工质热物性对脉动热管运行性能的影响

工质热物性显著影响脉动热管的流动与传热特性。本文通过理论计算及实验研究,定性分析了工质热物性对临界直径、毛细滞后阻力、启动运行及传热极限等方面的影响。研究表明,为保证脉动热管的运行性能,在设计阶段应综合考虑工质、管材及管径大小等因素。首先,根据使用场合的热流密度及运行温度高低合理选取工质种类;然后,选用合适的管壁材料,尽可能减少液塞与管壁之间前、后接触角不同引起的毛细滞后阻力;最后,确定管内直径范围。本文工作旨在为脉动热管的设计和选用提供一些依据和参考。     

相变换热系统的能量流模型及其应用

工质在换热过程中发生相变时,其物性参数将发生剧烈变化,增大了换热系统性能分析和优化的复杂度。本文以顺流、逆流和叉流三种典型换热器为研究对象,在考虑工质发生相变的前提下,构建了与其对应的等效热阻网络图(能量流模型),获得了换热器的换热量与结构/运行参数以及工质物性间的直接物理联系。以此为基础,对于含相变工质的换热系统,通过构建其整体能量流模型,结合基尔霍夫电压、电流定律明确了系统中各独立设计参数间的整体约束关系,并应用拉格朗日乘子法实现了相变换热系统的性能优化。     

基于AR功率谱的振荡热管循环运行特性分析

本文可视化实验观测了振荡热管在准稳定运行状态下管内工质的循环运行模式,并引入现代自回归(AR)模型功率谱分析方法分析了两种工质循环运行模式下振荡热管壁温振荡信号的频谱特性。研究表明:不同循环运行模式下振荡热管各工作段壁温的时域振荡信号各具特征,其AR功率谱密度图能够有效反映振荡热管循环运行的频谱特性并提取壁温时域振荡信号中的主频信息,它可以成为辨识振荡热管内工质循环运行模式的有效工具。     

考虑接触角滞后的脉动热管工质运动特性研究

将汽、液塞工质接触角滞后毛细阻力引入Ma等的模型中,并在考虑管间压力不平衡影响下建立了描述脉动热管工质运动特性的数学模型。模拟结果发现,脉动热管启动后在小于1 s的短时间内即可进入稳定周期振荡阶段。在稳定振荡过程中,充液率、管长和冷/热段温差对管内工质运动位移及速度影响显著。本研究有助于更好地理解脉动热管振荡运动特性和运行机理。     

平板热管在毛细极限下的传热能力研究

建立了多孔毛细芯结构的平板热管在冷凝段不发生堵塞的情况下流动和传热的理论模型,分析了热管在毛细限下的最大传热量和热阻的变化.结果表明,丝网目数的增加和工作温度的升高会增大热管的传热能力,热管工质为水时的传热性能优于工质为丙酮和乙醇时的情况.     

低沸点工质板式脉动热管传热特性研究

针对电子设备需要在较低的温度下工作的要求,本文对采用R141b与R600a等低沸点工质,槽道边长为1 mm的板式脉动热管进行传热实验研究。结果表明,对比丙酮工质脉动热管,在不同加热功率下,低沸点工质脉动热管启动时间短,启动温度低,正常运行时冷热端温差小,热端温度低,热阻小。低沸点工质能大幅提高微通道脉动热管传热性能,R600a为工质时,脉动热管启动时间最短仅需要12 s,正常运行时,R141b为工质脉动热管冷热端温度差最小为0.8℃。     

氮工质低温脉动热管的数值模拟

低温制冷机被广泛应用于超导体冷却、低温医疗、低温液体贮存等方面,但受到只能在冷头处提供冷量的限制。脉动热管作为一种灵活高效的传热元件,可以与低温制冷机配合以实现分布式冷却和长距离冷量传送。低温工质在物性上与常温工质有很大不同,这使得以氮、氢为代表工质的低温脉动热管的传热和振荡特性有别于以水、乙醇为代表工质的常温脉动热管。针对脉动热管中的长液塞典型流动现象,建立了多气泡-液塞的闭式脉动热管模型,给出了以氮为工质时装置的振荡和传热特性,结果显示氮工质的低温脉动热管与水的脉动热管相比,其内部的长液塞具有更高的振荡频率,且具有更小的传热温差。     

