Intermittent Bubble Research Articles

Numerical investigation of the multiphase flow and loading state of underwater semiclosed initial interrupted bubbles

The pulsation of bubbles and the impact load from reverse flow, generated by the evolution of semiclosed initial intermittent bubble multiphase flow during underwater launches, are crucial factors affecting launch safety. This paper employs the mixture multiphase flow model and the interphase heat and mass transfer model to simulate the interaction between the gas inside a partially enclosed cylinder and the water medium outside the cylinder, combined with simulation and piggybacking experiments, to analyze the flow process and load state. The numerical model is further utilized to study the evolution of the multiphase flow field of the semienclosed initial intermittent bubble, the pulsating load of the bubble, the impact load of the inverted water flow, and the influence of structural dimensions on the load. The results show that the initial intermittent bubble in the mouth of the cylinder experiences an expansion–contraction–expansion pulsation process, and as the migration of the interface between the phases results in significant pressure pulsation, the peak pulsation can exceed twice the pressure difference between the initial gas pressure inside the cylinder and the hydrostatic pressure at the mouth of the cylinder. At the late stage of bubble pulsation, a large amount of water with pulsating bubbles flows into the semiclosed cylinder, and the pulsation-induced velocity and gravity are used to form a high-speed inverted water flow. The interaction between the inverted water and the gas inside the cylinder generates an oscillating shock load where the maximum shock load is significantly greater than the ambient pressure load. Additionally, the effect of structural dimensions on the load state under the same intermittent conditions is examined.

Business Cycle Variations in Manager and Investor Sentiment Indices

I find that the highly regarded investor and manager sentiment indices demonstrate both cyclical and persistent variations. The presence of cyclicality in the orthogonalized indices suggests the existence of feedback loops connecting sentiment with economic or market outcomes. For example, optimistic sentiment can stimulate increased consumer spending and investment, thereby fostering economic growth and further boosting sentiment. These feedback loops have the potential to amplify cyclical sentiment trends and increase the volatility of economic and market cycles, leading to persistent cycles driven by feedback mechanisms. Importantly, my results remain robust against potential mean reversion resulting from heuristic behaviors such as herding and overreaction, as well as against random behavior arising from intermittent bubbles characterized by near-rational learning and potential overextrapolation bias.

Experimental and simulation study of the pulsation characteristics of underwater semiclosed initial intermittent bubbles

Bubbles at the cylinder outlet are a typical feature of the underwater ejection process. The interaction between gas and water is turbulent and results in an unstable bubble interface. In this work, experimental and numerical methods were used to determine the evolution of underwater semiclosed initial intermittent bubbles and their pressure propagation characteristics. Direct measurements of the interfacial migration behaviour of the bubbles were made using a high-speed video camera, and the variation in the pressure law in the flow field was obtained using a pressure sensor. The bubble pulsation characteristics were also analysed in conjunction with numerical simulations. The results show that the bubble at the mouth of the cylinder underwent the process of expansion, contraction, necking, and fracture under the coupled effect of the inertial motion of the liquid phase and the pressure inside the bubble and exhibited obvious periodic evolution characteristics. The flow instability driven by the velocity and density gradient gradually destabilised the bubble boundary, resulting in the phenomenon of necking of the gas cluster. Simulations were carried out for different diaphragm opening states to investigate the effects of the diaphragm cracking state on bubble evolution and pressure fluctuations.

Visual observations of steam–air submerged horizontal jets at low mass flux

Steam jet condensation at low mass flux is important especially in start-up, shutdown or accident conditions of various applications. Visual experiments of steam–air submerged jets through horizontal pipe were conducted in the ranges of mass flux 0–––20 kg/m2s, air mass fraction 0–––0.02, and water temperature 20 − 80℃. In pure steam jets, three condensation regimes of no bubbling, intermittent bubbling, and continuous bubbling were identified in steam jets. In no bubbling regime, rolling up and billows of plane shear flow were observed. In intermittent bubbling regime, large bubble was generated, detached and collapsed intermittently, accompanied by fluid oscillations. The bubble forming frequency increased with the rise of water temperature. Condensation heat transfer coefficients tends to decrease as the steam mass flux increases. In continuous bubbling, fluid oscillation no longer occurred. The bubble forming frequency decreased with the rise of water temperature. Condensation heat transfer coefficients increase as the steam mass flux increases. In the cases with shallow submerged depth, air-entrained vortex, surface water jets, and splash were observed after bubble condensation. In steam–air jets, condensation became stable and small bubbles increased. The condensation regime transitioned from intermittent bubbling to continuous bubbling earlier.

