水平梯度表面能材料表面上的滴状凝结换热系数

本文在均质表面的单个球缺形液滴换热模型和液滴通用尺度分布规律的基础上,结合梯度表面能材料表面的液滴分布和凝结换热特性,得到了一维水平梯度表面能材料表面上的滴状凝结换热计算式。在此基础上,研究了壁面过冷度、接触角梯度、工质物性等参数对梯度表面能材料表面滴状凝结换热性能的影响。结果表明:随着过冷度的增加和凝结工质汽化潜热的增大和表面张力的减小和接触角梯度的增大,平均表面凝结换热系数会增大。     

小液滴撞击壁面传热特性数值分析

小液滴撞击壁面现象在喷雾冷却等领域都有广泛应用.为研究小液滴(微米)撞击热壁面(非沸腾区)传热过程,建立了二维液滴撞壁瞬态模型,并采用相场方法对小液滴换热过程中对流热通量和导热热通量的大小进行了对比.研究结果表明:液滴撞击壁面初期形成“冷斑”,有利于小液滴与壁面的传热;小液滴撞击壁面过程中热通量峰值存在于三相接触点附近,数量级在105—106 W/m²;小液滴撞击壁面过程中受壁面浸润性和液滴尺寸对传导热通量的影响较为显著,而速度和液滴尺寸对对流热通量的影响较为显著;大多数情况下,小液滴撞击壁面传导热通量数量级在103—105 W/m²,对流热通量数量级在104—106 W/m²,对流热通量大于传导热通量,在整个换热过程中占据主导地位.     

气液双热源耦合换热器性能研究

设计了一种由管翅式换热器和套管式换热器耦合而成的气液双源耦合式换热器,该换热器可以实现一种介质同时与气态热源和液态热源进行同步耦合换热.对该换热器进行了详细的介绍,并对其耦合换热特性及该换热器在耦合热源热泵空调中应用时的制热工况进行了的性能测试.研究结果证明,使用该气液双热源耦合式换热器的耦合热源热泵空调系统,气液双热...     

纳米变截面结构的导热性质

采用分子动力学方法模拟了固态氩的纳米变截面结构的导热性质,研究发现纳米变截面材料的热阻和热流的大小与方向都相关:当纳米结构沿热流的方向为渐缩时,纳米结构的热阻随热流的增加而增大,而当纳米结构沿热流的方向为渐扩时,纳米结构的热阻随热流的增加呈减小的趋势;当热流较大时,热流沿渐缩方向时的热阻明显大于热流沿渐扩方向时的热阻,但当热流较小时纳米变截面结构的热阻和热流方向的关系不大.最后依据热质的运动和传递理论的动能效应对该现象进行了分析解释.     

混合工质高温水源热泵计算机模拟

针对高温混合工质热水热泵,本文提出了纯质及混合工质的热泵模拟程序;本程序详细考虑了混合工质纯传递特性对换热的影响,在只输入热泵系统结构参数以及外部换热参数的条件下,应用本程序能进行热泵系统冷热水温度、换热器温度场、制冷制热量及系统的性能参数计算。     

间歇热源驱动下的吸附式制冷系统运行特性研究

本文以一个连续回热型吸附式制冷系统为例,通过对间歇热源驱动下的系统运行过程的动态仿真,分析了热源的变化及其热源中的蓄热对于系统解吸过程的影响,提出了热源间断时间的判断方法以及在间歇热源驱动下的系统的控制方案。     

Calculation of the Thermal Resistance of a Heat Distributer in the Cooling System of a Heat-Loaded Element

Numerical simulation is performed for heat transfer in a heat distributer of a thermoelectric cooling system, which is located between the heat-loaded element and the thermoelectric module, for matching their sizes and for heat flux equalization. The dependences of the characteristic values of temperature and thermal resistance of the copper and aluminum heat distributer on its thickness and on the size of the heatloaded element. Comparative analysis is carried out for determining the effect of the thermal conductivity of the material and geometrical parameters on the heat resistance. The optimal thickness of the heat distributer depending on the size of the heat-loaded element is determined.     

Numerical simulation of anode heat transfer of nitrogen arc utilizing two-temperature chemical non-equilibrium model

A detailed understanding of anode heat transfer is important for the optimization of arc processing technology. In this paper, a two-temperature chemical non-equilibrium model considering the collisionless space charge sheath is developed to investigate the anode heat transfer of nitrogen free-burning arc. The temperature, total heat flux and different heat flux components are analyzed in detail under different arc currents and anode materials. It is found that the arc current can affect the parameter distributions of anode region by changing plasma characteristics in arc column. As the arc current increases from 100 A to 200 A, the total anode heat flux increases, however, the maximum electron condensation heat flux decreases due to the arc expansion. The anode materials have a significant effect on the temperature and heat flux distributions in the anode region. The total heat flux on thoriated tungsten anode is lower than that on copper anode, while the maximum temperature is higher. The power transferred to thoriated tungsten anode, ranked in descending order, is heat flux from heavy-species, electron condensation heat, heat flux from electrons and ion recombination heat. However, the electron condensation heat makes the largest contribution for power transferred to copper anode.     

