# Study on bubble visualization of gas-evolving electrolysis in forced convective electrolyte

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### Abstract

Electrolysis has been applied to many industrial fields because of the simple configuration and various usages. The bubble on the surface of electrodes is one of the most important factors that reduce the transport of electrons in the channel. In this study, the nucleation process of bubbles on electrodes against the time and the characteristics of bubble motion right after departure from the electrode were analyzed according to the Reynolds number of convective electrolytes. To verify the influence of the flow convection, the bubble behavior such as size and motion was analyzed by image processing. For an efficient configuration, the length of the electrode could be designed using empirical equations about the thickness of the bubble layer.

### Graphic abstract

## List of symbols

- \(a\)
Change rate of bubble velocity (m/s

^{2})- \(\Delta c_{\text{b}}\)
Concentration difference at bubble [\({\text{mol}}/{\text{m}}^{3}\)]

*D*Diffusion coefficient (m/s

^{2})- \(\tilde{D}\)
Diameter of bubble (m)

- \(D_{\text{h}}\)
Hydraulic diameter (m)

*H*Bubble height (m)

*h*Distance between electrodes (m)

- \(j\)
Current density (A/m

^{2})- \(k_{\text{b}}\)
Mass transfer coefficient at gas–liquid interface (m/s)

- \(k\)
Empirical constant for time-dependent bubble diameter

- \(l\)
Dimensionless length of electrode

- \(L\)
Length of electrode (m)

*m*Mass of bubble (kg)

*M*Molar mass of gas (kg/mol)

- \(P\)
Pressure (Pa)

- \(P_{\text{E}}\)
Electrical power (W)

- \(P_{\text{H}}\)
Hydraulic power (W)

- \(P_{\text{R}}\)
Ratio between electric and hydraulic power

- \(Q\)
Flow rate of liquid (m

^{3}/s)*R*Ideal gas constant (J/K mol)

*t*Time (s)

*T*Thermodynamic temperature (K)

*U*Mean velocity of liquid (m/s)

- \(v\)
Velocity of bubble (m/s)

*W*Width of electrode (m)

- \(Y\)
Distance between electrodes (m)

- Z
Velocity ratio

*Ja*Jakob number, Eq. (1)

*Re*Reynolds number of electrolyte

- \(Re_{\text{v}}\)
Reynolds number of bubble, Eq. (4)

- \(Sc\)
Schmidt number, Eq. (4)

- \(Sh\)
Sherwood number, Eq. (4)

- \(\gamma\)
Density ratio

- \(\delta_{\text{b}}\)
Thickness of bubble layer

- \(\mu\)
Kinematic viscosity

- \(\rho\)
Density (kg/m

^{3})- \(\theta\)
Contact angle between bubble and electrode

## Subscripts

- s
Kind of gas (\({\text{O}}_{2}\) or \({\text{H}}_{2}\))

- L
Liquid

## Notes

### Acknowledgements

This work was supported by the Basic Science Research Program through the National Research Foundation, Korea (2019R1A2C2003176).

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