Experimental demonstration of a multi-stage boiling heat extraction concept for high-temperature metallic phase change thermal energy storage in electric vehicles

Abstract

Thermal energy storage using metallic phase change materials is a promising technology for enhancing the thermal management of electric vehicles in cold environments. However, the high operating temperature range of such systems poses challenges for thermal discharge, especially when transferring heat to the vehicle's coolant circuit. This study proposes a novel multi-stage boiling heat extraction concept for thermal discharge and presents a prototype design with experimental validation. The lab-scale storage system utilizes an aluminum‑silicon alloy housed in a box-shaped graphite container. Heat extraction is achieved through a closed-loop boiling and condensing cycle using water as the working fluid, where the extracted heat is controllable and can be shut off as needed. Experiments were conducted successfully across an operating temperature range of 650 °C to 100 °C. High specific heat discharge rates were achieved at various storage temperatures—high, medium, and low—with peak values exceeding 20 W/cm^2. The system effectively utilizes both the latent and sensible heat of the storage material, demonstrating high efficiency and low pumping power requirements. Under pressure-tight conditions, the absolute pressure in the discharge system remained below 1.4 bar. The experimental results confirm the functionality of this novel concept, overcoming the challenges of transferring high-temperature storage heat to a vehicle's coolant circuit and providing a viable technical solution for future applications.