摘要:

A plane-symmetric, gray model of coal particle suspensions is developed to test the accuracy of the low-order discrete ordinates and flux methods and of the differential approximation for calculating the radiant energy transport in multiply scattering and heat generating media bounded by diffusely reflecting surfaces. Results obtained by these three approximate techniques are compared with those computed by a high-order discrete ordinates method. In this study, the internal heat generation function is represented by a constant model and a diffusion-limited Arrhenius model; however, the solution method presented is applicable to arbitrary nonlinear and temperature-dependent heat production rates, ft is shown that the accuracy of flux methods decreases while the accuracy of the differential approximation increases with increasing optical thickness of the suspension. The approximate methods are found to yield more accurate results for temperature profiles than for profiles of the radiation intensity. With the Arrhenius heat generation model, particle suspensions are shown to ignite only if their optical thickness exceeds a critical value, which varies with the temperature and reflectivity of the bounding walls. The differential and flux methods tend to overpredict the critical size of the system required for ignition.

ISSN:0149-5720    

DOI:10.1080/10407788208913446

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

This paper considers the development of self-adaptive solution algorithms for nonlinear heat conduction. By reinterpreting the incremental successive substitution and Newton Raphson procedures as methods involving extrapolations bound by open constraint surfaces, specialized closed constraints are developed that significantly improve the efficiency and stability of such schemes. This is achieved by introducing closed ellipsoidal surfaces to control the size of successive iterations. In particular, due to the nature of the ellipsoidal bound employed, the resulting closed constrained incremental successive substitution and Newton Raphson algorithms are self-adaptive, intrinsically stable, as well as far more efficient than the open versions. Because of the generality of the constrained schemes developed, all the various types of non-linearity common to heat transfer can be treated. To demonstrate the new algorithms developed here, benchmark examples are presented and comparisons are made with traditional schemes.

ISSN:0149-5720    

DOI:10.1080/10407788208913447

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

The nonlinear inverse heat conduction problem is the calculation of surface heat fluxes and temperatures by utilizing measured interior temperatures in opaque solids possessing temperature-variable thermal properties. The most widely used numerical method for this problem was developed by Beck. The new sequential procedure presented here reduces the number of computer calculations by a factor of 3 or 4.

ISSN:0149-5720    

DOI:10.1080/10407788208913448

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

The three-dimensional laminar mixed convection boundary layer on a vertical heated surface exposed to a horizontal cross flow was investigated by using a full three-dimensional finite-difference code, local similarity, and a first-order perturbation solution. The full three-dimensional equations were solved by a modified version of the box scheme of Keller and Cebeci. The results indicate that natural convection dominates near the lower leading edge of the surface and at large values of the horizontal coordinate, whereas forced convection dominates near the vertical leading edge and at large values of the vertical coordinate. In comparing the approximate methods of local similarity and first-order perturbation, where the perturbation parameter was taken to be α = gcβ ΔTK/w2∞,, it was found that local similarity yielded more accurate results and required less computer time and programming effort.

ISSN:0149-5720    

DOI:10.1080/10407788208913449

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

An instant nonsimilarity method is proposed for the analysis of unsteady thermal boundary layers. The method is an improvement on the instant similarity method, which assumes that similarity solutions are obtained instantly by deleting time derivative terms that cause nonsimilarity in the boundary-layer energy equation. A basic feature of the nonsimilarity solution is that the nonsimilar terms in the conservation equations are retained without approximation, while those in derived auxiliary equations are selectively neglected. Therefore, more accurate results are obtained. The method is illustrated by analyzing the problems of unsteady laminar forced convection heat transfer from a rotating disk and at the two- and three-dimensional stagnation points due to a step change in surface temperature. The flow is steady and incompressible and has constant physical properties. Numerical results are compared with data from the literature. Excellent agreement is obtained at both short and long times.

ISSN:0149-5720    

DOI:10.1080/10407788208913450

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

The non-Fourier model for heat transfer leads to a hyperbolic evolution problem describing the temperature solution. A one-dimensional case is considered for such a propagating heat wave reflected at a boundary. A primary goal is investigation of the effectiveness of numerical solution techniques for the case of a propagating heat front and the influence of different boundary conditions. Finite elements are employed in space and alternative time integration schemes are studied, including ordinary differential equation system integrators. The effect of solution “roughness” on the error and oscillations before and after reflection is examined and rates of convergence are numerically determined.

ISSN:0149-5720    

DOI:10.1080/10407788208913451

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

Laminar natural and mixed convection around a heated cylinder placed within confining walls is investigated numerically. The numerical scheme involves the use of a cylindrical network of nodes in the vicinity of the cylinder with a Cartesian mesh covering the remainder of the flow domain. Results are obtained for the streamlines, isotherms, and heat transfer coefficients. Effects of varying the ratio of width across the walls to cylinder diameter are also investigated. The results obtained are of direct use, for instance, in the design of certain thermal energy storage devices and ocean thermal energy conversion units under investigation.

ISSN:0149-5720    

DOI:10.1080/10407788208913452

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

The vortex instability of laminar mixed convection flow over isothermal, inclined flat plates is investigated by the linear stability theory. Critical Grashof and Reynolds numbers that predict the first occurrence of vortex rolls are obtained for fluids having a Prandtl number of 0.7 under various buoyancy force intensities and over a range of angles of inclination. It is found that at a given angle of inclination the flow becomes more susceptible to the vortex mode of instability as the buoyancy force increases. However, for a given bouyancy force intensity, the susceptibility of the flow to the vortex mode of instability decreases as the plate is tilted from the horizontal toward the vertical orientation, finally attaining the absolutely stable condition when the plate is vertical. The results are also compared with analytical results for the wave mode of instability.

ISSN:0149-5720    

DOI:10.1080/10407788208913453

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

A polynomial approximation method for the solution of heat transfer by conduction and radiation in an absorbing, emitting, and isotropically scattering medium has been developed. Consideration is given to a one-dimensional system bounded by two parallel gray, diffuse, isothermal walls. A function f(t) representing the relation between incident radiation and temperature is defined and approximated by a polynomial equation over the entire optical thickness. The integrodifferential equation is transformed, by introducing radiation operators, into simple expressions, which are then solved iteratively. The method of solution is shown to be relatively simple and converges very quickly to the exact solutions.

ISSN:0149-5720    

DOI:10.1080/10407788208913454

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

The transient temperature distribution of two semi-infinite media at different temperatures that are suddenly brought into contact is investigated. The effect of thermal radiation in the hot medium is considered. Solutions are obtained by a hybrid technique, using an explicit fourth-order Runge-Kutta method for the time variable and the finite-difference method for the space variable. A variable grid spacing system utilizing hyperbolic sine functions is incorporated to extend the computational boundary as well as to minimize the computation time and the number of nodal points. The technique is shown to be relatively simple and accurate, and illustrative solutions are presented for the transient contact temperature after sudden contact of molten uranium with molten sodium.

ISSN:0149-5720    

DOI:10.1080/10407788208913455

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor