Bubble Dynamics Research Articles

Bubble Theory and its Applications in Underwater Explosion, Marine Cavitation, and Seismic Exploration

AbstractBubbles play crucial roles in various fields, including naval and ocean engineering, chemical engineering, and biochemical engineering. Numerous theoretical analyses, numerical simulations, and experimental studies have been conducted to reveal the mysteries of bubble motion and its mechanisms. These efforts have significantly advanced research in bubble dynamics, where theoretical study is an efficient method for bubble motion prediction. Since Lord Rayleigh introduced the theoretical model of single-bubble motion in incompressible fluid in 1917, theoretical studies have been pivotal in understanding bubble dynamics. This study provides a comprehensive review of the development and applicability of theoretical studies in bubble dynamics using typical theoretical bubble models across different periods as a focal point and an overview of bubble theory applications in underwater explosion, marine cavitation, and seismic exploration. This study aims to serve as a reference and catalyst for further advancements in theoretical analysis and practical applications of bubble theory across marine fields.

Insights Into Pool Boiling Heat Transfer on Minichannel Surfaces Through Point and Field Measurements

Abstract In this study, saturated pool boiling experiments were conducted on copper minichannel and flat surfaces at atmospheric pressure using water as the working fluid. The heat transfer performance was assessed through point measurements with a heater block, cartridge heaters, and thermocouples, as well as field measurements using a thin-foil heater and infrared thermography. Two copper minichannel surfaces with square cross sections of 1 mm (minichannel-1) and 2 mm (minichannel-2) side lengths were tested and compared to a flat surface. Minichannel-1 and minichannel-2 enhanced the critical heat flux (CHF) by 17% and 45%, respectively, and improved the heat transfer coefficient by 24–40% and 51–75%, respectively, compared to the flat surface. Minichannel-2 exhibited the lowest and most uniform boiling surface temperature, making it the best performer among the three. There was no significant change in departure frequency among the surfaces, and no significant change in departure diameter for the flat surface and minichannel-1. However, minichannel-2 had lower departure diameters due to its deeper channels, which prevented bubble coalescence and maintained low departure diameters. Additionally, minichannel-2 delayed vapor film formation by breaking it with its deeper fins, thereby improving CHF and slightly enhancing bubble dynamics. The enhancement in boiling heat transfer is primarily attributed to the increased surface area provided by the minichannels, with a minor contribution from improved bubble dynamics. However, the dominant factor in enhancing pool boiling heat transfer on minichannel surfaces is the increase in surface area.

A theoretical model for compressible bubble dynamics considering phase transition and migration

A novel theoretical model for bubble dynamics is established that simultaneously accounts for the liquid compressibility, phase transition, oscillation, migration, ambient flow field, etc. The bubble dynamics equations are presented in a unified and concise mathematical form, with clear physical meanings and extensibility. The bubble oscillation equation can be simplified to the Keller–Miksis equation by neglecting the effects of phase transition and bubble migration. The present theoretical model effectively captures the experimental results for bubbles generated in free fields, near free surfaces, adjacent to rigid walls, and in the vicinity of other bubbles. Based on the present theory, we explore the effect of the bubble content by changing the vapour proportion inside the cavitation bubble for an initial high-pressure bubble. It is found that the energy loss of the bubble shows a consistent increase with increasing Mach number and initial vapour proportion. However, the radiated pressure peak by the bubble at the collapse stage increases with decreasing Mach number and increasing vapour proportion. The energy analyses of the bubble reveal that the presence of vapour inside the bubble not only directly contributes to the energy loss of the bubble through phase transition but also intensifies the bubble collapse, which leads to greater radiation of energy into the surrounding flow field due to the fluid compressibility.

