Turbulent flow in pulsed extraction columns with internals of discs and rings: Turbulent kinetic energy and its dissipation rate during the pulsation

Turbulent energy parameters of single-phase pulsed flow in an extraction column with internals of immobile discs and rings (doughnuts) are studied. Simulation results are obtained by resolution of Reynolds equations coupled with k-epsilon model of turbulence. As far as pulsed flow is concerned, the evolution of space distribution of turbulent kinetic energy k and its dissipation rate epsilon during the pulsation is thoroughly studied. It is observed that the energy distribution on a contact stage changes periodically from rather homogeneous to highly inhomogeneous depending on instantaneous flow velocity. Significant difference between maximal and mean energy parameters is observed. it is supposed that the discrepancy between simulation and experimental results for the size of drops formed in the turbulent field might be attributed to mean energy presentation that smoothes the peak effects of a pulsed flow. Spatial zones and time intervals of high-turbulent kinetic energy are delimited presuming their dominant role for accurate foreseeing of size of drops in this type of equipment. It is shown that an "effective" energy level should be determined by selection over the high-energy time periods and zones in order to compensate the smoothing effect of mean energy level. The results obtained are useful for the calculation of drop size based on energy level at the stage, which is necessary for the determination of parameters of practical interest such as drop residence time and interphase mass transfer surface. (c) 2008 Elsevier B.V. All rights reserved.