Natural convection effects in solar stills

Abstract

This paper deals with a numerical simulation of natural convection flows in a triangular cavity submitted to a uniform heat flux using the Control Volume Finite Element Method. The aim of the study is to examine the thermal exchange by natural convection and effects of buoyancy forces on flow structure. The study provides useful informations on the flow structure sensitivity to the governing parameters, the Rayleigh number and the tilt angle, on the thermal exchange. In a basin still receiving a uniform heat flux, the results show that the bottom is not isotherm and the flow structure is sensitive to the cover tilt angle. Many recirculation zones can occur in the core of the cavity and the heat transfer is dependent on the flow structure. The results of this study can provide informations for the enhancement of the design of the energy systems such as solar water distillers and air conditioning systems. The physical problem concerns a two-dimensional incompressible fluid flow generated inside a triangular enclosure with isotherm upper walls and heated bottom. The hydrodynamic and thermal fields, the local Nusselt number, the temperature profile at the bottom and at the center of the cavity are investigated for a large range of Rayleigh number. The effect of the upper sides inclination is examined for the particular value of Ra=10 5.