Experimental study of thermal conductivity of textile materials included in the clothes of power structures and special agencies
When designing clothing for military sub-units that protects personnel from adverse environmental factors, it is necessary to know the various thermal properties of the materials from which it is produced. One of these properties is the thermal conductivity of fabrics, which largely determines the thermal protection characteristics of workwear. Any fabric has a complex heterogeneous structure formed by interweaving of threads and air inclusions, so the total heat flow in it includes three components: conductive heat transfer through the fibers, as well as molecular and radiant heat transfer in inter-fiber or through pores. The coefficient of thermal conductivity of a fabric is an equivalent or effective value that takes into account these features of heat transfer. In this article, an experimental study of the effective coefficient of thermal conductivity of a number of fabrics is undertaken using two different measurement methods: the stationary method of a flat layer and the non-stationary Express method of a regular cooling mode. The flat layer method used a scheme with a symmetrical arrangement of tissue samples relative to the electric heater; this allowed us to correctly determine the heat flux densities, and end heat leaks can be minimized and accounted for by calculation. This method is highly accurate. The method of regular cooling mode combines the relative simplicity of the experiment and acceptable measurement accuracy. It is based on the exponential nature of changes in the temperature of a tissue sample over time. In experiments, only the rate of cooling of the fabric is determined, which is uniquely related to its thickness and thermal properties. Sources of experimental errors are analyzed. It is shown that in the regular mode method, the main contribution to the thermal conductivity measurement error is made by contact thermal resistances at the points where tissue samples come into contact with the surface of the measuring device. A method for eliminating these resistances is proposed, which significantly improves the accuracy of experimental data.