Heat and moisture transfer and clothing thermal comfort

Abstract

This thesis is concerned with a systematic study of the dynamic coupled heat and moisture transfer in porous textiles and its influences on the clothing dynamic thermal comfort. The research aims to establish a knowledge framework for design and development of textiles and clothing for thermal function and comfort by theoretical study and experimental investigation. The research works have been carried out in the related knowledge areas such as neuropsychology, heat and moisture transfer in porous textiles, thermoregulation of human body and the perception of clothing dynamic thermal comfort. Significant results have been obtained as follows. The neuropsychological mechanisms of coolness and dampness perception to the touch of textiles have been investigated by conducting a series of psychophysical experiments and numerical simulations. The mechanism is hypothesized as a process involving a series of interactive physical, neurophysiological and neuropsychological processes and was confirmed by the experimental findings. Using the neuropsychological relationships derived from the experiments and models of heat and moisture transfer in textiles, numerical models have been developed to simulate and predict the coolness and dampness sensations from the neurophysiological responses of cutaneous thermoreceptors, which is determined from the heat and moisture exchange between the skin and fabrics. The simulation results are compared with the experimental measurements and good agreements are found between the two. To investigate and describe the complex coupling effect of heat and moisture transfer in porous textiles, a new mathematical model has been developed for isotropic textiles structure on the basis of the existing models. Heat and moisture transfer processes are considered being coupled by the phase change processes such as moisture sorption/desorption and evaporation/condensation inside the porous textile. The liquid water transfer and the thermal radiation inside the textile structure are also considered. The model has been validated by physical experiment. Further computational case studies have revealed complex interactions among different modes of moisture transport and the coupling effects between heat transfer and moisture transfer. Significant differences have been identified and the physical mechanisms are analyzed in detail between simulations with and without liquid water transfer inside the fabrics. To investigate the influences induced by different waterproof fabrics, a numerical model has been developed for clothing made of multilayer isotropic fabric assemblies with different waterproof fabrics bonded at the fabric surface. Significant effects of the waterproof fabrics at the outer surface on the heat and moisture transfer, and the water vapor condensation have been found. The isotropic model has been extended for the heat and moisture transfer in porous textiles of multiplayer anistropic assemblies by considering the roles played by different textile materials in each layer and heat and moisture exchanges between neighbored layers. Physical experiments on layered fabric assemblies with different liquid transfer properties and fiber types with different moisture sorption capability are conducted to validate the new model. The comparisons between the predicteded and experimental results show that thenew model can describe the coupled heat and moisture (vapor and liquid) transfer in the layered fabric assemblies with good accuracy. Significant influences of fibers and composite structures on the heat and moisture transfer processes have been illustrated clearly through the simulation. To fill the knowledge gap of the roles played by clothing in dynamic thennoregulation in a Human-Clothing-Environment system, a new one dimensional simulation model has been developed by interfacing the isotropic heat and moisture transfer model with an improved Gagge's two-node model. The mew model is able to describe how the processes of heat and moisture transfer in the clothing interact and influence the thermoregulatory responses of human body. The model is validated with the published experimental results. Analysis of the simulation cases show that for clothing made of fabrics with different heat and moisture transfer properties can influence the thermoregulatory responses even under the same environmental condition and physiological activities. Finally, an adaptive model has been developed to simulate the perception of dynamic clothing thermal comfort by integrating the mathematical models developed in previous chapters and fuzzy logic. A fuzzy inference system (FIS) was developed based on the measurement from a series of wear trials. Subjective perception of thermal comfort is predicted with fuzzy logic on the basis of the simulated results of thermal and moisture sensations as input variables, which are generated from a modeling system built on a series of mathematical models that simulate heat and moisture transfer in textiles, heat and moisture exchange between human skin and clothing system, thermoregulation of human body and neuropsychological responses. Thermal and moisture sensations are considered as two key factors that affect the overall clothing thermal comfort perception. The adaptive model can provide detailed information on the dynamic temperature and moisture distributions in the clothing system, the thermal physiological status of human body, neurophysiological responses of thermoreceptors, and the psychological thermal and moisture sensations, as well as dynamic perception of clothing thermal comfort. Good agreements are found between the predicted and experimental thermal and moisture sensations, and overall dynamic thermal comfort perception. The integrated adaptive mathematical model consists of different modules, which are expressed in various mathematical forms. Those expressions characterize the nature of the corresponding processes in the simulation. Therefore it is able to provide a comprehensive description of the dynamic thermal profiles and thermal comfort performance of the Human-Clothing-Environment system. In summery, a knowledge framework for thermal comfort and functional design of textiles and clothing has been established by carrying out a systematic study to investigate the mechanisms of interactive multiple processes involved in the perception of dynamic thermal comfort of clothing. The study includes the coupled heat and moisture transfer in the Human-Clothing-Enviroenment system, thermoregulatory processes of human body, neurophysiological responses of thermoreceptors and the psychological thermal and moisture sensations and perception of thermal comfort. Mathematical models for individual processes and the interactions amongst them have been improved or developed provide comprehensive information of the system status. The models can be developed as CAD tools for functional design of textiles and apparel products.