Convective-conductive Drying Characteristics of Thin Shrinkable Fibrous Layer Wetted with Aqueous Polymer Solution

摘要

Convective-conductive drying was investigated in a thin dewaxed cotton layer wetted with aqueous polyvinyl alcohol (PVA) solution and set on a polymer film base.Heated air was supplied to both the top of the cotton layer and the bottom of the polymer film.Drying rates were measured for several initial concentrations of PVA solution and two modes of air supply.One was high temperature air with high velocity to the top and low temperature air with low velocity to the bottom,and the other was the reverse.The wetted cotton layer shrank on drying and may be a model system for a coated layer in which small particles disperse.Under certain conditions,it was observed that a higher initial drying rate gave a longer overall drying time.Drying rates were also measured for a PVA solution layer with the same thickness as the wetted cotton layer.Comparison of the data for the two layers suggested that the drying of the wetted cotton layer takes place in three phases.The first is the period when there is no air void,which is observed on drying of the solution layer.In the second phase,a void is partly formed.In the last phase,a void is formed in the whole cotton layer,which is observed on drying of non-shrinking porous layer wetted with polymer solution.