Pressurised metered-dose inhaler spray structure

Sprays with and without ethanol issuing from a pressurised metered-dose inhalers (pMDI) are studied with Mie scattering, particle image velocimetry and laser extinction. Preliminary PIV measurements in the sagittal plane show that axial velocities are lower immediately downstream of the mouthpiece for ethanol-containing sprays at 50 ms after the start of actuation; further downstream, the velocity appears equal for both formulations. Vertical profiles of axial velocity collapse to a single curve when non-dimensionalised by peak velocity and distance from the atomising nozzle, suggesting that outside the mouthpiece the mean spray behaves like a self-similar turbulent jet. High turbulence intensities for the axial and vertical velocity fluctuations are measured, and found to decay with increasing axial distance from the nozzle. Laser extinction measurements downstream of the mouthpiece reveal an intermittent high amplitude fluctuation in spray density, an observation consistent with conjectures from prior studies of pMDIs with less temporal resolution. Propellant-only sprays are found to have higher fluctuations in absorption, indicative of a higher amplitude pulsation taking place in the nozzle.