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A Design Tool for Aerodynamic Lens Systems - Department of ...

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A DESIGN TOOL FOR AERODYNAMIC LENS SYSTEMS 333<br />

p1<br />

pressure upstream <strong>of</strong> an orifice<br />

p2<br />

fully recovered pressure downstream <strong>of</strong><br />

an orifice<br />

pfocusing<br />

pressure upstream <strong>of</strong> a lens <strong>for</strong> focusing<br />

particles <strong>of</strong> a given size<br />

pMa<br />

minimum pressure <strong>for</strong> flow to be subsonic<br />

pmax<br />

maximum operating pressure <strong>of</strong> an aerodynamic<br />

lens<br />

pKn<br />

minimum pressure <strong>for</strong> flow to be continuum<br />

Q volumetric flowrate<br />

Qi<br />

volumetric flowrate at stage i<br />

R universal gas constant<br />

Re flow Reynolds number based on orifice<br />

diameter<br />

Res<br />

flow Reynolds number based on spacer<br />

diameter<br />

ri<br />

critical initial particle radial position<br />

r pi<br />

particle initial radial location in an aerodynamic<br />

lens<br />

S Sutherland constant<br />

Sa<br />

particle axial stopping distance<br />

Sr<br />

particle radial stopping distance<br />

St Stokes number based on orifice diameter<br />

Sto<br />

Sts<br />

Sts50<br />

optimum Stokes number<br />

Stokes number based on spacer diameter<br />

Spacer Stokes number corresponding to<br />

a 50% impaction loss<br />

stage i includes lens i and the downstream<br />

spacer<br />

t<br />

T1<br />

TpF<br />

particle residence time<br />

temperate upstream <strong>of</strong> the lens<br />

particle frozen temperature in the jet expansion<br />

Tr<br />

u<br />

reference temperature in Sutherland’s<br />

Law<br />

average flow velocity at orifice entrance<br />

based on upstream flow conditions<br />

u p<br />

particle axial velocity<br />

Us<br />

va<br />

vpr<br />

average flow velocity in the spacer<br />

axial jet flow velocity<br />

particle terminal radial velocity in the<br />

vacuum chamber<br />

vr<br />

xc ≈ 1 −<br />

radial jet flow velocity<br />

� �p pressure drop across an orifice<br />

ηc<br />

particle contraction factor<br />

ηc,i<br />

contraction factor at lens i<br />

ηt<br />

particle transmission efficiency<br />

ηt, diffusion, i penetration after diffusional loss at stage<br />

i<br />

ηt, GK, i<br />

penetration after loss at stage i estimated<br />

by Gormley-Kennedy equation<br />

ηt, orifice, i<br />

transmission efficiency after impaction<br />

losses on the orifice plate i<br />

ηt, spacer, i<br />

transmission efficiency after impaction<br />

loss to spacer i<br />

θ jet opening angle<br />

λ1<br />

mean free path <strong>of</strong> the gas molecules upstream<br />

<strong>of</strong> the orifice<br />

µ carrier gas viscosity<br />

ξ =<br />

� γ<br />

2 γ −1<br />

γ +1<br />

xrms<br />

particle root mean square displacement<br />

due to diffusion<br />

xrms,i<br />

root mean square displacement between<br />

lenses i and i+1<br />

Y<br />

β = d f /ds<br />

γ<br />

orifice flow expansion factor<br />

constriction ratio<br />

specific heat ratio <strong>of</strong> the carrier gas<br />

Dils,i<br />

Qi<br />

dimensionless diffusion deposition parameter<br />

ρ1<br />

carrier gas density upstream <strong>of</strong> the aerodynamic<br />

lens<br />

ρp<br />

particle material density<br />

τ particle relaxation time<br />

REFERENCES<br />

Back, L. H., and Roschke, E. J. (1972). Shear-Layer Flow Regimes and Wave<br />

Instabilities and Reattachment Lengths Downstream <strong>of</strong> an Abrupt Circular<br />

Channel Expansion, J. App. Mech. 94:677–681.<br />

Bean, H. S. (1971). Fluid Meters: Their Theory and Applications (Report <strong>of</strong><br />

ASME research committee on fluid meters). New York, ASME.<br />

Cheng, Y. S., and Dahneke, B. E. (1979). Properties <strong>of</strong> Continuum Source Particle<br />

Beam. II. Beams Generated in Capillary Expansions, J. Aerosol Sci.<br />

10:363–368.<br />

Dahneke, B. E., and Cheng, Y. S. (1979). Properties <strong>of</strong> Continuum Source<br />

Particle Beam. I. Calculation Methods and Results, J. Aerosol Sci. 10:257–<br />

274.<br />

Di Fonzo, F., Gidwani, A., Fan, M. H., Neumann, A., Iordanoglou, D. I.,<br />

Heberlein, J. V. R., McMurry, P. H., Girshick, S. L., Tymiak, N., Gerberich,<br />

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Patterned Microstructures, Appl. Phys. Lett. 77(6):910–912.<br />

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Generation <strong>of</strong> Nano-Sized Free Standing Single Crystal Silicon Particles,<br />

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Drewnick, F., Hings, S. S., DeCarlo, P., Jayne, J. T., Gonin, M., Fuhrer, K.,<br />

Weimer, S., Jimenez, J. L., Demerjian, K. L., Borrmann, S., and Worsnop, D.<br />

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Instrument Description and First Field Deployment, Aerosol Sci. Technol.<br />

39(7):637–658.<br />

Eichler, T., de Juan, L., and Fernández de la Mora, J. (1998). Improvement <strong>of</strong><br />

the Resolution <strong>of</strong> TSI’s 3071 DMA via Redesigned Sheath Air and Aerosol<br />

Inlets, Aerosol Sci. Technol. 29(1):39–49.<br />

Fernández de la Mora, J., and Riesco-Chueca, P. (1988). <strong>Aerodynamic</strong> Focusing<br />

<strong>of</strong> Particles in a Carrier Gas, J. Fluid Mech. 195:1–21.<br />

Fernández de la Mora, J., Rosell-Llompart, J., and Riesco-Chueca, P. (1989).<br />

<strong>Aerodynamic</strong> Focusing <strong>of</strong> Particles and Molecules in Seeded Supersonic Jets.<br />

in Rarefied Gas Dynamics: Physical Phenomena, Progress in Astronautics &<br />

Aeronautics. E. P. Muntz, D. P. Weaver, and D. H. Campbell, eds., Washington,<br />

DC, AIAA. 117:247–277.

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