Pressure drop characteristics for turbulent flow in a straight circular tube situated downstream of a bend

Experiments are performed to quantify the effects of a bend on the pressure distributions and friction factors in a straight tube situated downstream of a bend. Results are reported for parametric values of the Reynolds number (5000-80 000), bend turn angle (0, 90, and 180 deg), and the flow delivery configuration at the inlet of the bend (either a hydrodynamic development tube or a sharp-edged inlet). The 0 deg turn angle corresponds to the no-bend case, which serves as a baseline against which the with-bend cases are compared. It is found that the substantial circumferential pressure variations which exist in a bend dissipate almost immediately when the flow passes from the bend into the downstream-positioned straight tube. With the bend in place, the axial pressure gradients in the entrance region of the tube are smaller than the fully developed gradients at the lower Reynolds numbers and larger at the higher Reynolds numbers. A lengthwise-linear pressure variation is attained for all cases at an axial distance of 20 diameters or less from the tube inlet. Compared with the measured no-bend baseline values, the fully developed with-bend friction factors display deviations no greater than 9%, but with larger deviations (up to 18%) when compared to straight-tube correlations from the literature.