Boiling Heat Transfer in Battery Electric vehicles

In this paper the feedback stabilisation of a boiling-based cooling scheme is discussed. Application of such cooling schemes in practical setups is greatly limited by the formation of a thermally insulating vapour film on the to-be-cooled device, called burn-out. In this study a first step is made, to check the viability of such cooling systems, already used in high performance electronics, applied to Electric Vehicles (EVs). It can be used for instance for the cooling of high heat flux transistors and for the thermal homogenisation of battery packs. Thereto, the unstable transition to burn-out is stabilised by controlling the pressure inside the boiling chamber, with which boiling (and thus creation of the thermally insulating vapour film) can be stimulated or suppressed. The feedback law used to do this is based on the dominant modes of the temperature field of the thermally conducting element, i.e. the heater, between the device and the boiling liquid. As not all states used in this feedback law can be measured, an observer or "state-estimator" must be implemented in the control strategy. The observer is a copy of the nonlinear boiling model with an additional term to assure convergence of observer to system state. Simulations are performed to demonstrate controller efficiency on the nonlinear cooling device. This puts forth the boiling-based cooling scheme as viable for application in EVs, enabling increased cooling and thermal-homogenisation capacities compared to conventional thermal management methods. The nextstep should be experiments to proof the principle on battery cells/packs and high heat flux transistors.