Role of Clothing:
Clothing is the most important necessity of day-to-day human life. Without food a person can survive for few days but without clothing it is no possible to survive in the civilized environment. The role of clothing are multipurpose. For example, to protect human body from different environmental conditions, to lead civilized life, to feel comfort, to increase attractiveness, to save human body from unusual situation etc. If we want to understand the role of clothing and design of clothing etc. We should understand the physical aspects of clothing. In this article, I will discuss, process of maintaining constant body temperature and role of clothing.
Role of Clothing for Maintaining Body Temperature:
As food is necessary to survive, clothing is also necessary to maintain body temperature to a correct rate. The food materials used by human are digested by physiological process. The digested food provides heat and energy to human body. To retain that heat in the body to a correct level, clothing and the design of clothing is very important. The design of clothing should be such that it can protect human body from any adverse environmental condition as well as the body movement of any part is comfortable. As per medical science, human body core temperature should be 370C and skin temperature should be 330C to feel comfortable. Skin temperature may vary from place to place of human body; e.g. lowest at leaf of feet and hands, and highest at under arms. When body temperature drops, then skins of hand, leg, body, face etc starts working to squeeze blood cells to protect loss of body temperature and to maintain constant core temperature of body and brain at 370C. Change of body core temperature only for +/-20C causes discomfort to human and for +/-40C needs help of a doctor. It is necessary to know the methods of temperature loss from human body to design the clothing for human comfort.
Basically there are four methods of temperature loss from human body. The methods are as follows:
- Perspiration and respiration
Human body losses temperature constantly by the above mentioned methods and gains temperature from foods through metabolic activities. The balance between gain and loss of human body temperature is maintained automatically by physiological process. If at any time this temperature is not maintained, the person feels discomfortable. When a person physically works hard, his or her body temperature rises rapidly, to balance the body temperature, sweating occurs automatically. As a result the body temperature again becomes balanced. The methods of temperature loss from human body are discussed below.
A. Heat loss from human body through clothing by conduction method:
Loss of heat from human body can occur through any medium. Clothing is made from various types of fibers. In clothing, there are fiber and air in different proportions. Volume of fiber is normally less than the volume of air in any clothing. In a very tightly spun yarn, volume of fiber may be upto 60% and volume of air is 40%. In a very compactly woven fabric, volume of fiber may be upto 40% and volume of air is 60%. So, when heat is lost by conduction method through the clothing, it is lost both through the fiber and air.
Loss of heat through the clothing is expressed by thermal resistance and thermal resistance is expressed as TOG value. Higher the value of TOG higher the thermal resistance, means lower the heat loss. In America and many other countries, thermal resistance is expressed as CLO value. The relation between TOG and CLO value can be expressed as follows:
CLO x 1.55 = TOG value
It is seen that, lower the volume of fiber in a clothing with respect of volume of clothing, higher the thermal resistance of that clothing, means lower the heat loss through the clothing. Loss of heat by conduction method through the clothing also depends on type of fibers in the clothing. For example, cotton clothing feels comparatively cool, whereas clothing made from wool, polyester, polypropylene are worm. The reasons behind such fact is that the cotton fibers remain in flat condition in the fabric, hence large area of cotton fibers comes in contact to body and heat loss by conduction method is higher, as a result cotton feels cool. Polyester, wool and polypropylene fibers remain in crimped condition in the fabric, hence area of contact of those fibers with body is less and heat loss by conduction method is less and feels worm during use. If viscose mixed fabric surface is hairy, for example VILOFT, which is made from blend of polyester and viscose fiber, feels worm during use, as because area of contact of such clothing is less due to hairy surface of fabrics.
B. Loss of heat through clothing by convection method from human body:
Experimental result shows that the heat loss by convection method is accounted 10% to 15% of total heat loss from human body through clothing. But in reality heat loss from human body by convection method may be little bit higher through the clothing, as because forced convection due to body movement is not considered.
C. Loss of heat through clothing by radiation method from human body:
Heat radiation means infrared radiation or microwave radiation. All the materials take part in radiation. Heat loss by radiation method can be explained by following theory.
E = e𝛿T4
E = Amount of heat energy loss.
T = Temperature0K
𝛿 = Constant
e = Emissivity of body
Value of ‘e’ depends on nature of the surface of body and due to variation of color of the same body. All the materials are staying in the sea of radiation, hence heat loss or heat gain depends on some factors, which are:
- Temperature of body
- Surrounding temperature of body
- Emissivity of different materials
Real heat loss or gain by radiation method depends mainly on the difference between body temperature and surrounding atmospheric temperature. So it is seen that heat loss by radiation method from human body is less from the clothed areas and more from the uncovered area like face, hands, leaf etc. in a certain environment a person wearing light clothing will loss more heat by radiation method than a person wearing heavy clothing is almost absorbed by the clothing and vapor. Relative humidity between the clothing and body may be 70 to 80% depending on time and situation. It is estimated that heat loss from human body by radiation method may vary from 5% to 50% of total heat loss.
D. Heat loss from human body by perspiration and respiration method:
Generation of body temperature depends on physical activity level of human body. Human body temperature generation may be 6 to 10 times higher than the normal temperature generation, depending on the physical activity level. When a person is at complete rest situation, heat loss through vapor (respiration) is accounted from 25% of the total heat loss by the body. Two third portion of that 25% is lost through body skin. Under this situation, heat loss as vapor form is counted approximately 15 watts and total heat loss is counted 60 watts.
When sweating occurs, heat loss by vapor form may be upto 300 watts and during very hard physical work it may be upto 500 watt. 500 watts heat loss is equivalents to loss of 19000 rams vapor per 24 hours from human body. Under that circumstances, a portion of heat loss as sweating and vapor from human body is passed through fabric and clothing. The process of human body heat loss by sweating and vapor form works as one of the mechanism of temperature balance. Heat loss in vapor form through clothing depends on following factors:
- Amount of clothing worn
- Vapor permeability through clothing
- Difference between body skin temperature and surrounding atmospheric temperature.
If surrounding environment temperature reaches to freezing point, then vapor may convert to water molecule or sweating, if present in between body surface and clothing. Under these circumstances, discomfortness will happen and heat loss by conduction method will increase. In reality, when clothing is worn, due to body movement, force pumping occurs and the worn moist air in between body surface and clothing passes through the opening areas of clothing like collar, cuff, bottom openings etc.
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