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FUNDAMENTS OF DESIGN OF FABRICS AND GARMENTS WITH DEMANDED THERMOPHYSIOLOGICAL COMFORT by Prof. Lubos Hes, PhD., DSc, University of Liberec, Czech Republic, – PowerPoint PPT presentation

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Title: Prezentace aplikace PowerPoint


1
FUNDAMENTS OF DESIGN OF FABRICS AND GARMENTS WITH
DEMANDED THERMOPHYSIOLOGICAL COMFORT   by Prof.
Lubos Hes, PhD., DSc, University of Liberec,
Czech Republic, e-mail luboshes_at_vslib.cz
2
1.HIGH ADDED VALUE CLOTHING AND GARMENTS DESIGNED
BY THE APPLI CATION OF COMFORT SCIENCES   Due to
increasing sales of functional and protective
clothing, clothing comfort and the related
evaluation methods became very important in
recent years.   Comfort perceived by human
senses eyes, ears, touch, nose.   Comfort
defined as the absence of perceived pain- and
discomfort. A new concept of garments with
defined, but not maximal comfort level for young
healthy people, sportsmen under training scheme
etc.  
3
1.1. Components of clothing comfort
psychological, sensorial (or tactile) and
thermophysiological comfort.   2. PSYCHOLOGICAL
COMFORT geographical (climatic), economical,
hi-storical, cultural, social and individual
aspects.   2.1.Components of psychological
comfort Climatic aspects typical (daily)
clothing should at first respect the climatic
requirements Economical aspects Resources,
technology of food and objects manu-facture,
skills, political system
4
Historical aspects Inclination to products made
of natural materials, to products simulating
nature, to products of natural smell. Tradition
in lifestyle and fashion Cultural aspects
religion, habits (in Arabic countries women are
fully covered) Social aspects age,
qualification, social class, rank or position in
this class Individual and group aspects the
effect of fashion, style, colours and lustre,
trends, personal preferences
5
3.SENSORIAL COMFORT 3.1.Stephen's law, skin
sensors perceived sensation P (sound, lightning,
climate) is proportional to the magnitude of
physical stimulus I according to the
relation   P d In

(1)   Skin temperature (Kraus
Ruffini) sensors sensors for 38 to 43OC, cold
sensors for 15 to 35OC, low sensitivity between
35 and 38OC. Adaptability with acclimatisation.
6
Sensors for pressure and pain. No sensor for
humidity (substituted by feeling of cold and
pressure).
Fig. 1 Schematic section view of human skin
7
1)Hair sheath 2)Hair
3)Smooth muscles 4)Fat gland
5)Skin vein 6)Sweat gland
7)Touch sensor 8)Higher temperature sensor by
Ruffini 9)Vater-Paccini sensor of pressure and
pull 10)Lower temperature sensor by
Krause 11)Free ends of nerves
8
3.1.1.Sensory properties of fabrics and their
division into mechanical, thermal and complex
properties. Dynamic (Newton) force F N/m2given
by acceleration a m/s2 of a fabric mass m
kg/m2 F m . a
(2)
  and friction forces generated while wearing
clothing. Ergonomic approach to garment
design.   3.2.Survey of mechanical properties of
fabrics. Basic equations Hook's Law for
extension and shear, typical load-extension
curves for various fabrics, parameters, which
determine the fibres and fabrics bending
rigidity.
9
Mechanical properties of fabrics assessed
manually when purchasing a cloth or garment in a
shop 1.    Fabrics thickness and
compressibility (between 2 fingers,
immedia-tely) 2.    Warm-cool feeling of fabric
(within several seconds, by fingers or when
fabric lies on the table) 3.    Friction force
and perfile (when moving a finger against fabric
surface) 4.    Bending rigidity (bending among 3
fingers) 5.    Extensibility (pulling between
both hands) 6.    Shear rigidity (with both hands
when fabric lies on the table)
10
Relation for the deformation y (in the axis
perpendicular to the fabric plane) of an inclined
fibre protruding from a fabric under the angle a
between the fibre (of diameter 2r and length l)
and a fabric, when the fibre is bent by a force F
perpendicular to a fabric   y F l3 cos2a sina
/ 3 E I
(3)
where the inertia momentum I m4 of a fibre is
I p d4 / 64
(4)
11
The equations indicate, that the fibre
deformation is proportional to the 3rd power of
the fibre length and indirectly proportional to
the 4th power of its diameter. That is why the
micro-fibre fabrics, even if the protruding
fibres are short, deform easily under pressure to
certain extend and partially copy the acting
body. Thus, the contact area is always large, the
amount of heat taken away form the contacting
body is high and the contact feeling is cool, in
spite of the smooth and pleasantly soft surface.
Similar phenomenon appears after the enzymatic or
chemical treatment of fabrics this relatively
drastic action results in the disintegration of
the fibre ending into several fine micro-fibrils,
which behave as micro-fibres.
12
Then, the enzymatic treated fabrics reveal also
cool feeling (high thermal absorptivity),
accompanied by smooth, pleasant feeling. The
bending rigidity B of such fabrics, however, is
sometimes too low, as follows from the
consideration placed at the end of this
chapter.   On the other hand, any mechanical
treating of fabrics, like brushing or carding,
brings the warmer feeling, because the original
compact and smooth plane surface of dense woven
fabrics with high mass and hence high thermal
capacity is being replaced by the irregular
surface featuring lower mass, irregular thickness
of a structure composed of some soft and
13
easily deformed fibres, but some surface fibres
are not split, and due to their relatively big
diameter and short length they do not bend easily
under pressure, thus conserving the surface less
compressible, but full of thermal insulating air
pores of low thermal absorptivity. 3.3. Yarn and
fabrics hardness (compressibility) as a function
of their packing coefficient µ A new expression
for yarn hardness or compression modulus Ec Mpa
according to NECKAR (Prof. B. Neckar, Tech. Univ.
of Liberec), k means the proportionality
parameter in Mpa, depending on fibre material and
processing,
14
µO means the lowest possible level of packing,
e.g. 0,8 for cotton yarns   Eck3µ312(µ/µo)3/
1-(µ/µo)34 (5) Bending
rigidity of fabrics is an important fabric
comfort parameter, since sometimes garments
require low bending rigidity (silhouette skirts,
pullovers, socks, all kinds of underwear), but
good appearance e.g. of men's suits, trousers
etc. is based on fabrics of higher and defined
bending rigidity B. In the classical mechanics of
elastic solids, the bending rigidity is given by
a product of the purely material parameter E Pa
called initial elastic modulus, and the inertia
momentum I m4, given by the fabric structure
and dimen-sions.
15
For the high density woven fabric of thickness h
and of width b the fabric bending rigidity, under
certain assumptions, the fabric bending rigidity
may be estimated by the following expression   B
E . I , I b.h3/12
(6)
16
3.4. Drape angle - a new method of drape
determination One of the parameters, which
characterises the wearing comfort of clothes is
fabric drape. Due to easy way of its evaluation
by means of the Cuisicks instrument an increased
attention is dedicated to this parameter, but the
proper device is quite large and requires
relatively complicated opto-electronic system.
Also the proper measuring procedure is time
consuming. That is why we cannot find this
instrument or any similar drapemeter in the
factory labs, they are used in the textile
research units only.
17
3.4. Drape angle - a new method of drape
determination One of the parameters, which
characterises the wearing comfort of clothes is
fabric drape. Due to easy way of its evaluation
by means of the Cuisicks instrument an increased
attention is dedicated to this parameter, but the
proper device is quite large and requires
relatively complicated opto-electronic system.
Also the proper measuring procedure is time
consuming. That is why we cannot find this
instrument or any similar drapemeter in the
factory labs, they are used in the textile
research units only.
18
Fig. 2 Measurement of Drape Angle
19
Fig. 2 Measurement of Drape Angle by means of a
special tool (table) and moving this sample
towards the sharp (90O) corner of the table in
such way, that the axis of the 90o angle
coincides with the warp or weft direction. The
fabric motion stops, when the peak of the corner
reaches the center of the sample. Then the fabric
folds and forms a direct edge, whose inclination
f against the horizontal plane we measure. The
sin f value measured by means of simple ruler
see the Fig.2-then characterizes the level of
drape. The fact, that this parameter, in some
extend, does not depend on the length of the
inclined fabric edge indicates,
20
that this inclination is a certain fabric
property, which depends on composition, mass and
structure of the fabric. A certain evidence, that
this inclination may characterize the fabric
drape results from the fact, that materials like
paper with high shear stiffness do not fold in
our test, they just bend, and hence do not create
the drape edge.   Theory of fabric drape
According to the Niwa and Seto regression
equation given below,   DA DAC0 C1
(B/W)0,33 C2 (G/W) 0,33 (6)

