The influence of slip conditions, wall properties and heat transfer on MHD peristaltic transport

The effects of both wall slip conditions and heat transfer on peristaltic flow of MHD Newtonian fluid in a porous channel with elastic wall properties have been studied under the assumptions of long-wavelength and low-Reynolds number. The analytical solution has been derived for the stream function and temperature. The results for velocity, temperature, stream function and heat transfer coefficient obtained in the analysis have been evaluated numerically and discussed briefly. The numerical result shows that more trapped bolus appears with increasing Knudsen number.     

颗粒物料传热传质过程的数值仿真与实验研究

转筒干燥器的主体是略带倾斜并能回转的圆筒体，是一种既受高温加热又兼输送的设备，它的应用十分广泛。该文较为系统地进行了转筒干燥器物料的传热传质过程的分析，并进行了试验研究。利用质量平衡方程、能量平衡方程、传热方程和传质方程，建立了颗粒物料在转筒干燥器干燥过程中的传热传质数学模型，该模型能够较好地预测干燥过程中物料颗粒的温度和含湿量的变化，仿真结果与实验结果吻合良好。该仿真程序对此类问题的研究具有参考价值。     

A comparison between a linear- and a non-linear three-dimensional thermal analysis of a radial gas turbine wheel

Various rotating components of a gas turbine engine are subjected to high temperatures as well as high centrifugal forces. Abrupt temperature variations often introduce thermal stresses. These must of course be considered when the designer is faced with the problem of predicting the low cycle fatigue life of the relevant component.Particularly at higher temperatures the material behaviour is non-linear and may influence the accuracy of the computed results. Both the thermal conductivity- and the heat capacity properties become more and more temperature-dependent in higher temperature regions. In addition, convective heat transfer at heat exposed surfaces are temperature-dependent.This paper describes a linear- and two non-linear three-dimensional temperature field analyses of a radial gas turbine wheel. In one of the non-linear analyses the material properties were made temperature-dependent, whereas the second non-linear analysis had constant material properties but temperature-dependent heat transfer coefficients.The results obtained show that for the analyzed gas turbine wheel, a linear analysis will produce results which deviate insignificantly from the results obtained in a much costlier non-linear analysis. This is true for material properties and convective heat transfer coefficients that are non-linear only to a moderate extent. It is also fair to assume that this may be concluded for heat conduction problems of the same category, e.g. analysis of other machinery components, nuclear reactor design problems, etc.     

Analysis of radiation-natural convection in a divided enclosure using the lattice Boltzmann method

A numerical hybrid lattice-Boltzmann equation finite-difference is used to study the radiation-natural convection phenomena in a square cavity, differentially heated, with partition of finite thickness and varying height located vertically at the center of the cavity. The results obtained show that the radiation exchange produces a rise in the heat transfer. The average Nusselt number and the throughflow strength increase when the gap width (w), maximal difference temperature (ΔT) and cavity width (L) get larger. Effects of different parameters on streamlines, temperature fields, average Nusselt number and throughflow strength are discussed.     

Numerical analysis of dual-phase-lag heat transfer in a layered cylinder with nonlinear interface boundary conditions

To accommodate the micro-structural effect, this work analyzes the heat transfer induced by a pulsed surface heating in a two-layered solid cylinder with the dual-phase-lag model. The interface thermal resistance is specified with the radiation boundary condition model. Due to the difference in the relaxation times between two dissimilar materials, the strong nonlinearity of the interfacial boundary condition, and the singularity at the center axis, it introduces the complexity and causes some mathematical difficulties to analyze the present problem. Thus a numerical scheme is developed. Results show the lagging thermal behavior is affected with the geometry effect and the interface thermal resistance and depends on the magnitude of the relaxation times more than the ratio value between the relaxation times. The microstructure effect would destroy the structure of thermal wave. The propagation speed of thermal wave is independent of the interface thermal resistance and the microstructure effect.     

