About Cooling Tower
A cooling tower is a specialized heat exchanger in which air and water are brought into direct contact with each other in order to reduce the water’s temperature. As this occurs, a small volume of water is evaporated, reducing the temperature of the water being circulated through the tower.
Water, which has been heated by an industrial process or in an air-conditioning condenser, is pumped to the cooling tower through pipes. The water sprays through nozzles onto banks of material called “fill,” which slows the flow of water through the cooling tower, and exposes as much water surface area as possible for maximum air-water contact. As the water flows through the cooling tower, it is exposed to air, which is being pulled through the tower by the electric motor-driven fan.
When the water and air meet, a small amount of water is evaporated, creating a cooling action. The cooled water is then pumped back to the condenser or process equipment where it absorbs heat. It will then be pumped back to the cooling tower to be cooled once again.
Purpose of Cooling Tower
Cooling towers are used to remove heat from a number of sources such as heated process material or machinery. A traditional residential HVAC system is not large enough or designed to handle industrial jobs properly. Industrial cooling towers are primarily used to remove heat from the water systems in natural gas plants, petroleum refineries, petrochemical plants, and food processing plants.
How Does the Cooling Tower Works?
Warm water from industrial equipment, commercial ac system or any other heat source enters the tower and spreads evenly at the top. As the water flows down the tower, the equipment fill spreads it over a large area to increase the water-air contact, thus enhancing heat transfer via evaporation.
A large volume of air is constantly moving along the fill courtesy of large fans in the tower. As evaporation takes place, the water loses heat. It eventually enters the tower sump at the bottom. The cool water then goes back to cool the initial heat source and the cycle repeats. For the sake of system dilution, of portion of the system water goes to the drain through a bleed-off valve. The makeup line feeds the cooling tower with fresh water for replenishment.
You will not note these processes easily because their simultaneous occurrence creates a continuous loop. The figure below shows the process in a typical cooling tower.
Efficient Operation of Cooling Tower
Cooling towers may be generally cost-effective for industrial cooling compared to other options, but efficiency challenge can be a letdown. Monitoring the efficiency factor is crucial as it ensures the following:
- Reduced water consumption
- Energy savings
- Extended equipment service life
- Reduced operating costs
To keep the cooling tower running efficiently, three things are important: understand the type of cooling tower you are using, use chemicals efficiently and track down system water loss.
Terminology in Cooling Tower
Drift: From a cooling tower water lost due to liquid droplets entrained in the exhaust air. It is independent of water lost by evaporation.
Heat exchange/ Condenser – It is a device for transferring heat from one substance to another.
Concentration : The process of increasing solids per unit volume of solution also the amount of material dissolved in a unit volume of solution.
Usually concentration of liquid in cooling tower occurs due to evaporation that cools the water. It is normally expressed directly as (parts per million) ppm or indirectly as mhos conductivity.
Air Blows: By the opening in cooling tower through which air enters a tower.
Blowdown: Water discharged from the system of cooling tower to control concentration of salts or other impurities in the circulating water
Evaporation loss: In the process of cooling tower system, water evaporated from the circulating water into the atmosphere.
Makeup : Water added to the circulating water in cooling tower system to replace water lost by evaporation, blowdown, drift and leakage
Drift eliminators: An assembly constructed of plastic, cement board, wood, or other material that minimize the entrained water moisture from the discharged air.
Cooling water : Water circulated through a cooling system to remove heat from certain areas.
Exhaust air : The mixture of air and its associated vapor leaving the cooling tower system
Louvers : Members installed horizontally in a cooling tower wall to provide openings through which the air enters into the system while also containing the falling water within the tower. Usually Louvers are installed at an angle to the direction of air flow to the cooling tower.
Design Consideration of Cooling Tower
The efficiency of this device depends essentially on climatic conditions, in particular the wet-bulb temperature and the relative humidity of the ambient air.
The required cooling tower design and size will be a function of following values
a) Cooling range
b) Web bulb temperature
c) Approach to wet bulb temperature
d) Mass flowrate of water (Circulation rate)
e) Air velocity through tower or individual tower cell
f) Tower height
The performance of cooling towers is estimated by approach and range. During the performance assessment, portable monitoring instruments are used to measure the following parameters:
a) Dry bulb temperature of air
b) Wet bulb temperature of air
c) Cooling tower inlet water temperature
d) Cooling tower outlet water temperature
e) Electrical readings of pump and fan motors
f) Exhaust air temperature
g) Water flow rate
h) Air flow rate
Cooling Tower Approach
Approach: The difference between the Cooling Tower Outlet water (Cold Water Temperature) and ambient Wet Bulb Temperature is called as Approach of Cooling Tower.
Approach of cooling tower = Cooling tower outlet water – Wet bulb temperature
Cooling Tower Range
Range: The difference between the cooling tower inlet temperature (Hot Water Temperature) and cooling tower outlet temperature (Cold water temperature) is called Range of Cooling Tower.
Range of cooling tower = Cooling tower inlet temperature – Cooling tower outlet temperature
Applications of Cooling Tower
The cooling tower system is common in many industries, chief among them being power, commercial, HVAC and industrial. In the industrial setup, the system rejects heat from machinery, heated process material among other sources. Specifically, industrial cooling towers are common in food processing plants, petroleum refineries, natural gas plants and petrochemical plants.
- Water Cooled Air Compressors
- Plastic Injection & Blow Moulding Machine
- Die Casting Machine
- Refrigeration and Chilling Plant
- Cold Storage
- Anodizing Processes Plant
- Electrical Power generation plant
- Water Cooled Air Conditioning systems and Vam Machine