Hemaka Bandulasena | Loughborough University (original) (raw)
Papers by Hemaka Bandulasena
Industrial & Engineering Chemistry Research, Sep 16, 2021
Emulsions formed by mixing reactant streams inside microdroplets are efficient micro-scale reacto... more Emulsions formed by mixing reactant streams inside microdroplets are efficient micro-scale reactors for synthesis of nano/micro-particles/crystals due to small quantities of reagents confined within each droplet and separation of droplet contents from the reactor walls. In this work, the synthesis of size-tuneable gold nanoparticles (AuNPs) within emulsion droplets generated in a three-phase glass capillary microfluidic device was investigated experimentally and numerically using computational fluid dynamics (CFD). AuNPs were produced by micromixing two aqueous streams, 1.15 mM HAuCl4 containing 1% polyvinylpyrrolidone capping agent and 20 mM ascorbic acid solutions, inside monodispersed droplets created by 3D counter-current flow focusing in a medium-chain triglyceride. The mean particle size of AuNPs was tuneable in the range between 26 and 56 nm and depended on the degree of premixing of the reactant streams shortly before droplet generation, and the mixing efficiency within droplets, which was controlled by hydrodynamic conditions within the microfluidic device. The CFD results were compared and validated against experimental observations and revealed the presence of a recirculation zone near the outer wall of the injection capillary tip. The mixing efficiency was higher at smaller droplet size causing a reduction in the particle size of the AuNPs.
Langmuir, May 12, 2022
Liquid foams are highly complex systems consisting of gas bubbles trapped within a solution of su... more Liquid foams are highly complex systems consisting of gas bubbles trapped within a solution of surfactant. Electroosmotic effects may be employed to induce fluid flows within the foam structure and impact its stability. The impact of external electric fields on the stability of a horizontally oriented monolayer of foam (2D foam) composed of anionic, cationic, nonionic, and zwitterionic surfactants was investigated, probing the effects of changing the gas−liquid and solid−liquid interfaces. Time-lapse recordings were analyzed to investigate the evolution of foam over time subject to varying electric field strengths. Numerical simulations of electroosmotic flow of the same system were performed using the finite element method. Foam stability was affected by the presence of an external electric field in all cases and depended on the surfactant type, strength of the electric field, and the solid material used to construct the foam cell. For the myristyltrimethylammonium bromide (MTAB) foam in a glass cell, the time to collapse 50% of the foam was increased from ∼25 min under no electric field to ∼85 min under an electric field strength of 2000 V/m. In comparison, all other surfactants trialed exhibited faster foam collapse under external electric fields. Numerical simulations provided insight as to how different zeta potentials at the gas−liquid and solid−liquid interfaces affect fluid flow in different elements of the foam structure under external electric fields, leading to a more stable or unstable foam.
This is a poster presented at the Joint Conference of COST ACTIONS TD1208 “Electrical discharges ... more This is a poster presented at the Joint Conference of COST ACTIONS TD1208 “Electrical discharges with liquids for future applications” & MP1101 Biomedical Applications of Atmospheric Pressure Plasma Technology
Langmuir, Jan 19, 2020
Electrokinetic transport of a charged dye within a free liquid film stabilized by a cationic surf... more Electrokinetic transport of a charged dye within a free liquid film stabilized by a cationic surfactant, trimethyl-(tetradecyl)ammonium bromide, subjected to an external electric field was investigated. Confocal laser scanning microscopy was used to visualize fluorescein isothiocyanate (FITC) separation within the stabilized liquid film. Numerical simulations were performed using the finite element method to model the dynamics of charged dye separation fronts observed in the experiments. Because of the electrochemical reactions at the electrodes, significant spatial and temporal pH changes were observed within the liquid film. These local pH changes could affect the local zeta potential at the gas−liquid and solid−liquid film boundaries; hence, the flow field was found to be highly dynamic and complex. The charged dye (FITC) used in the experiments is pH-sensitive, and therefore, electrophoresis of the dye also depended on the local pH. The pH and the electroosmotic flow field predicted from the numerical simulations were useful for understanding charged dye separation near both the anode and the cathode.
The flow field within a free liquid film under an applied external electric field was measured us... more The flow field within a free liquid film under an applied external electric field was measured using confocal micro-PIV system. Free liquid films of thickness ∼ 200 μm were formed in a rectangular frame with electrodes in direct contact with the fluid and stabilised by cationic surfactant. The flow field induced by an external electric field of ∼1600 V/m was visualised using 2 μm tracer particles on several depth wise planes. The observed particle velocities were used to determine the fluid velocities within the film by accounting for the electrophoresis of the tracer particles.
