Underwater Bubble Research Articles

Fluid–structure interactions between a near-field underwater explosion bubble and a suspended plate

During near-field underwater explosions, the structural response induced by the shock wave and bubble load significantly affects the bubble collapse and jet characteristics. The effect of fluid–structure interaction (FSI) may increase the damage potential of the structure. In this study, we conduct experiments examining the interaction between small-charge underwater explosion bubbles and a suspended plate under different initial detonation distances. The morphological evolution of the bubble and the structural response are recorded using a high-speed camera and strain gauges, respectively. In addition, the bubble dynamic behaviors are simulated using the finite volume method, and an FSI model is established based on the overset mesh technology. The model is verified by comparisons between the experimental and numerical results. The physical mechanism affecting the bubble collapse pattern is revealed. The influence of the distance parameter γ between the bubble and the plate on the jet pattern and structure load is systematically studied. The findings presented in this study provide a reference for bubble-related fields and transient gas–liquid–structure interactions.

Facile Fabrication of Single-Layer Janus Membrane for Underwater Bubble Unidirectional Transport

Janus membranes with superwetting play an important role in many fields, such as oil/water separation, unidirectional fluid transportation, microfluidic devices, intelligent ion valve, mass/heat transfer applications, etc. Although there has been some progress in the preparation of the Janus membranes with unidirectional penetration, it still remains a great difficulty for facile fabrication of two dimensional Janus membranes with a large pore structure and stable bubble unidirectional transport in the water. Herein, a signal-layer Janus membrane with superwetting is fabricated via the method of liquid-regulated hydrophobic modification strategy. The resultant Janus mesh achieves underwater unidirectional penetration. Namely, Underwater bubbles can pass unidirectionally from superhydrophobic side to hydrophilic side, but are blocked from passing through in the opposite direction. Thus, this Janus membrane with the unidirectional underwater bubbles penetration “diode” performance. We believe this work can promote the development of multi-dimensional Janus materials for fluid directional transport.

Laser Microfabrication of Janus Tapered Aluminum Foil for Self‐Driven Transportation of Bubbles

The multidimensional regulation of the directional transport of bubbles is of great importance in the field of subsea gas extraction, with the increased complexity of controlling the direction of underwater bubble transport making it more challenging. Herein, drawing on a variety of bionic technologies, nanosecond laser processing combined with a low surface energy reagent modification to prepare porous hydrophobic/superhydrophobic Janus tapered aluminum foil (JTAF) is used. The wettability gradient of JTAF promotes unidirectionally self‐driven penetration of bubbles, and the shape gradient facilitates self‐driven transport of bubbles from the tip to the root. The synergistic effect of the two gradient forces endows bubbles with unidirectional self‐driven transport capability in both the buoyancy direction and the antibuoyancy direction. Finally, the JTAFs are used as bipolar electrodes in electrolysis cells to achieve gas generation, self‐driven transport, and collection processes by electrolyzing saturated saltwater. This simple, low‐cost, controlled approach to laser processing of the JTAF has tremendous potential for underwater self‐driven gas transport and is a promising tool for solving energy and environmental problems.

Bio‐inspired spontaneous splitting of underwater bubbles along a superhydrophobic open pathway without perturbation

AbstractBubbles are pervasive in aqueous media, and on account of numerous advantages of tiny bubbles, efficient bubble splitting is favorable in a wide range of applications. However, underwater bubble splitting faces a lot of challenges because bubbles tend to coalesce during the rising due to the action of buoyancy and surface energy, and the consumption of considerable external energy is needed. Inspired by the bubble bursting phenomenon on the feathers of high‐speed swimming penguins, we proposed a new bubble splitting strategy based on the energy conversion of bubble transportation on superhydrophobic open pathways. A porous superhydrophobic coating was first developed via a bubble‐template assisted fabrication method, which provides hierarchical micro/nanostructures and robust air plastron. Gas bubbles can transport along the superhydrophobic open pathways without perturbation, and split into smaller ones by taking advantage of the potential energy contributed by buoyancy. By controlling the superhydrophobic pathway, the size of the split bubbles can be controlled precisely. We also demonstrated that a bubble splitting device could be applied in underwater reactions where an enhanced gas−liquid mass transfer is desired. This bubble splitting strategy may offer new prospects for underwater bubble manipulation and unfold a potential in many bubble‐involved fields.

