FC-72在浸泡于液池中的微小圆管内的沸腾传热

本文对浸泡于FC-72液池中的两个微小圆管进行了沸腾实验研究,得到了沸腾曲线和传热系数,并用DV摄像机拍摄到了圆管出口处的沸腾状况,研究了管道尺寸对沸腾传热特性的影响。实验结果显示,管道尺寸对沸腾传热特性有显著的影响。传热系数和CHF随着管道尺寸的缩小而减小.直径为1.10mm的圆管出口处在低热负荷加热时发生了汽泡阻塞,并导致了剧烈的沸腾滞后现象。     

FC-72在竖直壁面上及微小三角型通道内的沸腾传热

本文对浸在FC-72液池中的竖直壁面及两个微小三角形通道进行了沸腾实验研究,考虑了管道尺寸对沸腾传热特性的影响。两个微小三角形通道的边长分别为1.5和2.5 mm,水力直径分别为0.87和1.44 mm,长度50 mm,采用铜块上开V型沟槽,再覆盖上透明的玻璃片构成。热流密度由贴在铜块背后的膜状加热器提供。实验得到了沸腾曲线和传热系数,并用DV摄影机拍摄到了沸腾状况。实验结果显示,管道尺寸对沸腾传热特性有显著的影响,CHF值随通道尺寸的减小而减小,小通道在低热流密度时传热系数较大。     

微槽道中纳米流体沸腾换热特性研究

为研究纳米流体在微槽道中的沸腾换热特性及规律,分别以去离子水和体积浓度为0.2%、0.5%的水基Al2O3纳米流体为工质进行试验,研究质量流速、热流密度、进口过冷度、槽道尺寸等因素对沸腾传热系数的影响及其两相摩擦压降与出口干度的关联分析和沸腾换热关联式对比拟合.试验结果表明:在一定热流密度和质量流速下,传热系数随槽道尺...     

载气汽油在水平螺旋扁管管束中的沸腾换热

以汽油-空气为介质,在不凝性气体质量含量不超过5%时,对导程为200mm的螺旋扁管管束中的沸腾换热进行了实验研究,分析了沸腾换热系数随两相质量流量的变化规律以及流动压降随空气流量的变化规律。得到了相应条件下,载气汽油在该导程的螺旋扁管管束中的沸腾换热实验关联式。     

聚变堆偏滤器过冷水流动沸腾强化换热性能研究

选择欧拉多相流模型和非平衡沸腾模型,用Fluent 软件对单边受热竖直向上平滑管进行了过冷流动沸腾换热的数值分析。研究了不同质量流速、进口温度和热流密度对对流换热系数和空泡份额的影响,并分析了它们对传热恶化的影响。     

An experimental investigation on pool boiling heat transfer enhancement using Cu-Al2O3 nano-composite coating

Pool boiling heat transfer performances of Cu-Al₂O₃-coated copper surfaces have been studied experimentally for its potential use in heat transfer applications. In the present study, a two-step electrochemical deposition method is examined. This method provides an easy control on surface properties such as porosity and coating thickness. The deposition method is studied carefully and responsible surface morphology parameters are reported. After performing the pool boiling experiments on coated surfaces with DI water, the maximum critical heat flux of 1800 kW/m² and heat transfer coefficient of 193 kW/m² K, which are 68% and 260% higher than that of bare surface, respectively.     

气粒两相流传热问题的光滑离散颗粒流体动力学方法数值模拟

在气粒两相流动问题中,颗粒间以及气体与颗粒间的传热问题不可忽略.光滑离散颗粒流体动力学(SDPH)模型作为一种新的求解气粒两相流动问题的方法,已经成功应用于模拟风沙运动等问题.在此基础上,提出了SDPH方法的热传导模型,模拟了气粒两相流动问题中的热传导过程以及颗粒蒸发过程.首先引入各相的能量方程,利用有限差分与光滑粒子流体动力学一阶导数相结合的方法,处理各相内部热传导项中的二阶导数问题,基于气粒两相间温度差及对流换热系数计算颗粒与气体间的热传导量,推导得到了含热传导模型的气粒两相流SDPH计算方程组,模拟计算了圆盘形颗粒团算例及鼓泡流化床内部热传导算例,并与双流体模型计算结果进行对比,结果基本符合;其次利用离散液滴模型中的颗粒蒸发传质传热定律计算颗粒的蒸发过程,数值模拟了颗粒射流蒸发过程,并与离散颗粒模型结果进行对比,两者符合得较好,验证了该方法的准确性及实用性.     

