(186a) Studies on Ionic Mass Transfer with Coaxially Placed String of Spheres as Turbulence Promoter in Homogeneous Flow

STUDIES ON IONIC MASS TRANSFER WITH COAXIALLY PLACED STRING OF SPHERES AS TURBULENCE PROMOTER IN HOMOGENEOUS FLOW

Avinash. B., Raju, CH. A. I., Rajendra Prasad, P., Sujatha, V. and Sarveswara Rao, S. Department of Chemical Engineering, College of Engineering, Andhra University, Visakhapatnam ? 530 003, Andhra Pradesh, India.

ABSTRACT

The process of development of the ionic mass transfer in a system is of immense theoretical and practical significance. This is an attempt to analyze and improve the performance of a mass transfer system. Several techniques have been adopted and tested by several workers to find out the level of augmentation. The use of surface promoters, swirl generators, inserts promoters, vibration of reacting surface and pulsation of fluids are few among the techniques practiced.

The use of insert promoters has gained much importance among the techniques mentioned above. Several works were published in literature using the string of discs, cones, spiral coils and twisted tapes mounted on a central rod as insert promoters and augmentation in mass transfer coefficients were reported. The present study is envisaged to obtain higher augmentation by the insertion of a coaxially placed string of spheres as turbulence promoter in homogeneous flow of fluid through a circular conduit. Diffusion controlled electrochemical redox reaction for the potassium ferri-ferro cyanide couple was chosen for the study. The geometric parameters covered in the study are the diameter of the sphere and the spacing between the spheres.

The experimental unit consists of a main unit consisting of an entrance calming section, a test section and an exit calming section and rotameters, a centrifugal pump and a recirculating tank. The experimental measurements consist of flow rate, temperature, limiting current and the pressure drop. The calculated data consist of velocity, limiting current density, mass transfer coefficients, Reynolds number, Schmidt number, JD factor, friction factor and other pertinent geometric groups.

The study is based on 3000 limiting current measurements obtained by varying the flow rate and geometric characteristics of the promoter. The magnitude of augmentation due to the presence of promoter was obtained. The study reveals that the limiting current density and hence the mass transfer coefficient increased with the increase in velocity. The increase in sphere diameter and the decrease in the spacing between the spheres increased the mass transfer coefficient. The friction factor increased with the increase in diameter of the sphere.

The data are correlated using the JD, Re and the geometric parameters of the promoter. The momentum transfer data are correlated using R(h+), Re and the geometric parameters. The following correlations are developed and presented hereunder.

JD = 1.06 (Re)-0.33 (ds/D)0.14 (S/D)-0.05 R(h+) = 0.06 (Re)-0.03 (ds/D)0.13 (S/D)-0.05

The present study is compared with the earlier works on string of discs and string of cones.