Talking about the principle of heat exchange and thermal stability of electric motor
Temperature rise is an important performance index of the motor. When the motor is running, it is a heating element. How does the motor dissipate heat to achieve the final balance? In general, heat is radiated from the surface of the heating element to the surrounding medium. One way; one is radiation; the other is convection by means of air or other cooling medium. In the motor, the latter usually dominates.
Radiation cooling
Convection cooling
The heat dissipation from the solid surface in direct contact with the fluid can be found. When the temperature of the solid surface is not equal to the temperature of the fluid, heat exchange occurs between them, and heat is transferred from the high temperature object to the low temperature object. This exchange heat is actually both conduction and convection, but is collectively referred to as convective heat transfer. In a motor, the heat generated in a core, winding, or other heat-generating component is carried away by cooling fluid (air, hydrogen, water, oil, etc.) flowing through one or more surfaces of these components: Forms are widely available in motor cooling systems. The heat dissipation capability of this form of heat dissipation depends primarily on the state of motion of the fluid on the solid surface.
When the fluid moves in a laminar flow, the fluid only flows parallel to the solid surface. If the fluid is divided into a plurality of flow layers parallel to the solid surface, there is no exchange of fluid between the layers, and in this direction perpendicular to the solid surface, the transfer of heat mainly depends on conduction.
Since the thermal conductivity of the fluid is small, the heat dissipation of the solid surface during laminar flow is poor. When the fluid moves in a turbulent motion, the fluid parts no longer maintain the movement parallel to the solid surface, and the irregular vortex is made in all directions at the average flow velocity, at which time the heat transfer mainly depends on the convection.
Since the thermal resistance during convection heat transfer is relatively small, the heat dissipation capability of the solid surface when the fluid is subjected to turbulent flow is remarkably improved. In the case of turbulence, there is still a laminar thin layer near the solid surface, but the larger the flow rate of the fluid, the thinner the laminar layer and the higher the surface heat dissipation capability. When convective heat is dissipated, the surface heat dissipation capability is also related to the physical properties of the cooling medium (such as thermal conductivity, specific heat, severity, etc.) as well as the geometry and size of the solid surface and its location in the fluid.
