Operating principle of ultrasonic humidifier

Physical conditions/advantages

BOGA GmbH is a manufacturer of high-quality humidification systems according to the ultrasonic principle. Our devices are used in all industrial sectors and branches - see reference list. In the following text you will find some explanations concerning the humidification principle.


Information on ultrasonic humidification

Air conditioning by ultrasound has become more and more important within the last few years and gained more market segments. There are so many advantages of ultrasonic humidification that the higher purchase price will soon amortise compared to classical systems, especially due to its extremely low operating costs.

The operating principle and the advantages of our humidifiers working according to the ultrasonic principle compared to classical humidification systems are as follows.


Operating principle:

a) Physical conditions

When certain crystals are deformed by mechanical stress, electrical charge is build up proportionally on them, producing an electric field strength in the crystal.

Jacques and Pierre Curie discovered this phenomenon in 1880. Even the reversal of this so-called piezoelectric effect or Piezo-effect is possible; materials change their dimensions under the influence of an electric field.

Ceramic piezoelectric materials are hard, chemically inactive and completely insensitive to humidity or other atmospheric influences.

The human ear is able to hear frequencies between 16-20.000 Hz. All higher frequencies are called ultrasound.

Vibrations occur as a result of pressure changes. Repeated pressure increase and decrease produce different sound waves.

In order to use ultrasound waves for air humidification, electrical energy must be transformed into mechanical energy. This is done in the piezoelectric transformer (also called ultrasonic generator or transducer).

Therefore, a vibration unit consists of the resonant circuit, in which the high frequency of about 1.7 MHz is produced, and the piezoelectric transformer which transforms the electrical frequency into a proportional mechanical vibration.

Due to their physical nature, sound waves consist of mechanical vibrations of compressible media. These vibrations occur due to a displacement of equilibrium of the particles of a compressible material. Due to their own mobility and gravitation these particles are periodically moving to and fro their original position. Sound waves are tied to a medium and cannot exist in a vacuum.

The Piezo-ceramic transformers are attached to the bottom of the water reservoir of the humidifier. With excitation of this transformer the water transports the ultrasound vibrations to the boundary layer water-air. Constant compression /decompression of the water column above the transformer causes cavitation in the immediate vicinity of the water surface. Crossed capillary waves are formed, from which very small mist droplets (aerosols) are cast off in the wave crest.

The aerosols are blown out by the air blast in the humidifier and very soon mingle with the surrounding air. They have a very small diameter (~ 0.001 - 0.005 mm) and therefore form a freely floating mist. The average droplet diameter depends on the surface tension s and the density r of the medium as well as on the excitation frequency. The higher the excitation frequency, the smaller the average droplet diameter.




b) Operation of the ultrasonic air humidifier

Advantages: