Question 71 : Prandtl number for most of dry gases is about
1. 150
2. 0.001
3. 70
4. 0.72
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Question 72 : In a heat exchanger with steam outside the tubes, a liquid gets heated to 45°C, when its flow velocity in the tubes is 2 m/s. If the flow velocity is reduced to 1 m/s, other things remaining the same, the temperature of the exit liquid will be
1. more than 45°C
2. equal to 45°C
3. initially decreases and remains constant thereafter.
4. less than 45°C
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Question 73 : The heat transfer co-efficient in film type condensation is __________ that for dropwise condensation
1. greater than
2. lower than
3. half
4. is same as
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Question 74 : Prandtl number is the reciprocal of
1. Thermal diffusivity x Mass diffusivity
2. Thermal diffusivity/Momentum diffusivity
3. thermal diffusivity x Momentum
4. Mass diffusivity x Momentum diffusivity
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Question 75 : Pick out the wrong statement.
1. The value of hydrostatic head increases with increase in vacuum in the effect in a multiple effect evaporator system.
2. Entering velocity of the liquid in the tubes of natural circulation evaporators is in the range of 0.3 to 0.9 metre/second.
3. Duhring's plot is used for calculating the concentration of solution.
4. In a multiple effect evaporation system, the number of effects is limited by the total boiling point rise.
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Question 76 : In Fourier's law, the proportionality constant is called the
1. thermal diffusivity
2. heat transfer co-efficient
3. thermal conductivity
4. Stefan-Boltzman constant
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Question 77 : Duhring's plot' is of use in
1. leaching
2. absorption
3. evaporation
4. extractive distillation
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Question 78 : Which has the lowest Prandtl number ?
1. Liquid metal
2. Aqueous solution
3. Lube oil
4. Water
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