Experimental Investigation on Heat Transfer Enhancement of Latent Heat Storage System Containing Spherical Capsules with Internal Hollow and Solid fins

Latent heat storage has high storage density with a smaller temperature swing. However many practical problems are encountered. A common problem in latent heat thermal storage is the poor conductivity of the phase change materials (PCMs). To increase the heat transfer rate and to reduce the charging time, extended surfaces such as fins are used. In the present work experiments are conducted to study the performance of latent heat thermal energy storage system (LHTS) to store heat energy in PCM (Paraffin) filled spherical capsules provided with following fin configurations: a) Internal hollow cylindrical fins, b) Internal solid cylindrical fins and c) No fins. Paraffin with a melting point of 61 degrees C was used in the investigation because it is appropriate for thermal storage applications. Water is used as heat transfer fluid (HTF) to transfer heat from source to TES tank. Time-based variations of the temperature distribution for HTF and PCM have been studied for different configurations of spherical capsules, different flow rates & inlet temperature of HTF. It is observed that when HTF inlet temperature is varied from 65 degrees C to 70 degrees C the charging time is reduced by 25% for without fins, 28% for internal hollow cylindrical fins and 23% for internal solid cylindrical fins. When flow rate is varied from 4 lpm to 6 lpm for same HTF inlet temperature of 70 degrees C charging time is reduced by minimum percentage. The performance parameters such as instantaneous heat stored, cumulative heat stored and system efficiency are also studied.