Rapid Fabrication of Efficient and Stable Microporous Electrodes for Practical Alkaline Water Electrolysis

Efficient and stable electrode is paramount for advancing practical alkaline water electrolysis (AWE) technology. In this study, we employed a rapid and scalable laser texturing process to create microporous nickel electrodes, demonstrating promising catalytic performances for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The alkaline electrolyzer cell (AEL) incorporating laser-textured electrodes (NP-LT30) exhibited a remarkable improvement, with voltage drops exceeding 300 mV under a current density of 1 A cm−1, compared to conventional perforated Ni plate electrodes (NP) based cell. This enhancement resulted from a substantial boost in mass transport, as unveiled by in-situ electrochemical impedance analysis. Of particular note is the unique multi-channel porous structure within the NP-LT30 electrode, enabling rapid mass transport through an innovative convection mode driven by an intermittent bubble eruption (IBE) mechanism, outperforming the traditional convection mode. Furthermore, AEL using NP-LT30 electrodes demonstrated exceptional durability, maintaining performance at 1.0 A cm–2 for an impressive 300 hours. This study highlights the capability of the multi-channel structure within NP-LT30 electrodes to expedite mass transport in practical AWE applications significantly. Moreover, the cost-effective and scalable nature of laser-textured porous electrodes positions them for commercialization, enabling the production of highly efficient electrodes for practical AWE implementation.

Multifractality and Universality of Thermal Fluctuations in Terrestrial and Microgravity Pool Boiling

Abstract Nucleation site interaction in pool boiling is well known to cause intermittent bubble growth and departure. Such interactions can cause long-term temporal correlations in spatio-temporal fluctuations of temperature and heat flux and may affect the conditions leading to the onset of boiling crisis. In this study, we check for the presence of such long-term correlations. A multifractal analysis is carried out on heat flux fluctuations recorded in pool boiling experiments under terrestrial and microgravity conditions. The Hurst exponent is shown to progressively decrease as the wall temperature is increased, attaining a value close to 0.5 near the onset of boiling crisis. This trend persists for multiple pressures and levels of bulk subcooling and may serve as an indicator of proximity to the boiling crisis. Similar experiments performed with an identical setup under terrestrial gravity conditions are shown to exhibit similar trends.

Curie point depth analysis of aeromagnetic data of Kasane region in northwest Botswana and surrounding regions for geothermal investigation of Kasane Hot Spring

The Kasane Hot Spring with discharge temperatures of 43–50 °C is characterized by intermittent bubbling accompanied by white precipitant within its vicinity. The hot spring discharges mainly along Chobe River which meets the Zambezi River at the tip of northwest Botswana. In this study the Curie point depth (CPD) was estimated using the spectral centroid method of aeromagnetic data at Kasane Hot Spring and the surrounding regions. The upward continued aeromagnetic data were analyzed to obtain depths to the bottom (CPD) of the magnetic sources. The CPD values were then used to compute the geothermal gradient, subsurface crustal heat flow including radiogenic heat flow distribution in the region.According to the obtained results, the depth to the magnetic bottom varies from 6 to 22 km. These depths are comparable to those obtained from recent regional study of the Okavango Rift Zone. The areas with shallow CPDs of demagnetized rocks at depth are located around Kasane Hot Spring, where high heat flow values in the range 70–90 mW/m2 were recorded. Moreover, the radiogenic heat production values between 0.50 and 0.60 μWm-3 within the same region may also provide an extra contribution to the geothermal potential of Kasane Hot Spring. The correlation of estimated shallow CPDs with high geothermal gradient, high heat flows, and radiogenic heat flow values at area within Kasane region indicate possible geothermal resource. The CPDs values obtained may be associated with the seismic events in the region and surroundings. The mean earthquake depth of events that occurred within Kasane and surrounding areas from 1987 to 1991 is 10 km, while the mean Curie Point Depth is approximately 11 km. These seismic events in the area could be responsible for possible thermal accumulation at Kasane Hot Spring, resulting in high heat flow values in the area.

Multiple dynamic regimes in a coarsening foam

Intermittent dynamics driven by internal stress imbalances in disordered systems is a fascinating yet poorly understood phenomenon. Here, we study it for a coarsening foam. By exploiting differential dynamic microscopy and particle tracking we determine the dynamical characteristics of the foam at different ages in reciprocal and direct space, respectively. At all wavevectors q investigated, the intermediate scattering function exhibits a compressed exponential decay. However, the access to unprecedentedly small values of q highlights the existence of two distinct regimes for the q-dependence of the foam relaxation rate Γ(q). At high q, Γ(q) ∼ q consistent with directionally-persistent and intermittent bubble displacements. At low q, we find the surprising scaling Γ(q) ∼ q δ , with δ = 1.6 ± 0.2. The analysis of the bubble displacement distribution in real space reveals the existence of a displacement cut-off of the order of the bubble diameter. Introducing such cut-off length in an existing model, describing stress-driven dynamics in disordered systems, fully accounts for the observed behavior in direct and reciprocal space.

Improved bubbling for membrane fouling control in filtration of palm oil mill effluent anaerobic digester sludge

Application of anaerobic membrane bioreactor is strictly limited by the membrane fouling because of the fouling prone nature of the feed. This study evaluates a method to enhance the effectiveness of a bubbling system for fouling control in filtration of anaerobic digestion sludge treating palm oil mill effluent using a tilted panel system. Such system is expected to enhance the role of biogas recirculation as the bubbling fluid for membrane fouling control. Effect of tilting angle, bubbling rate, intermittent bubbling period, and panel switching period was investigated. The energy consumption for applying such system was also estimated. Results show that the tilted panel with bubbling remarkably enhance permeability by more than double of the vertical system to reach a maximum value of 87 Lm−2h−1bar−1, the highest value reported so far. The panel switching mechanism helps to enhance the system throughput by allowing two-sided membrane panel with intermittently bubbling, in the expense of mechanical switching energy. The estimation of energy consumption of the system has been estimated at 0.247 kWhm−3, corresponding to 0.3 % of total electricity generated from anaerobic treatment of POME, very attractive for full-scale implementation.

Effect of bubble characteristics and nozzle size on the membrane distillation enhanced by gas–liquid two-phase flow

Abstract This study investigates the membrane performance and fouling control in bubble-assisted sweeping gas membrane distillation with high concentration saline (333 K saturated solution) as feed. The results show that a longer bubbling interval (3 min) at a fixed bubbling duration of 30 s can most efficiently increase the flux enhancement ratio up to 1.518. Next, the flux increases with the gas flow rate under a relatively lower level, but tends to plateau after the threshold level (1.2 L·min−1). Compared to the non-bubbling case, the permeate flux reaches up to 1.623-fold at a higher bubble relative humidity of 80%. It was also found that greater flux enhancement can be achieved and, meanwhile, dramatic flux decline can be delayed for an intermittent bubbling system with a smaller nozzle size. These results accord well with the observations of fouling deposition in situ on the membrane surface with scanning electron microscope (SEM).

Numerical Simulation of Gas-Liquid Flow in a Bubble Column by Intermittent Aeration in Newtonian Liquid/Non-Newtonian Liquid

The dynamic behaviors of gas-liquid two-phase flow were simulated in a lab-scale intermittent bubble column by Euler-Euler two-fluid model coupled with the PBM (population balance model) using two different liquid phases, i.e., Newtonian fluid (water)/non-Newtonian fluid (activated sludge). When non-Newtonian fluid was used during intermittent aeration, some interesting results were obtained. Two symmetric vortexes existed in the time-averaged flow field; the vertical time-averaged velocity of the liquid phase decreased with increasing anaerobic time; the average gas holdup distribution was like a trapezoid with long upper side and short lower side and affected by the dynamic viscosity of the liquid phase. Compared with non-Newtonian fluid, the use of Newtonian fluid as the liquid phase led to a more complicated time-averaged flow field structure and vertical time-averaged velocity distribution, higher average gas holdup, and the asymmetric column-shaped gas holdup distribution with increasing anaerobic time. For different liquid phases, the instantaneous flow field, instantaneous vertical velocity, and instantaneous gas holdup distribution all periodically changed with anaerobic time; however, different from Newtonian liquid phase, non-Newtonian liquid phase had no periodic oscillating instantaneous horizontal velocity.

