UNIT – I
1. Define diffusion.
Diffusion is the movement, under the influence of a physical stimulus, of an individual
component through a mixture. The most common cause of diffusion is a concentration gradient
of the diffusing component.
2. What is thermal diffusion?
Diffusion generally caused by activity gradient sometimes it occurs by temperature is
thermal diffusion.
3. What is forced diffusion?
When the molecule as diffusion is induced by an external field, it is said to be forced
diffusion. Generally thermal and forced diffusion are uncommon in chemical engineering only
diffusion under concentration gradient is considered
4. Define eddy diffusion.
Diffusion also takes place when fluids of different compositions are mixed. The first step in
mixing is often mass transfer caused by the eddy motion characteristic of turbulent flow. This is
called eddy diffusion.
5. What is the role of diffusion in mass transfer?
In all the mass-transfer operations and often in both phase and often in both phases. In
distillation the low boiler diffuses through the liquid phase to the interface and away from the
interface into the vapour. In leatering diffusion of solute through the solid phase is followed by
diffusion into the liquid. In liquid extinction the solute diffuses through the raffinate phase to
the interface. In crystallization, solute diffuses through the mother liquorto the crystals. In
humidification there is no diffusion through the liquid phase.
6. Explain theory of diffusion?.
Here the attention is focused on diffusion in a direction perpendicular to the interface
between the phases and at a definite location in the equipment. Generally, steady state is
assumed, and concentrations at any point do not change with time.
7. What is the difference between heat transfer and mass transfer?
It arises from the fact that heat is not a substance but energy in transit, whereas diffusion is
the physical flow of material.
Heat transfer is based on one temperature gradient but in ass transfer there are different
concentration gradients.
8. What are the diffusion quantities?
They are,





Velocity (u)
Flux across the plane (N)
Flux relature to a plane of zero velocity (J)
Concentration (c)
Concentration gradiert (dc/db)
9. What is a diffusion co efficient?
The diffusivity or diffusion coefficient, DAB of a constituent A in solution in B, which is a
measure of its diffusive mobility, is then defined as the ratio of its fluex JA to its concentration
gradient.
Here DAB is the diffusivity
10. What is Fick’s first law?
JA =  DAB
CA
xA
 C DAB
z
z
Which is Fick’s first law written for the Z direction. The negative sign emphasizes that diffusion
occurs in the direction of a drop in concentration.
11. What is interstitial mechanism in the diffusion of solids
Interstitial sites are places between the atoms of a crystal lattice small diffusing solute a forms
may pass from an intestinal site to the next when the matrix atoms of the crystal lattice move
aspect temporarily to provide the necessary space.
12. What is vacancy mechanism?
If lattice sites are unoccupied an a form in an adjacent site may jump into such a vacancy.
13. What is interstitially mechanism?
In this care a large atom occupying an interstitial site pushes one of its lattice neighbours
into as interstitial position and moves into the vacancy thus produced.
14. What is crowd -ion mechanism?
An extra a form is a chain of close – packed a forms can displace several a forms in the line
from their equilibrium position, thus producing a diffusion flux.
15. Define diffusion along group boundaries.
The diffusion in a single – crystal metal is always substantially smaller than that for a multicrystalline sample because the latter has diffusion along the grain boudace’s which is nothing
but the crystal interfaces.
16. What is an unsteady state operation?
In an unsteady state operation the concentrations at any point in the apparatus change with
time.
17. What is a steady - state operation?
In a steady –state operation concentrations at any position in the apparatus remain constant
with the passage of time
18. What is stage wise operation?
In an insoluble phase if the phase are separated by mechanical means the entire. Operation
and the equipment repaired to carry it out are said to constitute one state.
19. Write continuity equation.
For a fluid of constant density the result is,
  2t  2t  2t 
t
t
t t
Q
ur  uy  uz

 



x
y
Z Q
 x 2 y 2 z 2  PCP
where  = k/lcp and Q is the rate of heat generation within the fluid per unit volume firm a
chemical reduction.
20. Give equation for steady state molecular diffusion in fluids.
NA 
NA DABc
NA /( Na  NB)  CA2 / c
/n
NA  NB Z
NA /( NA  NB)CA / C.
21. Give the equation for steady – state diffusion of A through non- diffusing B.
NA 

DAB Pt  

 PA1  PA 2 

RTZ PB m 
1
substitute A diffuses by the virtue of its concentration gradiest, - dpA / de substance B is
also diffusing relative to the average molar velocity at a flux J, which depends upon

d p B / d 2. but like a fish which swims upstream at the same velocity as the water flows
downstream NB = 0 relative to a fixed place.
22. What is steady-state equimolal counter diffusion?
This frequently per fairs in distillation operations NA = - N3 = conil we have,
NA 

DAB 
( PA1  PA2 )
RTZ
23. Define steady – state diffusion in multi – component mixtures.
It can be effectively handled by using an effective diffusivity where it can be synthesized
firm its binary diffusivities.
n
DA, n 
NA  YA N
i A
n
1
 DAi  yNA  yANi 
i A
24. Give the expression, when the diffusion is in stageart conditions.
PAm 
1  yA