空浴式汽化器基础传热问题及研究现状评述

对我国空浴式汽化器的研究和使用现状进行了评述;分析了空浴式汽化器涉及的流动沸腾、凝华结霜、自然对流等传热过程及各过程之间的相互耦合关系;提出了综合研究各传热过程及相互制约关系的新思路,拟在前期工作的基础上研究管内的汽液两相流及沸腾传热过程、管外的霜层生长及导热规律,以及翅片管内外的耦合传热规律.     

Quantification of the water boiling heat transfer in micro-structures by image analysis

The heat transfer performance of a micro-vaporizer has been measured by conventional methods (using temperatures, flow rates, effective power input). The study was carried out for laminar flow in channels (5 mm×3 cm×200 μm) micro-structured with square obstacles to increase the specific area. The results show that high heat transfer coefficients (1300– 2500 W m⁻²/C⁻¹) can be reached in such a micro-structured channel. Image analysis was done to estimate the volume vapour fraction, which can be converted into the mass vapour fraction using a slip ratio and avoids the need for any temperature or electric power input measurements. The estimation of this slip ratio is discussed in this paper.     

二氧化碳管内沸腾换热系数关联式的分析

了解管内流动沸腾特性并准确地预测出其换热系数,对设计紧凑、高效的CO2蒸发换热器有着至关重要的作用.文中分析了几个国内外已公开发表的换热关联式,并将预测结果与实验数据进行对比和误差分析,比较后发现Yoon2004、Jung关联式的预测精度相对较高,但各关联式对干涸后的换热系数预测普遍有较大偏差,有待进一步的改进.     

池沸腾传热的数学分析

在统计方法的基础上,对于池沸腾换热的传热机理提出了一个数学模型. 在没有增加新的经验常数的条件下,从该模型中可得到池沸腾热流密度是壁面过热度、活化穴最小与最大尺寸、流体的接触角与流体物理特性的函数. 该模型可以较好地解释润湿性如何影响沸腾热流密度. 对不同的接触角,模型预测的结果与实验相符合. 关键词： 池沸腾 传热 数学模型     

液氮流动沸腾换热研究综述

作为一种优良的低温冷却剂,液氮在航天、电子工业、超导磁体和超导电缆冷却及低温生物医疗等领域应用广泛。在这些应用中,准确预测液氮的流动沸腾换热特性对于系统设计和安全运行十分重要。该文主要介绍了液氮流动沸腾换热的特点,对已有的实验和数值模拟结果进行了归纳;并比较了四个液氮流动沸腾换热计算关联式的预测情况,以及关联式中干度、质量流量、热流密度和压力对换热系数的影响;指出了有待进一步研究的课题。     

The use of enhanced surface in flow boiling heat transfer in a rectangular minichannel

The results of flow boiling heat transfer in a 1-mm-deep vertical minichannel are presented. The heating element for an FC-72 laminar flow in a minichannel is a single-sided enhanced foil with various depressions; liquid crystal thermography was used for measuring temperature distribution of the foil. The void fraction and vapor quality were determined for some cross-sections of two-phase flow images. Results presented in the form of boiling curves were analyzed. Both typical and untypical shapes of boiling curves were found. The suitability of classical methods of two-phase pressure drop determination using experimental verification was confirmed.     

