Microbubble cloud generation from fluidic oscillation: underpinning fluid dynamics

Microbubbles received an intensive study for various generation mechanisms in the 1990s. The state of the art is currently perceived as being the Venturi method, which pumps both gas and liquid. As the density of liquids are usually a thousand fold higher than gases, it is inherently less energy efficient than the recently patented mechanism by the PI that produces microbubbles on the scale of the pore (as small as 20 microns) with high holdup (~40% is achievable currently), uniformly sized and spaced so non-coalescent, plumes with less energy use than the same flow rate of fine bubbles (1-2mm). For the smallest scale of microbubbles, industrial processes use the saturated liquid release method (6 bar compression), with nucleation of 30-60 micron bubbles, but with high coalescence rates so a very wide range of bubble sizes in a turbulent flow are created. We estimate that our fluidic oscillation method saves 90-95% of the electricity with a similar savings in the capital cost (no expensive saturation system and large pumps are needed to pump the saturated liquid). Field trials are underway to demonstrate the feasibility of replacing solids removal systems in water purification by this method. We have identified at least 25 potential applications and over 40 companies interested in the technology.The difficulty is that the industrial applications and engineering implementations are outstripping our fundamental understanding of the mechanism for microbubble generation and how it depends on the situation, operating conditions, and the controlling fluidic circuit design. We believe that there are potential medical applications (drug delivery, gas exchange in the blood) if the methodology can be extended to nanoscale bubbles with the same features of monodispersity and energy efficiency. In order to understand how to match the microbubble transfer requirement to the fluidic circuitry and generation devices for the various applications identified already, we must build computational models that are accurate predictors, as well as validating them and understanding the dynamics qualitatively from visualization and velocimetry studies under many representative conditions.Because of the extremely low cost of microbubbles produced by this methodology, mixing and gas transfer mechanisms that have never previously used microbubbles, is possible. Without accurate engineering design tools and a thorough scientific understanding, the implementation of such systems will be hit or miss and even when they work as in all our successful applications to date, they are certainly not optimal. As the technology is disruptive in that the change of infrastructure to exploit the potential energy and capital savings will drive change across several industries, the design and implementation protocols adopted at early stages become set in stone . But if the processes implemented are non-optimal, these non-optimalities will persist through at least one capital cycle. There are many instances in engineering of systems where the rules of design have not changed for a century (since they work), even though re-visiting them could achieve substantial savings. Thus, this proposal is extremely timely as design flaws adopted now may be long term costly, even though the potential improvement over current practise is breath-taking.In this proposal, we will bring to bear the state-of-the-art in flow visualization and velocimetry, with multiphase flow and engineering modelling, and a range of experimentation in fluidic circuitry and resultant microbubble dynamics, some of which has been pioneered by the investigators, to develop the full toolset to design microbubble generation systems tuned to the application system dynamics.

The impact plan focuses on the commercial exploitation path for energy efficient microbubble generation and low power consumption, high yield plasma microreactors (other technology patented by the PI and used in conjunction with microbubble dispersal). The current plan is to spin out a company this year to exploit the greater than 40 industrial contacts in more than ten application areas for these technologies, frequently combined as discussed in the generic beneficiary description. The University of Sheffield has a company incubator (fusionIP) which has been planning the commercial development of these patents over the past 18 months, and expects to spin out a company this summer for commercial management of the patents and to engage with potential endusers and commercial partners to arrange the engineering design, installation, commissioning and operational knowledge to have the technologies taken up. The supply chain is in place for microbubble applications, but not yet for ozone-UV dosing applications. The list of applications currently under R&D investigation with potential endusers and partners includes: 1. Algal biofuels production. 2. Biodiesel production. 3. Wastewater aeration. 4. Anaerobic digestor intensification for more biogas production and removal of CO2 to upgrade fuel quality. 5. Anammox (ammonia removal) intensification. 6. Solids removal by flotation in water purification (replacing dissolved air flotation). 7. Solids removal by flotation in minerals separations. 8. Intensified evaporation / heat transfer, such as in desalination. 9. Yeast production. 10. Beer and bioethanol production. 11. Ozone dosing for water purification -- organics removal, disinfection. 12. Ozone dosing for wastewater disinfection. 13. Dual ozone-UV breakdown of organics such as pesticides or metallocyanides. 14. Dual ozone-UV breakdown of biochemical byproducts in bioreactors. 15. Aeration of fish farms (aquaculture). 16. Ozone dosing in HF for cleaning solution for silicon wafers. 17. Microbubble dosing / extraction replacing gas-liquid spargers/scrubbers in commodity chemicals production, potentially CO2 dissolution in carbon capture systems. 18. Selective oxidation based on control of ozone levels in organic synthesis or for analytic chemistry (ozonolysis). 19. Gas-lift enhanced oil recovery (requires 30-50 micron size bubbles, cheaply produced) 20. CO2 flooding for enhanced oil recovery with microbubbles which avoids the channelling instability. 21. Hot gas microbubble injection for enhanced oil recovery which achieves similar improvement. 22. Oil-water separation enhancement by flotation effect for offshore separators and oil spill remediation. 23. Drag reduction in oil pipelines. 24. Fats, oils, and grease effluent separation as a feedstock for biodiesel. 25. Microfoam production for processed foods. 26. Oxygenation of oxygen depleted water recycled through PEM hydrogen fuel cells.