atw - International Journal for Nuclear Power | 04.2023

atw Vol. 68 (2023) | Ausgabe 4 ı Juni
(cf. size class around 1.3 µm). This behavior might
indicate that the change in weighting of the deposition
mechanisms with increasing particle diameter,
might be shifted to larger particle diameters by the
mixed aerosol compared to the results with CsI
(cf. Fig. 6).
Nevertheless, the retention efficiency for particles
below 0.5 µm is for the mixed aerosol above 70 %
whereas in the tests with CsI the retention efficiency
in this region is at most 62 %.
Figure 8 shows the retention efficiency plotted over
the aerodynamic diameter for three experiments
with a submergence of 1.5 m. The experiments differ
in the aerosol material used. The results for the
experiments conducted with CsI are given by the
blue line, the results for SnO 2 by the green line and
the measurements for the mixed aerosol are given
by the yellow line in Fig. 8.
of CsI. The third test series investigates the retention
efficiency of CsI for a nozzle submergence of
1.5 m and different carrier gas feed rates. These investigations
are repeated in the fourth test series,
using a mixed-aerosol instead of CsI. Former experiments
performed with SnO 2 in the SAAB test vessel
are taken into account in a discussion, where the
behaviour of mixed-aerosols is compared to a single
component aerosol.
Pool scrubbing experiments on the retention efficiency
of a mixed aerosol (SnO 2 and CsI) were
conducted in the SAAB test facility at Research
Centre Juelich. To investigate the mixed aerosols’
influence on the particle retention behaviour, the
results are compared to experiments with CsI.
Boundary conditions such as volume flow rate and
height were also varied to investigate their influence
on the retention efficiency. In the experiments
with CsI increasing the submergence is a key to increase
the retention efficiency especially for smaller
particles. Increasing the gas velocity shows a different
effect for very small particles.
RESEARCH AUS DEN AND UNTERNEHMEN
INNOVATION 75
Contrary to the expectation that the retention efficiency
increases with residence time, all heights
show relatively high retention efficiencies of more
than 70 % for the mixed aerosol for all size classes.
Only small deviations are observed.
| Fig. 8
Retention efficiency for three different aerosols plotted over the aerodynamic
diameter.
It is noticeable that the mixed aerosol is much better
retained than the individual substances. For the
individual substances SnO 2 and CsI a filter gap at a
specific aerodynamic diameter is observed, whereas
for the mixed aerosol there is a plateau between
0.5 µm and 1.2 µm where the retention efficiency
is reduced.
However, it must also be considered that the input
mass concentration was highest for the mixed aerosol
(cf. Fig. 2).
Conclusion and Outlook
Four test series are presented in this section, comprising
seventeen individual (quasi-) stationary test
phases. The first test series deals with the retention
efficiency of CsI that is injected with 20 m³ nitrogen
per hour by different nozzle submergences in the
water layer of the test vessel. Those tests are repeated
in the second test series but using a mixed-aerosol
(consisting of ~60 % CsI and ~40 % SnO 2 ) instead
The rather high retention of the mixed aerosol might
have been caused by different mechanisms. Three
different interpretations have been developed.
Firstly, that during the experiment the partial density
of the water next to the aerosol stream might
have been higher, because of the soluble CsI. Dissolved
CsI could act as scrubbing liquid for SnO 2 ,
and the retention efficiency would rise. The second
theory is that a mixed aerosol might build coarser
particles due to agglomeration, and therefore more
particles would be retained by inertial impaction at
the inlet. The third theory is that the initial number
concentration of the mixed aerosol was much higher
than in the single aerosol tests, so the particle interactions
inside a rising bubble would have been
much higher and more particles would have been
retained, e.g. due to Brownian diffusion or centrifugal
impaction.
For varying the inlet flow rate it is observed that
the retention efficiency of the mixed aerosol is significantly
higher than in the tests with the single
aerosol CsI. Increasing the inlet flow causes the integral
retention to rise. Nevertheless, with increasing
the inlet flow rate and therefore the inlet velocity
the filter gap is shifted from 0.5 µm to smaller
Research and Innovation
Experimental Investigation on the Pool Scrubbing Behaviour of soluble and mixed Aerosol Components ı René Vennemann, Michael Klauck, Tobias Jankowski, Hans-Josef Aus den Allelein, Unternehmen
Marco K. Koch