Influence of heat transfer fluid on thermal performance improvement of latent heat storage unit with helical fins

Abstract

The helical fins can improve the hampering effect of classical fins on the convection flows of latent heat storage units (LHSU) as an innovative design, but their thermal performance improvement was largely affected by the operational conditions of heat transfer fluid (HTF), especially for fluid temperature and velocity. Based on this, an experimental system was established to measure thermal performance of latent heat storage units with perforated and solid helical fins (PHF-LHSU and SHF-LHSU). Two inlet temperatures were considered as 65 °C and 75 °C in the charge process and 20 °C and 30 °C in the discharge process, while three velocities were employed as 0.5 L/min, 1.0 L/min and 1.5 L/min. Experimental results showed PHF-LHSU exhibited the higher thermal performance than SHF-LHSU, especially in temperature response and average Nusselt number. Increasing HTF temperature from 65 °C to 75 °C increased melting rate, the average heat flux, Nusselt number and thermal efficiency by 25.4%–31.6%, 65.9%–70.6%, 15.9–25.9% and 9.7%–11.6% in the charge process, while reducing HTF temperature from 30 °C to 20 °C lowered the solidifying rate, the average heat flux and thermal efficiency by 39.3%–47.4%, 52.5%–56.6%, and 30.7%–35.3% in the discharge process. The HTF velocity had the certain effects on thermal properties and with the HTF velocity increasing from 0.5 L/min to 1.5 L/min, the thermal efficiency was increased by 3.9%–4.7%.