Thermal comfort of football dressesin dry and wet state

 

Lubos HesTechnical University of Liberec

Czech Republic e-mail: luboshes@gmail.com

 

 

  

   

Football dresses historySince 1908: football belongs to an official Olympic sport Today: considered the most popular sport at all, due to its good financial accessibilityThere are 207 football associations in the World under the umbrella of FIFA Football empire: empire of peace, even in the period of wars and political disharmony

Football dresses: serve to distin-guish the rival teams and empha-sise the team images.

Fig. 2 Dress of L. Andrade during the match with Buenos Aires, 1910

Football dresses - composition 

Today, with so many football teams: it is not easy do design an original dress, especially when the dress structure is clearly defined and compulsory. Originally: all dresses made of cotton – see the national dress Uruguay of José Leandro Andrede from the twen-ties of 20. century.

Onset of synthetic materials: at seventies of the last century

Fig. 3 Permitted modern dresses should involve long sleeves

Primary positive property of cotton: pleasant handle, but did not compensate:•the exceeding sweat sorption•permanent cooling effect•long time of drying •high mass of the wet dress and increase of the dress dimensions.

At the beginning:polyamide (PAD) was used, butlater was replaced by polyester(PES), due to its hydrophobicity,UV + abrasion resistance, hightenacity, excellent coloration etc.

First PES coarse fibres: quite unpleasant in hand, causing skin irritation due to high bending rigidity (10 times higher then for same fineness cotton fibres). Sportsmen complained on allergy and had to use fine underwear. Today: prevailing PES microfibers knits exhibit good softness, no underwear is necessary.Modern dresses consist of different parts, where each satisfies specific function, according to its location on the body.

Modern design of performancegarments (sport dresses): 

Higher price of garments with high added value, made ofperformance or smart fabrics, should be based on higher protection and comfort properties.

Garment prototypes should be tested in terms of their protection and comfort parameters by means of new testing instruments,

Testing of comfort properties of final products (dresses) should be non-destructive, to enable economical comparison of various products, here dresses

The biggest problem ofknown measuring methods:requirement on cutting ofsamples of given dimensions,which results in destructionof the garment.  

Strategy of the Dept. of textile Marketing of TU Liberec: to promote and in some cases to develop relatively cheap and user-friendly instruments, which measure the garment comfort properties without the necessity to destroy the garments. Also smaller dimensions of specimens reduce the testing costs.

Such instruments, in fu-ture, can be used also inlarge shopping centersand specialised shops,to enable the testingthe basic comfort characteristics in front of the customer.

As an example of such simple user friendly instrument, serves thePERMETEST instrument (by SENSORA)

Survey of comfort characteristics of fabrics and garments, which are tested Properties of textile fabrics and garments embrace both purely mechanical properties and heat / moisture transfer properties. Complex effect of these properties characterise comfort properties of fabrics.  Properties, which involve the effect of fabric humidity on selected mechanical parameters along with the effect of deformation properties and contact force of garments on the user’s perception during the garment wearing we call sensorial properties.

More simple is the fabric hand or handle, generally perceived by hands, where fromtransfer properties just warm-cool feeling is involved. 

Heat/moisture transfer properties involve steady state and transient properties, which contribute to thermal equilibrium of human thermal engine - our body.

. Tactile (hand) characteristics of fabrics:

   Friction + profile   Thickness + compressibility Bending + shearing stiffness (at low and large deformations)   Elasticity, tenacity   Warm-cool feeling (transient contact heat transfer)

Thermo-physiological comfort characteristics of fabrics+ garments:

 Steady-state local thermal insulation parameters (thermal resistance and conductivity) Steady-state total thermal resistance (including ventilation effects) Steady-state local and total moisture transfer parameters (evaporation resistance) Transient moisture transfer (moisture absorbtivity)    

 Determination of Water vapour permeability by means of the PERMETESTinstrument (non-gravimetric method with electric output) This instrument is the so called skin model, which simulates dry and wet human skin in terms of its thermal feeling and serves for determination of water vapour and thermal resistance of fabrics. If the instrument is used in laboratories with standard air conditions, then it offers reasonable precision of measurement. Results of measurement are expressed in units defined in the ISO Standard 11092. The instrument principle is following:

