Scientific Basics of an Insulator- Quincy and Crescent Bar Home Inspections
Scientific Basics of an Insulator- Quincy and Crescent Bar Home Inspections
The basic principle of any insulator is its ability to limit the transfer of heat energy.
Heat is the energy exchange between two thermodynamic systems which differ in temperature. Like the Sun to the earth or your bare body to snow. The transfer of thermal energy will always go from the system of higher temperature to the colder system. When the two systems have reached a thermodynamic equilibrium (same temperature) they will cease to exchange thermal energy.
Heat moves by three basic ways: conduction, convection, and radiation. The first two mechanisms need an intervening medium to work and this is where insulation plays its major role. Insulators can be any material or means by which any or all of the three heat transfer mechanisms can be interrupted.
Conduction
Heat energy is stored in molecules as vibrations. The more the molecules vibrate the higher temperature. In some materials, it is easy for one molecule to make its neighbors start to vibrate. The neighbor molecule then makes more molecules vibrate. Before long all the molecules are vibrating (is a party!). Now the whole object has a higher temperature. This is heat conduction. Metals are very good at this as well as many liquids.
Convection
Convection is the movement of molecules within fluids (i.e. liquids, gases) and rheids (a solid material that deforms by viscous flow like lava).
For convection, warmed atoms and/or molecules which are free to move about like those in a gas or liquid circulate through the medium in a rather predictable route. It cannot take place in solids, since neither bulk current flows nor significant diffusion can take place in solids
Radiation
In radiation is heat energy that is transmitted via electromagnetic waves. The radioactive process requires no medium. In other words, radiation (for example, light and heat) can move through empty space (like between my ears ; ).
How Insulators Work
For conduction the best insulator is a vacuum, completely empty space. If there are no molecules, there can be no vibrations. A very good insulator is air. Gasses such as air do no transfer heat very well because the molecules are so far apart from each other.
With convection heat we want to use a poor heat conductor with as many dead air spaces we can create. Things like cellulose, fiberglass and foam board insulation work well because they interfere with the convective flow essential to that mechanism. The tiny air (or gas) filled spaces in the insulator limit heat flow because they greatly extend the time necessary for convective and conductive flow to occur.
For heat to move through these materials each cell, which there are millions, must relay the heat across it. The longer it takes, the slower the heat flow.
In the case of radiation we want heat radiation to be bounced off a substance rather than being absorbed by it. This is how a thermos bottle works or those shiny emergency heat blankets work. The shiny mirrored surface reflects heat (electromagnetic waves) back toward the source. Hot things in a thermos stay hot because heat is reflected back toward the hot contents and cool things stay cool because the heat from the outside is reflected away from the contents.
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