Basic concept of cooling tower and factors affecting in cooling Tower performance.

Cooling Tower Types

Cooling towers fall into two main categories: Natural draft and Mechanical draft.

Natural draft towers use very large concrete chimneys to introduce air through the media. Due to the large size of these towers, they are generally used for water flow rates above 45,000 m3/hr. These types of towers are used only by utility power stations.

Mechanical draft towers utilize large fans to force or suck air through circulated water. The water falls downward over fill surfaces, which help increase the contact time between the water and the air this helps maximize heat transfer between the two. Cooling rates of Mechanical draft towers depend upon their fan diameter and speed of operation
.

Mechanical draft towers are available in the following airflow arrangements:

1. Counter flows induced draft.

2. Counter flow forced draft.

3. Cross flow induced draft.

Glossary of Cooling Tower Terms

Approach
It is the difference between cold-water temperature (sump) and wet bulb temperature.

Approach = Outlet temp - Wet Bulb Temp.

Range

It is the difference between Inlet water temperature and outlet water temperature.

Range = Inlet temp. - Outlet temp.

Fill or Packing

The structural system, which keeps the water evenly, distributed as it falls through the tower.

Wet Bulb temperature

The wet bulb temperature of the air is the lowest temperature at which water can be cooled by evaporation. The wet bulb temperature is also the dew point of the ambient air.

Dew point temperature
The dew point of the air, which is also the coldest temperature to which water can be cooled by passing it through air. Wet bulb temperature is normally determined by using a psychrometer that contains a thermometer in contact with a water wetted wick.

Blow down  

It is the controlled discharge of recirculating water to waste that is necessary to limit the solids in the system.

Blow down =evaporation loss/C.O.C.-1