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Views: 8 Author: Site Editor Publish Time: 2022-09-22 Origin: Site
As electric vehicles become an unstoppable trend due to their zero emissions and high tank-to-wheel efficiency, improving battery performance, cost, life, and safety has become increasingly important. And battery thermal management systems (BTMS) are critical to battery performance, which is essential to the overall performance of the powertrain systems in electric vehicles (EVs) and hybrid electric vehicles (HEVs). BTMS technologies include:
· Air cooling systems.
· Liquid cooling systems.
· Direct refrigerant cooling systems.
· Phase change material (PCM).
· Thermoelectrics.
· Heat pipe cooling.
Air systems use air as the thermal medium. The inlet air can come directly from the atmosphere or the cabin or be conditioned air after the air conditioning heater or evaporator. The former is called a passive air system, and the latter is active. Active systems can provide additional cooling or heating power. Passive systems can provide hundreds of watts of cooling or heating power, while active systems are limited to 1 kW of power.
Both cases are called forced air systems because, the air is supplied by a blower.
Liquid cooling is a cooling system in which water is used as a coolant to cool the cell. And liquid cooling is the most commonly used cooling system because of its convenient design and good cooling performance. There are usually two groups of liquids used in thermal management systems. One is a dielectric fluid (direct contact fluid) that can directly contact the battery monomer, such as mineral oil. The other is conductive fluids (indirect contact fluids) that can only indirectly contact the cell, such as a mixture of ethylene glycol and water. In both groups, indirect contact systems are preferred to better isolate the battery module from its surroundings for better safety performance. The liquid systems can also be divided into passive and active systems using different heat sinks for cooling.
In terms of liquid cooling, Winshare Thermal has been one of the world's leading and most professional suppliers of the liquid cold plate, brazed type, extruded type, copper, and aluminum cold plate can be customized.
Like the active liquid system, the Direct Refrigerant System (DRS) consists of an A/C loop, but the DRS uses the refrigerant directly as the heat transfer fluid circulating through the cell.
Phase change materials absorb heat throughout the melting process and conserve it as latent heat until it reaches a maximum. In addition, PCM always binds for some time, the temperature remains at the melting point, and then the temperature increase is delayed. Therefore, PCM is used as a conductor and buffer in BTMS. In addition, the PCM is always combined with another BTMS system (e.g., liquid or air-cooled) to manage the cell temperature.
The thermoelectric module converts voltage to temperature difference and vice versa. The former effect is used here. This means that it transfers heat through the module by directly consuming electricity. Two fans are installed to improve heat transfer by forced convection. Combining a passive air system with a thermoelectric module, the combined system can cool the battery to even lower than the inlet air temperature. However, the power is still limited to around a few hundred watts, less than a kilowatt. The main issue of this cooling is the system's safety, which can be a problem in emergencies. A short circuit could occur due to a coolant leak on the battery cell, leading to vehicle failure and being fatal. In addition, the capillary tube must have a minimum diameter to maintain sufficient pressure drop and avoid clogging.
In addition to thermoelectric modules, heat pipes are another way to upgrade passive air systems. The flat copper housing of the heat pipe is under partial vacuum. The capillary structure is made of sintered copper powder. The heat pipe uses water as the working fluid. Due to the low internal pressure, the water on the evaporator side absorbs heat and turns into steam below 100°C. The water on the condenser radiates the heat around and turns into liquid again. This cycle is repeated over and over again.