21
the drape coefficient should depend not only on
the fabric bending stiffness, shear stiffness and
fabric mass, but also on the levels of their
bending and shear hysteresis. Recently, the
effect of fabric mechanical properties on drape
coefficient was analyzed in 2003 by Militky and
Hes.   Experimental determination of correlation
between Drape angle and Drape coefficient To
confirm the principal correlation between the new
Drape angle (DA) method and Drape coefficient
(DC) according to the Cuisicks method, 90 woven
fabrics made of cotton, linen, viscose and their
blends with nylon and polyester were tested by
the mentioned procedures. Square mass of these
samples varied from 50 g/m2 to 390 g/m2.
22
Every sample was measured 8 times. whereas the
axis of the table corner is perpendicular to the
fabric edge Separate measurments along the weft
and warp directions were made. The edge length in
first series of measurement reaches 5 cm, in the
second series it was 10 cm.  
From the presented figures follows, that best
correlation of the new Drape Angle method with
the Cuisick classical method exhibit the C/E
sample orientation for the edge length 5 cm.
23
Fig. 3 - Correlation between the DC and DA
methods
24
The correlation coefficient for the weft
direction was R 0,717, and for the warp
direction the R reached 0,759. Unfortunately, we
cannot directly correlate any of this direction
with the Cuisick Drape coefficient, since the
Drape coefficient involves the whole fabric.
Therefore, we have also correlated the average
value of DA for weft aned warp directions with
the DC data, with the resulting level of
correlation coefficient R 0,767. Since this
result was verified for very large set of
fabrics, the practical verification of the new
method can be considered as verified.
Nevertheless, other unpublished results show,
that this new simple and cheap method may
emphasize more the effect of shear rigidity then
the classical method,
25
which is a positive result, since the evaluation
of shear rigidity of fabrics by other methods is
quite complicated. 3.5.Methods of objective
evaluation of sensorial comfort of garments and
fabrics   German method of objective evaluation
of complex sensorial comfort of worn garments
based on large experimental investigation. I is
called index, independently of its dimension. The
scales for TK (Wear Comfort, in German
Tragekomfort) extends from 1 to 6, where 1 is the
best level, 6 is the worst level).
26
Sensorial comfort

( 7)
where particular parameters mean imt index
of water vapour transmission io surface
index nk
number of contact points ik index
of lepivosti iB
index of wetting s
bending rigidity

27
Numerical values of constants ?1 -2,537 ?5
1,71.10-3 ?2 1,88.10-2 ?6 3,86.10-2 ?3
2,29.10-3 ? 0,36 ?4 2,09.10-2
28
Determination of thermophysiological comfort is
similar

(8) imt index of water vapour
transmission Fi dynamic vater vapour
absorbtion Kd liquid moisture buffering
coefficient ?T temperature buffering
coefficient K.min-1 Kf moisture
permeability g.m-2.hmbar-1
Numerical values of constants ?1 -5,640 ?4
-4,512 ?2 -0,375 ?5 -4,532 ?3
-1,587 ? 11,553  
29
Kf moisture permeability
g.m-2.hmbar-1 Numerical values of
constants ?1 -5,640 ?4 -4,512 ?2 -0,375
?5 -4,532 ?3 -1,587 ? 11,553   Total
comfort   TKtot 0,35 . TKH 0,65 . TKT
30
3.6.Objective measurements of tactile mechanical
properties (FOM) of fabrics by means of Kawabata
(KES) instruments and their correlation to Handle
Values evaluation   4 measuring modulus, 16
parameters measured.         Fabric friction
and perfil measurement         Fabric
load/extension and shear force/shear angle
dependences         Fabric thickness and
compressibility measurement         Fabric
beding rigididy dependence on curvature
determination  
31
Comparison of Hand Values with FOM parameters.
Assesment of Total Hand Values. Kawabata-Niwa
regression equations for fabrics.
  3.6.1.Determination of friction coefficient of
textile fabrics Friction coefficient belongs to
the important parameters of textile fabrics, and
its value affects both their behavior during
confectioning, and their contact comfort
parameter called handle. Feeling of friction
influences customers opinion when buying new
cloth for suits or skirts, and the possibility of
its precise objective evaluation even in shops
and markets would mean strong tool of textile
marketing.
32
Unfortunately, common instruments for the
friction assessment are too large, and their
operation is cumbersome. The aim of research
based on the above mentioned torque measuring
instrument was to design a small portable
instrument which is easy to operate. New
measuring method of the fabric friction
measurement The principle of the instrument
depends in manual application of mechanical
torque momentum by means of hand rotation and the
measurement of the peak value of this momentum
applied in the specific friction torque measuring
tool.
33
The measuring unit was designed in mechanical
version, electronic analogue version and also in
electronic digital version. All instrument
versions should exhibit the possibility of
recording the peak value of the applied torque
momentum. The mechanical version, equipped by
the testing needle (1) used also for the hardness
measurements in yarn packages, is displayed in
the Fig. 4. The principle of recording the peak
torque momentum depends in the use of torque
spring inside the instrument body (2).
34
1
Fig. 4a. The measuring unit equipped by a needle
for the measurement of the package hardness
35
The more is turned the instrument handle (3), the
higher is the torque momentum in the main shaft
of the instrument. The maximum angular
displacement, and hence the maximum momentum, is
then displayed by the extreme position of the
slippage dial (pointer).   The electronic
versions of the instrument are based on torque
the ultra-thin wall tube, whose small angular
deformation is measured by means of special
strain gages, fixed on the tube wall under the
45o slope. The strain gages are fully temperature
compensated. One end of the tube is manually
turned, the other end carries the proper
measuring tool.
36
The strain gages signal is conducted to the
Wheatstone bridge and the processed by means of a
digital micro-controller or PC together with an
A/D converter. As shown in Fig 4b, surface of
the ring shaped body of diameters D and d, rubs
against the flat surface due to the force P. The
torque momentum M of this dry clutch and
consequently the friction coefficient ? are given
by the following equations  

37
Fig. 4b Geometry of the friction ring used in
the tester
38
The force P causing the pressure p results from
the mass of the measuring ring (here, the mass
inertia affects partially the level of the
momentum M at the beginning of the measurement)
or may be assured by other, recently developed
method, which is not negatively influenced by the
ring mass.   3.7. FOM by means of the FAST
instruments and related snake diagrams
39
3.8. Non traditional methods of FOM Pulling a
fabric through a short hollow cylinder of approx.
15 mm diameter and recording the pulling force as
a function of the fabric displacement reflects
the effect of several mechanical properties, but
the specific calibration is almost impossible.
  Also pulling a fabric strip by a moving
straight edge into a gap of certain width
(Handle-O-Meter) reveals a mixed effect of fabric
bending rigidity, compressibility and surface
friction.
40
L. Hes and Yi Li (Hong Kong Polytechnic
University) designed and manufactured an
intelligent Hand Simulator, which should measure
in one step and on one sample all thermal and
mechanical fabric characteristic commonly
detected by a customer when buying the cloth and
compare these characteristic with the subjective
ones.
41
3.9. Instruments For the Evaluation of Thermal
Contact Feeling of Textile Fabrics Warm-cool
feeling means the feeling we get when the human
skin touches shortly any object, in our case
textile or other fabric used in clothing,
furniture or carpets. It was found, that this
parameter characterises well the transient
thermal feeling which we get in the moment, when
we put on the undergarment, shirts, gloves or
other textile products. Since this feeling
strongly affects the choice of people when buying
the clothes or gar-ments, the objective
assessment of this feeling became very important
in the last decade.
42
The first instrument, which was able to evaluate
the warm-cool feeling of fabrics objectively, was
developed by YONEDA and KAWABATA in 1983. They
have introduced the maximum level of the contact
heat flow qmax W/m2K as a measure of this
transient thermal characteristics, and KAWABATA
has published the first objectively determined
values describing the thermal-contact properties
of textile fabrics. Their instrument, called
THERMO-LABO, was commercialised. In 1986 an other
instrument for the objective evaluation of
warm-cool feeling of fabrics, but of different
concept, was completed at the Technical
University in Liberec.
43
This computer controlled semi-automatic
instrument called ALAMBETA calculates all the
statistic parameters of the measurement and
exhibits the instrument auto-diagnostics, which
avoids faulty instrument operation. The whole
measurement procedure, including the measurement
of thermal con-ductivity , thermal resistance R,
qmax, sample thickness and the results
evaluation, lasts less than 3 -5 min. As the
objective measure of warm-cool feeling of
fabrics, so called thermal absorptivity b
Ws1/2/m2K was introduced. The meaning of this
parameter (formerly used in the civil engineering
and ergonomics) is explained in next paragraph.
44
Fig. 5 Heat flow between a skin and a fabric
45
Provided that the time of thermal contact between
human skin and a fabric is short, textile fabric
was idealised to a semi-infinite body of thermal
capacity cJ/m3 and initial temperature t2.
Transient temperature field between human skin
(characterised by a constant temperature t1) and
a fabric is then given by the following partial
differential equation   (t / ) a ( 2t / x2)

(9)
46
and can be used for the calculation of the
initial level of heat flow q passing between the
skin (characterised by a constant temperature t1)
and textile fabric according to the next
equation, whose derivation for the boundary
condition of 1st order is similar to derivation
of the Eq. (10)   qdyn b ( t1 - t2 ) / ( ? ?
)1/2 (10)
47
Thus derived thermal absorptivity b Ws1/2/m2K
is given by the relation   b (c)1/2

