IMAGING
`
`TECHNOLOGIES
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`PROCEEDINGSOF
`THE SECOND INTERNATIONAL CONFERENCE
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`Sponsored by
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`Technical Council on Computer Practices
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`FOREWORD
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`
`
`Contents
`
`ference Participant.ssssssssssoccccssseecsesecsersseseecesnseeceesnmessessseceessoneeseeenssecsunessessnassesuassseeseae ix
`
`Submitted Papers
`Using Imaging Technologies in Experimental GeotechmicS.........cccsssecsssseeseesecensreeeneee
`-Henderickus GB. Allersma
`Measurement of Displacement Field by “Matching Method” and Observation
`Strain Localization in Soft ROCK ........cccssssssssessessssssscssssseseesnssssssassscansnesnennensenssesenesaneee LO
`- H.Horii, K. Takamatsu,J. Inoue, and N. Sasaki
`umerical Image Processing in Cetriftuge Testing........cssssscsssssssssrsssscssssnnrosenessnsnsnansessseees20
`Jean Charrier, Jean-Marc Moliard, and Jacques Garnier
`‘AnAttempt to Compare Image Processing and Stereophotogrammetry
`in, Geotechnical Centrifuge Models ........csssscccssssssssseceenssacenspassasesssnsassacessauscsnsereerdetensenenes30
`“* Pierre Chambon, Louis-Marie Cottineau, and Jacques Desrues
`*Determination ofVoid Fabric Tensor of Soils Without Radial Sampling Bias.........000.40
`. Balasingam Muhunthan and Eyad Masad
`
`
`
`
`
`
`
`Fourier Morphological Descriptors of Aggregate Profiles..........cscssssssssssassnssssecesenssssses76
`'
`Lin-Bing Wang, James S. Lai, and J. David Frost
`
`
`' Methods for Soil Characterization from Tages of Grain Assemblies.......ssccesseeseerrees88
`Roman D. Hryciw, Ali M. Ghalib, and Scott A. Raschke
`
`. Application of Digital Image Analysis for Size Distribution Measurements
`- OF Microbubbles...csssassssssssscsssssssensessseessesedsucsseeessisauserssseccursssrsarsesssaccanensersssesssesssesceaaes 106
`Susan E. Burns, Sotira Yiacoumi, J. David Frost, and Costas Tsouris
`
`cent Studies in Geotechnical Emage Amalysis.......:.cscscssesssrssassesssssssssacsessesssssssssssuserersnnes56
`“" D. Luo, X. Leng, X. Xue, A-E. Henderson, J. Cowan, J-E.S. Macleod, and
`“PB Smart
`Geo-Material Characterization Using Digital Micrograph Amalysis.....sssssssssssssssssseseireOO
`Dayakar Penumadu and Ian Hazen
`
`:
`
`A Model for Imaging Assisted Automation of Infrastructure Maintemance..............0+108
`Carl Haas, Young-Suk Kim, and Richard Greer
`
`Fuzzy Logic Distress Classifier for Pavement Emaging.........s.ssssccesscseseesessssstescscanonnsvesess148
`Gary R. Smith and Chien-Liang Lin
`Pavement Condition Assessment Using Ground Penetrating Radar.....sssssssssessssserverd 28
`Michael Heiler and Sue McNeil
`
`Segmentation Algorithm Using Iterative Clipping for Processing Noisy Pavement
`EMMAQES o..ccccscessennsunvensnsnensnencsevesnensstatasssseneasaeaesesediuaenesssssensarevessasseneneneaeaenssusssssasasasesssessensaansns 138
`
`

