Heat Transfer
Three solid objects of the same material and of equal mass-a sphere, a cylinder (length = diameter) and a cube are at 500°C initially. These are dropped in a quenching bath containing a large volume of cooling oil each attaining the bath temperature eventually. The time required for 90% change in temperature is the smallest for

Cube
Sphere
Equal for all the three
Cylinder

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Heat Transfer
Prandtl number is the ratio of

Thermal diffusivity to mass diffusivity
Thermal diffusivity to momentum diffusivity
Momentum diffusivity to thermal diffusivity
Momentum diffusivity to mass diffusivity

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Heat Transfer
In a gas-liquid shell and tube heat exchanger, the

Gases under high pressure are routed through the tube side, because high pressure gases are corrosive in nature
All of these
Gases to be heated/cooled is normally routed through the shell side, because the corrosion caused by the cooling water or steam condensate remain localised to the tubes
Presence of a non-condensible gas decreases the condensing film co-efficient

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Heat Transfer
In a heat exchanger, one transfer unit means

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

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