Power battery cooling solution
Current new energy vehicles are basically powered directly or indirectly by battery packs. According to the energy source and power composition, electric vehicles can be divided into pure electric vehicles (EV, Electric Vehicle) and hybrid electric vehicles (HEV, Hybrid Electric Vehicle) and Fuel Cell Electric Vehicle (FCEV, Fuel Cell Electric Vehicle), no matter which form of new energy vehicle, the thermal management of the battery pack is a very important part of its design.
Physical parameters of lithium batteries
Processing technology introduction
Our battery pack liquid cooling solution mainly uses buried tube and microchannel technology. The buried tube process is to make full use of the high thermal conductivity of copper. We use the method of slotting on the aluminum plate and then embedding the copper tube. The micro-channel method is to increase the convective heat transfer coefficient of the internal flow, and let the coolant take away the heat more quickly and evenly.
1 Buried pipe: one side is attached to the heating device, the copper pipe and the slotted aluminum plate are interference fit, and the copper pipe is flattened and milled to ensure a better fit.
2.Micro-channel: The micro-channel structure is obtained by means of profile mold or machining, and then sealed with welding process, which can fully improve the convective heat transfer coefficient between the internal fluid and the wall, and greatly improve the heat transfer efficiency.
Battery specification (lithium iron phosphate battery)
Battery type: lithium iron phosphate
Rated capacity: 55Ah
Nominal voltage: 3.2V
DC internal resistance: 2mΩ
Battery size: 136mm x 199mm x 28.5mm
Maximum continuous charge current: 3C
Maximum continuous discharge current : 5C
Waterway and battery pack model
Base material: AL6063-T6 Pipe material: copper T2
Using 2 parallel 120 strings, the entire battery system is divided into 4 cooling units, and now one unit is subjected to thermal analysis.
The heat loss of lithium iron phosphate batteries mainly comes from internal resistance and reaction heat. The charging and discharging processes are different, and vary with different SOCs. The loss data of the battery cells of this project is shown in the figure below.
Loss data in charging mode
Loss data in discharge mode
Boundary conditions
Refrigerant: 50% ethylene glycol aqueous solution by volume
Refrigerant temperature: 25℃
Volume flow rate: 4L/min
To Design requirements
Flow resistance is less than 10Kpa
The battery temperature rise is less than 20℃, and the temperature difference between the batteries is less than 5℃
Cloud map of flow field distribution
Cloud map of battery surface temperature distribution during charging
During the charging process of the battery pack, when the SOC is 70%-80%, the temperature is the highest. The maximum temperature of the battery pack is about 35°C, the temperature rise is about 10°C, and the temperature difference between the battery packs is about 3°C, which can meet the design requirements.
The maximum surface temperature of each battery pack changes with time during the charging process
Cloud map of battery surface temperature distribution during charging
During the battery pack discharge process, when the SOC is 0-10%, the temperature is the highest. The maximum temperature of the battery pack is about 43°C, the temperature rise is about 18°C, and the temperature difference between the battery packs is about 5°C, which can meet the design requirements.
The maximum surface temperature of each battery pack changes with time during the discharge process.
In conclusion
1. At a volume flow of 4L/min, the flow resistance of the pipeline is about 3Kpa, which can meet the design requirements;
2. Calculate according to the charge and discharge rate of 1C, the working conditions are relatively severe (1 hour continuous work, complete the charge and discharge), the maximum temperature of the battery pack in the charging mode is about 35 ℃, the temperature rise is about 10 ℃, between the battery packs The temperature difference is about 3℃, which can meet the design requirements;
3. In the discharge mode, the maximum temperature of the battery pack is about 43℃, the temperature rise is about 18℃, and the temperature difference between the battery packs is about 5℃, which can also meet the design requirements, but only 5%-10% of the battery power remains. In this case, the temperature of the battery will increase significantly.
