Hydrodynamics of Secondary Settling Tanks and Increasing Their Performance Using Baffles

Abstract

Generally, the flow in settling tanks is stratified, but the effect of buoyancy force on the flow field depends on the inlet concentration of particles and flow bulk velocity. A common approach for increasing settling tanks performance is to use baffles which can reduce effects of the unfavorable phenomena such as short circuiting between inlet and outlet and density currents in primary and secondary settling tanks, respectively. The suitable position of the baffles is related to the importance of buoyancy force. As a result, effects of inlet Reynolds and Froude numbers on the strength of buoyancy force are studied for a secondary settling tank and the results show that neither Reynolds nor Froude numbers are sufficient to be considered alone. Effect of buoyancy force on the suitable baffle position is also investigated. Results show that in high Reynolds numbers, the flow field and baffle position are not affected by the inlet Froude number.