Boiling heat transfer of refrigerant R-21 in upward flow in plate-fin heat exchanger

The article presents the results of experimental investigation of boiling heat transfer of refrigerant R-21 in upward flow in a vertical plate-fin heat exchanger with transverse size of the channels that is smaller than the capillary constant. The heat transfer coefficients obtained in ranges of small mass velocities and low heat fluxes, which are typical of the industry, have been poorly studied yet. The characteristic patterns of the upward liquid-vapor flow in the heat exchanger channels and the regions of their existence are detected. The obtained data show a weak dependence of heat transfer coefficient on equilibrium vapor quality, mass flow rate, and heat flux density and do not correspond to calculations by the known heat transfer models. A possible reason for this behavior is a decisive influence of evaporation of thin liquid films on the heat transfer at low heat flux.     

热管换热器用于LED冷却系统的实验研究

研发了一系列将发光二极管(LED)散热与热管传热相结合的用于大功率LED冷却的热管散热器,并对其传热性能进行了实验研究。结果表明,该系列热管散热器具有良好的散热能力,能将节点温度控制在70℃以下,满足了大功率LED对结点温度的控制要求;实验结果还表明,翅片结构不同,换热器散热能力明显不同,所研发系列异形翅片热管换热器的散热能力明显高于目前常用的普通矩形翅片热管换热器,其中以外翻形翅片热管换热器散热能力最好;还研究了热管换热器工作倾角对其散热能力的影响,并给出了热管排布数量、翅片材质及结构对换热器散热性能、换热装置体积、成本及质量的影响。     

U型管传热量影响因素的数值模拟研究

地下换热器是地源热泵的重要组成部分,竖直U型管是最常见的地下换热器形式. U型管与土壤间的传热受诸多因素的影响.为分析这些因素对于U型管传热的影响,本文建立了地源热泵竖直U型管地下换热器的三维全尺寸数值模型,在此基础上采用CFD软件FLUENT对U型管的埋管深度、进口水温、管内流速等一系列因素在冬夏不同工况下对U型管传热量的影响进行了数值模拟研究.经过整理分析得出的各种因素对传热量影响可以为优化工程设计提供依据.     

HL-2M装置第一壁传热结构设计及传热性能测试

在 HL-2M 第一壁传热结构设计中,利用导热管的轴向快速导热特性及较短的传热路径,将面对等离 子体的第一壁表面热量快速传至真空室内壁上。第一壁背板和真空室内壁上分别焊接导热铜块作为冷热连接端, 导热管嵌入其内,导热管与铜块之间增垫导热金属箔并用压板固定压紧,以增强接触界面传热。根据此传热结构 设计,设计加工了相应的传热性能测试试验件。通过对试验件进行传热性能测试及实验条件外推可知,试验件冷 热端面间的最大传热功率为 4kW,端面间最大对流换热系数为 6kW·m^‒2。     

Experimental and numerical investigation on the exergy and entransy performance of a novel plate heat exchanger

There has been increased attention on various types of plate heat exchangers because of their high efficiency and compactness. This article presents an investigation of heat transfer and fluid flow performance of a novel plate heat exchanger based on numeric studies and experimental tests. Parameters of the novel plate heat exchanger are analyzed and discussed. The thermo-hydraulic transfer performance of different plate heat exchangers is comprehensively analyzed using the exergy and entransy principle. The results indicate that the novel plate heat exchanger has better thermo-hydraulic transfer performance than the smooth plate heat exchanger. The result of this study provides a paradigm for the optimal design of plate heat exchangers.     

离散发热器件基于(火积)耗散率最小和最高温度最小的构形优化比较

建立了导热基座上圆柱体离散发热器件的三维湍流散热模型,基于构形理论,考虑空气变物性及可压缩性和黏性耗散,研究了器件材料的热导率、热源强度和流体流速对器件最高温度、基于(火积)耗散定义的当量热阻和平均Nu数的影响.结果表明:在总发热功率一定的条件下,以器件最高温度和当量热阻为性能指标进行热设计,均存在最优热源强度分布使得散热性能最优.当各热源强度相同且热源热导率小于基座热导率时,提高热源热导率可明显改善散热性能;将热源热导率沿流动方向从低到高布置可降低器件最高温度,而将热源热导率均匀布置可使当量热阻最小.所得结果可为实际热设计中不同材质和不同发热率的电子器件最优布置提供理论支撑.     

