Number Of Microbubbles Research Articles

Minimising microbubble size through oscillation frequency control

Microbubbles are bubbles below 1mm in size and have been extensively deployed in industrial settings to improve gaseous exchange between gas and liquid phases. The high surface to volume ratio offered by microbubbles enables them to enhance transport phenomena and therefore can be used to reduce energy demands in many applications including, waste water aeration, froth flotation, oil emulsion separations and evaporation dynamics. Microbubbles can be produced by passing a gas stream through a micro-porous diffuser placed at the gas–liquid interface. Previous work has shown that oscillating this gas steam can reduce the bubble size and therefore increase energy savings. In this work we show that it is possible to further reduce microbubble size (and consequently maximise the number of bubbles) by varying the frequency of the oscillating gas supply. Three different microbubble generation systems have been investigated; an acoustic oscillation system and a mesh membrane, a fluidic oscillator coupled to a single orifice membrane and a fluidic oscillator coupled to a commercially available ceramic diffuser. In all three bubble generation methods there is an optimum oscillation frequency at which the bubble size is minimised and the number of microbubbles maximised. In some cases a reduction in bubble size of up to 73% was achieved compared with non-optimal operating frequencies. The frequency at which this optimum occurs is dependent on the bubble generation system; more specifically the geometry of the system, the type micro-porous diffuser and the gas flow rate. This work proves that by tuning industrial microbubble generators to their optimal oscillation frequency will result in a reduction of microbubble size and increase their number density. This will further improve gaseous exchange rates and therefore improve the efficiency of the industrial processes where they are being employed to produce bubbles, leading to a reduction in associated energy costs and an increase in the overall economic and energetic feasibility of these processes.

Temperature is key to yield and stability of BSA stabilized microbubbles

The effect of preparation and storage parameters on the number, size and stability of microbubbles covered with bovine serum albumin (BSA) was investigated. A large number of microbubbles with a high stability was obtained at protein concentration of 7.5% or higher, at pH between 5 and 6, at an ionic strength of 1.0 M and at a preheating temperature of 55–60 °C. Microbubbles stored at 4 °C were more stable than those stored at room temperature. This was observed for a specific commercial BSA batch. We found that optimal preparation parameters strongly depend on the batch. Certain BSA batches were found not to lead to microbubbles at all. Microbubbles made with different protein concentration and preheating temperatures shrunk in time to a radius between 300 nm and 350 nm, after which the size remained constant during further storage. We argue that the constant final size can be explained by a thickening of the microbubble shell as a result of the microbubble shrinkage, thereby withstanding the Laplace pressure. The effects of protein concentration, pH and ionic strength on the number of microbubbles directly after sonication can be ascribed to the influence of these parameters on the adsorption speed and ability to cover the surface of air bubbles formed during sonication with enough protein to stabilize the bubble against coalescence and dissolution. We suggest that the effect of temperature during sonication on the formation of microbubbles can be related to thermally induced protein–protein interaction at the air–water interface.

Body Positions in the Diagnosis of Right-to-Left Shunt by Contrast Transcranial Doppler

Contrast transcranial Doppler (c-TCD) is sensitive in detecting right-to-left shunt (RLS). However, the methodology and ideal posture are controversial. Consecutive migraine patients were prospectively examined for RLS using c-TCD. Each patient was examined while at rest and subsequently with the Valsalva maneuver (VM) in three positions: supine, left lateral decubitus and right lateral decubitus. RLS was diagnosed with at least one microbubble detected at any position. RLS was highest in the left lateral decubitus position, both during rest and with VM. The left lateral decubitus position was associated with the highest total number of microbubbles and greater shunt grades. Patients who tested positive in the other two positions had the lowest index position failure rate during rest in the left lateral decubitus position. In some patients in whom RLS is detected at rest, it may not be detected (false negative) under VM. To ensure c-TCD's the sensitivity to RLS, testing in the left lateral decubitus position at rest and under VM is suggested; testing in other positions is necessary to avoid false negatives.

