环路热管技术的研究热点和发展趋势

综述了环路热管技术近20年的主要理论和实验研究内容,分析了当前的研究热点,包括环路热管启动特性研究,以温度滞后和温度波动现象为代表的暂态特性研究,新型毛细芯的研制和毛细结构的优化,蒸发器内的强化传热和可视化研究,以及高级环路热管、混合冷却环路、多蒸发器混合环路热管、低温环路热管等新型环路热管技术。     

复合结构毛细蒸发器传热特性研究

研制了复合结构毛细蒸发器环路热管,实验研究了环路热管的启动性能与运行特性,通过与单一结构毛细蒸发器环路热管对比,表明复合结构毛细蒸发器环路热管传热功率密度得到了提高,热阻明显降低.但在低功率下启动时,复合结构毛细蒸发器环路热管的温度波动现象加剧.     

CO_2两相回路启动过程阶段蒸发和干烧现象分析

采用并联蒸发器作为传热元件,并联冷凝器作为散热部件,建立了包括热量收集、传递与排散的机械泵驱动两相回路集成试验系统,并对该系统的热启动进行实验研究.实验结果表明:(1)在冷工况、低热流密度的情况下,采用长程毛细管结构的蒸发器对分布式小热源进行集热时,会出现阶段性形核沸腾蒸发,并且上游过热液体形核沸腾后会导致下游出现干烧现象.(2)对于该系统,并联蒸发器相同热量同时启动是相对较好的启动方式.     

平板式mLHP的仿真与实验研究

环路热管是一种靠蒸发器的毛细芯产生毛细力来驱动回路运行,利用工质相变来传递热量的高效传热装置.本文研制了一套不锈钢外壳,以氨为工质的小型平板式环路热管(mLHP),并着重研究其在不同热负荷条件下启动特性及变工况条件下的稳定运行特征,通过对平板 mLHP 运行机制理论分析,建立了合理的数学物理模型,实现了对整个系统动态仿真.实验结果表明,小型平板式 mLHP 可以在不同热流密度下快速启动,并具有良好的适应变热负荷能力.实现了平板式 mLHP 系统中各个主要节点的压力、温度和流量的动态仿真,与实验数据对比,仿真结果和实验数据吻合较好,加深了对 LHP 系统运行机理的理解.通过实验和动态仿真结果对系统结构进行优化,为应用在电子器件散热的高效率平板式 mLHP 系统的设计与优化提供依据.     

小型平板CPL蒸发器耦合计算及优化设计研究

本文建立了小型平板CPL蒸发器毛细多孔芯内汽液两相流动与传热的模型以及金属外壁和工质区的导热模型,并进行耦合求解.分析了金属侧壁效应对蒸发器性能的影响,提出小型平板CPL存在着侧壁效应传热极限.数值结果表明,工质蒸发发生在多孔芯加热表面附近,蒸发器采用单一金属外壁时由于侧壁效应导致系统传热极限低,而上壁采用导热系数大,侧壁及下壁采用导热系数小的新型结构能够明显的提高系统的传热能力,同时使加热表面的温度维持在较低的水平.     

机械式冷藏车蒸发器结霜特性的研究

机械冷藏车蒸发器结霜会增加传热热阻和减小换热量,必须对结霜过程进行深入了解。建立了一个机械冷藏车蒸发器结霜的数学模型,并计算了结霜量、蒸发器换热量随时间的变化过程。获得了各个入口空气参数对蒸发器结霜厚度和换热量的影响规律。研究发现结霜严重地影响了蒸发器换热性能。     

水平管降膜蒸发器传热优化研究

基于分布参数方法,对大型制冷系统中的水平管外降膜蒸发进行了传热优化数值模拟计算.在计算中,分析了饱和的液态制冷剂R134a在水平的铜管束外流动蒸发的换热特性.模型考虑了不同的管子类型和2流程不同管程布置对蒸发器换热特性的影响,结果表明,蒸发器采用Turbo-EHP管的性能高于其它管;不同管程布置对蒸发器性能的影响比较大,其中,下进上出管程布置的换热性能优于其它管程布置.同时,本文考虑了传热管外"干斑"对换热的影响.本文结论对于大型制冷系统中的降膜蒸发器传热优化设计具有指导性意义.     