yi

i  B DA, i
n
1
n
yi
 DAi
iB
25. What is an effusion?
The gaseous diffusion is also known as effusion. Here, the membrane micro-porous. If a gas
mixture whose components are pf different mokalae weight is brought into contact with such a
diaphrapn the various components of the gas pair through the pores of rates dependent upon
the mollule weights. This leads to different compositions on opposite sides of the membrane.
26. What is permeation?
In permeation, the member is not porous and the gas transmitted through the membrare
first deisolves in it then diffures through. Separation in this case is brought by difference in
solubility of the components
27. What are the types of solid diffusion?
The various types of solid diffusion are
 Diffusion through polymers.
 Diffusion through crystalline solids
 Diffusion in porous solids
28. When will the hydrodynamic flow of gores occur?
If there is a difference is absolute pressure across a power solid, a hydrodynamic flow of gas
through the solid will occur.
29. Define krudren diffusion.
Knudres diffusion is not known for liquids, but important reductions in diffusion rates
occur when the molecular size of the diffusing solute becomes significant relative to the pare
size of the solid.
30. What is surface diffusion?
Surface diffusion is a phenomenon accompanying adsorption of solutes onto the surface of
the pores of the solid. It is an activated diffusion involving the jumping of adsorbed modules
firm one adsorption site to another.
31. Discuss the velocities in diffusion.
Several velocities are needed to describe the movements of individual substances and of the
total phase. Since absolute motion has no meaning any velocity must be based on as arbitrary
state of rest. In this, velocity without qualification refers to the velocity relative to the interface
between the phases and is that apparent. To as observes at rest with respect to the interface.
32. What is turbulent diffusion?
In a turbulent stream, the moving eddies transport matter firm one location to another, just
as they transport momentum and heat energy. For momentum transfer and heat transfer in
turbulent streams, the equation for mass transfer is,
JAt = -  N
c
p
33. Discuses on prediction of diffusivities.
Diffusivities are best estimated by experimental measurements, and where such information
is available where such information is available for the system of interest, it should be used
directly. Often the derived values are not available. However they must be estimated from
published correlations. Sometimes a value is available for one set of conditions of temperature
and pressure.
34. Briefly explain equimolal diffusion.
For equimolal diffusion in gases the net volumetric and molar flours are zero and the
equation is
NA  JA 
DV
( Ai  C A )
BT
35. What is Schmidt number?
The ratio of the kinematic viscosity to the molecular diffusivity is known as the Schmidt
number and it is designated by Sc
Sc 
u


DV  dv
36. What is prandtl number?
Prandtl number is defined as the ratio of the kinematic viscosity to the thermal diffusivity
Pr 
U




cpm


P [k / ( p)

37. Give the expression for diffusivity of dilute solution for of non- electrolytes.
For dilute solutions of nonelectrolytes the empirical correlation of wilke and chang,
DAB =
(117.3x1013 )(QM &)0.5 7
V 0.6
Where, DAB = Diffusity of A.
MB= Moloculare weigh of solvent
T = Temperature
 = Viscosity
Q = Arrociation factor.
38. Give the expression for the diffusivity of liquids in concentrated solution.
The diffusivity in concentrated solutions differ from that in dilute solutions because of
change in viscosity with concentration and also because of changes in the degree of non ideality
of the solution.

d log ya 
DA  ( DBA ) xf ( DAB M B ) xb  

d log xA 

39. Write a note on rate coefficient.
The rate coefficients for the various components in a given phase will differ from each other
to the greatest extent under conditions where molecular diffusion prevails, but even then the
difference is not really large.
40. Write a short note on diffusion through polymers.
In many respects, diffusion of solutes through certain types of polymeric solids is more like
diffusion through liquid solutions than any one of the other solid – diffusion phenomena, at
least for the permanent gases as solutes.
41. Write a short note on diffusion in porous solids.
The solid may be in the form of a porous barrier or membrane separating two bodies of
fluid, as in the case of gaseous diffusion. Here, the solute movement may be by diffusion from
one fluid body to the other by the virtue of a concentration gradient or it may be hydrodynamic
as a result of pressure difference.
42. Write a short note on diffusion through crystalline solids.
The mechanisms of diffusion vary greatly depending upon the crystalline structure and the
nature of the solute. For crystals with lattices of cubic symmetry, the diffusivity is isotropic, but
not so for non-cubic crystals.
43. Write a note on steady state diffusion in multi-component mixtures.
They can be frequently handled by using an effective diffusivity, where the effective
diffusivity, of a component can be synthesized from its binary diffusivities with each other
constants.
44. What is the significance of diffusion?
This diffusion is significant when it is considered that we frequently wish to obtain products
which we nearly pure substances, where the ratio of components nay be of the order of 1,000 or
10,000 to 1 or even lasper.
Therefore we depend almost entirely upon the differences in concentration which exist at
equilibrium, and not upon the difference in transfer coefficient for making separations.
45. Write a note on concentration.
Concentration means mass per unit volume. Mass may be in kilograms or pounds and
volume in cubic meters or cubic feet. Kilogram moles or pound mole are often used as a
measure of the almost of solute present.
46. Define diffusional sublayer:
The region close to the wall where moleculer diffusivity exceeds eddy diffusivity of
mass has been termed the diffusional sublayer.
47. What is the physical basis of mass transfer to occur ?
On the basis of an appropriate physical model of mass transfer. The distribution of
liquid mass is the effective diffusion boundary layer of a whirled unidirectional stream is
determined, with the resistance of the liquid phase to mass transfer.
UNIT – II
1. Define Gas absorption.
Gas absorption is an operation in which a gas mixture is contacted with a liquid for the
purposes of dissolving one or more components of the gas and to provide a solution of them in
the liquid.
2. Give one-eg for gas absorption.
Gas from by product coke ovens is washed with H20 to remove NH3 and again with an
oil to remove benzene and toluene vapours.
3. Define Raoult’s law.
When the gas mixture in equilibrium with an ideal solution also follows ideal gas law,
the partial pressure p * of a solute gas A equals the product of its vapor pressure P at the same
temperature and its mole fraction in the solution x.
p*  px
4. Define Absorption Factor.
Absorption factor A =
L
slope of operating line

mG slope of equilibrium curve
5. What happens when pressure drops is high in absorber?
For absorber, high pressure drops results in high operating cost.
6. Write down the expression for the height of packing.
Z = NLOG HLOG
Where
Z = height of packing
NLOG = no. of overall gas transfer unit
HLOG = height of an overall gas transfer unit.
7. When will be the operating line and Equilibrium curve will be straight for an absorber?
In an absorber, both equilibrium curve and operating line will be straight for dilute
solution and non isothermal operation.
8. What is the relation between the individual film coefficients and the overall mass transfer
coefficient?
1
1
H