相变换热混合工质板翅式换热器流动与传热数值模拟

采用由SRK方程计算得出的混合工质物性参数,将具有相变两相流体物性分三部分处理,得出混合工质分段物性数据拟合曲线,并输入FLUENT软件的材料物性数据文件中,作为数值模拟物性参数数据。在上述物性数据处理的基础上,对混合工质天然气液化装置中换热器采用分段方式进行稳态数值模拟研究,得到沿长度方向一定温度下传热系数、压力梯度的变化曲线。通过与MUSE软件数据比较,计算结果有一定合理性,所得结论为有相变换热的混合工质低温板翅式换热器的设计和优化提供一定参考。     

脉动热管的结构改进及其传热特性的实验研究

通过观察脉动热管的运行过程,并分析其存在的缺点,提出对脉动热管的结构进行改进,合理匹配各通道内的 流动阻力,实现工质在热管里的稳定单向流动,以改善加热段的供液情况,提高脉动热管传热性能。并对充灌率、倾角和 通道大小对改进型脉动热管的传热性能的影响进行了实验研究。     

基于管排组合的热管换热器温度分布的研究

建立了热管废热锅炉的换热器模型,研究了在各种管排组合方案下的分离式热管换热器的工质温度分布、管壁温度分布、烟气温度分布及热回收量等,结果表明,调整管排组合是解决工质温度过高和低温腐蚀问题的一种有效方法.     

液相斯特林机工质的热力学与热物理性质的计算

介绍了液相斯特林机用液相工质的性质。并以工质 RC31 8作为算例 ,介绍了液相工质的热力学性质和热物理性质的数值计算 ,计算结果与已有的实验结果吻合较好。该文也将是研究和开发低品位热源液相热声热机的重要参考。     

热管技术在金属模具均温散热上的应用

热管作为一种高效的传热元件,其优异的导热性能,在模具行业有着越来越大的作用。简述了在热管的工作原理,较为系统地介绍热管技术在模具行业上的应用,并且将热管冷却方式和传统模具冷却方法进行了比较。介绍热管技术在热流道系统中应用的进展,热管技术在注塑模中的应用,以及在铸造模具行业中的应用。     

分离式螺旋热管在蓄冷系统的换热特性分析

阐述了分离式螺旋热管的换热特性,并提出了将螺旋热管应用于蓄冷系统的新方案。建立了分离式螺旋热管的换热模型,分析了热流密度、充液率以及几何尺寸对螺旋热管管内换热的影响,为螺旋热管结构的优化以及在蓄冷系统的应用提供了理论依据。     

Investigation on thermal performance of a high-temperature heat-pipe thermal protection structure

Sharp leading edges with a millimeter-scale radius are required for hypersonic vehicles from aerodynamic reasons. However, with the leading edges being so sharp, stagnation regions at wing and tail leading edges suffer a hostile thermal environment. Therefore, a high-temperature heat pipe is considered to be integrated into the structure of the leading edge to reduce the temperature of the stagnation point. In this paper, a superalloy-refractory composite-container-“wall” combined with the wick and working fluid structure is proposed, which is proved to be a feasible design of a heat pipe for the semi-passive thermal protection system (TPS). The effects of different material of the exterior surface on the temperature distributions are investigated. The effect of the half wedge angle, the design length and porosity of the wick is also investigated to find the effect of the geometry of the structure of the leading edge on the operation of the heat pipe.     