Thermal Performance of a Capillary Pumped Loop for Automotive Cooling

The design and test results for a capillary pumped loop (CPL) for thermal management of up to 210 W at the source and heat transfer over a distance of 1 m are discussed. The design configuration of the CPL evaporator consists of an internally grooved aluminum evaporator, 31.70-mm outer diameter and 500-mm long, fitted with a porous ultra-high molecular weight polyethylene wick, 8- to 15-μm pore radius, and 38% porous volume. Heat was transferred using a stainless steel tube of 4.5-mm internal diameter for vapor and liquid lines. High-grade acetone (99.99% pure) was used as the heat transfer fluid inside the loop. In the tests, thermal characteristics of the CPL were specifically studied with respect to the temperature control capability using an active thermal device on the reservoir and to the start-up process through pressure priming of the capillary evaporator. The loop was able to start-up successfully at both low and high heat loads, although proper priming of the wick structure before start-up was necessary to attain low evaporator temperatures during steady-state operation. While maintaining constant reservoir temperature through active means, the loop was able to control evaporator temperature within 55 ± 3°C, even with changing input heat from 30 to 210 W. Total thermal resistance from the evaporator surface to the surroundings was 0.19° to 1.15° C/W with the minimum value achieved at the maximum heat load of 210 W. This study is intended to illustrate the thermal potential of the CPL as an effective temperature control device in automotive applications.     

工质对平板型LHP运行特性影响的实验研究

本文研制了一套以不锈钢丝网为毛细芯的平板式蒸发器、风冷管翅式冷凝器的环路热管,并着重研究其以甲醇和丙酮为工质时运行特性的差异。实验结果表明,小型平板式LHP具有良好的启动特性和适应变热负荷能力,在相同的工况条件下,以丙酮为工质的LHP温度波动较小,系统启动较快且蒸发器壁面温度较低,但其极限热负荷能力低于甲醇。     

微矩形槽平板热管的设计制造及性能分析

目前微槽平板热管成为热管研究和开发的重点。文中简要介绍了平板热管的设计要点及制造工艺,并通过实验,对设计制作的平板热管进行了性能测试。得出如下结论:该平板热管具有良好的启动特性和工作特性;在设计中要注意工质与管壳材料的相容性;制作时要严格控制清洗、检漏、充装等关键工序以保证制作质量。     

太阳能光伏光热扁管式蒸发器性能分析

根据太阳能光伏光热蒸发器与制冷系统之间的能量平衡,建立了光伏光热扁管式蒸发器性能的数理模型。该模型考虑了光伏光热扁管式蒸发器的传热系数变化,并分析了太阳辐射强度、环境温度、制冷循环的蒸发温度对光伏光热扁管式蒸发器的电池板温度、电池板光电转换效率、电池板发电功率以及光伏光热蒸发器散热量的影响。     

Coefficient de transfert, à l'interface de vaporisation,d'une boucle fluide diphasique à pompage thermocapillaire

Heat transfer coefficient at vaporisation interface of a two phase capillary loop. In this article, we present the results of heat transfer coefficient measurements at the vaporisation interface of a capillary pumped two-phase loop for two different types of evaporators and various powers. High contact between the evaporator wall and the porous wick, which induces capillary pumping, prevents vapor from escaping and being forced back into the wick and inhibits the device starting up. First, the surface state of the evaporator wall, then the minimum distance between wall and porous wick necessary to optimize operating conditions have been established.     

Influence of nucleation on the flow boiling heat transfer coefficient of a refrigerant mixture under varied heat flux conditions

The influence of nucleation on the flow boiling heat transfer coefficient of R-134a/R-290/R-600a refrigerant mixture is experimentally studied in a smooth horizontal tube of 12.7 mm diameter. The heat transfer coefficients are experimentally measured for stratified flow patterns under a varied heat flux condition; a condition found in the evaporator of refrigerators and deep freezers. The experiments are conducted in a counter-current heat exchanger test section. By regulating the flow rate and inlet temperature of acetone, which is the heating fluid flowing in the outer tube, a varied heat flux is provided to the refrigerant flowing in the inner tube. The refrigerant mass flow rate is fixed between 3 and 5 g s⁻¹ and its inlet temperature between −8.59 and 5.33°C, which corresponds to a pressure of 3.2 to 5 bar. The significance of nucleate boiling prevailing in the above-mentioned evaporators is highlighted. The experimental heat transfer coefficients are also compared with well known heat transfer correlations.     

平板型环路热管应用于LED的启动特性研究

本文将平板型环路热管应用于大功率LED的散热,通过实验研究了加热位置、放置方式和功率对启动特性的影响.蒸发器内的汽液分布影响着从蒸发器到补偿器的热泄漏,从而影响启动特性.如果非有效蒸发区内的液态工质量越多,则热泄漏越小,环路热管越容易启动.此外,补偿器内工质往液管流动,相当于补偿器对外做功,自身能量有减少的趋势,促使形成循环所需的更大压差.     

