Saturday, December 31, 2016

Thermal Clothing | Various Heat Transfer Process through Clothing

Thermal clothing is not common clothing it is such kind of cloth which is used to feel cool or warm in conditional environment. So, it is also called environmental clothing. The property of clothing depends on the thermal properties of raw materials, structure of cloth, finishing process. Most of the case cotton feels cool and wool feels warm.

Thermal clothing:
The clothing which feels cool at hot weather & feels warm at cool weather is called thermal clothing. The basic properties of these clothing depend on thermal properties of the fiber, thickness, fabric structure, density of the clothing. It is an important example for clothing comfort.

Cotton fiber feels cool due to its flat condition on fabric but wool, wool mix yarn feels warm due to its crimped condition in fabrics.
Thermal clothing
Fig: Thermal clothing
Now a days the different coated fabrics such as polyurethane fiber, polyester fiber, pvc etc used as thermal clothing. These are used as thermal clothing for their excellent water absorbency property, wicking property. Here PVC is very costly. So polyester and polyurethane are used mostly.

Depending factor of thermal clothing:
  1. Structure is a factor; knit structure is better than woven
  2. Thermal properties depend on fabrics fittings, thickness, environmental condition
Different heat transfer process:

  1. Heat transfer rate is measured by thermal resistant.
  2. Heat is lost through fiber and still air.
  3. Thermal resistant is express by Tog value.
  4. Higher Tog value Higher thermal resistant
  5. In America or other countries CLO value is used.
When heat is losing by passing air through clothing is known as heat loss by convection process. There are many openings area in our garments, warm air between clothing and body skin is mostly passed through that open area (collar, cuff, bottom). So heat loss by convection process is very poor . It is counted (10%-15%) to the total heat loss from our body.

Heat loss through radiation system is measured by following formula:

E = Relative radiation power x Stephens constant x Temperature (power 4)

Radiation process depends on:
  1. Fabric density.
  2. Fabric thickness.
  3. Fabric color.
  4. Amount of cloth worn.
  5. Temperature of body.
  6. Surroundings temperature.
  7. Emissivity of materials.
Depending parameter of perspiration and respiration:
  1. Amount of clothing worn
  2. Air permeability
  3. Difference between atmospheric temp and body temperature
  4. Opening area of clothing
  5. Wicking properties of Clothing.