EXPERIMENTAL AND NUMERICAL STUDY OF A PASSIVE COLD THERMAL ENERGY STORAGE SYSTEM

Abstract

Water scarcity and the inefficiencies of current cooling systems highlight the need for alternative cooling solutions. This study presents a cold thermal energy storage (CTES) system designed to store cold thermal energy during nighttime and release it during daytime operations. The experimental setup consists of three primary components: a hot water heat transfer fluid (HTF) conduit for melting, a vertical phase change material (PCM) tank, and an air-cooling section for solidification. Heat pipes were employed to facilitate cold thermal energy transfer from the PCM to the HTF during discharge (melting) and from the cold air to the PCM during charge (solidification). Two operational scenarios, charging (solidification) and discharging (melting), were investigated, with three distinct HTF inlet temperatures of 45°C, 50°C, and 55°C and two HTF mass flowrates of 8.2 kg/s and 5 kg/s. Local temperature measurements were collected, melting and solidification times were monitored, and thermal resistance of the systems were calculated. Results indicate that thermal resistance tends to decrease as the mass flow rate of the HTF or the HTF temperature increases, and that the useful energy exchanged by the PCM per discharge cycle is around 236–253 kJ. In addition, a transient three-dimensional numerical model was developed in ANSYS-FLUENT to provide insights into the underlying physics. The phase change was simulated using the enthalpy-porosity approach, with computational results showing reasonable agreement with experimental data. This study demonstrates a compact CTES module that stores off-peak “cold” in a PCM via heat pipes and releases it on demand, improving efficiency relative to purely mechanical cooling. The approach is a good fit for industrial, residential and data center cooling, enabling peak load management and short-duration backup while reducing water and energy use.