential tool to improve continuously the thermal properties of the material. Heat is transferred in fibrous materials by four different transfer mechanisms: conduction through air, conduction through fibres, thermal radiation and convection. In a particular temperature range the conduction through air can be regarded as a constant, and conduction through fibres is an insignificant part of the total heat transfer. Radiation, however, constitutes 25-40% of the total heat transfer in light fibrous materials. In Denmark and a number of other countries convection in fibrous materials is considered as non-existent when calculating heat transmission as well as when designing building structures. Two heat transfer mechanisms have been the focus of the current project: radiation heat transfer and convection. The radiation analysis serves to develop a model that can be used in further work to gain a wider knowledge of the way in which the morphology of the fibrous material, i.e. fibre diameter distribution, fibre orientation distribution etc., influences the radiation heat transfer under different conditions. The convection investigation serves to examine whether considering convection as non-existent is a fair assumption to use in present and future building structures. The assumption applied in practically is that convection makes a notable difference only in very thick insulation, at external temperatures below -20 deg. C, and at very low densities. For lager thickness dimensions the resulting heat transfer through the

  20. Evaluation of heat transfer enhancement in air-heating collectors

    Energy Technology Data Exchange (ETDEWEB)

    Mattox, D. L.

    1979-06-01

    The present research effort was initiated for the purpose of increasing the thermal efficiency of air heating solar collectors through identification and development of optimum design and operation criteria for solar absorber-to-air heat exchangers. Initially this effort took the form of a solar collector systems analysis to evaluate the impact of various techniques for enhancing the heat transfer between the absorber and air stream on overall thermal performance of the entire solar collector. This systems analysis resulted in the selection of solar collector designs providing ducted cooling air on the absorber shaded side as a base line. A transient heat transfer analysis of a complete solar air heating collector was used to demonstrate that an optimum absorber-to-air heat exchanger design could be provided with several interrupted fin configurations. Additional analyses were performed to establish that the maximum solar collector thermal performance to required pumping power was realized for a Reynolds number range of 1000 to 2000. This Reynolds number range was used to establish a theoretical design limit curve for maximum thermal performance versus required pumping power for all interrupted fin designs as published in the open literature. Heat and momentum transfer empirical relationships were defined for scaling the state-of-the-art high conductance fin designs identified from a compact configuration to the less compact designs needed for solar collectors.

  1. Prediction of Heat Transfer Performance on Horizontal U-Shaped Heat Exchanger in Passive Safety System Using MARS

    Energy Technology Data Exchange (ETDEWEB)

    Jeon, Seong-Su; Hong, Soon-Joon [FNC Tech, Yongin (Korea, Republic of); Cho, Hyoung-Kyu; Park, Goon-Cherl [Seoul National University, Seoul (Korea, Republic of)

    2015-10-15

    The design and the safety analysis of the passive safety systems are performed mainly using the best-estimate thermal-hydraulic analysis codes such as RELAP5 and MARS. This study developed the heat transfer model package for the horizontal U-shaped HX submerged in a pool by improving the horizontal in-tube condensation model and developing the outside-tube natural convective nucleate boiling model. This paper presents the HX model package and the validation results against the passive safety system-related experimental data of PASCAL and ATLAS-PAFS. This study developed the heat transfer model package of the horizontal U-shaped HX submerged in a pool in order to obtain a reliable prediction of the HX heat removal performance of the passive safety system, especially PAFS, using MARS. From the validation results, the proposed model package provided the improved prediction of HX performance (condensation, natural convective nucleate boiling, and heat removal rate of the HX) compared to the default model in MARS.

  2. CFD ANALYSIS FOR HEAT TRANSFER BETWEEN COPPER ENCAPSULATED PHASE CHANGE MATERIAL AND HEAT TRANSFER FLUID

    Directory of Open Access Journals (Sweden)

    M.Premkumar

    2013-03-01

    Full Text Available Heat transfer plays an important role in the enhancement of thermal energy storage in phase change material (PCM. The effective utilization of solar thermal energy can be obtained by proper storage of that energy. There are various techniques for the enhancement solar thermal storage in phase change material such as introductionof wire brushes, honey comb structure, fins and packed bed storage. In this study the analysis of heat transfer between PCM and heat transfer fluids (HTF with Spherical and cylindrical finned encapsulations made of copper are done using computational fluid dynamic (CFD analysis software GAMBIT and Fluent 6.2. The analysis is done in two modes as charging and discharging. During the charging mode the input is given in terms of temperature to the heat transfer fluid and the amount of heat transfer inside the PCM encapsulation is taken as output. During the discharging process the output temperature in the PCM is given as input and the amount of heat transferred to the heat transfer fluid is noted. The results from CFD analysis conclude that the heat transfer is more in finned encapsulations than that of without finned encapsulations and the copper sphere with fins is considered to be the best out of all other encapsulations.

