Bubble Discharge Research Articles

CFD Investigation on Movement Features of Hydrogen Bubble under Microgravity Environment

A designed cryogenic upper stage adopted liquid hydrogen and liquid oxygen (LH2/LO2) as an aerospace propellant. During a zero-gravity coast period in space, the wall heat leakage into the delivery tube could induce liquid propellant evaporation and two-phase flow phenomenon, so that a bubble discharge operation must be employed prior to engine restart. In this study, a CFD approach was utilized to numerically study the bubble discharge behaviors inside the LH2 delivery tube of the upper stage. The bubble motion properties under two different schemes, including positive acceleration effect and circulation flow operation, were analyzed and discussed. The results showed that the boiled hydrogen bubbles could increase to the size of the tube inner diameter and distribute randomly within the entire tube volume, and that, in order for the bubble to spill upward under the acceleration effect, a higher acceleration level than the needed value of acquiring liquid–vapor separation inside the propellant tank should be provided. When creating an acceleration level of 10−3 g0, most of the bubbles could spill upward within 700 s. Significantly, the bubbles could not be completely expelled in the created acceleration condition since a number of small bubbles always stagnate in the bulk liquid region. In the circulation flow operation, the gas volume reduction was mainly attributed to two mechanisms: the vapor condensation effect; and bubble discharge effect. For the case with a circulation flow rate of 0.2 kg/s, a complete bubble discharge purpose was reached within 820 s, while a large bubble stagnation in the spherical distributor occupied a remarkable proportion of the total time. In addition, both the liquid flow rate and liquid subcooling exert important effects on bubble performance. When applying a high circulation flow, the gas volume reduction is mainly due to the inertial effect of liquid flow, but the bubble stagnation in the spherical distributor still affects the total discharge time. The liquid subcooling influence on the gas volume reduction is more significant in smaller circulation flow cases. Generally, the present study provides valuable conclusions on bubble motions inside a LH2 delivery tube in microgravity, and the results could be beneficial to the sequence design of engine restart for the cryogenic upper stage.

Degradation of methylene blue by pulsed nanosecond discharge in Ar, O2, and N2 gaseous bubbles in water: Evaluation of direct and postprocessing modes

Dye-based water pollution is a subject of great concern as it has been linked to many health hazards. Considering their stable structures, some dyes, such as methylene blue (MB), cannot be easily removed from water. However, recent studies show that plasma-assisted processing has great potential for eliminating these dyes from water bodies. Among the different configurations of plasmas, discharges in gaseous bubbles in water are particularly promising in terms of water processing. The bubble-liquid discontinuity in such plasmas significantly facilitates the occurrence of discharge, and the modification of gas composition allows for controlling induced chemical reactions. In this study, we investigate the degradation of MB using pulsed discharges (amplitude of 20 kV, pulse duration of 500 ns, and repetition rate of 1 kHz) in Ar, O2, and N2 gaseous bubbles dispersed in water. The degradation of MB is evaluated in the direct mode, i.e., MB is present in the water during discharge as well as in the postprocessing mode, i.e., MB is added to water after plasma processing. Based on the obtained results, the most and least efficient degradation rates measured in the direct mode are achieved with O2 and N2 bubbles, respectively. Meanwhile, in the case of the postprocessing mode, degradation with N2 bubbles is initially more efficient than that with O2 or Ar. However, after hundreds of hours, higher degradation efficiency (up to 100%) is observed with O2 and Ar gas bubbles and not with N2. The findings reported herein are of great importance, particularly considering that plasma processing is complementary to the conventional techniques used in water depollution applications.

