Basic Psychrometric Processes

The psychrometric processes are performed in the air to change their psychometric properties. It is used widely for air conditioning and cooling and heating purposes. Now the question arises what are these psychrometric properties? The process is called psychrometric because it is used to obtain some very essential attributes of a scientific term. 

Some psychrometric properties done in air are: humidification of air and also dehumidification, mixing of different streams of air, heating, and cooling of the air, sensible heat removal, mixing of two different streams flowing, dry bulb temperature and wet bulb temperature, and many more.  

To understand the psychometric properties a psychrometric chart is used which makes it easy to understand. We’ll discuss those soon. Till then let us understand first some of the basic psychrometric processes so that we could know what these are.

Cooling of Air

It is generally called sensible cooling of air and is widely used in refrigerators, air conditioners, coolers, and other cooling devices. This is the process where the hot gases are removed from the room or container only to decrease the temperature. And there is no change in the moisture of the air inside. Overall if we see there is only a change in enthalpy of the air, obviously a decrease in enthalpy. 

In a water cooler, if we see it, it also removes heat but it does not comes  undercooling of water. Instead the psychrometric process of an air cooler is said to be sensible heat removal of air. What happens here is that there is high energy unstable water falling from sides of the water cooler and also there is stable low energy air which removes the energy of water. How this happens is that when air loses its kinetic energy its speed reduces and captures water. I want to remove water from its surface so it evaporates water and it uses its sensible heat to evaporate it and reach its maximum WBT (wet bulb temperature). It provides its latent heat to water reaching its maximum WBT and comes out of the fan. This process goes on continuously by which an air cooler provides us with cold air in summer. And since air removes from its molecule it is known as sensible heat removal. 

Heating of Air 

The sensible heating of air is another psychrometric process done in the air, here the temperature of the air is raised by using an electric heating coil or by using a hot refrigerant. And by keeping the moisture of the air the same. While this process continues the DB (dry bulb) and WB (wet bulb) of the air is rose. Whereas the DP point is kept constant. 

This phenomenon is used in air heaters or comfort air conditioners. For industrial purposes in various industries. 

In the psychrometric chart, for sensible cooling the DB temperature decreases (goes right to left) whereas in sensible heating it’s the opposite. DB value increases (goes left to right). After studying how to read the psychrometric chart you could refer to the link mentioned above and understand the sensible cooling too. 

Humidification and Dehumidification of air

This process is the addition or removal of moisture in the air without altering the temperature or DB(dry bulb) value of air. The humidity level in the chart is divided into two forms, relative humidity, and specific humidity. While increasing moisture, the relative humidity level increases from 1 to 2, and the specific humidity level increases from W1 to W2. While in the removal of humidity the scenario is the complete opposite. Both the values decrease. 

In the psychrometric chart, the relative humidity lines are represented by curves. 

Conclusion

To sum up, psychrometric processes are the processes performed in mechanical devices for changes in the property of air. Using a psychrometric chart it becomes very easy to understand these psychrometric processes which are done by experimenting with the thermometer bulb in dry and wet conditions using various kinds of air with various properties.