effect of drag reducing agents - polymers and surfactants alone and in combination on efflux time in gravity-driven flow systems

Determination of efflux time for draining water, a newtonian liquid from a large cylindrical open tank through a hole located at the center of the bottom of the tank has been used to study the effect of the addition of water-soluble drag-reducing agents. two polymers (polyacryl amide, (pam) and guar gum), two surfactants (lauryl sulfate and surf excel), and mixed solutions of guar gum and surf excel were studied.  four different concentrations of drag-reducing agents were considered for their impact on efflux time. there is a maximum of 1.3% reduction in efflux time (i.e drag reduction) with the addition of aqueous solutions of poly acryl amide while there is 2.8% maximum drag reduction due to guar gum. in the presence of aqueous solutions of lauryl sulfate surfactant, there is an increase in efflux time i.e (enhancement of drag) while there is a maximum of 2.3% drag reduction when aqueous solutions of surf excel are used.  with the mixed solutions of surf excel and guar gum, a maximum drag reduction of 2.9% has been observed.  this suggests that drag reduction is possible in the tank. and also, at the contraction point at the bottom of the tank. in the concentration ranges considered, polymers either had no effect or reduced drag while the same conclusion cannot be drawn in the case of surfactant solutions.