Bubble Diffusion Research Articles

The Formation Mechanism of Martensite and Type II Boundary in 52M/SA508-3 Joints under Different Pulse Frequencies and Their Effects on Helium Bubbles

The white bright band (WBB) in the 52M/SA508-3 pulsed TIG joint is clearly visible after metallographic etching. Increased pulse frequency leads to enhancing oscillation of the molten pool and promoting deeper heat penetration. This results in the formation of the δ/γ phase boundary, facilitating martensite and Type II boundary formation within the WBB. High-frequency pulsing refines grain structure and increases grain boundaries, inhibiting helium bubble diffusion and growth. As frequency rises from 15 kHz to 50 kHz, WBB width increases from 20 μm to 35 μm, martensite proportion from 0% to 77.1%, and austenite grain size decreases 26.1%.

Effects of oxygen levels and temperature on growth and physiology of pikeperch juveniles cultured in a recirculating aquaculture system

This study aimed to understand how environmental factors, specifically water temperature and oxygen saturation, affect the growth performance and physiology of pikeperch (Sander lucioperca) juveniles in recirculating aquaculture systems (RASs). Given the importance of optimising growth conditions in aquaculture to maximise efficiency, it aims to assess whether different combinations of oxygen levels and temperatures can enhance growth while maintaining the physiological health and welfare of the fish. The experimental design included the culturing pikeperch juveniles (22.7 ± 7.1 g) were exposed to hypoxia (78 ± 14%), normoxia (105 ± 12%), and hyperoxia (140 ± 18%) conditions for 72 days. This was conducted at two temperatures, 20 °C and 23 °C, each in a separate but identical RAS. The level of oxygen supply was controlled with micro bubble diffusers on the bottom of each tank. The hyperoxia at 23 °C positively affected total length, BW, specific growth rate, feed intake and feed conservation rate (FCR). The slowest growth and feed intake, along with the highest FCR, were observed in hypoxia at 20 °C. Fish reared under 23 °C exhibited significantly higher visceral-somatic index (3.54 ± 0.83 at 23 °C and 2.76 ± 0.73 at 20 °C) regardless of oxygen levels. It was primarily responsible for the observed growth difference (Final BW: 58.3 ± 18.8 g at 23 °C and 53.0 ± 18.3 g at 20 °C). The water temperature also affected haematocrit, haemoglobin, leucocyte count, mean corpuscular haemoglobin, mean corpuscular volume (MCV) of the blood cells; the concentration of lymphocytes, neutrophile granulocyte bands and segments. Among biochemical markers, temperature affected cytoplasmic and mitochondrial enzymes, ammonia and triglyceride levels in blood plasma. Elevated antioxidant activity was observed in muscle, intestine and liver tissues. Oxygen levels demonstrated significant effects on growth, feed intake and conversion, the MCV of the blood cells, the concentration of the glucose, lactate and ammonia in blood plasma, and antioxidant biomarkers in the liver tissue. The analysis indicated a significant effect of oxygen on energy metabolism. The results showed hyperoxia under 23 °C create conditions for the highest growth and feed intake, high feed utilisation. There are, however, concerns about the physiological conditions and welfare of intensively cultured pikeperch juveniles, as higher feed intake led to increased visceral fat content in the body, elevated antioxidant activity in the liver, muscle and intestine tissues, morphology of blood cell, and energy metabolism.

Vertical Conductive Metal-Organic Framework Single-Crystalline Nanowire Arrays for Efficient Electrocatalytic Hydrogen Evolution.