Estimation of critical dimensions for a trapezoidal-shaped steel fin using hybrid differential evolution algorithm

This paper deals with the inverse prediction of parameters in a trapezoidal fin with temperature-dependent thermal conductivity and heat transfer coefficient. Three critical dimensions along with the relevant heat transfer coefficient at the fin base have been simultaneously predicted for satisfying a given temperature distribution on the surface of the trapezoidal fin. The inverse problem is solved by a hybrid differential evolution-nonlinear programming (DE-NLP) optimization method. For a given fin material which is considered to be stainless steel, it is found from the present study that many feasible dimensions exist which satisfy a given temperature distribution, thereby providing flexibility in selecting any dimensions from the available alternatives by appropriately regulating the base heat transfer coefficient. A very good estimation of the unknown parameters has been obtained even for temperature distribution involving random measurement errors which is confirmed by the comparisons of the reconstructed distributions. It is concluded that for a given fin material, the hybrid DE-NLP algorithm satisfactorily estimates feasible dimensions of a trapezoidal fin even with random measurement error of 11 %.

     

Double-diffusive and Soret-induced convection of a micropolar fluid in a vertical channel

This paper reports an investigation of the fully developed natural convection heat and mass transfer of a micropolar fluid in a vertical channel. Asymmetric temperature and concentration boundary conditions are applied to the walls of the channel. The cases of double diffusion and Soret-induced convection are both considered. The governing parameters for the problem are the buoyancy ratio and the various material parameters of the micropolar fluid. The resulting non-dimensional boundary value problem is solved analytically in closed form using MAPLE software. A numerical solution of the time dependent governing equations is demonstrated to be in good agreement with the analytical model. The influence of the governing parameters on the fluid flow as well as heat and solute transfers is demonstrated to be significant.     

On dual-phase-lag magneto-thermo-viscoelasticity theory with memory-dependent derivative

A new mathematical model of generalized magneto-thermo-viscoelasticity theories with memory-dependent derivatives (MDD) of dual-phase-lag heat conduction law is developed. The equations for one-dimensional problems including heat sources are cast into matrix form using the state space and Laplace transform techniques. The resulting formulation is applied to a problem for the whole space with a plane distribution of heat sources. It is also applied to a perfect conducting semi-space problem with a traction-free surface and plane distribution of heat sources located inside the medium. The inversion of the Laplace transforms is carried out using a numerical approach. Numerical results for the temperature, displacement, stress and heat flux distributions as well as the induced magnetic and electric fields are given and illustrated graphically. A comparison is made with the results obtained in the coupled theory. The impacts of the MDD heat transfer parameter and Alfven velocity on a viscoelastic material, for example, poly (methyl methacrylate) (Perspex) are discussed.

     

Mixed convection in a wall plume

The mixed convection flow that arises due to a finite heated element located on a vertical adiabatic surface in an external flow, aligned with the surface, is studied analytically. The problem is of particular interest in electronic circuitry cooling and in heat removal in various manufacturing systems. The boundary layer flow is studied to determine the heat transfer from the heated element, the temperature decay downstream and the flow field that results. Numerical results are obtained, employing finite difference methods for a wide range of the mixed convection parameter. The pure natural convection problem is studied first and the results obtained are compared with earlier studies on wall plumes. The effect of mixed convection on the heat transfer and fluid flow characteristics is studied in detail. The temperature at the heated element surface is studied as a function of the mixed convection parameter. The effect of the inclusion of radiative loss on the temperature and flow fields is also examined.     

