Dielectric liquids or fluids, hereafter a quick definition:

 

Dielectric liquids refer for example to an insulating oil or an insulating liquid. These liquids are most often derived from organic compounds originally from natural products such as vegetable oils or petroleum derivatives.

The term dielectric can be defined as an environment which does not contain electrical charges that can move macroscopically. This environment is therefore not electrically conductive and could be even considered as an electrical insulator. We can cite various dielectric environments such as: vacuum, glass, dry wood, many plastics, etc.

Currently, mineral oils occupy nearly 95% of this market, which is mainly dedicated to transformers. Extracted from petroleum crudes, they represent several million tons per year. There is also another family of fluids, more recent, resulting from chemical processes: hydrofluoroolefins or hydrofluoroethers.

Dielectric liquids, which can also be called dielectric fluids, are used in many fields such as electrical engineering, power electronics; for various purposes such as electrical insulation, cooling, elimination of partial discharges, etc. They make it possible to design new processes and new technological solutions, particularly in the field of EV batteries.

 

When dielectric liquids overshadow glycol water

 

For a long time cooled only by air, the majority of battery-powered electric cars are now equipped with a glycol water cooling system. This cooling system, described as indirect, uses water-glycol as a heat conductive fluid. The fluid flows through a cooling plate attached to the battery, connective heat transfer occurs between the fluid and the cooling plates, drawing heat heat from the cooling plate to the fluid. In turn, the cooling plate draws heat from the battery cells thus cooling it.

Economical, reliable and above all, more efficient than air cooling, the glycol water cooling system has always been presented as the best solution on the market. The glycol, once added to the water, avoids the risk of ice formation, it enabled manufacturers to guarantee the operation of the cooling circuit even in case of low temperatures and frost.

However, water-glycol cooling also has certain limitations:

1) Poor temperature homogeneity between cells.

At the entrance of the cooling circuit, the glycol water is injected cold. However, throughout its journey, it heats up and does not allow the cells located at the end of the circuit to be cooled at the same temperature as those upstream.

2) A limited thermal performance.

Cooling being indirect : separated by a metal plate and contact thermal resistances, the glycol water cooling systems cannot ensure a direct and optimal heat transfer from the cell to the fluid.

3) Temperature gradient

Glycol cooling also involves a large temperature gradient in the cell: the cell often being cooled only on one side.

Limited by insufficient performance, these drawbacks impact mostly (significantly) the charging time of a battery at values around 30 minutes for 80% recharge for the best cold plates. Thus, as rapid recharging is perceived as the lever for democratization of the electric vehicle and as all manufacturers are seeking to approach recharging times of less than 10 minutes, it seems obvious that glycol water is not a solution for the future.

Les cellules immergées dans un liquide diélectriques

A more recent solution, immersion cooling is an innovative system using the fluid in direct contact with cells. Using a dielectric liquid to immerse the battery cells, this system is more adapted to users expectations, with performances that make the glycol water redden…

Made possible thanks to the use of dielectric liquids, immersion cooling pushes the limits of glycol water and guarantees a temperature harmony between all the cells, an excellent thermal performance and a very limited thermal gradient.

By immersing the battery in a dielectric liquid, all the cells are immersed and cooled at a constant and controlled temperature.

 

 

Maximum temperature between the cells and its homogeneity, factor of all success

 

The key to this innovative solution is battery immersion cooling, which opens the door to ultra-fast recharging. Where it was previously unthinkable to reduce the charging time at the risk of drastically reducing the lifetime of the cells, it is now possible to recharge 80% of a battery in less than 10 minutes.

Le liquide diélectrique diminue l'emballement thermique d'une cellule et empêche sa propagation vers les autres cellules

In addition, beyond recharging, safety is also greatly improved. The dielectric liquids used in a thermal management system guarantee a constant and optimal temperature. It has the huge advantage of stopping the start of fires within the battery and avoiding the propagation of thermal runaway from one cell to neighbouring cells.

Finally, while the previous coldplate solutions simply avoid freezing, the best dielectric liquids used in immersion cooling allow the battery to operate in extreme conditions: by a quicker start in very cold conditions (-40°C) as well as no degradation in very hot conditions (+50°C).

 

 

 

Dielectric liquids: a real technological revolution for future users and professionals in the sector.

 

In the field of electric batteries, the use of dielectric liquids has made it possible to introduce the immersion cooling process.

A real revolution, dielectric fluids therefore improve a large number of key points: recharging time, safety, performance, life span, etc.

While there are still many brakes on the purchase of an electric vehicle, most of which are linked to the constraints of the battery. Dielectric liquids offer users great prospects: faster, further, safer and longer-lasting.

As for the professionals of the sector, always looking for the most economical and compact solution, dielectric fluids also make it possible to develop smaller, lighter and therefore less expensive batteries with immersion cooling.

Thus, whether for cars, buses, trucks, aeronautics, material handling equipment, public transport, the use of dielectric fluids in immersion cooling will speed up the transition to electric vehicles. This solution is also expected to gain significant market share in a rapidly growing sector.

 


 

More information on: e-mersiv.com

 

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