Numerical study and optimization of the new concept of a solar air heater with a closed-cycle heat recovery system

Abstract

The increased efficiency of solar air heaters has been of great importance in recent years. In this study, the effects of environmental parameters on the performance of a new generation of combined solar air heaters were investigated. Using a novel method in an optimization algorithm, the mixing ratio of fresh air and heated air from this type of heater’s reheat system was optimized. The differential equation was modified for this geometry and boundary conditions. As part of the study, the heat recovery system and the preheating of inlet air were applied to increase the efficiency of the air heater. A version of the air heater with a heat recovery system and a version without one were analyzed using Reynolds numbers in the range of 1000 to 8000. In addition, the recovery and preheating cycles were set to close and open, respectively. Note that an air heat exchanger is responsible for transferring the recovery system’s fluid energy to the air heater inlet fluid. The calculations of the numerical modeling of air heaters and closed-cycle recovery systems were independently performed in this study. The research study’s results showed that adding a recovery system to a solar air heater increased the efficiency and the Nusselt number by 15.23% and 7.8%, respectively. The mean temperature of the air heater was dependent on the mixing rate between fresh inlet air and heated air in the heat exchanger in the recovery cycle. In addition, the results indicated that through optimization, the Nu could be increased up to 23%.