Investigation of bubble interaction in a temporal and spatial heat flux partitioning model for subcooled flow boiling

CFD methodology for subcooled flow boiling is significantly affected by the heat flux partitioning model, which plays a crucial role in predicting the mass source term generated by wall boiling of the liquid phase. Although numerous models have been proposed, most research efforts have focused on the spatial dimensions of boiling heat transfer mechanisms, neglecting the temporal aspect. This study presents a heat flux partitioning model for subcooled flow boiling that considers both temporal and spatial dimensions. The model accounts for the contribution of heat flux from the superheated liquid layer during the bubble growth stage, liquid convection during the bubble wait stage within the bubble influence area in the temporal dimension, and heat flux from the overlapping area of bubble influence in the spatial dimension. An approach was developed to determine the bubble influence area by considering the bubble interaction based on the stochastic nature of nucleation sites on the heated wall, verified by the Monte Carlo method. The bubble dynamics parameters were experimentally derived to reduce the uncertainty associated with the boiling sub-models on the calculation. A comparative analysis of boiling curves and wall heat flux partitioning was conducted between the present model and the RPI model under various flow conditions. The results indicate that both models could reasonably predict the boiling curve. However, the RPI model tends to over-predict the proportion of evaporative heat flux, which is considered a weakness. Based on physical principles, the present model accurately captures the fundamental trend of wall heat flux partitioning. This research enhances the understanding of subcooled flow boiling and increases confidence in multiphase CFD methodology predictions.

Unveiling the fundamentals of flow boiling heat transfer enhancement on structured surfaces.

Micro- and nanostructured surfaces offer the potential to enhance two-phase heat transfer. However, the mechanisms behind these enhancements are not well-understood due to insufficient diagnostic methods, leading to reliance on trial-and-error surface development. We introduce in situ boroscopy to investigate microscale bubble dynamics during flow boiling nucleation and subsequent flow regime development. This method was applied in saturated flow boiling experiments within chemically etched aluminum and copper tubes. Although the surfaces have self-similar surface structures, our findings revealed varied heat transfer coefficient enhancements, with increases of up to 391% on aluminum and 41% on copper. Using boroscopy, we identified key mechanisms of heat transfer enhancement. We further used mercury porosimetry to determine the impact of pore size distribution on thermal performance. The boroscopy technique introduced here not only elucidates the underlying processes of flow boiling heat transfer enhancement but also has potential applications for the study of other two-phase phenomena.

Assessment of Cavitation Erosion Using Combined Numerical and Experimental Approach

This paper aims to numerically assess the cavitation damage of hydrodynamic machines and hydraulic components and its development in time, based on cavitation erosion tests with samples of used materials. The theoretical part of this paper is devoted to the numerical simulation of unsteady multiphase flow by means of computational fluid dynamics (CFD) and to the prediction of the erosive effects of the collapses of cavitation bubbles in the vicinity of solid surfaces. Compressible unsteady Reynolds-averaged Navier–Stokes equations (URANS) are solved together with the Zwart cavitation model. To describe the destructive collapses of vapor bubbles, the modeling of cavitation bubble dynamics along selected streamlines or trajectories is applied. The hybrid Euler–Lagrange approach with one-way coupling and the full Rayleigh–Plesset equation (R–P) are therefore utilized. This paper also describes the experimental apparatus with a rotating disc used to reach genuine hydrodynamic cavitation and conditions similar to those of hydrodynamic machines. The simulations are compared with the obtained experimental data, with good agreement. The proposed methodology enables the application of the results of erosion tests to the real geometry of hydraulic machines and to reliably predict the locations and magnitude of cavitation erosion, so as to select appropriate materials or material treatments for endangered parts.

The structure and dynamics of the laminar separation bubble

A novel selective mode decomposition, proper orthogonal decomposition and dynamic mode decomposition methods are used to analyse large-eddy simulation data of the flow field about a NACA0012 airfoil at low Reynolds numbers of $5\times 10^4$ and $9\times 10^4$ , and at near-stall conditions. The objective of the analysis is to investigate the structure of the laminar separation bubble (LSB) and its associated low-frequency flow oscillation (LFO). It is shown that the flow field can be decomposed into three dominant flow modes: two low-frequency modes (LFO-Mode-1 and LFO-Mode-2) that govern an interplay of a triad of vortices and sustain the LFO phenomenon, and a high-frequency oscillating (HFO) mode featuring travelling Kelvin–Helmholtz waves along the wake of the airfoil. The structure and dynamics of the LSB depend on the energy content of these three dominant flow modes. At angles of attack lower than the stall angle of attack and above the angle of a full stall, the flow is dominated by the HFO mode. At angles of attack above the stall angle of attack the LFO-Mode-2 overtakes the HFO mode, triggers instability in the LSB and initiates the LFO phenomenon. Previous studies peg the structure, stability and bursting conditions of the separation bubble to local flow parameters. However, the amplitude of these local flow parameters is dependent on the energy content of the three dominant flow modes. Thus, the present work proposes a more robust bursting criterion that is based on global eigenmodes.

