Dimensionless Group
Dimensionless ratios that compare the rate of momentum transport to the rate of mass transport in a fluid flow characterize mass transfer systems. The schmidt number relates the kinematic viscosity of the fluid to the molecular diffusion coefficient of the diffusing species. It is used to analyze the behavior of boundary layers where evaporation or chemical absorption occurs.
This group is calculated as the ratio of momentum diffusivity to mass diffusivity.
Boundary Layer
When the value of this ratio is high, momentum penetrates much deeper into the boundary layer than the chemical concentration profile. The schmidt number determines the relative thickness of the velocity and concentration boundary layers on the fabric surface. In air-water systems typical of textile stenters, the value of this group is approximately zero point six.
This constant is a primary input in equations that predict moisture evaporation rates.
Textile Drying
Modeling the drying of solvent-treated fabrics or high-temperature dyeing processes requires precise knowledge of this ratio for the specific vapor-gas mixture. By using the schmidt number, engineering software calculates the mass transfer coefficient and optimizes the exhaust flow rates. This helps to prevent the buildup of solvent vapors while minimizing heat loss from the dryer.
The calculation is critical for maintaining safe operating limits and reducing energy costs.
Operating Limit
The value of this ratio changes with temperature because both viscosity and diffusion coefficients are temperature-dependent. At very high temperatures, the relationship becomes highly non-linear.
