Thomas Daly1, 2, Tony Mallett1, Daniel McCluskey2 & Darragh Murnane2
1Bespak, Bergen Way, King’s Lynn, PE30 2JJ, United Kingdom
2University of Hertfordshire, College Lane, Hatfield, AL10 9AB, United Kingdom
Summary
The refill phase of pressurised Metered Dose Inhalers (pMDIs), which immediately follows actuation, remains significantly less studied compared to the actuation stage, where dose delivery and aerosol spray characteristics have typically been the focus. This study used Computational Fluid Dynamics (CFD) to analyse the transient behaviour of a capillary retention metering valve using both current (HFA-134a, HFA-227ea) and next-generation low Global Warming Potential (GWP) propellants (HFA-152a, HFO-1234ze(E)). The simulation captured transient data, including metering chamber pressure, temperature, and liquid fill percent over an initial 300 ms duration. Reopening of the metering chamber to the canister reservoir was included in the simulation and a Eulerian multiphase mixture method was employed. Results indicate clear differences between the filling performance of propellants. HFA-152a achieved the highest liquid fill level (88.3% at 300 ms), followed by HFA-134a (87.1%), HFO-1234ze(E) (75.9%), and HFA-227ea (65.7%).
The development of this model provides a framework for exploring metering valve geometries and a foundation for evaluating formulation-specific refill dynamics for capillary retention metering valves but can be easily extended to primeless metering valves. Ongoing and future work will include sensitivity analysis of model inputs and mesh optimisation to enhance simulation accuracy. Experimental data will be obtained from high-speed x-ray imaging to validate the transient metering chamber liquid fill level during refill.