250+ TOP MCQs on Evaporators – Types of Feeding and Answers

Heat Transfer Operations Multiple Choice Questions on “Evaporators – Types of Feeding”.

1. What do we mean by types of feeding in an evaporator?
a) Total number of different types of feed available
b) Types of steam temperature applied
c) Types of recycle feed applied
d) Types of product extracted

Answer: c
Clarification: The statement of types of feed in evaporator defines the way of arranging the recycle feed from one evaporator to two or more other evaporators is known as a type of feed.

2. Which one of the following is not a type of feeding in an evaporator?
a) Forward feed
b) Backward feed
c) Convoluted feed
d) Mixed feed

Answer: c
Clarification: There are four types of feed which are currently in industrial use which are –

1. Forward feed
2. Backward feed
3. Parallel feed
4. Mixed feed.

3. Parallel feed is almost the same as forward feed in an evaporator.
a) True
b) False

Answer: b
Clarification: No, the statement is wrong. In forward feed the feed is taken in series where the product of a particular single effect is the feed to the other, whereas the parallel feed setup has independent feed supply to each unit.

4. Why do we use more than one type of feeding in an evaporator?
a) To increase the feed efficiency
b) To increase the efficiency of the steam used
c) To decrease the steam consumption per unit mass of feed
d) To increase the steam consumption per unit mass of feed

Answer: c
Clarification: The steam consumption can be reduced to a low value if we use evaporators in series as it would then reuse the vapour from the first one to heat the second one, hence considerable reducing the consumption.

5. The product concentration in a forward feed evaporator _________ as we move to successive evaporators.
a) Increases
b) Decreases
c) Remains same
d) Is different for each

Answer: a
Clarification: The forward feed setup has series connection where the product of a particular single effect is the feed to the other. Hence the product concentration increases with each subsequent evaporator.

6. The product concentration in a backward feed evaporator _________ as we move to successive evaporators.
a) Increases
b) Decreases
c) Remains same
d) Is different for each

Answer: b
Clarification: The backward feed setup has series connection where the product of a particular single effect is the feed to the other in the opposite direction, i.e. from back to front. Hence the product concentration decreases with each subsequent evaporator.

7. For mass balance in the forward pass evaporator, select the correct option.
a) F = E₃ + P₃
b) F = E₁ + E₂ + E₃ + P₃
c) F = P₁ + P₂ + P₃
d) F = E₁ + E₂ + E₃ + P₁ + P₂ + P₃

Answer: b
Clarification: The mass balance is F = E₁ + E₂ + E₃ + P₃ because the product of a particular setup is the feed for another and if we join the whole setup as one, we see F entering and E₁ + E₂ + E₃ + P₃ leaving.

8. Which evaporator uses the maximum number of pumps for its operation?
a) Forward feed
b) Backward feed
c) Parallel feed
d) Mixed feed

Answer: b
Clarification: The backward feed evaporator requires a pump between each pair of effects to transfer liquid from lower pressure effects to higher pressure effects and this is in maximum effect only in backward feed and to an extent in the mixed feed.