Thermal characteristics of a small-scale medium- and high-temperature latent heat storage system at different inlet flow rates and their influencing factors

Abstract

This study investigates the impact of heat transfer fluids (HTFs) operational parameters on latent heat storage (LHS) systems, focusing on medium and high-temperature storage. A small-scale, visualized setup with a compact shell-and-tube heat exchanger, featuring helical fins, was constructed to enhance heat exchange. Dense thermocouples and flow meters recorded temperature and flow data of the phase-change material (solar salt) and HTF (heat transfer oil) during charging and discharging cycles, enabling detailed thermal analysis.Results show that higher HTF flow rates significantly reduce cycle time. Increasing the flow rate from 15 to 35 L/min decreased the discharging time from 176.5 to 146.4 min, a 17 % reduction, and improved energy injection/extraction efficiency. Lower rates, however, stabilize energy output and slightly increase cycle efficiency (from 51.58 % at 15 L/min to 52.45 % at 35 L/min). Additionally, the study identified a correlation between storage temperatures and flow rates: higher temperatures boost the efficiency of high flow rates in reducing melting time, while lower temperatures enhance the positive effects of low flow rates on circulation efficiency. These findings provide essential guidance for parameter selection in LHS system engineering applications.