Abstract:

Objective The selection of fiber or yarn material is very important for the design of thermal-moisture comfort textiles. Compared with traditional yarns, nanofiber core-spun yarns have both the mechanical properties of traditional yarns and the surface effect and small size effect of nanofibers, which is beneficial for preparing thermal-moisture management textiles. In order to control thermal-moisture management performance of nanofiber core-spun yarn, the theoretical research on thermal-moisture transfer is indispensable. However, the current theoretical research on thermal-moisture management of nanofiber core-spun yarns mainly focuses on the experimental research or mathematical model research, and lacks the simulation research on thermal-moisture transfer process.

Method The finite element software COMSOL, which is suitable for multi-physics coupling, is selected to model and simulate the yarn section direction by finite element simulation method. The section of cotton yarn and nanofiber core-spun yarn are modeled and parameterized, and the thermal-moisture transfer process of yarn section is quantitatively studied by the configuration of laminar flow and heat transfer physical field.

Results The cross-section models with different parameters of traditional yarn (cotton yarn) and nanofiber (polyacrylonitrile nanofiber) core-spun yarn were established by using the geometric modeling function of COMSOL software, after multi-physical field coupling numerical calculation. Under the condition of the same inflow velocity, the average outflow velocity of PAN nanofiber core-spun yarn was 0.006 8 m/s, while that of cotton yarn was 0.005 3 m/s. At the center line position of the model, when the temperature was the same, the nanofiber core-spun yarn transferred farther, indicating that PAN nanofiber core-spun yarn had faster thermal transfer capacity than the cotton yarn. In order to explore the effect of nanofiber content on the thermal and moisture coupling transfer performance of yarns, a physical model of a yarn with nanofiber core and with different layers was designed. The simulation results show that increasing the number of nanofiber layers (less than 4 layers) can improve the boundary flow rate of the nanofiber cored yarn and speed up the water transfer process, mainly because the increase of the number of nanofiber layers leads to the increase of water transfer distance. In addition, thermal transfer across yarn sections was not significantly different due to the small difference in water transfer velocity. To explore the effect of pore size on the thermal-moisture coupling transfer of nanofiber core-spun yarns, physical models of four types of nanofiber core-spun yarns with different pore sizes were established. With apertures from 3.9 to 0.9 μm, the average water transfer velocity of nanofiber core-spun yarn gradually was changed from 0.006 8 m/s to 0.01 m/s, and the water transfer velocity was almost doubled compared with cotton yarn. Due to the difference in water transfer, the heat transfer distance became larger. Through the above results, it is further proved that there is a positive correlation between heat and humidity coupling transfer.

Conclusion The finite element software COMSOL, which is suitable for multi-physical field coupling, is used to model the longitudinal cross-section direction of yarn and simulate the coupled thermal-moisture transfer process along the yarn cross-section direction, and the speed of thermal and moisture transfer in yarn is quantitatively studied. The theoretical results show that the thermal only transfers half of the distance when the water is transferred to the boundary during the same time, indicating that the water transfer speed is faster than the heat transfer. At the same inflow rate, the moisture transfer rate is higher through the PAN nanofiber core-spun yarn due to the introduction of nanofibers, which is 28.3% higher than that of cotton yarn. The influence of nanofiber content and nanofiber diameter on the thermal-moisture coupling transfer performance was explored. The thermal-moisture coupling transfer speed of nanofiber core-spun yarn (about 11.8%) when the number of nanofiber layers is increased to four layers, but the effect is not significant. With the decrease of the diameter of the nanofiber and the increase of the number of the aperture, the moisture transfer rate of the nanofiber core-spun yarn is increased to 90% (compared with cotton yarn), and the thermal rate is increased significantly, which further proves that the moisture transfer and heat transfer of the nanofiber core-spun yarn present a positive correlation. Through the simulation of thermal-moisture coupling transfer process of nanofiber core-spun yarn, the mechnaism and influencing factors of thermal and moisture transfer in yarn cross-section direction are revealed, which provides ideas for the design of functional textiles such as moisture absorption and quick drying, waterproof and permeable.

Key words: nanofiber core-spun yarn, coupled thermal-moisture transfer, simulation, functional textile, thermal comfort management