Combined effects of temperature and Reynolds number on drag-reducing characteristics of a cationic surfactant solution

The drag-reducing characteristics in the turbulent channel flow of dilute cationic surfactant solution, cetyltrimethyl ammonium chloride (CTAC)/sodium salicylate (NaSal) aqueous solution, were experimentally investigated in a closed loop fluid flow facility at different temperatures. The mass concentrations of the surfactant solution ranged from 75 to 200ppm, and the temperatures ranged from 15 to 55°C. The cationic surfactant solution showed a great drag-reducing ability, which was greatly affected by concentration, temperature, and Reynolds number. It was found that there existed a critical temperature T _c in each solution at different concentrations. Above T _c, drag-reduction level decreases and reaches the behaviour of water flow without drag-reducing ability. A new temperature parameters T _f, was proposed, and the difference between T _c and T _f can represent the effective temperature range for the drag reduction at a certain Reynolds number. The variation tendency of T _f and T _c with Reynolds numbers can give the guidance of selecting effective drag reduction range to the practical application in the district heating systems (DHS). It was supposed that temperature and shear stress are two kind of energy applied on the surfactant microstructure, which can be helpful to the surfactant network formation or dissociation depending on their values.