Water Treatment Using Discharge Generated in Cavitation Field with Micro Bubble Cloud

SUMMARYA new method of wastewater treatment using electric discharge in the water cavitation field formed by a large number of micro bubbles generated by high‐speed water flow is proposed in this paper. Indigo carmine solution, which is a type of dye, with a concentration of 9 mg/liter was used as the specimen solution for demonstration of water treatment. The total volume of solution and the average speed of solution in the cavitation field were 20 liters and about 7.4 m/s, respectively. An absorbance decrease rate of 96% was obtained in 50 min of treatment time at the electrode distance of 2 mm and discharge power of 16 W. It was also found that the efficiency of decolorization was improved by changing the electrode location. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 186(4): 1–10, 2014; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22483

Effects of coupling, bubble size, and spatial arrangement on chaotic dynamics of microbubble cluster in ultrasonic fields

Microbubble clustering may occur when bubbles become bound to targeted surfaces or are grouped by acoustic radiation forces in medical diagnostic applications. The ability to identify the formation of such clusters from the ultrasound echoes may be of practical use. Nonlinear numerical simulations were performed on clusters of microbubbles modeled by the modified Keller-Miksis equations. Encapsulated bubbles were considered to mimic practical applications but the aim of the study was to examine the effects of inter-bubble spacing and bubble size on the dynamical behavior of the cluster and to see if chaotic or bifurcation characteristics could be helpful in diagnostics. It was found that as microbubbles were clustered closer together, their oscillation amplitude for a given applied ultrasound power was reduced, and for inter-bubble spacing smaller than about ten bubble radii nonlinear subharmonics and ultraharmonics were eliminated. For clustered microbubbles, as for isolated microbubbles, an increase in the applied acoustic power caused bifurcations and transition to chaos. The bifurcations preceding chaotic behavior were identified by Floquet analysis and confirmed to be of the period-doubling type. It was found that as the number of microbubbles in a cluster increased, regularization occurred at lower ultrasound power and more windows of order appeared.

Quantitative Investigation of Flocs Flotation Removal and Hydrocyclonic Separation for the Washing Water Treatment

A new hydrocyclone and gas-flotation device was designed and tested for the treatment of the wash water containing the flocs. The device separates particles and removes flocs simultaneously. The gas-generator equipment can produce a large number of micro-bubbles, and the bubbles adhere to the impure flocs particles. This makes the density of the bubble-floc less than that of water, and their buoyancy enables particle separation and removal of suspended flocs. To achieve a high efficiency of flocs removal and particle separation, some of the factors that influence the separation efficiency (such as the gas-liquid pressure difference, gas-liquid ratio, underflow split ratio, water pressure, inlet flow rate, and the contact time of the gas and particles, bubble size, and number of bubbles) were investigated. The results showed that there is an optimum combination of multi-dimensional parameters; good particle separation and a high efficiency of flocs removal were achieved.

The Effects of Pressure on Gases in Solution: Possible Insights to Improve Microbubble Filtration for Extracorporeal Circulation

Improvements in micropore arterial line filter designs used for extracorporeal circulation are still needed because microbubbles larger than the rated pore sizes are being detected beyond the filter outlet. Linked to principles governing the function of micropore filters, fluid pressures contained in extracorporeal circuits also influence the behavior of gas bubbles and the extent to which they are carried in a fluid flow. To better understand the relationship between pressure and microbubble behavior, two ex vivo test circuits with and without inline resistance were designed to assess changes in microbubble load with changes in pressure. Ultrasound Doppler probes were used to measure and compare the quality and quantity of microbubbles generated in each test circuit. Analysis of microbubble load was separated into two distinct phases, the time periods during and immediately after bubble generation. Although microbubble number decreased similarly in both test circuits, changes in microbubble volume were significant only in the test circuit with inline resistance. The test circuit with inline resistance also showed a decrease in the rate of volume transferred across each ultrasound Doppler probe and the microbubble number and size range measured in the postbubble generation period. The present research proposes that fluid pressures contained in extracorporeal circuits may be used to affect gases in solution as a possible method to improve microbubble filtration during extracorporeal circulation.

