Experimental investigation on performances and characteristics of nitrogen-charged cryogenic loop heat pipe with wick-mounted condenser

A cryogenic loop heat pipe (CLHP) provides a highly efficient thermal-conductive link between a cryogenic heat source such as an infrared detector and a cryogenic heat sink like a cryocooler in a spacecraft. The CLHP inherently has a large thermal inertia by the influence of latent heat during phase changes and large heat-transfer coefficients in boiling and condensing of working fluid in cryogenic operating temperatures. This paper presents the experimental results of the nitrogen-charged CLHP which adopts the compact cylindrical wick-mounted condenser and its operational characteristics. The improved compact condenser design was proposed and analyzed comparatively. The recovery of the CLHP to normal state after freezing of the working fluid was verified, and the specific matching characteristic of the heat loads on the primary and secondary evaporators were investigated. The thermal performance and thermal-hydraulic behavior of the CLHP with 680 mm effective heat transport length by stepwise heat-loads were analyzed including state-keeping head load change. The effective thermal conductivity of the CLHP was 112,393 W/(m.K) across 680 mm effective length with 3.1 K temperature difference, which is about 230 times higher than that of a pure copper rod (RRR = 300) in 100 K with 12.17 W heat load.