摘要:

An optimal design strategy is developed for the Bridgman crystallization process through the formulation of a nonlinear program. The objective function and constraints are designed to optimize the conditions for the growth of crystals with nearly flat melt-crystal interfaces. The decision variables are the temperatures of the hot and cold zones, the size of the thermal barrier, and the thickness of the crucible. The equations for momentum and energy transport in the melt, for conduction in the crystal and crucible, and the energy balance at the melt-crystal interface are solved using finite elements. The nonlinear program is solved using the controlled random search technique. Results are presented for the growth of GaAs crystals.

ISSN:1040-7782    

DOI:10.1080/10407789608913790

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The dual reciprocity boundary element method (DRBEM) is implemented to solve three-dimensional transient heat conduction problems in the presence of arbitrary sources, typically as these problems arise in materials processing. The DRBEM has a major advantage over conventional BEM, since it avoids the computation of volume integrals. These integrals stem from transient, nonlinear, and/or source terms. Thus there is no rued to discretize the inner domain, since only a number of internal points are needed for the computation. The validity of the method is assessed upon comparison with results from benchmark problems where analytical solutions exist. There is generally good agreement. Comparison against finite element results is also favorable. Calculations are carried out in order to assess the influence of the number and location of internal nodes. The influence of the ratio of the numbers of internal to boundary nodes is also examined.

ISSN:1040-7782    

DOI:10.1080/10407789608913791

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

A numerical investigation has been carried out for conjugate forced convection heat transfer in tubes with multiple obstructions. The investigation included the ranges of Reynolds number Re, thermal conductivity ratio kr, and the distance between two obstructions d of 50-600, 0.3-3.0, and 2.0-8.0, respectively. A fluid Prandtl number Pr of 7.56 is used. The obstructions create recirculation flow / back flow in the tube with increase and decrease of local heat transfer rates. Reversal in the direction of heat transfer occurs at certain locations of the tube due to the presence of the obstructions. At high values of Re and d, reversal in the direction of heat transfer occurs on the outer wall after the second obstruction. The overall heat transfer rate decreases with the decrease of kr.

ISSN:1040-7782    

DOI:10.1080/10407789608913792

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The phenomenological analysis of free surface transport through porous media is presented. A finite difference scheme using the Marker and Cell (MAC) method is employed to investigate the momentum and energy transport in a porous channel involving free surface transport phenomena. To the best of the authors' knowledge, this is the first investigation of free surface momentum and energy transport through porous media and is also the first application of the MAC method for exploring the free surface transport phenomena in a porous medium. Limiting case comparisons are made with an existing analytical solution for flow through a channel filled with a porous medium. Excellent agreement is obtained for both the temperature and velocity distributions. Temporal free surface positions are also compared and verified against an existing analytical solution. A detailed analysis of the encroachment of two immiscible fluids in a porous channel using Darcy's model is presented. The effects of pressure differences and permeabilities on free surface transport through a porous medium are investigated. The effect of the free surface transport in porous media on the energy transfer is also explored.

ISSN:1040-7782    

DOI:10.1080/10407789608913793

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Heat transfer is examined for channel flow of mixed convection between two parallel plates with two hot blocks within. The numerical method SIMPLE-C is used. The influence on flow field and heat transfer capacity with respect to elevations of two hat blocks is investigated. The elevations of and distance between hot blocks are varied in an attempt to understand their influence on mixed convection. The Reynolds, Richardson, and Prandtl numbers are also varied in order to study the influence on flow field and temperature distribution. It is observed that heat transfer capacity increases as the distance between two hot blocks increases. For different arrangements, to make heat transfer of the second hot block be independent of the first, the distance varies. However, such distances can be reduced dramatically with a staggered arrangement. The heat transfer capacity increases effectively with increasing Reynolds number. Heat transfer and flow type are greatly affected by various fluids.

ISSN:1040-7782    

DOI:10.1080/10407789608913794

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The laminar mixed convection in the entrance region of horizontal straight ducts of an annular cross section is studied by means of a generally applicable finite element procedure based on the parabolized simplification of the Navier-Stokes and energy equations and on the Boussinesq approximation of the buoyancy term. The procedure is validated through comparisons of computed results with available data from the literature. New results concern annuli with radius ratios equal to 0.25, 0.5, and 0.75 subjected to the fundamental boundary condition of the second and the third kinds, for Prandtl numbers equal to 0.7 and 7, and different values of Grashof number.

ISSN:1040-7782    

DOI:10.1080/10407789608913795

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

ISSN:1040-7782    

DOI:10.1080/10407789608913789

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor