Prof. Wei-keng Lin Explains the Four Thermal Management Solutions for Electric Vehicles

There are four broad types of electric vehicle thermal management solutions: air cooling, liquid cooling, direct cooling and phase change material cooling.


I.Air cooling
Air cooling is a form of heat dissipation that uses low temperature air as a medium to reduce the temperature of a battery by heat convection, and is classified into natural convection and forced convection. The technology adopts natural airflow or fans to cool the battery with the vehicle's own evaporator, making the system simple and easy to maintain. It was widely applied in early electric vehicles, such as the Nissan Leaf and Soul EV, and is now also widely used in electric buses and electric logistics vehicles.

II.Liquid cooling
Liquid cooling is used to reduce the battery temperature by indirectly exchanging heat with the battery through the cooling fluid and carrying away the heat generated by the battery. The chosen liquid (currently the mainstream is ethylene glycol) has a high thermal conductivity and a high specific heat, which has a significant effect on reducing the maximum temperature and improving the temperature uniformity of the battery pack, while the thermal management system is relatively small in size. The liquid cooling system is more flexible: the cell unit or module can be immersed in liquid, or a cooling channel can be installed between the battery modules, or a cold plate can be used at the bottom of the battery. When the battery is in direct contact with the liquid, the liquid must be insulated (e.g. mineral oil) to avoid short circuits. At the same time, demand for the airtightness of the liquid cooling system is also higher. In addition, there are requirements for mechanical strength, vibration resistance and longevity. Liquid cooling is currently the preferred solution for many electric passenger cars, typically the BMW i3, Tesla and Chevrolet Volt.

III.Direct cooling
Direct cooling involves the use of refrigerants (R134, etc.) to evaporate latent heat, creating an air conditioning system in the vehicle or battery system and installing the evaporator of the air conditioning system in the battery system. The refrigerant evaporates in the evaporator and quickly and efficiently carries the heat away from the battery system, completing the thermal management of the battery system. The most typical electric vehicle with thermal management solutions by direct cooling is the BMW i3 (i3 comes with either liquid cooling or direct cooling options).


IV.Phase change material (PCM) cooling
Phase change materials are materials that change their physical properties with temperature and can provide latent heat. The process of changing physical properties is known as phase change, where the PCM absorbs or releases a large amount of latent heat. In the case of solid-liquid phase change, for example, the phase change from solid to liquid occurs when the melting temperature is reached by heating. During the melting process, the PCM absorbs and stores a large amount of latent heat, which, if applied to a battery pack, can lead to a significant drop in internal temperature. Common phase change materials include paraffin, advanced fatty acids, polyolefins and alcohols. Gogoro Inc is currently using paraffin wax to absorb heat and even out the temperature of battery packs for its own electric scooters.

Editorial staff T-Global Marketing

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