Many process industries and power plants include cooling towers, which are an essential component. The water lost to evaporation is replaced using the make-up water supply. The cooling tower receives hot water from the condenser and heat exchanger. Water is returned to the condenser/exchangers or to other units for further processing, after cooling in the cooling tower.
How to determine the Cooling Tower Efficiency?
Let us undergo over the fundamental ideas of cooling towers, several kinds of cooling towers, and the formula for calculating cooling tower efficiency.
Components of the cooling towers
Drift:Water loss from a cooling tower due to liquid droplets entrained in exhaust air is known as drift. It is unaffected by the water that evaporates.
Condenser:A device for transferring heat from one substance to another is a heat exchanger or condenser.
Concentration: It is the process of increasing both the amount of material dissolved, and the number of solids per unit volume of solution.
Evaporation: It cools the water, typically causes liquid concentration in cooling towers. Directly or indirectly, it is typically stated as (parts per million) ppm or mhos conductivity.
Cooling tower entrance:By the cooling tower entrance where air enters a tower, the air blows.
Blowdown:Water is released from the cooling tower system during a blowdown, to reduce the amount of salts or other contaminants in the circulating water.
Cooling tower system:Water evaporated from the circulating water into the atmosphere,is as a result of the cooling tower system.Water is added to the cooling tower system's circulating water, to make up for water lost to evaporation, blowdown, drift, and leaks.
Drift eliminators: An assembly made of plastic, cement board, wood, or another material that reduces the amount of moisture, which is entrained in the air that is evacuated.
Cooling water: To remove heat from particular places, water is circulated through a cooling system.
Exhaust air: The vapour and-air mixture that is expelled from the cooling tower system.
Louvers: Structures that are horizontally inserted into the wall of a cooling tower to create openings for air, to enter the system and to catch falling water inside the tower. Louvers are often positioned at an angle to the airflow direction, to the cooling tower.
Cooling tower types
Cooling towers are often divided into two categories.
1. A cooling tower with mechanical draught
2. A cooling tower with natural draught
1. Cooling tower with mechanical draught
Mechanical draught cooling towers are increasingly frequently employed for cooling water. Large fans are used in these mechanical draught cooling towers, to push air through the moving water.
Water flows downward across fill surfaces, lengthening the duration that the water and air are in touch. By doing this, the air and water can transmit heat more effectively.
Two types of mechanical draught water-cooling towers are:
· Forced draught: At the air inlet of this cooling tower, there are fans.
· Induced draught: At the air exhaust of this cooling tower, there are fans.
Cooling tower with forced draught
These resemble a huge rectangular concrete building. Sprays of water are created after the water is pumped to the top. It comes down in the shape of rain on successive layers of wood, polystyrene, or metal louvers, with notches and ribs to break up the flow.
The water travels through each level until arriving at the pond at the bottom of the structure, where the cold water pump draws it.Fans positioned at the base of the tower create air circulation, in forced draught cooling towers.
Tower with induced draught for cooling
At the top of the tower, there are fans that are used to circulate the air.In general, induced draught cooling towers are categorised as counter current or cross flow towers, based on how the air flows in relation to the water.
Although, the cross flow tower can be operated with a lower power need or at higher vapour velocities, the counter current tower is anticipated to be more efficient.
2. Water-cooling tower with natural draught
The cooling tower is typically covered in laths of wood or brush. In this very big tower, the hot water comes into contact with a natural draught that encourages cooling of the water, by convection and evaporation.
The air circulation in a natural draught cooling tower is caused by the difference in pressure, between the air inside and outside the cooling tower.
Design factors for cooling towers
The effectiveness of this device is largely dependent on the weather, particularly the temperature and the relative humidity, of the surrounding air.
Design and size of the necessary cooling tower will depend on the following factors:
· Cooling range
· Bulb temperature
· Water mass flowrate (Circulation rate)
· Air speed via the tower or each tower cell
· Tower height
Performance assessment in cooling towers
Approach and range are used to estimate cooling tower performance. The following parameters are measured by portable monitoring devices, during the performance assessment:
a) The air's dry bulb temperature
b) Air temperature at the wet bulb
c) Inlet water temperature of cooling towers
d) Water temperature at the cooling tower outlet
e) Electrical readings from the fan and pump motors
f) Temperature of exhaust air
g) The flow of water
h) Airflow velocity
Considerations for the operation of cooling tower (Cooling tower mass balance)
The mass balance of the cooling towers provides information on the system's need for make-up water. The need for cooling tower makeup is due to water losses via drift, evaporation, and blowdown.
Total water losses (M) equals the sum of the following-
Drift Losses (D), Evaporation Losses (E), and Blow Down Losses (B)
M = D + E + B
“M” is the amount of make-up water needed in m3/hr.
“D” is for Drift Loss in m3/hr.
“E” is loss from evaporation in m3/hr.
“B” is the blowdown in m3/hr.
Drift Losses (D) or Windage
Drift losses may be assumed to be:
D = 0.3 - 1.0 % of Circulating water (C), for a natural draft cooling tower.
D = 0.1 - 0.3 % of Circulating water (C), for an induced draft cooling tower.
D = 0.01 %or less of Circulating water (C), if the cooling tower has windage drift eliminators.
Blowdown or draw off in cooling towers
As cooling water circulates, a portion of it evaporates in the cooling tower, increasing the number of solids per unit volume of solution, as well as the amount of material dissolved in a unit volume of solution.
Blow down or Draw off is used to manage the Concentration Cycle. The formula can be used to determine blowdown.
B = E/ (COC-1)
B= Blow Down in m3/hr.
E = Evaporation Loss in m3/hr.
COC= Cycle of Concentration.
Calculations of Cooling Tower Efficiency
This cooling tower system's effectiveness is based on the local climate, particularly the wet-bulb temperature and the relative humidity of the surrounding air.
Design and size of the necessary cooling tower will depend on the following factors:
· Cooling range
· Wet bulb temperature
· Water mass flowrate
· Air speed via the tower or each tower cell
· Tower height
Cooling Tower Approach
The cooling tower approach is the difference in temperature between the water leaving the cooling tower (cold water temperature), and the surrounding wet bulb temperature.
Approach of cooling tower = Wet bulb temperature - Cooling tower outlet water
Cooling Tower Range
The range of a cooling tower is the difference between the temperatures at the intake (hot water temperature), and outflow (cold water temperature) of the cooling tower.
Range of cooling tower = Inlet temperature of cooling tower - Outlet temperature of cooling tower
The efficiency of the cooling towers will typically range from 65 to 70%. In comparison to winter, the ambient air wet bulb temperature rises in the summer, which limits cooling tower efficiency.
Conclusion
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Why should you select Netsol Water as the manufacturer of your water treatment systems?
We are the leading producer and supplier of commercial RO Plants, industrial RO systems, water softeners, etc., in India. Our system is exceptionally reliable and cost-effective for use in an industrial environment. We work with each of our clients to give high-quality filtration systems at affordable pricing since, we are aware that you need the best systems available, at fair and competitive prices.
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