Industrial & Engineering Chemistry Research, 2020
Product inhibition and the cost of downstream separations are two main barriers in using lignocel... more Product inhibition and the cost of downstream separations are two main barriers in using lignocellulosic biomass for bioethanol production. If bioethanol can be continuously removed from fermentation broth without affecting the fermentation process, significant gains can be achieved with bioethanol yields and process efficiency. Hot microbubble clouds generated by energy efficient means have been used to remove ethanol from dilute ethanol−water mixtures (∼4% [v/v]) maintained at 60°C, and the effect of key operating parameters on the stripping rate has been studied. Numerical simulations of a hot microbubble rising in a dilute ethanol−water mixture were also performed to understand the instantaneous concentrations within the gas phase. Increasing the inlet gas temperature from 90 to 150°C and decreasing the liquid height in the unit from 50 to 5 mm both increased the ethanol stripping rate. However, the benefit of increasing the gas temperature for maximum ethanol removal depended on the liquid height in the unit. Under all operating conditions, ethanol concentration was reduced below ∼2% [v/v] within ∼25 min of operation, demonstrating the potential of hot microbubble stripping for product removal from lignocellulosic fermenters. Implemented effectively in a fermenter, this technology could intensify the bioethanol production process and improve process economics.
Colloids and interfaces, May 4, 2023
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
Chemical Engineering Science, 2021
Novel organic synthesis routes that circumvent the need for a catalyst and reduce unwanted by-pro... more Novel organic synthesis routes that circumvent the need for a catalyst and reduce unwanted by-products are highly sought by industry. A novel microfluidic plasma reactor that generates a dielectric barrier discharge (DBD) plasma in the vicinity of the gas-liquid interface and facilitate a chemical reaction at the interface of microbubbles has been used for transstilbene epoxidation. Three different operating strategies were implemented to optimise the transfer of species selectivity: single pass, multi-pass and continuous recirculation. The effect of initial trans-stilbene concentration, oxygen content in the feed gas mixture and reaction time on the epoxide formation was studied to optimise the chemical reaction. The optimum operating conditions were found to be short bubble-liquid contact times (~2 s) with frequent exposure to freshly generated microbubbles containing reactive species by continuous liquid recirculation, and under these conditions the overall epoxide yield was ~94% with an overall epoxide selectivity of 10:1.
Colloids and Interfaces
A novel electrophoretic separation technique is presented, where continuous electrophoretic separ... more A novel electrophoretic separation technique is presented, where continuous electrophoretic separation is demonstrated using free flowing liquid foams. Continuous foam electrophoresis combines the principle of capillary electrophoresis and interactions between analytes and the electrical double layer, with the ability of Free Flow Electrophoresis to continuously separate and recover analytes automatically. A liquid foam is used to provide a network of deformable micro and nano channels with a high surface area, presenting a novel platform for electrophoresis, where interfacial phenomena could be exploited to modify analyte migration. The main purpose of this paper is to present a proof-of-concept study and provide fundamental understanding of a complex foam system in continuous separation mode, i.e., flowing liquid foam under an external electric field with electrophoresis and chemical reactions at the electrodes continuously changing the system. Liquid foam is generated using a mix...
Supplementary Information Files for 'An integrated microfluidic chip for generation and trans... more Supplementary Information Files for 'An integrated microfluidic chip for generation and transfer of reactive species using gas plasma'<br>Abstract:Reactive species produced by atmospheric pressure plasma (APP) are useful in many applications including disinfection, pretreatment, catalysis, detection and chemical synthesis. Most highly reactive species produced by plasma, such as <b><sup>·</sup></b>OH, <sup>1</sup>O<sub>2</sub> and , are short-lived; therefore, in-situ generation is essential to transfer plasma products to the liquid phase efficiently. A novel microfluidic device that generates a dielectric barrier discharge (DBD) plasma at the gas-liquid interface and disperses the reactive species generated using microbubbles of ca. 200 µm in diameter has been developed and tested. As the bubble size affects the mass transfer performance of the device, the effect of operating parameters and plasma discharge on generated ...
Supplementary information files for "A comparison of azimuthal and axial oscillation microfi... more Supplementary information files for "A comparison of azimuthal and axial oscillation microfiltration using surface and matrix types of microfilters with a cake-slurry shear plane exhibiting non-Newtonian behaviour"<br>AbstractThe mode of application of oscillation, axial or azimuthal, did not influence filtration performance, when filtering a calcite mineral with a d<sub>32</sub> value of 2.7 µm. The equilibrium flux and deposit thickness correlated with shear stress, regardless of: filter type (metal slotted surface filter or homogeneous sintered filter); and mode of oscillation. Shear stress values up to 240 Pa were used and the particle compact believed to be at, or near, the deposited solids showed non-Newtonian flow behaviour described by the Herschel-Bulkley equation. The shear was computed using Comsol® to model the shear at, and near, the oscillating surface. The peak shear (maximum value) was used in the correlation for flux, which appeared to fi...
Proceedings of the 6th International Conference on Fluid Flow, Heat and Mass Transfer (FFHMT'19), Jun 1, 2019
We consider liquid in a cylindrical beaker and study the deformation of its surface under the inf... more We consider liquid in a cylindrical beaker and study the deformation of its surface under the influence of an impinging gas jet. Analyzing such a system not only is of fundamental theoretical interest, but also of industrial importance, e.g., in metallurgical applications. The solution of the full set of governing equations is computationally expensive. Therefore, to obtain initial insight into relevant regimes and timescales of the system, we first derive a reduced-order model (a thin-film equation) based on the long-wave assumption and on appropriate decoupling the gas problem from that for the liquid and taking into account a disjoining pressure. We also perform direct numerical simulations (DNS) of the full governing equations using two different approaches, the Computational Fluid Dynamics (CFD) package in COMSOL and the volume-of-fluid Gerris package. The DNS are used to validate the results for the thinfilm equation and also to investigate the regimes that are beyond the range of validity of this equation. We additionally compare the computational results with experiments and find good agreement.
Chemical Engineering Research and Design, 2017
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service... more This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ELECTROPHORESIS, 2017
Fluid flow profiles in free liquid films stabilised by anionic and cationic surfactants under an ... more Fluid flow profiles in free liquid films stabilised by anionic and cationic surfactants under an external electric field were investigated. Depthwise velocity fields were measured at the mid region of the
Current Opinion in Colloid & Interface Science, 2018
Procedures used in Electrokinetic investigations of surfactant-laden interfaces, liquid films and... more Procedures used in Electrokinetic investigations of surfactant-laden interfaces, liquid films and foam system. Cocis (2018),
Plasma Sources Science and Technology
In this study we examine both the effect of changing the applied voltage waveform shape and the m... more In this study we examine both the effect of changing the applied voltage waveform shape and the modulation on-time on the amount of ozone dissolved within a liquid in a DBD bubble reactor. In this device, the discharge forms at the gas liquid interface allowing for effective transfer of the plasma effluent into the liquid. To produce different voltage waveforms, a multilevel inverter power supply capable of generating arbitrary waveforms without switching-on and switching-off transients has been used. Of the four waveforms used in the study (sinusoidal, sawtooth, square and short-pulse), the square waveform was found to be the most efficient at producing the highest ozone concentration for a fixed peak voltage and average power. To determine the effect of the modulation on-time, the number of cycles during the on-time were increased from 1 up to 1000, adjusting the off-time accordingly to maintain the same duty cycle. Shorter on-time periods were found to be more efficient. Experimental and computational results indicate that the time between subsequent discharges is critical for increased ozone generation efficacy, as this needs to be long enough for ozone produced in one discharge event to diffuse away from the discharge region before the next discharge event occurs, thereby avoiding its partial destruction in the plasma. This insight provides a valuable criterion for the optimization of DBD reactors used in novel biomedical, agricultural and environmental applications.
CO2 is concentrated in steel plant exhaust gases, providing the opportunity for biochemical fixin... more CO2 is concentrated in steel plant exhaust gases, providing the opportunity for biochemical fixing by photosynthetic plants such as algae. Yet with the technologies currently available, algal farming would require a large surface area (100s of hectares), to process a commercially significant volume of CO2 from a typical steel plant. The limitations in the processing are the dissolution rate of CO2 in water, which requires a substantial height (34m) for a partial transfer, the slow growth rate of algae with inhibition by the O2 by-product, and the low density of biomass produced. In this work the feasibility of using steel plant stack gases, rich in CO2, as a feedstock for sequestrating CO2 and growing algal biomass, using an intensified bioreactor design was demonstrated. The novel bioreactor equipped with air lift loop exploited a recently invented micro-bubble generation technique which achieved a high transfer rate across the gas-liquid interface and therefore accelerated CO2 dis...
