In this study, an effect of an additive on a bend loss was examined. Measurements of pressure distributions along pipes connected to pipe bends were performed using a drag-reducing surfactant solution. The additive used is being commercialized as a drag reducer and it has a non-degrading or rapidly repairable nature. Dimensions of the apparatus are pipe diameters d = 5, 10, 15 mm, radius ratios R/r = 20, 40, 60, 100, and a bend angle θ = 180 degree. It has been confirmed that total bend loss coefficients for water can be expressed by the equation deduced by Ito. When the surfactant solution is used, remarkable drag reduction was recognized in the inlet and the exit straight pipes. Pressure recovery length for the surfactant solution after the passage of the bend is longer than that for water. The curve of total bend loss coefficients for the surfactant solution intersects that for water. The former is larger than the latter at low Reynolds number and is smaller at high Reynolds number. The coefficients don’t depend on the pipe diameter but they depend on the radius ratio. It is shown that total bend loss coefficients for the surfactant solution can be expressed by a single curve and the empirical formula is deduced.

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