DESIGN ASPECTS OF A LATENT HEAT STORAGE UNIT FOR HEAT PRODUCTION SHIFTING AT A COGENERATION PLANT

摘要

In the present study, a latent heat thermal energy storage (LHTES) unit with two different configurations (a shell-and-tube design using spiral coils as tubes and an encapsulation design using commercial capsules) are investigated and compared over their thermal performance for providing heat storage and recovery. The designed latent heat storage unit is to be implemented at an existing (cogeneration plant for heat production shifting purposes. The design procedure involves several aspects of theoretical investigations: the determination of suitable melting point of the employed phase-change material (PCM); the selection of heat exchanger configuration; and (he prediction of the units' transient charging/discharging thermal behavior under operating conditions set by the cogeneration plant. Numerical approaches are used in this study to estimate the heat transfer conditions in PCMs as well as the transient charging/discharging thermal power of the entire unit. The accumulative stored/released energy throughout a charging process of three hours and a discharging process of one hour is also calculated. With the cylindrical containment tank in the same geometry, the spiral coil design exhibits a 52%-bigher total heat storage capacity than the encapsulation design, and the simulation results show that it can store a higher amount of heat by 20% after first three hours of charging. For discharging, however, the encapsulation design exhibits a higher completion rate of 96% than the spiral coil design (53%) alter first hour of discharging. Besides, the heat recovery capacity with the encapsulation design is 26% higher. The spiral coil design therefore shows advantage in the charging mode in terms of higher storage capacity while the encapsulation design outperforms when discharging due to is higher discharge rate within the given discharge operating duration of one hour.