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.
