Experiment and Analysis of Combined Heat and Water Vapor Transfer Through Clothes with Condensation

Abstract

A series of experiments is performed on the combined heat and water vapor transfer through fabric at simulated high altitudes. A considerable water vapor concentration difference is imposed between the water vapor source and the environment, so that condensation takes place in the specimen. A new analytical expression for the rate of condensation in textile materials is derived by considering the combined heat and mass transfer between the specimen and the environment. Although the amount of condensation in textiles can not be correlated well by primitive parameters such as temperature or water vapor concentration differences, good agreement can be obtained between the condensation mass flux measured experimentally and that calculated by means of the derived expression.If water vapor concentration in a garment exceeds saturation level) condensation takes place in the garment. When condensation occurs, heat released from the body to the environment is enhanced through the increased heat conduction of the liquid water. Thus, condensation is not only a significant discomfort factor in daily life, but also a significant survival factor in severely low temperature environments, such as polar regions and very high altitudes. Our previous work [3] experimentally indicated that the condensation mass flux increases with increasing altitude. This is due to both water vapor diffusion resistance and the saturated water vapor condensation decrease because of decreasing temperature with increasing; altitude. This indicates that a decrease in the water vapor resistance not only enhances condensation in clothes; but also discomfort and the chance of hypothermia due to the low thermal resistance of wet clothes. Therefore, condensation in clothing has to be prevented, especially at high altitudes.The water vapor transfer rate is determined by the concentration gradient, while the vapor saturation concentration is determined by the temperature level. Thus, both water vapor concentration and temperature gradient are determinant factors in water vapor transfer and condensation in clothing. Lotens et al. [6] developed a heat and water vapor transfer model with condensation and solved it numerically in order to estimate the condensation rate in clothes. They obtained good agreement for thermal resistance between their experiments and calculations, while agreement was less satisfactory for water vapor resistance or the amount of condensation in clothes by experiment. Therefore, more exact predictions of condensation are needed to develop comfortable and safe clothing systems. Lotens and Pieters [5] presented a set of heat and mass balance equations including condensation, which they solved numerically by an iterative method. To our

A simple theoretical model of heat and moisture transport in multi-layer garments in cool ambient air

“…Lotens, et al verified the essential correctness of their model by showing that computed results were in substantial agreement with three sets of data for human subjects who performed both light and heavy exercise while wearing either a semi-permeable or an impermeable outer garment. Fukazawa, et al (2003b) validated their model by showing that calculated mass fluxes were in good agreement with fluxes measured in a flat-plate apparatus (Fukazawa, et al, 2003a). Temperature, water vapour pressure, and total pressure (which affects the resistance to mass transfer) were varied over a considerable range of conditions.…”

“…While those variables are conceptually interesting, their practical utility is limited because they are not defined in terms of clothing properties and conditions on the skin and in ambient air. A conceptually elegant, but computationally demanding, analysis of moisture transport in clothing was described in 1986 by Farnworth, and a much simpler quasi-steady-state analysis was published in 1995 by Lotens, et al The approach developed by Lotens, et al was modified by Fukazawa, et al (2003b) to obtain an analytical solution, although the final result still appears to involve some computation. Both papers compare theoretical results with experimental data.…”

“…The principal difference between our approach and the approaches employed by Lotens, et al (1995) and Fukazawa, et al (2003b) is that neither of those authors considered the effect of an air space separating inner and outer garments, and they assumed a priori that condensation occurs at a particular location within the garment. Lotens, et al assumed that condensation occurs at the inner garment-outer garment interface when the outer garment permeability for water vapour is much lower than the permeability of the inner garment.…”

Protection From Steam at High Pressures: Development of a Test Device and Protocol

“…By examining the rate of heat and moisture transfer through fabrics during steam exposure, and through understanding the mechanisms of such, differences among FR clothing materials can be evaluated and improved clothing systems can be developed. Although extensive research has been conducted to understand mechanisms of heat and vapour transfer through different clothing systems, most has focused on transfer from human skin towards the environment with relatively low heat fluxes [2,3,4,5,6,7]. Li [2] concluded that the transfer of energy in mostly porous textile assemblies was governed by conduction by air and fibers, convection and radiation, while moisture transfer mechanisms included vapour diffusion in void space, moisture absorption by fibers, evaporation, and capillary effects.…”

“…Fukazawa, Kawamura, Tochihara, et al [5] investigated the combined heat and water vapour transfer rate through clothes with condensation at simulated high altitudes; they found that the water vapour transfer rate was determined by the concentration gradient, while the saturation concentration was temperature dependent. Thus they concluded that the water vapour concentration and temperature gradient were the determinant factors in water vapour transfer and condensation in clothing.…”