The cooling tower is nothing but a device used to reduce the heat and increase production efficiency. In simple words, it is used to cool industrial hot water. Its size ranges from tiny to massive towers based on the requirement.
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A cooling tower’s main function is to remove heat from water by evaporating a little amount of it. The mixture of warm and cooler water leads to latent heat evaporation causing the water to cool. A commercial cooling tower has an average life expectancy of 15-20 years.
Several industries use a cooling tower, such as chemical manufacturing plants, primary metals processing plants, petroleum refineries, rubber products manufacturing plants, tobacco manufacturing plants, glass manufacturing plants, and textile manufacturing plants.
The cooling tower provides high cooling efficiency, needs less maintenance, consists of reliability and sustainability, and can be operated for a longer duration. Now, let us have a look at a few questions that will help you get clear with the idea behind cooling towers.
1. What is a cooling tower?
A cooling tower is nothing but a heat exchanger. It extracts waste heat to the atmosphere by cooling the water stream to a lower temperature. Water begins to cool when it comes into contact with air. In this way, the same amount of water is evaporated and thereby cool down the hot water.
2. What are the different types of cooling towers?
There are two types of cooling towers:
3. What is an Evaporative cooling tower?
Cooling is provided via an evaporative cooling tower based on a design wet-bulb temperature. This cooling tower can cool water to 85 degrees Fahrenheit. It is the most economical option for cooling a large amount of water.
4. What is entering wet-bulb temperature (EWBT)?
EWBT is nothing but a device that measures the level of humidity in the air entering the cooling tower. The higher the temperature of the wet bulb, the more moisture exists in the air. The cooling tower needs to be larger with a high wet-bulb temperature compared to a lower wet-bulb temperature.
5. What is the difference between ‘counterflow’ and ‘cross flow’ cooling towers?
In a counterflow cooling tower, air travels vertically upwards through the fill and makes intimate contact with water. Hence, both air and water are in opposite directions. In a crossflow tower, air passes through the fill horizontally, crossing the downwards water flow.
6. Why choose the FRP cooling tower?
FRP (fibreglass reinforced polyester) is mixed with a gel coating that protects the cooling tower from direct UV rays. Additionally, it also provides a higher resistance to rot and decay to all FRP portions. Hence, FRP cooling tower manufacture is considered in extreme climate conditions.
7. How do Cooling Towers Operate in Cold and Sub-zero Weather?
In cold weather, the cooling tower is operated with a heat load. The operating water flow is directly bypassed to the cold-water basin to prevent icing if the heat load drops too low. The water flow is maintained over the cooling tower.
8. What is the difference between a ‘Force Draft’ and ‘Induced Draft’ cooling tower?
A Force-draft cooling tower imparts an agitation system that forces air into the tower, and fans are positioned on the side of the cooling water. Meanwhile, induced draft tower works by pulling air from the building and fans are located on the top of the cooling tower.
9. How is Water Loss Calculated in Cooling Tower?
There are three types of water loss in the cooling tower: drift, evaporation, and blowdown. Drift loss is while circulating water for the natural draft tower. Evaporation loss is simple as it sounds, water loss due to evaporation. Blowdown loss is during circulating water that lowers the concentration of solids.
10. What is Cooling Tower Drift?
Drift is undesirable loss of water to the environment through tiny, unevaporated droplets in the existing cooling tower stream. These water droplets carry minerals, microorganisms, debris, and chemicals from the circulating water. Hence, it potentially impacts the environment.
11. What is the regulating organization for cooling tower technology, and where can you learn more about the cooling tower industry?
There’s a worldwide industry named Cooling Technology Institute (CTI) authorized on cooling tower technology. In this institute, there are manufactures, owners/operators, and supplies providing facilities for the cooling tower. Moreover, you can get more information on CTI guidelines and specifications on the CTI site.
12. How to clean Air Inlet Louvers of Cooling Tower?
The best method to remove the minerals from the air inlet louvres is to remove the louvre equipment and let them soak in the cold-water basin of the unit. The chemicals present in the water treatment unit will neutralize and dissolve the minerals buildup. The time depends on the severity of the buildup.
7-What is the function of drift eliminators?
Drift eliminators fitted at the top of the tower capture water droplets trapped in air & water vapour mixture.
Drift is water that is carried away from the tower in the form of droplets with the air discharged from the tower.
8-What is the function of fills?
Fills situated just below the drift eliminator facilitate the heat transfer by maximizing the contact between air & water particles.
9-What are the two types fills used in cooling towers?
Splash type fills & Film type fills
Splash type fills: Are made up of plastics or wooden materials. These are fitted on splash bars .These splash break the water particles into small particles to increase the surface contact area with air.
Film type fills: These are made of plastic materials, the water particle falling on this forms small films, which increases heat transfer by making contact area larger.