Vapor Channel Oscillations in Laser Lithotripsy.

Laser-based endoscopic procedures present special challenges to deliver energy for ablation or coagulation of target tissues. When optical fiber-target quasi-contact (< 0.5 mm distance) cannot be maintained or is undesirable, the creation of intervening vapor bubbles and channels provide for the necessary transmission of laser energy to the target. This work investigates the characteristics and the dynamics of vapor channels that directly affect ablation efficiency and ablation rate and are known to effect stone movement, all of which impact procedure efficiency and safety. A simplified, experimental model for thulium fiber laser (1940 nm) lithotripsy consists of a water-filled cuvette and a vertically oriented laser fiber (200 μm core diameter) with its tip at 9 mm for "quasi-free" bubble generation and at vapor channel working distances 1-5 mm from and centered on the transparent cuvette bottom simulating a target's surface. Laser power transmission is recorded and synchronized with video frames from a high-speed camera (24,260 frames per second) to capture the induced vapor channels' and bubbles' development. Laser-induced channel transmission from 0% to 100% for 1, 2, and 3 mm fiber-target distances undergoes oscillations with average periods of 0.32, 0.64, and 1.0 ms, respectively, for 500 W laser output power. For fixed fiber-target distances of 0.5, 1, and 2 mm, the variation of these average oscillation frequencies across laser powers from 500 to 1000 W is much smaller, not exceeding 14%. For fiber-target distances in the range of 1-5 mm, the fraction of the 500 W laser's total pulse energy delivered to the target for 1, 2, and 3 ms pulses linearly decreases from 0.78 to less than 0.2. The channel and bubble dynamics begin with a spherical seed bubble expansion centered on the distal fiber tip that evolves into a pear shape whose surface exhibits periodic irregularities attributable to laser beam interruption by water droplets within the developing bubble. The study of laser-induced channel oscillations provides quantitative information relating fiber-target distance to channel oscillation frequency and energy transmission onto a target. These oscillations directly effect ablation efficiency and ablation rates that are important parameters for the optimization of a procedure's safety and duration. Insights that may lead to further reduction in retropulsion are also presented. Lasers Surg. Med. 00:00-00, 2024. © 2024 Wiley Periodicals LLC.

Numerical investigation on the liquid jet and the dynamics of the near-wall cavitation bubble under an acoustic field

The dynamics of the near-wall cavitation bubble in an acoustic field are the fundamental forms of acoustic cavitation, which has been associated with promising applications in ultrasonic cleaning, chemical engineering, and food processing. However, the potential physical mechanisms for acoustic cavitation-induced surface cleaning have not been fully elucidated. The dynamics of an ultrasonically driven near-wall cavitation bubble are numerically investigated by employing a compressible two-phase model implemented in OpenFOAM. The corresponding validation of the current model containing the acoustic field was performed by comparison with experimental and state-of-the-art theoretical results. Compared to the state without the acoustic field, the acoustic field can enhance the near-wall bubble collapse due to its stretching effect, causing higher jet velocities and shorter collapse intervals. The jet velocity in the acoustic field increases by 80.2%, and the collapse time reduces by 40.9% compared to those without an acoustic field for γ = 1.1. In addition, the effects of the stand-off distances (γ), acoustic pressure wave frequency (f), and initial pressure (p*) on the bubble dynamic behaviors were analyzed in depth. The results indicate that cavitation effects (e.g., pressure loads at the wall center and the maximal bubble temperature) are weakened with the increase in the frequency (f) owing to the shorter oscillation periods. Furthermore, the maximum radius of bubble expansion and the collapse time decrease with increasing f and increase with increasing p*. The bubble maximum radius reduces by 12.6% when f increases by 62.5% and increases by 20.5% when p* increases by 74%.

VOF-based modeling study of surface oscillation behavior and gas–liquid stirring dynamics in the bottom-blown reactors

Gas bottom-blown reactors are widely employed in the chemical, metallurgical, and biochemical industries due to their superior mixing capabilities. This study numerically investigates the gas–liquid flow hydrodynamics and bubble dynamics in a bottom-blown system with a circular boundary using the volume of fluid approach. Following the experimental validation of the mathematical model, the study evaluates the effects of gas flow rates, liquid heights, and fluid medium properties on both the dynamics of the bubble swarm and the mixing characteristics of the flow field. The results indicate that: (1) Rising bubbles disturb the fluid, generating numerous vortices that facilitate momentum transfer for effective gas stirring; (2) The height of the liquid surface oscillation during the bottom-blown process exhibits significant temporal variation, with the peak showing clear lateral swings; (3) Due to the nonlinear interactions involving bubble coalescence and breakup during their ascent, along with constructive and destructive interference between liquid surface waves, the liquid surface can exhibit violent fluctuations at certain moments; (4) Bubble size and aspect ratio significantly influence liquid surface oscillations; (5) The bubble rising path displays instability due to vortex shedding, with some vortices forming at locations where the bubble shape changes abruptly. A bubble velocity prediction equation is proposed: uc=σ5.2737Lcρc4.2737/16156μl9.5475.

Investigation of surfactant-laden bubble migration dynamics in self-rewetting fluids using lattice Boltzmann method

Self-rewetting fluids (SRFs), such as aqueous solutions of long-chain alcohols, show anomalous nonlinear (quadratic) variations of surface tension with temperature involving a positive gradient in certain ranges, leading to different thermocapillary convection compared to normal fluids (NFs). They have recently been used for enhancing thermal transport, especially in microfluidics and microgravity applications. Moreover, surface-active materials or surfactants can significantly alter interfacial dynamics by their adsorption on fluid interfaces. The coupled effects of temperature- and surfactant-induced Marangoni stresses, which arise due to surface tension gradients, on migration bubbles in SRFs remain unexplored. We use a robust lattice Boltzmann method based on central moments to simulate the two-fluid motions, capture interfaces, and compute the transport of energy and surfactant concentration fields, and systematically study the surfactant-laden bubble dynamics in SRFs. When compared to motion of bubbles in NFs, in which they continuously migrate without a stationary behavior, our results show that they exhibit dramatically different characteristics in SRFs in many different ways. Not only is the bubble motion directed toward the minimum temperature location in SRFs, but, more importantly, the bubble attains an equilibrium position. In the absence of surfactants, such an equilibrium position arises at the minimum reference temperature occurring at the center of the domain. The addition of surfactants moves the equilibrium location further upstream, which is controlled by the magnitude of the Gibbs elasticity parameter that determines the magnitude of the surface tension variation with surfactant concentration. The parabolic dependence of surface tension in SRF is parameterized by a quadratic sensitivity coefficient, which modulates this behavior. The lower this quantity, the greater is the role of surfactants modifying the equilibrium position of the bubble in SRF. Furthermore, the streamwise gradient in the surfactant concentration field influences the transient characteristics in approaching the terminal state of the bubble. These findings provide new means to potentially manipulate the bubble dynamics, and especially to tune its equilibrium states, in microchannels and other applications by exploiting the interplay between surfactants and SRFs.

Machine learning-inspired study of dynamical parameters of single vapor bubble under nucleate flow boiling regime

