Subject:- Refrigeration and Air Conditioning

Topic:- Vapor Compression Refrigeration System

Difficulty:- High

Working of Cooling Tower

The function of cooling towers is to cool the hot water pumped from the condenser of refrigeration system. Then the same water can be used again and again to cool the condenser.

Cooling is achieved by means of heat transfer to atmospheric air. The principle is similar to the evaporative condenser. The air surrounding falling water droplets from spray nozzles causes some of the droplets to evaporate. These evaporating droplets absorb latent heat of evaporation from the remaining water and also small amount of sensible heat and thus cools it.

The cooled water collects in a pond or sump and is recirculated through the condenser. Approach

This is defined as the difference in temperature of water leaving cooling tower and the wet-bulb temperature of the entering air. It should be as low as possible.

Tower Approach= $t_wo-t_wb$

Where $t_wo$= temperature of water leaving cooling tower

$t_wb$= WBT of air entering

Range

This is defined as the difference between inlet (hot) water temperature and outlet (cold) water temperature to the cooling tower. It should be as high as possible.

Tower Range=$t_wo-t_wi$

Wher $t_wi$= temperature of water entering cooling tower

Tower Efficiency

It is defined as ratio of actual increase in air temperature $(t_ao-t_ai)$ to maximum theoretically possible drop in air temperature $(t_ai-t_wb)$

$η\frac{(t_ao-t_ai)}{(t_ai-t_wb})$

Where $t_ao$= temperature of air at outlet

$t_ai$= temperature of air at inlet