Nucleate Pool Boiling Heat Transfer of Pure Refrigerants and Binary Mixtures

Heat transfer coefficients in nucleate boiling on a smooth flat surface were measured for pure fluids of R-134a, propane, isobutane and their binary mixtures at different pressure from 0.1 to 0.6 MPa. Series of experiments with different heat flux and mixture concentrations were carried out. The influences of pressure and heat flux on the heat transfer coefficient for different pure fluids were studied. Isobutane and propane were used to make up binary mixtures. Compared to the pure components, binary mixtures show lower heat transfer coefficients. This reduction was more pronounced as the heat flux increasing. Several heat transfer correlations are obtained for different pure refrigerants and their binary mixtures.     

Nucleate Pool Boiling of Pure Liquids and Binary Mixtures ：Part I—Analytical Model for Boiling Heat Transfer of Pure Liquids on Smooth Tubes

A mechanism is proposed for nucleate pool boiling heat transfer along with a general model for both pure liquids and binary mixtures. A combined physical model of bubble growth is also proposed along with a corresponding bubble growth model for pure liquids on smooth tubes. Using the general model and the bubble growth model for pure liquids, an analytical model for nucleate pool boiling heat transfer of pure liquids on smooth tubes is developed.     

A Study of the Influence of Solid Particles on Boiling Hysteresis

Experiments have been performed to determine the effects on boiling hysteresis of locally fluidized particlescontained in a liquid that serves as coolant for electronic equipment.The results show that locally fluidizedparticles can diminish boiling hysteresis.     

Nucleate Pool Boiling of Pure Liquids and Binary Mixtures：PartI－Analytical Model for Boiling Heat Transfer of Pure Liquids on Smooth Tubes

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Influence of Tube‘s Diameter on Boling Heat Transfer Performance in Small Diameter Tubes

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.     

Investigation of Enhanced Boiling Heat Transfer from Porous Surfaces

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

INTanDUCTI0NBoilingheattransferandcriticalheatflux(CHF)inaconfinednarrowspacehavebeenstudiedexperi-melltallybyanumberofinvestigatorsinthepastfewdecades.However,thereisnoanypopularlyacceptedmodelintheheattransferinnarrowspaceboiling,althoughsomepopularknowledgeabouttheboilingheattransferinthenarrowspacehavebeenacceptedbymanyresearchers.Theknowledgecanbecon-cludedasthatthenucleateboilingheattransferisenhancedatlowheatfluxregionanddeterioratedathighheatfiuxregi0nespeciallyatCHF.Theenhanceme…     

Influence of Tube's Diameter on Boiling Heat TransferPerformance in Small Diameter Tubes

INTaoDUCTIONReclitlydry-troeeVaPoratorofairconditioningmaChineandreffigeratorhavebeendevefoPinginthedirectionofusingsmalldiamtertube.TheHITACHICo.conductedaserlesofeVaPoratfonhe8ttransferexperimeats,usingthethinwallcoppertubesofinnerdiamter9.52nun,8mm,7mmand5nunre-spectivelytheworkingmediawasHCFC22(qualityx=o.6)I'].TheresulthasshoWnthatheeVaPo-rationheattransfercoefficielltsweresghcatlyincreasedwiththedecreasingoftubediameter.EVaThorationheattransfercoefficientofa5.onuninnerdiare…     

Boiling on a Tube Bundle: Part II—Heat Transfer and Pressure Drop

An extensive experimental study was undertaken to measure nucleate pool boiling heat transfer coefficients, local bundle boiling heat transfer coefficients, and two-phase bundle pressure drops for R134a and R236fa on one plain tube bundle configuration. The experimental database allowed the refinement of frictional pressure drop models previously developed at the Laboratory of Heat and Mass Transfer. Together with the new onset of dryout prediction method presented in part I (preceding article in this issue), this constitutes a significant improvement in such prediction methods. The local bundle boiling heat transfer data highlighted the dependency of the heat transfer coefficient on the heat flux as expected for the present conditions. The new method was proposed and worked well versus the present database and was also validated against additional refrigerants from independent studies. It was proven to also work reasonably well for falling film evaporation data, proving the new prediction method is applicable for a wide range of operating conditions.     

Critical Heat Flux in Flow Boiling—Review of the Current Understanding and Experimental Approaches

ABSTRACT

A comprehensive review of current literature on subcooled flow boiling with a focus on the mechanistic modeling of the departure from nucleate boiling is presented. This review covers parametric trends, other reviews on the topic, previous modeling approaches, applicable measurement techniques for two-phase flow, and an extensive literature review on mechanistic models for the prediction of critical heat flux (CHF). The models have been carefully deconstructed to give an overview about differences and similarities in the respective modeling approaches. Drawing on previously successful application of measurement techniques for two-phase flow, recommendations for future experimental investigation regarding specific parameters of the respective models are given for the refinement of the current modeling approaches of CHF phenomena.     

