برج خنک کننده (کولینگ تاور) چیست؟

The cooling tower is one of the most common equipment for cooling water. A cooling tower is one of the types of heat exchangers in which water and air come into contact with each other to reduce the water temperature. Cooling towers are used in industrial refrigeration systems, including power plants, petrochemicals, food production, and also in air conditioning. The basis of cooling in this equipment is water evaporation. Therefore, it does not have good efficiency in areas with humid climate and is not usually used.

انواع کاربرد برج خنک کننده (کولینگ تاور)

Water that has been heated during industrial processes or in the condenser of air conditioning systems is pumped to the cooling tower for cooling. Cooling towers are designed and produced in different models and dimensions, each of these models has its own limitations and advantages. Therefore, whether in industrial use or air conditioning, it is important to fully evaluate the usage conditions.

The cooling tower is one of the peripheral equipments that is used along with the cold water chiller and the absorption chiller. In the past, metal and galvanized cooling towers were mostly used, which have now been replaced by fiberglass towers. In chilled water chillers, the temperature of the water entering the cooling tower is usually between 30 and 45 degrees Celsius, and the temperature leaving the tower is 25 to 35 degrees.

Some industrial processes are exothermic and many devices have high temperature sensitivity, so it is necessary to control their temperature during operation and remove excess heat. Otherwise, the efficiency of the device will be affected and the production of the collection will be reduced. For this reason, cooling is of particular importance in industries. Cooling towers, as one of the cooling equipments, are of great interest due to low repair costs, no pollution to the environment, no harm to humans, low energy consumption, long durability, variety of capacity, etc.

نحوه کار برج خنک کننده (کولینگ تاور)

The way cooling towers work varies based on the type of tower. But in general, the cooling process in towers happens for 2 reasons

The temperature difference between ambient air and hot water entering the tower
Evaporation of water and latent heat required for evaporation (hot process water or an intermediate water)

In the rest of the article, we will talk about the types of towers and the cooling method in each, but we will explain one of the most common methods in this section. Before that, it is necessary to get acquainted with the concept of wet temperature. Wet Bulb Temperature is the temperature at which the air humidity is saturated and 100%. In fact, the wet temperature is the lowest temperature that a volume of air can reach by evaporating water.

In this method, the cooling process in the cooling tower is done by evaporating some of the water flow inside the tower. The hot process water enters the cooling tower from the top and is in contact with the cool air. As a result of direct contact of water with air flow, part of the particles evaporates. In this process, the latent heat of evaporation is obtained from the water flow and the temperature of the remaining water decreases. In addition to decreasing the water temperature, the moist temperature and the latent heat of the air also increase

The efficiency of the cooling tower in the process of lowering the water temperature depends on the relative humidity of the air entering the tower. The lower the air humidity, the more volume of water evaporates and the more latent heat of evaporation is absorbed from the water flow. This is the reason why the cooling tower is not efficient in humid and humid environments. It should be kept in mind that in the best weather conditions, even in hot and dry areas, the difference in water temperature at the entrance and exit of the tower does not exceed 10 degrees Celsius. Of course, in industrial applications, if the temperature entering the tower is high and we expect a large temperature drop, it is better to connect several cooling towers together.

Due to the high importance of the cooling tower in the industry as well as refrigeration, many efforts have been made in recent years to improve the quality of this equipment. Among the measures taken by the manufacturers are reducing electricity consumption, reducing water consumption, reducing the amount of sedimentation and increasing the useful life of the device. One of the recently used cooling tower models is closed-circuit cooling towers, which have had a significant impact on reducing water consumption and sedimentation.

اجزای اصلی برج خنک کننده

Cooling towers consist of different parts, the most important of which can be listed below.

Cooling tower packing

Cooling tower packing is one of the most important components in cooling towers. Their role is to create a heat exchange surface between hot water droplets and cool air in the heat transfer process. The function of the packing is similar to that of the water cooler bags, which increases the surface of contact and collision between water and air; In this way, water is splashed on these surfaces and the surfaces become wet. In addition to creating a heat exchange surface, this also reduces the speed of movement of water particles, and air and water come into contact with each other for a longer time. Packings play a significant role in the water cooling process, so that if they become clogged, the efficiency of the tower will decrease and the temperature of the cool water coming out of the cooling tower will clearly increase.

Water spray nozzles

In the water inlet collector to the tower (a pipe in which a number of outlets are installed), there are nozzles that are responsible for the uniform distribution of water inside the tower and on the packings. These nozzles make water pulverize (turn water into many drops) and increase the contact surface of water with air. Another advantage of these nozzles is reducing the water pressure and thus reducing the evaporation temperature.

