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REFRIGERATION TOWERS AND EVAPORATIVE CONDENSERS (I)

REFRIGERATION TOWERS
AND EVAPORATIVE CONDENSERS
1. INTRODUCTION
Cooling towers are mechanical systems designed to cool water bodies in processes that require heat dissipation.

The principle of cooling of these equipment is based on evaporation, the equipment produces a cloud of water droplets either by spraying, or by free fall that is put in contact with a current of air. The surface evaporation of a small part of the water induced by the contact with the air, results in the cooling of the rest of the water falling into the raft at a lower temperature than the spray.
The most common use of these equipments is associated to the refrigeration systems, both in air
However, in the industrial field, these devices are used for the cooling of any part of a process that generates heat and is dissipated (for example, grinding that generate heat by friction, cooling of exothermic reactions, waste heat dissipation in power plants, etc.).

Evaporative condensers are equipment, by structure and function, very similar to cooling towers, but the main difference lies in the use and mode of operation. Condensers are intended for the condensation of gases in general (butane, propane, butylene, pentane, CO2, water vapor, etc.) as well as the condensation of refrigerant gases in industrial air conditioning and cooling systems. The water is sprayed directly onto a system of ducts in the interior of which circulates a refrigerant initially in the gaseous state and which, through the cooling of the water, becomes liquid. The refrigerant circulates through a totally independent circuit without contact with the water.

        Figure 1. Schematic of a tower as part of a cooling system of a building
In Figure 1 that corresponds to a tower as part of a cooling system of a building three circuits are appreciated:
1. The first circuit moves the water of condensation stored in the tower balsa to the heat exchanger (condenser) where the refrigerant gas condenses. In condensation the refrigerant gives off heat to the water which is in turn transported back to the tower where it is sprayed and is brought into contact with the upward air stream to achieve its partial evaporation cooling. This is the only circuit really
dangerous from the point of view of transmission of legionellosis, since it is the only one that can emit aerosols
to the environment.
2. The second circuit, transports the refrigerant, a chemical compound that has the particularity of yielding or absorbing large amount of heat when it changes state. To facilitate the change of state the refrigerant is subjected to pressure changes, a compressor increases the pressure of the refrigerant in the gaseous state and it begins to condense by yielding heat that is absorbed through the indirect contact with the cold water coming from the raft of the tower. The pressure is released by means of an expansion valve which produces the change of liquid to gas of the refrigerant in the evaporator, as well as its cooling. At this point the refrigerant is brought into contact with a third water circuit.
3. The third circuit is responsible for transporting the cooled water in the evaporator to the cold batteries of the so-called air treatment units (UTA). The batteries allow the indirect contact (through tubes and fins similar to a vehicle radiator) of the water cooled with the interior air of the rooms to be conditioned, producing a continuous cooling of the air.

Figure 2 shows a single water circuit that constantly carries out a cycle in which a spray is produced to promote its partial evaporation and therefore decrease its temperature upon falling to the raft.
The water of the refrigerated balsa is sent to the point of the industrial process to be cooled and is brought into contact through a heat exchanger or similar system, normally there is no mixing of the water with the elements to be cooled but a indirect contact through pipes, exchangers, cooling shirts, bathrooms, etc.

2. TECHNICAL DEVELOPMENT
Cooling systems due to water evaporation have been used for industrial and / or air conditioning purposes since the beginning of the last century. The principles and techniques have not varied substantially since the basis of the system is very simple, however especially in recent years there has been a substantial evolution in the quality of materials and accessibility of facilities.
Currently the know-how has led to the elimination of the use of cellulose, wood or fiber cement fillings that were previously quite common. Current legislation does not allow the use of these materials because they favor microbiological growth.
3. DESCRIPTION
This section describes the types of towers for different categories and the specific terminology of these
facilities.
3.1 Cooling towers
There are equipment of various sizes and structures depending on the power to be dissipated, the manufacturer, materials, etc., however we could classify cooling towers in two broad categories:

• Natural draft
equipment • Equipment with mechanical ventilation.

To be continued………