Modeling of gas flow inside and outside the nozzle used in spray deposition

In spray deposition, the flow pattern of atomizing gas plays an important role in the atomization process. In the present investigation, gas flow inside and outside the nozzle is analyzed numerically using a commercial computational fluid dynamics software Fluent®. Analysis is carried out for various nozzle configurations, protrusion lengths of the melt delivery tube and applied gas pressures. Two types of nozzle configurations are considered, the first one is a convergent nozzle and in the second one, a small parallel portion of various lengths is attached at the end of the convergent nozzle. The analysis shows that pressure, velocity, temperature and density of atomizing gas at the nozzle exit does not change much for various nozzle configurations, whereas turbulent kinetic energy is drastically reduced when a parallel portion is attached at the end of the convergent nozzle. A protrusion length between 2 and 3 mm is found to be optimum for the nozzles with a parallel portion at the end of the nozzle as it gives rise to lowest aspiration pressure, which assists in melt flowing out of the delivery tube. A decrease in aspiration pressure with increase in protrusion length from 0 to 2 mm is experimentally verified.