Air Bubble Injection Research Articles

Antibiotics Degradation and Bacteria Inactivation in Water by Cold Atmospheric Plasma Discharges Above and Below Water Surface

Cold atmospheric plasma discharges in air above air–water surface interface and discharges inside water with injection of air bubbles, show interesting properties for water purification. Water parameters during plasma treatment get different values depending on discharge schemes. Detailed measurements of water parameters during plasma applications as pH, oxidation–reduction potential, total dissolved solids and conductivity are essential in understanding micropollutants degradation mechanisms in water. E. coli bacteria in water have been eliminated faster by plasma discharges produced in water than in air above it. Degradations of two antibiotics oxytetracycline hydrochloride (OTC) and doxycycline hyclate (DXC) in water solution are faster for plasma generated below solution surface than above it with appearance of one degradation product for OTC and two for DXC along plasma treatment time. Degradations are enhanced in the solution after 200 h following plasma treatment for the two antibiotics. H2O2 concentration can give a good indication of plasma effectiveness on different pollutants as it is a relatively stable compound. For water purification, contributions of two factors have to be identified namely water acidity with certain pH value and concentrations of reactive species generated in water. For plasma discharges inside water with air bubbles the most pronounced effect is the increasing value of H2O2 generated in water, while for plasma discharges above water the effect of water acidity induced by low pH is more dominant regarding pollutants degradations.

Effects of Air Bubble Injection on the Efficiency of a Flat Plate Solar Collector: An Experimental Study for the Open Flow System

Effects of Air Bubble Injection on the Efficiency of a Flat Plate Solar Collector: An Experimental Study for the Open Flow System

Effect of air bubble injection on the thermal performance of a flat plate solar collector

Air bubble injection has been proved to be a simple and effective heat transfer enhancement technique in liquid-to-liquid heat exchangers. This study aimed to investigate the technique experimentally as a possible method for augmenting the thermal performance of a flat plate solar collector in the climatic conditions of Najaf city, Iraq. Air was injected as small bubbles into the riser tubes of the solar collector with three different flow rates Qa=1,1.5and2LPM and was compared with no air injection Qa=0LPM. The flat plate solar collector had dimensions of 1000 × 2000 × 80 mm (length, width and thickness respectively) and contained seven riser tubes of 8 mm internal diameter and 0.6 mm thickness. A perforated silicon tube (with holes of 0.5 mm diameter) was used for the air injection. Tap water was used as a working fluid and the experiments were repeated three times for each air flow rate. The experimental results showed that the injected air significantly improved the thermal performance of the solar collector. Its efficiency was enhanced by about 16.5%, 69.2% and 68.8% for the injected air flow rates of 1 LPM, 1.5 LPM and 2 LPM respectively.

Solar still distillation enhancement through water surface perturbation

Solar still water production enhancement was measured in experimental single-slope basin-type solar stills (BTSS) by perturbing the water surface of the still. The perturbation is achieved by the injection of air bubbles into the water basin, which produces surface ripples, thus increasing the overall evaporative surface area and stimulating the mass transfer coefficient. Overall, distilled water production is therefore enhanced as the evaporation improves. The position and flowrate of the air bubble injectors do not seem to affect the amount of evaporation increase. Two very low-tilt covered, shallow BTSS were operated simultaneously side by side. Only one of them was subjected to mass transfer enhancement, in order to produce conclusive mass transfer enhancement results. These results can be accommodated in a computer simulation program with the introduction of a simple intensification factor. Experimental work was carried out in the semi-desert, water-starved, highly insolated region of La Paz, BCS, Mexico.

Analysis of coiled tube waste heat storage tank under water injection

Abstract In this paper, attempts are made to increase the heat transfer in the hot water storage tank via water injection into the storage water. With new water injection system, increasing mixing effect especially around the coiled tube was aimed. The experimental study was conducted to obtain the effect of different velocity (0.03 ≤ V ≤ 1.3), different flow pressures and different outlet hole diameters on dimensionless temperature distribution, Nusselt number and second law efficiency. The results showed, depending on the velocity, water injection into the tank provided an increase in the range of 15–60% for the Nusselt number. The highest enhancement in average Nusselt number occurred when the V = 1.3 m/s. The highest decrease in the second law efficiency was observed around 5% for the 1 mm hole diameter. In addition, the water injection method compared with air bubble injection method in the literature. The comparison indicated, average Nusselt number of the air bubble method 0.6% higher than the water injection method but second law efficiency and average dimensionless temperature 1.7% and 25.7% respectively less than the water injection method.

Novel Technique For The Management Of Macroperforation During Deep Anterior Lamellar Keratoplasty.

PurposeTo describe the outcomes of a case series of patients who underwent a novel technique for managing macroperforation during deep anterior lamellar keratoplasty (DALK).MethodsNine eyes of 9 patients with advanced keratoconus who underwent DALK comprised the case series. A macroperforation occurred in all eyes during DALK. The stromal patch suturing technique was used to manage all cases; a large piece of the previously excised stromal tissue was sutured to the edge of the trephine to seal the perforation. The technical aspects of the procedure are described and data are presented on the visual outcomes, endothelial microscopy, and postoperative complications at last postoperative visit (average 18 months; range, 7 to 23 months).ResultsAll 9 cases were managed successfully with the stromal patch suturing technique. Postoperatively, the graft was clear in all cases. At day 1, seven eyes had a Descemet’s membrane detachment, 3 of these eyes resolved spontaneously within 2 weeks and 4 required air bubble injection for successful reattachment. At last follow up seven eyes had a corrected distance visual acuity of 20/30 or better and 2 eyes had 20/40 vision. The average endothelial cell count was 2162 cell/mm2. There were no cases with excessive inflammation or vascularisation during the postoperative follow-up.ConclusionThe stromal patch suturing technique was successfully used to manage intraoperative macroperforation during DALK. This technique resulted in endothelial changes that were consistent with uncomplicated DALK and function visual acuity of 20/40 or better in all cases with no postoperative sequelae.

