Experimental investigation on phase change material based thermal storage system for solar air heating applications

Many types of solar air heaters have been developed in India and their performance has been studied in detail. In solar dryers the drying process largely depends on the varying local weather conditions, resulting in a poor quality of the dried product. To eliminate the fluctuations in the temperature of the hot air, solar collectors are integrated with the Phase Change Material (PCM) based thermal storage unit. The present study is aimed at investigating the feasibility of using a latent heat storage unit with HS 58, an inorganic salt based phase change material, to store the excess solar energy, and release it when the energy availability is inadequate during poor weather conditions, and to extend the period of utilisation beyond the sunshine hours. Experiments were conducted to evaluate the charging and discharging characteristics of the storage unit. The effects of inlet flow rate during the charging and discharging processes were measured and reported. For the storage tank configuration and PCM ball size considered in the present investigation, the mass flow rate of 200 kg/h is able to provide a near uniform rate of heat transfer during charging and discharging processes. Further, low mass flow rate is able to utilise the maximum capacity of the storage system and to supply heat for a longer duration.

► Collector efficiency is higher at higher mass flow rates.
► Low mass flow rate is preferred for uniform heat flux for longer duration.
► Maximum capacity of the storage is utilized at low mass flow rate.
► Selection of PCM with suitable phase change temperature avoids over heating of air.