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Details for article 15 of 16 found articles
| Title: |
THERMAL TAYLOR DISPERSION PHENOMENA IN NONADIABATIC SYSTEMS |
| Author: |
Batycky, Richard P. Edwards, David A. Brenner, Howard |
| Appeared in: |
Chemical engineering communications |
| Paging: | Volume 130 (1994) nr. 1 pages 53-104 |
| Year: |
1994 |
| Contents: |
This paper outlines or general 'one-dimensional' theory of convective-conductive internal energy transport phenomena in complex, multidimensional, nonadiabatic systems whose rate of heat loss to their surroundings is characterized by a 'Newton's law of cooling' heat transfer coefficient h. Taylor dispersion theory is used to effect the coarse-graining ofthe microscale thermal problem, therby producing an effective-medium theory of the mean thermal transport process. Both ducts ('continuous' systems) and model packed beds (spatially periodic systems) are analyzed. Expressions are derived for the macroscale thermal propagation velocity vector U¯* and effective thermal dispersivity dyadic α¯* in terms of the prescribed microscale data. Additionally, an expression is obtained for a third macrotransport coefficient, H¯*, representing the effective or overall macroscale heat transfer coefficient, and distinct from the microscale heat transfer coefficient h. (This is the same type of quantity as arises in so-called 'fin' problems.) Furthermore, it is shown that when solving the nonadiabatic macrotransport equation Jot the mean temperature T¯, parameterized by the effective-medium phenomenological coefficients H¯*, U¯* and α¯*, it becomes necessary to employ a fictitious mean initial temperature distribution in place ofthe true one. A paradigm is developed for calculating this fictitious mean initial temperature field from the prescribed initial microscale temperature field By way of example, calculations are presented for flow in a circular tube with heat loss to isothermal surroundings. In addition to providing numerical values for H¯* in terms of the pertinent microscale phenomenological data, these calculations show that U¯* and α¯* for nonadiabatic systems may differ sensibly from their adiabatic counterparts (calculated in two previous papers), as they now also depend funaionally upon the heat transfer coefficient h. Numerical results are also presented for the Darcy-scale thermophysical parameters H¯*, U¯* and α¯* for two-dimensional pressure-driven flow through model packed beds composed of periodic arrays of circular cylinders. For both duct and porous media flow problems, the thermal propagation velocity vector U¯* is shown to differ from the mean fluid velocity vector V¯—that is, the mean velocity ofthe carrier fluid. Depending upon particular circumstances, | U¯* | may be larger or smaller than | V¯ |. |
| Publisher: |
Taylor & Francis |
| Source file: |
Elektronische Wetenschappelijke Tijdschriften |
Details for article 15 of 16 found articles
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