Thermal Analysis for Heat Transfer Enhancement in Perforated Pin Fins of Various Shapes with Staggered Arrays

The present work investigates the enhancement of heat transfer rate through staggered pin fins of different shapes with different perforation geometries, namely circular, diamond shaped and elliptical type. Three dimensional computational fluid dynamics simulation has been carried out to analyze the effects of fin geometry and dimension of perforation as well as the shape of fin to enhance heat transfer rate against pressure loss. Results show that the heat transfer rates of perforated fins up to certain perforation number and size are always greater than the solid ones and with the change of fin shape and perforation geometry heat transfer rate also improves significantly. On the other hand pressure drop through heat sink decreases not only with increasing perforation number but also with the size of perforation. Moreover, variation of pressure drop of perforated fins is influenced with fin geometry.     

A Double Decomposition Method for Solving the Annular Hyperbolic Profile Fins With Variable Thermal Conductivity

In this article, the double decomposition method is used to analyze the annular hyperbolic profile fins with variable thermal conductivity. The double decomposition method is an advantageous way to solve the nonlinear problem. The solution gained by the double decomposition method is in the form of infinite power series, and the variable thermal conductivity is considered to have a linear relation with temperature. The results from the exact model solution are compared with the constant thermal conductivity case. The parameters that affect the fin performance and temperature distribution strongly are identified.     

基于接触非线性的金具安全销极限承载力分析

基于输电线路防灾减灾金具的设计,考虑金具之间的接触,建立了碗头挂板、联板、安全销的整体有限元模型,采用增量有限元法分析了安全销上的接触应力,验证了模型的正确性。对安全销的应力分布及极限承载力分析表明,通过调整安全销的槽深,可得到不同孔径比下安全销的极限承载力,确定了在外荷载达到塔线分离荷载前实现塔线分离的安全销尺寸,为安全销的改进提供了合理、有效的方法。     

Transient Thermal Stress Analysis of Orthotropic Functionally Graded Materials with a Crack

The transient thermal fracture problem of a crack (perpendicular to the gradient direction) in a graded orthotropic strip is investigated. Most of the materials properties are assumed to vary as an exponential function of thickness direction. The transient two-dimensional temperature problem is analyzed by the methods of Laplace and Fourier transformations. A system of singular integral equations are obtained and solved numerically. Numerical results are figured out to show the variation of the temperature on the crack faces and extended line and stress intensity factors for different material parameters with dimensionless time.     

Thermal Modeling of the Effect of Interstitial Fluid on Contact Resistance between Two Dissimilar Materials

Contact resistance between two dissimilar materials of finite thickness is formulated as two cylinders in contact over an area at their centers. The noncontact gap between the two cylinders is assumed to be filled with a thermally conducting fluid. The lateral surfaces are insulated, while the top and bottom surfaces are kept at constant temperatures. Heat diffusion equations in the cylinders are transformed to two integral equations for the heat flux through the contact and noncontact areas with the interstitial fluid conductance as a parameter. The integral equations are solved numerically. Therefore, no assumption on the heat flux distribution on the contact and noncontact surfaces is made. An expression for the dimensionless overall resistance is developed using the rate of heat transfer through the contact and noncontact areas. The effects of the length of the cylinders and the gap conductance on the overall and contact resistances were evaluated. Radial heat flux and temperature distributions over the contact and noncontact regions were determined. The results are reported in dimensionless form convenient for a parametric study and design analysis.     

多种分析方法在热经济性分析中的应用

针对扰动对汽轮机组运行热经济性的影响,结合实际情况对不同机组不同扰动下进行分析,给出了3种计算方法(热平衡法,等效焓降法,矩阵分析法).     

堇青石基透波材料的抗热震性能分析

随着微波技术的发展,透波材料成为材料制备领域的研究热点。堇青石具有热膨胀系数低、热导率小、介电常数低、抗热震性能好及化学稳定性好等优点,将其作为微波冶金的承载体材料,满足了微波冶金过程的使用要求和适用条件。采用MgO、Al_2O_3、SiO_2三种原料,同时添加部分纳米SiO_2粉体代替工业SiO_2,在不同的原料配比下微波烧结合成Mg-Al-Si-O系堇青石基透波材料,并测定分析所得样品在未热震前、热震4次及热震8次的测试下,样品的弯曲强度及抗热震性能的变化。     

