Efficiency analysis of straight fin with variable heat transfer coefficient and thermal conductivity

In this study, one type of applicable analytical method, differential transformation method (DTM), is used to evaluate the efficiency and behavior of a straight fin with variable thermal conductivity and heat transfer coefficient. Fins are widely used to enhance heat transfer between primary surface and the environment in many industrial applications. The performance of such a surface is significantly affected by variable thermal conductivity and heat transfer coefficient, particularly for large temperature differences. General heat transfer equation related to the fin is derived and dimensionalized. The concept of differential transformation is briefly introduced, and then this method is employed to derive solutions of nonlinear equations. Results are evaluated for several cases such as: laminar film boiling or condensation, forced convection, laminar natural convection, turbulent natural convection, nucleate boiling, and radiation. The obtained results from DTM are compared with the numerical solution to verify the accuracy of the proposed method. The effects of design parameters on temperature and efficiency are evaluated by some figures. The major aim of the present study, which is exclusive for this article, is to find the effect of the modes of heat transfer on fin efficiency. It has been shown that for radiation heat transfer, thermal efficiency reaches its maximum value.     

端面泵浦固体激光棒内温度分布的研究

在分析了端面泵浦、周边冷却的固体激光棒内生热及致冷机制的基础上,将轴对称系统内的热传导问题简化为仅考虑径向热流的一维方程,并推导出“大礼帽”型光束泵浦及高斯光束泵浦两种情况下激光棒内温度分布的表达式。结果表明,在同样的光束尺寸下,利用高斯光束泵浦将导致棒内更加剧烈和更加不均匀的温度变化。文中对讨论进行了无因次处理,以使所获得的结论能够适用于不同的激光材料。     

Discussion on Temperature Profile in End-pumped Laser Rods

在分析了端面泵浦、周边冷却的固体激光棒内生热及致冷机制的基础上，将轴对称系统内的热传导问题简化为仅考虑径向热流的一维方程，并推导出“大礼帽”型光束泵浦及高斯光束泵浦两种情况下激光棒内温度分布的表达式。结果表明，在同样的光束尺寸下，利用高斯光束泵浦将导致棒内更加剧烈和更加不均匀的温度变化。文中对讨论进行了无因次处理，以使所获得的结论能够适用于不同的激光材料。     

铠装K型热电偶动态响应误差补偿研究

提出了一种利用同一可高频调制的高功率C02激光器发出的连续激光和脉冲激光作为激励热源,在同一系统中进行辐射温度计（红外探测器）静态校准和被校表面温度传感器动态校准的新方法,由于高速辐射温度计的频率响应特性优于被校温度传感器,因此以前者的响应作为真值来校准后者并获取系统误差的修正值,避免了因传感器安装环境差异及热物性的变化所产生的误差,解决了表面温度传感器动态校准的溯源难题。利用该方法对K型热电偶进行了动态校准实验,建立了数学模型,获得了该热电偶的频率特性和动态性能指标,对该传感器的动态特性进行补偿。     

基于瞬态传热的含裂缝环形锻件传热模型

针对目前热态锻件存在的裂缝问题,提出了一种基于传热理论的含裂缝锻件传热模型。首先,基于微元体的传热特性,推导满足微元体热平衡关系的导热微分方程,并以瞬时热流量为中介变量,对传热系数、热导率进行了修正。其次,设定环形锻件内外环境边界条件、裂缝有限空间自然对流边界条件,进而建立了多边界条件下含裂缝的热态环形锻件传热模型,利用分离变量法求解该传热模型。最后,应用有限元软件对含不同尺寸裂缝的环形锻件传热模型进行模拟,通过试验验证了仿真分析及传热模型的可行性。     

A numerical model for simulating temperature and speed effects in hot extrusion of rod