  3. Axial flow heat exchanger devices and methods for heat transfer using axial flow devices

    Energy Technology Data Exchange (ETDEWEB)

    Koplow, Jeffrey P.

    2016-02-16

    Systems and methods described herein are directed to rotary heat exchangers configured to transfer heat to a heat transfer medium flowing in substantially axial direction within the heat exchangers. Exemplary heat exchangers include a heat conducting structure which is configured to be in thermal contact with a thermal load or a thermal sink, and a heat transfer structure rotatably coupled to the heat conducting structure to form a gap region between the heat conducting structure and the heat transfer structure, the heat transfer structure being configured to rotate during operation of the device. In example devices heat may be transferred across the gap region from a heated axial flow of the heat transfer medium to a cool stationary heat conducting structure, or from a heated stationary conducting structure to a cool axial flow of the heat transfer medium.

  4. Boiling flow through diverging microchannel

    Indian Academy of Sciences (India)

    V S Duryodhan; S G Singh; Amit Agrawal

    2013-12-01

    An experimental study of flow boiling through diverging microchannel has been carried out in this work, with the aim of understanding boiling in nonuniform cross-section microchannel. Diverging microchannel of 4° of divergence angle and 146 m hydraulic diameter (calculated at mid-length) has been employed for the present study with deionised water as working fluid. Effect of mass flux (118–1182 kg/m2-s) and heat flux (1.6–19.2 W/cm2) on single and two-phase pressure drop and average heat transfer coefficient has been studied. Concurrently, flow visualization is carried out to document the various flow regimes and to correlate the pressure drop and average heat transfer coefficient to the underlying flow regime. Four flow regimes have been identified from the measurements: bubbly, slug, slug–annular and periodic dry-out/rewetting. Variation of pressure drop with heat flux shows one maxima which corresponds to transition from bubbly to slug flow. It is shown that significantly large heat transfer coefficient (up to 107 kW/m2-K) can be attained for such systems, for small pressure drop penalty and with good flow stability.

  5. Electromagnetic Heat Transfer in Artificial Materials

    Science.gov (United States)

    Woods, Lilia; Drosdoff, David; Phan, Anh

    2014-03-01

    Electromagnetic energy exchange has found promising new opportunities by greatly enhancing the heat transfer between bodies via radiation in the near-field regime. The greatest heat transfer occurs when the bodies support surface plasmons or polaritons that share the same resonant frequency. It has been shown, however, that 2-D materials such as graphene can have their surface plasmons tuned by modifying the chemical potential and temperature. This allows for tuning its resonance with other systems. In this talk, we investigated the electromagnetic radiation in metamaterials characterized by a strong magnetic response. We study theoretically Pendry-like and magnetically active metamaterial/graphene composites. The possibility for enhancing or inhibiting the heat transfer via the graphene properties is investigated.

  6. Below and above boiling point comparison of microwave irradiation and conductive heating for municipal sludge digestion under identical heating/cooling profiles.

    Science.gov (United States)

    Hosseini Koupaie, E; Eskicioglu, C

    2015-01-01

    This research provides a comprehensive comparison between microwave (MW) and conductive heating (CH) sludge pretreatments under identical heating/cooling profiles at below and above boiling point temperatures. Previous comparison studies were constrained to an uncontrolled or a single heating rate due to lack of a CH equipment simulating MW under identical thermal profiles. In this research, a novel custom-built pressure-sealed vessel which could simulate MW pretreatment under identical heating/cooling profiles was used for CH pretreatment. No statistically significant difference was proven between MW and CH pretreatments in terms of sludge solubilization, anaerobic biogas yield and organics biodegradation rate (p-value>0.05), while statistically significant effects of temperature and heating rate were observed (p-valueheating/cooling rates) was controlled.

