Drag reduction by polymer additives in gravity driven flow

A mathematical equation was developed, based on macroscopic balances, to compute efflux time for the case of gravity draining of a Newtonian liquid from a large cylindrical tank through an exit pipe located at the centre of the bottom of the tank, the flow in the pipe line being turbulent. The equation was fine tuned with the experimental data and an empirical equation for friction factor was proposed. The proposed equation will be of use in arriving at the minimum time required for draining the tank. The effect of addition of watersoluble polymer, polyacrylamide, on drag reduction was investigated for the cases of partly laminar (when draining through the cylindrical tank), partly turbulent (while draining through the exit pipe), gravity driven once through flows and % reduction in efflux time was reported. The concentration of polymer on drag reduction was also established from the experimental data.