Circulating water spray humidifiers
- Air humidifiers -
The circulating water spray humidifier, also called an air washer, is the classic among humidifier systems. The water quantity atomised within the airflow is several times greater than the water flow required for humidification. The water that is not evaporated is captured in a tank and channelled back to the nozzles.
Application areas for circulating water spray humidifiers
- High increase in humidity (1.0 to 10g/kg and more)
- From small to large volumes of air (1,000 to 2,000,000 m³/h)
- Air purification (wash-out effect!)
- Operation by means of municipal water
- Low-maintenance spray nozzles through large flow cross-sections
- Low-maintenance pump
- Automatic level control
- Automatic draining with hygienic flushing
- Automatic elutriation
- Physical sterilisation (UV immersion lamps, UV reactor)
- Chemical sterilisation (hydrogen peroxide, chlorine dioxide)
Using a centrifugal pump, water is withdrawn from a water tank placed below the airflow and sprayed in relatively large droplets via nozzles at a low pressure (2.5-3.0 bar). Part of the water evaporates at the surface of the droplets, thereby causing the air to be humidified. The larger part of the water bound in the droplet falls back into the water tank. On their way through the airflow, the droplets absorb particles and harmful gases from the air. This wash-out effect causes the air pollutants to accumulate in the water tank.
The water evaporation causes an additional concentration of air pollutants in the water tank. To ensure constant water quality, it is therefore not sufficient simply to replace the evaporated water portion. Depending on the extent of pollution of the air, a further quantity of water is required to extract contaminants from the water tank. This additional water requirement is described via the elutriation rate, with the water required for contaminant extraction being expressed as a ratio of the evaporated quantity of water.
With regard to conventional humidification tasks, the maximum elutriation rate for demineralised water is approx. half the amount of water required for humidification, while that for municipal water is approx. the double amount.
To prevent the pump from running dry, the minimum allowable water level is constantly monitored via a fill-level sensor. The fresh water supply, and hence the water level in the water tank, is controlled mechanically via a float valve. Electronically controlled level regulation is also possible as an enhanced feature. 2 additional fill-level sensors are fitted in this case. A min sensor monitors the lower water level in the water tank and, if the water drops below this level, opens a solenoid valve in the fresh water supply. As soon as the upper water level is detected via a max sensor, the solenoid valve closes the water supply. In many cases, a further sensor, which acts as an overflow alarm in indicating an imminent tank overflow, is provided.
The air enters the humidifier via the rectifier. Special eliminators at the outlet of the humidifier prevent the droplets from being discharged with the airflow.