Spray-Cooling in Electric Mobility - Application-Oriented Characterisation of the Heat Transfer of Oils with a New Measuring Method
Zentrum für Wärmemanagement (ZFW)
Prof. Dr.-Ing. Andreas Griesinger
Electrically powered vehicles require a sophisticated heat management system. Especially the cooling of the actual drive must be safe and efficient. Water-glycol circuits are typically used for this purpose. With their high heat capacity and simultaneously good thermal conductivity, water-glycol mixtures are ideally suited for cooling tasks. In addition to a cooling circuit, a lubrication circuit for moving drive components is also required in vehicles. In the future, it may be possible to dispense with the water-glycol circuit and instead use the oil that is already available for lubrication for cooling. By reducing to only one fluid circuit, the system complexity can be minimised and the costs in development and production can be reduced considerably. To achieve this, the cooling system must be modified in such a way that the fundamentally poorer heat transfer properties of oils are compensated and become attractive for cooling. An increased cooling effect can be achieved by direct spray cooling onto the open structures of the components to be cooled. This strategy is made possible by the electrical insulation effect of oils.
Within the planned research project the approach of direct spray cooling with oils on open electrical and electronic components will be analysed and optimised. For this purpose, a newly designed measuring method will be used to quantify the heat transfer between any solid surface and the oil (based on the thermal transient method). Compared to conventional methods, this measuring method offers the advantage of analysing the actual heat path. Thus, the measurement results can be directly transferred to practical applications. Heat transfer follows highly complex physical relationships and is influenced by a large number of different system and operating parameters. A systematic, metrological investigation provides information about the influence of individual parameters and their interactions. The transformation of these interrelationships into mathematical correlations (so-called Nussel equations) enables a simple and quick advance calculation of the heat transfer during spray cooling. The results of these investigations will serve the industry in the future as a basis for the development of oils suitable for cooling and lubrication, including the necessary additives.
The IGF application was submitted for evaluation.