  7. Coupled Seepage and Heat Transfer Intake Model

    Institute of Scientific and Technical Information of China (English)

    WU Junhua; YOU Shijun; ZHANG Huan; LI Haishan

    2009-01-01

    In the beach well intake system, heat is transferred from soil to fluid when seawater is filtered through the aquifer, providing higher temperature source water to the seawater source heat pump (SWHP) system in winter. A 3-D coupled seepage and heat transfer model for studying beach well intake system is established by adopting the computer code FLUENT. Numerical results of this model are compared with the experimental results under the same conditions. Based on the experiment-verified coupled model, numerical simulation of the supply water temperature is studied over a heating season. Results show that the minimum temperature of supply water is 275.2 K when this intake system continuously provides seawater with flow rate of 35 m3/h to SWHP. Results also indicate that the supply water temperature is higher than seawater, and that the minimum temperature of supply water lags behind seawater, ensuring effective and reliable operation of SWHP.

  8. Low-temperature heat transfer in nanowires.

    Science.gov (United States)

    Glavin, B A

    2001-05-07

    A new regime of low-temperature heat transfer in suspended nanowires is predicted. It takes place when (i) only "acoustic" phonon modes of the wire are thermally populated and (ii) phonons are subject to the effective elastic scattering. Qualitatively, the main peculiarities of heat transfer originate due to the appearance of the flexural modes with high density of states in the wire phonon spectrum. They give rise to the T(1/2) temperature dependence of the wire thermal conductance. Experimental situations where the new regime is likely to be detected are discussed.

  9. Heat transfer applications for the practicing engineer

    CERN Document Server

    Theodore, Louis

    2011-01-01

    This book serves as a training tool for individuals in industry and academia involved with heat transfer applications. Although the literature is inundated with texts emphasizing theory and theoretical derivations, the goal of this book is to present the subject of heat transfer from a strictly pragmatic point of view. The book is divided into four Parts: Introduction, Principles, Equipment Design Procedures and Applications, and ABET-related Topics. The first Part provides a series of chapters concerned with introductory topics that are required when solving most engineering problems, inclu

  10. Convective heat transfer during dendritic growth

    Science.gov (United States)

    Glicksman, M. E.; Huang, S. C.

    1979-01-01

    Axial growth rate measurements were carried out at 17 levels of supercooling between 0.043 C and 2 C, a temperature range in which convection, instead of diffusion, becomes the controlling mechanism of heat transfer in the dentritic growth process. The growth velocity, normalized to that expected for pure diffusive heat transfer, displays a dependence on orientation. The ratio of the observed growth velocity to that for convection-free growth and the coefficients of supercooling are formulated. The dependence of normalized growth rate in supercooling is described for downward growing dendrites. These experimental correlations can be justified theoretically only to a limited extent.

  11. Microscale surface modifications for heat transfer enhancement.

    Science.gov (United States)

    Bostanci, Huseyin; Singh, Virendra; Kizito, John P; Rini, Daniel P; Seal, Sudipta; Chow, Louis C

    2013-10-09

    In this experimental study, two surface modification techniques were investigated for their effect on heat transfer enhancement. One of the methods employed the particle (grit) blasting to create microscale indentations, while the other used plasma spray coating to create microscale protrusions on Al 6061 (aluminum alloy 6061) samples. The test surfaces were characterized using scanning electron microscopy (SEM) and confocal scanning laser microscopy. Because of the surface modifications, the actual surface area was increased up to 2.8× compared to the projected base area, and the arithmetic mean roughness value (Ra) was determined to vary from 0.3 μm for the reference smooth surface to 19.5 μm for the modified surfaces. Selected samples with modified surfaces along with the reference smooth surface were then evaluated for their heat transfer performance in spray cooling tests. The cooling system had vapor-atomizing nozzles and used anhydrous ammonia as the coolant in order to achieve heat fluxes up to 500 W/cm(2) representing a thermal management setting for high power systems. Experimental results showed that the microscale surface modifications enhanced heat transfer coefficients up to 76% at 500 W/cm(2) compared to the smooth surface and demonstrated the benefits of these practical surface modification techniques to enhance two-phase heat transfer process.