SAMPLE

THERMAL INSULATION

TEMPERATURE SENSOR

TEMPERATURE SENSOR

WIND CHANNEL

RELATIVE HUMIDITY SENSOR

FAN

HEATING ELEMENT

INSTRUM. BODY

WATER INLET

POROUS LAYER WHICH SIMULATES THE HUMAN

SKIN

MEASURING HEAD

Working principle of the PERMETEST skin model

Slightly curved porous surface is moistened and exposed in a wind channel to parallel air flow of adjustable velocity. A tested sample is located on the wetted area

of diameter about 80 mm. The amount of evaporation heat taken away

from the active porous surface is measured by a special power sensing integrated system. The measurement time is very short – full

signal is achieved within several minutes. The instrument body can be heated above the

room temperature or kept at the room temperature to maintain the isothermal working conditions.

At the beginning of the measurement, the measuring head is covered by semi-permeable foil to keep the measured garment dry.

Then, heat flow value qo without a sample is

registered. In the next step, the full-size garment is inserted (without being cut to special shape) between the head and the orifice in the bottom of the channel. When the signal gets steady, the level of qs, which quantifies heat loses of wet

measuring head covered by a sample, is registered. Both values then serve for calculation (made by a micro-PC) of the following parameters of garment water vapour permeability:

Relative water vapour permeability P is a non-standardized, but practical parameter (P = 100% presents the permeability of free measuring surface). It is given by the relationship P = 100 ( qs / qo) [ % ]

Water vapour resistance Ret (as defined in ISO

11092) expresses the equation Ret = (Pm – Pa) (qv

-1- qo-1

) [ m2Pa/W]

 The values Pm and Pa in this equation represent

the water vapour saturate partial pressure in Pascals valid for ambient temperature ta and actual

partial water vapour pressure in a laboratory.

The instrument also measuresthermal resistance Ret [m

2K/W]

of garments, similarly as given by the ISO standard 11092.  How the sample dimensions affect the measurementprecision? Is here any effect of moisture conduction alongthe sample surface resultingin (incorrectly) higher watervapourpermeability, then incase of the cut sample?  Systematic measurements of relative water vapour permeability on samples with varying dimensions proved, that the effect of sample dimensions (diameter) is not very strong - Variation coefficients in most cases did not exceed 5%, which confirms good measurement precision for this kind of measurement.

The PERMETEST non-destructive fast Skin Model

Warm - cool feeling andMoisture absorbtivityevaluation by means ofthe ALAMBETA tester 

The apparatus used in this study enables the measurement of thermal conductivity, thermal absorbtivity, thermal resistance and sample thickness.

Thermal absorbtivity b of fabricswas introduced by L. Hes (1987)to characterise thermal feeling (heat flow level) during short timecontactof human skin with the fabric surface. For time of thermalcontact τ between the human skinand the fabric shorter then severalseconds, the measured fabric can be simplified into semi-infinite homogenous mass with thermal capacity ρc [J/m3] and initial temperature t2. Unsteady temperature

field between the human skin (with temperature t1) and fabric with respect to of boundary conditions offers a relationship, which enables to determine the heat flow q [W/m2] course passing through the fabric:

q = b (t1 – t2) / (π τ)1/2, b = (λρc)1/2 [Ws1/2/m2K]

where ρc [J/m3] is thermal capacity of the fabric and the term b presents thermal absorbtivity of fabrics.

