Immersed-cooling Concepts for Electric Vehicle Battery Packs using Viscoelastic Heat Transfer Liquids (I-BAT)

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The penetration of plug-in EVs on the world market faces considerable technological challenges. The performance of battery electric drives is influenced among other things by the power density and efficiency of the EV Battery Thermal System (BTMS), the heating and cooling system for batteries and power electronics. Lithium-ion batteries require a temperature of 15-60 °C for optimal operation, with high demands on temperature uniformity between the cells. The power density of the battery cooling systems has to be doubled compared to the state of the art to enable powerful and compact drives. The tight integration in vehicles means that only minimal cross-sections are available for the liquid coolants used. This challenge is met by innovative coolants, which have shown considerable potential for increasing the cooling effect and reducing pump losses in basic investigations. The subject of work is the synthesis and characterization of mineral oil-based coolants with optimal rheological and thermal properties suitable for EV BTMS. The novel fluids to improve heat transfer consist of a viscoelastic liquid carrier matrix with suspended nanoparticles. The dielectric nature of mineral oils allows the realization of immersion cooling systems with improved heat transfer rates compared to current devices with indirect cooling. In addition, viscoelastic additives can give the flow a controllable non-Newtonian character, resulting in reduced friction losses leading to 10-20% less pressure loss. At the same time, the selective amplification of specific types of coherent secondary flows favors a further increase in heat transfer. Overall, the proposed research aims at doubling thermal performance. The newly developed nanocoolants will be tested in a BTMS prototype to prove that these improments have the potential to revolutionize the relevant transport sector.