Uniaxial model for gas-loaded variable conductance heat pipe performance; the effects of vapor flow, friction and inertia

A uniaxial model for the transient performance of gas-loaded variable conductance heat pipes is described. The model is steady-state and accounts for diffusion at the vapor-gas interface, inertia and friction of the moving vapor, and radial conduction in the wall and wick. Calculations show that: diffusion is negligible; inertial effects are considerable in the operating range characterized by low vapor pressure. Friction, causing velocity increase of subsonic flow, enhances the impact of inertia and widens the operating range. Results of calculations with a flat front model (the uniaxial model in the limit of zero diffusivity) predict performance and controllability figures that considerably differ from those predicted by models which neglect inertia and friction.