NUMERICAL INVESTIGATION OF HEAT TRANSFER UNDER CONFINED IMPINGING TURBULENT SLOT JETS

This work numerically in vestigates confined impinging turbulent slot jets. Eight turbulence models, including one standard and seven low-Reynolds-number k-epsilon models, are employed and tested to predict the heat transfer performance of multiple impinging jets. Validation results indicate that the prediction by each turbulence model depends on grid distribution and numerical scheme used in spatial discretization. In addition, spent fluid exits are set between impinging jets to reduce the cross-flow effect in degradation of the heat transfer of downstream impinging jets. The overall heat transfer performance can be enhanced by proper spent fluid removal.     

NUMERICAL ANALYSIS OF CONVECTIVE HEAT TRANSFER FROM A MOVING PLATE COOLED BY AN ARRAY OF SUBMERGED PLANAR JETS

Abstract

A numerical model is developed to determine convective heat transfer distributions for an array of submerged planar jets impinging on a uniform heat flux or constant temperature moving surface where the surface motion is directed perpendicular to the jet planes. Unlike prior related work, the model accounts for the interaction between neighboring jets in the array without imposition of an imposed cross flow. The effects of surface speed, nozzle separation distance within an array, nozzle height, and Reynolds number on the flow field, coefficient of friction, and Nusselt number are investigated. Results suggest that neglecting surface motion effects can lead to overestimates of heat transfer.     

HYDROMAGNETIC FLOW AND HEAT TRANSFER OF A HEAT-GENERATING FLUID OVER A SURFACE EMBEDDED IN A POROUS MEDIUM

Similarity solutions for the laminar boundary-layer equations describing steady hydromagnetic two-dimensional flow and heat transfer in a stationary electrically-conducting and heat-generating fluid driven by a continuously moving porous surface immersed in a fluid-saturated porous medium are obtained. The flow is exposed to a transverse magnetic field and the surface is moving with a constant velocity. Fluid suction or injection is imposed at the wall. The dimensionless similar equations are solved numerically by an implicit finite-difference method. The numerical flow and heat transfer results are illustrated graphically for various parametric conditions to show special features of the solutions. Favorable comparisons with previously published work confirm the correctness of the numerical results. © 1997 Elsevier Science Ltd     

余热锅炉鳍片管受热面传热特性

文中介绍了在一热态试验台上进行余热锅炉鳍片管受热面传热特性试验研究的结果,对于大型余热锅炉的设计和运用具有重要意义。     

LARGE-EDDY SIMULATION OF HEAT TRANSFER OVER A BACKWARD-FACING STEP

A large-eddy simulation (LES) of the flow over a backward-facing step was conducted to investigate the heat transfer phenomena in the reattachment zone. The Navier-Stokes equations for an incompressible fluid with the temperature field considered as a passive scalar are solved using a second-order accurate scheme in space and time. An original coupling is used with a previous simulation to impose a fully turbulent flow at the entrance of the domain. The mixed scale subgrid model is used for the momentum equations while a scalar subgrid diffusivity model is employed for the temperature equation. The Reynolds number based on the velocity at the entrance of the domain and the step height is 7,432. The mean velocity field shows clearly that the shear layer issued from the step impacts the wall defining a recirculation zone, in which the reversed flow spreads into the original shear layer. A second recirculation region is found behind the step and acted like an obstacle for the first reversal flow. The mean reattachment length is well correlated to the maximum Nusselt number. The examination of the mean temperature field proves that the mixing behind the step is weak. The temperature fluctuations are important in the shear layer and in a zone issued from the reattachment point and stretched toward the region of reversed flow. Two main frequencies are identified: a high one due to the vortex shedding of the shear layer and a low one corresponding to the drift of the reattachment point.     

