A comparison of classical nucleation theory and thermal phase change based condensation models

Abstract

In this work, we perform numerical simulations of the condensation process of CO2 inside a converging-diverging nozzle. We use Ansys Fluent for the simulation work. The real gas properties of CO2 are generated in tabular form (including metastable states) using NIST Refprop. We compare the distribution of physical quantities during the high-speed, compressible flow of CO2 inside a nozzle under the Classical Nucleation Theory (CNT) and the Thermal Phase Change (TPC) models. The CNT model is known to be accurate but computationally expensive while the TPC model is computationally cheaper. We observe that the TPC model predicts a knee in the pressure distribution near the throat of the nozzle while CNT predicts a continuous decrease in the pressure. The two solvers predict slightly different temperature, supercooling and liquid mass fraction values in the diverging part of the nozzle. The compressible, phase change simulations under high speed conditions can be performed quickly with the TPC solver. Overall, the TPC based solver appears to be a reliable alternative to the CNT based model.