Acceleration-induced depriming of external artery heat pipes

Abstract

Analysis T WO external artery heat pipes are currently under consideration for use as radiator elements on Space Station Freedom.* Both of these utilize a liquid and vapor channel connected by a longitudinal slot to provide axial pumping, Fig. 1. Although previous analytical and experimental investigations have demonstrated that these heat pipes will prime properly iii a zero-g environment, little is known about the effect of accelerations caused by orbital attitude adjustments or docking maneuvers. These accelerations, particularly longitudinal accelerations, could result in redistribution of the working fluid and dry out of the evaporator. This would require a reduction in the evaporator heat flux to allow rewetting. In the present work, an analytical investigation was conducted to determine what reduction in heat flux would be required and the effect of short-term longitudinal accelerations on the liquid/vapor interface. Assuming the heat pipe is properly primed and operating normally in a zero-g environment, the most damaging accelerations will be those occurring along the longitudinal axis because these are most likely to deprime the liquid channel. When the magnitude and/or duration of the acceleration is sufficient, liquid will flow out of the liquid channel through the connecting slot and accumulate in the end of the liquid and vapor channels, opposite the direction of acceleration. Because this flow may occur quite rapidly, some of the liquid may remain in the slot or adhere to the surface of the liquid and vapor channels forming a thin liquid film flowing along the length of the heat pipe. Although the flow of liquid out of the liquid channel and into the vapor channel is the most significant, the flow