The higher is thermal absorbtivity of the fabric, the cooler is its feeling. In the textile praxis this parameter ranges from 20 Ws1/2/m2K for fine nonwoven webs to

600 Ws1/2/m2K for heavy wet fabrics.

Thermal resistance R depends on fabric thickness h and thermal conductivity λ:

R = h/λ [m2K/W]

Computer-controlled instrument ALAMBETA for fast measurement of thermal insulation and thermal-contact properties of compressible

materials like textile fabrics

Experimental partThere are 4 manufacturersof football dresses in Czech Republics : Alea Sportswear, (Písek), Jadberg (Napajedla), LoMa sport (Broumov), Panartex (Prague). In this research 6 dresses of different design and composition were studied:

●Manchester United- chest +armpit + belly●Munique dress 1860 of 1988●Czech National dress ● Red dress● Sport Club Kladno, Czech Republic● Blue dress

Testing procedure and experimental results The dresses were measured 4times in dry state and thermalabsorbtivity was measured atthe next to skin surface in wetstate also. The wet measurement simulated the so called sweating impulse, depending in application of 0,3 water with 1% of detergent in to the measuring area centre. The proper measurement was carried out after 1 minute delay, to get rid of the effect of moistening heat. After 1 minute also the wet spot diameter was determined.

 

Thermal conductivity λ

53,3

52,1

45,544,8

39,4 39,3 38,5

36,8

25

30

35

40

45

50

55

60

65

λ [mW/m.K]

Red dress of 1988

Blue Dress of 1970

Munique of 1999

Manchest. U.(chest)

SC Kladno of 2006

Manch. U. (armpit)

Czech nat. dress

Manchester U.(belly)

r [m2K/W] Thermal resistance r18,3

15

11,1 10,8 10,7

9,4

8,2

7,1

0

2

4

6

8

10

12

14

16

18

20

r

Red dress of 1988

Blue dress of 1970

Munique dress of 1999

Manchester U.(belly)

SC Kladno of 2006

Czech Rep. training

Manchester U. armpit

Manchester U. chest

MUC CZN MUA MUB MUN RED SCK BLU

Thermal absorbtivity values b [Ws1/2/m2K] in dry state (blue) and wet state (red)

Diameter of the wetted area (mm)

29

25

21

18

16

15

10

8

SC Kladno

Blue dress of 1970

Manchester U.(belly)

Manchester U.(chest)

Czech rep.training

Red dress of 1988

Manch. U. armpit

Munique 1860

72,58

72

70,83

65,45

65,15

63,6

57,36

53,03

40

50

60

70

Relative water vapour permeability [%]

Manchester U. (chest)

Manchester U. (armpit)

Manchester U. (belly)

SK Kladno

Czech Rep.

Munique 1860

Blue dress of 1970

Red dress of 1988

Evaluation of resultsThe oldest cotton dresses with highest thickness exhi- bits highest thermal resistance, but with the disadvan-tage of high square mass. High thermal insulationis here also the disadvantage. The lowest thermalinsulation exhibits the Manchester United dress.

As regards the water vapour permeability, the highest levels ofers the Manchster United dress made of Coolmax (PES), whereas the lowest levels exhibit the two old cotton dresses.

Thermal absorbtivity

The MU PES dress exhibited at some body parts (chest, armpit)the required coolest feeling, provided that after the cooling period the fabric gets dry rapidlyand protects the body against post treatment chill. Unfortunately, the cooling effect on the back has not been measured.

Thanks to the rib structure, the warmest feeling showed the cotton dresses, despite the reduced distribution of moisture along the fabric plane. However, cotton fabrics turn dry after quite a long time, which is one of their most serious disadvantages.

Conclusions  This study presents the first part of the systematic

experimental research of comfort properties of football dresses, focused on determination of their dry thermal properties and thermal absorbtivity after single sweating impulse.

From the presented results follows, that thermal comfort properties of the dresses both in dry state (thermal resistance) and wet state (thermal absorbtivity) vary substantially according to dress composition and structure (design). Also water vapour permeability of the studied dresses depends strongly on their composition.

In the next step, also the effect of moisture on thermal insulation properties and water vapour permeability will be systematically investigated.

Acknowledgements

The Czech Ministryof Education Supported Mr. Paul Smith, designer MU partially this studywithin the Grantof SPECIFIC RESEARCH and the author also thanks to Mr. Lukáš Killar for his experimental work (BSc, 2007)