Research on bubble pulsation and jet loading characteristics during a near-field underwater explosion

<p indent="0mm">To deeply study the bubble jet phenomenon occurring during the near-field underwater explosion, this study performed an underwater explosion test of small equivalent TNT exploding at the bottom of a clamped square plate. The load time–history curve of the bubble jet was successfully measured by the method employing an array wall pressure sensor. The experimental results show that the peak value of the bubble pulsation pressure at the bottom center of the clamped square plate is not significantly different from the peak value of the jet pressure. However, the duration of the jet pressure is 21.36 times that of the bubble pulsation pressure. The bubble pulsation pressure and its duration slightly attenuate, while the jet pressure and its duration attenuate faster with the increasing distance from the sensor to the center, indicating a quite concentrated range of jet load. Further, the numerical simulation of the whole process from the explosion to the bubble jet formation was performed via the Abaqus software. The bubble evolution process and the bubble jet load time-history curve obtained by the simulation are consistent with the experimental results. Finally, the distribution law of the specific impulse of the bubble jet, the evolution law of the bubble jet shape, and the change law of the head speed of the bubble jet during the near-field underwater explosion bubble pulsation process are obtained through numerical simulation. This work can provide a basis for the destructive strike of surface ship structures using bubble jets formed by a near-field underwater explosion.

Control of the shape of bubble growth on underwater substrates with different sizes of superhydrophobic circles

Inspired by the everyday experience of changing the shape of a blown-up balloon by imposing a constraint, a method to control the shape of underwater bubbles is proposed by tangential constraint forces generated by the wettability difference (WD), and two bubble growth modes are distinguished based on the tangential constraint force strength and the minimum apparent contact angle (CA) of the bubble after the WD constraint. First, the critical growth shape of the bubble with a combined shape of a vertical cylinder and hemispherical top is identified, and its corresponding critical contact radius RCritical = 2.7 mm is solved by the Young–Laplace equation. Then, the effects of the radii of the superhydrophobic circle (SBC) on the bubble growth shapes are studied experimentally. The result shows that as the SBC radius decreases, the minimum apparent CA of the bubble decreases, and the minimum tangential constraint forces increase. Therefore, the bubble growth mode changes from the bell mode (with a minimum apparent CA greater than 90°) with a weaker constraint to the Ω mode (with a minimum apparent CA less than 90°) with a stronger constraint, and the bubble growth shape tends toward spherical from a flattened sphere. The maximum bubble trapping rate, Laplace pressure difference at the apex and bottom of the bubble, the aspect ratio, and the bubble filling ratio also increase as the SBC radius deceases. Furthermore, our results suggest that the proper WD-patterned arrays on underwater substrates can enhance their application efficiency, and the size of SBCS # R4 is probably the best choice in all cases.

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.

A continuous underwater bubble localization method using passive acoustic array beamforming

The bubble is an effective carrier of underwater gas leakage detection, and its rapid localization is of great significance. In this paper, a continuous underwater bubble localization method using passive acoustic array beamforming is proposed. A specific array of hydrophones was constructed to capture the bubble acoustic signal. The signal of finite length is obtained by introducing the time window. Then, the time delay compensation is carried out according to the positions of the hydrophones in the array to estimate the direction of arrival. The influence of shape, number, and aperture of the hydrophone array on the algorithm performance is studied by simulation. Moreover, the experiment was carried out in a cuboid transparent tempered glass water tank in the laboratory, and a field programmable gate array is used as the core control unit of the data processing system to complete the signal acquisition and the algorithm execution. The localization results show that the passive acoustic cross array beamforming algorithm can accurately and stably estimate the leakage direction at different positions.

