The scope of thermal insulation.
Control heat transfer, and prevent heat loss or increase inside a building to reduce energy consumption and maintain adequate living comfort.
How does heat transfer occur.
From hot to cold, always.
The heat flow represents the movement of heat and has only one direction, which sees the propagation from hot areas to cold areas.
This movement is what causes a drop in temperature inside buildings in winter, and a rise in temperatures in summer periods.
Heat transmission occurs by one or more of the following mechanisms:
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propagation by conduction;
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propagation by convection;
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propagation by radiation.
Insulating materials are designed to reduce heat transfer.
Propagation by conduction.
Through elements in solid, liquid or gaseous state.
This propagation modality sees the transmission of heat through one or more elements in direct contact (remember that this always happens from the hot element to the cold element).
The amount of heat propagated in a body, in a given time interval, is directly proportional to the thermal conductivity of the material itself and to the temperature differential between the two elements in question.
The lower the conductivity of the material, the greater the heat propagation time, the more the material will be a good insulator.
The lower the λ value of a material, the greater its ability to resist the propagation of heat by conduction.
Propagation by convection.
Through bodies in liquid and gaseous state.
This modality of propagation (non-existent for bodies in a solid state and absent in a vacuum) occurs inside gases or liquids, when the molecules inside them overheat, generating a variation in terms of density (i.e. when the hot air becomes less dense and tends to go upwards, the "natural convection" occurs, but the same result is obtained with wind or artificial means, incurring in "forced convection").
The amount of heat transmitted by a body (liquid or gaseous) depends on the heat difference between the two bodies, the incident speed and the area of the exposed surface. A wall exposed to a cold and strong wind will cool down faster than a wall exposed to a cold but moderate wind.
A material with a closed cell structure inhibits thermal convection within the cell itself. When the cellular structure is very fine and the cells are very small, thermal convection and the propagation of heat to nearby cells is further reduced.
Propagation by radiation.
Also in the absence of solid, liquid or gaseous bodies.
This modality of propagation sees the transmission of heat, in the form of energy, between two bodies through space. It does not require a direct contact between the bodies that exchange heat and does not need a channel to propagate.
It is a phenomenon that does not occur at every temperature, but only at fairly high temperatures, or at very close distances, and only in these cases will its contribution exceed that of the other transmission modes.
