Fluid Dynamics
Fluid mechanical force acts upon textiles suspended in liquid media during high-velocity washing or dyeing operations. This force, characterized as hydrodynamic shear stress, arises from the relative velocity between the moving fluid and the solid fabric surface. It is a factor in determining the rate of boundary-layer mass transfer during rinsing.
High levels of this stress can also deform the yarn structure.
Stress Boundary
Nozzle diameters and pump flow rates determine the intensity of the force applied to the textile rope. As the liquid travels through the restricted nozzle, it accelerates and exerts a shearing force on the fabric outer surface. This mechanical interaction helps to dislodge unbound dye molecules and surface impurities from the fibers.
However, if the force exceeds the cohesive limit of the yarn, it pulls loose fibers from the surface, causing pilling and fuzzing. In knitted structures, this force can also distort the loop shape, leading to dimensional instability in the finished garment. Operators adjust nozzle clearances to control the pressure gradient according to fabric weight.
Fabric Alteration
Loose fiber generation is particularly severe in low-twist spun yarns subjected to high stress levels. Filament yarns, which have higher structural cohesion, resist this action much better than staple fiber products. Testing the fabric surface before and after processing reveals the extent of the physical alteration.
Controlling fluid forces prevents structural damage during wet processing.
Process Management
Adjusting the pump speed allows mills to match the fluid dynamics to the specific fabric construction. Gentle treatment parameters protect delicate wool or silk blends from felting and distortion. Consistent pressure control ensures reproducible results across different production batches.
