Manipulation of pMDI spray morphology via orifice length variation with propellants HFA134a, HFA227, HFA152a and HFO1234ze(E)

Spray structure and development are important influences on the performance of pressurized metered dose inhalers (pMDIs) [1]. Spray atomization plays a pivotal role in determining droplet size and distribution. The spray pattern impacts droplet deposition [2], altering the delivered dosage. Orifice configuration, which determines the initial conditions for the spray, is thus a crucial design parameter in determining pMDI spray development. With the transition to low-global warming potential (GWP) propellants such as HFA152a and HFO1234ze(E) now underway [3], manipulation of the pMDI orifice provides an alternative route to in vitro bioequivalence with respect to factors such as plume pattern, geometry and velocity [4]. This study investigates the influence of orifice length-to-diameter ratio as a controlling parameter for pMDI sprays across current and novel propellants using a high-speed imaging technique.