`

` SIZE DISTRIBUTION MEASUREMENTS OF MICROBUBELES
`
`101
`
`Application of Digital Image Analysis for Size Distribution
`Measurements of Microbubbles
`
`Susan E. Burns, Sotira Yiacoumi', J. David Frost’, and Costas Tsouris?
`
`This work employs digital image analysis to measure the size distribution of
`microbubbles generated by the process of electroflotation for use in solid/liquid
`separation processes. Microbubbles are used for separations in the mineral
`processing industry and also in the treatment of potable water and wastewater. As
`the bubbles move upward in a solid/liquid column due to buoyancy,particles collide
`with and attach to the bubbles and are carried to the surface of the column where they
`are removed by skimming. The removal efficiency of solids is strongly affected by
`the size of the bubbles. In general, higher separation is achieved by a smaller bubble
`The primary focus of this study was to characterize the size and size
`distribution of bubbles generated in electroflotation using image analysis. The study
`found that bubble diameter increased slightly as the current density applied to the
`system was increased. Additionally, electroflotation produces a uniform bubble size
`with narrow distribution which optimizes the removaloffine particles from solution,
`
`Many environmental and industrial treatment processes rely on the separation
`of solid particles from liquid solutions. Traditionally, solid particles are removed by
`sedimentation; however, sedimentation does not work well for low density particles
`like clay minerals, spores, and coagulated fulvic acids (Edzwaldet al., 1992; Malley
`and Edzwald, 1991; Letterman, 1987). As a result, a method known as flotation,
`which floats rather than sediments low density particles,
`is being used more
`In flotation, small gas bubbles are generated at the bottom of the water
`column to be treated. The microbubbles then tise to the surface of the liquid through
`buoyancy. As the bubbles rise, they collide with and adsorb to particles in the
`
`~ solution; consequently, the low density solids are floated to the top of the column for
`removal by skimming. The process offlotation is known as dissolved air flotation if
`the microbubbles are produced by pressurizing air into water, as dispersed air
`flotation if the bubbles are produced by forcing gas through a Sparger, and as
`electroflotation if the bubbles are produced through the electrolysis of water. This
`-, study will focus on bubbles generated by electroflotation,
`
`Electroflotation has been used by the mineral processing industry for the
`recovery of mineral particles (Ketkar et al., 1991), and in environmental and
`industrial processes for the separation ofoil from oil/water emulsions (Hosny, 1992;
`Balmer and Foulds, 1986), and for the removal of coagulated heavy metals from
`‘. solution (Srinivasan and Subbaiyan, 1989: Ramadorai and Hanten, 1986).
`In all of
`these applications, the removal efficiency is sttongly affected by the size of the
`generated bubbles. Smaller bubbles have a longerresidence time in the system, have
`a larger surface area, and are more likely to adhere to solids after a collision (de Rijk
`Set al., 1994). Consequently, the treatment process is optimized by generating the
`smallest diameter bubbles possible.
`
`This paper examines the effect of the process variables of voltage, current,
`” ‘and ionic strength on the size of the bubbles generated during electroflotation.
`Bubble images were recorded with a long-distance, high-magnification microscope,
`and were printed and imported into a digital image analysis system for measurement
`of equivalent bubble diameter. The average equivalent circular diameter for was
`calculated for each experimental condition; additionally, the volume distribution of
`the bubbles wascalculated for each experiment.
`
`Experimental
`
`The rectangular test cell used in the experiments ofthis study was made of
`Plexiglas with dimensions of 58.4 cm by 7.6 cm by 2.5 cm.
`Inflow and outflow
`ports were drilled in the top and bottom ofthe cell and it was mounted vertically in
`order to allow gas flow out the top. After the cell was filled with the test solution, a
`soap-film flow meter was attached to one outflow port to measure gas flow rate and
`the remaining outflow ports were sealed. The electrodes used in the experiments
`were polished graphite electrodes (7.6 cm by 2.5 cm by 1.3 cm) and were mounted at
`the bottom ofthe cell with a separation of 13 cm. Electrical leads were attached to
`the electrodes using conductive epoxy, and then connected to an external power
`-
`supply.
`
`
`" Graduate Research Assistant and Associate Professors, respectively, Georgia Institute of
`
`Twenty eight experiments were performed using aqueous solutions of
`
`

`

`distance microscope with a magnification of approximately 230 times attached to a
`video camera, monitor, and VCR. The calibration factor was a wire of known
`diameter. The experiments performed at 0.001 M did not produce a significant gas
`flow rate; consequently, only the results for the experiments performed at 0.1 and
`0.01 M are reported in this paper.
`where # = sample size, Z,/7
`=
`i
`=
`+
`ai
`ron «/2=confidence interval, o = standard deviation, and E =p
`
`
`The gas bubbles producedin electroflotation form through the electrolysis of
`water by the following redox reactions:
`
`n=(Ze|E
`
`?
`
`Results
`
`
`
`IMAGING TECHNOLOGIES
`
`H,O->2H* +60, (g)+2e7
`2H,0+2e° >20H” +H,(g)
`
`Anode(+)
`Cathode(—)
`
`The oxygen and hydrogen gas dissolve into the liquid surrounding the electrodes;
`when the liquid becomes supersaturated with gas, bubbles begin to form on the
`electrode surface (Verhaart et al., 1980). The camera was focused on the bottom
`electrode in the test cell and two experiments were performed at cach power level. In
`the first experiment,
`the bottom electrode was the anode, and in the second
`experiment the electrical
`leads were reversed making the bottom electrode the
`cathode. This configuration was used because it prevented the mixing of oxygen and
`hydrogen bubbles during videotaping. A light source was set up behind the cell to
`produce contrast between the bubbles and the solution in the recorded images.
`
`Image Processing and Analysis
`
`After the experiments were completed, the images were printed to hard copy
`using a video copy processor and imported into a Quantimet Q570 Digital Image
`Processor. The printed images were gray-scale pictures of dark bubbles on a light
`background because the light source behind the cell was blocked by the bubbles but
`passed through the aqueous solution. After the images were acquired by the image
`processor, they were converted from gray-scale into digital images and a minimal
`amount of image processing was performed.
`In someinstances, background noise
`ocewred on the images and was erased. Additionally, sometimes two bubbles*
`touched each other on the images. In this case, the bubbles were either separated and
`analyzed individually, or were eliminated from the image. No other
`image
`processing was performed on the bubble pictures. Because not all of the bubbies
`were citcular in cross-section, the image analyzer measured the area of each bubble
`and converted that to an equivalent circular diameter for the output.
`
`A statically valid sample size was chosen for analysis by first determining the
`error in the measurement. Measurements of one experiment were performed twice
`
`
`
`103
`
`(1)
`
`
`
`di
`Figure 1 showsa plot of the equivalent circular
`x diameter of oxygen bubbles
`as a function of current density. The figure shows a trend of slightly increasing
`'. bubble diameter with increasing current density applied to the system. This is
`conststent with other electroflotation results using metallic electrodes (Brandon
`and
`Kelsall, 1985; Janssen and Hoogland, 1973: Landolt et al., 1970), The formationof
`bubbles in electroflotation is an inhomogeneous, or sutface controlled process vathe
`than a homogeneous process where the bubbles form out of solution without the
`presence of a surface. Previous research has found that bubbles will form at the
`location of scratches and pits on the electrode surface (Janssen and Hoogland 1973,
`Glas and Westwater, 1964) which illustrates the importance of the surf
`characteristics of the electrodes.
`In this study, the electrodes were not polished
`_ between successive experiments which most likely explains the scatter seen in the
`average bubble diameter measurements, because the application of current wil! affect
`the surface characteristics of the electrode, Average oxygen and hydrogen bubble
`diameters measured in the experiments ranged from 17.1 to 37.9 um, which is
`consistent with the size of bubbles produced on stainless steel and platinum
`‘electrodes (Ketkar et al., 1991).
`
`Diameter
`AverageBubble
`
`
`0
`
`20
`
`40
`
`60
`
`80
`
`100
`
`

`

`IMAGING TECHNOLOGIES
`
`No clear trends in bubble size were seen as a function of voltage or as a
`function of ionic strength; however,
`the volume of gas generated was a strong
`function of both powerinput to the system and of ionic strength of the surrounding
`medium. As would be expected,
`the generation of hydrogen and oxygen gas
`increased as both the power input to the system was increased and as the ionic
`strength of the aqueous medium was increased.
`
`The volume distribution of the generated bubbles was also plotted for
`comparison between the experimental conditions. Figures 2 and 3 show the volume
`
`1.0
`
`0.8
`
`0.6
`
`0.4
`
`0.2
`
`SIZE DISTRIBUTION MEASUREMENTS OF MICROBUBBLES
`
`105
`
`distribution of both the oxygen and hydrogen bubbles produced at ionic strengths of
`0.1 and 0.01 M and at powerlevels ranging from 0.255 to 2.070 W. Thedistribution
`plots show that electroflotation produces bubbles with fairly uniform diameters. The
`most common range in bubble diameters is approximately 60 tm, which is a rather
`narrow distribution for flotation methods. Additionally, the majority of the bubbles
`produced have diameters smaller than 50 jim which increases the removal efficienc
`of fine particles from the solution. However, as was seen with average bubble
`diameter, no distinct trends in the distribution are seen as functions ofeither power or
`lonic strength.
`
`
`
` Figure 2(b). Cumulative volume distribution for oxygen bubbles: i = 9.1 M.
`
`0
`
`50
`
`400
`
`450
`
`0
`
`Bubble Diameter (um)
`
`Figure 2(a). Cumulative volume distribution for hydrogen bubbles: I = 0.1 M.
`
`
`
`CumulativeVolume
`
`
`
`CumulativeVolume
`
`Distribution
`
`150
`
`100
`
`50
`
`Bubble Diameter(11m)
`
`0
`
`Distribution
`Distribution 0.0|ennsthetin
`
`CumulativeVolume
`CumulativeVolume
`
`Distribution
`0.0
`
`100
`50
`Bubbie Diameter(:m)
`
`150
`
`1.0
`
`0.8
`
`0.6
`
`0.4
`
`0.2
`
`0
`
`100
`50
`Bubble Diameter(um)
`
`150
`
`

