An analysis of the air-jet yarn texturing process. Part 4, Fluid forces acting on the filaments and the effects of filament cross-sectional area and shape

Fluid (drag) forces acting on filaments in an air-flow are theoretically analysed, and equations to calculate them are derived. Drag forces acting on filaments are shown to vary with the filament cross-section, the position of the filaments across the nozzle, and the local air velocity. Since finer filaments have a smaller inertial resistance to fluid forces and have lower stiffness, yarns with finer filaments are shown to be more suitable for air-jet texturing. Theoretical modelling of a lament as it emerges from the nozzle shows that, for filaments with identical linear densities, those with cross sections having reduced bending and torsional stiffness, such as elhpt1c cross-sections, may be more suitable for air-jet texturing.