Heat Transfer
A long iron rod initially at a temperature of 20°C has one end dipped in boiling water (100°C) at time, t = 0. The curved surface of the rod is insulated so that heat conduction is one dimensional in the axial direction. The temperature at a distance 100 mm from the dipped end becomes 40°C at time, t = 200 s. The same temperature is achieved at a distance of 200 mm from the dipped end at time

t = 283 s
t = 400 s
t = 356 s
t = 800 s

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Heat Transfer
A 10 cm dia steam pipe, carrying steam at 180°C, is covered with an insulation (conductivity = 0.6 W/m.°C). It losses heat to the surroundings at 30°C. Assume a heat transfer co-efficient of 0.8 W/m².°C for heat transfer from surface to the surroundings. Neglect wall resistance of the pipe and film resistance of steam. If the insulation thickness is 2 cms, the rate of heat loss from this insulated pipe will be

Less than the steam pipe with 5 cms insulation
Equal to that of the uninsulated steam pipe
Greater than that for uninsulated steam pipe
Less than that of the uninsulated steam pipe

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Heat Transfer
Water always boils when its

Vapour pressure equals 76 cm of Hg
Saturated vapour pressure is less than the atmospheric pressure
Temperature reaches 100° C
Saturated vapour pressure equals the external pressure on its surface

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