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


bAt low velocity


cWhen fluid flows past a smooth surface


dNone of these



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


bCondensate is corrosive in nature


cLower pressure drop through the exchanger is desired


dTemperature of the incoming vapor is very high



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


bCube


cSphere


dAll will cool at the same rate


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


b10 minutes


c20 minutes


d40 minutes


View Answer 5 minutes

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


aIncreases the rate of condensation


bDecreases thermal resistance


cIs desirable to increase the film co-efficient


dNone of these


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


b2K/h0


chi/K


d2hi/K


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


bCounter flow with process stream on tube side


cParallel flow with process stream on shell side


dParallel flow with process stream on tube side



Natural convection is characterised by__________________?


aGrashoff number


bPeclet number


cReynolds number


dPrandtl number


View Answer Grashoff number

The unit of heat transfer co-efficient is_________________?


aBTU/hr. ft2°F


bBTU/hr. °F. ft


cBTU/hr. °F


dBTU/hr. ft


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


b34.4


c26.8


d25


View Answer 34.4

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