Numerical and experimental investigation on a latent heat thermal storage device featuring flat micro heat pipe arrays with offset strip fins

Abstract

In this paper, a latent heat thermal storage device is designed and manufactured. The device uses flat micro heat pipe arrays as the core heat transfer element, multichannel flat pipes as the heat transfer fluid channel to provide and remove heat, and offset strip fins to strengthen the heat exchange of the phase change material side. The performance of the device under different operating conditions was explored, and a 3D computational fluid dynamic model of the device is established. The model is simplified by using the method of equivalent thermal conductivity and equivalent specific heat capacity. The performance of a latent heat storage unit under small temperature difference is also studied. Results show that the inlet temperature of fluid has a great influence on the performance of the device. During charging process, when the fluid temperature changes from 63 °C to 73 °C, the charging power increases from 921.1 W to 1302.1 W (41.3%). During discharging process, when the fluid temperature decreases from 18 °C to 8 °C, the discharging power increases from 831.1 W to 1210.5 W (48.9%). Regarding the flow rate, when the fluid flow rate increases from 2 L/min to 3 L/min (50%), the average charging power increases from 1,069.2 W to 1,199.3 W (12.2%), and the average discharging power increases from 895.1 W to 1,068.3 W (19.3%). Simulation results show that the phase change material in the thermal storage unit can melt completely when the temperature difference is 4 °C, but the melting time is longer when the heat transfer temperature difference is less than 6 °C. Heat transfer temperature difference refers to the variance between the heat transfer fluid inlet temperature and the phase change material phase transition temperature. The main thermal resistance is concentrated in the part where multichannel flat pipes transfer heat to the flat micro heat pipe arrays and the phase change material side.