Two-Phase Mach Numbers in Heat Pipe Analysis

Abstract

E analyzing one-dimensional flow of a compressible two-phase ixture in a heat pipe of constant vapor passage diameter D, Levy uses several plausible assumptions to obtain approximate digital integration of his equations. His solutions suggest without explicit proof infinite gradients in various properties at the downstream end of the evaporator. In this paper the gradients are re-examined after transforming them in terms of an equilibrium two-phase Mach number. It is then shown that the assumption of a uniform mass injection rate me = nDpgVn, where Vn is the radial mass injection velocity, apparently leads to infinite gradients; however, second law analysis rules out a constant me as well as a uniform heat addition rate per unit length of evaporator, Qe = me(hfg + Vn/2), leaving the gradients indeterminate. The subscripts / and g denote liquid and vapor phases.