INAUGURAL–DISSERTATION zur Erlangung der Doktorwürde der ...

62 4. Results and Discussion
3
3
Veloctiy [m/s]
2.5
2
1.5
1
u[1] = 1.09 m/s, r[1] = 24 µm
u[2] = 1.94 m/s, r[2] = 86 µm
u[3] = 2.76 m/s, r[3] = 143 µm
Velocity [m/s]
2.5
2
1.5
1
u[1] = 1.09 m/s, r[1] = 24 µm
u[2] = 1.94 m/s, r[2] = 86 µm
u[3] = 2.76 m/s, r[3] = 143 µm
0.5
0.5
0
0 0.2 0.4 0.6 0.8 1
Time [s]
0
0 1 2 3 4 5
Time [s]
Fig. 4.8: Velocity profiles of three droplets with different initial radii and velocities
under the influence of drag alone (left) and drag and gravity (right).
follow the streamlines of the gas after reaching a steady value, cf. left side of Fig. 4.8.
On the other hand, when the droplets encounter gravity in addition to drag force applied
by the surrounding gas, the droplet velocity initially decreases due to drag and
then increases linearly due to gravity as seen in right part of Fig. 4.8. In a previous
study [198, 200], it has been shown that the moderate droplet evaporation under the
present conditions does not significantly influence droplet velocity.
140
130
Experiment - 80 kg/h
Evaporation - 80 kg/h
Evaporation and Coalescence - 80 kg/h
Experiment - 150 kg/h
Evaporation - 150 kg/h
Evaporation and Coalescence - 150 kg/h
Sauter mean diameter [µm]
120
110
100
90
80
70
0.14 0.28 0.42 0.56 0.7 0.84
Position [m]
Fig. 4.9: Effect of liquid inflow rates on Sauter mean diameter computed with and
without coalescence.