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Machine Design MCQ Set 1

1. Relation between the slope of two operating line in the give figure.
mass-transfer-interview-questions-answers-freshers-q1
a) Equal
b) Un equal
c) 1>2
d) 2>1

View Answer

Answer: a [Reason:] There are parallel operating lines so the slope will be same.

2. Only small equipments is required for co-current process.
a) True
b) False

View Answer

Answer: b [Reason:] Only for the counter current process, the mean of driving force is large so small equipment is needed.

3. Find the concentration representation in the equilibrium distribution curve given below.
mass-transfer-interview-questions-answers-freshers-q3
a) Mole ratio
b) Mass ratio
c) Mole fraction
d) None of the mentioned

View Answer

Answer: c [Reason:] The operating line is a curve, so the representation must be in mole or mass fraction.

4. Find the slope of the operating line from the figure below.
mass-transfer-interview-questions-answers-freshers-q4
If, Ls,Gs- non diffusing solvent
X,Y- Concentrations in mole ratio
x,y- concentration in mole fraction

a) Ls/Gs
b) –Ls/Gs
c) Gs/Ls
d) –Gs/Ls

View Answer

Answer: a [Reason:] Gs(Y1)+Ls(X2)= Gs(Y2)+ls(X1) Y1-Y2= Ls/Gs(X1-X2) So the slope of the operating line is Ls/Gs

5. Find the driving force at the point (P) in the equilibrium distribution curve given below.
mass-transfer-interview-questions-answers-freshers-q5
a) Zero
b) Infinity
c) One
d) Greater than one

View Answer

Answer:a [Reason:] Here, the operating line touches the equilibrium line the mass transfer rates becomes zero. So the driving force will be zero at the point P.

6. The driving force line between the operating line and the equilibrium line depends on
a) Relative diffusion resistance
b) Relative mass resistance
c) Cumulative resistance
d) None of the mentioned

View Answer

Answer: a [Reason:] As the driving force changes continuously at every point in a counter current process, the relative diffusion resistance is taken into consideration.

7. Removal of ammonia from the air with water is an example of counter-current process.
a) True
b) False

View Answer

Answer: a [Reason:] Here, the ammonia + air is sent through one side and water is sent through other end.

8. For Air-Water system Lewis Number equals to
a) Approx 1
b) 0
c) Infinity
d) 0 to 1

View Answer

Answer: a [Reason:] For air-water system the simultaneous heat and mass transfer takes place. Therefore the Schmidt number (Sc) and Prandtl number (Pr) become equal. Lewis number= (Sc/Pr) equals to 1.

Machine Design MCQ Set 2

1. The Ponchon Savorit method is applicable for determining negligible heat loss.
a) True
b) False

View Answer

Answer: a [Reason:] As this method includes enthalpy concentration data it helps to determine the negligible heat loss.

2. External reflux ratio is used for Ponchon Savorit method.
a) True
b) False

View Answer

Answer: b [Reason:] Here the reflux ratio is based on the flow rates of the final plates of the enriching section or stripping section; so internal reflux ratio comes to the part.

3. Find the heat removed by the condenser if the net heat out of the condenser is 25000 J and the total moles are 25.
a) 1000 J
b) 10000 J
c) 5000 J
d) 2000 J

View Answer

Answer: a [Reason:] Heat removed by the condenser = net heat out/ net moles out = 25000 J/ 25 = 1000.

4. From the enthalpy-concentration diagram find the location of heat removed by the condenser.
mass-transfer-question-bank-q4
a) X
b) Y
c) Z
d) None of the mentioned

View Answer

Answer: a [Reason:] X is the heat removed by the condenser where the net heat removed by the net moles out can be determined.

5. Find the internal reflux ratio by analysing the below fractionator.
mass-transfer-question-bank-q5
a) 0.8
b) 1.25
c) 1.2
d) 1

View Answer

Answer: b [Reason:] Internal reflux ratio = 50/40 = 1.25.

6. Estimate the heat removed by the condenser.
mass-transfer-question-bank-q6
a) 20 KJ/Kg
b) 22 KJ/Kg
c) 24 KJ/Kg
d) 0

View Answer

Answer: b [Reason:] Heat removed by the condenser = Qc/D + Hd = 50/25 + 20 = 20 KJ/Kg.

7. Find the distillate rate by analysing the fractionator given below.
mass-transfer-question-bank-q7
a) 10 KJ
b) 20 KJ
c) 30 KJ
d) 40 KJ

View Answer

Answer: c [Reason:] We have to calculate from n th tray L*HL + G* Hg = DQ Q=(50*20 + 40*10)/20 = 30 KJ.

8. The fictitious stream is the difference in the flow rates of the nth tray.
a) True
b) False

View Answer

Answer: a [Reason:] Fictitious stream = Gn+1 – Ln (Represented by delta).

9. Ponchon Savorit method do not include enthalpy concentration diagram.
a) True
b) False

View Answer

Answer: b [Reason:] The heat losses or heat used by the condenser or reboiler determined only by enthalpy concentration data.

10. Find the flow rate of liquid entering into the enriching section if the internal reflux ratio is 1.5 times min. Given minimum reflux ratio is 0.95 and the gas flow rate is 35 mol/hr.
a) 49.87 mol/hr
b) 22.167 mol/hr
c) 55.26 mol/hr
d) None of the mentioned

View Answer

Answer: a [Reason:] Internal reflux ratio = Liquid flow rate/ gas flow rate ( in n th plate of section) 1.5 *0.95 = L/35 L= 49.87 mol/hr.

Machine Design MCQ Set 3

1. Device where two insoluble phases are brought into contact is known as
a) Trays
b) Stage
c) Cascade
d) Sieves

View Answer

Answer: b [Reason:] The stage is a single device where the phases are allowed to contact each other.

2. Ideal stages are also known as
a) Equilibrium or Theoretical stages
b) Equilibrium or Actual stages
c) Differential or Theoretical stages
d) Differential or Actual stages

View Answer

Answer: a [Reason:] Ideal stages are always equilibrium stages. Actual stages are practical stages hence theoretical stages are Ideal stages.

3. More than one stages are interconnected to form
a) Trays
b) Sieves
c) Cascades
d) Multiple stage

View Answer

Answer: c [Reason:] More than one stage is cascades.

4. The main purpose of cascades is
a) To get maximum conversion
b) To increase mass transfer rates
c) To get more efficiency
d) None of the mentioned

View Answer

Answer: b [Reason:] Though all the above mention is applicable, the main purpose is to increase the extent of mass transfer.

5. (Yn- Yn-1)/ (Yn*-Yn-1) is
a) Fractional overall
b) Murphree stage
c) Stage
d) Tray

View Answer

Answer: b [Reason:] The leaving stream is in equilibrium with its actual concentration. It is known as Murphree stage efficiency.

6. Find the number of stage(s)
mass-transfer-questions-answers-cascade-stages-q6
Where,
Y- Mole Ratio of gas phase
X- Mole Ratio of liquid phase

a) 1
b) 2
c) 1 to 2
d) No stage

View Answer

Answer: a [Reason:] one operating line = one stage.

7. Murphree efficiency is defined as the number of equilibrium stages to the number of real stages.
a) True
b) False

View Answer

Answer: a [Reason:] Fractional overall efficiency gives the ratio of equilibrium stage to real stage.

8. Find the value of y in an ideal single stage absorber is used to remove ammonia from gas with water as solvent. Its representation is given below
mass-transfer-questions-answers-cascade-stages-q8
Here,
y0=0.2, the molar gas flow rates of liquid and gas mixture in (moles/sec) are 4 and 2. The equilibrium relation between y and x is given by y = 0.2x. The solvent water is pure.
a) 1/10
b) 1/20
c) 2/110
d) 2/220

View Answer

Answer: b [Reason:] 2 (0.2) + 4(0) = 2 (y*) + 4(x) As y= 0.2x 0.4= 0.4x + 4x x= (1/11) y= 2/110.

9. ______________ is defined as the number of equilibrium stages to the number of real stages.
a) Murphree stage efficiency
b) Fractional overall efficiency
c) Stage efficiency
d) Overall efficiency

View Answer

Answer: b [Reason:] Fractional overall efficiency gives the ratio of equilibrium stage to real stage.

10. Find the Murphree stage efficiency for the following co-current operation with equilibrium leaving gas phase concentration Y*= 0.8.
mass-transfer-questions-answers-cascade-stages-q10
Where,
G and L are gas and liquid flow rates
Y and X are concentration in mole ratio (Y1=0.2, Y2=0.4, X1= 0.6, X2=0.8)
a) 25%
b) 50%
c) 75%
d) 100%

View Answer

Answer: a [Reason:] Murphree stage efficiency is= (Y2- Y1)/(Y2*- Y1) Given gas phase leaving stream in equilibrium Y2*= 0.8 Then, Murphree stage efficiency is (0.2/0.8) x 100 Murphree stage efficiency is 25%.

Machine Design MCQ Set 4

1. In which of the following conditions mass transfer will occur spontaneously? C and z is concentration and distance respectively.
a) dC/dz>0
b) dC/dz<0
c) dC/dz=0
d) None of the Mentioned

View Answer

Answer: b [Reason:] Mass transfer occurs in the direction of decreasing concentration.

