The document defines key terms related to psychrometrics, which is the science of moist air properties and processes. It explains that atmospheric air contains a mixture of gases including nitrogen, oxygen, carbon dioxide and water vapor. Moist air contains both air and water vapor, while saturated air contains the maximum possible amount of water vapor. Other terms defined include humidity, dry bulb temperature, wet bulb temperature, relative humidity, vapor pressure, specific humidity, dew point temperature, and enthalpy. The document concludes by explaining that a psychrometric chart graphically represents various psychrometric properties and processes on a single plot.

1. BY
AMULYA .Y

2. Definitions
 Psychrometrics: Psychrometrics is the science of moist
air properties and processes.
 Psycrometry: It is the study of properties of mixture of
air and water vapour.
 Air contains Nitrogen,Oxygen,Carbon dioxide and
small amount of some other gases.
 Atmospheric Air: Atmospheric air contains mixture of
air, water vapour and some dust particles.
 Dry air: Air with no water vapour.

3.  Moist Air: Contains mixture of air and water vapour.
 Saturated Air: If air contains maximum water vapour
then it is called saturated air.
 Moisture: The amount of water vapour present in air in
liquid phase.
 Humidity: The amount of water vapour present in air
in gaseous state.
 Hygrometer is the device used to measure humidity or
the amount of water vapour in the air.

4.  Dry bulb temperature: It is the temperature of moist
air measured using standard thermometer.
 Saturated vapour pressure: Saturated partial pressure
of water vapour at dry bulb temperature.
 Wet bulb temperature: It is the temperature recorded
when the bulb of thermometer is covered with wet
cloth.

5.  Relative Humidity: Relative humidity is the ratio of
amount of water vapour the air can hold to the total
amount of water vapour the air holds. It is denoted by
φ.
 φ=0 dry air
 φ= 1 saturated air
 Humidity ratio: The ratio of water vapour present in
1kg of dry air. It is represented by W.
 Vapour pressure: It is the pressure of water vapour
which would exert if it exists alone at same
temperature and volume of atmospheric air.

6.  Specific humidity: The amount of water vapour
present in dry air. Also called as humidity ratio.
 Dew point temperature: The temperature at which the
moist starts to condense. Also known as saturated
temperature.
 Enthalpy: It is the heat content of a system. Enthalpy
of moist air is sum of enthalpies of dry air and water
vapour. It is represented by h

7.  Adiabatic saturation temperature: The temperature at
which water gets evaporated and bring the air to
saturation at same temperature.
 Degree of saturation: The ratio of humidity ratio to the
humidity ratio of saturated mixture at same pressure
and temperature. It is denoted by µ.

8. Psychrometric chart
 Psychrometric chart is the graphical representation of
psychrometric processes such as physical and
thermodynamic properties of air and water vapour.
 These include dry bulb and wet bulb temperatures,
relative humidity,enthalpy,dew point temperature.

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