(11)   As it can be see, the level of thermal
absorptivity depends neither on the temperature
gradient between the fabric and skin, nor on the
measurement time. This value just depends on the
contact pressure, which also correspond to the
real situation. The pressure is adjustable.
48
The simplified scheme of the instrument is shown
on Fig. 6. The principle of first version of this
instrument depends in the application of ultra
thin heat flow sensor 4, which is attached to a
metal block 2 with constant temperature, which
differs from the sample temperature. When the
measurement starts, the measuring head 1
containing the mentioned heat flow sensor drops
down and touches the planar measured sample 5,
which is located on the instrument base 6 under
the measuring head. In this moment, the surface
temperature of the sample suddenly changes and
the instrument computer registers the heat flow
course. Simultaneously, a photoelectric sensor
measures the sample thickness.
49
All the data are then processed in the computer
according to an original programme, which
involves the mathematical model characterising
the transient temperature field in thin slab
subjected to different boundary conditions. To
simulate the real conditions of warm-cool feeling
evaluation, the instrument measuring head is
heated to 32ºC (see the heater 3 and the
thermometer 8), which correspond to the average
human skin temperature, while the fabric is kept
at the room temperature 22ºC. Similarly, the time
constant of the heat flow sensor, which measures
directly the heat flow between the automatically
moved measuring head and the fabrics, exhibit
similar value (0,07 sec), as the human skin.
Thus, the full signal response is achieved within
0,2 sec.
50
Fig. 6 Principle of the ALAMBETA instrument
51
The validity of thermal absorptivity as a new
warm-cool feeling parameter of fabrics was
confirmed by several tests where the results of
relative subjective feeling of 100 persons were
compared with the values of thermal absorptivity
found by means of the ALAMBETA instrument. It was
found, that practical values of thermal
absorptivity of dry fabrics range from 20 to 300,
see Tab. 1. The higher is this value, the
cooler feeling represents.
52
Tab. 1
53
(No Transcript)
54
(No Transcript)
55
As results from the table, the thermal - contact
feeling of the fabrics is strongly affected by
their structure and composition. It was found,
that fibres and fibre polymers of higher moisture
regain, provide also cooler feeling. Therefore,
the warmest feelings can be achieved at fabrics
made from PVC, PP, PAN, whereas viscose, flax,
cotton and PAD fibers show the coolest feeling.
Which feeling is better, depends on customer for
hot summer garments cooler (cotton) feeling is
demanded, whereas in the north of Europe warmer
clothing, based on the PES/wool is preferred.
56
An important aspect of the warm-cool feeling
evaluation is the change of this feeling when the
textile product gets wet. Because the time of the
warm-cool feeling evaluation of samples in the
ALAMBETA instrument is very short, less than 3
minutes, the evaluation of humid samples is
reliable (the sample does not turn dry during the
measurement). Because the thermal conductivity
and thermal capacity of water is much higher than
these of dry textile structure, the negative
feeling of coolness of garments moistened by
sweat can exceed 1000.
57
Since the thermal absorptivity is mainly the
superficial property, its level can be changed by
any superficial or finishing treatment, like
raising, brushing and coating. The instrument was
commercialised by the Czech SENSORA company.
58
3.10. Moisture absorbtivity of fabric Many people
believe, that 100 cotton underwear (t-shirts)
provide the best thermal contact comfort, even in
hot days, due to its easy and fast sweat sorption
(wetting), and their experience based on common
life of a clerk or a bussinesman confirms this
statement. Nevertheless, when the wearer has to
exhibit some physical effort, the excess of the
sweat keeps accumulated in the cotton fabric in
the proximity of sweating glands for long time
and causes thermal discomfort. On the other hand,
when we wear the PES/cotton fabrics in hot day,
the thermal discomfort, appears as well (even
without physical effort), but such fabric gets
dry soon.
59
Some customers believe, that both fabrics differ
in their water vapour permeability mainly. In
order to explain the effect of this parameter,
various underwear fabrics were measured in this
study. From the measurements made on the
PERMETEST (Sensora) instrument (see in Tab. 2)
resulted, that water-vapour permeability of the
measured underwear fabrics depends more on their
mass per area then on their composition, and that
in all cases the relative vapour permeability was
very good, exceeding 15.
60
The next parameter in question is the moisture
sorption capacity (absorbency) of shirt fabrics.
There are some other methods to determine this
parameter. Nevertheless, the moisture absorbency
characterises just the specific moisture
retention corresponding to the state of full
saturation of the fabric volume by water or
sweat, and is directly proportional to the fabric
mass. No transient aspects are considered here,
and no different boundary conditions of moisture
transmission between the skin and a fabric are
respected. A survey of other techniques to
measure transplanar liquid transport into fabrics
published Kissa in 1995.
61
Nevertheless, all the found measuring methods are
not suitable for simple standard measurements of
transient fabric wetting, due to quite complicate
preparation of the measurements and poor dynamic
properties of some of these methods. Moreover,
the reduced comfort caused by wearing e.g. the
PES/cotton shirts in hot day is felt mainly in
the moment, when the suddenly wetted fabric
touches the skin. Consequently, local cool
feeling occurs, which is considered unpleasant.
Within the con-tact time, heat is transferred by
conduction through a thin intermediate layer,
created by wet outstanding fibres. Thus, the
boundary condition approximates to the heat
transfer of 1st order, which should be respected
within a measuring method in question.
62
Therefore, the first objective of the research
work was to develop a method of an indirect
experimental determination of the so called
surface moisture absorptivity B?, whose higher
level apparently increases the contact comfort of
wet fabrics and on the contrary. Such parameter
should present an integral factor, embracing the
effect of moisture surface adhesion (given by
the contact angle ) and the moisture conduction
(depending on capillary forces). The highest
surface moisture absorptivity appears in the
moment, when the adhesion and conduction
mechanisms, which in some cases act again each
other, create a specific synergic effect.
63
Introduction of Moisture Absorptivity The amount
of liquid inside any porous structure or textile
fabric can be expressed in terms of the fabric
free volume saturation s. Thus, for s 0 the
fabric is dry, and for s 1 all the pores are
full of a liquid. In this case, the saturation
propagation within a fabric, either along its
surface, but also perpendicularly to its surface,
can be characterised by the classical partial
differential equation of diffusion
processes (?s / ??) A ( ?2s / ?x2)
(12)
64
where A m2/sec is so called moisture
diffusivity. This parameter is for textile
fabrics sometimes moisture dependent due to
swelling. The solution of equation of this kind
for A const is generally known. If we consider
just short time moisture conduction, then we can
convert a textile fabric to a semiinfinite body,
where the 1st order boundary condition is
applied. In this case, the moisture saturation
propagation in the x direction is given by the
equation   s erfc (x /2 A1/2?1/2)
(13)
65
The experimental determination of the moisture
diffusivity from the moisture propagation along
the measured fabric is possible. Unfortunately,
the moisture diffusivity in this form does not
characterise the volumetric capacity V of the
fabric expressed in this case in m3/m2s to
conduct the moisture (sweat) from the contacted
skin away towards a fabric interior. To cope
with this task, a Darcy law modified for the
saturation gradient should be introduced as
follows   V - ?s (?s/?x)
(14)
66
where ?s m2/s is the volumetric moisture flow
conductivity, which is proportional to the fabric
permeability. In the next step, we should remind,
that in the first Ficks diffusion law, which is
used to express the mass flow in the form
formally identical with Eq. (14), the same
diffusion coefficient D occurs, as in the second
Ficks law for transient mass transfer by
diffusion. By simplifying the problem solved to a
simple diffusion, we can express the moisture
flow conductivity in Eq. (14) ?s by means of the
moisture diffusivity A. From applying this
relation in equation (13) follows V
A1/2(?s/?1/2?1/2)
(15)
67
The first term in this equation fully
characterises the fabric ability to absorb the
moisture from any moist surface which contacts
the fabric. Then this so called moisture
absorptivity B m3 s1/2 is defined by the next
relation B A1/2
(16)