A Correction Factor-Based General Thermal Resistance Formula for Heat Exchanger Design and Performance Analysis

Methods for the analysis of heat exchangers with various flow arrangements modeling, design, and performance are essential for heat transfer system modeling and its integration with other energy system models. This paper proposes the use of the linear-transfer law for the heat exchanger design and performance analysis as a function of the thermal resistance related to the ratio of a linear temperature difference to the total heat transfer rate. Additionally, we derived a correction factor that represents the influence of the flow arrangement on the heat transfer performance by the effective thermal conductance, as a function of correction factor, heat transfer coefficient, and surface area. Based on the effective thermal conductance, we propose the hot-end NTU and cold-end NTU for deriving a standardized and general thermal resistance formula for different types of heat exchangers by the combination of the correction factor with linear-transfer law. Moreover, for parallel-flow, cross-flow, and 1-2 Tubular Exchanger Manufacturers Association(TEMA) E shell-and-tube heat exchangers, we derived and obtained alternative correction factor expressions without introducing any temperatures. Two cases about heat exchanger design and performance analysis show that the calculation processes using the correction factor-based general thermal resistance are straightforward without any iteration and the calculation results are accurate. Finally, the experimental validation shows that the general thermal resistance formula is appropriate for analyzing the heat transfer performance. That is, the correction factor-based general thermal resistance formula provides a standardized model for heat exchanger analysis and heat transfer/integrated energy system modeling using the heat current method.     

A Comparison of ODE Solution Methods for Spacecraft Thermal Problems

Abstract

In spacecraft thermal design and analysis practice, the lumped-parameter network formulation is used extensively to construct mathematical models. The models lake the form of a system of coupled, nonlinear, first-order ordinary differential equations (ODEs). The number of equations may vary from a few tens to a few thousands. It is necessary to solve these equations in an efficient and economical way. This article reviews various methods available for the numerical solution of ODEs. General-purpose codes available for this are discussed. Numerical experiments are conducted to investigate the efficiency of various methods. The results indicate that the Crank-Nicholson method with provision for automatic selection of step size to control the local truncation error is a very good choice for the solution of spacecraft thermal problems.     

Thermal characteristics of an underground cold-water reservoir: Analytical and experimental studies

The thermal characteristics of an underground cold-water reservoir are investigated analytically and experimentally. An analytical solution is developed for the temperature distribution in the reservoir by assuming a linearized boundary condition at the water surface. The results are compared with the experimental measurements which have been conducted in a cistern located in the city of Yazd. Very good agreements between the analytical and the experimental results at various times during the withdrawal cycle are observed, ensuring the accuracy of the analytical solution obtained for the linearized boundary condition. The results show that a stable thermal stratification is preserved in the reservoir throughout the entire course of the withdrawal cycle. During this period, the outside temperature reaches as high as 42 °C, while cool water with the temperature varying from 12 to 13 °C is easily available from the underground water reservoir under investigation.     

某柴油机飞轮壳及其连接板结合面漏油故障分析及解决措施

本文阐述了某一柴油机飞轮壳及其连接板结合面漏油故障的分析思路和过程,借助有限元方法查找该处漏油的根本原因,并提出有效的解决方案。     

接触热阻的方法在活塞组耦合模型有限元分析中的应用

在有限元分析中,与单件模型相比,耦合模型的分析结果更加精确。本文建立了活塞、活塞环、活塞销、缸套的耦合模型,采用接触对、设定接触热阻的方法对耦合模型进行了二维和三维瞬态温度场的分析。通过计算结果与测量值的对比,表明耦合模型的瞬态分析通过设定接触热阻的方法能够精确地反映活塞组的热负荷分布情况。     

Analysis of the Correlation between the Level of Contact Degradation and the Dynamic Resistance Curve in Circuit Breakers

The DRM （dynamic contact resistance measurement） in high voltage circuit breakers is a manner of evaluating the internal ageing condition of the chamber. DRM is similar to static contact resistance measurement testing, but instead of measuring a single value when the breaker contacts are closed （static value）, the ohmic resistance is measured at various contact positions, from the beginning of the contact opening until a complete separation of the contacts. The relationship between the contact resistances of the new circuit breaker and the ageing circuit breaker in operation provides subsidy for the evaluation of both the main and arcing contact conditions. This research aims to analyze the correlation between the various levels of degradation of the contacts and the configuration of the DRM curve. This work considers curve samples from new acceleration tests. breaker chamber contacts and different levels of degradation by     

