Predicting Inlet Roundness of Hydroentangling Nozzles Using CFD Simulations

摘要

Hydroentangling process uses cone-capillary nozzles to direct high-energy waterjets against loose fiber webs. For hydroentangling to be feasible at higher pressures, it is important that waterjets maintain their intact length for an appreciable distance downstream of the nozzle. Hydroentangling nozzles produce constricted waterjets. A constricted waterjet is a laminar stream that is resulted from a detached flow inside the nozzle. When flow detaches from the nozzle wall, it is enveloped by an air gap and so is protected from cavitation or wall-induced turbulence. A sharp inlet edge is required to produce waterjets of such characteristics, which is a difficult proposition given the manufacturing constraints. The inlet sharpness is also affected with running time and the high operating pressures. In this work, steady-state two-phase CFD simulations were performed on cone-capillary nozzles with inlet roundness ranging from 0 to 0.2 to predict the nozzle's discharge coefficient. Discharge coefficients obtained from these simulations were found to increase with increasing the inlet roundness. We obtained a simple expression for predicting the nozzle inlet roundness by measuring its discharge coefficient at high pressures. The predicted inlet radius of curvature is compared with the actual nozzle dimensions reported by the manufacturer.