Recently, considerable interest has developed in surfactant additives for use in district heating and cooling systems to lower the pumping energy requirement. Many studies in the case of surfactant solutions have been done for the flow behavior in a circular pipe. However, few studies have been conducted on flow near a rotating disk in surfactant solutions. In this paper, the flow characteristics near an enclosed rotating disk in surfactant solutions were studied by applying flow visualization techniques and analyzed by applying the momentum integral equations which are related to the three boundary layer problem. The test surfactant solution was Ethoquad 0/12 with sodium salicylate at a concentration of 200ppm and a temperature of 18°C. The flow patterns were obtained at Re = 2.5×105 and 3.5×105 so that the Reynolds number range corresponds with the transition region to turbulent flow in the boundary layer on the rotating disk for Newtonian fluids. Consequently, it has been clarified that the amplitude of the circular vortex on the rotating disk was reduced and the flow direction near the disk was turned outward to the circumferential direction comparing with that of tap water. In additional, the limiting maximum drag reduction asymptote for a moment coefficient of a rotating disk was obtained by applying the momentum integral equation for drag-reducing solutions based on previous papers on circular pipe flow.

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