ABSTRACT
Conduction is the mode of heat transfer due to temperature gradient in a stationary medium. The medium may be a solid or a fluid. When a temperature gradient exists in a body, there will be energy transfer from the high-temperature region to the low-temperature region. This kind of energy transfer is termed conduction and the heat transfer per unit area (normal to the direction of heat flow) is proportional to the temperature gradient. That is, the heat flux q˙ (the amount of heat transferred per unit area per unit time) is given by
q˙x ∝ ∂T ∂x
or
q˙x = −k ∂T ∂x
(2.1)
where k is the proportionality constant, q˙x is the heat flux and ∂T/∂x is the temperature gradient in the direction of heat flow. The positive constant k is called the thermal conductivity of the material, and the minus sign indicates that the heat must flow from a higher-temperature region to a lowertemperature region. Equation (2.1) is called the Fourier’s law of heat conduction. The thermal conductivity has the units of watts per meter kelvin [W/(m K)]. It can be expressed as [W/(m ◦C)]. This is because, k appears in the relation involving temperature difference.
