9. Questions for Practice

  • The resistance wire of a 1200 W hair dryer is 80 cm long and has a diameter of 0.3 cm. Determine:

    • the rate of heat generation in the wire per unit volume, in W/cm\(^3\), and

    • the heat flux on the outer surface of the wire as a result of this heat generation.

    (Ans: 212 W/cm\(^3\); 15.9 W/cm\(^2\).)

  • A 2 kW resistance heat with thermal conductivity \(k=15\) W/(m.K), diameter \(D=4\) mm, and length \(L=0.5\) m is used to boil water. If the outer surface temperature of the resistance wire is (Ts=105\( \circ \) C), determine the temperature at the center of the wire. Assume steady state operation, with uniform generation of heat. (Ans: 126\( \circ \) C)