Experimental characterization of a vertical shell-and-tube latent heat thermal energy storage with dual-tube finned tubes for evaporation at temperatures about 133 ◦C

Kurzfassung

Significant progress has been made in the development of latent heat thermal energy storage technologies for process industry and power plant sector applications, and storage systems in the megawatt range have been demonstrated on a pilot scale. Cost-effective storage materials have low thermal conductivities, and a central task in the realization of economical storage technologies is to find cost-effective solutions for heat transfer during the charging and discharging process. In the current state of the art, parallel tube heat exchangers with finned tubes are integrated into the storage material. This publication describes a modified storage unit in which a vertical shell-and-tube type heat exchanger with a novel dual-tube finned tube design is used to enable charging and discharging with different working fluids by condensing and evaporating them. This can increase the efficiency of the storage process and simplify the overall system by reducing integration equipment needs. The focus here is on the experimental characterization of the discharging process of the latent heat thermal energy storage, showing data from experiments with a mixture of potassium nitrate and lithium nitrate (KNO3-LiNO3) as the phase change material with a phase change temperature of about 133 ◦C and R1233zd(E) as the heat transfer fluid. An extensive parameter study was carried out to investigate the transient heat flow rate profile and temperature distribution in the storage, as well as the corresponding outlet condition under rarely-reported nonnominal conditions. The results show that the latent heat thermal energy storage is capable of storing up to 124 kWh of heat in a temperature range of 104 to 139 ◦C with a maximum heat flow rate of up to 90 kW. Furthermore, it is shown that the maximum heat flow rate, the duration of a constant heat flow rate and superheating can be controlled by adjusting the mass flow rate. The outcomes of this study contribute to improved design and operating strategies for future passive latent heat storage technologies and can serve for numerical model validation.