Hydropower plants have the ability to cause high levels of total dissolved gas (TDG) supersaturation in the river downstream the plant. This occurs when high amounts of air get trapped and pressurized inside the hydroelectric system. Gas supersaturation in water, if it reaches a certain level, increases fish mortality and impacts surrounding habitats. Using power ultrasound to enhance the degassing process is a potential solution, to avoid water with high levels of dissolved air getting discharged in rivers downstream hydropower plants.
Power ultrasound, which is a low-frequency, high-intensity ultrasound wave, is able to initiate acoustic cavitation. Acoustic cavitation is briefly described as the formation, growth, and violent collapse of gas bubbles as a result of pressure waves traveling through a fluid. This process has the ability to enhance the natural degassing process and lower the TDG saturation level in a water body. In order to make power ultrasound an efficient technology, the different parameters that effect the degassing process are to be evaluated and tested in a laboratory environment. This may include sound intensity, TDG saturation level, and flow velocities.
In this thesis, an experimental procedure to produce and degas gas supersaturated water is developed. In a first setup different parameters to increase the amount of TDG in a water mass are tested. Subsequently, the produced gas supersaturated water is used to test the degassing effect of power ultrasound in an open flow channel. The effect of different initial TDG saturation levels and ultrasound amplitudes on the degassing process is evaluated.
To conclude the results show that the degassing effect depends on the TDG saturation level and the ultrasound amplitude. Further, it is shown that the highest sound intensity does not lead to the best degassing effect as a result of dampening effects. Moreover, the limits of the used experimental setup are evaluated and the weakness of the TDG measuring principle is pointed out.