Design 2 Flashcards
The minimum plate spacing in most of the pertroleum refinery distillation columns (of dia > 3 ft) is normally __________ inches.
18
Joint efficiency (J) for a seamless pipe is
1
For a given design of bubble cap, the number of bubble caps to be used per tray is set by the
allowable gas velocity through the slots.
The shell side pressure drop in a shell and tube heat exchanger is maximum for __________ baffle.
orifice
The function of manholes provided in the shell of a distillation column is to
give access to the individual trays for cleaning, maintenance and installation.
Back-trapping in a distillation column results due to
excessive liquid gradient over the tray.
For a cylinderical vessel of moderate height, the weld joint efficiency for joints parallel to the cylinderical axis is given as 1.0, while for joints along the girth (circumference) it is given as 0.8. In calculating the shell wall thickness using code formula for an internally pressurised cylinderical vessel, what value of weld joint efficiency should be used ?
0.8
Diameter of bubble caps used in high pressure columns is __________ as compared to that used in identical vacuum columns.
more
The ideal size of round bubble caps to be used in industrial distillation column having a diameter of 3-6 metres is __________ cms.
15
Lap joints are preferred for plates having thickness __________ mm.
> 3
In a distillation column, minimum clearance to be maintained betweeen the overflow weir and the last row of the bubble caps is __________ cms.
7.5
Which of the following lengths of heat exchanger tubes are normally not used in practice ?
10 metres
A pipe is generally made of circular cross-section, because a circular cross-section has the
both (a) & (b).
higher structural strength.
lowest surface area requirement for a given volume.
In case of a shell and tube heat exchanger, the effect of L/D on inside film heat transfer co-efficient (hi) vanishes after a Reynold number of
10000
Equivalent diameter for heat transfer calculation for a duct of square cross-section having each side as ‘d’ will be
d
A cylindrical storage tank can have a self supported conical roof,
if its diameter is less than 15-20metres.
For high pressure process equipments/vessels, the connected nozzle should be
flanged
Smoker’s equation for the calculation of number of equilibrium stages in a continuous binary distillation column is used, when the
relative volatility is close to one (e.g., separation of close boiling isomers).
Column support for the roof of cylindrical storage tank must be provided for
large diameter tanks.
For a cylinderical internally pressurised vessel, which of the following closure types would withstand highest pressure, if each closure is of the same material and thickness ?
ellipsoidal (2 : 1)
In inclined long tube vertical evaporators, the tubes are inclined at an angle of
45°
In a continuous distillation column, the optimum reflux ratio ranges from __________ times the minimum reflux ratio.
1.1 to 1.5
The wall thickness for a large high pressure pipeline is determined by the consideration of the
circumferential pipewall tension.
In the case of a shell and tube heat exchanger, the logarithmic mean temperature difference
is always less than arithmetic average value.
Skirt support is the most suitable for supporting __________ vessels.
tall vertical
Baffles may be eliminated for
high viscosity liquids (> 600 poise).
Generally, as the length of the liquid path on a tray is increased beyond 5 ft, the overall column efficiency
increases
In packed absorption tower, onset of flooding usually occurs at a pressure drop of about __________ mm of water column per metre height of packing.
50-75
For pipe flows, head is proportional to __________ at constant capacity (where D = pipe diameter ).
1/D5
Friction factor for turbulent flow in a new pipe is given by
f=0.04/(Re)^0.16
The minimum tray spacing in distillation column of diameter less than 3 ft is normally __________ inches.
6
Oxygen carrying pipelines in chemical industries are coloured with __________ colour.
blue
Normally, the ratio of the total riser area to the tower cross sectional area (for bubble cap towers of diameter more than 3 ft) is around
0.1-0.2
Pick out the wrong statement about the design of seive plate column and the bubble cap column.
Weir height for a bubble cap plate column is the same as that for a seive plate column.
Maximum size of the raschig rings used in a packed tower is about __________ of the coloumn diameter.
1/30th
Longitundinal stress induced in a thin walled cylindrical storage vessel is
pD/4t
The type of stress developed in a metallic bar on subjecting it to a change in temperature without allowing it to be deformed is __________ stress.
thermal
The safe distance of habitation from a hazardous chemical plant (TLV of its product < 1000 ppm) should be about __________ kms.
25
Corrosion allowance in the design of pressure vessel/chemical equipment is not necessary, if
both(b) & (c).
wall thickness is > 30 mm.
material of construction is high alloy steel.
Maximum allowable vapour velocity in a bubble cap tower is determined by the
entrainment considerations.
Pick out the wrong statement pertaining to a shell and tube heat exchanger.
Disk and doughnut baffle is the most commonly used baffle.
