Rotating Heat Pipes
The Rotating Heat Pipe (RHP) is a two phase heat transfer device that is designed to cool machinery by removing heat through a rotating shaft. As shown in Figure 1 below, heat input to the evaporator vaporizes the working fluid. As in a normal heat pipe, the vapor travels down the heat pipe to the condenser, where heat is removed as the vapor condenses. While a normal heat pipe uses a wick to return the condensate, a rotating heat pipe uses centrifugal forces. The inside of the heat pipe is a conical frustum, with the evaporator inside diameter (I.D.) larger than the condenser I.D. A portion of the centrifugal force is directed along the heat pipe wall, due to the slight taper. A copper-methanol rotating heat pipe is shown in Figure 2.
Rotating Heat Pipes can be used to remove heat generated in motors and other rotating machinery, e.g., electric motor/stator heat build-up, gear heat loads, bearing heat generation, etc. Most shaft are made of steel or stainless steel and have poor thermal conductivity. By implementing heat pipes into the shaft, the effective thermal conductivity can be increased with little strength/weight penalty
Figure 3 and Figure 4 show a rotating heat pipe test apparatus developed by ACT. It is capable of testing at rotational speeds up to 10,000 RPM, with an IR heater capable of 4kW supplying heat to the evaporator, and a liquid cooled condenser. RTD temperature sensors and high speed slip ring are used with a Keithley DAQ system to provide real time data readings.