Humidifiers for laboratory rooms. Traditional humidifiers. From a practical point of view, points related to the operation of the humidifier

Comfortable humidity in any room

Traditional (classic) humidifiers are one of the most common types of such devices. Simple design and low power consumption make these humidifiers affordable for a wide range of customers, while effectively coping with functions such as humidification and air purification.

Traditional Humidifiers have another name - cold-type humidifiers. They got their second name from the principle of operation, which is based on the natural process of evaporation. Water in a traditional humidifier is poured into a special tank, from which it then enters the tray onto the evaporative elements (humidifying cartridges). The fan built into the case sucks in air from the room and drives it through the cartridges. The air returns to the room already humidified and cleaned of dust. Some modern models of humidifiers are additionally equipped with antibacterial filters that kill pathogens and provide deep air purification. In premium models, you can even find options such as air ionization or evaporation sterilization.

The only significant drawback of traditional humidifiers can be considered their ultimate performance - such an air conditioner is able to humidify the air in the room up to 60%. This is sufficient in most cases of domestic use of the device (since a humidity level of 45-55% is considered comfortable for a person). An exception may be the use of a humidifier only to create a special microclimate with a high level of humidity (in winter gardens, indoor greenhouses, laboratories, etc.)

The main advantages of modern classic air humidifiers:

compact, attractive design;
high performance with low power consumption;
low noise level;
uniform distribution of humidified air throughout the room;
simplicity and ease of management

In our online store are presented traditional humidifiers the best modern manufacturers of climate equipment, incl. such recognized market leaders as Atmos, Air-O-Swiss, Aircomfort and others. Prices vary depending on the power of the model, the area of wetting and the number of options available. Compact desktop models are available for humidification of small rooms up to 20 sq.m and powerful units with tanks up to 30 l, capable of effectively humidifying residential or office premises up to 100 sq.m.

is the amount of water vapor in the air. In everyday life, we usually remember it only by listening to the weather forecast.

Employees and institutions have a completely different attitude to the humidity of the air in the room. Due to the lack of moisture in the air, forced humidification has to be done in clinics, industrial and food enterprises, using industrial, semi-industrial or household installations.

Humidity is not only one of the parameters, but also mandatory, provided for, deviation from which is unacceptable.

When air humidity decreases, static electricity builds up. Electronic devices that are sensitive to their effects are easily damaged. To reduce the risk of electrostatic charges, the relative humidity of the air should be maintained at a level of at least 30%.

A decrease in humidity has a negative effect on the well-being of people, especially those who suffer from allergies and asthma: in winter, a significant amount of dust accumulates in the dry indoor air.

Humidity plays an important role in most technological processes. The rate of many chemical reactions depends on relative humidity. Air humidity at the level of 40-60% will exclude the development of microorganisms and the reproduction of bacteria.

Getting the right microclimate in a laboratory or clean room without a humidifier is problematic. Dry air comes regardless of whether we like it or not:

in cold weather when the heating is turned on;
in the summer heat;
due to the peculiarities of production;
in connection with heat transfer during operation of the equipment;
due to the hygroscopic nature of the raw material, which absorbs moisture from the air.

If it is impossible to change the weather and production technology, then it is possible to neutralize the consequences and restore the loss of moisture with the help of air humidifiers.

Long live hydration

Air humidification creates comfortable and healthy living conditions for people, increasing labor productivity. The required amount of moisture in the atmosphere of the production facility ensures the reliable flow of technological processes, the quality of finished products does not suffer, sanitary norms and rules are observed.

Use natural methods to humidify the air - small fountains, aquariums - effectively in small household premises. In all other cases, the problem of moisture is solved differently.

Humidification in laboratories and clean rooms is recommended using industrial or semi-industrial humidification systems. There are three main ways to moisturize:

adiabatic.
Isothermal.
Ultrasonic.

The advantages of adiabatic humidification include low energy consumption. Simultaneously with hydration occurs. Systems operating on the principle of adiabatic humidification have high productivity, do not emit harmful impurities into the atmosphere, and 90% of the volume of water is used for its intended purpose. Saturation of air with moisture occurs without the use of a source of thermal energy.

Isothermal humidifiers operate on the principle of a steam generator: water vapor is produced by heating and evaporating water. Purified and softened water is required for normal operation. These devices are very energy intensive: about 750 W of electricity is spent on the production of 1 kg/h of moisture. The advantages of this type of devices include high performance and low noise level.

