Heat pipes are highly efficient heat transfer devices that have been applied to electric motors in several studies and inventions. Heat pipes use a phase change heat transfer mechanism, which is a passive heat transfer method from the heat source to the heat sink with very low thermal resistance.
As shown in Figure 1, the liquid in the tube evaporates vapor and flows to the condensing end after one end is heated, and the condensing end is subjected to the convection of air or liquid to transfer heat, and the internal steam liquefies and flows to the heating end, and circulates.
Figure 1: How heat pipes work
As shown in Figure 2, one end of the heat pipe is in close contact with the winding, and the other end is inserted into the cooling channel arranged in the front end cover, and the end cover water channel is connected in series with the casing water channel. Through the establishment of CFD finite element model and prototype experimental verification, the comparative results show that the indirect cooling method of heat pipe has obvious advantages over the traditional casing water jacket cooling, and the current density is increased by 50%.
Figure 2: Indirect cooling method of heat pipes
Ref. [3] designed the heat pipe in a U-shaped structure to shorten the axial length of the motor, as shown in Figure 3. The heat pipe cooling design adopts axial conduction heat, and the heat is not dissipated outward through the stator core and the casing, but through the slot design, the heat pipe conducts heat and dissipates heat with the heat dissipation wings. The analysis results show that when the wind speed is 4m/s, the winding temperature can be suppressed within 100°C, and the current density can reach 12.5A/mm². However, due to the U-shaped structure of the heat pipe, the scheme needs to be further optimized due to the inefficient use of its shaft conduction heat capacity, combined with the structural characteristics of the motor.
Figure3. Structure of a motor with a U-shaped heat pipe
In the future, it may be widely used in MV motor production in China, SIMO motor, best drive solution!