Effect of Air Permeability and Water Vapor Permeability upon Simultaneous Heat and Mass Transfer in Simulated Clothing Systems.

Abstract

The effect of air and vapor permeability of material on heat and mass transfer in clothing systems has been investigated with experimental and theoretical model. When size of air space is set very small e. g. about 5mm, water vapor condensation occurs. In such a case, water vapor permeability has more effect on heat and mass transfer than air permeability. In comparison with vapor impermeable fabric, vapor permeable fabric decreases the amount of condensation heat flux. In other word, such a fabric can keep lows the temperature and the amount of absolute water vapor concentration in microclimate, high values of which cause humid and heat stress sensation to wearer. The numerical analysis shows that the velocity of convective flow in microclimate is highly related to air permeability of fabric. However, the convective flow rate in microclimate under an air impermeable clothing is faster than that of a permeable clothing, especially inlet at the lower edge. Additionally, for a garment without air and vapor permeability, only the pathway through the openings is available. This shows that thermal insulation and water vapor resistance of clothing-system are determined not only by fabric properties but also by constructive factors as how to wear, such as condition of upper and lower opening, size of air space of microclimate.