Cooling Tower Basics: Types, Working Principle, Losses, and Design Parameters

What Is a Cooling Tower?

A cooling tower is a heat rejection device that removes heat from warm process or HVAC water and releases it to the atmosphere. A small portion of water evaporates and carries away heat. The cooled water is collected in a basin and returned to the system.

How It Works

1. Distribution: warm water is distributed over fill media.
2. Surface area: film/droplet formation increases heat transfer area.
3. Airflow: fan (or natural draft) moves air through wetted surfaces.
4. Heat transfer: sensible + partial evaporation cools the water.
5. Collection: cooled water returns to the loop.

Counterflow vs Crossflow

Counterflow: air moves upward while water moves downward. Crossflow: air moves horizontally/diagonally relative to falling water.

Open vs Closed Circuit

Open circuit towers directly expose process water to air. Closed circuit towers keep process fluid inside a coil while spray water + air reject heat.

Key Design Metrics

• Range: hot-water inlet minus cold-water outlet.
• Approach: cold-water outlet minus wet-bulb temperature.
• Wet-bulb: practical performance limit for evaporative cooling.

Water Losses

• Evaporation: inherent heat removal mechanism.
• Drift: droplets carried out with exhaust air; reduced by drift eliminators.
• Blowdown: controlled purge to manage dissolved solids (TDS).

Operation and Maintenance

• Water treatment (scale/corrosion/biological control) is essential.
• Periodic inspections: nozzles, fill, drift eliminators, fan/motor group, basin hygiene.