Partial Discharge Characteristics and Deterioration Mechanisms of Bubble-Containing Oil-Impregnated Paper

Bubbles, as typical defects of oil–paper insulation systems, pose a great threat to the insulation state. In this article, the characteristics and mechanisms of the partial discharge (PD) inception, evolution, and induced breakdown of bubbles embedded between oil-impregnated paper (OIP) layers are investigated. The results show that the PD inception has a significant statistical time delay due to the lack of free electrons. The PD inception time delay (PDTD) follows an exponential distribution and leads to the large dispersion of the PD inception voltage (PDIV), which follows a Weibull distribution. The changes in PD behavior [charge, repetition rate, pulse current waveform, and phase-resolved PD (PRPD)] over time all show two separable stages (stages 1 and 2). The continuous recording of bubble area and gas composition under PD reveals that the evolution of bubble PD is attributed to the change in gas composition rather than the change in surface conditions as believed by researchers. The OIP breakdown induced by bubble PD indicates two breakdown modes, fast and slow, which correspond to direct-induced breakdown in stage 1 and cumulative-damage breakdown in stage 2. The former occurs because of the severe distortion of the electric field by the space charge at the head of the discharge channel inside the bubble, whereas the latter occurs because of the gradual deterioration of the OIP due to the continuous PD action. This study increases our understanding of the mechanisms of bubble discharge and of oil–paper insulation deterioration, and it provides guidance for fault diagnoses.

Dynamics of Rising Bubbles and Their Impact with Viscoelastic Fluid Interfaces.

Bubble dynamics plays a significant role in a wide range of industrial fields, such as food, pharmacy and chemical engineering. The physicochemical properties of complex fluids can greatly affect the speed with which bubbles rise, and the lifetime of bubbles, which in turn can affect the efficiency of food and drug manufacturing and also sewage purification. Therefore, it is of great scientific and practical significance to study the influence mechanism of nanoparticles and surfactants on bubble rising and impact in a complex fluid interface. This paper selects a mixed dispersion liquid of nanoparticles (SiO2) and a surfactant (SDS) as the objects of the study, observes in real-time the entire processes of bubbles rising, impact at the gas-liquid interface, and rupture, and analyzes the dynamic mechanism of bubble impact in a complex fluid interface. By analyzing the morphological changes of the rising bubbles, the rising velocity and the lifetime of the bubbles, it is found that the surfactant molecules are distributed in the ultrapure water liquid pool and the liquid film surrounding the bubbles. Such distribution can reduce the viscoelasticity between bubbles and the liquid surface, and lower the surface tension of the liquid, which can reduce the rising velocity of bubbles, delay the drainage process of bubbles on a liquid surface, and enhance the lifetime of bubbles. If the liquid surface is covered with nanoparticles, a reticulate structure will be formed on the bubble liquid film, which can inhibit bubble discharge and prolong bubble lifetime. In addition, the influence of such a reticulate structure on liquid surface tension is limited and its function is far smaller than a surfactant.

Three-Dimensional Open Water Microchannel Transpiration Mimetics.

The key problem that hinders the water transportation performance and application of microchannels is the annoying gaslock. Realizing liquid transport without the gaslock requires a specially designed pump and a channel system, as well as the reduction of gas concentration in liquids. In nature, to eat viscous nectar with high efficiency, hummingbirds use their open geometric tongue for nectar-sucking. Inspired by hummingbirds' tongue, we report a bionic open microchannel that discharges unwanted gas inside the microchannel from the opening without influencing its fluidic performance. The opening can also be used for extrusion of oil droplets in microchannels, indicating great potential applications in oil-water separation and chemical slow release, especially for bubble discharge in microchannels. Most significantly, a mimicked "leaf" with our bionic open microchannnels exhibits marvelous "transpiration" performance when irradiated by a laser. Our work provides a new strategy for the fabrication of open microchannels and sheds light on potential applications of multiphase phenomena in microchannels including oil-water separation, phase change heat and mass transfer, solar vapor generation, and precisely controllable drug delivery.

DISCHARGE IN GAS BUBBLES IN WATER AS A SOURCE OF AN INTENSIVE FACTORS’ COMPLEX FOR WATER DISINFECTION: COMPARISON EXPERIMENTAL AND COMPUTER MODELLING RESULTS

Computer simulation of the discharge process in an electric circuit, which contains a pulsed electric in gas bubbles in water, has been perf0rmed. The experimental oscillograms of voltage pulses are compared with the results of computer simulation of voltage pulses on the treated water layer. It is shown that the amplitudes of the voltage pulses directly on the layer of disinfected water in the reactor with a discharge in the gas bubbles are less than those measured in experiments using a capacitive voltage divider. Computer simulations have shown that the shape of the voltage on a layer of water differs significantly that at the point where it is measured by capacitive voltage. In addition, we have shown that the presence of long lines in the bit circuit of the plant must be taken into account. Given the presence of long lines in the bit circuit, the simulation results better correspond to experimental results. References 5, figures 7.

