AbstractThe longitudinal mixing of liquids flowing through straight pipes may be characterized by the coefficient of longitudinal dispersionK. In the case of pipings equipped with bends, the value ofKmust be extended by ΔKexpressing the more intense longitudinal mixing in bend areas. Physically, the value of ΔKis determined by the secondary flow in pipe bends.The dependence of ΔKupon the Reynolds numberNR= 15 180‐73 180/, the bend length /α = 30°.90°/ and the proportional bend curvature /R/D= 2‐6/ has been measured on a 50,8 mm ‐ diameter pipe. These dependences are expressed by empirical equations. Each of these partial results is further discussed from the view of relationships valid for secondary flows. The individual values of dependence are summarized in a final equation expressing the simultaneous effect of each observed variable upon the value of ΔK, i. e.\documentclass{article}\pagestyle{empty}\begin{document}$$ \Delta K = f/N_{Rc} ,\,R/D,\,\alpha /\,. $$\