A simple methods for prediction of textile fabrics thermal conductivity

Abstract

Paper presented at the 5th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 1-4 July, 2007.The prediction of the thermal conductivity of fibrous structures is important for design purposes of new fabrics and prediction of their thermal comfort. It is well known that physiological comfort is strongly connected with the thermal comfort. There is a lot of fabrics’ properties which influence the thermal comfort. Thermal insulation properties characterized by thermal resistance or thermal conductivity belong to the most important ones. There exists a plenty of various models for prediction of thermal conductivity of multiphase materials which can be used for prediction of textile fabrics thermal conductivity. Tai deduced mathematical expressions for the equivalent thermal conductivity of two and three-dimensional orthogonally fibre-reinforced composites in a one-dimensional heat flow model. Tai showed that whether a square slab model or a cylindrical fibre model is used makes little difference to the heat flux; while the fibre volume fraction matters. Transversal heat conductivity of fibrous composites is dependent on the yarn shape and fabric macroscopic porosity. Krach and Advani investigated the effect of void volume and shape on the effective conductivity of a unidirectional sample of a 3-phase composite using a numerical approach consisting of a unit cell. Their findings clearly showed that the influence of porosity on thermal conductivity could not be described solely by the void volume. Militky used the plain weave cell model for prediction of cotton type fabrics thermal conductivity. Application of these models for systems in which in matrix phase replaced by air phase is complicated by fact that during measurement of thermal conductivity is fabric deformed, shape of yarns is not circular and therefore unit cell is then not precisely known. The simpler approach is to use estimated porosity and packing density as characteristics of fabrics porous structure. The main aim of this paper is prediction of textile fabrics thermal conductivity as function of material (fibre type) and construction parameters (porosity or packing density). The relations between thermal conductivity and sound velocity or electrical conductivity are mentioned. Some approaches to predict thermal conductivity of multiphase systems with specific geometrical arrangements are shown. A measurement of the thermal conductivity is performed by the Alambeta apparatus. The set of cotton fabrics with plain weave and varying fineness of weft yarns is used as experimental material. The relations between total volume porosity and thermal conductivity of cotton weaves are predicted.