Cyclic characteristics of water thermocline storage tank with encapsulated PCM packed bed

Abstract

Thermal energy storage (TES) with phase change materials is a promising approach for combined heat and power plants to enhance the electricity peak regulation capability and maintain stable heat-supply at the same time. Its cyclic performance is important under practical working conditions, however was rarely investigated. An experimental study on the thermocline TES was presented employing encapsulated paraffin wax packed bed as heat storage media and water as heat transfer fluid (HTF). The cyclic characteristics were revealed experimentally with consecutive charging/discharging processes. Convergence behavior was observed during the cyclic operation. It was found that the end-of-charging/discharging temperature distribution, charging/discharging duration and utilization rate of each cycle tend to be stable as the cycle number increases. It is believed that such behavior stems from the difference between the initial status and the end-of-charging/discharging criteria. The influences of flow rate of HTF, working temperature and initial status on the operational performance were investigated. The results indicated that the initial status had no significant impact on the TES performance after the convergence reached. Larger flow rate of HTF resulted in lower utilization rate and longer duration of each cycle. Especially the cyclic operation performance was strongly depended on the completeness of charging/discharging. These results may be helpful to understand such promising thermal energy storage technology, as well as the design and improvement of its auxiliary system.