  12. Experimental determination of stator endwall heat transfer

    Science.gov (United States)

    Boyle, Robert J.; Russell, Louis M.

    1989-01-01

    Local Stanton numbers were experimentally determined for the endwall surface of a turbine vane possage. A six vane linear cascade having vanes with an axial chord of 13.81 cm was used. Resutls were obtained for Reynolds numbers based on inlet velocity and axial chord between 75,000 and 495,000. The test section was connected to a low pressure exhaust system. Ambient air was drawn into the test section, inlet velocity was controlled up to a maximum of 59.4 m/sec. The effect of the inlet boundary layer thickness on the endwall heat transfer was determined for a range of test section flow rates. The liquid crystal measurement technique was used to measure heat transfer. Endwall heat transfer was determined by applying electrical power to a foil heater attached to the cascade endwall. The temperature at which the liquid crystal exhibited a specific color was known from a calibration test. Lines showing this specific color were isotherms, and because of uniform heat generation they were also lines of nearly constant heat transfer. Endwall static pressures were measured, along with surveys of total pressure and flow angles at the inlet and exit of the cascade.

  13. Natural convective heat transfer from square cylinder

    Science.gov (United States)

    Novomestský, Marcel; Smatanová, Helena; Kapjor, Andrej

    2016-06-01

    This article is concerned with natural convective heat transfer from square cylinder mounted on a plane adiabatic base, the cylinders having an exposed cylinder surface according to different horizontal angle. The cylinder receives heat from a radiating heater which results in a buoyant flow. There are many industrial applications, including refrigeration, ventilation and the cooling of electrical components, for which the present study may be applicable

  14. Electrically Driven Liquid Film Boiling Experiment

    Science.gov (United States)

    Didion, Jeffrey R.

    2016-01-01

    This presentation presents the science background and ground based results that form the basis of the Electrically Driven Liquid Film Boiling Experiment. This is an ISS experiment that is manifested for 2021. Objective: Characterize the effects of gravity on the interaction of electric and flow fields in the presence of phase change specifically pertaining to: a) The effects of microgravity on the electrically generated two-phase flow. b) The effects of microgravity on electrically driven liquid film boiling (includes extreme heat fluxes). Electro-wetting of the boiling section will repel the bubbles away from the heated surface in microgravity environment. Relevance/Impact: Provides phenomenological foundation for the development of electric field based two-phase thermal management systems leveraging EHD, permitting optimization of heat transfer surface area to volume ratios as well as achievement of high heat transfer coefficients thus resulting in system mass and volume savings. EHD replaces buoyancy or flow driven bubble removal from heated surface. Development Approach: Conduct preliminary experiments in low gravity and ground-based facilities to refine technique and obtain preliminary data for model development. ISS environment required to characterize electro-wetting effect on nucleate boiling and CHF in the absence of gravity. Will operate in the FIR - designed for autonomous operation.

  15. Pool boiling on the superhydrophilic surface with TiO2 nanotube arrays

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    Surface with TiO2 nanotube arrays(TNTAs)is superhydrophilic and of great specific area.This paper investigates the pool boiling characteristics at the thermal interface with TNTAs.The results show that the TNTAs interface can enhance the pool boiling heat transfer compared to the pure Ti metal plate.The bubbles formed at the initial nucleation state are very small and released in higher frequency.The pool boiling heat transfer enhancement at the TNTAs interface may be attributed to the high density of nucleate site,high intrinsic heating area of nanotubes layer,superhydrophilicity and the vertically oriented nanotube structure.

  16. Heat flux sensors for infrared thermography in convective heat transfer.

    Science.gov (United States)

    Carlomagno, Giovanni Maria; de Luca, Luigi; Cardone, Gennaro; Astarita, Tommaso

    2014-11-07

    This paper reviews the most dependable heat flux sensors, which can be used with InfraRed (IR) thermography to measure convective heat transfer coefficient distributions, and some of their applications performed by the authors' research group at the University of Naples Federico II. After recalling the basic principles that make IR thermography work, the various heat flux sensors to be used with it are presented and discussed, describing their capability to investigate complex thermo-fluid-dynamic flows. Several applications to streams, which range from natural convection to hypersonic flows, are also described.