A Numerical Study on the Heat Transfer Enhancement Behavior of Water-Microparticles Suspension

The heat transfer enhancement characteristics of water with polystyrene particles are examined in the present numerical study. The numerical study is conducted in the hydrodynamically fully developed turbulent flows within a circular duct with the wall boundary condition of a constant heat flux. The thermal conductivity of the turbulent flow obtained by the Reynolds analogy is 1000 times as much as the thermal conductivity of water. On the contrary, the enhancement of thermal conductivity caused by water-microparticles suspension is relatively low. Slight enhancements of the local Nusselt number are obtained in the numerical calculations of Newtonian turbulent flows with the micro-convection effects, thus showing large deviations from the experimental data. The numerical results in non-Newtonian flows are in agreement with the experimental data. Thus, the main cause for the enhancement of the heat transfer of the suspension might be not due to the micro-convection effects but to the non-Newtonian effects     

Effect of Radiative Heat Transfer on Indoor—Fire

The importance of radiative heat transfer in the simulation of indoor-fire has been studied.Computer codeshave been developed based on four-flux model and discrete transfer model,respectively.Evaluation of the codesagainst exact analytic solution and experimental data shows that the discrete transfer model gives numericalresults with acceptable accuracy while the four-flux model underpredicts the heat fluxes although the gen-eral trend is reasonable.Numerical studies have been performed of two-dimensional,axisymmetric turbulent,buoyancy-controlled indoor fire.The computational results show that neglecting radiation in the simulationcan cause overprediction of 500K in the maximum temperature and less uniform velocity field compared to theprediction by discrete transfer model.The four-flux method has been found to produce less uniform velocityand temperature values than discrete transfer model,but is more economic in computation.     

On the Numerical Modeling of Impinging Jets Heat Transfer—A Practical Approach

This article compares steady-state and transient simulations in predicting impinging jet heat transfer. The configurations tested are H/D = 2 and 6, Re = 10,000, 20,000, 23,000, and 30,000. The variables considered are: turbulence model (LES, k-?, k-ω, V2F), discretization schemes, mesh density and topology, inlet velocity profile, and turbulence. The V2F model performs best for the steady state simulations. The inlet velocity profile plays an important role. Mesh topology and distribution is also important. The turbulence created in the shear layer plays a stronger role than the inlet turbulence. The LES model reproduces the turbulent structures with a useful degree of accuracy.     

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

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 field numerical calculations have been carried out, and heat transfer coefficient correlations along full-flow-path derived. The results show that heat transfer performance of boiling two-phase flow could be significantly augmented 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.     

Undergraduate Education in Heat Transfer—A Point of View

During the past three decades, many new technologies have enhanced the application of heat transfer, while other technologies (computational and measurement) have strongly influenced its practice. These developments present the heat transfer instructor with many options, and compromises must be made in deciding what balance should be reached in presenting heat transfer principles, establishing their relationship to thermal system behavior, and introducing modern tools of heat transfer analysis and measurement. In this paper, reasonable goals of a first course in heat transfer are identified and prioritized. Highest priority is assigned to those goals which enhance the student's understanding of basic principles and the skill to apply these principles in thermal system design and evaluation.     

Reexamination of Correlations for Nucleate SiteDistribution on Boiling Surface by Fractal Theory

INTRODUCTIONThenumberandspatia1distributionofnucleatesiteplaysaparticu1arimportantroleinmodelingorpred-icatingofnucleateboilingprocess.Thenucleatesitedistributiondensityappearsasanimportantterminalmostallthemechanisticnucleateboilingmodels[1].Inpastdecades,manyresearchersproposedvariousexperimentalcorrelations.Forexample,MikicandRohsenowl2],Biereta1.[3],WangandDhirl4]devel-opedsomeempiricalcorrelationsbetweenthecumula-tiveactivenucleatesitenumberandthecharacteristicsizesuchasthemouthdia…     

Experimental Investigations on Boiling Heat Transfer Inside Miniature Circular Tubes Immersed in FC-72

To investigate the size effect on the characteristics of boiling heat transfer, boiling behavior of FC-72 in heated vertical miniature circular tubes immersed in a liquid pool was experimentally studied. Two AISI 304 stainless steel tubes with inner diameters of 1.10 mm and 1.55 mm correspondingly, were heated by swirled Ni-Cr wire heaters and sealed in Lucite blocks by silicon adhesive. Both the top and the bottom ends of the circular test sections were open to the liquid pool. The boiling curves and heat transfer coefficients were obtained experimentally. The boiling behaviors at the outlets of the miniature tubes were also visualized with a digital video camera. Experimental results show that the tube geometry has a significant effect on the boiling characteristics. Vapor blocking at the outlet of the smaller circular tube with a diameter of 1.10 mm caused severe boiling hysteresis phenomena. The CHF decreased with reducing in tube size.     

Boiling Delay Phenomenon in a Thermosyphon Heat Sink and Its Effect on Device Performance

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Numerical Study of Heat Transfer Enhancement by Liquid Film on the Walls

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