★ 3N3 FTW!

Wednesday, April 7, 2010 12:15 PM

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CONDUCTION is heat transfer through a material as thermal energy moves from molecule to molecule through a substance; or from one object to an adjoining object. If you pick up the handle of a cast iron frying pan from a hot stove you’ll experience conduction! The heat reaches your hand via conduction from the burner to the bottom of the pan through the metal handle to your hand. Heat is conducted through the ceilings, walls and floors of homes. Effective insulation slows conduction by keeping heat out during summer and in during winter.

CONVECTION is the transfer of heat by a liquid or gas (such as air). Circulatory air motion due to warmer air rising and cooler air falling is a common mechanism by which thermal energy is transferred. An open chimney flue provides a good example of convective heat loss during the winter. Warm air will rise up the chimney and cold air will fall down into the home. The energy used to warm the air that escapes is lost. The cold air must now be heated. The greater the temperature difference between the inside and outside of the home, and the larger the openings in the home, the easier it is for air to move and the greater losses you will have due to convection. Convective heat loss occurs through cracks and holes in the home and gaps and voids in ceilings, walls, and floors—and in the insulation. Convection also occurs if air can circulate through the insulation — if insulation is to be effective, it must prevent air from flowing easily through it. Properly applied insulation reduces convective heat loss by resisting and minimizing air movement.
Norazlinda .