21-22 the Best Article on| Cooling Tower

Best Article on| Cooling Tower

In this post of Best Article on| Cooling Tower, we will discuss the following.

  1. How Cooling Tower Works?
  2. Types of Cooling Tower
  3. Factors affecting cooling tower performance
  4. Cooling Tower problems
Cooling Tower
21-22 the Best Article on| Cooling Tower 7

Theory of Cooling Tower

Best Article on| Cooling Tower
21-22 the Best Article on| Cooling Tower 8

Cooling Tower is equipment, for reducing the temperature of a water stream by withdrawing heat from the water and radiating it to the atmosphere.

The cooling tower works through evaporation. Some water evaporates with the air stream and radiates the heat to the atmosphere, and the remaining water cools down. Cooling tower reduces the circulation water temperature near to ambient wet bulb temperature.

Cooling Tower Types

  1. Natural Draft Cooling Tower
  2. Mechanical Draft Cooling Tower 

Cooling Tower Natural Draft type

Natural draft cooling tower is an open direct contact system that utilizes the difference in temperature between the Ambient air and the hotter air inside the tower. Air movement occurs due to the differences in densities between the air entering the tower and the air present inside the tower. Hot moist air is denser than the cool air, rises upward through the tower, and the cool air from outside will fall, creating a constant airflow cycle.

Due to the layout of the cooling tower, there is no requirement for a cooling fan.

 The tower shell is a concrete design with a height of more than 200 Mtrs. Captive power plants makes use of natural draft cooling towers. 

Natural draft cooling towers are of the following two types.

  1. Cross flow Tower-In a cross flow type tower air flows across the falling water and the location of the fill is outside the tower.
  2. Counter flow tower;- In this type of tower flow of air is through falling water and the location of the fill is inside the tower.

Counter flow (Induced draft) cooling towers are more efficient than cross flow (Forced draft) cooling towers.

Mechanical Draft Cooling Tower 

In a mechanical draft cooling tower, the circulation of air is through fans. This type of cooling tower uses either propeller fans or centrifugal fans. Comparatively, these types of cooling towers are more effective and can be installed inside the building.

Power consumption in mechanical draft cooling towers is more than the natural draft cooling towers.

Mechanical draft cooling towers are with maximum heat transfer between air to water.

Connected heat load determines the range of the cooling tower.

Terminology in cooling towers (Best Article on| Cooling Tower)

Best Article on| Cooling Tower
21-22 the Best Article on| Cooling Tower 9

Range;- Range is the difference between the water inlet and outlet temperature. The high cooling tower range indicates the effective reduction of water temperature and the cooling tower is performing well.

The formula for the calculation of the range

Cooling Tower Range (0C) = [Cooling water inlet temp. (0C)- Cooling water outlet temp. (0C)]

Wet bulb Temperature

Wet bulb temperature is the key factor for the Performance of evaporative type cooling machine. WBT is the controlling factor for the minimum cold water temperature to which water will be cooling down by evaporative method. Wet bulb temperature of the air inlet to the cooling tower regulates the operating temperature limits in the plant, process and system.

Approach;- Cooling water outlet cold water temperature and ambient wet bulb ( Wb) temperature difference is Approach in CT. The lower approach is the indication of an efficient cooling tower.

The approach is a better indicator of CT performance than the range.

The formula for the calculation of Approach

Cooling Tower Approach (0C) = [Cooling water outlet temp (0C) – Wet bulb temp. (0C)

Effectiveness;- Effectiveness is the ratio between range and ideal range, the difference between cooling water inlet temperature and ambient wet-bulb temperature.

The formula for the calculation of effectiveness

Cooling Tower Effectiveness (%) = 100x (CW temp- CW outlet temp)/ (CW inlet temp- WB temp)

Cooling Capacity; Product of mass flow rate of water, specific heat and Temperature difference is the cooling Tower capacity, Heat rejected in kCal/Hr.

 Evaporation Loss;- Evaporation loss is the quantity of water evaporation for cooling purposes.

The formula for the calculation of Evaporation loss

Evaporation loss (m3/hr)=0.00085×1.8x circulation ratio (m3/hr) x (T1-T2) 

T1-T2= Inlet and outlet water temperature temp difference.

