Effect of the thermo-physical properties of the working fluid on the performance of a 1-m long cryogenic horizontal pulsating heat pipe

Abstract

The growing industry of high-temperature superconducting magnets needs to be accompanied by the development of new cryogenic cooling techniques characterized by low fluid consumption, lightness, and adaptability. For this purpose, cryogenic pulsating heat pipes have been studied over the last decade as possible thermal links generally associated with cryocoolers. This paper presents the thermal performance of a one-meter long horizontal pulsating heat pipe using argon as working fluid. Operating at temperatures between 88 and 110 K, the system is able to transfer up to 25 W of heat load and attains a maximum equivalent thermal conductivity of 85 kW/m.K at 20 W. The experimental results have been compared with previous experiments using nitrogen and neon as working fluids. Analyzing in detail the pressure evolution and temperature distribution of the central capillary tube of the adiabatic part, differences in the thermo-hydraulic behavior of the fluid are observed and can be linked to the thermo-physical properties of these three fluids. When operating with neon, the circulation of the fluid in the PHP is more dynamic, ensured by a larger amounts of vapor, while the heat is mainly carried by sensible heat through the liquid parts. With nitrogen, the heat is more transferred by phase change processes than with the two other fluids, which requires a higher filling ratio for the boiling and condensation phenomena leading to the highest filling ratio. The PHP with argon has heat transfer characteristics and filling ratios that lie between the other two fluids due to the combinations of its thermophysical properties, i.e. leading to an intermediate filling ratio but having the slowest fluid motion due to its thermo-physical properties associated with the fluid movement.