Water-cooled Motors Freeze Out Heat
Faik k. Ibrahim, published November 7, 2002
Machine Design, www.machinedesign.com
Induction motors cooled only by water can handle situations that would otherwise stymie conventional air-cooled units.
induction motors are designed to deliver a high power-to-weight ratio.
They serve in a variety of applications and may be good alternatives to
ordinary air-cooled motors, especially where the temperature is high. And
they frequently make sense in situations that call for minimal size and
weight. Finally, they are also less noisy than fan-cooled motors and are highly
One application for water-cooled motors has been in testing scale models of airplane designs. The motor drives the propeller while technicians check lift, drag, movement, and so forth. In this case, the water-cooled version got the nod because of its small size. Water-cooled motors have also found a spot driving pumps to cool nuclear reactors. Mining and tunnel drilling are candidate uses as well.
The average horsepower-per-pound for a water-cooled motor is 1.9. In contrast, the average for a still-air-cooled motor is 0.3 hp/lb. Water-cooled units can range in output from about 2 to 2000 hp or more. Their physical size can be 2 inches diameter on the low end to about 50 inches or more. Size, of course, depends on the application.
Water-cooled motor designs have many of the same components found in ordinary induction motors. But the design of the various components can be quite different.
Heat transfer in water-cooled motors is
essentially by conduction only. That means all motor components must be
designed to keep thermal resistivity low.
Probably the most obvious difference in construction is the water jacket. The motor water jacket consists of a housing, ribs, cover, two water connectors, and two seals. Water hoses connect to the inlet and outlet connectors. the staggered ribs force water to circulate between the motor and housing. In addition, water-cooled motors have a heat shield surrounding the bearings on their shaft.