化工过程仿真培训系统中的换热器模型

本文讨论了化工过程仿真培训系统中的换热器的动态模型，着重比较了两种稳态模拟与动态补偿相结合的仿真算法－基于平均传热温差和基于传热单元数的仿真算法。分析了基于平均传热温差的仿真算法存在的问题，讨论了基于传热单元数的仿真算法中有关参数的确定方法，最后给出仿真实例。     

Level set topology optimization of cooling and heating devices using a simplified convection model

This paper studies topology optimization of convective heat transfer problems in two and three dimensions. The convective fluxes are approximated by Newton’s Law of Cooling (NLC). The geometry is described by a Level Set Method (LSM) and the temperature field is predicted by the eXtended Finite Element Method (XFEM). A constraint on the spatial gradient of the level set field is introduced to penalize small, sub-element-size geometric features. Numerical studies show that the LSM-XFEM provides improved accuracy over previously studied density methods and LSMs using Ersatz material models. It is shown that the NLC model with an iso-thermal fluid phase may over predict the convective heat flux and thus promote the formation of very thin fluid channels, depending on the Biot number characterizing the heat transfer problem. Approximating the temperature field in the fluid phase by a diffusive model mitigates this issue but an explicit feature size control is still necessary to prevent the formation of small solid members, in particular at low Biot numbers. The proposed constraint on the gradient of the level set field is shown to suppress sub-element-size features but necessitates a continuation strategy to prevent the optimization process from stagnating as geometric features merge.     

Optimal Allocation of Heat Exchanger Investment

The optimal allocation of a given investment capital to the heat exchanging inventory is studied for heat engines, refrigerators and heat pumps. The study is based on an endoreversible model operating between two constant temperature heat reservoirs at optimal thermodynamic performance, which is either minimal entropy production or maximum power production. The analysis accounts for the fact that the actual costs of heat exchangers equipment is subject to the material, design and operating conditions of the heat exchangers so that the dependence between the costs and heat transfer coefficients generally needs to be considered as nonlinear and different for the hot and cold side of the system. Contrary to existing results showing no difference between cyclic and stationary operation for Newtonian heat transfer we find one. This result also pertains to non-Newtonian heat transfer.     

基于接触测温的太阳能重力热管温差测量方法与装置研究

热管温差是太阳能重力热管传热性能中的重要标志.通过正交实验研究温差随热管倾斜角度、充液比、水浴温度和热管蒸发段加热长度变化对太阳能重力热管温差的影响,得到了影响温差显著性因素.为解决太阳能重力热管温差尚无自动化在线监测的现状,提出了太阳能重力热管温差测量方法,该方法一次能够检测多支太阳能重力热管.结合生产厂家和国标要求,设计了一套太阳能重力热管温差批量化测量方案,并对该方案进行了不确定度评估.     

GPU-based model predictive control for continuous casting spray cooling control system using particle swarm optimization

Model predictive control (MPC) for spray cooling control system requires a repeated online solution of an optimization problem that includes partial differential equations (PDEs). To simulate the future temperature behavior of steel billets, 3D dynamic heat transfer model is used. The special solution domain of PDEs has led to large computation cost, which is the main challenge in the real-time practical application of spray cooling control system. Meanwhile, the heat transfer coefficients need to be identified using the measured surface temperature. This work presents a two-level parallel solution method implemented on a Graphics processing unit (GPU) for MPC of spray cooling control systems and a weighted least squares modified conjugate gradient method (WLS–MCG) for identification of heat transfer coefficients. Two-level parallel solution method consists of parallel-based heat transfer model and stream parallel particle swarm optimization (PSO). PSO is used to solve the optimization problem. WLS–MCG consists of the weighted least squares (WLS) and modified conjugate gradient method (MCG). The experimental results show that the two-level parallel solution method has good computational performance and achieves satisfactory control performance.     

