Download - psychrometer 2.pptx
-
7/27/2019 psychrometer 2.pptx
1/19
1
-
7/27/2019 psychrometer 2.pptx
2/19
2
Psychrometry : It is the branch of science which deals with the study of
the mixture of dry air and water vapor. In air conditioning estimations air is
taken as a mixture of dry air and water vapor.
The principles ofpsychrometryapply to any physical system consisting of
gas-vapor mixtures.
The Pschrometry terms:
Dry airMoist air
Saturated air
Degree of Saturation
Humidity
Absolute HumidityRelative Humidity
Dry bulb temperature
Wet bulb temperature
Dew point Temperature
Dew point Depression
-
7/27/2019 psychrometer 2.pptx
3/19
3
Moist Air : The mixture of dry air and water vapor. The quantity of water vapor
present in air is known as moisture.
Saturated Air : When moist air contains maximum amount of water vapor that it
can hold, it is called saturated air.
Unsaturated Air : Moist air which is not saturated.
Humidity Ratio : The weight of water vapor per unit weight of dry air in avapor air mixture. It is also called Specific Humidity.
Degree of Saturation : The ratio of the prevailing humidity ratio of moist air to
the humidity ratio of saturated air at the same temperature and pressure.
Relative Humidity : The ratio of actual weight of water vapor in a given
volume to the weight of water vapor contained in the same volume at the same
temperature when the air is saturated.
-
7/27/2019 psychrometer 2.pptx
4/19
4
A Sling Psychrometer is
used to measure relative
humidity.
Following are the pschrometry relationship:
1. Specific Humidity, humidity ratio & moisture content.2. Degree of Saturation or percentage humidity
3. Relative Humidity
4. Pressure of Water vapour
5. Vapour density & absolute humidity
-
7/27/2019 psychrometer 2.pptx
5/19
5
Psychrometer Parts:
Dry Bulb Thermometer
Wet Bulb Thermometer
Reservoir and StockingWETDRY
-
7/27/2019 psychrometer 2.pptx
6/19
6
Dry-bulb Temperature : The temperature which is recorded by a
thermometer whose reading is not affected by the humidity ratio or
by thermal radiation.
Wet-bulb Temperature : The temperature which is recorded by a
thermometer when its bulb is covered with wet cloth and is exposed to a
current of moving air. The difference between dry-bulb temperature and
wet-bulb temperature is known as wet-bulb depression.
Dew Point Temperature : The saturation temperature which corresponds to the
existing humidity ratio and barometric pressure. Generally dew point
temperature is taken to be the temperature at which condensation will just begin
when the moist air mixture under consideration is cooled at constant pressure.
Enthalpy of Air: It is the Total heat of air.
It is considered that the enthalpy of moist air is a concern of Air conditioning
Engineer.
-
7/27/2019 psychrometer 2.pptx
7/19
7
-
7/27/2019 psychrometer 2.pptx
8/19
8
On the side of the psychrometer is
a sliding scale which calculates
relative humidity for us.
Align the dry-bulb reading with thewet-bulb reading. The arrow will point
to the relative humidity reading on the
center scale. Its easy!
-
7/27/2019 psychrometer 2.pptx
9/19
9
Using our wet- and dry-
bulb temperatures, we can
consult tables made by
scientists
to determine humidityand saturation value.
Psychometric Chart : The graphical representation of various thermodynamic
properties of moist air. In this abscissa represents dry bulb temperature and ordinate
represents specific humidity.
-
7/27/2019 psychrometer 2.pptx
10/19
10
Psychometric Processes : The various processes which are involved in air
conditioning to change the psychometric properties of air according to requirement.
-
7/27/2019 psychrometer 2.pptx
11/19
11
-
7/27/2019 psychrometer 2.pptx
12/19
12
But why do we sling it
around
and
around?
-
7/27/2019 psychrometer 2.pptx
13/19
13
What happens to your skin when you
sweat and then stand in a breeze?
-
7/27/2019 psychrometer 2.pptx
14/19
14
-
7/27/2019 psychrometer 2.pptx
15/19
15
As the wet-bulb thermometer goes through the air
1. Water
evaporates
2. Energy is
used; water
changesfrom liquid to
vapor
3. Wet-bulb temperature goes down
-
7/27/2019 psychrometer 2.pptx
16/19
16
What influences how
much the wet-bulb
temperature goes
down?
Humidity
Temperature
-
7/27/2019 psychrometer 2.pptx
17/19
17
Now we can calculate relative humidity!
-
7/27/2019 psychrometer 2.pptx
18/19
18
Partial Relative Humidity Chart for 30 CDifference Between
Dry Bulb and Wet Bulb
Temperatures
Relative Humidity
None 100%
0.5 96%
1.0 93%
1.5 89%
9.0 44%
9.5 42%
14.5 19%
15.0 17%
18.0 5%
Fortunately, we dont have to do all this every time
-
7/27/2019 psychrometer 2.pptx
19/19
For Help:
AMSTI-GLOBE The GLOBE Programwww.amsti.org/globe www.globe.gov
Judy Reeves Lynn VaughanAMSTI-GLOBE AMSTI-GLOBEResource Specialist Resource Specialist
[email protected] [email protected]
Robin Nelson Jerry CobbsAMSTI-GLOBE AMSTI-GLOBEAdministrator Technology Specialist
[email protected] [email protected]
http://www.amsti.org/globehttp://www.globe.gov/mailto:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]://www.globe.gov/http://www.amsti.org/globe