This work deals with the cooling of high-speed electric machines, such as motors and generators, through an air gap. It consists of numerical and experimental modelling of gas flow and heat transfer in an annular channel.
Velocity and temperature profiles are modelled in the air gap of a high-speed test machine. Local and mean heat transfer coefficients and total friction coefficients are attained for a smooth rotor-stator combination at a large velocity range.
The FINFLO software has been used in the flow solution. The annular channel is discretized as a sector mesh. Calculation is performed with constant mass flow rate on six rotational speeds. The effect of turbulence is calculated using three turbulence models. The friction coefficient and velocity factor are attained via total friction power.
The first part of the experimental section consists of finding the proper sensors and calibrating them in a straight pipe. After preliminary tests, a RdF-sensor is glued on the walls of stator and rotor surfaces. Telemetry is needed to be able to measure the heat transfer coefficients at the rotor. The mean heat transfer coefficients are measured in a test machine on four cooling air mass flow rates. The calculated values concerning the friction and heat transfer coefficients are compared with measured and semi-empirical data.
Heat is transferred from the hotter stator and rotor surfaces to the cooler air flow in the air gap.
On constant mass flow rate the rotor heat transfer coefficient attains a saturation point at a higher rotational speed, while the heat transfer coefficient of the stator grows uniformly.
The magnitudes of the heat transfer coefficients are almost constant with different turbulence models.
The theoretical and experimental research at LUT has resulted in one doctoral thesis (Kuosa)