Psychrometric chart/Psychrometric properties/Psychrometric Process

Psychometric chart:

• It is the study of properties of mixtures of air and water vapors.
• It only deals with air properties.

Properties of air:

• 1)Dry bulb temperature(DBT)
• 2)Wet-bulb temperature(WBT)
• 3)Specific humidity/absolute humidity/moisture content
• 4)Enthalpy
• 5)Relative humidity
• 6)Specific volume
• 7)Dew point temperature

Dry bulb temperature(DBT):

• The temperature measure by the thermometer when the bulb of the thermometer is in direct contact or directly exposed to the atmosphere. 
• The vertical lines are shown in the figure indicate dry bulb temperature lines and it increases from left to right.

Wet-bulb temperature(WBT):

• The WBT is the temperature ready by a thermometer covered in water-soaked cloth.
• At 100% relative humidity, the WBT is equal to the DBT and is lower at lower humidity.

Absolute humidity:

• It is the amount of moisture in grain present in 1 pound of dry air.

                                                               7000 grains = 1 pound of water

Enthalpy:

• It is expressed in BTU/pound of dry air and it is the energy content of moisture air.
• The enthalpy scale is located above the saturation curve.

Relative humidity:

• It is the ratio of moisture present in an air sample to the maximum moisture that it can hold at its saturation level.

Specific Volume:

• It is expressed as volume per unit weight.

Dew point temperature:

• The temperature by which unsaturated air can be converted into saturated air called a dew point temperature.

Psychrometric Process:

• 1)Sensible heating
• 2)Sensible cooling
• 3)Humidification
• 4)Dehumidification
• 5)Sensible heating and humidification
• 6)Sensible heating and dehumidification
• 7)Sensible cooling and humidification
• 8)Sensible cooling and dehumidification

Sensible heating:

• It is the process in which sensible heat is added to a given air sample at constant moisture content.

Sensible cooling:

• It is the process in which sensible heat is removed to a given air sample at constant moisture content.

Humidification:

• It is the process in which sensible moisture is added to a given air sample at the constant dry bulb temperature.

Dehumidification:

• It is the process in which sensible moisture is removed to a given air sample at the constant dry bulb temperature.

Sensible heating and humidification:

• It is the process in which sensible heat and moisture are increased.

Sensible heating and dehumidification:

• It is the process in which sensible heat is added but moisture is removed.

Sensible cooling and humidification:

• It is the process in which sensible heat is removed but moisture is added.

Sensible cooling and dehumidification:

• It is the process in which both sensible heat and moisture are removed from the given air sample.