Operating limits heat pipe viscous limit

At low temperatures, viscous forces are dominant in the vapor flow down the heat pipe. At very low operating temperature, the vapor pressure difference between the closed ends of the evaporator (the high-pressure region) may be extremely small. Because of the small pressure difference, the viscous forces within the vapor region may prove to be dominant and hence limit the heat pipe operation. From the 2-D analysis by Busse,... 

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