numerical investigation of the spiral solar air heater performance

This paper presents a new design of a spiral solar air heater with a 90 turning of the air inside the passageway assembled between the absorber and bottom plate for the purposes of mixing process and extending the surface of heat transfer that finally leads to higher performance. to enhance the thermal efficiency, an air gap is considered at the top of the solar collector to reduce heat loss. the proposed solar collector is simulated numerically by the finite element method using the comsol software. the set of governing equations for both forced and free convection turbulent air flows are solved based on the rng k–ε turbulence model. in the energy equation solution, the effect of surface-to-surface radiation as an important phenomenon in solar collectors is considered. numerical results reveal a high thermal efficiency of 75% for the test case with 100  solar heat flux and air mass flow rate of 0.01 kg/s. compared to the conventional smooth duct solar air heater with 35% thermal efficiency, the designed solar collector operates with higher performance, and a more than 100% increase in thermal efficiency is achieved due to the applied technique with the limitation of pressure drop which is increases about three times in spiral solar air heater.