What Is The Best Liquid For Cooling?
Overview of the liquid cooling principle
Cooling systems based on liquid heat exchange are more efficient than air systems and have a more uniform temperature inside the battery pack of an electric vehicle, but the systems are more complex. The heat transfer from the battery to the liquid phase, for example, can be accomplished by gluing metal to the walls of the container or by embedding it in the container walls.
Similarly, the entire heat transfer can be achieved using heat transfer from the liquid medium, i.e. by arranging pipes between battery modules or by arranging jackets around the modules to achieve heat exchange between the battery and the liquid, such as the designs Trumonytechs has for liquid cooling plates, serpentine bends attached to thermal conductive interface materials (thermal conductive silicone mats, thermal conductive gels, etc.) for heat exchange. At the same flow rate, most direct contact fluids (e.g. mineral oil/water) transfer heat at a much higher rate than air because of their thinner boundary layer and higher thermal conductivity. So in terms of the many ways to dissipate heat from power batteries today, liquid cooling is one of the most promising ways to develop.
Liquid cooling is divided into two ways: direct contact and non-direct contact. Mineral oil can be used as a direct contact heat transfer medium, while water or antifreeze can be used as a typical non-direct contact heat transfer medium. Liquid cooling must pass through a heat transfer facility such as a water jacket in order to cool the battery, which reduces the heat transfer efficiency to a certain extent.
On the choice of liquid cooling heat transfer media
The choice of heat transfer medium has a significant impact on the performance of the liquid-cooled thermal management system and the heat transfer medium should be determined prior to the design of the thermal management system.
Direct contact liquid cooling uses electrically insulated liquids with high thermal conductivity (e.g. silicone based oil, mineral oil) in direct contact with the single cell or module, which can well solve the problem of module temperature homogenisation, but as the insulating liquid is usually relatively viscous, the flow rate will not be very high, thus limiting its heat exchange effect. and the way in which the fluid flows through the cell.
In the case of the liquid cooling plates and serpentine bends we have at Trumonytechs, for example, in indirect contact liquid cooling, the fluid flows inside the pipe and comes into direct contact with the battery through the thermal conductivity interface material, for example, transferring heat through the thermal conductivity interface material and cooling the battery by transporting it through the fluid flow heat exchanger.
As there is no insulation requirement and no flow rate restriction, liquids with high thermal conductivity but poor insulation can be used and the heat transfer effect is very good. However, the temperature uniformity is somewhat worse than with direct contact liquid cooling. In order to prevent leakage causing a short circuit, this method has higher requirements for the sealing of the pipes. The main heat transfer media generally chosen are water, glycol, silicone, paraffin, etc.
Regardless of the type of liquid cooling system used, one problem is that there are gaps between the battery cells and the arrangement piping or the jacket around the module arrangement, and air is an undesirable medium for heat transfer, where thermal conductive silicone sheets can eliminate this obstruction to heat transfer.
The benefits of filling the gap between the battery and the pipe with electrically insulating heat-conducting material
- Changing the form of contact between the battery and the heat sink pipe from line contact to surface contact, improving the efficiency of heat transfer.
- It is conducive to increasing the temperature homogeneity between individual cells.
- It is beneficial to increase the overall heat capacity of the battery pack, thus reducing the overall average temperature.
The liquid cooling system for power batteries can be designed using liquid cooling plates, serpentine bends with heat-conductive interface materials (thermal conductive silicone mats, thermal conductive gels, etc.) for heat exchange to achieve higher efficiency in heat transfer.
Trumonytechs liquid cooling solutions
Trumonytechs’ thermal conductive silicone Pad is the best auxiliary material for water-cooling solutions because of its good insulating properties and high resilience, which can effectively avoid the problem of vibration and friction breakage between the cells and the potential short circuit between the cells.
The battery generates a lot of heat during operation, which is transferred by the heat-conducting silicone Pad to the water-cooling tube, which in turn transfers it to the cooling liquid, which flows through the battery pack and removes the heat quickly by means of a pressure pump or cooling fan.