Variable-conductance behavior in two-phase binary thermosyphons

Two-phase closed thermosyphons using hinarymixture working fluids can provide equal or superior variable-conductance performance compared to conventional gas-loaded heat pipes. This analysis of binary reflux thermosyphons examines both ideal binary devices, in which no mixing or diffusion occurs in the liquid film and the vapor flow is laminar, and real devices in which some mixing occurs. The total pressure and evaporator temperature change only slightly over wide ranges of power input, reaching equilibrium at values which just allow complete condensation. Two empirical mixing parameters account for mixing in the vapor and film, providing good agreement with experimental data. Nomenclature A e,, = specific heat, J/kg C, = constant, equation (11) D = mass diffusivity, mZ/s E f = fugacity, Pa F 9 = gravitational acceleration, m/sz hl, = latent heat, Jjkg k = thermal conductivity, W/mK Le = Lewis number = k,/p,Dc, rn = film mixing parameter, equation (4) P = absolute pressure, Pa q = power input, W T = radial coordinate, m R Re = Reynolds number, equation (18) = Schmidt number = pJp-D = constant, equation (9), J/mo1