Consolidated theoretical/empirical predictive method for subcooled flow boiling in annuli with reference to thermal management of ultra-fast electric vehicle charging cables

Abstract

Ability to deliver very high electrical current through a charging cable is key to successful proliferation of electric vehicles (EVs). Associated with high current delivery is a host of thermal problems stemming from the need to remove enormous amounts of heat from the cable. This study seeks to develop a highly effective thermal management scheme based on subcooled flow boiling principles. The main objective is to develop a consolidated theoretical/empirical method for predicting the heat transfer and pressure drop characteristics of both laminar and turbulent flows though concentric circular annuli with uniformly heated inner wall and adiabatic outer wall. Although maintaining subcooled boiling along the entire cable is a key practical objective, this consolidated method is shown to be capable of tackling multiple flow regimes (single-phase liquid, subcooling boiling, saturated boiling, and single-phase vapor) and highly effective at predicting local surface and fluid temperatures. This method is then adopted to design and optimization of very high current EV charging cable cooling system using dielectric fluid HFE-7100 as coolant. Effects of various parameters, including electrical current, both wire and conduit sizes, inlet fluid temperature, and flow rate are carefully addressed and recommendations made for effective and robust overall system design.