Hardware Updates

• Light Scattering developments External trigger and software for ToF system

• Black carbon detection module SP2-AMS black carbon mass measurement.

• Lens Modeling and Testing

Particle Lens Work

Leah William, Dagmar Trimborn, Sally Ng, Tim Onasch, Elena de la Rosa Blanco

ARI

Dahai Tang, Ken Smith MIT

Jennifer McInnisCornell University

Aerodynamic Lens Systems Investigated Models and Measurements

• Standard lens• High Pressure lenses (PM2.5)• Nano-particle lenses (Wang/McMurray

design)• Inlet design, pin hole • Valve assembly design

Model Studies Have Investigated:Standard lens• Effect of the lens pressure through a change of inlet pressure or a change

of the critical orifice sizeHigh Pressure lens• Effect of different valve assembly system• Effect of the lens aperture and nozzle diameterNano-particle lens (Wang et al 2005)• Effect of carrier gas molecular weight

For each of the 3 lens systems• Effect of laminar vs. turbulent model• Effect of different Brownian methods• FLUENT used for CFD calculations

Particle Transmission versus Collection in Aerodynamic Lens

Aerodynamic Size

CE/

Tran

smis

sion

Target

TransmissionNo Collection

No Transmission or Collection

Large particle losses are controlled by the pin-hole

Small particle losses are controlled by geometry and Brownian diffusion

Figure 10. Experimental results for DEHS (solid circles), NH4NO3 (triangles) and NaNO3 (squares) at an ambient pressure of 585 torr. The solid line is the Fluent modeling result for 585 torr and is re-plotted from Figure 7.

Liu, P.S.K., R. Deng, K.A. Smith, L.R. Williams, J.T. Jayne, M.R. Canagaratna, K. Moore, T.B. Onasch, D.R. Worsnop, and T. Deshler, Transmission Efficiency of an Aerodynamic Focusing Lens System: Comparison of Model Calculations and Laboratory Measurements for the Aerodyne Aerosol Mass Spectrometer, Aerosol Science and Technology, 41(8):721-733, 2006.

1.2

1.0

0.8

0.6

0.4

0.2

0.0

Lens

Tra

nsm

issi

on E

ffici

ency

EL

102 3 4 5 6 7 8 9

1002 3 4 5 6 7 8 9

10002

Dva (nm)

Mass Method: NH4NO3 DEHS NaNO3 Fluent

Results for Standard Lens

Liu et al. (2006)

Figure 1a. Drawing of the lens system which is composed of the pinhole assembly, the valve body and the lens assembly.

450mm

3.8mm OD

7”, 178mm6.055”, 154mm

FEDCBA100 µm Orifice

15D

1.6mm ID

Figure 1b. Structure used in the Fluent simulations, including the lens system, particle flight chamber and vaporizer. The diameters of the apertures are given in Table 1.

Standard Lens System

Liu et al. (2006)

Must model the “System”

-0.36 -0.30 -0.24 -0.18 -0.12 -0.06 0.00-0.015

-0.010

-0.005

0.000

0.005

0.010

0.015

Nozzle

Diameter of pinhole is 80/100/120 microns.Diameters of connection and lens tube are 4.4mm.Diameter of the nozzle is 1.0mm.

LensConnectionPinhole

Y (m

)

X (m)

Constant bore of 4.4 mm from orifice to lens entrance.“New Inlet”

HP Lens requires constant bore

CFD Calculations and Experimental Measurements

Good agreement between calculated and measured transmission efficiency.

1.5

1.0

0.5

0.0

Tran

smis

sion

Effi

cien

cy

1012 3 4 5 6 7 8

1022 3 4 5 6 7 8

1032 3 4 5 6 7 8

104Dva [ nm ]

High Pressure Lens PSL from Atomizer Lens#0 PSL from Nebulizer Lens#0 PSL from Atomizer Lens#2 NH4NO3 Lens#2 NH4NO3 Lens#2 SN2

CFD calculations

HP Lens

Effect of lens pressure for High Pressure lens

101 102 103 104

0.0

0.2

0.4

0.6

0.8

1.0

PLens[Torr] PInlet[Torr] Orifice [um] 18.6 760 120 13.3 760 100 7.1 760 70 9.3 504 100 7.2 385 100 5.3 261 100

Tran

smis

sion

Effi

cien

cy

dp [ nm ]

Small Particle lens

Nano-particle lens geometries

Four lenses

Collection efficiencyC

E

Effect of different Brownian models

McMurry “Nano” Lens Geometry

Effect of carrier gas for nano-particle lens performance

“Spot Measurements” for Visual Characterization of Lens Performance

Keith and Frank….We have gotten really good at measuring

spots!

Isolation Valve and Removable Lucite rod

LensAMS Chamber

Another way to look at focusing: BWP Data for HPLv2 SN5 and Standard Lens

2.0

1.5

1.0

0.5

0.0

Sig

nal (

arb.

uni

ts)

-2.0 -1.0 0.0 1.0 2.0BW P position (mm)

BW P Data for HPLv2 SN50.5 mm wireSize-selected NH4NO3

100 nm 300 nm 500 nm

40

30

20

10

0

Nor

mal

ized

sig

nal

-2.0 -1.0 0.0 1.0 2.0BWP Position (mm)

BW P Data for Standard Lens0.5 mm wireSize-selected NH4NO3

80 nm 150 nm 300 nm 450 nm

Red circle is projection of vaporizer on plexiglass surface.

Standard Lens

HP Lens

Photographs of “Spots”Polydisperse NH4NO3 with different “Identical” HP lenses

SN #0 SN #1

SN #3SN #2

Machining tolerances are critical

Lens #3, turned whole lens

270°

90°

0°

180°

Lens SN#3, NH4NO3

100nm 250nm

500nm400nm300nm

200nm150nmpoly

450nm350nm

HP V2 Lens, 3000nm

Trajectories for 3000 nm particles for HPLv2.

13 torr lens pressure

Impaction losses predicted on low pressure side of 100um pin hole

Particle loss on the back plane of the critical orifice (NH4NO3,varied particle size, 5min)

300nm 400nm 500nm

800nm700nm600nm

Critical orifice - φ100um HP LensCollector

Summary• Small particles focusing ultimately limited by Brownian diffusion.

• Large particle TE and CE limited by impaction. • Agreement between model and measurement is not perfect but agrees qualitatively. Need to refine calculations.

• HP lens cuts off too soon on small size end for ambient work.

• Overall goal is to “widen” the transmission window. Can we combine Standard and HP lens?

• Lens development is an ongoing effort.