Chemical Engineering MCQs

Page No. 452

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


aAt high fluid velocity

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bAt low velocity

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cWhen fluid flows past a smooth surface

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dNone of these

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Condensing film co-efficient for steam on horizontal tubes ranges from 5000 to 15000 Kcal/hr.m2.°C. Condensation of vapor is carried out inside the tube in a shell and tube heat exchanger, when the_________________?


aHigher condensing film co-efficient is desired

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bCondensate is corrosive in nature

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cLower pressure drop through the exchanger is desired

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dTemperature of the incoming vapor is very high

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A cube, sphere & a thin circular plate (all having same mass and made of same material) are all heated to 300°C and allowed to cool in natural air. Which one will cool the slowest ?


aCube

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bCube

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cSphere

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dAll will cool at the same rate

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View Answer Sphere

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 ?


a5 minutes

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b10 minutes

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c20 minutes

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d40 minutes

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View Answer 5 minutes

Presence of a non-condensing gas in a condensing vapour___________________?


aIncreases the rate of condensation

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bDecreases thermal resistance

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cIs desirable to increase the film co-efficient

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dNone of these

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View Answer None of these

The critical radius of insulation for cylindrical pipe is (where, hi = heat transfer coefficient at inside of the pipe) ?


aK/h0

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b2K/h0

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chi/K

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d2hi/K

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View Answer K/h0

A process stream of dilute aqueous solution flowing at the rate of10 Kg.s-1 is to be heated. Steam condensate at 95°C is available for heating purpose, also at a rate of 10 Kg.s-1. A 1 – 1 shell and tube heat exchanger is available. The best arrangement is_______________?


aCounter flow with process stream on shell side

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bCounter flow with process stream on tube side

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cParallel flow with process stream on shell side

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dParallel flow with process stream on tube side

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Natural convection is characterised by__________________?


aGrashoff number

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bPeclet number

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cReynolds number

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dPrandtl number

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View Answer Grashoff number

The unit of heat transfer co-efficient is_________________?


aBTU/hr. ft2°F

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bBTU/hr. °F. ft

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cBTU/hr. °F

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dBTU/hr. ft

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View Answer BTU/hr. ft2°F

In Joule’s experiment, an insulated container contains 20 kg of water initially at 25°C. It is stirred by an agitator, which is made to turn by a slowly falling body weighing 40 kg through a height of 4 m. The process is repeated 500 times. The acceleration due to gravity is 9.8 ms-2. Neglecting the heat capacity of agitator, the temperature of water (in °C) is________________?


a40.5

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b34.4

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c26.8

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d25

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View Answer 34.4

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