Development of Meter-scale O-shaped and U-shaped Oscillating Heat Pipes for GAPS

Meter-scale Oscillating Heat Pipe (OHP) has been developed for the General Anti Particle Spectrometer (GAPS) project. Two types of the OHP routing have been investigated. One is a U-shaped routing and the other is an O-shaped routing. For the operation at low temperature, R410A was used as the working fluid. As the result of the investigation, we verified for the first time that both the meter-scale O-shaped and U-shaped OHPs can transfer heat in gravity at low temperature. Between the heat input section and the radiator section, the thermal conductance larger than 10 W/K was achieved under particular sets of conditions. In terms of thermal characteristics, the O-shaped OHP showed better performance than the U-shaped OHP. The O-shaped OHP started up more quickly than the U-shaped OHP at low temperature. The temperature uniformity of the O-shaped-OHP heating section was also better without drying-out at around the top of the heating section. The U-shaped OHP could transfer heat at temperatures above around 240 K, and the O-shaped OHP could transfer heat at temperatures above around 210 K. We consider the O-shaped OHP utilizes the gravity to assist the circulation of the working fluid resulting in better performance.