Conduction

# Conduction - Consider a composite slab is made up out of...

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Conduction Consider the slab of material shown in Figure 17.3. The left end of the beam is maintained at a temperature T H ; the right end of the beam is maintained at a temperature T C . As a result of the temperature difference heat will flow through the slab, from its hot end to its cold end. Experimentally it is shown that the rate of heat transfer (Q/t) is proportional to the cross- sectional area of the slab, proportional to the temperature difference, and inversely proportional to the length of the slab Here, k is the thermal conductivity , which is a constant that depends on the type of material. Large values of k define good heat conductors. The thermal resistance R is related to the thermal conductivity k in the following manner Figure 17.3. Conduction. Thus, the lower the thermal conductivity of the material, the higher the thermal resistance R. From the definition of R it immediately follows that

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Unformatted text preview: Consider a composite slab is made up out of two different materials, with length L 1 and L 2 , and with thermal conductivity k 1 and k 2 , is placed between two heat baths (see Figure 17.4). Suppose that the temperature of the interface between the two slabs is equal to T x . The amount of heat flowing from T H to T x is given by The amount of heat flowing from T x to T C is given by Of course, the heat flowing through slab 1 must equal the heat flowing through slab 2. Thus Figure 17.4. Heat transport through a composite slab. This equation can be used to obtain the temperature at the interface between slab 1 and slab 2: The heat flowing through the slab can now be calculated easily A composite slab therefore has a thermal resistance equal to the sum of the thermal resistance of each of the individual slabs....
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## This document was uploaded on 11/25/2011.

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Conduction - Consider a composite slab is made up out of...

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