Cooling tower fan

A fan is used to forcibly move the air inside the cooling towers. In cooling towers, axial fans or centrifugal fans are used. The axial fan (suction) is installed at the top of the tower and creates an axial flow, and the centrifugal fan (blower) is installed in front of the device.

Other important components of the cooling tower are:

Ports of inlet water – outlet cold water – compensation water – drain water
Electro-Motor
Dropper or dripper
Cold and cool water storage pan
Water distribution pipes
Compensating water inlet float
Electric heater (element), in industrial towers

انواع برج خنک کننده (کولینگ تاور)

Cooling towers have different types in terms of body type. Cooling towers can be concrete, galvanized or fiberglass. Today, mostly fiberglass (composite) cooling towers are used. In addition to this, cooling towers are usually classified based on the cooling mechanism, the type of air flow, as well as the material and structure. The variety of cooling towers in structure, cooling mechanism, etc. has caused many industries in different regions and climatic conditions to consider this product as a main choice for them.

Types of cooling towers based on heat transfer mechanism

A) Dry cooling tower

In dry cooling towers, they only use the difference in water temperature and dry air temperature for cooling, and water does not play a role in cooling. In these towers, hot water flows inside finned coils and air flows outside the surface of these coils. The heat of the water is first transferred to the surface of the coil and blades, and then it is transferred to the air as the air passes over these surfaces and the cooling operation takes place. This system does not consume any water and is a suitable option for low water areas.

b) Wet cooling tower

In wet cooling towers, water is responsible for cooling. In fact, the evaporation of some water leads to cooling and lowering the temperature. In this way, with the evaporation of some water, the amount of relative humidity and also the wet temperature of the air increases. This model is the most common type of cooling tower. In order to save water consumption, drippers are used in all wet cooling towers. The dripper returns some of the evaporated water particles that are leaving the tower along with the air to the system.

Types of cooling towers based on structure

A) Open circuit cooling tower

In open circuit cooling towers, which are wet tower types, the contact between process water and air is completely direct. These towers are offered in two models based on flow arrangement: cross flow and counter flow; Open-circuit cooling tower with counter current has more efficiency than counter current.

In this type, the water sprayed from the nozzles is distributed on the surface of the packing and a thin film is formed. In this way, this thin layer of water is in contact with the air and evaporation is done. In this method, the air cools the water in two ways. The first method of heat transfer between water and air is due to the temperature difference between water and air (of course, if the dry air temperature is lower than the water temperature). The next method is to evaporate part of the water particles and provide the required latent heat from other water particles. Finally, the cool water is accumulated in the pan at the bottom of the tower and exits the cooling tower through the outlet port.

In the open circuit cooling towers, to prevent hot water droplets from exiting from the top of the nozzle, a device called a drip catcher is installed. It should be noted that in open circuit cooling towers due to evaporation of water, the concentration of minerals in water increases; For this reason, it is necessary to use make-up water to compensate the volume of evaporated water. On the other hand, it is necessary to de-harden this water so that the increase in concentration of minerals does not cause a problem for the efficiency of the tower and other equipment.

b) Closed circuit cooling tower

In these closed circuit towers, the contact between hot water and air is not direct. There are coils installed inside the cooling tower, where hot water flows through these coils, and the air passing over the surface of the coil absorbs the heat of the water; Of course, the condition of heat transfer between air and coils is that the dry air temperature is lower compared to the surface temperature of the pipes. For this reason, closed-circuit cooling towers are not efficient in hot and dry areas.

The mechanism of these closed or so-called dry cooling towers is similar to an air condenser. The air flow in this model is more axial. Due to the indirect connection between air and water, water does not evaporate and prevents water loss.

c) Hybrid cooling tower

The hybrid cooling tower is a collection of wet cooling towers and a combination of the two previous systems. In these towers, hot water flows inside the coils and the air flow is perpendicular to the coils from the bottom to the top of the tower. In addition, water is sprayed on the surface of the pipes from the top of the tower with the help of nozzles. The water droplets in contact with the hot body of the tube evaporate and the temperature of the water inside the tube decreases. Air flow around the coils provides conditions for faster and better water evaporation. On the other hand, if the dry air temperature is lower than the surface temperature of the pipes, the heat transfer between the two also helps to cool the water inside the pipe. In the cold seasons of the year and spring, the sprinkler system can be turned off.

The surface of Towerhybrid cooling coils is without fins; Because despite the water splash, the surface of the fins will quickly get sedimented and clog the fin.

Types of cooling towers based on the type of air movement

Cooling towers are divided into two categories, forced and natural, based on the type of air movement.

