Flow Regime in Helical Long-Path Emitters

The applicability of the Darcy-Weisbach equation combined with the Poiseville friction coefficient for describing the flow parameters in helical long-path emitters was tested under laboratory conditions. The results show that this equation fails to predict the pressure drop and mean flow velocities in these emitters. Based on previous work reported in the literature it is suggested that the water flowing through a helical flow path is subjected to centrifugal forces that distort the symmetrical axial flow velocity distribution. As a result the friction forces in helical long-path emitters are significantly larger than those in straight long tubes. The experimental results were in good agreement with the functional relationships predicted by the theory of flow through helical tubes. An empirical equation for computing the pressure drop and mean flow velocity in helical long-path emitters was developed and successfully tested.