Theoretical investigations of hydrogen, nitrogen, and oxygen homogenous and annular wick heat pipes

In any heat pipe, the capillary pressure developed at the liquid-vapour interface balances the sum of the various pressure drops throughout the pipe. This study analyses the different contributions to pressure drop for both homogenous wick and annular wick heat pipes operating at low temperatures. The pressure drop in the wick structure is of primary importance for a homogenous wick heat pipe. The heat transfer capacity of an annular-wick heat pipe is strongly affected by the interphase pressure drop due to non-zero evaporation and condensation rates at the liquid-vapour interfaces. Theoretical heat transfer rates as functions of the vapour temperature have been computed for both homogenous and annular wick structures of heat pipes using hydrogen, nitrogen, and oxygen as working fluids. The heat transfer capacity of the annular wick design is more than an order of magnitude higher than that of the corresponding homogenous wick design.