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Mass transfer characteristics of electrochemical reactors employing gas evolving mesh electrodes

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Abstract

Mass transfer rates were measured at a single screen and a fixed bed of closely packed screens for the simultaneous cathodic reduction of K3Fe(CN)6 and anodic oxidation of K4Fe(CN)6 in alkaline solution with H2 and O2 evolution, respectively. Variables studied were gas discharge rate, number of screens per bed and position of the electrode (vertical and horizontal). For single screen electrodes, the mass transfer coefficient was related to the gas discharge rate by the equations:

$$\begin{gathered} K = aV^{0.190} , for H_2 evolving electrodes, \hfill \\ K = aV^{0.469} , for O_2 evolving electrodes \hfill \\ \end{gathered} $$

. Electrode position was found to have no effect on the rate of mass transfer for single and multiscreen electrodes in the case of H2 and O2 evolution. Mass transfer coefficients were found to increase with an increasing number of screens per bed in the case of H2 evolution, while in the case of O2 evolution the mass transfer coefficient decreased with an increasing number of screens per bed. A mathematical model was formulated to account for the behaviour of the H2 evolving electrode which, unlike the O2 evolving electrode, did not obey the penetration model. Power consumption calculations have shown that the beneficial effect of mass transfer enhancement is outweighed by the increase in the voltage drop due to gas evolution in the bed electrode.

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Abbreviations

a, ā :

constants

A :

electrode area, cm2

C :

concentration, mol cm−3

D :

diffusivity, cm2s−1

F :

Faraday's constant

g :

gravitational acceleration cm s−2

Gr :

Grashof number,Gr=(gL 3/v 2)(Δρ/\(\bar \rho\))

i :

current, A

K :

mass transfer coefficient, cm s−1

L :

electrode length, cm

Sc :

Schmidt number,Sc=μ/ρD

Sh :

Sherwood number,Sh=KL/D

V :

gas volume discharge rate, cm3 cm−2 min−1

Z :

number of electrons in reaction

ε :

void fraction

μ :

viscosity, g cm−1 s−1

v :

kinematic viscosity cm2 s−1

ρ :

density, g cm−3

g:

gas phase (subscript)

l:

liquid phase (subscript)

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Author notes

  1. G. H. Sedahmed

    Present address: Chemical Engineering Department, Alexandria University, Alexandria, Egypt

Authors and Affiliations

  1. Chemical Engineering Department, McMaster University, Hamilton, Ontario, Canada

    G. H. Sedahmed & L. W. Shemilt

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  1. G. H. Sedahmed
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Sedahmed, G.H., Shemilt, L.W. Mass transfer characteristics of electrochemical reactors employing gas evolving mesh electrodes. J Appl Electrochem 14, 123–130 (1984). https://doi.org/10.1007/BF00611269

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