Drag Reduction in the Flow of Aqueous Solutions of a Mixture of Cocamidopropyl Betaine and Cocamide DEA

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 degrees 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 degrees C, however, above 25 degrees 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 Re-c(,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 tau(w,c)(0) corresponding to the critical value of Re-c(,0) is approximately independent of pipe diameter. The critical value of the Re-c(,0) number has been linked to the clouding of CAPB/DEA solutions.

Automated summary

This study presents results of rheological tests and pressure drop measurements during the flow of aqueous solutions of a mixture of drag reducing surfactants through straight pipes. The formation of wormlike micelles was observed at temperatures below 10 degrees C. Drag reduction in the solutions was noted between 3 to 45 degrees C, with decreasing effectiveness at temperatures above 25 degrees C. The critical value of Re-c(,0) number for drag reduction onset was found to be dependent on temperature, pipe diameter, and surfactant weight ratio. The critical value of Re-c(,0) number has been linked to the clouding of CAPB/DEA solutions.