&
KG K g Kl
1
1
1


K L K l H Kg
where
KG = overall mass transfer coefficient based on gas phase
KL = overall mass transfer coefficient based on liquid phase.
Kg = gas film mass transfer coefficient
Kl = liquid film mass transfer coefficient
H = Henry’s law constant.
9. What condition HTU and HETP will be equal?
HETP is numerically equal to HTU, only when the operating line and equilibrium lines are
parallel.
10. What is the uses of co-current absorbers?
Co-current absorbers are usually used when the gas to be dissolved in the liquid is a
pure substance.
11. What is the valve of absorption factor?
Desirable value of absorption factors in an absorber is > 1.
12. When will be the tower height in absorber will increase?
For the same system if the same liquid used in an absorber is decreased, the tower
height in absorber will increase.
13. What is the range of Absorption factor?
The most economical absorption factors, A will be in the range from 1.25 to 2.
14. Define stripping factors.
It is defined as the reciprocal of absorption factor.
S
1
A
15. What will be the temperature in the absorption?
For absorption, an exothermic r x n, the temperature tends to rise and for stripping, an
endothermic r x n, the temperature tends to fall.
16. What is the Gas velocity in Absorber?
The design velocity is normally specified at about 60% of the flooding value.
17. What will be the operating pressure in absorber?
In general an absorber should be operated at the highest pressure consistent with the
requirement of other steps in the process.
18. Write down the formula for NTU.
Number of Transfer unit (NTU or HLOG) is a measure of difficulty of the separation. If the
NTU’s are large, the separation is hard.
N LOG 
y1
dy
1
1  y2
 y  y *  2 ln 1  y
1
y2
19. Write down the formula for HTU.
Height of Transfer unit (HTU or HLOG) give an ideal of efficiency of the equipment.
HTU =
G
k y a 1  y  
A small HTU is a good tower, implying a large surface area per unit volume.
20. What is the practical range of HTU?
It tends to be between 0.3 meter to 1 meter.
21. What is the Relation between overall and individual transfer units?
1
N LOG

1
mG 1

N LG
L N LL
H LOG  H LG 
mG
H LL
L
22. What are the common packings used in the absorption?
1.
2.
3.
4.
5.
Berl saddle and Raschig rings are older types of packing that are not used nowadays.
Intalox saddles are somewhat like Berl saddles where bed porosity increases.
Super Intalox saddles made up of plastic or ceramic form.
Pall rings are made from thin metal and have 90% void fraction and low pr drop.
Hypak metal and flexi rings are similar in shape.
23. What is the diameter of rasching rings used in packed tower?
Diameter of rasching rings used in packed lower in industry is normally around 2
inches.
24. When will the exothermic rxn take place in absorption?
1. pr = sc; % change in heat & mass transfer flux will be the same for a given change in the
degree of turbulence
2. pr = sc = 1, total mass, momentum and thermal diffusivity will be the same.
25. What happens when absorption with evolution of heat as compared to isothermal
absorption?
(i)
Decreased solute solubility.
(ii)
Large minimum liquid to gas L
(iii)
Large number of trays.
 G  ratio.
27. What is value of rasching ring?
Rasching ring =
Diameter
1
height
28. Define gas solubility.
The gas solubility should be high, increasing the rate of absorption and decreasing the
quantity of solvent.
29. Give some Example used in gas solubility.
(i) Hydrocarbon oil are used to remove benzene from coke-oven gas.
(ii) Hydrogen sulfide can be removed from gas mixtures using ethanolamine solutions.
30. What is condition used in volatility?
The solvent should have low vapor pressure since the gas leaving an absorption
operation is saturate with the solvent and much may be lost.
31. When will be the operating line straight?
The operating line is straight only when plotted in terms of the mole ratio unit.
32. When will be the operating line is curve?
The operating line is cure when plotted in terms of mole fraction and partial pressure.
33. What is the Equation of line in an absorber?
 P1 
 y
 x1
y 
x 
Gs  1 

  Ls 
  Gs 

 1  y1 1  y 
 1  x1 1  x 
 Pt  P1 
34. Where will the operating line lie in an stripper and absorber?
The operating line lies above the equilibrium curve in an absorber where as the
operating line lies below the equilibrium curve.
35. What is the principle applied to stripper?
The operating line which anywhere touches the equilibrium curve represents a
maximum ratio of liquid to gas and a maximum exit gas concentration.
36. When will be the operating will be negative?
When gas and liquid flow concurrently, the operating line has a negative slope
 Ls
Gs
.
37. Define ideal tray or theoretical tray.
It is defined as one where the average composition of all the gas leaving the tray is in
equilibrium with the average composition of all the liquid leaving the tray.
38. What is the formula for the number of equilibrium trays in terms of mole fraction of an
absorber?
 mx0  1  1 
y
log  Np 1
 Number of 
1   
y1  mx0  A  A 



 Equilibrium  N P 
log A
 trays



39. What is the formula for Np of an stripper?
y


xo  Np 1  1  1 

m 1
log 

yNp 1  S  S 
x

 Np

m
NP 
log S
40. Define number of real tray D.

