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Title: A fluidic oscillator based on a new mechanism for microbubble generation and developing microbubble stripping for separation phenomena
Author: Desai, Pratik
ISNI:       0000 0004 7428 2522
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2018
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Microbubbles, gas-liquid interfaces sized between 1μm and 1000μm, exhibit high levels of transport phenomena due to their high surface-area to volume ratio. The thesis describes the underpinning understanding of bubble generation, the invention and benchmarking of a novel fluidic oscillator, the visualisation dynamics associated with the sizing of high throughput microbubble clouds, and the development and application of hot microbubble injection in thin liquid layers for ammonia-water, and ammonia-rich wastewater). Successful design and implementation of a novel technology relies on developing the field around it. The chapters detailed herein demonstrate the path taken and the understanding developed. New understanding is developed for microbubble generation mediated by oscillator flow that the generation frequency of the bubbles coupled with the amplitude required for bubble detachment is imperative for significantly reducing the bubble size. A 'sweet spot' is observed where bubble size reduced dramatically - sweet spot (volume-average size -60μm,number-average7μm)reduction in bubble size compared to conventional steady flow(volume-average size-800μm, number-average-300μm)from oscillatory flow (volume-average-size-180μm,number-average-14μm) is demonstrated. A new fluidic oscillator is invented-Desai-Zimmerman-Fluidic-Oscillator- (DZFO) which retains all the advantageous properties of other oscillators but has several important features/improvements including - higher pulse amplitude (4-10 times higher), lower frictional losses, new switching mechanism, higher frequency attainable (20kHz), constructive/destructive wave formation, asymmetric gas mixing, and lower onset of oscillation (< 1slpm) with crisper momentum pulse transfer. These properties also make the DZFO better at microbubble generation and smaller bubbles are generated compared to other oscillators. A mechanism is proposed for this new oscillator and an experimental campaign carried out to support the mechanism and benchmark it with the other oscillators. The DZFO is based on a new mode of oscillation, acoustic resonant mode, which is different to the ones typically used to categorise different oscillators. Acoustic bubble spectrometry has been compared to laser diffraction and optical methods for visualising high throughput microbubble clouds and has been deemed to be the most effective at inferring bubble size distributions for these scenarios. Hearing bubbles is much better than directly visualising them. Microbubble stripping of ammonia from ammonia-water systems and ammonia rich liquor systems was developed and benchmarked with an industrial comparator (air stripping). The mass transfer rates were over 1000-3000 times higher for microbubble stripping compared to air stripping for ammonia-water systems and over 15000 times higher for ammonia-rich liquor. Stripping of nearly 100% ammonia was achieved in less than 30 minutes of contact time (as opposed to 95% in 100h for air stripping), and removal of ammonia at a pH less than 9 was achieved which is a first in literature. A new understanding for the ammonia removal process was developed.
Supervisor: Zimmerman, W. B. J. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available