Performance augmentation of solar air heater using absorber with multi-functional encapsulated PCM tubes

Abstract

Under fluctuating solar radiation, attaining higher air temperatures for an extended period using solar air heaters (SAH) is challenging. The current study deals with the heat transfer enhancement of a SAH using an absorber with phase change material (PCM). The proposed SAH has an absorber of aluminum sheet with inclined and stagger-arranged multi-functional heat storage tubes encapsulated with PCM. Experiments were conducted using commercial paraffin wax as PCM at varying air flow rates of 0.01 kg/s, 0.02 kg/s, and 0.03 kg/s, and results are compared with SAH with a plain absorber. The SAH using heat storage yields higher air temperature and energy efficiency than the plain absorber. The attained peak air temperature for PCM-integrated and plain absorbers is 64 °C and 58 °C at the airflow rate of 0.01 kg/s. SAH's average heat transfer coefficient at 0.03 kg/s with PCM is 27.7 W/m2K, which is 252 % higher than the plain absorber. The energy efficiency of the proposed SAH is higher due to higher useful energy absorption and lower heat loss. Maximum energy efficiency for the SAH with the proposed and plain absorber is 77.7 % and 62.5 %, respectively, at 0.03 kg/s. The improved thermohydraulic efficiency illustrates that increased heat output counterweights the pressure drop penalty. The proposed absorber has a more significant annual useful energy cost and a shorter payback period than the plain absorber. Thus, the present study of SAH with PCM could help attain higher outlet air temperature by minimal investment towards sustainable development.