Question

A composite refrigerator wall is composed of 2 in of cork board sandwiched between a 1/2 in thick layer of oak and a 1/32 in thick layer of aluminum lining on the inner surface. The average convection heat transfer coefficients at the interior and exterior wall are 4 and 1.5 Btu/h ft^2 F, respectively. Draw the thermal circuit.

Answer 1

Step 1: convert units.

2 in = 0.17 ft

1/2 in = 0.042 ft

1/32 in = 0.0026 ft

Step 2: Draw the problem

Remember, heat comes from the external wall to the inner wall, as follows:

Step 3: Draw the thermal circuit. So, you'll have different temperatures in points 4 to 1. Every change in temperature is a node and what happens in between are resistences. Resistence is given by the thick (delta x) of the layer divide by the k coefficient and the area. When doing your calculation remember that the area is not what your seeing in front, but it is the larger part of the wall. For example, if the wall is 10 ft high, 5 ft width and has a thick of 2 ft (delta x), the area is: 10 ft * 5 ft.

Hope this helps!