Abstract
A garmet is one of the most important factors in order to predict and control the man and thermal environment system, but the property of garments, especially the moisture pemeability has not been well clarified to apply to the thermal equilibrium equation of man and his thermal environment. In general, garments not only act heat resistance, but also play the role of the moisture permeation resistivity. Whereas clo value may be commonly used as a unit for heat resistance, a practical unit for the moisture permeation resistivity has not been established. From the heat transmission and mass transfer theory, the evaporative heat loss H_e from the human skin to his environment is given by H_e=M・L=κ/(0.18Gη+1/α_c)(x_s-x_a) where M: rate of diffusive vapor flow [g/m^2・h] L: latent heat of water evaporation [kcal/g] κ: modified Lewis relation's factor [deg/(g/kg)] α_c: convective heat transfer coefficient [kcal/m^2・h・deg] G: clo value (1clo=0.18m^2・h・deg/kcal)[-] η: moisture permeability coefficient of clo-thing [-] x_s, x_a: vapor pressure of skin and air [g-vapor/kg-dry air] While in consideration of mass diffusivity into real textiles the diffusive vapor flow M can be expressed as follows. M=1/(l_gR_w(t_s+273)/μ・D_w)(x_s-x_a) where l_g: thickness of clothing [m] R_w: gas constant for water vapor [(g/kg)m^3/g・deg] D_w: mass diffusion coefficient of vapor into air [m^2/h] t_s: skin temperature [℃] μ: rate of air volume in clothing [-] From above mentioned equations and the relationship of l_g=0.03(0.18G)^<9/8>, the moisture permeability coefficient of clothing η is η=1.644(0.18G)^<1/8> under the condition that rate of air volume in clothing is 0.7 and that the temperature range limits to our daily life. Using a dry and a wet cylinder which produce about 84kcal/m^2・h heat flux, cotton, acrylic fiber and wool cloth which are utilized generally were examined. It was confirmed that η value is little difference between low and high air velocity. And it was disclosed that despite of kinds of clothes η values follow the same equation. Taking into account accuracy of clo value, η value fixes 1.5 in our daily life clothing for practical purpose. Further, the relationship of the moisture permeability coefficient η with the moisture transmission resistance R from Beaker method, the permeability index i_m by Woodcock (1962) and the permeation efficiency factor F_<pcl> by Nishi and Gagge (1970) were discussed.