Heat transfer performance of nucleate boiling is interlinked with the departure dynamics of vapor bubbles, which also serves as the basis for heat transfer partitioning schemes and bubble growth models. Given the fast transients and multiple bubble ebullition cycles, boiling experiments lead to voluminous data that are to be analysed for determining the bubble dynamic parameters, and subsequently, the boiling heat transfer rates. Conventional approach of manual handling of such temporal and spatially-resolved experimental data is inherently time-consuming and error-prone. In the backdrop of these limitations, importance of machine learning algorithms gets highlighted in making the entire process automated and accurate as they minimize the need of any human intervention. The present work explores the potential of machine learning techniques towards quantifying the bubble departure characteristics and heat transfer partitioning during nucleate flow boiling. Water-based experiments have been conducted in a vertical channel under varying subcooling levels (ΔTsub = 2, 5, and 8 K) and flow rates (Re = 2400, and 3600). Mask R-CNN machine learning (ML) model is employed to evaluate the temporal variations of dynamical parameters of vapor bubbles and departure characteristics. The bubble departure characteristics as well as the corresponding evaporative and convective heat transfer rates, as retrieved through ML-generated masks, showed a strong dependence on the level of bulk fluid subcooling and flow rates. Heat transfer partitioning analysis revealed a competing interplay between the evaporative and condensation components of overall boiling heat transfer rates. These findings demonstrate the potential of ML techniques towards optimizing the thermal performance of boiling phenomena that have significant implications in a range of critical engineering applications.

Experimental study on effect of elastic-rigid composite boundary on shockwave from cavitation bubble collapse

Understanding the mechanisms behind the cavitation erosion resistance of elastic materials is the basis for the development of new cavitation erosion resistance materials. This paper employs underwater low-voltage discharge to induce cavitation bubble, combined with high-speed photography, shadowgraph methods, and transient pressure measurement systems to experimentally investigate the evolution and intensity of shockwave from bubble collapse near elastic-rigid composite boundary. Under the condition of constant elastic material thickness, with the bubble–wall distance increasing, shockwave shape evolves from multi-layers to single-layer. The peak pressure of the shockwave shows a trend of decreasing, then increasing, and finally stabilizing with increase in the bubble–wall distance. Furthermore, it was found that the elastic-rigid composite boundary causes the shockwave to reflect twice. As the material thickness increases, the intensity of the first reflected shockwave from the elastic surface decreases initially, then increases, and eventually stabilizes. However, that of the second reflected shockwave decreases. The total energy of the two reflections at the elastic interface is less than 4% of the mechanical energy of the bubble at its maximum volume. Finally, after the energy dissipation by the two reflections and material deformation, the elastic layer substrate withstands over 70% of the total mechanical energy of the cavitation bubble. There is an optimal elastic material thickness to minimize the shockwave load on the elastic layer substrate under the condition that the elastic-rigid composite boundary does not affect the evolution of cavitation bubble shape. These findings are significant for understanding bubble dynamics near elastic-rigid composite boundaries and provide theoretical support for developing cavitation erosion-resistant materials in engineering.

Ultrasonic dissolution of solid Al in liquid Sn during soldering: Modeling and equation, trend prediction, accelerating effect

Soldering of ceramics/metals using an inactive commercial solder with the advantage of low cost has wide application prospects. The dissolution behavior of base metal could not be quantified, which has been a basic issue for the joining design. This work investigated the dissolution of the solid Al in liquid Sn with and without the ultrasound. The physical model for the dissolving process was established based on the experiments. The relationship equation of the average concentration of Al (Ca) and soldering time was derived by using the Nernst-Brunner principle. The key parameters of limiting solubility (C0L) and dissolution rate constant (K) were obtained through dissolving experiments of liquid Sn to solid Al. The calculation results show that the effect of soldering temperature, and thickness Sn layer on the Al concentration (Ca) and dissolution rate (dCa/dt) under ultrasound is weaker than that without ultrasound. Compared to the condition without ultrasound, the value K, the maximum value of Ca and dCa/dt was increased by 5.8 times, 4.5 times, and 52 times at 250 °C under the ultrasound action, respectively, and the activation energy of dissolution was reduced by 41 %. The mechanism of ultrasonically accelerating dissolution of the solid Al by the liquid Sn has been revealed by using the bubble dynamics principle. It will provide a guideline for the design of soldering ceramics/metals using an inactive commercial solder.