Comparison of the physicochemical properties and inactivation against tumor cells of PAW induced by underwater single-hole and multi-hole bubble plasma

Plasma-activated water (PAW) regarded as a green alternative is of great interest in biomedicine due to the presence of a rich diversity of aqueous reactive oxygen and nitrogen species (RONS). Optimizing the reactor parameter is an important approach to regulate RONS in PAW to obtain better biological effects. This work mainly focuses on the number of micro holes of the plasma device to realize underwater bubble discharge. By comparing single-hole and multi-hole plasma under the same pulse voltage, the multi-hole plasma would produce a better discharge characteristic, and the prepared PAW presents superior physicochemical properties to realize high level RONS production by means of microbubbles to increase the contact area with water molecules. Furthermore, the A549 lung carcinoma cells are used to verify the inactivation effect induced by PAW treated by underwater single-hole and multi-hole bubble plasma, respectively, and the results show that the multi-hole plasma would induce cell apoptosis reaching up to 57.4%, while only 31.2% apoptosis efficiency for single-hole plasma. This mainly contributes to the high concentration of key species (NO2 −, H2O2, ONOO−/O2 −, and ·OH) produced by multi-hole plasma. This study is helpful to insight into the influence of underwater bubble on chemistry activity of PAW, and promoting the wide applications in biomedical field.

Utility of low-cost recreational-grade echosounders in imaging and characterizing bubbly coastal submarine groundwater discharge

Despite the growing knowledge on the significance of submarine groundwater discharge (SGD), mapping its occurrence is a continuing challenge. This study explores the capability and applicability of low-cost, off-the-shelf, recreational-grade echosounders (RGESs) to image different types and locate point sources of bubbly coastal SGD. Standard and systematic methodologies for efficient imaging and processing were established. The use of RGES was validated using a research-grade side scan sonar (RGSSS), continuous resistivity profiling, conductivity-temperature-depth casting, and MantaCam and SCUBA diving surveys. Lower frequencies (77/83 kHz) of RGESs showed more distinct acoustic signatures of bubbly SGD, as these were nearly the same as the effective resonance frequency of the bubbles. The clusters of bubbly discharges have higher backscatter strength than the water column noise, resulting in the definitive and convenient manual detection of SGD features. Hence, showing more accurate point sources of SGD. Three types of known SGD occurrence were identified and characterized based on acoustic behavior and spatial distribution: 1) sparse, discrete and sporadic discharge over wide area, 2) curtain, high and continuous bubble concentrations from widespread discharge, and 3) spring, direct bubble discharge from intense seafloor degassing at a single point source. These results showed that RGES provides a good alternative for more efficient and cost-effective preliminary coastal SGD works. Additional research on areas with water-dominated discharge but no bubbling is recommended.

Differentiation of communities of macroinvertebrates and cottoid fish associated with methane seeps of different bottom landscapes of Lake Baikal

The paper presents the results of the study of communities of macroinvertebrates and cottoid fish inhabiting methane seeps of Lake Baikal. For the analysis, we used video surveillance and collection of animals carried out with the help of "Mir" deep-water submersible, as well as NIOZ-type box-corer samplers from the board of a research vessel. Posolskaya Bank and Saint Petersburg methane seeps are located in different basins (southern and middle) and at different depths (300–500 m and ~ 1400 m), characterized by the different underwater landscapes (slope of underwater upland and hills formed by gas hydrates), by the structure of gas hydrates and their depth location in sediments, as well as the composition of microbial mats and communities of microorganisms of bottom sediments. Both seeps are characterized by bubble discharge of methane gas and the formation of highly productive communities of large invertebrates and cottoid fish on seep habitats. Seep animal communities consisted of species-depleted invertebrates and fish of the surrounding deep-water benthal of the Lake. We showed the similarities and differences in the composition of the faunas of two seeps, as well as the quantitative characteristics of taxonomic groups of macroinvertebrates and cottoid fishes. Obligate species have not been revealed on the methane seep Posolskaya Bank. For the methane seep Saint Petersburg, the gastropod species Kobeltocochlea tamarae Sitnikova, Teterina et Maximova, 2021 (Caenogastropoda: Benedictiidae) was designated as an obligate species; among bottom cottoid fishes, Neocottus werestschagini (Taliev, 1953) (Cottoidei: Abyssocottidae) had possible a transitional state to obligate. We presented the data on the assimilation by seep animals of mixed photo- and chemosynthetic food with different proportions of methane-derived carbon. A hypothesis has been substantiated that deep-water seep areas could serve as refugium for the preservation of endemic fauna during the Pliocene-Pleistocene glaciations of Lake Baikal.

