Electrochemical, photographic, luminescent and acoustic characterisation of cavitation
Electrochemical, photographic, luminescent and acoustic characterisation of cavitation
Initially, the sound field generated in the cylindrical ultrasonic reactor is characterised both theoretically and experimentally. The sound field is considered with a variable operating frequency. An acoustic model is developed to predict the spatial distribution of acoustic pressure, which is compared with experimental measurements of the spatial characteristics of luminescent emission from the cell. A sound speed (averaged in space and time) within the cavitation environment in the range of 868 - 1063 m s-1 was calculated for the first time. The implications for chemical activity within ultrasonic cells of this nature are discussed.
Chemical activity within the acoustically characterised model ultrasonic reactor is then investigated. A novel electrochemical technique is presented for the detection of radicals (OH* and H*) produced as the result of cavitation induced by ultrasound. A study of four example reactions is reported; evidence of OH* formation is found through the Weissler reaction, the Fricke reaction and the detection of H2O2; evidence for the production of H* is obtained by a Cu+2/Cu+ system. In all cases, redox active materials trap the oxidative or reductive radicals. Electrochemical detection within a flow cell is then used to sense redox active products of the reactions between a chosen trapping agent and radicals produced within an ultrasonically irradiated solution. The detectors are seen to be sensitive and to work reproducibly within an acoustically characterised cavitation environment.
The electrochemical sensors were then used to investigate the frequency dependence of the production of radicals in the model ultrasonic reactor. Radical production is shown to be highly frequency dependent in the range of 20 kHz to 160 kHz ultrasound. However, the dominant frequency dependence is not of the chemistry per se, but is a function of the ability of the acoustic reactor to provide sufficient inertial cavitation. MBS(C)L appears to predict at which frequency chemical activity should be expected to be most efficient within a particular cell. The variation of the rate of these reactions is correlated to MBS(C)L as a function of the frequency with a resolution of 1 kHz. The results obtained are discussed with reference to the acoustics, in particular to the modal nature of the cell employed.
The electrochemical radical sensors were then tested in a "standard" Branson ultrasonic bath (40 kHz) with a "standard liquid", designed by NPL (National Physics Laboratory). This was part of an attempt to develop a reference sensor for cavitation. Three sensors were successfully tested including the Weissler reaction, multi bubble sonoluminescence (MBSL) and multi bubble sonochemiluminescence (MBSCL). The results achieved from the study including those obtained by the various partners are critically analysed.
University of Southampton
Power, John Francis
77e153c6-6a9b-4a7c-aa48-98f6413b86f2
2003
Power, John Francis
77e153c6-6a9b-4a7c-aa48-98f6413b86f2
Power, John Francis
(2003)
Electrochemical, photographic, luminescent and acoustic characterisation of cavitation.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
Initially, the sound field generated in the cylindrical ultrasonic reactor is characterised both theoretically and experimentally. The sound field is considered with a variable operating frequency. An acoustic model is developed to predict the spatial distribution of acoustic pressure, which is compared with experimental measurements of the spatial characteristics of luminescent emission from the cell. A sound speed (averaged in space and time) within the cavitation environment in the range of 868 - 1063 m s-1 was calculated for the first time. The implications for chemical activity within ultrasonic cells of this nature are discussed.
Chemical activity within the acoustically characterised model ultrasonic reactor is then investigated. A novel electrochemical technique is presented for the detection of radicals (OH* and H*) produced as the result of cavitation induced by ultrasound. A study of four example reactions is reported; evidence of OH* formation is found through the Weissler reaction, the Fricke reaction and the detection of H2O2; evidence for the production of H* is obtained by a Cu+2/Cu+ system. In all cases, redox active materials trap the oxidative or reductive radicals. Electrochemical detection within a flow cell is then used to sense redox active products of the reactions between a chosen trapping agent and radicals produced within an ultrasonically irradiated solution. The detectors are seen to be sensitive and to work reproducibly within an acoustically characterised cavitation environment.
The electrochemical sensors were then used to investigate the frequency dependence of the production of radicals in the model ultrasonic reactor. Radical production is shown to be highly frequency dependent in the range of 20 kHz to 160 kHz ultrasound. However, the dominant frequency dependence is not of the chemistry per se, but is a function of the ability of the acoustic reactor to provide sufficient inertial cavitation. MBS(C)L appears to predict at which frequency chemical activity should be expected to be most efficient within a particular cell. The variation of the rate of these reactions is correlated to MBS(C)L as a function of the frequency with a resolution of 1 kHz. The results obtained are discussed with reference to the acoustics, in particular to the modal nature of the cell employed.
The electrochemical radical sensors were then tested in a "standard" Branson ultrasonic bath (40 kHz) with a "standard liquid", designed by NPL (National Physics Laboratory). This was part of an attempt to develop a reference sensor for cavitation. Three sensors were successfully tested including the Weissler reaction, multi bubble sonoluminescence (MBSL) and multi bubble sonochemiluminescence (MBSCL). The results achieved from the study including those obtained by the various partners are critically analysed.
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Published date: 2003
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Local EPrints ID: 465007
URI: http://eprints.soton.ac.uk/id/eprint/465007
PURE UUID: a580b478-1c5e-4fe9-90c1-59b658128dd7
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Date deposited: 05 Jul 2022 00:16
Last modified: 16 Mar 2024 19:53
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Author:
John Francis Power
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