Experimental study on pressure drop fluctuations for boiling flow at various gravity levels

Experiments were conducted on the pressure drop fluctuations of R245fa boiling through a horizontal microchannel with a diameter of 0.94 mm and a heated length of 170 mm at various gravity levels. The visualization results show that under inlet saturation conditions, three typical periodic oscillation modes are observed: continuous two-phase flow, bubbly/annular alternating flow, and churn/annular alternating flow. The flow oscillation characteristics within the channel are closely related to bubble dynamics, the vapor–liquid interface evolution, and the upstream compressible vapor volume. It has also been found that increasing the mass flux or decreasing the heat flux can enhance the suppression effect on pressure drop oscillation. In addition, under inlet subcooling conditions, although the total pressure drop increases with the increase in gravity level (1–2.78 g), and the amplitude of pressure drop fluctuation first increases and then decreases with the increase in gravity level, with the transition point occurring approximately at an = 1.10 g. The impact of gravity level on the amplitude of pressure drop fluctuation is primarily determined by the relative dominance of bubbly flow and annular flow within the channel.

Combined ANFIS and numerical methods to reveal the mass transfer mechanism of ultrasound-enhanced extraction of proteins from millet

Millet protein, as a promising plant-based protein substitute source, is an excellent basis for essential amino acids compared to commonly consumed staple grains. Compared with the traditional extraction process, ultrasound has been used to enhance the extraction efficiency of various plant-based proteins. To reveal the mechanism of ultrasound-enhanced extraction of proteins, adaptive neuro-fuzzy inference system (ANFIS) algorithm and numerical simulation based on Fick’s law were applied to illustrate the mass transfer behavior of millet proteins under different ultrasonic conditions including solid–liquid ratios (S/L ratios), pH and acoustic energy density levels (AED). The results showed that AED dominated the changes in effective diffusion coefficient (De), showing a positive correlation relationship (p < 0.05). Specifically, when the AED was 47.07 W/cm2, the De value increased by 95 % compared to that of 23.47 W/cm2. Meanwhile, the ANFIS model successfully predicted protein yields across all investigated parameters, achieving a coefficient of determination (R2) greater than 0.97. This model also elucidated the interactions among four critical factors, among which pH and S/L ratios were the main factors affecting protein yield. Concerning the ultrasonic cavitation bubble dynamics, the bubble collapse efficiency enhanced with an increase in AED, and therefore high AED ultrasound can significantly enhance the cavitation effect. Additionally, the results of the yields and physical properties of millet protein also indicated that in contrast with the traditional extraction methods, the ultrasound impactfully improved extraction yield (by 165 %), and combined with pH condition, it decreased the protein particle size (from 813.55 nm to 299.30 nm) without altering the molecular weight distribution. This study offers a novel perspective on the mechanism underlying ultrasound-enhanced protein extraction, drawing upon principles of ultrasonics and extraction processes. The insights gained can serve as a foundation for the food industry to upscale the extraction process, potentially enhancing efficiency and yield.

Near-field underwater explosion and its interaction with a sandwich composite plate

Polymeric composite sandwich materials are critical for marine structures, but their behavior under near-field underwater explosions is not well understood. This study investigates the dynamic response of carbon-fiber-reinforced sandwich composites with varying core densities subjected to near-field underwater explosions. Lab-scale experiments were conducted at two explosive stand-off distances using high-speed imaging and Digital Image Correlation (DIC) to capture the evolution of gas bubble dynamics, surface cavitation, and structural deformation. Results showed that reducing the stand-off distance led to a 0.7 ms increase in gas bubble period, along with an 80 mm increase in horizontal migration of the bubble, while vertical migration remained unaffected. The interaction between the gas bubble and surface cavitation, driven by fluid-structure interaction (FSI), significantly influenced the structural response. In particular, the simultaneous collapse of the gas bubble and surface cavitation resulted in higher localized impulsive loading, causing catastrophic failure in low-density core panels. Meanwhile, panels with higher core densities exhibited a 40 % reduction in out-of-plane deflection, demonstrating enhanced resistance to blast loading. This study provides new insights into the fluid-structure interaction mechanisms that occur during near-field underwater explosions and offers a basis for improving the design of marine structures by optimizing material selection and geometric configurations. These findings contribute to a deeper understanding of shock mitigation strategies in composite materials and inform future research in marine structural design under extreme loading conditions.

Needle-Free Targeted Injections Using Bubble Laser Technology in Therapeutics.

This work explores bubble laser technology as an alternative to needles in injection systems for vaccination, cancer treatment, insulin delivery, and catheter hygiene. The technology leverages laser-induced microfiltration and bubble dynamics to create high-speed pneumatic jets that penetrate the skin without needles, addressing discomfort, infection risk, and needle-related concerns. The system's performance is analyzed based on laser wavelength, pulse duration, and Gaussian beam droplet size. The findings indicate a significant increase in spot size at 1064 nm compared with 400 nm, consistent with the diffraction theory. Induced bubble dynamics reveal bubble generation, jetting, and fluid interactions as the Weber number increases, as well as jet velocity and fluid inertia. For femtosecond pulses, increasing the pulse duration from 100 to 1500 fs reduces the bubble lifespan from 0.8 to 0.3 arbitrary units, and the collapse pressure decreases from 2.1 to 0.4 bar. For picosecond pulses, the bubble lifetime decreases from 0.9 to 0.5 arbitrary units, and the pressure drop decreases from 2.0 to 0.4 bar as the pulse length extends from 2000 to 8000 ps. Jet formation in laser jet injection systems is enhanced by short pulses in water that produce longer-lasting bubbles. Drug delivery based on the Rayleigh-Plesset equation is characterized by a low-pressure collapse and short bubble lifetime. Thus, this relationship suggests that bubble laser technology can provide a more controlled and safer method of needle-free procedures, increasing compliance and reducing tissue trauma.

Real Case Study of 600 m3 Bubble Column Fermentations: Spatially Resolved Simulations Unveil Optimization Potentials for l-Phenylalanine Production With Escherichia coli.

Large-scale fermentations (»100 m³) often encounter concentration gradients which may significantly affect microbial activities and production performance. Reliably investigating such scenarios in silico would allow to optimize bioproduction. But related simulations are very rare in particular for large bubble columns. Here, we pioneer the spatially resolved investigation of a 600 m³ bubble column operating for Escherichia coli based l-phenylalanine fed-batch production. Microbial kinetics are derived from experimental data. Advanced Euler-Lagrange (EL) computational fluid dynamics (CFD) simulations are applied to track individual bubble dynamics that result from a recently developed bubble breakage model. Thereon, the complex nonlinear characteristics of hydrodynamics, mass transfer, and microbial activities are simulated for large scale and compared with real data. As a key characteristic, zones for upriser, downcomer, and circulation cells were identified that dominate mixing and mass transfer. This results in complex gradients of glucose, dissolved oxygen, and microbial rates dividing the bioreactor into sections. Consequently, alternate feed designs are evaluated splitting real feed rates in two feeds at different locations. The opposite reversed installation of feed spots and spargers improved the product synthesis by 6.24% while alternate scenarios increased the growth rate by 11.05%. The results demonstrate how sophisticated, spatially resolved simulations of hydrodynamics, mass transfer, and microbial kinetics help to optimize bioreactors in silico.

Directional enhancement of underwater impact and bubble loads in neighbor two-phase fluid domains charge

The loading characteristics of underwater explosions and the dynamic behavior of bubbles are directly related to the charge structure. This study proposes a unique charge structure in a gas–liquid two-phase fluid domain. Numerical methods are used to investigate the effects of fluid layer thickness and gas–liquid ratio on underwater explosion shock wave load, bubble dynamics, and bubble pulsation load. The results show that the two-phase fluid layer significantly enhances the directional release of shock wave energy and bubble pulsation load. During the shock wave phase, a lagging wave effect appears in the liquid layer direction, causing a secondary high-energy shock, significantly increasing the specific impulse. The gas layer direction may form a pressure relief channel effect, enhancing the shock wave peak pressure. For the bubble motion phase, differences in the physical properties of the fluid layer medium lead to irregular bubble boundary movements, promoting bubble tearing and rupture. The gaseous medium converts the accumulated shock wave energy into the internal energy of the bubble, increasing its volume potential. Although this characteristic reduces the pulsation frequency, it significantly increases the specific impulse. Altering the fluid layer medium can control explosion loads and bubble movement, offering new insights for ocean engineering applications.