Comparing Dynamic and Static Methods for Measuring Thermal Conductive Properties of Textiles

Abstract

Dynamic and a static methods for measuring thermal conductivity of textiles have been developed, and the measuring processes and results are described in detail in this paper. Three different textile materials are used for the actual test. and the data are analyzed, illustrated, and compared. Moreover, a theoretical model is used to obtain the temperature-time curves as predictions corresponding to the dynamic method, and comparisons of the theoretical predictions and experimental results are provided. The static and dynamic methods are also compared, and their applicability to porous media like textiles is discussed.The importance of the thermal properties of textiles is indisputable, and extensive research work has been done in this area. Hager [ 12 ] investigated, both experimentally and theoretically, the effects of radiant heat transfer on the thermal insulation of textiles. In a series of papers, Rees and colleagues [6, 22, 23 developed a thermal transmission apparatus for measuring the thermal properties of textiles, and analyzed the effects of various factors on the warmth or comfort of clothing from the viewpoint of thermal equilibrium between a human body and the clothing. Famworth [ 11 ] proposed a theoretical model to predict the combined conductive and radiative heat flow through textiles. Stuart and Holcombe [ 26 ] studied the heat transfer through fiber beds by means of radiation and conduction. They reported that a portion of the radiated heat is absorbed by fibers in its path, resulting in a shadowing effect along the projected path. They then derived the heat transfer equations that take this shadowing effect into account.Many of these studies involved the development of instruments for measuring textile thermal properties. Although recently several new techniques have emerged for thermal property measurement, including the heat pulse [ 3,19 ] , heat balance ( 16 ] , heat wave [ 2 ] , photothermal [ 7). and photoacoustic {! 7 ] methods, the approach that uses a hot plate and a thermocouple remains an effective technique for textile materials. After reviewing previous research and existing experimental devices for measuring fabric thermal properties, Martin and Lamb [ 18 ) developed a dynamic measurement apparatus. Two layers of measured material are heated up to 125°C and then placed between two metal plates at room temperature. The temperature decrease at the center line of the sample is recorded and thermal diffusivity is thus calculated, but the method has some problems. First, the material being measured is heated to a rather high temperature, which may significantly change its composition as well as its thermal properties. The high temperature also induces intense radiant heat transfer. which is difficult to take into account. Further, it is hard to determine exactly the time and temperature of the beginning of the cooling process because of the time required to mount the sample, during which irregular cooling occurs. In addition, heat transport between the sample and the metal plates gener...

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