Thermal comfort moisture

The guarded hot-plate method can be modified to perform dry and wet heat transfer testing (sweating skin model). Some plates contain simulated sweat glands and use a pumping mechanism to deUver water to the plate surface. Thermal comfort properties that can be deterrnined from this test are do, permeabihty index (/ ), and comfort limits. PermeabiUty index indicates moisture—heat permeabiUty through the fabric on a scale of 0 (completely impermeable) to 1 (completely permeable). This parameter indicates the effect of skin moisture on heat loss. Comfort limits are the predicted metaboHc activity levels that may be sustained while maintaining body thermal comfort in the test environment. 

Humans seek and want thermal comfort, even at work in industrial settings. Clothing, activities, posture, location, and shelter are chosen, adjusted, altered, and sought consciously and unconsciously to reduce discomforts and enable us to focus more on the other tasks of life. Discomfort can contribute to mistakes, productivity decreases, and industrial accidents. " Thermal discomfort results from the physiological strain of thermoregulation. The strain can be in the form of altered body temperatures, sweating and excessive skin moisture, muscle tension and stiffness, shivering, and loss of dexterity. A small... 

Air conditioning The process of air treatment in which the temperature, moisture content, purity, and distribution is controlled to set conditions. The resulting conditions may be chosen for human thermal comfort or to meet the requirements of a manufacturing process... 

Thermal comfort exists if the human body is in thermal equilibrium with its environment, implying a constant temperature of the body. Comfort is mainly determined by the construction of a garment, in particular by its thermal insulation and by moisture transfer. 

Rossi S provided an extensive review of methods to characterise clothing comfort and discussed the thermal and tactile properties of flame retardant garments, with special attention paid to the problem of sweat accumulation in the garments and its influence on thermal protection. Rossi also outlined factors influencing thermal comfort and discussed the protection/comfort contradiction as well as test methods for heat and moisture transfer. 

It is noteworthy that each of these has an outer fabric containing meta- and para-aramid blends (see Chapter 8) for good fire protection and durability. However, a number of inner layers, whether joined to the outer or part of the Uner comprising breathable polyurethane or PTFE membranes, are also a common feature. Thirdly, the use of thermally insulative nonwoven interlayers and comfortable meta-aramid/FR viscose innermost linings are also present. It is the ordering and exact interlayer compositions that appear to be the major differences, while each design attempts to provide the common properties of fire resistance, thermal insulation, moisture transport, and comfort. 

Other applications can be found in the thermal comfort of seating furniture. The heat flux of the body through a seat into the environment is essentially reduced, leading to a rapid temperature increase in the microclimate. A reduction in moisture transfer from the body through the seat, resulting in a substantial increase in microclimate moisture, would also be apparent... 

In addition, thermal comfort is also an important factor in buildings this is linked to the following four physical factors the ambient room air temperature, the average temperature of room-enclosing surfaces, moisture content and movement of air within the room. 

Sampath, M., Aruputharaj, A., SenthiUcumar, M., Nalankilli, G., 2012. Analysis of thermal comfort characteristics of moisture management finished knitted fabrics made from different yams. J. Ind. Text. 42, 19-33. 

As a final test sequence, to evaluate all performance aspects of a military uniform for a cold environment, subject wearing trials are conducted in a climatic chamber that simulates realistic temperatures and physical activity/metaboUc rates. The subject is equipped with numerous temperature and humidity sensors on the skin that judge his or her subjective thermal and moisture sensation as weU as the resulting overall comfort in distinct time periods and varying conditions. The subjective perceptions of the wearer and the measured temperature and moisture data are compared and subsequently correlated with the data from the Skin Model and thermal manikin. This fully validates the wear trials. 

Moisture accumulation. Some textile fibers (eg, cotton, wool) are hydrophilic in nature. Due to this, a fabric may absorb moisture (sweat) generated from wearers bodies and accumulate it in its structure. The thermal conductivity of moisture is much higher than the thermal conductivity of air or fibers. This may cause rapid transmission of metabolic heat from wearers bodies to the ambient environment that can result in better thermal comfort for wearers under some conditions (Barker et al., 2006 Song et al, 2011). In this context, it is necessary to remember that absorbed moisture in cotton and wool may not always increase the amount of interstitial free water inside the fabric and this situation may not cause the rapid transmission of metabolic heat from wearers bodies. Additionally, rapid loss of metabolic heat may not always lead to thermal comfort for wearers. 

Lee et al. explored the application of zinc oxide nanoparticles to polypropylene nonwoven fabrics via electrospinning as one approach to impart UV-protective properties. In addition, moisture and air vapor transport characteristics of layered clothing systems with various levels of electrospun mat area density are assessed to observe the consequence of electrospun web layers on thermal comfort level of the layered structures (Fig. 14.6c) [56]. Ultrafine cellulose fibers from natural cotton lines, whose degree of polymerization was above 10,000, were electrospun. The cellulose nanotibers treated with the hydrothermal incorporation of Ce02 nanoparticles into the nanofiber substrate surface showed good UV-shielding properties... 

The concept of clothing comfort and the factors influencing the same have been investigated by various researchers since 1930s till present date. Many investigations have been carried out to study the thermal and moisture properties of textile materials. Researchers have worked on the effect of various properties of textile materials on their transport values. 

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