Films fills may be flat, corrugated or horizontal type. Film type fills are more efficient than splash type fills
10-What is the function of lowers in cooling towers?
11-What are the different types fans used in cooling tower?
12-What type of blades used for propeller type fans?
Fixed pitch & variable pitch blades.
13-What is the material of construction of CT blades?
Generally Blades are of Aluminium or FRP (Fibre Reinforced Plastic)
14-Why do the cooling towers used in power plant
Cooling towers used for cooling
15-Why do the Mechanical draft cooling towers some time installed inside the buildings?
Because, mechanical draft cooling towers do not depend on atmospheric air
16-Briefly explain the cooling tower working procedure?
Hot water from various plant appliances is sent to cooling tower hot basin, where water distributed into various cells through pipe lines & water is being sprayed on fills. While falling downward water, comes in contact with cold air that was sucked, forced or naturally drafted by cooling tower. Thus exposure of hot water to cold air converts water vapour & the remaining water falls down in sump for recirculation.
The vapour is pulled by fans & expelled to atmosphere. Such loss of water due to vapour is added through fresh same quality make up water.
17-What is the function of sluice valves
Sluice valves are used to isolate the cooling towers sumps of different cells for cleaning or any maintenance purpose.
18-What are the various pipe lines connected to cooling towers?
19-What is the blade angle of CT fans usually set?
It is in the range of 12 to 140
20-What is the function of fore bay in cooling tower?
It is a water sump or canal provided to connect the different cells & to provide suction water to cooling water pumps.
21-What are the reasons for drift loss in cooling towers?
Note:
22-For which type fill height required is very less?
Film type fills
26-Distinguish between cooling towers having film type fills & flash type fills
Sl No.
Film type fills
Flash type fills
1
Fill height required less
Fill height required more
2
Pump static head required is less
Pump static head required is more
3
Motor power consumption is less
Motor power consumption is more
27-What is the maximum speed of cooling tower fans for induced counter flow film type CTs?
It’s generally 125 rpm to 175 rpm
28-Define Range & Approach in cooling towers?
Range: It is the difference between cooling tower inlet and out let water temperature
Range = T2-T1
Where T1 = Cooling tower outlet cold water temperature in deg C
T2 = Cooling tower inlet hot water temperature in deg C
Approach: It is the difference between cooling tower outlet cold water temperature (T2 or Tc) and wet bulb temperature (Twb)
Approach = T2-Twb or Tc-Twb
29-Define the term cooling tower effectiveness?
CT effectiveness = Range X 100 / (Range + Approach)
30-How do you measure the Cooling tower capacity?
It is measured in terms of heat rejected.
Heat rejected = Mass of circulating water X Specific heat of water Cp X Range
40-What do you mean by evaporation loss in cooling towers?
It is the evaporation of circulating water during cooling duty
Evaporation loss = 0. X 1.8 X Water circulation rate X Range
1.8 is taken as 1.8 m3 of water is rejected on every 10, kcal heat rejected
Evaporation Rate is the fraction of the circulating water that is evaporated in the cooling process.
A typical design evaporation rate is about 1% for every 12.5°C range at typical design conditions.
It will vary with the season, in colder weather there is more sensible heat transfer from the water to the air, and therefore less evaporation.
The evaporation rate has a direct impact on the cooling tower makeup water requirements.
41-What do you mean by cycles of concentrations (COC) in CT
It is the ratio of dissolved solids in circulating cooling water to the dissolved solids in makeup water
It is given as
COC = Conductivity in circulation water / Conductivity in makeup water
If you want to learn more, please visit our website how to size a cooling tower.
OR
COC = Chloride in circulation water / Chloride in makeup water
42-How do you calculate the blow down loss in CT?
Blow down loss = Evaporation loss / (COC-1)
43-Heat rejection of a counter flow induced draft cooling tower is kcal/hr & circulation rate of cooling water is m3/hr. Calculate the cooling water temperature differences (range)
We have Range = Heat load (heat rejection) / Circulation rate X Specific heat Cp
Range = / ( X X 1)
Range = 10.36
44-Calculate the approach of cooling tower having effectiveness 75% & cooling water temperature difference 7 deg C
We have,
Effectiveness = Range / (Range + Approach)
0.75 = 7 / (7+Approach)
Approach = 2.33
45-Inlet & outlet temperatures of circulating cooling water of a induced draft cooling towers are 38 deg C & 31 deg C respectively. The hygrometer shows 27 deg C wet bulb temperature, calculate the cooling tower efficiency.