Another type of artificial humidifier, ultrasonic. The operation of the device is based on the process of cavitation, the use of the energy of high-frequency vibrations of water molecules. It turns into cold steam, saturating the air with moisture as much as possible. For the device is completed. The ultrasonic humidifier consumes little energy, reduces the air temperature in the room by 1-2 degrees, and works absolutely silently.

When choosing a humidification system, performance, energy intensity class, environmental friendliness, technical parameters of the room in which it is installed are taken into account.

There is a humidifier, no problems

A humidifier is an air conditioning device used to increase the humidity of indoor air.

Proper humidification of the air is a necessary condition for the safe presence of a person in a dwelling or industrial premises. Insufficient or excessive humidity will equally adversely affect well-being and performance. There can be no question of any technologically correct and competent production process if the regulatory requirements of the standards for the microclimate of laboratories and clean rooms are not met.

Humidification in clean rooms by spraying microscopic, no more than 5 microns, drops of moisture into them simultaneously reduces the ambient temperature. Passing from a liquid to a gaseous state, water takes the energy of the air, cooling it.

The humidification system will create the required level of humidity in clean rooms and laboratories automatically and absolutely silently. Create a comfortable, healthy microclimate at your workplace, it's easy!

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High accuracy of maintaining air humidity, in conditions of maximum hygiene - throughout the entire humidification process.

High precision control of air humidity and hygiene.

Rooms that have been assigned a cleanliness class require an impeccable microclimate, with precise control of temperature and humidity conditions. It is also possible to achieve high levels of hygiene with the involvement of steam humidifiers, as well as with adiabatic air humidifiers. For the former (isothermal systems), water quality will play a less significant role in process hygiene, but rather in ensuring the reliability of the steam cylinder and the life of the heating elements. For adiabatic systems, water quality is the main element on which maximum hygiene will depend.

Humidification systems and air humidity standards for clean rooms.

30-50% R.H. Pharmaceuticals - production, drug preparations.

40-50% RH. Electronics - production or server rooms (DPC).

40-60% RH. Medicine - diagnostic centers, hospitals.

40-90 RH%. Laboratories - research, pilot production.

Today, a clean room can be seen not only in a medical institution or laboratory. There are rooms that are assigned standards and cleanliness classes in almost every office in the form of a server room or in the production of electronic components, in industry or agriculture. Hygiene classes and cleanliness standards may differ in relation to the content of suspended particles, aerosols or bacteria in the air. Humidification systems are also subject to high hygiene requirements, where the first, priority requirement will be the requirement for the quality of the water with which the humidification unit will work.

Sterile Humidification Systems: operate in a high hygiene mode, use purified water and control humidity to within 1% RH.

The second requirement would be; the process of preparation of water vapor and the method of their delivery to the air of a clean room. The path from the preparation of water vapor to the saturation of the air mass with it should be the shortest and without stagnant zones. Water must not stagnate in the duct or inside the humidifier unit, as this may cause the growth of mold and fungus spores. The water must be purified or completely demineralised.

Ask a Question.

One of the most complex and science-intensive processes in the field of ventilation and air conditioning is its humidification. determined by a number of fundamental documents of a regulatory and reference nature.

Successful engineering and technical implementation of air humidification systems requires the correct choice of methods and means of steam generation used, compliance with fairly strict requirements for its distribution inside the serviced premises or inside the supply part of the ventilation system, as well as proper organization of excess moisture drainage.

From a practical point of view, points related to the operation of the humidifier

Of particular importance is the use of feed water of appropriate quality.. The requirements for this are fundamentally different for humidifiers, the principle of operation and design of which are very diverse. Unfortunately, this issue has not yet been adequately covered in the literature, which in some cases leads to operational errors and premature failure of expensive technical equipment.

Notable Publications relate mostly to water treatment in heating systems and hot water supply of buildings, which differs significantly from water treatment in air humidification systems. This article is an attempt to clarify the essence of the requirements for the quality of feed water for the main types of humidifiers by analyzing the physicochemical characteristics of the behavior of substances of varying degrees of solubility during the transition of water to steam, implemented in one way or another. The presented materials are quite general in nature, covering almost all known methods of air humidification. However, based on the personal experience of the author, the considered specific design versions of the units are limited to the range supplied by CAREL, which includes humidifiers of various types in a wide range of operating principles used.

There are two main ways to humidify the air in practice: isothermal and adiabatic.