  17. Heat Flux Sensors for Infrared Thermography in Convective Heat Transfer

    Directory of Open Access Journals (Sweden)

    Giovanni Maria Carlomagno

    2014-11-01

    Full Text Available This paper reviews the most dependable heat flux sensors, which can be used with InfraRed (IR thermography to measure convective heat transfer coefficient distributions, and some of their applications performed by the authors’ research group at the University of Naples Federico II. After recalling the basic principles that make IR thermography work, the various heat flux sensors to be used with it are presented and discussed, describing their capability to investigate complex thermo-fluid-dynamic flows. Several applications to streams, which range from natural convection to hypersonic flows, are also described.

  18. 8. Innovative Technologies: Two-Phase Heat Transfer in Water-Based Nanofluids for Nuclear Applications Final Report

    Energy Technology Data Exchange (ETDEWEB)

    Buongiorno, Jacopo; Hu, Lin-wen

    2009-07-31

    Nanofluids are colloidal dispersions of nanoparticles in water. Many studies have reported very significant enhancement (up to 200%) of the Critical Heat Flux (CHF) in pool boiling of nanofluids (You et al. 2003, Vassallo et al. 2004, Bang and Chang 2005, Kim et al. 2006, Kim et al. 2007). These observations have generated considerable interest in nanofluids as potential coolants for more compact and efficient thermal management systems. Potential Light Water Reactor applications include the primary coolant, safety systems and severe accident management strategies, as reported in other papers (Buongiorno et al. 2008 and 2009). However, the situation of interest in reactor applications is often flow boiling, for which no nanofluid data have been reported so far. In this project we investigated the potential of nanofluids to enhance CHF in flow boiling. Subcooled flow boiling heat transfer and CHF experiments were performed with low concentrations of alumina, zinc oxide, and diamond nanoparticles in water (≤ 0.1 % by volume) at atmospheric pressure. It was found that for comparable test conditions the values of the nanofluid and water heat transfer coefficient (HTC) are similar (within ±20%). The HTC increased with mass flux and heat flux for water and nanofluids alike, as expected in flow boiling. The CHF tests were conducted at 0.1 MPa and at three different mass fluxes (1500, 2000, 2500 kg/m2s) under subcooled conditions. The maximum CHF enhancement was 53%, 53% and 38% for alumina, zinc oxide and diamond, respectively, always obtained at the highest mass flux. A post-mortem analysis of the boiling surface reveals that its morphology is altered by deposition of the particles during nanofluids boiling. A confocal-microscopy-based examination of the test section revealed that nanoparticles deposition not only changes the number of micro-cavities on the surface, but also the surface wettability. A simple model was used to estimate the ensuing nucleation site

  19. In-Cylinder Heat Transfer Modelling

    Directory of Open Access Journals (Sweden)

    Žák Zdeněk

    2016-12-01

    Full Text Available The goal of the paper is to discuss specific features of the in-cylinder heat transfer calculation based on widely used empirical formulas. The potential of in-house codes compared with commercially available software packages is presented. The principles of user models in the GT-SUITE environment are also explained. The results of calibrated models are briefly discussed.

  20. Endwall convective heat transfer for bluff bodies

    DEFF Research Database (Denmark)

    Wang, Lei; Salewski, Mirko; Sundén, Bengt

    2012-01-01

    The endwall heat transfer characteristics of forced flow past bluff bodies have been investigated using liquid crystal thermography (LCT). The bluff body is placed in a rectangular channel with both its ends attached to the endwalls. The Reynolds number varies from 50,000 to 100,000. In this study...

  1. Forced Convection Heat Transfer in Circular Pipes

    Science.gov (United States)

    Tosun, Ismail

    2007-01-01

    One of the pitfalls of engineering education is to lose the physical insight of the problem while tackling the mathematical part. Forced convection heat transfer (the Graetz-Nusselt problem) certainly falls into this category. The equation of energy together with the equation of motion leads to a partial differential equation subject to various…

  2. Conjugate problems in convective heat transfer

    CERN Document Server

    Dorfman, Abram S

    2009-01-01

    The conjugate heat transfer (CHT) problem takes into account the thermal interaction between a body and fluid flowing over or through it, a key consideration in both mechanical and aerospace engineering. Presenting more than 100 solutions of non-isothermal and CHT problems, this title considers the approximate solutions of CHT problems.

