1. An electric immersion heater, 10 mm in diameter and 300 mm long, is rated at 550 W. If the heater is horizon- tally positioned in a large tank of water at 20°C, estimate its surface temperature. Estimate the surface temperature if the heater is accidentally operated in air at 20°C.
2. The maximum surface temperature of the 20-mm- diameter shaft of a motor operating in ambient air at 27°C should not exceed 87°C. Because of power dissi- pation within the motor housing, it is desirable to reject as much heat as possible through the shaft to the ambi- ent air. In this problem, we will investigate several methods for heat removal.
For the prescribed conditions. Thermophysical properties associated with the liquid state of the paraffin are k = 0.15 W/m · K, /3 = 8 X 10-4 K-1, p = 770 kg/m3, v = 5 X 10-6 m2/s, and a = 8.85 X 10-8 m2/s.