Chemical Engineering MCQs

Page No. 424

Pick out the wrong statement pertaining to a shell and tube heat exchanger ?


aThe minimum value of baffle spacing is 50 mm

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bThe maximum value of baffle spacing is equal to the I.D. of the shell

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cThe maximum unsupported tube span is generally about 75 times tube diameter, but is reduced to about 60 times for aluminium, copper & alloys of these

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dDisk and doughnut baffle is the most commonly used baffle

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Pick out the wrong statement. In an agitated vertical cylindrical reaction vessel, the___________________?


aRatio of liquid depth to tank diameter (i.e. the filling ratio) recommended for most purposes is 1

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bFilling ratio for dispersing gas in a liquid is 2 for sufficiently long contact period

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cFlat bottom and conical bottom vessels have low agitation efficiency for agitation of heavy solids in liquids

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dDished bottom vessel has very high power consumption

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Pick out the correct statement ?


aWhen highly corrosive fluids are to be handled, the plate towers prove to be cheaper and easier to construct than packed tower

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bPacked towers are generally preferred over plate towers, if the liquids have a foaming tendency

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cThe pressure drop through the packed towers is generally more than the pressure drop through plate towers designed for same duty

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dNone of these

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Pick out the wrong statement pertaining to the use of valve tray, seive tray and bubble cap trays in continuous distillation column ?


aBubble cap trays though most expensive are the best in situations, where low vapour rates is to be handled and a positive liquid seal is essential at all flow rates

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bMurphree efficiency of all the three trays are nearly equal, however the peak efficiency is generally higher for sieve and valve trays than the bubble cap

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cMaintenance cost for valve and sieve trays are comparatively more than bubble cap tray due to their relatively complicated construction features

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dValve trays have the highest turn down ratio (i.e. the ratio of the highest to the lowest vapour flow rates) and thus provide the maximum flexible operating range

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Pick out the wrong statement about the design of a sieve plate column ?


aAn increased weir height improves the tray efficiency at the cost of high plate pressure drop; optimum wear height being 40-90 mm for column pressure above atmospheric and 6-12 mm for vacuum columns

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bFor segmental downcomers, the chord length is 60-80% of the column diameter. An initial value of downcomer area of 12% is taken in the design

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cWidth of the calming section provided at the inlet and outlet sides of the plate is 75 mm for column diameter below 1.5 metres and 100 mm for larger diameter columns

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dMinimum recommended downcomer residence time for the disengagement of entrained vapour is the same for both foaming and non-foaming liquids, which is about 20 seconds

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Pick out the wrong statement?


aSafety valves are provided in heat exchangers for removal of non-condensable

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bLiquid metals and Dowtherm are used for very high temperature heating

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cIn a shell and tube heat exchanger, high pressure fluid is generally routed through the tube

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dA loop seal or U-seal is provided in a vertical condenser sub-cooler to prevent quick draining of the condensate

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Pick out the wrong statement pertaining to ‘Horton sphere’ used for the storage of liquid ammonia ?


aDiameter of Horton sphere is normally 6 to 25 metres and it is supported by 6 to 12 nos. tubular or rolled section column

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bThickness of spherical shell is half that of the cylindrical vessel under same operating pressure condition. Besides, the ratio of surface area to volume is less for sphere than any other shape; hence insulation required is less

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cHorton sphere is used for the storage of gases and volatile liquid at a moderate pressure of 1 to 10 kg/cm2

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dHorton sphere is used for the storage of liquid at sub-zero temperature at very high pressure upto 200 kg/cm2

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Pick out the wrong statement about distillation operation__________________?


aDistillation under vacuum is a substitute for steam distillation

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bIn differential (simple) distillation, the vapour is removed as soon as it is formed without appreciable condensation

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cIn flash (equilibrium) distillation, a definite fraction of liquid is vaporised in such a way that the evolved vapour & residual liquids are in equilibrium with each other

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dFlash distillation, differential distillation & steam distillation are all continuous distillation processes

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Pick out the correct statement ?


a1 kcal/hr.m.°C is equal to 1 BTU/hr. ft.°F

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bIn steady state heat conduction, the only property of the substance which determines the temperature distribution, is the thermal conductivity

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cIn unsteady state heat conduction, heat flows in the direction of temperature rise

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dIn heat transfer by forced convection, Grashoff number is very important

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Pick out the wrong statement ?


aHeat transfer from a hot body to cold body by the emission of heat waves is called radiation

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bFilmwise condensation takes place on non-wettable surfaces

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cThe boiling point of a solution is affected by liquid head as well as boiling point elevation

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dNone of these

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