ID 75

Effect of ambient pressure on ultrasonic atomization

 

Abstract:

To better understand the physical processes behind ultrasonic atomization, some experiments are performed nebulizing different liquids inside a pressurized chamber. Sprays are generated using a commercial piezoceramic disk with a resonance frequency of 1.65 MHz. The disk is excited with a sinusoidal signal with voltage amplitude that goes up to 60 V. Sprays are visually characterized analyzing instantaneous images. A Onda HNR-500 hydrophone is also used to measure the wave propagation inside the liquid. Pressure in the chamber is varied between -0.85 bar(g) and 4 bar(g). In general, it is observed that atomization is progressively inhibited as chamber pressure increases, until it eventually disappears when a certain value is reached. This limit varies, depending on the nature of the atomized liquid. Some effects can also be detected when pressure is decreased below atmospheric. However, this reduction is not sufficient to trigger the atomization in all the analyzed cases. For example, propanol cannot be nebulized in any condition. Results are examined in relation to the physical properties of the working fluids, namely water and several alkanes and alcohols. Liquid temperature appears also to be a relevant parameter controlling the atomization efficiency.