Experimental Analysis of Supercritical Startup of Nitrogen/Stainless Steel Cryogenic Heat Pipe

Abstract

An experimental investigation of the supercritical startup of a nitrogen/stainless steel cryogenic heat pipe is presented. A detailed description of the experimental setup used for this investigation is presented, and several data sets for the transient axial temperature distribution of the heat pipe are shown. A transient, one-dimensional model developed for microgravity environment available in the literature is used to obtain the internal pressure and working fluid axial distribution. The results showed that cryogenic heat pipes are very sensitive to parasitic heat loads (e.g., heat convection), even in rarefied atmospheres, and the parasitic heat loads can significantly change the operational temperature of the cryogenic heat pipe. The effects of parasitic heat loads must be accurately considered during the design stages. Also, the fluid charge plays an important role in the determination of the initial thermodynamic state of the cryogenic heat pipe. An excess of fluid charge may prevent a successful startup due to an increased vapor pressure, whereas a deficiency may prevent the startup due to lack of working fluid to sufficiently prime the heat pipe.