Civil Engineering Reference
In-Depth Information
s
¼
L
transverse
L
where
L
transverse
length of the path transversed by fluid
L
body length of the path transversed by fluid
In describing the properties of porous materials, pore shape factors are some-
times introduced, relating the behaviour of real pore shapes to that which would be
obtained for circular pores. In the case of an oval shape with longer axis a and
shorter axis b, the pore shape factor is defined as
d
¼
b
a
For a fibrous material, the fibre is often described by a convenient parameter
called ''fibre aspect ratio'' which is defined as a ratio of fibre length to diameter as
s
¼
l
f
D
f
where l
f
; fibre length, D
f
; fibre diameter
For example, the aspect ratio of the dispersed fibre is about 75 (Home
2012
).
5.2 Models
It has been reported widely that moisture problem is one of the most serious
factors in building and housing industry. Over the last decade, moisture failures in
building systems have reached billions of Euros in damages in Europe, many of
which involved the deterioration of sheathing panels. Additionally, excess mois-
ture in envelopes can lead to the presence of moulds which results in poor indoor
air. However, despite of the vast research work on heat transfer in vegetable
fibrous insulation, little has been done on the coupled heat and moisture transfer
until 1980s. This subsection is devoted to modelling heat and moisture transfer in
fibrous insulation materials.
The engineering analysis of the heat and moisture transfer in porous media can
be dated as early as 1920s in the fields of drying science. The transport behaviour
of porous media is largely governed by the interactions among coexisting com-
ponents. These interactions occur through interfaces. Theoretically, transport
processes in a porous medium domain may be described for a continuum at the
microscopic level as taking into account the multiphase nature of the material.
However, this is impractical because of our inability to describe the complex
geometry and trace a large number of interfacial boundaries of the porous domain
although by lattice gas or lattice Boltzmann method made such a description
