Boundary Layer Hydrodynamics and Mass Transfer Rates in Flax Roving Swelling
Hydynamic boundary layer reduction in wet-spinning troughs accelerates core hydration, stabilizing swelling and lowering yarn count CV percent.
Sherwood Number
Mass Transport
Dimensionless ratios comparing convective mass transfer to molecular diffusion describe the efficiency of chemical movement into flax fibres. The sherwood number indicates how effectively a flowing chemical bath transports bleaching agents, dyes, or enzymes to the surface of the flax roving. High values indicate that convective flow dominates the transport process, leading to shorter treatment times.
Chemical Treatment
Dyeing and bleaching uniformity depend on maintaining a high rate of mass transfer at the fiber boundary. A low sherwood number suggests that the process is limited by slow molecular diffusion through the stagnant liquid layer, which can cause uneven chemical uptake and patchy coloration. By increasing the pump flow rate or using jet nozzles, the convective transport is enhanced, which raises the value of this dimensionless ratio and ensures a rapid and uniform chemical distribution.
This acceleration of chemical delivery is particularly important during the initial stages of the dyeing cycle when the dye molecules are rapidly absorbed by the flax cellulose.
Process Optimization
Industrial wet processing lines use these flow ratios to minimize water and energy consumption. Optimizing the sherwood number allows mills to reduce the duration of the washing and bleaching cycles without compromising the quality of the finished linen yarn. This optimization is achieved by adjusting the flow rate to match the specific diffusion characteristics of the flax fiber grade being processed.