Section 2 Flashcards
Needle valves are generally not used for
very large diameter pipes.
high pressure throttling service.
very accurate flow control.
smaller sizes of pipe.
very large diameter pipes.
Height equivalent to a theoretical plate (HETP) is the height of packing that will give the same separation as one theoretical plate in gas-liquid mass transfer operations like distillation, absorption/stripping and humidification/dehumidification. HETP which is experimentally determined, depends upon the
flow rates of each fluid.
type and size of packing.
concentration of each fluid.
all a, b & c.
all a, b & c.
Pick out the wrong statement.
Safety valves are provided in heat exchangers for removal of non-conden-sables.
Liquid metals and dowtherm are used for very high temperature heating.
In a shell and tube heat exchanger, high pressure fluid is generally routed through the tube.
A loop seal or U-seal is provided in a vertical condenser sub-cooler to prevent quick draining of the condensate.
Safety valves are provided in heat exchangers for removal of non-conden-sables.
With increase in gas flow rate to fabric surface area ratio (Nm3/hr/m2 fabric surface area), the size & the cost of a bag filter
increases
decreases
remain unaffected
none of these
decreases
A head comprises of straight flange section, corner torus, section and central dished section. Crown radius and knuckle radius in a head is related respectively to the
central dished section and corner torus section.
corner torus section and central dished section.
central dished section and straight flange section.
straight flange section and corner torus section
central dished section and corner torus section.
Number of evaporators which can be used in service in a multiple effect evaporation system is limited by the
practical limit reached, due to low heat transfer rate because of inadequate temperature difference.
economic limit reached, when the plant cost exceeds the saving of steam.
both (a) & (b).
both (a) & (b).
Which of the following is used to set the diameter of the distillation column ?
Number of theorectical plates.
Static submergence.
Allowable vapour velocity.
Length of straight rectangular weir on cross-flow tray.
Allowable vapour velocity.
Ponchon Savarit method is based on the use of enthalpy concentration diagram, which contains the bubble point curve (saturated liquid curve), dew point curve (saturated vapour curve) and equilibrium tie lines. As compared to McCabe-Thiele’s method, this method
is more accurate in finding the number of equilibrium stages.
accounts for the enthalpy changes in the process.
facilitates direct calculation of heat load on reboiler & condenser from, the diagram used in this method.
all ‘a’, ‘b’ & ‘c’.
all ‘a’, ‘b’ & ‘c’.
The optimum size ratio for two mixed reactors in series depends on the kinetics of the reaction and the conversion level. For reaction orders more than one, the
equal sized reactors are the best.
smaller reactor should come first.
larger reactor should come first.
none of these.
smaller reactor should come first.
In a shell and tube heat exchanger, tube side __________ of the mass velocity.
heat transfer co-efficient is proportional to 0.8th power
pressure drop is proportional to the square
both ‘a’ & ‘b’
neither ‘a’ nor ‘b’
both ‘a’ & ‘b’
Which of the following is not a graphical method (but is an analytical method) for the calculation of theoretical number of stages in case of continuous binary distillation?
Sorel-Lewis method.
McCabe-Thiele’s method.
Ponchon-Savarit method.
none of these.
Sorel-Lewis method.
Saddle supports are used for supporting __________ vessels.
horizontal cylinderical
tall vertical
thick walled vertical
thick spherical
horizontal cylinderical
The diameter of a propeller agitator used in agitation tank ranges from __________ percent of the tank diameter and its peripherial speed is normally 300 to 500 metres/minute.
5 to 10
15 to 30
40 to 50
55 to 75
15 to 30
In packed towers provided with saddle packing, liquid redistributors are positioned at every __________ times column diameter or 6 metres whichever is less.
2-3
5-8
10-15
20-25
5-8
Optimum reflux ratio in a continuous distillation column is determined by the
maximum permissible vapour velocity.
flooding limit of the column.
total cost consideration (fixed cost of the column plus the cooling water & steam cost).
none of these.
total cost consideration (fixed cost of the column plus the cooling water & steam cost).
Cooling water fouling factors vary in the range of 0.001 to 0.003
(BTU/hr.ft2 . °F)^-1
(kcal/hr.m2 .°C)^-1
(W/m2.°K)^-1
(kcal/hr. m. °C)^-1
(BTU/hr.ft2 . °F)^-1
Minimum recommended baffle spacing in a shell and tube heat exchanger is about (where, D = shell diameter )
0.2 D
0.5 D
0.66 D
0.80 D
0.2 D
The maximum liquid gradient over a tray must not exceed
0.5” -1.25”.
2”-3.5”.
5”.
half the tray spacing.
0.5” -1.25”.
An underdesigned steam trap will
waste steam.
destroy itself of acceleration wear due to rapid recycling.
back up condensate and cause water hammer in steam line.
none of these.
back up condensate and cause water hammer in steam line.
The slope of the feed line in distillation opeartion is given by (where, q = fraction of the feed stream that is liquid.)
-q
-q/(1-q)
-q/(q-1)
none of these
-q/(1-q)
Speed of industrial paddle agitator ranges from __________ rpm.
