Comparative Study of Heat Transfer and Water Vapor Permeability at Three Laboratories
Final rept. Nov 1989-Jan 1991
ARMY NATICK RESEARCH DEVELOPMENT AND ENGINEERING CENTER MA
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Heat transfer and water vapor transport measurements of materials were performed by three laboratories on-site at the U.S. Army Natick Research, Development and Engineering Center and compared. All three laboratories determine the thermal and water vapor transport properties of clothing materials and evaluate them for their intended use. Differences in test procedures and equipment result in different reported properties this study evaluated which factors are most important. It was found that the air speed over the guarded hot plate is the biggest source of discrepancies in reported material property results. The effect of air speed can be understood by examining the relative proportions of heat lost by convection and evaporation, which increase at higher air speeds, and the heat lost by radiation, which remains constant. The thermal and water vapor transport data generated by the three laboratories agree well if the variation in air speed over the plate is taken into account. A small bias between laboratories does exist, but is not significant for most materials. Measured intrinsic properties should agree within 10 for all the laboratories. Better agreement is possible if identical test conditions are used by all three laboratories.