Combined Action of Gas Radiation and Airfoil Shaped Ribs in Improvement of Solar Heater Performance

A novel design of solar air heater is proposed in this paper based on the simultaneous exploitation of radiating gas and also airfoil-shaped ribs. Using participating gases with high radiative characteristics concerning the usual working gas, namely air, could show a more promising improvement in thermal performance, especially while this technique is combined with extending surface area. This new concept is demonstrated by simultaneous solution of the radiative transfer equation considering both the diffuse and collimated beams coupled with momentum, energy, and continuity equations. The set of governing equations are solved using the finite element method in a steady-state condition by the COMSOL Multi-physics. The well-known  model is used in calculations of turbulent stress and heat flux in numerical simulation. Through the presented results, radiative gas proved its full potential to serve as a future working gas in solar gas heaters. Its combination with the airfoil-shaped ribs shows magnificent 88% thermal efficiency and gas outlet temperature up to 85°C in the test cases. The contributions of airfoil-shaped ribs and also the gas radiation to increase thermal performance are computed equal to 7% and 66%, respectively.