Produce Gas Bubbles Research Articles

Gas-liquid hydrodynamics of a fractal flow mixer

Gas-liquid hydrodynamics of a micro-structured device (fractal flow mixer) was experimentally investigated. Experiments were conducted for a range of liquid-to-gas superficial velocity ratios (VSL/VSG). High-speed imaging was used to identify the flow regimes inside the microchannels of the device at different VSL/VSG. At different VSL/VSG, two or more flow regimes were observed simultaneously in different micro-channels. Consequently, a new flow regime map was developed. An optical probe was used to measure the bubble mean size and velocity. The effect of the VSL/VSG towards the bubble mean size, mean velocity, and frequency were analyzed. The bubble mean size decreases with the increase of the VSL/VSG, which can be attributed to the uniform shearing of gas slugs across all channels. To check the consistency of the fractal flow mixer in producing gas bubbles over a single experiment run, the global relative standard deviation (RSD) was used. The fractal flow mixer was able to generate equal flow distribution across the 16 outlets and maintain a Taylor flow over a range of VSL/VSG. . However, depending on the VSL/VSG, the GB and GS vary to a certain extent, governed by the capillary effect and the back-pressure.

Boosting cell performance and optimizing gas distribution of flow-through microfluidic fuel cells by adjusting flow configuration

Microfluidic fuel cells (MFCs) with flow-through porous electrodes produce gas bubbles under acidic condition, which undoubtedly cover the catalyst surface, hinder the fuel transport and increase the ionic transfer resistance between electrodes. Herein, an effective approach is proposed to optimize the gas bubble distribution and reduce their influence on cell performance. Different from the flow configuration in the conventional flow-through MFCs, the reactant solutions flow from the microchannel between the anode and the cathode to the external channel through porous electrodes. After adjusting the flow configuration, the nucleation and distribution of gas bubbles are changed from the microchannel between anode and cathode to the external one, leading to a decreased ionic transfer resistance between the anode and the cathode. As a result, compared with the MFC with the conventional flow configuration, the maximum power density of the MFC with the new configuration (MFC-N) is increased by 52.9%, and a higher fuel utilization rate is achieved. Moreover, the MFC-N reaches a more stable voltage even at a high current density of 80 mA cm−2. The proposed flow configuration is a good and feasible method for gas management and performance enhancement in the flow-through MFCs.

Bubbles help male flowers overcome obstacles during pollination in Hydrilla verticillata.

Pollination in many aquatic plants takes place on the water surface, and the male flowers or stamens often produce gas bubbles underwater; however, the generation mechanism and function of these bubbles are unknown. A common submerged plant, Hydrilla verticillata, was used as experimental material to observe the structure of male flowers, analyze the process of bubble generation, and simulate the movement process of the male flower with attached gas bubble in water. The aerenchyma inside the male plants of H. verticillata transported the gas produced by the plant's branches during photosynthesis to the male flower, and the formed gas bubbles became attached to the edge of the perianth. The gas accumulation rate in the attached bubbles increased with light intensity. Once the bubble diameter increased to approximately 3.3 mm, the male flowers with the bubble detached from the plant and floated to the water surface. The removal of the attached bubbles did not affect the male flower detached from the plant; however, the surfacing of male flowers without gas bubbles was easily prevented by the plant's branches in the water, and they could not reach the water surface to complete pollen dispersal. The gas bubbles produced by male flowers of H. verticillata came from the gas produced by branches under light. These bubbles can help ascending male flowers bypass the obstacles in water and reach the surface to complete pollination.

Corrosion Engineering on Iron Foam toward Efficiently Electrocatalytic Overall Water Splitting Powered by Sustainable Energy

AbstractExploiting highly effective and low‐cost electrocatalysts for the hydrogen evolution reaction (HER) is a pressing challenge for the development of sustainable hydrogen energy. In this work, a facile and industrially compatible one‐pot corrosion strategy for the rapid synthesis of amorphous RuO2‐decorated FeOOH nanosheets on iron foam (FFNaRu) within 1 h is reported. Corrosion is a common and inevitable phenomenon that occurs on metal surfaces without electricity input, high temperature, and tedious synthetic procedures. The FFNaRu electrode is superhydrophilic and aerophobic, which guarantees intimate contact with the electrolyte and accelerates the instantaneous escape of produced gas bubbles during the electrocatalytic process. Moreover, the strong electronic interactions between RuO2 and FeOOH promote the electrocatalytic process via dramatically improving the electrochemical interfacial properties. Thus, the FFNaRu electrocatalyst presents excellent catalytic activity towards the HER (30 mV at 10 mA cm–2) and overall water‐splitting (230 mV at 10 mA cm–2) in 1 M KOH. The overall water‐splitting could be simply powered by sustainable and intermittent sunlight, wind, and thermal energies motivated Stirling engine. Density functional theory calculations confirm that coupling effects between RuO2 and FeOOH are also responsible for promoting the electrocatalytic HER performance.

Identification of lactic acid bacteria from etawa goat milk kopelma Darussalam Village, Banda Aceh

Identification of Lactic Acid Bacteria (LAB) has been carried out based on the catalase test and Gram staining of Etawa pure Goat Milk samples that obtained from Kopelma Village, Darussalam District, Banda Aceh City, Aceh Province. De Man, Rogosa, Sharpe Agar (MRSA) media was used for LAB isolation. There were 10 isolates of goat milk bacteria that used for microscopic characteristics, morphological observations, catalase test and Gram staining. Based on the microscopic test, it was explained that all colonies had similar characteristics, that having a round shape, convex surface shape, 1-2 mm diameter and cream color. In the catalase test, the results were negative, because all isolates did not produce gas bubbles after dripped with H2O2 solution. The morphological results showed that all isolates were Gram positive, marked by purple cells and bacilli cells. Based on the Gram staining and the shape of the bacillus cells, it were suspected that milk isolates are candidates for the genus Lactobacillus. Microscopic diagnosis is only a provisional presumption. Therefore, it needs a conclusive diagnosis, such as biochemical properties which are important factors that must be carried out for the next stage.

Removal of landfill leachate ultraviolet quenching substances by electricity induced humic acid precipitation and electrooxidation in a membrane electrochemical reactor

Persistent UV quenching substances (UVQS) in landfill leachate can affect the effectiveness of UV disinfection in domestic wastewater treatment systems when leachate is being co-treated. As a result, effective onsite leachate pre-treatment will have to be implemented to reduce the UV quenching capability. Herein, a membrane electrochemical reactor (MER) was developed and investigated for treating UV quenching organics contained in landfill leachate. Compared to a control reactor that did not have a membrane separator, the MER achieved significantly higher removals of both dissolved organic carbon (61.5 ± 4.1%) and UV254nm absorbance (63.4 ± 8.4%). This enhanced performance was likely due to the combined effects of humic acid precipitation and augmented oxidation of organics. The MER was able to remove 89.1 ± 2.9% of total nitrogen from the leachate while recovering about 51% of the influent ammonia in the catholyte, in comparison to 38.1 ± 4.4% of total nitrogen removal by the control reactor. The MER consumed significantly less electrical energy with specific energy consumption of 70.62 kWh kg−1 DOC or 33.03 kWh kg−1 sCOD, compared to that of the control reactor (211.8 kWh kg−1 DOC or 55.02 kWh kg−1 sCOD). A current density of 20 mA cm−2 was considered optimal in terms of both UVQS removal and energy efficiency. Consideration should be given to the spacing of electrodes to minimize internal resistance and also to avoid trapping of the produced gas bubbles. These results collectively suggest that the MER is a promising onsite pretreatment approach for landfill leachate and further exploration of this technology should be encouraged.

Microstructures and Mechanical Study of Mg Alloy Foam Based on Mg-Zn-Ca-CaCO3 System

Magnesium alloy, a material that has potential to use some applications such as aerospace components, computer parts, and mobile phones. Magnesium alloy can also be a popular candidate as an orthopedic implant material for biodegradability, non-toxicity, and mechanical and physical properties that are excellent. Magnesium, one of the main macro elements required for the proper functioning of the human organism, is used to test the materials for biodegradable implants. The main objective of this study was to find out the microstructure, and mechanical characteristics of the Mg-Ca-Zn-CaCO3 alloy as porous implant materials are biodegradable. The presence of CaCO3 on the alloy functions as a foaming agent expected to produce gas bubbles during manufacturing process taken place that will form pores in the alloy. Mg-Ca-Zn-CaCO3 alloy was made by powder metallurgy method with three variations of composition (96Mg-Ca-3Zn-CaCO3, 91Mg-Ca-3Zn-5CaCO3, and 86Mg-Ca-3Zn-10CaCO3 wt%). Milling process was by using a shaker mill for 2 hours to produce a powder size distribution which was more homogeneous. The mixed powder was uniaxially pressed at a pressure of 100 MPa for 2 minutes and 200 MPa for 3 minutes into green compacts with dimensions of 10 mm in diameter and 10 mm in length. The sintering process was carried out at 650°C with a variation of holding time of 10 and 15 hours, and then the specimens were cooled down at room temperature. Microstructural analysis was performed by using X-Ray diffraction technique and Scanning electron microscopy equipped with an energy disperse spectrometry (EDS). The mechanical characteristics were analyzed by using Universal Testing Machine. The density and porosity of specimen were further measured by using Archimedes method. The results show that the optimum microstructure and mechanical characteristics are the holding time of 10 hours. The value of compression was 208.398 N/mm2, the density was 1.63 g/cc and a porosity was 18% on the composition of 86Mg-Ca-3Zn-10CaCO3 wt%.

