Air - Humidifier / Air - Washer
General notes 1. General functions In spray humidifiers, also known as air washers or jet chambers, the air is brought into direct contact with flowing or atomised water. There is thus a transfer of material in addition to the transfer of heat. Depending on the temperature of the water, this means that any changes in the air condition are possible: heating, cooling, humidification and drying. Given that there are so many possible changes in the air condition, air washers are primarily used in air-conditioning systems, in which it is the adiabatic change of state (humidification and cooling) of the air that is of maximum importance. In contrast, washing or cleaning of the air in air washers only applies to coarse dust particles and a few gases, such as SO2, SO4. Designs In jet humidifiers, the water is atomised through spray diffusers to form a dense mist of water droplets. The air then flows through this mist. The jet chambers consist of a tank and a housing, both made from stainless steel or plastic, and at least one jet assembly and a pump. The tank height is 300 mm to 600 mm. It is equipped with an overflow, drain and mechanical float valve for the incoming flow of water. It also has desludging lines. The housing on which the tank is mounted has two sides and a top. Air flows through it horizontally at 1 to 4 m/s or, in special cases (high-speed washer) up to 7 m/s. The pump that extracts the water from the tank is generally mounted on a plinth or bracket beside the washer. Inside, the jets are arranged on one or two levels. The water is supplied to these jets by collecting and distributing pipes. The jet pipes are made primarily from plastic or stainless steel and have holes to which the jets are fitted using assembly clamps. Jet pressures in excess of 3.5 bar should be avoided to prevent the occurrence of ultrafine aerosols which cannot be separated out by the droplet separator and could damage downstream components. Depending on the design, the jets spray either against or with the air flow, or indeed in both directions. The jets are roughly 600 mm apart. There can be 4 6 jets per m 2 on the jet assembly depending on the jet diameter. The jets atomise the water supplied at a pressure of 0.1 to 3.5 bar from openings 4 to 10 mm wide. This creates a more or less dense rain or mist of small and tiny water droplets Two rows of jets should be used for larger volumes of water. The same applies to follow-up controls in order to increase the control range. A droplet separator is provided at the end of the washer to prevent the entrainment of water droplets by the air. This droplet separator generally consists of specially-shaped separator profiles with protruding catch heads that separate the droplets from the air when they hit the heads. Droplet separators (rectifiers) are generally provided on the air inlet side as well to prevent droplets emerging if the air flow is uneven. Other components of the washer include a tightly-closing inspection door with observation window, a watertight light and a mechanical float valve for automatically topping up with fresh water. Seite 2 von 5
2. Adiabatic washers If the washer works as an adiabatic humidifier, then circulating water can be used. The pump sucks the water from the tank and pumps it through the distributor pipes to the jets. A screen filter should be provided at the suction point. Adiabatic washers are essentially dependent on the associated water temperature (can be controlled by RH, C or TP). The low water temperatures, which are generally always lower than the initial temperatures from the washer, mean that water is absorbed into the air (by evaporation) which in turn cools the air. The reverse would be the case if the water temperature were higher. In this case the air will be heated, and the relative humidity can be increased (the temperature curve may remain the same as the setpoint on the temperature line, but the relative humidity increases). Another situation is cooling of the air (cold water below 10 ). Cooling: the relative humidity increases, the air is dehumidified and condensate is formed. 2.1 System with washer and humidifier functions In addition to the standard air humidifiers, we can also supply air washers with additional humidifier functions. These are used to wash out dust, ink mist, air impurities, chemicals, etc. These systems are generally equipped with a middle separator that prewashes the majority of the impurities, thus reducing the load on the downstream end separator. - Reduces the level of fouling at the end separator - Increases operational reliability (water seeping through) - Extends the maintenance intervals Electronic components also allow partial cleaning (replacement of water) to be carried out during operation, depending on the operating mode and the substances to be washed out. The evaporated water is pure (contains no chemicals), so any solids dissolved in the water (limescale, chlorides, magnesium, manganese, etc) remain in circulation. The fresh water that is added to compensate for the volume lost introduces further solid matter into the system, with the result that the concentration quickly rises (known as "thickening ) to inadmissible levels. The consequence is limescale, generally at the droplet separators, which greatly affects their effectiveness. Attention: Regular cleaning and inspection of the washer are important. (housing, separator profiles, jets, etc). Seite 3 von 5
3. Desludging Desludging (desalination) of part of the circulating water helps to prevent an unwanted concentration of solids. Part of the concentrated (thickened) water is replaced with fresh water, which reduces the thickening. This desalination can be achieved in different ways: Manually Continuously (e.g. overflow) When a specific volume is reached When a specific conductance is reached 4. Elimination of bacteria and algae To eliminate bacteria and algae, the circulating water can be sterilised by UV light, either by lamps immersed in the trough or by a separate UV system. Chemical disinfection is also possible. Automatic dosing of disinfectant at regular intervals ensures that the washer is permanently sterile. We recommend that you have a study carried out by and obtain advice from a qualified organisation. Continuous desalination, e.g. by constant removal of overflow or manual desludging of the water, is suitable for reducing thickening. Controlled thickening is desirable in order to save water. This requires automation and the ability to control the process, which is achieved by a system that is controlled by specific volumes or conductance values. When a defined volume of fresh water is reached, the volume-controlled system desludges a defined volume of water via a solenoid valve or electric drive for a defined period of time. This option works, but it relates solely to the thickening of the water at the set time. Any change in the fresh water will also change the thickening, but the system will not take this into account. Conductance-based desalination continuously measures the quality of the water by means of a measuring probe. The conductance is a measure of the ability of the water to carry current. The more salts are dissolved in the water, the better current is able to flow (as there is less resistance) and the higher the conductance (high concentration = higher conductance and vice versa). A conductance-controlled system can be used to set a predefined limit that must not be exceeded. When the limit is reached, a motor-driven ball valve opens and the desludging continues until the value falls below the limit once more. Any change in the fresh water thus will have no negative effect on the circulating water. Seite 4 von 5
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