Deck 14: Gas-Vapor Mixtures and Air-Conditioning

Question 1

A room is filled with saturated moist air at 20°C and a total pressure of 90 kPa. If the mass of dry air in the room is 100 kg, the mass of water vapor is

A)1.52 kg
B)2.60 kg
C)1.62 kg
D)1.66 kg
E)4.21 kg

Answer 1

1.66 kg

Question 2

A room contains 40 kg of dry air and 0.5 kg of water vapor at 20°C and 95 kPa total pressure. The relative humidity of air in the room is

A)1.2%
B)2.5%
C)80%
D)56%
E)72%

Answer 2

80%

Question 3

A 35-m³ room contains air at 25°C and a total pressure of 90 kPa with a relative humidity of 85%. The mass of dry air in the room is

A)30.4 kg
B)35.7 kg
C)36.8 kg
D)41.3 kg
E)426 kg

Answer 3

35.7 kg

Question 4

A room contains air at 25°C and a total pressure of 87.0 kPa with a relative humidity of 85%. The partial pressure of dry air is

A)2.69 kPa
B)83.8 kPa
C)84.3 kPa
D)74.0 kPa
E)87.0 kPa

Question 5

The air in a house is at 25°C and 72 percent relative humidity. Now the air is cooled at constant pressure. The temperature at which the moisture in the air will start condensing is

A)8.7°C
B)15.3°C
C)18.0°C
D)19.6°C
E)21.2°C

Question 6

On the psychrometric chart, a cooling and dehumidification process appears as a line that is

A)horizontal to the left,
B)vertical downward,
C)diagonal upwards to the right (NE direction)
D)diagonal upwards to the left (NW direction)
E)diagonal downwards to the left (SW direction)

Question 7

On the psychrometric chart, a simple heating process (no humidification or dehumidification) appears as a line that is

A)horizontal to the right,
B)horizontal to the left,
C)vertical upward,
D)diagonal upwards to the right (NE direction)
E)diagonal downwards to the right (SE direction)

Question 8

Air in a space heating system is heated while being humidified by steam injection. On the psychrometric chart, this process will appear as a line that is

A)horizontal to the right,
B)vertical upward,
C)diagonal upwards to the right (NE direction)
D)diagonal upwards to the left (NW direction)
E)diagonal downwards to the right (SE direction)

Question 9

Air is cooled and dehumidified as it flows over the coils of a refrigeration system at 90 kPa from 25°C and a humidity ratio of 0.021 kg/kg dry air to 15°C and a humidity ratio of 0.015 kg/kg dry air. If the mass flow rate of dry air is 0.7 kg/s, the rate of heat removal from the air is

A)6.8 kJ/s
B)11 kJ/s
C)45 kJ/s
D)32 kJ/s
E)18 kJ/s

Question 10

Air at a total pressure of 85 kPa, 15°C, and 70 percent relative humidity is heated and humidified to 25°C and 60 percent relative humidity by introducing water vapor. If the mass flow rate of dry air is 4.6 kg/s, the rate at which steam is added to the air is

A)0.025 kg/s
B)0.0054 kg/s
C)3.22 kg/s
D)0 kg/s
E)0.18 kg/s