Heat Transfer
The thermal boundary layer at NPr > 1

Is thinner than hydrodynamic boundary layer
Is thicker than hydrodynamic boundary layer
And the hydrodynamic boundary layer are identical
Disappears

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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

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

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