Heat and mass fluxes in the presence of fast exothermic superficial reaction

In this paper heat and mass transfer phenomena are studied in a catalytic monolith with a fast exothermic reaction taking place at the walls at fully developing laminar flow for different values of the kinetic parameters. A two-dimensional model has been adopted to simulate the behaviour of the monolith reactor. The unsteady Navier-Stokes equations have been discretized by adopting the control volume approach and solved by means of the CFD-ACE+ package. The model surface reaction is parametrically varied to account for the effects of the perturbation generated by heat production associated with the reaction on flow field, temperature and concentration profiles and then on transport. Results show that Nu and Sh trends are not monotonic functions but that there exists a transfer enhancement due to the perturbation of the flow field. This increase is shown to be dependent on the kinetics parameters of the surface reaction. We show that the definition of the new driving force we previously proposed, which relates the transfer coefficients to the adiabatic temperature rise, is also able to describe the effect of the kinetic parameters if the pre-exponential factor and the activation energy are included in the correlation.