Flow field measurement inside the mouthpiece of the Spiros inhaler using particle image velocimetry

Flow field distributions inside the mouthpiece of a Spiros inhaler, a dry powder inhaler delivering therapeutic powders to airways, were investigated by means of the particle image velocimetry technique. The aim of the study was to obtain flow patterns inside the mouthpiece at various flow rates for characterizing dynamics related to drug dispersion. Particle image velocimetry results revealed a strong turbulent flow structure in the mouthpiece at all the flow rates tested, ranging from 15 lpm to 35 lpm. Strong counter-clockwise rotating flow, as viewed from downstream, prevailed due to upstream tangential air injection introduced into the mouthpiece by 4 holes equally spaced along the perimeter. The air jets were designed to introduce high kinetic energy along the wall of the mouthpiece in an attempt to prevent particle deposition onto the wall, thus reducing drug losses, by creating a circulating sheath of air along the surface. Experimental results indicated that excess core flow mixing prior to the full formation of the sheath of air caused particle collisions with the mouthpiece wall as a result of the strong tangential air injection.