Mass Transfer online quiz on “Design of Fractionator with Mc-cabe Thiele Method”.
1. The Enriching section operating line intercept at the origin in McCabe-Thiele method when
a) Reflux ratio = Zero
b) Reflux ratio= Infinity
c) Reflux ratio= One
d) Reflux ratio= 1.5 to 2 times Reflux minimum
Answer: b
Clarification: When the Enriching section operating line intercept at origin then the operating line will become the diagonal line (45 degree line) that means all the condenser product are refluxed( No distillate). i.e. Reflux ratio =(R/D) if D=0 then reflux ratio tends to infinity that gives a minimum number of trays for designing the distillation column.
2. If the feed enters the distillation column at its dew point, then the slope of the Flash vaporization operating line is
a) Infinity
b) 0
c) 1
d) Between 0 and 1
Answer: b
Clarification: If the feed at dew point means the feed condition is saturated vapour so the enthalpy of feed is same as the enthalpy of the vapour. Therefore the slope of the Q-line is 0. Since Q-line is the Flash vaporization operating line.
3. If there is no reflux to a fractionating column then
a) Large condenser size is needed
b) Less reboiler size needed
c) Minimum number of trays
d) None of the mentioned
Answer: a
Clarification: Because if there is no reflux stream to the continuous distillation column then the entire vapour product after condensed from the condenser becomes a distillate but practically it is not possible but as per the theory in order to get all the vapour as distillate the condenser must be so large which is economically cost more.
4. After leaving the condenser if the liquid is at bubble point then which of the following is correct?
a) Same concentration of distillate and reflux
b) Different concentration of distillate and reflux
c) No latent heat is removed
d) None of the mentioned
Answer: a
Clarification: Since the latent heats are alone removed by the condenser so the concentration of liquid entering the condenser and the concentration leaving the condenser are same.
5. McCabe –Thiele method excludes ________ information.
a) Entropy
b) Enthalpy
c) Flow rate
d) Number of theoretical stages
Answer: b
Clarification: Ponchon-Savarit method alone includes enthalpy concentration data.
6. Non-equimolal flow rates are maintained in the fractionator obeying McCabe-Thiele method.
a) True
b) False
Answer: b
Clarification: According to McCabe’s assumptions only equimolal flow rates of both liquid and gas are maintained.
7. Heat losses are avoided in McCabe-Thiele method.
a) True
b) False
Answer: a
Clarification: According to the assumptions of McCabe-Thiele method the heat losses are avoided.
8. Find the point P in this enriching section.
a) Xd/R-1
b) Xd/R+1
c) R/Xd-1
d) R/Xd+1
Where, Xd- concentration of distillate and R- reflux ratio
Answer: b
Clarification: Since the intercept obtained from the derivation for McCabe method is Xd/R+1.
9. The slope of the operating line of the enriching section is R/R+1.
a) True
b) False
Answer: a
Clarification: Since the slope obtained from the derivation for McCabe method is R/R+1. Where, R- reflux ratio.
10. Find the slope of the operating line of the top section of Fractionator if Reflux ratio is 2.
Hint: use McCabe Thiele method is applicable
a) 0.57
b) 0.67
c) 0.77
d) 0.87
Answer: b
Clarification: Slope =R/R+1 = 2/3 = 0.67.
11. Look the below figure and find the possibility of measurement.
a) Maximum number of trays
b) Minimum number of trays
c) Single stage
d) None of the mentioned
Answer: b
Clarification: the operating line meets the 45 degree diagonal line we can determine the minimum number of trays because there is no reflux.
12. Find the location of condenser from the figure below.
a) P
b) R
c) S
d) No condenser
Answer: a
Clarification: Condenser always present in the top near the distillate.
13. In order to find the total number of theoretical trays we usually add one stage additional for ___________
a) Condenser
b) Reboiler
c) Condenser or Reboiler
d) No additional trays
Answer: c
Clarification: It is necessary to include condenser or reboiler since the separation may occur in such locations.