Skin and inner layer of clothing

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A .Tahan PhD

Ready Made Garment Technology Dep't.

Faculty of Applied ArtsDamietta University, Damietta,

Egypttahan@mans.edu.eg

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Thermo-physiological Wear Comfort Due To The Heat And

Sweat Transfer From Body Skin In Consequences Of The Properties Of Clothing

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Waste heat from body skin must be dissipated all the time and whenever necessary, aided by evaporation of sweat from the skin.

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Clothing has, as one of its main functions, the control of heat and moisture transfer from the body to the environment.

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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.

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Skin Microclimate and

inner layer of clothing

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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,

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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

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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.

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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

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Fig (5)

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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 velocityFabric has its insulative ability as water and air permeability ,absorbency ,wickability and other properties related to thermal comfort

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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.

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Textile materials

Fabric physical properties:

1. Weight per Unit Area

2. Air Permeability

3. Water Permeability

4. Moisture Regains

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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. RepresentedThe phenomena of TESV (Thermal Effective Specific Volume). K= f/m m3/sec .kg,

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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.

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S4 T1/3

T1/2

P1/1

P1/1

117

T2/2

T1/3

S4

S4 120

T1/3

T2/2

P1/1

P1/1

141

T2/2

T1/3

S4

141

Effect of Fabric Construction vrs TESV (thermal insulation)

cotton

dry wet moistTESV

Fabric construction

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S4 T1/3 T1/2 P1/1100

P1/1 100

T2/2 T1/3 S4 117

S4 T1/3 T2/2 P1/1 120

P1/1 T2/2 T1/3 S4 141

0

0.5

1

1.5

2

2.5

3

3.5

4

Effect of Fabric Construction vrs(TESV)

at maximum hloding water

COTTON

C/POLY

Th

erm

al E

ffect

ive

Sp

eci

fic V

olu

me

(m3

/se

c.m

/kg

)

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Considering1. Conduction 2. Convection, 3. Radiation And 4. Vapour Transfer Diffusity

through the garment

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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 transferQR = Radiation Heat transfer QC = Convection Heat transfer QCd = Conduction Heat transfer

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Heat Transfer by Conduction

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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.),

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Heat transfer By Convection:

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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

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Heat Transfer by Radiation

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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

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Heat transfer By Evaporation QE

it depends upon the vapour pressure difference between the skin surface ,the microclimate with garment and the surrounding air.

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QE=A2 Φε (Ps-PA)

2../ mPakgGTpCcch

Φ Sweat transfer coefficient Cp Air specific heat transfer equal (1003.5 k j/kg. k) [33]

convective heat transfer Coefficient = 6 watt/m2

ρ Air vapour sweat concentration

Ps = vapour pressure at skin temperature (Ts), PA = vapour pressure at ambient temperature (TA) ambient temperature

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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

Temperature of the skin

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20 21 22 23 24 25 Ta

31.1 31.4 31.7 32 32.2 32.5 Ts

26 27 28 29 30 31 Ta

32.75 33 33.3 33.5 33.8 34.1 Ts

Skin Temperature

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The final equation (25 parameters)

)23(

])22)((

1[121

])

21)((

2293.0[

)()(

ATCTATCTMF

G

Kf

NNsLcLC

APspREBodyAATsTM

GarmentA

Q

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.

radiationGarment

Skin Pressure and microclimate

Skin temprature and microclimate

ConvectionConduction

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P1/1

100

T2/2

T1/3

S4

117

S4

T1/3

T2/2

P1/1 120

P1/1

T2/2

T1/3

S4

141

0500

100015002000250030003500400045005000

100

T2/2

S4

S4 T1/3P1/1

T2/2T2/2

T1/3

117

S4

120

P1/1

T1/3

141

Effect of Fabric Strcture vsHeat Transfer( watt)Cotton Fabric

(6 year)

wet

dry

moist

Fabric structure Fig 6

Hea

t tra

nsfe

r (K

.wat

t)

35

0

250

500

750

1000

1250

1500

1750

2000

100 117 120 141

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

Fabric Structure Fig (9)

Hea

t Tra

nsfe

r (K

.wat

t)

COTTONthat is due to the pressure differences between the skin pressure and the ambient pressure where it reached up to 5 times the dry condition.

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0

500

1000

1500

2000

2500

100 117 141

Effect of Fabric Structure at Different Conditionsvs Heat Transfer

Cotton/poly 6 Year

Dry RH20

Wet RH20

Fabric Structure Fig ( 10 )

Hea

t T

rans

fer

(K.w

att)

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.

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Conclusion

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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.

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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.

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The work presented here is only a limited set of conditions such fabric material, construction ,ambient condition and the metabolic of the human body .

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Thank you for your interesting