Surfactant turbulent drag reduction in an enclosed rotating disk apparatus

An enclosed rotating disk apparatus (RDA) with rotational speed up to 5,500 rpm and with temperature control from ?5 to 55 degree C was designed to screen the turbulent drag reducing effectiveness of small samples of newly synthesized drag reducing additives. First, the rotating disk was calibrated with water using both logarithmic and power law models. Then experiments were carried out to measure the frictional torque reduction for a drag reducing aqueous cationic surfactant system (5 mM Ethoquad O12 with 12.5 mM sodium salicylate) over a range of Re. The maximum drag reduction at 30 degree C was about 47% at Re = 1.90x10 super(6). For the first time, results with the RDA were compared with those in a circular pipe flow system. They showed similar trends indicating it is a useful screening device for small samples, giving conservative estimates of surfactant effectiveness compared with pipe flow.