单根热管蓄冰研究

从技术角度研究和探讨了热管做为冰蓄冷装置的适用性,建立了单根热管蓄冰过程的数学模型,提出了蒸发段与冷凝段的长度配比;进行了一系列的实验,得到了不同工况下蓄冰厚度与时间之间的关系;结果表明热管蓄冰装置有着非常良好的蓄冰性能,为热管冰蓄冷装置的推广应用,提供整个装置的最优配置模式参数及强有力的理论依据及实验支撑。     

The performance analysis of a micro-/nanoscaled quantum heat engine

A new model of micro-/nanoscaled heat engines consisting of two thin long tubes with the same length but different sizes of cross section, which are filled up with ideal quantum gases and operated between two heat reservoirs, is put forward. The working fluid of the heat engine cycle goes through four processes, which include two isothermal processes and two isobaric processes with constant longitudinal pressure. General expressions for the power output and efficiency of the cycle are derived, based on the thermodynamic properties of confined ideal quantum gases. The influence of the size effect on the power output and efficiency is discussed. The differences between the heat engines working with the ideal Bose gas and Fermi gas are revealed. The performance of the heat engines operating at weak gas degeneracy and high temperatures is further analyzed. The results obtained are more general and significant than those in the current literature.     

以TFE-[BMIm][Br]为工质对的吸收式制冷循环性能分析

本文选择含离子液体体系TFE-[BMIm][Br]作为吸收式制冷循环的工质体系,基于文献数据给出了计算TFE-[BMIm][Br]热物性模型,建立并联双效吸收式制冷循环的模拟程序,分别考察了四种双效并联制冷流程中溶液换热器的热交换效率、蒸发温度、吸收温度以及发生温度对系统性能、溶液循环倍率以及系统操作压力的影响.探索新工质对TFE-[BMIm][Br]的可行性,确定了TFE-[BMIm][Br]双效并联吸收式制冷循环的适宜的运行操作范围以及适宜的流程方案.     

尺度效应对脉动热管启动和运行的影响

建立了脉动热管启动和运行的物理和数学模型,关联了新汽泡的产生条件和毛细管内已有汽泡之问的关系,从而发现了尺度效应如何影响脉动热管启动和运行的规律.已有汽泡的形状强烈影响脉动热管的启动和运行,小汽泡更利于新汽泡的产生.脉动热管的优化设计可以通过对壁面粗糙度的加工、形成的汽泡尺度的控制和工质的匹配选择等来实现.结果对于脉动热管的设计具有重要参考价值.     

Parametric optimum analysis of an irreversible Ericsson cryogenic refrigeration cycle working with an ideal Fermi gas

An irreversible model of an Ericsson cryogenic refrigeration cycle working with an ideal Fermi gas is established, which is composed of two isothermal and two isobaric processes. The influence of both the quantum degeneracy and the finite-rate heat transfer between the working fluid and the heat reservoirs on the performance of the cycle is investigated, based on the theory of statistical mechanics and thermodynamic properties of an ideal Fermi gas. The inherent regeneration losses of the cycle are analyzed. Expressions for several important performance parameters such as the coefficient of performance, cooling rate and power input are derived. By using numerical solutions, the cooling rate of the cycle is optimized for a given power input. The maximum cooling rate and the corresponding parameters are calculated numerically. The optimal regions of the coefficient of performance and power input are determined. Especially, the optimal performance of the cycle in the strong and weak gas degeneracy cases and the high temperature limit is discussed in detail. The analytic expressions of some optimized parameters are derived. Some optimum criteria are given. The distinctions and connections between the Ericsson refrigeration cycles working with the Fermi and classical gases are revealed.      

Structural and thermodynamic properties of inhomogeneous fluids in rectangular corrugated nano-pores

Based on the free-energy average method, an area-weighted effective potential is derived for rectangular corrugated nano-pore. With the obtained potential, classical density functional theory is employed to investigate the structural and thermodynamic properties of confined Lennard-Jones fluid in rectangular corrugated slit pores. Firstly, influence of pore geometry on the adsorptive potential is calculated and analyzed. Further, thermodynamic properties including excess adsorption, solvation force, surface free energy and thermodynamic response functions are systematically investigated. It is found that pore geometry can largely modulate the structure of the confined fluids, which in turn influences other thermodynamic properties. In addition, the results show that different geometric elements have different influences on the confined fluids. The work provides an effective route to investigate the effect of roughness on confined fluids. It is expected to shed light on further understanding about interfacial phenomena near rough walls, and then provide useful clues for the design and characterization of novel materials.