Isothermal Humidification occurs at a constant temperature (∆t = 0), i.e. when the relative humidity of the air increases, its temperature remains unchanged. Saturated steam enters the air directly. The phase transition of water from a liquid to a vapor state is carried out due to an external heat source. Depending on the way the external heat is realized, the following types of isothermal air humidifiers are distinguished:

with submersible electrodes (HomeSteam, HumiSteam);
with electric heating elements (HeaterSteam);
gas humidifiers (GaSteam).

Adiabatic Humidification Only on the content of harmful substances in drinking water 724 indicators are normalized. General requirements for the development of methods for their determination are regulated by GOST 8.556-91. From the point of view of the use of water in air humidification systems, not all of the indicators mentioned above are of significant importance.

The most important are only ten indicators, discussed in detail below:

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Total dissolved solids in water(Total Dissolved Solids, TDS)

The amount of substances dissolved in water depends on their physicochemical properties, the mineral composition of the soils through which they infiltrate, temperature, time of contact with minerals, and the pH of the infiltration medium. TDS is measured in mg/l, which is equivalent to one part per million (parts per million, ppm) by weight. In nature, TDS of water ranges from tens to 35,000 mg/l, which corresponds to the most saline sea water. According to current sanitary and hygienic requirements, drinking water should contain no more than 2000 mg/l of dissolved substances. On fig. Figure 1 shows, on a logarithmic scale, the solubility of a number of chemicals (electrolytes) most commonly found in water under natural conditions as a function of temperature. It is noteworthy that, unlike most salts (chlorides, sulfates, sodium carbonate) present in water, two of them (calcium carbonate CaCO3 and magnesium hydroxide Mg(OH)2) have relatively low solubility. As a result, these chemical compounds form the bulk of the solid residue. Another characteristic concerns calcium sulfate (CaSO4), whose solubility, unlike most other salts, decreases with increasing water temperature.

Total hardness (TH)

The total hardness of water is determined by the amount of calcium and magnesium salts dissolved in it, and is divided into the following two parts:

constant (non-carbonate) hardness, determined by the content of sulfates and chlorides of calcium and magnesium, which remain dissolved in water at elevated temperatures;
variable (carbonate) hardness, determined by the content of calcium and magnesium bicarbonates, which, at a certain temperature and / or pressure, participate in the following chemical processes, which play a key role in the formation of a solid residue.

Сa(HCO3)2 ↔CaCO3 + H2O + CO2, (1) Mg(HCO3)2 ↔Mg(OH)2 + 2 CO2.

With a decrease in the content of dissolved carbon dioxide, the chemical balance of these processes shifts to the right, leading to the formation of poorly soluble calcium carbonate and magnesium hydroxide from calcium and magnesium bicarbonates, which precipitate from the water solution with the formation of a solid residue. The intensity of the considered processes also depends on the pH of the water, temperature, pressure, and some other factors. It should be borne in mind that the solubility of carbon dioxide sharply decreases with increasing temperature, as a result of which, when water is heated, a shift in the balance of processes to the right is accompanied by the formation, as indicated above, of a solid residue. The concentration of carbon dioxide also decreases with decreasing pressure, which, for example, due to the above-mentioned shift of the considered processes (1) to the right, causes the formation of solid deposits in the mouths of the nozzles of air humidifiers of the spray type (atomizers). Moreover, the greater the speed in the nozzle and, accordingly, according to the Bernoulli law, the deeper the rarefaction, the more intense the formation of solid deposits. This is especially true for atomizers without the use of compressed air (HumiFog), which are characterized by a maximum speed at the mouth of a nozzle with a diameter of no more than 0.2 mm. Finally, the higher the pH of the water (the more alkaline), the lower the solubility of calcium carbonate and the more solid residue formed. Due to the predominant role of CaCO3 in the formation of solid residue, the measure of water hardness is determined by the content of Ca (ion) or its chemical compounds. The existing variety of units of measurement of stiffness is summarized in Table. 1. In the USA, the following classification of hardness of water intended for household needs has been adopted:

0.1-0.5 mg-eq / l - almost soft water;
0.5-1.0 mg-eq / l - soft water;
1.0-2.0 mg-eq/l - water of low hardness;
2.0-3.0 mg-eq / l - hard water;
3.0 mg-eq/l - very hard water. In Europe, water hardness is classified as follows:
TH 4°fH (0.8 meq/l) - very soft water;
TH = 4-8°fH (0.8-1.6 meq/l) - soft water;
TH \u003d 8-12 ° fH (1.6-2.4 mg-eq / l) - water of medium hardness;
TH = 12-18°fH (2.4-3.6 meq/l) - almost hard water;
TH = 18-30°fH (3.6-6.0 meq/l) - hard water;
TH 30°fH (6.0 meq/l) - very hard water.

Domestic water hardness standards have significantly different values. According to the sanitary rules and norms SanPiN 2.1.4.559-96 "Drinking water. Hygienic requirements for water quality in centralized drinking water supply systems. Quality control" (clause 4.4.1), the maximum permissible water hardness is 7 mg-eq / l. At the same time, this value can be increased to 10 mg-eq/l by decision of the chief state sanitary doctor in the relevant territory for a specific water supply system based on the results of an assessment of the sanitary and epidemiological situation in the settlement and the water treatment technology used. According to SanPiN 2.1.4.1116-02 "Drinking water. Hygienic requirements for the quality of water packaged in containers. Quality control" (clause 4.7), the standard for the physiological usefulness of drinking water in terms of hardness should be in the range of 1.5-7 mg-eq / l. At the same time, the quality standard for packaged waters of the first category is characterized by a hardness value of 7 mg-eq / l and the highest category - 1.5-7 mg-eq / l. According to GOST 2874-82 "Drinking water. Hygienic requirements and quality control" (clause 1.5.2), water hardness should not exceed 7 mg-eq / l. At the same time, for water supply systems that supply water without special treatment, in agreement with the bodies of the sanitary and epidemiological service, water hardness of up to 10 mg-eq / l is allowed. Thus, it can be stated that in Russia the use of water of extreme hardness is allowed, which must be taken into account when operating air humidifiers of all types.

In particular this applies adiabatic humidifiers, unconditionally requiring appropriate water treatment.

As for isothermal (steam) humidifiers, it should be borne in mind that a certain degree of water hardness is a positive factor contributing to the passivation of metal surfaces (zinc, carbon steel) due to the formation of a protective film that contributes to the inhibition of corrosion developing under the action of chlorides present. In this regard, for isothermal humidifiers of the electrode type, in some cases, limit values are set not only for the maximum, but also for the minimum values of the hardness of the water used. It should be noted that in Russia the water used varies significantly in terms of hardness, often exceeding the above standards. For example:

the highest water hardness (up to 20-30 mg-eq/l) is typical for Kalmykia, the southern regions of Russia and the Caucasus;
in the underground waters of the Central District (including the Moscow region), water hardness ranges from 3 to 10 mg-eq/l;
in the northern regions of Russia, water hardness is low: in the range from 0.5 to 2 mg-eq/l;
water hardness in St. Petersburg does not exceed 1 mg-eq/l;
the hardness of rain and melt water ranges from 0.5 to 0.8 mg-eq/l;
Moscow water has a hardness of 2-3 mg-eq/l.

Dry residue at 180°C(Dry residue at 180°C, R180)
This indicator quantifies dry residue after complete evaporation of water and heating to 180°C, differing from total dissolved solids (TDS) in the contribution made by dissociating, volatilizing and adsorbing chemicals. These are, for example, CO2 present in bicarbonates and H2O contained in hydrated salt molecules. The difference (TDS - R180) is proportional to the content of bicarbonates in the water used. In drinking water, R180 values not exceeding 1500 mg/l are recommended.

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Natural water sources are classified as follows:

R180 200 mg/l - weak mineralization;
R180 200-1000 mg/l - medium mineralization;
R180 1000 mg/l - high mineralization

Conductivity at 20°C(Specific conductivity at 20°C, σ20)
The specific conductivity of water characterizes the resistance to flowing electric current, being dependent on the content of electrolytes dissolved in it, which in natural water are mainly inorganic salts. The unit of measure for specific conductivity is µSiemens/cm (µS/cm). The specific conductivity of pure water is extremely low (about 0.05 µS/cm at 20°C), increasing significantly with the concentration of dissolved salts. It should be noted that the conductivity is strongly dependent on temperature, as shown in Fig. 2. As a result, conductivity is indicated at a standard temperature value of 20°C (rarely 25°C) and is indicated by the symbol σ20. If σ20 is known, then the values of σt°C corresponding to the temperature t, expressed in °C, are determined by the formula: σt°Cσ20 = 1 + α20 t - 20, (2) where: α20 is the temperature coefficient ( α20 ≈0.025). Knowing σ20, TDS and R180 values can be approximately estimated using empirical formulas: TDS ≈0.93 σ20, R180 ≈0.65 σ20. (3) It should be noted that if the TDS estimate in this way has a small error, then the R180 estimate has a much lower accuracy and depends significantly on the content of bicarbonates in relation to other electrolytes.

