摘要:

A newly developed two-phase mixture model is applied, in conjunction with a control-volume-based finite difference method, to numerically investigate boiling with thermal convection in a porous layer heated from below. The numerical procedure employs a fixed grid and avoids tracking explicitly the moving interface between the liquid and two-phase regions. Numerical results are obtained to shed light on the intricate interactions between boiling and natural convection as well as to explain experimental observations. Four distinct flow patterns that were observed in previous experiments are predicted. A quantitative comparison of the predicted and measured vapor volume fraction in the porous bed shows good agreement. The numerical results also agree with published linear stability results. In addition, the present study documents the effects of important parameters such as Rayleigh number, bottom heat flux, and aspect ratio.

ISSN:1040-7782    

DOI:10.1080/10407789408955999

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The present paper deals with non-Darcian, forced convection, boundary layer flow over a wedge with a variable free stream, taking into account the effects of connective inertia, solid boundary, and porous inertia as well as Darcyflow resistance. Three novel methods, namely, the extended series method together with Shanks' transformation, the local nonsimilarity method, and the finite difference approximations combined with the Keller box method, are employed to integrate local nonsimilarity momentum and energy equations governing the flow. The results thus obtained are compared with the local skin friction and the local Nussett number at the surface. Effects of different physical parameters on the local rate of heat transfer coefficient against the Darcy drag parameter ξ are examined for fluids of Prandtl number σa ranging from 0.7 to 100.0.

ISSN:1040-7782    

DOI:10.1080/10407789408956000

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A hybrid adaptive gridding procedure is applied to the computation of two-dimensional, turbulent, recirculating flows. The procedure combines both the local refinement method and the global moving grid method. The moving grid method is applied to obtain the initial adaptive solution. The local refinement method is then used on the targe error regions flagged by using the weight function approach. The test cases are a backward facing step flow, a two-dimensional side jet flow, and an axisymmetric swirling flow. By comparing with the fine uniform grid solution, the numerical efficiencies ranging from 20 to 40 are obtained in these test problems. The most attractive feature of the procedure is its ease of application.

ISSN:1040-7782    

DOI:10.1080/10407789408956001

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Laboratory and numerical experiments were conducted in order to study the flow within an isothermal parailelepipcdic test room. The air is injected through a complex diffiiser (made of 84 nozzles) near the ceiling and is evacuated through a rectangular exit just below the inlet. Measurements were performed on a hydraulic model at 1/6 scale. The parameters were determined according to a Reynolds similitude. Both laser Doppler anemometry and flow visualization were used. Numerical simulations were carried out using the EOL-3D software developed at the Institute National de Recherche et de Sécurité. A comparison between experimental results and numerical predictions is presented.

ISSN:1040-7782    

DOI:10.1080/10407789408956002

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A general applicable method is presented to determine conductivity properties of repetitive heterogeneous structures from the material properties of their constituents. The method is an extension of an analysis given by Rayleigh and is demonstrated to determine the global conductivity of a regularly perforated brass plate used as a flat-flame holder. The method is also applicable to other analogous transport properties in a wide variety of geometrical configurations.

ISSN:1040-7782    

DOI:10.1080/10407789408956003

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The countercurrent flow of gas and water in a short horizontal pipe is studied numerically with a two-phase flow model. It is observed that the onset of flooding cannot be predicted at low liquid flow rates using conventional one-dimensional equations. The conventional equations yield the same underestimated results as the Taitel-Dukler criterion. Utilizing physical reasoning, improved equations have been derived. The basic idea is that the distribution of the phase velocities should not be treated as uniform in the cross-sectional area occupied by phases but transverse dependencies for the velocities should be allowed. By comparing measurement data and calculated results, it is shown that flooding transition can be predicted accurately with these equations.

ISSN:1040-7782    

DOI:10.1080/10407789408956004

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

This paper presents a numerical analysis of natural convection-dominated melting from a wall of finite conductance. A computational methodology based on a stream function / vorticity / temperature formulation is presented. The irregular shape of the moving solid-liquid phase front is treated with generalized curvilinear coordinates. The model is then employed to investigate the interaction between convection in the cavity filled with phase change material (PCM) and conduction in the heated wall. Experiments are carried out for Rayleigh numbers between 2.03 × 105and 4.60 × 109, wall-PCM thermal diffusivity ratios α between 1.0 and 1000.0, and dimensionless wall thicknesses w between 0.005 and 0.25. The results indicate that for α < 10 and increasing wall thickness, conduction plays a significant role in the melting process. It delays the onset of buoyancy-driven convection and, as a result, slows down melting. In return, buoyancy-driven motion of the melt influences conduction heat transfer across the wall.

ISSN:1040-7782    

DOI:10.1080/10407789408956005

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor