Air humidification in clean rooms. Humidification of “clean rooms”: hospitals, clinics Humidifier for laboratory

House

In a city where there is more than enough gas and stench, you can often find air humidifiers in apartments. These installations create the required degree of humidity in the room, thereby purifying oxygen from harmful impurities and creating optimal conditions for a healthy life.

Humidifiers are necessary in homes with small children, as well as in places where elderly people and people with disabilities with respiratory problems live. The right humidity in the air will help them overcome an exacerbation of the disease and help them cope with the disease faster.

The Importance of Humidifiers

Universal air humidifiers are electrically powered and most of them have LED backlight, displaying the degree of humidity in the room. The functionality of such devices is varied:

  • different design, which can be selected as desired;
  • convenient removable water tank;
  • built-in timer;
  • varying degrees the power of the device, which can be controlled according to the situation;
  • The size of the humidifier depends on the area of ​​the room;
  • various models - steam, ultrasonic and mechanical;
  • air ionization will help protect against harmful bacteria;
  • automatic shutdown when the tank is empty.

Very often, air humidifiers are recommended by doctors for children's rooms, especially in winter. if the humidity at this time is not higher than 40%, then there is a risk of colds and inflammatory diseases. When choosing a humidifier, pay attention to the following:

  • original design and perhaps a built-in night light will cheer up any child and adult;
  • the inhaler-ionizer function will allow you to use essential oils and also cleanse the air of germs;
  • It is necessary to have a hygrostat, which will help assess the level of humidity in the room.

Description of the problem

The correct level of humidity in a cleanroom manufacturing environment is essential to maintaining production standards, research and waste minimization.

Even small changes in humidity levels can cause surfaces, substances and materials to dry out more quickly and lead to the build-up of static charges that can cause equipment to malfunction or fail.

Precise humidity settings often cannot be achieved using standard humidification equipment that we use in the office or at home, in such cases specialized humidification systems are used.

Laboratory humidifiers

The humidity indicator refers to the amount of water vapor in the atmosphere.

Humidifiers are tools that increase humidity levels.

There are many types of humidifiers depending on the needs and requirements.

A laboratory humidifier is an important device used in various laboratories to maintain the desired humidity level.

In such rooms, the ability to clearly regulate the humidity, as well as the uninterrupted operation of the device, is very important, since any deviations or failures can lead to distortion in its operation, which is not acceptable.

Below are some of the important benefits of a laboratory humidifier.

Improves atmospheric conditions


Laboratory humidifiers increase the level of humidity in the laboratory, which is necessary for carrying out a number of tests or tasks. Some tests require controlled atmospheric conditions and required humidity levels. By improving air quality, these humidifiers help in conducting experiments and tests under desired atmospheric conditions.

Reduces static electricity


During the winter season, when the air is dry, there is a high chance of feeling static discharge as a result of touching certain objects.

When static electricity charges on metal furniture and door handles, it can be very irritating. Besides, static charges may damage electrical laboratory instruments.

The use of laboratory humidifiers avoids all these problems and also provides controlled and favorable air humidity in medical and clinical laboratories.

Reduces the likelihood of illness


People tend to get sick and become more susceptible to a number of problems such as colds and flu when humidity levels drop to a significant extent. In such a situation, it becomes necessary to increase the humidity level to a favorable level to avoid susceptibility to infection.


Often wooden furniture and wooden appliances become unusable due to low humidity levels. By using laboratory humidifiers, the problem can be radically reduced.

Thus, laboratory humidifiers prevent wear of wooden instruments and furniture, and also protect people from diseases.

Improves work efficiency


Often, doctors and other laboratory workers work for long hours, which subsequently causes fatigue.

This may affect operating efficiency, especially if humidity levels drop to significant levels.

By increasing humidity levels, laboratory humidifiers help reduce the amount of fatigue experienced by people working in the laboratory.

Solutions options

In small spaces you can best use ultrasonic humidifiers , they have a number of advantages:

  • Ease of operation and maintenance;
  • Reliability of design and simplicity of technology;
  • High-quality fine mist;
  • Eliminates the possibility of oil getting into splashed water.

Fog generators (humidifiers) high pressure

The most advanced technology in agriculture. Its principle is based on spraying water through nozzles and their instant evaporation. Their advantages:

  • Low specific electrical energy costs;
  • Uniform humidification of the entire room;
  • Possibility of installing a piping system and nozzles according to wishes;
  • The piping and nozzle system can be easily disassembled without the use of special tools;
  • The generated fog cools the room.

High pressure humidifiers. The system of pipelines and nozzles is assembled and mounted under the ceiling, the pipelines are connected with collet clamps, without the use of special tools. This allows you to assemble a humidification system according to the individual dimensions of the customer.

The system can be controlled remotely using an external control module with a remote humidity sensor. Simple assembly instructions allow you to install the humidifier yourself. The pump is connected to a 220 V network, and water is supplied to it.

When using ultrasonic duct humidifiers, mist is supplied into the room through an air duct. It is most effective to install the steam duct directly under the ventilation, as shown in the figure. This contributes to the most effective humidification of the entire volume of the room.

In the high pressure pump, it is necessary to periodically check the oil level and, if necessary, add to the required level.

You can use regular machine oil. Operating the pump without oil is unacceptable.

Over time, the nozzles will become clogged with salt deposits, so they need to be soaked in a special solution.

Options

Modernization is already possible installed system high pressure humidification in the future by connecting additional sections of pipelines with nozzles or installing a more powerful pump.

This can be done in case of production expansion, when the current system capacity is not enough to maintain the desired humidity level.

In the room with mushrooms, sanitary and hygienic conditions must be maintained, therefore, together with the humidification system, it is possible to install air ozonizers.

Final words

With the benefits of a laboratory humidifier, more and more laboratories are using a humidifier to maintain the required humidity, improve operating efficiency and achieve accurate research results.

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

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

Important from a practical point of view aspects associated with the operation of a humidifier

It is particularly important to use feed water of appropriate quality. The requirements imposed in this case are fundamentally different for humidifiers, the operating principle and design of which are very diverse. Unfortunately, this question 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 and hot water supply systems 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 through analysis physical and chemical characteristics behavior of substances of varying degrees of solubility during the transition of water into steam, realized in one way or another. The presented materials are quite general in nature, covering almost all known methods of air humidification. However, based on personal experience author, the specific design versions of the units considered are limited to the range supplied by CAREL, which includes air humidifiers various types in a wide range of operating principles used.

There are two main methods of air humidification in practical use: 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. Directly enters the air saturated steam. The phase transition of water from liquid to vapor state is carried out due to an external heat source. Depending on the method of implementing external heat, 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 standardized . General requirements the development of methods for their determination is regulated by GOST 8.556-91. From the point of view of using water in air humidification systems, not all of the indicators mentioned above are significant.

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 in weight quantities is equivalent to one part per million (parts per million, ppm). In nature TDS 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 must contain no more than 2000 mg/l of dissolved substances. In Fig. 1 on a logarithmic scale shows the solubility of the series depending on temperature chemicals(electrolytes) most often present in water under natural conditions. Noteworthy is the fact 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. Other characteristic feature concerns calcium sulfate (CaSO4), the solubility of which, 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 calcium and magnesium sulfates and chlorides remaining dissolved in water at elevated temperature;
  • 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 that play a key role in the formation of 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 to form a solid residue. The intensity of the processes considered 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 processes considered (1) to the right, causes the formation of solid deposits at the mouths of the nozzles of spray-type air humidifiers (atomisers). Moreover, the higher the speed in the nozzle and, accordingly, according to Bernoulli’s law, the deeper the vacuum, 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 (more alkaline), the less 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 for measuring stiffness is summarized in table. 1. In the USA, the following classification of water hardness intended for domestic 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 mEq/l - hard water;
  • 3.0 mEq/L is 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 = 8-12°fH (1.6-2.4 mEq/l) - water of medium hardness;
  • TH = 12-18°fH (2.4-3.6 mEq/l) - practically 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 characterized by significantly different values. According to sanitary rules and regulations SanPiN 2.1.4.559-96 "Drinking water. Hygienic requirements for water quality of centralized drinking water supply systems. Quality control" (clause 4.4.1), the maximum permissible water hardness is 7 mEq/l. At the same time, this value can be increased to 10 mg-eq/l by decree 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 locality and the applied water treatment technology. 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 mEq/ l. At the same time, the quality standard for packaged waters of the first category is characterized by a hardness value of 7 mEq/l and highest category- 1.5-7 mEq/l. According to GOST 2874-82 "Drinking water. Hygienic requirements and quality control" (clause 1.5.2), water hardness should not exceed 7 mEq/l. At the same time, for water supply systems that supply water without special treatment, in agreement with the sanitary and epidemiological service authorities, water hardness of up to 10 mEq/l is allowed. Thus, it can be stated that in Russia the use of extremely hard water is allowed, which must be taken into account when operating air humidifiers of all types.

This especially applies to adiabatic humidifiers, which certainly require appropriate water treatment.

Regarding isothermal (steam) humidifiers, It should be borne in mind that a certain degree of water hardness is a positive factor contributing to passivation metal surfaces(zinc, carbon steel) due to the formed protective film, helping to inhibit corrosion that develops under the influence of the chlorides present. In this regard, for isothermal electrode-type humidifiers, in some cases, limit values ​​are set not only for the maximum, but also for the minimum hardness values ​​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 mEq/l) is typical for Kalmykia, the southern regions of Russia and the Caucasus;
  • in groundwater in the Central region (including the Moscow region), water hardness ranges from 3 to 10 mEq/l;
  • in the northern regions of Russia, water hardness is low: ranging from 0.5 to 2 mEq/l;
  • water hardness in St. Petersburg does not exceed 1 mEq/l;
  • the hardness of rain and melt water ranges from 0.5 to 0.8 mEq/l;
  • Moscow water has a hardness of 2-3 mEq/l.

Dry residue at 180°C(Dry residue at 180°C, R180)
This indicator quantitatively characterizes dry residue after complete evaporation of water and heating to 180°C, different from total number dissolved solids (TDS) in water by the contribution made by dissociating, volatilizing and absorbing chemical compounds. These are, for example, CO2 present in bicarbonates and H2O contained in hydrated salt molecules. The difference (TDS - R180) is proportional to the bicarbonate content of 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 - average mineralization;
  • R180 1000 mg/l - high mineralization

Specific conductivity at 20°C(Specific conductivity at 20°C, σ20)
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 measurement for specific conductivity is μSiemens/cm (μS/cm). Conductivity clean water extremely low (about 0.05 µS/cm at 20°C), increasing significantly depending on the concentration of dissolved salts. It should be noted that 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 (less often 25°C) and is designated by the symbol σ20. If σ20 is known, then the values ​​of σt°C corresponding to temperature t, expressed in °C, will be determined by the formula: σt°Cσ20 = 1 + α20 t - 20, (2) where: α20 is the temperature coefficient ( α20 ≈0.025). Knowing σ20, the values ​​of TDS and R180 can be approximately estimated using empirical formulas: TDS ≈0.93 σ20, R180 ≈0.65 σ20. (3) It should be noted that while estimating TDS in this way has a small error, estimating R180 has much less accuracy and is significantly dependent on the bicarbonate content relative 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 = 7. At lower values, acidic properties appear, and, conversely, at higher values, alkaline properties appear. An 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 intensity of corrosion increases significantly, while in an alkaline environment at pH above 12, the intensity of corrosion is also slightly increased. Corrosive activity in an acidic environment increases with increasing temperature. It should be kept in mind 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-)

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 submersible electrodes, enhances the above effect. Chlorides are especially active when the water hardness is insufficient. It was previously indicated that the presence of calcium and magnesium ions has a passivating effect, inhibiting corrosion, especially at elevated temperatures. In Fig. Figure 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 negatively 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 the formation of slurry, surface deposits and/or secondary corrosion, which requires their removal, especially when working with adiabatic humidifiers using reverse osmosis water treatment, since otherwise rapid clogging of the membranes occurs.

Silicon dioxide(Silica, SiO2)

Silicon dioxide (silica) can be found in water in a colloidal or partially dissolved state. The amount of SiO2 can vary from trace amounts to tens of mg/l. Typically, the amount of SiO2 is increased in soft water and in the presence of an alkaline environment (pH 7). The presence of SiO2 has a particularly negative effect on the operation of isothermal humidifiers due to the formation of a hard, difficult-to-remove deposit consisting of silicon dioxide or calcium silicate formed. Residual chlorine (Cl-) The presence of residual chlorine in water is usually due to the disinfection of drinking water and for all types of humidifiers it is limited to minimum values ​​in order to avoid the appearance of pungent odors entering the humidified rooms along with moisture vapor. In addition, free chlorine leads to corrosion of metals through the formation of chlorides. Calcium sulphate (CaSO4) Calcium sulfate, present in natural water, has a low degree of solubility, and therefore is prone to sediment 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 (hemihydrate).
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As shown in Fig. 5, at temperatures below 42°C, dihydrate sulfate has reduced solubility compared to anhydrous calcium sulfate.

In isothermal humidifiers At water temperatures corresponding to the boiling point, calcium sulfate may be present in the following forms:

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

Excessive amounts of calcium sulfate precipitate, forming a paste-like mass that, under certain conditions, has a tendency to harden. Summary data on the limit values ​​of the feed water parameters discussed above for various types of air humidifiers are presented in the following series of tables. It should be borne in mind 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 coating on the heating element.

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

  • pressure from 0.1 to 0.8 MPa (1-8 bar), temperature from 1 to 40°C, flow rate not lower than 0.6 l/min (nominal value for nutrient solenoid valve);
  • hardness no more than 40°fH (which corresponds to 400 mg/l CaCO3), specific conductivity 125-1250 µS/cm;
  • absence organic compounds;
  • feed water parameters must be within the specified limits (Table 2)


Not recommended:
1. Use of spring water, industrial water or refrigeration circuit 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 should not have unpleasant smell, contain corrosive agents or excessive amounts of mineral salts. The humidifier can operate on tap or demineralized water having the following characteristics (Table 3).


Not recommended:
1. Use of spring water, process 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 Humidifying the air with such water can cause allergic reactions in others.

Gas humidifiers
Gas humidifiers can operate on water having 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, because they are potentially harmful substances.

Adiabatic (spray) humidifiers (atomisers), operating on compressed air Adiabatic humidifiers type MC can operate on both tap and demineralized 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 rooms where sterility is required.

1 Adiabatic (spray) humidifiers(atomizers) operating on high pressure water
HumiFog humidifiers can only operate with demineralized water (Table 5). For this purpose, as a rule, water treatment is used that meets the parameters listed below. The first three parameters play a primary role and must be observed under all conditions. When the specific electrical conductivity of water is below 30 µS/cm, it is recommended to use a pump unit made entirely of stainless steel.

2 Adiabatic centrifugal (disc) humidifiers
DS direct humidifiers do not use water as such. With their help, the existing steam is supplied to the humidification section of central air conditioners or to the supply air ducts. As is obvious from consideration of the above information, in some cases it is desirable, and in some of them, appropriate water treatment by replacing, converting 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 technical maintenance. The main objectives of water treatment are to reduce, to a certain extent, corrosion activity and the formation of salt deposits in the form of scale, sludge and solid sediment. The nature and degree of water treatment depend on the ratio of the actual parameters of the available water and those required for each of the humidifiers discussed above. Let us consider sequentially the main methods of water treatment used.

Water softening

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This method reduces water hardness without changing the amount of electrolyte dissolved in the water. In this case, the ions responsible for excess hardness are replaced. In particular, calcium (Ca) and magnesium (Mg) ions are replaced by sodium (Na) ions, which prevents the formation of limescale 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 water softening process 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, ions responsible for excess hardness (in this case Ca++) are fixed on ion exchange resins and Na+ ions are dissolved. Since ion exchange resins are gradually saturated with calcium and magnesium ions, their effectiveness decreases over time and requires regeneration, which is carried out by backwashing with a dilute solution of sodium chloride (table salt):
ReCa + 2 NaCl →ReNa2 + CaCl2. (6)
The calcium or magnesium chlorides formed are soluble and are carried away with the rinsing water. At the same time, it should be taken into account that softened water has increased chemical corrosive activity, as well as increased specific conductivity, which intensifies the electrochemical processes taking place. In Fig. 6 shown in comparatively corrosive effects of hard, softened and demineralized water. Please be aware that despite the patented Anti Foaming System (AFS), the use of soft water in all types of isothermal humidifiers may result in foam formation and ultimately malfunction. As a result, water softening during water treatment in air humidification systems is not so much of independent importance, but serves as an auxiliary means of reducing water hardness before its demineralization, which is widely used to ensure the operation of adiabatic humidifiers.

