Variable-Conductance Behavior in Two-Phase Binary Thermosyphons

Two-phase closed thermosyphons using binary mixtures of working fluids can provide equal or superior variable-conductance performance compared to gas-loaded heal pipes. This analysis of binary reflux thermosyphons examines both ideal devices, where no mixing or diffusion occurs in the liquid film and the vapor flow is laminar, and real devices, where some mixing occurs. The total pressure and evaporator temperature change only slightly over wide ranges of power input, reaching equilibrium at values that just allow complete condensation. By introducing two empirical mixing parameters, mixing in the vapor and film can be accounted for, providing good agreement with experimental measurements.