Effect of heat load to a capillary starter pump on the thermal characteristics of a 2-m nitrogen cryogenic loop heat pipe

Abstract

A thermal characteristic of a nitrogen-charged cryogenic loop heat pipe (CLHP) with an auxiliary loop and a capillary starter pump (CSP) was investigated in this study. One of the advantages of CLHPs is their high heat transfer capability over a long distance. However, there are only few studies on CLHPs with heat transfer lengths over 1 m. The effect of the CSP heat loads on the heat transfer characteristics has not been studied for the long-distance CLHPs, so far. To determine them, a 2-m nitrogen CLHP operating at 80 K–100 K was developed. The designed evaporator and CSP had stainless steel porous wicks with a pore radius of 1.0 µm and a permeability of 1.3 × 10−13 m2. The lengths of the vapor line and liquid line were 2000 mm. Experiments were conducted with CSP heat loads of 0, 2, and 4 W under horizontal condition. Based on the results, the CLHP successfully demonstrated a supercritical start-up when the heat loads to the evaporator and CSP were 4 W. The CLHP stably operated when evaporator heat loads of 4–24 W were applied while the operating temperature was within 80 K–86 K. The maximum heat transfer capability was 24 W for the CSP heat loads of 0, 2, and 4 W. On the other hand, the thermal resistance tended to be higher as the CSP heat load increased. The minimum CLHP thermal resistance was 0.064 K/W when the CSP heat load was 0 W. In addition, the effect of CSP heat load on the temperature difference between two compensation chambers and between the CSP and the condenser was discussed.