2. Which among the following is always true for mass transfer to occur?
a) Difference in concentration
b) Difference in Pressure
c) Difference in temperature.
d) Difference in chemical potential.

View Answer

Answer: d [Reason:] Mass transfer occurs to attain an equilibrium position or to minimize the energy of the system. Mass occur can occur even if there is no difference in concentration, pressure and temperature. Example: – A ball rolls down a slope to minimize its potential energy.

3. A solution contains 0.3 moles of solute A, 0.2 moles of B and 0.5 moles of C. What will be the mole fraction of A in the mixture?
a) 0.3
b) 0.2
c) 0.5
d) 1

View Answer

Answer: a [Reason:] Mole Fraction of A= Moles of A/Total moles

Paragraph for question Numbers (4-6)

A gas mixture containing 21% O2 and 79% N2 flows through a pipe of circular cross-section of diameter 2cm at atmospheric pressure. The velocity of O2 is 0.04m/s and N2 is 0.035m/s.

4. What is the value of molar average velocity (m/s) of the mixture?
a) 0.036
b) 0.035
c) 0.034
d) 0.033

View Answer

Answer: a [Reason:] Molar average velocity= (C1u1+C2u2+……….)/C =y1u1+y2u2….. = 0.21*0.04+0.79*0.035 =0.036

5. What will be the value of mass average velocity (m/s)?
a) 0.981
b) 0.891
c) 0.985
d) 0.857

View Answer

Answer: a [Reason:] Mass average velocity= (ρ1u12u2)/ ρ ρ1= (p1*M1)/RT ρ= (p*M)/RT. Dividing these two equations ρ1/ ρ = (p1*M1)/pM =(y1*M1)/M M=y1*M1+y2*M2=0.79*28+0.21*32=28.84 Mass average velocity= (y1*M1*u1+y2*M2*u2)/M = (0.21*32*0.04+0.79*0.035)/28.84 = 0.981

6. What is the value of Volume average velocity?
a) 0.036
b) 0.035
c) 0.034
d) 0.033

View Answer

Answer: a [Reason:] Volume average velocity= Molar average velocity.

7. In a gas mixture if molecular weights of all the species are equal than which one will be more, Mass average velocity or Molar average velocity?
a) Mass average velocity
b) Molar average velocity
c) Both will have the same value
d) Nothing definite can be said

View Answer

Answer: c [Reason:] Average molar mass of the mixture=M(x1+x2+………+ xn)=M (x1+x2+………+ xn=1) Mass average velocity=Σuiρi/ρ=uiPui/P Molar average velocity=Σciui/c=ρuiPi/P (P=cRT).

8. The velocity of various components of mixture(21% A, 78% B and 1% C) are:
Velocity is in the form: v⃗=xi+yj+zk

Velocity of component A= (0.1, 0, 0)
Velocity of component B= (0, 0.1, 0)
Velocity of component B= (0, 0, 0.1)
Calculate the value of average molar velocity?
a) (0.021, 0.078, 0.01)
b) (0.1, 0.1, 0.1)
c) (0, 0 ,0)
d) (0.079, 0.021, 0.01)

View Answer

Answer: a [Reason:] Molar average velocity = (c1u1+c2u2+c3u3)/C.

9. Calculate the value of mass average velocity in the previous question?
a) (0.0235, 0.0764, 0.00007)
b) (0.021, 0.078, 0.01)
c) (0.1, 0.1 0.1)
d) (0.079, 0.021, 0.01)

View Answer

Answer: a [Reason:] (y1*M1*u1+y2*M2*u2)/M.

10. For the calculation of Mass average velocity, which velocity of the molecule is used?
a) Instantaneous Velocity
b) Mean Velocity
c) Instantaneous Velocity as well as Mean Velocity
d) Bulk velocity of the mixture

View Answer

Answer: b [Reason:] None.

11. Which among the following can be the unit of Flux?
a) Kg*m-2*s-1
b) Kg*m2*s-1
c) Kg*m2*s1
d) Kg*m*s2

View Answer

Answer:a [Reason:] Dimension analysis. Flux= rate at which a species passes through a unit area, in unit time.

12. A molecule in a mixture moves with a velocity of 0.03m/s in (+x) direction. The concentration of the particle is 0.5 mol/liter. A observer is running in (-x) direction with a velocity of 2m/s. calculate the value of molar flux (mol/m2.s) relative to the observer.
a) 0.015
b) 15
c) 1.015
d) 1015

View Answer

Answer: d [Reason:] Molar flux with respect to observer= C(u-U) (C=500mol/m3, u=0.03m/s, U= (-) 2m/s).

