Assessment of Heat and Mass Transfers by the Evaporation of a Large Impoundment under Dry and Hot Climate: Case of Burkina Faso

Abstract

This paper aims to report a numerical study of the assessment of heat and mass transfers by evaporation of a large impoundment under Burkina Faso climate conditions. This impoundment is considered as a parallelepiped which upper face, in contact with the ambient environment and subject to solar radiation, is the seat of a natural convection-based evaporation. The intensity of this evaporation is modeled by a correlation in the literature. Transfers into water are made by natural convection. They are caused by temperature differences due to solar radiation and ambient conditions (wind, hygrometry of the air,) on water. These transfers are described by the Navier-Stokes equations and energy and the initial and boundary conditions associated with them. The finite volume method and the SIMPLE algorithm were used for speed-pressure coupling. The systems of algebraic equations deduced from the discretization of transfer equations and boundary conditions associated with them are solved with Thomas’ algorithm, the SIMPLE algorithm and an iterative procedure because evaporated water quantity depends on the temperature and concentration of water vapor at the surface of the impoundment which are the unknowns of the problem. The numerical model developed is validated in relation to previous work and experimental data from Burkina Faso meteorology. The results obtained concern the evolution of the evaporated water flux under dense solar flows, a relative humidity of the air proportional to the wind speed and also the evolution of the evaporated water flux against the solar flux density for high relative moisture content. Also the evolution of the evaporated water flow against the depth of the impoundment for a solar flux density, relative humidity and the temperature of the surface of the body of water is given. The determination of evaporated water flux for typical years was calculated on a 10-year period. The results obtained show that the flux of evaporated water increases with a high solar flux rate and decreases for a high relative humidity level.