Influence of pressure transducer protrusion depth on pressure measurements of shock waves in shock tubes

This note investigates how small changes in the protrusion depth of a pressure transducer affect the pressure measurement of a moving shock wave. Measurements are undertaken with Kistler, Kulite, and PCB sensors in flush, recessed, and protruded sensor positions. Measurements of both absolute pressure and Mach number are shown to be insensitive to sensor protrusion depth. An assessment of sensor response time indicates a significantly shorter reaction time for the Kulite and PCB sensors compared with the Kistler sensor.

Drug distribution transients in solution and suspension-based pressurised metered dose inhaler sprays

This paper presents in situ time-resolved drug mass fraction measurements in pressurised metered dose inhaler (PMDI) sprays, using a novel combination of synchrotron X-ray fluorescence and scattering. Equivalent suspension and solution formulations of ipratropium bromide in HFA-134a propellant were considered. Measurements were made both inside the expansion chamber behind the nozzle orifice, and in the first few millimeters of the spray where droplet and particle formation occur. We observed a consistent spike in drug mass fraction at the beginning of the spray when the first fluid exits the nozzle orifice. Approximately 20% of the total delivered dose exits the nozzle in the first 0.1 s of the spray. The drug mass fraction in the droplets immediately upon exiting the nozzle peaked at approximately 50% of the canister mass fraction, asymptoting to approximately 20% of the canister concentration. The effect is due to a change in the drug mass fraction inside the droplets, rather than changes in droplet size or distribution. The transient was found to originate inside the expansion chamber. We propose that this effect may be a major contributor to low delivery efficiency in PMDIs, and have important implications for oropharyngeal deposition and inhalation technique. This highlights the importance of expansion chamber and nozzle design on the structure of PMDI sprays, and indicates areas of focus that may lead to improvement in drug delivery outcomes.