A cooling tower is used to remove excess heat that is generated in large industrial and commercial units by cooling the area by lowering the temperature.
Here, in this article, you will learn and study the working of different types of cooling towers in brief.
Working of Cooling Towers
In powerplants and industries, a large amount of heat is continuously dissipated due to industrial processes and heavy machines. This heat must be taken out into the environment by means of a heat exchange process. This heat exchange process is the basic principle of cooling tower technology.
As shown in the figure-1 below, the working of the cooling tower system involves the influx of the warm water into the tower system which then gets evenly spread at the top. The equipment spreads the hot water entered over a large area thus increasing the water-air contact. This water-air contact helps to enhance the heat transfer by means of evaporation.
A large volume of air is constantly flowing through the large fans present in the tower system. Water loses its heat as the evaporation proceeds and this warm air then enters the tower sump present at the bottom and the warm air is let out.
The cooled water moves back to the initial source of heat generation and, further, the cycle repeats. All these processes occur simultaneously in a continuous loop.
Classification of Cooling Towers
Latest technologies present a large variety of cooling towers in different types and sizes. Some categories of cooling towers include:
- Shape characterised cooling tower
- Cooling tower based on the method of heat transfer
- Atmospheric cooling tower
- Mechanical draft cooling tower
- Air-flow characterised cooling tower
Mainly, there are three types of cooling towers based on how air or the water passes through them. They are :
- Crossflow Cooling Towers
- Counter-flow Cooling Towers
- Hyperbolic Cooling Towers
1. Crossflow Cooling Towers
In this type, a splash fill is used to make the air flow in horizontal path over the stream of water from the upper reservoirs. This is the most expensive cooling tower system with less maintenance. One main disadvantage of this system is that it is more susceptible to frost action when compared to other types.
2. Counter-flow Cooling tower
Here, the in-flowing air takes a vertical path over the splash fill as the water streams from the reservoirs present above. The system is smaller than crossflow. As more energy is required to push air up against the downward flowing water, the system is costly.
3. Hyperbolic Cooling Towers
This is a well-built system with a minimum amount of resources. As these require few resources, large-scale tasks within big power plants can be managed efficiently.
Selection of Cooling Towers
The selection of cooling towers can be conducted based on the following features :
- System Operation
There are several important factors that govern the operation of a cooling tower :
- The dry-bulb and wet-bulb temperatures of the air.
- The temperature of warm water.
- The efficiency of contact between air and water in terms of the volumetric mass transfer coefficient and the contact time between the air and the water.
- The uniformity of distribution of the phases within the tower.
- The air pressure drop.
- The desired temperature of the cooled water.
The material selection of cooling tower is also important. Cooling towers tend to be corrosive since they are always in direct contact with the water. Proper material selection or additional water treatment is then needed to keep the cooling tower safe.
Applications of Cooling Towers
The chief applications of cooling towers are in:
- Power Plants
- Commercial, HVAC and Industrial applications
- Cold Storage
- Electrical Power generation plants
- Die casting machine
- Water cooled air compressors
Structural Stability of Cooling Towers
The cooling towers are susceptible to wind damage and several other failures. Special building codes are made to take into consideration these effects and provide structural support to the system.