Intelligent thermal protective clothing

Abstract

The aim of this study is to develop sound scientific understanding of the physical mechanisms involved in designing intelligent thermal protective clothing (TPC) for protecting human body from the cold environment. The effects of functional materials on the temperature and humidity distributions in protective clothing as well as the human physiological responses have been studied by carrying out computational simulations, experimental investigations, and wear trial experiments. To reveal the knowledge gaps and ensure the originality of this study, a critical search of literature is reviewed in relevant areas, including neurophysiological and neuropsychological mechanisms of thermal comfort, human thermoregulation, physical mechanisms of heat and moisture transfer, smart and functional materials and intelligent clothing. To study the effects of functional materials, computational simulations, laboratory experiments have been conducted. The dynamic heat and moisture transfer processes in TPC assemblies were simulated by using the thermal functional CAD software in which comprehensive models were incorporated with consideration of the complex physical mechanisms involved in terms of water vapor diffusion, heat conduction and radiation, liquid water transfer, moisture sorption/desorption, condensation/evaporations, phase changes and self heating elements. Engineering functional design approach was employed to design and simulate the dynamic heat and moisture processes in commercial TPC system, with consideration of the moisture management function, addition of phase change materials and further addition of temperature control system. The simulated temperature and humidity distributions in TPC systems indicates that applications of these functional fabrics, smart materials and active temperature control systems have significant impact on their thermal functional and comfort performances. To validate the theoretical predictions of computational simulations, laboratory experiments have been carried out by designing and setting an experimental apparatus in a climatic chamber controlled at -15 oC. The results of objective experimental measurements confirmed the numerical simulation results. Further, independent temperature control systems were developed with monitoring and automatic temperature control that were interfaced with a PDA system via bluetooth wireless communications. Then, the functions of the temperature control systems were tested by using the apparatus with and without application of PCM in clothing systems. The test results confirmed further that active temperature control system can significantly change the moisture and temperature distributions to enlarge the dry zone, and that PCM can regulate temperature and save energy consumption in the temperature control system up to 33%. Then, four prototypes of TPC were design and developed, including commercial TPC, moisture management TPC, smart TPC and intelligent TPC by the use of moisture management fabrics, PCM and the temperature control systems developed earlier. To reveal the effects of design parameters on body thermoregulatory and physiological responses and to validate the simulation predictions and objective experimental measurements on human subjects, wear trials were conducted and results were analyzed and compared in details. The wear trial results confirmed the computational simulations that the fabric moisture management properties of fabrics in clothing systems can significantly affect the humidity and temperature distribution and comfort of clothing. The moisture management functional design of clothing system can allow effective transfer of moisture and latent heat loss to keep the clothing microclimate dry and comfortable. Thus the performance of protective clothing can be greatly improved if it is systematically designed. The water vapor permeability and moisture management of fabrics are indeed very important to prevent water condensation in the clothing and ultimately to ensure improved superior thermal functional and comfort-related performance. The effects of PCM application in TPC were analyzed in-depth in a variety of ways. The experimental results from the wear trials confirmed that computational simulations in that PCM applied in clothing system temperature can enhance thermal regulating effect and influence the temperatures and humidity distributions in TPC. PCM applied in clothing system also decreased the temperature change rate at the back skin, and decreased the temperature impact induced by the environmental temperature change and change in physical activities. The effects of active temperature control were also analyzed. These results clearly indicated that temperature control could significantly improve the temperature regulation function and decrease the absolute humidity of the microclimate, making subjects more comfortable in the extreme cold environment. The effects of different thermal engineering design of TPC on physiological responses and stresses were analyzed as well. The experimental results showed that the properties of fabrics of the clothing system had significant effects on the physiological stresses. The moisture management design in the functional cold protective clothing seemed to significantly reduce the heart rate, the absolute humidity of the skin surface, the peak temperatures of the ear canal, the forehead skin surface, the chest skin surface, and the back skin surface. The clothing system coated with phase change material had significant influence on temperature regulation function, and could reduce the temperature change rates of the ear canal, the chest skin, and the back skin when changes occurred in environmental temperature or the activity level of participants. The temperature control system did keep the body temperatures of participants much more steady and make the participants feel more comfortable. The results demonstrated the importance of managing the moisture transport in TPC systems with smart thermal regulation and active temperature control functions in order to keep the core temperature constant, minimize physiological stresses and keep the wearer comfortable in extremely cold environment. Through this systematic study, sound scientific understanding of the complex coupled physical mechanisms has been established for identifying the impacts of various engineering design factors such as moisture management systems, temperature regulating with PCM and active temperature control systems on functional performance of intelligent thermal protective clothing.