Transferts simultanés de chaleur et de masse en convection mixte confinée
Goni Boulama, Mahaman Kiari
The effects of thermal and solutal buoyancy forces on a laminar, steady state flow of a binary gas mixture between two large and inclined parallel plates are investigated. Great attention is paid for the proper formulation of the governing conservation equations. Thus, usually omitted terms such as the axial diffusion of momentum, energy and chemical species are incorporated in the model.The resolution has been performed via a numerical code based on the finite volume method. This code is first thoroughly validated by a series of tests and comparisons with available results. Different combinations of the boundary conditions have been considered and the corresponding solutions are presented and discussed. It has therefore been shown that species diffusion and channel inclination significantly influence the velocity, temperature and species concentration profiles as well as the pressure drop and the heat transfer processes. Under certain conditions, flow reversal has been observed. On the other hand, an exact analytical solution has been derived for the fully developed flow region and for the combinations of boundary conditions of the numerical study. In the case of first kind thermal and solutal wall conditions, the solution is expressed as a function of the unique parameter (Gr[subscript T]* + Gr[subscript M]*)/Re which combines the two buoyancy effects as well as the channel inclination. However, when the walls are subjected to uniform heat fluxes and uniform species concentrations, the solution is a function of three independent parameters (Gr[subscript T]*/Re, Gr[subscript M] */Re and q[subscript 1] / q[subscript 2]). In all cases, the precise flow reversal criteria, the flow field profiles and the asymptotic values of the friction factors, the Nusselt and Sherwood numbers have been obtained, thereby providing a straightforward validation for the above numerical observations. This analytical solution has also been utilized in order to identify the sources and to calculate the amount of irreversible losses encountered in such flows. This thesis also presents an approximate analytical solution for the one-dimensional evolutions of the dependent variables in a direct-contact heat and mass exchanger with evaporation or condensation.The proposed solution is based on truncated power series expansions and is less restrictive than all currently available such studies.
- Génie – Thèses