30 n MOTORS May 2025 www.drivesncontrols.com Air or liquid cooling: which is best? Electric motors generate heat due to energy losses during operation – the more stress, the more the machine radiates heat that needs to be displaced. This makes it crucial to keep operating temperatures in an optimal range. If unchecked, this heat can lead to shortand long-term degradation of the motor. Excessive heat can warp mechanical components or damage bearings, leading to operational issues. There is also a signicant dierence in performance under hot conditions, so nding the right cooling system is imperative for energy eciency. The longer an electric motor is subject to incorrect cooling, the shorter will be its operating life as wear and tear will be accelerated. Prolonged exposure to high temperatures can deteriorate insulation materials, posing a risk to both operation and safety. Without sucient insulation material, electrical shorts can cause a machine to fail, while ammable components might be exposed continuously to high temperatures. A rotary fan is the simplest method to move hot air around a motor, promoting convection that allows cooler air to replace it. The uncomplicated layout of a fan system reduces the number of components and potential failure points, ensuring greater reliability and ease of troubleshooting. Installation and maintenance are also easy and cost-eective, requiring fewer resources to be committed to start and keep such systems running. A lightweight design also makes fans ideal for agile or mobile tasks. Cool, compact and consistent Liquid cooling takes advantage of the high heat capacity in uids such as water and certain oils to absorb the heat energy emitted by electric motors. This can be done by funnelling the cooling system through the heat source itself or via a jacket that covers the entire motor, which greatly improves the cooling eciency. This more direct method of dissipating heat also allows more control over the temperature, regulating the environment of the electric motor to a consistent level. The eciency of liquid cooling also leads to design exibilities in terms of compactness and shape. Making the choice between air and liquid cooling will often come down to each system’s limitations and challenges. Air cooling has a comparatively lower performance, that might not keep up with electric motors that produce high heat intensities. If the design requires tight or enclosed spaces where air currents are harder to generate, a fan-based system will struggle. A generally hot operational environment might also make it hard to generate the necessary convection to cool down the motor. The simple nature of fan cooling lends itself to lightweight, simple designs such as portable power tools and drones. With liquid cooling, the complexity produces a higher initial investment that might not be appropriate for smaller projects. On a similar note, more expertise is needed to perform maintenance checks and repairs. Depending on the uid choice, liquid cooling can also be sensitive to extreme temperatures, where there are risks of freezing or evaporation. This makes applications such as high-performance industrial machinery or electric vehicles an appropriate setting, demanding high thermal dissipation with relative environmental consistency. Practical experience under application conditions is the most valuable data that can help when deciding between air or liquid cooling, however this is not always possible especially when starting a project from scratch. To get around this, it is best to talk to industry experts and be inspired by proven modern designs. n *CWIEME Berlin, the international coil winding and electrical manufacturing event, takes place in Berlin, Germany from 3–5 June. https://berlin.cwiemeevents.com/home The two main ways of cooling electric motors are to use fans or liquids. Nicola Acampora, head of growth at the organiser of the CWIEME* exhibition, looks at the pros and cons of the two approaches to cooling. Liquid cooling of electric motors can be more ecient than air cooling, but it is more complex. Image: ABB
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