Industrial & Engineering Chemistry Research, Sep 16, 2021
Emulsions formed by mixing reactant streams inside microdroplets are efficient micro-scale reacto... more Emulsions formed by mixing reactant streams inside microdroplets are efficient micro-scale reactors for synthesis of nano/micro-particles/crystals due to small quantities of reagents confined within each droplet and separation of droplet contents from the reactor walls. In this work, the synthesis of size-tuneable gold nanoparticles (AuNPs) within emulsion droplets generated in a three-phase glass capillary microfluidic device was investigated experimentally and numerically using computational fluid dynamics (CFD). AuNPs were produced by micromixing two aqueous streams, 1.15 mM HAuCl4 containing 1% polyvinylpyrrolidone capping agent and 20 mM ascorbic acid solutions, inside monodispersed droplets created by 3D counter-current flow focusing in a medium-chain triglyceride. The mean particle size of AuNPs was tuneable in the range between 26 and 56 nm and depended on the degree of premixing of the reactant streams shortly before droplet generation, and the mixing efficiency within droplets, which was controlled by hydrodynamic conditions within the microfluidic device. The CFD results were compared and validated against experimental observations and revealed the presence of a recirculation zone near the outer wall of the injection capillary tip. The mixing efficiency was higher at smaller droplet size causing a reduction in the particle size of the AuNPs.
Langmuir, May 12, 2022
Liquid foams are highly complex systems consisting of gas bubbles trapped within a solution of su... more Liquid foams are highly complex systems consisting of gas bubbles trapped within a solution of surfactant. Electroosmotic effects may be employed to induce fluid flows within the foam structure and impact its stability. The impact of external electric fields on the stability of a horizontally oriented monolayer of foam (2D foam) composed of anionic, cationic, nonionic, and zwitterionic surfactants was investigated, probing the effects of changing the gas−liquid and solid−liquid interfaces. Time-lapse recordings were analyzed to investigate the evolution of foam over time subject to varying electric field strengths. Numerical simulations of electroosmotic flow of the same system were performed using the finite element method. Foam stability was affected by the presence of an external electric field in all cases and depended on the surfactant type, strength of the electric field, and the solid material used to construct the foam cell. For the myristyltrimethylammonium bromide (MTAB) foam in a glass cell, the time to collapse 50% of the foam was increased from ∼25 min under no electric field to ∼85 min under an electric field strength of 2000 V/m. In comparison, all other surfactants trialed exhibited faster foam collapse under external electric fields. Numerical simulations provided insight as to how different zeta potentials at the gas−liquid and solid−liquid interfaces affect fluid flow in different elements of the foam structure under external electric fields, leading to a more stable or unstable foam.
This is a poster presented at the Joint Conference of COST ACTIONS TD1208 “Electrical discharges ... more This is a poster presented at the Joint Conference of COST ACTIONS TD1208 “Electrical discharges with liquids for future applications” & MP1101 Biomedical Applications of Atmospheric Pressure Plasma Technology
Langmuir, Jan 19, 2020
Electrokinetic transport of a charged dye within a free liquid film stabilized by a cationic surf... more Electrokinetic transport of a charged dye within a free liquid film stabilized by a cationic surfactant, trimethyl-(tetradecyl)ammonium bromide, subjected to an external electric field was investigated. Confocal laser scanning microscopy was used to visualize fluorescein isothiocyanate (FITC) separation within the stabilized liquid film. Numerical simulations were performed using the finite element method to model the dynamics of charged dye separation fronts observed in the experiments. Because of the electrochemical reactions at the electrodes, significant spatial and temporal pH changes were observed within the liquid film. These local pH changes could affect the local zeta potential at the gas−liquid and solid−liquid film boundaries; hence, the flow field was found to be highly dynamic and complex. The charged dye (FITC) used in the experiments is pH-sensitive, and therefore, electrophoresis of the dye also depended on the local pH. The pH and the electroosmotic flow field predicted from the numerical simulations were useful for understanding charged dye separation near both the anode and the cathode.
The flow field within a free liquid film under an applied external electric field was measured us... more The flow field within a free liquid film under an applied external electric field was measured using confocal micro-PIV system. Free liquid films of thickness ∼ 200 μm were formed in a rectangular frame with electrodes in direct contact with the fluid and stabilised by cationic surfactant. The flow field induced by an external electric field of ∼1600 V/m was visualised using 2 μm tracer particles on several depth wise planes. The observed particle velocities were used to determine the fluid velocities within the film by accounting for the electrophoresis of the tracer particles.