Microbubble Phenomenon in the Grease Lubricating Film Induced by Micro-Oscillation

A microbubble phenomenon induced by micro-oscillation in the grease lubricating film confined within a nanogap between a highly polished steel ball and a smooth glass disc has been observed with an interferometer. Experimental results show that when the micro-oscillation frequency is a constant value, the microbubble number increases with the micro-oscillation amplitude. When the micro-oscillation amplitude is a constant value, the microbubble number increases with the micro-oscillation frequency when the latter is lower than the critical value and decreases with the micro-oscillation frequency when it is higher than the critical value. Theoretical models and analyses have been used to discuss the bubble formation and describe the characteristics of bubble movement.

Microembolism and Catheter Ablation I

Background— Cerebral diffusion-weighted MRI lesions have been observed after catheter ablation of atrial fibrillation. We hypothesized that conditions predisposing to microembolization could be identified using a porcine model of pulmonary vein ablation and an extracorporeal circulation loop. Methods and Results— Ablations of the pulmonary veins were performed in 18 swine with echo monitoring. The femoral artery and vein were cannulated and an extracorporeal circulation loop with 2 ultrasonic bubble detectors and a 73-μm filter were placed in series. Microemboli and microbubbles were compared between ablation with an irrigated radiofrequency system (Biosense-Webster) and a phased radiofrequency multielectrode system (pulmonary vein ablation catheter [PVAC], Medtronic, Inc, Carlsbad, CA) in unipolar and 3 blended unipolar/bipolar modes. Animal pathology was examined. The size and number of microbubbles observed during ablation ranged from 30 to 180 μm and 0 to 3253 bubbles per ablation. Microbubble volumes with PVAC (29.1 nL) were greater than with irrigated radiofrequency (0.4 nL; P =0.045), and greatest with type II or III microbubbles on transesophageal echocardiography. Ablation with the PVAC showed fewest microbubbles in the unipolar mode ( P =0.012 versus bipolar). The most occurred during bipolar energy delivery with overlap of proximal and distal electrodes (median microbubble volume, 1744 nL; interquartile range, 737–4082 nL; maximum, 19 516 nL). No cerebral MRI lesions were seen, but 2 animals had renal embolization. Conclusions— Left atrial ablation with irrigated radiofrequency and PVAC catheters in swine is associated with microbubble and microembolus production. Avoiding overlap of electrodes 1 and 10 on PVAC should reduce the microembolic burden associated with this procedure.

Bubble Behavior and Flow Structure on Bubble Collapse Phenomena in a Venturi Tube

A micro-bubble generator with a venturi tube generates a large number of micro-bubbles with a diameter of 10 μm ― 1 mm by bubble collapse. The bubble collapse is caused by pressure recovery in the diverging region of the venturi tube. The pressure recovery is expected to be a shock for supersonic flow in gas-liquid two-phase flow. However, a profile of Mach numbers to flow direction of the venturi tube has not been estimated experimentally. The present study reveals mechanisms of a bubble collapse. In order to achieve the objectives, we observe bubble behavior with the bubble collapse. In addition, we measure pressure and volumetric void fraction profiles in the flow direction. Pressure is measured by a differential pressure gauge. Void fraction is measured by a constant electric current method and Maxwell' s theory. From these measurements, gas-liquid mixture velocity, sonic speed and Mach number are estimated. In experimental results, bubble collapse is observed with high liquid inlet velocity. When bubble collapse is caused, bubbles expand once into a divergence region of the venturi tube. After that, they contracted rapidly and broken up into a great number of tiny bubbles. Pressure decreases sharply around the throat and increase at the bubble collapse point. On the other hand, the void fraction increase downstream from the throat and decrease around the bubble collapse point. From these results, it is confirmed that the flow is supersonic flow between the throat and the bubble collapse point, while it becomes subsonic flow downstream of the point. Therefore, it is proposed that a shock is present at the bubble collapse point.

