A. If sufficient residence time (around 8 seconds) is not provided to the downcoming liquid in
the downcomer, it may entrain some vapour
B. The liquid head in the downcomer should not be greater than one half the plate spacing to
avoid flooding
C. The discharge end of the downcomer must project far enough into the tray liquid so that no
gas bubbles can enter the open end and by pass the bubble caps
D. None of these
Related Mcqs:
- Pick out the wrong statement pertaining to the design of a horizontal tube evaporator ?
A. It is unsuitable for concentrating those liquids, which form a scale or deposit salt
B. It is suitable for process, in which the final product is a liquor instead of solid
C. Its usual dimensions are: tube dia = 2-3 cms; evaporator body dia = 1-4 metres and evaporator
height = 2.5-4 metres
D. Liquor flows inside the tube, while the steam is outside submerging the tube - Pick out the wrong statement ?
A. In a flanged and standard dished head, the crown radius is ≤ shell outside diameter
B. In a flanged and shallow dished head, the crown radius is > shell outside diameter
C. Flat head covers are most suitable for larger vessels operating at very high pressure
D. Flanged only head is a type of flat head in which gradual change in the shape at the centre results in reduced local stresses - Pick out the wrong statement?
A. The tensile strength of a brittle material is less than its compressive strength
B. The compressive strength of a ductile material is less than its tensile strength
C. In a thick cylindrical shell, the hoop stress is maximum at the inner radius
D. The value of crushing load is more than that of buckling load for long columns - Pick out the wrong statement ?
A. Plate efficiency increases with increase in superficial vapour velocity till entrainment limit
B. Increase in depth of the liquid about the slots increases the plate efficiency, particularly if the liquid depth is < 1"
C. Too small a plate spacing can cause a low efficiency, if the vapour velocity is greater than the allowable value
D. None of these - Pick out the wrong statement?
A. In practical operation, distillation towers having diameter 3-6 metres equipped with bubble cap (round) size of 15 cms are used
B. Height of packing in a packed tower is about 3 times the column diameter for raschig rings and about 5 to 10 times the column diameter for saddle packing
C. In a sieve tray, the minimum hole diameter is equal to the tray thickness
D. In a stainless steel sieve tray, the minimum hole diameter is equal to 10 times the plate thickness - Pick out the wrong statement pertaining to the design of a long tube vertical evaporator ?
A. Tube dia is 3-6 cms, while tube length in 3-6 metres
B. Steam is fed to the shell, whereas the liquor is filled inside the tube
C. Liquor level is maintained at 1/3rd to 1/2 of the height of the tube
D. None of these - Pick out the wrong statement pertaining to the design of a basket type evaporator ?
A. It is used for high viscosity liquor having large rate of scaling
B. The tube bundle is suspended on bracket
C. There is no central downtake
D. Downtake is formed by the annular space between the bundle and the shell - Pick out the wrong statement pertaining to a shell and tube heat exchanger ?
A. The minimum value of baffle spacing is 50 mm
B. The maximum value of baffle spacing is equal to the I.D. of the shell
C. The maximum unsupported tube span is generally about 75 times tube diameter, but is reduced to about 60 times for aluminium, copper & alloys of these
D. Disk and doughnut baffle is the most commonly used baffle - Pick out the wrong statement pertaining to the use of valve tray, seive tray and bubble cap trays in continuous distillation column ?
A. Bubble 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
B. Murphree 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
C. Maintenance cost for valve and sieve trays are comparatively more than bubble cap tray due to their relatively complicated construction features
D. Valve 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 - Pick out the wrong statement about distillation operation__________________?
A. Distillation under vacuum is a substitute for steam distillation
B. In differential (simple) distillation, the vapour is removed as soon as it is formed without appreciable condensation
C. In 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
D. Flash distillation, differential distillation & steam distillation are all continuous distillation processes
