Heat and Moisture Transfer Modeling and Performance Evaluation of Hygroscopic Fabrics for Thermal Comfort Across Different Body Parts in Extreme Heat

Abstract Extreme heat exposure in medical and occupational settings can elevate thermal strain, impair task performance, and increase dehydration risk, particularly when protective clothing restricts ventilation and traps moisture near the skin. This study presents a one-dimensional coupled heat-moisture transfer model to evaluate hygroscopic natural fabrics for wearable cooling applications. Fabric properties for linen, ramie, bamboo, tencel, and hemp were obtained from recent literature, and simulations were performed for ambient temperatures of 38–45 °C, relative humidity (RH) of 90–95%, and wind speeds of 0–10 m/s over a 60 min exposure period. The numerical model describes transient heat conduction and vapor diffusion in the skin and fabric system, with latent cooling effects due to evaporation at the skin interface. The results indicate that the cooling rate is enhanced by wind speed and inversely affected by relative humidity, as the vapor pressure driving force is diminished. Linen fabric presented the highest cooling rate, followed by ramie and bamboo fabrics, with maximum temperature reductions of 5.1 °C, 4.1 °C, and 3.4 °C, respectively, while Tencel and hemp fabrics presented lower rates of 2.5 °C and 2.3 °C. The cooling rate in the body regions is not uniform, with the thigh presenting the maximum temperature reduction of 2.6 °C at 90% RH, while the upper arm and forearm presented lower values at near-saturated conditions. The rate of cooling benefit rose sharply until about 6 m/s and then reached a point of diminishing returns as the speed of airflow further increased. The results of this study can be used as quantitative information for fabric screening and region-targeted design of medical workwear.