`

`SIZE DISTRIBUTION MEASUREMENTS OF MICROBUBBLES
`
`107
`
`es, Jnfernati
`
`E
`
`i
`
`etterman, R.D, (1987). An Overview of Filtration, Journal
`
`onventional
`
`Treatment, Journal of
`
`the Ameri
`
`lati
`
`oO
`
`uents
`
`tati
`
`i
`
`j
`
`j
`
`i
`
`
`
`IMAGING TECHNOLOGIES
`
`image analysis provided an efficient method for measuring the
`average equivalent diameter of microbubbles produced by electroflotation. The use
`of automated measuring processes allowed for the rapid determination of bubble size
`and eliminated the measurement errors which can occur in manual measurements.
`Because the measurement process is faster using an image analyzer than manual
`measurements, a larger sample space can be used and/or more experiments can be
`performed allowing for more complete data sets.
`In these experiments, the average bubbie diameter increased as the current
`density applied to the system was increased, No trends were identified in bubble
`diameter as a function of either power or ionic strength of the aqueous medium;
`however, gas flow rate increased as both power and ionic strength were increased.
`The volume distribution of the generated bubbles showed that electrofletation
`produces bubbles with fairly uniform diameters and narrow ranges. Again, no trends
`were identified in distribution as functions ofeither power or ionic strength.
`
`Acknowledgmenis
`The authors thank Ken Thomasfor his assistance with equipment preparation.
`Partial financial support from the Division of Chemical Sciences, Office of Energy
`Sciences, US Department of Energy, under contract DE-AC05-960R22464 with
`Lockheed Martin Energy Research Corp., is gratefully acknowledged.
`
`©
`
`from Oil-in-Water
`(1986). Separating Oil
`Balmer, L. M. and Foulds, A. W.
`Emulsions by Ftectroflocculation/Electroflotation, Filiration and Separation,
`Vol. 6, pp. 366-370.
`.
`Brandon, N.P.
`and Kelsall, GH.
`(1985). Growth Kinetics of Bubbles
`Electrogenerated at Microelectrodes, Journal of Applied Electrochemistry,
`Vol. 15, pp. 475-484.
`pe Rijk, 5.E, VAN DER Graaf, HM., and pen Blanken (1994). Bubble Size in
`Flotation Thickening, Water Research, Vol. 28, No. 2, pp. 465-473.
`Edzwald, J.K., Walsh, J.P., Kaminski, G.S., and Dunn, HJ. (1992). Flocculation and -
`Air Requirements for Dissolved Air Flotation, Journal ofthe American Water
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`Glas, J.P. and Westwater, J.W. (1964). Measurement of the Growth of Electrolytic:
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`Bubbles, International Journal ofHeat and Mass Transfer, Vol. 7, pp. 1427
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`
`from Oil/Water Emulsions Using and
`(1992). Separation of Oil
`Hosny, A.Y.
`itrati
`Electroflotation Cell
`wi
`WoL Sp Taos with Insoluble Electrodes, Filtration and Separation,
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`Janssen, L. J. J. and Hoogland, J. G. (1973). The Effect of Electrolytically Evolved
`Gas Bubbles on the Thickness of the Diffusi
`imi
`tera, VoL 18, yp. 843-550,
`sion Layer - Il, Electrochimica
`
`
`. seeareaerTunan. R., ae Venkatachalam, 8. (1991). Electroflotation of
`qu
`ational Journal ofMineral Processing, Vol. 31, pp. 127-
`
`
`Landolt, D., Acosta, R., Muller, R.H., and Tobias, C.W. (1970). An Optical Study of
`Cathodic Hydrogen Evolution in High-Rate Electrolysis, Journal of the
`
`L
`Electrochemical Society, Vol. 117, No. 6, pp. 839-845
`
`Works Association, Vol. 12, pp. 26-32.
`_Hournal ofhe American Water
`
`: Malley,JP. ane iowa JK.
`(1991). Laboratory Comparison of DAF with
`:
`Vol. 8 pp 36-61
`if
`rican Water Works Association,
`
`
`: Ramadoral,G.an faten|. P. (1986). Removal ofMolybdenum and Heavy Metals
`aid9-134
`y
`Flotation, Minerals and Metallurgical Processing, August,
`
`
`S. Srinivasen Vv. and Subbaiyan, M. (1989). Electroflotation Studies on Cu, Ni, Zn, and
`with Ammonium Dodecyl Dithiocarbamate, Separation Science and
`
`Technology, Vol. 24, No. 1&2, pp. 145-150.
`- Verhaart, H.F.A., pe Jonge, R.M., and van Straten, S.1.D. (1980). Growth Rate of a
`Gas Bubble During Electrolysis
`i
`iqui
`ysis in Supersaturated Liquid,
`Jnr
`j
`Journal ofHeat andMass Transfer, Vol. 23, pp. 293-299.
`pi Nernaiones
`
`
`
`