In-silico prediction of pMDI performance with low-GWP propellants HFA-152a and HFO-1234ze(E)

The transition to low greenhouse warming potential propellants for pressurised metered dose inhalers will necessarily require a redesign of the nozzle orifice to compensate for changes in physicochemical properties such as reduced vapour pressure, density, and increased saturation temperature. New propellants have reduced spray momentum, reduced flash-evaporation, altered spray morphology resulting in larger primary droplet size at the orifice. Investigating these phenomena is challenging due to the large parameter space for orifice and actuator design and multiple propellant candidates that must be searched in order to find an optimal arrangement. A cost-effective solution to this problem is the use of in silico models which can search the parameter space quickly by running dozens of detailed computational fluid dynamics simulations on hundreds to thousands of processors. We present the first results of a parametric study of the effect of orifice diameter and length for solution formulations with propellants HFA-134a, HFA-152 and HFO-1234ze(E). The simulations are capable of capturing trends in near-orifice spray structure and accurately predicting droplet size. We show that manipulation of the orifice geometry may be able to compensate for the differences between propellants.