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Flashcards in Psychrometrics Deck (42):

What is psychometrics?

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


What is atmospheric air?

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


What is dry air?

Is atmospheric air with all water vapor and contaminants removed.


Is dry air's composition constant?

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


What factors cause dry air's composition to vary?

Time, geographic location, and altitude.


What is moist air?

Is a binary mixture of dry air and water vapor.


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



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

Dry air.


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

The temperature and pressure.


What is saturation?

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


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

Altitude, geographic location and weather conditions.


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

Sea level


What is the standard temperature and barometric pressure?

15 C and 101.325 kPa.


How does temperature vary with altitude?

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


What is the troposphere and what is its range?

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


In what region of altitude is the temperature constant?

In the lower reaches of the stratosphere.


What is the stratosphere?

The region above the troposphere.


How does dry air behave in the troposphere?

It behaves as a perfect gas.


What is the humidity ratio?

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


What is specific humidity ratio?

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


What is the absolute humidity ratio?

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


What is the density?

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


What is saturation humidity ratio?

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


What is the degree of saturation?

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


What is the relative humidity?

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


What is the Dew Point Temperature?

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


What is thermodynamic wet bulb temperature?

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.


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

The ideal gas law.


Could each part of the moist air be considered ideal?

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


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



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

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


What is the specific volume?

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


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

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


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

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


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

It stays the same.


When does moisture condensation occur in moist air?

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


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

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


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

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


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

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


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

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.


What is air conditioning for a space usually determined by?

(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.


What is the sensible heat gain equal to?

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