EV Batteries Conference Review:

The IMechE’s international battery conference was held at the Kia Oval, London on November 9th & 10th 2021. We were delighted to be a sponsor of the event arranged by the IMechE. It was great to see some familiar faces, existing customers and many new faces too, whilst enjoying the fantastic view of the Oval throughout! Read on for our summary of the topics covered, from dielectric to cold plate cooling solutions.

Dielectric fluids for Immersive cooling:

The last 12 months have seen the rapid pace of development continue around cells, packs and the all-important topic of thermal management. We have seen a number of companies emerge in the world of immersive cooling, so were intrigued to see where the market as a whole is, in terms of immersive cooling adoption and use cases.

For those who are new to immersive cooling, this is the use of a non-conductive dielectric fluid to immerse the cells, either fully or partially and the busbars, in a non-conductive coolant. This coolant has a relatively low viscosity compared to a traditional oil, so we see many applications successfully using a “traditional” water pump product, rather than a specific oil pump. Note that it is important to be mindful of the properties of the fluid you are using when trying new fluids to avoid issues with the materials in the pump seals.

Typically water pumps are centrifugal and are limited by pressure whilst delivering relatively large flow rates, whereas the electronic oil pump is a gear pump (positive displacement) and therefore delivers far higher pressure, but is limited by flow rate.

The trade-off of flow vs pressure is not a new one, but the use of a dielectric fluid does create an interesting pump choice question, one where the answer is typically provided by the internal design of the cooling pack and its associated pressure / restriction to the flow. Whereas traditional pump selection is determined by the fluid’s properties, operating temperatures and then “limited” by the pumps performance.

There was an excellent presentation from Dr Richard Pearson, Senior Advisor, EV and Mobility at BP that comprehensively covered use cases and strategies for immersive dielectric cooling.

What impact does a Dielectric have on the Heat Exchangers?

Modern dielectric fluids are very compatible with traditional cooling circuits, typically the heat exchanger is a radiator when the pressure is low (water pump applications) and an oil cooler when the pressure is high (oil pump applications).

Dielectric considerations:

Cost, weight and complexity vs the benefits…

The general consensus from the industry is that immersive cooling is the way to go for high C charge and discharge, whether this be motorsport or rapid charging. Fears over high weight were somewhat alleviated during the presentations from Ricardo Plc in collaboration with M&I Materials and WMG (Warwick Manufacturing Group). Their presentation also demonstrated a cost comparison against cold plate cooling which prompts some interesting discussion. However, serious R&D is required in order to optimise a pack to this level, therefore immersive cooling probably won’t be your first battery pack, but certainly one to aspire to if your application demands it. Further work is ongoing to evaluate the increased life expectancy and additional range benefits for a battery pack with immersive cooling.

Cold plate cooling by comparison:

By comparison, cold plate battery thermal management solutions are not dead in the water (glycol), not by a long shot. Not only is this one of the most popular current cooling techniques, it is also set to stay for some time. Many OEMs and battery pack manufacturers can maintain acceptable cell temperatures throughout the pack with a water glycol cooling loop and a cold plate with 3 to 5 C charge / discharge rates.

For now, we’ll leave the topic of cold plate cooling, as that is somewhat of a more mature technique, but we always welcome a discussion about specific applications if customer questions arise.