1. INTRODUCTION

1.1. Types of heat exchangers

COOLING TOWERS

The cooling towers are a type of heat exchanger is to remove heat from a hot water stream through cold and dry air that circulates through the tower.
Hot water may fall as rain and heat exchange with cold air, vaporizes a portion of it, removing it from the tower in the form of water vapour.
The cooling towers are classified according to the form of air supply:

- Towers of natural circulation

- Atmospheric: The air movement depends on the wind and the effect aspiring of the sprinklers. Used in smaller installations. It depends on the prevailing winds by the air movement.

-Tyre natural: the flow of air required is obtained as a result of density differences between the cooler air from the outside and moist on the inside of the tower. They use tall chimneys to get the shot you want. Due to the large size of these towers is used for water flow over 200000gpm. It is widely used in power stations. Here is how a natural draft cooling tower with:

- Towers of tyre mechanic

The hot water that reaches the tower is sprayed by a sprinkler system letting down the flow of water through some holes.
The air used for cooling water is taken from the tower of any of the following ways:

- Tyre induced: it sucks air through the tower by a fan located at the top of the tower. They are the most commonly used. Below is the operation of induced draft towers:

- Tyre forced:the air force by a fan located at the bottom of the tower and is discharged to the top-Below is the performance of forced draft towers:

-Other: cross-flow towers. The air enters the sides of the tower flowing horizontally through the water falls. These towers need more air and have an operating cost lower than the towers against the current. Below is the operation of cross-flow towers: