冷却水中重悬浮颗粒影响沸腾传热的试验研究

试验研究了冷却水中添加氧化铁(Fe3O4/Fe2O3)颗粒在高温钢坯冷却过程中影响沸腾传热的性质。系统分析了冷却水(悬浮液)喷淋初速度、加入重颗粒的粒径、质量分数等因素对热钢坯温度下降强度、传热热流密度、沸腾传热系数、过冷沸腾长度等参数的影响,总结了冷却水中引入重悬浮颗粒用以强化沸腾传热的优化方案。     

声空化场下纳米颗粒对沸腾传热影响的实验研究

作者以添加有纳米颗粒的丙桐溶液为工质,首次通过实验系统地研究了声空化场方向及强度,液体过冷度,纳米材料浓度和光照射等对水平圆管沸腾传热的影响,对其进行了机理分析。     

水平管束沸腾传热增强的研究

本文分别以单组份和双组份为沸腾工质,对水平管束的沸腾传热进行了研宄,并提出了从水平管束底部引入惰性气体的方法,研究了由此引起的传热增强。实验结果表明引入惰气使传热膜系数得到很大的提高,作者对此传热增强的机理进行了分析。     

多孔表面强化沸腾传热的研究

一、前言 当前全世界普遍重视节省能源,降低产品能耗已成为重要的研究课题。构成节能对象的机器设备中,有众多的热交换器,因此,研究提高现有传热设备的性能和探求新的强化方法,对于降低能耗具有重要意义。     

CaCO3垢的形成对池核沸腾传热的影响

在一水平圆形加热表面上通过实验考察了饱和池核沸腾和过冷池核沸腾时CaCO3垢的生成对传热的影响。结果表明，在饱和池核沸腾和过冷池核沸腾的初始阶段沸腾传热系数均呈先降低后升高、达到一个最大值后稳定降低的趋势，而且在初始阶段出现了负污垢热阻现象。在相同操作条件下，过冷池核沸腾传热系数明显低于饱和池核沸腾传热系数。在分析污垢的生成和生长影响表面活化中心的基础上，对污垢的形成对沸腾传热的影响进行了机理分析。     

缸盖冷却水的沸腾传热模型

针对缸盖水腔内的冷却水流动沸腾传热计算,本文介绍了两种沸腾传热模型。模型认为流动沸腾总传热量等于泡核沸腾和单相流对流传热之和,介绍了常用的Chen模型,然后介绍了一种基于加权叠加方法基础上的。计算过冷流动沸腾传热的新模型Franz模型。     

水平窄空间沸腾传热的实验研究

通过对五种尺寸的窄空间试验元件分别以水和乙醇做工质进行实验。研究了窄空间间距、窄空间尺寸、不同工质及不同热流密度对窄空间沸腾性能的影响。结果表明：当窄空间尺寸与热流通等因素组合恰当时。其换热系数可比大空间池沸腾提高3～6倍；临界热流密度有所降低。     

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。     

柴油机非水冷却介质自然对流沸腾传热特性的研究

对于采用非水冷介质的高温冷却水及少冷却柴油机的研究，目前尚需了解冷却介质温度的提高，及冷却介质的性质差异，对柴油机的传热及零部件热状况的影响。本模拟柴油机工作条件，对机油，柴油及不同配比的乙二醇水溶液等液体的自然对流沸腾热特性进行了试验研究，揭示了各种因素对传热的影响，通过对试验数据的回归分析得出了３种非水冷却介质自然对流沸腾传热关系式。     

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。     

Boiling heat transfer characteristics of R-113 in a vertical small diameter tube under natural circulation condition

Boiling heat transfer characteristics of freon R-113 are experimentally investigated in a vertical small diameter tube, D=1.45 mm and L=100 mm at a wide pressure range of 19-269 kPa under natural circulation condition. Except the entrance region of the test section, the flow regime is annular in view of the measured vapor flux. The pool boiling correlations of Stephan and Abdelsalam and McNelly equally well predict the experimental data within an error of ±20%. No enhancement of heat transfer coefficient is obtained although D/B is less than 1.5, which differs from the finding of Klimenko.     

Hydrodynamics and heat transfer in swirl flow under conditions of one-side heating. Part 2: Boiling heat transfer. Critical heat fluxes

The paper gives the basic results of experimental investigation of boiling heat transfer in heat-absorbing devices of the ITER thermonuclear reactor, which are subjected to one-side heating. The experimental data on heat transfer at nucleate and film boiling and on critical heat fluxes are obtained in the following range of parameters of water flow: pressure p = 0.7–2.0 MPa, mass flux G = 340–25 000 kg/(m² s), and water temperature at the inlet T_in = 20–60 °C. A twisted tape is inserted in the circular channel in order to form swirling flow of water. The investigations are performed for tapes with different values of flow swirl coefficient, as well for test sections without a tape. Appropriate calculation formulas are derived, which reliably generalize the experimental data.     

高饱和蒸发压力氨喷雾冷却沸腾传热特性

利用冷却工质的相变蒸发带走大量热量的喷雾相变冷却技术成为大功率电子元件散热需求的最佳途径.建立了双喷嘴阵列氨喷雾相变冷却实验系统,研究了饱和蒸发压力以及进口流量对氨喷雾相变冷却传热特性的影响规律.实验结果表明:在氨喷雾相变冷却过程中,维持较高的饱和蒸发压力有利于传热系数提高,过热度降低;流量对传热特性影响较大,低流量时...     

