Ultrasonic humidifiers are one of the most environmentally friendly products that can be used in data centers
Ultrasonic humidifiers operate according to the principle of "Ultrasonic Atomization".
Fig. 1: The humidifier is switched on. The oscillator amplitude is positive.
Fig. 2: The oscillator amplitude is negative. The inertia of the water creates a vacuum.
Fig. 3: After approx. 10 amplitudes, the ultrasonic humidifier reaches 100 % of its output.
A piezoelectric transducer immersed in a water bed, converts a high frequency, electronic signal into a high frequency mechanical oscillation. As the oscillation speed is increased to a level where the water particles can no longer follow the oscillating surface, a momentary vacuum and strong compression occur, leading to the explosive formation of air bubbles (cavitation). At cavitation, broken capillary waves are generated, and tiny (1 micron diameter) droplets break the surface tension of the water and are quickly dissipated into the air, taking vapor form and absorbed into the air stream.
The principle of ultrasonic humidification is based on the superimposition of two effects:
1. Cavitation bubble implosion
The change in amplitude of the oscillator gives rise to powerful water hammers that release tiny cavitation bubbles. The implosion of the bubbles on the surface emits tiny water aerosols into the ambient air.
2. Capillary wave theory
The ultrasonic oscillators generate regularly formed Rayleigh surface waves in the water tank. Minute water aerosols are also emitted into the ambient air on the crests of these waves.
By superimposing these two effects, the use of ultrasonic humidifiers enables a homogeneous aerosol mist to be produced with minimal energy consumption.