Computational simulations on through-drying of yarn packages with superheated steam

Abstract

Industries need different types of drying technologies for their processes. The most traditional and commonly used one is to employ hot air as the drying medium. However, recent research has proved that superheated steam has higher drying capacity than hot air, because the specific heat capacity and heat conductivity of steam are higher than air. In addition, it has been found that using steam as drying medium can prevent surface hardening. Therefore, steam drying can preserve the quality of products better. This is especially important to heat-sensitive materials, like fruits and textiles. There are lots of research studies on drying process design using superheated steam, however, most of the studies were based on the jet impingement approach. In this research, an alternative approach of using steam for yarn package drying is studied. Superheated steam is generated from saturated steam and passes through the wetted yarn packages by establishing a pressure gradient between the up and down stream of the process. Computational fluid dynamics (CFD) analysis has been carried out using ANSYS 13 to model the heat and mass transfer process for the entire drying cycle, and to determine analytical solutions to quantify the residual water in the packages against cycle time. An industrial grade dryer prototype has been built to support experimental tests. Experimental results have been empirically used to assist the assignment of viscous resistance factor for CFD simulation studies. In the simulation process, the yarn packages have been assumed to be porous homogeneous. The drying rate under different pressures gradients between the up and down stream has been observed. The ultimate goals from the CFD results are to explore mathematical relationships in the drying process and predict the fastest drying rate with minimum amount of steam used.