Heat Transfer

91. Critical value of the _________ number governs the transition from laminar to turbulent flow in free convection heat transfer.

1. Grashoff
2. Reynolds
3. Both 'a' & 'b'
4. Prandtl & Grashoff

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92. Crystal size in a continuous crystalliser depends upon the

1. Rate of heat transfer
2. Degree of turbulence
3. Degree of super-saturation
4. All (A), (B) and (C)

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93. Crystallisation of solids from a homogeneous solution is a/an _________ process.

1. Exothermic
2. Mildly endothermic
3. Highly endothermic
4. None of these

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94. Dittus-Boelter equation cannot be used for molten metals mainly due to its very low

1. Prandtl number
2. Grashoff number
3. Thermal conductivity
4. Viscosity

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95. Dittus-Boelter equation used for the determination of heat transfer co-efficient is valid

1. For fluids in laminar flow
2. For fluids in turbulent flow
3. When Grashoff number is very important
4. For liquid metals

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96. Double pipe heat exchangers are preferably useful, when

1. High viscosity liquid is to be cooled
2. Requirement of heat transfer area is low
3. Overall heat transfer co-efficient is very high
4. A corrosive liquid is to be heated

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97. Double pipe heat exchangers are used

1. When heat transfer area required is very high
2. When heat transfer area required is very low, i.e. (100-200 ft₂).
3. Because it occupies less floor area
4. Because it is less costly

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98. Dropwise condensation is promoted on a/an _________ surface.

1. Glazed
2. Oily
3. Coated
4. Smooth

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99. Dropwise condensation occurs on _________ surfaces.

1. Clean and dirt free
2. Smooth clean
3. Contaminated cooling
4. Polished

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100. Duhring‟s rule is important in solving problems on

1. Distillation
2. Crystallisation
3. Evaporation
4. Humidification

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