Underwater Fast Bubble Generating on Pitaya Thorn and Enhanced Biomimetic Gas Collection

AbstractUnderwater bubble is vital to various applications and many technologies are applied for realizing efficient interfacial bubble generating. Here, the unique underwater bubble generating by the thorn of pitaya is reported. Extensive bubbles are generated underwater within few seconds on the thorn surface. Microbumps and dual‐scale ribs grow on the thorn surface, constructing the unique dual‐scale groove configuration along the thorn surface. Microbumps equip groove with width gradient. The mechanism of how geometric configuration of groove and surface wettability affect the bubble generating is investigated. Bioinspired study shows that groove configuration can generate bubble within 2 ms by reassembling gas column within groove, which lowers the energy barrier of bubble generating and accelerated gas molecular diffusion toward bubble. Dual‐scale groove is beneficial for strengthening surface hydrophobicity and is favorable for reassembling. Besides, width gradient induces the discrepancy of interface curvature along the groove and further accelerates the bubble generating. Accordingly, the dual‐scale gradient groove can speed up bubble generating by ≈800%. Especially, the biomimetic combinational groove can realize enhanced underwater gas collection. This research reveals a new mechanism of fast bubble generating which is of great potential for the applications based on underwater bubbles.

Investigation of the Effect of Nozzle on Underwater Detonation Shock Wave and Bubble Pulsation

The subject of a gas jet generated by underwater detonation is an important issue in the field of underwater propulsion. The experimental system of underwater detonation is established, which utilizes a high-speed camera to record the morphological changes in bubbles and various pressure sensors to measure the flow field pressure. The effect of nozzles and the pressure of the flow field are analyzed thoroughly. The comparison of the bubble and field pressure shows that the shrinking nozzle increases the peak pressure of the transmitted shock wave generated by underwater detonation compared with that of the straight nozzle. Simultaneously, the water–air mixing phenomenon caused by the gas jet is enhanced. Under the influence of the reflected shock wave and the converging angle of the nozzle, the pulsation process of the bubble is inhibited enormously, which results in the bubble energy being substantially below that of the straight nozzle. The bubble pulsation period is 24.2 ms when the shrinking nozzle is installed, and the pressure of the bubble pulsation is quite small, only 9.8 kPa. On the contrary, the expansion angle increases the velocity of the gas jet, suppressing the water–gas mixing phenomenon while enhancing the bubble pulsation process. The bubble pulsation period is 33.0 ms when the expanding nozzle is equipped, which is larger than the 31.2 ms of the straight nozzle and the bubble pulsation pressure is higher, at 26.1 kPa. Although the bubble energy is increased when the expanding nozzle is installed, thus generating a higher pulsation pressure, the peak pressure and direction of the shock wave are changed in the water.

Underwater Directional and Continuous Manipulation of Gas Bubbles on Superaerophobic Magnetically Responsive Microcilia Array

AbstractThe manipulation of underwater bubbles is of great significance in scientific research and industrial applications since they are ubiquitous and inevitable in production and life, for example, in agriculture and industry processes. Unfortunately, in an aqueous environment, the bubbles are mainly dominated by buoyancy and move upward, which makes the manipulation of bubbles difficult. To this end, numerous materials have been designed to manipulate bubbles. However, almost all of the existing materials are based on the superaerophilic surface, which has low controllability of bubble and cannot switch the transport velocity. Therefore, realizing the efficient, non‐destructive, and reversible manipulation of bubbles remains a great challenge. Herein, a novel strategy combining the superaerophobic wettability with magnetic response microcilia structure surface to achieve efficient, lossless, and reversible manipulation of bubbles is proposed. The surface can not only realize the non‐destructive manipulation of bubbles with different volumes, but also adjust the bubble transport velocity by adjusting the magnetic field. This study provides a reference for the application of bubbles in more fields and provides a basis for the development and research of expanding the application of microfluidic technology in the future.

Highly synergetic effect for norfloxacin degradation by coupling underwater bubble plasma formation with a Fe (III)–S (IV) system

• Coupling plasma with Fe (III)–S (IV) system can efficiently remediate NOR and prolong it during plasma-off. • Underwater bubble plasma accelerates radical chain reactions and improves the transfer efficiency. • Enhanced NOR degradation is attributed to the presence of • OH and SO 4 •− . • • OH and SO 4 •− can be regenerated by chain reactions through plasma-generated effects. • The synergetic degradation mechanism and possible contribution of approaches are proposed. Antibiotics are widely used to treat or prevent infectious diseases in human and veterinary medicine. Excessive residues in the aquatic environment lead to increasingly prominent antibiotic pollution; therefore, it is urgent to develop sustainable strategies for rapidly degrading antibiotics. In this study, a highly synergetic effect for norfloxacin (NOR) remediation is achieved by coupling underwater bubble plasma formation with a Fe (III)–S (IV) system due to the efficient utilization of reactive species in chain reactions. The degradation rate using synergetic approach can reach 76.4% within 50 min discharge, and further increases significantly to 94.4% after 5 h post-discharge. The effects of pulsed peak voltage and Fe (III)/S (IV) dosage on NOR removal are characterized. The existence of hydroxyl radicals ( • OH) and sulfate radicals (SO 4 •− ) are proved by electron spin resonance spectrometer (ESR) during degradation. Furthermore, radical scavenger experiments demonstrate that • OH and SO 4 •− play a crucial role in degradation. Underwater bubble plasma provides the oxic and acidic liquid environment for the Fe (III)–S (IV) system to accelerate the self-perpetuating chain reactions. These reactions not only introduce SO 4 •− and generate more • OH during plasma-on, but also induce their regeneration and further prolong the degradation process during plasma-off through plasma-generated effects. Finally, the degradation intermediates of NOR are identified, and a possible degradation pathway is proposed. The possible contribution weight of each approach on the degradation rate is speculated. These new findings offer promising applications for developing a technology with real potential for the treatment of organic compounds in industrial wastewater treatment.

Polarization Reconstruction Algorithm of Target Based on the Analysis of Noise in Complex Underwater Environment

How to effectively eliminate interference such as scattering, absorption, and attenuation is a hot topic of underwater photoelectric detection at present. Around the hot issues, this paper carries out studying the method of polarization-imaging recovery in a dynamic complex underwater environment from the theory of underwater radiation transfer, and numerical simulation of imaging interference characteristics to the simulation of underwater environment experiment. First, by conducting the analysis and simulation of scattering characteristics of underwater suspension particles and bubble by using the theory of radiation transfer, and taking advantage of quantitative description on changing tendency of radiation intensity and polarization properties of light waves in turbid water under the condition of scattering interference. Second, by constructing an underwater target polarization reconstruction model on the basis of the Mueller matrix analysis, and taking target polarization characteristic into reconstruction model on the basis of classical Schechner’s model, automatically estimating polarization information of target by the method of covariance. Finally, by building a polarization imaging system in the simulated complex underwater environment that contains bubble and suspended particles, obtaining reconstructed results with different underwater environments and different materials of target. According to experiment results, and compared with other traditional methods, using the proposed method in this paper can get higher resolution and higher contrast of target in the reconstructed result.

Experimental research of underwater explosion bubble dynamics between two parallel plates with various distances

In this article, the complex dynamics of underwater explosion bubble between two parallel plates is studied experimentally. The time and length scales of a mini-charge underwater explosion bubble are larger than those of laser-induced bubbles and spark-generated bubbles. The evolution of a bubble with dimensionless distance γ from 0.2 to 0.8 is captured using a high-speed camera in side view. Two different forms of collapse are discussed in detail. The bubble collapses at the center of two plates at a small dimensionless distance γ. With the increase of γ, the bubble splits into two sub-bubbles before collapsing and reverse jets penetrate sub-bubbles. The first pulsation periods of an underwater explosion bubble between two parallel plates are 30% to 50% larger than that of a free field bubble. The dimensionless period decreases on the whole with the increasing γ. The generation of sub-bubbles shortens whole first pulsation period of bubble significantly between γ=0.47 and γ=0.53.

Anisotropic Sliding Behaviors of Gas Bubbles upon Ferrofluid‐Infused Orthonormal Tracks (FOTs) Under Magnetic Stimuli

AbstractManipulating gas bubbles in aqueous environment exhibits both scientific and technological significance in pressure sensors, mineral flotation, and sewage disposal. Recently, the emerging ferrofluid liquid‐infused porous surfaces (FLIPS) with excellent bubble magnetism‐responsive functions have attracted great attention. Although current studies have focused on the isotropic bubble motion on FLIPS, the dynamic bubble slipping behaviors on anisotropic FLIPS has not been clarified yet. Herein, a kind of ferrofluid‐infused orthonormal tracks (FOTs) with periodic micro‐grooved structures by one‐step femtosecond laser ablation is reported, exhibiting anisotropic slipping behaviors of underwater bubbles along two orthogonal directions on FOTs. Further investigation suggests that the bubble slipping distance, that is, the interfacial resistance, is subject to the ferrofluid infusion and the external driving velocities. It is revealed that the disparity of slipping resistance is mainly related to the interfacial dissipation and the anisotropic menisci reshaped by magnetic stimuli along two orthonormal directions of FOTs. Finally, relying on the anisotropic slipping motion of gas bubbles, typical applications including bubble screening and bubble‐assisted optical shutter are demonstrated. This study should provide new insight into bubble slipping dynamics on lubricant‐infused surfaces and prompt the development of optofluidics.

