INAUGURAL–DISSERTATION zur Erlangung der Doktorwürde der ...
INAUGURAL–DISSERTATION zur Erlangung der Doktorwürde der ...
INAUGURAL–DISSERTATION zur Erlangung der Doktorwürde der ...
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72 4. Results and Discussion<br />
160<br />
140<br />
DQMOM<br />
DDM<br />
Experiment<br />
Sauter mean diameter [µm]<br />
120<br />
100<br />
80<br />
60<br />
40<br />
20<br />
0<br />
-120 -80 -40 0 40 80 120<br />
Radial position [mm]<br />
Fig. 4.20: Experimental and numerical profiles of the Sauter mean diameter at the cross<br />
section of 0.16 m distance from the nozzle exit for 120 kg/h.<br />
profiles of Sauter mean diameter at cross sections of 0.12 m and 0.16 m away from<br />
the nozzle exit are shown in Figs. 4.19 and 4.20. An increased liquid flow rate causes<br />
a somewhat decreased droplet size: For a given liquid, increased mass flow rate leads<br />
to higher pressure drop in the atomizer, which decreases liquid sheet size and breakup<br />
length to yield smaller particles as can be seen when compared with Fig. 4.18.<br />
At the cross section of 0.12 m, it can be seen that DQMOM performs better than the<br />
DDM results as DDM overpredicts the experimental values. The scattering behavior<br />
of DQMOM simulation results near the centerline is observed in this case, too. As the<br />
droplets move to the next cross section, a decrease in large size droplets is evident,<br />
which is predicted by both DQMOM and DDM. The results show that the DQMOM<br />
shows better agreement with experiment, while DDM predicts somewhat higher values<br />
than the experiment at corresponding radial positions [205].<br />
The overall shape of a hollow cone spray is captured quite nicely by both methods,<br />
although some deviations are observed, particularly in DQMOM as compared to<br />
experimental profile. This is possibly due to the post-processing of the experimental<br />
data as explained in Subsection 4.2.2, which is done to correct the number frequency<br />
at every measuring position to rule out the fluctuations in the effective cross sectional<br />
area of the measuring volume for the larger droplet sizes [207]. This correction of experimental<br />
data is position dependent, whereas DQMOM and DDM results account<br />
for these corrections for the initial condition but not at positions further downstream.<br />
Another reason for the discrepancies in the DQMOM results may be due to the fact<br />
that the spray equations are not yet fully coupled to the gas phase.