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University of Newcastle

1. Sarkar, Md Shahjahan Kaisar Alam. Electroflotation: its application to water treatment and mineral processing.

Degree: PhD, 2012, University of Newcastle

Research Doctorate - Doctor of Philosophy (PhD)

Flotation of particles of diameter less than 10 μm is important economically yet recovery is very poor in conventional flotation machines where the bubble diameter is typically greater than 600 μm. Many studies have reported that flotation recovery of fine particles increases with decreased bubble size. Electroflotation can create very fine hydrogen and oxygen bubbles and may be a viable option to recover very fine particles. This study aims to develop an increased understanding of the principles of electroflotation and to use this knowledge to float very fine particles. The interaction between the gas phase with the mineral surface may bring about changes in the surface properties of the mineral, which can be either beneficial or detrimental in improving the flotation recovery. To investigate this interaction, flotation recovery of silica between air and molecular hydrogen was performed in a laboratory Denver, type D12, flotation machine. For both gases, the pH of the suspension, gas flow rate, concentration of collector and frother, solids concentration, particle size and speed of impeller were kept constant. Almost identical recoveries were obtained for both gases, suggesting that gas composition played no significant role in silica flotation. There is wide variation in the reported measurements of bubble size in electroflotation, and uncertainty with the influence of electrode curvature, surface preparation and current density on bubble size have made it difficult to effectively design an efficient electroflotation system for fine particle recovery. Experiments were performed in a viewing cell that allowed direct visualization of hydrogen bubbles being generated and transported away from platinum wire electrodes of 90, 120 and 190 μm in diameter. It was found that the detached bubble diameter varied between 15-23 μm in diameter, and for each wire diameter, was little influenced by the applied current in the range 150-350 A/m². The measurements were consistent with those predicted from a simple force-balance analysis based on a H2-Pt-0.2M Na₂SO₄ contact angle of 0.18°. Interestingly, upon detachment the bubble size increased rapidly, recording up to an 8-fold increase in volume in the first few millimetres of rise, before approaching a steady state diameter of between 30-50 μm in the bulk. This increase in bubble size was found to be mostly due to the transfer of dissolve hydrogen into the growing bubble while moving through the electrolyte that was super-saturated with dissolved hydrogen. The equilibrium bulk diameter was found to be a function of the rate of hydrogen production, bubble nucleation rate, and dissolved gas concentration field. Consequently, it was concluded that in order to optimise electroflotation performance the cell geometry needed to be designed to optimise the contact between the supersaturated liquid and the rising bubble plume. By doing this, the volumetric flux of bubbles will be maximised leading to improved flotation performance. The…

Advisors/Committee Members: University of Newcastle. Faculty of Engineering and Built Environment, School of Engineering.

Subjects/Keywords: bubble size; detachment diameter; bulk diameter; recovery; bubble particle aggregare; bubble surface coverage; current density; bubble flux; hydrogen bubble generation

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Sarkar, M. S. K. A. (2012). Electroflotation: its application to water treatment and mineral processing. (Doctoral Dissertation). University of Newcastle. Retrieved from http://hdl.handle.net/1959.13/930125

Chicago Manual of Style (16th Edition):

Sarkar, Md Shahjahan Kaisar Alam. “Electroflotation: its application to water treatment and mineral processing.” 2012. Doctoral Dissertation, University of Newcastle. Accessed December 14, 2019. http://hdl.handle.net/1959.13/930125.

MLA Handbook (7th Edition):

Sarkar, Md Shahjahan Kaisar Alam. “Electroflotation: its application to water treatment and mineral processing.” 2012. Web. 14 Dec 2019.

Vancouver:

Sarkar MSKA. Electroflotation: its application to water treatment and mineral processing. [Internet] [Doctoral dissertation]. University of Newcastle; 2012. [cited 2019 Dec 14]. Available from: http://hdl.handle.net/1959.13/930125.

Council of Science Editors:

Sarkar MSKA. Electroflotation: its application to water treatment and mineral processing. [Doctoral Dissertation]. University of Newcastle; 2012. Available from: http://hdl.handle.net/1959.13/930125


INP Toulouse

2. Montout, Michaël. Contribution au développement d'une Approche Prédictive Locale de la crise d'ébullition : Contribution to the development of a Local Predictive Approach of the boiling crisis.

