DPI Flow Visualization: Initial Experimental Results Rob Tuley John Shrimpton

Introduction Motivation Experimental Simplifications Experimental Design & Procedure Some Results Evacuation Timescales Scope and Limitations Conclusions Future work

Motivation To gain a better understanding of how and why the Diskus pocket evacuation occurs. Ultimate aim is to computationally simulate this process – this is the first exploratory set of experiments to produce a data-set to validate these simulations.

Simplifications - Inhalation Inhalation simulated by a linear pressure ramp. time pressure ACTUAL INHALATIONSIMULATED INHALATION

Simplifications - Geometry We tested 4 different geometries, although the results from only two are being presented today: Square U-bendDiskus Replica fully developed turbulent in-flow approx real-scale pocket geometry exact. includes ‘cross-hairs’ at in-flow and out-flow.

Experiment Design Experimental rig designed in a modular fashion for added flexibility. inhalatorpocket geometry power supply and vacuum pressure source. log pressure sensor data optical setup

Geometry modules

Pocket filling Excess powder ‘swiped’ off from surface. Low compression.

Inhalator module Pressure is controlled through a PI control feedback loop.

Optical Setup The square U-bend geometry is backlit with a halogen 1kW floodlight. Diskus replica is front lit with the same halogen flood.

Complete Setup

The two variables examined during the course of the experiments were: Pressure ramp gradient – 4 different ramps were examined, both steeper and shallower than the average real inhalation ramp of -30kPa/s. Powder type – 4 powders were chosen with various shape and cohesive properties… Parameter Space time pressure Pulse -30kPa/s -10kPa/s -3.33kPa/s

Powders Glass particles 0-50  m Nearly perfectly spherical. Small cohesion forces. Aluminium particles 0-44  m Non-spherical flakes. Small cohesion forces. Lactose 6% fines blend Non-spherical. Medium cohesion forces. Lactose 15.8% fines blend Non-spherical. Large cohesion forces.

Video Results pocket channel pocket channel Straight U-bend Diskus Replica

Square U-bend flow features Transient ‘blow-back’ effect

Diskus Replica flow features Strong influence of cross-hairs

Key Points No visible difference in evacuation between glass and aluminium particles. Two modes of evacuation – ‘EROSION’ (glass/aluminium) and ‘FRACTURE’ (15.8% fines lactose). Lactose 6.5% fines behaviour lies between these two extremes. Differences evident between the two geometries considered, but type of pocket evacuation and powder behaviour visibly similar. Difficult to quantify effect of pressure ramps…

Intensity Post-processing Area processed: Normalised intensity = 0 Normalised intensity = 1

Evacuation Timescales

Evacuation Pressures

Pressure Ramps - Glass

Pressure Ramps - Lactose

Key Points Aluminium and glass evacuations are quantifiably equivalent. Lactose 15.8% fines blend seem to evacuate based on instantaneous pressure, not gradient. Glass/Aluminium evacuations, and to a lesser extent lactose 6% fines blend seem to be influenced by pressure gradient, but this may be due to hidden 3D effects.

Scope Various pocket geometries can be connected to the simulated inhalation apparatus. Labview software PI control feedback loop means any pressure profile can be simulated. Running the software on a faster PC and DAQ card would give better control loop performance. Options to use various optical setups/different lighting, etc.

Current Limitations There can be a certain amount of delay in the pressure control PI loop. With the current setup there is a high noise-to- signal ratio from the pressure sensors. Backlighting provides a 2D visualization – possibility that certain 3D effects might be hidden. Difficult to quantify possible leakage effects. Pocket filling method could be improved. Repeatability…

Repeatability Each parameter combination was repeated a total of three times. Some parameter combinations were repeated after a gap of a few days and changed geometries. Examine glass and lactose 15.8% fines, at time 0.09s and 0.06s respectively, -30kPa/s.

Repeatability (glass 0-50  m)

Repeatability (lactose 15.8% fines)

Conclusions The evacuation of the simplified 2D U-shaped geometry is similar to the evacuation from the 3D Diskus replica geometry. Cohesion has a much more important effect on the pocket evacuation than shape. The evacuation of lactose is based on instantaneous pressure, not on pressure gradient. This conclusion cannot be extended to any of the other particle types. A clearer understanding has been achieved of the timescales and pressures required for particle evacuation.

Future Work Using more sophisticated camera equipment from EPSRC, better resolution images possible (approx 1000 x 1000 pixels). This batch of experimental results not analysed fully quantitatively at present, but possibility of using techniques such as PIV or variance maps on future results. Experiment with a wider range of lactose blends? Data to be used on a validation basis for computational simulations.

Discussion Data CD with a copy of this presentation and further experiment description and results available from Mark Palmer. Questions?

Extras