Issue link: https://www.e-digitaleditions.com/i/1515319
14 February 2024 Inhalation sity of the gas and its high vapor pressure. ese act together to enhance entrainment of the surrounding air and turbulent mixing in the spray, increasing the likelihood of mouthpiece and actuator deposition. In recent work (not shown), we have demonstrated that HFO-1234ze(E) formulations show greater plume variability from shot to shot [21], which we attribute to reduced mixing of the spray with ambient air. Other recent work has shown that spray stability changes are primarily initiated at the orifice [21]. Most importantly, we have also observed in simu- lations that the stability and repeatability challenges observed in these experimental studies can be min- imized by making minor modifications in orifice geometry (such as orifice length or diameter), pro- viding a route to adjustment of low-GWP pMDIs toward equivalence with existing formulations [22]. Matured aerosol performance e most important consequence of propellant choice is its effect on the matured aerosol since spray event and the shot-to-shot repeatability from one spray to the next for a range of formulations. e results of our preliminary analysis are shown in Figure 3 for BDP solution formulations with 8% w/w ethanol co-solvent as described above. e schematic (top left) shows the region of the actuator observed in the high-speed images (top right). e colored panels in the lower portion of the figure show the average plume structure, temporal stability and shot-to-shot repeatability of the spray plumes (top row to bottom row, respectively). ese were obtained from statis- tical analysis of the high-speed imaging data. e column headings name the propellants. All other hardware, formulation and ambient properties were held constant across the tests. Our data show that the average plume structure does not vary greatly with propellant change, and the presence of co- solvent acts to moderate the differences between propel- lants. However, the higher-order statistics reveal more interesting differences. HFA-152a formula- tions show more unstable plume behavior over time than HFA-134a. is is likely due to the lower den- High speed image Flow 5 mm Statistical analysis HFA-134a HFA-152a HFO-1234ze(E) 0 10 20 0 10 20 0 10 20 Distance from orifice (mm) 0 10 20 0 10 20 0 10 20 0 10 20 0 10 20 0 10 20 -2 0 2 4 6 8 -2 0 2 4 6 8 -2 0 2 4 6 8 -2 0 2 4 6 8 -2 0 2 4 6 8 -2 0 2 4 6 8 -2 0 2 4 6 8 -2 0 2 4 6 8 -2 0 2 4 6 8 Repeatability Stability Average 0.6 0.4 0.2 0 0.02 0.01 0 0.2 0.1 0 Figure 3 High-speed analysis of ex-orifice plume structure for matched hardware with various formulations. The formulations contained 8% w/w ethanol and 2.0 mg/mL BDP in each propellant. The horizontal and vertical axes are given in mm relative to the location of the orifice.