NM provided an update at work conducted at Vectura to support Darryl’s investigations, and provided an industry perspective on using ΔP measurements for in-use impactor monitoring.

Vectura are currently gathering data on their in-use NGI’s to determine whether the ΔP measurements are sensitive enough to detect atypical impactor results. They are currently awaiting mensuration of the uncleaned NGI to determine correlation of ΔP with changes in nozzle diameter.

The presentation raised the following observations:

• JTS asked if analytical noise could mask ΔP effects? (team concluded that more data is needed to assess this)
• CB raised the issue of whether the MOC performance could be assessed in any way
• JM/DR commented that if shown to be useful this could form the basis of a future system suitability test

MC/DR commented that the issue of whether impactor manufacturing tolerance limits were appropriate for in-use limits. If these could be widened would ΔP be more useful?

• JM commented that that AIM is under consideration for inclusion in the Ph Eur, and is being discussed by the USP
• HM asked whether the impactor group can recommend suitable AIM options for future effective use, and that perhaps the questionnaire data could inform this process?
• CB commented that the AIM questionnaire has provided background information for the CFD programme and highlighted the divergent approaches in use. Everybody should be encouraged to publish available data which may help the industry to focus on a reduced number of key devices going forward
• MC commented that AIM is probably in Wider use than our current knowledge indicates (possibly during early phase development when considered low risk)

The group took an action to gather more information regarding which devices are in use, with a view to designing a more specific questionnaire to gauge wealth of available data, and to consider circulating the questionnaire to users outside of the impactor group (Copley may be able to help with this if we decide to explore this option). The group should also consider whether a new workshop (perhaps at a future DDL?) would be useful to present new data to a wider audience.

Current Projects Report

• HV is currently drafting a publication to cover the study of transient flow in the impactor.
• HV provided a summary of CFD project modelling flow and particle deposition in the rNGI – Inclusion of filter at stage 3 of the impactor, induces a significant ΔP at stage 3 in steady state. Future work will study transient flow but this is complex to do.
• Model of flow & particle deposition in FSI – HV reported successful development of transient and steady state models

Modelling of particle deposition – HV reported that Steady flow model reveals complex flow distribution in single nozzle impactor and that Collection efficiency curves can be matched to data by adjusting models of turbulence and particle restitution behaviour.

Future Studies

Four options for future work were presented, of these option 3 – Study effect of low, medium and high resistance on transient flow through cascade impactors – was preferred.