Acrolab was asked to develop a new thermal management concept to improve the efficiency and reliability of a battery electric (BE) thermal management system, other than air-cooling and liquid-coolant cooling systems, used in Battery Electric Vehicles (BEV). In order to optimize the performance of the (BEV) battery we were required to maintain the optimal operating temperature of the battery.

If the batteries were too hot they would have a shorter lifespan and if they were too cold they would lose power or energy capacity, or both.

Determining the Coolant Method

For the BE thermal management systems that are currently being used, air cooling has the advantage of a simpler system and can tolerate a small air leak in the system but the disadvantage is that it provides lower cooling efficiency and is less compact. On the other hand, the liquid coolant cooling has the advantage of providing higher cooling efficiency and is more compact but the disadvantage is that it cannot tolerate any leaks in the system.

Acrolab Initial Evaluation

After initial review, Acrolab determined that the first concept would be a two-phase flow BE thermal management system. This concept would provide a higher heat transfer coefficient inside the cold plate and a more compact design.

This application was both unique and novel from an Acrolab perspective and was the first time that Acrolab had been approached to develop such a complicated thermal management system in this sector.

As a Result of This Engagement, we Identified Four Major Obstacles;

  • The first obstacle was to design a different, more novel system than similar ones we had previously worked on. This new system had to be more efficient, more reliable and had to meet the client’s specifications in order for the system to work in commercial vehicles. We also had to highlight the competitive advantages of this new system over the other systems.
  • The second obstacle was this system being used in a commercial vehicle which had to be tested under all conditions. A major component of this concept was the cold plate (evaporator) where the heat inside the battery was removed by the two-phase system.
  • The third obstacle was that under very cold weather conditions the plate would act as a heat plate for the battery.
  • The fourth obstacle was choosing the appropriate working fluid for the proposed two-phase system because it had to be compatible with the materials used and also be safe under normal and sub-normal conditions.

Acrolab Final Solutions

After lengthy discussions with the client and various detailed internal discussions, Acrolab settled on three viable solutions which we presented to the client for their review and consideration.

These three options consisted of:

1.  A simplified Isobar® heat pipe (HP) concept,
2.  A capillary pumped loop (CPL) heat pipe concept, and
3.  A mechanical pump assisted two-phase loop (2MPDL) concept.

The detailed presentation materials were prepared and it was agreed to continue work on the thermal interface system used between the cold plate and the stacks. After testing all three different systems, we further developed the concept that best suited the BE thermal management system, assisting us in developing similar systems for the future.