Performance investigation of a lab-scale latent heat storage prototype - Experimental results

This paper presents the performance tests carried out on a lab-scale latent heat storage (LHS) prototype during charging and discharging processes. The storage unit is a shell-and-tube type heat exchanger with embedded finned tubes, designed for an LHS capacity of 10 MJ. A ternary mixture comprising of potassium nitrate, sodium nitrate and sodium nitrite in the weight proportion of 53:7:40 is used as the phase change material (PCM). Hi-Tech Therm 60 is used as the heat transfer fluid (HTF). Performance parameters viz., melt fraction, charging/discharging time and energy storage/discharge rate were evaluated at different operating conditions. The effects of HTF inlet temperature and flow rate on the storage characteristics of LHS prototype were analyzed. It is observed that the temperature variation in the angular direction of the prototype during charging process is significant. This is due to the natural convection heat transfer that occurred around the molten layer of PCM while melting. During the discharging process, the angular temperature variation is negligible as the solidification phenomenon is controlled mainly by the conduction heat transfer. It took about 124 min/131 min for charging/discharging of the LHS prototype.