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Acidity and alkalinity(Acidity and alkalinity, pH)

Acidity is determined by H+ ions, which are extremely aggressive towards metals, especially zinc and carbon steel. Neutral water has a pH value of 7. Lower values are acidic, while higher values are alkaline. The acidic environment leads to the dissolution of the protective oxide film, which contributes to the development of corrosion. As shown in fig. 3, at pH values below 6.5, the corrosion rate increases significantly, while in an alkaline environment at a pH of more than 12, the corrosion rate also increases slightly. Corrosive activity in an acidic environment increases with increasing temperature. It should be noted that at pH< 7 (кислотная среда) латунный сплав теряет цинк, в результате чего образуются поры и латунь становится ломкой. Интенсивность данного вида коррозии зависит от процентного содержания цинка. Алюминий ведет себя иным образом, поскольку на его поверхности образуется защитная пленка, сохраняющая устойчивость при значениях pH от 4 до 8,5.

chlorides(Chlorides, Cl-)

The chloride ions present in water cause corrosion of metals, especially zinc and carbon steel, interacting with metal atoms after the destruction of the surface protective film formed by a mixture of oxides, hydroxides and other alkaline salts formed due to the presence of dissolved CO2 in water and the presence of impurities in atmospheric air . The presence of electromagnetic fields characteristic of isothermal (steam) humidifiers with immersed electrodes enhances the above effect. Chlorides are especially active when water hardness is insufficient. Previously, it was indicated that the presence of calcium and magnesium ions has a passivating effect, inhibiting corrosion, especially at elevated temperatures. On fig. 4 schematically shows the inhibitory effect of temporary hardness in terms of the corrosive effect of chlorides on zinc. In addition, it should be noted that a significant amount of chlorides intensifies foaming, which adversely affects the operation of isothermal humidifiers of all types (with immersed electrodes, with electric heating elements, gas).

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Iron + Manganese(Iron + Manganese, Fe + Mn)

The presence of these elements causes suspended slurry formation, surface deposits and/or secondary corrosion, which suggests the need to remove them, especially when working with adiabatic humidifiers using reverse osmosis water treatment, otherwise the membranes will quickly clog.

Silica(Silica, SiO2)

Silicon dioxide (silica) can be contained in water in a colloidal or partially dissolved state. The amount of SiO2 can vary from trace amounts to tens of mg/l. Usually the amount of SiO2 is increased in soft water and in the presence of an alkaline environment (pH 7). The presence of SiO2 is particularly detrimental to the operation of isothermal humidifiers due to the formation of a hard, difficult to remove precipitate consisting of silica or the resulting calcium silicate. Residual chlorine (Cl-) The presence of residual chlorine in water is usually due to the disinfection of drinking water and is limited to minimum values for all types of humidifiers in order to avoid the appearance of pungent odors entering the humidified premises along with moisture vapor. In addition, free chlorine, through the formation of chlorides, leads to corrosion of metals. Calcium sulfate (Calcium sulphate, CaSO4) Calcium sulfate, present in natural water, has a low degree of solubility, and therefore it is prone to precipitate formation.
Calcium sulfate is present in two stable forms:

anhydrous calcium sulfate, called anhydrite;
calcium sulfate dihydrate CaSO4 2H2O, known as chalk, which dehydrates at temperatures above 97.3°C to form CaSO4 1/2H2O (semihydrate).

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As shown in fig. 5, at temperatures below 42° C., sulfate dihydrate has a reduced solubility compared to anhydrous calcium sulfate.

In isothermal humidifiers at the boiling point of water, calcium sulfate may be present in the following forms:

a hemihydrate which at 100°C has a solubility of about 1650 ppm, which corresponds to about 1500 ppm in terms of calcium sulfate anhydrite;
anhydrite, which at 100°C has a solubility of about 600 ppm.

Excess calcium sulfate precipitates out, forming a pasty mass, under certain conditions, having a tendency to harden. A summary of the limit values for the feed water parameters discussed above for different types of humidifiers is presented in the following series of tables. It should be taken into account that isothermal humidifiers with immersed electrodes can be equipped with cylinders designed to operate on standard water and water with a reduced salt content. Electrically heated isothermal humidifiers may or may not have a Teflon coated heating element.

Isothermal (steam) humidifiers with immersed electrodes The humidifier is connected to the water mains with the following parameters:

pressure from 0.1 to 0.8 MPa (1-8 bar), temperature from 1 to 40°C, flow rate not less than 0.6 l/min (nominal value for the supply solenoid valve);
hardness not more than 40°fH (corresponding to 400 mg/l CaCO3), specific conductivity 125-1250 μS/cm;
absence of organic compounds;
feed water parameters must lie within the specified limits (Table 2)

Not recommended:
1. Use of spring water, industrial water or refrigeration water, as well as potentially chemically or bacterially contaminated water;
2. Adding disinfectants or anti-corrosion additives to the water, which are potentially harmful substances.

Humidifiers with electric heating elements The feed water on which the humidifier operates must not have an unpleasant odor, contain corrosive agents or excessive amounts of mineral salts. The humidifier can operate on tap or demineralized water, which has the following characteristics (Table 3).

Not recommended:
1. Use of spring water, industrial water, water from cooling towers, as well as water with chemical or bacteriological contamination;
2. Adding disinfectant and anti-corrosion additives to the water, because moistening the air with such water can cause allergic reactions in others.

Gas humidifiers
Gas humidifiers can operate on water with the following characteristics (Table 4). To reduce the frequency of maintenance of the steam cylinder and heat exchanger, namely their cleaning, the use of demineralized water is recommended.

Not recommended:
1. Use of spring water, industrial water or water from refrigeration circuits, as well as potentially chemically or bacterially contaminated water;
2. Adding disinfectants or anti-corrosion additives to the water, as they are potentially harmful substances.

Adiabatic (spray) humidifiers (atomizers), Compressed air humidifiers Type MC adiabatic humidifiers can be operated with both tap water and demineralised water, which is free of bacteria and salts found in ordinary water. This makes it possible to use humidifiers of this type in hospitals, pharmacies, operating rooms, laboratories and other special areas where sterility is required.

1 Adiabatic (spray) humidifiers(atomizers) operating on high pressure water
HumiFog humidifiers can only be operated with demineralized water (Table 5). For this purpose, as a rule, water treatment is used, corresponding to the parameters listed below. The first three parameters are of paramount importance and must be respected under all conditions. For water conductivity below 30 µS/cm, it is recommended to use a pump unit made entirely of stainless steel.

2 Adiabatic centrifugal (disk) humidifiers
DS direct humidifiers do not use water as such. With their help, the already existing steam is supplied to the humidification section of the central air conditioners or to the supply air ducts. As is obvious from the consideration of the above information, in a number of cases it is desirable, and in some of them, appropriate water treatment is required by replacing, transforming or removing certain chemical elements or compounds dissolved in the feed water. This prevents premature failure of the humidifiers used, increases the service life of consumables and materials such as steam cylinders, and reduces the amount of work associated with periodic maintenance. The main tasks of water treatment are to reduce to a certain extent the corrosive activity and the formation of salt deposits in the form of scale, sludge and solid sediments. The nature and degree of water treatment depends on the ratio of the actual parameters of the water available and required for each of the humidifiers discussed above. Consider sequentially the main methods of water treatment used.

Water softening

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This method reduces the hardness of the water without changing the amount of electrolyte dissolved in the water. In this case, the replacement of ions responsible for excess rigidity is carried out. In particular, calcium (Ca) and magnesium (Mg) ions are replaced by sodium (Na) ions, which prevents the formation of lime deposits when water is heated, since, unlike calcium and magnesium carbonates, which form a variable component of hardness, sodium carbonate remains dissolved in water when elevated temperature. Typically, the process of water softening is implemented using ion exchange resins. When using sodium ion exchange resins (ReNa), the chemical reactions are as follows, constant hardness:

2 ReNa + CaSO4 →Re2Ca + Na2SO4, (4) variable hardness:
2 ReNa + Ca(HCO3)2 →Re2Ca + NaHCO3.(5)

Thus, the ions responsible for excessive hardness (in this case, Ca++) and the dissolution of Na+ ions are fixed on the ion exchange resins. Since ion exchange resins are gradually saturated with calcium and magnesium ions, their effectiveness decreases over time and regeneration is required, which is carried out by backwashing with a dilute sodium chloride solution (table salt):
ReCa + 2 NaCl →ReNa2 + CaCl2. (6)
The resulting calcium or magnesium chlorides are soluble and are carried away with the washing water. At the same time, it should be taken into account that softened water has an increased chemical corrosiveness, as well as an increased specific conductivity, which intensifies the electrochemical processes taking place. On fig. 6 shows in comparative terms the corrosive effect of hard, softened and demineralized water. Please note that despite the patented Anti Foaming System (AFS), the use of softened water in isothermal humidifiers of all types can cause foaming and eventually malfunction. As a result, water softening during water treatment in air humidification systems is not so much of independent importance as it serves as an auxiliary means of reducing water hardness before its demineralization, which is widely used to ensure the operation of adiabatic type humidifiers.

Polyphosphate treatment
This method allows you to "bind" hardness salts for a while, preventing them from falling out in the form of scale for some time. Polyphosphates have the ability to form bonds with CaCO3 crystals, keeping them in a state of suspension and, thereby, stopping the process of their aggregation (formation of chelate bonds). However, it should be borne in mind that this mechanism is operable only at temperatures not exceeding 70-75°C. At higher temperatures there is a tendency to hydrolysis and the efficiency of the method is sharply reduced. It should be borne in mind that water treatment with polyphosphates does not reduce the amount of dissolved salts, so the use of such water, as in the previous case, in isothermal humidifiers can lead to foaming and, consequently, to their unstable operation.

Magnetic or electric air conditioning
Under the action of strong magnetic fields, an allotropic modification of salt crystals occurs, which is responsible for the variable hardness, as a result of which the scale-forming salts turn into finely dispersed sludge, which is not deposited on surfaces and is not prone to the formation of compact forms. Similar phenomena take place when using electrical discharges, which reduce the ability of precipitated salts to aggregate. However, to date, there are no sufficiently reliable data on the efficiency of such devices, especially at high temperatures close to the boiling point.

Demineralization
The water treatment methods discussed above do not change the amount of chemicals dissolved in the water and, therefore, do not completely solve the problems that arise. When operating isothermal humidifiers, they can reduce the amount of solid deposits that are most relevant to water softening methods. Demineralization, carried out by extracting substances dissolved in water in one way or another, has a limited effect for isothermal humidifiers with immersed electrodes, since the principle of their operation is based on the flow of electric current in a salt solution. However, for all other types of air humidifiers, demineralization is the most radical method of water treatment, especially for adiabatic humidifiers. It can also be fully applied to electrically heated isothermal humidifiers and gas humidifiers, where other water treatment methods discussed above, while reducing the amount of solid deposits, create the accompanying problems associated with an increase in the concentration of strong electrolytes when the water evaporates. One of the negative aspects associated with the lack of water demineralization is the formation of a finely dispersed salt aerosol when moisture is supplied to the serviced premises. This applies to the greatest extent to the electronics industry ("clean" rooms) and medical institutions (eye microsurgery, obstetrics and gynecology). With the help of demineralization, this problem can be completely avoided, except for the use of isothermal humidifiers with immersed electrodes. The degree of demineralization is usually estimated from the specific conductivity, which is approximately proportional to the total concentration of dissolved electrolytes in the following ratios (Table 7).

In nature, water with a specific conductivity of less than 80-100 µS/cm is almost never found. Ultra-high demineralization is necessary in exceptional cases (bacteriological laboratories, crystal growth chambers). In most practical applications, however, a sufficiently high and very high degree of demineralization is observed. The highest degree of demineralization (up to the theoretically achievable) is provided by distillation of water, incl. double and triple. However, this process is costly, both in terms of capital costs and operating costs. In this regard, for the purpose of water treatment during air humidification, the following two methods of demineralization are most widely used:

Reverse osmosis
In this method, water is pumped at high pressure through a semi-permeable membrane with pores less than 0.05 µm in diameter. Most of the dissolved ions are filtered on the membrane. Depending on the membrane used and other characteristics of the filtration process carried out, between 90% and 98% of the ions dissolved in the water are removed. Achieving a higher demineralization efficiency in this case is problematic. The possibility of carrying out the reverse osmosis process fully automatically, as well as the absence of the need for the use of chemicals, make it particularly attractive for the purposes under consideration. The process is quite economical, consuming electricity in the amount of 1-2 kWh per 1 m3 of treated water. The cost of equipment is constantly decreasing due to the increase in the volume of its production due to the constant expansion of areas of use. Reverse osmosis, however, is vulnerable if the treated water is very hard and/or contains a large amount of mechanical impurities. In this regard, in order to increase the service life of the membranes used, it is often necessary to pre-soften the water or its polyphosphate treatment or magnetic / electrical conditioning and filtration.

