2 research outputs found
A cross-industry assessment of the flow rate-elapsed time profiles of test equipment typically used for dry-powder inhaler (DPI) testing: Part 2ā analysis of transient air flow in the testing of DPIs with compendial cascade impactors
We describe a computational model that captures the physics of the unsteady airflow start-up that accompanies the testing of dry-powder inhalers (DPI) with cascade
impactors (CIs) specifically when following methods described in the pharmacopeial
compendia. This transient has been measured in a multi-organization study for a wide
range of conditions and reported in a companion article. The DPI test system is simulated
as a series of flow resistances, starting with the inhaler itself, including each stage of the
CI, and finishing with the prescribed flow control valve, wherein the flow is held at sonic
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velocity. The resulting non-dimensional equations indicate the relative importance of the
several flow resistances. The model agrees well with the available experimental data for
the Next Generation Impactor (NGIā¢) and qualitatively with the available data from a
variety of the configurations of the Andersen 8-stage cascade impactor (ACI), including
the typical 4-kPa pressure drop across an entry fixed orifice mimicking surrogate low-,
medium- and high-resistance DPIs. The model indicates that the start-up times for the
NGI and for the ACI are very reasonably estimated by a simple āreference time,ā given in
equation (26) and, for an inlet flow rate of 60 L/min, having a value of 277 ms and 113
ms for the NGI and ACI (60-L/min configuration), respectively. The model also enables a
baseline, universal design curve for the flow rise-time performance of testing DPIs with
the NGI (Figures 9a,b), because this impactor requires no change of components for any
inlet flow rate
A cross-industry assessment of the flow rate-time profiles of test equipment typically used for dry-powder inhaler (DPI) testing: Part 1 ā compendial apparatuses
We report a cross-industry study characterizing flow rate-time profiles of equipment used for testing dry-powder inhalers
(DPIs). Nine organizations used the same thermal mass flow sensor to record flow rate-time profiles at the inlet of
individual participant compendial DPI test systems including either sample collection tubes (SCT), the Andersen 8-stage
non-viable impactor (ACI) or the Next Generation Impactor (NGIā¢) with and without pre-separator (PS). The plan
included some tests with a surrogate DPI consisting of one of three inlet orifices chosen to generate a 4-kPa pressure drop
at each of the target final flow rates of 30, 60, and 90 l.minā1, simulating the pressure drop typical of high-, medium-, and
low-resistance DPIs. When a particular surrogate DPI was present at the inlet, rise times to 90% of these target flow rates
(t90) were shortest at the highest target flow rate, and decreased linearly with decreasing apparatus internal volume,
following the order: NGI-PS>NGI>ACI-PS>ACI>SCT. A flow acceleration parameter was also evaluated, expressed as
the slope between the rise times when the flow rate attained 20% and 80% of each final steady flow rate (slopet20/80).
Flow acceleration was smallest at the lowest target flow rate, decreasing exponentially with increasing internal volume.
Measurements were also made without the surrogate DPI, providing a reference condition with no resistance at the inlet
to the apparatus. These flow rate-rise time profiles will be useful for those involved in evaluating equipment for
characterizing DPIs and in understanding the behavior of these inhalers in development or commercial production