底部局部加热多孔介质自然对流传热的格子Boltzmann模拟

运用格子Boltzmann方法研究了底部局部加热多孔介质方腔的自然对流传热.方腔的上壁面为低温热源,下壁面为局部高温热源,左右壁面为绝热条件.重点分析了高温热源位置a及尺寸b对多孔介质方腔自然对流传热性能的影响,提出了平均Nusselt数Nu和位置a及尺寸b的拟合关系式.研究结果表明:高温热源位置及尺寸对多孔介质方腔内自然对流传热性质的影响很大,且存在最佳高温热源位置(a=4/16)和尺寸(b=0.75),以达到最强的对流换热强度(Nu_(max)≈10.35)和最大的对流换热量(Q_(max)≈5.69).     

空气源热泵除霜性能的实验研究

空气源热泵目前应用十分广泛,但是冬季热泵翅片管式蒸发器表面结霜会对其性能造成很大危害。因此除霜性能是影响热泵整体性能的重要因素之一。为了解决热泵除霜问题,实验测量了风冷热泵除霜的性能,研究了热泵除霜时各主要部件的性能变化,研究结论对热泵系统除霜研究具有重要的参考价值。     

Experimental study of heat transfer of dielectric liquid perfluorohexane at flowboiling in a microchannel heat exchanger

Presented are results of an experimental study of local heat transfer characteristics in boiling of the dielectric liquid perfluorohexane under forced convection in a horizontal microchannel heat exchanger. The experiments with a copper microchannel heat exchanger comprising 21 channels with sections of 335 × 930 μm were conducted with a mass velocity of 250 to 1000 kg/m²s and a heat flux through the outer wall of the heat exchanger of 3 to 60 W/cm². The dependence of the local heat transfer coefficient on the heat flux density on the inner wall of the microchannels was established, as well as the critical heat flux. The experimental data are compared with calculations based on known models of heat transfer.     

高温及超高温热管的启动特性和传热极限

根据局部高温、高热流加热等特殊场合的需求,设计、加工了钠高温热管及锂超高温热管,并对热管的启动和极限特性进行了研究。高温及超高温热管能够顺利启动,但启动时应注意可能到来的声速传热极限。端部加热启动时,端部附近管体部分会形成一段等效的加热段,可以将工质从启动时的固体状态到全部熔化形成相变传热及流动循环的时间确定为启动时间。热管的传热极限特性表明,超高温热管应工作在更高的温度和更大的热流密度。热管的结构和工艺优化有利于启动和运行。     

Modeling and Performance Optimization of an Irreversible Two-Stage Combined Thermal Brownian Heat Engine

Based on finite time thermodynamics, an irreversible combined thermal Brownian heat engine model is established in this paper. The model consists of two thermal Brownian heat engines which are operating in tandem with thermal contact with three heat reservoirs. The rates of heat transfer are finite between the heat engine and the reservoir. Considering the heat leakage and the losses caused by kinetic energy change of particles, the formulas of steady current, power output and efficiency are derived. The power output and efficiency of combined heat engine are smaller than that of single heat engine operating between reservoirs with same temperatures. When the potential filed is free from external load, the effects of asymmetry of the potential, barrier height and heat leakage on the performance of the combined heat engine are analyzed. When the potential field is free from external load, the effects of basic design parameters on the performance of the combined heat engine are analyzed. The optimal power and efficiency are obtained by optimizing the barrier heights of two heat engines. The optimal working regions are obtained. There is optimal temperature ratio which maximize the overall power output or efficiency. When the potential filed is subjected to external load, effect of external load is analyzed. The steady current decreases versus external load; the power output and efficiency are monotonically increasing versus external load.     

超临界CO2在烧结多孔圆管中换热的实验研究

本文对超临界压力二氧化碳在烧结多孔介质的竖直圆管中的对流换热进行了实验研究。分析了入口温度超过准临界温度、颗粒直径为0．2-0．28 mm的多孔圆管中,压力、流量、热流密度以及流动方向对超临界二氧化碳对流换热的影响。结果表明,准临界点附近剧烈变物性的影响使得超临界二氧化碳在多孔结构中的对流换热非常复杂。对流换热随着温度远离准临界温度和热流密度的增加不断减弱;流量对对流换热的影响比较复杂。在准临界温度附近,浮升力对换热有一定的影响。