摘要:

A theoretical study of the heating effectiveness of a composite porous radiant burner (PRB) is conducted. A one-dimensional laminar premixed flame model incorporating a radiatively participating inert porous medium consisting of two layers of different properties is used to describe the heat release/transfer processes. Combined conductive, connective, and radiative heat transfer is considered. The spherical harmonics method with die P-3 approximation is used to model the radiation part. A multistep reaction mechanism for premixed methane-air combustion is employed. A parametric study is carried out to determine the effect of the radiative properties of the two porous layers on burner performance. Calculations indicate that a significant improvement in the radiative output of a PRB can be attained by optimizing the burner properties upstream and downstream of the flame. Generally, the upstream layer should be of lower porosity, shorter length, and higher optical thickness than the downstream layer. Also, the upstream layer should be highly scattering, while the downstream layer should be nonscattering.

ISSN:1040-7782    

DOI:10.1080/10407789608913837

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

A set of coupled heat, mass, and pressure transfer equations proposed by Luikov [1] was employed to model the heat, mass, and pressure transfer phenomenon in a capillary porous body. A two-dimensional finite element model was formulated to solve the system of equations. The simulated results agreed well with the exact solutions. The finite element model was then used to study the sensitivity of the parameters in Luikov's heat, mass, and pressure transfer system and to estimate the key parameters identified (the thermal conductivity kqand the coefficient of moisture conductivity km) for Norway spruce. The two-dimensional finite element model was further used to predict the temperature, moisture, and pressure variation during drying of Norway spruce. The mass average moisture content and temperature at the geometric center of a Norway spruce sample were measured at different drying temperatures. The predicted results agreed very well with the experimental results for all of the drying conditions considered.

ISSN:1040-7782    

DOI:10.1080/10407789608913838

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Five algorithms of the Krylov subspace method and three preconditioning techniques art presented. Applications of the Krylov subspace method were illustrated in solving four example problems. The matrix inversion example snowed that the Krylov subspace method can be viewed as a direct method. It was demonstrated that, in solving an example problem of heat conduction with a constant source term, incomplete lower-upper (LU) (ILU) decomposition and polynomial preconditioning could substantially reduce the number of iterations. Also, linear relationships were observed between the iteration number and the equation number. It was also found that double preconditioning using a fifth-order polynomial and ILU decomposition could further reduce the computing time. The generalized minimal residual (GMRES) method with double preconditioning was compared with such iterative methods as alternating direction implicit (ADI) and Gauss-Seidel. The results showed that the GMRES method only required fractions of the computing time required by ADI or Gauss-Seidel method. Example problems of heat conduction with an Arrhenius source term and cavity flow were also solved by the GMRES method with preconditioning. Converged solutions were obtained with one or two iterations for the momentum equation of cavity flow considered, and three to six iterations for the pressure Poisson equation. Further effort seems to be warranted to explore the implementation of the Krylov subspace method for the finite difference modeling of heat transfer and fluid flow problems.

ISSN:1040-7782    

DOI:10.1080/10407789608913839

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Numerical calculations were carried out for natural convection of low-Prandtl-number fluid. These calculations include the inertial terms that were approximated by six kinds of schemes, i.e., upwind scheme, hybrid scheme, second-order central difference method, Kawamura-Kuwahara scheme, Utopia scheme, and fourth-order central difference method. The average Nusselt number depended significantly on the schemes. The occurrence of oscillatory flow also depended on the schemes for inertial terms. Higher order up-winding approximations for inertial terms appear to be required to calculate natural convection of low-Prandtl-number fluids like liquid metal, even if the Rayleigh number is not large enough.

ISSN:1040-7782    

DOI:10.1080/10407789608913840

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The present study is concerned with the buoyancy-driven airflow in an cumulus between two asymmetrically heated horizontal eccentric elliptical cylinders. Flow patterns and heat transfer characteristics for various geometric configurations and heating conditions are predicted. The governing equations are discretized with the finite volume method on a curvilinear grid system generated numerically by the body-fitted coordinate transformation. Dependence of the equivalent conductivity on the physical and geometric parameters, such as the Rayleigh number, the dimensionless eccentricity, and the ratio of the areas of the cylinders, has been evaluated. Results show that, for Ra > 104, the strength of the buoyancy-driven fluid motion as well as the enhancement in the heat transfer becomes appreciable. Among the nine possible geometric configurations considered in this study, case Vv exhibits the highest heat transfer performance. For some special cases, the numerical solutions are compared with existing information, and close agreement has been found.

ISSN:1040-7782    

DOI:10.1080/10407789608913841

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

This article presents a numerical study of upward fluid flow and the corresponding convective heat transfer in a vertical porous annulus. The study investigated the effects of the inertia term, thermal dispersion, variable porosity, variable properties, buoyancy, particle diameter, and fluid pressure on the flow and heat transfer. The heat transfer augmentation produced by the porous matrix was also analyzed. It was found that for the conditions studied, the effect of thermal dispersion and variable porosity had to be considered. For Ree ≥ 5, the flow inertia had nonnegligible influence on the flow field and local heat transfer coefficient near the inlet (x / L ≤ 0.02). When Ree ≥ 400, the flow inertia significantly influenced the overall friction factor in the vertical porous annulus. The porous medium greatly enhanced the heat transfer coefficient and also sharply increased the friction resistance. At supercritical pressures (25 Mpa), variable properties significantly influenced the heat transfer.

ISSN:1040-7782    

DOI:10.1080/10407789608913842

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor