Mass Transfer Flashcards
Mass transfer rate between two fluid phases does not necessarily depend on the __________ of the two phases.
a. chemical properties
b. physical properties
c. degree of turbulence
d. interfacial area
a. chemical properties
In a solution containing 0.30 Kg mole of solute and 600 kg of solvent, the molality is
a. 0.50
b. 0.60
c. 2
d. 1
a. 0.50
Fenske equation determines the
a. maximum number of ideal plates.
b. height of the distillation column.
c. minimum number of theoretical plates.
d. optimum reflux ratio.
c. minimum number of theoretical plates.
The term “cooling range” in a cooling tower refers to the difference in the temperature of
a. cold water leaving the tower and the wet bulb temperature of the surrounding air.
b. hot water entering the tower and the wet bulb temperature of the surrounding air.
c. hot water entering the tower and the cooled water leaving the tower.
d. none of these
c. hot water entering the tower and the cooled water leaving the tower.
Which of the following is the most suitable for extraction in a system having very low density difference ?
a. Mixer-settler extractor
b. Centrifugal extractor
c. Pulsed extractor
d. Packed extraction tower
b. Centrifugal extractor
Total reflux in a distillation operation requires minimum
a. reboiler load
b. number of plates
c. condenser load
d. all (a), (b) and (c)
number of plates
The amount of steam required per unit quantity of distillate in case of steam distillation will be reduced by
a. raising the temperature.
b. lowering the total pressure.
c. both (a) and (b).
d. neither (a) nor (b).
c. both (a) and (b).
The difference of wet bulb temperature and adiabatic saturation temperature of unsaturated mixture of any system is
a. +ve
b. -ve
c. zero
d. none of these
a. +ve
Fenske’s equation for determining the minimum number of theoretical stages in distillation column holds good, when the
a. relative volatility is reasonably constant.
b. mixture (to be separated) shows negative deviation from ideality.
c. mixture (to be separated) shows positive deviation from ideality.
d. multicomponent distillation is involved.
a. relative volatility is reasonably constant.
When the temperature and humidity of air is low, we usually use __________ draft cooling tower.
a. natural
b. forced
c. induced
d. none of these
a. natural
Pick out the correct statement.
a. In case of liquid-liquid extraction, no separation is possible, if the selectivity of the solvent used is unity.
b. With increase in temperature, the selectivity of the solvent used in solvent extraction decreases.
c. The selectivity of solvent used in solvent extraction is unity at the plait point.
d. all (a), (b) and (c).
d. all (a), (b) and (c).
__________ columns are used for liquid dispersion in a continuous gas phase.
a. Packed
b, Pulse
c. Bubble cap
d. Sieve plate
a. Packed
Overall efficiency of the distillation column is
a. the ratio of number of ideal plates to actual plates.
b. the ratio of number of actual plates to ideal plates.
c. same as the Murphree efficiency.
d. always more than the point efficiency.
a. the ratio of number of ideal plates to actual plates.
On addition of solute in the solvent, the __________ of the solution decreases.
a. boiling point
b. freezing point
c. vapour pressure
d. both (b) and (c)
d. both (b) and (c)
Which is the controlling factor for a drum drier?
a. Diffusion
b. Heat transfer
c. Both (a) and (b)
d. Neither (a) nor (b)
b. Heat transfer
Drying operation under vacuum is carried out to
a. dry those materials which have very high unbound moisture content.
b. reduce drying temperature.
c. increase drying temperature.
d. dry materials having high bound moisture content.
b. reduce drying temperature.
Air initially at 101. 3 kPa and 40°C and with a relative humidity of 50%, is cooled at constant pressure to 30°C. The cooled air has a
a. higher dew point.
b. higher absolute (specific) humidity.
c. higher relative humidity
d. higher wet bulb temperature.
c. higher relative humidity
*As the temperature decreases the relative humidity increases.
Temperature decrease of gas then vapour pressures also decrease.
Relative humidity= partial pressure of vapour in water air mixture /vapour pressure of pure water.
Separation of two or more components of a liquid solution can not be achieved by
a. fractional crystallisation
b. liquid extraction
c. absorption
d. evaporation
c. absorption
At minimum reflux ratio for a given separation
a. number of plates is zero.
b. number of plates is infinity.
c. minimum number of the theoretical plates is required.
d. separation is most efficient.
b. number of plates is infinity.
*At minimum reflux ratio number of plates infinites. When reflux ratio is increased theoretical requirement plates is decreases.
At minimum reflux ratio maximum number of trays minimum reboiler and condenser load.
At total reflux i.e., D=0 minimum number of trays and maximum reboiler and condenser loads.
Stefan’s law describes the mass transfer by
a. diffusion
b. bulk flow
c. both ‘a’ & ‘b’
d. neither ‘a’ nor ‘b’
c. both ‘a’ & ‘b’
Relative humidity is the ratio of the
a.partial pressure of the vapour to the vapour pressure of the liquid at room temperature.
b. partial pressure of the vapour to the vapour pressure of the liquid at gas temperature.
c. actual humidity to saturation humidity.
d. none of these
b. partial pressure of the vapour to the vapour pressure of the liquid at gas temperature.
**For this question, the answer should be C.
Because first of all, it is correct. Secondly, in the B part it is said that vapour pressure of any liquid which is not true because the humidity is measured for water vapours only and not any liquid.
In batch distillation with constant reflux, overhead product composition __________ with time.
a. increases
b. decreases
c. does not vary
d. may increase on decrease, depends on the system.
b. decreases
*Here the reflux is constant so at first as the composition decreases with time the overhead product composition diseases.
If the reflux is increased the the composition of the more volatile can be kept at constant.
Psychrometry deals with the properties of gas-vapor mixture. Humidity can be determined by the measurement of the __________ of a fibre.
a. electrical resistance
b. thermal conductivity
c. strength
d. none of these.
a. electrical resistance
.
*Thermal conductivity is the property of a given substance. It may be reported as certain quantity in literature, for fibre, but not for Fibre + Water mixture (Humid fibre). Hence, it is easier to measure resistance (=V/I) directly rather than extrapolating the resistivity values for the mixture.
Heat in BTU necessary to increase the temperature of 1 lb of gas and its accompanying vapour by 1°F is called the
a. latent heat
b. humid heat
c. specific heat
d. sensible heat
c. specific heat
**The right answer is humid heat.The right answer is humid heat.
Specific heat would have been the answer if the total mass of air+vapor would have been 1 lb but in question mass of air only is 1 lb hence the total mass of air + vapour will be greater than 1 lb.
To increase the absorption factor, (where, G = gas flow rate, S = solvent flow rate)
a. increase both ‘G’ and ‘S’.
b. decrease both ‘G’ and ‘S’.
c. increase ‘S’ and decrease ‘G’.
d. increase ‘G’ and decrease ‘S’
c. increase ‘S’ and decrease ‘G’.
*Absorption factor: A = S/(mG).
Dew point of a gas-vapour mixture
a. increases with temperature rise.
b. decreases with temperature rise.
c. decreases with decrease in pressure.
d. increases with increase in pressure.
c. decreases with decrease in pressure.
The mass diffusivity, the thermal diffusivity and the eddy momentum diffusivity are same for, NPr = NSc = __________
a. 1
b. 0.5
c. 10
d. 0
a. 1
In a packed absorption tower, if the equilibrium and operating lines are both straight lines, then the ratio, HETP/HTUOG __________ the absorption factor.
a. increases with increase in
b. is one at unity value of
c. both (a) and (b)
d. neither (a) nor (b)
c. both (a) and (b)
Height equivalent to a theoretical plate (HETP).
Height of a transfer unit (HTU).
1/HETP = (1/HTU[OG] + 1/HTU[OL]).
HTU[OG] = HTU[G] + S*HTU[L].
HTU[OL] =HTU[G]/S + HTU[L].
Where,
S= strriping factor = mG/L.
Which of the following plays an important role in problems of simultaneous heat and mass transfer ?
a. Lewis number
b. Schmidt number
c. Prandtl number
d. Sherwood number
a. Lewis number
In case of an absorber, the operating
a. line always lies above the equilibrium curve.
b. line always lies below the equilibrium curve.
c. line can be either above or below the equilibrium curve.
d. `velocity is more than the loading velocity.
a. line always lies above the equilibrium curve.
As the reflux ratio in a distillation column is increased from the minimum, the
a. slope of the operating line in stripping section decreases.
b. number of plates decreases very slowly first and then more and more rapidly.
c. total cost first decreases and then increases.
d. liquid flow increases while the vapor flow decreases for a system.
c. total cost first decreases and then increases.
- Total cost = operating cost + fixed cost.
Here first fixed cost decreases due to no of theoretical plate decreases but operation cost increases due to high reflux rate for which condenser duty and reboiler duty increases.
As the boil up ratio increases, then slope in stripping section decreases, as both boil up ratio and reflux ratio are different, so option A is incorrect. Moreover, option B, we can’t say how slowly or rapidly it decreases, so the most appropriate answer is option C.
Absorption factor is defined as (where, S1 = slope of the operating line S2 = slope of the equilibrium curve)
a. S2/S1
b. S1/S2
c. S1 - S2
d. S1 x S2
b. S1/S2
*Absorption factor, A = (Slope of operating line)/(Slope of equilibrium curve).
= S1/S2.
= (L/G)/m.
= L/mG.
Stripping factor S = 1/A.
A plait point is the point on the solubility curve, where the tie line reduces to a point. What is the number of plait point for a ternary system containing two pairs of partially miscible liquids ?
a. 0
b. 1
c. 2
d. 3
a. 0
*No plait point can exist in the ternary diagram where two pairs of partially miscible liquids exist.
It should be zero because looking at the binodal curve for two pair partially soluble liquid there’s nowhere we can find the plait point.
Which of the following remains constant during sensible cooling process ?
a. Specific humidity
b. Partial pressure of vapour
c. Both (a) and (b)
d. Neither (a) nor (b)
c. Both (a) and (b)
*The sensible cooling of air is the process in which only the sensible heat of the air is removed so as to reduce its temperature, and there is no change in the moisture content (kg/kg of dry air) of the air.
Heat transfer without phase change.
Physical absorption is
a. an irreversible phenomenon.
b. a reversible phenomenon.
c. accompanied by evolution of heat.
d. both (b) and (c)
d. both (b) and (c)
Make up water is required in a cooling tower to replace the water lost by
a. evaporation
b. drift
c. blowdown and leakage
d. all (a), (b) and (c)
d. all (a), (b) and (c)
*Drift is water lost from cooling towers as liquid droplets are entrained in the exhaust air.
Blowdown is draining of cooling water from the system for reducing the scale formation in line.
In cooling tower the cooling water circulated due to this increases the chance of scale in pipe line. For preventing from this some of cooling water drained time to time and fresh cooling water make up.
Which of the following quantities need not be fixed before starting the design of a co-current absorber ?
a. Heat gain or loss
b. Flow rate of entering liquid
c. Flow rate of gas
d. None of these
b. Flow rate of entering liquid
Mass transfer co-efficient of liquid is
a. affected more by temperature than that for gases.
b. affected much less by temperature than that for gases.
c. not affected by the temperature.
d. none of these.
a. affected more by temperature than that for gases.
*For gas M.T.C directly proportional to Dab/T. And Dab proportional to T^1.5 so M.T.C proportional to T^0.5. And liquid M.T.C proportional to Dab and Dab proportional to T. So M.T.C directly proportional to T. Option A is correct.
Absorption accompanied with chemical reaction is exemplified by the absorption of
a. ammonia in water.
b. benzol present in coke oven gas by wash oil.
c. SO2 in alkaline solution.
d. all (a), (b) and (c).
c. SO2 in alkaline solution.
Which of the following unit operations makes use of Thiele-Geddes equation ?
a. Liquid-liquid extraction
b. Solid-liquid extraction
c. Multicomponent absorption with chemical reaction
d. Multicomponent distillation.
d. Multicomponent distillation.
Which of the following liquid-vapor contacting devices provides maximum contact surface area for a particular duty ?
a. Sieve plate column
b. Bubble cap column
c. Randomly packed column
d. Wetted wall column
d. Wetted wall column
The equipment frequently used for adiabatic humidification-cooling operation with recirculating liquid is
a. natural draft cooling tower
b. induced draft cooling tower
c. spray chamber
d. none of these
c. spray chamber
*The cooling effect is achieved solely through the evaporation of water, which cools the air and increases its humidity without any external heat input or removal.
Also, denoted as adiabatic cooling.
Chemisorption (chemical adsorption) is
a. same as “Van der Waals” adsorption.
b. characterised by adsorption of heat.
c. an irreversible phenomenon.
d. a reversible phenomenon.
c. an irreversible phenomenon.
*Chemical adsorption, also known as chemisorption, solid materials is achieved by substantial sharing of electrons between the surface of adsorbent and adsorbate to create a covalent or ionic bond. Thus, chemical adsorption may not be fully reversible and could require high energy for regeneration.
The rate of solid-liquid extraction is limited by the
a. phase change of the solute as it dissolves in the solvent.
b. diffusion of the solute through the solvent in the pores to the outside of the particle.
c. diffusion of the solute from the solution in contact with the particle to the main bulk of the solution.
d. all ‘a’, ‘b’ & ‘c’.
d. all ‘a’, ‘b’ & ‘c’.
Raoult’s law applies to the
a. all liquid solutions
b. non-ideal solution only.
c. non-volatile solute.
d. solvents.
d. solvents.
*Raoult’s law expressed by;
Psolution= Xsolvent * Psolvent.
In distillation columns, the number of bubble caps per tray primarily depends upon the
a. allowable liquid velocity.
b. allowable gas velocity.
c. allowable gas and liquid velocities.
d. feed composition.
c. allowable gas and liquid velocities.
In distillation, overhead product contains
a. only one component
b. two components
c. any number of components
d. only saturated liquid
c. any number of components
With increase in pressure, the relative volatility for a binary system
a. increases.
b. decreases.
c. remains same.
d. either (a) or (b), depends on the system.
b. decreases.
Low viscosity absorbent is preferred for reasons of
a. rapid absorption rates and good heat transfer characteristics.
b. improved flooding characteristics.
c. low pressure drop on pumping.
d. all (a), (b) and (c).
d. all (a), (b) and (c).
Mass transfer co-efficient (K) and diffusivity (D) are related according to film theory as
a. K ∝ D
b. K ∝D
c. K ∝ D1.5
d. K ∝ D2
a. K ∝ D
Flim theory by Lewis and Whitman= k proportional to D.
Penetration theory by Higbie = k proportional to D^0.5.
Surface renewal by Dankwarts = k proportional to D^0.5.
Film Theory: k=D/S (D= diffusivity, S = film thickness).
Penetration Theory: k=√(D/πt) –> instantaneous mass transfer coefficient.(t= time)
k=2√(D/πt) –> average mass transfer coefficient.
Surface Renewal Theory: k=√(D*S) –> (S= surface renewal rate).
The McCabe Δ L law states that the
a. molar heats of vaporisation of components are nearly equal.
b. linear crystal growth rate depends on the degree of supersaturation.
c. linear crystal growth rate does not depend on the crystal size.
d. linear crystal growth rate depends on the crystal size.
c. linear crystal growth rate does not depend on the crystal size.
*Where L is a characteristic single dimension of the crystal, such as length. It has been shown that geometrically similar crystals of the same material grow at the rate described by independent of crystal size. This is known as the delta L law.
Bollman extractor
a. is a static bed leaching equipment.
b. is used for extraction of oil from oilseed.
c. is a centrifugal extractor.
d. employs only counter-current extraction.
b. is used for extraction of oil from oilseed.
*Bollman Extractor is mainly used for the recovery of additional oil from the residues obtained after mechanical pressing of solids.
The Bollman Extractor essentially consists of a vapour-tight vertical chamber in which a series of perforated baskets are attached to a chain conveyor.
The relation, Sc = Pr = 1, is valid, when the mechanism of __________ transfer is same.
a. heat and mass
b. mass and momentum
c. heat and momentum
d. heat, momentum and mass
a. heat and mass
**Option D is correct as the Schmidt Number is a ratio of momentum diffusivity and mass diffusivity, so if Sc = 1, then momentum and mass diffusivities should be the same, whereas the Prandtl number is a ratio of momentum diffusivity and heat diffusivity.
So, Pr = 1 implies heat diffusivity and momentum diffusivity are equal. So all three differences are the same in this case.
A coalescer in a mixer-settler liquid-liquid extraction coloumn
a. comprises of thin bed of substances of extended surface having high porosity.
b. helps in increasing the bubble size entering the settler.
c. helps in increasing the settling rate of the bubbles.
d. all ‘a’, ‘b’, & ‘c’.
d. all ‘a’, ‘b’, & ‘c’.
*A coalescer is a device which induces coalescence (Coalescence is the process by which two or more droplets, bubbles or particles merge during contact to form a single daughter droplet, bubble or particle) in a medium. They are primarily used to separate emulsions into their components via various processes, operating in reverse to an emulsifier.
For the same feed, feed quality and separation (in a distillation column), with the increase of total pressure, the number of ideal plates will
a. increase
b. decrease
c. remain same
d. data insufficient, can’t be predicted
a. increase
*With increase in pressure, Relative volatility decreases which leads to requirement of Large number of plates for the desired separation.
Pick out the correct statement.
a. Ponchan-Savarit method is more accurate than McCabe-Thiele method to determine the number of theoretical stages required for the separation of non-ideal binary system by distillation.
b. A sharp decrease in pressure drop is an indication of flooding in a distillation coloumn.
c. Solvent used in extractive distillation should be of high volatility.
d. Flash distillation is suitable for separating components which have very close boiling temperature.
a. Ponchan-Savarit method is more accurate than McCabe-Thiele method to determine the number of theoretical stages required for the separation of non-ideal binary system by distillation.
*This is because Ponchan-Savarit method takes energy balance of the system into account which is not considered in McCabe-Thiele method because of this the dew point bubble point curves are not straight and the latent heat of vapourisation is not a constant.
Weeping (caused by low vapour flow) is indicated by a sharp pressure drop in the column and reduced separation efficiency.
Flooding (caused by excessive vapour flow) is detected by sharp increases in column differential pressure and significant decrease in separation efficiency.
When the liquid phase and vapour phase of a binary system obeys Raoult’s and Dalton’s law respectively, the relative volatility is the ratio of
a. vapour pressure of component A to that of component B.
b. vapour pressure of component A to the total pressure.
c. vapour pressure of component A to the partial pressure of A.
d. partial pressure of component A to the total pressure.
a. vapour pressure of component A to that of component B.
*Raults law- partial pressure equals to the product of vapour pressure and the mole fraction in the liquid phase.
Dalton’s law- total pressure exerted by gaseous mixture is equals to the individual partial pressures exerted by the components in the gas.
The operation involved when the soluble material is largely on the surface of an insoluble solid and is merely washed off by the solvent is called
a. decoction
b. percolation
c. elutriation or elution
d. none of these
*Percolation: The slow passage of a liquid through a filtering medium.
Decoction: A concentrated liquor resulting from heating or boiling a substance, especially a medicinal preparation made from a plant.
Elutriation is a process for separating particles based on their size, shape and density, using a stream of gas or liquid flowing in a direction usually opposite to the direction of sedimentation. This method is mainly used for particles smaller than 1 μm.
In the constant rate period of the rate of drying curve for batch drying,
a. cracks develop on the surface of the solid.
b. rate of drying decreases abruptly.
c. surface evaporation of unbound moisture occurs.
d. none of these.
c. surface evaporation of unbound moisture occurs.
It takes 6 hours to dry a wet solid from 50% moisture content to the critical moisture content of 15%. How much longer it will take to dry the solid to 10% moisture content, under the same drying conditions? (The equilibrium moisture content of the solid is 5%).
a. 15 min
b. 51 min
c. 71 min
d. 94 min
c. 71 min
*Ss-mass of solid on a dry basis.
A-surface area per unit dry solid.
Nc-critical drying rate.
tc = (Ss/ANc)*(X1 - Xc)(1).
tc = time for constant drying.
We required moisture % 10. Which is < Xc.
Further drying will done by linear falling rate period.
(Ss/ANc) = tc /(X1 - Xc) =(6/(0.50 -0.15)) = 17.14.
tF = (Ss/ANc)(Xc “ X)ln((X1-X)/(X2-X))
where tF = falling rate period.
X = equilibrium moisture content.
X1 = INITIAL MOISTURE CONTENT =0.15.
X2 = FINAL MOISTURE CONTENT = 0.10.
tF = 1.1881 hr =71.28 min.
Agitator is provided in a crystalliser for
a. avoiding deposition on cooler surfaces.
b. formation of nuclei.
c. crystal growth.
d. all (a), (b) and (c).
d. all (a), (b) and (c).
