Paul Mavros - Profile on Academia.edu (original) (raw)

Papers by Paul Mavros

Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2014

This article appeared in a journal published by Elsevier. The attached copy is furnished to the a... more This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/authorsrights

Chemical engineering research & design, Nov 1, 1997

A n agitation index, based on velocity measurem ents obtained from laser Doppler velocimetry or o... more A n agitation index, based on velocity measurem ents obtained from laser Doppler velocimetry or other sim ilar techniques, is proposed as an objective m easure of the effectiveness of a particular agitator in inducing¯ow in a stirred vessel. This index is calcul ated by ® rst generating a cell structure based on the measurem ent grid, and then assigning each velocity to the entire correspondin g cell; the volum e-weighted sum of velocities yields then the agitation index, which represents the volume-average velocity as a percentage of the im peller tip velocity. The usefulness of this objective measure of the quality of agitation in a stirred vessel is illustrated by applying it ® rst to the case where three different agitators have to be graded in term s of effectiveness in inducing¯ow , and then to the case of determining the clearance of two agitators located on the same shaft correspondin g to the optim um liquid circulation.

Internal Recirculation and Mixing in Flotation Columns

Chemical Engineering Research & Design, 1995

The effect of column height and internal baffling on the mixing of the liquid phase inside the co... more The effect of column height and internal baffling on the mixing of the liquid phase inside the collection zone of flotation columns was investigated by RTD and the mixed cells-in-series-with-backflow and the axial dispersion models were used to interpret the experimental results. The increase in column height subtly affected the mixing process, by influencing the transition from plug-flow-like to mixed flow conditions. The backflow was calculated in all cases as approximately 10% of the net incoming liquid flow, and 4 to 14 perfectly mixed cells were found to represent the collection zone liquid-phase RTDs, with the higher number of cells corresponding to high liquid and low gas flowrates. Vertical baffles were found to enhance rather than attenuate the collection zone mixing

Structured stochastic flow model for interpreting flow-follower data from a stirred vessel

Minerals Engineering, Nov 1, 1993

A mixed zones-in-series model, allowing for backflow between adjacent zones, has been used to des... more A mixed zones-in-series model, allowing for backflow between adjacent zones, has been used to describe the flow structure established in the collection zone of a flotation column. Experimental residence time distribution data were used to quantify the baclfllow parameter (2), using the tracer breakthrough time," this parameter was shown to depend essentially only on the supeoqcial liquid velocity and the column diameter (d c) and the following correlation was obtained : /l = 0.347 exp(O.303dc) uL-(O'S30+O'O348dO. The circulation velocity of the additional circulatory flow induced by the gas stream was also determined," the experimental results were well corroborated by predictions using theoretical axial velocity models.

Colour removal from aqueous solutions. Part I. Flotation

Environmental Technology, Jul 1, 1994

The removal of colours from aqueous solutions and/or dispersions has been studied by dispersed‐ai... more The removal of colours from aqueous solutions and/or dispersions has been studied by dispersed‐air flotation, in a semi‐batch flotation column. Three colours were used for the experiments: Basic Yellow 28 (acidic), Direct Black 22 (basic) and Disperse Orange 30 (dispersion colour). All three were effectively removed by flotation within 15 to 30 min. Sodium lauryl sulfate and dodecylamine were found to be effective as collectors in the removal of colour, which was also found to be related to the pH of the solution and the amount of collector added to it, with high collector dosages causing the process to become pH‐independent.

Analysis of unsteady tracer dispersion and mixing in a stirred vessel using interconnected networks of ideal flow zones

Minerals Engineering, Dec 1, 1993

Arsenic-rich, gold-bearing pyrite concentrates may be further enriched in arsenic W assist subseq... more Arsenic-rich, gold-bearing pyrite concentrates may be further enriched in arsenic W assist subsequent Au beneficiation. Among several amines tested in refloating a local Chalkidiki pyrite concentrate, 2-coco 2-methyl ammonium chloride proved successful by raising the grade from 9% to 22%, although total solids recovery was low. The use of a frothstabilizing frother was also beneficial to the process. Optimum hydrodynamic conditions were : intermediate pulp fiowrate, low wash water and gas flowrate; the latter abated the mixing~dispersion process in the collection zone.

Chemical engineering research & design, 2005

Chemical engineering, a highly intellectual scientific discipline, is changing. While a large num... more Chemical engineering, a highly intellectual scientific discipline, is changing. While a large number of processes are well established, optimized and standardized, new needs have to be addressed. A summary of the new challenges and pressures faced by chemical engineering research is presented here. '. .. a form of sustainable development which meets the needs of the present without compromising the ability of future generations to meet their own needs'.