Boiling heat transfer on large diamond and SiC heaters: The influence of thermal wall properties

Pool boiling experiments were performed on large synthetic diamond and SiC substrates with integrated heating and temperature sensor elements. The boiling fluid was pure water at atmospheric pressure. The two heating substrates were identical with regard to geometry and design, and were mainly comparable in terms of surface roughness and static contact angle. This enabled the influence of the thermal heating wall properties on the resulting heat transfer to be investigated directly. The extraordinarily high value of the thermal conductivity of the synthetic diamond heater led systematically to higher mean heat transfer rates within the nucleate boiling regime compared to the SiC material. Strong thermal fluctuations due to the growth and detachment of vapor bubbles were recorded for both heaters. Indications for the existence of a local heat flux reversal from the liquid to the wall have been found by means of re-condensation phenomena and direct temperature measurements during boiling.     

Evaporation heat transfer of steady thin film in micro capillary tubes of micron scale

This paper reports that the heat transfer mechanism of phase change in a capillary tube belongs to liquid film conduction and surface evaporation. The surface evaporation is influenced by vapor temperature, vapor‐liquid interfacial temperature, and vapor‐liquid pressure difference. In the vapor‐liquid flow mechanism, flow is effected by both the gradient of disjoining pressure, and the gradient of capillary pressure. The mechanism of vapor‐liquid interaction consists of the shear stress caused by momentum transfer owing to evaporation, and frictional shear stress due to the velocity difference between vapor and liquid. In the model presented for a capillary tube, the heat transfer, vapor‐liquid flow, and their interaction are more comprehensively considered. The thin film profile and heat transfer characteristics have close relations with a capillary radius and heat transfer power. The results of calculation indicate that the length of the evaporating interfacial region decreases to some extent with decreasing capillary radius and increasing heat transfer power. © 2002 Wiley Periodicals, Inc. Heat Trans Asian Res, 31(7): 513–523, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ).DOI 10.1002/htj.10050     

循环流态化自动清洗式换热器的传热强化

液-固流态化传热强化的机理尚未完全清楚,已有文献对流态化粒子的粒度与传热系数的影响关系有较大分歧。从传热强化角度对水-沙流态化自动清洗的运行参数进行优化试验研究,得到的结果是:沙子粒度不是愈细愈好,而是D p 2mm(8目)左右为好;粒子体积分数以2.4%比较好;流速在0.2~0.28 m/s(R e为6 000~9 000)较好。虽然粒子体积分数低,但是在优化条件下的流态化传热强化幅度几乎可以达到一倍左右,并且阻力又很低。     

An Experimental Study of Condensation Heat Transfer in Sub-Millimeter Rectangular Tubes

The characteristics of local heat transfer and pressure drops were experimentally investigated using condensing R134a two-phase flow, in single rectangular tubes, with hydraulic diameter of 0.494, 0.658, and 0.972 mm. New experimental techniques were used to measure the in-tube condensation heat transfer coefficient especially for the low heat and mass flows. Tests were performed for a mass flux of 100, 200, 400, and 600 kg/m2s, a heat flux of 5 to 20 kW/m2, and a saturation temperature of 40℃. In this study, effect of heat flux, mass flux, vapor qualities, and hydraulic diameter on flow condensation were investigated and the experimental local condensation heat transfer coefficients and frictional pressure drop are shown. The experimental data of condensation Nusselt number are compared with previous correlations, most of which are proposed for the condensation of pure refrigerant in a relatively large inner diameter round tubes.     

Interfacial suction effects of a porous layer on filmwise condensation heat transfer enhancement

Considering the liquid transverse suction effect at the porous layer interface, a mathematical model was presented to investigate the influence of the porous layer characteristic parameters on condensation heat transfer. The results revealed that the enhancement ratio increased with the increase of the porous layer thickness and permeability. The effective thermal conductivity of the porous layer was, however, of little significance for condensation heat transfer enhancement. Also, the enhancement mechanism was analyzed by comparing the thermal resistances within the external condensate film and the porous layer. © 2002 Wiley Periodicals, Inc. Heat Trans Asian Res, 31(7): 568–577, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10058     

Characterization of heat transfer modes of tube side convective condensation under the influence of an applied DC voltage

An experimental study was performed to determine the modes of heat transfer in horizontal tube side convective condensation under an applied DC high voltage. Experiments were performed with R134a in a horizontal, single-pass, counter-current heat exchanger. A 8 kV DC voltage was applied through a central rod electrode with the tube wall grounded for mass flux in the range 45–156 kg/m² s. The average quality across the test section was 45%, which corresponds to an initially stratified flow with the liquid level below the central electrode. The high-voltage electric field results in an interfacial electric body force which extracts the liquid from the bottom stratum towards the vapour core. This results in a phase redistribution with a resultant increase in heat transfer. The increase in heat transfer can be attributed to a change of the heat transfer mode in the lower section of the tube from convective condensation to film condensation.     

Boiling heat transfer coefficients inside a vertical smooth tube for the water/lithium bromide mixture

This paper describes the experimental results obtained on the heat transfer in forced convective boiling for the water/lithium bromide mixture flowing upward in a vertical tube uniformly heated. The concentration range for the mixture was from 48.1 to 57.7 wt%. Correlations were proposed to correlate the experimental local heat transfer coefficients. The results showed that the local heat transfer coefficients are strongly dependent on Bo, 1/X_tt and 1/x at the analysed conditions. It was observed that the average heat transfer coefficients increased for the mixture with a decrease of the solution concentration or an increase of the mass flux. Copyright © 2002 John Wiley & Sons, Ltd.