# What Is Adiabatic Cooling: Working, Process, Several Facts Around It

It is not necessary for a system to transfer heat in order to perform work. This article discusses about what is adiabatic cooling.

In adiabatic cooling, the pressure inside the system reduces due to which volume increases. This causes the system to do work on the surroundings. In adiabatic process, heat is not transferred but work is still done in the form of moving walls or boundary of the system.

## What is adiabatic cooling system?

Adiabatic cooling is a type of thermodynamic process in which the temperature of the working fluid reduces without any transfer of heat between system and surroundings.

This happens when pressure of the system reduces and volume expands. The walls of system are adiabatic so they do not let heat escape or enter the system. Though they can move in order to perform work.

Though cooling takes place, it is not necessary that heat transfer takes place. In adiabatic cooling, heat transfer does not take place but temperature of the system decreases.

There are three types of adiabatic cooling process, they are-

• Direct adiabatic cooling: This is also called as wet bulb cooling. In this process, there is direct interaction between air and water.
• Indirect adiabatic cooling: This is also called as evaporative cooling. In this process, water is evaporated in a column of air that is different from the air which is used for cooling.
• Two stage adiabatic cooling: As the name suggests, it uses two stages to complete the cooling process. First stage is indirect adiabatic cooling and other stage is direct adiabatic cooling. Combining both the processes helps us achieve cooling faster.

The benefits of air-cooled chillers are as follows-

• The process is automated so the need of human interference is reduced so it does not need continuous inspection or operator.
• Energy savings are higher so it is cost effective and gets more profit to the company.
• It is greener technology and has very less impact on environment. This is because it creates minimal waste while operating.
• These systems are cost effective and easy to use. Hence, the installation process and setting up time does not take much time.
• The user interface is very simple making it easy to use.

Above benefits make air cooled chillers a desirable device for cooling purposes. Many industries use air chillers and save huge sum of money by using cost effective chillers.

## How does adiabatic air cooling occur?

The adiabatic air cooling occurs when the pressure of the system is reduced which results in volume expansion.

The adiabatic walls of the system prevent heat to enter or escape. Due to the pressure drop, work is done on the system reducing the internal energy of the system. Internal energy being function of temperature, temperature also decreases as internal energy decreases.

This way adiabatic air cooling takes place.

## What is adiabatic cooling extrusion?

Extrusion means squeezing out the working material into a cavity to make desirable shapes. For example, wires can be made out of extrusion.

Adiabatic means no heat transfer takes place. Extrusion is done by pushing the working material into a cavity or out of cavity with the use of an extruder. In adiabatic cooling extrusion, the extruder operates without the input or extraction of heat.

## Adiabatic cooling vs evaporative cooling

Adiabatic cooling and evaporative cooling are different. Below section explains in brief about what is adiabatic cooling and what is evaporative cooling.

• Adiabatic cooling: Adiabatic cooling is the process in which temperature is reduced at the expense of change in air pressure and increase in volume.
• Evaporative cooling: In evaporative cooling, a large fan draws warm air through moisture rich pads. The temperature of air is reduced as the water inside the pad is evaporated.

## What do you mean lapse rate?

The word lapse refers to decrease in certain quantity. In adiabatic process, lapse rate refers to decrease in certain quantity. In this case, usually temperature in Earth’s atmosphere.

The lapse rate can be defined as the rate at which a particular parameter usually temperature decreases with altitude.

Mathematically, lapse rate can be defined as-

Where,

The Greek symbol Gamma refers to lapse rate in SI units that is temperature, T divided by altitude, Z (in m).

## What is the dry adiabatic rate of cooling for rising air?

Dry refers to the absence of water content in air. Dry air has a dryness fraction of 100% and wetness fraction of 0%.

The dry adiabatic rate of cooling for rising air is given below-

Where,

The Greek symbol Gamma refers to lapse rate in SI units that is temperature, T divided by altitude, Z (in m).

g represents gravitational pull and Cp represents specific heat at constant pressure.

## What is moist adiabatic lapse rate?

The word moist refers to anything which contains water content in it. Moist adiabatic lapse rate.Water has a certain latent heat of vaporisation due to which it affects the rate of convection in Earth’s atmosphere.

Mathematically, moist adiabatic lapse rate can be written as-

Where,

Greek letter Gamma represents wet lapse rate

g is Earth’s gravitational acceleration

Hv is heat of vapourisation

R in the numerator represents specific heat of dry air

R in the denominator represents specific heat of wet air

Cpd is the specific heat of dry air at constant pressure

T is temperature in K

## What is environmental lapse rate?

Environmental lapse rate or ELR can be defined as the rate of decrease of temperature with altitude in stagnant atmosphere.

The international standard atmosphere has a temperature lapse rate of 6.50 degrees celsius/km from sea level to an altitude of 11km.  However, the temperature of the air in atmosphere doesn’t always reduce at uniform rate with height as there can be inversions layer of air in which the temperature increases with altitude.

Overall, the concept of lapse rate was meant for troposphere only. Eventually it was confirmed that it can be used in any parcel of gas that is affected by gravity.

Image credits: Wikipedia

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