Abstract
The present investigation aims to devise a thermal management system (TMS) for electric vehicles able to improve on limitations like charging time and all-electric range, together with the safety and environmental impact of the chosen thermal medium. A research gap is identified, as focus is often on addressing system thermal performance without considering that the thermal medium must not only provide suitable performances, but also must not add risks to both passengers and the environment. Thus, this work proposes an innovative cooling system including graphite sheets and a Loop Heat Pipe, filled with Novec™ 649 as working fluid, due to its exceptional environmental properties (GWP = 1 − ODP = 0) and safety features (non-flammable, non-toxic, dielectric). A three-cell module experimental demonstrator was built to compare temperatures when the proposed TMS is run with Novec™ 649 and ethanol. Results of testing over a bespoke fast charge driving cycle show that Novec™ 649 gave a faster start-up and a slightly higher maximum temperature (0.7 °C), meaning that the gains in safety and lower environmental impact brought by Novec™ 649 came without lowering the thermal performance. Finally, the TMS was tested under three different fast charge conditions (1C, 2C, 3C), obtaining maximum temperatures of 28.4 °C, 36.3 °C and 46.4 °C, respectively.
Highlights
The evident deteriorating of planetary conditions during the last 40 years has pushed governments worldwide to take actions to reduce the emissions of greenhouse gases (GHG)
A Loop Heat Pipe (LHP), as shown in Figure 1, is a two-phase passive thermal device, evacuated and partially filled with a working fluid whose motion is ensured by capillarity due to the positive pressure gradient arising in the evaporator section
The LHP evaporator was obtained from Thercon, Russia, and the rest of the and piping made in copper, with the exception of the stainless steel hydraulic unions
Summary
The evident deteriorating of planetary conditions during the last 40 years has pushed governments worldwide to take actions to reduce the emissions of greenhouse gases (GHG). Liquid-based TMS used a various range of working fluids, such as water [18,19], an ethylene glycol-water mixture [20,21], and refrigerants (R134a) [22,23], which have issues in of being electrical conductors, flammable, and have very high GWPs (1300), respectively From this analysis of the current research on EV TMS, what emerges is a lack of an efficient cooling method for TMS that considers the thermal performance and the safety and environmental impact of the cooling medium. In this work, a thermal management system with LHPs and graphite sheets is proposed together with the use of a novel synthetic fluid NovecTM 649, developed by 3MTM This design allows for excellent cooling performance with no parasitic power consumption (due the passive nature of the LHP), thereby ideally increasing the all-electric range of the vehicle and allowing for shorter fast charge times.
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