A numerical model of the open-width coupling drying process for cotton fabrics based on the theory of heat and mass transfer in porous media

In order to reveal the physical drying characteristics of various kinds of cotton fabrics and further provide theoretical guides for designing drying equipment and improving drying technologies, a finite element model is built that is able to describe coupling of the drying process between fabrics and environment. Specifically, three kinds of cotton fabrics mesoscopic structures parameters and mechanical properties are firstly measured and then these fabrics are equivalent to porous media, and the equivalent media can characterize the fabrics precisely. Then, the formulas for calculating the convection heat transfer and thermodynamic properties of fabrics are also improved and verified by corresponding experiments. The results shows that the improved formulas can calculate the properties more accurately. Next, we apply this model to analyze the regular change of surface temperature and water content with time during the drying process of three kinds of fabrics under different technologies. The results indicates that the coupled heat and mass transfer of drying processes are obviously affected by liquid phase transition. In addition, with higher wind temperature, the velocity of water evaporation inside fabrics is faster and, when water content inside fabric becomes lower in the drying process, the velocity of water evaporation decreases. The numerical values agrees well with the corresponding experimental values: The mean absolute error of water content inside fabric in the drying process is less than 1.51 g, while the average absolute error of fabric surface temperature is about 1.63℃, which means this model can precisely capture the coupling drying process of various kinds of cotton fabrics inside the oven. It is expected that the model can be applied for providing theoretical guidance for designing structures of drying equipment and improving drying technologies.