*Macmillan Encyclopedia of Energy*. Copyright © 2001-2006 by Macmillan Reference USA, an imprint of the Gale Group. All rights reserved.

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## Conduction

When a temperature difference exists in or across a body, an energy transfer occurs from the high-temperature region to the low-temperature region. This heat transfer, q, which can occur in gases, liquids, and solids, depends on a change in temperature, ΔT, over a distance, Δx (i.e., ΔT/Δx) and a positive constant, k, which is called the thermal conductivity of the material. In equation form, the rate of conductive heat transfer per unit area is written as where q is heat transfer, A is normal (or perpendicular to flow of heat), k is thermal conductivity, ΔT is the change in temperature, and Δx is the change in the distance in the direction of the flow. The minus sign is needed to ensure that the heat transfer is positive when heat is transferred from the high-temperature to the low-temperature regions of...

This section contains 2,775 words(approx. 10 pages at 300 words per page) |