  3. Determination of the convective heat transfer coefficient

    NARCIS (Netherlands)

    Spierings, D.; Bosman, F.; Peters, T.; Plasschaert, F.

    1987-01-01

    The value of the convective heat transfer coefficient (htc) is determined under different loading conditions by using a computer aided method. The thermal load has been applied mathematically as well as experimentally to the coronal surface of an axisymmetric tooth model. To verify the assumptions m

  4. Heat Transfer and Thermodynamics: a Compilation

    Science.gov (United States)

    1974-01-01

    A compilation is presented for the dissemination of information on technological developments which have potential utility outside the aerospace and nuclear communities. Studies include theories and mechanical considerations in the transfer of heat and the thermodynamic properties of matter and the causes and effects of certain interactions.

  5. Convective heat transfer of nanofluids with correlations

    Institute of Scientific and Technical Information of China (English)

    Lazarus Godson Asirvatham; Balakrishnan Raja; Dhasan Mohan Lal; Somchai Wongwises

    2011-01-01

    To investigate the convective heat transfer of nanofluids,experiments were performed using silver-water nanofluids under laminar,transition and turbulent flow regimes in a horizontal 4.3 mm inner-diameter tube-in-tube counter-current heat transfer test section.The volume concentration of the nanoparticles varied from 0.3% to 0.9% in steps of 0.3%,and the effects of thermo-physical properties,inlet temperature,volume concentration,and mass flow rate on heat transfer coefficient were investigated.Experiments showed that the suspended nanoparticles remarkably increased the convective heat transfer coefficient,by as much as 28.7% and 69.3% for 0.3% and 0.9% of silver content,respectively.Based on the experimental results a correlation was developed to predict the Nusselt number of the silver-water nanofluid,with ±10% agreement between experiments and prediction.

  6. Heat transfer interface between a high temperature heat source and a heat sink

    Energy Technology Data Exchange (ETDEWEB)

    du Pre, F.K.; Jaspers, H.A.

    1977-10-11

    A heat-transfer interface between and separating a high temperature heat source and a heat sink is formed by the adjacent walls of the heat source and heat sink with a thin gap between these walls and helium gas sealed in the gap, the walls preferably defining concentric hemispheres; this interface being particularly feasible as separable walls of the heater portion of a Stirling engine and a heat source.

  7. Heat Transfer Analysis of Fin Tube

    Energy Technology Data Exchange (ETDEWEB)

    Jeon, Woo-Jin [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of); Choi, Cheng-Ryul [ELSOLTEC Co., Yongin (Korea, Republic of)

    2015-10-15

    This paper describes a preliminary numerical analysis of fin tube used for a heat exchanger of the air-water cooling system. The internal flow in a fin tube is steam and the external of the fin is cooled by air. Cooling system in a nuclear power plant can be divided into two categories; 1) active pump driven system powered by alternating current and 2) passive cooling system drived by natural circulation phenomena. After the accident in Hukushima Nuclear Power Plants, the importance of the passive cooling system that can provide a long-term cooling of reactor decay heat during station blackout condition is emphasized. However, the effectiveness of passive cooling system based on cooling water is limited by the capacity of water storage tank. To overcome the limit due to the exhaustion of the cooling water, an natural convection air cooling system is proposed. As the air operated cooling system utilizes natural circulation phenomena of air, it does not require cooling water. However, the heat transfer area of the air operated cooling system should be increased much as the heat removal capacity per unit area is much lower than that of water cooling system. The air-water combined cooling system can resolve this excess increase of the heat transfer area in the air operated cooling system. This air-water cooling system can be also used in the passive containment cooling system. The effect of design parameters such as fin tube arrangement, the fin height, and pitch has been analyzed and the chimney effect on the simulation of heat transfer in a heat exchanger is evaluated. The internal flows in a fin tube heat exchanger for natural circulation flow condition and forced convection (suction) condition were investigated.

  8. Evaporative Heat Transfer Mechanisms within a Heat Melt Compactor

    Science.gov (United States)

    Golliher, Eric L.; Gotti, Daniel J.; Rymut, Joseph Edward; Nguyen, Brian K; Owens, Jay C.; Pace, Gregory S.; Fisher, John W.; Hong, Andrew E.