Mixing and Hydrodynamics in Flotation Cells

Springer eBooks, 1992

Industrial & Engineering Chemistry Research, May 19, 2006

The hydrodynamics of a continuous-flow stirred tank reactor (CFSTR) have been studied through RTD... more The hydrodynamics of a continuous-flow stirred tank reactor (CFSTR) have been studied through RTD measurements, visual tracing, and CFD simulations, for an axial-flow and two radial-flow impellers (Mixel TT and Rushton and NS turbines), to investigate how the combination of impeller choice and operating conditions (flow rates, agitator speed) affect the vessel hydrodynamics and flow nonideality. The portion of the total vessel volume being perfectly mixed decreases considerably as the vessel utilization is forced by decreasing the vessel retention time; at the same time the amount of feed bypassing/short-circuiting increases, too, especially in the case of axial-flow impellers. Qualitative and quantitative results are obtained, leading to conclusions about the suitability of particular impeller-vessel configuration combinations.

Minerals Engineering, Jul 1, 1993

The dispersion number, characterising mixing, has been determined in flotation columns of interna... more The dispersion number, characterising mixing, has been determined in flotation columns of internal diameters varying from 2.5 to 11.0 cm; results are compared with literature data and a correlation : Nd = 0.0194 exp(0.267 dc) UL "0.56 (uL superficial liquid velocity) was found to correlate satisfactorily all data for columns having diameters less than 14 cm, for superficial gas and liquid velocities in the usual flotation column range (0.5-3.o cm/s). Keywords Flotation column, dispersion number, axial dispersion. * The term "flotation" rather than "bubble" column implies that some of the features of the column (e.g. gas sparger) and the operating conditions (superficial gas and liquid velocities) are those pertaining to flotation rather than bubble columns.

The experimental and computational techniques available lately have yielded a large amount of inf... more The experimental and computational techniques available lately have yielded a large amount of information regarding the flow conditions in stirred vessels; it is widely accepted nowadays that the characteristics of the solid products of the reactions occurring in stirred vessels, e.g. size distribution, porosity, specific surface area, among others, are affected by the turbulent conditions in them [ 1 ]. Thus, it becomes important to understand the way that various mixing process parameters, like the type of impeller used, the location and rate of addition of the various reactants etc. affect the morphology of the solid particles. Ideally, we would like to be able eventually to choose the appropriate mixing vessel configuration and operating conditions to obtain a particulate material with predefined properties.

Water Encyclopedia , Oct 15, 2005

Mixing is one of the primary processes involved in water and wastewater treatment. In this articl... more Mixing is one of the primary processes involved in water and wastewater treatment. In this article, the state of the art in mixing and impeller design is presented.

International Journal of Mineral Processing, May 1, 1993

Arsenopyrite has been selectively floated from pyrite by an unconventional amonic collector (sodr... more Arsenopyrite has been selectively floated from pyrite by an unconventional amonic collector (sodram dodecylsulphonate), at the pH range of about 4. The floatablllty expenments were conducted mainly in a Halhmond cell with an industrial auriferous bulk pyrite-arsenopynte concentrate. The addition of permanganate, a common oxidizing agent, enhanced the selectivity of the process; the system was also studied by electroloneUc measurements. The separation was further enhanced by the use of methyl isobutylketone as a frother A synergtsm ofiomc and non-ionic surfactant was apparent, causing meanwhde a decrease m reagents consumption

Recovery of Co²⁺Ions from Aqueous Solutions by Froth Flotation. Part II. CoS Precipitation

Separation Science and Technology, 1995

Canadian Journal of Chemical Engineering, May 19, 2008

Chemical engineering research & design, 2011

The analysis of velocity data in a stirred vessel, obtained experimentally in this work by laser ... more The analysis of velocity data in a stirred vessel, obtained experimentally in this work by laser Doppler velocimetry, as well as from the literature, shows that the dissolution of a surfactant with a long alkyl chain-in this work, hexadecyl trimethyl ammonium bromide-and a counter ion with an aromatic group-in this work, sodium salicylate-can modify the mean and r.m.s. velocities of the liquid, a phenomenon similar to the drag reduction observed in tubular flows. The magnitude and importance of this effect depend on the concentration of the surfactant-counterion mixture and on the localization of the element of fluid in the vessel, i.e., in a zone close to the impeller or farther away from it, but not in a monotonic fashion.

International Journal of Mineral Processing, Jun 1, 1989

The mixing process of the liquid phase in a gas-liquid flotation column and the effect of the flo... more The mixing process of the liquid phase in a gas-liquid flotation column and the effect of the flowrates on it have been investigated. The increase of the gas and liquid flowrates had opposite effects: the former enhanced the mixing process, whereas the latter caused the behaviour of the column to approach plug flow. A mixed zones-in-series model is proposed for interpreting the experimental results, which involves two parameters: the number of zones and the ratio of backwards to net liquid flow. In this way, the mixing was related to the backflow and the increase in mixing was due to an intense internal recirculation. The model was able to predict accurately the column behaviour in the experimental range investigated. Its major advantage lies in its structured description of the column contents.

A New Hybrid Flotation—Microfiltration Cell

Separation Science and Technology, Oct 1, 2006