A) Cooling tower with forced air movement

In these towers, in order to move the air, they use an external agent, which is the axial fan or centrifuge, and in this way, the air flows in a forced convention way. The forced flow cooling tower can be placed anywhere in the building.

b) Cooling tower with natural air movement

In these towers with natural displacement (Natural Convention), air flow is based on the law of buoyancy. According to this law, the air at the bottom of the tower is heated due to heat absorption and thus becomes lighter. Light air also moves upwards and gives way to cold air. In order to move air better, these towers are built very high and have a height of about 100 to 150 meters. In large industries such as steelmaking, iron smelting, petrochemical, etc., cooling towers with natural flow are usually used.

Types of cooling towers based on flow arrangement

Cooling towers are classified into two categories, cross flow and asymmetrical flow, based on flow arrangement.

A) Cooling tower with asymmetric flow

In these towers, air flow and water flow are parallel and opposite to each other. The water is sprayed downwards by the nozzles connected to the collector placed on the top of the tower, and the air flows from the bottom to the top.

b) Cross flow cooling tower

In these towers, the air flow enters horizontally from the sides of the tower. Water also flows through the nozzles in a vertical direction and towards the bottom of the tower. In this way, two perpendicular currents come into contact with each other. In this method, the contact time between air and water is less than the previous method; Therefore, the efficiency of the cooling tower with cross flow is lower than that of the non-uniform flow.

عوامل موثر در تعیین ظرفیت برج خنک کننده

One of the important parameters in purchasing cooling towers is determining the tower capacity. Some important factors to determine the capacity are:

Dry temperature and relative humidity of the installation site
Equipment cooling fluid
Circulating water flow
The temperature of the water entering the cooling tower
The required temperature of the water leaving the cooling tower

Common cooling tower problems

Sometimes the performance and efficiency of the cooling tower has problems or the energy consumption of the device increases. In these cases, it is necessary to quickly troubleshoot the cooling tower. Some of the most common problems of these towers are:

Cooling tower leakage

Installing cooling towers is a specialized activity and requires an expert. After the correct installation of the device, it is necessary to seal around it so that there is no leakage. Of course, sometimes, despite observing the installation and sealing tips, there is this problem that finding the reason is also very expensive.

Deposition of the cooling tower

One of the most common problems of open circuit cooling towers is sedimentation on the internal surfaces. Its cause is the evaporation of part of the water and as a result the concentration of minerals increases. The presence of these minerals inside the tower leads to the creation of limestone layers in the walls. Of course, this problem is not unique to open circuit cooling towers and can be seen in all towers. In addition, the high hardness of water in some regions of our country is another factor of sedimentation in cooling towers, which needs to be used with equipment such as water hardness, drainage and PH adjustment device and adding chemicals to water.

Dust entering the cooling tower

Usually, the dust in the air enters the tower and is placed on various surfaces, including packings. Over time, if these surfaces are not cleaned, the dust becomes a deposited layer and reduces the efficiency of the device.

Microorganism contamination (Legionella)

Due to the high humidity and the concentration of minerals, there is always a possibility of growing and forming a layer of algae (harmful bacteria) on the surfaces, especially the tower pan. These layers, in addition to reducing the level of heat transfer and thus reducing the efficiency of the device, also cause water pollution. If after sampling the water, the presence of pollution in the water is confirmed, it is necessary to solve this problem by using chemicals.

Lots of vibrations and noise

Due to the presence of large fans in this equipment, vibration and noise are normal. Of course, sometimes fan problems lead to an increase in the amount of vibration and noise produced. Measures such as using mechanical shock absorbers in the supporting chassis to dampen vibrations, installing pipe shock absorbers in the pipe connection areas, changing the fan, etc., can reduce the amount of vibration and noise.

Water consumption in cooling towers is one of the most important challenges in this equipment. Of course, measures such as hybrid or combined system, use of temperature sensor and installation of inverter drive, use of motor handle and shock absorber, multi-cell design, etc. have led to the reduction of water consumption.

Evaporator is actually the last equipment in the cooling cycle that the refrigerant enters after passing through the expansion valve and exchanges heat with water. Usually, two types of evaporators are used in compression chillers.

برج خنک کننده باردصنعت

Baredsanat production group, with expertise in designing and producing all kinds of air conditioning and cooling systems, has the ability to design and produce fiberglass cooling towers in various capacities, according to the needs of our dear customers. Baredsanat cooling towers are provided with a valid 5-year warranty, including all equipment and accessories, as well as 10 years of after-sales service.

You can find out about the technical information of the products produced by Bared Sanat by visiting the fiberglass package rooftop purchase page. The price of the Baredsanat cooling tower varies based on the type of capacity and the brand of equipment used. You can contact the experts of the collection to get the exact price.

Registration request for free consultation Contact experts: 09120662381

4 November, 2020/0 Comments

cooling tower