摘要:

The present work examines mathematical modeling and simulation of drying and pyrolysis of porous media. The equation system presented is basic for modeling of heat and mass transfer in porous media when drying and pyrolysis appear. The set of differential and algebraic equations is discretized in space by first-order upwinding and central differencing, and is integrated in time by the differential/algebraic equation solver named DASSL. The developed program system is tested by simulating drying and pyrolysis of wood, and hence necessary submodels for the transport and physical properties of wood are given. The simulations are done for one-dimensional transient problems in Cartesian coordinates. Two examples are shown, one with pure drying at moderate temperature and one with combined drying and pyrolysis at high temperature.

ISSN:1040-7782    

DOI:10.1080/10407789608913796

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

This article proposes a model for estimating the effect of the overall thermal resistance of the absorber and the coolant on a solar thermal energy system utilizing advanced heat transfer mediums. Two equations can be used to model a dynamic system: one for the maximum conversion efficiency and one to specify the constraint that, in quasi-steady state, the net energy collected must be transferred to the coolant. These two equations define a constrained optimization problem in two variables, the fluid and the absorber temperatures. The results present interesting implications for liquid metal, direct absorption, and solar evaporating systems.

ISSN:1040-7782    

DOI:10.1080/10407789608913797

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

A numerical method has been developed for the prediction of coupled heat and mass transfer and related processes in porous media exposed to elevated temperatures. The computer model predictions have been validated against experimental results of carbonate aggregate concrete slabs subjected to the ASTM E119 standard fire exposure. Output from the model depicts the coupled relationships between the temperature, moisture content, and pore pressure histories and distributions. This article investigates the numerical effect of grid spacing on the pore pressure fluctuations and the influence of the pore pressure on the spalling potential of concrete exposed to elevated temperatures.

ISSN:1040-7782    

DOI:10.1080/10407789608913798

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

We study numerically the steady state laminar mixed convection around a sphere heated by a nonuniform flux in a Newtonian fluid. The sphere rotates around its vertical axis. The governing transfer equations in this three-dimensional problem are solved by using the method of Cebeci-Keller. Three types of convection are considered: pure rotation, pure natural convection, and mixed convection. The profiles of the coefficients of heat transfer and local friction, as well as the profiles of temperature, will be determined for various distributions of a heat flux. In the case of a two-dimensional problem, our results agree with those in the literature.

ISSN:1040-7782    

DOI:10.1080/10407789608913799

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

An anisotropic two-equation model is proposed to determine turbulent heat flux in a channel flow up to the wall. The turbulent heat fluxes are given in the form of an anisotropic eddy diffusivity representation in which both the isotropic and anisotropic eddy diffusivities of heat are expressed using the temperature variance $t2$, the dissipation rate of temperature fluctuations ϵt, and the velocity gradient. The proposed model is tested through application to an incompressible, two-dimensional, turbulent channel flow with the neglect of buoyant heat transfer. Calculated results are compared with the direct numerical simulation data. It is disclosed from the study that the proposed anisotropic $t2$-ϵt, heat transfer model predicts reasonably well the distributions of the time-averaged temperature, normal and streamwise turbulent heat fluxes, temperature variance, dissipation rates, and these near-wall budgets.

ISSN:1040-7782    

DOI:10.1080/10407789608913800

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor