This is the first step in a two-step problem. Assume that a long aluminum extrusion having dimensions shown in the following figure has been heated uniformly to 150°C. It is necessary to determine the time required for this extrusion to cool to a maximum temperature of 40°C in ambient still air with a temperature of 20°C. For the initial estimate, use an average heat transfer coefficient from Table 1.3. After you have studied convection heat transfer, you will be asked to reconsider this problem with convection heat transfer coefficients calculated from information learned in Chapter 6.

Data from in Table 1.3

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4 cm 1 cm. 4 cm 1 cm