68
Many researchers have already measured the
time-dependent longitudinal wicking of fabrics.
From these results, the moisture diffusivity A
could be determined and its square root used for
the calculation of the spontaneous moisture
uptake according to Eq. 15. Nevertheless, this
approach may produce inaccurate results, since
longitudinal wicking rates not always correlate
with the corresponding transplanar ones, due to
the complexity of the wicking processes, which
besides the diffusion processes include capillary
penetration of moisture inside fabrics, and also
moisture absorption of the fibre surface.
69
Indirect Method of the Moisture Absorptivity
Measurement The suggested method is based on the
objective evaluation of warm-cool feeling
perceived by a wearer of a cloth, which suddenly
comes into contact with a wetted skin. In this
moment, the cotton fabric absorbs the liquid
sweat rapidly, and conducts it away from the
fabric surface towards to the fabric inerroir.
Due to high adhesion forces, the sweat keeps
accumulated in the fabric close the places where
the sweat was generated. If the amount of sweat
is not too high, within a short time the moisture
concentration close to the fabric contact surface
reduces, and the wearer feels the pleasant
contact of nearly dry fabric.
70
The other mechanism of achieving the pleasant dry
feeling of underwear and shirts is based on the
use of PES microfibres, which, due to higher
surface, absorb in some extend the humidity also,
but the liquid sweat is rapidly distributed by
capillary forces in larger area surrounding the
perspiration zone, thus reducing the average
relative humidity of fabric under the limit,
which would result in unpleasant wet feeling.
Unfortunately, this mechanism requires also some
additional dymamic contact forces typical for
sport activities. In the case of blended fabrics
containing too much poorly absorbing PES fibres
of common section and fineness, the sweat keeps
adhered on the skin, and provokes an unpleasant
cool feeling due to sweat evaporation.
71
The suggested method is based on the objective
evaluation of cool feeling effect within an
experimental procedure, which simulates the real
fabric wearing conditions described above.
  Methodology of the Indirect Measurement of the
Fabric Moisture Absorptivity The intention of
this research was to characterise the contact
comfort felt by a wearer of a shirt during a hot
day. For this purpose, a special thin interface
fabric was found, which should simulate the
effect of a sudden sweat discharge on the skin.
72
This sweat simulator should be thin, in order not
to influence (in dry state) the thermal capacity
of the measured fabric, but this interface fabric
should absorb a certain amount of liquid injected
in the centre of this interface fabric and it
should distribute the liquid fast and uniformly
within a circle of approx. 50 mm diameter. After
some trials, a thin PES Coolmax knit was found to
fulfil all demands.
73
At the beginning of the measurement, the ALAMBETA
instrument is switched on and the measured
underwear is placed on the measuring base of the
instrument. Then, the volume of 0,2 ml of water
(containing detergent) was injected on the centre
of the interface fabric surface, covered by the
viscose fibres. Within one minute, the liquid
distributed uniformly within a circle of 45-50
mm, and stopped. When this occurred, this
interface fabric was inserted into the space
between the measured sample and the centre of the
measuring head of the instrument - see Fig. 7. At
the same time, the interface fabric and the
measuring head of the instrument dropped down
towards to the measured underwear or shirt
fabric.
74
Within a few seconds, the liquid from the
interface fabric was more (in case of pure cotton
shirt) or less (in other cases) taken away by
absorption into the lower fabric. If this fabric
exhibits low absorption, the thermal capacity of
the interface fabric is maintained quite large
and the initial level of thermal absorptivity b
is significantly higher.   In the case of
measurement of warm-cool feeling on pure cotton
fabrics, characterised by higher moisture
absorptivity, the moisture is rapidly distributed
within the whole thickness of the fabric, so that
the interface fabric gets nearly dry, and the
instrument shows a lower level of the resulting
thermal absorptivity.
75
Fig. 7 - Simulation of the underwear wetting and
wicking by means of the ALAMBETA instrument
76
Theoretical Analysis of the Underwear Wicking and
Wetting Effect on Cool Feeling In the new
version of the ALAMBETA, not only one, but two
heat flow sensors are applied, as shown on Fig.
7- see the second sensor. This enables to
simplify the heat flow signals evaluation and
moreover, the instrument can check the level of
heat, which is during the measurement conducted
away (in the surrounding air) from the sample.
This increases the measurement precision.  
77
During the measurement, the computer integrates
the heat QW passing through both heat flow
sensors, which is accumulated inside the measured
sample, according to the Eq. 17   Q q(?) d?
q1 qo) d?
(17)
78
The measurement finishes for the time level T,
when q1 (T) equals qo (T). Then, the heat Q
causes the increase of the average temperature
inside the measured sample, as follows   Q
moco (t1 to)
(18)
79

This equation then yields the surface related
heat capacity moco J/ m2. Simultaneously, the
sample thickness hmm is measured and used for
the determination of the fabric heat capacity
?oco J/m3 from the equation   ?oco moco/h

