PROBLEMS

5.2-1.

Temperature Response in Cooling a Wire. A small copper wire with a diameter of 0.792 mm and initially at 366.5 K is suddenly immersed in a liquid held constant at 311 K. The convection coefficient h = 85.2 W/m2 · K. The physical properties can be assumed constant and are k = 374 W/m · K, cp = 0.389 kJ/kg · K, and ρ = 8890 kg/m3.

  1. Determine the time in seconds for the average temperature of the wire to drop to 338.8 K (one-half the initial temperature difference).

  2. Do the same but for h = 11.36 W/m2 · K.

  3. For part (b), calculate the total amount of heat removed for a wire 1.0 m long.

A1: Ans. (a) t = 5.66 s
5.2-2.

Quenching Lead Shot in a Bath. Lead shot having an average diameter of 5.1 mm is at an initial temperature of 204.4°C. To ...

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