| The role of nozzle geometry in the formation of constricted hydroentangling waterjets, waterjets resulting from detached nozzle flows, is the main focus of this research. It is demonstrated that the characteristics of such waterjets mainly depend on the operating pressure and the nozzle geometry. In the first part of this study, flow of water through sharp-edge cone-capillary hydroentangling nozzles is simulated for different Reynolds numbers. For such nozzles, at high Reynolds numbers, the critical capillary length is found to be about 70% of the nozzle diameter, below which a constricted waterjet forms without cavitation. In the second part of the study, the cavitation phenomenon inside the above nozzles for 5700 < Re < 25600) is simulated. The shear-stress contours at the inlet together with the SEM elemental analysis indicated that stress-induced corrosion is the major cause of nozzle wear. In the third part of the study, different micro-nozzles with inlet roundness ranging from 0 to 0.18 were considered to obtain an expression for relating the nozzle's inlet roundness to its discharge coefficient. A good agreement between the numerical and experimental data is observed. The fourth part of the study discusses the possibility of obtaining a fluctuating impact force during the steady-state operation of a constricted waterjet. Characteristics of waterjets in the so-called 1st wind-induced breakup regime are briefly explained and the impaction between such streams and a smooth flat plate is discussed. The impulsive impact force for the discrete portion of these waterjets is found to be about 4 times greater than that of the continuous portion. The last part of this study deals with the presence of jet-marks on the surface of hydroentangled nonwoven fabrics, which is usually regarded as an undesirable outcome of the process. It is demonstrated that a waterjet curtain made of two rows of staggered jets where the jets in the 2 nd row are smaller in diameter than those in the 1st row can help minimize these jet-marks. |
