Thermodynamic Modeling of Bifunctional Dye Hydrolysis under High Shear Boundary Layer Flow
High fluid shear compresses boundary layers, accelerating hydroxyl mass transfer and driving hydrolytic dyestuff loss in bifunctional reactive dyeing.
Convective Mass Transport
Bulk Movement
Movement of dye molecules through the bulk liquid occurs primarily through the forced circulation of the dye liquor within the vessel. Effective convective mass transport ensures that the concentration of dye and chemical auxiliaries remains uniform throughout the entire volume of the machine. This mechanism is far more efficient than simple molecular diffusion for moving large quantities of chemicals over long distances within the dye bath during a production cycle.
Hydrodynamic Force
Kinetic energy from the pump drives the liquid through the fabric gaps and around the yarn bundles. Higher flow rates increase the effectiveness of convective mass transport, which reduces the time required for the dye bath to reach equilibrium. In package dyeing, this force must be high enough to penetrate the inner layers of the yarn wound onto the perforated tube.
Transport Variable
Pump pressure and liquor ratio determine the volume of fluid passing through a given section of fabric per minute. If the convective mass transport is insufficient, localized depletion of dye occurs, resulting in lighter shades in the center of the fabric rope or the interior of the yarn package.
Dyeing Consistency
Uniformity in the finished product depends on the ability of the machine to maintain constant chemical levels at every contact point. Modern control systems monitor flow sensors to ensure that the circulation remains within the parameters required for the specific weight and density of the textile batch.