摘要:

A nonstationary coupled problem is considered for thermoelasticity of a plane layer of semi-transparent gray, absorbing, radiating, and isotropically scattering elastic material. One of the boundary layers is heated by an external flow of radiation energy and convection at constant intensity. To solve the problem numerically, a vector modification of the Thomas method is used. The thermal and strain fields in the half-transparent material have been determined. Their interaction manifests itself by temperature pulsations and quantitative variation in the values of thermoelastic stresses of an object. A wide range of optic parameters are considered for the medium and the conditions of heat transfer with the environment.

ISSN:1040-7782    

DOI:10.1080/10407789208944875

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The effect of spectral radiative properties of fly-ash particles on radiative heat transfer through an inhomogeneous planar layer near the walls of a combustion system is investigated. The spectral absorption and scattering coefficients, as well as the scattering phase function of the particles, are obtained from the Lorenz-Mie theory as functions of temperature and particle diameter. These data are employed in the solution of the radiative transfer equation, which is modeled using a double spherical harmonics approximation. In the calculations, a linearly anisotropic scattering phase function is used. It is shown that, if the medium temperature distribution is nonuniform, the divergence of the radiative flux term calculated using the spectral fly-ash properties differs significantly from that obtained using constant properties. This means that if fly-ash properties are assumed wavelength independent, a coupled radiation-convection heat transfer analysis would underestimate the gas temperature near the walls of a typical furnace. On the other hand, the temperature dependency of the fly-ash radiative properties is quite weak and can safely be neglected.

ISSN:1040-7782    

DOI:10.1080/10407789208944876

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The flow of Newtonian and power law fluids through beds of particles has been investigated by solving the equations of continuity and momentum in the framework of the free-surface cell model. The finite-element method has been used for predicting the flow fields in terms of the primitive variables u, p, and v. Theoretical estimates of drag for assemblages of particles are obtained for wide ranges of physical and kinematic conditions: 10−3≤ Re ≤ 100, 0.4 ≤ n ≤ /, and 0.3 ≤ ε ≤ 0.9. The accuracy of the numerical scheme has been tested using known analytical results for creeping Newtonian flow. The drag results obtained herein can be used successfully to predict the friction factor for flow in fixed and fluidized beds and the minimum ftuidizalion velocity for a given liquid-solid system.

ISSN:1040-7782    

DOI:10.1080/10407789208944877

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The boundary element technique is used to solve the steady state convection-diffusion problem with constant velocity in a two-dimensional domain with a free interface. These problems arise in a number of important heat transfer applications involving melting or solidification, such as bulk crystal growth in Bridgman furnaces. The boundary element approach reduces the dimension of the problem, thereby improving the computational efficiency, and is particularly well suited to free-surface problems in which the position and shape of the solid-liquid interface are of primary importance. Results are presented for a case study problem representing solidification in a two-dimensional, rectangular configuration.

ISSN:1040-7782    

DOI:10.1080/10407789208944878

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

This paper presents the results of a numerical investigation of conjugate conduction and laminar mixed convection in vertical pipes for upward flow and uniform wall heat flux. The Prandtl number was fixed at 5; the Grashof number, based on heat flux, was set at 5000; and Reynolds numbers of 1 and 10 were used. Results are presented for four different values of solid-to-fluid thermal conductivity ratio K and three different values of wall thickness-to-pipe diameter ratio Δ. The effects of axial conduction in the pipe wall are quite pronounced when K and Δ are high and Re is low. In one case, upstream axial wall conduction distorted the parabolic velocity profile at the entrance of an upstream section to the point that the centerline velocity was negative at the entrance of the heated section, which established a zone of recirculation. Experimental flow visualization results and corresponding numerical predictions of these recirculation zones are also presented.

ISSN:1040-7782    

DOI:10.1080/10407789208944879

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Studies of hyperbolic heat conduction have so far been limited mostly to one-dimensional frameworks. For two-dimensional problems, the reflection and interaction of oblique thermal waves and complicated geometries present a challenge. This paper describes a numerical solution of two-dimensional hyperbolic heat conduction by high-resolution schemes. First, the governing equations are transformed from Cartesian coordinates into generalized curvilinear coordinates. Then the dependent variables are cast in a characteristic form that decouples the original system equation into scalar equations. Two-dimensional high-resolution numerical schemes, suck as total variational diminishing ( TVD) are built up by forming symmetrical products of one-dimensional difference operators on each individual wave. Three examples are used to demonstrate the unique feature of complicated interaction of two-dimensional thermal waves.

ISSN:1040-7782    

DOI:10.1080/10407789208944880

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The optimal heating rate is sought for a plate with temperature-dependent thermal conductivity and an internally located continuous plane heat source. At the final specified time tf, the final temperature distribution Tf(x) should approximate as closely as possible a specified uniform temperature Td, and a minimum amount of energy should be used for the heating. We determine the location and the timewise variation of the strength of the plane heat source that satisfy such requirements.

ISSN:1040-7782    

DOI:10.1080/10407789208944881

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The main purpose of this work is to evaluate the values of diffusion coefficients at control-volume faces, using the finite-volume method, in transport problems that include diffusion processes. A heat conduction problem in a composite slab with linearly temperature-dependent conductivity, which has a closed-form solution, is selected for demonstration. It is found that the harmonic mean operation performs better than the arithmetic mean operation in evaluating the interface diffusion coefficients. Moreover, if we intend to obtain the information at some specific interfaces with abrupt changes of diffusion coefficients, the recommended grid layout is arranged such that each specific interface contains a grid node. This arrangement can give more accurate predictions at these unusual interfaces.

ISSN:1040-7782    

DOI:10.1080/10407789208944882

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor