COMPARISON OF INTERFACE-FOLLOWING TECHNIQUES FOR NUMERICAL ANALYSIS OF PHASE-CHANGE PROBLEMS

The Semi-Implicit Method for Pressure-Linked Equations (SIMPLE)algorithm for heat transfer and fluid flow problems is extended to time-periodic situations. A vectorized line group method for solving the system of associated algebraic equations in a rectangular two-dimensional computational domain is developed to speed up the computations. A multiblock procedure with the line group method is used to solve a piston-driven oscillating heat transfer problem. The numerical results obtained show some interesting new phenomena and agree with analytical results where such comparisons are possible.     

地板辐射采暖空间温度场的数值模拟

根据地板采暖的特点，建立数学模型，采用有限差分法，模拟地板辐射采暖中地板温度场的变化关系。通过与实测结果进行比较和调整，可有效地控制供暖温度，取得了满意的结果，为工程设计提供比较准确的方法。     

埋地管道温度特性数值模拟与相似性实验研究

针对含内热源的埋地管道,建立了管道与周围土壤之间的传热模型。模型考虑了地表温度随季节变化,采用数值计算方法编制程序进行计算,得出管道温度随年代的变化规律。根据实际模型,建立缩小的相似性实验台进行验证,结果表明数值计算具有很好的准确性。最后,利用本模型预测了电力隧道在无通风条件下连续运行50a内的温度变化情况。     

SSL水电站交通洞温度测试及节能潜力分析

通过对埋深约250m的北京SSL地下水电站交通洞换热特性5d的连续现场实时监测,分析了洞内空气温度随距洞口距离的变化规律及交通洞的节能潜力,测试结果表明地下交通洞对送风空气有明显的降温和升温效果。测试发现夏天1000m温降最大约达6℃,温升近3℃;每km最大供冷能力可达380kW以上,供热能力达140kW以上,且在交通洞末端靠近主厂房处温度维持在约23℃,北京SSL水电站利用地下隧洞节能潜力巨大,在夏季及冬季可以部分或全部替代空调冷热源,具有显著节能意义。     

MULTIPLE TRANSIENT POINT HEAT SOURCES IDENTIFICATION IN HEAT DIFFUSION: APPLICATION TO NUMERICAL TWO- AND THREE-DIMENSIONAL PROBLEMS

This article deals with an inverse problem, which consists of the location and strength identification of multiple-point heat sources in transient heat conduction. The identification procedure is based on a boundary integral formulation using space and time Green functions. The discretized problem is nonlinear if the location of the point heat sources is unknown. In order to reduce the sensitivity of the solution to errors, we use the future time step procedure associated to a Tikhonov regularization procedure. The proposed numerical approach is applied to numerical two- and three-dimensional examples.     

MESHLESS EFG METHOD IN THREE-DIMENSIONAL HEAT TRANSFER PROBLEMS: A NUMERICAL COMPARISON,COST AND ERROR ANALYSIS

The present analysis deals with the numerical solution of three-dimensional heat transfer problems using a meshless element-free Galerkin (EFG) method. The EFG method utilizes the moving least-square (MLS) approximation to approximate the unknown function of temperature T(x) with T ^h (x). The approximants are constructed by using a weight function, a monomial basis, and a set of coefficients that depends on position. A variational method is used to obtain the discrete equations. The essential boundary conditions are enforced using the Lagrange multiplier method. MATLAB codes have been developed to obtain the numerical results for a model problem of three-dimensional heat transfer in orthotropic materials using different EFG weight functions. Three new weight functions, exponential, elliptical, and cosine, are proposed. A numerical comparison is made among the results obtained using proposed (exponential, elliptical, and cosine) and existing (quadratic) weight functions for a model problem. L₂ error is calculated for the proposed and existing EFG weight functions using 125 nodes. FORTRAN software has also been developed and executed on a PARAM 10000 supercomputing machine to obtain the computational cost of the EFG method. The computational cost of the EFG method is obtained for different orders of Gaussian quadrature and for different values of scaling parameter. The effect of scaling parameter on EFG results (temperature values) is also discussed in detail. The effectiveness of EFG method is shown by comparing the EFG results with those obtained by the finite-element method.     

重庆地区太阳能资源的建筑应用潜力分析

以重庆地区的气象资料为基础,从太阳月总辐射、日照时长、云量、太阳高度角等方面,对太阳能资源的分布特点、应用措施及潜力进行了分析.结果表明,重庆地区太阳能资源具有明显的季节性;5～9月份的太阳能热水可满足标准要求;对遮阳与采光的太阳能应用要兼顾用与控,东、西向窗的面积应尽量减少,而南向窗宜设置活动式水平外遮阳;夏季在太阳能辅助通风时室内通风速度可提高14%～40%,明显改善室内热湿环境和空气品质.     

