Performance of a medium temperature eutectic solder packed bed latent heat storage system for domestic applications

Abstract

Abstract A packed bed latent heat storage system consisting of aluminum encapsulated eutectic solder (Sn63Pb37) capsules is experimentally evaluated during charging and discharging cycles. Sunflower Oil is used as the heat transfer fluid in the experiments. The effect of the flow-rate on the charging performance is evaluated using three charging flow-rates namely; 4 ml/s (low), 6 ml/s (medium) and 8 ml/s (high). The storage system is also evaluated with three different set heater charging temperatures (260 °C (low), 280 °C (medium) and 300 °C (high)). Discharging experiments are performed with the three different flow-rates to evaluate the effect of the flow-rate on the discharging characteristics. Charging and discharging results are presented in terms of the axial storage tank profiles, the energy rates and the exergy rates. The overall performance of the storage system is evaluated in terms of the energy and exergy storage efficiencies. The charging energy and exergy rates are seen to increase with the charging flow-rate at the expense of a greater charging duration since higher flow-rates tend to cool down the heater. The best charging flow-rate of 6 ml/s is suggested which ensures a reasonable duration of charging, reasonable thermal stratification and reasonably high energy and exergy charging rates. The effect of the set heater temperature on the charging energy and exergy rates is insignificant as compared to the effect of the flow-rate. The best set charging temperature of 280 °C is also suggested by the experimental tests. Increasing the flow-rate results in faster heat transfer with higher peak energy and exergy rates during discharging. However, the stored energy and exergy is utilized for a shorter duration as compared to the lowest flow-rate. Energy and exergy storage efficiencies decrease with an increase in the flow-rate and the highest flow-rate shows the lowest values due to the longer charging duration and the shorter discharging duration. The set heater charging temperature shows only a marginal effect on the energy and exergy storage efficiencies. A comparison of the energy and exergy rates of the solder during charging and discharging with adipic acid shows slightly better performance during charging cycles for adipic acid. For discharging cycles, the solder shows a better performance.