Modeling of heterogeneous heat transfer in fabrics

Thermal comfort, an important factor when designing fabric, is strongly related to heat transfer in the fabric. Fabric is not homogeneous because the constituent yarns are interlaced at a certain weave angle, and the contact area between yarns varies. Therefore, heat transfer along the yarn in the fabric is not yet well understood. In this study, we developed a heterogeneous fabric model in which heat transfer along the longitudinal and transverse directions of the yarn is treated independently, and proposed a method for estimating the contact heat transfer coefficients for yarns. The geometrical fabric structure was constructed based on the cross section of three fabrics observed with a three-dimensional microscope. The parameters used were the mass density, specific heat, and thermal conductivity of the fibers and air. The heat flow calculated using the model was compared with that measured experimentally. Fairly good agreement was observed, verifying the validity of this heterogeneous model. The simulation results indicated that when the anisotropy of the fiber thermal conductivity is high, heat is transferred significantly faster along the longitudinal direction than along the transverse direction of the yarn, and the equilibrium temperature distribution is strongly influenced by heat transfer in the longitudinal direction.