Near-monodisperse spray

An attractive feature of rotary atomization is the nearly uniform droplets produced with small disks at high rotational speeds and low liquid flow rates. Therefore, rotary atomization is probably the most generally successful method for producing moderately monodisperse sprays over a wide range of droplet sizes. The mean... 

Another example of dryer selection is related to the choice of a suitable atomizer for a spray dryer. A spray dryer is indicated when a pumpable slurry, solution, or suspension is to be reduced to a free-flowing powder. With proper choice of atomizer, spray chamber design, gas temperature, and flow rate it is possible to engineer powders of desired particle size and size distribution. Table 47.2 shows how the choice of the atomizer affects chamber design, size, as well as energy consumption of atomization and particle size distribution. The newly developed two-fluid sonic nozzles appear to be especially attractive choices when nearly monodisperse powders need to be produced from relatively moderate viscosity feeds (e.g., under 250 cP) at capacities up to 80 t/h by using multiple nozzles. More examples may be found in Kudra and Mujumdar [20]. 

Custom-made SFD towers and apparatuses have been designed, built and improved to produce nearly monodisperse, low-density lyophilisate powders suitable for pulmonary dmg delivery. Spray-freeze-dried particles were characterized regarding their mean geometric particle size, aerodynamic behaviour, surface morphology and interior structure, API (protein) stabihty, powder flowability and reconstitution characteristics. 

It should be noted that some problems may arise in the techniques or devices for producing monodisperse or near-monodis-perse sprays. One of the problems is droplet coalescence. Initially uniform droplets may coalesce rapidly to create doublets or triplets, particularly in a dense and turbulent spray, deteriorating the monodispersity of the droplets. This problem may be lessened by using appropriate dispersion air around the spray.[88] Another problem is non-spherical droplet shapes that make estimations of monodispersity difficult. 

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