热能精确传导无铅手工焊接的关键

随着无铅焊接时代的到来,由于无铅焊料具有熔点高、焊接工艺窗口窄和锡含量高等诸多特点,故对应用于无铅焊接的焊接制程提出了更高的要求。同时,为确保电路板组件的完整性和其上面的热敏感器件的质量和可靠性,对焊接工具也提出了更大的挑战。由此可见,高效和精确的热能传导才能在焊接速度与功率控制之间达到平衡,从而成为获得高焊接质量的关键所在。

电厂熔岩储能装置的结构优化与技术实现

本文主要阐述电厂熔岩储能装置的结构优化与技术实现,重点分析熔岩储能装置的工作原理及其各组成部分,包括加热系统、储能模块、热交换系统和保温系统。基于优化设计策略,提出改进热能传导路径、优化储能模块的几何结构以及改良保温系统的方法,旨在提高熔岩储能装置的整体效率与稳定性。通过选用高比热容、优异热稳定性且成本较低的熔岩材料,进一步提升储能装置的经济性和实用性,为未来电厂实际储能优化应用提供可行性的参考方案。

Analyses on performances of heat and multilayer reflection insulators

This research was conducted to study the performances of the heat and multilayer reflection insulators used for buildings in South Korea to realize eco-friendly, low-energy-consumption, green construction, and to contribute to energy consumption reduction in buildings and to the nation＇s greenhouse gas emission reduction policy （targeting 30% reduction compared to BAUCousiness as usual） by 2020）. The heat insulation performance test is about the temperatures on surfaces of test piece. The high air temperature and the low air temperature were measured to determine the overall heat transfer coefficient and thermal conductivity. The conclusions are drawn that the heat transmission coefficients for each type of existing reflection insulator are： A-1 （0.045 W/（m-K））, A-2 （0.031 W/（m.K））, A-3 （0.042 W/（m.K））, A-4 （0.078 W/（m.K））, and the average heat conductivity is 0.049 W/（m-K）; The heat conductivity for each type of Styrofoam insulator are 0.030 W/（m.K） for B-l, 0.032 W/（m-K） for B-2, 0.037 W/（m＇K） for B-3, 0.037 W/（m.K） for B-4, and the average heat conductivity is 0.035 W/（m＇K） regardless of the thickness of the insulator; The heat conductivity values of the multilayer reflection insulators are converted based on the thickness and type C-1 （0.020 W/（m.K））, C-2 （0.018 W/（m.K））, C-3 （0.016 W/（m.K））, and C-4 （0.012 W/（m.K））; The multilayer reflection insulator keeps the indoor-side surface temperature high （during winter） or low （in summer）, enhances the comfort of the building occupants, and conducts heating and moisture resistance to prevent dew condensation on the glass-outer-wall surface.

A comprehensive comparison on vibration and heat transfer of two elastic heat transfer tube bundles

Elastic heat transfer tube bundles are widely used in the field of flow-induced vibration heat transfer enhancement. Two types of mainly used tube bundles, the planar elastic tube bundle and the conical spiral tube bundle were comprehensively compared in the condition of the same shell side diameter. The natural mode characteristics, the effect of fluid-structure interaction, the stress distribution, the comprehensive heat transfer performance and the secondary fluid flow of the two elastic tube bundles were all concluded and compared. The results show that the natural frequency and the critical velocity of vibration buckling of the planar elastic tube bundle are larger than those of the conical spiral tube bundle, while the stress distribution and the comprehensive heat transfer performance of the conical spiral tube bundle are relatively better.

冰冻寒冷地区水泥生产线电伴热带保温技术研究

针对当前电伴热带保温设计体系不完善、缺乏相关标准技术图集的现状,重点结合"一带一路"哈萨克斯坦水泥生产线建设项目的实际工作经验提炼而成。对在冰冻寒冷地区地下冻层埋设工艺管线有关使用电伴热带技术的设计、施工等方面展开深入的研究。首次在工业、民用建筑绝热保温领域内提出使用电伴热带保温结构中设计热能储蓄传导层、热能二次反馈层、绝缘密封层和保温保冷绝热结构的新理念,进一步推广使用电伴热带技术应用领域。此项技术荣获国家四项发明专利,解决了多年来水泥工艺管线无法应用电伴热带技术埋设介质管线的技术难题。

Analysis of steady heat conduction for 3D axisymmetric functionally graded circular plate

The thermal conduction behavior of the three-dimensional axisymmetric functionally graded circular plate was studied under thermal loads on its top and bottom surfaces. Material properties were taken to be arbitrary distribution functions of the thickness. A temperature function that satisfies thermal boundary conditions at the edges and the variable separation method were used to reduce equation governing the steady state heat conduction to an ordinary differential equation （ODE） in the thickness coordinate which was solved analytically. Next, resulting variable coefficients ODE due to arbitrary distribution of material properties along thickness coordinate was also solved by the Peano-Baker series. Some numerical examples were given to demonstrate the accuracy, efficiency of the present model, mad to investigate the influence of different distributions of material properties on the temperature field. The numerical results confirm that the influence of different material distributions, gradient indices and thickness of plate to temperature field in plate can not be ignored.

Performance enhancement of filled-type solar collector with U-tube

In order to increase the efficiency of solar collector, a methodology is proposed based on the analysis of its influencing factors, such as thermal conductivity of filled layer, structure forms of filled layer and heat loss coefficient. The results of analysis show that the heat transfer between pipes in evacuated tube is one of the most important factors, which can lead to the decrease of the outlet temperature of working fluid. In order to eliminate the negative influence of the heat transfer between pipes, the hollow filled-type evacuated tube with U-tube(HUFET) was developed, and the heat transfer characteristics of HUFET were analyzed by theoretical and experimental studies. The results show that the thermal resistances decrease with the increase of the thermal conductivity of filled layer. When the thermal conductivity is over 10 W/(m·K), the change of thermal resistances is very little.Furthermore, the larger the thermal conductivity of filled layer, the less the rate of the energy transfer between the two pipes to the total energy transfer, which is between the absorber tube and the working fluid. There is a little difference between the efficiencies of HUFET and UFET, with the efficiency of HUFET 2.4% higher than that of UFET. Meanwhile, the validation of the model developed was confirmed by the experiment.

Thermal properties of open-celled aluminum foams prepared by two infiltration casting methods

Contrastive research was carried out to study the thermal properties of open-celled aluminum foams prepared by counter-gravity infiltration casting system and the traditional process respectively.The experimental results show that the thermal conductivity coefficients of aluminum foams prepared by two different infiltration methods have similar increasing trend with the increase of particle size;along with the reducing porosity,the thermal conductivity coefficients will be enhanced oppositely.However,with the same particle size,the open-celled aluminum foam prepared by the former method has a higher thermal conductivity coefficient obviously.It is largely because that the sample prepared by counter-gravity infiltration casting has a lower void content and better dense crystallization of metal-matrix after the constant pressure process.

Effects of thermal transport properties on temperature distribution within silicon wafer

A combined conduction and radiation heat transfer model was used to simulate the heat transfer within wafer and investigate the effect of thermal transport properties on temperature non-uniformity within wafer surface. It is found that the increased conductivities in both doped and undoped regions help reduce the temperature difference across the wafer surface. However, the doped layer conductivity has little effect on the overall temperature distribution and difference. The temperature level and difference on the top surface drop suddenly when absorption coefficient changes from 104 to 103 m-1. When the absorption coefficient is less or equal to 103 m-1, the temperature level and difference do not change much. The emissivity has the dominant effect on the top surface temperature level and difference. Higher surface emissivity can easily increase the temperature level of the wafer surface. After using the improved property data, the overall temperature level reduces by about 200 K from the basis case. The results will help improve the current understanding of the energy transport in the rapid thermal processing and the wafer temperature monitor and control level.

UO2-BeO Composite Fuel Thermal Property and Performance Modeling

An enhanced thermal conductivity UO2-BeO composite nuclear fuel was studied. A methodology to generate ANSYS （an engineering simulation software） FEM （finite element method） thermal models of enhanced thermal conductivity oxide nuclear fuels was developed. The results showed significant increase in the fuel thermal conductivities and have good agreement with the measured ones. Thus BeO is one of the promising candidates for fabricating two-phase high thermal conductivity ceramic nuclear fuels with UO2. The reactor performance analysis showed that the decrease in centerline temperature was 250-350 K depending on different fabrication methods for the UO2-BeO composite fuel, and thus we can improve nuclear reactors＇ performance and safety, and high-level radioactive waste generation for the existing and next generation nuclear reactors.

基于SPH-FDM耦合算法的非饱和岩土介质中瞬态导热问题数值模拟

光滑粒子法是近些年来发展起来的一种新的数值计算方法,已经成功应用到多种工程和物理问题的求解中.为修正光滑粒子法计算域边界附近粒子近似缺陷及弥补边界条件处理方法的不足,将有限差分法耦合到光滑粒子法中,使所求解问题在整个计算域上的函数近似精度达到二阶,从而提高计算的求解精度;然后基于有限差分算法处理边界条件的思想来处理定解问题中的第二、第三类边界条件,使复杂边值问题的计算可以归于第一类边值问题的框架下求解.采用光滑粒子-有限差分耦合算法计算了各类不同边界条件下的导热问题,通过和解析解的对比表明,相比传统光滑粒子法,耦合算法能够直接施加各类边界条件,计算结果精度高,求解过程可靠有效.最后模拟了非饱和岩土介质内的热能传输问题,得到了岩土介质中随时间变化的温度演化特点,并分析了隔热层对导热过程的影响以及隔热层导热性质不同情况下的温度分布特征.

广东深圳中信城市广场

作为综合性、智能化建筑，该工程外装饰采用多种几何形体和互相交错的弧线，根据建筑的地理位置，在外墙材料选取上以环保、节能为前提，在追求大面积采光及观光要求的同时满足了节能隔音要求。

Three-Dimensional Heat Transfer Analysis for A Thermal Energy Storage Canister

High temperature latent thermal storage is one of the critical techniques for a solar dynamic power system. This paper presents results from heat transfer analysis of a phase change salt containment canister A three-dimensional analysis program is developed to model heat transfer in a PCM canister. Analysis include effects of asymmetric circumference heat flux, conduction in canister walls, liquid PCM and solid PCM, void volume change and void location, and conduction and radiation across PCM vapor void. The PCM phase change process is modeled using the enthalpy method and the simulation results are compared with those of other two- dimensional investigations. It’s shown that there are large difference with two-dimensional analysis, therefore the three-dimensional model is necessary for system design of high temperature latent thermal storage.

Magnetic-field enhanced high-thermoelectric performance in topological Dirac semimetal Cd3As2 crystal

Thermoelectric materials can be used to convert heat to electric power through the Seebeck effect. We study magneto-thermoelectric figure of merit （ZT） in three-dimensional Dirac semimetal Cd3A 5 2 crystal. It is found that enhancement of power factor and reduction of thermal conductivity can be realized at the same time through magnetic field although magnetoresistivity is greatly increased. ZT can be highly enhanced from 0.17 to 1.1 by more than six times around 350 K under a perpendicular magnetic field of 7 T. The huge enhancement of ZT by magnetic field arises from the linear Dirac band with large Fermi velocity and the large electric thermal conductivity in CdsA 5 2. Our work paves a new way to greatly enhance the thermoelectric performance in the quantum topological materials.

Constructal entransy dissipation rate minimization for umbrella-shaped assembly of cylindrical fins

Umbrella-shaped assembly of cylindrical fins is optimized by adopting analytical method and taking dimensionless mean thermal resistance (MTR) as performance index. The optimal construct of umbrella-shaped assembly is obtained. The results show that the heat conductance performance of the assembly becomes ever worse with ever greater number of elemental cylindrical fins,the umbrella-shaped assembly reduces to cylindrical fin in some values of design parameters,and the diameters’ dependence on design parameters is weak for the optimized assembly. An equivalent thermal resistance defined based on entransy dissipation rate (EDR) reflects an average heat transfer effect of the assembly. The constructal design corresponding to the minimum EDR (or MTR) should be adopted for designing an assembly of fins in engineering at the limit safe condition.

Constructal entransy dissipation rate minimization for leaf-like fins

Based on constructal theory,the constructs of the leaf-like fins are optimized by taking minimum entransy dissipation rate(for the fixed total thermal current,i.e.,the equivalent thermal resistance) as optimization objective.The optimal constructs of the leaf-like fins with minimum dimensionless equivalent thermal resistance are obtained.The results show that there exists an optimal elemental leaf-like fin number,which leads to an optimal global heat conduction performance of the first order leaf-like fin.The Biot number has little effects on the optimal elemental fin number,optimal ratios of length and width of the elemental and first order leaf-like fins;with the increase of the thermal conductivity ratio of the vein and blade,the optimal elemental fin number and optimal ratio of the length and width of the elemental leaf-like fin increase,and the optimal shape of the first order leaf-like fin becomes tubbier.The optimal construct based on entransy dissipation rate minimization is obviously different from that based on maximum temperature difference minimization.The dimensionless equivalent thermal resistance based on entransy dissipation rate minimization is reduced by 11.54% compared to that based on maximum temperature difference minimization,and the global heat conduction performance of the leaf-like fin is effectively improved.For the same volumes of the elemental and first order leaf-like fins,the minimum dimensionless equivalent thermal resistance of the first order of the leaf-like fin is reduced by 30.10% compared to that of the elemental leaf-like fin,and the global heat conduction performance of the first order leaf-like fin is obviously better than that of the elemental leaf-like fin.Essentially,this is because the temperature gradient field of the first order leaf-like fin based on entransy dissipation rate minimization is more homogenous than that of the elemental leaf-like fin.The dimensionless equivalent thermal resistance defined based on entransy dissipation rate reflects the average heat transfer performance of the leaf-like fin,and can provide some guidelines for the thermal design of the fins from the viewpoint of heat transfer optimization.

Existence of Classical Solutions to a Stationary Simplified Quantum Energy-Transport Model in 1-Dimensional Space

The existence of classical solutions to a stationary simplified quantum energytransport model for semiconductor devices in 1-dimensional space is proved.The model consists of a nonlinear elliptic third-order equation for the electron density,including a temperature derivative,an elliptic nonlinear heat equation for the electron temperature,and the Poisson equation for the electric potential.The proof is based on an exponential variable transformation and the Leray-Schauder fixed-point theorem.

Exact Variational Principle For 3-D Unsteady Heat Conduction With Second Sound

The exact variational formulation of the extended unsteady heat conduction equation with finite propagation speed （the 2nd sound speed） of hyperbolic type is derived herein via a systematic and natural way. Moreover, the boundary- and the physically acceptable initial-value conditions are accommodated in the variational principle by a novel method suggested just recently. In this way a perfect justification of the variational theory of transient heat conduction and a rigorous theoretical basis for the finite element analysis of heat conduction are provided.

Heat Loss Calculation of Compound Honeycomb Solar Collector

A simplified technique is described for calculating the heat loss coefficient from the absorber of the solar flat-plate collector with a combined honeycomb.The problem is treated in two ways:the coupled mode and the decoupled mode.In the analysis,the cell wall and glass cover are assumed to be specularly reflecting and diffusely emitting surfaces,while the absorber is a diffusely reflecting and emitting surface.The influences of emissivities of the absorber and the cell wall as well as the aspect ratio on the heat loss coefficient are predicted.The theoretical results are compared with experimental data reported in the literature,and the agreement is good.

Electrical and thermal transport properties of CdO ceramics

High temperature electrical and thermal transport properties,that is,electrical conductivity,Seebeck coefficient and thermal conductivity,of CdO ceramics have been investigated.Because of the good electrical properties and low thermal conductivity,the dimensionless figure-of-merit ZT of the CdO ceramics reaches 0.34 at 1023 K.This value is comparable to the best reported ZT for the n-type oxide ceramic thermoelectric materials and remains as potential to be further improved by porosity controlling or nanostructuring.