The construction of crystalline metal-organic frameworks with regular architectures supportive of enhanced mass transport and bubble diffusion is imperative for electrocatalytic applications; however, this poses a formidable challenge. Here, a method is presented that confines the growth of nano-architectures to the liquid-liquid interface. Using this method, vertically oriented single crystalline nanowire arrays of an Ag-benzenehexathiol (BHT) conductive metal-organic framework (MOF) are fabricated via an "in-plane self-limiting and out-of-plane epitaxial growth" mechanism. This material has excellent electrocatalytic features, including highly exposed active sites, intrinsically high electrical conductivity, and superhydrophilic and superaerophobic properties. Leveraging these advantages, the carefully designed material demonstrates superior electrocatalytic hydrogen evolution activity, resulting in a low Tafel slope of 66mVdec-1 and a low overpotential of 275mV at a high current density of 1Acm-2. Finite element analysis (FEA) and in situ microscopic verification indicates that the nanowire array structure significantly enhances the electrolyte transport kinetics and promotes the rapid release of gas bubbles. The findings highlight the potential of using MOF-based ordered nanoarray structures for advanced electrocatalytic applications.

Revamping of a Full-Scale Membrane Plant for Landfill Leachate Pretreatment Using Partial Nitritation.

This paper describes a case study involving a revamping of a full-scale membrane bioreactor that treats landfill leachate and other liquid wastes. The main change was the introduction of nitritation/denitritation in alternating cycles instead of the classic denitrification/nitrification process, together with the installation of fine bubble diffusers, a reduction in the volume of the biological compartment, and an increase in the equalization volume. The most significant results were obtained for the biological compartment, with a decrease in the specific energy consumption of 46.6%. At the same time, the removal efficiency of COD, BOD, and TN substantially remained the same before and after plant revamping, while the removal efficiency of TP increased over the years, reaching an average value of almost 71%. Regarding the ultrafiltration unit, the specific flux (or permeability) was characterized by an increasing trend. At the same time, the specific energy consumption of this section decreased by 9.4%. These results led to the conclusion that the changes introduced with the revamp led to a more stable process, a reduction in membrane fouling, and important energy savings.

Energy-efficient bubble aeration guided by bubble dynamics model: From bubble formation at submerged orifice to oxygen utilization during uprising

Bubble aeration is a significant consumer of energy in wastewater treatment processes. Optimizing oxygen transfer, from an energy usage perspective, is crucial in the development of clean production techniques and for the stimulation of the circular economy. Although large efforts have been made in enhancing this process, particularly in ameliorating bubble diffusers, a main problem lies in energy wastage due to over-pursuing ultra-fine bubble generation. In this study, a dynamic model, that integrated both bubble expansion and detachment at submerged orifices, and consequential oxygen utilization during the uprising, was developed in order to better facilitate energy savings during the control of bubble generation. We demonstrate through calibrated models that bubble formation is governed by many factors including gas flow rate, orifice radius, surface tension, liquid viscosity, and surface wettability. Small bubbles are more prone to form when subjected to conditions of high wettability, small orifice size and low flow rate, since the bubbles are easily detached by the increasing upward forces in these scenarios. The oxygen transfer during the rising process was calculated as a function of bubble size, gas type and water depth. Bubbles with a radius smaller than a threshold value can shrink and collapse while below the water surface and thus provide 100% oxygen utilization. The threshold values of bubble radius are determined to be 150 μm and 250 μm at 5 m and 15 m initial water depth, respectively. The parameter set for bubble generation in order to obtain the desired bubble size may then be inversely determined by our bubble formation model, and it's considered as optimal aeration strategy to realize precise aeration. With these results, our study highlights the viability of the approach employing the proposed model in order to direct energy-efficient bubble generation.

Influence of bubble size on perfluorooctanesulfonic acid degradation in a pilot scale non-thermal plasma treatment reactor

A 25L working volume non-thermal plasma-based treatment reactor was trialled to destroy per- and polyfluoroalkyl substances (PFAS) utilising argon bubbles to transport PFAS to the surface to be destroyed with plasma interaction at the argon-liquid interface. The breakdown rate of PFAS and the system's overall energy efficiency could be improved while minimising gas usage by utilising small bubbles (0.6–0.7 mm d32) to maximise the transport of PFAS to the plasma discharge for destruction. Vertically scaling the treatment reactor dimensions increases the overall liquid height and dwell time for bubbles to contact and transport PFAS molecules to the surface. The removal rate of perfluorooctane sulfonate (PFOS) correlated with the total surface area of the gas. Significant concentration gradients of PFOS could be observed when sampling from different liquid heights within the 25 L reactor. A one-dimensional model of mass transfer to the surface of rising bubbles was developed and gave good predictions of the overall rates of PFOS breakdown with modelled time constants of 0.14–0.18 min−1 versus 0.16 ± 0.01 min−1 for the fine bubble diffuser, and 0.048–0.053 min−1 versus 0.06 min−1 for the medium bubble diffuser. The time constant compared favourably with similar experiments at the 2 L scale of 0.11 min−1.

