#### Convective Heat Transfer over a Flat Plate: Example Problems

Try to solve these problems before watching the solutions in the screencasts.

##### Example Problem 1

A simplified version of a solar cell consists of a very thin semiconducting silicon layer. A layer of protective glass is glued to the silicon by an adhesive. The solar cell is 0.5 m long and 0.2 m wide. The air temperature is 25°C. It blows over the solar cell at a speed of 5 m/s. Calculate the average heat transfer coefficient, *h̅*. Report your answer in units of W/m^{2}-K.

**NOTE:** In this screencast, the kinematic viscosity is off by an order of magnitude. The number used is 1.7e^{-6} m^{2}/s, but it’s actually more like 1.7e^{-5} m^{2}/s for air. This makes the Reynolds number 10x smaller and makes the actual flow laminar. The general procedure remains the same, but one should select a laminar flow correlation for this problem. The value computed is: h_bar = 38.6 W/m^{2}-K, but 12 W/m^{2}-K is more realistic.

##### Example Problem 2

Calculate the surface temperature of a motorcycle cooling fin attached to a motorcycle engine traveling at U_{∞} = 40 km/h (25 mph). The ambient air is T_{∞} = 27°C (81°F). Model the fin as a flat plate that is L = 5 cm long. To simplify the problem, assume the temperature of the fin is uniform along its length. Start by calculating h̅ using an appropriate correlation. Then calculate q′, which is the heat transferred per unit length of the fin, in units of W/m, which you can use in this expression: q′ = 2h̅L(T_{s }− T_{∞} ). The factor of 2 is used because heat is transferred from both sides of the fin.