Abstract
The birefringences of dilute cationic surfactant solution were measured to investigate for the time characteristics of the solution casing drag reduction in a pipe flow. The concentration of surfactants was kept constant at 500ppm and shear rate ranged from 10 to 500s^<-1>. From the present results, the build-up time reaching shear induced structure (SIS) of micelles is found to be very long and it can be estimated from the results that the entry length required for flow fully developing in a pipe is longer than 1,250 times of pipe diameter. The SIS retardation and relaxation times also indicate that longer pipe is required for discussions on fully developed flow of drag-reducing surfactant solution.