 1 
log 1  EMGE   1 
Equilibrium trays
 A 

Eo 

real trays
1
log  
 A
41. Expand HETP.
Height equivalents to an equilibrium stage, Height equivalent to an Theoretical plate.
42. CO2 can be absorbed by heated charcoal.
43. The process employing desorption of the absorbed solute by a solvent is called elution
44. What happens when absorption factor increases?
To increase absorption factor, increase ‘s’ and decrease ‘G’
Where
S – Solvent flow rate
G – Gas flow rate
45. Absorption factor method is used to calculate the number of ideal stages when the
operating and equilibrium lines are parallel.
46. What are all the parameters, which determines the Gas-Bubble diameter?
The rize of gas bubbles depends upon the rate of flow through the orificer, the orifice
diameter, the fluid properties, & the extent of turbulence prevailing in the liquid.
47. Define sparger.
A sparger is a device for introducing a stream of gas in the form of small bubbler in to a liquid.
48. What is called Gas-holdup?
Gas hold-up (QG) is meant the volume fraction of the gas-liquid mixture in the vessel
which is occupied by the gas.
49. What is meant by swarms of Gas Bubbles?
The behaviors of large number of bubbles Gowded together is different from that of
isolated bubbles. Ring velocities are smaller because of crowding, & bubble diameter may be
attired by liquid turbulence, which causer bubble breakup, & by walescene of coding bubbles.
50. What are all the parameters fixed before an absenting column design?
The quantities which are ordinarily fixed before an absorber design is started are the
following:
1) Rate of flow, composition, & temperature of entering gas.
2) Composition and temperature of entering liquid (but not slow rate)
3) Pressure of operation.
4) Heat gain or less.
51. What is called “Reboiler”?
The heat exchanger where a portion of the rich oil is heated is called a reboiler.
52. What is meant by “Reglux”?
A stream returned to a cercade of stage, as represented by the frags in the absorber. For
the purposes of obtaining an enrichment beyond that detained by counter current contact with
the feed to the cascade, is called reflux.
53. Define Plait Point ?
Composition conditions in which the three coexisting phases of partially soluble
components of a three phase liquid system approach each other in composition.
UNIT – III
1. Define Distillation.
It is a method of separating the components substance between a gas and a liquid phase, applied to
cases where all components are preset in both phases.
2. Give one example for the Distillation:
In the separation of a solution of common salt and water, the water can be completely vaporized from
the solution without removal of salt – since the latter is for all practical purpose quite nonvolatile at the
prevailing conditions.
3. Define Relative volatility.
It is the ratio of the concentration ratio of A and B one phase to that in the other is a measure of the
separability,
y*1-x 
α= 





1-y*  x

4. What is the value of Relative volatility ?
i)
ii)
iii)
The value of  will ordinarily change as x varies from 0 to 1.
Y*=x at x=00r1 =1 and no separation is possible.
The larger the value of  above unit, greater the degree of separability.
5. Define Raoult’s law.
For an ideal solution, the equilibrium partial pressure P * of a constituent at a fixed temperature equals
the product of its vapor pressure P when pure at its temperature and its mole fraction in the liquid.
PA*  PA x; PB*  PB x
vapor phase is ideal
Pt  PA*  PB*  PA x  PA 1  x  x  y  1
y=1-x
6. What is the Relative volatility for ideal solution?
It is the ratio of vapour pressure of component A to its vapour pressure of component B

PA
PB
7. Where is Raoult’s law is applied?
It is applicable to the ideal solution and solvents
8. Define Henry’s law.
It is defined as the partial pressure of a component over a solution is proportional to its mole fraction in
the liquid.
9. What are uses of flash distillation?
It is used for multi components systems like crude refining.
10. Define positive deviations from ideality.
It is the mixture whose total pressure is greater than that computed for ideality.
11. Write down the Rayleigh equation.
F
dL
F
laf L  ln W 
XF
dx
 y * x
xw
12. What is the equation of Differential condensation?
yD
F
dy
ln  
D yF y  x *
13. Write down the constant Relative volatility.
ln
x 1  xW 
1  xW
F
1

ln F
 ln
W   1 xW 1  xF 
1  xF
14. Define Reflux Ratio.
R
It is the molar ratio of reflux to distillation
L
D
15. Define surface tension- positive systems.
The more volatile component has the lower surface tension, the surface tension increases down the
packing becomes more stable and mass transfer become larger.
16. Write down the Fenske’s Equation.
log
Nm  1 
xD 1  xw
1  xD xW
log av
It is used to determine the minimum number of theoretical plants.
17. Relative volatility does not change appreciably with the change in temperature.
18. In batch distillation wilk constant reflux, overhead product composition decreases wilk time.
19. In rectifying section of a continuous distillation column, the vapour is enriched wilk high boilers.
20. What is the reflux ratio of the continuous rectification for a binary mixture.
For a binary mixture wilk low relative volatility, continuous rectification to get pure products will require
high reflux ratio.
21. When will be the low relative volatility in the distillation?
For binary mixture with low relative volatility, an azeotrope may be formed during distillation.
22. Give one eg for azeotrope distillation.
Alcohol is dehydrated.
23. What is the purpose of entrainer in azeotropic distillation?
Entrainer used in azeotropic distillation should form a low boiling a zoetrope with one of the
constituents of a mixture.
24. Give one eg for steam distillation and its uses.
Rose oil is extracted from rose and is used to separate high boiling substance from non volatile
impurities and the product must be immiscible with walir.
25. What are the uses of molecular distillation?
It is used to measure heat – sensitive materials very low pressure distillation.
26. Write down the langmair equation.


1
NA  1006PA 

 2 AR 'T 
0.5
27. What are the assumption made in MCcabe – Thiele Method and the assumption are
(i)
(ii)
Molal vaporization and over flow
It is used to find molal units for Materials and energy balance.
28. What is the slope of feed line in Mc Cable Thiele method?
The slope of feed line m=-1/f
Where f- moles of vapour present per mole of feed.
29. Draw the diagram for the q line for feed condition in distillation.
30. What is the slope of the
distillation column?
feed line to a
Feed condition
i) Liquid below B.pt
slope
ii) Saturated liquid
q>1
iii) Mixture of Liquid and vapour 0<q<1
iv) Saturated vapour
q=0
v)Superheated vapour
q<0
31. What is the uses of Absorption factor method?
It is used to calculate the number of ideal stages, when both operating and equilibrium line are parallel.
32. As the reflux Ratio decreases, the number of plate.
Decreases
33. Tower diameter may be decreased by use of increased .
Tray spacing
34. Define priming:
It is due to the presence of foam throughout the space between trays
35. Define over all efficiency of the distillation colomn.
It is the ratio of number of ideal plate to actual plates.
36. What is the use of ponchan – savarit method?
It is used to determine the fractional equipment based on both enthalpy and material Balance.
37. Why Reboiler is considered as theoretical plate?
Reboiler is considered as one theoretical plate because of the assumption that vapour and liquid leaving
the reboiler are in equilibrium.
38. What is the function of plate efficiency?
It is a function of the mass transfer between the liquid and vapour.
39. What is meant by Back – trapping?
Back – trapping in a distillation column decrease the tray efficiency.
40. Weeping in a distillation column result due to very low gas velocity.
41. What are the causes of channeling in a packed tower?
i)
ii)
Mal distribution of liquid
Non – uniformly of packing
42. What is value of reflux ratio, when the number of theoretical plates in a distillation is minimum?
Infinity
43. If the path of liquid across the plate is very long as in case of large diameter tower, Murphree.
efficiency can be >100 percent.
44. What is the use of cox chart?
It is useful in the design of distillation column.
45. It Rm is the minimum reflux ratio, the optimum.
reflux ratio may be 1.2 to 1.5 Rm
46. Define murphree efficiency .