Normally, the plate thickness of the bottoms and roofs of vertically cylindrical storage vessels as compared to that of the cylindrical shell is
less
The practical representative values of HETP for a number of commercial operations lies within a range of __________ metre.
0.4-0.9
Of the pressure vessels, with same thickness but different diameters, which one withstands higher pressure ?
Smaller dia vessel.
Reflux ratio variation in a distillation column is between
minimum and infinity
Width and depth of grooves in the tube sheet holes normally are __________ inch respectively.
1/8 and 1/64
In condenser, the cooling water is passed in the tube side in a pass arrangement, because
it reduces heat transfer area.
In packed towers provided with pall rings liquid redistributors are positioned at heights of every 6 metres or 5-10 times the column diameter, whichever is less. Maximum size of the pall rings should not exceed __________ of the column diameter.
1/10-1/15th
Height of the flights in the rotary drier is in the range of
0.08 to 0.12 d
Vapor velocity in a distillation column for non-foaming mixture is in the range of __________ times the flooding velocity.
0.6 to 0.7
Cylindrical storage tanks used for the storage of volatile liquids (e.g., naphtha) have __________ roofs.
floating
Pick out the wrong statement.
Plate efficiency increases with increase in superficial vapour velocity till entrainment limit.
Increase in depth of the liquid about the slots increases the plate efficiency, particularly if the liquid depth is < 1”.
Too small a plate spacing can cause a low efficiency, if the vapour velocity is greater than the allowable value.
none of these.
none of these.
Pick out the wrong statement.
In practical operation, distillation towers having diameter 3-6 metres equipped with bubble cap (round) size of 15 cms are used.
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.
In a seive tray, the minimum hole diameter is equal to the tray thickness.
In a stainless steel seive tray, the minimum hole diameter is equal to 10 times the plate thickness.
In a stainless steel seive tray, the minimum hole diameter is equal to 10 times the plate thickness.
In the downcomer of a distillation column, the minimum recommended residence time is about __________ seconds.
2.5
5
For identical situation, condensing film coefficient in case of a horizontal condenser is almost __________ the value expected in case of vertical condenser.
thrice
Diameter of rivet hole (d, mm) and the plate thickness (t, mm) are related by Unwin’s formula as
d = 1.6 sqrt(t)
A binary liquid azeotropic mixture has boiling point lower than either of the components, when it shows __________ deviation from Raoult’s Law.
positive
In which of the following evaporators, steam is fed inside the tube while the liquor is outside the tube ?
Horizontal tube evaporator
A single pass air heater is connected to a two pass unit. For the air flow rate and other conditions remaining the same, the film heat transfer co-efficient for air will vary in the ratio of
2^0.8
In a multipass shell and tube heat exchanger, the baffles on shell side is primarily provided for
creating turbulence.
For turbine agitator, the impeller diameter is about
0.3 to 0.5 d
In a shell and tube heat exchanger having triangular pitch, the shell side equivalent diameter is given by
4(0.86P^2- pid^2/4)/pid
If a single tube pass heat exchanger is converted to two passes; for the same flow rate, the pressure drop per unit length in tube side will __________ times.
increase by 2^1.6
Pick out the wrong statement pertaining to the design of a long tube vertical evaporator.
Tube dia is 3-6 cms, while tube length in 3-6 metres.
Steam is fed to the shell, whereas the liquor is filled inside the tube.
Liquor level is maintained at l/3rd to 1/2 of the height of the tube.
none of these.
none of these.
Which of the following is the most common type of baffle used in industrial shell and tube heat exchanger ?
25% cut segmental baffle.
What is the minimum recommended ligament for square pitch arrangement in case of heat exchangers ?
6.5 mm
Pick out the correct statement
Centre to centre distance between two consecutives rivets in a row is called the pitch.
A rivetted joint made in overlapping plates is called butt joint.
Hole size drilled in rivetted plates is less than the actual size of the rivet.
none of these.
Centre to centre distance between two consecutives rivets in a row is called the pitch.
Safety valves are provided in chemical equipments to guard against excessive
pressure/pressure fluctuation
The equivalent diameter for pressure drop is __________ that for heat transfer.
not related with
Most of the storage vessels/tanks are made cylindrical, because of the fact that a cylinder
both (a) and (b).
has greater structural strength.
is easy to fabricate.
The distance between the top of the slots and the liquid surface when the static liquid is just ready to flow over the overflow weir is called
static submergence
Liquid gradient over the tray results due to the
resistance offered to flow of liquids by caps & risers and the flow of gas.
The centre to centre distance between two consecutive baffles in a shell and tube heat exchanger is called the baffle pitch or baffle spacing, which is more than 1/5th the I.D. of the shell. Which of the following is not a function of the baffles ?
To increase the tube side heat transfer co-efficient by inducing turbulence.
