Thermophysical properties of textiles

Thermal Conductivity. The most frequently investigated thermophysical property of textiles is thermal conductance, or U, the heat flux without convection transfer (usually expressed as calories/meters2 x seconds x °C), or its reciprocal, thermal resistance. Thermal conductivity, or k, is thermal conductance normalized with respect to the heat flux per unit degree temperature across unit thickness of the material (expressed in calories/ meters x seconds x °C). Many studies have demonstrated that thermal conductance primarily depends on fabric thickness and air present in the material however, the conductivity of air accounts for the greater part of the conductivity values observed (1 2,... 

Many investigators have proposed and utilized instrumentation that measures the thermophysical properties of textiles. One fundamental classification system for such instruments is based on the state of the heat flow involved (a) constant temperature,... 

Recent studies demonstrate that the thermophysical properties of textiles may be improved or even optimized. Such studies offer a variety of physical, chemical, and physicochemical approaches for conducting further research on the thermal characteristics of textiles that can be applied toward energy conservation. 

Research on optimizing thermal characteristics of drapes should include the use of the innovative technology acquired from a knowledge of the thermophysical properties of textiles the assessment of the relative importance of conductive, convective, and radiant properties of draperies in relation to their energy-conserving efficiency under summer and winter conditions the variation of the amount of convective air flow and determination of its influence on other thermophysical properties and the measurement of surface radiation of curtains and other textile interiors by remote sensing devices. 

Thermophysical Properties. Several investigators have focused their work on evaluation of the thermophysical properties of clothing assemblies and either related the results to mannequins or wear trials or discounted the need for such trials and elaborate models. Total thermal resistance of a clothed body to heat transfer from the body to surrounding air was considered to be the sum of three properties thermal resistance of the textile, thermal resistance to heat transfer at the textile surface, and thermal resistance of the air interlayer. Relationships between thermal resistance of clothing assemblies, air permeability, wind speed, and assembly thickness were also explored (5J). A method for calculating the effects of wind speed on thermal resistance of clothing claims to be as reliable as tests that use mannequins (58). 

However, use of the special thermophysical properties of PCMs to improve the thermal insulation of textile materials only became possible by entrapping them in microcapsules, each with a diameter of 1 pm to 6 pm. 

In addition to wool, other hygroscopic textile materials such as cotton and linen underwent a threefold increase in their specific heat at constant vapor pressure. The relatively high specific heats derived from equations in the study, which are considered to represent those incurred in actual use of the hygroscopic textiles, explain the well-known buffering action of these fabrics toward sudden changes in indoor or outdoor temperatures (2l). A compilation of the specific heat of a variety of textile fibers at 20-200°C indicates that considerable variation in the values of this thermophysical property occurs with different fibers (e.g., a value of 0.157 for glass and 0.1 9 cal/g.°C for Nylon 66 are reported), and that additional research is needed to establish the extent to which specific heat affects the characteristics of thermal transmission in textiles (22). 

During this period, there was a limited amount of cooperative industrial R D under rather special circumstances. For example, the chemical and petroleum industry agreed to support development of the thermophysical and chemical properties of materials at several universities. Some regulated industries also supported joint R D in such institutions as the Institute of Gas Technology at the Illinois Institute of Technology and in the Electric Power Research Institute. A few traditional sectors whose firms had little or no indigenous R D capability also supported joint R D efforts, as in the textile and pulp and paper industries. 

Yoo S, Barker RL. Comfort properties of heat-resistant protective workwear in varying conditions of physical activity and environment. Part I thermophysical and sensorial properties of fabrics. Textil Res J 2005 75 523-32. 

---