Experimental Study on Periodical Fluctuations of the Diffuse Vapor/Gas Front during Operation of a Gas-Loaded Heat Pipe

A test sequence with two gas-loaded heat pipes of different geometry with external noncondensable gas reservoirs was performed in order to detect, analyze and classify conjugated and detached fluctuations of evaporator temperature, operating temperature and the position of the vapor/gas front after start-up. The fluctuations become noticeable at operation with more than half of the condenser open and gain force the more the front approaches the condenser end. It was found that amplitude, frequency and polarity of the fluctuations also depend on the magnitude of a heat load step change, the gas charge and the working fluid. A method is mentioned of how to dampen the fluctuations.