Heat Transfer
A steel sphere of radius 0.1 m at 400°K is immersed in an oil at 300°K. If the centre of the sphere reaches 350°K in 20 minutes, how long will it take for a 0.05 m radius steel sphere to reach the same temperature (at the centre) under identical conditions ? Assume that the conductive heat transfer co-efficient is infinitely large.

5 minutes
20 minutes
10 minutes
40 minutes

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Heat Transfer
In a shell and tube heat exchanger,

The temperature drops in the two fluids and the wall are proportional to individual resistances
The temperature drop is inversely proportional to the resistance across which the drop occurs
The relationship is not generalised
There is no relationship between temperature drop and resistance

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Heat Transfer
In a heat exchanger, one transfer unit means

None of these
A section of the exchanger in which change in temperature of one stream equals the average driving force in the section
Both A and B
The size of the exchanger in which heat transfer rate is 1 kcal/hr

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Heat Transfer
Heat transfer by conduction results due to the transfer of free electrons, kinetic energy & vibrational energy from one molecule to another. Conduction heat transfer can not take place

Both B & C
From one part of a body to the another part of the same body
Between two bodies not in physical contact with each other
Between two bodies in physical contact with each other

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