Visualization of two-phase flow and temperature characteristics of an active liquid-feed direct methanol fuel cell with diverse flow fields

Direct methanol fuel cell (DMFC) is a promising power source for portable applications. This study aims to reveal the two-phase flow characteristics of an active liquid-feed DMFC by using the visualization method. Different flow fields based on the serpentine, parallel and porous patterns and their effects on reactant and product managements are experimentally investigated. Results show that the performance of serpentine flow field is closely influenced by the change of methanol feed rate but the parallel pattern shows less sensitivity. The use of serpentine flow field enables the fuel cell to be operated with a higher methanol concentration. A higher methanol feed rate promotes removal of the produced gas bubbles. The oxygen feed rate has a negligible effect on the fuel cell with a cathode serpentine flow field but produces a more obvious performance difference in the case of parallel pattern. The visualization tests indicate that the use of a higher oxygen flow rate is helpful in water removal. The temperature characteristics of the anode serpentine channel are evaluated and how the temperature behaviors relate to different operating conditions are accordingly discussed.

Mechanism of Electrochemical Delamination of Two-Dimensional Materials from Their Native Substrates by Bubbling.

A capacitor-based circuit model is proposed to explain the electrochemical delamination of two-dimensional materials from their native substrates where produced gas bubbles squeeze into the interface. The delamination is actually the electric breakdown of the capacitor formed between the solution and substrate. To facilitate the procedure, the backside of the ubstrate has to be shielded so that the capacitor breakdown voltage can be reached. The screening effect can be induced either by nonreactive ions around the electrode or, more effectively, by an undetachable insulator. This mechanism serves as a guideline for the surface science and applications involving the bubbling delamination.

Synthesis, Characterization and Applications of a New Prussian Blue Type Material

AbstractThis work reports on a material synthesized via 1‐butyl‐3‐methylimidazolium tetrachloroferrate and K3[Fe(CN)6]. Its structure and properties were characterized by IR, XPS, AFM and CV, which was inferred as Prussian Blue Type (PBT) material with particle size distribution between 80–120 nm and spike‐like aggregation from the characterization results. PBT is insoluble in acetone, water and ethanol uniformly, which gives magnetic properties. It can be reacted with 30 % H2O2, and produce gas bubbles when a voltage is applied. Modified on the glassy carbon electrode, the material showed obviously electrocatalytic activity to sodium nitrite, which has potential application prospect for sensors.

BiotecVisions 2012, November

BiotecVisions 2012, November

Gas bubble formation in the cytoplasm of a fermenting yeast

Current paradigms assume that gas bubbles cannot be formed within yeasts although these workhorses of the baking and brewing industries vigorously produce and release CO2 gas. We show that yeasts produce gas bubbles that fill a significant part of the cell. The missing link between intracellular CO2 production by glycolysis and eventual CO2 release from cells has therefore been resolved. Yeasts may serve as model to study CO2 behavior under pressurized conditions that may impact on fermentation biotechnology.

Influence of pore structural properties of current collectors on the performance of proton exchange membrane electrolyzer

The effect of pore structural properties (porosity and pore diameter) of current collectors in proton exchange membrane (PEM) electrolyzers on electrolysis performance was experimentally evaluated by using various titanium (Ti)-felt substrates with different porosities and pore diameters (measured by capillary flow porometry) as the anode current collectors. The current–potential (j–ΔV) characteristics were measured, and overpotential analysis was performed based on the j–ΔV characteristics and the cell resistance (Rcell) data. The results showed that (1) the effect of the decrease in water supply on the membrane resistance due to produced gas bubbles is limited when the mean pore diameter of the anode current collector is less than 50μm, but might appear at the concentration overpotential, and (2) enhancing the uniform and sufficient contact between the current collector and the electrode reduces not only the contact resistance but also the activation overpotential.

Application of magnetic resonance imaging (MRI) to study the anatomy and reproductive condition of live Sydney rock oyster, Saccostrea glomerata (Gould)

Magnetic resonance imaging (MRI), a non-invasive technique, was used to study the soft tissue of live Sydney rock oysters (Saccostrea glomerata). The oysters were farmed in Port Stephens, Australia and the research was carried out during 2008–2011. MRI was performed on a Varian UNITY plus 300MHz spectrometer with a wide bore Oxford magnet system (7.05Tesla) equipped with a Varian Millipede microimaging probe. Relaxation parameters (T1 and T2) were found to be dependent on the type of tissue and also reflected seasonal changes in reproductive status of the gonad. The variation in T1 values of different types of soft tissue was used judiciously to optimise contrast in MR images. The MR images of live oysters revealed anatomical details of the gills and the labial palps that are consistent with the feeding mechanism of bivalves. An empirical equation (y=4.2x+14.9) was derived by traditional methods which describes the relationship between the condition index (y) of oysters and the percentage volume of soft tissue (x). A significant correlation (R2=0.871, P<0.01, n=5) was obtained between measurements of percentage volume of soft tissue by MRI and the traditional method. Hence, it was concluded that MRI is useful in determining the condition index of live oysters. An interesting observation from MR images was the development of gas bubbles within emersed oysters. Analysis of this gas revealed an elevated concentration of carbon dioxide (2760ppm after 3days of emersion and 6300 ppm after 8days). It was concluded that oysters produce gas bubbles by a physiological process for removing CO2 from soft tissue. The research findings presented here suggest that MRI, due to its non-invasive nature, could prove to be a unique tool for oyster research.

Ebullition‐Facilitated Transport of Manufactured Gas Plant Tar from Contaminated Sediment

Manufactured gas plant (MGP) tar and wastewater solids historically were discharged into the Penobscot River, Maine,USA, via a sewer at the Bangor Landing site. The tar and wastewater solids accumulated in riverbed sediment over a 5-hectare area downstream from the sewer outfall. Much of the tarry sediment is a hardened mass at the bottom of the river, but in part of the tar deposit (the active zone), the tar remains unhardened. In the active zone, anaerobic biodegradation of organic matter generates methane and carbon dioxide; as gas accumulates and migrates upward, it entrains tar, eventually dragging the tar from the sediment to surface water. Understanding the migration mechanisms in different portions of the tar deposit is critical for modeling the risk posed by the tar at the Bangor Landing site, because during gas-facilitated tar migration, the tar is brought to the water surface, instead of remaining in the sediment. Tar migration from sediment poses a potential human health risk because of the high concentrations of polycyclic aromatic hydrocarbons in the tar. Migration from sediment to the water surface greatly increases the potential exposure of human and ecological receptors to tar that reaches the water surface. In order for tar to migrate from sediment to surface water, three conditions are necessary: the sediment must contain liquid tar, the sediment must produce gas bubbles, and the gas must come into contact with the tarry sediment. Failure to consider facilitated transport of MGP tar from sediment can cause underestimation of site risk and can lead to failure of remedial measures.

Denitrification activity of Bradyrhizobium sp. isolated from Argentine soybean cultivated soils

Two hundred and fifty strains, all of them representatives of native Bradyrhizobium sp., isolated from soils cultivated with soybean have been characterized by their denitrification activity. In addition, the denitrification potential of those soils was also measured by evaluating the most-probable-number (MPN) of denitrifying bacteria and the denitrification enzyme assay (DEA). Of the 250 isolates tested, 73 were scored as probable denitrifiers by a preliminary screening method. Only 41 were considered denitrifiers because they produced gas bubbles in Durham tubes, cultures reached an absorbance of more than 0.1 and NO3− and NO2− were not present. Ten of these 41 were selected to confirm denitrification and to study denitrification genes. According to N2O production and cell protein concentration with NO3−, the isolates could be differentiated in three categories of denitrifiers. The presence of the napA, nirK, norC and nosZ genes was detected by production of a diagnostic PCR product using specific primers. RFLP from the 16S-23S rDNA spacer region (IGS) revealed that denitrifiers strains could be characterized as Bradyrhizobium japonicum and strains which were non-respiratory denitrifiers as B. elkanii.

Colloid fabrication by co-extrusion

We propose a novel technique that allows assembling composite particles by manipulating three (initially fluid) phases, e.g. gas bubbles or liquid droplets (phase 1) in one liquid (phase 3), coated by another one (phase 2). In this way, we can control (i) the type of disperse phase fluid and its flow rate, (ii) the type of the coating material, its composition, and its flow rate, and (iii) the type of the continuous phase and its composition. All this gives us numerous opportunities to prepare new disperse systems with interesting applications. We describe two sets of experiments. In the first one we produce gas bubbles coated with oil. In the second one we produce stable foam that is stabilized by a surfactant formed in situ on the surface of each separate bubble. The surfactant is formed by a chemical reaction between a fatty acid solution spread on the bubble surface and an aqueous solution of NaOH as a continuous phase. The foam grows linearly with time during the supply of the fatty acid solution. When we stop the supply of the fatty acid the foam growth stops. The simple examples show that with carefully chosen phases and precise control of the experimental conditions we can produce a whole range of different colloids: composite capsules, shell particles or fluid dispersions, etc.

Fixation of heavy contaminants of a dirty bomb attack: Studies with uranium and metal simulants

AbstractAsphalt emulsions were evaluated as a means to immobilize radiological contaminants deposited on urban surfaces after a dirty bomb attack. Contaminated surfaces would be sprayed with thin coatings of asphalt emulsion to encapsulate the radioactive particles until the site can be safely remediated. This research investigated applications of an asphalt emulsion (Topein C, Encapco Technologies, LLC, Napa, CA) to treat (zero‐valent) iron, lead, and uranium powders on various building material surfaces. Initial studies found that some of the building materials (limestone, concrete, and metal) reacted with the emulsion producing gas bubbles, which formed 0.001 to 1 cm vesicles in the cured asphalt emulsion. These vesicles, however, did not expose the building material surface, and the reaction appeared to aid in the setting of the emulsion. Powdered lead did not react with the asphalt emulsion, but iron powder and uranium did. Iron powder and the emulsion formed vesicles up to 0.5 mm (but not exposing the building material surface), while the uranium (U3O8) had a moderate reaction when compared with to the lead and iron powders. Scanning electron micrographs showed that the lead powder formed nonreactive layers adjacent to the concrete surface while iron particles were evenly distributed in the asphalt matrix due to the reaction with the asphalt, indicating that the physical and chemical reactions between the iron metal particles, asphalt, and concrete affected particle distribution in the asphalt matrix. A vertical operation sediment tube was used to determine the flowing shear stress durability of the asphalt/metal/substrate complex. The asphalt treatment with iron had no loss at the shear range tested (0.1–2.5 Pa), while the asphalt stabilized powdered lead lost 8% asphalt and lead at 2.5 Pa mean shear stress applied for 5 h. The chemical reaction between asphalt emulsion and iron increased the resistance of the asphalt/metal/substrate complex to shear when compared with lead. Some hydrogen was formed in reactions with iron, but the amount formed was well below the lower flammability limit. Treatment of uranium indicated that the emulsion was effective at reducing leaching of the uranium 10 fold. These experiments indicate that asphalt emulsions may be a viable means for containing metallic or dense radiological contaminants on common building materials. © 2007 American Institute of Chemical Engineers Environ Prog 26:94–103, 2007

In-vitro- und In-vivo-Untersuchungen zur Presbyopiebehandlung mit Femtosekundenlasern

Ultrashort (femtosecond) laser pulses can generate precise cuts in biological tissue without damaging the surface. The application of femtosecond laser technology at the lens was evaluated with respect to a possible treatment of presbyopia. Femtosecond laser lentotomy was performed on 150 pig lenses in vitro. Cutting geometry and laser settings were optimized to generate smooth cuts with a minimum of produced gas bubbles. Four rabbit lenses were treated afterwards in vivo and were controlled for 3 months post-treatment. The lenses were then extracted and evaluated. With suitable laser settings, light scattering due to residual gas bubbles could be almost completely avoided in pig lenses. A pulse energy of less than 1.2 microJ and a cutting geometry with spot separations of more than 5 microm are important. The rabbit lenses stayed macroscopically clear for 3 months in vivo. Only the cell structures directly adjacent to the laser focus were cut; structures 5-10 microm away appeared to be intact. No cataract formation occurred during this time. Femtosecond laser application allows precise and smooth cuts inside pig and rabbit lenses without damage to adjacent tissue.

Ultrasound detectable instrument with bubble generator

Ultrasound detectable instrument including a bubble generator having two elements which, upon contact with each other in the presence of a fluid, react with each other to produce gas bubbles which may be detected by sonic imaging equipment. The two elements comprise first and second radially displaced layers of the elements within a fluid permeable carrier material.