*7.1.6 Ultraviolet radiation*

The sterilization of water by ultraviolet radiation (UV) is a potentially useful method to avoid the formation of the biofouling film and as a cleaning technique. Its principle of operation is based on attacking the deoxyribonucleic acid (DNA) of the cells, causing their death. In this way, the amount of microorganisms present in the cooling water flow is minimized.

This treatment is very effective against microorganisms in the larval stage, and their environmental impact is zero [5]. On the contrary, the useful life of UV lamps is limited (approximately 8 months), and the cost of operation and maintenance is high, which is why it is not normally used in industrial installations that require a large flow of water to treat [79].

In order to reduce the treatment and broaden the spectrum of organisms attacked, it is usually combined with another chemical or physical method [5].

### *7.1.7 Ultrasound*

These are acoustic waves whose mode of action is based on the creation of vibrations to generate cavitation bubbles. The size of the bubbles can be increased by means of compression-decompression cycles until reaching a critical value at which they explode transforming their energy into heat. These microexplosions produce a disturbance in the surface that breaks the cohesion forces of the deposits to the surface causing their detachment [5]. Inside the cavitation bubbles, the temperature and pressure conditions can reach 5000°C and 500–2500 bar [80, 81], so that even water molecules decompose generating HO- and H+ radicals. The radicals formed can be recombined in the same way or react with substances present in the medium causing their degradation. Obviously, the generation of radicals is facilitated if in the medium there are molecules that break easily, such as ozone or hydrogen peroxide, which also act as usual precursors of hydroxyl radicals in the oxidation processes. The greater the effectiveness of ultrasound treatments, the higher their frequency (100 Hz and 100 MHz).

This antifouling treatment is effective against microorganisms in the larval stage and also has no environmental impact. On the contrary, the high cost of the ultrasonic units must be added to the energy cost of the installation.

#### *7.1.8 Filtering systems*

These systems are considered complementary methods for the elimination of biofouling in any industrial facility. The filtrate prevents larvae of mussels, crustaceans, and other organisms from entering the circuits of refrigeration systems and therefore develops into a biofouling film.

In cooling water conduction systems, the most commonly used filters are of the panel type for flow rates of less than 10 m3 s<sup>−</sup><sup>1</sup> and of the drum type for higher flow rates [40]. Before the installation, the overall cost/benefit of the system must be analyzed due to the pressure drop produced in the installation [79].

#### *7.1.9 Injection of fresh water in seawater systems*

The microorganisms present in the biofilm feed on the nutrients existing in the water through osmotic processes through a semipermeable membrane. When injecting fresh water, the saline concentration of the water is modified, and the pressure inside the cells increases, causing death [5]. According to Cho et al. [82], the exposure time must be high, reaching 48 hours for the mussel *Mytilus californianus* and 63 hours for the mussel *Mytilus edulis*. This method is used in piping systems of refrigeration systems that remain out of service for long periods [83].

#### *7.1.10 Inserts in the tubes*

This system consists of inserting a helical element, whose vibration, distortion of flow, or rotation mitigate the growth of biofouling adhering on the inner surface of the tubes [5].

**81**

*Fouling in Heat Exchangers*

ness of biofouling.

*7.1.11 Circulation of polymers*

reduces its thickness [87, 88].

surfaces of the exchanger.

pipes are air, water, and water steam.

**7.2 Offline systems**

and CO3<sup>2</sup>

*DOI: http://dx.doi.org/10.5772/intechopen.88079*

This system can present the following variants [84]:

• SPIRELF®. Metallic helical element attached to the ends of the tube and adjusted to its length. When the fluid circulates inside the tube, it vibrates

• FIXOTAL® or HITRAN®. They use metallic helical elements that are fixed inside the tubes, improving the turbulent effect on the wall to reduce the thick-

• TURBOTAL®. Rigid helical device that is inserted into the tubes and uses the

The insertion of metal elements inside the tubes has proven to be an effective method to prevent the formation of biofouling in heat exchangers of different industrial processes [84]. However, the use of this type of device means increasing the cost of the equipment and its maintenance, as well as a higher consumption of

The method consists of introducing polymer fibers entrained by the fluid stream in order to erode and detach the layer of adhered deposits. According to Bott [5], its effectiveness on the process of forming the biofouling film in the tubes of a heat exchanger depends on the concentration of fibers and the speed of the flow of cooling water. The biggest drawback is that of removing the fibers from the effluent