Air bubble curtain improves the welfare of captive rainbow trout fry and fingerlings

Fish welfare is becoming a priority for the fish farming industry. The search for practical, easy-to-implement methods to promote farmed fish welfare is therefore essential. Environmental enrichment aims to improve the psychological and physiological needs of a captive animal by increasing the complexity of its environment. During previous studies, we observed that fish seemed to be positively affected by short diffusions of air bubbles. In this study, we evaluated the effects of an innovative enrichment strategy consisting of introducing into the tank at the earliest stages of life, a pipe generating a curtain of air bubbles. Using rainbow trout (Oncorhynchus mykiss) as a captive fish model, we compared the short- (∼7 weeks) and long-term (∼21 weeks) effects of this bubble curtain diffused for one hour four times a day (Bubble condition) to a standard condition without bubbles (Control) on fish growth, aggressive and abnormal behaviors, as well as on fish motivation to access a bubble curtain, their emotional responses and their learning abilities. We found that bubble diffusion decreased aggressive and abnormal behaviors during diffusions in both the short-term and the long-term experiments. In the long-term experiment, this decrease was also observed during feedings and neutral periods when no bubble was diffused. Bubbles were found to be attractive for young Control fish (bubble-naive fish) subjected to a motivation test in the short-term experiment. When subjected to the emotional reactivity test, Bubble fish seemed less fearful, exhibiting a lower maximum velocity than Control fish in the long-term experiment only. However, the other behavioral parameters measured during this test, appetite and plasma cortisol levels were similar between treatments, irrespective of the experimental period. The latency to consume the reward observed in the spatial learning test in the long-term experiment was decreased in Bubble fish compared with Control fish, showing enhanced learning abilities in fish that experienced bubbles for 21 weeks. Growth parameters and fin erosion index did not differ between treatments. We conclude that repeated bubble diffusions act as an environmental enrichment for fish, combining physical, occupational, and sensory enrichment via the tactile stimulations provided by the air bubbles. This type of enrichment had a positive impact on the behavior of farmed rainbow trout in the long term, and would make it possible to integrate the notion of “positive welfare” into fish farms, while guaranteeing easy technical maintenance.

Hierarchical FeOxHy@Ni3B hybrid for efficient alkaline oxygen evolution at high current density

Electrocatalysts with high activity and long-term durability are vital toward large-scale hydrogen production from electrocatalytic water splitting. Here, the self-supported electrode (FeOxHy@Ni3B/NF) with hierarchical heterostructure was simply prepared by using Ni3B chunks grown on nickel foam as substrate to in situ form vertical FeOxHy nanosheets. Such hybrid shows efficient oxygen evolution reaction activity with overpotentials as low as 267 and 249 mV at 100 mA cm−2 in 1 M KOH solution and 30 wt% KOH solution, respectively. Meanwhile, it also exhibits excellent catalytic stability, sustaining catalysis at 500 mA cm−2 in 1 M KOH solution for 200 h, and even for 200 h at 1000 mA cm−2 in 30 wt% KOH solution. Further experimental results reveal that the FeOxHy@Ni3B/NF is endowed with superhydrophilic and superaerophobic surface properties, which not only provide more mass transport channels, as well as facilitated the diffusion of reaction intermediates and gas bubbles. Also, it holds faster reaction kinetics, more accessible active sites and accelerated electron transfer rates due to strong synergistic interactions at the heterogeneous interface.

Bubble Unidirectional Transportation on Multipath Aerophilic Surfaces by Adjusting the Surface Microstructure.

Comprehending and controlling the behavior of bubbles on solid surfaces is of significant importance in various fields including catalysis and drag reduction, both industrially and scientifically. Herein, Inspired by the superaerophilic properties of the lotus leaf surface, a series of asymmetrically patterned aerophilic surfaces were prepared by utilizing a facile mask-spraying method for directional transport of underwater bubbles. The ability of bubbles to undergo self-driven transportation in an asymmetric pattern is attributed to the natural tendency of bubbles to move toward regions with lower surface energy. In this work, the microstructure of the aerophilic surface is demonstrated as a critical element that influences the self-driven transport of bubbles toward regions of lower surface energy. The microstructure characteristic affects the energy barrier of forming a continuous gas film on the final regions. We classify three distinct bubble behaviors on the aerophilic surface, which align with three different underwater gas film evolution states: Model I, Model II, and Model III. Furthermore, utilizing the energy difference between the energy barrier that forms a continuous gas film and the gas-gas merging, gas-liquid microreaction in a specific destination on the multiple paths can be easily realized by preinjecting a bubble in the final region. This work provides a new view of the microevolutionary process for the diffusion, transport, and merging behavior of bubbles upon contact with an aerophilic pattern surface.

Einstein–Stokes relation for small bubbles at the nanoscale

As the physicochemical properties of ultrafine bubble systems are governed by their size, it is crucial to determine the size and distribution of such bubble systems. At present, the size or size distribution of nanometer-sized bubbles in suspension is often measured by either dynamic light scattering or the nanoparticle tracking analysis. Both techniques determine the bubble size via the Einstein–Stokes equation based on the theory of the Brownian motion. However, it is not yet clear to which extent the Einstein–Stokes equation is applicable for such ultrafine bubbles. In this work, using atomic molecular dynamics simulation, we evaluate the applicability of the Einstein–Stokes equation for gas nanobubbles with a diameter less than 10 nm, and for a comparative analysis, both vacuum nanobubbles and copper nanoparticles are also considered. The simulation results demonstrate that the diffusion coefficient for rigid nanoparticles in water is found to be highly consistent with the Einstein–Stokes equation, with slight deviation only found for nanoparticle with a radius less than 1 nm. For nanobubbles, including both methane and vacuum nanobubbles, however, large deviation from the Einstein–Stokes equation is found for the bubble radius larger than 3 nm. The deviation is attributed to the deformability of large nanobubbles that leads to a cushioning effect for collision-induced bubble diffusion.

1D/3D hierarchical carbon skeleton confined NiFe nanoparticles with optimized three-phase interfaces as tri-functional electrocatalysts

Multilevel 1D/3D CNTs/carbon spheres with hydrophilicity can promote the infiltration of an electrolyte into the interior and guide bubble diffusion, thus constructing an optimal gas–solid–liquid interface to enhance the electrocatalytic process.

Ozone and photodynamic inactivation of norovirus surrogate bacteriophage MS2 in fresh Brazilian berries and surfaces

This study assessed the efficacy of ozone (bubble diffusion in water; 6.25 ppm) and photodynamic inactivation (PDT) using curcumin (75 μM) as photosensitizer (LED emission 430–470 nm; 33.6 mW/cm2 irradiance; 16.1, 20.2, and 24.2 J/cm2 light dose) against the Norovirus surrogate bacteriophage MS2 in Brazilian berries (black mulberry and pitanga) and surfaces (glass and stainless steel). Contaminated berries and surfaces were immersed in ozonized water or exposed to PDT-curcumin for different time intervals. Transmission electron microscopy was used to assess the effects of the treatments on MS2 viral particles. The MS2 inactivation by ozone and PDT-curcumin varied with the fruit and the surface tested. Ozone reduced the MS2 titer up to 3.6 log PFU/g in black mulberry and 4.1 log PFU/g in pitanga. On surfaces, the MS2 reduction by ozone reached 3.6 and 4.8 log PFU/cm2 on glass and stainless steel, respectively. PDT-curcumin reduced the MS2 3.2 and 4.8 log PFU/g in black mulberry and pitanga and 2.7 and 3.3 log PFU/cm2 on glass and stainless steel, respectively. MS2 particles were disintegrated by exposure of MS2 to ozone and PDT-curcumin on pitanga. Results can contribute to establishing effective practices for controlling NoV in fruits and surfaces, estimated based on MS2 bacteriophage behavior.

