Lab-size aerosol lidar chamber: on the road to...

Defence Research andDevelopment Canada

Recherche et développementpour la défense Canada Canada

Lab-size aerosol lidar chamber: on the road to optimization

Sylvie ButeauSupporting team: D. Nadeau, J.-R. Simard, C. Laflamme, P. Lahaie, G. Roy,

P. Mathieu

SBWG July 2010 (Dstl, UK)

Defence R&D Canada • R & D pour la défense Canada

Presentation focus

Artefact source findings and improvements

Original chamber design

System limitations/artefacts


Lab-size chamber: original design

Short-range bi-axial LIDAR system (355nm) Closed system: control over the environment Dissemination of liquids and dissolved powders

Particles counter

TelescopeBeamBeam expanderexpanderMixingMixing

chamberchamber

Main ChamberSpectrometer

ICCD


Artifact 1: Laser power drop


Artifact 1: power drop mitigation

Temperature Ctrl

Heating pads

Thermocouple

Thermal-compensation process + new chiller


Artifact 2: wet dissemination

Low signal to noise ratio versus concentration

Collison Nebuliser


Mitigation (#2): dry dissemination

Higher signal to noise ratio versus concentration

Air injection


Particle size distribution: wet versus dry BG

WetDry

Only few aggregatesMany small particles (32%)

More aggregates Less small particles (3%)


Source of the higher LIF signal (wet/dry)?

Particle size distribution

Aerosol quantum yield


LIDAR equation for a fluorescent target

λλλ

λλ

πσ ,0

0

4A a

aaaaaa PNNE Ψ⋅⋅=⋅∝

0000 ,ra

,ac

,aeoc2

0 0pu NAEn λλλλλλλ σξ a

rroe

r rttttr

Δ⋅=raE,, 0λλ

Energydelivered Geometry

OpticsAtmosphere

Columnthickness

Aerosolproperties

Collected Energy

approximations

⋅⋅=i

iiAa dnrN 2π

Plot LIF metric vs NA

0λaslope Ψ∝

Projected area weighted concentration


Higher LIF signal for dry versus wet BG

Wet Dry

Higher quantum yield for dry BG versus wet BG


Artifact 3: Limited control over dissemination

Difficult to replicate a given dissemination

scheme

Low control over the concentration within

the chamber

Old BG dry


Mitigation (#3): Design of new disseminator

Small Scale Powder Disperser (SSPD)

In-house design (D. Nadeau); Dissemination of dry sample; Fully automated dissemination; Controlled by adapted software; Sealed enclosure.

Disseminated quantity adjustment:

Plate groove; Plate speed; Injected air pressure


Mitigation (#3): SSPD disseminator

Better control over the dissemination scheme


SSPD disseminator: particle size distribution

SSPD is effective to minimize particle aggregates

Dry Old BG


Artifact 4: LIF-APS correlation non-linearityNew BG dry (BHI media)

No impact on the signature extraction

Limitation on the cross-section

evaluation


Artifact 4: Possible sources

APS saturation effect

Bleaching effects

APS sampling effectiveness

Dissemination in-homogeneity

Particle size distribution evolution


Artifact 4 : APS saturation?

APS saturation will produce non-linearity (at a higher level than the default setting of 1Mppl)

Old BG dry (SSPD)


Artifact 4 : Bleaching effects?

Difficult to isolate the bleaching effect contribution with the actual set-up following variable testing conditions


Artifact 4 : APS sampling effectiveness?

Particle velocity and their Stokes number (Stk) may vary significantly due to injection of air during dissemination

In –chamber air flow

APS sampling

(90°)


Mitigation (#4): LIF- APS non-linearity

Possible bleaching effect No recirculation of the material (open loop chamber) Adjust flow velocity for minimum bleaching effects More testing is needed to assess the bleaching properties

APS sampling Relocate the APS sampling input Adjust in-chamber flow velocity with the APS sampling flow This will be implement only in the new chamber design

APS saturation Ensure the concentration levels are below 1 Mppl


Other system design observations

In coming flow

Air injection

(SSPD)

Injection orientation interfere with the circling

particle flow

Mixing chamber geometry not optimum for material aerosolization


Conclusion

System artefacts and limitations

Acquiring data and gaining expertise with the

original chamber

Investigations

Optimised design for the next

chamberFluorescence cross-section evaluation

Lab-size aerosol lidar chamber: on the road to...

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