NATURAL-CONVECTION MASS-TRANSFER AT A VERTICAL ARRAY OF CLOSELY-SPACED HORIZONTAL CYLINDERS WITH SPECIAL REFERENCE TO ELECTROCHEMICAL REACTOR DESIGN

Natural convection mass transfer at a vertical array of closely-spaced horizontal cylinders was studied by an electrochemical technique invo lving the measurement of the limiting current of the cathodic depositi on of copper from acidified copper sulfate solution. Various combinati ons of solution concentration, cylinder diameter, and number of cylind ers per array were used including experiments on single cylinders. Res ults for single cylinders are correlated in the range 1.5 x 10(7) < Sc . Gr < 1.3 x 10(10) by the equation Sh = 0.231(Sc . Gr)(0.283). The t ransfer coefficient at the array was found to decrease with increasing number of cylinders, pass through a minimum, and then increase with f urther increase in the number of cylinders per array; the mass transfe r coefficient increased with increasing cylinder diameter in the array . Mass transfer data for different arrays were correlated for the rang e 6.3 x 10(9) < Sc . Gr < 3.63 x 10(10) by the equation Sh = 0.455(Sc . Gr)(0.25) and for the range 6.3 x 10(10) < Sc . Gr < 3.63 x 10(12) b y the equation Sh = 0.0064(Sc . Gr)(0.42). The characteristic length u sed in the above correlations was obtained by dividing the array area by the perimeter projected onto a horizontal plane. Practical implicat ions of the present results in designing electrochemical reactors with heat transfer facilities are highlighted.