(19)
80
The consequent steady state measurement of heat
flow passing through the sample then enables the
easy determination of the coefficient of thermal
conductivity ?W/m.K and the fabric thermal
resistance Rm2K/W. The warm-cool feeling
parameter - thermal absorptivity, then follows
from Eq. 11.
81
In the next step, the mentioned measuring
principle will be applied in the simple analysis
of the wetting and wicking simulation. In this
case, heat balance of the space between both heat
flow sensors should include the effect of heat
capacity per area m1c1 of the interface fabric
and ist initial moisture Mwcw, provided that the
measuring head has just dropped down and
completed the thermal contact between the
interface and underwear fabrics   QM (moco
m1c1 Mwcw)(t1 to) (20)
82
Within a few seconds, the moisture will be
absorbed by the underwear and distributed in its
volume. In fabrics exhibiting good moisture
conduction the sweat will be transported by the
capillary action outside the area of heat flow
sensors. Hence, the effective moisture content in
central part of the underwear will be reduced to
lower level mw, thus reducing the volumetric
thermal capacity of the system consisting of
interface fabric and underwear. The integral heat
detected by both heat flow sensor will be as
follows   Qm (moco m1c1 mwcw)(t1
to) (21)
83
Because mw ? Mw, and due to the fact, that the
specific heat of water cw is very high approx.
3 times higher than that of fabrics, even small
differences in the moisture amount absorbed form
the sweat simulating fabric and conducted away
form the sensing area of heat flow sensors will
result in relative big changes in heat capacity
of various tested fabric system and hence in big
changes in their thermal absorptivity levels. In
fact, the resulting sensitivity will be even
bigger, due to varying evaporation effects, which
were not considered in this simple analysis (the
more moisture keeps in the interface fabric after
contact, the cooler is ist surface, and the
higher is the resulting thermal absorptivity).
84
Experimental Results The composition of the
investigated plane fabrics varied from 100
cotton to 100 PES or PP fibres. Medium values of
the results are shown in the following Table
2.   Tab. 2. Cool feeling (thermal absorptivity)
of various fabrics measured by the ALAMBETA
instrument when simulating their sudden thermal
contact with wetted skin, pressure 200 Pa  
85
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88
Results Evaluation         With an increasing
portion of PES fibres in common woven shirt
fabrics increases the unpleasant cool feeling (i.
e. increases thermal absorptivity) when worn in
conditions of surface wetting, which matches the
practical experience of wearing the tested
shirts.         Special smart fabrics with
improved thermal comfort properties like double
layered knits or T shirts knitted from Coolmax or
Coolplus (Taiwan) modified PES fibres reveal more
pleasant contact feeling in conditions of
superficial wetting.
89
        Exceptionally some cotton/PES blend
fabrics made from common fibres may exhibit
relatively good thermal contact comfort in the
wet state, even with quite high portion of PES
fibres, due to some unknown effect or due to a
special fabric structure (confirmed by wearers).
        Cotton shirt weaves containing too much
chemical agents deposited inside the fabric may
show worse contact comfort feeling in the wet
state, in spite of the fact, that their
steady-state water vapour permeability keeps very
high.
90
4.Thermophysiological clothing comfort -
principles
Fig. 8 Thermoregulation system
of human body
91
4.1.Environmental parameters of human life air
relative humidity f, air velocity vA, dry
thermometer (or air) temperature tA, wet bulb
(thermo-meter) temperature tWB (strongly
dependent on fand vA, and globe temperature tG,
which is measured in centre of big black globe,
thus expressing the effect of solar radiation.
The integral environmental effect expressed in
terms of the wet bulb globe temperature tWBG
tWBG 0,7 tWB 0,2 tG 0,1 tA
(21)
92
Examples of groups of environmental parameters,
which offer the thermo-physiological comfort
under various physical activities, provided that
the level of the radiation temperature (emitted
e.g. by warmer walls) does not exceed the dry air
(environmental) temperature tA for more then 2OC
 
93
Administrative work tA 21OC3OC,
f 55 15,vA 0,1 m/s Light manual work,
standing tA 19OC3OC,f 55 15, vA 0,2
m/s Heavy manual work tA
18OC3OC,f 50 15, vA 0,4 m/s Very
heavy work tA 7OC3OC, f
50 15, vA 0,5 m/s
94
4.2.Fundaments of human thermal physiology Human
body as a thermal engine with the efficiency ?
(5-25).
Fig. 9 Human body as a thermal machine
95
Muscles transforming chemical energy into
labour L J (up to 50x increase from the resting
level). Energy carriers carbohydrates (18 kJ/g),
fats (40 kJ/g) and proteins (19 kJ/g). Food
processing stomach         absorption
in small intestines         transport by blood
        transformation into energy in cells or
storing as glycogen (C6H10O5) or fat.
96
Muscles work energy input converts
adenosine diphosphate -ADP into adenosine
triphosphate (ATP). Most easily used energy
carrier glucose . Aerobic metabolism (most
effective) C6H12O6 6O2 6 CO2 6 H2O
energy (690 kcal/mole). Anaerobic metabolism
lactic acids released. Energy storage fat,
16-22 of the body weight in a man, 22-34 in a
woman (15-20 in sportsmen). Much less stored
energy in glycogen and glucose. Protein amino
acids used for energy just in vital conditions
(death of cells involved).
97
Basal metabolism approx. 1,1 W /kg of
body weight, minimum metabolic power Mmin
reaching 50-100 W., heart rate 60-80 /min.
Resting metabolism 1, 25 W /kg of body weight,
corresponding to the oxygen consumption 0,0035 L
/min/kg of body weight (which is called 1 MET).
Heavy work requirements even more then 10 W /kg
of body weight, heart rate exceeding 120 /min,
muscles consuming up to 70 oxygen available,
brain always 5, internal organs suffering. Heart
pumping rate from 25 litre/min to 40 litre/min
for sportsmen. Temperature set points in
hypothalamus 37OC for core, 33OC for skin.

