1. Why direct heating by hot air cannot be done in some cases?
- 1) The material can degrade
- 2) High temperature not required
- 3) Low temperature not required
- 4) Conduction gives best results
Answer: 1)
Explanation: Since some materials are thermally degradable, direct heating techniques cannot be employed.
2. When are drum dryers used?
- 1) When the material is too thick for spray dryer and too thin for rotary dryer
- 2) When the material is too thick for rotary dryer and too thin for spray dryer
- 3) When the material is not biodegradable
- 4) When large crystal size is to be obtained
Answer: 1)
Explanation: Drum dryers are used when the material is too thick for spray dryer and too thin for rotary dryer.
3. How is heating achieved in drum dryers?
- 1) By heating the drums
- 2) By conduction
- 3) By passing steam through hollow screws
- 4) By passing steam through the conveyer belt
Answer: 3)
Explanation: Heating is achieved in the drum dryers by passing heat through the hollow screws.
4. What is the drum dryer called if it is open to the atmosphere?
- 1) Open dryer
- 2) Box dryer
- 3) Trough dryer
- 4) Trench dryer
Answer: 3)
Explanation: When a drum dryer is open to the atmosphere it is called as trough dryer.
5. Which materials are not used in drying in a freeze dryer?
- 1) Seafood
- 2) Fruits
- 3) Pharmaceuticals
- 4) Dyes
Answer: 4)
Explanation: Dyes are not used to dry in freeze dryer.
6. How the liquid does gets separated in freeze dryer?
- 1) Boiling
- 2) Distillation
- 3) Freezing and crystallization
- 4) Evaporation
Answer: 3)
Explanation: The material is first frozen so that the liquid gets frozen and is separated as crystals.
7. Heat sensitive or easily oxidizable materials are dried by:
- 1) Flash dryer
- 2) Drum dryer
- 3) Fluidized bed dryer
- 4) Rotary dryer
Answer: 1)
Explanation: Since the contact time is less the flash dryer can be used to dry heat sensitive or easily oxidizable materials.
8. With what is the feed introduced in the spary dryer?
- 1) Spray
- 2) Atomizer
- 3) Nucleator
- 4) Heat exchanger
Answer: 2)
Explanation: A spray dryer is used to dry the atomized droplets of a feed that may be
a solution or a slurry of fine particles. It consists of a big drying chamber in which the feed is introduced through an atomizer at the top.
9. What is the use of a high pressure nozzle or a whirling disk in a spray dryer?
- 1) Increasing contact time
- 2) Decreasing contact time
- 3) Agitation
- 4) Atomization
Answer: 4)
Explanation: Atomization is done by a high pressure nozzle or a whirling disk.
10. Which dryer used radiation for drying?
- 1) Spray dryer
- 2) Drum dryer
- 3) Flash dryer
- 4) Microwave dryer
Answer: 4)
Explanation: A microwave dryer uses long wavelength radiation of the order of radio waves.
The material is heated throughout by the radiation that penetrates into it.