y n  y n 1
y n*  y n 1
where yn – actual concentracation of vapour leaving platen yn+1 = actual concentraction vapour entering
plate n
y*n = Concentration of vapour in equilibrium with liquid leaving down pipe from plate n.
47. Define local efficiency .
'
y n ' y n 1
'
y en
 y 'n 1
Where
Y’n – concentration of vapour leaving specific location on plate n
Y’n+1- concentration of vapour leaving entering plate n at same location
Y’en- concentration of vapour leaving in equilibrium with liquid with liquid at same location.
’ cannot be greater than 1 or 100%
y’n cannot be greater than y’en
48. What is meant by hetero a zoetrope?
A liquid mixture of average composition L, which produces a vapor of the same composition, is
some times called as hetero zoetrope.
49. Define Dew Print.
It is the temperature at which contention will first occur (i.e., vapour begins to condense) when
the vapour-goes mixture is cooled at constant pressure. At this temperatures the gas is saturated with
vapour.
50. Define Bubble point.
It is the temperature at which the first bubble starts to appears (i.e., liquid begins to vapour).
51. Where the feed fray is located in the diagram?
The material & enthalpy balance from which the curves are derived dictate that the step wire
construction must change operating lines at the tray where the feed is to be introduced.
52. What is meant by multiple feeds? When it will happens?
There are occasions when two or more feeds composed of the same substances but of different
concentrations require distillation to give the same distillate & residue products.
53. What is meant by Total Reflux or Infinite reflux ratio?
As the reflux ratio R=L/D is increased, the ratio L/G increase, until ultimately, when R = , L/G =
1 and the operating lines of both reactions of the column coincide. With the 45o diagonal.
54. What is meant by minimum reflux ratio?
The minimum reflux ratio Rm is the minimum reflux ratio which will require an infinite number
of trays for the reparation desired, and it corresponds, to the minimum receiver heat & condenser
cooling capacity for the reparation.
55. What are the applications of steam Distillation?
 Manufacture of essential oils
 Used in petroleum refineries
 Production of consumer food products such as sprayable or aerosolized condiments.
56. What is Flash Evaporation ?
Flash Evaporation is the partial vapour occurs when a saturated liquid stream undergoes a
reduction in pressure by passing through a throttling device. This is the simple process in unit operation.
UNIT – IV
1. Define Liquid – liquid extraction.
Separations involving the contact of two insoluble liquid phases.
2. Give some e.g. for extraction.
If an acetone- H2o solution is shaken in a separators funnel with CC14. The liquids allowed to settle a
large portion of the acetone will be found in the CC14 rich phase and will have been separated from the
H2o.
3. What is the combination of properties for a good solvent for extraction?
Good solvent for
Extraction
high selectivity, low viscosity, large
- distribution coefficient, high
Inliofacial tension.
4. How the solvent is selected in Extraction?
The solvent used in solvent extraction should be >1
The solvent used in liquid extraction should be <1
5. Which extractors in a system having very low density difference?
Centrifugal extractor
6. What component will be in the apex of an equilateral triangular coordinate?
The apex of an equilateral – triangular coordinate represents a pure component.
7. What is the principle used in counter current liquid extractor?
In a counter current liquid extractor only one of the liquids may be pumped at any desired rate.
8. What will be the reflux ratio is increased in a continuous counter current extraction is increased the
number of stages decrease?
As the reflux ratio, in a continuous counter current extraction is increased the number of stages
decrease.
9. In extraction as the temperature increases the area of heterogeneity (area covered by bimodal
curve decreases.
10. What is the uses of pulsed column extractor?
Radio active nuclear waste is treated in pulsed column extractor.
11. What is the uses of Boll man extractor?
Boll man extractor is used for extraction of oil from oilseed.
12. The solvent used in liquid extraction should not have high latent heat of vaporization because its
recovery cost by distillation may be prohibitively high.
13. Sides of equilateral triangular coordinates represent a binary mixture.
14. Fractional solvent extraction employs two solvents.
15. When the solvent dissolves very little of solute then large quantities of solvent in required to
extract the solute.
16. Define fractional Extractor.
A solution of acetic Acid and acetone can be separated by adding it to the insoluble mixture of H2o and
cc14. After shaking and setting bolt acetone and Acetic Acid will be found in both liquid phases, but in
different proportions.
17. Heat sensitive materials with high latent heat of vaporization may be economically separated
using liquid extraction
18. Define feed, solvent.
The solution which is to be extracted is called the feed.
The liquid with which the feed is contacted in the solvent.
19. Define Extract and raffinate.
The solvent rich product of the operated is called extract.
The residual liquid from which solute has been removed is the raffinate.
20. Given some e.g. for double solvent fractional extraction.
Mixture of Para and ortho nitro benzoic acids can be separated by distributing them between the
insoluble liquids chloroform and H2o. The CC14 dissolves the Para isomer & H2o the ortho isomer.
21. What are the uses of liquid extraction?
Metal separation such as uranium-vanadium, hafnium – zirconium and tungsten – molybdenum and
fission products of atomic energy process.
22. Give some e.g. for one pair partially soluble.
i) Water – chloroform – acetone
ii) Benzene – water – acetic acid.
23. Define sol tropic.
The direction of the tie line slope changes and one tie tube will be horizontal.
24. Define Distribution coefficient.
It is the ratio of mole fraction of vapor at equilibrium to its mole fraction of liquid.
25. Give some e.g. For two pairs partially soluble.
