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You searched for subject:(bubble surface flux). Showing records 1 – 3 of 3 total matches.

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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 (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 February 24, 2020. 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. 24 Feb 2020.

Vancouver:

Sarkar MSKA. Electroflotation: its application to water treatment and mineral processing. [Internet] [Doctoral dissertation]. University of Newcastle; 2012. [cited 2020 Feb 24]. 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


University of Lund

2. Cao, Zhen. Pool Boiling on Structured Surfaces: Heat Transfer and Critical Heat Flux : -Experiments and Mechanistic Modelling.

Degree: 2019, University of Lund

In this thesis, pool boiling heat transfer was experimentally studied on structured surfaces with dielectric liquids (HFE-7200, NOVEC-649, FC-72), organic liquids (Acetone, Pentane) and deionized water.In the first step, nanoparticle coatings on copper surfaces were prepared by an electrophoretic deposition method, with Cu-Zn nanoparticles (100 nm) and Cu nanoparticles (150 nm). Two types of nanoparticle-coating surfaces were prepared, namely nanoparticle coatings uniformly deposited on smooth surfaces and nanoparticle coatings partially deposited on smoothsurfaces. Pool boiling of HFE-7200 and acetone was tested on the coating surfaces. It is found that pool boiling heat transfer coefficients are significantly enhanced by nanoparticle coatings. However, the uniform coating cannot enhance the critical heat flux, while the partially-deposited coating can enhance critical heat flux. Mechanistic heat transfer models were developed to predict the heat transfer coefficients, considering natural convection, transient heat conduction, microlayer evaporation and micro convection, while the critical heat flux was analyzed from the point of wickability and hydrodynamic instability.In the following step, microporous coatings on copper surfaces were generated by an electrochemical deposition method, with electrolyte solutions (CuSO4+H2SO4). Pool boiling of HFE-7200, NOVEC-649 and water was tested. The results show that heat transfer coefficients and critical heat flux are enhanced, and the heat transfer coefficients are obviously dependent on deposition-relevant parameters, like deposition time and electrolyte concentration. Heat transfer coefficients were discussed mechanistically and empirically by a mechanistic model and correlations, while the critical heat flux was predicted by a modified force balance model which considers the forces exerted on vapor and assumes occurrence of the critical heat flux when the vapor expands on surfaces.Finally, hybrid micro/nano structures were fabricated on copper surfaces by femtosecond laser machining and electrophoretic deposition, and on silicon wafers by dry etching and electrostatic deposition. Pool boiling of acetone and FC-72 was investigated on the copper surfaces and the silicon wafers, respectively. It is found that the hybrid structures induce higher heat transfer coefficients than sole structures and wickability plays an important role on enhancement of the critical heat flux.

Subjects/Keywords: pool boiling; heat transfer; critical heat flux; bubble dynamics; surface modification

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

APA (6th Edition):

Cao, Z. (2019). Pool Boiling on Structured Surfaces: Heat Transfer and Critical Heat Flux : -Experiments and Mechanistic Modelling. (Doctoral Dissertation). University of Lund. Retrieved from https://lup.lub.lu.se/record/4476ab29-a1b6-41e6-9446-771360de710c ; https://portal.research.lu.se/ws/files/70150598/Thesis_Zhen.pdf

Chicago Manual of Style (16th Edition):

Cao, Zhen. “Pool Boiling on Structured Surfaces: Heat Transfer and Critical Heat Flux : -Experiments and Mechanistic Modelling.” 2019. Doctoral Dissertation, University of Lund. Accessed February 24, 2020. https://lup.lub.lu.se/record/4476ab29-a1b6-41e6-9446-771360de710c ; https://portal.research.lu.se/ws/files/70150598/Thesis_Zhen.pdf.

MLA Handbook (7th Edition):

Cao, Zhen. “Pool Boiling on Structured Surfaces: Heat Transfer and Critical Heat Flux : -Experiments and Mechanistic Modelling.” 2019. Web. 24 Feb 2020.

Vancouver:

Cao Z. Pool Boiling on Structured Surfaces: Heat Transfer and Critical Heat Flux : -Experiments and Mechanistic Modelling. [Internet] [Doctoral dissertation]. University of Lund; 2019. [cited 2020 Feb 24]. Available from: https://lup.lub.lu.se/record/4476ab29-a1b6-41e6-9446-771360de710c ; https://portal.research.lu.se/ws/files/70150598/Thesis_Zhen.pdf.

