A Note on the Gas Distribution in a Cylindrical Gas-Loaded Heat Pipe

Abstract

A gas-loaded heat pipe, which contains a fixed quantity of noncondensible gas in addition to the primary heat transfer fluid, is known to have distinct advantages over conventional fixed-conductance heat pipes for thermal control under variable evaporator load conditions (Brennan and Kroliczek, 1979). In order to predict the thermal performance of such a heat pipe, it is necessary to determine the concentration distribution of the noncondensible gas inside the pipe, which is governed by the intricate balance between convective flow and mass diffusion. For the simplest pipe circular in geometry, a two-dimensional configuration must be employed for its analysis. The flat-front model, though extensively used for the initial design of variable-conductance heat pipes (Marcus, 1972), represents the simplest of all approaches by ignoring diffusion altogether. The one-dimensional model of Edwards and Marcus (1972) takes into account diffusion in the axial direction but neglects the effect on the gas distribution due to radial diffusion. The partial solution to the exact two-dimensional formulation given by Peterson and Tien (1989) has emphatically revealed the importance of the radial dependence of the gas distribution on the condenser performance of the heat pipe. As a first step directed toward solving the steady-state two-dimensional problem ofmore » simultaneous heat and mass transfer at the presence of diffusion within a gas-loaded heat pipe of circular cross section, this brief note reports a consistent method for determining the radial dependence of the noncondensible gas concentration distribution. The authors present discussions in the context of heat pipes having a sealed condenser end and a uniform circumferential wick.« less