相对湿度对空调中翅片管蒸发器性能的影响

基于换热器几何结构参数以及流路布置等相同的3HP商用空调,在空调工况下,研究了相对湿度对R22替代制冷剂R407C、R410A、R32以及R290在蒸发器内的流动和传热性能的影响规律。研究表明:在一定的条件下,增加环境相对湿度,这五种制冷剂对应蒸发器换热量、压降和质量流量均增加,其中R407C蒸发器换热量最大,R290和R32蒸发器压降和制冷剂质量流量均小于R22蒸发器。在低湿度环境下(约20—30%相对湿度),显热换热占主导因素。随着相对湿度的增加,显然换热减少,潜热换热增强且起主导因素。在满足换热量的要求下,R290在协调压降与质量流量具有一定的优势且满足现行工质替代理念,可以作为现有商用空调的环保型替代工质。     

小型平板CPL蒸发器预热驱动过程研究

分析了小型平板CPL蒸发器毛细多孔芯上下表面温差对启动的影响,建立了蒸发器满液启动的数学模型.结果表明,对不同的金属外壁,多孔芯上下表面平均温差存在一个最大值,铜壁时,温差较小,侧壁效应明显;采用不锈钢壁及上壁铜、侧壁下壁不锈钢时,温差大,侧壁效应小;采用不锈钢外壁时蒸发器加热面的温度过高.上壁采用导热系数大、侧壁下壁为导热系数小的金属对小型平板CPL蒸发器的正常启动以及降低加热表面温度非常有利.     

The optimal design of integrated evaporation systems

The heat integration of evaporators with overall processes leads to optimal designs very different from optimal stand-alone designs. The grand composite curve has been previously suggested for assessing alternative evaporator integration schemes. This paper demonstrates that if the effect of the evaporator integration on the overall capital-energy trade-off is ignored then misleading conclusions can be obtained. A procedure is suggested which takes account of this capital-energy trade-off. Design complications such as boiling point rise and latent heat changes which have often been ignored in the past in the grand composite approach are also considered.     

EXPERIMENTAL STUDY OF THE HEAT TRANSFER CHARACTERISTICS OF A TWO-PHASE DOUBLE-LOOP THERMOSYPHON

An experimental study is presented for the heat transfer characteristics of a rectangular, two-phase, double-loop thermosyphon with water-steam as the working fluid. The evaporator was installed in the middle branch and shared by the two condensers. Local temperature measurements of the core fluid and the wall were made, and the overall heat transfer coefficients of the evaporator, the condensers, and the loop system were obtained and correlated in terms of the fluid properties, heat flux conditions, and the liquid charge level V⁺. Results show that the overall heat transfer coefficients increase with decreasing V⁺ and increasing heat flux. The heat transfer performance of the entire system can be viewed as a parallel combination of the thermal resistances of the evaporator and two condensers. Results also confirm the previous findings that if the liquid charge level is below the fractional volume of the bottom connecting tubes, an overheat phenomenon will take place.     

Computer simulation of a combined cycle power plant

This paper presents the simulation procedure developed to predict the performance of a combined cycle power plant from given performance characteristics of its main components. In order that the procedure could be validated, the simulation technique has been applied to a typical combined cycle power plant (having a dual pressure bottoming cycle) manufactured by a prominent company. The characteristics of the standard equipment like the air compressor, steam and gas turbines, various pumps, etc. have been taken from the manufacturer's catalogues and converted into appropriate equations based on theoretical understanding. The performance of various heat exchangers (like economizers, superheaters, evaporators, etc.) has been determined by using the effectiveness concept after evaluating the overall heat transfer coefficient by using appropriate correlations from literature. The strategy of system simulation is obtained by judiciously interlinking the information flow diagrams of various components and thus the task is finally reduced to that of solving nine non-linear equations for nine variables. The predicted performance of the system is seen to be in good agreement with in good agreement with its rated performance.     

低温工况下结霜对翅片管蒸发器性能影响的实验研究

翅片管蒸发器的结霜将增加空气压降 ,增大传热热阻 ,从而直接影响到蒸发器的效率及空气侧平均换热系数。文中就低温工况下结霜对蒸发器性能的影响进行了测试研究 ,为翅片管蒸发器的设计应用提供了重要依据