Numerical investigation on spilling upward performance of hydrogen bubbles inside a delivery tube under low-gravity environment

A typical cryogenic upper stage mission requires a reliable liquid–gas phase separation prior to engine restart in space, and auxiliary engines are usually used to provide positive acceleration effect to satisfy vapor-free liquid supplement purpose. To assist thruster logic design for an upper stage, bubble distribution inside a delivery tube and bubble spilling behaviors should be known previously. In the present paper, a CFD approach is adopted to numerically study the bubble generation and bubble movement in liquid hydrogen (LH2) delivery tube under microgravity, and the bubble spilling upward behaviors under different situations are significantly analyzed. The results show that space heat from surroundings brings about liquid evaporation inside the delivery tube, and weak convection effect induced by bubble generation process could result in random bubble distribution in the whole tube range. The maximum bubble reaches the size of tube inner diameter. Under positive acceleration effect, the bubbles spill upward and bring about gas amount decrease in the delivery tube range. Moreover, the bubble spilling upward is not a continuous process, and only the big bubble discharge exerts a significant contribution to the gas amount decrease. In addition, the tube layout and the initial gas amount have slight influence on the bubble discharge performance, but the space acceleration level plays the primary effect on this process. For the present objective, the acceleration with 10−3g0 could drive the bubble to be discharged within 700 s. When the acceleration increases to 10−1g0, the required time correspondingly decreases to less than 100 s. Under the acceleration level of 10−4g0, however, the bubble could not spill upward any more but a vapor amount increase phenomenon is observed. Generally, the present work provides an opportunity to understand the bubble properties inside the cryogenic delivery tube in microgravity, and the results on acceleration influence as well as acceleration period are beneficial to the sequence design of space engine restart.

Absolute OH density and gas temperature measurements by laser induced fluorescence in a microsecond pulsed discharge generated in a conductive NaCl solution

Electrical discharges in bubbles in liquid water have been extensively investigated for many applications including water treatment and often the OH radical is considered to be a key enabler of many applications. Nonetheless, to date, no OH density measurements have been reported for discharges in bubbles or in liquids in general. In this paper, we report an investigation of discharges in bubbles by laser-induced fluorescence (LIF). The plasma was generated by applying a microsecond voltage pulse to a needle electrode submerged in an aqueous NaCl solution in a Hele-Shaw cell. To determine the gas temperature and OH radical density, a LIF model resolving the energy transfer at the rotational level was implemented. Gas compositions at different gas temperature were obtained with a 0-D kinetics model. The LIF model also enabled us to explain the non-equilibrium rotational distribution of the OH ground state by LIF. Gas temperatures and OH radical densities up to 4900 ± 800 K and 3.2 ± 0.5 × 1017 cm−3 are consistent with conditions favoring thermally driven reactions in the plasma-filled vapor bubble.

Stress response of Escherichia coli and Listeria innocua to plasma treatment

This research aimed to define the inactivation and stress response of Escherichia coli MG1655-K12 and Listeria innocua ATCC 33091 cells after the treatment by liquid phase plasma discharges in bubbles. Variations of frequency (60, 90, and 120 Hz), gas (argon or air), and processing time (5 and 10 min) have been proposed to determine their influence after the plasma treatment on E. coli and L. innocua cells. The most effective inactivation was achieved at the 60 Hz, input gas argon, and 10 min of treatment time for the E. coli sample (7.3 log10 CFU/mL). Transmission electron microscopy figures illustrated death cells and cells with well-defined cell walls and membranes despite the conducted treatment. Proteomics analysis provided insights into the molecular response mechanisms underlying the plasma treatment regime. This study demonstrated that plasma treatment caused significant alterations in proteome and indicated the proteins that may play important roles in recovering treated cells. Identified proteins were classified into six functional groups: stress response, regulation of gene expression, translation, metabolism, sugar transport, and cell division.

