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A thin-walled metal tank of surface area 5 m² is filled with water and houses a 1 kW immersion heater. The tank is wrapped in a 4 cm thick layer of insulation (thermal conductivity 0.2 W/m/K). In the steady state the outer surface of the insulation is at 25 deg C. Find the temperature of the tank wall.

1. 45 deg C
2. 65 deg C
3. 75 deg C
4. 85 deg C

Correct answer: 65 deg C

Solution

deltaT = P d/(k A) = 1000*0.04/(0.2*5) = 40 deg C, so the tank is at 25 + 40 = 65 deg C.

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