Module 2: Air Conditioning Psychrometric Fundamentals Flashcards

Vocabulary flashcards covering the thermodynamic composition of air and psychrometric properties based on the lecture notes.

Atmospheric air

Air that contains nitrogen, oxygen, carbon dioxide, water vapor, other gases, and miscellaneous contaminants such as dust, pollen, and smoke; it is used for ventilation.

Dry air

Air exists when all contaminants and water vapor have been removed; by volume, it contains about $78\%$ nitrogen, $21\%$ oxygen, and $1\%$ other gases.

Moist air

A mixture of dry air and water vapor that, for practical purposes, can be considered equal to atmospheric air under normal conditions.

Dry Bulb Temperature (DBT)

The temperature measured with a standard thermometer that has no water on its surface; it is the actual temperature of the air mixture.

Wet bulb temperature (WBT)

A temperature associated with the moisture content of the air measured by surrounding a thermometer with a wet wick; it is always lower than dry bulb temperature except at saturation.

Dew point temperature

The temperature at which water will begin to condense out of moist air, obtained by finding the corresponding saturation temperature of the calculated vapor pressure ($P_v$).

Enthalpy

The measure of heat energy in the air due to sensible heat or latent heat, calculated as the sum of latent energy and sensible energy.

Sensible heat

The heat or energy in the air that is due to the temperature of the air.

Latent heat

The heat or energy in the air that is due to the moisture of the air.

Dalton's Law of Partial Pressure

A principle stating that the existing pressure of the air is the sum of individual partial pressures of dry air and vapor content: $P = P_a + P_v$, where $P_a$ is the partial pressure of dry air and $P_v$ is the partial pressure of vapor.

Humidity ratio ($w$)

A unitless value defined as the mass of water vapor in a given volume of mixture to the mass of dry air in the same volume, calculated as $w = 0.622 \frac{P_v}{P - P_v}$.

Relative humidity ($\phi$)

The ratio of the partial pressure of the vapor ($P_v$) in the mixture to the saturation pressure ($P_s$) at the same temperature, expressed as a percentage.

Degree of saturation ($\mu$)

The ratio between the actual humidity ratio of sample air ($w$) and the humidity ratio when it is saturated ($w_s$) at the given dry bulb temperature ($DBT$).

Density of moist air

The mass of the mixture per unit volume, calculated using the partial pressures and gas constants as $\frac{P_a}{R_a T} + \frac{P_v}{R_v T}$.

Specific volume

The property of moist air that is the reciprocal of the value for density.

Enthalpy of moist air (empirical equation)

The enthalpy of the mixture calculated as $h = 1.005t + w(2500 + 1.88t)$ in $kJ/kg_{d.a.}$, where $t$ is the dry bulb temperature in $^{\circ}C$.

$R_a$ (Gas constant for dry air)

The universal gas constant ($R_u = 8.3145\,kJ/kmol\cdot K$) divided by the molecular weight of air ($M_a = 28.96$).

$R_v$ (Gas constant for water vapor)

The universal gas constant ($R_u = 8.3145\,kJ/kmol\cdot K$) divided by the molecular weight of water ($M_v = 18$).