Conference Year

2016

Keywords

Latent heat storage, Phase Change Materials, Buffer storage, Liquid cooling system, Peak load

Abstract

The progressive electrification in automotive and aircraft industry results in increasing power densities and waste heat of power electronics. Due to higher power densities air cooling systems are substituted by more effective but in many cases heavier liquid cooling systems. Since the weight of cooling systems is a crucial aspect during the design process of vehicles, the dimensions of the cooling systems should be minimized. The dynamics of power electronics’ waste heat implies often short periods of high waste heat, so-called peaks. Cooling systems are usually designed for maximum waste heat.  This leads to an oversized cooling system for a wide range of operating points. Latent Heat Storages (LHS) compensates peaks and enables a downgrade of the cooling system, which in turn reduces the cooling system weight. The integration of a Composite Latent Heat Storage (CLHS) into a liquid cooling system is investigated experimentally at Hamburg University of Technology. The main objective is to analyze the implementation of a LHS as a buffer storage under different boundary conditions. The test rig is designed for a maximum waste heat of 500 W, resulting in a maximum heat flux density of 20.8 W/cm². The heat is applied by three cartridge heaters embedded into an aluminium body representing a power electronics module. The latent heat storage uses paraffin as Phase Change Materials (PCM). On the one hand paraffins allow a light-weight storage, but on the other hand they have a very low thermal conductivity, therefore a finned aluminum structure is used to improve the transport of the waste heat into the PCM. The power electronics dummy is fixed between the latent heat storage and a cold plate. The temperature is measured on both contact surfaces of the LHS. The cooling cycle is a one-phase cooling cycle with a heat exchanger as heat sink, a tank, a cold plate and a pump, which provides a maximum mass flow rate of 1200 kg/h. The coolant is Propylene-Glycol-Water (PGW) in a mixture of 60/40. The dynamics of the waste heat are given by a laboratory power supply. The paper presents the results of tests showing the influence of different waste heat load progressions including the melting and the solidification. All tests are performed for a CLHS and a Sensible Heat Storage (SHS) made of aluminium. The focus is on the buffering of the thermal energy in order to reduce the required mass flow rate and in consequence the weight.

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