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The Thermal Fluid Sciences Group @ UNT can simultaneously evaluate evaporative cooling efficacy arising from heat- and mass-transport of dilute water vapor through porous barrier materials presenting a resistance of 30 s/m or greater at atmospheric pressure. For textiles, fabrics, and membranes we can provide human thermal comfort data similar to ASTM F 1868, the sweating hot plate method. However, existing textile thermal comfort tests cannot measure both heat- and mass-transport simultaneously and do not provide complete thermal management data for specimens under study. In addition, our approach allows cooling to be gauged over a range of surface input heat fluxes from 50 W/m2 up to 2000 W/m2.
Our equipment provides steady-state heat balance closures to within ± 8% for practically realistic heat loads. We can therefore predict actual heat removal rates and associated human comfort parameters to ± 8% or better.
Water vapor mass transport rates at atmospheric pressure through porous barriers with channels ranging from 1 micron to sub-nanometer can be accurately interrogated by our approach, provided samples present a mass transport resistance of 30 s/m or greater. Moreover, our experimental method returns intrinsic coefficients for diffusion of latent heat carriers through the micro-truss voids at ambient pressure. These results are entirely free of parasitic apparatus and environmental artifacts, which (if not accounted for) can provide misleading data.
Other gas permeability measurements draw a vacuum on one or both sides of a sample under study, which yields results unrepresentative of true diffusion mass transport under realistic atmospheric conditions. By contrast, our approach measures latent heat carrier transport in air under ambient pressure conditions. The resulting data is therefore directly applicable to engineering design of real systems that must function under atmospheric pressure conditions.
For more information, please read our White Paper covering the TFS Group's capabilities for measuring self cooling body armor wearer comfort.