    2013-01-01

    This paper will discuss the status of microgravity analysis and testing for the development of a Heat Melt Compactor (HMC). Since fluids behave completely differently in microgravity, the evaporation process for the HMC is expected to be different than in 1-g. A thermal model is developed to support the design and operation of the HMC. Also, low-gravity aircraft flight data is described to assess the point at which water may be squeezed out of the HMC during microgravity operation. For optimum heat transfer operation of the HMC, the compaction process should stop prior to any water exiting the HMC, but nevertheless seek to compact as much as possible to cause high heat transfer and therefore shorter evaporation times.

  9. Heat transfer in high density electronics packaging

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    In order to get an insight into the thermal characteristic and to evaluate the thermal reliability of the "System in Packaging"(SIP), a new solution of electronics packaging, a heat transfer model of SIP was developed to predict the heat dissipation capacity and to investigate the effect of different factors on the temperature distribution in the electronics. The affecting parameters under consideration include the thermophysical properties of the substrates, the coefficient of convection heat transfer, the thickness of the chip, and the density of power dissipation. ALGOR, a kind of finite element analysis software,was used to do the model simulation. Based on the sinulation and analysis of the heat conduction and convection resistance, criteria for the thermal design were established and possible measurement for enhancing power dissipation was provided, The results show that the heat transfer model provides a new and effective way to the thermal design and thermal analysis of SIP and to the mechanical analysis for the further investigation of SIP.

  10. Numerical Modeling of Ablation Heat Transfer

    Science.gov (United States)

    Ewing, Mark E.; Laker, Travis S.; Walker, David T.

    2013-01-01

    A unique numerical method has been developed for solving one-dimensional ablation heat transfer problems. This paper provides a comprehensive description of the method, along with detailed derivations of the governing equations. This methodology supports solutions for traditional ablation modeling including such effects as heat transfer, material decomposition, pyrolysis gas permeation and heat exchange, and thermochemical surface erosion. The numerical scheme utilizes a control-volume approach with a variable grid to account for surface movement. This method directly supports implementation of nontraditional models such as material swelling and mechanical erosion, extending capabilities for modeling complex ablation phenomena. Verifications of the numerical implementation are provided using analytical solutions, code comparisons, and the method of manufactured solutions. These verifications are used to demonstrate solution accuracy and proper error convergence rates. A simple demonstration of a mechanical erosion (spallation) model is also provided to illustrate the unique capabilities of the method.

  11. Transient Heat Transfer from a Wire Inserted into a Vertically Mounted Pipe to Forced Flow Liquid Hydrogen

    Science.gov (United States)

    Tatsumoto, Hideki; Shirai, Yasuyuki; Shiotsu, Masahiro; Naruo, Yoshihiro; Kobayashi, Hiroaki; Inatani, Yoshifumi

    The transient heat transfer from a Pt-Co wire heater inserted into a vertically mounted pipe, through which forced flow subcooled liquid hydrogen was passed, is measured by increasing the exponential heat input with various time periods at a pressure of 0.7 MPa and an inlet temperature of 21 K. The flow velocities range from 0.8 to 5.5 m/s. For shorter periods, the non-boiling heat transfer becomes higher than that given by the Dittus-Boelter equation due to the transient conductive heat transfer contribution. In addition, the transient critical heat flux (CHF) becomes higher than the steady-state CHF. The effect of the flow velocity and period on the transient CHF heat flux is also clarified.

  12. Some stakes in heat transfer; Quelques enjeux en transferts thermiques

    Energy Technology Data Exchange (ETDEWEB)

    Saulnier, J.B. [Ecole Nationale Superieure de Mecanique et d`Aerotechnique (ENSMA), 86 - Poitiers (France). Laboratoire d`Etudes Thermiques (LET)

    1998-10-01

    Heat transfer is strongly involved in many scientific and technologic domains and the French heat transfer laboratories and networks cooperating is this field are first located. The analysis of the main industrial activities demanding heat transfer competence helps on first to identify some up-to-date technological challenges. It appears clearly that connections are to be reinforced between disciplines like heat transfer, fluid mechanics, combustion, material science, optics, biology... Scientific objectives are then scanned through, by spitting the research activities between mature topics (radiation, particularly in semi-transparent media; convection and thermo-convective instabilities; heat transfer in porous media...), emerging (heat transfer with change of phase, convective heat transfer enhancement by active control in the boundary layer, inverse techniques...) and incipient ones. Among some promising new topics, let us mention microscale heat transfer, and also bio-heat transfer. (authors)

  13. Review of heat transfer problems associated with magnetically-confined fusion reactor concepts

    Energy Technology Data Exchange (ETDEWEB)

    Hoffman, M.A.; Werner, R.W.; Carlson, G.A.; Cornish, D.N.