Pneumorachis, A Rare Post-Traumatic Complication

The presence of air in the spinal canal defines pneumorachis, which is a rarely reported entity; exceptionally, it is found during a road traffic accident (MVA). We present the case of a 36-year-old patient who suffered an MVA. The work-up showed multiple fractures of the cephalic extremity, pneumocephalus, pulmonary contusions, pneumomediastinum, moderate bilateral hemopneumothorax, thoracic vertebral and costal fractures and moderate cervicothoracic pneumorachis. Spinal lesions are thought to be the cause of this pneumorachis. Lesions of the parietal pleura and meninges are thought to be responsible for air escaping from the pleural space into the spinal canal from D2 to D7. Although rare, the literature reports similar observations of post-traumatic pneumorachis. The diffusion of air bubbles into the spinal canal is a direct consequence of the rupture of a solid organ and a spinal lesion. The discovery of air bubbles should therefore prompt a search for other lesions that may explain their formation.

Vertical diffusion of bubbles injected beneath a flat-bottomed ship for frictional drag reduction

There has been concern about the short effective distance of frictional drag reduction achieved by air lubrication, but recent model ship experiments have shown over 30 m longer than our expectation. Also, the reduction ratio can be improved through the artificial generation of void waves appearing beneath the hull. These topics relate to the spatiotemporal bubble distribution and an understanding of them requires clarification of the distribution. In this study, optical probes were used to measure the distributions of bubble states beneath a 20-m long flat-bottomed ship towed with 6–8 m/s. The measurements explained the long effective distance of drag reduction and the process of void wave generation and development. The drag reduction ratio was about 7–25% and mainly depended on the void fraction within 10 mm of the hull. The vertical distribution of the void fraction remained unchanged over long downstream distances. The development of void waves was affected by the streamwise velocity difference between bubble clusters near the hull. The velocity was determined by the number density of the bubbles, decreasing to the half of ship speed until reaching a certain number density, 100 per meter in our experiments, and then becoming constant at higher density.

Facile synthesis of hierarchically ordered Mo2C/Co3Mo3C@C nanosheet heterostructure: A highly durable pH universal electrocatalyst for hydrogen evolution reaction and overall alkaline water splitting

Developing cost-effective, high-efficiency, earth-abundant electrode materials for hydrogen evolution reaction (HER) operating in wide pH range electrolytes is significant for large-scale hydrogen generation. However, the rational design of highly stable electrocatalysts with robust performance remains challenging. Herein, in-situ construction of hierarchically ordered Mo2C/Co3Mo3C nanosheet heterostructure (CMC/MC@C) is achieved by the simple pyrolysis method. The optimized Co1Mo1C/550 catalyst achieves a low HER overpotential of 86, 102, and 323 mV at 10 mA cm−2 current density in 1.0 M KOH, 0.5 M H2SO4, and 0.1 M PBS solutions, respectively, with robust durability over 48 h. Benefiting from the bifunctionality of Co1Mo1C/550, the electrocatalyst achieves a current density of 10 mA cm−2 at a low overpotential of 336 mV towards the oxygen evolution reaction (OER) and 1.597 V for overall water splitting in a 1.0 M KOH solution. The exceptional performance of the as-prepared catalyst is primarily attributable to the strong synergistic relationship between Co3Mo3C and Mo2C particles, hierarchically ordered porous carbon nanosheet structure, and superhydrophilic electrode surface, which not only provide rich exposed active sites but also boost the access of electrolytes and the diffusion of H2 bubbles, thereby effectively enhancing the HER and OER performances. This study offers a new approach to the rational design of various transition metal-based carbide electrode materials via the structural optimization strategy for reliable and efficient universal pH catalysts towards HER and overall alkaline water splitting.

