Psychrometrics

Question 1

What is psychometrics?

Answer 1

The a subject that uses thermodynamic properties to analyze conditions and processes involving moist air.

Question 2

What is atmospheric air?

Answer 2

Air that contains many gaseous components as well as water vapor and miscellaneous contaminants.

Question 3

What is dry air?

Answer 3

Is atmospheric air with all water vapor and contaminants removed.

Question 4

Is dry air’s composition constant?

Answer 4

Yes, its composition is relatively constant, but it still varies slightly.

Question 5

What factors cause dry air’s composition to vary?

Answer 5

Time, geographic location, and altitude.

Question 6

What is moist air?

Answer 6

Is a binary mixture of dry air and water vapor.

Question 7

What is the least amount of water vapor that can be present in moist air?

Answer 7

Zero

Question 8

What is moist air considered when it has no water vapor?

Answer 8

Dry air.

Question 9

What is the maximum amount of water vapor that can be present in moist dependent on?

Answer 9

The temperature and pressure.

Question 10

What is saturation?

Answer 10

A state of neutral equilibrium between moist air and the condensed water phase.

Question 11

What causes the temperature and barometric pressure of atmospheric air to vary?

Answer 11

Altitude, geographic location and weather conditions.

Question 12

What level is considered to be the standard for barometric pressure and temperature?

Answer 12

Sea level

Question 13

What is the standard temperature and barometric pressure?

Answer 13

15 C and 101.325 kPa.

Question 14

How does temperature vary with altitude?

Answer 14

Temperature is assumed to decrease with increasing altitude throughout the troposphere.

Question 15

What is the troposphere and what is its range?

Answer 15

The lower atmosphere and it ranges from sea level to the start of the stratosphere.

Question 16

In what region of altitude is the temperature constant?

Answer 16

In the lower reaches of the stratosphere.

Question 17

What is the stratosphere?

Answer 17

The region above the troposphere.

Question 18

How does dry air behave in the troposphere?

Answer 18

It behaves as a perfect gas.

Question 19

What is the humidity ratio?

Answer 19

The ratio of the mass of water vapor to the mass of dry air in moist air.

Question 20

What is specific humidity ratio?

Answer 20

The ratio of the mass of water vapor to total mass of the moist air.

Question 21

What is the absolute humidity ratio?

Answer 21

The ratio of the mass of water vapor to the total volume of the moist air.

Question 22

What is the density?

Answer 22

The ratio of the total mass to total volume of moist air.

Question 23

What is saturation humidity ratio?

Answer 23

The humidity ratio of moist air saturated with respect to water (or ice) at the same temperature and pressure.

Question 24

What is the degree of saturation?

Answer 24

The ratio of air humidity ratio to humidity ratio of saturated moist air at the same temperature and
pressure.

Question 25

What is the relative humidity?

Answer 25

The ratio of the mole fraction of water vapor in a given moist air sample to the mole fraction in an air
sample saturated at the same temperature and pressure

Question 26

What is the Dew Point Temperature?

Answer 26

The temperature of moist air saturated at a given pressure, with the same humidity ratio as that of the
given sample of moist air.

Question 27

What is thermodynamic wet bulb temperature?

Answer 27

The temperature at which water (liquid or solid), by evaporating into moist air at a given dry bulb
temperature and humidity ratio, can bring air to saturation adiabatically at the same temperature while total pressure is constant.

Question 28

What law does the most air obey when it is considered a perfect gas?

Answer 28

The ideal gas law.

Question 29

Could each part of the moist air be considered ideal?

Answer 29

Yes the dry air and water vapor can be considered ideal.

Question 30

Can the ideal gas law be used for each part of moist air?

Answer 30

Yes

Question 31

How is the ideal gas law effected when each part is considered separately?

Answer 31

The partial pressure and their individual mass or moles are used.

Question 32

What is the specific volume?

Answer 32

The ratio of the total volume to the mass of the dry air.

Question 33

What is the enthalpy of a mixture of perfect gases equal to?

Answer 33

It is equal to the sum of the individual partial enthalpies of the components.

Question 34

What happens to moist air during adiabatic saturation, in a constant pressure process?

Answer 34

The humidity ratio, enthalpy and mass of water vapor in the moist air sample increases to the thermodynamic wet bulb temperature values.

Question 35

What happens to the humidity ratio for moist air that goes through a strictly heating or cooling process?

Answer 35

It stays the same.

Question 36

When does moisture condensation occur in moist air?

Answer 36

Moisture condensation occurs when moist air is cooled to a temperature below its initial dew point.

Question 37

What is the temperature range from which water condensation can be removed from the moist air?

Answer 37

The temperature ranges from its initial dew point temperature to its final saturation temperature.

Question 38

At what temperature is the condensed water extracted from the moist air?

Answer 38

It is assumed that condensed water is cooled to the final air temperature before it drains from the system.

Question 39

Where does the state point of a resulting mixture of two adiabatic moist air streams lie on?

Answer 39

The state point of the resulting mixture lies on the straight line connecting the state points of the two streams being mixed.

Question 40

Where on the line does the state point of a resulting mixture of two adiabatic moist air streams lie on?

Answer 40

It is the point that divides the line into two segments, in the same ratio as the masses of dry air in the two streams.

Question 41

What is air conditioning for a space usually determined by?

Answer 41

(1) the quantity of moist air to be supplied, and
(2) the supply air condition necessary to remove given amounts of energy and water from the space at the exhaust condition specified.

Question 42

What is the sensible heat gain equal to?

Answer 42

The total sum of added energy from all the heat sources.