Friction Factors for Flow of Drag Reducing Solutions of Micellar Surfactant Additives in Straight Circular Pipes and Conventional Globe Valves

摘要

Experiments were carried out in order to investigate pressure drops due to friction and form for flow of water with micellar drag reducing additives Arquad S-50, CTAB and CTAC, which were prepared in various different concentrations. The rheological behavior of these solutions was studied on a coaxial cylinder rheometer. Standard experimental data evaluation in the form of flow curves disclosed a pattern in which, in the low shear rate range, a nonlinear shear stress decrease with increasing shear rates was observed. For still higher shear rates, shear stress values approached asymptotically constant, shear-independent, values. Therefore, in the low shear rate region, experimental data were described with sufficient accuracy by means of the simple power-law model. A closed-loop experimental stand consisted of a 2700 mm long stabilization section followed either by a 3000 mm long straight, stainless circular tube, (15, 20, and 25 mm I.D.) or with a conventional globe valve. Results are presented in the form of Darcy-Weissbach friction factor vs. the generalized Reynolds number Reg. Also, it is worth to note that the pressure loss reduction in the lower shear-rate range in pipes occurs due to the pseudoplastic behavior of the solutions rather than due to the drag-reduction mechanism in the proper (Toms) sense of the word.