1. What is Cooling Tower TR?
TR means “Tons of Refrigeration.”
Cooling Tower TR is the heat removal capacity expressed in Tons of Refrigeration, where 1 TR = 12,000 BTU/hr.
It is a unit to express the cooling capacity of a cooling tower.
Definition:
1 TR = Heat required to melt 1 ton of ice in 24 hours at 0°C.
In cooling systems, 1 TR = 12,000 BTU/hr ≈ 3.517 kW ≈ 3024 kcal/hr.
In Cooling Towers:
TR indicates how much heat the tower can reject from circulating water.
Used to size and rate cooling towers for HVAC, process, and industrial applications.
Example:
A 100 TR cooling tower can reject heat equivalent to 100 tons of refrigeration load.
2. How do you calculate Cooling Tower TR?
Cooling tower TR is calculated using water flow rate × specific heat × temperature drop, divided by 3024.
Formula:
Where:
m = Water flow rate (kg/hr)
Cp = Specific heat of water (≈ 1 kcal/kg°C)
ΔT = Cooling range (Hot water temp – Cold water temp, °C)
3024 = kcal/hr equivalent of 1 TR
Simplified (if flow in m³/hr):
Example:
Water flow = 300 m³/hr
Hot water temp = 40°C, Cold water temp = 32°C
ΔT = 8°C
3. How do you calculate cooling tower efficiency?
Cooling tower efficiency = Actual cooling achieved ÷ Maximum possible cooling × 100.
Definition: Cooling tower efficiency indicates how effectively a tower cools water compared to the maximum possible cooling.
Formula:
Where:
Thot = Hot water temperature entering tower
Tcold= Cold water temperature leaving tower
Twb= Ambient wet bulb temperature
Key Points:
Efficiency depends on approach (cold water temp – wet bulb temp).
Closer the cold water temperature is to wet bulb, higher the efficiency.
Practical efficiency usually ranges 65–75%; 100% is not achievable.
Q. How does a Natural Draft Cooling Tower work?
No fans are required; it relies purely on natural air circulation, making it energy-efficient and suitable for large power plants.
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It works on the chimney effect – hot air inside the tower rises naturally, pulling in cool air from the bottom.
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Warm water from the plant is sprayed at the top of the tower.
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The water falls through fill material, which increases contact surface with air.
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Cool air enters from the bottom, meets falling water, and absorbs heat → part of the water evaporates, cooling the rest.
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The warm, moist air rises out through the tall chimney due to density difference.
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The cooled water collects at the basin at the bottom and is recirculated back to the plant.
Q: How is heat transfer done in a cooling tower? Explain the heat transfer mechanism.
1. Basic Concept:
A cooling tower removes heat from hot water coming from industrial equipment or condensers by transferring heat to the atmosphere.
2. Types of Heat Transfer Involved:
(a) Evaporative Cooling (Major):
Around 70–80% of heat is removed by evaporation of a small portion of water.
When a small amount of water evaporates, it absorbs latent heat of vaporization from the remaining water, reducing its temperature.
(b) Sensible Heat Transfer:
The remaining 20–30% of heat is transferred by direct contact between air and water (air absorbs heat due to temperature difference).
3. Heat Transfer Mechanism (Stepwise):
1. Hot water from the plant is sprayed or distributed at the top of the tower.
2. Air enters from the bottom or sides (either by fan or natural draft).
3. Contact between air and water occurs through fill media, increasing surface area for heat exchange.
4. A portion of water evaporates, absorbing heat (latent heat transfer).
5. The cooled water collects at the bottom basin and is recirculated back to the process.
6. Warm, moist air exits from the top of the tower.
4. Final Outcome:
The system efficiently reduces water temperature by 5–10°C (approx) using evaporative and convective heat transfer.
Example:
Cooling tower works on the principle of evaporative and convective heat transfer, where heat from hot water is removed by partial evaporation and direct air–water contact, ensuring efficient process cooling.
Q: What is R.I. in a cooling tower?
R.I. in a cooling tower represents the temperature drop across the tower, showing how effectively the tower removes heat — a key indicator of its operational efficiency.
1. Full Form:
R.I. stands for Range Indicator (or sometimes Range Index) in a cooling tower.
2. Definition:
It indicates the temperature difference between the hot water entering and the cold water leaving the cooling tower.
3. Formula:
4. Purpose:
R.I. helps to evaluate the cooling performance or heat removal capacity of the tower.
A higher R.I. means better cooling efficiency, assuming ambient conditions are constant.
5. Typical Range:
Normally between 4°C to 10°C, depending on tower design and load.
6. Application:
Used for performance monitoring, process optimization, and detecting issues like reduced airflow or scaling.
Q: Which chemicals are used for which type of problem in cooling tower treatment?
In cooling tower water treatment, scale inhibitors, corrosion inhibitors, biocides, dispersants, and pH controllers are used as per the specific problem — ensuring efficient heat transfer, long equipment life, and reliable operation.
1. Scale Formation:
Problem: Deposition of calcium and magnesium salts on heat transfer surfaces reduces efficiency.
Chemical Used: Scale inhibitors (e.g., phosphonates, polyphosphates, polymers).
Function: Prevents crystallization and deposition of hardness salts.
2. Corrosion:
Problem: Metal surface damage due to oxidation and electrochemical reactions.
Chemical Used: Corrosion inhibitors (e.g., chromates, molybdates, phosphates, azoles).
Function: Forms a protective film on metal surfaces to prevent rusting and pitting.
3. Algae and Biological Growth:
Problem: Growth of algae, bacteria, and slime reduces water flow and efficiency.
Chemical Used: Biocides and algaecides (e.g., chlorine, bromine, isothiazolin, glutaraldehyde).
Function: Kills and controls microorganisms in the water system.
4. Fouling:
Problem: Accumulation of suspended solids, dust, and organic matter.
Chemical Used: Dispersants or antifoulants (e.g., polyacrylate - based polymers).
Function: Keeps particles in suspension and prevents deposition.
5. pH Control:
Problem: High or low pH causing corrosion or scale.
Chemical Used:
Acid (e.g., sulfuric acid) → to reduce pH.
Caustic (e.g., NaOH) → to increase pH.
Function: Maintains optimum pH (usually 6.5–8.5) for system stability.
