竖直矩形窄缝内流动沸腾压降实验与模型研究

本文实验研究了水在间隙为2.1、2.2、3.6 mm的垂直矩形窄通道内流动沸腾压降,包括入口过冷的情况,得到了在不同操作条件下压降随热流密度的变化曲线,同时分析了曲线变化的原因.实验结果发现:在实验参数范围内,流动沸腾的压降随着质量流速、热流密度和入口干度增加而增大;随着窄缝间隙的增大而减小.窄通道内的压降计算与大通道有显著不同,本文针对窄通道的特点,修正了传统的压降计算模型,模型预测值与实验结果比较,误差在±15.4%之内.     

螺旋管内高压汽水两相流动沸腾干涸点的研究

在较宽的实验参数范围内(系统压力P=8～15 MPa,质量流速G=800～1800 kg·m~(-2)·s~(-1),壁面热流密度q_w=200～950 kW·m~(-2))对一立式螺旋管内(管内径为10 mm,螺旋直径为300 mm,节距为50 mm)汽水两相流动沸腾干涸特性进行了实验研究。通过研究,获得了干涸发生时螺旋管圈壁温的分布特征以及压力、质量流速和壁面热流密度这三个参数对临界干度的影响规律。同时在实验数据的基础上,提出了一个适用于计算螺旋管内高压高含汽率工况下汽水两相流临界干度的经验关系式。     

窄通道内热薄燃料表面火焰传播特性研究

利用实验和数值模拟对微重力和常重力条件下高度为14mm和10mm的窄通道内热薄纸张表面火焰传播特性进行了研究。不同重力条件下窄通道内火焰传播速度随气流速度变化的规律符合得较好,说明地面窄通道实验能够模拟微重力条件下材料表面火焰传播的主要特征。地面窄通道中浮力流动速度的最大值约为5cm／s,与常规实验通道（高度较大）相比...     

多孔细径微肋管内CO2流动蒸发换热特性的研究

对亚临界二氧化碳在带有微肋的微细通道内的蒸发换热特性进行了实验研究.实验段为长0.6 m,内径1.7 mm的八孔带0.16 mm高微肋的铝制扁管.实验中参数的变化为:蒸发温度1～15 ℃,质量流速100～300 kg/m2s,热流密度1.67～8.33 kW/m2,干度0.1～0.9.实验结果表明,二氧化碳在带有微肋的微细通道中的蒸发换热系数高于其在光滑微细通道内的换热.二氧化碳的流动蒸发换热系数主要受热流密度和蒸发温度的影响,基本上是换热系数随热流密度及蒸发温度的增加而增加,但同时临界干度前移及滞后,而质量流速对换热系数的影响较弱;压力损失随质量流速和热流密度的增加以及蒸发温度的降低而增加.     

环形小通道内过冷沸腾的气泡行为研究

本文对去离子水在竖直环形小通道内流动过冷沸腾时的气泡行为进行了可视化研究,观察到了气泡在流动沸腾过程中的生长,合并,脱离,滑移及气泡脱离壁面后的运动等现象,并结合气泡动力学理论模型及气泡滑移模型,对实验结果进行了对比分析,总结了本实验通道中气泡行为的特性。     

竖直矩形窄缝通道过冷流动沸腾的实验研究

本文以去离子水为实验工质,对常压下竖直窄缝通道内过冷流动沸腾的气泡特性进行了实验研究。通过可视化实验分析发现,汽化核心密度主要受壁面过热度影响,气泡脱离直径受壁面过热度、主流过冷度以及质量流速影响。拟合了汽化核心密度和气泡脱离直径的经验关系式,预测结果与实验值误差较小。     

基于微小通道尺度效应的冷板沸腾换热数值研究

选用R134a、R123、水三种不同的介质,分别对不同流速和不同通道尺寸下微小通道冷板的流动沸腾换热进行数值模拟研究,分析了介质、流速及通道尺寸对换热器流动沸腾换热性能的影响。研究发现:微小通道冷板的通道宽度为1mm时,采用8mm的通道肋高和低流速的R134a介质,既能控制加热表面温升,又能有效地将利用介质的沸腾换热和流动换热。     