Underwater bubble plume image generative model based on noise prior and multi conditional labels

The characteristics of underwater bubble plume dispersion behavior are important to assess and manage potential risks of underwater gas pipelines. In order to generate sufficient image samples for underwater bubble plume research based on artificial intelligence, we try to design an optimized generative adversarial network. In this paper, a novel underwater bubble plume image generative model that combines noise prior and multi conditional labels is proposed and evaluated using different testing dataset. In the proposed framework, the noise prior which contains the image attributes and the category features are trained with the help of VAEs, prior noise and multi conditional labels are utilized to construct the generative and discriminative models. Finally, 3 types of the underwater bubble plume images generated from the experiment is contrasted and evaluated. The experimental results show that，compared with the existing methods text2img and CGANs，the FID values of the generated images are reduced by 97.4% and 22.8% on SUIM dataset, and the FID values are reduced by 97.4% and 22.8% on BUBBLE dataset, our proposed framework achieves satisfactory and promising performance.

Electrically Induced Underwater Superaerophilicity/Superaerophobicity Switching on Polypyrrole-Coated Mesh Films for Selective Bubble Permeation.

Recently, materials with controllable superwettability have attracted much attention. However, almost all studies focused on controlling wetting of water and oil; research on underwater gas bubble wetting control is still rare. Herein, we report a mesh film prepared by coating polypyrrole (PPy) film on Ti mesh. Briefly, the film mesh is underwater superaerophilic when PPy is doped with perfluorooctanesulfonate ions (PFOS- ), and becomes underwater superaerophobic as the PFOS- are removed. The transition of the wettability can be triggered by electrical stimuli, which is attributed to the cooperative effect between the rough structure and chemical components variation. The controllable wettability allows adjustable bubble permeation. It can be envisioned that the film will provide potential applications in the future, such as underwater bubble capture/release and microfluidic devices.

Study on Vector Radiative Transmission Characteristics of Polarization Optics in Underwater Bubble Environment

Study on Vector Radiative Transmission Characteristics of Polarization Optics in Underwater Bubble Environment

Violet Phosphorus-Fe3o4 as a Novel Photocatalysis-Self-Fenton System Coupled with Underwater Bubble Plasma to Efficiently Remove Norfloxacin in Wastewater

Violet Phosphorus-Fe3o4 as a Novel Photocatalysis-Self-Fenton System Coupled with Underwater Bubble Plasma to Efficiently Remove Norfloxacin in Wastewater

Real‐Time Monitoring and Quantification of Underwater Superhydrophobicity

AbstractLong‐lasting underwater superhydrophobicity involves stable‐in‐time air layer trapped and retained between a submersed surface and the overlying liquid. Due to its underwater nature, it is rather difficult to accurately observe this air layer in submerged systems, let alone to measure it. Here, white light reflectance spectroscopy is used for real‐time monitoring (acquisition speed 50–200 ms) of underwater superhydrophobicity as well as for the calculation of the entrapped air layer thickness on “everlasting” underwater polymeric superhydrophobic surfaces fabricated by plasma micro‐nanotexturing. The proposed method enables real‐time monitoring and accurate calculation of air layers with thicknesses ranging from a few nanometers to several tens of micrometers involving small underwater bubbles. In addition, different scale topographies of superhydrophobic plasma micro‐nanotextured surfaces are tested and found to retain underwater superhydrophobicity for at least 60 days. As a demonstration, the air layer thickness is also monitored in real time when titrating water with low surface tension liquids. Among several topographies tested, a superhydrophobic surface exhibiting hierarchical topography and a high roughness ratio is able to retain a stable air layer when submersed in liquids with surface tension down to 44 mN m−1.