Delivery of ultrasound cavitation therapy with a modified clinical scanner

Ultrasound-induced bioeffects from stable and inertial cavitation of microbubbles in tumors have been shown to enhance systemic drug delivery. However, the high pressures and long cycle lengths needed for cavitation treatment are not available on current clinical ultrasound scanners. Here, we implement acoustic conditions (1.6 MHz, 12-500 cycles, <3 MPa, 10-200 Hz PRF) suitable for cavitation treatments (USCTx) on the S5-1 probe of a Philips EPIQ scanner. Hydrophone measurements confirmed the acoustic conditions. Passive cavitation detection (PCD) in solutions and tissue mimicking phantoms containing microbubbles demonstrated the spatial and temporal extent of the produced cavitation with 20 consecutive pulses. Inertial cavitation was observed at peak negative pressures of ∼0.5 MPa and ∼0.9 MPa in the solutions and phantoms, respectively. At low PRFs (<100 Hz), inertial cavitation was only observed within the first 5-10 pulses for both media, suggesting USCTx may generate most bioeffects in the first few pulses. The higher PRFs sustained cavitation activity for a greater duration, consistent with gas diffusion of micron size bubbles after shell disruption with the first pulse. Having implemented USCTx with a clinical scanner and confirmed the produced cavitation in vitro, we plan to evaluate this technique in an upcoming mouse study.

Self-supported crystalline-amorphous composites of metal phosphate and NiS for high-performance water electrolysis under industrial conditions

Developing affordable and efficient electrocatalysts toward water electrolysis under industrial conditions is crucial for large-scale production of green hydrogen. In this regard, we propose a facile and mild method to construct crystalline-amorphous composites of metal phosphate (MPi) and NiS on nickel foam (NF) for practical water electrolysis. The as-prepared electrodes exhibit excellent performance, achieving a remarkable current density of 1000 mA cm–2 at the ultralow overpotential of 345 and 223 mV for FePi-NiS/NF (oxygen evolution reaction, OER) and NiCoPi-NiS/NF (hydrogen evolution reaction, HER), respectively. The composites can undergo an in-situ transformation into highly active and targeted species under high current density, which possess a unique pore structure interconnected by nanosheets that provides an abundance of catalytic sites and open channels for efficient bubble diffusion. When operated under industrial conditions (6 M KOH, 70 °C), the assembled electrode requires only 1.712 V to attain a current density of 1000 mA cm−2. The electrodes also demonstrate exceptional performance in alkaline electrolysis with an anion exchange membrane (AEMWE) when scaled up to a larger size (area: ≈ 25 cm2). Specifically, they achieve a substantial current of 12.5 A at 1.87 V with a high energy efficiency of 79.2 % and remarkable durability over 30 h under industrial electrolysis conditions (1 M KOH, 50 °C), outperforming benchmark Pt/C/NF || IrO2/NF electrodes with energy saving of 0.215 kWh Nm–3. This work provides a cost-effective and efficient strategy for designing and constructing stable and active catalysts for water electrolysis under harsh industrial conditions.

Pre‐Eruptive Outgassing and Pressurization, and Post‐Fragmentation Bubble Nucleation, Recorded by Vesicles in Breadcrust Bombs From Vulcanian Activity at Guagua Pichincha Volcano, Ecuador

