Effect of wall roughness solar chimney absorber on natural ventilation rates

Abstract

In the present study, a numerical analysis of a vertical solar chimney with different shapes of absorber wall is carried out. The absorber wall is structured in four cases. The first case is a smooth wall. The other cases are rough structure cases A, B and C. Case A is a wall with roughness of a triangular profile. Case B is identical to case A but has a curvature profile connection to the base. Case C is a wall with a rectangular roughness and a curve profile at its base. The chimney gap varies from 10 cm to 50 cm, the uniform heat flux is varied from 200W/m2 to 600W/m2 and Rayleigh number changes from 3.9×1012 to 1.2×1013. These cases are tested under isothermal glazing wall boundary condition. The optimum case is tested under adiabatic and convective glazing wall boundary conditions and compared to the isothermal boundary condition. The results show that the air flow rate of case A is higher than that in cases B and C by 6.9% and 3.5%; respectively at heat flux of 600W/m2 and chimney gap of 20 cm. The optimum conditions that maximize air flow rate in a solar chimney of case A is obtained at chimney gap of 40 cm compared to the other gaps at all heat fluxes. For case A at heat flux of 600W/m2 and chimney gap of 40 cm, the mass flow rate increases by 71.9%, 52.8%, 21.9% and 2.5% than chimney gaps of 10 cm, 20 cm, 30 cm and 50 cm; respectively. The solar chimney of rough absorber wall case A shows backflow at chimney exit for a gap of 50 cm in the isothermal boundary condition compared to the other boundary conditions. A higher air flow rate is obtained in an adiabatic glazing wall condition while lower air flow rate is obtained in the condition of isothermal glazing wall.