Effects of FLIRT on Bubble Growth in Man

Recompression during decompression has been suggested to possibly reduce the risk of decompression sickness (DCS). The main objective of the current study was to investigate the effects of FLIRT (First Line Intermittent Recompression Technique) on bubble detection in man. 29 divers underwent 2 simulated dives in a dry recompression chamber to a depth of 40 msw (500 kPa ambient pressure) in random order. A Buehlmann-based decompression profile served as control and was compared to an experimental profile with intermittent recompression during decompression (FLIRT). Circulating bubbles in the right ventricular outflow tract (RVOT) were monitored by Doppler ultrasound and quantified using the Spencer scoring algorithm. Heat shock protein 70 (HSP70), thrombocytes, D-Dimers and serum osmolarity were analyzed before and 120 min after the dive. Both dive profiles elicited bubbles in most subjects (range Spencer 0-4). However, no statistically significant difference was found in bubble scores between the control and the experimental dive procedure. There was no significant change in either HSP70, thrombocytes, and D-Dimers. None of the divers had clinical signs or symptoms suggestive of DCS. We conclude that FLIRT did not significantly alter the number of microbubbles and thus may not be considered superior to classical decompression in regards of preventing DCS.

A High Blood Level in the Air Trap Reduces Microemboli During Hemodialysis

Previous studies have demonstrated the presence of air microemboli in the dialysis circuit and in the venous circulation of the patients during hemodialysis. In vitro studies indicate that a high blood level in the venous air trap reduces the extent of microbubble formation. The purpose of this study was to examine whether air microbubbles can be detected in the patient's access and if so, whether the degree of microbubble formation can be altered by changing the blood level in the venous air trap. This was a randomized, double-blinded, interventional study of 20 chronic hemodialysis patients. The patients were assigned to hemodialysis with either an elevated or a low blood level in the air trap. The investigator and the patient were blinded to the settings. The numbers of microbubbles were measured at the site of the arteriovenous (AV) access for 2 min with the aid of an ultrasonic Doppler device. The blood level in the air trap was then altered to the opposite setting and a new measurement was carried out after an equilibration period of 30 min. Median (range) for the number of microbubbles measured with the high air trap level and the low air trap level in AV access was 2.5 (0-80) compared with 17.5 (0-77), respectively (P = 0.044). The degree of microbubble formation in hemodialysis patients with AV access was reduced significantly if the blood level in the air trap was kept high. The exposure of potentially harmful air microbubbles was thereby significantly reduced. This measure can be performed with no additional healthcare cost.

Water Treatment using Discharge Generated in Cavitation Field with Micro Bubble Cloud

SUMMARY A new method of wastewater treatment using electric discharge in the water cavitation field formed by a large number of micro bubbles generated by high-speed water flow is proposed in this paper. Indigo carmine solution, which is a type of dye, with a concentration of 9 mg/liter was used as the specimen solution for demonstration of water treatment. The total volume of solution and the average speed of solution in the cavitation field were 20 liters and about 7.4 m/s, respectively. An absorbance decrease rate of 96% was obtained in 50 min of treatment time at the electrode distance of 2 mm and discharge power of 16 W. It was also found that the efficiency of decolorization was improved by changing the electrode location. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 186(4): 1–10, 2014; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22483

Enhancement of microbubble generation in a pressurized dissolution process by packing the nozzle with porous ceramics

The pressurized dissolution method is often used for microbubble generation. However, the main disadvantage of this method is that a large amount of energy (more than 0.3 MPa) is required to generate many microbubbles, each of which have a diameter of several dozen μm. To overcome this problem, we investigated the effectiveness of porous ceramic when used as the packing material in the pressurized dissolution method. The results showed that when compared with the control (no porous ceramics), use of porous ceramics resulted in a 39% increase in the number of microbubbles. Furthermore, when this system was used for the flotation separation of artificial suspended solids and activated sludge, the level of separation achieved with porous ceramics at 0.15 MPa was the same as that achieved using no porous ceramics at 0.25 MPa. It was estimated that the use of porous ceramics led to a 40% reduction in the energy required for the dissolved air flotation, with subsequent decreases in the operating cost.

0212 ベンチュリ管式マイクロバブル生成法における気泡微細化時の界面不安定性と流動特性(OS2 機能性流体とその先進応用,オーガナイズドセッション)

The micro-bubble generator with a venturi tube generates a large number of micro-bubbles by bubble breakup phenomena. The bubble breakup is caused by a shock with pressure recovery in the diverging region of the venturi. However, a profile of Mach numbers in the flow direction of the venturi has not been estimated experimentally. In the present study, the profiles are estimated by measurements of pressure and void fraction profiles in the flow direction. In the experimental results, Mach numbers are higher than 1 between the throat and the bubble breakup point, and the numbers are lower than 1 downstream of the breakup point. It is proposed that the shock is present at the bubble breakup point. In addition, the breakup from the top to the bottom of a bubble surface is observed. This results means that the shock with pressure recovery causes the bubble breakup.

Factors related to recurrence of paradoxical cerebral embolism due to patent foramen ovale

Patent foramen ovale (PFO) is an important etiology of ischemic stroke in young adults. We investigated factors contributing to recurrent ischemic stroke in patients with PFO. Subjects comprised 47 patients (mean age, 56.8 ± 14.2 years; range 23-74 years) with ischemic stroke due to PFO who were admitted to our hospital between April 2007 and February 2011. Mean duration of follow-up was 34.5 ± 13 months. Recurrence occurred in 11 cases. Annual recurrence rate was 23.4%. We investigated relationships between recurrence of ischemic stroke and size of PFO (large, >4 mm; medium, 2-3.9 mm; small, <1.9 mm; absent group), maximal number of microbubbles (determined as the number of microembolic signals: small, 0-5; moderate, 6-25; and multiple, ≥ 26), massive bubble on contrast transesophageal echocardiography or atrial septal aneurysm, D-dimer level and antithrombotic therapy. Univariate analysis showed size of the PFO (P = 0.013), number of microbubbles (P = 0.021), and presence of a massive bubble on echocardiography (P = 0.04) were related to recurrence of ischemic stroke. Logistic analysis identified size of the PFO (P < 0.05) and massive bubble on echocardiography (P < 0.05) as factors related to recurrence of ischemic stroke. In conclusion, size of the PFO and presence of a massive bubble were considered to be factors associated with recurrence of ischemic stroke due to PFO.

A new biophysical decompression model for estimating the risk of articular bends during and after decompression

The biophysical models that intend to predict the risk of decompression sickness after a change of pressure are not numerous. Few approaches focus in particular on joints as target tissues, with the aim to describe properly the mechanisms inducing pain. Nevertheless, for this type of decompression incidents, called articular bends, no model proved to fit the empirical results for a broad range of exposures and decompression procedures. We present here an original biophysical decompression model for describing the occurrence of articular bends. A target joint is broken down into two parts that exchange inert gases with the blood by perfusion and with each other by diffusion over distances of a few millimetres. This diffusion pathway allows the slow amplification of microbubbles growing during and after decompression, consistent with the possible delayed occurrence of bends. The diffusion coefficients introduced into this model are larger than those introduced into most modern decompression models. Their value remains physical (#10 −9 m 2/s). Inert gas exchanges and the formation, amplification and resorption of microbubbles during and after decompression were simulated. We used a critical gas volume criterion for predicting the occurrence of bends. A risk database extracted from COMEX experience and other published studies were used for the correlation of model parameters not known a priori. We considered a large range of exposure, and the commonly used inert gases nitrogen and helium. This correlation phase identified the worst biophysical conformations most likely to lead to the formation, in tissues such as tendons, of a large number of microbubbles recruited from pre-existing gas nuclei during decompression. The risk of bends occurrence was found to be linked to the total separated gas volume generated during and after decompression. A clamping phenomenon occurs soon after the start of decompression, greatly slowing the gas exchanges controlled especially by the oxygen window. This model, which reproduces many empirical findings, may be considered both descriptive and predictive.

Modeling and simulation of multiple bubble entrainment and interactions with two dimensional vortical flows

