What is Thermal Insulation:
- Any material that retards or Resistance to the flow of heat through it is known as Thermal Insulation
- Insulating material that has Extremely low thermal conductivity.
- Insulation maintains the lower temperature inside the duct by insulating it from the warmer ambient air temperature and vice versa.
The function of Thermal Insulator:
- To resist the flow of heat from the surrounding
- To make possible better control of temperature in the refrigerated space.
- To minimize temperature fluctuation
- To prevent water vapor condensation.
- To minimize water vapor transmission
- To give a better surface finish.
- To absorb vibration and noise.
- To reduce the spreading of the fire and flames in case of fire hazard.
Properties of heat-insulating material
- The properties of materials can be divided into the following four categories:
- Physical properties
- Chemical Properties
- Mechanical Properties
- Thermal properties
1. Physical properties:
- These properties include density, porosity, moisture, resistance, coefficient of thermal expansion, low odor level, inflammability, compactness, and surface tension.
- An insulating material should have the following physical properties
- It should have low density (to decrease its weight).
- Not process its own odor nor should it pick up odor particles placed in the refrigerated space.
- It resists moisture penetration.
- It should repel vermin and insects.
- Not be flammable otherwise it may prove dangerous in presence of electric wiring etc.
2. Chemical properties:
- These properties enable insulation to retain its own structure in a hostile environment and also prevent it from being corrosive to substances.
- An insulation material that is to be used in industry must possess adequate resistance to acidic and corrosive gases.
3. Mechanical properties:
- It requires generally high abrasion resistance and hardness, and good compressive strength.
- The properties depend on the type of insulating material used.
4. Thermal properties:
These properties of insulating material are the most important properties.
1. Thermal conductivity
- The ability of a material to retard the flow of heat is given by its thermal conductivity.
- It should be low in the case of a thermal insulator.
2. Heat capacity
- It is essentially a measure of heat absorbed for a certain temperature rise and should be concordant with the use.
3. Thermal diffusivity
- It is a measure of the rate of progression of temperature raise in an insulating material when specific heat energy is available at one of its surfaces.
4. Combustibility
- It is characterized by flash point, smoke index, fire point, etc. To reduce fire hazards a low combustibility is necessary.
Requirements of thermally insulating material:
- Thermal stability
- Chemical stability
- Physical stability
- Low thermal conductivity
- Resistance to moisture
- Low specific heat
- Low specific gravity
- Odorless
- Resistance to vibration and shock
- Noninflammability
- The porous and fibrous texture
- Economical to its initial cost
Classification of thermal insulating materials:
- Organic heat insulator
- Cork
- Cotton wool
- Rubber foam sawdust
- Rice husk
- Polystrene
- Urethane
- Phenotherm etc.
- Inorganic heat insulator
2. Inorganic heat insulator
- Glass wool
- Slag wool
- Ceramic products
- Asbestos etc.
