Electric vehicles are expected to increase in number and help reduce the emissions of the transport sector. To improve the efficiency and driving range of these vehicles, the power density of the drive train (motor, gearbox, power electronics, battery) has to increase. Due to the decrease in volume and increase in power, the heat dissipation per volume increases, making it harder to cool these drivetrain components. This is particularly an issue for the power electronics (see Fig. 1), as these will heat up to temperatures above 175°C and break down if not properly cooled. Current solutions use water-glycol mixtures as coolant to achieve the desired cooling rate.
Fig. 1: Infineon power module
A new research project, SingleOilCnL, aims to decrease the volume of the drivetrain by eliminating the water-glycol circuit and using the available lubrication oil circuit as a combined lubrication and cooling circuit. As oils are worse heat transfer fluids than water-glycol mixtures, this implementation puts more strain on the cooling of the power electronics. Therefore, new advanced heat sinks have to be designed and tested, utilizing oil as cooling medium. Some examples of improved heat sinks already available on the market utilize pin fins and improved channel geometries (Fig. 2), but these types are not optimized for use with oil coolants. The SingleOilCnL research project is a collaboration of Ghent University with Flanders Make, Dana, Siemens, Diabatix and Lubrizol.
Fig. 2: Pin fin (left) and 'ShowerPower' (right) heat sink design
Due to the high viscosity of oil, the flow is mainly laminar. CFD simulations in ANSYS Fluent on different techniques to enhance the laminar flow heat transfer are done. The goal of these simulations is to evaluate the performance of different techniques (fins, vortex generators, baffles, turbulators) and optimize the thermohydraulic design (heat transfer versus pumping power).
This project aids in achieving sustainable development goal (SDG) 7: affordable and clean energy, by enabling the replacement of fossil fuels by renewable electricity as an energy source for the transport sector.