Cooling tower is a special type of heat exchanger which rejects waste heat to the atmosphere by making direct contact between air and water to lower down the temperature of water. It works on basic principle of heat transfer due to evaporation. It is mostly use to cool down large amount of water so it recirculate again for cyclic operation. cooling towers are used in many industries like thermal power station, chemical industries, refineries etc. According to the requirement and weather conditions, there are various types of cooling towers available. Today we will discuss about all of them.
Let’s start leaning its types.
Types of Cooling Tower:
It is generally categorized according to its working and applications. Various types of it given below.
1.) Categorized by Air to water flow:
a.) Crossflow cooling tower:
As the name implies in cross flow cooling tower air flow perpendicular to the water flow. Air enters the tower from vertical faces to meet the fill located inside the tower and hot water enters the basin located at the top of the tower. Gravity distributes the water uniformly through the nozzle across the fill upright the air flow. Turbulent air passing through the fill causes water to pass into an open area which improves the contact between air and water resulting effective cooling. The air is taken out from the system by an induce for force draft system.
1. Lower operation cost due to low pumping head
2. Minimum maintenance
3. Low energy consumption
1. Maximum water overturn
2. Easily build up the dirt into the fill of tower.
1. Widely used in heating process in chemical industry
2. Used in Aluminium die casting and air compressor
b.) Counterflow cooling tower:
In this type of cooling tower air flows in opposite direction to the water flow. Air is drawn from the bottom of the cooling tower near the fill and pulls into open space of tower. Water passes downward into the fill media parallel but opposite to the air direction which increases the contact area as well as contact time. Cooling air drawn out heat from the water and increases heat transfer.
1. More efficient air to water contact due to droplet distribution.
2. Maximum tower performance.
1. More noise production due to spraying and falling water.
2. Uneasy maintenance and difficult to clean up.
1. Refineries and natural gas processing plants.
2.) Categorized by drawing air through the tower:
a.) Natural draft cooling tower:
Natural draft cooling tower basically removes waste heat from the system and release it into the atmosphere. In this process hot water enters through the series of pumps to the top area of tower near hot water inlet. Series of nozzles connected to the hot water inlet used to sprays water over the fill and distributed throughout the tower. Simultaneously air is introduced from the bottom of the tower flowing in upward direction. It then circulated inside the cooling tower by natural convection. While flowing down water emits heat due to evaporation which mixes with the air flowing upward causing water to cool down. Cooled water is collected into the basin and then used for cooling various hot process fluid.
1. Less operating and maintenance cost.
2. Safe to operate.
3. Energy efficient.
1. Not adoptable with every climate conditions.
2. Large space is required to install.
3. High initial Cost.
1. Used in power stations and for process cooling applications.
b.) Mechanical draft cooling tower
Mechanical draft cooling tower utilizes mechanical devices such as fan or blower to move air through the tower. It is classified into two types.
I.) Forced Draft cooling tower:
In forces draft cooling tower air is blown through tower with the help of a fan located at the bottom of tower. Hot water enters from top of the tower. Counter flow of air and water in the fill results in a heat transfer. It uses atmospheric cooling with wet technology. This type of cooling tower removes low potential heat generated during production process and having limited application due to recirculation difficulties.
1. Easy maintenance as it has better access to the fan, drives and motor.
2. Suitable for high air resistance.
1. Higher fan power requirement.
2. It may be susceptible to recirculation.
1. Petrochemical industry and energy industry.
II.) Induced Draft:
It works similar to the forces draft cooling tower except little difference. In this type of tower, air is introduced from the bottom and water enters from the top. Water gets spread throughout the tower with the help of spray distribution header. Fan is situated at air outlet which draws air across the fill at high level and drawn through the baffled area by fan which causes cooling of the water. Time of contact is greater in induced draft which also improves heat transfer area.
1. Less recirculation as compare to Forced draft.
2. Does not require large space to install.
1. Fan, motor and drives located in moist air stream so electrical protection is required.
2. More maintenance required and corrosion is likely.
1. Best suitable for A/C plants, chemical industries and sugar industries.
3.) Categorized by Heat transfer method:
a.) Dry cooling tower:
It utilizes air instead of water so named as Dry cooling tower. It transfer heat to the atmosphere without evaporation and consumption of water is relatively less. This type of cooling tower operates by convective heat transfer through a surface which separates fluid from the air. It is most suitable for cooling of processing liquid.
1. Only frequent maintenance is needed.
2. A large amount of water gets conserved.
1. It tends to produce large mechanical noise.
1. It is used in power generation units.
2. Suitable in heat treatment furnace in forging unit.
b.) Wet cooling tower:
Wet cooling tower is otherwise known as Open circuit cooling tower. It operates on evaporative cooling. Water to be cooled is pumped from the plant and distributed over the fill. Water vapor are added into the air which lowers the temperature pf water as well as air. Fills plays important role in providing better heat transfer by increasing contact surface as well as contact time.
1. Thermal efficiency and net power output is high.
1. Operating cost is little high.
1. Petrochemical, oil refinery and thermal power plant.
c.) Fluid cooler:
It is also known as Closed circuit cooling tower. It operates on similar principle as open circuit cooling tower only difference is that process fluid does not contact cooling air. Two separate external fluid circuits and coil are present inside the fluid cooler. Coil isolates the process fluid from outside air to keep it contamination free. Internal circuit circulates process fluid inside the coil and External circuits circulate water over the coil mixing with outside air. Heat is transferred from the internal circuit to water and then to the atmosphere by evaporating water.
1. Reduced pumping requirement and cost.
2. It conserves more space due to compact design.
1. Slightly expensive.
2. It can be heavier and larger than open circuit cooling tower.
1. It is used for heating, ventilation and air conditioning in refrigeration industry.
This is all about what is cooling tower and types of cooling tower. If you have any query regarding this article, ask by commenting. If you like this article, don’t forget to share it on social networks with your friends. Subscribe our website for more informative articles. Thanks for reading it.