Polyphosphate treatment
This method allows you to temporarily “bind” the hardness salts, 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 only operational at temperatures not exceeding 70-75°C. With more high temperatures there is a tendency to hydrolysis and the effectiveness of the method is sharply reduced. It should be borne in mind that treating water with polyphosphates does not reduce the amount of dissolved salts, therefore 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 electrical conditioning
Under the influence of strong magnetic fields, allotropic modification salt crystals responsible for variable hardness, as a result of which scale-forming salts turn into finely dispersed slurry, which is not deposited on surfaces and is not prone to the formation of compact forms. Similar phenomena occur when using electrical discharges, reducing the ability of precipitated salts to aggregate. However, until now there is no sufficiently reliable data regarding the efficiency of this type of device, 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 water and, therefore, do not completely solve the problems that arise. When operating isothermal humidifiers, they can reduce the amount of solid deposits formed, which is especially true for 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 their principle of 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 type air humidifiers. It can also be fully applied to isothermal humidifiers with electric heating elements and gas humidifiers, in which other water treatment methods discussed above, while reducing the amount of solid deposits formed, create associated problems associated with an increase in the concentration of strong electrolytes during water evaporation. One of the negative aspects associated with the lack of demineralization of water is the formation of a finely dispersed salt aerosol when moisture is supplied to the serviced premises. This applies to the greatest extent to enterprises in the electronics industry (clean rooms) and medical institutions (eye microsurgery, obstetrics and gynecology). With the help of demineralization, this problem can be completely avoided, with the exception of the use of isothermal humidifiers with immersed electrodes. The degree of demineralization is usually assessed by specific conductivity, which is approximately proportional to the total concentration of dissolved electrolytes in the following ratios (Table 7).

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

Reverse osmosis
In this method, water is pumped under high pressure through a semi-permeable membrane with pores having a diameter of less than 0.05 microns. Most of the dissolved ions are filtered on the membrane. Depending on the membrane used and other characteristics of the filtration process performed, between 90% and 98% of the ions dissolved in the water are removed. Achieving higher demineralization efficiency is problematic. The ability to carry out the reverse osmosis process completely automatically, as well as the absence of the need to use chemical reagents, 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 an increase in the volume of its production due to the constant expansion of areas of use. Reverse osmosis, however, is vulnerable if the water being treated 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, preliminary water softening or polyphosphate treatment or magnetic/electric conditioning and filtration are often required.

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 hydroxyl ions for anions of dissolved salts. Cation ion exchange resins (cation exchange resins, polymer acids) exchange one hydrogen ion for a cation of a solute that comes into contact with the resin (for example, Na++, Ca++, Al+++). Anionic ion exchange resins (anion exchange resins, polymer bases) exchange one hydroxyl ion (hydroxyl group) for the corresponding anion (for example, 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 look like this in a cation exchange column:

Rice. 7

2 ReH + CaCO3 →Re2Ca + H2CO3, (7) in the anion exchange column 2 ReH + H2CO3 →Re2CO3 +H2O. (8) As ion exchange resins consume hydrogen ions and/or hydroxyl groups, they must be subjected to a regeneration process using hydrochloric acid cation exchange column 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 installation without compromising the quality of cleaning. In addition, the ion exchanger layer works as a filter for purifying water from mechanical impurities.

The efficiency of demineralization by this method is comparable to distillation. At the same time, the operating costs inherent in deionization are significantly lower compared to distillation. Theoretically, water demineralized by the methods considered (reverse osmosis, deionization) is chemically neutral (pH = 7), but it easily dissolves various substances, with whom she subsequently comes into contact. In practice, demineralized water is slightly acidic due to the demineralization process itself. This occurs as a result of the fact that residual amounts of ions and gas impurities lower the pH. In the case of reverse osmosis, this is explained by the differential selectivity of the membranes. In the case of deionization, these residual amounts are due to depletion or disruption of the integrity of the ion exchanger columns. In case increased acidity water can dissolve metal oxides, opening the way for corrosion. Carbon steel and zinc are especially susceptible to corrosion. A typical phenomenon, as noted earlier, is the loss of zinc from 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 presents a diagram mutually linking the considered indicators of water quality, air humidification methods and water treatment methods. For each humidification method, black rays determine a set of water quality indicators, the quantitative values ​​of which must be ensured within specified limits. Colored rays indicate 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 were 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 regarding the content of salts dissolved in water is the ultrasonic method of air humidification (HumiSonic, HSU), for which the priority is the use of distillate, or, at a minimum, the use of deionization or reverse osmosis. Water treatment is also mandatory for atomizers operating on high-pressure water (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. Other methods of air humidification can be used tap water without its preparation if, for the entire set of specific water quality indicators, their quantitative values ​​are within specified limits. Otherwise, it is recommended to use water treatment methods in accordance with the designated priorities. As for direct-acting humidifiers (UltimateSteam, DS), they are powered by ready-made steam and in the conditions shown in Fig. 7 diagrams have no formal connections with water quality indicators and water treatment methods.

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