Aerosol deposit characterization via nuclear imaging Pierre-Colin Gervais, Nathalie Bardin-Monnier & Dominique Thomas ´) Laboratoire R´ eactions et G´ enie des Proc´ ed´ es (LRGP - upr 3349 CNRS - Nancy Universite SAFE (Safety, Aerosols, Filtration and Explosions), 1 rue Grandville, BP 20401, 54 001 Nancy Cedex, France.
Introduction
Pleated Filter
Results
Fibrous pleated filters are widely used in aerosol filtration because of : • their high effective surface area • their low overall dimension
Pleated filters are manufactured by Camfil Farr SAS (France). Their characteristics are presented in Tables 1 and 2.
➥ The exploitation of PET will be performed with NanCycloTEP. ➥ A monodispersed radioactive aerosol will be generated using Sinclair-LaMer generator and a radioactive tracer.
Fibrous pleated filters clogging by solid particles can be divided in 3 main periods (Fig. 1) : ➥ the depth filtration : particles trapped within the medium, no ∆P ր ➥ the surface filtration : formation of a filtration cake at the medium surface ➥ the filtration surface decrease : particles trapped on the filter surface, abrupt ∆P ր
➥ Technetium 99m is used to generate based DiEthyl-Hexyl-Sebacate aerosol. Particle size analysis : 0,5 T
7000
T
0,4
6500
T
6000
filtration surface decrease
P/
4500
4000
fiber bend [µm] 0.6
3000
depth filtration
2000
1500 0,00
0,25
0,50
0,75
1,00
1,25
1,50
1,75
2,00
2,25
thickness (Z) [µm] 521 ± 31
packing density (α)
0,2
99
=220°C NaCl+
Tc
Sat
=220°C NaCl
Sat
99
=235°C NaCl+
Sat
Tc
=235°C NaCl
Sat
0,1
0.071 ± 0, 006
2,50
0,1
)
1
10
Particle diameter ( m)
Tab 2 : Filter characteristics
Fig 1 : ∆P evolution as a function of collected mass
The challenge is to increase the lifetime of such filters by delaying the beginning of the surface decrease period. Surface observations of pleated filters after clogging allows to show different behaviors according to the operating conditions (filtration velocity Vf and particle diameter dp)
Fig 2 : Filtration surface decrease [1]
T
=200°C NaCl
Sat
0,0
-2
m (g.cm
T
Tc
Sat
Tab 1 : Medium characteristics
surface filtration
3500
-0,25
dV/V
Fig 4 : Picture of pleated filter
5000
2500
T
0,3
P0
5500
99
=200°C NaCl+
pleat height [mm] 27.5
filtration area [m2] 0.42
nominal flow rate [m3.h−1] 43
Experimental Setup Positron Emission Tomography (PET), developed by NanCycloTEP a will perform the visualization of aerosol deposit.
Fig 6 : Volumetric particle size distribution
We can produce different particles size between 1 and 10 microns as a function of generator parameters.
Conclusion • Observations of initial deposit on pleated filters with a nondestructive method will permit to complete the understanding of aerosol spatial deposit mechanisms on the whole pleat height.
A mobile bench is currently in design : • big particles and/or high velocities : the particles, under the effect of inertia, would tend to settle preferentially in the pleat bottom. • small particles and/or low velocities : the particles are arranged progressively causing a faster complete filling : ∆P ր++
• In parallel with this work, a numerical approach will be performed in order to study the two-phase flow. • Experimental results will allow to validate local velocity analysis using the voxel-based CFD R a. Virtual material design and code GeoDict property simulation will allow us to develop a complete clogging predictive model.
5,5
25 V =0.5m/s f
20
5,0
V =1m/s f
d =1 m p
d =4 m p
P0
P0
4,5
4,0
15
Fig 5 : Experimental Setup
P/
P/
3,5
10
a. developed at Fraunhofer ITWM in Kaiserslautern, Germany
3,0
2,5
5
Experimental set-up consists of :
References
– (1) Monodispersed aerosol generator PALAS MAG 2010 – (2) Filter holder containing the test filter R Basis designed with CFD code Fluent – (3) Light scattering spectrometer system WELAS PALAS digital 2000H – (4) Differential pressure transducer
[1] Aur´elie Joubert. Performances des filtres pliss´es a` ´ Tr`es Haute Efficacit´ e en fonction de l’humidit´e relative de l’air. PhD thesis, Institut National Polytechnique de Lorraire, novembre 2009.
2,0
d =8 m p
0 0
50
100
150
200
250
m (g.cm
-2
)
300
350
400
V =5cm/s f
1,5
0
20
40
60
80
100
120
140
m (g.cm
-2
160
180
200
220
240
)
Fig 3 : Illustration of Vf and dp influence on clogging. (From Del Fabbro’s experimental values [2])
To keep the particle structuring intact, a nonintrusive and nondestructive method needs to be used. We present the implementation of an original aerosol deposit characterization via nuclear imaging.
a. Medical imaging unit of Nancy teaching hospital, France
[2] Lætitia Del Fabbro. Mod´elisation des ´ecoulements d’air et du colmatage des filtres pliss´es par des a´erosols solides. PhD thesis, Universit´e Paris XII, juin 2001.
