All about cooling tower

Cooling towers are a special type of heat exchangers in which water and air are in direct contact to reduce the water temperature. These types of equipment have different types in terms of construction type, body shape and material, heat transfer method, water, and airflow arrangement, and airflow suction type, and each of them has features and limitations, and various applications. The use of cooling towers is not limited to various industries, refineries, and power plants, and cooling towers are also used in the air conditioning systems of residential and office complexes. Since it will be possible to choose the most suitable type of cooling tower by knowing the applications, limitations, advantages, and disadvantages of its types, below are the applications, limitations, advantages, and disadvantages of the most important types of cooling towers based on two main classification parameters ( The arrangement of airflow and the type of airflow suction) are discussed.

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Classification of cooling towers based on the arrangement of water and airflow Cross Flow Cooling Towers

In the cooling tower, with the cross-flow of water, due to the force of gravity, it falls through the perforated plate or tower nozzles to evenly distribute the water between the inner surfaces of the cooling tower. The air also enters the tower simultaneously and horizontally and flows outwards by the fans installed outside the tower, as a result, the water and air collide with each other in a crosswise manner and after the evaporation of a part of the water, transfer Heat is transferred from water to air. The cooled water is also accumulated at the bottom of the tower and sent to other equipment for use.

Figure 1- Cross flow cooling tower

Table 1- Applications and limitations of cross-flow cooling tower

Table 2- Advantages and disadvantages of cross-flow cooling tower

Counter Flow Cooling Towers

In the cooling tower with the opposite flow, the air flows in the opposite direction, and at the same time as the water falls down the tower, it passes through the inner surfaces of the tower. The airflow enters from the bottom of the tower and is pulled up vertically due to the suction of the fan. Circulating water is also distributed on the inner surfaces of the tower through the spray nozzles, and after non-uniform and maximum contact, heat transfer takes place and cool water enters the end part of the tower. The important point in these towers is the use of nozzles to spray the water flow so that the water pressure can overcome the airflow in front and move downwards. Also, the height of these towers should be such that the water distribution on the tower surfaces is done well and the water has a chance to cool down. The thermal efficiency of counter-flow cooling towers in places with low relative humidity is higher than the cross-flow type, and most new towers are designed as counter-flow.

Figure 2- Counterflow cooling tower

Table 3- Applications and limitations of counter flow cooling tower

Table 4- Advantages and disadvantages of counter flow cooling tower

 Classification of cooling towers based on the type of airflow suction, cooling towers with natural suction (Natural Draft)

In the cooling tower, the air naturally flows from the bottom to the top of the tower due to the temperature difference and consequently the density difference between the hot air inside the tower and the cool air outside with natural suction. The hot water enters from the top of the tower and after being sprayed inside the tower through the nozzles, it comes into contact with the air in a different direction, and as a result, part of it evaporates and cools. Over time, the temperature of the air inside the tower rises due to the exchange of heat with hot water, and the difference in temperature and density of the air inside and outside the tower increases, and the natural air suction continues with greater intensity. Cooling towers with natural suction are made of concrete and have large dimensions and are expensive to build.

Figure 3- Cooling tower with natural suction

Table 5- Applications and limitations of cooling tower with natural suction

Table 6- Advantages and disadvantages of cooling tower with natural suction

Cooling towers with a mechanical draft (Mechanical Draft)

In cooling towers with mechanical suction, unlike cooling towers with a natural flow, the air flows using a fan (fans). The presence of fans in these towers has made it possible to change the amount of airflow, and in this way, more stability can be created in the weather conditions. Cooling towers with their mechanical suction are divided into the following two groups.

Cooling towers with a forced draft (Forced Draft)

In the cooling tower with forced suction, the fan is located in the air intake area at the bottom of the tower and blows the air upwards. Water also enters from the top of the tower and due to the non-directional contact of water and air and evaporation of a part of it, the water is cooled. The location of the fan in the air intake area can cause hot air to circulate and return to the tower, which has led to the lower cooling efficiency of these towers compared to cooling towers with induction suction.

Figure 4- Cooling tower with forced suction

Table 7-Applications and limitations of forced suction cooling tower

Table 8- Advantages and disadvantages of cooling tower with forced suction

Cooling towers with an induced draft (Induced Draft)

The difference between this tower and the cooling tower with forced suction is the location of the fan, which is installed at the top of the tower. In cooling towers with induction suction, there are fans at the air outlet that draw the air into the tower and direct it outside. Therefore, the air is pulled up by the fan from the bottom inlets and the water enters from the top and is sprayed inside the tower. Due to the location of the fan, the air exits at a high speed and the air enters at a low speed, and this problem reduces the possibility of air circulation and return. Also, the position of the fan at the entrance of the hot air stream provides good protection against the freezing of mechanical equipment. The cooling tower with induction suction has a high efficiency, which is due to the greater contact surface of water and air. The capacity of these towers is around 3 to 160,000 cubic meters per hour (15 to 700,000 gallons per minute). Induced suction and asymmetric flow cooling tower is the most widely used tower in the process industries, capable of producing chilled water with a temperature of 1 °C (2 °F) higher than the ambient bubble temperature.

Figure 5- Cross flow cooling tower with induction suction

Figure 6- Counterflow cooling tower with induction suction

Table 9- Applications and limitations of cooling tower with induction suction

Table 10- Advantages and disadvantages of cooling tower with induction suction

You can also read the article FIBERGLASS COOLING TOWER for more information.

Final speech

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