98
Temperature limits over 45OCcoagulation of
proteins, 0OCbreaking cell aparts due to ice
crystals. Deviation of core temperature 37OC 2
OC affects body functions, deviations 6OC are
lethal.
Sudomotor nervous pathways control the sweat
glands activities only, the vasomotor system
brings about the vascular dilation, constriction
or shunting, thus affecting the heat distribution
throughout the body.
99
Sweating level mp kg/min, up to 10 kg/day as
the function of real skin (tS gt 32O C)
temperature and core (nuclei) temperature (tN gt
37OC) due to increased environmental temperature
tE mp F1 (tS - 32 ) F2 (tN - 37)
(22)
100
4.2.1.Definition of thermal comfort for lying or
resting human body thermal equilibrium, no
muscular shivering nor vasodilatation, no
principal sweating (relatively dry skin), skin
temperature between 32 and 34OC, no heat storage
or loses. Changes of stored (accumulated) heat
  ?QACcspec.(0.35?tS0.65tN),cspec3300J/kg.K
(23)
101
4.3.Equation of steady - state thermal
equilibrium of human body expressed in heat/time
J/sec units, it means in power Q?W units.
(Mmin L/?- L)/ADu (M - L)/ ADu

(24) (M-L)/ADu qcond qconv qrad - qres,c -
qres,e - qins -persp 0 (25)
102
Meaning of new symbols ADu is the surface of
the average human body, 1,8m2. qconv heat flow
W/m2 by convection from the skin surface
qconv a Fcl (tsk ta) ADu
(26) a 2,38 (tsk
ta)0,25 for natural convection
a 3,5 5,2 var for
forced convection at var 0-1 m/s a
8,7var0,6 for forced
convection at var over 1 m/s
103
  qcond given by Eq. 28, at walking just 5 -10
w. qrad given by Eq. 35 qres,c cooling by
respiratory convection qres,c
cp Va (tex ta) ADu, which can be expressed
through metabolic power M as
qres,c 0,0014 M (tex ta)
104
qres,e cooling by evaporation at respiration
qres,e L Va (Wex Wa) ADu, which
can be expressed through metabolic power M as
qres,e 0,0173 M ( pex pa)
  qins cooling by insensible and permanent
evaporation from skin pores, approx.0,15 W/1 kg
of body mass   qpersp intensive cooling by means
of principal sweating glands controlled by brain
hypothalamus (sudomotor pathways) through
adrenalin level, and by means of smaller glands
in
105
palms and soles   qpersp w (pwv,sat
pwv,out)/Revap,tot   w means here skin
wettedness, given by fraction of the wetted skin
skin surface related to total skin surface   The
heat and moisture transfer mechanisms applied in
the human body thermal balance are explained in
the next text in more detail.
106
4.4.Fundaments of heat transfer between human
body and environ- ment by conduction,
convection and radiation   4.4.1.Principal
relations describing the heat conduction Fourier'
s law, expressing the proportionality among heat
flow q W/m2K, thermal conductivity ?W/m.K and
temperature gradient ?t/?x   q -
?.?t/?x
(27)
107
Relation for thermal resistance R m2K/W of
fabrics, thin air layers and other plane
materials of thickness h m   R h
/?
(28)   Thermal resistance of air layer in
clothing maximum for h 5mm.   Total thermal
resistance of clothing RCL consisting of full
area individual layers   RCL R1 R2
R3 . . .
(29)
108
Fig. 10 Heat flow through
clothing layers
109
Total heat flow - heat power QW through a
clothing of area ACL by conduction within the
temperature gradient ?t tS - tE is then given
by the equation   Q? ACL . q ?t . ACL / RTOT,
where RTOT RCL RE (30)   4.4.2.Principal
relations describing the heat convection Heat is
transferred by particles of fluids moving with
the velocity v m/s. The thermal boundary layer
thickness dis thick for the laminar fluid flow
and becomes thinner for the turbulent flow,
110
when the Reynolds dimensionless number Re exceeds
2300 for any object of characteristic dimension d
m.   Re vd/?, where ?m2/s means
the dynamic viscosity of the fluid.
111
The heat transfer coefficient aC W/m2K is
relatively low for natural convection, and
increases for forced convection. For the
conditions typical for the use of clothing, the
heat transfer coefficient can be also given by a
simplified equation for all air velocities  
aC 8,3 vv
(30)   The Newton's law for the heat
flow transferred by any kind of convection or
conduction is as follows   q aC (t1 -
t2) or q (t1 - t2) /Rcl
(31)
112
where Rcl means thermal resistance of
garment or clothing.
Convection thermal boundary
layer presents important external thermal
resistance   Rbl 1/aC