13. In the previous question what will be the value of flux (mol/m2.s) with respect to a stationary observer?
a) 0.015
b) 15
c) 1.015
d) 1015

View Answer

Answer: b [Reason:] Here U=0.

14. Under which of the following conditions mass average velocity and molar average velocity are equal?
a) In a very dilute solution
b) If molecular weights of all the species are equal
c) Always different
d) In dilute solutions as well as in solutions in which all components have same molecular weights

View Answer

Answer: d [Reason:] None.

15. The mass flow rate of a component in a mixture in X-direction is 2kg/s. The area vector at a particular cross-section is (1.1, 3.2, 5.4) cm2. Calculate the value of flux (kg/cm2.s) through the cross-section.
a) 0.31
b) 2.2
c) 1.82
d) 6.45

View Answer

Answer: c [Reason:] For flux calculation area normal to the flow direction should be taken into account.

Machine Design MCQ Set 5

1. The ratio of mass concentration of species A to the total mass density of the mixture is known as
a) Mass density
b) Concentration
c) Mole fraction
d) Mass fraction

View Answer

Answer: d [Reason:] It is defined as p a/p.

2. For a binary mixture of species A and B, the mass average velocity is defined as
a) 2 p a V a + p b V b/ p
b) p a V a + p b V b/ p
c) p a V a + 2 p b V b/ p
d) p a V a + p b V b/ 2 p

View Answer

Answer: b [Reason:] p a V a + p b V b/ p a + p b = p a V a + p b V b/ p.

3. The ratio of number of moles of species A to the total number of moles of the mixture is known as
a) Mole fraction
b) Mass fraction
c) Partial pressure
d) Mass density

View Answer

Answer: a [Reason:] It is defined as n a/n.

4. A binary mixture of oxygen and nitrogen with partial pressures in the ratio 0.21 and 0.79 is contained in a vessel at 300 K. If the total pressure of the mixture is 1 * 10 5 N/m2, find molar concentration of oxygen
a) 8.42 * 10 -1 kg mol/m3
b) 8.42 * 10 -2 kg mol/m3
c) 8.42 * 10 -3 kg mol/m3
d) 8.42 * 10 -4 kg mol/m3

View Answer

Answer: c [Reason:] 0.21 * 10 5/8341 * 300 = 8.42 * 10 -3 kg mol/m3.

5. For a binary mixture of species A and B, the molar average velocity is defined as
a) n a V a + n b V b
b) n a V a + n b V b/n
c) n a V a + n b V b/2 n
d) n a V a + 2 n b V b/n

View Answer

Answer: b [Reason:] n A V A + n B V B/n A + n B = n A V A + n B V B/n.

6. Given diagram shows diffusion of water vapor through air. Identify the correct statement
mass-transfer-questions-answers-concentrations-velocities-fluxes-q6
a) The water evaporates and diffuses downward
b) The water does not evaporates but diffuses upward
c) The water evaporates and diffuses upward
d) The water does not evaporates but diffuses downward

View Answer

Answer: c [Reason:] The slight movement of air over the top of the tube does not bring about any change in the concentration profile of air.

7. A binary mixture of oxygen and nitrogen with partial pressures in the ratio 0.21 and 0.79 is contained in a vessel at 300 K. If the total pressure of the mixture is 1 * 10 5 N/m2, find overall mass density
a) 4.156 kg/m3
b) 3.156 kg/m3
c) 2.156 kg/m3
d) 1.156 kg/m3

View Answer

Answer: d [Reason:] For oxygen = 0.269 kg/m3 and for nitrogen = 0.887 kg/m3.

8. A binary mixture of oxygen and nitrogen with partial pressures in the ratio 0.21 and 0.79 is contained in a vessel at 300 K. If the total pressure of the mixture is 1 * 10 5 N/m2, find molar fraction of nitrogen
a) 0.79
b) 0.21
c) 0.23
d) 0.13

View Answer

Answer: a [Reason:] Molar fraction is equal to the partial pressure.

9. A binary mixture of oxygen and nitrogen with partial pressures in the ratio 0.21 and 0.79 is contained in a vessel at 300 K. If the total pressure of the mixture is 1 * 10 5 N/m2, find mass fraction of oxygen
a) 0.133
b) 0.233
c) 0.333
d) 0.433

View Answer

Answer: b [Reason:] 0.269/1.156 = 0.233.

10. A binary mixture of oxygen and nitrogen with partial pressures in the ratio 0.21 and 0.79 is contained in a vessel at 300 K. If the total pressure of the mixture is 1 * 10 5 N/m2, find the average molecular weight of the mixture
a) 28.84
b) 29.84
c) 30.84
d) 31.84

View Answer

Answer: a [Reason:] (0.21) (32) + (0.79) (28) = 28.84.

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