Types of insulation:

Types of insulation:

1. Flake insulation (fine particles)
2. Fibrous insulation (Glass or rock wool)
3. Granular insulation (Magnesia or cork)
4. Cellular insulation (rubber or plastic)
5. Reflective insulation (Foils)

Heat transfer through insulation:

The heat transfer through insulation takes place by conduction, convection and radiation, because most of the insulations used are of low density and high porosity. The insulating material reduces the heat transfer by replacing the short path of low resistance by a long path of high resistance. Most of the insulating materials provide small pockets of air through which the heat is transferred. These pockets in the insulating material are formed by flaked fibers and cells of material itself.

The heat flow by conduction is reduced due to the long path followed through the insulating material and due to very low conductivities of air gaps and material itself. The heat flow by radiation is also considerably less because most of the insulating materials are opaque to radiation.

If there is no continuous path for the circulation of air inside the insulating material, then the heat flow by convection is more or less neglected. The heat transfer by convection through insulation material generally takes place in material like glass wool which provides continuous path for air flow. Every care should be taken to remove the air from such material before use.

When the insulation is applied to the hot surface, the moisture from the insulation is vapourised and vapour pressure near the hot surface is increased and it tries to escape into the low pressure ambient air. Thus the heated surface tries to dry out the insulation contact with it. The moisture is always present in the insulation and its content depends upon this temperature and pressure of surrounding air.

The moisture content in the insulating material which is in contact with hot surface also changes due to the constant change of ambient air conditions on account of time of the day and season.

The weather barrier is always provided on the insulation to prevent the absorption of moisture by insulation from the atmospheric air. The barrier material provided on the insulation used on hot surface should not be a good vapour barrier, otherwise the vapour pushed out from hot surface will condense on the inner surface of vapour barrier and rusting will occur on inside surface of the barrier.

In our project model the layers of insulation provided are shown in figure, where aluminium foil is used for reflective insulation. After providing 8 layers of insulation the box can be treated as insulated box, which acts as a barrier for radiative heat transfer.