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Engineering ToolBox > Conductive Heat Transfer
Conduction take place when a temperature gradient exists in a solid (or stationary fluid) medium.
Energy is transferred from the more energetic to the less energetic molecules when neighboring molecules collide. Conductive heat flow occur in the direction of decreasing temperature because higher temperature are associated with higher molecular energy.
The equation used to express heat transfer by conduction is known as Fourier's Law and is expressed as:
q = k A dT / s (1)
where
q = heat transferred per unit time (W, Btu/hr)
A = heat transfer area (m2, ft2)
k = thermal conductivity of the material (W/m.K or W/m.oC, Btu/(hr oF ft2/ft))
dT = Temperature difference across the material (K or oC, oF)
s = material thickness (m, ft)
A plane wall constructed of solid iron with a thermal conductivity of 70 W/moC and a thickness of 50 mm with a surface area of 1 m by 1 m. The temperature is 150oC on one side and 80oC on the other.
The heat transfer can be calculated as:
q = (70 W/m.oC) (1 m 1 m) (150oC - 80oC) / (0.05 m)
= 98,000 W or 98 kW