Application of computational fluid dynamic simulations to spray-freezing operations

Spray-freezing is an important precursor to spray-freeze-drying operations. A 3-D CFD simulation for spray-freezing was developed and was used to identify design improvements to avoid problems such as high particle temperatures and low particle collection efficiencies. This model included the latent heat of fusion by increasing the effective specific heat capacity of the particles over the temperature range -10 to 0 ºC. The model was also able to track particles to calculate particle residence time distributions and outlet particle collection efficiencies. The simulation predictions agreed reasonably well with experimentally measured gas temperatures (obtained by thermocouple measurements) and droplet velocities (obtained by Phase Doppler Anemometry). Both solid and hollow cone sprays were simulated, and the results suggested that a hollow cone spray was more effective in cooling the particles uniformly, but yielded low particle collection efficiency (13%). This could be partially overcome by increasing the diameter of the product outlet to give particle collection efficiencies of 57%. The solid cone spray appeared to show slightly better collection efficiencies for a narrow outlet spray-freezing rig, although the freezing was less uniform.