混合润湿性柱状纳米结构对铜板上纳米氩膜沸腾传热的影响

混合润湿性对固/液相互作用有显著影响,因此对提高相变过程中的传热速率有积极作用.采用分子动力学模拟方法研究了柱状纳米结构表面混合润湿性对池沸腾传热的影响.分析了混合润湿性和纳米结构柱高对液体起始沸腾时间和温度的影响及其机理.结果表明,疏水比例和柱高会影响爆沸的起始温度和时间.与纯亲水壁相比,增加疏水比改变了固液界面性质,可以降低沸腾温度,更容易突破势能壁垒,使液体起始沸腾时间提前,并且随着疏水比的增加,不同柱高下的沸腾温度降低;当疏水比相同时,增加柱高扩大了混合润湿性的影响,也能降低沸腾起始温度并使液体起始沸腾时间提前.这为设计微纳粗糙结构和混合润湿表面以强化沸腾传热提供了思路.     

EHD强化微槽道两相流传热动力学研究

以去离子水为工质,对当量直径分别为1.33mm和2mm的竖直矩形微槽道进行了EHD两相流饱和沸腾传热实验研究,运用分维数、关联维数和Kolmogorov熵对槽道进出口压差波动信号进行了动力学研究,分析了槽道尺寸和外加高压电场对传热系数和非线性特征量的影响规律,结果表明:有无电场情况下,各系统均具有非线性混沌特性,并且有外加高压电场系统的混沌程度比无外加高压电场系统的混沌程度更强烈,槽道尺寸越小,系统的混沌程度越强烈,混沌程度越强烈的系统对应的传热系数越大。     

载气汽油蒸汽在水平圆管内的冷凝

研究了空气质量含量在2%~13%,汽油蒸汽和空气的混合气体在水平管内的冷凝换热。并分析了不凝气体质量分数对管内冷凝换热的影响规律。得到Co随Re变化的冷凝换热系数的实验关联式。     

Heat transfer in boundary layer stagnation-point flow towards a shrinking sheet with non-uniform heat flux

In this paper, the effect of non-uniform heat flux on heat transfer in boundary layer stagnation-point flow over a shrinking sheet is studied. The variable boundary heat fluxes are considered of two types: direct power-law variation with the distance along the sheet and inverse power-law variation with the distance. The governing partial differential equations (PDEs) are transformed into non linear self-similar ordinary differential equations (ODEs) by similarity transformations, and then those are solved using very efficient shooting method. The direct variation and inverse variation of heat flux along the sheet have completely different effects on the temperature distribution. Moreover, the heat transfer characteristics in the presence of non-uniform heat flux for several values of physical parameters are also found to be interesting.     

Experimental Investigation of Heat Transfer in Two-phase Flow Boiling

In this article, an experimental investigation is performed to measure the boiling heat transfer coefficient of water flow in a microchannel with a hydraulic diameter of 500 μm. Experimental tests are conducted with heat fluxes ranging from 100 to 400 kW/m², vapor quality from 0 to 0.2, and mass fluxes of 200, 400, and 600 kg/m²s. Also, this study has modified the liquid Froude number to present a flow pattern transition toward an annular flow. Experimental results show that the flow boiling heat transfer coefficient is not dependent on mass flux and vapor quality but on heat flux to a certain degree. The measured heat transfer coefficient is compared with a few available correlations proposed for macroscales, and it is found that previous correlations have overestimated the flow boiling heat transfer coefficient for the test conditions considered in this work. This article proposes a new correlation model regarding the boiling heat transfer coefficient in mini- and microchannels using boiling number, Reynolds number, and modified Froude number.     

Heat transfer and Marangoni flow in a circular heat pipe using self-rewetting fluids

In this study, Marangoni flow and heat transfer enhancement in a heat pipe have been investigated. The experiments were carried out at different heat inputs. A constant temperature water bath was used at the condenser section at three temperature levels. Heat transfer coefficients and thermal resistances of the heat pipe were measured for pure water and water/butanol solutions. The experimental results confirmed that the heat pipe filled with butanol solutions showed better thermal performance than the water-filled heat pipe. At maximum heat flux, 25% heat transfer improvement was obtained when 7 wt% butanol solution was used instead of pure water.