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
A setup was developed at Ghent University to experimentally measure the thermohydraulic performance of different heat sink designs. As the oil is also used as a lubricant, it is expected that the coolant can be subject to fouling and degradation. The goal of this thesis is to experimentally determine the effects of fouling and oil degradation on the cooling performance. This is done by devising a methodology to artificially introduce fouling and oil degradation. Measurements are done to determine the effect on the thermohydraulic performance. A model based on the physical phenomena and the perceived effects is made to predict the effects for different heat sink designs.
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.