A NUMERICAL STUDY OF THE HEAT TRANSFER TO FLUID FLOW THROUGH CIRCULAR POROUS PASSAGES

A detailed numerical study of heat transfer to a fluid passing through a saturated porous medium is the subject of this study. The Green's function solution method is selected in order to accomplish this task. The interesting features of this methodology are the focus of this article. As a test case, primary consideration is given to the computation of heat transfer to a fluid flowing through a circular passage with impermeable walls filled with porous materials. The analysis includes the heating/cooling effects due to a temperature change at the wall of the passage. In addition, the contributions of frictional heating are examined.     

ANALYSIS OF A MOVING HEATED PUNCH OVER THE SURFACE OF A THERMOELASTIC HALF-SPACE

Analysis of a healed punch moving over the surface of a thermoelastic half-space is carried out for temperature and stress distribution in the medium. The formulation results in a mixed boundary-value problem independent of time in a moving nondimensional coordinate system. Exponential Fourier transforms are applied and the resulting system solved to obtain a general solution in terms of the functions expressed in the form of inverse Fourier transforms. Specifically, closed-form solutions are obtained for flat, cylindrical, and wedge punches. For a uniform temperature distribution the results derived agree with those available in the literature. Also, in the case of a concentrated force moving on the surface of an elastic half-space the solution obtained agrees with that in the literature.     

TRANSIENT THERMAL STRESSES IN A RECTANGULAR PLATE DUE TO NONUNIFORM HEAT TRANSFER COEFFICIENTS

Abstract

The linear problems of transient temperature and thermal stresses in a thin, finite, rectangular plate subjected to heat losses due to nonuniform heat transfer coefficients on the upper and lower plate surfaces are solved by a direct power series approach through the application of the Lanczos-Chebyshev and the discrete least-squares methods. A numerical example demonstrates the accuracies that can be achieved by using only a small number of terms.     

空气-沙子移动床换热器传热特性实验研究

面向太阳能热发电系统,建立一种空气-沙子移动床换热器实验平台,对其在不同参数下进行传热性能的实验研究.并基于实验数据,利用线性回归拟合得到表观气固传热系数的关联式,其整个实验工况预测值与实验值的平均误差为3.57％.研究结果表明:较高雷诺数可提升空气-沙子移动床换热器的传热效能,空气进口温度为281℃时,空气-沙子移动...     

间壁式耐火砖大型换热器传热计算的数值解法

以实际生产使用的间壁式耐火砖大型换热器为例,运用数值方法进行了换热器的传热计算,通过建立热计算模型,巧妙地选择计算模块,进行网络划分及边界条件的处理,采用有限差分方法对传热和流动的教学方程组织进行离散,并应用迭代法求出娄值解,计算取得了满意的结果。     

NUMERICAL SIMULATION OF TRANSIENT COOLING OF A HOT SOLID BY AN IMPINGING FREE SURFACE JET

This paper treats transient cooling of a hot solid by an impinging circular free surface liquid jet. The flow and thermal fields in the liquid as well as the temperature distributions in the hot solid have been predicted numerically. The Navier-Stokes equations for incompressible fluid flow in an axisymmetric coordinate system and the transient heat conduction equation for a solid have been solved by a finite difference method. The hydrodynamics of the liquid film and the heat transfer processes have been investigated to understand the physics of the phenomena.     

NUMERICAL INVESTIGATION OF CONVECTION HEAT TRANSFER IN A HEATED ROOM

We describe numerical investigation of airflow and temperature field in a room with a convective heat source. The simulation involves using computational fluid dynamics (CFD) to validate different turbulence models, i.e., the standard k- k model and the low Reynolds number k- k model. The comparisons between computations and experiments show good and acceptable agreement. It can be concluded that the CFD simulations can capture the main flow features and provide satisfactory results. It can be seen that the thermal wall jet created by the heat source greatly influences airflow pattern and temperature field in the room. It can also be seen that the advanced turbulence model may produce better results than the standard one under a suitable mesh scheme.     