1 to 5
20 to 100
500 to 750
1000 to 2000
20 to 100
__________ strain is measured using a ‘strain rosetter’.
Volumetric
Shear
Linear
none of these
Linear
Thin spherical shells subjected to internal pressure, develop __________ stresses.
radial
circumferential
both (a) & (b)
neither (a) nor (b)
radial
With increase in the reflux ratio for a fixed production from a continuous binary distillation column, the __________ decreases.
fixed charges initially
running cost of cooling water for condenser
vapour & liquid load both
running cost of steam for reboiler
fixed charges initially
The slope of operating line in the rectifying section of a distillation column is unity, if the reflux ratio is
0
∞
1
minimum
∞
Vertical vessels are not supported by
brackets
skirts
columns
saddles
saddles
With increase in pressure drop (for a given particle size), the dust collection efficiency of a cyclone separator will
increase
decrease
remain unaffected
increase or decrease depending on the nature of the dust.
increase
Spherical shaped pressure vessel is considered to be the most ideal, because it can
withstand higher pressure for a given metallic shell thickness.
be fabricated very easily.
be designed without wind load considerations.
be supported very easily.
withstand higher pressure for a given metallic shell thickness.
An adequate clearance between the tray and the shell wall of a distillation column is provided to
drain the liquid from the tray when the unit is not in operation.
allow for thermal expansion and facilitate installation.
avoid back-trapping.
none of these.
allow for thermal expansion and facilitate installation.
Overall tray efficiency of a distillation column is the ratio of the number of
overall gas transfer units to the number of ideal trays required.
ideal trays required to the number of real trays required.
real trays required to the number of ideal trays required.
none of these.
ideal trays required to the number of real trays required.
Pick out the wrong statement about the design of a sieve plate column.
An 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.
For 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.
Width 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.
Minimum 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.
Minimum 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.
Generally, no corrosion allowance in wall thickness of a part is required, if the thickness is more than __________ mm.
10
20
30
5
30
Multiple blade paddle agitator is used for mixing high viscosity liquids/paste in which the paddle diameter is commonly 0.8 times the tank diameter. However, the width of the blade is in the range of __________ times the paddle diameter.
0.1 to 0.25
0.3 to 0.5
0.5 to 0.6
0.65 to 0.80
0.1 to 0.25
In a __________ rivetted joint, the rivets in the various rows are opposite to each other.
zig-zag
chain
diamond
none of these
chain
Pick out the wrong statement:
The tensile strength of a brittle material is less than its compressive strength.
The compressive strength of a ductile materia] is less than its tensile strength.
In a thick cylindrical shell, the hoop stress is maximum at the inner radius.
The value of crushing load is more than that of buckling load for long colmns.
The value of crushing load is more than that of buckling load for long colmns.
Generally, elliptical dished heads
are manufactured on 2:1 ratio of major to minor axis and is recommended to be used for pressure vessels operating above a pressure of 1.5 MN/m2.
resist half the pressure rating compared to hemi spherical head provided on the cylindrical shell of the same thickness and diameter.
are approximately as strong as seamless cylindrical shell having the corresponding I.D and O.D.
all (a), (b) and (c)
all (a), (b) and (c)
Pick out the wrong statement pertaining to the comparative evaluation of performance of the packed tower and the plate tower.
Plate tower is perferred, if interstage cooling is required to remove heats of reaction or solution.
Plate tower is preferred over packed tower, if the operation involves liquids containing dispersed solids.
The total weight of a dry plate tower is usually much more than that of a dry packed tower designed for the same duty.
In operations involving large temperature changes. (e.g. distillation), plate towers are preferred over packed towers as the packing may be crushed due to large temperature changes.
The total weight of a dry plate tower is usually much more than that of a dry packed tower designed for the same duty
The circumferential (hoop) stress in a thin walled cylinderical vessel under internal pressure is
pd/2t
pd/4t
pd/t
pd/3t
pd/2t
Le/D for fully open gate valves would be
much more than that for fully open globe valves.
much less (say 2% than that for fully open globe valves).
around 7.
both (b) and (c).
both (b) and (c).
LMTD correction factor is used in heat exchanger design for
double pipe heat exchanger.
multipass shell and tube heat exchanger.
fouling fluids.
counter flow of hot and cold fluids.
multipass shell and tube heat exchanger.
Floating head heat exchangers are used for the
heat transfer between corrosive fluids.
cases where temperature difference between the shell and the tubes is more (>50°C).
co-current heat transfer systems.
counter-current heat transfer systems.
cases where temperature difference between the shell and the tubes is more (>50°C).
The most common standard size of bubble caps used in industrial operation is
1” dia cap with 0.5” dia riser.
6” dia cap with 4” dia riser.
8” dia cap with 1” dia riser.
4” dia cap with 8” dia riser.
6” dia cap with 4” dia riser.
Compensation against openings in process vessels for giving inlet and outlet connections, for providing sight glasses and manholes etc. is provided for strength and rigidity. The most efficient type of compensation is of __________ type.
nozzle or rim
flared out
fluid in
ring plate
nozzle or rim
In case of a continuous distillation column, increase in reflux ratio may result in the
lower fixed charges for the column.
greater cost for the reboiler heat supply.
greater cost for the condenser coolant.
all (a), (b) and (c).
all (a), (b) and (c).
In a distillation column, the minimum residence time for liquid in the downspout is about __________ seconds.
1
8
80
180
8
Thickness of the frame of a plate and frame filter as compared to that of plates is
less
same
more
either (a) or (b)
more
Which of the following factors affect the pressure drop in a co-current gas-liquid absorption packed tower ?
Size, shape, orientation and surface of the packing particles.
Density and viscosity of fluids.
Fluid flow rates.
All (a), (b) and (c).
All (a), (b) and (c).
The thickness of heat transfer plates used in the plate type heat exchanger ranges from __________ mm, pressed in a single piece provided with grooves & corrugations.
0.3 to 0.8
1.25 to 3.125
3.5 to 7.0
8-12
1.25 to 3.125
Rivets are generally specified by the
head diameter
shank diameter
overall length
none of these
shank diameter
Length to diameter ratio of most rotary driers is in the range of
1 to 2
4 to 10
10 to 20
20 to 30
4 to 10
