👉All About-Psychrometry
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| All About-Psychrometry |
Psychrometric Properties of Air is a term, which is generally used to study environmental air.
Basically to design one of the best HVAC systems one must understand all about psychrometry Properties of Air.
As we know that managing a comfortable temperature which brings comfort to human is achieved only if we study the behaviour of Psychrometric Properties Of Air.
Well, psychrometric Properties of air is a branch of engineering science which deals with the study of the air.
Basically, air atmospheric condition is not fixed all the time. It keeps on changing with the zones, sessions, country, state, even a small region has different air atmospheric conditions.
So depending on this condition, an HVAC system, design and execution is decided.
which need a strong foundation of psychometric properties of air knowledge.
Before playing with temperature we need to understand the properties of the air which will surely help to achieve our goal of maintaining a comfortable temperature.
What is HVAC:https://bit.ly/2ZMkmSo
Laws Of Thermodynamics:https://bit.ly/2OaHdSi
PSYCHROMETRY PROPERTIES OF AIR 😕😕??
PSYCHROMETRY PROPERTIES OF AIR is basically the study of atmospheric air which help us to understand its different properties.
Basically, the atmospheric air that surrounds us in not only air but it is a mixture of dry air and water vapour which is called as moist air.
The study of moist air is called as psychrometry.
It is a Greek word which means the study of air.
Well, we are clear 😮!!! what is psychrometry and what are we going to deal with.
As it is a study of atmospheric air which is a mixture of dry air and water vapour, which has certain properties which have been found after study of the atmospheric air.
So let us understand its properties.
PSYCHROMETRIC PROPERTIES OF AIR
- DRY BULB TEMPERATURE
- WET BULB TEMPERATURE
- DEW POINT TEMPERATURE
- HUMIDITY RATIO/SPECIFIC HUMIDITY
- RELATIVE HUMIDITY
- SATURATED AIR
- ENTHALPY OF AIR
This is the properties which are very important to find, to maintain a comfortable temperature.
Well, to maintain the best design in HVAC it is necessary to calculate the amount of sensible heat and latent heat, which help us to understand what type of system one must select to overcome this heat loads.
Well, it is not necessary to find all properties of the following but only two parameters are enough to understand the other properties using either a psychrometry Properties of air graph or other platforms like psychrometric software.
To find these two properties of the air we use a device which is called as hygrometer or sling psychrometer.
But before that, it is very important to study these Psychrometric properties of air ….
So let us start!!!!!!!!!!!
DRY BULB TEMPERATURE (DBT)
DRY BULB TEMPERATURE which is also called as DBT.
It is normal temperature of the air which is indicated by the thermometer. This temperature will measure the sensible heat of air.
DBT lines are shown vertically in the graph.
To understand what is DBT lets take an example of a normal thermometer which indicates your body temperature in the same way DBT is used to measure the atmospheric normal temperature.
WET BULB TEMPERATURE (WBT)
WET BULB TEMPERATURE is also called as WBT.
The temperature sensed by a thermometer through a glass bulb which indicated the temperature is wrapped with the water-soaked wick, which is rapidly moving in the air.
WBT lines are shown inclined on the psychometric Properties Of Air graph.
The most important thing is that WBT always has less temperature than that of the DBT.
Have confusion 😕😕😕😕????
Lets clear it...
Let us understand the WBT process by an example
So when you take a shower🚿 and come out of the bathroom you have some glimpse of water stuck to your body and when you come in contact with the air you will find cold, whereas without a glimpse of water you will not feel so cold.
I hope you got it what is a dry bulb and what is wet bulb temperature!
If not, lets clear it, well from the above example the period when we feel cold after taking a shower is called a WBT.
And when we move without a glimpse of water we feel less cold as compared to after shower that is DBT.
Well, hope we are clear what is DBT and WBT.
Basically, this parameter or properties are very important to find, so that we can achieve other properties by a graph or other software.
DO YOU HAVE QUESTION WHY WE FEEL COOL WHEN WE COME OUT OF SHOWER🚿 ?????
Well, we have water particles on our body, that means we are wet, so when the atmospheric air comes in contact with our body it absorbs the water from your body which is called as evaporation.
This evaporation of water from our body generates a coolness which is one of the principles of air conditioning.
Similarly, earthen pots which have a pores in it, when we put water on the surface of the earthen pots the process of evaporation takes place which cools the water fill in the pots.
This is one of the examples of the natural cooling process using evaporation.
Hope we are clear with its so let us move on to the next properties...
DEW POINT TEMPERATURE (DPT)
Dew point temperature is a temperature at which water vapour in the atmosphere begins to condense if the air was cooled at constant pressure.
It is the temperature at which air moisture or water vapour leaves the air and condenses on an object.
DPT is shown horizontally in the psychometric Properties of air graph.
To understand it we have an example like dew form on grass and plant leaves.
During winter you will find the objects in the early morning is surrounded with droplets of water which is the presence of atmospheric air.
Similarly, if you remove a bottle of water from the refrigerator you will find the droplet of water around it after sometimes.
Hope we have understood with this example, what it is….
HUMIDITY RATIO
It is also called as specific humidity or moisture content.
It can be expressed as the mass of water vapour present in 1 kg of dry air.
HUMIDITY RATIO is shown horizontally in the psychometric properties of air graph.
Generally expressed as grains/kilogram of dry air.
This is a very important parameter to find out the latent heat present in the atmosphere which helps to decide how to overcome the heat load.
1lb =7000grains.
RELATIVE HUMIDITY (RH)
The relative humidity is basically a comparison of actual to an ideal parameter.
I know you may be confused by this wording don’t worry we will resolve it.
It is a ratio of the actual amount of water vapour present in atmospheric air to the ideal amount of water vapour or maximum possible water vapour present in atmospheric air.
RELATIVE HUMIDITY is shown with a curve in the psychometric graph.
It is expressed in %
Generally, 50% of RH is suitable for human comfort ……
SATURATED AIR
Saturated air is the temperature at which dry bulb, wet bulb and dew point temperature are same or equal, then the air is said to be saturated.
SATURATED AIR is shown with a curve on the top curve of the Psychometric graph.
This curve is also called a saturation curve.
It can hold no moisture when the air is in a saturated condition.
Saturation is the extreme condition of the atmospheric air when it removes the moisture content in it.
ENTHALPY
Enthalpy is a type of energy which content in an object, according to thermodynamics. In the same way atmospheric air to have some energy contained in it.
ENTHALPY are shown inclined in the psychometric graph.
And the atmospheric air is a mixture of water vapour and dry air.
Hence total enthalpy is the addition of dry and water vapour enthalpy.
H total =H dry air + H water vapour.
Now let see the real psychrometric chart.
PSYCHOMETRIC CHART
To find all properties of air it is necessary that you find two properties manually or from any reference book.
These two properties are generally DBT and WBT or any other properties, which help us to find all remaining properties.
Find DBT and WBT temperature and find the point where two temperature in psychometric lines meet.
The point where is meet mark it and find other properties using this graph.
PSYCHOMETRIC SOFTWARE
Just put the value of DBT and anyone other parameters like WBT or RH or humidity ratio etc will get the result as shown.
This is basically carrier software which I generally used for faster process.
After putting two known properties of the air we will find remaining as shown in the figure.
😇Hope you like this article and have to gain knowledge about this study of air.
This parameter is very important to understand for better design and understanding of a section of the system to overcome the heat load and provide the desired comfort to the desired space.
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