A cooling tower is a special heat exchanger in which air and water are brought directly exposed to each other to reduce the temperature of the water. As this happens, a small amount of water evaporates that reduces the temperature of the water being circulating through the tower.
In the chemical industry, the temperature may rise to 1000 degrees celsius; there are processes where temperature sensitivity is essential.
Any rise of these temperatures may damage the plant accessories and it is essential to control the temperatures.
The temperature is reduced by circulating cold water and through heat exchanges, the temperature is control.
Introduction to cooling tower:
The principle behind the cooling is simply evaporation.
As the water falls down the column, due to temperature difference due to the driving force, the water droplets lose the heat as latent heat of vaporization, thus decreasing the temperature of the water.
In this process, there is water loss due to evaporation; to reduce this loss, a small amount of water stream is to be continuously added.
In a cooling tower, water is sprayed from the top of a column (to maximize the interracial surface area for heat transfer) and collected at the bottom of the tower.
Types of Cooling Towers:
Natural draft cooling tower:
Natural draft makes use of a boom by a long chimney.
Warm, moist air naturally will increase due to the density difference of the cooler exterior air.
It is much less dense than hot air on a similar temperature and pressure, this moist air produces a present of air through the surge tower.
Natural draft towers are sometimes about 400 feet high, depending on the differential pressure between the cold air outside and the hot humid air contained in the tower because of the driving force.
No fans are used.
Forced Draft Cooling Tower:
In forced draft cooling towers, a fan is attached to induce wind flow, thus increasing efficiency.
Few cooling towers also have structures packing’s to increase the interfacial area of heat transfer to achieve a smaller volume of cooling towers for a given cooling operation.
In forced draft counter-flow towers, where the fan is installed lower on the side of the tower and pushes air into a matrix.
It is the matrix where the incoming warm water is sprayed, cooled, the airflow goes up while water flow goes down.
Such towers use more horsepower than other types and they are installed indoors to be ducted outdoors and generally used for tight-space conditions.
The forced-draft tower has an application in evaporation cooler, whereby there is a spray sump.
Still, the fluid-cooled is not open to the atmosphere, but it is contained in piping and passes through a heat exchanger.
Induced Draft Counterflow Cooling Tower:
In Induced-draft counter-flow towers, the fan is on top and pulls air into a matrix onto which is sprayed the incoming warm water to be cooled.
The airflow goes up while water flow goes down, hence counter-flow. The fans for these tend to be larger but lower horsepower and more significant than forced-draft towers.
These are the large vase-shaped concrete towers usually associated with nuclear power plants.
They operate on a principle of surface evaporation with the natural draft. Air is drawn in by stack effect and cools by more passive evaporation.
Induced draft cross Cooling TowerS:
An induced draft cooling tower is a mechanical draft cooling tower, which is more efficient than a forced draft cooling tower because it uses 50% less energy than constrained draft designs.
This is a draw-through arrangement, where the fan at the top fills the air.
Working of cooling tower:
Also read: Culverts, Surge Tank & Spillway
Application of Cooling Tower:
Chilling Plant: The chiller plant is a centralized system that cools the air in the building and provides the air conditioning portion of the HVAC system.
Diesel Engine & Gas Engine: They are internal combustion engine in which ignition of the fuel is caused by the elevated temperature of the air in the cylinder by mechanical compression.
Natural Gas Engine: It is also the internal combustion engine that runs on gaseous fuels, i.e. coal gas, biogas, landfill gas, or natural gas.
Cold Storage: Cold storage is a means of keeping things at the right temperature.
Bio Gas Plant: Biogas plants depend on anaerobic digestion as it is a fermentation process in which waste is digested by microbes to produce methane gas.
Vacuum Pumps: A vacuum pump is a device that extracts gas molecules from a sealed volume to repel a partial vacuum.
Also read: Fish Ladder, Canal & Batching Plant
Cooling tower systems are currently found in almost every industry; higher water ﬂow rates will decrease the efﬁciency and the tower characteristics.