Comfort of Clothing. Rajesh Mishra & Jiri Militky Technical University of Liberec Liberec, Czech Republic

Transcription

1 Comfort of Clothing Rajesh Mishra & Jiri Militky Technical University of Liberec Liberec, Czech Republic

2 Comfort Physical comfort - Mechanical Physiological comfort - Transmission Psychological comfort - Aesthetic

3 Issues associated with comfort Material characteristics Thermal science Environmental variants Human body physiology Mind and body interaction

4 Expectations from Fabric for Garment Aesthetic performance Intrinsic performance Utility performance

5 Aesthetic performance Aesthetic performance in terms of : colour, design, texture and appearance in made-up form.

6 Intrinsic performance Intrinsic performance comprising of : Mechanical comfort expressed in fabric hand Thermo-physiological comfort associated with : transmission of heat, moisture and air.

7 Utility performance Utility performance associated with : durability and serviceability of the garment measured in terms of : abrasion resistance, pilling resistance, fastness properties, wash and wear etc. Also includes Tailorability

8 Requirements in fabrics for Clothing AESTHETIC PERFORMANCE Color Design Texture Appearance in garment form QUALITY OF FABRICS FOR CLOTHING INTRINSIC AND ESSENTIAL PERFORMANCE Mechanical and Tactile Comfort as Judged by Hand Environmental Comfort which depends on movement of heat, moisture, air UTILITY PERFORMANCE Strength Abrasion resistance Pilling resistance Washing and Wear etc.

9 Total effect on human being To appreciate their total effect, it is necessary to consider how the mind and body interact to maximize comfort for any human being.

10 Considerations for comfort The way body and brain mechanisms achieve comfort for the attainment of thermal equilibrium Role of moisture in this process Extreme hot or cold environments can be prevented by using textiles Understanding choice of fibre type, construction factors and treatment mode in selecting a material to provide the optimum comfort level achievable.

11 Technical University of Liberec 2013 TEXTILE TESTING

12 Technical University of Liberec 2013 TEXTILE TESTING

13 Technical University of Liberec 2013 TEXTILE TESTING

14 Technical University of Liberec 2013 TEXTILE TESTING

15 Technical University of Liberec 2013 TEXTILE TESTING

16 Technical University of Liberec 2013 TEXTILE TESTING

17 Technical University of Liberec 2013 TEXTILE TESTING

18 Technical University of Liberec 2013 TEXTILE TESTING

19 Technical University of Liberec 2013 TEXTILE TESTING

20 Thermal Comfort definition According to ISO 7730 Thermal Comfort is That condition of mind which expresses satisfaction with the thermal environment. This is achieved when there is a balance between the energy produced by a human being and the energy lost to the environment

21 Functions of Clothing Protect the body against excessive heat loss Keep out detrimental environmental and weather effects Enhance the appearance

22 Role of Clothing Clothing is designed to maintain a hygienic and comfortable zone about the human body in which one feels well, even if inner or outer influences change rapidly Clothing helps in achieving the thermal balance between the heat production by the body and heat transmission to the environment

23 Human-Clothing-Environment Radiative Heat Transfer Environment Clothing system Convective Heat Transfer Microclimate Core Skin Conductive Heat Transfer

24 COMFORT ZONE The zone in which the temperature, moisture and air circulation are properly matched so as to maintain the thermal and the moisture balance is called the comfort zone Moisture transfer from skin through clothing ideally in vapour form is necessary for comfort

25 Body Environment Interaction Body Heat and Moisture Vapour Production Clothing Environment

26 Processes Involved Physical Physiological Neurophysiological Thermophysiological Psychological

27 The Processes Involved In Sensations And Attitudes On Comfort Physical processes Pressure stimuli mechanical behavior Tactile stimuli mechanical behavior clothing & environment Physiological processes body & skin Neurophysiological processes: Sensory responses of nerve endings to stimuli thermal, pressure, pain, Thermophysiological processes: sweating, blood flow control, shivering Psychological processes brain Visual stimuli color, light reflection, design Perception of sensation from thermal, pressure and pain and combination of various synthetic stimuli. Evaluate and weigh various sensations. Overall perception Comfort/Discomfort

28 Metabolic Heat Production Teaching: 1.6 Met Sleeping: 0.8 Met Running: 9.5 Met 1 Met = W /m 2 of body surface

29 Environmental Factors Air Temperature Mean Body Temperature Mean Relative Air Velocity Ambient Humidity

30 Effect of Wind It has been observed that wind induces a reduction in thermal insulation of fabrics Ia=ambient insulation Ic=clothing insulation In cold temperature, wind causes rapid cooling of skin temperature which is known as the Wind Chill Effect

31 Wind Chill Effect W = the wind chill index, based on the Celsius temperature scale Tair = the air temperature in degrees Celsius ( C)( V10m = the wind speed at 10 metres (standard anemometer height), in kilometres per hour (km/h)

32 Thermal Comfort The actual combination of skin temperature and the body s core temperature provide a sensation of thermal neutrality The fulfillment of the body s energy balance: the heat produced by the metabolism should be equal to the amount of heat lost from the body

33 Human Body Temperature Normal body temperature in humans is C ( F). Hypothermia is defined as any body temperature below 35.0 C (95.0 F). Heat stroke is defined as a temperature of greater than 42 C (107 F) due to environmental heat exposure with lack of thermoregulations

34 Thermal Comfort Body Hypothermia Core Heat Stroke 37 o C Skin Temperature 33 o C Tolerance (20-30 o C)

35 Thermal Management Mechanism of Human Body When body becomes too warm Vasodilation of blood vessels Increased blood flow through the skin and subsequent sweating When the body becomes too cold Vasoconstriction of blood vessels Stimulating the muscles, which causes shivering

36 Factors Affecting Heat Transfer from Skin The Fit of The Garment Proportion of Body Surface Area Covered Geometry of Human Body Body Movements

37 Heat Transfer Mechanism Dry Heat Transfer Conduction Convection Radiation Evaporative Heat Transfer Moisture Transmission Vapour Transmission

38 Heat Transfer Mechanism Heat flows through materials depend on their thermal conductivity but this is not the case in textile structure. Most textile fibres have similar value of thermal conductivity and the more important one is the nature of textile structures

39 What is important in textile structures for heat flow Insulation is governed by the bulk structure of a fabric, rather than by any of its individual parts, and air has a much higher insulation value than fibres. Thus, the thermal insulation is governed exclusively by the amount of entrapped air within a structure.

