Direction: Water (specifie heat, c = 4.18 kJ/kgK) enters a pipe at a rate 0.01 kg/s and a temperature of 20°C. The pipe, of diameter 50 mm and length 3 m, is subjected to a wall heat flux q"w in W/m2.
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If q"w = 5000 and the convection heat transfer coefficient at the pipe outlet is 1000 W/m2K, the temperature in °C at the inner surface of the pipe at the outlet is
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- 71
- 76
- 79
- 81
Correct Option: D
q"w = 5000 w/m2
h = 1000 w/m2k
Heat transfer through pipe wall, Q = q"w × surface area
= 5000 × π × d × l
= 5000 × 3.14 × 0.05 × 3 = 2355 W
Q = mCP (T0 –Ti), amount of heat gained by the water
2355 = 0.01 × 4180 (T0 – 20)
T0 = 76.33°C
q"w = h( Tso - To)
5000 = 1000 (Tso – 76.33)
Tso = 81°C
