Click image to open full size
Cooling Tower Reference Cheat Sheet
A printable reference covering cooling tower types, airflow layouts, range, approach, effectiveness, water losses, cycles of concentration, and blowdown for grades 11-12.
Related Tools
Related Worksheets
Cooling towers remove waste heat from water by bringing warm water into contact with moving air. This reference helps engineering students compare tower types, read airflow diagrams, and use the main performance formulas. It is useful for HVAC, power plant, manufacturing, and process cooling problems. Students need it because cooling tower calculations connect thermodynamics, fluid flow, and water treatment in one system. The most important performance ideas are range, approach, heat load, and effectiveness. Range measures how much the water cools, while approach compares the leaving water temperature to the entering air wet-bulb temperature. Water losses include evaporation, drift, and blowdown, and they determine the required makeup water. Cycles of concentration help engineers control dissolved solids so scaling, corrosion, and biological growth stay within safe limits.
Key Facts
- Cooling tower range is Range = hot water temperature - cold water temperature.
- Cooling tower approach is Approach = cold water temperature - entering air wet-bulb temperature.
- Heat removed from water is Q = m dot water x cp x (T hot - T cold), where cp for water is about 4.186 kJ/kg C.
- Cooling tower effectiveness is Effectiveness = Range / (Range + Approach).
- Evaporation loss can be estimated as E = 0.001 x circulation rate x Range in degrees F for many practical water-cooling estimates.
- Cycles of concentration are COC = dissolved solids in circulating water / dissolved solids in makeup water.
- Blowdown can be estimated as B = E / (COC - 1) when drift and other losses are ignored.
- Makeup water is M = evaporation loss + drift loss + blowdown loss.
Vocabulary
- Cooling tower
- A heat rejection device that cools circulating water by transferring heat from the water to air.
- Wet-bulb temperature
- The lowest temperature air can reach by evaporative cooling under the current humidity conditions.
- Range
- The temperature drop of water as it passes through the cooling tower.
- Approach
- The temperature difference between the cold water leaving the tower and the entering air wet-bulb temperature.
- Drift
- Small liquid water droplets carried out of the cooling tower by the air stream.
- Blowdown
- Water intentionally drained from the circulating loop to control dissolved minerals and impurities.
Common Mistakes to Avoid
- Using dry-bulb temperature instead of wet-bulb temperature for approach is wrong because evaporative cooling depends mainly on wet-bulb temperature.
- Confusing range with approach is wrong because range compares hot and cold water temperatures, while approach compares cold water to entering air wet-bulb temperature.
- Ignoring blowdown is wrong because dissolved solids concentrate as water evaporates, which can cause scale, corrosion, and poor heat transfer.
- Assuming a smaller approach is always easy to achieve is wrong because a low approach usually needs more tower area, more airflow, or higher cost.
- Forgetting consistent units in Q = m dot x cp x delta T is wrong because mixed units can give a heat load that is off by large factors.
Practice Questions
- 1 A cooling tower receives water at 38 C and sends it back at 29 C. What is the cooling tower range?
- 2 The cold water temperature is 28 C and the entering air wet-bulb temperature is 23 C. What is the approach?
- 3 A tower circulates 50 kg/s of water with cp = 4.186 kJ/kg C and cools it from 35 C to 27 C. What heat load is removed in kW?
- 4 Why does a humid day usually make it harder for a cooling tower to produce very cold leaving water?