Deionization
In accordance with this method, layers of ion exchange resins (columns of ion exchangers) are used to remove solutes, which have the ability to exchange hydrogen ions for cations and hydroxide ions for anions of dissolved salts. Cationic ion exchange resins (cationites, polymeric acids) exchange one hydrogen ion for the cation of the solute that comes into contact with the resin (eg Na++, Ca++, Al+++). Anionic ion exchange resins (anion exchangers, polymeric bases) exchange one hydroxyl ion (hydroxyl group) for the corresponding anion (eg Cl-). Hydrogen ions released by cation exchangers and hydroxyl groups released by anion exchangers form water molecules. Using calcium carbonate (CaCO3) as an example, the chemical reactions are as follows, in a cation exchanger column:

Rice. 7

2 ReH + CaCO3 →Re2Ca + H2CO3, (7) in the anion exchanger column 2 ReH + H2CO3 →Re2CO3 +H2O. (8) As the ion exchange resins consume hydrogen ions and/or hydroxyl groups, they should be subjected to a regeneration process using hydrochloric acid cation exchanger treatment:

Re2Ca + 2 HCl →2 ReH + CaCl2. (9) The anion exchanger column is treated with sodium hydroxide (caustic soda): Re2CO3 + 2 NaOH →(10) →2 ReOH + Na2CO3. The regeneration process ends with washing, which ensures the removal of salts formed as a result of the considered chemical reactions. In modern demineralizers, the water flow is organized "from top to bottom", which prevents the separation of the gravel layer and ensures continuous operation of the plant without compromising the quality of cleaning. In addition, the ionite layer works as a filter for water purification from mechanical impurities.

The efficiency of demineralization by this method is comparable to that of distillation. At the same time, the operating costs inherent in deionization are significantly lower compared to distillation. Theoretically, water demineralized by the considered methods (reverse osmosis, deionization) is chemically neutral (pH = 7), but various substances with which it subsequently contacts are easily dissolved in it. In practice, demineralized water is slightly acidic due to the demineralization process itself. This is due to the fact that residual amounts of ions and gaseous impurities lower the pH. In the case of reverse osmosis, this is due to the differential selectivity of the membranes. In the case of deionization, these residual amounts are due to the depletion or violation of the integrity of the columns of ion exchangers. In the case of increased acidity, water can dissolve metal oxides, opening the way for corrosion. Carbon steel and zinc are particularly susceptible to corrosion. A typical phenomenon is, as noted earlier, the loss of zinc by a brass alloy. Water having a specific conductivity of less than 20-30 µS/cm should not come into contact with carbon steel, zinc and brass. In conclusion, in fig. Figure 7 shows a diagram that interconnects the considered indicators of water quality, methods of air humidification and methods of water treatment. For each moistening method, black rays determine a set of water quality indicators, the quantitative values of which must be maintained within the specified limits. Colored beams define water treatment methods recommended, if necessary, for each of the considered methods of air humidification. At the same time, the priorities of the recommended water treatment methods are determined. Colored arcs also, taking into account priorities, identify auxiliary water treatment methods recommended for preliminary reduction of water hardness, which is subject to further treatment by reverse osmosis. The most critical in terms of the content of dissolved salts in water is the ultrasonic method of air humidification (HumiSonic, HSU), for which the use of distillate is a priority, or at least the use of deionization or reverse osmosis. Water treatment is also mandatory for high-pressure atomizers (HumiFog, UA). In this case, the use of reverse osmosis provides satisfactory results. More expensive water treatment methods such as deionization and distillation are also possible. The remaining methods of air humidification allow the use of tap water without its preparation if, for the entire set of specific indicators of water quality, their quantitative values are within the specified limits. Otherwise, it is recommended to use water treatment methods in accordance with the identified priorities. As for humidifiers of direct action (UltimateSteam, DS), they are fed with ready-made steam and in the one shown in fig. 7 in the scheme do not have formal links with water quality indicators and water treatment methods.

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