Numerical investigation of natural convection solar air heater with different fins shape

In this paper, natural convection of air in solar air heaters with rectangular, triangular and elliptical fins is numerically investigated. Finite volume method is used to discretize the governing equations in the three dimensional domain, the Realizable K-ε model is used for closing the turbulence equations and Business model is utilized for simulating buoyancy force. Effect of inclination angle on mass flow rate and thermal performance of solar air heaters is studied. The results showed that Optimum angles to obtain the highest mass flow rate occur in the range of 45o<β<60o for triangular and elliptical fins and 50o<β<75o for rectangular fins. Also the reverse flow angle of inclination, beyond which the solar air heater is not able to deliver hot air is obtained for different fin shapes. The results showed that rectangular fin lead to the narrowest range of applicable inclination angles (45o<β<90o) and the widest range belongs to the elliptical fins with the range of 33.75o<β<90o. Results revealed that the solar air heater with rectangular fins has the best thermal performance and yet the lowest mass flow rate. Also the results revealed that thermal performance of solar air heaters with rectangular fins is slightly higher than that of heaters containing two other fin shapes in the same dimensions.