    1976-04-01

    Conceptual design studies of possible fusion reactor configurations have revealed a host of interesting and sometimes extremely difficult heat transfer problems. The general requirements imposed on the coolant system for heat removal of the thermonuclear power from the reactor are discussed. In particular, the constraints imposed by the fusion plasma, neutronics, structure and magnetic field environment are described with emphasis on those aspects which are unusual or unique to fusion reactors. Then the particular heat transfer characteristics of various possible coolants including lithium, flibe, boiling alkali metals, and helium are discussed in the context of these general fusion reactor requirements. Some specific areas where further experimental and/or theoretical work is necessary are listed for each coolant along with references to the pertinent research already accomplished. Specialized heat transfer problems of the plasma injection and removal systems are also described. Finally, the challenging heat transfer problems associated with the superconducting magnets are reviewed, and once again some of the key unsolved heat transfer problems are enumerated.

  14. Effect of Uniformly and Nonuniformly Coated Al2O3 Nanoparticles over Glass Tube Heater on Pool Boiling

    Directory of Open Access Journals (Sweden)

    Nitin Doifode

    2016-01-01

    Full Text Available Effect of uniformly and nonuniformly coated Al2O3 nanoparticles over plain glass tube heater on pool boiling heat transfer was studied experimentally. A borosilicate glass tube coated with Al2O3 nanoparticle was used as test heater. The boiling behaviour was studied by using high speed camera. Result obtained for pool boiling shows enhancement in heat transfer for nanoparticle coated surface heater and compared with plain glass tube heater. Also heat transfer coefficient for nonuniformly coated nanoparticles was studied and compared with uniformly coated and plain glass tube. Coating effect of nanoparticles over glass tube increases its surface roughness and thereby creates more nucleation sites.

  15. Boiling of HFE-7100 on a Straight Pin Fin

    Institute of Scientific and Technical Information of China (English)

    Z. W. Liu; W.W. Lin; D.J. Lee; J.P. Hsu

    2001-01-01

    This paper deals with an experimental investigation of pin fin boiling of saturated and subcooled HFE-7100 under atmospheric pressure. Fin base temperature and heat flux data are measured along with the fin tip temperature. The basic features of boiling stability of HFE-7100 boiling on pin fin had been reported for the first time. For a given liquid/heating surface combination there exist upper steady-state (USS) branch and lower steady-state (LSS)branch, and a large, unstable regime located in between. Zones with different stability characteristics are mapped according to boiling on fins with different aspect ratios. Liquid subcooling can largely enhance heat transfer performance. A longer fin can provide a safer operation.

  16. Heat transfer and pressure drop in an annular channel with downflow

    Science.gov (United States)

    Dolan, F. X.; Crowley, C. J.; Qureshi, Z. H.

    The onset of a flow instability (OFI) determines the minimum flow rate for cooling in the flow channels of a nuclear fuel assembly. A test facility was constructed with full-scale models (length and diameter) of annular flow channels incorporating many instruments to measure heat transfer and pressure drop with downflow in the annulus. Tests were performed both with and without axial centering ribs at prototypical values of pressure, flow rate and uniform wall heat flux. The axial ribs have the effect of subdividing the annulus into quadrants, so the problem becomes one of parallel channel flow, unlike previous experiments in tubes (upflow and downflow). Other tests were performed to determine the effects if any of asymmetric and non-uniform circumferential wall heating, operating pressure level and dissolved gas concentration. Data from the tests are compared with models for channel heat transfer and pressure drop profiles in several regimes of wall heating from single-phase forced convection through partially and fully developed nucleate boiling. Minimum stable flow rates were experimentally determined as a function of wall heat flux and heat distribution and compared with the model for the transition to fully developed boiling which is a key criterion in determining the OFI condition in the channel. The heat transfer results in the channel without ribs are in excellent agreement with predictions fro