Drying of Porous Media. The Case of Cotton Fabrics.

The focus of this PhD thesis is on clothes drying in home laundry, an energy-intensive operation of high societal impact due the high associated costs and carbon footprint. The main goal of this work is to improve the basic understanding of drying of cotton fabrics by combining classical thermal analysis with microscopy techniques. In particular, the proposed approach is to regard cotton fabrics as a porous medium where water can penetrate at different spatial scales. The well-known constant rate (CRP) and falling rate (FRP) phases of the drying process were related to cotton fabric porosity and our results show that drying is faster in a cotton fabric as compared to a dish filled with water with the same area of the fabric, during the CRP. Drying rate in fabrics can be enhanced by surfactants in diluted regime, in a concentration-dependent way. These effects were correlated with an increase of the interfacial area due to a decrease of the contact angle induced by the surfactant, by a single capillary model. All the drying curves overlap in the FRP, showing negligible effects of surfactants on drying rate. Both CRP and FRP can be qualitatively explained by considering the fiber as the base element of a multi-scale porous medium. Moreover, a single capillary model is proposed to study the evaporation process.