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the thermal performance of a heat pipe depends strongly on its orientation in operation relative to gravity. for a specific orientation, this performance is determined by the wick structure present inside the heat pipe. wick structures exhibiting low capillary pressure perform best in gravity-assisted applications, where the evaporator is located below the condenser.

however, a wick structure producing high capillary pressure will be needed if a heat pipe is to be operated in a gravity adverse orientation. a previous qpedia article detailed how a heat pipe’s performance is really dependent on both orientation and wick structure [1].

this article builds on that same topic, as it presents a review of experimental results obtained with heat pipes, in the shape of round cross sections, in different orientations [2], [3]. the results are compared with data published in the literature [4], [5]. 

click here for the full article in pdf, free.