Experimental analysis and numerical modeling of solar air heater with helical flow path

In the present research, effect of helical channeling on the performance of a solar heater is investigated both experimentally and numerically. The innovation of this research is designing a triangular cross-section channel, in such a way to establish a helical air flow through the air heater, in which the flow exchanges heat with the bottom and the top of the absorber plate. Once finished with measuring various thermal parameters of the system experimentally at two different flowrates, overall heat transfer coefficient and thermal efficiency of the system are calculated. It is followed by numerical modeling of the flow inside the air heater which has 3% maximum error compared to experimental data. The results indicate that, the average thermal efficiency of a double pass solar air heater with helical channeling is estimated 14.7% higher than simple duct and 8.6% higher than double pass-finned solar air heaters with the same mass flow rate. For the mass flow rate of 0.026 kg/s the day average of overall heat transfer coefficient and thermal efficiency of the system are obtained 65.14 W/m2 K and 55.4% respectively. Numerical aspect shows that Vortexes are formed at turning points inside the air heater, increasing heat exchange and pressure drop locally. Furthermore, as far as the application of the air heater in dryers is concerned, one can use nitrogen rather than air to maintain quality of the product while achieving the same heat exchange performance.