Air-Conditioning Questions and Answers – Psychrometric Terms

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This set of Air-Conditioning Multiple Choice Questions & Answers (MCQs) focuses on “Psychrometric Terms”.

1. What is the mixture of a number of gases?
a) Moist air
b) Dry air
c) Fresh air
d) Saturated air
View Answer

Answer: b
Explanation: Dry air is the mixture of a number of gases like nitrogen, oxygen, carbon dioxide, hydrogen, etc. These gases have different proportion in this mixture by which the properties may alter.
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2. Which of the following has the maximum contribution in the dry air?
a) Nitrogen
b) Argon
c) Carbon dioxide
d) Hydrogen
View Answer

Answer: a
Explanation: Dry air is the mixture of a number of gases like nitrogen, oxygen, carbon dioxide, hydrogen, etc. In this mixture, nitrogen has the maximum contribution. Nitrogen is approximately 78.03 % by volume and 75.47 % by mass in this mixture.

3. Nitrogen and Argon have a major portion in the dry air.
a) False
b) True
View Answer

Answer: a
Explanation: Dry air is the mixture of a number of gases like nitrogen, oxygen, carbon dioxide, hydrogen, etc. In this mixture, nitrogen has the maximum contribution. Nitrogen is approximately 78.03 % by volume and 75.47 % by mass in this mixture. Oxygen is approximately 20.99 % by volume and 23.19 % by mass in the mixture. But the argon has a very little portion in the mixture. So, Nitrogen and Oxygen have a major portion in the dry air.
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4. Mixture of dry air and water vapor is __________
a) moist air
b) dry air
c) fresh air
d) saturated air
View Answer

Answer: a
Explanation: If water vapor is present in a larger amount in the dry air, then the type of air is called as moist air. The amount of water vapor present in the air depends upon the absolute pressure and temperature of the mixture.

5. Specific humidity and absolute humidity have the same unit.
a) False
b) True
View Answer

Answer: a
Explanation: Humidity ratio or Specific humidity is the mass of water vapor present in 1 kg of dry air. It is generally expressed in, g / kg of dry air and absolute humidity is the mass of water present in 1 m3 of dry air. It is generally expressed in, g / m3 of dry air.
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6. The mixture of dry air and water vapor called when the air has diffused the maximum amount of water vapor into it is called ________
a) dry air
b) moist air
c) saturated air
d) specific humidity
View Answer

Answer: c
Explanation: Saturated air is the mixture of dry air and water vapor when the air has diffused the maximum amount of water vapor into it. The water vapors occur in the form of superheated steam as an invisible gas.

7. What is the ratio of actual mass of water vapor in a unit mass of dry air to the mass of water vapor in the same mass of dry air when it is saturated at the same temperature?
a) Moist air
b) Dry air
c) Degree of saturation
d) Saturated air
View Answer

Answer: c
Explanation: The ratio of actual mass of water vapor in a unit mass of dry air to the mass of water vapor in the same mass of dry air when it is saturated at the same temperature is called as the degree of saturation.

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8. What is the mass of water vapor present in 1 kg of dry air called?
a) Specific Humidity
b) Relative humidity
c) Degree of saturation
d) Saturated air
View Answer

Answer: a
Explanation: Humidity ratio or Specific humidity is the mass of water vapor present in 1 kg of dry air. It is generally expressed in, g / kg of dry air. Mathematically, W = mv / ma.

9. What is the ratio of actual mass of water vapor in a given volume of moist air to the mass of water vapor in the same volume of saturated air at the same pressure and temperature?
a) Specific Humidity
b) Relative humidity
c) Degree of saturation
d) Saturated air
View Answer

Answer: b
Explanation: Relative humidity is the ratio of actual mass of water vapor in a given volume of moist air to the mass of water vapor in the same volume of saturated air. It can be represented as,
∅ = mv / ms = pv / ps.
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10. What is the temperature of air recorded by a thermometer, when the moisture present in it starts condensing?
a) DBT
b) WBT
c) DPT
d) WBD
View Answer

Answer: c
Explanation: DPT i.e., Dew Point Temperature is the temperature at which the moisture in it begins to condense. It can also be defined as the temperature corresponding to the partial pressure of water vapor.

11. What is the mixture of dry air and water vapor called when the air has diffused the maximum amount of water vapor into it?
a) Dry air
b) Moist air
c) Saturated air
d) Specific humidity
View Answer

Answer: c
Explanation: Saturated air is the mixture of dry air and water vapor when the air has diffused the maximum amount of water vapor into it. The water vapors occur in the form of superheated steam as an invisible gas.

12. What is the temperature of air recorded by thermometer when it is not affected by the moisture present in it?
a) WBT
b) DBT
c) DPT
d) Sub-zero Temperature
View Answer

Answer: b
Explanation: DBT means Dry Bulb Temperature is the temperature of the air recorded by thermometer and is not affected by moisture in it.

13. For unsaturated air, the value of DPT is _________ WBT.
a) less than
b) more than
c) equal to
d) much more than
View Answer

Answer: a
Explanation: Moist air containing moisture in the superheated state then the air is called unsaturated air. In such a situation, the dew point temperature is less than the wet-bulb temperature.

14. What is the difference between DBT and WBT called?
a) DPD
b) DBD
c) Degree of saturation
d) WBD
View Answer

Answer: d
Explanation: The difference between dry bulb temperature and wet bulb temperature is called wet-bulb depression. It indicates the relative humidity of the air.

15. If wet-bulb depression is zero, then the relative humidity is also zero.
a) False
b) True
View Answer

Answer: a
Explanation: The difference between dry bulb temperature and wet bulb temperature is called wet-bulb depression. It indicates the relative humidity of the air. So, if the wet-bulb depression is zero, then the relative humidity is 100 % or 1.0.

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Manish Bhojasia - Founder & CTO at Sanfoundry
Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He is Linux Kernel Developer & SAN Architect and is passionate about competency developments in these areas. He lives in Bangalore and delivers focused training sessions to IT professionals in Linux Kernel, Linux Debugging, Linux Device Drivers, Linux Networking, Linux Storage, Advanced C Programming, SAN Storage Technologies, SCSI Internals & Storage Protocols such as iSCSI & Fiber Channel. Stay connected with him @ LinkedIn | Youtube | Instagram | Facebook | Twitter