Heat Insulating Materials
The purpose of thermal insulation is to restrict the heat transfer from warmer to cooler areas. Transfer of heat takes place by three processes- the convection, the radiation and, the conduction.
Convection
In convection, heat is transferred from one place to another by the movement and mixing of liquids or gases.
Radiation
Radiation is the process of transferring heat in a similar manner to that in which light is transmitted, i.e., by means of invisible wave radiation. The extent to which a building material radiates heat is mainly dependent on the emissivity of the surface, on the temperature of the surface, and on the temperature of the surrounding surfaces; metals have very low emissivities.
Conduction
Conduction is a process whereby heat is passed on between adjacent stationary particles of matter. The conductivity of building materials depends upon their density and porosity, and upon their content. Since bulk densities of materials vary inversely to their air contents, those materials which enclose a high proportion of air in their structure are generally better heat insulators.
Water is a good heat conductor, if present in the material, makes the material a poor insulator.
The commonly used heat-insulating materials work on the principle of either air spaces formed between structural components, surface insulation, or internal insulation.
Well Known Products of Heat Insulation
- Aerated concrete
- Gypsum boards
- Fibre boards
- Asbestos cement boards
- Chipboards
- Corkboards
- Foam plastic
- Aluminium foil
- Reflecting paints
- Expanded blast furnace slag
- Vermiculate*
- Fibreglass
- Glass wool
- Cavity wall, though costly
Properties of Heat Insulating Materials
Heat insulating materials should be impermeable to water, fireproof, resistance to insect attacks, have low thermal conductivity (0.0228 kCals-cm/m2oC). Since a good heat insulating material has a porous structure the strength is lowered affecting the stability.
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