Chemistry Reference
In-Depth Information
Table 3.2
Scale-up parameters in lab- and industrial-scale SDRs.
Disc
diameter
(m)
Disc
speed
(rpm)
Throughput
(cm
3
/s)
Mean
disc
residence
time
(s)
a
Film
thickness
at disc
edge
(
m
m)
a
Surface
area per
unit
volume
(m
2
/m
3
)
Lab-scale SDR
0.2
400
20
0.2
82
8200
Industrial-scale SDR
1
127
50
2.0
82
8200
a
Assumes liquid properties similar to those of water.
3.3 Characteristics of SDRs
The characteristic features of fluid flow in the SDR are described in this section.
3.3.1 Thin-film Flow and Surface Waves
Film thicknesses of the order of 50-500
m
m are typical for the films flowing on the surface
of a horizontal disc rotating at speeds of between 200 and 2000 rpm. As expressed in
Equation 3.4, film thickness is dependent on a range of operational parameters, such as the
disc speed and diameter, and the liquid flow rate and physical properties (density and
viscosity). For a given liquid at a fixed radial position on a disc, the disc speed (represented
by the angular velocity,
v
) is a more influential parameter than the flow rate, Q, in
determining the film thickness, as
d /v
2/3
Q
1/3
. The effects of increasing the disc speed
and liquid flow rate are illustrated in Figure 3.6. It is also clear from Equation 3.4 and
Figure 3.6 that, for set values of Q and
v
, the film becomes thinner the further away the
liquid is from the centre.
The conditions giving rise to the wave-associated flow regimes on rotating discs have
been extensively studied. One of the most recent studies was by Woods [18], who carried
out a comprehensive theoretical and experimental examination of the formation and
500
20ml/s, 500rpm
400
5ml/s, 500rpm
20ml/s, 2000rpm
300
5ml/s, 2000rpm
200
100
0
0
10
20
30
40
50
60
70
80
Disc Radius [mm]
Figure 3.6
Film thickness variation for water at room temperature on a smooth disc [17].
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