Mass transfer coefficients between a liquid and column wall of an electrochemical cell were computed from the limiting current measurements made at the point electrodes fixed flush with the inner surface of the column wall. Twisted tapes of varying width and pitch served as insert promoter elements. The employed test section, which acted as electrochemical cell, consisted of a perspex tube of 6.73 cm inner diameter. 34 point electrodes were fixed to the test section. The liquid used was an electrolyte belonging to the Ferri-Ferrocyanide redox system. Addition of Carboxy Methyl Cellulose (CMC) sodium sulphate increased the viscosity of the solution. Analysis of the data obtained revealed that an increase in tape width increased the mass transfer coefficient. A decrease in mass transfer coefficient was observed with increase in tape pitch and CMC concentration. The data were correlated using regression analysis.

Use of several augmentative methods for enhancement of heat and mass transfer rates is ubiquitous in process and manufacturing industries. The augmentation in heat and mass transfer rates results in the reduction of the size of operating equipment, often with improved performance. This indeed lessens the burden of capital to be invested. The various methods employed for achieving augmentation of heat and mass transfer rates have been summarized by Bergles (1998). Broadly these methods are classified as: passive enhancement techniques, active enhancement techniques and compound enhancement techniques. Passive techniques do not require any external power. Active techniques need the application of external power. Simultaneous application of two or more techniques is called as compound enhancement technique. Use of treated surfaces, rough surfaces, extended surfaces, displaced devices, swirl flow devices, coiled tubes, surface tension devices etc., come under passive enhancement techniques. Using mechanical aids, surface vibration, fluid vibration, electrostatic fields, suction, injection and additives for fluids form the active enhancement techniques. Detailed information on all these techniques is presented by Bergles (1998). A good review of passive enhancement methods was also provided by Dewan et al. (2004). In general, passive methods are preferred to active methods for better cost-effectiveness. Among all the passive methods, the technique of employing displaced devices is widely in use. A comprehensive review on employing twisted tapes and coiled wires as heat transfer enhancement devices was presented by Dewan et al. (2004).

Enhancement of mass transfer rates was investigated by employing displaced promoters such as crossflow elements (Bhaskara Sarma et al., 1986), coiled wires (Rajendra Prasad et al., 2004), string of spheres (Sitaraman, 1977), string of cones (Sarveswara Rao and Raju, 1986), string of discs (Venkateswarlu et al., 2000) and helical tape on a rod (Sujatha et al., 1997). In all these investigations, the mass transfer between the column wall and the flowing liquid electrolyte was measured by a limiting current technique. The limiting current technique was first employed by Lin et al. (1951) for the measurement of mass transfer coefficient between an annular rod and flowing electrolyte.

Chemical Engineering Journal, Mass Transfer, Electrochemical Cell, Regression Analysis, Manufacturing Industries, Surface Tension Devices, Passive Techniques, Carboxy Methyl Cellulose, Newtonian Liquid, CMC Concentration, Twisted Tapes.