Heat transfer is the energy flow that occurs between bodies as a result of a temperature difference. There are three commonly accepted modes of heat transfer: conduction, convection, and radiation. Although it is common to have two or even all three modes of heat transfer present in a given process, we will initiate the discussion as though each mode of heat transfer is distinct.

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...