环形通道内爆轰波的起爆机制

旋转爆轰发动机环形燃烧室和预爆轰管的设计是影响发动机点火性能的关键因素。为了获得环形燃烧室中的起爆机制，使用多帧短时开快门摄像法，研究了不同含量氩气稀释的乙炔-氧气爆轰波经直管道沿切向进入环形通道中的传播过程和模式，重点关注爆轰波的失效和重新起爆机制。通过分析胞格模式发现环形通道内爆轰波的传播模式可以分为亚临界、临界和超临界3种状态。环形通道内爆轰波在顺时针和逆时针方向同时传播，根据初始压力和环形管道宽度的不同，会出现完全熄爆模式、熄爆-重新起爆模式和完全不熄爆模式，对应亚临界、临界和超临界3种状态。3种状态在顺时针和逆时针方向出现的顺序并不一致，相比较而言逆时针方向更易熄爆。研究同时也发现重新起爆通过两种方式实现：一种是通过解耦爆轰波与内壁面的反射以及其后的横向爆轰波，另外一种是通过燃烧转爆轰。通过分析直管的临界管径发现，随着环形通道宽度的增大，对于高浓度或低浓度氩气稀释的乙炔-氧气爆轰波，其临界管径均趋近于经典衍射问题中不稳定爆轰波的临界管径。实验研究结论将为旋转爆轰发动机燃烧室和预爆轰管的结构设计提供技术支持。     

垂直环形通道中低质量流速下弥散流传热实验研究

本文对低压、低质量流速下垂直环形通道中弥散流沸腾传热进行了理论分析和实验研究。本实验使用热块技术建立了稳定的于涸后传热工况,利用分离式抽汽热偶测量蒸汽的过热度,并在相同的流动、传热及入口参数条件下移动热块得到汽相温度沿轴向变化曲线,获得了七十余组的壁温及汽温实验数据。本文还推导出了一维的垂直环形通道的弥散流沸腾传热的计算模型,它同本实验数据吻合良好。     

窄缝通道中液氮的沸腾传热研究:第二部分:窄缝通道尺寸对液氮临界热流密度(CHF)的影响

在实验的基础上对窄缝通道中液氮的临界热流密度进行了实验研究.实验针对3个不同长度和间距尺寸的窄缝通道在多方位倾角的情况下进行.系统研究了窄缝的方位倾角和窄缝的几何尺寸对临界热流密度的影响,同时对液氮的膜态沸腾进行了研究.     

自然循环加热段内摩擦阻力及对流传热的实验研究

以常压去离子水为工质,对自然循环工况下上升加热段内单相水的摩擦阻力及对流传热特性进行了实验研究.结果表明,自然循环工况下加热段内由浮升力引起的自由流动对摩擦阻力及对流传热特性有重要影响,自然循环与强制循环二种工况下加热段内的摩阻系数及对流换热系数存在明显差别;并且,自然循环工况下加热段内的摩擦阻力存在滞后现象.通过实验提出了计算自然循环工况下加热段内单相水的摩阻系数及对流换热系数的经验关系式.     

竖直窄环隙通道内的强迫对流换热

本文在常压下,以水为工质,对三种尺寸的竖直窄环隙流道进行了单相强迫对流换热实验研究。结果表明,窄隙流道内的换热在低雷诺数区表现出与普通流道不同的多变特性,而在高雷诺数区与普通流道相近。温差对换热的影响具有两重性。窄隙流道使紊流换热区域扩大,当流道间隙足够小时,换热没有明显的过渡区和层流区,均表现为紊流换热的特征。本文提供的经验公式可以在较宽的参数范围内关联实验数据。     

BOILING HEAT TRANSFER MECHANISMS IN A HORIZONTAL TUBE BUNDLE

The effect of thermal environment on boiling heat transfer performance in a section of a horizontal tube bundle was investigated using R-113 as the working fluid. The in-line tube bundle has five columns and 27 rows with a pitch-to-diameter ratio of 1.3. Heal transfer coefficients obtained from the instrumented tube in the tube bundle with only one tube heated while the other tubes remained unhealed and with all the lubes in the bundle heated are reported for a range of heat flux, pressure, mass flow rate, and quality. The results showed that heat transfer coefficient of a tube in a heated bundle is slightly higher than that in an unhealed bundle, with the variation of heat transfer coefficient decreasing as heat flux, mass flow rate, or pressure increased. It was also found that higher quality would tend to improve the heat transfer. However, the effect of quality disappeared as heat flux, mass flow rate, and pressure increased. Based on the experimental data, the mechanism of the heat transfer augment due to thermal environment was analyzed. It was proposed that fluid agitation and thin liquid film formation are two main factors for a heated bundle to have better transfer performance than an unhealed bundle,     

