Theory of the axial dry-out heat flux of gravity-assist heat pipes with capillary flow

A theory for the axial dry-out heat flux of gravity-assist heat pipes with capillary flow is developed by deriving formulas for the limiting case of incompressible flow, with the assumption that no entrainment and boiling occurs, and a numerical solution is presented for the case of compressible inertia flow. A decrease in the axial dry-out heat flux occurs in each case by an increase in the relative contribution of gravity to the total pumping force. Thus, the total pumping force required for reaching the same limit rises with a corresponding increase in the ratio of the gravity to capillary pumping forces. It is proposed that this theory be used for an experimental investigation of the significance of entrainment from capillary structures in gravity-assist heat pipes.