Electrical discharge in gas bubbles in gel

The development of electrical discharge in gas bubbles immersed in a liquid or a gel depends on the combination of the conductivity and dielectric properties of the medium as well as on the composition of the gas in the bubbles. The interest in a discharge in hydrogels is strongly stimulated by its use in combination with plasma in biology and medicine. Here, we use the electrical measurements of the current waveform and fast imaging and demonstrate the correlation between the discharge propagation in the bubble and the time evolution of the discharge current. We demonstrate experimentally that, if the dielectric constant is low and the conductivity is high (short time constant), then the discharge continues to propagate and to increase in brightness and the current continues to grow until the applied voltage is removed. The quenching of the discharge typical for dielectric barrier discharge is not observed and the effects are similar in hydrogels and in water. A simple circuit model is used to explore the dependence of the current waveform on the parameters of the medium and plasma. The shape of the current pulse significantly affects the amount of energy produced by the discharge and hence is an important property for the design and monitoring of plasma sources used for water decontamination and for plasma activation of gels.

Ultra-high synergetic intensity for humic acid removal by coupling bubble discharge with activated carbon

Humic acid (HA) removal research focuses on the global water treatment industry. In this work, efficient HA degradation with an ultra-high synergetic intensity is achieved by combined bubble discharge with activated carbon (AC). Adding AC to the discharge greatly improves HA removal efficiency and degradation speed; the synergetic intensity reaches 651.52% in the combined system, and the adsorption residual on AC is 4.52%. After 90 min of treatment, the HA removal efficiency reaches 98.90%, 31.29%, and 7.61% in the plasma-AC combined, solo bubble discharge, and solo AC adsorption systems, respectively. During the plasma process, the number of pore structures and active sites and the amount of oxygen-containing functional groups on the AC surface increase, resulting in a higher adsorption capacity to reactive species (H2O2 and O3) and HA and promoting interactions on the AC surface. For HA mineralization, the presence of AC greatly promotes the destruction of aromatic structures and chromophoric HA functional groups.

Partial discharge characteristics of bubble flow under AC non-uniform electric field in FC-72

In the present study, a test chamber filled with perfluorohexane (FC-72) is set up to investigate partial discharge (PD) in phase-cooling bubbles. Under the non-uniform electric field with needle point-to-hemisphere electrodes, thermal bubbles are generated from the needle point. The difference between PD with and without the bubbles is analyzed to identify features of the discharge in the bubbles. It is observed that the bubbles reduce the PD inception and intensify the discharge. A model of bubble motion is established to investigate bubble behavior in an electric field. Based on the observation of the flow and streamer patterns, a mechanism of PD in bubble flow is established and confirmed by phase-distribution of PDs with bubble transit time.

Formation Rate and Energy Yield of Hydroxyl Radicals in Water under the Action of Gas-Discharge Plasma

The kinetics of hydroxyl radical formation in water under the action of a pulsed discharge in vapor-gas bubbles formed near the surface of a graphite electrode immersed into water is studied. The reaction of potassium hexacyanoferrate(II) oxidation is used to determine the concentration and formation rate of OH radicals in the liquid phase. The power dissipated in the discharge is estimated from measurements of the time dependences of the current through the discharge cell, the voltage applied to the electrodes, and the integrated intensity of the discharge radiation. The yields of OH radicals per 100 eV of the energy applied to the plasma are calculated. It is found that, with an increase in power from 13 to 100 W, the rate of radical generation increases within the range of (2.8–34.8) × 10–7 mol/(L s). The radical yield weakly depends on power and is equal to 0.12 ± 0.03 particles/100 eV.

