微尺度通道内流动沸腾研究综述

阐述了微尺度通道内传热问题出现的工程背景——高密度微电子器件的冷却。对当前国内外微尺度通道内流动沸腾换热特性的研究现状进行了归纳。突出分析了工质种类、微尺度通道的几何参数和工质的工况参数等对微尺度通道内流动沸腾换热特性的影响。同时分析了微尺度通道内流动沸腾换热的强化机理、流动阻力特性、压降关联式和沸腾换热关联式的理论和实验研究。最后根据分析对今后的工作提出了一些建议。     

外加电场强化苯自然对流和沸腾换热的试验研究

对沉浸在非极性有机液体工质苯中的平板表面自然对流和沸腾换热的外加电场强化进行了试验，得出了自然对流和沸腾换热的换热系数、强化效果与电场电压、热流密度的关系。试验数据表明外加电场对平板表面苯的自然对流换热和沸腾换热都有一定的强化效果，但外加电场对平板表面苯自然对流换热的强化效果明显好于对沸腾换热的强化效果；且平板表面苯的自然对流换热的强化效果与试验所给定的热流密度无关，而外加电场对平板表面苯的沸腾换热的强化效果随热流密度的增大而减弱。     

微通道和小通道内流动沸腾换热的研究

介绍了小通道、微通道内流动沸腾换热机理的最新进展，其中包括国内外学者对各种形状的单通道小通道内流动沸腾现象的解释及其对换热系数影响的各种不同看法，以及微通道内流动沸腾换热现象研究的概况；还介绍了小通道和微通道内流型转变的研究现状，指出了各研究者研究结果的差异，并提出要进一步探索小通道微通道内流动沸腾换热现象，必须借助更先进的观测手段等。     

垂直矩形窄通道流动沸腾换热特性实验研究

流动沸腾换热是典型的两相流问题。窄通道与常规通道相比较,其流动沸腾换热系数有较大提高,换热机理也更加复杂。针对截面为250 mm×5 mm的竖直矩形窄缝通道,在低压、入口温度过冷、不同质量流速及加热功率密度的条件下,对水流动沸腾换热特性进行实验研究。通过实验分析可知:入口温度27～60℃、质量流速2.22～3.49 kg/(m2.s)及加热功率密度0～12 kW/m2对饱和沸腾起始点和过冷段长度有重要影响;高的空泡份额和通道结构的限制使汽液两相流动不稳定而影响换热系数,换热系数随着功率的增大而减小,流体进入完全对流沸腾阶段;由于实验段通道顶部结构的限制,干度的增加不会出现干涸点,换热不会得到恶化,换热系数随着功率的增大基本不变。     

紧凑型强化传热管管束受限空间内沸腾强化换热特性

采用满液式蒸发换热器，利用强化传热管管束受限空间内早期沸腾强化机理，将中小热负荷条件下的自然对流换热转化为核沸腾换热。其换热性能大大优于降膜式蒸发换热器。对紧凑型滚压表面传热管管束在受限空间内沸腾强化换热进行实验研究，确认了满液式蒸发换热器使用紧凑型滚压强化管束具有良好的换热性能，在小管间距时有显著的沸腾换热复合强化效应。     

多孔表面新型复杂结构优化沸腾传热的实验研究

报道了R11在烧结多孔表面开槽时沸腾传热的实验研究，实验发现，与普通槽道和双空隙层多孔表面相比，沸腾换热增强，沸腾表现为液体灌注、槽道起泡、底部蒸干三个区，对特定的多孔层，开槽可获得更好的换热效果。带槽道的多孔表面实验件与均匀多孔表面相比，在相同壁面过热度（θ）条件下，热流密度（q）提高2－10倍，临界热流密度提高2－4倍。     

高低热导率相间表面强化饱和池沸腾的格子玻尔兹曼模拟

采用格子玻尔兹曼方法模拟高低热导率相间表面的饱和池沸腾过程,研究不同表面高低热导率区域热导率比值、低热导率区域宽度和深度对沸腾换热性能的影响。对比均匀热导率表面与高低热导率相间表面的沸腾曲线发现：高低热导率相间表面的沸腾过程可被分为5个阶段,并且其临界热流密度最高可达均匀表面的12倍;高低热导率相间可促使表面维持一定的温度差异,从而保持明显的气液流动;随着低热导率区域宽度增大,气液分离更加明显,低热导率区域宽度存在一个最优值,其与毛细长度的量级接近;随着低热导率区域的深度增大,表面过热度的差异更加明显。     

内表面烧结型多孔管的流动沸腾换热

采用流动沸腾传热试验平台,研究了2 m长铁基烧结型内表面多孔管竖直管内流动沸腾传热特性,利用流动沸腾传热学基本原理及公式计算了传热过程中的热通量、沸腾传热系数及相关参数,并考察了过热度和流速对多孔管流动沸腾传热性能的影响.结果表明:烧结型表面多孔管的流动沸腾传热能力优于同条件下的光滑管,内表面沸腾传热系数是同尺寸光滑管...     

微/小通道内沸腾换热研究综述

微／小通道紧凑式蒸发器的应用越来越广泛，对其换热特性的深刻认识和进一步研究已成为当前亟待解决的课题，而目前涉及微／小尺度通道内沸腾换热特性和流动方面的研究尚处于起步阶段：本文介绍了近年来国内外微／小通道内沸腾换热方面的研究状况，并指出了该研究领域有待于深入开展研究的内容。     

微通道内流动沸腾特性研究

对国内外微通道流动和换热的研究实验作了总结,阐述了影响微通道换热系数的因素,如热流密度、过热度和干度等.对去离子水在内径为0.65 mm、长为102 mm的圆形管道内流动沸腾换热进行了实验研究,得到了局部换热系数随干度的变化关系,进而根据换热系数的变化趋势讨论了饱和流动沸腾区微通道内主导的换热机制.结果表明:从换热系数随干度的变化关系很难判定主导的换热机制;将实验数据与已发表的预测关联式进行了比较,发现大多关联式都失效,说明基于常规理论的模型不再适用于微通道.     

Comparison of Six Typical Correlations for Upward Flow Boiling Heat Transfer with Kerosene in a Vertical Smooth Tube

The present article is aimed at evaluating six typical flow boiling heat transfer correlations selected from the open literature with experimental results. The selected correlations are correlations of Chen, Shah, Gungor and Winterton, Liu and Winterton, Klimenko, and Kandlikar. Experiments of upward flow boiling heat transfer with kerosene in a vertical smooth tube were conducted. The test tube has a length of 2.5 m and its outer and inner diameters are 19 mm and 15 mm, respectively. The experiments were performed at an absolute atmospheric pressure of 3. The input heat flux ranged from 28.5 to 93.75 kW/m² and the mass fluxes were selected at 410, 610, and 810 kg/m² s, respectively. The experimental flow boiling heat transfer coefficients were compared with flow boiling heat transfer coefficients calculated with the six typical correlations. By comparison, the most suitable correlations are recommended for the calculation of flow boiling heat transfer coefficients with kerosene in a smooth tube.     

Heat transfer and pressure drop during flow boiling of pure refrigerants and refrigerant/oil mixtures in tube with porous coating

The experimental stand and procedure for flow boiling investigations are described. Experimental data for pure R22, R134a, R407C and their mixtures with polyester oil FUCHS Reniso/Triton SEZ 32 in a tube with porous coating and smooth, stainless steel reference tube are presented. Mass fraction of oil was equal to 1% or 5%. During the tests inlet vapour quality was set at 0 and outlet quality at 0.7. Mass velocity varied from about 250 to 500 kg/m²s. The experiments have been conducted for average saturation temperature 0 °C. In the case of flow boiling of pure refrigerants, the application of a porous coating on inner surface of a tube results in higher average heat transfer coefficient and simultaneously in lower pressure drop in comparison with the flow boiling in a smooth tube for the same mass velocity. Correlation equation for heat transfer coefficient calculation during the flow boiling of pure refrigerants inside a tube with porous coating has been proposed.     

Flow boiling characteristics of refrigerant mixture R22/R114 in the annulus of enhanced surface tubing

The paper presents an experimental study of flow boiling heat transfer characteristics of refrigerant mixture R22/R114 in the annuli of a horizontal enhanced surface tubing evaporator. The test section had an inner tube bore diameter of 17.3 mm, an envelope diameter of 28.6 mm and an outer smooth tube of 32.3 mm internal diameter. The ranges of heat flux and mass velocity covered in the tests were 5–25 kW/m² and 180–290 kg/m²/s, respectively, at a pressure of 570 kPa. The enhanced surface tubing data shows a significant enhancement of the heat transfer compared with an equivalent smooth tube depending on the mixture components and their concentrations. Correlations are proposed to predict such heat transfer characteristics as the average heat transfer coefficients as well as pressure drops of R22/R114 nonazeotropic refrigerant mixture flow boiling inside enhanced surface tubing. In addition, it was found that the refrigerant mixture's pressure drop is a weak function of the mixture composition.     