40 Which structural parameters are important for better insulation in Textiles Fibre : which have an irregular surface, a non-circular cross-section, high levels of unevenness or a convoluted form will produce materials with better insulation Yarns : which are loosely twisted, irregular, hairy and fancy will be better insulators Fabrics : which are loose in structure, soft, thick, porous or textured will generally insulate better than those which are flat, boardy, thin or level-surfaced Cloth : clothing system consists of many garments layered over each other than if it is a single-layer garment of the same total thickness and weight

41 Which structural parameters are important for minimum heat retention in Textiles Fibre : straight, uniform, even fibres Yarns : straight, uniform, even, tightly twisted yarns to make thin, flat, open fabrics Fabric : thin, flat, open fabrics Garment : single thin layer garment to allow heat to escape efficiently Garment design : design which provides ample ventilation to permit the free movement of air over the surface of the body will allow convection currents to flow over the skin, removing heat more rapidly.

42 Factors Influencing Thermal Resistance of Fabrics The most important factor which influences the dry thermal resistance of a fabric is the Thickness Cover factor, surface roughness, finishing or coating materials used on the fabric may also have some effect

43 Thermal Resistance of Clothing Clothing consists of a number of fabric layers Thermal resistance of a combination of garments is more than the sum of the thermal resistance of individual items Additional layers of air are trapped between fabrics Boundary layer of still air over outer surface of clothing

44 Water vapour Permeability Water vapour is constantly being released by the skin For comfort, this vapour should be able to easily escape from within the clothing microclimate to outside through the fabric Vapour transmission takes place by diffusion In general, fabrics having high vapour permeability have low resistance to air flow and rain water Breathable fabrics have solved the problem

45 Moisture and Clothing Perspiration Insensible Sensible Insensible: under normal atmospheric conditions and at rest, human body continuously produces perspirations which evaporates within skin layers and is emitted in the form of water vapour Sensible: Liquid sweat

46 Moisture and Clothing Vapour permeability and air permeability are not equivalent in case of hygroscopic textile materials The rate at which water vapour passes through a fibre depends on the nature of the fibre Hydrophilicity of the fibre becomes an important criterion in case of dense fabric construction Wicking behaviour of fabric is also important in the moisture management of the clothing

47 Which cloths are important from MVTR point of view Sportswear casual wear Protective textiles from comfort point of view Surgical gown, Masks etc.

48 Liquid moisture flow through textile materials Liquid moisture flow through textile materials is controlled by two processes: wetting wicking Wetting is the initial process, involved in fluid spreading and it is controlled by the surface energies of the involved solid and liquid As water wets the fibre, the water enters the inter fibre capillary channel and is dragged along by capillary pressure.

49 Capillary pressure through textile material The magnitude of the capillary pressure is given by the Laplace equation: γ P is the pressure developed in the capillary channel R c γ θ LV P 2 γ c o s θ is the radius of the capillary formed in the fibrous structure represents the surface tension at the interface between the various combinations of fibre(s), liquid (L) and air (V) = is the contact angle between the liquid drop and fibre surface cosθ L V R c is the resultant surface tension between fibre and liquid interface

50 Perspiration and thermal balance Perspiration of human body should be transferred to the atmosphere in order to maintain the thermal balance of the human body.

51 Factors of vapor transmission that maintain Thermo-physiological comfort index Parameters of vapor transmission that maintain the thermo-physiological comfort index : Absorption-desorption Diffusion and convection of vapour perspiration Wetting and wicking of liquid perspiration

52 Moisture Vapour Transmission Rate (MVTR) through any clothing The moisture vapor transmission rate (MVTR) through any clothing item depends on : Moisture content of the fabric Type of material used Perspiration rate Atmospheric stimuli like temperature, wind speed and relative humidity.

53 Air Transmission Fabric interstices,pore size and their distribution are prime factors for air transfer. Factors which influence air flow are: Yarn crimp Yarn flattening Yarn twist Fibre fineness Cross-sectional shape of the fibre

54 Comfort Measurement Method for predicting thermal comfort of fabric comprises of a provision of a perspiring hot plate to simulate the skin hermoregulatory responses of a human fluid flow through the fluid input source and a power flux through the thermal input source to correspond to human perspiring and thermal output level placing a fabric on top of the perspiring hot plate

55 Comfort Measurement temperature of the top surface of the plate as the temperature changes to simulate the skin surface thermoregulatory responses can be observed. The temperature profile is analyzed and the comfort level of the fabric from the results is determined

56 Research in Comfort Functional clothing Advanced Materials Fibre Engineering

57 Technical University of Liberec 2013 TEXTILE TESTING

58 Concluding Remarks Clothing protects from cold or heat to maintain body thermal comfort throughout the full range of human activities

59 Concluding Remarks Comfort can be affected by any variation of the following parameters beyond certain tolerances: Person Clothing Environment Activity

60 Concluding Remarks The design of the clothing, the tactile and thermal insulation behaviour of the fabric assembly and the moisture management capabilities of the clothing affect the comfort.

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