离散发热器件基于(火积)耗散率最小和最高温度最小的构形优化比较

建立了导热基座上圆柱体离散发热器件的三维湍流散热模型,基于构形理论,考虑空气变物性及可压缩性和黏性耗散,研究了器件材料的热导率、热源强度和流体流速对器件最高温度、基于(火积)耗散定义的当量热阻和平均Nu数的影响.结果表明:在总发热功率一定的条件下,以器件最高温度和当量热阻为性能指标进行热设计,均存在最优热源强度分布使得散热性能最优.当各热源强度相同且热源热导率小于基座热导率时,提高热源热导率可明显改善散热性能;将热源热导率沿流动方向从低到高布置可降低器件最高温度,而将热源热导率均匀布置可使当量热阻最小.所得结果可为实际热设计中不同材质和不同发热率的电子器件最优布置提供理论支撑.     

Criticality of D=2 and D=3 Ising models: cluster structure versus populations

The energy and the specific heat of two- and three-dimensional Ising systems are analyzed in terms of cluster properties. The energy and the specific heat are decomposed into two components, which are defined by quantities pertaining to cluster populations and cluster structure expressed in terms of average cluster perimeters. It is shown that the structural component of the energy as well as of the specific heat represents the dominant contribution. Indications are presented that the critical exponent of structural and populational components of specific heat matches the exponent of the entire specific heat.     

微型热管的研究进展

微型热管是伴随微电子技术的发展而发展起来的一门新兴技术,是有效冷却高热流密度电子器件的主要途径之一。阐述常用的微型热管即脉动热管、微槽平板热管、环路热管的研究现状和进展,总结微型热管研究所面临的困难和挑战,指出微型热管的发展趋势,认为必将广泛应用于电子器件冷却、航空航天及计算机等领域。     

离子推力器空心阴极热特性模拟分析

对离子推力器空心阴极进行了热分析。利用ANSYS有限元软件对阴极罩开启/闭合状态下的空心阴极热启动过程和达到稳态工作时温度场分布进行了模拟,结果表明稳态工作时空心阴极内部能量主要损耗在热阻丝和阴极顶部分,并且阴极罩及热屏是降低空心阴极温度损耗提高其热效率的关键部件,采用阴极罩及热屏后使得空心阴极的总体温度值提升了2.3%~13.2%,其中发射体温度提升2.3%~4.2%,热实验得出的实验数据与模拟结果基本一致,研究结果对空心阴极的优化设计提供参考。     

Effective conductivity and skew Brownian motion

We consider heat conduction in a periodic body which is composed of finitely many different components. The effective conductivity is represented in terms of skew Brownian motion. The representation formula is a fluctuation-dissipation relation. The dissipation term in this formula is related to the transmission of heat through the surface separating the different components of the body; it is described by the skew reflections of Brownian motion at these surfaces. The problems caused by the discontinuity of the microscopic conductivity are handled in the framework of Dirichlet forms.     

Hall and Ion-Slip Effects in MHD Couette Flow with Heat Transfer

An analysis of the MHD Couette flow on taking into account the Hall and the ion-slip effects has been carried out for fully developed flow. Exact solutions to the velocity components, magnetic field components, axial and transverse components of the skin-friction, temperature and the rate of heat transfer have been derived. The numerical values of the transverse induced pressure gradient, the skin friction and the rate of heat transfer are entered in tables and the others have been shown on graphs. It has been observed that the flow may become unstable when M is small and ?e (Hall parameter) and ?i (ion-slip parameter) are large or at large value of M.     

Energy and Entropy Analyses of a Pilot-Scale Dual Heating HDH Desalination System

This study focuses on energy and entropy analysis to theoretically investigate the performance of a pilot scale dual heated humidification-dehumidification (HDH) desalination system. Two cases of HDH systems are considered in the analysis. The first case is a dual heated (DH) cycle consisting of 1.59 kW air heater and 1.42 kW water heater with a heat rate ratio of 0.89 (CAOW-DH-I). Whereas the second case is a dual heated HDH cycle comprising of 1.59 kW air heater and 2.82 kW water heater with a heat rate ratio of 1.77 (CAOW-DH-II). As a first step, mathematical code was developed based on heat and mass transfer and entropy generation within the major components of the system. The code was validated against the experimental data obtained from a pilot scale HDH system and was found to be in a good agreement with the experimental results. Theoretical results revealed that there is an optimal mass flowrate ratio at which GOR is maximized, and entropy generation is minimized. Furthermore, the degree of irreversibility within the humidifier component is low and approaches zero, while the specific entropy generation within other components are relatively high and are of the same order of magnitude. Entropy analysis also showed that the dual heated system with heat rate ratio greater than unity is better than the one with heat rate ratio less than unity.     

红外光学系统内部构件热辐射分析

红外光学系统的内部构件由于呈现于光路之中,其表面热辐射将会通过光学系统到达探测像面而引起背景辐射噪声。本文利用LightTools分析软件对一套折反式红外光学系统内部机械构件的主要表面的热辐射进行了分析,得到了探测像面接收到的热辐射的量级。分析了三种不同的表面反射率的情况,能够用于指导如何进行表面处理和结构设计的改善。     

Modeling of methane steam reforming in a microchannel subject to multicomponent diffusion

Catalytic methane steam reforming in a slot microchannel under external heat supply to the mixture reacting on walls is considered based on numerical simulation of a complete system of Navier-Stokes equations. Three ways of heat supply to channel walls are represented, namely, a uniform heat flux, a heat flux linearly decreasing in channel length, and a heat flux following the reaction rate profile of the main reaction. The thermophysical parameters of the mixture depend on its temperature and composition. Two diffusion models are considered, namely, models with equal and different diffusion coefficients for each mixture component. It is shown that consideration of multicomponent diffusion does not practically affect the concentration of the components and the methane reforming at the outlet. For the above-mentioned ways of heat supply, the methane reforming with a heat flux linearly decreasing in channel length is most significant.     

三效吸收制冷循环的性能分析和优化

本文建立了使用溴化锂溶液作为工质的三种流程的三级三效吸收制冷循环模型,进行了性能比较计算,结果表明并联流程循环的性能系数ＣＯＰ最高;同时本文进一步对并联流程和串联流程的三效吸收制冷循环分别进行了关于溶液分配率和总体热交换面积分配率的优化计算,得到了不同设计工况时面积分配率与ＣＯＰ的关系,为三效吸收循环的最优设计提供了理论依据。     

Shear-driven heat flow in absence of a temperature gradient

Jaynesian statistical inference is used to predict that steady, non-uniform Couette flow in a simple liquid will generate a heat flux proportional to the gradient of the square of the strain-rate when the temperature gradient is negligible. The heat flux is divided into phonon and self-diffusion components, with the latter coupling to the elastic strain and inelastic strain-rate. Operators for all these are substituted into the information-theoretic phase-space distribution. By taking moments of an exact equation for this distribution derived by Robertson, one obtains an evolution equation for the self-diffusion component of the heat flux which, in a steady state, predicts shear-driven heat flow. Received 10 September 1998     

Nonequilibrium thermodynamics of stochastic systems with odd and even variables

The total entropy production of stochastic systems can be divided into three quantities. The first corresponds to the excess heat, while the second two comprise the housekeeping heat. We denote these two components the transient and generalized housekeeping heat and we obtain an integral fluctuation theorem for the latter, valid for all Markovian stochastic dynamics. A previously reported formalism is obtained when the stationary probability distribution is symmetric for all variables that are odd under time reversal, which restricts consideration of directional variables such as velocity.     

Numerical modelling of heat transfer in plasma shaft electric furnace at utilization of anthropogenic waste

The mathematical model of heat transfer between the counter flows of gas and porous batch of anthropogenic wastes in the working area of a shaft furnace is presented. This model considers chemical transformations in separate batch components and radiation heat transfer between the gas and solid phases. Results of calculations are presented.     

Thermo-frigopompe à absorption pour production simultanée de chaleur et de fraîcheur utiles

Absorption heat-cold-pump for simultaneous production of useful heat and coolness. A new absorption heat-cold-pump for the simultaneous production of useful cold (12 °C – 7 °C) and of useful heat (80 °C – 85 °C) is presented. The system operates with a couple of components with comparable volatilities, for example the following saturated hydrocarbons, butane + hexane, butane + octane, butane + decane, propane + octane. The working pair is separated in a rectification column. The components are remixed in a reverse-rectification column fitted with an incorporated heat exchanger. The COP and the exergy efficiency are presented for a number of modelized internal structures of the heat-cold-pump.     

Progress on adsorption heat pumps

Adsorption heat-pump and refrigeration systems present many interesting characteristics such as noiseless, non-corrosive and environmentally friendly components; besides, adsorption machines efficiently use heat as primary energy. For these reasons the research activities in this sector are still increasing to solve the crucial points that make these systems not yet for the market. In this paper an update of the research trends is presented. The results and the most important recommendations are mainly related to improving the heat transfer inside the machine, to find an economic compromise between mass and heat transfer and to practically realize efficient and cheap regenerative systems.     

Evaporation of uniformly strained substitutional-interstitial solid solutions

The equilibrium vapor pressures and evaporation heat of subtitutional-interstitial solid solution components are calculated. The effect of uniform strain on the foregoing characteristics is discussed.     

Evaporation of a particle into chemically reactive carrier gas

After a general discussion and classification of physicochemical processes contributing to aerosol particle formation, evaporation of a particle into chemically active carrier gas is studied in more detail. The vapor flux from the particle surface is shown to increase if the carrier gas contains components reacting with the evaporated molecules. A method for determining the chemical correction to the Maxwell formula for evaporated flux is proposed. The correction to the heat balance of the evaporation process due to heat production by the chemical reaction is considered. The temperature of the particle is found to depend on the total evaporated flux, specific heat of the reaction, and the latent heat of evaporation. Main results are listed in the concluding part of the paper.     

Uniformity principle of temperature difference field in heat transfer optimization

The uniformity principle of temperature difference field is very useful in heat exchanger analyses and optimizations.In this paper, we analyze some other heat transfer optimization problems in the thermal management system of spacecrafts,including the cooling of thermal components, the one-stream series-wound heat exchanger network, the volume-to-point heat conduction problem, and the radiative heat transfer optimization problem, and have found that the uniformity principle of temperature difference field also holds. When the design objectives under the given constraints are achieved, the distributions of the temperature difference fields are uniform. The principle reflects the characteristic of the distribution of potential in the heat transfer optimization problems. It is also shown that the principle is consistent with the entransy theory. Therefore, although the principle is intuitive and phenomenological, the entransy theory can be the physical basis of the principle.     

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。     

90W太阳能LED路灯的设计及优化

针对LED在灯具配光、散热等方面达不到实用要求,无法真正体现出经济节能的问题,参照已有太阳能LED路灯产品,根据相关国家标准和行业标准,确定90 W太阳能LED路灯系统的技术指标和性能要求,在此基础上进行初步设计。对系统中的主要部件进行设计论证和选型,得出一个可行的设计方案,通过MATLAB软件对LED的照度分布和灯具的配光进行仿真,并就配光和散热这两个方面对系统进行优化,使其符合道路照明要求。