Chemistry Reference
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Figure 5.9
Initial and final distributions of molecules in the centre of the channel after
282 fs (the flow is from left to right). Left: low flow rate. Right: high flow rate.
been removed from the images. From these images, it is clear that the molecules
in the high flow rate stream have moved further than those in the low flow rate
stream. It is also noticeable that the high flow molecules have not dispersed as
much as those in the low flow. This is confirmed by looking at a histogram plot of
the distribution of the molecules, shown in Figure 5.10.
In Figure 5.10, the frequency has been normalized for the number of molecules
in each band, as the low and high flow examples contained a slightly different
number of molecules. These results highlight the fact that there is a substantial
difference between the distributions of the two regimes. The standard deviation of
the low flow rate simulation is 0
.
0443, whereas the high flow value is substantially
lower, at 0
0302.
The same test performed with a horizontal band, between
y
.
=
6
.
0 nm and
y
0 nm, allows an examination of the way in which the molecules diffuse
vertically, perpendicular to the solid boundaries. Figure 5.11 shows the initial and
final plots. In these figures, the distribution of molecules in the low and high flow
rates in the
y
direction is visibly the same in both cases. Figure 5.12 shows a
histogram of the data collected, along with the initial position of the band. The
graph shows that the majority of molecules have diffused in different directions
in the low and high cases, but the distributions of the molecules after a short time
are almost identical. The low flow rate gives a standard deviation of 0
=
9
.
.
0320 and
the high flow rate gives a value of 0.0304.
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