Effect of on the Membrane Distillation of PVDF Membrane Material Enhanced by Gas-Liquid Two-Phase Flow

This study investigates the membrane performance and fouling control in the bubble-assisted sweeping gas membrane distillation with high concentration saline (333 K saturated solution) as feed. The results show that longer bubbling interval (3 min) at a fixed bubbling duration of 30s can most efficiently increase the the flux enhancement ratio up to 1.518. Next, the flux increases with the gas flowrate under a relatively lower level, but tends to a plateau after the threshold level (1.2 L•min-1). Compared to non-bubbling case, the permeate flux reaches up to 1.623 fold at a higher bubble relative humidity of 80 %. It was also found that greater flux enhancement can be achieved and meanwhile dramatic flux decline can be delayed for an intermittent bubbling system with a smaller nozzle size. These results accord well with the observations of fouling deposition in situ on the membrane surface with SEM.

Lu Yu: the past and future of condensed matter physics

Abstract Lu Yu, a distinguished theoretical physicist at the Institute of Physics (IOP) of Chinese Academy of Sciences (CAS), has witnessed the development of Chinese physics over the past five decades, from the difficult period of 1960s when physicists worked in a ‘half-fed’ state to the present flowering springtime of Chinese physics in which many breakthroughs at the frontier of physics are attracting international recognition. He considers these achievements to be not merely ‘intermittent bubbles’, but the cumulative result of sustained governmental support of basic research over the past decades. In his area of condensed-matter physics, Yu sees ‘a big deep-rooted tree with many branches—some old branches have withered away, but new shoots continue to appear’. In a recent interview with NSR, Yu reflected upon the recent history of condensed-matter physics in China—what has been accomplished and what lies ahead—and his view on the development of physics in general.

The Zannone Giant Pockmark: First evidence of a giant complex seeping structure in shallow-water, central Mediterranean Sea, Italy

An active giant pockmark located offshore Zannone Island (central Tyrrhenian Sea, Italy), is analyzed by very high resolution multibeam bathymetry, high resolution seismic profiles, ROV video observations, sediment and water sampling. The active fluid emission area is located on the outer shelf, between 110 and 130 m water depth, and affects the Late Quaternary lowstand and highstand deposits resting on rocky bedrock. A variety of fluid-escape features characterizes the area, including the Zannone giant pockmark, several smaller pockmarks, hummocky terrains and areas of positive relief. Ground-truth video data show active seepages, bacterial communities, widespread lithified pavements, mounds, and cone-shaped structures. Evidence of active seepage includes both continuous and intermittent bubble release from the seafloor and a well-defined plume rising 70 m above the seafloor. The Zannone giant pockmark is about 900 × 500 m (surface of some 0.5 km2). It represents the first evidence of an active shallow-water seepage area in the central Tyrrhenian Sea (Italy) and the first record of a morphologically complex giant pockmark in the entire Mediterranean Sea. Some speculations on processes originating the observed features are explored, including possible occurrence of multiple eruption events, processes of fluidization–liquefaction and minor slides that may have modified the original morphology. Factors peculiar to the study area – shallow depth, thin sedimentary cover resting on a faulted rocky basement, seeping occurring through non-cohesive sandy sediments – appear to have been key to the formation and morphology of the Zannone giant pockmark.

Influence Factors of Calcium Carbonate Whiskers Prepared by Intermittent Bubbling Method

Calcium carbonate whiskers were successfully prepared in the MgC12-Ca(OH)2-CO2 system by a intermittent bubbling method and characterized by X-ray diffraction and scanning electron microscopy. The results demonstrated that aragonite style calcium carbonate whiskers with well morphology, large aspect ratio and smooth surface can be obtained by controlling technical conditions such as reaction temperature, concentration of Ca(OH)2 and amount of additives and under the conditions of CO2 flow velocity of 3.4ml/min/gCa(OH)2, flow of CO2 to air ratio of 1:4, stirring speed of 240 r/min.

Reuse of Organic Matter from Coagulated Sludge Using a Membrane-Coupled Anaerobic Organic Acid Fermentor in Advanced Municipal Wastewater Treatment

Abstract This study focused on the development of an advanced municipal wastewater treatment process using a membrane-coupled anaerobic organic acid fermentor (MAOF) to remove dissolved organic matter from coagulated sludge. Intermittent ozone bubbling was effective in preventing increases in permeation resistance that were caused by particle accumulation on the membrane surface and in maintaining a high permeation flux. With regard to taxonomy, approximately 20 isolates were identified in the MAOF and are believed to represent the principal cell types in the fermentor. MAOF, coupled with intermittent ozone bubbling, is an effective system that can be implemented to recover organic matter that is used in biological denitrification or other basic materials.

