Experiments on comparative performance of water thermocline storage tank with and without encapsulated paraffin wax packed bed

摘要

The electric power load regulation capability is significantly weakened by combined heat and power (CHP) despite of its energy saving benefit. The application of thermal energy storage (TES) has been proved effective to improve this situation. Combining the advantages of conventional water TES tank and larger heat storage density of latent heat storage using phase change material (PCM), the performance of a water TES tank with encapsulated paraffin wax packed bed is experimentally investigated. Having appropriate phase change temperature, it is designed to charge heat by heat exchanger with the steam turbine extraction and provide hot water to the district heating network. To discuss the feasibility of this TES technology, a comparison with conventional water TES tank is shown. Aiming at the stratification performance and efficiency of both TES systems with and without PCM packed bed, the factors including dimensionless temperature, thermocline thickness, charging/discharging power and energy efficiency are analyzed. The results indicate that the performance of PCM-water tank is not as good as the water tank in stratification, but the advantage of encapsulated paraffin wax packed bed is obvious especially when operating at small flow rate, releasing much more thermal energy with qualified hot water. During the discharging process, the outlet water temperature stays close to the phase change temperature for much longer time. In practical application, to take advantage of the latent heat storage, it is suggested to employ the phase change material whose phase change temperature is properly larger than the required heat-supply temperature.