الفهرس 
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Abstract
The present work is concerned with the study of the mass transfer behaviour of an electrochemlcal reactor suitable for pollution control of waste streams containing metallic ions. The reactor involves a fixed bed electrode made of closely packed screens and stirred by gas sparging. The rate of mass transfer at the fixed bed electrode was determined by measuring the limiting current of the cathodic reduction of K3Fe(CN)6 in a large excess of NaOH Variables studied were t
1- Electrolyte concentration and the physical properties of the solution (Viscosity, density and diffusivity).
2- Air flow rate •
J- Number of screens forming the packed bed electrode (thickness of the bed) •
4- Position of the fixed bed electrode (horizontal or vertical ).
The study revealed the following results: br>1- At relatively low air velocities, the limiting current and mass transfer coefficient increase with air velocity by a factor ranging from 5.6 to 10.8 over the natural convection value depending on the operating conditions; at relatively high gas velocities the limiting current and the mass transfer coefficient show little dependence on air velocity.
2- The mass transfer coefficient can be related to the gas velocity by the equation I K = a V <n ranges from 0.3785 to 0.0708 depending on the number of screens forming the bed •
J- Mass transfer data at horizontal fixed beds was found to fit the equation:
-0.25 l. -0.35
J = 0.25 (Fr.Re ) (Id)
4- Mass transfer data at vertical fixed beds can be represented by the equation I 0.28 J a 0.184 (Fr.Re )
” -0.28 ( t../d) br>5- The effect of gas velocity on the total cell voltage at different electrolyte concentrations show that air sparging within the range of air velocities used in the present work (0.,0212-0.6)66 cm/s)has no deleterious effect on the total cell voltage.
6- Power consumption calculations have shown that air stirring consumes more power than mechanical stirring for the same rate of mass transfer (i.e. the same rate of production) except for thin vertical beds where gas stirring is cheaper than mechanical stirring. br>7- An Industrial reactor based on the use of air stirred t~in vertical stacked screens as the working electrode is suggested for wastewater treatment .