几种典型流动条件对平板转捩过程影响的数值模拟

采用作者构造的k方程转捩湍流模型，数值模拟了较大跨度来流湍流度情况、不同来流湍流度时几种不同顺、逆压梯度存在情况、壁面存在不同热交换强度情况下平板的转捩流动过程．与实验结果对比表明，新模型具有较好地模拟转捩流动能力。     

Experimental investigation of 3-dimensional wavy liquid films under the coupled influence of thermo-capillary and electrostatic forces

Three-dimensional interfacial waves developing on the free surface of falling liquid films are known to intensify heat and mass transfer. In this context, the present paper studies the effect of electrostatic as well as of thermo-capillary forces on a falling film of a dielectric liquid. Therefore, measurements of the local film thickness using a confocal chromatic imaging method were performed under isothermal and heated conditions. The experimental results show that both forces destabilize the flow. It is found, that the application of an additional electric field under heating conditions enhances the generation of rivulets, thereby reducing the overall heat transfer coefficient.     

Flow patterns and flowboiling heat transfer of freon R318C in an annular minichannel

This paper deals with experimental results on flowboiling heat transfer of liquid moving in an annular channel with unilateral central heating under the conditions of a significant effect of capillary forces on the flow modes and heat transfer. Experiments were carried out on boiling freon R318C in an annular channel with a gap of 0.95 mm and transparent outer wall. The inner wall was heated by the electric current. The local heat transfer coefficients and flow modes are presented. The critical film thickness corresponding to suppression of nucleate boiling was determined.     

Convection sous-vestimentaire. Analyse dimensionnelle et mesure des flux échangés

This article presents an experimental study that quantifies heat and mass transfers between the skin and a fabric layer. The experiment is carried out with a sponge plate heated to skin temperature, about 35°C, and saturated in moisture. Analysis by holographic interferometry provides the determination of the convective heat fluxes. Radiative flows are calculated by the radiosity method. We show the influence of the underclothing air layer, and that of the fabric using different textiles. The radiative properties also modify the underwear exchanges. The influence of mass transfer on convective phenomena was studied by comparison with a dry plate. The results that are obtained, under the form of heat fluxes, are analysed. They can be used to create a data base to check the validation of models treating heat exchanges between skin and clothes.     

非均匀加热立式螺旋管内沸腾传热恶化特性研究

本文主要开展非均匀加热螺旋管内沸腾传热恶化特性实验研究。实验参数范围为:热流密度15~55 kW·m^-2;质量流速190~400 kg·m^-2·s^-1;压力0.8~1.1 MPa。实验包括一个均匀加热实验段及两个非均匀加热实验段,三个实验段尺寸一致,不均匀度分别为1.0,1.2和1.4。实验过程中共获得三种壁温飞升现象,而且发现随着质量流速及不均匀度的增大传热恶化位置逐渐向内侧管圈偏移,并由此导致非均匀加热螺旋管内初始烧干干度随着质量流速的变化规律与均匀加热螺旋管恰好相反。     

Experimental studies of influence of the turbulent flow structure on temperature distribution in a compact heat exchanger

Results of experimental investigation of temperature distribution over the surface of a complex heat exchanger (the Frenkel packing type) are presented. Measurements were carried out in the air flow between two sheets with triangular corrugations directed at 90° to each other. Measurements were carried out by the microthermocouples glued on the heated outer surface. The effect of Reynolds numbers, a gap between corrugated sheets, and substitution of one corrugated sheet by the smooth one on temperature distribution over the heat exchanger surface in the turbulent air flow is analysed. According to the performed experiments, there is a significant effect of a gap and applied perturbations on the type of temperature distribution over the perimeter of a heated cell.     

Experimental Investigation of Jet Stabilization in Near-Axis Region of Plasma Reactor

The paper presents the results of experimental investigations of aerodynamics and heat transfer in a vortex plasma reactor with gas jet injection along its axis. The process of mixing under quasi-isothermal conditions (injection of slightly heated jet) and inhomogeneous conditions (injection of helium and argon) as well as with the injection along the axis of plasma jet is studied consistently. A detailed comparison of temperature fields and concentrations is presented for these conditions. The process of jet expansion is shown to be defined mainly by three factors — centrifugal mass forces, buoyancy forces and initial velocity shift in a jet at the chamber inlet. The end flows contribute considerably to the process of jet mass transfer with peripheral flow.