Diffusion Coefficient
The dimensionless ratio of momentum diffusivity to mass diffusivity governs the relative thickness of velocity and concentration boundary layers in flowing fluids. In the chemical finishing of linen textiles, the schmidt number describes the behavior of bleaching and dyeing solutions as they flow through the dense yarn packages.
Dyeing Process
Liquid transport within a pressurized yarn package depends on the flow rate of the liquid and the diffusion rate of the solute. A high schmidt number indicates that mass transfer is dominated by slow molecular diffusion rather than fluid convection. In high-temperature scouring of flax yarns, this condition requires longer cycle times to achieve uniform removal of natural pectins and waxes.
Process Optimization
Dyehouse laboratories calculate this value to determine the optimal agitation speed and pumping frequency during yarn package dyeing. The test procedure log records the temperature and viscosity of the liquor, which directly influence the schmidt number during the execution of the dye cycle. By keeping this value within the calculated limits, the mill prevents uneven dye distribution and avoids shade variation across the inner, middle and outer layers of the wound yarn package.
The resulting fabric must meet the buyer’s color fastness and uniformity specifications before export.
