Section 5 Flashcards
__________ tower is the most suitable gas-liquid contacting device involving highly corrosive fluids.
Sieve plate
Packed
Bubble cap plate
None of these
Packed
At equal mass velocities, the values of film co-efficients for gases as compared to that for liquids are generally.
higher
lower
same
unpredictable
lower
The ratio of the largest load in a test to the original cross-sectional area of the test specimen is called the __________ stress.
yield point
breaking
ultimate
none of these
ultimate
Baffle spacing is generally __________ the I.D. of the shell.
more than
not greater than
not less than one fifth of
both (b) and (c)
both (b) and (c)
The wall thickness of thin cylindrical shell with hemispherical ends is __________ that of the spherical ends.
equal to
more than
less than
either (b) or (c); depends on maximum permissible internal pressure
more than
A ‘rupture disc’ is provided in chemical equipments as an accessory meant for
relieving excess pressure.
creating turbulence.
enhancing mixing rate.
avoiding vortex formation.
relieving excess pressure.
In a vertical short tube evaporator (Calendria type), the
tube dia of 2.5-7.5 cms, tube length of 75-200 cms and cylinderical drum dia of 1-6 metres are normally used.
area of central downtake is equal to 40 to 100% of total cross-sectional area of the surrounding tube.
liquor is inside the tube while the steam is outside the tube.
all (a), (b) & (c).
all (a), (b) & (c).
In a multipass shell and tube heat exchanger, the problem of differential expansion between the shell and tube passes is taken care of by using a
U-bend
floating head tube sheet
either (a) or (b)
neither (a) nor (b)
either (a) or (b)
In a shell and tube heat exchanger, the shortest centre to centre distance between the adjacent tubes is
called tube pitch.
called tube clearance.
always less than the diameter of the tube.
none of these.
called tube pitch.
Any shell opening greater than 5 cms for a storage tank must be reinforced for reason of
preventing the local overstressing of the shell around the opening.
reduction of discontinuity in shape at the junction.
making the joint leak proof.
none of these.
preventing the local overstressing of the shell around the opening.
Minimum tube pitch recommended for shell and tube heat exchangers is about __________ times the outside diameter of the tube.
1.25
1.75
2.5
3.5
1.25
Liquid redistribution should be done in a packed tower packed with raschig rings every 6 metres or __________ times the column diameter, whichever is lower.
2.5-3.0
5-7.5
10-12.5
15-20
2.5-3.0
Slope of countercurrent flow rotary drier is in the range of __________ meter/metre.
0 to 0.08
0 to 0.8
0 to 1.5
0 to 2.2
0 to 0.08
In case of saddle packing (e.g., berl and intralox saddles), the maximum size of the packing should not exceed __________ of the column diameter.
l/5th
l/15th
l/30th
l/50th
l/15th
Seamless pipe is made
from rolled strips formed into cylinders and seam-welded.
by extrusion & casting into static and centrifugal molds.
by forging a solid round, piercing it by simultaneously rotating & forcing it over a piercer point and further reducing it by rolling gas drawing.
both (b) and (c).
both (b) and (c).
The thermal stress in a metallic bar does not depend upon the
changes in temperature.
cross-sectional area.
both (a) and (b).
neither (a) nor (b).
cross-sectional area.
The minimum baffle height should be
equal to the impeller diameter.
twice the impeller diameter.
twice the tank diameter.
3/4 of the tank height.
twice the impeller diameter.
For turbulent flow (NRe > 2100) of low viscosity fluid (μ > 20cp) in steel pipes, the optimum inside pipe diameter is given by(where, Q = fluid flow rate, ft3/sec.ρ = fluid density, lb/ft3 μ = fluid viscosity, centipoise Di = optimum inside pipe diameter, inches)
Di, opt = 3.9 Q^0.45 ρ^0.13
Di, opt = 3.9 Q^0.45 . μ^0.95
Di, opt = 4.7 Q^0.36 . μ^3.2 ρ^0.13
Di, opt = 3 Q^0.36 . μ^0.88
Di, opt = 3.9 Q^0.45 ρ^0.13
To avoid the tearing off the plate of an edge, the margin (i.e., the minimum distance from the centre of the rivet hole to the nearest edge of the plate) should be equal to
0.5 d
d
1.5 d
2.5 d
1.5 d
The normal range of velocity of water in pipes is __________ m/sec.
0.1-0.5
1-2
10-50
15-30
1-2
Baffles are provided in a shell and tube heat exchanger to increase the turbulence and velocity of the shell side fluid. Which of the following shaped baffles does not fall in the category of transverse baffle ?
Segmental baffle
Flat plate extending across the wall
Disk type baffle
Helical type baffle
Flat plate extending across the wall
A certain pressure vessel manufacturer avoids doing reinforcements calculations for openings by always providing a reinforcing pad extending upto double the diameter of the opening and of the same material and thickness as that of the shell wall. If area compensation is accepted as a code guideline, his approach leads to safe design
only if the opening is on spherical vessel.
only if the opening is on a vertical cylinderical vessel.
only if the opening is on a horizontal cylinderical vessel.
irrespective of the shape of the vessel.
irrespective of the shape of the vessel.
