A bubble curtain model applied in chlorate electrolysis

voidage stops increasing due to the transition of homogeneous regime to heterogeneous regime of the
gas-liquid dispersion. In the homogeneous regime the electrolyte contains small bubbles all of the same
order of magnitude. In the heterogeneous regime these small bubbles start to coalesce and break up
again. This process makes that there will be both small and big bubbles in the electrolyte. Due to this
coalescence the voidage will no longer increase with rising current density.
The limiting voidage is influenced by the type of the electrolyte and its concentration.[8] Factors that
benefit or inhibit coalescence will also be responsible for the value of the limiting voidage. The concept of
coalescence is further investigated in a separate chapter (see chapter 4.5). In this work the point of
transition from homogeneous to heterogeneous regime or differently stated the limiting voidage is
searched for by increasing the current density and measuring when the voidage stops increasing.
The void fraction can be estimated using the superficial gas and liquid velocities instead of the volumes of
gas and liquid using the equations below. The explanation for this replacement is that if v gas ≪ v liquid ,
which can be seen in Equation (4.39), the gas bubble can be assumed not moving compared with the
dispersion velocity.
ε =
V gas
v gas
=
(4.43)
V gas +V liquid v gas +v liquid
v g = I
.
RT 1
.
2F P T −P water sw
(4.44)
I = i. L. w (4.45)
The combination of Equation (4.44) and Equation (4.45) results in the equation below.
ε =
1
1+ 2 F s v liquid P T −P water
i.R.T.L
(4.46)
The width of the electrode is denoted as w, the length as L and the distance of the electrode gap is s.
When taking this into account, the cross section surface between electrodes has a surface of sw and the
surface of the electrode equals Lw . Equation (4.46) will be used in the for the calculations of the
conductivity in chapter 4.8.
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