New technical solution for using ultrasound and aeration to reduce gas supersaturation inside the hydropower plant


Power dissipated by ultrasound (PUS) has been shown to affect the concentration of dissolved gas in liquids. However in the literature no systematic studies have been carried out to investigate the effect and rate of degassing at various ultrasonic frequencies ultrasonic powers and intensities, solution residence times and pressures.  

The main research questions are as follows:

  • Does PUS degas effectively solution oversaturated with gas, and if so, to what extent?
  • What are the active zone residence times and how does this correlate with PUS frequency and power?
  • What are the kinetic properties in degassing supersaturated air-water solution? Is it possible to treat water flows from hydropower plants?

The parameters required to describe and to optimize ultrasonic reactors, gas-liquid transfer at various ultrasonic frequencies, powers, durations, volumes, flowrates and pressures will be studied. The study will use different testing gases at several concentrations e.g. dissolved dioxygen (O2), dissolved dinitrogen (N2), dissolved argon (Ar), dissolved carbon dioxide (CO2) and air to understand bubble growth and degassing efficiency. The size and number of gas bubbles in the absence and presence of ultrasound will be studied under several gas types and concentrations under various operating conditions. A mathematical model will be developed to predict the level of degassing at several ultrasonic frequencies, power and irradiated volumes.

The research tasks are as follows:

  1. Develop a theoretical model for the reduction of gas supersaturation.
  2. Laboratory test at a small and medium scale.
  3. Large scale tests in the laboratory and/or at a hydropower plant

The effect of ultrasonication on liquid degassing under the various operating conditions will be determined by investigating the release of the dissolved gases by Gas Chromatography coupled with a Mass Spectrometer for gas.  Dissolved O2 concentration will be measured with the help of an oximeter.  pH and water conductivity will be measured in all experiments. Ultrafast imaging will be employed to understand bubble formation and growth in the absence and presence of ultrasound under the various operating conditions. The number of bubbles will be measured by Dynamic Light Scattering. The effect of ultrasonication on tank walls will be studied by imaging and Scanning Electron Microscope.
Aeration will be tested by the same experiment design and evaluation methods. Aeration of the turbine will be used to stimulate an increased degassing of the supersaturated water.

This will be tested in pipe flow in the Waterpower Laboratory and/or in a hydropower plant. 

Se the live stream from the experiments in the laboratory



Bjørn Winther Solemslie, Researcher, NINA

Leader work package 1