i) Chlorobenzene - H2o – methyl ketene.
26. Give some e.g. for two partially soluble liquids and one solid.
i) naphthalene – anatine – isooctane
27. Define selectively.
B=
wL fraction c inE  / wL fraction A in E 
wt fraction C in R  / wt fraction A in R 
yE * w t fraction A in R 
B=
xR wt fraction A in E 
28. What are the two types of mixers?
i) Flow mixer or line mixers
ii) Mixing vessels
di
is
29. The impeller – tank – diameter ratio T
in the range 0.25 to 0.33.
30. What are the types of stage type equipment?
i) Single – stage mixer setter and multistage cascades
ii) Sieve tray, Multistage towers
31. What is the diameter of dispersed droplets in the Emulsion?
The diameter of the dispersed droplets is the order of 1 to 1.5 um, whereas dispersions of particle
diameter 1mm or larger usually sediment.
32. What is the mass-transfer effectiveness in save tray?
i) Axial mixing of the condition the continuous phase as confirmed as to the region between trays and
does not spread throughout the tower from stage to stage.
ii) Dispersed phase droplets coalesce.
33. Which are materials is used to make coals?
It is a mixture of cotton fiber and glass wool or cotton and Dynes fiber.
34. What are the uses of coalesced?
It is used to increase the size of the droplets and settling rate.
35. What is the morphed efficiency in extract composition?
EME 
ym  ym  1
ym*  ym  1
36. What type of impellers is used?
Flat – blade turbine type.
37. Give one best e.g. for solvent recovery by extraction.
Amyl acetate
38. What are the types of stage wise contact Extractor?
i) Single stage extraction
ii) Multistage crosscurrent
iii) Continuous countercurrent “multi stage”
39. Give some e.g. for extractor.
Aromatic and paraffin hydrocarbon of nearly the same molecular weight are impossible to separate by
distillation because their vapor pressure are nearly the same but they can readily be separated by
extraction with any of a number of solvents e.g. liquid sulfur dioxide diethyl or suffocate.
40. What is the total material balance in single stage extraction?
F  s1  M1  E1  R1
41. What is the material balance for single stage extraction?
E1 
M1  xm1  x1 
y1  x1
42. What is the angle used in the operating live?
450
43. Sketch the single stage extraction.
44. Draw the flow sheet for three stage extraction.
45. Draw morphed
efficiency in stage efficiency.
stage
46. Define
Leaching ?
It is the process by which the soluble materials in the soil such as salts, nutrients, pesticide
chemicals or contamitants are washed into a lower layer of soil and are dissolved and carried away.
47. Applications of leaching ?
 Used in gold recovery process
 Used in silver extraction process
 Used for milk pasteurization
 Used for agricultural drying
 Used for fish drying
48. Tray efficiency ?
For a vapour liquid separation process considaing that both liquid and vapour phase are mixed
perfectly a measure of the efficiency of distillation of the component is tray efficiency.
UNIT – V
1. Define Adsorption.
Adsorption is a fluid solid operation it is a process in which one or more components of a liquid
or gaseous mixture adhere to the solid surface with which it is brought in contact due to force of
attraction between the molecules of the solid and the component adsorbed. The solid is known as
adsorbent and the component adsorbed is known as adsorbate.
2. Draw the single stage operation diagram.
Ss ADSORBENT
Solvent
Ls
Xo
1
Ls
Yo
Y1
Ss
Operating line
Y0
X1
Equilibrium curve
Y
Y1
slope 
X0 X1
3. What are the two types of Adsorption?
Ss
Ls
1. Physical adsorption
2. Chemical adsorption
4. What are the Natures of Adsorbent?
It is usually in granular form varying in size from roughly 12mm in diameter to as small as 50um.
5. What are the commonly used Adsorbents?
1. Fuller’s earth
3. Baynite
2. Activated days
4. Bone char
6. Draw the Adsorption isotherm showing hysteresis.
P-equilibrium
Adsorption
Partial pressure
Desorption
Kg adsorbed / Kg adsorbent
7. What is differential heat of adsorption?
It is defined as the heat liberated at constant temperature when unit quantity of vapour is
adsorbed upon a large quantity of solid already containing adsorbate.
Equilibrium solute
concentration in liquid
8. Draw the Typical Adsorption isotherms for diluty solution.
Wt.solute apparently adsorbed
9. Write Freundlieh Equation.
/wt adsorbent
C   k   Co  C  
n
where   Co  C   is the apparent adsorption per unit
mass of adsorbent and k and n are constant.
10. What is heat of wetting?
When a adsorbed solid is immersed in a pure liquid, the evolution of heat is known as heat of
wetting.
11. What is split feed treatment?
The removed of a given amount of solute can be a accomplished with greater economy of
adsorbent if the solution is treated with separate small batches of adsorbent rather than in a single
batch with filteration between each stage.
12. What is elution?
Desorption of the adsorbed solute by solvent is called elution.
13. What is eluate?
The effluent stream containing the desorbed solute and eluting solvent is the eluate.
14. Physical Adsorption is ____________
i) a reversible phenomenon
ii) accompanied by evolution heat
15. Chemical Adsorption is _____________
An irreversible phenomenon
16. What happens when the Rate of adsorption increases?
Ttemperature decreases
17. When adsorption hysteresis is observed the desorption equilibrium pressure is _____ that
obtained by adsorption.
Always lower than
18. Which adsorbent is used to decolourise yellow glycerine?
Activated carbon
19. Freundlich equation applies to the adsorption of solute from __________
Dilute solution, over a small concentration range.
20. Explain Freundlich adsorption theorem.
At a particular temperature, the relation between the magnitude of adsorption and pressure
can be expressed mathematically by empirical equation.
a
= KPn
a
= Amount of gas adsorbed per unit mass of the adsorbent
P
= pressure
K & n = are constant
21. What is adsorption isotherm?
The variation of adsorption with pressure at a given constant temperature is called as
Adsorption isotherm.
-78oC
adsorption
-28oC
mass of absorbent
0oC
22. Write the B.E.T theory equation of Adsorption.
Pr
P
Vtotal  Po  P 
1