A high vapour velocity is required for high plate efficiency in a seive plate coloumn. The satisfactory value of operating vapor velocity for design purpose in seive plate column is about __________ percent of the flooding velocity.
80
The approximate liquid depth in an agitation tank is equal to (where, d = tank diameter)
d
Baffle width is normally taken as __________ times the tank diameter.
0.1-0.12
A cylinderical pressure vessel of volume 6 πm3 has to be designed to withstand a maximum internal pressure of 10 atm. The allowable design stress of the material is 125N/mm2 and corrosion allowance is 2 mm. The thickness of the vessel for a length/diameter ratio of 3 will be close to
10 mm
Which of the following packing materials provides for maximum mass transfer ?
Cross-partition rings.
__________ of water makes it a widely used coolant in heat exchangers.
High specific heat
The equivalent diameter for fluid flow through a channel of constant non-circular cross section of area ‘A’ is given by (where, P = perimeter of the channel in contact with the fluid)
4 A/P
Fouling factor must be included in the calculation of over all design heat transfer coefficient, when the liquid
containing suspended solids flows at low velocity.
Lug support is meant for supporting __________ vessels.
small
Overall mass transfer co-efficient in case of absorption of __________ in water is based on the gas film co-efficient only, as the mass transfer process is gas film (phase) controlling.
NH3
Which tube arrangement in a heat exchanger would facilitate highest heat transfer rate ?
Triangular pitch.
In case of 1.5” heat exchanger tubes, the inside flow area __________ with decrease in BWG.
decreases
Cylindrical pressure vessels in horizontal condition is generally supported on a __________ support.
saddle
Pressure drop per tray in the atmospheric distillation column is about __________ psi.
0.07 - 0.12
Welded joint efficiency in the design of chemical process equipment is taken as
0.85
The thickness of segmental baffles (25 -35% cut truncated plates usually) is generally __________ the tube wall thickness.
twice
The safe height (h) to diameter (d) ratio (i.e., h/d) for liquid/petro fuel storage tank of capacity more than 45 kilolitres is less than
1
For given number of passes, pitch & tube diameter, the maximum number of tubes that can be accommodated in a shell of tripled inside diameter will be __________ times.
considerably more than 9
The ratio of linear stress to linear strain is termed as the
modulus of elasticity
__________ head is the most economical for cylindrical vessels designed for operating at high pressure (> 15 atm.).
Ellipsoidal
Bubble cap plate column is
a finite stage contactor.
In seive plate column, holes are drilled or punched in sizes ranging from 2.5 to 12 mm (5 mm being widely used). The hole pitch is normally __________ times the hole diameter to give the required hole area.
2.5 to 4.0
Pick out the wrong statement.
Rivetting provides a permanent fastening method.
The joint made by overlapping of one plate over the other, and then rivetting the two plates together with two rows of rivets is called ‘double rivetted butt joint’.
Shank diameter of the rivets should be less than the size of the hole drilled in the plate for rivetting.
The efficiency of a rivetted joint is the ratio of the strength of the rivetted joint to the strength of the solid plate.
The joint made by overlapping of one plate over the other, and then rivetting the two plates together with two rows of rivets is called ‘double rivetted butt joint’.
The force due to wind load acting on a tall vessel depends upon its
shape.
outside diameter.
height.
all (a), (b) & (c).
Bubble cap diameter used for the distillation column having diameter ranging from 1.5 to 4.5 metres is about __________ mm.
100
Power required for agitation depends upon the
height & properties of the liquid.
agitator type & speed of agitation.
size of agitator & the tank.
all (a), (b) and (c).
Tube height in a calendria type evaporator is normally less than __________ metres.
2
Pick out the wrong statement.
Lug supports are less expensive than other type of supports.
A pipe is differentiated from a tube by the fact that a pipe has a greater wall thickness compared to the tube.
A reducer is used to change the direction of a pipe in a straight run.
The method of fixing tubes to a tube sheet by expanding is called ‘tube rolling’.
A reducer is used to change the direction of a pipe in a straight run.
For a 25 mm hole drilled in plates to be rivetted, the shank diameter of the rivet should be __________ mm.
23
Optimum economic pipe diameter for fluid flow is determined by the
total cost considerations (pumping cost plus fixed cost of the pipe).
total cost considerations (pumping cost plus fixed cost of the pipe).
250 to 500
Vertical storage vessels are never supported by __________ support.
saddle
In a double pipe (concentric) heat exchanger, the hydraulic radius for heat transfer (for a fluid flowing through the annulus) would be
more than that for fluid flow.