In this paper, a two-dimensional numerical model with upper-bound coupled thermal analysis has been developed. The model is capable of simulating the hot rod extrusion process with variable ram speeds. The temperature distributions and the speed effects in hot extrusion are predicted in detail by the proposed numerical model. A generalized kinematically-admissible velocity field without velocity discontinuity is adopted. The temperatures are calculated by considering simultaneously the heat generation due to deformation and friction and heat transfer. A finite-difference method with an implicit time integration scheme is utilized to solve the two-dimensional heat conduction problem. Two mathematical models for variable ram speed profiles are proposd. Ram speed profiles satisfying the exit temperature and the load requirements are obtained. The proposed numerical simulation has been demonstrated to be a powerful tool for the design of hot extrusion processes.     

高压燃气涡轮叶栅热辐射特性研究

采用商用软件CFX11.0的不同湍流模型对NASA-Markll高压燃气气冷涡轮叶栅进行气热耦合换热计算,得出最佳湍流模型。针对不同涡轮叶栅前进口总温进行考虑和不考虑热辐射的数值计算,着重分析叶栅流道内热辐射效应随涡轮前入口温度的变化情况,得出在实际的高温高压气冷涡轮叶栅耦合换热计算时,辐射热流应当作为源项加入到方程中。这样能够更准确地得出叶片内部温度分布,为热应力计算以及寿命预估提供准确的边界条件。     

改进烟花算法计算热态轴类锻件内圆柱体空洞缺陷深度

针对高温状态下热态轴类锻件内部产生的圆柱体空洞缺陷测量困难的问题，提出基于改进的烟花算法检测空洞深度方法。根据锻件的内部微元模型和瞬态温度场传热微分方程推导圆柱体空洞温度场与空洞半径关系的微分方程，利用分离变量法求解；对烟花算法进行改进，以提高圆柱体空洞深度检测精度；构造缺陷深度的目标函数进行测试，得到最优解的相对误差为2.5%。最后，运用所提方法、PSO算法和传统的烟花算法于同一深度的空洞分别进行检测，验证所提方法的可行性。     

淬火过程换热系数反求法的有限元实现

在淬火过程的数值模拟中,换热系数的正确求解是工件温度场、应力/应变场模拟结果和实际相符的先决条件.分析换热系数反求法的数学模型,并采用有限元法实现该数学模型的求解.与有限差分求解法比较,用有限元方法求解的换热系数曲线连续、平滑,结果可靠,而且编程量小,用求得的换热系数计算试件中心的温度场变化曲线,计算结果和实测数据吻合.     

UNIFIED APPROACH AND INTERACTIVE PROGRAM FOR THERMAL ANALYSIS OF VARIOUS MANUFACTURING PROCESSES WITH APPLICATION TO MACHINING

Analytical approach to thermal aspects of various manufacturing processes, such as machining, grinding, polishing, welding, heat treatment, laser processing, and tribology was used by many researchers between the late 1930s and early 1940s. That was the golden period when Blok introduced the heat partition concept in 1937; Jaeger developed the heat source method in 1942; and Rosenthal introduced the moving heat source theory in 1946. Starting from the Fourier's partial differential equation (PDE) of heat conduction, researchers have addressed various manufacturing processes using different approaches, namely, separation of variables, Fourier transform, Laplace transform, Bessel function, and Green's function methods. Consequently, it has become difficult to conceive a unified analytical approach of the various manufacturing processes based on the review of the literature as one approach differs from the other quite significantly and integration of them would be a formidable task, if not an impossible task. In contrast, using the Jaeger's classical heat source method and appropriate heat source (shape, size, and distribution) we developed a unified analytical approach to address the thermal aspects of various manufacturing processes. Such an approach, to the best of our knowledge, has never been attempted before and lends itself to the development of a user friendly interactive programming software that can be extremely valuable in practice. In this paper, we used Jaeger's classical heat source method, modified Hahn's oblique moving heat source for the shear plane heat source, Blok's ingenious heat partition method, and Chao and Trigger's functional analysis approach to illustrate the analysis of the temperature distribution in the work material, chip, and cutting tool in machining.     