Experimental observation of interfacial oscillations and self-organization derived from streamer-driven mechanical perturbation of a gas–liquid boundary

Plasma discharges in bubbles remain an active area of research because of the associated applications in environmental remediation, agriculture and chemical processing. Plasmas in contact with the gas–liquid interface can drive chemical and physical processes, one of which is the mechanical surface perturbation leading to the formation of capillary waves. Using a 2D discharge cell, capillary waves on the surface of a 2D bubble are investigated. This study reports the observation of interfacial capillary waves on the gas–liquid interface excited by nanosecond pulsed plasma discharges. The capillary waves appear to be initiated by streamers coming into contact with the interface, with surface tension playing the role of the restoring force and viscosity contributing to damping. The waves propagating along the bubble’s surface alter the bubble’s shape. This capillary wave mode was found to be dependent on bubble size and plasma pulse frequency. Sympathetic resonant oscillations were also observed in adjacent bubbles, which indicate that capillary waves can drive acoustic oscillations and ultimately drive large-scale fluid effects. Additionally, strong surface perturbation was observed to modify the breakdown gap and as a result, led to self-organization of subsequent plasma streamers, which in turn sustains the capillary waves. In effect, plasma streamers and capillary waves are positively coupled to each other as a form of feedback, thus give insight into the interplay between plasma and fluid effects.

Application of a Passive Acoustic Method for Detection and Estimation of Shallow-Water Bubble Gas Emissions

A passive acoustic method for estimating the flow of underwater bubble gas emissions for shallow water areas has been proposed and tested. The method is based on the connection between the frequency of the acoustic signal produced by a gas bubble when it separates from the underwater outlet channel and the size of the bubble. In the conducted laboratory experiments acoustic signals with frequencies in the range from 2.7 to 0.4 kHz were recorded during generation of bubbles with a size from 2 to 15 mm within the fluid. The analysis of acoustic recordings made near existing shallow-water seeps in Laspi Bay showed a series of short audio signals produced by the released methane bubbles of 0.5–2s duration, grouped into packages containing approximately ten pulses. For the two investigated seeps, the frequency peaked at 1 and 1.4 kHz. According to a theoretical estimate, the bubbles generating such a signal are 7 and 5 mm in diameter, respectively. Taking the intensity of the bubble discharge into account, the calculated gas flows were 40 and 6 liters per day, respectively.

Mechanism of partial discharges in free helium bubbles in transformer oil

Partial discharges (PD) in floating bubbles and in microspheres made from thin glass walls in transformer oil were studied experimentally and theoretically. In a test cell, the PD occurrence was a very rare event. Sometimes PD in bubbles occurred after exposure for more than 10 hours at a voltage that corresponds to a value three times the voltage in accordance with Paschen's law. In the case of a glass microsphere, PD takes place at a voltage according to Paschen's law after several hours but afterwards PD occurs more frequently. The reason for this is in the starting electrons which initiate the first avalanche. It is shown with 100 keV X-rays that PD occurs in all bubbles and its inception voltage corresponds to Paschen's law. Theoretical analysis shows that, at the conditions of PD occurrence in helium bubbles, breakdown fits the streamer mechanism. Registrations of electrical and optical signals of PD were performed to estimate apparent and true charges and the number of radiated photons. As a result of the evaluation, the number of electrons is approximately equal to the number of photons.

Plasma-Driven Reactive Species Production and Transport in a 2-D Discharge Cell

A 2-D cell was employed to study the plasma–liquid interface. Chemical probes were used to compare the chemical reactivity induced by both air and argon plasma discharges in bubbles. Methyl orange and potassium iodide-starch solutions were used to visualize the propagation of acidic and oxidative fronts into the bulk liquid beyond the interface. Acidic and oxidative fronts were observed for both air and argon plasmas, indicating that charge exchange and electron impact processes at the interface are crucial to plasma-induced reactivity in liquids. Absorption spectrophotometry of indigo trisulfonate was performed to measure the transport of oxidative species, primarily aqueous ozone, and hydroxyl radicals, from plasma to the liquid region. Chemical reactivity at the interface can be transported far into the bulk liquid region due to plasma-induced fluid flow.