This set of Dairy Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Deareator”
1. Aeration in milk doesn’t occur in which of the following states?
a) Dispersed state
b) Dissolved state
c) Chemically bound state
d) Crystal state
Explanation: Air in milk occurs in three states namely Dispersed; Dissolved; and chemically bound.
2. Milk in udder contains what percentage of gases?
Explanation: The total volume of air in milk in the udder can be some 4.5 – 6 %, of which O2 constitutes about 0.1%, N2 (nitrogen) about 1% and CO2 3.5 – 4.9%.
3. Dispersed air in milk cause problems.
Explanation: It is not unusual for incoming milk to contain 10% air by volume or even more. Finely and coarsely dispersed air predominates at this stage. Dispersed air causes problems.
4. Aeration leads to ______ in volumetric measurement of milk.
Explanation: Inaccuracy in volumetric measurement of milk is observed due to dispersion of air in the milk.
5. Which among the following are the problem associated with aeration in milk?
I) Incrustation of heating surfaces in pasteurizers (fouling)
II) Reduced skimming efficiency in separators
III) Loss of precision in automatic in-line standardization
IV) Inaccurate in-line fat standardization
a) I), II) and III)
b) I) and II)
c) I), II), III) and IV)
d) I) only
Explanation: The basic problems caused by dispersed air are Inaccuracy in volumetric measurement of milk, incrustation of heating surfaces in pasteurizers (fouling), reduced skimming efficiency in separators, loss of precision in automatic in-line standardization and concentration of air in cream, causing inaccurate in-line fat standardization.
6. In order to make milk pass through air eliminator, the inlet of the cylindrical vessel must be located at a ______ level than the outlet pipe of the milk tank on the vehicle.
Explanation: The inlet of the cylindrical vessel must be located at a lower level than the outlet pipe of the milk tank(s) on the vehicle, as the milk should not be pumped into the vessel but transferred to it by gravity.
7. Efficiency of milk deaerator depends on which of the following factor?
a) Fat content
c) Fat globule size
d) Dispersion of air
Explanation: The deaeration system can be manually or automatically operated. In both cases, the efficiency of air elimination depends very much on how finely dispersed the air is. The smallest air bubbles cannot be removed.
8. Which law forms the basis of working of deaerator?
a) James law
b) Planck law
c) Law of thermodynamic
d) Henry law
Explanation: According to William Henry in 1803 its state, that gas solubility in a solution decreases as the gas partial pressure above the solution decreases. The solubility of a gas dissolved in a liquid is directly proportional to the partial pressure of the gas.
9. Solubility of gases decrease with ________ in solution temperature.
c) No change
d) Increase and decrease
Explanation: Solubility of gases decrease with an increase in solution temperature and or decrease in pressure. The solubility of gas in a solution decreases as the temperature of the solution rises and approaches saturation temperature.
10. Which of the deaerator have application in the dairy industry?
a) Tray type
b) Vacuum type
c) Spray type
d) Bubble type
Explanation: Vacuum deaeration has been used successfully to expel dissolved air and finely dispersed air bubbles from milk. Warm (Preheated) milk is fed into an expansion vessel in which the vacuum level is adjusted to a level equivalent to a boiling point.
11. Components of vacuum deaerator are?
II) Vacuum pump
III) Pump unit
a) I) only
b) II) only
c) III) only
d) I), II) and III)
Explanation: A vacuum deaerator consists of three main components a vacuum deaerator, a vacuum pump unit and a pump unit.
12. What is the oxygen content of commercial mixed raw milk?
Explanation: Commercial mixed raw milk constitutes about 0.47% of oxygen in it. The total volume of air in milk in the udder can be some 4.5 – 6 %, of which oxygen constitutes about 0.1%.
13. What is the nitrogen content of commercial mixed raw milk?
Explanation: Commercial mixed raw milk constitutes about 1.29% of nitrogen in it. The total volume of air in milk in the udder can be some 4.5 – 6 %, of which nitrogen constitutes about 1%.
14. What is the carbon dioxide content of commercial mixed raw milk?
Explanation: Commercial mixed raw milk constitutes about 4.45% of carbon dioxide in it. The total volume of air in milk in the udder can be some 4.5 – 6 %, of which carbon dioxide constitutes about 3.5- 4.9%.
15. Factors that lead to excess air in milk are?
a) Gravity and temperature
b) Temperature and atmospheric pressure
c) Temperature and volume
d) Volume and pressure
Explanation: The equilibrium that prevails between three states of aggregation is determined by temperature and atmospheric pressure. The rise in temperature during pasteurization for instance, dissolved air goes from solution to dispersion causing the problem.
Sanfoundry Global Education & Learning Series – Dairy Engineering.
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