Heat Transfer
The Grashoff number is defined as the ratio of the

inertial to viscous forces.
buoyancy to viscous forces
buoyancy to inertial forces
buoyancy to surface tension forces

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Heat Transfer
Extended heat transfer surface like fins are used to increase the heat transfer rate. Fin efficiency is defined as the ratio of heat transferred across the fin surface to the theoretical heat transfer across an equal area held at the

Surrounding temperature
Temperature of the fin end
Constant temperature equal to that of the base
Average temperature of the fin

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Heat Transfer
A hollow sphere and a solid sphere of the same material and equal radii are heated to the same temperature. In this case,

Both B & C
Both will absorb equal amount of radiation from the surrounding in the beginning
The cooling rate will be the same for the two spheres and hence the two spheres will have equal temperatures at any instant
Both the spheres will emit equal amount of radiation per unit time in the beginning

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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
Less than that of the uninsulated steam pipe
Greater than that for uninsulated steam pipe

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