Psychrometrics and Air Properties Vocabulary

Vocabulary flashcards covering key psychrometric terms, formulas, units, and thermodynamic concepts of moist air from the lecture.

Specific Humidity

The mass of water vapour present per unit mass of vair ($g/kg\text{ of vair}$).

Apparent Specific Humidity (ASH)

The mass of water vapour present per unit mass of dry air ($g/kg\,\text{d.a.}$).

Relative Humidity

The ratio of the partial pressure of water vapour actually present to the saturated vapour pressure at constant temperature, usually expressed as a percentage ($\% = \frac{P_v}{SVP}$).

True Density of vair

The mass of a sample per unit volume of vair ($kg/m^3\text{ of vair}$).

Apparent Specific Volume

The volume of a sample of vair per unit mass quantity of dry air ($m^3/kg\,\text{d.a.}$).

Super Heat

The amount or degree of temperature required to raise the wet-bulb temperature of a quantity of vair to its dry-bulb temperature ($T_{db} - T_{wb}$).

Enthalpy of vair

The sum of all the internal sensible energies plus pressure energy (latent heat) of the dry air and water vapour components, measured as total heat added from a datum temperature of $0^\circ C$ ($kJ/kg\,\text{d.a.}$).

Components of Enthalpy (H)

The components comprising total enthalpy: a) Heat of air from $0^\circ C \rightarrow T_{db}$ (@P), b) Heat of water vapour from $0^\circ C \rightarrow T_{wb}$ (@P), c) Heat of vaporization from $H_2O$ at $T_{wb}$, and d) Super Heat of water vapour from $T_{wb} \rightarrow T_{db}$.

Dry-bulb Temperature

A measure of the sensible internal energy measured by a conventional thermometer in $^\circ C$.

Wet-bulb Temperature

The temperature measured by a thermometer whose bulb is covered by a wetted wick and exposed to an airflow of $3\,m/s$; together with dry-bulb temperature, it measures the evaporative capacity of the air ($^\circ C$).

Dew-Point Temperature

The temperature to which air must be cooled for condensation to just begin, at which temperature the vair is saturated ($^\circ C$).

Partial Pressure

The pressure that a single component of an air/water vapour sample would exert on the walls of the container if it were present alone in that container at constant temperature ($kPa$).

Total Pressure

The sum of all partial pressures of dry air and water vapour ($P_a + P_v$), measured in $kPa$.

Vapour Pressure

The partial pressure exerted by the water vapour present in a quantity of vair ($kPa$).

Saturated Vapour Pressure

The partial pressure exerted by water vapour when it is saturated.

Absolute Humidity

The mass of water vapour present per unit volume of vair ($g/m^3\text{ of vair}$).