NUMERICAL METHOD FOR HEAT TRANSFER,FLUID FLOW,AND STRESS ANALYSIS IN PHASE-CHANGE PROBLEMS

This work presents a finite-volume method for simultaneous prediction of physical phenomena occurring during a solid / liquid phase change, including buoyancy-driven flow in the liquid, deformation and stresses in the solid, and heat transfer in both the liquid and solid parts of the solution domain. The liquid is treated as a Newtonian incompressible fluid and it is assumed that the solid behaves as a thermoelastic body, although other constitutive equations for liquid and / or solid could easily be incorporated. The method solves integral equations of mass, momentum, and energy balance discretized on numerical meshes consisting of cells of arbitrary polyhedral shape. The method is validated by comparing numerical results with analytical solutions and available measurement data.     

SENSITIVITY ANALYSIS IN THERMO-ELASTIC-PLASTIC PROBLEMS

The design sensitivity of a thermo-elastic-plastic system is considered. The continuum approach and resulting finite element formulations are described. Sensitivity is obtained by an incremental load approach for nonlinear response analysis. Kinematic and isotropic hardening in thermo-elasto-plasticity are discussed. The control volume approach is to analyze shape and nonshape design. The direct differentiation method is adopted to obtain the design sensitivity expression for the response variables. Analytical examples demonstrate the developed sensitivity procedure. The design sensitivity formulas are discretized to implement it as a computer program with isoparametric finite elements. Numerical examples are presented to calculate the design sensitivity.     

A NEW METHOD FOR NUMERICAL TREATMENT OF DIFFUSION COEFFICIENTS AT CONTROL-VOLUME SURFACES

ABSTRACT

Diffusion coefficients at control-volume surfaces are required for numerical simulation of convection-diffusion equations. Various interpolation methods for these diffusion coefficients are briefly discussed and compared with the analytical solutions of both pure diffusion and convection-diffusion problems. It is found that the harmonic mean method is not as accurate and reliable as is supposed. A new method is thus developed. Extensive numerical comparisons are given for both the harmonic mean and the present method, and the results show that the method proposed is accurate, reliable, and easy to use.     

STOCHASTIC FINITE-ELEMENT ANALYSIS OF COUPLED HEAT AND MASS TRANSFER PROBLEMS WITH RANDOM FIELD PARAMETERS

A first-order perturbation algorithm for the computation of mean values and variances of transient temperature and moisture fields during coupled heat and mass transfer problems with random field parameters has been developed and implemented. The algorithm is based on the Galerkin finite-element discretization of Luikov's heat and mass transfer equations for capillary porous bodies and is computationally less demanding than the Monte Carlo method. The algorithm has been programmed in MATLAB and applied to a published test case of a drying process for soybean kernels. The simulations indicate that the stochastic fluctuations of the thermophysical properties and the process conditions may cause a considerable level of uncertainty in the predicted temperatures and moisture contents inside the product.     

NUMERICAL ANALYSIS OF NATURAL CONVECTION IN CAVITIES WITH VARIABLE POROSITY

This work analyzes the effects of variable porosity on the heat transfer by natural convection, in a cavity with isothermal vertical walls and adiabatic horizontal ones and a porous medium inside. The hydrodynamic field in the porous medium is modelled according to the general model obtained by Brinkman's and Forchheimer's terms. An exponential variation of the porosity near the walls was considered. The equations in terms of the real variables were numerically solved by the finite-volume method, with a staggered variables arrangement. The pressure-velocity coupling was treated with the PRIME algorithm. The simulations involved both Darcian (Da = 10 -7 ) and non-Darcian flows (Da = 10 -6 ). In each case, the modified Rayleigh range (Ra m = Ra 2 Da) was from 10 to 1,000, and from 100 to 5,000, respectively. For the numerical simulation we considered Pr = 1, Rk = 1, A = 1, and k X = 0.36. The results are shown through streamlines and isotherms and velocity and temperatures profiles. This shows that the generalized method with variable porosity means an increase in the average Nusselt number. For physical validation, some experimental sets were simulated in which glass was the porous medium, and water, alcohol, and transformer oil were used as the fluids. The simulated results indicate that the adopted model reduces the discrepancy in the experimental results obtained with water and alcohol. We proposed a correlation to evaluate the average Nusselt number as a function of six parameters: Rayleigh number, Prandtl number, the dimensionless particle diameter, thermal conductivity ratio between solid and fluid phase, porosity, and the aspect ratio of the cavity.     

A METHOD FOR PREDICTING AND MINIMIZING NUMERICAL DIFFUSION

Finite-difference numerical techniques based on control volumes provide the most commonly applied method for solution of heat and mass transfer problems. These first-order solutions are prone to substantial inaccuracy introduced by numerical diffusion effects, From a Lagrangian viewpoint, the inaccuracy of interpolation in space and time creates this diffusion. Here, Taylor series expansions for streamwise and cross-stream interpolation processes give numerical diffusion coefficients. These simple coefficients can be used to adjust physical diffusion coefficients, providing second-order accuracy for convection in control volume solutions. The diffusion correction functions derived here are particularly useful for transient solutions.     

