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

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

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Heat Transfer
In regenerative air preheater (as practised in heating of coke ovens), the heat is transferred

By direct contact of hot flue gas with air
Through a metallic wall
None of these
By heating an intermediate material (like chequor bricks) and then heating the air from this hot material

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