The previous article took an in-depth look at how to safely cool down the Tesla Powerwall battery. In this blog, we will learn about the core technologies for cooling batteries and their types.
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In the past two years, energy storage liquid-cooled battery systems have been recognized by users and integrators due to their good temperature control consistency and strong heat dissipation capabilities.
It has become a trend for liquid-cooled battery systems to gradually replace air-cooled battery systems.
It’s not complicated to use liquid cooling technology for Tesla Powerwall batteries.
In the field of electric vehicles, most power battery packs use liquid cooling.
The design of the energy storage liquid-cooled battery pack also draws on the mature technology of power liquid-cooled battery packs.
When the Tesla Powerwall battery system is running, the battery generates some heat, and the heat is transferred through the contact between the battery or module and the surface of the plate-shaped aluminum heat sink.
It is eventually carried away by the coolant passing through the internal flow channel of the liquid cooling plate.
Generally, the liquid cooling plate is required to have high heat dissipation power, which can promptly dissipate the excess heat generated during the operation of the Tesla Powerwall lithium battery, avoid excessive temperature rise, and have high reliability.
The power batteries of road vehicles are subject to relatively harsh working environments such as vibration, impact, and alternating high and low temperatures.
Therefore, the reliability and strength of the liquid cooling plate seal are important.
The heat dissipation design of the liquid cooling plate must be precise to avoid excessive temperature differences within the system. This is the performance requirement of the Tesla Powerwall lithium battery itself.
The liquid cooling plate also has strict requirements on its weight, which comes from the pursuit of energy density of the power battery system.
At present, the main types of liquid cooling plates in the new energy market include the following:
1. Harmonica tube liquid cooling plate
The harmonica tube liquid cooling plate has the advantages of low cost, lightweight, relatively simple structure, and high production efficiency.
However, due to its single flow channel, small contact area, and thin pipe wall, its heat exchange effect is average and its load-bearing capacity is poor.
2. Stamped liquid cooling plate
The stamped liquid cooling plate has the advantages of arbitrarily designed flow channels, large contact area, good heat exchange effect, high production efficiency, good pressure resistance, and strength, etc.
However, because it requires mold opening, the cost is high and it requires flatness. High and difficult to install.
3. Inflated liquid cooling plate
Inflated liquid cooling plates have the advantages of low cost, good heat exchange effect, and high production efficiency.
However, because their materials are soft, they have major shortcomings in terms of pressure resistance and strength.
4. Parallel flow tube liquid cooling belt
The parallel flow tube liquid cooling strip has the advantages of good heat exchange effect.
And is suitable for cylindrical cells, but its cost is high due to its complex structure.
5. Profile plus friction stir welding
This kind of liquid cooling plate formed by connecting profiles through friction stir welding has the advantages of good reliability, good load-bearing capacity, good surface flatness, and good heat exchange effect.
However, due to its thick thickness and complicated processing methods, it is costly and It is heavy, and takes up a lot of space.
Design principles of liquid cooling heat sink:
1) Selection of substrate: Try to avoid having two metals with large electrode potential differences in a system to reduce electrochemical corrosion.
2) Selection of liquid cooling plate types: Select based on the structure of the liquid cooling system and whether it can bear heavy loads
3) Determination of flow rate: Since the water-cooled system is relatively large, simulation analysis of the entire system is generally not performed.
Instead, the water cooling radiator flow is set first, and then the water pump is matched according to the corresponding system flow resistance.
After the total heat and the physical parameters of the workpiece material are determined, the flow rate is inversely proportional to the temperature rise.
If the temperature rise is high, the heat exchanger power design of the water cooling system must be larger.
If the temperature rise is too low, a larger water pump needs to be selected.
Therefore, if the temperature rise is too high or too low, it will cause an increase in costs.
Based on economic considerations, there is often an economical temperature rise range, which simultaneously determines the flow rate of the radiator.
4) Design of flow channel section: According to theoretical derivation, the convection thermal resistance is positively correlated with the hydraulic diameter of the section.
That is to say, other conditions being equal, the larger the hydraulic diameter, the greater the convective thermal resistance.
According to the hydraulic diameter formula D=4A/P, where A is the cross-sectional area of the flow channel and P is the cross-sectional circumference of the flow channel.
Then, under the condition that the cross-sectional areas are equal, the larger the circumference, the smaller the hydraulic diameter, and the smaller the convection thermal resistance.
Challenge:
The first is that liquid cooling systems are more expensive. Compared with air-cooled energy storage battery packs, liquid-cooled battery packs have a liquid-cooled heat sink.
Due to rising raw material prices, the price and cost of Tesla Powerwall battery packs have increased.
In addition, the current market price of a liquid-cooled unit with the same cooling capacity is 4-5 times that of an air-cooled air-conditioning unit.
Then, since the protection level of the liquid-cooled battery pack is IP67 fully enclosed if thermal runaway occurs inside the battery pack, the original container-level gas flooding fire extinguishing will not work and cannot effectively extinguish the fire.
The fire extinguishing agent needs to be sprayed into the battery pack, and the targeted and precise injection can effectively extinguish the fire.
If you need to achieve pack-level detection, monitoring, and fire extinguishing, the fire protection system you choose is also very expensive.
There are more detection devices, the construction of pipelines and lines is difficult, and the system is also complex.
The above two major problems are also the main factors restricting the development of energy storage liquid-cooled battery systems.
Of course, with the expansion of the energy storage application market, the price of related auxiliary equipment will gradually decrease due to the increase in quantity.
We will reduce costs and increase efficiency through product design.
PVMars engineers will demonstrate their R&D innovation capabilities and promote the further development of the energy storage industry.
