Multiphase heat and mass transfer through hygroscopic porous media with applications to clothing materials

Accurate models for heat and mass transfer through porous textile-based materials are important for applications such as filtration, clothing systems, textile preforms for composites, and industrial processes involved in manufacturing textiles and textile-based commodities. Many natural and man-made textile materials are hygroscopic to some degree; their transport properties, physical structure, and transient behavior are often highly dependent on the total amount and rate at which water is absorbed into the polymeric matrix.; The approach presented in this thesis relied on both modeling and experiment. A set of partial differential equations describing time-dependent heat and mass transfer through porous hygroscopic materials was developed. In a hygroscopic porous medium, water may exist in vapor or liquid form in the pore spaces or in bound form when it has been absorbed by the solid. Factors such as the swelling of the solid due to water imbibition, and the heat of sorption evolved when the water is absorbed by the polymeric matrix, were incorporated into the conservation and transport equations. A numerical code to solve the set of nonlinear coupled equations was developed, and applied to an experimental apparatus designed to simulate transient and steady-state convection/diffusion conditions for textile materials.; Experimental measurements of air permeability and diffusion properties as a function of relative humidity provided fundamental data on the changes in transport properties as hygroscopic textile fibers swell and decrease the free gas phase volume within the porous structure. When these relations were incorporated into the numerical model, it was possible to directly compare the predictions of the numerical code with results generated in the experimental apparatus. Results are shown for hygroscopic porous textiles under several conditions. Under pure mass diffusion conditions, the temperature changes of hygroscopic textiles subjected to step changes in environmental relative humidity are shown to agree very well with the numerical predictions. These temperature changes are due to sorption of water vapor from the flows on both sides of the material, and relate to textile fiber equilibrium sorption isotherms and sorption kinetics, as well as the physical structure and thermal properties of the textile. Under conditions of a vapor concentration gradient and a pressure gradient across the fabric, which results in combined diffusion and convection, it is shown that fiber swelling has a very large effect on the total vapor mass flux across the textile layer. Also shown are results for step changes in both vapor concentration, and pressure drop across the textile layers, where the time-dependent transport properties are again influenced by the sorption kinetics and volume changes of the textile fibers.; The textile layer model was integrated with an existing human thermal physiology model to provide appropriate boundary conditions for the clothing system. The human thermal control model provides skin temperature, core temperature, skin heat flux, and water vapor flux, along with liquid water accumulation at the skin surface. The integrated model couples the dynamic behavior of the clothing system to the human physiology of heat regulation. This provided the opportunity to systematically examine a number of clothing parameters which are traditionally not included in steady-state thermal physiology studies, and to determine their potential importance under various conditions of human work rates and environmental conditions.