Elastic failure of a material occurs, when the tensile stress equals yield strength, yield point or the elastic limit. Also, the elastic failure occurs according to maximum strain theory, when the maximum tensile strain equals (where, σ = yield strength and E = modulus of elasticity)
σ/E
In a pressure vessel containing multiple openings of various dimensions at different parts, stress concentration at the edges of the opening is maximum which becomes negligibly small beyond the area covered by __________ times the hole diameter.
two
What is the slope of the feed line, if the feed to a distillation column is a saturated liquid ?
∞
Liquid gradient over a tray can be minimised by
providing a higher skirt clearance or a higher weir.
decreasing the number of rows of caps through which the liquid flows or by decreasing the velocity of liquid flow past the caps or by reducing the distance along the tray through which the liquid must flow.
using split flow, radial flow or cascade flow for column diameter large than 4 ft.
all (a), (b) and (c).
In a shell and tube heat exchanger for a given heat transfer surface area, smaller diameter tubes are favoured as compared to larger diameter ones ; because the smaller diameter tubes
can be fitted into a smaller shell diameter hence the cost of the heat exchanger would be less.
for 90° elbow (medium radius) and 90°square elbow would be respectively around
25 and 60
__________ heat exchanger is also known as ‘hair pin type’ exchanger,
Double pipe
What is the value of ‘q’ for saturated vapor feed to a distillation column ?(where q = fraction of the feed stream that is liquid.)
0
In hydrostatic testing of welded pipe (for leakage, strength etc.) the ratio of minimum hydrostatic test pressure to internal design pressure is around
1.5
Frame thickness in the plate and frame filter press is normally in the range of __________ inches.
0.25 to 8
Cylinderical shell thickness of rotary drier is generally __________ mm.
6-8
The ratio of lateral strain to linear strain is termed as the
Poisson’s ratio
The distance between the centre of a rivet hole to the nearest edge of the plate is called
margin
Mc Cable Thiele method used for finding theoretical stages in a distillation column assumes that the
sensible heat differences are small, because the temperature changes from tray to tray is small.
Trouton’s rule is applicable.
liquid/vapor loading across the column remains constant.
all (a), (b) and (c).
A minimum clearance of about __________ mm is maintained between the distillation column wall and the bubble cap.
38
Pick out the wrong statement.
If sufficient residence time (around 8 seconds) is not proivided to the downcoming liquid in the downcomer, it may entrain some vapour.
The liquid head in the downcomer should not be greater than one half the plate spacing to avoid flooding.
The dischare 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.
none of these.
none of these.
Pick out the wrong statement pertaining to shell and tube heat exchanger.
Clearance between shell & baffles and between tube & baffles should be minimum to avoid by-passing of the fluid, but it should be enough to permit the removal of tube bundle.
Baffles are supported independently of the tubes by tie rods and positioned by spacers.
Tie rods are fixed at one end in the tube sheet by making blind holes and the minimum number of tie rods is 4 with at least 10 mm diameter.
Bracket supports are used for horizontal shell, while saddle support is used for vertical shell.
Bracket supports are used for horizontal shell, while saddle support is used for vertical shell.
Wind load consideration in the design of a support can be neglected, when the vessel is
short (< 2 m) and housed indoor.
Souders Brown equation given by, , is used for the calculation of the __________ in a continuous distillation column.
diameter of the bubble cap column
The ratio of volumes of the mixed reactor to the plug flow reactor (for identical feed composition, flow rate, conversion, and for all positive reaction orders) is always
> 1
Steam economy is defined as the amount of evaporation per unit amount of steam used, while the capacity is the total evaporation obtained per hour. Use of multiple effect in evaporation
ncreases capacity.
increases economy.
L/D for a Tee (used as elbow, entering run) would be around
60
Log mean temperature difference in case of multi-pass shell and tube heat exchanger is always
less than arithmetic mean value.
Practical dividing line between a ductile and brittle materials is suggested, when the ultimate elongation is about 5%. Generally, larger the knuckle radius, stronger is the corner torus section of a head. The knuckle radius provided should be less than __________ of the head.
6% of I.D.
3 times the thickness
either (a) or (b), whichever is larger
Tubes are fixed to the tube sheet (a thick circular metallic plate) by the method of tube rolling and brazing (non-removable) or ferrule connection (removable). Thickness of the tube, sheet is normally __________ the outside diameter of the tube but in no case it should be less than 22 mm (7/8”).
equal to
A shell may by termed as thin if its thickness to diameter ratio is less than 0.1. The factor which can be neglected in the calculation of membrane stresses is
bending
Scale up problem in design based on the similarity concept takes into account __________ similarity.
geometrical
kinematic
dynamic
all (a), (b) and (c)
__________ closure is the weakest enclosure for cylindrical vessels.
Conical or flat plate
Which of the following efficiencies can be greater than 100% ?
Murphree plate efficiency.
