Question 1

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

Accepted Answer

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

Question 2

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

Accepted Answer

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

Question 3

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

Accepted Answer

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)  C

Question 4

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

Accepted Answer

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 5

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

Accepted Answer

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

Question 6

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

Accepted Answer

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

Question 7

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

Accepted Answer

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

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

Accepted Answer

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

Question 9

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

Accepted Answer

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

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

Accepted Answer

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

Exam 14: Gas-Vapor Mixtures and Air-Conditioning