NUMERICAL ANALYSIS OF THERMAL STRESSES IN A NONLINEAR THERMOELASTIC THICK CYLINDRICAL SHELL AND CUBE

Numerical analysis of static thermal stresses in a nonlinear, isotropic, thermaelas-tic, thick cylindrical shell and a cube is presented using the nonlinear thermoelas-ticity. The geometrical relations, equilibrium equations, and Fourier's law are linear while the constitutive relations accounting for the id-order elastic moduli and the temperature-dependent 2d-order elastic moduli and coefficient of thermal expansion are nonlinear. Nonlinear effects are numerically investigated for a cylindrical shell and a cube made of D54S aluminum alloy.

     

POTENTIAL FUNCTION METHOD FOR PIEZOTHERMOELASTIC PROBLEMS OF SOLIDS OF CRYSTAL CLASS 6 mm IN CYLINDRICAL COORDINATES

A potential function method for three-dimensional asymmetric problems of piezoiher-moelasticity of hexagonal materials of crystal class 6 mm in cylindrical coordinates is proposed. The method employs two piezothermoelaslic potential functions, four piezoelastic potential functions, and a piezoelectric potential function. One of the piezother-moelastic potentials and the four piezoelastic potential functions are governed by simple uncoupled differential equations, which are derived from the stress equations of equilibrium and the equation of electrostatics. The remaining piezothermoelastic function and the piezoelectric potential function are expressed in terms of the previously obtained piezothermoelastic function. As an illustrative example, the problem of an infinite, thin piezothermoelastic plate subjected to axisymmetric surface heating is analyzed. Numerical results are obtained for the stresses and the electric potential in a cadmium selenide plate. The thermally induced stress distributions are compared with those obtained when the piezo-effect is ignored.     

热管式吸热器单元热管传热的数值模拟分析

热管式吸热器的热性能分析对吸热器设计有着重要意义，但由于其相变过程与热管传热的耦合作用十分复杂，至今仍是很少有人深入研究的领域。本文基于焓法建立单元热管耦合传热的物理和数学模型，模拟计算了热管壁温、蓄热容器壁温、循环工质出口温度及相变材料熔化率等参数，并与基本型吸热器进行比较，验证了热管吸热器明显改善了温度分布的均匀性和相变材料的熔化率。     

NUMERICAL ANALYSIS OF CONVECTIVE HEAT TRANSFER IN THE ENTRANCE REGION OF CUSPED DUCTS

Abstract

This study presents the numerical solution of connective heat transfer in the thermal entrance region of cusped ducts. These ducts are formed contiguously by assembling three, four, or five cylindrical rods having the same diameter next to each other. The ducts are also subjected to a constant wall temperature. The solution to the discretization of these duct geometries is obtained by using the numerically generated boundary fitted coordinate system. According to this method, the complex domain in the physical plane is transformed into a regular square domain in the computational plane. The finite difference method based on the control volume is then used to discretize the transformed governing equation. To prove the validity of the results, the present method is also used to obtain the convective heat transfer solution in the entrance region of square and equilateral triangular ducts. Comparison of the results for square and equilateral triangular ducts with available data published in the open literature gives excellent agreement. The representative curves illustrating variations of the bulk temperature and Nusselt numbers with pertinent parameters are plotted for the three different duct geometries.     

HIGH-PRECISION NUMERICAL SIMULATION WITH AUTOADAPTATIVE GRID TECHNIQUE IN NONLINEAR THERMAL DIFFUSION

Many engineering problems concern the determination of a steady state solution in the case with strong thermal gradients, and results obtained using the finite-element technique are sometimes inaccurate, particularly for nonlinear problems with unadapted meshes. Building on previous results in linear problems, we propose an autoadaptative technique for nonlinear cases that uses quasi-Newtonian iterations to reevaluate an interpolation error estimation. We perfected an automatic refinement technique to solve the nonlinear thermal problem of temperature calculus in a cast-iron cylinder head of a diesel engine.     

风力机叶片三维流动特性与气动性能的数值分析

采用基于雷诺平均的三维可压N-S方程,对美国国家可再生能源实验室开发的PhaseⅥ实验风力机叶片在7m/s来流下的绕流流场进行全三维数值模拟.通过对数值模拟得到的叶片表面压力分布与实验测量值的比较,验证了数值模拟的有效性,并在此基础上分析了叶片各截面的失速情况、叶片的三维绕流特性以及叶展方向上的升阻力系数与功率分布.数值模拟数据显示,相比简单的对二维数值模拟结果进行堆叠,全三维的数值模拟能够更准确的反映叶片绕流的气动特性.