Automotive Thermal Management Systems

          The role of the automotive thermal management system is becoming increasingly important. In the early days of automotive research, there was no such sub-field as thermal management, but rather the air conditioning system, which regulated cabin temperature, and the cooling system, which helped to cool the engine. Later on, automotive consumers have gradually increased their demand for air conditioning comfort and energy saving, and countries have also gradually raised their requirements on fuel consumption and emissions. Moreover, with the rapid development of new energy vehicles under the wave of vehicle electrification/intelligence, and the issues of range and safety of new energy vehicles being particularly prominent, automotive thermal management is becoming more and more important, hence the high certainty of future demand in the thermal management industry.
Automotive thermal management is the management of heat to achieve cabin temperature rise and fall and the normal operation of various systems in the vehicle. The temperature rise and fall of the cabin is mainly achieved through the vehicle air-conditioning system, while the normal operation of the vehicle systems is primarily realized through other thermal management systems. The specific composition of the thermal management systems of conventional vehicles and new energy vehicles is somewhat different. As new energy vehicles are developing at a rapid pace, companies that are able to grasp the opportunity to upgrade the thermal management systems for new energy vehicles are expected to see rapid growth.
A battery thermal management system monitors the temperature of the battery and actively controls it as required. The temperature of the battery environment determines the performance of the battery. If the temperature is too high, the battery life may be reduced or even cause safety concerns; if the temperature is too low, the battery discharge capacity will be weakened and the battery life will be diminished.
Therefore, thermal management of the battery is required, firstly by measuring and determining the optimum operating temperature range of the battery, then by calculating the battery thermal field and predicting the temperature during operation, and based on this information selecting the heat transfer medium of the battery pack and designing the heat dissipation structure to keep the temperature of the battery within the optimum range during operation. For example, the blade battery uses an innovative approach to battery thermal management, with the blade battery's liquid cooling plate positioned above the cells and a thermal conductivity layer between the cells. This solution has a much larger heat exchange area than a traditional square cell, which effectively transfers the heat from the cell to the cold plate, making the blade battery better at thermal management.
Battery thermal management systems are classified by technology type into liquid cooling systems (including direct liquid-cooling systems and independent circulating liquid-cooling systems), air-cooling systems and phase change material systems, of which phase change materials are currently in the research phase.

Table: the comparison of battery thermal management systems

Liquid cooling is the dominant technology route and is expected to remain so in the future
Depending on the technology, liquid-cooling systems can be divided into direct liquid-cooling systems and independent circulating liquid-cooling systems.
The direct liquid-cooling system feeds a plate evaporator inside the battery pack with refrigerant R134a and connects it to the air conditioning refrigerant circuit for evaporation and heat absorption to remove heat from the battery pack. The BMW i3, Audi A6 and Mercedes-Benz S400 are some of the representative models using this system. 
The independent circulating liquid-cooling system is fitted with a separate coolant (water-glycol) circuit for the batteries. When the battery temperature is low (38-45°C), it is being cooled by a heat sink. When the battery temperature is high (above 45°C), cooling is accomplished by heat exchange between the battery chiller and the air conditioning refrigerant circuit. When the battery temperature is too low, a heater on the circuit, such as a PTC heater, comes into operation to heat the battery. The JAC iEV7S, BYD Song and Chevrolet Bolt are some of the representative models using this system.

Author Professor Wei-Keng Lin Education｜Ph.D., University of Maryland Occupation｜Professor, National Tsing Hua University  Specialty｜Electronic package heat dissipation, Heat pipe, Loop heat pipes(CPL，LHP，PHP), Energy-saving design, Solar heat storage and cooling, Heat flow system, Cooling of electronic components, Two-phase flow, Heat transfer elements of artificial satellite and high-altitude flying object