相变换热适时动态过程数值模拟

以冷凝器为例,建立了分区和分流型的适时动态分布参数模型,模型建立过程中考虑流体的适时物性参数、湿区含液量、流动压力损失以及管壁蓄热等细节,使模型的准确性和通用性显著提高。在模拟过程中,计算机根据制冷剂状态自动由所建立的物性数据库中查取对应物性参数。模型采用显式方程组,求解速度快。由该模型可进行冷凝换热过程非稳态性能研究,获得换热过程冷、热流体温度、压力和冷凝状态等随时间变化的过程。通过实验验证表明,所建立的模型具有较高的准确性。     

流体变物性对带肋套管内耦合换热的影响

数值模拟了变物性带均布纵肋的同心套管换热芯的导热和对流换热耦合问题三维温度场和流场以及Nu数，与常物性下的结果进行了对比。对微型燃气轮机回热器．必须考虑物性的变化对流动和传热的影响。在相同质量流量和几何条件下．考虑物性变化时的平均Nu与常物性时要小很多。变物性对摩擦系数影响非常大．温度升高摩擦阻力也增大。在相同的Re下．变物性和常物性时的平均Nu相差很小．其比值在0．97～0．99之间．因此在常物性时所得的平均Nu．仍具有参考价值。     

人工神经元网络在汽液物性参数拟合中的应用

在热能系统的模拟与综合中,必须首先解决物性参数的计算问题。本文分析了现有物性参数的一些常用计算方法,提出了利用人工神经元网络对具有静态特性的物性参数进行拟合的计算机方法。在简单介绍人工神经元网络,特别是BP算法的基础上,通过对饱和水蒸汽的物性参数进行拟合的实例分析,认为人工神经元网络对于具有静态特性的饱和水蒸汽的物性参数具有很好的拟合效果,非常适合于实际的工程应用,对于其它具有静态特性的气体或液体的物性参数拟合也有参考价值。     

基于LabVIEW的水与水蒸汽物性参数计算软件开发研究

对水蒸汽物性计算区域IF97及计算公式模型进行了详细阐述,基于MALTAB编写了水与水蒸汽物性参数的计算程序,建立了水与水蒸汽的物性参数动态链接库。基于LabVIEW开发了水与水蒸汽物性参数计算软件界面。对比结果分析表明,该软件计算的结果与2007年国际水与水蒸汽表中的数据完全吻合,说明此软件具有很高的计算准确性,可应用于工程实际中的水与水蒸汽物性参数计算。     

两种深层岩土热物性测试方法的比较

通过对现场热物性测试和现场冷热量测试两种测试方法的对比,说明了各自在深层岩土热物性测试的优缺点。结合实际工程,对两种方法在测试中出现的问题进行分析,指出了现场热物性测试是一种适用范围更广的测试方法。     

热物性参数对钢坯炉内加热模型精度的影响分析

热物性参数直接影响钢坯的导热过程,在模拟钢坯炉内加热过程如果热物性参数选取不合理,势必造成计算结果严重失真,导致模型精度不高。针对某一钢种的热物性参数进行了实测,并将各种方法获得的热物性参数应用于钢坯加热过程的数值模拟计算,对比分析其对钢坯炉内加热过程模拟计算精度的影响。     

缸盖材料温变效应的理论与试验研究

采用数值仿真分析手段,研究了高热流密度条件下蠕墨铸铁平板内部传热状态随物性的变化。结果表明:在常物性和变物性2种不同的假设条件下,平板稳态传热的温度场分布存在显著差异。为了验证仿真分析结果,搭建了试验测试台架,材料常物性假设条件下的数值仿真结果相对试验实测数据的误差最高可达12%,而变物性计算条件下的数值仿真结果与试验数据误差在2%以内。且在某一热流密度范围内,常物性设置的计算结果非常接近变物性设置计算结果及实测值,即在该热流密度范围内的仿真可以用适当温度下的常物性设置来代替变物性设置,以简化计算。在此基础上,针对某机型缸盖结构设计方案,分别计算了常物性和变物性条件下缸盖火力面的温度分布。结果与平板仿真结果吻合,常物性与变物性之间的误差最高为7.03%。     

热力过程中工质热物性的确定方法讨论

在对热力过程进行分析时,经常需要确定工质在过程中热物性的变化,以热物性参数一焓为例,用余函数法和热力学中的经验公式,阐述了确定比焓的变化的另一种方法,也即确定热力过程中工质热物性的另一种方法。     

ORC系统热力性能计算程序开发

在有机朗肯循环(ORC)系统设计理论基础上,结合Matlab 2010a平台及REFPROP(工质物性)8.0数据库,编写了低品位余热发电ORC系统热力性能的计算程序。参照实例的设计参数,运用该程序进行了ORC系统的设计,并将程序运算结果与实际运行参数进行了对比。结果表明,该程序具有工质筛选、系统循环热力计算以及设备初步选型等应用功能,且运算结果准确。     

基于Web的水与水蒸汽热物性计算程序开发

在课题组已有流体热物性远程计算系统的研究基础上,进一步开展了针对水的热物性远程计算模块的研究,实现了IAPWS-95高精度水与水蒸汽的热物性数据计算,扩充了流体物理与化学性质数据资源平台,并完善了单一流体的热物性远程计算方法,为今后开展类似研究积累了经验。     

Food thermophysical property models

The design engineer must predict the thermophysical properties of foods in order to design food storage and refrigeration equipment and estimate process times for refrigerating, freezing, heating or drying of foods. Since the thermophysical properties of foods are strongly dependent upon chemical composition and temperature, composition based models provide a means of estimating these properties. Numerous models of this type have been proposed and the designer of food processing equipment is thus faced with the challenge of selecting appropriate models from the plethora of those available. This paper describes selected food thermophysical property models and evaluates their performance by comparing their results to experimental thermophysical property data. The results given in this paper will be of value to the design engineer in the selection of appropriate food thermophysical property models.     

Natural convection due to horizontal temperature and concentration gradients—1. Variable thermophysical property effects

Typically for single component fluids, the variation of thermophysical properties is negligible except in the presence of large temperature differences, and, therefore, has no appreciable effect on the heat transfer. In contradistinction, thermophysical properties can vary significantly due to concentration differences which affect the heat and mass transfer. This work examines the effects of thermophysical property variation on the heat and mass transfer in a cavity due to natural convection driven by combined thermal and solutal buoyancy forces. Results indicate that thermophysical property variations can appreciably influence heat and mass transfer and velocity distribution.     

高温气冷堆氦气透平循环工质的热物性

在高温气冷堆氦气透平直接循环中,氦气既是堆芯的冷却剂,又是循环工质。氦气热物性数据来源多样且互相不一致,对目前应用较多的5种氦气热物性参数计算方法进行了比较分析。     

Thermodynamic and thermophysical effects enabling high-forced convection heat transfer coefficients in supercritical fluids

Abstract

The strong variation of thermophysical properties of working fluids operating in the vicinity of the critical point makes this thermodynamic domain attractive to several energy applications. Therefore, herein a two-dimensional numerical method is used to investigate the effect of local thermophysical property variations on the local and overall thermal performance of internal convective heat transfer in a pipe in 324 operational conditions. Focusing on carbon dioxide and water as heat transfer fluids, an association of the variation of key thermophysical properties with thermohydraulic performance metrics is proposed, namely: (a) the local and (b) mean convective heat transfer coefficient and (c) the maximal temperature obtained at the tube wall. It is shown that there is an optimal combination of parameters such as mass flow rate, operating pressure, wall heat flux, and inlet temperature that, when properly selected, allow for a minimal maximal wall temperature. As expected, optimality is strongly associated with the Widom—or pseudo critical—line that extends from the critical point. Interestingly, however, contrary to what is observed in constant-property fluids, high heat transfer coefficient or minimal maximum temperature lead to different sets of optimal operating conditions. This difference is explained by how thermophysical properties vary locally along heat exchangers, which significantly affects overall heat transfer.     