Industrial & Engineering Chemistry Research, 2020
Product inhibition and the cost of downstream separations are two main barriers in using lignocel... more Product inhibition and the cost of downstream separations are two main barriers in using lignocellulosic biomass for bioethanol production. If bioethanol can be continuously removed from fermentation broth without affecting the fermentation process, significant gains can be achieved with bioethanol yields and process efficiency. Hot microbubble clouds generated by energy efficient means have been used to remove ethanol from dilute ethanol−water mixtures (∼4% [v/v]) maintained at 60°C, and the effect of key operating parameters on the stripping rate has been studied. Numerical simulations of a hot microbubble rising in a dilute ethanol−water mixture were also performed to understand the instantaneous concentrations within the gas phase. Increasing the inlet gas temperature from 90 to 150°C and decreasing the liquid height in the unit from 50 to 5 mm both increased the ethanol stripping rate. However, the benefit of increasing the gas temperature for maximum ethanol removal depended on the liquid height in the unit. Under all operating conditions, ethanol concentration was reduced below ∼2% [v/v] within ∼25 min of operation, demonstrating the potential of hot microbubble stripping for product removal from lignocellulosic fermenters. Implemented effectively in a fermenter, this technology could intensify the bioethanol production process and improve process economics.
Colloids and interfaces, May 4, 2023
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
Chemical Engineering Science, 2021
Novel organic synthesis routes that circumvent the need for a catalyst and reduce unwanted by-pro... more Novel organic synthesis routes that circumvent the need for a catalyst and reduce unwanted by-products are highly sought by industry. A novel microfluidic plasma reactor that generates a dielectric barrier discharge (DBD) plasma in the vicinity of the gas-liquid interface and facilitate a chemical reaction at the interface of microbubbles has been used for transstilbene epoxidation. Three different operating strategies were implemented to optimise the transfer of species selectivity: single pass, multi-pass and continuous recirculation. The effect of initial trans-stilbene concentration, oxygen content in the feed gas mixture and reaction time on the epoxide formation was studied to optimise the chemical reaction. The optimum operating conditions were found to be short bubble-liquid contact times (~2 s) with frequent exposure to freshly generated microbubbles containing reactive species by continuous liquid recirculation, and under these conditions the overall epoxide yield was ~94% with an overall epoxide selectivity of 10:1.
Colloids and Interfaces
A novel electrophoretic separation technique is presented, where continuous electrophoretic separ... more A novel electrophoretic separation technique is presented, where continuous electrophoretic separation is demonstrated using free flowing liquid foams. Continuous foam electrophoresis combines the principle of capillary electrophoresis and interactions between analytes and the electrical double layer, with the ability of Free Flow Electrophoresis to continuously separate and recover analytes automatically. A liquid foam is used to provide a network of deformable micro and nano channels with a high surface area, presenting a novel platform for electrophoresis, where interfacial phenomena could be exploited to modify analyte migration. The main purpose of this paper is to present a proof-of-concept study and provide fundamental understanding of a complex foam system in continuous separation mode, i.e., flowing liquid foam under an external electric field with electrophoresis and chemical reactions at the electrodes continuously changing the system. Liquid foam is generated using a mix...
Supplementary Information Files for 'An integrated microfluidic chip for generation and trans... more Supplementary Information Files for 'An integrated microfluidic chip for generation and transfer of reactive species using gas plasma'<br>Abstract:Reactive species produced by atmospheric pressure plasma (APP) are useful in many applications including disinfection, pretreatment, catalysis, detection and chemical synthesis. Most highly reactive species produced by plasma, such as <b><sup>·</sup></b>OH, <sup>1</sup>O<sub>2</sub> and , are short-lived; therefore, in-situ generation is essential to transfer plasma products to the liquid phase efficiently. A novel microfluidic device that generates a dielectric barrier discharge (DBD) plasma at the gas-liquid interface and disperses the reactive species generated using microbubbles of ca. 200 µm in diameter has been developed and tested. As the bubble size affects the mass transfer performance of the device, the effect of operating parameters and plasma discharge on generated ...
