Monte Carlo ray-tracing simulation for radiative heat transfer in turbulent fluctuating media under the optically thin fluctuation approximation

The Monte Carlo ray-tracing method (MCRT) based on the concept of radiation distribution factor is extended to solve radiative heat transfer problem in turbulent fluctuating media under the optically thin fluctuation approximation. A one-dimensional non-scattering turbulent fluctuating media is considered, in which the mean temperature and absorption coefficient distribution are assumed and the shape of probability density function is given. The distribution of the time-averaged volume radiation heat source is solved by MCRT and direct integration method. It is shown that the results of MCRT based on the concept of radiation distribution factor agree with these of integration solution very well, but results of MCRT based on the concept of radiative transfer coefficient do not agree with these of integration solution. The solution of time-averaged radiative transfer equation by the concept of radiative transfer coefficient should be treated with caution.     

纳米流体介质导热机理初探

纳米流体导热行为具有许多奇异的特性，结合纳米流体的特点和微尺度传热学原理，研究了 热流在纳米颗粒内波动式及非限域的热传导特性、纳米颗粒在悬浮液内的布朗运动、颗粒- 液体界面上液膜层原子的有规则排列、以及纳米颗粒的团簇形成及移动等四方面因素对纳米 流体导热系数的影响. 关键词： 纳米流体 导热     

风冷热泵冷热水机组动态过程仿真

本文给出了风冷热泵冷热水机组动态过程模型。系统的高、低压段被分成制冷剂侧、管壁、以及水或空气侧三个控制容积。针对每个控制容积建立了质量和能量平衡的微分方程。由于压缩机、热力膨胀阀阀体、以及四通换向阀具有较小的热惯性,因而采用稳态模型描述压缩过程、膨胀过程、以及内泄露过程。膨胀阀感温包中的制冷剂温度对于蒸发器出口温度的延迟用一阶惯性环节来描述。通过“预测-校正”和“自适应步长”方法实现系统仿真。仿真结果与测试数据吻合良好。     

Si微电阻桥温度分布与热传导特性的显微Raman光谱研究

采用显微Raman光谱方法对红外目标模拟器中重掺杂Si微电阻桥单元的热传导特性进行研究，根据Si桥的实际特性建立相应的Raman散射模型，通过测量Raman峰位的移动得到高功率激光辐照下测量点的温度.对Si桥桥面分别进行了沿某些特殊线段的逐点线扫描和覆盖全部桥面的面扫描，得到各点的温升及其分布.用基于有限元分析的软件结合Si桥结构参数对各测量点的温升进行了模拟计算，其结果在热导分布的基本趋势上与实验相一致.实验细致地揭示了热导分布的局域起伏，反映出实际器件的不均匀性，为改进器件设计、优化器件性能提供了实验依据. 关键词： Raman光谱 Si桥 温度分布 热导     

板状激光振荡介质温度场和应力场的数值模拟

以非均匀内热源模型为基础,并考虑材料的导热系数和热膨胀系数的温度相关性,利用有限元方法,对板状激光振荡介质在不同功率和冷却强度下的温度和热应力分布进行了数值模拟及分析。根据计算结果提出了最大有效换热系数的概念,指出换热系数超过最大有效换热系数后,继续强化传热对减小高功率激光器的热效应已无明显效果。以此得出采用常规冷却技术所允许的最大泵浦加热功率。     

新型制冷机冷凝器壳侧的传热强化研究

针对现行制冷机冷凝器的不足 ,设计了适用于冷凝传热的新型折流杆冷凝器的壳程内部结构 ,并分析了其传热强化机理。在重力控制条件下 ,对不同内部支承结构与管束组合的冷凝器进行了传热实验研究 ,得到了水蒸汽在冷凝器壳侧的冷凝传热特性曲线。采用冷凝传热强化因子的概念 ,建立了预测该种折流杆冷凝器壳侧冷凝传热膜系数的计算公式 ,为折流杆冷疑器在制冷系统中的设计应用提供了理论依据。     

轴流泵端壁区域流动三维粘性数值计算

本文采用通用流场分析软件FLUENT,基于N-S方程,选用RNG κ—ε湍流模型与SIMPLEC算法,对轴流泵叶轮内部(及端壁间隙)流动进行了三维粘性数值计算。通过实验验证,表明数值计算结果和实测数据吻合较好。详细分析了叶顶附近流场形态以及叶轮出口轴向、周向速度分布,进行了性能预估。并给出了实验装置图。     

Fourier regularization for a backward heat equation

In this paper a simple and convenient new regularization method for solving backward heat equation—Fourier regularization method is given. Meanwhile, some quite sharp error estimates between the approximate solution and exact solution are provided. A numerical example also shows that the method works effectively.     

Chip-calorimeter for small samples

A method for measuring heat capacities of small samples using a chip-calorimeter and a heat pulse technique is described. The theoretical background to calculate the heat transport properties and the heat capacity of the sample from the pulse response function is given. Problems and potentials of the method are discussed. An example is given.     

Specific heat and related thermophysical properties of liquid Fe-Cu-Mo alloy

The specific heat and related thermophysical properties of liquid Fe77.5Cu13Mo9.5 monotectic alloy were investigated by an electromagnetic levitation drop calorimeter over a wide temperature range from 1482 to 1818 K. A maximum undercooling of 221 K (0.13 Tm) was achieved and the specific heat was determined as 44.71 J·mol-1·K-1. The excess specific heat, enthalpy change, entropy change and Gibbs free energy difference of this alloy were calculated on the basis of experimental results. It was found that the calculated results by traditional estimating methods can only describe the solidification process under low undercooling conditions. Only the experimental results can reflect the reality under high undercooling conditions. Meanwhile, the thermal diffusivity, thermal conductivity, and sound speed were derived from the present experimental results. Furthermore, the solidified microstructural morphology was examined, which consists of (Fe) and (Cu) phases. The calculated interface energy was applied to exploring the correlation between competitive nucleation and solidification microstructure within monotectic alloy.