热质的运动与传递-微尺度导热中的热质动能效应

基于热质(热量的当量动质量)的概念,通过建立和分析热质的运动方程得到了反映热质动能变化的稳态导热微分方程,表明Fourier导热定律只有在热质的动能变化相对热质势能变化很小而可以忽略时才成立;在高热流密度和低温的情况下热质的动能变化不可忽略,这种动能效应表现为热流密度和温度梯度不再成线性关系.动能效应也导致Fourier导热定律不能通过热流和温度梯度准确地获得物体的导热系数,本文基于热质运动方程给出了导热系数动能效应的修正式.最后针对高热流密度和低温一维稳态导热进行了分子动力学模拟验证.     

平板在任意周期表面热扰动作用下的非Fourier热传导的求解与分析

分析了平板前表面遭受任意周期热扰动这类非Fourier传热情形下的温度响应. 采用双曲型热传导方程描述平板表面温度急速变化时的热传导问题. 为求解此类方程, 首先 利用分离变量法和Duhamel积分原理, 得到了平板前表面遭受突变热流和简谐热流两种情况下的解析解.然后, 在此基础上应用Fourier级数展开法和叠加原理, 获得了平板前表面热流任意周期变化时非Fourier热传导下温度场的解析表达式. 利用得到的解析表达式进行数值模拟, 分析了不同热松弛时间、 不同时刻和不同位置对温度响应的影响, 讨论了非Fourier热传导模型所给出的温度响应与Fourier热传导模型的差别. 这种方法能够处理许多在生产实际中具有周期边界条件的非Fourier热传导问题. 关键词： 非Fourier 热传导 周期变化 温度响应 平板     

Experimental investigation of heat transfer in a rivulet on the inclined foil

Heat transfer at rivulet water flow over the constantan foil with the length of 80 mm, width of 35 mm, and thickness of 25 mm was studied experimentally. The foil surface temperature was measured by an IR-scanner. Distributions of heat flux density on the surface of the foil, where the liquid flowed, were obtained. To determine the heat flux density from the foil to liquid near the contact line, the Cauchy problem was solved for the stationary heat equation using the thermographic data. Calculation results showed that the maximal heat flux occurs in the area of the contact line and exceeds the average heat flux from the entire foil surface by several times. This is explained by the influx of heat from the periphery of foil to the rivulet due to the relatively high value of heat conductivity coefficient of the foil material and high evaporation rate in the region of the contact line.     

竖直微槽道内沸腾换热CHF实验研究

对于沸腾换热,一个主要的约束条件就是临界热流密度(Critical Heat Flux,简称CHF)。这个约束条件对沸腾换热量有一个最高值的限制。文中对矩形微槽道中的流动沸腾临界热流密度进行了实验研究。实验数据是在不同尺寸(0.15mm;0.4mm;1mm)微槽道中,在较大范围的面积质量流速和不同进口过冷度下,以去离子水为工质得到的。实验过程中发现,达到CHF时,靠近出口壁面温度会突然升高,此时传热效率迅速下降。实验数据分析结果表明:CHF随质量流量的增加而增加;进口过冷度对CHF没有明显影响;CHF随着出口干度的增加而降低。     

Variation character of stagnation point heat flux for hypersonic pointed bodies from continuum to rarefied flow states and its bridge function study

This paper is a research on the variation character of stagnation point heat flux for hypersonic pointed bodies from continuum to rarefied flow states by using theoretical analysis and numerical simulation methods. The newly developed near space hypersonic cruise vehicles have sharp noses and wingtips, which desires exact and relatively simple methods to estimate the stagnation point heat flux. With the decrease of the curvature radius of the leading edge, the flow becomes rarefied gradually, and viscous interaction effects and rarefied gas effects come forth successively, which results in that the classical Fay-Riddell equation under continuum hypothesis will become invalid and the variation of stagnation point heat flux is characterized by a new trend. The heat flux approaches the free molecular flow limit instead of an infinite value when the curvature radius of the leading edge tends to 0. The physical mechanism behind this phenomenon remains in need of theoretical study. Firstly, due to the fact that the whole flow regime can be described by Boltzmann equation, the continuum and rarefied flow are analyzed under a uniform framework. A relationship is established between the molecular collision insufficiency in rarefied flow and the failure of Fourier’s heat conduction law along with the increasing significance of the nonlinear heat flux. Then based on an inspiration drew from Burnett approximation, control factors are grasped and a specific heat flux expression containing the nonlinear term is designed in the stagnation region of hypersonic leading edge. Together with flow pattern analysis, the ratio of nonlinear to linear heat flux W _r is theoretically obtained as a parameter which reflects the influence of nonlinear factors, i.e. a criterion to classify the hypersonic rarefied flows. Ultimately, based on the characteristic parameter W _r , a bridge function with physical background is constructed, which predicts comparative reasonable results in coincidence well with DSMC and experimental data in the whole flow regime.     

高温超导磁通跳跃过程中的磁致伸缩效应

文中基于超导磁通动力学理论,考虑电磁力与热激活对磁通运动的影响,基本模型包括由等效电阻率随超导体温度和磁场变化的磁通扩散方程,以及比热随超导体温度变化的热传导方程组成.在此基础上,用数值方法求解了这组非线性磁热耦合方程,主要研究了有磁通跳跃状发生状态时环境温度和外磁场速度对于高温超导磁致伸缩的影响.结果表明:磁通进入超...     

Thermal Performance Enhancement of Thermosyphon Heat Pipe with Binary Working Fluids

Thermal performance of a thermosyphon heat pipe using ethanol-water and TEG-water with variations of parameters such as the mixture content, the pipe diameter, and the working temperature have been studied in this research work. From the experiments, it is found that at low temperature of heat source (less than 80^oC), the ethanol-water mixture has a higher heat transfer rate than that of water and close to that of pure ethanol. In the case of TEG-water mixture, the heat transfer rate of the thermosyphon varies with the content of TEG in the mixture, and it is found that TEG in the mixture can increase the critical heat flux due to the flooding limit in a small thermosyphon. The boiling equation of Rohsenow and the condensation equation of Nusselt are modified to predict the heat transfer coefficients inside the thermosyphon. For the mixtures, the weighted average of the heat transfer coefficient of each component can be used to predict the total heat transfer coefficient. Furthermore, it is found that Faghri's equation can be used to predict the critical heat flux due to the flooding limit of the thermosyphon with the binary mixtures.     

高温超导体磁通跳跃数值模拟

文中基于超导磁通动力学理论,考虑电磁力与热激活对磁通运动的影响,基本物理模型由等效电阻率随超导体温度和磁场变化的磁通扩散方程,以及比热随超导体温度变化的热传导方程组成。在此基础上,用差分法数值求解了这一复杂非线性系统的磁热耦合控制方程,得到了与实验观测结果基本一致的数值模拟结果。结果还表明：外加磁场变化速度、超导体初始温度以及超导尺寸对于磁通跳跃均产生明显的影响。     

超急速传热时球体内非稳态热传导的非傅里叶效应

本文分析了球形物体表面加有一突然温度变化这类超急速传热情形下的热波传播特性．基于超急速传热条件下，热流矢的传播和温度梯度的形成之间存在时间延迟的概念，本文采用双曲型热传导方程来描述该高度非稳态热传导问题，得到了球体内部温度分布的解析表达式．同时将所得解与抛物型热传导方程的解进行了比较，分析了其热传导的非傅里叶效应与产生条件．     

Heat transport properties within living biological tissues with temperature-dependent thermal properties

Understanding of the heat transport within living biological tissues is crucial to effective heat treatments. The heat transport properties of living biological tissues with temperature-dependent properties are explored in this paper. Taking into account of variable physical properties, the governing equation of temperature is first derived in the context of the dual-phase-lags model (DPL). An effective method, according to the Laplace transform and a linearization technique, is then employed to solve this nonlinear governing equation. The temperature distribution of a biological tissue exposed to a pulsed heat flux on its exterior boundary, which frequently happens in various heat treatments, is predicted and analyzed. The results state that a lower temperature can be predicted when temperature dependence is considered in the heating process. The contributions of key thermal parameters are different and dependent on the ratio of phase lag and the amplitude of the exterior pulsed heat flux.     

Onset of superfluidity far from equilibrium: dynamical effects on the correlation length

Nonlinear heat conduction has recently been measured near the superfluid transition in pure ⁴He at very low heat flux Q. Since both dynamic effects and gravity limit the divergence of the superfluid correlation length near the transition at low-Q, these measurements must be repeated in the microgravity environment in order to observe the dynamic effects in isolation. Comparison of the microgravity data to similar data obtained on Earth will provide experimental insight into the effect of gravity on this nonlinear conduction region at low heat flux where theoretical predictions are lacking. While some measurement advantages exist in the microgravity laboratory, it is the study of the direct effect of gravity on the nonlinear conduction measurements that motivate the microgravity need.     

水射流冷却过程中表面热流密度的预测

建立了由内部一点测量温度值,选取多个时间步长计算未知的表面热流密度与换热系数的导热反问题算法。该算法采用有限容积法离散方程,附加源项法处理边界条件。将该计算模型应用于求解浸没水射流冷却过程中表面热流密度,将计算温度值与实验测温值进行比较验证了算法的正确性。在此基础上分析了水射流冲击过程中薄钢片表面热流密度随表面温度与时间的变化特性。     

一维大气边界层光学折射率结构常数的数值模式

 提出了一种大气光学折射率结构常数的数值模式。通过解大气边界层风速、位温度、绝对湿度预报方程,表面热平衡方程和土壤热传导方程，得到地表温度、表面层的动量通量、显热通量和潜热通量。再由Monin Obukhov相似理论，从湍流通量和温度结构常数的经验关系计算出折射率结构常数。     

Heat transfer analysis for stretching flow over a curved surface with magnetic field

The analysis of a viscous fluid flow and heat transfer is carried out under the influence of a constant applied magnetic field over a curved stretching sheet. Heat transfer analysis is carried out for two heating processes, namely, prescribed surface temperature (PST) and prescribed heat flux (PHF). The equations governing the flow are modeled in a curvilinear coordinate system (r, s, z). The nonlinear partial differential equations are then transformed to nonlinear ordinary differential equations by using similarity transformations. The obtained system of equations is solved numerically by a shooting method using Runge-Kutta algorithm. The interest lies in determining the influence of dimensionless radius of curvature on the velocity, temperature, skin friction, and rate of heat transfer at the wall prescribed by the Nusselt number. The effects of Hartmann number are also presented for the fluid properties of interest.     

Instrument for thermal radiation flux measurement in high temperature gas flow (Cuernavaca instrument)

A new instrument for hemispherical radiation heat flux measurement is proposed. It is based on the theory of blow of the boundary layer, taking into account that at the critical mass flow rate through the porous surface the thermal boundary layer is blown off and only radiation flux high temperature gases reaches the porous surface. With the measurement of blow of gas flow and the temperature of the porous material, the respective heat flux is obtained.     

加热探头圆柱上的液体微层厚度

1前言核态沸腾气泡形成时表面存在液体微层。虽然微层很薄,但对加热过程中的传热和气泡的产生具有重要影响。Lay和Dhirl‘］通过更细致的分析微层内的压力分布预言了微层的形状和热流,但考虑的仅是平板上气泡的液体微层。本文考虑了小的加热圆柱探针上气泡层的生长。当?..     

Effects of viscous dissipation and radiation on the thermal boundary layer over a nonlinearly stretching sheet

This Letter endeavours to complete an earlier numerical analysis for flow and heat transfer in a viscous fluid over a sheet nonlinearly stretched by extending the investigation in two directions. On one side, the effects of thermal radiation are included in the energy equation, and, on the other hand, the prescribed wall heat flux case (PHF case) is also analyzed. The governing partial differential equations are converted into nonlinear ordinary differential equations by a similarity transformation. The variations of dimensionless surface temperature as well as flow and heat-transfer characteristics with the governing dimensionless parameters of the problem, which include a nonlinearly stretching sheet, thermal radiation, viscous dissipation and power-law index of the wall temperature parameters, are graphed and tabulated.     

Transport bifurcation in a rotating tokamak plasma

The effect of flow shear on turbulent transport in tokamaks is studied numerically in the experimentally relevant limit of zero magnetic shear. It is found that the plasma is linearly stable for all nonzero flow shear values, but that subcritical turbulence can be sustained nonlinearly at a wide range of temperature gradients. Flow shear increases the nonlinear temperature gradient threshold for turbulence but also increases the sensitivity of the heat flux to changes in the temperature gradient, except over a small range near the threshold where the sensitivity is decreased. A bifurcation in the equilibrium gradients is found: for a given input of heat, it is possible, by varying the applied torque, to trigger a transition to significantly higher temperature and flow gradients.     

超临界注汽油井中蒸汽参数的数值计算

本文通过对动量方程、能量方程、散热方程等控制方程的离散求解,用稳态和瞬态相结合的方法,计算了超临界注汽油井地下垂直段、过渡段和水平段蒸汽参数（压力、温度等）和井简散热损失、压力降等随注入时间、注入流量和压力的变化规律．计算结果表明,随着井深的增加,蒸汽压力在垂直段和过渡段的前半部分是增加的,而在过渡段后半部分和水平段则减小,且同一井深位置随流量增加蒸汽压力减小,注入蒸汽压力高于２２ ＭＰａ时,井底蒸汽出口压力比入口高。同一井深位置每公斤蒸汽散热损失随流量的增加而减少,而随压力的增加无明显变化。井底蒸汽压力和温度在注入时间大约３天左右即趋于一稳定值,而井底热损失则随注入时间的增加而减少．     

Monte Carlo simulation of a hard-sphere gas in the planar Fourier flow with a gravity field

By means of the Direct Simulation Monte Carlo (DSMC) method, the Boltzmann equation is numerically solved for a gas of hard spheres enclosed between two parallel plates kept at different temperatures and subject to the action of a gravity field normal to the plates. The profiles of pressure, density, temperature and heat flux are seen to be quite sensitive to the value of the gravity acceleration g. If the gravity field and the heat flux are parallel (g > 0), the magnitudes of both the temperature gradient and the heat flux are smaller than in the opposite case (g < 0). When considering the actual heat flux relative to the value predicted by the Fourier law, it is seen that, if g > 0, the ratio increases as the reduced local field strength increases, while the opposite happens if g < 0. The simulation results are compared with theoretical predictions for Maxwell molecules.