STAGNATION POINT FLOW OF A CHEMICALLY REACTIVE FLUID IN A CATALYTIC POROUS BED

The heat transfer and reaction characteristics of a chemically reactiv e Bow near the stagnation point of a catalytic porous bed with finite thickness are investigated theoretically. Due to the catalytic effect, the activation energy is reduced such that chemical reaction in the b ed becomes possible even at relatively low flow temperatures. The stea dy state and initial transient period in the gas phase upstream and in the catalytic porous bed are studied using both the singular perturba tion method and the finite difference method. For the perturbation ana lysis, a single layer model is sufficient when the bed is relatively t hin, of the order of the characteristic thermal diffusion length scale . For a thick bed, a multiple layer analysis is necessary. Results fro m the steady-state analysis show that for a higher chemical reactivity , lower flow velocity gradient, lower activation energy, and lower mas s diffusion rate, the conversion rate from reactants to products is hi gher so that a thinner bed can be used to reach complete reaction. Mor eover, due to the high thermal conductivity of the solid porous materi al, temperature profiles are modified by the heat release through chem ical reaction only slightly for a thin bed. The flow temperature is af fected by the reaction more significantly for a thicker bed because mo re heat is released from the reaction, and the increased importance of convection effect. Numerical results for the transient case exhibit t he same characteristics as in the steady state. Copyright (C) 1996 Els evier Science Ltd.