Transfert couplé de chaleur et de masse par convection mixte avec changement de phase dans un canal
This thesis deals with a numerical study of laminar, mixed convection flow associated with mass transfer and phase change in a parallel plate channel. The plates are maintained at a constant uniform temperature and the lower plate is covered by thin liquid water film. The liquid film is assumed to be extremely thin and its temperature is equal to the wall temperature. A 2D fully elliptical model, associated with the Boussinesq assumption, is used to take into account axial diffusion. The solution of this mathematical model is based on the finite volume method and the velocity-pressure coupling is handled by the SIMPLER algorithm. Combined buoyancy forces effects on laminar mixed in symmetrical isothermal channel were investigated. Results show that buoyancy forces have an important effect on the hydrodynamic field as well as on the heat and mass transfer characteristics. Thus, for cold plates and an upward hot air flow, these forces induce a flow reversal near the plates for high air temperatures and mass fractions. Additionally, heat transfer associated with phase change (i.e. latent heat transfer) is more important compared with sensible heat transfer. Flow reversal was investigated in symmetrical isothermal vertical channel and asymmetrical isothermal inclined channel. For the inclined channel, only the lower plate is wetted by a thin liquid water film while the other one is impermeable. We discuss the effect of the buoyancy forces on the hydrodynamic, heat and mass fields. Thus, these forces induce a flow reversal when there intensities are important. It is established that heat transfer associated with phase change is, sometimes, more significant than sensible heat transfer. Furthermore, this importance depends on the mass fraction gradient. The conditions for the existence of flow reversal are presented in charts and analytical expressions. These charts specify the critical thermal Grashof number as a function of the Reynolds number for different values of the solutal Grashof number and different channel inclinations.
- Génie – Thèses