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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矩形窄缝流道内过冷沸腾汽泡行为的可视化

采用高速摄像仪,对矩形窄缝流道内过冷沸腾时的汽泡行为进行了可视化实验研究.分析了工况参数对汽泡成核起始点及其脱离直径的影响.结果表明:高过冷沸腾时,窄缝流道内加热面上产生了沿近壁面滑移的汽泡,这种滑移汽泡对窄缝流道内的换热产生了积极的作用,而且汽泡的滑移现象与主流流体的温度有着密切的关系,分析了产生这种滑移现象的原因.     

垂直矩形窄缝内的过冷流动沸腾换热性能

用高速摄像等方法研究了有压模化介质在单一垂直矩形窄缝流道内的气泡形态和传热情况 ,发现窄缝流动沸腾换热强化的原因在于流道尺寸较小 ,气泡的形状发生变化 ,增加了界面体积浓度 ,并强化了对加热面附近的扰动 ,使换热有所强化。通过与实际测量的壁温数据进行比较 ,发现用于计算大流道和池过冷沸腾换热的 Rohsenow关系式预测窄流道内高热流密度下的过冷流动沸腾换热的误差不大 ,但对于较低热流密度下的过冷流动沸腾时误差较大 ;通过最小二乘法对 Rohsenow关系式进行修正后 ,误差低于± 2 5 %。     

Enhancement of Boiling Heat Transfer Using Surface Vibration

An experimental investigation of the effect of mechanical vibrations of a copper flat circular surface on the pool boiling heat transfer coefficient of water at atmospheric pressure are presented in this paper. A vibration exciter was used to vibrate this copper test surface vertically. Effect of frequency and amplitude of vibration on the boiling heat transfer coefficient was studied. An increase in the heat transfer coefficient was observed at low frequency and amplitudes, at higher amplitude and frequency heat transfer deteriorates. Heat transfer coefficient increases up to 26% with vibration intensity, represented by vibrational Reynolds number.     

强化管外CFC11与HCFC123沸腾换热系数的对比试验研究

本文通过强化管外CFC11与HCFC123沸腾换热系数的对比试验分析与研究,分别得出了HCFC123与CFC11沸腾换热系数,并对这两种工质的实际应用情况进行了分析。     

微细通道内R290流动沸腾换热特性实验研究

对R290制冷剂在微细通道内的流动沸腾换热特性进行了实验研究。研究管径分别为1和2 mm,热流密度为20~65 k W/m~2,质量流率为100~200 kg/m~2·s,饱和温度为15和25℃,干度范围为0.1~0.9。通过实验数据分析管径、热流密度、质量流率、饱和温度对流动沸腾换热的影响。结果表明:随着管径的下降,换热系数呈现出大幅上升的趋势,其平均增幅为31%;随着热流密度的上升,换热系数呈现出大幅上升的趋势,其平均增幅达到了131%;随着质量流率的上升,换热系数呈现出小幅上升的趋势,其平均增幅为14%;随着饱和温度的上升,大部分换热系数呈现出小幅上升的趋势,其平均增幅为12.6%。     

Boiling heat transfer in a narrow space controlled by punched interference plate

An experiment on pool boiling in methanol was performed for a case in which the boiling space was controlled by an interference plate with many holes. The narrow space, 0.12 mm in thickness, between the heat transfer surface and the interference plate was hermetically sealed at the perimeter. Therefore, the vapor and liquid were only exchanged through the holes in the interference plate. The degree of superheat at the onset of boiling was 0.7 K without overshoot at 10‐mm plate thickness, 1‐mm hole diameter, and 3.85‐mm hole pitch. The critical heat flux obtained was the same value without the interference plate mentioned above. The interference plate disturbed free convection and a superheat layer was provided under small heat flux on the heat transfer surface. The critical bubble diameter for the onset of boiling was decreased as the temperature of the superheat layer was increased. Thus, the degree of superheat at the onset of boiling was decreased. © 2004 Wiley Periodicals, Inc. Heat Trans Asian Res, 33(7): 462–471, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20028     

Bubble growth and transient heat transfer at the onset of boiling

An experimental study was conducted to investigate transient local heat transfer around a bubble at onset of boiling on a thin glass heating plate immersed in saturated n-hexane at low pressure. Eight rapid response Cu-Ni thermocouples consisting of a vacuum deposited thin film were used to measure the temperature change of the heating surface. Simultaneous high-speed video photographs were also obtained. The surface temperatures near a nucleation site decreased rapidly owing to the evaporation of a thin layer (microlayer) of liquid formed beneath the bubble in the early period and the rate of bubble growth increased with increasing incipient boiling superheat (ΔT_IB). The thickness of the microlayer decreased markedly with increasing ΔT_IB. © 1998 Scripta Technica, Heat Trans Jpn Res, 26(7): 484–492, 1997     

5 mm微肋管内R404A流动沸腾换热特性研究

通过实验研究了R404A在5 mm微肋管内的流动沸腾换热特性。热流密度为5～25 kW/m~2、质量流速为200～500 kg/(m~2·s)、饱和温度为-5～5℃、干度为0.1～0.9。结果表明:提高饱和温度可以提高换热系数,在0.1～0.3低干度区提升作用较为明显,在0.3～0.6中干度区提升作用逐渐降低;随着质量流速的增大,换热系数呈上升趋势,其对换热系数的影响主要体现在中干度区;热流密度的增大也能够有效提升换热系数,同时使换热系数的峰值提前出现,加速干涸现象的发生。针对本实验数据,修正后的Gungor模型预测精度较高,修正系数为1.372,统计得出平均绝对偏差仅9.30%,高达98.18%的数据偏差度小于±30%。     

竖直矩形细通道内水沸腾换热的数值模拟

对宽度为1和O.1 mm竖直矩形细通道内的沸腾换热展开研究,通过数值模拟的方法探索汽泡生成、长大和脱离的过程;用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,计算中考虑了重力、表面张力和壁面黏性的作用.发现:通道宽度的不同对汽泡生长方式和汽泡形态产生很大影响,并由此导致临界热流密度...     

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

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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。     

强化管内沸腾换热实验研究

主要研究在低过热度下微槽对流动沸腾换热特性的影响,分别以单工质甲醇和甲醇与甲苯的混合物为工质对不同流量情况下光管、直槽管和螺旋槽管的流动沸腾换热特性进行了实验研究。研究结果表明：对单工质甲醇来说,螺旋槽管可以明显起到强化传热作用,而且流量越低,强化传热效果越明显。对混合工质来说,当流量较低时,螺旋槽管强化传热效果不明显,而在流量较高时,强化传热效果比较明显。无论是单工质还是混合工质,直槽管在实验所能达到的壁面温度条件下不能起到明显的强化传热效果。还给出了螺旋槽管强化传热的定性解释。     

强润湿性液体池沸腾传热的实验研究和机理分析

对强润湿性液体的池沸腾传热实验而言,本文提出了行之有效的实验程序,并严格按照实验程序进行了R113池沸腾传热的实验研究,具体研究了表现老化和液体过冷度对池沸腾传热曲线及起沸点的影响,实验中观察到了三个反常现象,最后,从强润湿性液体的沸腾传热机理的角度对其给出了相应的解释。     

强化传热管束狭窄空间内R_11的沸腾换热特性

对紧凑型滚压面传热管管束狭窄空间内R－11的沸腾强化换热进行了实验研究,确认了由紧凑型滚压强化管束组成的满液式蒸发换热器具有良好的换热性能。其原理是利用强化传热管管束狭窄空间提前从自然对流换热转换为旺盛核沸腾换热,实验结果确认了管束形成的狭窄空间和强化传热面两种强化技术对沸腾换热的强化效果不能简单叠加。     

考虑沸腾和缸内局部传热的缸盖流固耦合传热分析

以某商用车直列6缸柴油机作为研究对象,基于缸内传热模型获得内燃机缸盖和缸套的燃气侧局部传热边界条件;基于均相流沸腾传热模型获得水侧传热边界;实现水侧、燃气侧边界与结构温度场计算的耦合,并判断水腔内沸腾传热的状态。结果表明:缸盖温度计算值与实测值吻合,缸盖最高温度位于缸盖底面两个排气门之间;排气门之间的燃气传热系数和燃气温度均处于较高值,缸内局部传热显著;在缸盖底面中心和排气门附近水腔内的冷却水处于部分发展泡核沸腾状态。     

有扰流片的矩形通道内空气流动和传热过程的数值模拟

以高温透叶片尾部区内部冷却为应用背景，对带顺排、错排扰流片肋的通道内空气流动和传热过程进行了数值模拟。计算结果表明，在相同雷诺数下，错排扰流片的阻力系数比针肋和顺排绕流片的阻力因子均增大约2%，而冷却能力分别增大约50%和9%。     

电场作用下气泡的行为研究

为进一步揭示EHD强化沸腾换热机理，分析了电场作用下气泡的受力情况，综述了国内外对电场作用下气泡的行为研究成果，系统总结了电场对气泡行为及其动力学特性的影响，并对该领域的进一步研究提出了建议。     

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

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

Flow boiling of binary solution in horizontal tube

An experimental study of flow boiling of binary organic solution was conducted in a horizontal tube. An organic mixture of miscible fluids, chlorodifluoromethane (R22)–dimethylacetamide (DMAC) was circulated through the experimental system. The influence of the heat source, flow rate, solution concentration and operating pressure on the flow characteristics and the heat transfer coefficient was examined experimentally. Based on the experimental observation an appropriate flow pattern map was constructed. The experimental values of the heat transfer coefficient (HTC) were compared with predicted HTC obtained by several known correlations. Based on these comparisons the well know Dittus & Boelter correlation deviated up to 30%. A better agreement (up to 15%) was obtained by modified the Kattan et al. 10, 11 and 12 correlation. The modification includes using the Forster and Zuber correlation [21] for nucleate boiling HTC and multiplying the predicted HTC by a constant of 1.4.