Thermal analysis on porous evaporation composite wall integrated with solar chimney

Abstract

This paper introduces a composite wall integrated with a solar chimney and a wet porous layer for evaporation cooling without consumption of electrical power, in which the airflow is driven by the buoyancy force from solar chimney effect, and water for evaporation on surface is supplied by capillary forces in wet porous layer. A numerical study on heat and mass transfer in composite wall was conducted to analyze the impact of environmental conditions and composite wall structure on cooling performance. More convection between airflow and surface of porous layer under higher solar irradiation, and larger evaporation on surface of wet porous layer under lower relative humidity benefits for cooling to be obtained. The 3.3 or 2.1 K smaller temperature of indoor surface of composite wall below ambient occurs at about 12:30 in a sunny day. The effective cooling and cooling efficiency are defined to be evaluated the cooling performances in composite wall. The solid matrix material, thickness and porosity of wet porous layer relating to its thermal resistance and thermal capacity, as well as channel width and window-to-wall ratio relating to effects of airflow amount and evaporation surface size influence effective cooling and cooling efficiency greatly. The higher cooling and lower cooling efficiency occur in case with thinner porous wall at initial stage, and the cooling efficiency increases in case with thicker porous wall with thickness above 0.1 m. The larger cooling and lower cooling efficiency occur in cases with smaller channel width or window-to-wall ratio. All these results should be taken into account for the utilization of the porous evaporation composite wall integrated with solar chimney.