Numerical simulation of natural convection and condensation of humid air in a partially divided square cavity.
Résumé
Conjugate heat transfer by transient natural convection, conduction and surface condensation in a fully partitioned cavity in contact with a cold external ambient through a wall of finite thickness is numerically studied. The horizontal end walls are assumed adiabatic, and the hot vertical wall is kept at a constant and uniform temperature. A two-dimensional, double-diffusive, weakly compressible laminar flow of humid air is considered. Normal interface velocity components due to the concentration gradient at the surfaces are accounted for in the calculation of the mass of water vapor condensed. Owing to the temperature and mass fraction differences involved, the analysis is based on a low-Mach number formulation in order to account for the changes in mixture mass and thermodynamic pressure within the partitioned enclosure between the initial and steady states. Computations were carried out by using a finite volume method and focused on the effects of the fluid-to-partition thermal conductivity ratio (σ) and initial relative humidity (φ0). The heat and mass transfer with condensation are compared for conductivity ratio in the range 1 ≤ σ ≤ 103. Three initial humidities are then examined for a fixed conductivity ratio (σ = 10) to study the effects of condensation on the heat and mass transfer rates. It is shown that the conductivity ratio has a weak influence on the mass of water vapour condensed within the cold cell. A transient analysis on the effects of the initial relative humidity on the flow field and overall heat and mass transfer rates shows a much more appreciable effect.