基于热质运动概念的普适导热定律

根据爱因斯坦的质能等效关系式,热能具有的等效质量称为热质,从而在固态和气态介质中分别建立了声子气质量和热子气质量的概念.应用牛顿定律建立了含有驱动力、阻力和惯性力的热质(声子气或热子气)运动的动量守恒方程.由于热量在介质中的传递本质上就是热质(声子气和热子气)在介质中的运动,所以热质动量守恒方程就是普适的导热定律,能够统一描述各种条件下的导热规律.当热流密度不是很大从而热质惯性力可以忽略时,热质动量守恒方程就退化为傅里叶导热定律,这表明傅里叶导热定律是特殊条件下的导热定律,对于微纳尺度条件下的导热,热流密度可以极高,由速度空间变化引起的惯性力不能忽略,在稳态导热情况下也将出现非傅里叶导热,此时在计算或者实验中不能用热流密度除温度梯度求导热系数.在超快速加热条件下,必需考虑惯性力,与基于CV导热模型的波动方程相比,普适的导热定律增加了因速度空间变化引起的惯性力项,所以在介质中热波叠加时不会出现产生负温度的非物理现象,表明基于热质运动概念的普适导热定律更为合理. 关键词： 傅里叶导热定律 普适导热定律 热质运动 非傅里叶导热     

低温空气制冷系统中板翅换热器性能实验研究

对低温空气制冷系统中的散热器、回热器性能进行实验研究,测量不同工况条件下两个锯齿形板翅式换热器的换热效率及系统性能,分析了换热器低压侧和高压侧的空气流量对换热器及系统性能的影响。结果表明:(1)散热器低压侧空气流量是影响其效率的主要因素;(2)回热器效率随其低压侧空气流量的增大而增大,随其高压空气流量的增大而减小;(3)高压空气流量是影响制冷量的主要因素;在其它工况参数不变的条件下,高压空气流量增大7.9%,制冷量最大增加14.5%。     

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。     

Computation of the gas mass and heat fluxes in a rectangular channel in the free molecular regime

The problem of heat- and mass transfer in a long rectangular channel of a constant cross section is solved in the free molecular regime. The distributions of the mass flow rate and the heat flux vector over the channel cross section are calculated. The specific gas mass flux and heat flux are calculated. The results are compared with those obtained for nearly free molecular flows.     

The effect of magnetic fields on the stability of a cylindrical flow with mass and heat transfer

The effect of axial and radial magnetic fields on the Kelvin-Helmholtz stability of a cylindrical interface between the vapor and liquid phases of a fluid is studied when the vapor is hotter than the liquid and the two phases are enclosed between two cylindrical surfaces coaxial with the interface, and when there is mass and heat transfer across the interface. Both axisymmetric and asymmetric disturbances are considered. The linear dispersion relations are obtained and discussed. It is found that a uniform axial magnetic field has a stabilizing effect on the interface, while the effect of a radial magnetic field depends strongly on the choice of some physical parameters of the system. It is also found that the instability criterion is independent of heat and mass transfer coefficient, but it is different fromthat in the same problem without heat and mass transfer. Finally, the heat and mass transfer has a destabilizing influence on the system.     

Numerical solution to the plane heat-mass transfer problem in a system of focused radiation flux-liquid condensed substance film-oxidizer

The plane problem of heat and mass transfer in a focused radiation flux-liquid condensed substance film-oxidizer system is numerically solved. Peculiarities of heat and mass transfer at radiation energy absorption by a vapor-gas mixture near the liquid surface are analyzed. The influence of the radiation density distribution in a flux and the liquid and oxidizer parameters on the conditions of heat and mass transfer is assessed.     

冰的熔解热实验中冰水质量比的探讨

冰与温水质量比对冰的熔解热实验的成败起着关键作用。文章对冰水质量比进行测量和分析,得出了冰的熔解热实验中最适合的冰水质量比的范围约为1／12-1／5。     

External and internal problems of modeling the heat and mass transfer coefficients at particles motion in liquids

An approach to the determination of the heat and mass transfer coefficients from dispersed particles by the development of the hydrodynamic analogy is considered. The equations for computing the heat and mass transfer coefficients in continuous phase at a laminar regime of the flow around solid particles as well as the mass transfer coefficients in droplets are obtained. Comparisons with the experimental data of different authors are presented.     

微尺度水平管内沸腾换热特性研究

对不同质量分数下非共沸混合工质(R134a/R32)在微尺度管道内的流动沸腾换热特性进行了比较和分析,阐述了热流密度、质量流量和质量干度对换热的影响。结果表明:热流密度对换热的影响随着质量流量的增加而愈加明显;在质量分数为75%/25%和65%/35%时,换热系数随着质量流量的增大而增大;而质量分数为85%/15%时,换热系数随质量流量的变化先增加后减小;随着质量干度的增加,换热系数在各质量分数下基本上都呈上升趋势。     

R32/R134a在微通道内流动沸腾特性

研究非共沸混合工质R32/R134a(质量比,25%/75%)在水平微尺度通道内流动沸腾换热规律。在各种工况下进行了非共沸混合工质R32/R134a在水平微尺度管道内流动沸腾换热的实验,考察了质量流量G、热流密度q、质量干度x对微尺度通道内流动沸腾换热系数的影响。研究表明:在热流密度、质量流量都较低的区域,对细管道,换热系数与热流密度的关联度较大;而对微管道,换热系数受影响的因素比较多,并在干度为0.6时出现"干涸"现象,使得换热系数急剧下降。在质量流量高的区域,对细管道,热流密度对换热系数的影响很小;而对微尺度管道,当干度为0.06时换热系数发生转变,随质量干度的增加先减小后增大,热流密度增大到一定的阶段后,换热系数不再随热流密度变化。     

微尺度水平单管内流动沸腾特性实验研究

对非共沸混合工质R134a/R32(75/25)在水平微尺度管道内的流动沸腾换热实验结果进行了分析和讨论,以探究微细通道内流动沸腾换热的主导机制。对影响其换热的多种因素(热流密度、质量流量和质量干度)进行了分析,实验得出,当质量干度较低时,热流密度和质量流量共同控制着微尺度管内的换热方式,当热流密度的影响占主导地位时,管道内的换热以核态沸腾为主;当质量流量的影响占主导地位时,管道内的换热以强制对流为主。     

Effect of Coolant Temperature on the Condensation Heat Transfer in Air-Conditioning and Refrigeration Applications

This article directly investigates the effect of a cooling medium's coolant temperature on the condensation of the refrigerant R-134a. The study presents an experimental investigation into condensation heat transfer, vapor quality, and pressure drop of R-134a flowing through a commercial annular helicoidal pipe under the severe climatic conditions of a Kuwait summer. The quality of the refrigerant is calculated using the temperature and pressure obtained from the experiment. Measurements were performed for refrigerant mass fluxes ranging from 50 to 650 kg/m²s, with a cooling water flow Reynolds number range of 950 to 15,000 at a fixed gas saturation temperature of 42°C and cooling wall temperatures of 5°C, 10°C, and 20°C. The data shows that with an increase of refrigerant mass flux, the overall condensation heat transfer coefficients of R-134a increased, and the pressure drops also increased. However, with the increase of mass flux of cooling water, the refrigerant-side heat transfer coefficients decreased. Using low mass flux in a helicoidal tube improves the heat transfer coefficient. Furthermore, selecting low wall temperature for the cooling medium gives a higher refrigerant-side heat transfer coefficient.     

Measurement of effective specific heat of packed bed materials by the continuous flow electrical method

The theory of the continuous flow electrical method for the determination of specific heat of liquids has been extended to the measurements of effective specific heat of packed bed materials consisting of solid-liquid phase systems. Experimental data are reported showing the variation of effective specific heat with mass porosity and saturating liquid specific heat. The weighted arithmetic mean equation of constituent specific heats is in fair agreement with the measured values.     

Effects of fullerene coalescence on the thermal conductivity of carbon nanopeapods

The heat conduction and its dependence on fullerene coalescence in carbon nanopeapods (CNPs) have been investigated by equilibrium molecular dynamics simulations. The effects of fullerene coalescence on the thermal conductivity of CNPs were discussed under different temperatures. It is shown that the thermal conductivity of the CNPs decreases with the coalescence of encapsulated fullerene molecules. The thermal transmission mechanism of the effect of fullerene coalescence was analysed by the mass transfer contribution, the relative contributions of phonon oscillation frequencies to total heat current and the phonon vibrational density of states (VDOS). The mass transfer in CNPs is mainly attributed to the motion of encapsulated fullerene molecule and it gets more restricted with the coalescence of the fullerene. It shows that the low-frequency phonon modes below 20 THz contribute mostly to thermal conductivity in CNPs. The analysis of VDOS demonstrates that the dominating contribution to heat transfer is from the inner fullerene chain. With the coalescence of fullerene, the interfacial heat transfer between the CNT and fullerene chain is strengthened; however, the heat conduction of the fullerene chain decreases more rapidly at the same time.     