Electromagnetic fields have the ability to increase the interaction of the Ca2+

CaCO3. Below 35°C, CaCO3 precipitates in the form of aragonite instead of calcite, resulting in being less adherent and less insulating [3, 85, 86]. The precipitation process of CaCO3 reduces the superficial tension of the water, minimizing the adherence of microorganisms, and affects the intermolecular union of the extracellular polymers, weakening the matrix of the biofouling layer and diminishing its capacity of adhesion to the surface [7]. In addition, CaCO3 entrainment by the seawater flow produces an erosive effect on the weakened biofouling layer that

The use of online antifouling treatments does not prevent periodically scheduled stops in which aggressive cleaning methods are used to recover the efficiency of the tube at 100%. The frequency of scheduled stops is based on experience, and the

Brushing the surfaces of the heat exchanger in a dry or wet surface condition to eliminate adhering deposits. The cost of cleaning is high and involves access to the

Although the techniques used to clean the surfaces of an industrial heat exchanger are varied, the most common methods to clean the internal surface of the

*−* ions present in seawater, increasing their nucleation and precipitation in

water flow itself as the impeller of the rotating cleaning mechanism.

pumping energy due to the increase of load losses in the system.

before it is discharged into the natural environment.

*7.1.12 Treatments with electromagnetic fields*

cost/benefit ratio is derived from its application.

axially and radially, eliminating biofouling adhering to its walls.

*Inverse Heat Conduction and Heat Exchangers*

large flow of water to treat [79].

*7.1.7 Ultrasound*

*7.1.8 Filtering systems*

*7.1.10 Inserts in the tubes*

of the tubes [5].

therefore develops into a biofouling film.

panel type for flow rates of less than 10 m3

*7.1.9 Injection of fresh water in seawater systems*

This treatment is very effective against microorganisms in the larval stage, and their environmental impact is zero [5]. On the contrary, the useful life of UV lamps is limited (approximately 8 months), and the cost of operation and maintenance is high, which is why it is not normally used in industrial installations that require a

In order to reduce the treatment and broaden the spectrum of organisms attacked, it is usually combined with another chemical or physical method [5].

These are acoustic waves whose mode of action is based on the creation of vibrations to generate cavitation bubbles. The size of the bubbles can be increased by means of compression-decompression cycles until reaching a critical value at which they explode transforming their energy into heat. These microexplosions produce a disturbance in the surface that breaks the cohesion forces of the deposits to the surface causing their detachment [5]. Inside the cavitation bubbles, the temperature and pressure conditions can reach 5000°C and 500–2500 bar [80, 81], so that even water molecules decompose generating HO- and H+ radicals. The radicals formed can be recombined in the same way or react with substances present in the medium causing their degradation. Obviously, the generation of radicals is facilitated if in the medium there are molecules that break easily, such as ozone or hydrogen peroxide, which also act as usual precursors of hydroxyl radicals in the oxidation processes. The greater the effectiveness

of ultrasound treatments, the higher their frequency (100 Hz and 100 MHz).

sonic units must be added to the energy cost of the installation.

This antifouling treatment is effective against microorganisms in the larval stage and also has no environmental impact. On the contrary, the high cost of the ultra-

These systems are considered complementary methods for the elimination of biofouling in any industrial facility. The filtrate prevents larvae of mussels, crustaceans, and other organisms from entering the circuits of refrigeration systems and

In cooling water conduction systems, the most commonly used filters are of the

rates [40]. Before the installation, the overall cost/benefit of the system must be

The microorganisms present in the biofilm feed on the nutrients existing in the water through osmotic processes through a semipermeable membrane. When injecting fresh water, the saline concentration of the water is modified, and the pressure inside the cells increases, causing death [5]. According to Cho et al. [82], the exposure time must be high, reaching 48 hours for the mussel *Mytilus californianus* and 63 hours for the mussel *Mytilus edulis*. This method is used in piping systems of refrigeration systems that remain out of service for long periods [83].

This system consists of inserting a helical element, whose vibration, distortion of flow, or rotation mitigate the growth of biofouling adhering on the inner surface

analyzed due to the pressure drop produced in the installation [79].

s<sup>−</sup><sup>1</sup>

and of the drum type for higher flow

**80**

This system can present the following variants [84]:


The insertion of metal elements inside the tubes has proven to be an effective method to prevent the formation of biofouling in heat exchangers of different industrial processes [84]. However, the use of this type of device means increasing the cost of the equipment and its maintenance, as well as a higher consumption of pumping energy due to the increase of load losses in the system.
