(42e) Studies on Ionic Mass Transfer in Circular Tubes with Tangential Entry of Fluid through Curved Nozzles

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

ABSTRACT

Augmentation in mass transfer processes have received the attention of several augmentation techniques that have been adopted and tested to findout the level of augmentation for a given amount of energy. The salient factors that influence the selection of any technique are ease of operation, reduction in equipment size and increased output. Various techniques available in literature have been classified based on the means by which augmentation is achieved. For example significant improvement in coefficients were found to be achieved by the use of insert promoters that generate local turbulence in the vicinity of transfer surface. Turbulent flow fields are also generated by the vibration of the transfer surface or the flow field. In view of this the augmentation techniques are broadly classified as (a) the use of displaced promoters, vortex or swirl flow generators, surface promoters (b) vibration of transfer surface or fluid, rotation of transfer surface or fluid, the application of magnetic or electrostatic fields and the use of fluidized solids (c) use of fluidized beds in the presence of promoters.

Several studies were carried out using swirl flow generators like twisted tapes and tapes mounted on central rod in the flow medium. Adoption of entry region swirl flow generators like use of twisted tapes as internal at the entry region, single orifice across flow through conduits reported higher mass transfer augmentation.

In the present study mass and momentum transfer data were obtained using a swirl flow generator. The swirl was due to the tangential entry of fluid through curved nozzles serving as turbulence promoter. The promoters were made of copper tube of various sizes. Diffusion controlled electrochemical redox reaction for the system potassium ferri ferrocyanide couple was chosen for obtaining limiting current data. Pressure drop and limiting current measurements were obtained by varying the flow rate and nozzle diameter.

The following conclusions are drawn based on 1000 limiting current and pressure drop measurements. The study revealed that the mass transfer coefficient increased with increase in flow rate and diameter of the nozzle. The coefficients augmented from 418 percent to 1550 percent over the data obtained by Lin et al. for flow through smooth tubes. Friction factors were computed from the pressure drop measurements. It was found that friction factors decreased with Reynolds number and increase with diameter of the nozzle. The efficiency of the promoter is arrived by computing mass transfer augmentation factor and energy factors. The overall efficiency of the promoter is given as the ratio of augmentation factor and the energy factor. The data are correlated as

R (h+) = 0.614 Rem-0.899 (do.d) 0.214