62 are gaining other advantages in other areas as we don’t need a cold plate or thermal paste and we reduce the number of assembly steps at the OEM.” “These electric vehicles have more and longer hoses and tubes with smaller diameters regardless of the powertrain,” said Kyle St John, who works on pipe and hose designs as applications engineer for fluid conveyance at Danfoss. “The cooling has to travel to different parts of the vehicle with the battery in the middle and a motor at each end compared to a traditional centralised internal combustion engine vehicle. “Linking all the elements together raises the question of how you manage the rest of the systems, for example warming the battery and the cabin. With a two phase solution there will be little or no heat from the battery case to be used for the cabin. Now you don’t have a working fluid in the vehicle to use in other ways,” St John said. “The biggest factors that come to mind are cleanliness and the fluid type,” St John added. “These immersive cooling systems tend to be cleaner than a lot of other systems. There’s a lot of advancement in the fluids and analysis of what fits best; whether that is a different hose material or tubes made out of steel or aluminium for the cleanliness. “Customers determine the size of the hose or tube depending on the size of the system and that’s the key for more viscous fluids or longer runs in the hoses. As far as fluid compatibility goes right now there isn’t anything different but when you consider bend radius for smaller systems, that could change it.” Choice of fluid Carrar can use any low pressure refrigerant that is suitable for a high voltage system but needs a dielectric value at least 10 times higher than the battery pack voltage at 800V to 1000V. This means there are two candidate fluids commercially available. These are SF33, a proprietary hydrofluoroolefin (HFO) from Opteon and the R1233zd from Honeywell. “Because we use a low pressure range we can design the modules with lightweight polymer materials instead of aluminium, which is usually needed to transfer heat out of a pack,” said Friedman. “It also isolates from the outside temperature; this is why we can design very light systems and we can reduce the pack weight by 20 kg. That’s a lot for the OEMs. “For the refrigerant a single phase needs a lot of liquid but dual phase needs less so we are not changing the amount of cooling liquid in the vehicle,” Friedman added. “We are looking at both the passenger market and commercial vehicles but we assume the penetration will be for high end passenger vehicles. “On the commercial side, we designed a module for Volvo where we showed we prevent thermal runaway in a 14 kWh module with over 700 cells. That’s a big module measuring 60 x 60 cm and they have 36 of these modules in the battery pack with one condenser and one compressor per pack. Test results Castrol worked with Virtual Vehicle Research [VVR] in Graz, Austria on the comparative performance of indirect and single phase immersion cooling technologies. This research compared battery cooling via indirect water-glycol baseplate cooling with immersion cooling. The majority of today’s battery January/February 2024 | E-Mobility Engineering An immersion cooling system (Image courtesy of Valeo)
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