(254d) Multi-Phase Mathematical Modeling of Compressed CO2 Expansion through a Coanda Nozzle

A Coanda nozzle can be used to produce a high velocity mixture of air, gaseous CO₂, and dry ice particles from a supply of liquid CO_2. Such a process is effective (for instance) for residue-free rapid cooling or precision cleaning. A multiphase thermodynamic and computational fluid dynamics (CFD) analysis of this flow is presented for the purpose of optimizing the process parameters, which include the temperature of the liquid CO₂ supply, the flow rate, and the pressure and nozzle and air configuration.

Temperature, pressure, velocity and mass fraction profile distributions have been modeled on the spray-nozzle system. Flow characteristics have been quantified for dry ice particle sizes of 1.0x10^-3m, 1.0x10^-4m and 1.0x10^-5m. Maximum velocity and residence time as a function of inlet temperature have been simulated and quantified. The analysis suggests that as inlet CO₂ temperature increases, the maximum velocity increases and the particle residence time decreases. Decreasing dry ice particle size decreases the residence time in the nozzle channel. Overall, this study provides a basis for optimizing the temperature and velocity profiles, and thus the cooling or cleaning capacity of such Coanda devices.