The cycle of Concentration (C.O.C.);- The ratio of dissolved solids in circulating water to the dissolved solids in makeup water.

Blow down losses;- Blow down losses depend upon the cycle of concentration and evaporation losses. 

The formula for the Blow down losses

Blow down=Evaporation loss/ (C.O.C.-1)

Liquid gas ratio;- The ratio between the water and air mass flow rate is LG ratio


L/G= (h2-h1)/ (T1-T2)


L/G= ratio of liquid to gas mass flow ( kg/kg)

T1= Hot water temperature (0C)

T2= Cold water temperature (0C)

h2= enthalpy of air-water vapour mixture at exhaust wet bulb temperature ( kg/kg)

h1= enthalpy of air –water vapor mixture at inlet wet-bulb temperature (kg/kg)

Cooing tower performance effecting factors

  1. Heat Load
  2. Cooling Tower capacity
  3. Cooling tower range
  4. Wet bulb temperature
  5. Water flow and approach
  6. Filling media

Advantage of FRP blades (Best Article on| Cooling Tower)

  1. 20-30 % energy saving due to the aerodynamic profile of the blades
  2. Low starting torque on the motor due to the light weight of the blades low capacity motor requirement.
  3. Enhancement in the Life of the gearbox, motor and bearing.

Change in heat load affects the cooling Tower performance

Process to which cooling tower is connected determines the heat load. Desired process operating temperature levels decide the degree of cooling requirement. A low operating temperature is desirable to enhance the process efficiency and to improve the quality and quantity of product. But in Internal combustion engines the high temperatures are desirable.

The cost and size of cooling tower is directly proportional to the heat load.

Cooling Tower Problems

The unexpected rise in water temperature

1.   Low airflow. Correct the recommended airflow by adjusting the fan blade angle.

2.   Excessive water flow. Correct the water flow 

3.   Clogged or broken sprinklers. Clean/ change the sprinklers

4.   Water is not falling at fills. Correct the sprinklers and stop the leakages.

5.   Impediment of outside airflow. Check and clear the air obstructions.

6.   Fills coated with sludge/ scale. Clean the fills.

 Excessive vibration and Noise

1. Grease/ change the fan motor bearing.

2. Check the fan mounting. Tighten the mountings.

3. Other tower components are having contact with each other. Maintain the gap between various other components.

4. Vibration may be due to the unbalance fan. Check and correct the fan balancing.

5. Check and re-tighten the fan blocks

6. Check the shaft hub mounting for looseness. Re-tighten the shaft hub mounting

An unexpected reduction in cooling capacity

1. Check that motor hasn’t stopped. If the motor is in stopped condition, check the fuse, switch power, and switch control. Clean and adjust the components as per the requirement of action.

2. Check the fan spinning. If the has fan has stopped spinning, check for the nearing problems, change the bearing and remove any obstruction in the cooling tower fan.

3. Check for the unexpected lowering of motor RPM. Check for the defective starter, electrical load, and supply voltage. Take the necessary action according to the findings.

Water carries over the working level

1. Check the water flow for blockage through the filters. Unblock the flow

2. Adjust the speed and angle of sprinklers

3. Adjust the height of sprinklers concerning filter. Adjust the height as per the specifications.

Abnormal water conductivity 

1. Check the probe of the controller for cleanliness. Clean the probe with a dry and clean cloth.

2. Check the operation of the solenoid valve. If the solenoid is not operating due to any debris or for some other reason. Make the solenoid operational for fully closing.

3. Check for any leakages in the cooling tower system.

4. Check the priming of the chemical feed pump.

5. Carry out the adjustment of the chemical feed pump setting till the water conductivity is within acceptable limits.

Reduction in water flow below acceptable norms

1. Check the water distribution pipes for clogging and obstructions

2. Check and clean the water strainers/ filter

3. Check the operation of the water pump.

Unexpected water loss

1. Ensure the sprinkle rpm is within the specification range

2. Ensure the proper location of FRP/ PVC eliminators.

I sincerely thank the readers and hope the post will be useful.

Good Luck!!!

Hi, I’m Sham, Founder of marinediesel.co.in. A web site that provides authentic information regarding Marine Diesel Engines, and learn marine Engineering free with us

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