This set of Heat Transfer Operations Multiple Choice Questions & Answers (MCQs) focuses on “Common Dryers”.
1. Moisture content of a substance which exerts as equilibrium vapour pressure less than of the pure liquid at the same temperature is referred to as _________
a) Bound moisture
b) Unbound moisture
c) Moisture
d) Total Moisture
View Answer
Explanation: The bound moisture is the moisture that does not evaporate and is present during the falling rate period.
2. Moisture content of the solid which exerts an equilibrium vapour pressure equal to that of pure liquid at the given temperature is the ____________
a) Bound moisture
b) Unbound moisture
c) Moisture
d) Total Moisture
View Answer
Explanation: The unbound moisture is the moisture that evaporates and is lost during the constant rate period as given in the following diagram.
3. The moisture content of solid in excess of the equilibrium moisture content is referred as _______
a) Bound moisture
b) Free moisture
c) Moisture
d) Total Moisture
View Answer
Explanation: The free moisture is the moisture that evaporates and is lost during the constant rate period as given in the following diagram.
4. During drying, only __________ can be evaporated, which depends upon the vapour concentration in the gas.
a) Bound moisture
b) Fixed moisture
c) Free moisture
d) Total Moisture
View Answer
Explanation: The unbound or the free moisture is the water content of the substance that comes readily to the surface and gets evaporated during constant rate period.
5. The moisture contents of solid when it is in equilibrium with given partial pressure of vapour in gas phase is called as _____________
a) Equilibrium moisture content
b) Fixed moisture
c) Free moisture
d) Total Moisture
View Answer
Explanation: Equilibrium moisture content is the moisture content of solid when it is in equilibrium with given partial pressure of vapour in gas phase, this is the moisture content at that particular condition of the drying process.
6. Dryers heated by dielectric, radiant or microwave energy are _______________
a) Adiabatic
b) Non-Adiabatic
c) Isobaric
d) Isothermal
View Answer
Explanation: The microwave energy supplied is non-adiabatic in nature, i.e. the heat energy is not lost to the surroundings. It is not isothermal even though the temperature might be same.
7. Agitated vacuum dryers are a subcategory of/ can be referred to as _____________
a) Batch – Type Dryers
b) Continuous Dryers
c) Drum Dryers
d) Plate – type dryers
View Answer
Explanation: Agitated vacuum dryers are batch dryers as they cannot handle continuous flow of feed as the continuous feed dryers do such as drum dryers.
8. Which one of the following is not a batch dryer?
a) Agitated vacuum dryer
b) Tray dryer
c) Rotary dryer
d) Pan dryer
View Answer
Explanation: Rotary dryer is continuous feed dryer, the batch dryers can be classified as –
- Agitated vacuum dryer
- Tray dryer
- Pan dryer
9. ____________ involves the sublimation of water from ice under high vacuum at temperatures well below 0°C.
a) Freeze-drying
b) Flash drying
c) Furnace drying
d) Ice drying
View Answer
Explanation: Freeze drying is a dehydration process operated at very low temperature and pressure, on a feed which gets frozen after which the water is removed as ice by sublimation.
10. Which one of the following is best suited for heat sensitive feed?
a) Freeze-drying
b) Flash drying
c) Furnace drying
d) Ice drying
View Answer
Explanation: Freeze drying is a dehydration process operated at very low temperature and pressure, on a feed which gets frozen after which the water is removed as ice by sublimation. As we go by the definition, there is literally no use of high temperatures for drying rather very low temperatures, hence it is best suited for sensitive materials.
11. The atmospheric __________ has a jacketed round pan in which a stirrer or mill revolves slowly, driven from below.
a) Drum dryer
b) Pan – dryer
c) Agitated dryer
d) Furnace dryer
View Answer
Explanation: The jacketed pan mentioned in the given question tells us that the dryer is a pan dryer. It is a batch drying equipment best suited to produce crystal products.
12. Which one of the following batch-drying equipment can also be used as a crystallizer by passing cold liquid?
a) Drum dryer
b) Pan – dryer
c) Agitated dryer
d) Furnace dryer
View Answer
Explanation: The jacketed pan mentioned in the given question tells us that the dryer is a pan dryer. It is a batch drying equipment best suited to produce crystal products because the pan gives the ideal temperature and pressure conditions for crystallisation to occur.
13. Which one of the following batch-type dryer is the most versatile one, which can handle fouling to sensitive fluids?
a) Drum dryer
b) Pan – dryer
c) Agitated dryer
d) Furnace dryer
View Answer
Explanation: Agitated dryer is the most versatile dryer as it has the ability to handle large feed, fouling/scaling feeds, crystallising feed and many others by its advanced methods of blades.
14. Which one of the following batch-drying equipment has the least drying time/ residence time?
a) Drum dryer
b) Pan – dryer
c) Agitated vacuum dryer
d) Furnace dryer
View Answer
Explanation: Agitated dryer is the most versatile dryer as it has the ability to handle large feed, fouling/scaling feeds, crystallising feed and many others by its advanced methods of blades. It also has very low residence times as the scraping process of these dryers speeds up the process.
15. What is the name of the following dryer?
a) Drum dryer
b) Pan – dryer
c) Agitated vacuum dryer
d) Furnace dryer
View Answer
Explanation: A drum dryer as given in the diagram above, a mixture of feed having quality solid suspension which is to be dried, is fed to it from the top the rotating drums which there after forms a thin layer on the surface of the rotating drum, which then falls as a powdered product at the bottom.
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