Experimental study on charging characteristics of a latent heat thermal energy storage device integrated with finned helical coil and mechanical agitator

Abstract

With the continuous increase in the thermal load of avionics, traditional airborne heat sinks struggle to meet thermal management requirements. Using latent heat thermal energy storage (LHTES) for avionics thermal management shows great promise. However, the low thermal conductivity of most phase change materials (PCMs) severely restricts their charging and discharging rates. To address this issue, an enhanced LHTES device was developed by integrating a finned helical coil with a mechanical agitator. n-eicosane was selected as the PCM, and an ethylene glycol/water mixture (65/35 by volume) served as the heat transfer fluid (HTF). The effects of agitation speed (0–600 RPM), HTF inlet temperature (50–60 °C), and HTF flow rate (3.00–4.50 L/min) on device performance were investigated under two agitation strategies: delay-start (DS) and no-delay-start (NDS). Under the DS strategy, higher HTF flow rates and inlet temperatures led to higher PCM temperatures. At the same flow rate, faster agitation speeds increased PCM temperatures and accelerated equilibrium. Under the NDS strategy, latent heat transfer dominated in the first half of charging, with higher parameter values corresponding to lower PCM temperatures. In the second half, sensible heat transfer became dominant, reversing the trend. At HTF inlet temperatures of 50 °C and 55 °C, the NDS strategy provided significantly higher heat storage capacity than DS, with a maximum increase of 26.4 %. However, at 60 °C, the NDS strategy resulted in lower heat storage capacity, decreasing by up to 8.7 %. Additionally, the average heat storage power under the NDS strategy was consistently higher than that under the DS strategy, increasing by 37.7 %–90.7 %. This approach provides an innovative solution for enhancing the performance of LHTES devices.