(32) which
should be included into the total thermal
resistance RTOT. Sometimes we should also
consider the heat loses by radiation, given by
the linear radiation heat transfer coefficient
arad.
113
4.4.3.Principals of heat transfer by
radiation Generally, the heat flow passing
through clothing layers by IR radiation may reach
up to 10 - 15 of the total heat flow. In hot
days or countries, solar radiation, both visible
and invisible, causes principal
thermophysiological discomfort.
Radiation UV, µm Infrared waves
Ultrashort Short Radiofequences ?,
X 0,19-0,38 0,75 - 1000µm 1mm - 1 dm
0,1-2m 2 - 1500 m
Visible light 0,35
- 075 µm Log
wavelength ? ?
Fig. 11 Spectrum of electromagnetic radiation
114
Radiation heat is transferred by visible (light)
and invisible electromagnetic waves.The visible
part of the electromagnetic spectrum involves the
wavelength ? 0.4-0,75 micrometer (µ),where sun
emits approx. 50 of its thermal energy. White
garments reflects a good part of this thermal
energy. The resting 50 is radiated in the
invisible infrared (IR) part of the spectrum
(0,75 - 100 µ), mainly in the near infrared part
of the spectrum (till 2 µ). Here, the degree of
reflection ?lt1 already cannot be characterised by
a white colour - we cannot distinguish here any
colours, but any smooth surface reflexes IR
radiation better can a harsh, coarse surface.
The-refore, the protecti-ve clothing against heat
should be white (or of polished metal), and
smooth.
115
According to the Wien's law, the lower is the
absolute temperature TK of the heater, the
shorter is the wave-length ?MAX µ
corresponding to the maximum level of the emitted
energy, as follows   ?MAX . T 2890
(33)
Thus, heat flow transferred by radiation
between the sun and humans reaches its maximal
level for the green light (0,55 µm),whereas
clothed humans lose energy towards the common
environment at the wavelength approx. 10 µm. Some
special fibres contain ceramic particles,
116
which absorb the visible radiation with the
degree of emissivity (or absorbance) e1, whereas
for the IR radiation this dimension less
parameter is substantially lower then 1.
117
When calculating the heat flow q W/m2
transferred by IR radiation between two clothing
layers (garments), we can use the relation for
parallel planes with the emissivity levels e1,e2
and kept at temperatures T1 and T2 in IR
permeable environment as follows (s 5,67 x 10-8
is the radiation constant) q s(T14 -
T24 ) / (1/e1) (1/e2) - 1 (34)
118
In order to reduce the heat transferred through
clothing by radiation (e.g. in sleeping bags),
the textile layers can be coated by the vacuum
deposited aluminium.   Radiation heat flow
transferred between a (clothed) human of surface
absolute temperature TS and a homogeneous, cooler
environment of the average absolute temperature
TE is given by en expression q seS
(T14 - T24 ) ?4seS (T1 T2)/2 3 (t1- t2)
(35)
119
From the analogy with the convection heat
transfer, the linear radiation heat transfer
coefficient receives the form   arad
4seS (T1 T2)/2 3
(36)   High thermal resistance of
nonwoven fabrics is a frequent reason of their
applications in protective clothing, sleeping
bags and related technical textiles. New
standards and higher requirements result in the
necessity of determination of thermal resistance
of these insulation layers with higher precision.
Therefore, several new measuring instruments and
methods appeared recently to serve for these
purposes. Majority of them is based on the
evaluation of steady
120
or unsteady heat flow passing between two plates,
which embrace the measured fabric.   Should the
thin or low density fabrics be measured, the
portion of the heat transferred between the
plates by infrared radiation may reach 10-30 of
the total heat flow. Convection is generally
negligible. In this case, the radiation
properties of the plates should affect the
effective thermal resistance of the nonwoven
insulation layer. The first objective of the
next study is to determine the portion oh heat,
which, in common textile fabrics, is transferred
by infrared radiation. The main objective of the
paper is, however, the experimental determination
of the effect of the
121
surface emissivity of the measuring plates of the
thermal insulation measuring instrument, on the
measured thermal conductivity and thermal
resistance of selected relatively thin nonwoven
fabrics made of different materials.
The experimental procedure is based on a new
computer-controlled measuring instrument, which
measures the steady and transient thermal
characteristics of non-metallic materials within
one step. A brief description of this instrument
is given in the next chapter, along with the
brief theoretical analysis of the problem.
122
Thermal conductivity of textile
fabrics Thermal-insulation properties belong to
the basic properties of textiles fabrics and so
they have been studied and measured very
thoroughly. Similarly, the theoretical analysis
of heat transfer through fabrics was carried out
by several investigators and the most recent
papers were published by FARNWORTH, CAPS and
UMBACH, HES and STANEK. It was found that the
mechanisms of transfer of heat through textile
fabrics depend mainly on thermal conduction and
radiation. This was confirmed during an extensive
experimental investigation of heat transfer
through woven and nonwoven fabrics, which was
conducted at the Technical University of Liberec,
123
where the Grasshoff number Gr, describing the
effect of free convection, was always lower than
1000. Based on new theory and a new high
precision measuring instrument, HES and STANEK
derived the following formula for thermal
conductivity ? of textile fabrics with low
density   ? ?A ??1- ?
(37)
124
Here, the first term on the right hand side
expresses the transmission of heat by conduction
in air gaps (proportional to thermal conductivity
?A of air) and through the polyester fibres (with
a thermal conductivity ?PES 15 times higher than
that of air) oriented parallel with the surface.
The second term shows the heat conduction through
the fibres oriented perpendicular to the fabric
surface. The term µ represents the filling
coefficient of the fabric, and ? is the
(idealized) portion of fibres oriented vertically
to the isotherms in the fabric.
125
For the purpose of this paper, the more important
factor is the last right hand side term,
expressing the heat conducted by radiation, where
the classical dependence of heat flow on the 4th
power of temperature can be approximated by a
linear one   ?rad
(38)
126
Here, h is the thickness of the fabric, s is the
radiation constant, T the ave- rage temperature
in in the fabrics and e and r the emissivity and
radius of fibres.   As shown later, the portion
of heat flow transferred by radiation does not
exceed 20 of the total heat flow. Thus the
linearity of the mathematic model is conserved
and the following relation can be used   ?
?cond ?rad
(39)  
127
Nevertheless, in spite of the fairly low effect
of ?rad on total ?, the investigation of factors
influencing ?rad is important, because the
technological ways to reduce ?cond only (in order
to increase the insulation power of fabric) have
already been exhausted. As a result, many
researchers are now trying to reduce the?rad of
textiles. Because of the low contribution of?rad
to the total level of ?, the investigation of
this factor creates strict demands on the
sensitivity and precision of the experimental
technique.
128
The instruments generally used for the
measurement of thermal conductivity ? and thermal
resistance R of thin layers are not sufficiently
precise, because the changes in heat flow caused
by the low thermal resistance of fabrics are
nearly undetectable for classical instruments of
the BOCK (large skin model) type. A recently
developed instrument ALAMBETA, does not exhibit
this problem. Besides that, the new instrument
enables also the measurement of transient thermal
characteristics of textile fabrics, where one of
these characteristics can be used for objective
evaluation of warm or cool feeling. This is
important during short contact with the fabric,
or when wearing some fabrics (like trousers)
which come into intermittent thermal contact with
our skin.
129
Theoretical background of the experimental
procedure To investigate the portion p of
radiation heat flow transferred through textile
fabric, the next procedure can be applied   The
method is based on the fact, that ?rad increases
with the mean temperature T in the layer.
Therefore, for two different mean temperatures T
(supposing T1300 K and T2315 K, which can be
adjusted at the instrument) and after applying
Eq. (3) we get   for T T1 ?cond ?rad(T1)
?1
(40)
130
for TT2 ?cond ? ?air ?rad (T1) . (T2 /T1)
3 ?2
(41)   Subtracting both equations, we
obtain ?rad ( ?2 - ?1 ??air / (T2 /T1) 3
- 1
(42) The effect of
incre
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