Simulations of bubble entrainment and interactions with two dimensional vortical flows are preformed using a discrete element model. In this Eulerian-Lagrangian approach, solution to the carrier phase is obtained using direct numerical simulation whereas motion of subgrid bubbles is modeled using Lagrangian tracking. The volumetric displacement of the fluid by the finite size of the bubbles is modeled along with interphase momentum-exchange for a realistic coupling of the bubbles to the carrier phase. In order to assess the importance of this volumetric coupling effect, even at low overall volume loading, simulations of a small number of microbubbles entrained in a traveling vortex tube are studied in detail. The test case resembles the experiments conducted by Sridhar and Katz [JFM, 1999] on bubble entrainment in vortex rings. It is shown that under some conditions, the entrainment of eight small bubbles, 1100 μm or less in diameter, result in significant levels of vortex distortion when modeled using the volumetric coupling effect. Neglecting these effects, however, does not result in any vortex distortion due to entrained bubbles. The nondimensionalized vortex strength versus bubble settling locations are compared with experimental data to show collapse of the data along the trends observed in experiments only when the volumetric effects are modeled. Qualitative and quantitative assessments of this distortion observed with volumetric coupling are made using three methods; bubble induced vortex asymmetry, relative change in the decay of angular momentum, and relative change in the peak vorticity. It is found that in all cases the volumetric effects result in a relative increase of the vortex decay rate. The concept of a relative reaction force, defined as the ratio of net bubble to fluid reaction to the local driving force of the vortex, is introduced to analyze this effect. It is shown that the global increases in vortex decay rate are directly proportional to the magnitude of this highly local relative reaction force.

Dynamics Simulation of Microbubbles in Ultrasonic Wave Field Considering the Secondary Bjerknes Force

In order to control a large number of microbubbles with a pumping ultrasonic wave, it is essential to consider a bubble-to-bubble interaction. This paper proposes a simplified microbubble dynamics simulation method considered with bubble-to-bubble interaction in ultrasonic wave field. The microbubble dynamics is solved with difference method based on the Stokes’s low and the secondary Bjerknes force between microbubbles. The laminar flow is considered in the cylindrical calculation region. The effectiveness of the frequency sweep method in laminar flow is shown with simulation results. And a usefulness of this dynamics simulation is also discussed through the experimental result.

Valsalva maneuver in detection of right-to-left shunt by transcranial Doppler

Sir: We read with great interest the study by Lange et al (Arq Neuropsiquiatr 2010;68:410-3) regarding the effect of valsalva maneuver (VM) in right-to-left shunt (RLS) detection by transcranial Doppler (TCD). We wish to highlight some relevant issues. Trans-esophageal echocardiography (TEE) is considered the gold-standard for diagnosing RLS. Although, TEE provides anatomical details of RLS, the real-time travel of a thrombus has been observed rarely 1 . Limitations of TEE include the need of an expert echocardiographer, poor tolerance by patients and often insufficient VM due to sedation and endoscope in the throat. In contrast, TCD is reliable, performed without sedation and carries high sensitivity and specificity as compared to TEE 2 . We disagree with the finding that the timing of VM does not influence the diagnosis of RLS. Considerable variations exist in the methodology for RLS detection, especially the timing of VM during the test performance. While VM has been performed simultaneously with the contrast injection in some studies 3 , others initiated it after a delay of 3-5 seconds 2 . Substantial hemodynamic changes occur during the “Strain-phase” (amplifies inter-atrial leftto-right pressure-gradient and counteracts RLS) as well as the “release-phase” (reverses pressure gradient with sudden increase in venous return and right atrial pressure that facilitate RLS) 4 . Furthermore, VM causes considerable reduction, and even complete stoppage, of flow in proxi mal large veins. Thus, the injection of saline-air contrast mixture during VM into a proximal vein (with elevated pressure and near-stagnant flow) does not seem logical. Injection during VM theoretically seems counterproductive since the high venous-pressure might destroy some of the “microbubbles” in “saline-air” contrast mixture. This assumes further significance as the microbubbles creat ed during the vigorous shaking of the contrast mixture survive only for a short time. We believe that although, the timing of VM may not affect the detection of RLS, it might influence the functional grading of the shunt. Body position during the diagnosis of RLS needs special consideration. TEE, usually performed with patient lying in left-lateral position, is met with an adverse environment for air microbubbles - to travel from right atrium (at higher level) into the left atrium (at lower level) - thus challenging the basic physical fundamentals! We have demonstrated previously that multiple injections of contrast mixture during TCD are safe and “functional-grades” of RLS varies with body positions as larger number of microbubbles are detected in sitting position 5 . Larger studies with controlled conditions for various confounding factors are needed to develop a standardized protocol for RLS detection.