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Abstract
Experiments were conducted to investigate the effect of pertinent dynamic and geometric variables on wall-to-bulk mass transfer coefficient in two-phase upflow bubble column in the presence of a composite promoter. The liquid phase is an electrolyte consisting of equimolal solution of potassium ferrocyanide and ferricyanide of 0.01 N with 0.5 N sodium hydroxide. The gas phase is nitrogen and a 6.73 cm i.d. acrylic column was employed as the test section. Helical tapes of four different widths wound on central rods of three different diameters with five varying pitches were used as composite promoter elements along with annular rods of four different diameters. Measurement of limiting currents at point electrodes fixed flush with the inner surface of the test section facilitated the computation of wall-to-bulk mass transfer coefficients. The wall-to-bulk mass transfer coefficient was found to increase with increase in liquid and gas velocities in the presence of the promoter. The effect of rod diameter, tape width and tape pitch yielded improvements upto 40% at lower liquid and gas velocities. The entire data were correlated with the equation j D = 110.3 (Re)–0.8424 (Fr g )0.089.