Modeling and Testing of a Portable Thermal Battery

Portable energy storage will be a key challenge if electric vehicles become a large part of our future transportation system. A big limiting factor is vehicle range. Range can be further limited if heating and air conditioning systems are powered by the electric vehicle’s batteries. The use of electricity for HVAC can be minimized if a thermal battery can be substituted as the energy source to provide sufficient cabin heating and cooling. The aim of this project was to model, design, and fabricate a thermal storage battery for electric vehicles. Since cost and weight are the main considerations for a vehicular application — every attempt was made to minimize them in this design. Thus, the final thermal battery consists of a phase change material Erythritol (a sugar alcohol commonly used as artificial sweetener) as the storage medium sealed in an insulated, stainless steel cooking pot. Heat exchange to the thermal battery is accomplished via water (or low viscosity engine oil) which is pushed through a copper coil winding. A CFD model was used to determine the geometry (winding radius and number of coils) and flow conditions necessary to create adequate heat transfer. Testing of the fabricated design indicates that the prototype thermal battery module losses less than 5% per day and can provide enough heat to meet the demand of cruising passenger vehicle for up to 1 hour of full heating on a cold day. Other metrics, such as $/kJ and kJ/kg, are competitive with Lithium ion batteries for our prototype.