NE 342 Examination #3 Name:____________________________________
Opportunity #1: A wire is heated by electrical current and rejects this energy to air as
shown. The copper wire is generating 10 Watts per foot of length. One foot is 0.305 m.
a.
Find the energy dissipation per unit volume in the copper wire. 15pt
b. Find the temperature gradient, dT/dr, in the insulation at r equal to 2 mm. 15pt
c. Sketch the temperature distribution in the system from the centerline, r equal zero,
to the air. 20pt
Opportunity #2: Consider the engine left to cool in air after a drive to work.
a. Evaluate the Biot number, hL/k, for this situation. 20 pts
b. How long will it take the engine to cool to 40 C if the initial temperature after
stopping is 90 C? 3 pts