Cooling of Electrical Motors

Case Studies: Aerodynamics

The efficiency of electrical drives and motors can be enhanced by an efficient cooling. In this context the cooling of a three phase asynchronous motor, 2 pole, 1.3 kW, IE2, size 80 is exemplarily investigated. The cooling of the motor is by a radial impeller with straight blades on a plate. There are different sizes, shapes and numbers of the blades. There are different sizes and shapes for the plate. The (basically) cylindrical fan cover guides the airflow exiting the impeller in axial direction in order to cool the motor. Different geometries for radial impeller and fan cover were investigated in order to improve the motor cooling.
In experimental setups, the volume flow rate generated by the impeller as well as the motor temperature due to different efficiencies in cooling were investigated. Different commercial available impellers as well as own designs (produced by rapid prototyping (i.e. 3D printing)) were tested.
In numerical simulations (three dimensional transient incompressible Reynolds averaged Navier-Stokes (RANS) equations) the flow field for different impeller geometries was computed, looking for an optimal design for the motor cooling. In addition the resulting flow field was analysed to get an insight into the evolving flow patterns.
If only the impeller geometry is analysed (the fan casing and end cap geometry are fixed), the most influential parameter is the impeller diameter: with increasing diameter the fan performance increases but also the gap between impeller and fan cover decreases thus decreasing the volume flow rate and cooling efficiency. A blade number of eleven seems optimal. The influence of the other geometric parameters (shape and size of blade and plate) is of secondary importance.
The analysis of the computed flow fields reveals the critical design parameters for the motor cooling: the flow is choked in the gap between impeller and fan cover and the gap between fan cover and motor casing (end cap). An optimisation of the motor cooling has to involve the redesign of the fan cover and motor casing in order to achieve a significant increase in cooling efficiency.