This set of Food Engineering test focuses on “Evaporation-2”.
1. Statement 1: Horizontal tube evaporator is easy for cleaning.
Statement 2: Horizontal tube evaporator has a disadvantage of hindering agitation of the feed.
a) True, False
b) True, True
c) False, False
d) False, True
View Answer
Explanation: Horizontal tube evaporator is easy for cleaning as the evaporator part can be easily dismantled from the rest of the equipment parts. Horizontal tube evaporator has a disadvantage of hindering agitation of the feed as it is present outside the horizontal tubes.
2. Statement 1: In a rising film evaporator, the feed can be very viscous.
Statement 2: In a rising film evaporator, the feed cannot be heat sensitive.
a) True, False
b) True, True
c) False, False
d) False, True
View Answer
Explanation: In a rising film evaporator, the feed cannot be very viscous as the feed is made to flow against gravity. But, it can be heat sensitive because the residence time of the feed inside the evaporator is very low.
3. In a rising film evaporator, the temperature difference need not be as high as that in a falling film evaporator.
a) True
b) False
View Answer
Explanation: In a rising film evaporator, the temperature difference has to be high otherwise the vapor formation won’t be possible at a low residence time. Whereas, in a falling film evaporator, the temperature difference can be relatively lower than that in rising film. (It’s only comparative; the temperature difference in falling film is also required to be pretty high.)
4. Plate evaporators are used in recovering aroma from fruit juices.
a) True
b) False
View Answer
Explanation: Flash evaporators are used in recovering aroma from fruit juices. The juices are preheated and then flashed. The vapors are collected. They contain the aroma. These are made to condense onto a surface and hence the aroma is recovered.
5. Statement 1: Scraped surface evaporators are used in the dairy industry.
Statement 2: Plate evaporators can be used for viscous liquids.
a) True, False
b) True, True
c) False, False
d) False, True
View Answer
Explanation: Plate evaporators are used in the dairy industry as they have high temperature, short time operations and hence heat sensitive materials can be treated. Scraped surface evaporators can be used for viscous liquids as the scraper helps them in their motion.
6. Industry A is low on budget and is used in the sugar industry. Industry B wants to invest in a good evaporator. They are needed for meat extracts. Which evaporators will you suggest for each of them?
a) Forced circulation evaporator, forced circulation evaporator
b) Rising film evaporator forced circulation evaporator
c) Forced circulation evaporator, rising film evaporator
d) Rising film evaporator, rising film evaporator
View Answer
Explanation: Rising film evaporator is a low cost evaporator. It is also a single pass; hence heat sensitive sugars can be treated. Forced circulation evaporators are slightly more expensive. Also, they can be used for viscous materials like meat extracts.
7. A major reason as to why evaporators and their selection for different applications in the food industry is very important is because ______
a) Organoleptic characteristics of food is very important
b) Many food items are heat sensitive
c) Majority of them have high moisture content
d) All of the mentioned reasons
View Answer
Explanation: All the above mentioned reasons relevant to the question are true.
8. Desolventization which is done in certain evaporators is more similar to distillation than evaporation.
a) True
b) False
View Answer
Explanation: Desolventization involves the recovery of the vapors which is generally not done in evaporation. Hence it is more similar to distillation than evaporation.
9. In flashing of jams, the temperature of concentrated jam _____ on flashing. Also, the vapor pressure of the concentrated jam _____
a) Decreases, sustains combustion
b) Increases, sustains combustion
c) Decreases, does NOT sustain combustion
d) Increases, does NOT sustain combustion
View Answer
Explanation: In flashing of jams, the temperature of concentrated jam decreases on flashing as the source of ignition is the solvent itself. Also, the vapor pressure of the concentrated jam sustains combustion as the temperature is brought down to the flash point which is the lowest temperature at which the vapor pressure is just sufficient to sustain combustion.
10. In plate evaporator, the heat transfer coefficient is high in spite of low residence time because _____
a) It deals with high viscosity food items
b) It is economic
c) Feed is made to pass as thin film
d) All of the mentioned reasons
View Answer
Explanation: In plate evaporator, the heat transfer coefficient is high in spite of low residence time because the feed is made to pass as a thin film and hence it exposes a greater surface area for heat transfer.
Sanfoundry Global Education & Learning Series – Food Engineering.
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