A comparison of the equilibrium and the droplets based non-equilibrium compressible phase change solvers for condensation of carbon dioxide inside nozzles

Abstract

In the current work, we simulate the condensation of supercritical CO2 during its high speed flow inside two different converging-diverging nozzles. We use the homogeneous equilibrium method and the classical nucleation theory based non-equilibrium phase change model for this purpose. The simulation results indicate significant influence of the nozzle inlet condition, nozzle shape and the fluid thermophysical behaviour on the nonequilibrium conditions prevailing inside the nozzles. We observe very low, 0.15 K, supercooling for the flow of CO2 inside the Claudio Lettieri nozzle compared to the supercooling of 3 K observed for the Berana nozzle. Very high nucleation rate ( 1035 nucleation per m3 per second) is observed before the throat of the nozzles which remains confined to a very small axial distance. The nucleation rate takes much smaller values ( 107 nucleation per m3 per second) in rest of the nozzle. A maximum of 70 nano meter sized droplets with number densities of the order of 1021 droplets per m3 are predicted inside the nozzles. Liquid mass fraction values between 0.2 to 0.4 are predicted by the solvers inside the nozzles. These results will be useful to the engineering community involved in the design and fabrication of CO2 based systems.