1. Analysis of the Droplet Size Reduction in a pMDI Due to the Addition of a Turbulence Generating Nozzle by Michael P. Medlar Dr. Risa Robinson

2. Objective

3. To improve Medical Inhalation Therapy by reducing the median droplet size resulting from the pMDI through the addition of a turbulence generating nozzle

4. Abstract

6. Modeling

7. Flow Equations Governing equations Standard k-e turbulence model
Continuity:
where,
Navier-Stokes:
Transport of k:
Transport of e:

8. Huh Atomization Model
Considers turbulence as a primary part in the atomization process
Calculates PDF for secondary drop sizes, p(x)
where, f(x) is the turbulence energy spectrum and tA(x) is the atomization time scale

9. The turbulence energy spectrum is given as,
The atomization time scale is given as,
kavg, eavg, U, t, rf, and rg are input to find p(x)

10. Huh Atomization Model Analysis
This analysis was needed to determine the exit turbulence parameters that lead to a reduction in the median secondary drop size-low kavg/eavg at low kavg leads to a reduction in the median

11. Pressurized Metered-Dose Inhaler
Canister
Actuator
Actuator Orifice
Mouthpiece

12. Inhaler Internal Flow Passage
Inlet B.C.’s
V=2.34 m/s (normal to boundary)
I=5.7 % (turbulent intensity) I=0.16(Re)-1/8
L=1.155e-04 m (turbulent length scale) L=0.07l
Fluid Properties
rf = 1000 kg/m3
m = Pa-s
Outlet B.C.’s
Outflow condition assumes zero normal gradient for all flow properties except pressure (used when outlet conditions aren’t known and want to be determined)
Flow equation solved in CFD software package

13. Add-on Nozzle Flow equation solved in CFD software package
Inlet B.C.’s for add-on nozzle
Correspond to exit conditions of inhaler baseline model
Q=5.0e-06 m3/s
k=5.8 m2/s2
e=7.0e+04 m2/s3
Outlet B.C.’s for add-on nozzle
Outflow condition assumes zero normal gradient for all flow properties except pressure (used when outlet conditions aren’t known and want to be solved for)
Flow equation solved in CFD software package

14. Results

15. Inhaler Internal Flow Passage
Turbulent Kinetic Energy, k
Turbulent Kinetic Energy Dissipation Rate, e
kavg=5.8 m2/s2
eavg=7.0e+04 m2/s3
kavg/eavg=8.29e-05
Predicted Median Droplet Size-290 mm

16. Optimization of Add-on Nozzle
Based on h and s dimensions
Separation Point
Inlet
Outlet-fixed to keep outlet velocity same as baseline h
500 mm s
53o etch angle
Line of symmetry
1 mm

17. Optimization Results
Optimum dimensions are h=100 mm, s=350 mm

18. Add-on Nozzle Predicted Median Droplet Size-245 mm
Turbulent Kinetic Energy, k
Turbulent Kinetic Energy Dissipation Rate, e
kavg=60.8 m2/s2
eavg=8.13e+06 m2/s3
kavg/eavg=7.48e-06
Predicted Median Droplet Size-245 mm

19. Summary Current inhaler design-290 mm
Current inhaler with add-on nozzle-245 mm
Relative reduction of 15.5% in the median secondary drop size as predicted from the Huh Atomization Model based on turbulence effects alone

20. Conclusions

21. Fluent/Huh Atomization Model combination can be used to evaluate the significance of an add-on turbulence generating nozzle in reducing droplet size
Add-on turbulence generating nozzle can reduce the droplet sizes produced from the pMDI