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.     

Dynamic Behavior of Bubble Interface During Boiling

A brief review with discussions is conducted for some pertinent works, done and ongoing in the Laboratory of Phase-Change and Interfacial Phenomena at Tsinghua University, on interfacial behavior of vapor bubbles and interfacial transport phenomena during liquid nucleation boiling. From a sequence of experimental investigations, some new phenomena, particularly, the visually observed interfacial transport phenomena or processes including jet-like flows, bubble interaction and spatial scale effect, were described in this article. The interfacial effects and transport phenomena associated with surface tension gradients caused by temperature and concentration variations were theoretically analyzed to reveal the marked influence on bubble interfacial shape and dynamic behavior, the bubble dynamics including nucleation, bubble motion and coalescence. Several theoretical models and methods were proposed to describe the dynamic characteristics and explain the physics of interfacial phenomena/processes. The spe     

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.     

Spring Inserts for the Intensification of the Heat Exchange Process during Boiling in Vertical Tubes——Optimization of Geometric Parameters

The paper presents new criteria for calculation of heat transfer coefficients and flow resistance during boiling inside vertical tubes with spring inserts, developed on the basis of own experimental research. Calculations of the geometric parameters of the spring insert were carried out using the Nelder-Mead optimization method for various optimization criteria (maximizing the increase ratios for heat transfer coefficient and flow resistance, minimizing entropy, own optimization criterion). The results of optimization calculations were verified by the optimization procedures available in Statistica.     

High Heat Flux Burnout in Subcooled Flow Boiling

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Theoretical Aspects of Nucleate Pool Boiling with Dielectric Liquids

Direct cooling with inert,dielectric liquids may well become the technique of choice for the thermal manage-ment of future electronic systems.Due to the efficiency of phase-change processes and the simplicity of naturalcirculation,nucleate pool boiling is of great interest for this application.This paper examines the characteristicsof vapor bubbles and nucleate pool boiling of the dielectric liquids.The results provide a theoretical foundationfor understanding and interpreting the often complex empirical results reported in the literature.     

Liquid Jet Impingement Heat Transfer with or without Boiling

The purpose of this paper is to summarize the important studies in the area of impingement heat transfer with or without phase change, with emphasis on the research conducted at Beijing Polytechnic University mainly with circular jets. Heat transfer characteristics of single phase jets are discussed in detail. Comment is presented on boiling heat transfer of impinging jets for steady and transient states. Some special colling configurations of two-phase jets are also introduced.     

Investigation of Enhanced Boiling Heat Transfer from Porous Surfaces

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Enhanced Boiling Outside 8 × 3 Plain and Coated Tube Bundles

Experiments were conducted for pool boiling on the outside of 8 × 3 (eight rows and three columns) plain and coated tube (surface roughness = 8.279 μm) bundles for three different pitch distances with the distinct objective to study the behavior and the enhancement of boiling heat transfer in horizontal staggered tube bundles (of plain and coated tubes for different equilateral triangular arrangements) with heat flux values ranging from ～12 to 45 kW/m². At higher heat fluxes, coated and plain tube bundles had almost similar bundle average heat transfer coefficients at a given pitch distance, while at lower heat fluxes, the coated tube bundles have higher bundle average heat transfer coefficients as compared to that of the plain tube bundle. The coated tube bundles with the minimum pitch to diameter ratio of 1.4 exhibited the maximum bundle average heat transfer coefficients. The present study concludes that the bundle factor needs to be considered in the design of flooded evaporators.     

Boiling of HFE—7100 on a Straight Pin Fin

IntroductionSeveral books had summarized inveshgationsanalyzing fins with a consent heat tusfer coefficient(e.g., see Kem and Kraus[']). When boiling occurs on a fin,the heat transfer coefficient along the fin is definitely notconstant. Inveshgated by the Pioneering works of Haleyand Westwatefv and Lai and Hsu['l, fin boiling ProCesshas received extensive attention. ~sl41 and Liaw andYehul reviewed the related lit~. BOth the heattransfer rate from the fin base, as well as the feasibleoper…     

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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Nucleate Boiling in Large Arrays of Impinging Water Sprays

The nucleate boiling of subcooled water, under 100 cm² square arrays of impinging sprays, was experimentally investigated. Three types of commercially available full cone pressure nozzles, of distinct flow capacities, allowed for runs where the average impinging coolant mass flux spanned the 0.3–7.2 kg/m²-s range. Array geometry was varied adjusting nozzle-to-nozzle and nozzle-to-impingement surface distances. Experimental construction allowed for good drainage of spent coolant and unrestricted air entrainment to spray cones. The average heat flux through the heated, upward-facing, copper impingement surface was found to be equal to the sum of single-phase and nucleate boiling heat flux components. The phase-change component was experimentally observed to depend upon wall excess temperature only. The proposed heat transfer correlation reproduces original experimental data with a mean absolute error of 10.6%. Non-critical-heat-flux (non-CHF) cooling capacity and efficiencies of up to, respectively, 2000 kJ/kg and 83% were observed.     

Could Use of Soft Surfaces Augment Onset of Nucleate Boiling?

This work uses elementary theoretical arguments to estimate whether softening of the surface could be used, along with surface texture and chemistry, to control superheat required for onset of nucleate boiling. For an ideal, smooth surface a mild decrease of the required superheat is predicted. In turn, an approximate closed-form model of vapor trapping and bubble seeding from soft surface with conical cavities shows linear dependence between the required superheat and the substrate’s shear modulus. Based on these results, considerations involved in implementing soft coatings for boiling applications and relevant outstanding fundamental questions are also briefly discussed.     

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.     

Nucleate Boiling of n-Pentane in a Horizontal Confined Space

An experimental study was carried out on n-pentane nucleate boiling at atmospheric pressure and saturation temperature for different gap sizes. The boiling was investigated in a confined space delimited by two horizontal discs, a heated surface and an adiabatic surface, for distances varying between 0.1 mm and 13 mm. Tests were carried out on heated surfaces of 12 mm and 20 mm diameter. The effects of the gap size on the partial boiling curve and the diameter of the heated surface were studied. A dimensionless analysis was carried out and a correlation to describe the phenomenon of confined nucleate boiling is presented.     

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.     

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

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

High-Speed Visualization of Bubble Behaviors for Pool Boiling of R-141b

A visualization study on the behavior of bubbles has been carried out for pool boiling of R141b on a horizontal transparent heater at pressure 0.1 MPa. The behaviors of bubbles were recorded by a high-speed camera placed beneath the heater surface. The departure diameter, departure time of bubbles and nucleation site density at different heat flux were obtained. The visualization results show that bubble departure diameter and departure time decrease , while the nucleation site density increases as the heat flux increases. It is also observed that there is no liquid recruited into the microlayer in the experiment. Based on the experimental results, boiling curve for R141b was predicted by using the dynamic microlayer model. As a result, the agreement between the predictive result based on the dynamic microlayer model and the experiment data for boiling curve of R141b is good at high heat flux.     

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…     

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…