Measuring method of three thermophysical parameters of solids by a thermal probe with instantaneous point contact: Discussion about applicability and measuring conditions

An instrument for the measuring method reported in the previous paper is a handy tester for three thermophysical parameters of solids in situ. Discussions about measurement errors caused by not strictly satisfying the measuring conditions, such as size and shape of the testing body, and about optimum initial temperature difference between thermal probe and testing body have been done. As a result of the experiment varying the shape of a probe end, it is shown that the radius of the contacting surface on a testing body has no influence on measuring thermophysical parameters. © 2003 Wiley Periodicals, Inc. Heat Trans Asian Res, 32(3): 202–211, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10085     

Measuring method of three thermophysical parameters of solids by a thermal probe with instantaneous point contact: Measuring principle

A new method for instantaneous measurement of three thermophysical parameters of solids in situ is proposed. The measurement principle is based on a transient heat conduction model of a thermal probe point contacting a testing body. The measurement of temperature response has been made using the probe of a sheathed K‐type thermocouple in this experiment. Ratios of both thermal conductivity and thermal effusivity between the probe and the testing body are determined from curve‐fitting with the theoretical response to the measured one. As a result, it is shown that the measurement is reproducible and the accuracies of measured thermophysical parameters are good enough to apply this method to many kinds of solids. © 2003 Wiley Periodicals, Inc. Heat Trans Asian Res, 32(3): 191–201, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10084     

Effects of superheat and temperature-dependent thermophysical properties on evaporating thin liquid films in microchannels

A model based on the augmented Young–Laplace equation and the Clausius–Clapeyron equation was developed to describe the extended evaporating meniscus in a microchannel. The effects of the adsorbed film thickness, channel height and temperature-dependent thermophysical properties of the fluid are included in the model at wall superheats up to 50 K. The liquid flow is coupled with the vapor flow to obtain the mass transport across the liquid–vapor interface. The results show that the constant thermophysical property model greatly overestimates the liquid pressure difference and the total thin film heat transfer rate at higher superheats compared with the variable thermophysical property model. The adsorbed film thickness, which is controlled by the disjoining pressure limit, reaches a minimum near about 20 K superheat for water. The maximum film curvature and liquid pressure difference then decrease at superheats larger than 20 K. The effects of the capillary pressure limit produced by the channel height can be reduced by increasing the superheat.     

Thermophysical Properties of a New Environment Friendly Alternative—Trifluoroiodomethane

Trifluoroiodomethane (CF₃I) is considered as a promising refrigerant alternative, especially as a component in mixtures, to replace CFC-12. But reliable thermophysical property data for CF₃I are still limited. The investigations on thermophysical properties of CF₃I developed by us are summarized in this paper. Experimental data of critical parameters, and the correlations of saturated liquid and vapor density, enthalpy of vaporization, vapor pressure, PVT properties, second virial coefficient, ideal-gas heat capacity, surface tension, viscosity and thermal conductivity are given in the present paper.     

江西省地面气象遥测资料质量评估

根据相关要求，确定了自动气象站资料质量评估和差异评估的方法，对江西省16个基本、基准有线遥测气象站2003～2004年的遥测资料与同期的人工站观测资料进行评估分析，得出观测资料质量评估结论和数据差异情况，遥测站总体运行良好，观测资料连续可信。     

Convective heat transfer and second law analysis of non-Newtonian fluid flows with variable thermophysical properties in circular channels

This study presents an analytical solution, for fully developed non-Newtonian fluid flows in circular channels under isoflux thermal boundary conditions based on perturbation techniques. Since the physical properties are generally a function of temperature and may not be assumed constant under certain circumstances, the change in viscosity and thermal conductivity with temperature was taken into account. Viscous dissipation term was also included in the performed analysis. In this study, first closed form expressions for velocity, temperature distributions, and Nusselt numbers corresponding to constant thermophysical properties were given in terms of governing parameters. Then, numerical calculation was performed to obtain the values of Nusselt number and global entropy generation for variable thermophysical properties. The results revealed that neglecting the property variation significantly affects heat transfer characteristics and entropy generation, in which the deviation from the constant physical property assumption may reach up to about 32.6%.