Microscale simulation of phase change and evaporation behavior in heat and mass transfer of yarns

The heat and mass transfer characteristics during textile drying are critical factors affecting fabric quality and energy efficiency. To explore the microscopic mechanisms at the yarn scale, this study utilizes realistic cross-sectional morphology data of yarn obtained by scanning electron microscopy (SEM) to develop a microscale coupled heat-moisture-flow drying model for yarn. The model simulates the microscale evaporation and phase change dynamics inside the yarn during drying. It reveals the synergistic effects of fiber arrangement, pore distribution, and drying process parameters. It quantitatively analyzes the influence of temperature gradient, fiber volume fraction, fiber wettability and heat source type on the evaporation process. The results show a strong positive correlation between heat source temperature and drying efficiency. The evaporation front rate at 80 °C under contact drying is 34.59 % higher than at 60 °C. Fiber volume fraction exhibits a dual effect: although it improves thermal conductivity, the reduced porosity restricts moisture transport and evaporation, which decreases overall drying efficiency. Compared with hydrophilic fibers, hydrophobic fibers dry 14.89 % faster. Dual-heat-supply drying enhances the synergy between mass and heat transfer inside the yarn, resulting in 8.33 % and 14.44 % increase in internal drying rate compared to contact drying and double convection drying. Compared with time-domain nuclear magnetic resonance (TD-NMR) measurements. For contact and dual-heat-supply drying, this study’s microscale coupled heat-moisture-flow drying model shows relative moisture deviations of 6.62 % and 5.93 %. The R² values are 0.984 and 0.989, respectively. This confirms the model's reliability and accuracy.