In a __________ rivetted joint, the number of rivets decreases from the innermost row to the outermost row.
chain
diamond
zig-zag
none of these
diamond
Large process vessels operating under extreme temperature and pressure conditions are normally clad/ lined with materials like stainless steel, aluminium, nickel & its alloys, copper & its alloys and titanium. The cladding thickness is generally about __________ percent of the total thickness.
1 to 5
10 to 20
30 to 40
40 to 50
10 to 20
Heat transfer co-efficient for a horizontal condenser as compared to a vertical condenser operating under similar conditions is
same
less
about 3 times
about 0.33 times
about 3 times
Pick out the wrong statement pertaining to the design of the distillation column.
Generally, a skirt clerance of 0.5” to 1.5’ is recommended to prevent plugging of the slots by residue build up.
The purpose of the slot is to disperse the gas into the liquid in the form of small bubbles.
If sufficient slot area is not provided, the gas may pass through the skirt clearance.
none of these.
none of these.
The longitudinal stress induced in a thin walled cylinderical vessel under internal pressure is
pd/2t
pd/4t
pd/t
pd/8t
pd/4t
In distillation columns, bubble caps are held in place over trays by
rivets
a hold down bar
bolts
both (b) and (c)
both (b) and (c)
The buckling tendency of compression members is always in the direction of the
least radius of gyration.
axis of the load.
perpendicular to the axis of the load.
none of these.
least radius of gyration.
In case of plain carbon steel, butt welded joints are used for shell plate thickness ≤ __________ cms.
1.2
0.5
3.8
6.8
3.8
The average velocity in the tubes of a 1-4 heat exchanger is __________ times that in 1-1 heat exchanger having the same size & number of tubes and operated at same liquid flow rate.
2
1/2
4
1/4
4
Hoop (circumferential) stress induced in a thin walled ‘Horton Sphere’ used for the storage of liquid ammonia under pressure is
pD/2t
When one of the fluids is highly corrosive and has fouling tendency, it should
preferably flow inside the tube for its easier internal cleaning.
perferably flow outside the tube.
flow at a very slow velocity.
flow outside the tube, when the flow is counter-current and inside the tube when the flow is co-current.
preferably flow inside the tube for its easier internal cleaning.
The raio, (properller agitator dia)/(tank dia) is normally taken as
0.15-030
0.5-0.65
0.75-0.85
0.60-0.90
0.15-030
A/an __________ is used for changing the direction of a pipeline.
elbow
union
flange
disc compensator
elbow
Maximum plate efficiency is achieved in case of __________ flow.
split
cross
cascade
reverse
cross
The LMTD correction factor (FT) is defined as the
ratio of true temperature difference to the LMTD.
ratio of LMTD to the true temperature difference.
differenced of true temperature difference and the LMTD.
geometric mean of the true temperature difference and the LMTD.
ratio of true temperature difference to the LMTD.
The clearance between two tubes in a shell and tube heat exchanger is known as ‘ligament’, whose minimum value is __________ the outside diameter of the tube, but in no case it should be less than 4.5 mm.
equal to
half
one fourth
three fourth
one fourth
The ratio for the rate of washing to the final rate of filtration in a washing type of plate and frame filter is
0.25
0.50
0.75
1.25
0.25
Normally, the length to diameter ratio of rotary dryers varies form 4 to 10 and for its economic operation, the number of transfer units (NTU) for such dryers varies from
1.5-2.5
3.5-5.5
7.5-10.0
10-15
1.5-2.5
Value of Peclet number = 0, is the representative of
laminar flow.
complete back mixing.
plug flow.
eddy diffusivity = 0.
complete back mixing.
Poisson’s ratio of a material is the ratio of unit lateral strain to the unit axial elongation within its elastic limit. The value of Poisson’s ratio for structural and pressure vessel steel may be taken as
0.01
0.3
0.75
0.95
0.3
Removable connection of tubes to tube sheet is called
ferrule
socket
nipple
saddle
ferrule
Stress-strain diagram for low carbon steel/mild steel is shown below in the Fig.
The point ‘A’ on the Fig. represents the
breaking stress
ultimate stress
elastic limit
yield point
elastic limit
Typical static submergence for bubble cap plate column operating at atmospheric pressure may be around
2.5”
0.5”
5”
50% of the plate spacing
0.5”
In the allocated cap area, bubble caps are generally arranged on equilateral triangular pitch. Number of caps fixed on a plate is with a
clearance of 25-75 mm.
cap pitch of 1.3-2 times the cap diameter.
either ‘a’ or ‘b’.
neither ‘a’ nor ‘b’.
either ‘a’ or ‘b’.
The length of straight rectangular weir used on cross-flow trays is generally __________ the column diameter.
0.6-0.8 times
equal to
twice
2 ft irrespective of (for column > 3 ft diameter)
0.6-0.8 times
Le/D for couplings and unions would be
60
200
350
negligible
negligible
What is the slope of the operating line in the rectifying section of a distillation coloumn ?
0
∞
> 1
<1
<1
Stage efficiency for packed tower varies with the
type & size of packing.
fluid rates and fluid properties.
operating pressure and column diameter.
all (a), (b) and (c).
all (a), (b) and (c).
