Experimental Study of Simultaneous Charging and Discharging Process in Thermocline Phase Change Heat Storage System Based on Solar Energy

Abstract

As a renewable energy power generation method, concentrating solar power generation has a broad application prospect. Weather and fluctuation significantly affect the output power of concentrating solar power generation. A heat storage system can stabilize this fluctuation and generate continuous and stable power. Therefore, the research on heat storage systems is of great significance to the development of concentrating solar power generation. This paper mainly studies the operating characteristics of the heat storage system based on solar energy in simultaneous charging, the influence in the change in solar radiation intensity on the charging power and the discharging outlet temperature, and the feasibility of the heat storage tank as an inertial link to stabilize the fluctuation in solar energy and the discharging outlet temperature. In this study, an experimental system for heat storage was established, in which solar energy was used as the heat source, water was used as the heat transfer fluid, and paraffin was used as the phase change heat storage material. When the initial temperature is 50 °C and the charging flow rate is maintained at 0.7 m3/h, at the same time the discharging flow rate is 0.1 m3/h, 0.3 m3/h, and 0.5 m3/h, respectively. The results show that when the solar radiation intensity is lower than 548 W/m2, the curve of heat storage power is almost parallel to the curve of solar radiation intensity; when the solar radiation intensity is lower than 535 W/m2, the moving direction of the thermocline will change; the average discharging outlet temperature in each case is higher than the phase change temperature of the phase change material and this system can continuously supply hot water at more than 69 °C for more than 3 h 32 min; and increasing the discharging flow rate will increase the whole charging and discharging time, thicken the thermocline, and disturb the temperature field in the tank. The experimental analysis will be conducive to profoundly understanding the operation characteristics of the thermocline heat storage tank under the solar heat source and has reference value for the subsequent design of a more efficient heat storage system.

New Advances in Materials, Applications, and Design Optimization of Thermocline Heat Storage: Comprehensive Review

“…The schematic diagram of the thermocline is shown in Figure 3. In the literature, different methods define the thermocline zone, including the percentage of the maximum temperature difference in the fluid [8], absolute value of the temperature difference [9], or based on the magnitude of the temperature gradient. The thickness and stability of the thermocline significantly impact the performance of THS tanks, with thinner thermoclines leading to better tank performance.…”

“…During charging, the injection of thermal jets causes entrainment phenomena [10], resulting in convective heat transfer and fluid dynamic perturbations [11], leading to thermocline decay. Obtaining piston flow and the flattened thermocline shape during In the literature, different methods define the thermocline zone, including the percentage of the maximum temperature difference in the fluid [8], absolute value of the temperature difference [9], or based on the magnitude of the temperature gradient. The thickness and stability of the thermocline significantly impact the performance of THS tanks, with thinner thermoclines leading to better tank performance.…”

“…In the dynamic dual mode, the initial thermocline zone split into primary and secondary thermocline zones as it descended through the spiral discharge coil, and the thermocline zones expanded with increasing time and coil flow rate. Xi et al conducted experimental research on the SCAD process of a THS tank filled with PCM capsules, considering three cases where the charging flow rate remained constant at 0.7 m 3 /h, and the discharging flow rates were 0.1 m 3 /h, 0.3 m 3 /h, and 0.5 m 3 /h, respectively [9]. The results showed that an increase in the discharging flow rate would decrease the outlet temperature, increase the thermocline zone thickness, and alter the time of supplying hot water above 69 • C, indicating the existence of a 'perfect flow rate' based on specific discharging requirements.…”