5. Waste heat from body
skin must be dissipated
all the time and
whenever necessary,
aided by evaporation of
sweat from the skin.
5
6. Clothing has, as one of its
main functions, the control
of heat and moisture
transfer from the body to
the environment.
6
7. The physical properties of the
fabric’s material and
construction (structure &
design) as well as the physical
activities(metabolic) of the body
have been considered for the
way affecting the thermal
properties of the fabrics.
7
9. Firstly:
The passive system is such a Heat
flow from the central up to the skin
surface by the conduction and
vascular mechanism.
With the skin layer periphery, which
transports heat from heat producing
areas within the body to skin
surface,
9
10. the heat is transferred by skin
surface to the microclimate
between the body surface
layer and the garment layer
associated with the exchange
of heat by process of
conduction, radiation,
convection and evaporation to
the environment 10
11. Secondly,
the natural control system which
controls the skin blood flow, sweating
and shivering necessary heat to
maintain normal body temperature for
cooling.
The maximum value occurs when the
entire skin surface is 100% wet from
regulatory sweating.
11
12. Both depend on the evaporative
potential of the environment as a
function of
• air movement,
• vapour pressure gradient from
the skin surface through clothing
to ambient air and
• the resistance of clothing against
the sweat transfer of water vapour
12
14. In order to be comfortable
thermophysoliogically the
clothing microclimate should lie
in the range:
◦
35±2 c Temperature
50± 10% RH
25± 5 m/sec air velocity
Fabric has its insulative ability as
water and air permeability
,absorbency ,wickability
and other properties related to
thermal comfort
14
15. In this aspect, a mathematical
model has been developed to
describe the dynamic heat and
moisture transport behaviour of
the toddler 6 to 12 years old heat
transfers.
15
16. Textile materials
Fabric physical properties:
1. Weight per Unit Area
2. Air Permeability
3. Water Permeability
4. Moisture Regains
16
17. The yarn through the Garment swell
at high humidity could have a large
influence on the measured air
permeability for hygroscopic fibres
such as cotton, wool. Represented
The phenomena of TESV
(Thermal Effective Specific Volume).
K= f/m m3/sec .kg,
17
18. This relationship means, as water
accumulates through void spaces
of yarn-to-yarn and the fabric by
hydrophilic or hydrophilicphobic
groups,
there is absolutely changes in the
fabric dry thermal insulation.
18
19. Effect of Fabric Construction
vrs TESV (thermal insulation)
cotton
T dry wet moist
E
S
V S4
Fabric construction
19
20. Effect of Fabric Construction
vrs(TESV)
at maximum hloding water
4
Thermal Effective Specific 3.5 COTTON
Volume(m3/sec.m/kg)
3 C/POLY
2.5
2
1.5
1
0.5
0
S4 141
20
22. So the heat is produced by metabolism
Qm., by other way Qm = Heat dissipated
to the ambient due to the metabolic heat
production and the rate of working,
Qm = QE ± QR ± QC± QCd
QE = Evaporation Heat transfer
QR = Radiation Heat transfer
QC = Convection Heat transfer
QCd = Conduction Heat transfer
22
24. Qcd= AW(Ts-Ta)
Ta = ambiant air temperature,
Ts = skin temperature
A =surface area of garment
W = conduction heat transfer coefficient
of the used material (w/m2˚C.),
24
26. The rate of transfer by convection QC is
determined from Newton’s law of cooling
QC = A1 Ѱ (Tc – TA).
Where the convection heat transfer coefficient
Ѱ (w.m2/k ) it’s values depend on
• Garment fitting,
• Fabric design
• Nature of sweat motion through the fabric
structure and
26
28. The heat transfer by Radiation from
the body to the ambient condition
depends upon the mean radiant
temperature. The energy radiated
from the body is defined in terms of
its emissive power,
= 0.19038 K.m2 / w
28
29. Heat transfer By
Evaporation QE
it depends upon the vapour
pressure difference between the
skin surface ,the microclimate
with garment and the
surrounding air.
29
30. QE=A2 Φε (Ps-PA)
convective heat transfer Coefficient
= 6 watt/m2
hc
kg / Pa..m2
cC pGT
ρ Air vapour sweat concentration
Φ Sweat transfer coefficient
Cp Air specific heat transfer equal
(1003.5 k j/kg. k) [33]
Ps = vapour pressure at skin temperature (Ts),
PA = vapour pressure at ambient temperature
(TA) ambient temperature
30
31. Temperature of the skin
Metabolic Rate increases Up To
Four Or Five Times Setting-resting
Level
But For Clothed Subjects It Could
Follow The Equation :
Ts = 25.8 + 0.267 Ta
31
33. It was found the water vapour and heat transport characteristics of fabric
depend on water vapour absorption of fibres, the porosity, density and
thickness of fabrics.
The final equation (25 parameters)
Skin temprature Skin Pressure and
and microclimate microclimate
A
Garment (T T ) A E R ( ps P )
M s A Body A
Q (23)
1 K
0.293C 2 f 1 1
[ ]2 [ ]
( Lc Ls )( N N )
1 2 G
F M (T T )(T 2 T 2 )
C A C A
Convection
Garment Conduction radiation 33
35. Effect of Fabric Structure
vs Heat Transfer
Cotton 6 Year at different condition
Dry RH20 Wet RH20 Dry RH50 Wet RH50 Dry RH80 Wet RH80
2
1.75
Heat Transfer (K.watt)
1.5
1.25
1
0.75
0.5
0.25
0 100 117 120 141
Fabric Structure Fig (9)
COTTON
that is due to the pressure differences between the
skin pressure and the ambient pressure where it
reached up to 5 times the dry condition.
35
36. Effect of Fabric Structure at Different Conditions
vs Heat Transfer
Cotton/poly 6 Year
2.5
Dry RH20 Wet RH20
Dry RH50 Wet RH50
2 Dry RH80 Wet RH80
1.5
Heat Transfer (K.watt)
1
0.5
0 117
100 141
Fabric Structure Fig ( 10 )
the contribution of blended cotton is higher than the given
values by the pure cotton. This high humidity prevents rapid
evaporation of liquid water on the skin, gives the body the
sensation of heat, and eventually triggered the sweating in the
first place also causing uncomfortable feeling for the wearer.
36
39. It is important to realize that the fabric
setting as well as the fabric design
(especially satin) will play an import
part for absorbing water. The transfer
of water by means of fabric absorption
according to the physical properties
appears to be much more efficient way
to keep the water vapour pressure near
the skin very high. Consequently the
heat transfer is positively high.
39
40. It is believed that the model can not
only find applications in functional
clothing design, but also in other
scientific and engineering fields
involving heat and sweat transfer in
porous media.
40
41. The work presented here is only a
limited set of conditions such fabric
material, construction ,ambient
condition and the metabolic of the
human body .
41