Council of Science Editors:

Cao Z. Pool Boiling on Structured Surfaces: Heat Transfer and Critical Heat Flux : -Experiments and Mechanistic Modelling. [Doctoral Dissertation]. University of Lund; 2019. Available from: https://lup.lub.lu.se/record/4476ab29-a1b6-41e6-9446-771360de710c ; https://portal.research.lu.se/ws/files/70150598/Thesis_Zhen.pdf


University of Newcastle

3. Jiang, Kaiqi. Fast flotation in a reflux flotation cell.

Degree: PhD, 2017, University of Newcastle

Research Doctorate - Doctor of Philosophy (PhD)

The research undertaken in this study was based on a novel flotation device, the Reflux Flotation Cell (RFC). This system consists of multiple parallel inclined channels positioned below a vertical chamber. The inclined channels provide an effective increase in the cross-sectional area of the vessel, thus permitting enhanced bubble-liquid segregation efficiency when the bubbles are conveyed into the inclined channels. In this thesis, fast flotation is defined as simultaneously maximising three fundamental flotation aspects: the kinetics for particle collection by bubbles, the supply of bubble surface area flux for particle extraction, and the segregation of the fine bubbles from the tailings flow. Only one or two aspects can be addressed effectively using conventional flotation systems, hence those systems are constrained by the rate limiting aspect. The RFC, however, offers the potential to achieve increases in all three areas, meaning the concept of Fast Flotation can be achieved, delivering very high flotation rates per unit of vessel area. The study firstly addressed the hydrodynamics of the RFC. Drift flux theory was used to describe the performance of the conventional vertical flotation column, predicting the theoretical gas flux, liquid flux, and the bubble surface area flux under the flooding condition. The capacity advantage, developed from the Reflux Classifier to describe the enhanced processing rate using inclined channels, is utilised to estimate the enhancement of bubble surface area flux. The theory showed the bubble surface area flux of the RFC could be increased to well beyond the typical levels of conventional flotation systems under flooding condition. A series of experiments was conducted using the laboratory RFC based on the bubble-liquid system. The experimental work achieved a bubble surface area flux of about 600 m²/m²/s, more than an order of magnitude larger than achieved in conventional flotation. Another series of experiments, having the same operating conditions as in the RFC system, involved the use of a vertical column. Extreme gas fluxes of up to 5.5 cm/s, and feed fluxes of up to 16 cm/s were applied, significantly higher than the conventional operating ranges. The results showed the inclined channels greatly enhanced the bubble-liquid segregation, preserving the fraction of feed liquid reporting to overflow to well below 24%. By comparison, 50% to 80% of the feed liquid was conveyed to the overflow using the vertical column, driven by the need to prevent bubbles reporting to the underflow, thus exhibiting very inefficient segregation. Hydrodynamic investigation of the RFC system showed great potential to achieve fast flotation. Thus the second part of the study involved the processing of low pulp density fine coal slurries collected from the overflow of the hydrocyclone in a coal preparation plant. Three slurry pulp densities of 0.34 wt%, 3.0 wt%, and 5.2 wt% were processed. Very high feed fluxes in the range of 10 to 12 cm/s, more…

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

Subjects/Keywords: flotation; bubble surface flux; fine particle flotation; fast flotation; desliming flotation; coal tailing; inclined channels; segregation; reflux flotation cell; flotation kinetics; bubble–liquid segregation; bubble interfacial flux; inclined channels; coal

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

APA (6th Edition):

Jiang, K. (2017). Fast flotation in a reflux flotation cell. (Doctoral Dissertation). University of Newcastle. Retrieved from http://hdl.handle.net/1959.13/1342434

Chicago Manual of Style (16th Edition):

Jiang, Kaiqi. “Fast flotation in a reflux flotation cell.” 2017. Doctoral Dissertation, University of Newcastle. Accessed February 24, 2020. http://hdl.handle.net/1959.13/1342434.

MLA Handbook (7th Edition):

Jiang, Kaiqi. “Fast flotation in a reflux flotation cell.” 2017. Web. 24 Feb 2020.

Vancouver:

Jiang K. Fast flotation in a reflux flotation cell. [Internet] [Doctoral dissertation]. University of Newcastle; 2017. [cited 2020 Feb 24]. Available from: http://hdl.handle.net/1959.13/1342434.

Council of Science Editors:

Jiang K. Fast flotation in a reflux flotation cell. [Doctoral Dissertation]. University of Newcastle; 2017. Available from: http://hdl.handle.net/1959.13/1342434

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