Degree: Docteur es, Energétique et transferts, 2009, INP Toulouse

EDF vise à développer une « Approche Prédictive Locale » de la crise d'ébullition, i.e. une approche permettant d'élaborer des prédicteurs (empiriques) de flux critique basés sur des paramètres locaux fournis par le code NEPTUNE_CFD (pour les seuls écoulements à bulle dans un premier temps). Dans ce cadre général, ce travail de thèse a consisté à évaluer la modélisation du code NEPTUNE_CFD, sélectionnée pour simuler les écoulements bouillants à bulles,puis à l'enrichir. Ce dernier objectif nous a conduits à nous intéresser à la modélisation mécaniste de l'ébullition nucléée sous-saturée en convection forcée. Après une analyse bibliographique critique, nous avons identifié des améliorations physiques, en particulier la prise en compte du glissement des bulles le long de la paroi chauffante. Cette voie a nécessité le développement d'une approche de type « bilan des forces » pour renseigner le diamètre de détachement des bulles de leur site actif de nucléation et le diamètre de décollage des bulles de la paroi. Un nouveau modèle d'ébullition nucléée a, pour finir, été proposé, en relation avec ces développements, et évalué de manière préliminaire.

EDF aims at developing a "Local Predictive Approach" of the boiling crisis for PWR core configurations, i.e. an approach resulting in (empirical) critical heat flux predictors based on local parameters provided by NEPTUNE_CFD code (for boiling bubbly flows, only in a first stage). Within this general framework, this PhD work consisted in assess one modelling of NEPTUNE_CFD code selected to simulate boiling bubble flows, then improve it. The latter objective led us to focus on the mechanistic modelling of subcooled nucleate boiling in forced convection. After a literature review, we identified physical improvements to be accounted for, especially with respect to bubble sliding phenomenon along the heated wall. Subsequently, we developed a force balance model in order to provide needed closure laws related to bubble detachment diameter from the nucleation site and lift-off bubble diameter from the wall. A new boiling model including such developments was eventually proposed, and preliminary assessed

Advisors/Committee Members: Colin, Catherine (thesis director).

Subjects/Keywords: Modélisation; Ebullition nucléée; Bilan des forces; Glissement; Diamètres; Détachement; Décollage; Bulle; Modelling; Nucleate boiling; Force balance; Sliding bubble; Detachment diameter; Lift-off diameter

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Montout, M. (2009). Contribution au développement d'une Approche Prédictive Locale de la crise d'ébullition : Contribution to the development of a Local Predictive Approach of the boiling crisis. (Doctoral Dissertation). INP Toulouse. Retrieved from http://www.theses.fr/2009INPT010H

Chicago Manual of Style (16th Edition):

Montout, Michaël. “Contribution au développement d'une Approche Prédictive Locale de la crise d'ébullition : Contribution to the development of a Local Predictive Approach of the boiling crisis.” 2009. Doctoral Dissertation, INP Toulouse. Accessed December 14, 2019. http://www.theses.fr/2009INPT010H.

MLA Handbook (7th Edition):

Montout, Michaël. “Contribution au développement d'une Approche Prédictive Locale de la crise d'ébullition : Contribution to the development of a Local Predictive Approach of the boiling crisis.” 2009. Web. 14 Dec 2019.

Vancouver:

Montout M. Contribution au développement d'une Approche Prédictive Locale de la crise d'ébullition : Contribution to the development of a Local Predictive Approach of the boiling crisis. [Internet] [Doctoral dissertation]. INP Toulouse; 2009. [cited 2019 Dec 14]. Available from: http://www.theses.fr/2009INPT010H.

Council of Science Editors:

Montout M. Contribution au développement d'une Approche Prédictive Locale de la crise d'ébullition : Contribution to the development of a Local Predictive Approach of the boiling crisis. [Doctoral Dissertation]. INP Toulouse; 2009. Available from: http://www.theses.fr/2009INPT010H

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