We have,
CT effectiveness = Range X 100 / (Range + Approach)
Range = 38-31 = 7 deg C
Approach = 31-27 = 4 deg C
CT effectiveness = 7 X 100 / (7+4) = 63.63%
46-A cooling tower of circulation water flow M3/hr & temperature difference (range) 6 deg Calculate the heat load of a cooling tower
Heat rejected = Mass of circulating water X Specific heat of water Cp X Range
Heat load of cooling tower = X X 1 X 6 = kcal
47-A cooling tower having circulation water flow m3/hr & inlet and outlet circulating water temperatures are 36 & 29 deg C respectively. Calculate the evaporation loss in %
We have,
Evaporation loss = 0. X 1.8 X Water circulation rate X Range
Range = 36-29 = 7 deg C
Evaporation loss = 0. X 1.8 X X 7 = 37.21 M3/hr
% of evaporation loss = 37.21 X 100 / =1.07%
48-Calculate the blow blown loss of cooling tower, if its evaporation loss & COC are 0.8% & 5 respectively.
Blow down loss = Evaporation loss X 100 / (COC-1)
Blow down loss = 0.8 / (5-1) =0.2%
49-Calculate the COC of a cooling tower if Chloride & conductivity of circulating water are 147 ppm & 550 micS/cm and that of makeup water are 33 ppm & 90 micS/cm respectively
We have,
COC = Chloride in circulation water / Chloride in makeup water = 147 / 33 =4.45
COC = Conductivity in circulation water / Conductivity in makeup water = 550/90 =6.11
49- A cooling tower having circulation water flow m3/hr & inlet and outlet circulating water temperatures are 39 & 31 deg C respectively. Calculate the evaporation loss & blow down loss in %. Consider chloride level in circulating water & make up water are 155 ppm & 35ppm respectively.
We have
Evaporation loss = 0. X 1.8 X Water circulation rate X Range
Range = 39-31 = 8 deg C
Evaporation loss = 0. X 1.8 X X 8 = 78.34 M3/hr
% of evaporation loss = 78.34 X 100 / =1.22%
Blow down loss = Evaporation loss X 100 / (COC-1)
COC = Chloride in circulation water / Chloride in makeup water
COC = 155 / 35 = 4.4
Blow down loss = 1.22 / (4.4-1) =0.36%
48-A induced draft CT having cooling water circulation flow M3/hr, Calculate the quantity of makeup water required in a day. Assume evaporation, blow down & drift losses 0.9%, 0.2% & 0.003% respectively.
We have,
Evaporation loss = X 0.9/100 =64.8 M3/hr
Blow sown loss = X 0.2/100 =14.4 M3/hr
Drift loss = X 0.003/100 =0. M3/hr
Total make up water quantity = 64.8 + 14.4 + 0. =79.2 M3/hr
49-A Mechanical cooling tower operating at 5 COC is used to cool M3 of water required for the power plant auxiliaries from 37 deg C to 28 deg C at 24 deg C WBT.Calculate Range, approach, evaporation loss, blow down loss and make up water requirement.
We have,
1-Range = 37-28 = 9 deg C
2-Approach = 28-24 = 4 deg C
3-Evaporation water loss = 0. X 1.8 X X 9 =117.045 M3/hr
4-Blow down water loss =117.045 / (5-1) =29.26 M3
5-Make up water = 117.045 + 29.26 = 146.30 M3/hr
50-What do you mean by CT hold up of volume?
It is the operating water volume of CT including all cells & fore bays.
51-How do you decide the cooling tower hold up capacity?
Generally it is 25% of the circulating flow for safe operation.
That is if cooling tower required circulation water flow is M3/hr, then its hold up volume will be
X 25 / 100 = M3
52-What do you mean by liquid & gas ratio (L/G) in cooling towers?
It is the mass ratio of water (Liquid) flowing through the tower to the air (Gas) flow.Each tower will have a design water/air ratio.
An increase in this ratio will result in an increase of the approach, that is, warmer water will be leaving the tower.
L/G = (h2-h1)/(T2-T1)
L/G = liquid to gas mass flow ratio (kg/kg)
T2 = hot water temperature (°C)
T1 = cold-water temperature (°C)
h2 = enthalpy of air-water vapor mixture at exhaust wet
h1 = enthalpy of air-water vapor mixture at inlet wet-bulb temperature.
53-What are the types of heat transfer that occur in cooling towers?
Heat transfer in cooling towers occurs by two major mechanisms:
54-What are the various chemicals used in cooling water treatment?
SL No.
Chemicals
Use
1
Scale inhibitors
To prevent scaling
2
Corrosion inhibitor
To prevent corrosion
3
Bio dispersant
Bio-Dispersion
4
Sulphuric acid
To maintain pH level of water
5
Chlorine granules
To kill the bacteria
6
Oxidising biocides
Controls bio fouling in heat exchangers like Condensers, oil coolers)
7
Non- Oxidising biocides
To kill microorganisms
55-What are the various tests conducted for cooling water in CT?
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