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Published byChelsey Maddern Modified about 1 year ago

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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

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Objective

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

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Abstract

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Modeling

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

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

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The turbulence energy spectrum is given as, The atomization time scale is given as, k avg, avg, U, t, f, and g are input to find p(x)

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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 k avg / avg at low k avg leads to a reduction in the median

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Pressurized Metered-Dose Inhaler Canister Actuator Mouthpiece Actuator Orifice

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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 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) Fluid Properties f = 1000 kg/m3 = 0.001 Pa-s Flow equation solved in CFD software package

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Add-on Nozzle Inlet B.C.’s for add-on nozzle Correspond to exit conditions of inhaler baseline model Q=5.0e-06 m 3 /s k=5.8 m 2 /s 2 =7.0e+04 m 2 /s 3 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

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Results

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Inhaler Internal Flow Passage Turbulent Kinetic Energy, k Turbulent Kinetic Energy Dissipation Rate, k avg =5.8 m 2 /s 2 avg =7.0e+04 m 2 /s 3 k avg / avg =8.29e-05 Predicted Median Droplet Size-290 m

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

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Optimization Results Optimum dimensions are h=100 m, s=350 m

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Add-on Nozzle Turbulent Kinetic Energy, k Turbulent Kinetic Energy Dissipation Rate, k avg =60.8 m 2 /s 2 avg =8.13e+06 m 2 /s 3 k avg / avg =7.48e-06 Predicted Median Droplet Size-245 m

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

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Conclusions

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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

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