ISSN Online: 2377-424X
ISBN Print: 978-1-56700-421-2
International Heat Transfer Conference 15
Startup Characteristic of Loop Heat Pipes for Alpha Magnetic Spectrometer Cryocoolers
Abstract
The alpha magnetic spectrometer is one of the greatest scientific projects, with the main aim of searching for
dark matter and anti-matter. The alpha magnetic spectrometer uses four stirling cryocoolers to extract parasitic
heat from the shield around the helium-cooled magnet. Loop heat pipes, with propylene as the working fluid,
transfer heat from the cryocoolers. In this paper, we investigated the startup behaviors of the loop heat pipes
during thermal vacuum and thermal balance test in the large space simulator. Factors including liquid/vapor
distribution in the evaporator, filling rate of the compensation chamber, and LHP elevation were investigated.
Startup proved easier when vapor was present in the vapor grooves, whereas vapor in the evaporator core had an
adverse effect. When the vapor grooves are liquid-filled, the startup process can be divided into three stages:
heating of the loop heat pipe components before superheating establishes, nucleate boiling after superheating is
satisfied, and successful loop circulation. When the vapor grooves are vapor-filled, there are only two stages in
LHPs: nucleate boiling and loop circulation establishment. Examination of the effect of compensation chamber
filling rate on startup characteristics showed that reverse flow occurred when vapor was present in the
compensation chamber and startup proved difficult. Filling rate of the compensation chamber should be
sufficient to provide thorough wetting of the capillary structure, as otherwise wick dry-out may occur and
prevent loop heat pipe startup.