Titanium-Water Loop Heat Pipe Operating Characteristics Under Standard and Elevated Acceleration Fields

Abstract

An experiment has been developed to examine the behavior of a titanium-water loop heat pipe (LHP) under standard and elevated acceleration fields. The LHP was mounted on a 2.44 m diameter centrifuge table on edge with heat applied to the evaporator via a mica heater and heat rejected using a high-temperature polyalphaolefin oil (PAO) coolant loop. The LHP was tested under the following parametric ranges: heat load at the evaporator, 100 ≤ Qin ≤ 600 W; heat load at the compensation chamber, 0 ≤ Qcc ≤ 50 W; radial acceleration, 0 ≤ ar ≤ 10 g. For stationary operation, the evaporative heat transfer coefficient decreased monotonically with heat load while the thermal resistance decreased to a minimum then increased. Heat input to the compensation chamber was found to increase the evaporative heat transfer coefficient and decrease the thermal resistance for Qin = 500 W. Transient periodic flow reversal in the LHP was found for some cases, which was likely due to vapor bubble formation in the primary wick. Operation in an elevated acceleration environment revealed that dry-out was dependent on both Qin and ar, and the ability for the LHP to reprime after an acceleration event that induced dry-out was influenced by the evaporator temperature. The evaporative heat transfer coefficient and thermal resistance were found not to be significantly dependent on radial acceleration. However, the evaporator wall superheat was found to increase slightly with radial acceleration at high heat loads.