Use of internally resonant energy transfer from the symmetrical to anti-symmetrical modes of a curved beam isolator for enhancing the isolation performance and reducing the source mass translation vibration: Theory and experiment

This study aims to use the internally resonant energy transfer from the symmetrical to anti-symmetrical modes of a simply supported curved beam isolator to enhance the isolation performance and reduce the source mass vibration. The model is setup and based on the differential equation of the Euler-Bernoulli beam. The dynamic modal displacements and forces are then obtained from the model using a numerical integration method. The numerical and experimental results indicate that when the ratio of the resonant frequencies of the first bending symmetric and anti-symmetric modes is close to 2 and the excitation frequency is equal to the resonant frequency of the first symmetric mode, the contribution of the first anti-symmetric mode is significant, even though the curved beam and excitation are symmetrical. The net modal force induced by the first anti-symmetric mode acting on the ground is much smaller than that of the first symmetric mode because the two reaction forces at the beam ends induced by the first anti-symmetric mode are equal but opposite. Further, the source mass translational vibration is significantly reduced because it is placed on the node of the anti-symmetric mode.     

Thermal analysis on voltage responses of high-T c superconducting thin-films exposed to a pulse laser beam

One-dimensional radiation/conduction heat transfer model is employed to investigate thermal responses of HTSC thin-film detectors exposed to a pulse laser beam. The theoretical model includes local radiation absorption in the HTSC film based on the electromagnetic theory, thermal contact resistances at the interface between film and substrate, and nonuniform initial condition for the film/substrate temperature incurred by the Joule heating due to the bias current and inherent electrical resistance even before the radiation exposure. Using the steady-state conduction equation, the experimental resistance-temperature curve is corrected based on the real film temperatures instead of the substrate temperatures. The error involved in the estimation of the voltage jump based on the model without initial Joule heating could be significant near the transition temperature. Still there is a big discrepancy between the theoretical and experimental results, though the nonuniform initial condition model reduces the gap.     

用热源叠加原理研究圆孔车削温度场

基于移动热源法及热源叠加原理,对圆孔车削温度场进行研究。提出局部温度场和总温度场的分析方法,推导出瞬时圆环热源温度场的描述方程,为圆孔工件的工程实际热问题提供了理论计算方法。     

瞬态温度场灵敏度分析的精细积分法

结合有限元法,提出了线性和非线性瞬态温度场灵敏度分析的精细积分方法,在精细积分法求解线性和非线性温度场的基础上,采用敏度分析的半解析法,推导了瞬态温度场灵敏度的分析的精细积分列式,指出对于线性热导问题,精细积分法求解敏度方程同样具有稳定、高精度的数值特性,而且能够避免常规差分法的数值振荡现象,对于非线性热传导问题,提出了相应的求解办法,算例表明了算法的有效性。     

Simulation of the continuous casting process by a mathematical model

A computational three-dimensional (3D) heat transfer model has been developed and applied to calculate the temperature distribution and solid shell thickness profile of a continous cast slab in a steel plant. This developed model includes non-linear material properties of specific heat and thermal conductivity as well as phase changes during solidification. A general thermo-fluidmechanics computer program, PHOENICS, was employed to numerically solve the heat transfer equation with the associated source terms. The thermal profile and solid shell thickness calculated by mathematical model agree with those predicted by an industrial model and experimental measurements. The model could also be used to predict the optimum process parameters on casting speed, heat removal rates and associated water flow rates and roll force. These parameters could be monitored by suitable sensors and controlled through a feed back system that interfaced with the mathematical model and the sensors.     

