Characterisation of Differential Mobility Analysers for the Droplet Aerosol Analyser instrument
description
Transcript of Characterisation of Differential Mobility Analysers for the Droplet Aerosol Analyser instrument
Michael Gradmann
Supervisor: Maria Berghof, Staffan Sjörgenand Göran Frank
Examiner: Carl Erik Magnusson
Lund UniversityDepartment of Physics
Characterisation of Differential Mobility Analysers for the Droplet
Aerosol Analyser instrument
Understand mechanisms of climate and weather
Provide a reliable weather forecast Understand how and how much weather is
affected by humans
The DAA instrument
Measures size of cloud droplets Dries the droplets Measures number and size of the particles
(CCN)
→ unique data set
The DAA instrument
Sketch by Maria Berghof
Differential Mobility Analyser
Cylindrical capacitor Radial electrical field
Sheath air flow Uncurled, smooth
→ precise manufacturing required
Picture courtesy of [3]
Differential Mobility Analyser
Radial electrical field
Radial velocity
Differential notation
E= U
r∗ln r ar i er
vr r =U∗Z
r∗lnrar i
dt=
r∗lnrar i U∗Z
dr
Differential Mobility Analyser
Different differential notation
Integration, transposition
Electrical mobility
dz=
r∗lnr ar i U∗Z
v z dr
Z=
Q∗lnrar i 2∗U∗l
Z=neCC
3 d p
DMA preparation
Cleaning Check for scratches or
damages Mesh size checked
Mesh replaced Leak test
Picture courtesy of [3]
Set-up
Transfer function
Ideal triangular function
Losses and broadening because of imperfections inside the DMA
Picture courtesy of [2]
Transfer function
f , , Z 0 , Z =∗1Q s
Qa ZZ 0
−1;1− QaQs
≤ ZZ 0
≤1
f , , Z 0 , Z =∗1Q s
Qa −ZZ 0
1;1≤ ZZ 0
≤1QaQ s
f , , Z 0 , Z =0 ;ZZ 0
1−Qa
Qs
∨ ZZ 0
1Qa
Qs
Experimental method
Experimental method
Experimental method
Theoretical data can be calculated by
compared with measurement
λ, μ changed (iteration), until X² has its smallest value
X 2=∑i
exi−thi 2
n2 Z iN 1
=∫ f 1 1,1,Z ' 0 , Z ∗ f 2 2, 2,Z i , Z dZ
∫ f 1 1,1,Z ' 0 , Z dZ
Results
DMA name λa
μa
λb
μb
DMA1a 0.599 0.903 0.660 1.022
DMA2a 0.917 NA 0.811 1.056
DMA2b 0.934 0.942 0.980 0.756
DMA2c 0.838 0.783 0.904 0.885
DMA1b 0.953 0.910 0.969 0.832
DMA2d 0.686 0.710 0.786 0.714
DMA2e 0.821 0.942 0.842 0.881
DMA2f 0.858 NA 0.958 0.921
UDMA 0.896 0.781 0.962 0.873
Discussion
Too clean DMAs Turbulances caused by changed flow ratio Modifications added to DMAs (plastic
mount/mesh) Unstable particle number concentration
Discussion
Discussion
DMA name λa
μa
λb
μb
DMA2b 0.980 0.756
DMA1b 0.953 0.910 0.969 0.832
DMA2e 0.821 0.942
DMA2f 0.858 NA
Reliable results
Conclusion
Values for λ and μ depend on the stability of particle number concentration
Broad distribution of particle number has a larger effect than slow changes
The time a particle takes to reach a CPC is important
Perspective
Check of well known flow ratio to reproduce results published in [1] and [2]
Small changes made on the set-up Particle number concentration distribution could
be reduced to less than 2% Significantly better results
References
[1] Martin N.A. Karlsson, Bengt G. Martinsson, Methods to measure and predict the transfer function size dependence of individual DMAs, J. Aerosol Sci., 34, 603-625, 2003
[2] Bengt G. Martinsson, Martin N.A. Karlsson, and Göran Frank, Methodology to estimate the transfer function of individual Differential Mobility Analyzers, Aerosol Sci. Techn., 35, 815-823, 2001
[3] Anna Persson, Design av mätmetodik för droppaerosolanalysatorn, Examensarbete för Kandidatsexamen, Lunds Universitet, 2008
[4] William C. Hinds, Aerosol Technology, 2nd edition, Wiliey Interscience, 1999
[5] Göran Frank and Bengt G. Martinsson, An instrument for studies of the relation between cloud droplet size and dry residual particle size - The Droplet Aerosol Analyser, Proceedings of the International Conference on Cloud and Precipitation (Abstract), 2008
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