Heat Transfer

451. When does the heat generated by fluid friction becomes appreciable compared to the heat transferred between the fluids?

1. At high fluid velocity
2. At low velocity
3. When fluid flows past a smooth surface
4. None of these

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452. When the ratio of the Grashoff number and to the square of Reynolds number is one, the dominant mechanism of heat transfer is:

1. Free convection
2. Entry length problem in laminar forced conduction (developing thermal boundary layer)
3. Mixed convection (both free and forced)
4. Forced convection

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453. When vaporisation takes place directly at the heating surface, it is called

1. Film boiling
2. Nucleate boiling
3. Vapour binding
4. None of these

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454. When vaporisation takes place through a blanketting film of gas, the phenomenon is termed as _________ boiling.

1. Pool
2. Nucleate
3. Transition
4. Film

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455. When warm and cold liquids are mixed, the heat transfer is mainly by

1. Conduction
2. Convection
3. Radiation
4. Both (A) & (C)

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456. Which area is used in case of heat flow by conduction through a cylinder?

1. Logarithmic mean area
2. Arithmetic mean area
3. Geometric mean area
4. None of these

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457. Which characteristic of a fluid is not important in deciding its route in a shell and tube heat exchanger?

1. Corrosiveness
2. Fouling characteristic
3. Viscosity
4. None of these

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458. Which has the lowest Prandtl number?

1. Liquid metal
2. Aqueous solution
3. Water
4. Lube oil

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459. Which is the best tube arrangement (in a shell and tube heat exchanger) if the fluids are clean and non-fouling?

1. Square pitch
2. Triangular pitch
3. Diagonal square pitch
4. None of these

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460. Which is the most suitable for the concentration of foamy & frothy liquors?

1. Agitated film evaporator
2. Long tube vertical evaporator
3. Open pan evaporator
4. None of these

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