__________ diffusion is used for separating the isotopes of methane.
a. Thermal
b. Pressure
c. Concentration
d. Force
a. Thermal
Ordinary diffusion process is also called __________ diffusion.
a.pressure
b. thermal
c. concentration
d. forced.
c. concentration
Pick out the wrong statement.
a. Different solids have different equilibrium moisture curves.
b. Total condenser or reboiler is considered equivalent to one theoretical plate in McCabe-Thiele method of theoretical plate calculation for distillation column.
c. Heat removal load on cooler remains constant, even with increase of the reflux ratio in a distillation column.
d. Even a forced draft cooling tower can not cool water below the wet bulb temperature.
c. Heat removal load on cooler remains constant, even with increase of the reflux ratio in a distillation column.
Pick out the wrong statement pertaining to the rotary dryer.
a. Flights (located in the inside shell of rotary dryer) lift the material being dried and shower it down through the current of hot air/gases. It extends from the wall to a distance which is about 8-12% of the inside diameter of shell.
b. Hold up of a rotary drier is defined as the fraction of the dryer volume occupied by the solid at any instant. The best performance for rotary drier is obtained, when the hold up is in the range of 0.05 to 0.15.
c. Rotary dryer is suitable for drying sticky material.
d. Recommended peripherial speed of a rotary drier is in the range of 10 to 30 metres/minute.
c. Rotary dryer is suitable for drying sticky material.
The reason for preferring packed towers over plate towers in distillation practice is that the packed tower operation gives
a. low pressure drop and high hold up.
b. high pressure drop and low hold up.
c. low pressure drop and low hold up.
d. high pressure drop and high hold up.
c. low pressure drop and low hold up.
*Low-pressure drop. The packed tower has a higher voltage, so the pressure drop is lower than the plate tower. In the normal condition, the pressure drop of the plate tower is about 0.4 - 1.1 kPa per unit theoretical stage while the packed tower is about 0.01- 0.27 kPa. The low-pressure drop can not only save the operating cost but also save energy. It is very suitable for heat-sensitive material separation.
Low liquid hold-up quantity. Liquid hold-up quantity refers to the liquid quantity on the packing surface, internals and plates. The liquid hold-up quantity of the packed tower is less than 6% while the plate tower is higher to 8-12%. Though the higher liquid hold-up quantity can ensure the stable structure of materials and tower, it needs long operating hours, long operating periods and expensive operating costs, which is bad for the distillation process.
If the path of liquid across the plate is very long as in case of large diameter tower, Murphree efficiency can be __________ percent.
a. 100
b. > 100
c. < 100
d. none of these
b. > 100
Compound A is extracted from a solution of A + B into a pure solvent S. A Co-current unit is used for the liquid-liquid extraction. The inlet rate of the solution containing A is 200 moles of B/hr.m2 and the solvent flow, rate is 400 moles of S/m2. hr. The equilibrium data is represented by Y = 3X2 , where Y is in moles of a A/moles of B and X is in moles A/moles of S. The maximum percentage extraction achieved in the unit is
a. 25%
b. 50%
c. 70%
d. 90%
b. 50%
*400 mol of S ——————>400mol of S+x mole of A.
200 mol of B+a mol of A—–>200mol of B +(a-x) mol of A.
Given y = 3x^2.
(a-x)/200 = 3(x/400)^2.
a-x =(3/800)*2.
The maximum percentage of extraction can be achieved.
When a - x = x or a = 2x.
Maximum extraction=x/a=x/2x=0.5.
= 50%.
Raoult’s law is applicable to the
a. ideal solutions
b. real solutions
c. mixture of water and alcohol
d. non-ideal gases
a. ideal solutions
Weeping in a distillation column
a. increases tray efficiency.
b. provides large interfacial surface for mass transfer.
c. results due to very high gas velocity.
d. results due to very low gas velocity.
d. results due to very low gas velocity.
*This phenomenon is caused by low vapour flow. The pressure exerted by the vapour is insufficient to hold up the liquid on the tray. Therefore, liquid starts to leak through perforations. Excessive weeping will lead to dumping. That is the liquid on all trays will crash (dump) through to the base of the column (via a domino effect) and the column will have to be re-started. Weeping is indicated by a sharp pressure drop in the column and reduced separation efficiency.
In case of binary distillation, increasing the reflux ratio above optimum does not result in the increase of
a. area between operating line and 45° diagonal x-y diagram.
b. condenser and reboiler surfaces.
c. tower cross-section.
d. none of these.
a. area between operating line and 45° diagonal x-y diagram.
*The rays are not drawn between operating line & diagonal but drawn between operating line & equilibrium curve.
