Transient heat and mass transfer of single and dual-cartridge respirators under extreme hygrothermal conditions: A coupled CFD and experimental study

Under high-temperature and high-humidity conditions in mines combined with cyclic breathing by miners, the transient transport and accumulation of water vapor within the porous filter medium can significantly affect the hygrothermal state and aerodynamic performance of respirators. This study focuses on single- and dual-filter respirators and investigates water-vapor transport and condensation characteristics within the filter medium at different respiratory flow rates. A transient CFD model coupling Darcy–Forchheimer porous-medium flow, hygrothermal transfer, and condensation phase change was established and validated against experimental pressure-drop data. Response surface methodology was employed to analyze the effects of temperature, humidity, and respiratory intensity on filtration efficiency and inspiratory resistance. The results showed that respiratory intensity significantly altered the water-vapor transport state within the filter medium. Under high-flow cyclic breathing, the single-filter respirator exhibited greater moisture accumulation, with a peak relative humidity of 83.7%, markedly higher than the 59.9% observed for the dual-filter respirator. Structural differences further influenced aerodynamic and filtration performance: compared with the single-filter design, the dual-filter respirator showed an 8.12% lower increase in inspiratory resistance and over 15% less reduction in filtration efficiency under high-humidity conditions. Response surface analysis revealed distinct response patterns between the two structures, with the single-filter respirator being more sensitive to humidity variations, whereas the dual-filter respirator maintained more stable performance under combined high-humidity and high-respiratory-intensity conditions. These findings provide a scientific basis for the selection and structural optimization of mining respiratory protective equipment, offering practical value for safeguarding miners' occupational health.