Abstract
The study presents results of rheological tests and measurements of pressure drops occurring during the flow of aqueous solutions of a mixture of drag reducing surfactants: cocamidopropyl betaine (CAPB, zwitterionic surfactant) and cocamide DEA (nonionic surfactant) through straight pipes. Tests were carried out at different CAPB/DEA weight ratios and different total concentrations of surfactants in the solution. Rheological measurements demonstrate the formation of a shear-induced structure (SIS) in the temperature range below 10 °C, which provides evidence for the presence of wormlike micelles in CAPB/DEA solutions. Drag reduction was observed during the flow of CAPB/DEA solutions in the temperature range from 3 to 45 °C, however, above 25 °C the degree of drag reduction was markedly decreased. The lower temperature limit at which drag reduction occurs depends on the CAPB and DEA weight ratio in the solution. In the range of higher temperatures, during the flow of CAPB/DEA solutions (similarly to flexible-chain polymer solutions) the onset of drag reduction is noted above a certain critical value of the Rec,0 number, whose value depends on the temperature of the solution, diameter of the pipe and the weight ratio of surfactants. At the same time, the critical value of wall shear stress τw,c0 corresponding to the critical value of Rec,0 is approximately independent of pipe diameter. The critical value of the Rec,0 number has been linked to the clouding of CAPB/DEA solutions.
Highlights
The addition of small quantities of certain surfactants, polymers and their mixtures to water can dramatically reduce the frictional drag [1,2,3,4,5]
The present study shows results of rheological tests and measurements of pressure drops during the flow of aqueous solutions of a mixture of drag reducing surfactants: cocamidopropyl betaine (CAPB, a zwitterionic surfactant) and cocamide DEA through straight pipes
DEA solutions in pure water were cloudy in the temperature range which was applied for the experiments
Summary
The addition of small quantities of certain surfactants, polymers and their mixtures to water can dramatically reduce the frictional drag [1,2,3,4,5]. Polymer solutions degrade mechanically when shear stresses are applied. For this reason, they cannot be used in closed flow systems. Micellar microstructure undergoes the mechanical degradation above a critical shear stress τc. In contrast to the polymers, it has the ability to self recovery when the value of shear stress will be reduced below the critical value τc [6,7], solutions of surfactants may find application in district heating and cooling systems
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