泡沫金属对含油制冷剂管内流动沸腾换热特性的影响

实验研究了制冷剂-润滑油混合流体在内嵌泡沫金属圆管内流动沸腾的换热特性。泡沫金属为10ppi、90%孔隙率;制冷剂为R410A,润滑油为VG68,油浓度为0～5%。实验结果表明:纯制冷剂工况下,泡沫金属强化流动沸腾换热系数,换热系数提高30%～120%;含油工况下,泡沫金属只强化流动沸腾换热系数20%以下,在低质流密度或者高质流密度的高干度情况下出现恶化换热的情况。润滑油总是恶化制冷剂在内嵌泡沫金属圆管内流动沸腾的换热系数,换热系数最多恶化71%,且在低质流密度下对换热的恶化比在高质流密度工况下严重。     

Mathematical simulation of heat and mass transfer in a cylindrical channel versus the tangential momentum accommodation coefficient

The process of heat and mass transfer in a long cylindrical channel has been considered in terms of the mirror–diffuse model of the Maxwell boundary condition. The Hazen–Williams equation is used as a basic equation of the process kinetics. A constant temperature gradient is maintained in the channel. The heat and mass fluxes through the cross section of the channel versus the tangential momentum accommodation coefficient have been calculated in a wide range of the Knudsen number. The heat flux profiles have been constructed. A comparison with relevant published data has been carried out.     

Characteristics of conjugate heat and mass transfer in the flow of supersonic and hypersonic streams over blunt bodies

Problems associated with the formulation and solution of problems of conjugate heat and mass transfer in the supersonic and hypersonic motion of bodies are considered. The influence of the blunting geometry in streamline flow at different angles of attack, with gas injection into the shock layer, on the aerodynamic characteristics and the characteristics of heat and mass transfer is analyzed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 82–95, August, 1992.     

乳品行业低温余热回收系统性能分析

针对乳品行业排风风量大但品位低的特点,本文提出利用排风余热代替蒸汽来预热干燥空气的余热回收系统.在构建预热器、回热器和主加热器等部件热量流模型的基础上,建立了不包含中间节点参数的系统整体热量流模型.结合某奶粉厂运行数据对模型进行求解,结果表明,该系统将排风温度由90℃降低到42.58℃.在给定热负荷下,通过匹配中间回路...     

低品位烟气余热回收换热器热力学分析

低品位烟气余热回收过程存在冷凝现象,烟气的放热过程分为显热、潜热两部分。冷凝时,局部热流率和熵产率明显增大;增加水蒸气质量分数、冷却水质量流量和降低烟气入口温度都会导致烟气提前冷凝;存在最优冷却水质量流量使得热回收过程熵产数最小。另外,提出热回收效率评价烟气热回收程度,该指标受冷凝的影响很大。随着烟气中蒸汽质量分数的增加,冷凝过程的影响明显增强,因此,在低品位烟气的全热回收中必须考虑潜热的影响。     

水平螺旋管内超临界CO2冷却换热的数值模拟

采用RNG k-ε 湍流模型对超临界CO₂流体在内径为4 mm, 长度2000 mm, 节距为10 mm, 曲率为0.1的水平螺旋管内的冷却换热进行了数值模拟.研究了质量流量、热流量以及压力对换热系数的影响, 并和超临界CO₂在水平直管内的冷却换热进行了对比.研究结果表明, 超临界CO₂在水平螺旋管内流动产生的二次流强于水平直管内的二次流, 前者的换热系数大于后者; 换热系数随质量流量的增加而增大; 在似气体区, 换热系数随着热流量的增加而增大, 而在似液体区, 热流量对换热系数几乎没有影响; 换热系数峰值点随着压力的升高而下降, 并向高温区偏移.