外掺MgO对大体积混凝土温度应力的影响分析

采用三维有限元仿真计算程序对某碾压混凝土围堰掺M gO和不掺M gO两种方案进行了计算和分析,探讨了大体积混凝土掺用M gO后的温度应力分布特点,结果表明掺M gO后对基础强约束区混凝土温度应力有明显的补偿作用,是简化温控措施和减少温度应力裂缝的有效途径。为进一步研究碾压混凝土掺用M gO筑坝技术提供了重要参考。     

技术供水系统电控减压阀拒动原因分析及处理

针对水电厂现代化自动控制设备的增多及设备运行的可靠性影响水电机组的安全运行,介绍了新安江水电厂在技术改造过程中出现的电控减压阀拒动故障,分析了拒动原因并提出了改进方案.实际运行结果表明,改进方案效果较好,供借鉴.     

Comparison of a CFD Analysis and a Thermal Equivalent Circuit Model of a TEFC Induction Machine With Measurements

For a totally enclosed fan-cooled induction machine, two methods of numerical analysis are compared with measurements. The first numerical method is based on computational fluid dynamics (CFDs) and the second one uses a thermal equivalent circuit (TEC). For the analysis based on CFD, a 3-D induction machine including housing is modeled. The numeric solution of the flow equations is determined for stationary temperature distributions. For the TEC, a discretized one-and-a-half-dimensional model of the induction machine is considered. With the TEC model, stationary and transient operating conditions can be simulated. Measurement results are determined by iron–copper–nickel sensors embedded in the stator winding and the housing, as well as by an IR sensor for measuring the rotor temperature. With these measurement signals, stationary and transient operating conditions can be analyzed. For stationary operating conditions, additionally, the housing temperatures are determined by an IR camera. The investigated simulation and measurement methods reveal different local and global temperatures, and thus, only certain aspects and characteristics of the obtained temperatures can be compared. Nevertheless, certain conclusions can be drawn from comparing these aspects considering the actual restrictions of each of the applied methods.      

内燃机零部件热负荷研究的现状与展望

回顾并分析了内燃机零部件热负荷研究的现状，讨论并展望了尚待进一步研究的问题。     

Analysis of externally loaded bolted joints: Analytical,computational and experimental study

The behaviour of a simple single-bolted-joint under tensile separating loads is analysed using conventional analytical methods, a finite element approach and experimental techniques. The variation in bolt force with external load predicted by the finite element analysis conforms well to the experimental results. It is demonstrated that certain detailed features such as thread interaction do not need to be modelled to ensure useful results. Behaviour during the pre-loading phase of use agrees with previous long-standing studies. However, the pre-loading analysis does not carry over to the stage when external loading is applied, as is normally assumed and it is shown that the current, conventional analytical methods substantially over-predict the proportion of the external load carried by the bolt. The basic reason for this is shown to be related to the non-linear variation in contact conditions between the clamped members during the external loading stage.     

Criteria for Predicting Transitions in Free Convection Heat Transfer From Isothermal Convex Bodies in Fluids With Any Prandtl Number: A New Analytical Model

This article presents criteria for predicting transitions in free convection from isothermal convex bodies in fluids with any Prandtl number (conduction–laminar and laminar–turbulent transitions). Laminar–turbulent transition results for vertical plates happening in the vicinity of Grashof number 10⁹ in fluids with any Prandtl number and other geometries show that this criterion based on Grashof number is a better choice compared to that of the Rayleigh number, as the Prandtl number yields a large change in the transition Rayleigh number. Besides, for convex geometries other than vertical plates, the laminar–turbulent transition occurs at values slightly less than Grashof number 10⁹ owing to longitudinal vortices bringing about separation over their surface and helping laminar–turbulent transition to arise sooner. On the other side, the results of the conduction–laminar transition criterion for different convex bodies disclose that the Rayleigh number is superior to the Grashof number. Likewise, the present results for five different geometries over a wide range of Prandtl numbers are compared with the available experimental data, and excellent agreement is found. This reveals that the proposed criteria is powerful enough to predict the two transition phenomena in free convection heat transfer from isothermal convex bodies for a wide range of convex geometries in fluids with any Prandtl number.     

内燃机零部件热负荷研究的现状讨论与展望

回顾分析了内燃机零部件热负荷研究的现状，讨论并展望了尚待进一步研究的问题。