Dispersed flow film boiling in vertical narrow annular gaps

Dispersed flow film boiling heat transfer in vertical narrow annular gaps with gap sizes of 1.0, 1.5 and 2.0 mm was experimentally investigated with de-ionized water as the working fluid at low mass velocities. Comparisons of the experimental data with established correlations show that the correlations are not accurate for small gaps. The influences of the heating mode (only one tube heating or both tubes heated), the gap size and the tube diameter were analyzed. The data was correlated in the form of the Groeneveld equation with a modified wall temperature factor as use in the Polomik correlation and a modified gap size factor as use in the Yun and Muthu correlation. A new correlation was developed for dispersed flow film boiling heat transfer based on the experimental data for 1.0–2.0 mm gaps.     

Forced convective condensation and boiling of ternary non-azeotropic refrigerant mixtures inside water/refrigerant enhanced surface tubing

In this paper, an experimental study on the heat transfer characteristics of two-phase flow condensation and boiling of ternary non-azeotropic refrigerant mixtures, on water/refrigerant horizontal enhanced surface tubing, is presented. The enhanced surface tubing data showed a significant enhancement of the heat transfer compared to an equivalent smooth tube depending on the mixture components and their concentrations. Correlations were proposed to predict the heat transfer characteristics such as average heat transfer coefficients, as well as pressure drops of ternary non-azeotropic refrigerant mixture flow condensation, and boiling inside enhanced surface tubing. In addition, it was found that the refrigerant mixture's pressure drop is a weak function of the mixture's composition.     

Convective boiling heat transfer and two-phase flow characteristics inside a small horizontal helically coiled tubing once-through steam generator

The pressure drop and boiling heat transfer characteristics of steam-water two-phase flow were studied in a small horizontal helically coiled tubing once-through steam generator. The generator was constructed of a 9-mm ID 1Cr18Ni9Ti stainless steel tube with 292-mm coil diameter and 30-mm pitch. Experiments were performed in a range of steam qualities up to 0.95, system pressure 0.5-3.5 MPa, mass flux 236-943 kg/m²s and heat flux 0-900 kW/m². A new two-phase frictional pressure drop correlation was obtained from the experimental data using Chisholm’s B-coefficient method. The boiling heat transfer was found to be dependent on both of mass flux and heat flux. This implies that both the nucleation mechanism and the convection mechanism have the same importance to forced convective boiling heat transfer in a small horizontal helically coiled tube over the full range of steam qualities (pre-critical heat flux qualities of 0.1-0.9), which is different from the situations in larger helically coiled tube where the convection mechanism dominates at qualities typically >0.1. Traditional single parameter Lockhart-Martinelli type correlations failed to satisfactorily correlate present experimental data, and in this paper a new flow boiling heat transfer correlation was proposed to better correlate the experimental data.     

Experimental study on convective boiling heat transfer in vertical narrow-gap annular tube

IntroductionConvechve boiling or highly subcooled single-Phaseforced convention in micro-channels is an effeCtivecooling meChedsm with a wide ~ge of aPPlications.Among these are the COOling of such diverse system as. accelerator abets, high power resistive magnets,compact fission ~ cores, fusion ~ blankets,advanced space thermal management systems,manufachang and materials Processing OPerations, andhigh-density multi~chip modules in supe~ andOther modular eleCtronics. These devices involv…     

A complete evaluation method for the experimental data of flow boiling in smooth tubes

A complete solution for boiling phenomena in smooth tubes has been giving as a procedure regarding with the calculation of convective heat transfer coefficient and pressure drop using accurate experimental data validated by flow regime maps and sight glasses on the experimental facility. The experimental study is conducted in order to investigate the effect of operating parameters on flow boiling convective heat transfer coefficient and pressure drop of R134a. The smooth tube having 8.62 mm inner diameter and 1100 mm length is used in the experiments. The effect of mass flux, saturation temperature and heat flux is researched in the range of 290–381 kg/m² s, 15–22 °C and 10–15 kW/m², respectively. The experiments revealed that the heat transfer coefficient and pressure drop are significantly affected by mass flux for all tested conditions. Moreover, the experimental results are compared with well-known heat transfer coefficient and frictional pressure drop correlations given in the literature. In addition, 122 number of heat transfer and pressure drop raw experimental data is given for researchers to validate their theoretical models.     

Forced convective boiling of nonazeotropic refrigerant mixtures inside enhanced surface tubing

An experimental study on the characteristics of two phase flow boiling of pure refrigerants such as R12 and R22 as well as nonazeotropic refrigerant mixtures R22/R114 and R22/R152a inside horizontal enhanced surface tubing is presented. The enhanced surface tubing results showed a significant improvement of the heat transfer over that of an equivalent smooth tube, depending on the mixture components and their concentrations. Correlations are proposed to predict the heat transfer characteristics such as average heat transfer coefficients as well as pressure drops of nonazeotropic refrigerant mixture flow boiling inside enhanced surface tubing. In addition, it was found that the refrigerant mixtures pressure drop is a weak function of the mixture compositions.