LAMINAR IMPINGING JET HEAT TRANSFER WITH A PURELY VISCOUS INELASTIC FLUID

Laminar impinging flow heat transfer is considered with a purely viscous inelastic fluid. The rheology of the fluid is modeled using a strain rate dependent viscosity coupled with asymptotic Newtonian behavior in the zero shear limit. The velocity and temperature fields are computed numerically for a confined laminar axisymmetric impinging flow. Important features of the non-Newtonian developing flow field are described and contrasted with the Newtonian situation. It is demonstrated that very small departures from Newtonian rheology lead to qualitative changes in the Nusselt number distribution along the impinging surface. In particular, a mildly shear thinning fluid displays a pronounced off-stagnation point heat transfer maxima, a feature that is not observed with a Newtonian fluid. Hence, Newtonian fluid approximations cannot adequately describe experimental heat transfer measurements in such situations even though they may be deemed acceptable in terms of describing the velocity field in the incoming nozzle. Numerical results are presented to analyze the effect of the dimensionless nozzle-to-plate distance, the rheological parameters, and the Reynolds and Prandtl numbers on the magnitude of the off-stagnation point peak heat transfer rate. The influence of the rheology of the fluid is particularly significant at low nozzle-to-plate distances since the mean strain rate in the flow field increases as the nozzle-to-plate distance is reduced. The numerical heat transfer results are interpreted in the context of the developing flow field.     

二元固液相变过程的三维非稳态数值研究

对二元固液相变进行了传统热理论分析。建立了相变换热及两相流动过程的物理模型和数学模型,并进行了相应的数值求解。由模拟结果可见不同组分在固相和液相中的百分含量以及整场的温度、速度和压力分布等。     

NUMERICAL SIMULATION OF HEAT TRANSFER IN MIST FLOW

A numerical simulation of heat transfer over a row of tubes, in the presence of mist flow, is described. Computations include the solution of the flow field around the tubes, the prediction of the motion of water droplets, and the evaluation of the cooling effect of the water film on the tube surface. The entire analysis is carried out using FENSAP-ICE (Finite Element Navier-Stokes Analysis Package for In-flight icing), a simulation system developed by Newmerical Technologies for icing applications. The numerical model is described, including the Navier-Stokes solution, the water thin film computation, the droplet impingement prediction, and the conjugate heat transfer procedure. The predictions are verified against experimental data for different droplet mass flow rates, showing satisfactory agreement and allowing a useful insight in the physical characteristics of the problem.     

THE EFFECT OF THE GAS-GAP FORMATION DUE TO SHRINKAGE ON THE RATE OF HEAT TRANSFER DURING SOLIDIFICATION

A mathematical model is developed to investigate the gas-gap formation process at the metal-mold interface of a cylindrical casting during solidification. The governing equations are solved using an implicit finite difference technique. The effects of the gas gap on solidification time, surface temperature, temperature distributions, and position of solid-liquid interface are investigated.     

THREE-DIMENSIONAL TRANSIENT THERMAL STRESS ANALYSIS OF A NONHOMOGENEOUS HOLLOW CIRCULAR CYLINDER DUE TO A MOVING HEAT SOURCE IN THE AXIAL DIRECTION

In this paper, a theoretical analysis of a three-dimensional transient thermal stress problem is developed for a nonhomogeneous hollow circular cylinder due to a moving heat source in the axial direction from the inner and /or outer surfaces. Assuming that the hollow circular cylinder has nonhomogeneous thermal and mechanical material properties in the radial direction, the heat conduction problem and the associated thermoelastic behaviors for such nonhomogeneous medium are developed by introducing the theory of laminated composites as one of theoretical approximation. The transient heat conduction problem is treated with the help of the methods of Fourier cosine transformation and Laplace transformation, and the associated thermoelastic field is analyzed making use of the thermoelastic displacement potential, Michell's function, and the Boussinesq's function. Some numerical results for the temperature change and the stress distributions are shown in figures, and the effect of relaxing the thermal stress in the nonhomogeneous hollow circular cylinder and the influence of the velocity of a moving heat source are briefly discussed