Large eddy simulation of the bubbly ocean: New insights on subsurface bubble distribution and bubble‐mediated gas transfer

The evolution of bubbles in a turbulent oceanic boundary layer is simulated using a multi‐size multi‐gas bubble model coupled with a Large Eddy Simulation model. Bubbles injected by breaking waves are brought into the boundary layer by episodic bubble plumes, and they form near‐surface streaks in the convergence zone of Langmuir circulations. The equilibrium bubble distribution decays exponentially with depth and is a manifestation of intermittent bubble plumes whose bubble number density is at least one order of magnitude higher than the mean bubble number density. Bubble distribution in the injection zone is influenced by injection, turbulent transport, and dissolution. Bubble distribution below the injection zone is determined by the strength of turbulence and dissolution. For a given sea state, bubble e‐folding depth increases linearly with friction velocity. Wave age is an additional governing parameter for bubble e‐folding depth. The buoyancy of bubbles weakens both Langmuir circulations and near‐surface turbulent kinetic energy dissipation. The buoyancy effect increases with wind speed. Gas flux through bubbles depends on both wind speed and wave age. For a given sea state, the bubble flux increases with wind speed to the fifth power.

円柱後流渦による液体自由界面の振動と間欠的な気泡連行について

円柱後流渦による液体自由界面の振動と間欠的な気泡連行について

Microfiltration of algae ( Chlorella sorokiniana): Critical flux, fouling and transmission

Fouling and transmission studies of algae broth ( Chlorella sorokiniana) during cross-flow microfiltration were performed using direct microscopic observation technique. The flux stepping test was conducted for approximately 15 min interval and images were captured at the beginning and at the end of each flux step for further analysis of membrane surface coverage. The rate of membrane surface coverage was correlated to the rate of transmembrane pressure (TMP) rise. Results suggested that Direct Observation Through the Membrane (DOTM) technique was more sensitive to indicate the membrane fouling than TMP monitoring method. Deposition of microalgal cells started to occur even at a very low permeate flux. The layer of algal cells would eventually build up and might result in severe fouling. Despite this early deposition, TMP values remained low and would only increase when the fouling had become more pronounce. Lower fouling rate was achieved at higher cross-flow velocity. However, higher cross-flow velocity (CFV) also generated greater shear force which enhanced the transmission of extracellular polymeric substances (EPS). The particle removal due to bubble-induced shear was visualised with DOTM to provide better understanding. A significant reduction in fouling rate and near complete removal of microalgae could be achieved by applying continuous air bubbling. Based on TMP measurement, an intermittent aeration mode could achieve approximately identical performance as continuous bubbling mode. However, the recorded DOTM images indicated that intermittent bubbling mode could not completely maintain a cell-free surface.

Carotid Duplex Imaging on a Patient with a Temporary Left Ventricular Assist Device

Introduction In a carotid Duplex scan, the spectral Doppler examination is used to quantify stenosis by using the peak systolic and end diastolic velocities and ratios of the systolic velocities. The carotid spectral waveform is markedly different when a patient has a temporary left ventricular assist device (LVAD) that is nonpulsatile or continuous because of the oxygenated blood being redirected from the left atrium into the femoral artery via a centrifugal pump. This continuous-flow device provides complete circulatory support, preserving organ function and allowing quick restoration of hemodynamic stability. Case Report A 23-year-old man with idiopathic dilated cardiomyopathy, end-stage congestive heart failure, and cardiogenic shock required emergent placement of a TandemHeart temporary LVAD. Carotid Duplex imaging was performed the next day as a routine examination ordered for preheart transplant evaluation. No atherosclerotic disease was noted on B-mode images; however, intermittent bubbles were visualized and appeared as high-intensity transient signals within the Doppler spectral waveform. Flow was continuous in the carotid and vertebral arteries bilaterally. Discussion Percutaneous LVAD devices are increasingly being used as a short-term “bridge to cardiac transplantation.” Vascular sonographers should be aware that peripheral arterial flow will be nonpulsatile in patients who are sustained on these continuous flow devices. If significant disease is present we will need to rely on B-mode and color images and calculation of percent area or diameter reduction instead of waveform and velocity data.