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Professor Lin Weigeng explained: four thermal management solutions for electric vehicles

The current thermal management solutions for electric vehicles can be roughly divided into four types: air cooling, liquid cooling, direct cooling, and phase change material cooling.

 

I.            (Air cooling)

Air cooling is a heat dissipation method that uses low-temperature air as the medium and uses thermal convection to reduce the temperature of the battery. It is divided into natural convection and forced convection. This technology uses natural airflow or fan, and cooperates with the car’s own evaporator to cool the battery. The system has a simple structure and is easy to maintain. It was widely used in early electric vehicles, such as Nissan Leaf and Soul EV. widely adopted in adopted in current electric buses and electric logistics vehicles.

 

II.           (liquid cooling)

Liquid cooling is to indirectly exchange heat with the battery through the coolant, and take away the heat generated by the battery to reduce the battery temperature. The selected liquid (the current mainstream is ethylene glycol) has a large thermal conductivity and a large specific heat, which has a significant effect on reducing the maximum temperature and improving the temperature uniformity of the battery pack. At the same time, the volume of the thermal management system is relatively small. The liquid cooling system is more flexible in form: battery cells or modules can be immersed in liquid, cooling channels can also be set between battery modules, or a water-cooled plate can be used at the bottom of the battery. When the battery is in direct contact with liquid, the liquid must be insulated (such as mineral oil) to avoid short circuits. At the same time, the air-tightness requirements of the liquid cooling system are also high. In addition, it is the mechanical strength, vibration resistance, and life requirements. Liquid cooling is currently the preferred solution for many electric passenger cars. Typical products include BMW i3, Tesla, and Chevrolet Volt.

 

III.            (direct cooling)

Direct cooling uses the principle of the latent heat of evaporation of refrigerant (R134, etc.) to build an air-conditioning system in the vehicle or battery system. Install the evaporator of the air-conditioning system in the battery system. The refrigerant evaporates in the evaporator and quickly and efficiently removes the battery. The heat of the system is taken away to complete the thermal management of the battery system. At present, the most typical thermal management solution for electric vehicles through direct cooling is the BMW i3 (i3 has two cooling solutions, liquid cooling and direct cooling).

 

IV.            (PCM - Phase Change Material)

Phase change materials refer to substances that change physical properties with temperature changes and can provide latent heat. The process of transforming physical properties is called the phase change process. At this time, the phase change material will absorb or release a large amount of latent heat. Take the solid-liquid phase change as an example. When heated to the melting temperature, a phase change from solid to liquid occurs. During the melting process, the phase change material absorbs and stores a large amount of latent heat. The temperature dropped drastically. Common phase change materials are: paraffins, higher fatty acids, polyolefins, alcohols...etc. At present, Gogoro applies paraffin wax to the battery pack of its own electric locomotive to absorb heat and equalize the temperature.

 

 

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

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