Heat transfer characteristics in the heating section of a closed two-phase thermosyphon working with a binary mixture

A heat pipe with a working fluid of binary mixture is a more advantageous heat transfer device than a gas-loaded variable-conductance heat pipe controlling the temperature of the electric devices which is important in the recent industrial field. In the present study heat transfer characteristics of a closed two-phase thermosyphon, a gravity-assisted wickless heat pipe, was experimentally and analytically investigated. The working fluid was the mixture of ethanol and water. The axial temperature distribution at the heating wall obtained experimentally was very different from that in the case of a one-component (pure) working fluid. This is due to the axial distribution of the concentration of ethanol (the more volatile component). In order to estimate these concentration and temperature distributions, an analytical model was introduced, in which we took the vapor-liquid phase equilibrium of the binary mixture and the mass conservation of ethanol into consideration. The calculated results agreed well with the experimental data.