二维稳态传热问题的计算机仿真

热量传输现象在工程技术领域中广泛存在,对二维稳态传热情形下温度场分布的研究有重要现实意义。对于复杂几何形状的物体和非线性的边界条件,分析解法显得无能为力;相比之下,建立在有限元基础上的数值计算是有效和准确的。在传热和流体流动问题的数值计算方面,SIMPLE算法被广泛采用。通过VC和Matlab的混合编程用SIMPLE算法实现了对二维稳态传热问题的计算仿真,描述了温度场的分布。     

Optimal structure for heat and cold protection under transient heat conduction

A suitable combination of materials for sheltering a system from a sudden change of environmental temperature has been theoretically studied. The protective composite wall consists of two materials. An insulating material is placed on the outer surface, while, for the inner surface, materials that have good heat storage properties but negligible heat transfer resistance are chosen. The results show that by replacing some of the insulation material with a heat storage material, the temperature of the protected system can be maintained at a considerably lower level. Although the optimal thickness ratio X depends on the Biot number, Fourier number, and on the heat capacity ratio K _C, for a large number of thermal protection cases, the approximation X = 0.45 yields practically the minimum progress of the transient. If the Biot number is sufficiently small, it is better to replace all of the insulation material with a good heat storage material.     

温控伴热电缆温度采集与控制系统的研究

介绍了利用伴热电缆本身PTC热敏材料所具有的自调控温能力，再配上温度测控系统，从而克服由于受到传热因素的影响使PTC伴热电缆控温精度不高，启动电流过大的问题，提高控制等级和精度，节约电能。该成果可广泛应用于石油、化工、管道传输、公路机场积雪、农产品生产、民用等行业中。     

Formulation of the thermal problem

This paper describes the thermal problem and presents the experimental data for validation. The thermal problem involves validating a model for heat conduction in a solid. The mathematical model is based on one-dimensional, linear heat conduction in a solid slab, with heat flux boundary conditions. Experimental data from a series of material characterization, validation, and accreditation experiments related to the mathematical model are provided. The objective is to use the series of experiments to assess the model, and then use the model to predict regulatory performance relative to a regulatory requirement. The regulatory requirement is defined in terms of the probability that a surface temperature not exceed a specified temperature at the regulatory conditions.     

Pragmatism in semi-steady modular finite-grid simulation methodology for aerospace composites manufacturing

In this paper, practical aspects of employing the finite element/nodal control volume (FE/NCV) approach for modelling of prepreg moulding, resin transfer moulding and pultrusion of fibre reinforced polymer composites are discussed. Various NCV based formulations for simulating resin flow through fibrous media, resin cure, heat transfer in fabrication assemblies, changes in material properties with temperature and cure are explained. The development of a process-adaptive, modular, semi-steady simulation procedure that combines the benefits of a commercially available general-purpose FE package and user-defined computer programs for NCV grid is presented. The process is easily implementable for one-, two- or three-dimensional domains without re-meshing. Implications of ignoring the effects of the heat of exothermic cure reaction, the artificial loss of resin mass during the resin flow, and the die temperature on material properties are highlighted using example problems.     

A parameterized model of heat storage by lake sediments

A model of seasonal heat storage by lake sediments is proposed oriented at applications in climate modeling and at lake parameterization in numerical weather prediction. The computational efficiency is achieved by reformulating of the heat transfer problem as a set of ordinary differential equations for evolution of the temperature wave inside the upper sediment layer. Arising temperature and depth scales completely replace the conductivity of the sediment in the heat transfer equation and can be easily achieved from the lake water temperature observations without any data on the sediment thermal properties. The method is proposed for the scales estimation from the inverse solution of the model equations in special case of the constant water-sediment heat flux in ice-covered lakes. The method is tested on data from sediments of Lake Krasnoye, North-Western Russia. The long-term (1961–2002) modeling of temperature in German lakes Müggelsee and Heiligensee with a coupled one-dimensional model of lake water column and sediments has demonstrated an appreciable effect of the sediment heat storage on near-bottom temperatures in both lakes. Thus, incorporation of the sediment layer into lake temperature models can essentially improve, at low computational costs, the model performance, especially for shallow lakes. In addition, a better forecast of near-bottom temperature evolution on climatic scales can provide a better understanding of the response of lake benthic communities to global warming.