VmonoC

C 1  P 


Vmono C  Po 
Vtotal = The volume of gas adsorbed at the pressure P.
Vmow = Volume adsorbable when the surface of solid covered completely with a mono layer
23. State the various characteristics is features of physical adsorption.




physical adsorption is surface phenomenon
Adsorption occurs only at very low temperatures
Adsorption is a reversible process
It involves weak venda waals forces between molecules.
24. State the various characteristics features of Chemisorptions.
1. It involves chemical interaction between the surface
2. Atoms of the adsorbents and the atoms of the adsorbate.
3. It can occur at all temperature.
25. Define Diffusion.
In gaseous diffusion or effusion the membrane is microporous. If a gas mixture whose
components are of different molecular weight is brought into contact with such a diaphragm, the
various component of the gas pass through the pores at rates dependent upon the molecular weight.
26. Define permeation.
Liquid solution of alcohol and water is brought into contact with a suitable nonporous
membrane, in which the alcohol dissolve. After passage through the membrane the alcohol is vaporized.
27. Define Dialysis.
The separation of a crystalline substance form a colloid, by contact of their solution with a liquid
solvent with an membrane permeable only to the solvents and the dissolved crystalline substance.
28. Give some example for Dialysis.
Aqueous beet-sugar solution containing undesired colloidal material.
29. Define Fractional dialysis.
It is the separating two crystalline substance in solution makes use of the different in membrane
permeability for the substance.
30. Define osmosis
If a solution is separated from the pure solvent by a membrane which is permeable only to the
solvent the solvent diffuses into the solution.
31. Define electro electro dialysis.
If an electromotive force is applied across the membrane to assist to the diffusion of charged
particles.
32. Define reverse osmosis.
A pr to oppose the osmotic pr I the flow of solvent is reversed and the solvent and solute of a
solution can be separated.
33. Give example for reverse osmosis.
Desalination of sea H2O
34. Give example for permeation.
Fluorocarbon polymer member.
35. Define permeation.
The membrane is not porous, and the gas transmitted through the membrane first dissolves in it
and then diffuse through.
36. Define thermal diffusion.
The formation of a conc diffusion within a single liquid or gaseous phases by composition of a
temp gradient upon the fluid.
37. Define sweep diffusion.
If a condensable vapour such as steam is allowed to diffuse through a gas mixture, it is
preferentially carry one of the components along with it, thus making a separation by the operation is
known as sweep diffusion.
38. What is Atmolysis?
If the two zones with in the gas phase where the concentration are different arc separated by a
screen containing relatively large openings the operation is called atmolysis.
39. What is foam separation?
By forming a foam of large surface as by bubbling air through the solution as by collecting the
foam the solute can be concentrated. In this manner detergent have been separated from water. For
example: this operation is known as foam separation.
40. What is heat of wetting?
When an adsorbent solid is immersed in a pure liquid, the evolution of heat known as heat of
wetting.
41. The Adsorption of Nitrogen or hydrogen on chemical at temperature close to __________
-180oC.
42. Mow molecular adsorption postulated by ____
Langmuir
43. Draw the different types of Adsorption isotherms.
Amount
Type 1
Adsorbed
Pressure
Po
Amount
Adsorbed
Pressure
Po
44. What are the different types of operation?
Direct and indirect operation
45. What are the different types of phases separated by a membrane?
Gas-Gas, Gas-liquid, liquid-liquid.
46. Define drying.
Drying refers generally to the removal of moisture from a substance. It is so loosely and
inconsistently applied that some restriction in its meaning is necessary in the treatment to be given.
47. What is an equilibrium?
The moisture contained in a wet solid solution exerts a vapour pressure to an extent depending
upon the nature of the moisture, the nature of the solid, and the temperature. If then a wet solid is
exposed to a continuous supply of fresh gas containing a fixed partial pressure of the vapour P the solid
will either lose moisture by evaporation or gain moisture from the gas until the vapour pressure of the
moisture of the solid equals P . The solid and the gas are then in equilibrium.
48. What is board water?
Moisture present as a liquid solution of soluble portions of the solid and as a solid solution or
moisture held in small capillaries and reverses throughout the solid are otherwise a doubled upon the
surface such moisture is called found water.
49. What is a unbound water?
If exposed to saturated air, the wood may have any moisture content greaterthan 0.3 kg/kg dry
solid and moisture in excess of that at B, unbound water exerts the vapour pressure of pure water at the
prevailing temperature.
50. Give the curve for equilibrium water contact of some common solids at 25oC.
51. What is hypterexis?
Many solids exhibit different equilibrium-moisture characteristics depending upon whether the
equilibrium is reached by condensation or evaporation of the moisture.
52. What is regain?
The moisture picked up by a dry solid when exposed to moist air, the adsorption equilibrium, is
sometimes called regain.
53. Draw the curve for equilibrium water content of a sulfite pulp.
54. What are soluble solids?
Solids which are soluble in the liquid in question ordinarily show insignificant equilibrium moisture
content when expired to gases where partial pressure of vapour is less than that of the saturated
solution of the solid
55. Draw the curve for equilibrium moisture content of sodium nitrate at 25oC.
56. Define moisture content on
wet basis.
The moisture content of a solid or solution is usually described is terms of weight percent
moisture, and unless otherwise qualified this is ordinarily understood to be expressed on the wet basis.
57. What is moisture content on dry basis?
This is expressed as kg moisture per kg dry solid = x.
Percentage moisture, dry basis = 100 v.
58. Define equilibrium moisture.
If is denoted as X*. This is the moisture content of a substance when at equilibrium with a given partial
pressure of the vapour.
59. What is bound moisture?
This refers to the moisture contained by a substance which exerts an equilibrium vapour
pressure less than that of the pure liquid at the same temperature.
60. What is an unbound moisture?
This refers to the moisture contained by a substance which exerts an equilibrium vapour
pressure equal to that of the pure liquid at the same temperature.
61. What is free moisture?
Free moisture is that moisture contained by a substance is excess of the equilibrium moisture :
X – X* only free moisture can be evaporated, and the free moisture content of a solid depends i[pm the
vapour concentration in the gas.
62. What is batch drying?
Drying operations usually in fact a semi-batch process wherein a quantity of the substance to be
dried is expored to a continuously flowing stream of air into which the moisture evaporates.
63. On what basis, the drying is classified?
It is classified according to
 Equipment type.
 Nature of the drying process.
64. What are the major classifications?