Analysis of collapse in flattening a micro-grooved heat pipe by lateral compression

The collapse of thin-walled micro-grooved heat pipes is a common phenomenon in the tube flattening process, which seriously influences the heat transfer performance and appearance of heat pipe. At present, there is no other better method to solve this problem. A new method by heating the heat pipe is proposed to eliminate the collapse during the flattening process. The effectiveness of the proposed method is investigated through a theoretical model, a finite element(FE) analysis, and experimental method. Firstly, A theoretical model based on a deformation model of six plastic hinges and the Antoine equation of the working fluid is established to analyze the collapse of thin walls at different temperatures. Then, the FE simulation and experiments of flattening process at different temperatures are carried out and compared with theoretical model. Finally, the FE model is followed to study the loads of the plates at different temperatures and heights of flattened heat pipes. The results of the theoretical model conform to those of the FE simulation and experiments in the flattened zone. The collapse occurs at room temperature. As the temperature increases, the collapse decreases and finally disappears at approximately 130 ℃ for various heights of flattened heat pipes. The loads of the moving plate increase as the temperature increases. Thus, the reasonable temperature for eliminating the collapse and reducing the load is approximately 130 ℃. The advantage of the proposed method is that the collapse is reduced or eliminated by means of the thermal deformation characteristic of heat pipe itself instead of by external support. As a result, the heat transfer efficiency of heat pipe is raised.     

大型油浸式变压器绕组温度场分布特征提取方法研究

为解决绕组升温导致变压器过热故障,使变压器停止运行的问题,提出一种大型油浸式变压器绕组温度场分布特征提取方法。研究绕组和铁心 2 个热源的放热情况,采用有限元法计算放热状态下漏磁场值,获得变压器平均导热系数及热传导、对流、辐射 3 种散热温度场。根据绕组的放热、散热性能以及油流场情况计算出变压器各能量变化,根据湍能和能量方程的施密特数提取出绕组温度场分布特征。实验表明,该方法能够准确计算出温度场中的能量变化,提取到的温度分布特征与实际情况相符,能够完成高质量温度场分布特征提取工作。     

Real-time thermal characterization of 12 nl fluid samples in a microchannel

This work presents a novel method and a device for real-time simultaneous measurement of the thermal conductivity and heat capacity of 12 nl fluid samples. The device uses a micromachined thermal sensor composed of a microchannel and a thin-film probe. The method, based on the 3 omega technique, employs a multiparameter-fitting scheme to determine the thermal properties with numerical computation of heat transfer. The thermal properties of 12 nl samples have been measured successfully by the sensor. Furthermore, real-time thermal characterization of fluid samples flowing in a microchannel has been demonstrated, manifesting strong potential of the proposed technique as an in situ probe in various microfluidic applications.     

Numerical solution, simulation and testing of the thermal dynamic characteristics of ball-screws

This research focuses on the characteristics of how a ball-screw changes its temperature corresponding to the periodic change of the end-most heat source. Based on the theory of heat transfer, this paper supplies a numerical solution to the non-homogeneous equation of heat transfer through the group explicit (GE) finite difference approach. The temperature distribution for the ball-screw at different times and directions is shown. By simulating and modeling the temperature field and thermal deformation of the ball-screw under periodically varying heat sources, this paper describes the thermal dynamic characteristics of the ball-screw under such conditions. By testing the thermal dynamic characteristics of the ball-screw, the numerical solution is validated.     

异形坯连铸离线动态二冷控制模型的研究与开发

针对异型坯连铸二次冷却过程,基于凝固传热理论建立其二维凝固传热模型,采用非等间距网格离散空间区域,采用显式有限差分算法离散传热方程。以铸坯温度为控制目标建立了PID反馈控制模型。应用Visual Basic 6.0程序设计语言,开发了连铸二冷区离线动态配水控制软件,在铸坯拉速、浇铸温度和钢种发生变化后,该配水控制软件能够对进入二冷区的铸坯信息实行全程跟踪、记录、显示并动态地分配二冷各区的水量,保持铸坯温度分布的稳定。该软件界面友好、通用性强,运行结果证明其控制效果良好,从而为异型坯二冷水量实时动态控制系统的开发奠定了基础。