Psychrometry

This is about Psychrometry basics.

1. PSYCHROMETRY 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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