AbstractBreadcrust bombs formed during Vulcanian eruptions are assumed to originate from the shallow plug or dome. Their rim to core texture reflects the competition between cooling and degassing timescales, which results in a dense crust with isolated vesicles contrasting with a highly vesicular vesicle network in the interior. Due to relatively fast quenching, the crust can shed light on pre‐ and syn‐eruptive conditions prior to or during fragmentation, whereas the interior allows us to explore post‐fragmentation vesiculation. Investigation of pre‐ to post‐fragmentation processes in breadcrust bombs from the 1999 Vulcanian activity at Guagua Pichincha, Ecuador, via 2D and 3D textural analysis reveals a complex vesiculation history, with multiple, spatially localized nucleation and growth events. Large vesicles (Type 1), present in low number density in the crust, are interpreted as pre‐eruptive bubbles formed by outgassing and collapse of a permeable bubble network during ascent or stalling in the plug. Haloes of small, syn‐fragmentation vesicles (Type 2), distributed about large vesicles, are formed by pressurization and enrichment of volatiles in these haloes. The nature of the pressurization process in the plug is discussed in light of seismicity and ground deformation signals, and previous textural and chemical studies. A third population (Type 3) of post‐fragmentation small vesicles appears in the interior of the bomb, and growth and coalescence of Type 2 and 3 vesicles causes the transition from isolated to interconnected bubble network in the interior. We model the evolution of viscosity, bubble growth rate, diffusion timescales, bubble radius and porosity during fragmentation and cooling. These models reveal that thermal quenching dominates in the crust whereas the interior undergoes a viscosity quench caused by degassing, and that the transition from crust to interior corresponds to the onset of percolation and development of permeability in the bubble network.

Effects of a sidestream concentrated oxygen supply system on the membrane filtration performance of a high-loaded membrane bioreactor

To investigate the influence of high-pressure and shear effects introduced by a concentrated oxygen supply system on the membrane filtration performance, a laboratory-scale membrane bioreactor (MBR) fed artificial municipal wastewater was operated continuously for 80 days in four phases equipped with different aerations systems: (P1) bubble diffusers (days 0–40), (P2) concentrated oxygen supply system, the supersaturated dissolved oxygen (SDOX) (days 41–56), (P3) bubble diffusers (days 57–74), and (P4) SDOX (days 75–80). Various sludge physical-chemical parameters, visual inspection of the membrane, and permeability evaluations were performed. Results showed that the high-pressure effects contributed to fouling of the membranes compared to the bubble diffuser aeration system. Biofouling by microorganisms appeared to be the main contributor to the cake layer when bubble diffusers were used, while fouling by organic matter seemed to be the main contributor to the cake layer when SDOX was used. Small particle size distribution (PSD) (ranging from 1 to 10 and 1–50 μm in size) fractions are a main parameter affecting the intense fouling of membranes (e.g., formation of a dense and thin cake layer). However, PSD alone cannot explain the worsened membrane fouling tendency. Therefore, it can be assumed that a combination of several factors (which certainly includes PSD) led to the severe membrane fouling caused by the high-pressure and shear.

Applicability Analysis of a Multi-Filar Meander R-SFCL and an RSC-DCCB in an MMC-MTDC Grid

modular multilevel converters (MMC)-based high voltage direct current (HVDC) topology is an effective solution to solve the power transmission demand between countries. However, the initial fault current can rise to several tens of kA within a few ms by capacitor discharge during a fault. This fault current can permanently damage the converter components and cables. Therefore, to increase the stability of the system, the protection of the DC system is very important. DC system protection methods include circuit breaker technologies and current limiting technologies. We have selected a circuit breaker with combined resonant current source (RCS) and a resistive superconducting fault current limiter (SFCL) as protection methods for the DC system. The RSC-DC circuit breaker has no conduction power losses by on-state voltage drop. Therefore, it can provide stable interruption compared to a solid-state DC circuit breaker. Since the resistive SFCL has a very fast response time, it can effectively limit the rapidly rising initial fault current. We wound the superconducting tape by the multi-filar meander method. This method can increase the length of the superconducting tape used and speed up the bubble diffusion during quenching. We modeled an MMC-HVDC grid, resistive SFCL, and RCS DC circuit breaker using PSCAD/EMTDC. In this paper, the interrupting and current limiting characteristics are discussed when the resistive SFCL and the RCS-DC circuit breaker proposed by us are connected to the MMC-based MTDC grid. In the simulation, the current limiting factor of resistive SFCL was up to about 58%. In addition, the combination of resistive SFCL and RCS-DC circuit breaker can shorten the interruption time when the fault occurs.