Supplementary information files for "A comparison of azimuthal and axial oscillation microfi... more Supplementary information files for "A comparison of azimuthal and axial oscillation microfiltration using surface and matrix types of microfilters with a cake-slurry shear plane exhibiting non-Newtonian behaviour"<br>AbstractThe mode of application of oscillation, axial or azimuthal, did not influence filtration performance, when filtering a calcite mineral with a d<sub>32</sub> value of 2.7 µm. The equilibrium flux and deposit thickness correlated with shear stress, regardless of: filter type (metal slotted surface filter or homogeneous sintered filter); and mode of oscillation. Shear stress values up to 240 Pa were used and the particle compact believed to be at, or near, the deposited solids showed non-Newtonian flow behaviour described by the Herschel-Bulkley equation. The shear was computed using Comsol® to model the shear at, and near, the oscillating surface. The peak shear (maximum value) was used in the correlation for flux, which appeared to fi...
Proceedings of the 6th International Conference on Fluid Flow, Heat and Mass Transfer (FFHMT'19), Jun 1, 2019
We consider liquid in a cylindrical beaker and study the deformation of its surface under the inf... more We consider liquid in a cylindrical beaker and study the deformation of its surface under the influence of an impinging gas jet. Analyzing such a system not only is of fundamental theoretical interest, but also of industrial importance, e.g., in metallurgical applications. The solution of the full set of governing equations is computationally expensive. Therefore, to obtain initial insight into relevant regimes and timescales of the system, we first derive a reduced-order model (a thin-film equation) based on the long-wave assumption and on appropriate decoupling the gas problem from that for the liquid and taking into account a disjoining pressure. We also perform direct numerical simulations (DNS) of the full governing equations using two different approaches, the Computational Fluid Dynamics (CFD) package in COMSOL and the volume-of-fluid Gerris package. The DNS are used to validate the results for the thinfilm equation and also to investigate the regimes that are beyond the range of validity of this equation. We additionally compare the computational results with experiments and find good agreement.
Chemical Engineering Research and Design, 2017
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service... more This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ELECTROPHORESIS, 2017
Fluid flow profiles in free liquid films stabilised by anionic and cationic surfactants under an ... more Fluid flow profiles in free liquid films stabilised by anionic and cationic surfactants under an external electric field were investigated. Depthwise velocity fields were measured at the mid region of the
Current Opinion in Colloid & Interface Science, 2018
Procedures used in Electrokinetic investigations of surfactant-laden interfaces, liquid films and... more Procedures used in Electrokinetic investigations of surfactant-laden interfaces, liquid films and foam system. Cocis (2018),
Plasma Sources Science and Technology
In this study we examine both the effect of changing the applied voltage waveform shape and the m... more In this study we examine both the effect of changing the applied voltage waveform shape and the modulation on-time on the amount of ozone dissolved within a liquid in a DBD bubble reactor. In this device, the discharge forms at the gas liquid interface allowing for effective transfer of the plasma effluent into the liquid. To produce different voltage waveforms, a multilevel inverter power supply capable of generating arbitrary waveforms without switching-on and switching-off transients has been used. Of the four waveforms used in the study (sinusoidal, sawtooth, square and short-pulse), the square waveform was found to be the most efficient at producing the highest ozone concentration for a fixed peak voltage and average power. To determine the effect of the modulation on-time, the number of cycles during the on-time were increased from 1 up to 1000, adjusting the off-time accordingly to maintain the same duty cycle. Shorter on-time periods were found to be more efficient. Experimental and computational results indicate that the time between subsequent discharges is critical for increased ozone generation efficacy, as this needs to be long enough for ozone produced in one discharge event to diffuse away from the discharge region before the next discharge event occurs, thereby avoiding its partial destruction in the plasma. This insight provides a valuable criterion for the optimization of DBD reactors used in novel biomedical, agricultural and environmental applications.
CO2 is concentrated in steel plant exhaust gases, providing the opportunity for biochemical fixin... more CO2 is concentrated in steel plant exhaust gases, providing the opportunity for biochemical fixing by photosynthetic plants such as algae. Yet with the technologies currently available, algal farming would require a large surface area (100s of hectares), to process a commercially significant volume of CO2 from a typical steel plant. The limitations in the processing are the dissolution rate of CO2 in water, which requires a substantial height (34m) for a partial transfer, the slow growth rate of algae with inhibition by the O2 by-product, and the low density of biomass produced. In this work the feasibility of using steel plant stack gases, rich in CO2, as a feedstock for sequestrating CO2 and growing algal biomass, using an intensified bioreactor design was demonstrated. The novel bioreactor equipped with air lift loop exploited a recently invented micro-bubble generation technique which achieved a high transfer rate across the gas-liquid interface and therefore accelerated CO2 dis...