Drying Metric
Mass reduction measurements representing the quantity of water turned to vapor and removed from a fabric during drying determine the process endpoint. The evaporative mass loss is monitored to calculate the drying rate and the energy efficiency of the stenter. It reflects the transfer of liquid water from the yarn structure to the surrounding air.
This metric is expressed in kilograms of water evaporated per square metre of fabric per hour.
Transport Phenomenon
Energy supplied by the circulating hot air is consumed by the latent heat of vaporization of the water in the fabric. The resulting evaporative mass loss reduces the temperature of the wet textile, protecting the fibers from thermal damage. As long as free water exists on the surface, this evaporation rate remains constant.
Once the surface dries, the process enters the falling rate period.
Process Monitoring
Continuous moisture sensors at the exit of the stenter frame calculate the residual moisture to ensure the correct amount of drying. By tracking the evaporative mass loss along the different zones of the oven, the controller optimizes the burner output. This prevents over-drying, which can make cotton fibers brittle and reduce their mechanical strength.
Accurate evaporation control also reduces gas consumption.
Fiber Limit
Synthetic fibers with very low moisture regain exhibit rapid water release and low total mass reduction. The constant drying rate period for these materials is extremely short.
