This set of Heat Transfer Operations Multiple Choice Questions & Answers (MCQs) focuses on “Short Tube Vertical Evaporator”.
1. Short tube vertical evaporators are commonly used in sugar industries.
a) True
b) False
View Answer
Explanation: Short tube vertical evaporators are one of the oldest used evaporators and find its common use in evaporating sugarcane juice.
2. Short tube vertical evaporators are also known as __________
a) Plate type Evaporators
b) Calandria Evaporators
c) Basket evaporators
d) Falling film evaporators
View Answer
Explanation: Short tube evaporators have cylinders that hold the tubes and hence these types of evaporators are called calandria(cylindrical) evaporators.
3. What is the average tube length of short tube evaporators?
a) 4-10ft
b) 4-10m
c) 1-2ft
d) More than 10m
View Answer
Explanation: The average tube size of short tube evaporators are around 4-10ft for any industrial process, however it may change but the range remains the same.
4. The heating medium in the calandria of the short tube evaporator is usually _______
a) Gas at temperature just above 130℃
b) Steam
c) Gas at temperature just below 100℃
d) Gas at very high temperatures
View Answer
Explanation: Short tube evaporators use steam at 100℃ to boil the solution by avoiding nucleate boiling, because of which we cannot use other given options.
5. The central tube in the short tube evaporator known as down-comer has _________ diameter.
a) Larger
b) Smaller
c) Same
d) Very large
View Answer
Explanation: The central or down-comer has larger diameter to provide larger surface area for evaporation for the fluid that has reached the bottom but has not reached the desired concentration so it is recycled back to the down-comer.
6. The heating medium, steam in the case of short tube evaporator, is used in _______
a) Shell side
b) Tube side
c) Same side as that of the fluid
d) Any preferable side
View Answer
Explanation: The heating medium is kept in the shell side and the fluid passes through the tubes during which the fluid is heated to have effective evaporation.
7. The down-comer are of the short tube evaporator is about _______ of the total surface area.
a) 0-20%
b) 20-35%
c) 40-70%
d) 70-10%
View Answer
Explanation: The down-comer in a short tube evaporator has longer diameter due to which it has more surface area, which is approximately 40-70% of the total tube area.
8. Which one of the following is not an advantage of short tube evaporators?
a) Evaporator tubes expand the warming surface about 10 to 15 times than a steam jacketed pot
b) Low head space required
c) Corrosive fluids can be used as cleaning is easy
d) Relatively inexpensive to manufacture
View Answer
Explanation: In Short tube vertical evaporators, corrosive fluids cannot be used as the setup is not easy to dismantle and clean and hence we usually use cleaner fluids whose deposits can be removed by water.
9. The following are few demerits of using short tube vertical evaporators, select the incorrect one.
a) The fluid stays a long time above the tubes which takes long time to heat up
b) Corrosive fluids cannot be used as it increases cleaning cost
c) Convoluted tube increase the cost of manufacture
d) Very low heat transfer coefficients with thin fluids
View Answer
Explanation: The short tube evaporators are most commonly used with thin fluids as they do not scale and do not accumulate at the top. These fluids hence provide large heat transfer coefficients.
10. What is the direction of flow in the down-comer and the tubes?
a) Both downwards
b) Both upwards
c) Downward and upward respectively
d) Upward and downward respectively
View Answer
Explanation: The down-comer brings the fluid downward with a large area for maximum evaporation and the sends it upwards by the tubes to get heated.
11. Recognize the correct diagram of the flow directions in short tube evaporators.
a) 
b) 
c) 
d) 
View Answer
Explanation: The down-comer brings the fluid downward with a large area for maximum evaporation and the sends it upwards by the tubes to get heated.
12. Which one of the following is short tube evaporator?
a) 
b) 
c) 
d) 
View Answer
Explanation: The given answer is a short tube evaporator recognized from the direction of flow of the fluid in it. It has short tubes and vapour escapes from top.
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