Method of operation i.e. batch or continuous.
Method of supplying heat necessary for evaporation of the moisture.
Nature of the substance to be dried.
65. Give some examples for batch driers.
Some of the batch driers are
a) Direct driers
b) Indirect driers.
c) Freeze driers.
66. What are vacuum shelf driers?
There are tray driers whose cabiners, made of cast-iron or steel plates are fitted with tightly
closing dorts so that they can be operated at sub-atrospheric pressure.
67. What are vacuum rotary driers?
Vacuum rotary driers are steam-dedicated cylindrical shells, arranged horizontally, in which a slurry or
paste can be dried in vacuum.
68. What are agitated pan driers?
Agitated pan driers can be used to dry parts or slurries in small batches are shallow, circular
pans 1-2 m in diameter and 0.3 to 0.6 m deep with flat bottoms and vertical sides.
69. What is freeze-drying?
Substances which can’t be heated even to moderate temperature such food stuffs and certain
pharmaceuticals, can be dried by this method.
70. What is the alternate method of freeze-drying?
An alternate method of freeze-drying is flash vapourization this happens under-vacuum
conditions.
71. What are the conditions to be followed in drying tests?
The conditions are;

The sample should be similarly supported in a tray frame.

It should have the same ratio of drying to nondrying surface

It should be subjected to similar conditions of radiant-heat transfer.

The air should have the same temperature, humidity and velocity.
72. Give the curve for batch drying.
73. What is the equation for cross circulation drying?
The equation is,
Nc = Ky (y5 – y)
74. What is the time of drying?
The difference is times corresponding to the initial and final moisture contents from the curve.
75. What is the equation for the rate of drying?
The rate of drying equation is
N
 S S dx
Ad
76. What is constant rate period?
If the drying takes place entirely within the constant rate-period so that X1 & X2 > Xc and N = NC, Then,

SC ( x1  x2 )
ANc
77. What is falling rate period?
If X1 and X2 are both less than Xc, so that drying occurs under conditions of charging N.
78. Give the equation for falling rate period.

SC ( x  x*) X 1  X *
G
VC A
X2  X *
79. Define “effect of gas velocity”.
If radiation and conduction through the solid are negligible, Nc is proportional to G0.71 for parallel
flow of gas and to G0.37 for perpendicular flow. If radiation and conduction are present, the effect of gas
rate will be less important.
80. Define “effect of gas temperature”.
Increased air temperature increases the quantity TG-TS and hence increases Nc. In the absence of
radiation effects, if the variation of I over moderate temperature ranges is neglected. Nc is directly
proportional to (7G – 7s) directly proportional.
81. Define “effect of gas humidity”.
NC varies directly as ys – y and consequently increasing the humidity lowers the rate of drying.
Usually, changes in Y and TG involve simultaneous changes in 7s and Ys and the effects are the best
estimated by direct application.
82. Define “effect of thickness of drying solid”.
If heat conduction through the solid occurs the rate equation indicates lowered values of Nc
with increased solid thickers.
83. What are hygroscopic substances?
Substances containing bound water are often called “hydroscopic substances”.
84. Draw the plot of total moisture content and drying rate versus drying fire.
85. What is case – hardening?
Rapid drying may also make the surface of the shunker material hard and perhaps impervious,
enclosing the bulk of the solid so the interial moisture cannot be earily removed this effect is called
“care-hardening”.
86. What is critical moisture content?
The point at which the constant-rate period ends [whether or not the drying rate is truly
constant] is called the critical moisture content.
87. How the moisture is distributed in non-porous solids?
The moisture distinction in a typical non-porous solid is quantitatively consistent with that called
for by a assuming that the moisture flows by diffusion through the solids.
88. What are porous solids?
The moisture distribution is a porous solid during drying differs greatly from that indicated by
diffusion in a non-porous material.
Moisture flows through porous solids by capillarity and to some extent by surface diffusion.
89. What are tower dryers?
Tower driers contain a series of circular trays mounted one above the other on a central rotating
shaft solid feed dropped on the topmost tray is exposed to a stream of hot air or gas that pauses across
the tray. The solid is then scraped off and dropped to the tray below. It travels in this way through the
dryer, discharging as dry product from the bottom of the tower.
90. What is drum dryer?
A drum dryer consists of one or more heated metal rolls on the outside of which a thin layer of
liquid is evaporated to dryers. Dried solid is scraped off the rolls as they slowly revolve.
91. List out few example of adsorbents in general use.
 Fuller’s earths, * Activated days * Bauxite * Alumina
 Bone char * Decolorizing carbons * Gas-adsorbent carbon * molecular-screening activated
carbon
 Synthetic polymeric adsorbents * silica get * molecular river.
92. Define Integral heat of adsorption.
Integral heat of adsorption at any concentration of adsorbate upon the solid is designed as the
enthalpy of the adsorbate-adsorbent combination minus the sum of the enthalpies of unit weight of
pure solid adsorbent and sufficient pure adsorbed substance (before adsorption) to provide the required
concentration x, all at the same temperature.
93. Define the term Relative adsorptivity.
The reparation factor or relative adsorptivity, similar to relative volatility in distillation or
selectivity in liquid extraction, is obtained by dividing the equilibrium ratio of gas compositions in the
adsorbate by the ratio in the gas.
94. Define Desorption?
It is the phenomenon whereby a substance is released from or through a surface. This occurs in
a system being in the state of sorption equilibrium between bulk phase and an absorbing phase.