On regular and retrograde condensation in multiphase compressible flows

Abstract

Two distinctive condensation mechanisms of pure species, regular and retrograde condensation, are investigated using a one-fluid model and a homogeneous phase equilibrium model based on entropy maximization. Fluid dynamics simulations are performed to model the regular condensation process of ethylene in a converging nozzle, and the retrograde condensation process of a fluorinated compound in a shock tube. To our knowledge, the present simulations are the first CFD simulations of retrograde condensation processes. The simulations show reasonably good agreement with available experimental data both quantitatively and qualitatively, which confirms the consistency between the theory-guided simulations and experiments. For the supercritical injection problem, condensation is found to occur after continuous expansion when ethylene is brought into the two-phase region from a supercritical state. For the shock tube problem, both simulations and experiments show that condensation occurs after the high pressure reflected shock is formed from the end wall. Increase in the initial pressure ratio increases the incident shock strength and reinforces condensation by elevating the liquid volume fraction. A complete liquefaction shock is found at high incident shock Mach numbers when the compression is strong enough to send the fluid from the pure vapor to the pure liquid state by crossing the two-phase mixture region. After condensation, the condensed liquid phase is fully depleted as the pressure wave expands and the fluid is brought back to the vapor state though a continuous evaporation process.