A bubble curtain model applied in chlorate electrolysis

voltages are given for the model with bubble curtain compared to the model without. For lower current
densities, the differences in cell voltages are getting smaller.
The implementation of a bubble curtain or high liquid velocity will almost have no effect on the cell voltage
for low current densities. The biggest change in cell voltage occurs when bubble coverage on the cathode
is taken into account. Of course this depends on the value of the coverage on the cathode which was
taken as 0,5 here. Keeping the cathode surface free from bubbles has a higher impact on the total cell
voltage than increasing the liquid velocity to reduce the voidage.
In reality, the voidage, bubble curtain and bubble coverage are all effecting the cell voltage together. The
developed Equations serve to figure out their mutual importance. Different values can be used for the
parameters in the Equations to see their influence. Learning more about how the cell voltage is influenced
by different parameters will help to find a way to reduce the cell voltage or at least point out where the
biggest changes can be made.
4.10 Dissolving time of a small bubble
Close the cathode only small bubble appears as seen in Bollens work.[1] Further away from the cathode
the bubbles are larger (see Figure 10). Since coalescence does not occur, there must be another
explanation on how those larger bubbles of the size of 0,1 mm can exist and where they come from.
Once a bubble is formed, it gets bigger by diffusion and absorption of hydrogen from the liquid into the
bubble [13]. The larger a bubble becomes, the slower it can grow because the area/volume ratio is getting
smaller with a larger volume. The larger a bubble, the lower its inside pressure (see Eq.(4.10)). A large
bubble will absorb the hydrogen from a smaller bubble through the electrolyte because of the difference
of Laplace pressure of two bubbles of different size. The pressure gradient can be seen as the driving
force of the mechanism where a larger bubble will absorb the hydrogen from a smaller bubble. This
explains why larger bubbles only appear further away from the cathode since then they already had time
to grow. The speed at which the diameter of a dissolving bubble decreases is calculated. Together with
the diameter of the bubble, this speed will result in a certain time it takes for a big bubble to fully dissolve
a smaller bubble. Of course this way of reasoning is only acceptable if there is a large bubble near the
cathode and close enough to the small bubble.
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