Effects of gravity on gas-loaded variable conductance heat pipes

The effects of gravity on the operation of gas-loaded variable conductance heat pipes have been investigated. Experimental results have been obtained for three heat pipes (1.6 cm, 2.5 cm and 5 cm diameter) operating with methanol or Freon 113 as the working fluid and krypton or helium as the control gas. Results show that gravity tends to distort the axial temperature profiles on the small diameter pipe. For the large diameter pipe gravity has the effect of causing a stratification of the working fluid and non-condensible gas. These results seem to indicate that in certain cases the presently available design procedure will have to be modified to account for the effects of gravity on variable conductance heat pipe operation.