A novel CO2 thermal management system with battery two-phase (evaporative) cooling for electric vehicles

Development of electric vehicles promotes an increasing demand for battery cooling, and secondary loop with glycol aqueous is widely used. However, the cooling performance is restricted, and it is heavily affected by the thermal delay because of large heat capacities. Two-phase evaporative cooling was demonstrated to have a better performance, but was disturbed by the potential thermal runway propagation of battery, due to the instability of evaporative cooling in chiller. In the presented paper, an effective solution was proposed based on a novel evaporative cooling system with transcritical CO2 cycles, which could always avoid this problem by a simple control strategy. Moreover, a control logical was set up and it was easy to achieve the energy management for cabin and battery. A mathematical model was developed, and it was validated by experiment. The vapor quality, cooling performance and flow velocity distributions were investigated at different operation conditions. Results showed that it could better deal with the problem of potential overheating and difficult-control. Under the condition of 0.5 kW battery power, the flow vapor quality along the channel increased from 0.23 to 0.94 of the conventional systems, while it only ranged from 0.23 to 0.4 in the proposed system. Additionally, the presented systems had 13.5%higher COP at the ambient temperature of 35 °C. It could be used in electric vehicles thermal management systems for efficient battery cooling.