Diffusion Theories for the Design of Heat Setting Process in Fabric Drying

۱٫ Introduction
Hot air impingement is one of the most widely used methods for material drying. It is also
the most traditional drying approach used in industrial process for various kinds of
material, such as wood, paper, food, medicine and construction materials. Many research
studies have been carried out to see how it is effectively used to process different types of
material, and how it is implemented into the design of heat setting machines, such as spray
dryers, conveyor dryers, tunnel dryers, fluidized bed dryers and drum dryers.
To study hot air impingement in textile and clothing industries, modeling of porous type
fabric drying process would be the key study area. The heat and mass transfer principles are
used as tools to assist with the investigation of the hot air impingement mechanism. The
mechanism is usually treated as a mass transfer process of the moisture content from the
porous material to the impinging air. The transfer of moisture content from the fabric
material to the hot air stream is due to a heat transfer process under an in-equilibrium
condition. The change of water phases is traditionally described by linear heat transfer
equations. As a matter of fact, the driving force in the internal structure of porous materials
is not a simple direct proportional relationship between energy exchange and the phase
change of the interacting substances, i.e. air and water. Therefore non-linear analytical
models based on the physical properties of fabrics will be proposed in this study to provide
better simulation results. In the models, the parameters for modeling will be empirically
determined and used to describe the drying phenomenon down to microscopic levels. The
descriptions will involve the physical and mechanical properties of the drying materials
such as mass density, flow viscosity, thermal conductivity, diffusion properties, cohesive
properties and flow kinetics. Ip and Wan (2011) have suggested the strategies of using
analytical techniques to determine the modeling parameters, and these methods will be
investigated in greater depth in this research.