Effect of Working Fluid and Fluid Loading on the Performance of Rotating Heat Pipes

Abstract

<p>The steady state heat transfer performance of axially rotating heat pipes with methanol, ethanol and water as working fluid was measured for rotational speeds up to 4000 RPM, or centrifugal acceleration up to 150g, and heat transfer rates up to 0.7 kW. The measurements were used to characterize the effect of working fluid and fluid loading on the heat transfer performance of the rotating heat pipes with 10 internal condenser taper and straight adiabatic and evaporator sections. The effect of working fluid was examined for heat pipes where the liquid occupied approximately 19% of the pipe interior volume. In the heat pipes with ethanol and methanol as the working fluid, the thermal resistance of the heat pipes decreased as the heat flux increased before reaching a constant value. However, in the case of heat pipe with water, the thermal resistance increased with the increase in heat flux before appearing to reach a constant value. It was found that the thermal resistance of methanol and ethanol heat pipes were 50% to 80% larger than the thermal resistance of the water heat pipe.</p> <p>The effect of fluid loading was examined for three heat pipes using water as the working fluid where the liquid occupied approximately 6%, 7% and 19% of the pipe interior volume. It was found that the heat pipe with the lowest amount of water failed to operate. In this case, the thermal resistance was dramatically larger than the other heat pipes even at low heat fluxes. The heat pipe with 7% of water operated normally and had a thermal resistance smaller than the heat pipe with 19% of water.</p> <p>The experimental results were compared to predictions from an existing analytical model for high speed rotating heat pipes that accounts for natural convection heat transfer within the liquid film at the evaporator at high accelerations. The predictions from the model were in reasonable agreement with the experimental results for the heat pipes with water as the working fluid. The model over predicted the thermal resistance for the heat pipes with methanol and ethanol as the working fluids by 50% to 80%.</p>