As recycle ratio (L/D) increases, slop of enriching section will increases which drives off upper operating line far away from diagonal which results in an increase in area between both the line.
Wetted wall tower experiment determines the
a. molal diffusivity.
b. volumetric co-efficient.
c. mass transfer co-efficient.
d. none of these.
c. mass transfer co-efficient.
In McCabe-Thiele method, at infinite reflux ratio
a. the overhead product is minimum.
b. . both the operating lines coincide with diagonal.
c. both (a) and (b).
d. neither (a) nor (b).
a. the overhead product is minimum.
With decrease in the throughput (compared with the design capacity) for a bubble cap distillation column, its efficiency
a. increases
b. decreases
c. remains same
d. may increase or decrease ; depends on individual design
a. increases
Plate towers are preferred to packed towers, when large temperature changes are involved, because of the reason that the
a. packing may be crushed due to thermal expansion/contraction of the components of the equipments.
b. pressure drop in the equipment will be very high.
c. viscosity variation of the fluids may cause channeling/flooding.
d. none of these.
a. packing may be crushed due to thermal expansion/contraction of the components of the equipments.
The equilibrium liquid composition compared to the vapor composition in case of azeotropic mixture is
a. more
b. less
c. same
d. either more or less; depends on the system
c. same
Out of the following gas-liquid contacting devices, for a given set of operating conditions, gas pressure drop is the least in __________ tower.
a. wetted wall
b. bubble cap
c. perforated tray
d. packed
a. wetted wall
*The pressure drop of the wetted-wall column is significantly lower compared to the packed column.
Pick out the system with minimum boiling azeotrope at 1 atm.
a. benzene-toluene
b. ethyl alcohol-water
c. hydrochloric acid-water
d. all (a), (b) and (c)
The boiling points of C2H5OH and H2O are very close to each other
Free flowing granular materials can be best dried in a __________ drier.
a. rotary
b. cylinder
c. drum
d. freeze
a. rotary
In case of an ideal solution, the total vapor pressure varies __________ with the composition expressed as mole fraction
a. inversely
b. linearly
c. exponentially
d. none of these
b. linearly
Corresponding to Nusselt number in heat transfer, the dimensionless group in mass transfer is the __________ number.
a. Sherwood
b. Schmidt
c. Peclet
d. Stanton
a. Sherwood
If the specific heats of a gas and a vapor are 0.2KJ/Kg.°K and 1.5 KJ/Kg.°K respectively, and the humidity is 0.01; the humid heat in KJ/°Kg. is
a. 0.31
b. 0.107
c. 0.017
d. 0.215
d. 0.215
*Humid Heat = Sp heat of gas + (H * Sp.heat of vapour)
= 0.2+(0.01 * 1.5)=.215.
Liquid diffusivity is of the order of __________ cm2 /second.
a. 10.01
b. 0.1
c. 10-5 to 10-6
d. > 1
c. 10-5 to 10-6
*For liquid we have 10^-7 to 10^-9 m^2/s, then convert it into cm^2/ sec by multiplying 10^4.
For gas 10^-5.
For solids 10^-13 .
The solvent used in liquid extraction should not have high latent heat of vaporisation, because
a. the pressure drop and hence the pumping cost will be very high.
b. it cannot be recovered by distillation.
c. its recovery cost by distillation may be prohibitatively high.
d. it will decompose while recovering by distillation.
c. its recovery cost by distillation may be prohibitatively high.
At the same gas flow rate, the pressure drop in a packed tower being irrigated with liquid __________ that in dry packed tower.
a. is greater than
b. is lower than
c. is same as
d. cannot be predicted as data are insufficient
a. is greater than
Molarity is defined as the number of gm moles of solute per __________ of solvent.
a. litre
b. kg
c. gm
d. c.c
Molarity is defined as the number of gm moles of solute per __________ of solvent.
Molarity = (no.of gm moles of solute/ solutions in litres).
The value of Lewis number (Le = Sc/Pr) for air-water vapour system is around
a. 1
b. 0.24
c. 3.97
d. 600
a. 1
Which of the following T-H diagram is valid for dehumidification operation ?
*refer to Engineer cutie gc for reference
a
*We can take dehumdification as an example of water absorption from some gas lets say H2SO4 and water vapour mixture and hence we want to remove water from the mixture by using absorption.