Optimisation and evaluation of NTU and effectiveness of a helical coil tube heat exchanger with air injection

Air bubble injection has recently been confirmed as a beneficial technique for enhancing the thermal performance of a heat exchanger. The normal vertical motion of the bubbles due to buoyancy force leads to the entrainment of fluid from the shell side, thereby raising its velocity and turbulence level whilst improving the mix within the shell. Consequently, the thermal boundary layer that formed around the outer surface of the coil is disrupted, thus reducing heat transfer resistance and enhancing the heat transfer rate. Despite relatively considerable attention that has been given to assess this technique, numerous investigations have concentrated on only a few operational conditions. This consideration will be insufficient to understand the influence of air injection entirely on the thermal performance of a heat exchanger. Thus, this study aims to fill this gap by performing experiments over numerous operational conditions for hot and cold fluids and the injected air in a vertical counter-current coiled tube heat exchanger. The optimal air flow and the shell-side flow rates of the vertical coiled tube heat exchanger are determined, thus leading to the economic operation of a heat exchanger. Therefore, the implemented shell-side flow, air flow and coil-side flow rates were changed from 2 LPM to 10 LPM, from 0 to 10 LPM and from 1 LPM to 2 LPM, respectively, with three temperature differences (i.e., 20°C,30°Cand36°C). The number of heat transfer units (NTU) and the thermal effectiveness of the heat exchanger were investigated intensively. Results showed that the NTU and the effectiveness are influenced significantly by the injected air flow, shell-side flow and coil-side flow rates without noticeable effect on the temperature difference. In addition, the positive role of the injected air flow rate was diminished, and no further enhancement of NTU and effectiveness was observed when Qa>6LPM. The most effective shell-side flow rate was also 6 LPM. The maximum augmentation in the NTU and the effectiveness were 1.93 and 0.83, correspondingly, whilst the minimum value of the NTU and the effectiveness were 0.66 and 0.63, respectively.

Parametric CFD investigation of ALS technique on reduction in drag of bulk carrier

ABSTRACTDevelopment has been made in the field of Naval Architecture to enhance the fuel efficiency of ships by using techniques which reduces pressure drag at higher speeds. However, for slower moving vessels, the major concern is higher percentage of frictional drag. It is well-known fact that, frictional drag depends on the wetted surface area of a ship, viscosity and density of fluid flowing around it. Applications to change the viscosity and/or density and/or wetted surface area of the ship is need of an hour. In the Air lubrication system technique, alteration of above is possible by injecting air bubbles below the hull. In this study, numerical investigations into frictional drag reduction by injection of air bubbles were carried out in Star CCM+ for a 1:23 scaled model of a Bulk Carrier for two speeds and for different air injection rates using different diameters of series of injection holes.

Intracameral air injection after completion of phacoemulsification cataract surgery: Evaluation of corneal incisions with optical coherence tomography

PurposeTo evaluate the effects of air bubbles on clear corneal incision (CCI) in patients who had phacoemulsification surgery, and to compare this type of CCI architecture with patients who had no air bubbles after phacoemulsification surgery, using anterior segment optical coherence tomography (AS-OCT). MethodsEyes which had undergone uneventful phacoemulsification cataract surgery with implantation of a posterior chamber intraocular lens (IOL) were equally randomized into two groups. Group 1 comprised patients with anterior chamber air bubble injection after phacoemulsification, and Group 2 comprised patients who had undergone phacoemulsification surgery without anterior chamber air bubble. Postoperative evaluation included AS-OCT (Heidelberg Engineering, Germany) and pneumatic tonometry (Nidek NT-1000 Pneumatic Tonometer, Japan) in the 2nd hour, then at 1 week, and 1 month. Astigmatic changes assessed with corneal topography after phacoemulsification cataract surgeries were noted. ResultsEvaluation was made of 40 eyes of 28 patients (10 female, 18 male) as 20 eyes in Group 1 and 20 eyes in Group 2. On the first postoperative day, the endothelial gap rate was 13.3% in Group 1 and 57.1% in Group 2 (P = 0.02), and this continued until the 1-month follow-up examination. The Descemet's membrane detachment (DMD) rate was 0% in Group 1 and 42.8% in Group 2 on postoperative day 1 (P = 0.006), and this continued at the 1-month follow-up examination. At 1 month postoperatively, the rates of optical coherence tomography (OCT) parameters were similar. There were no significant differences between preoperative astigmatism and postoperative astigmatism in the group analyses. ConclusionIn this study, air bubbles decreased the rate of DMD and of endothelial and epithelial gap during the early postoperative period.

Coupled resonance of bubbles in spherical cavitation clouds

The interaction between bubbles in bubble group mainly acts on the other bubble through radiation sound pressure between the bubbles. In this paper, based on the bubble dynamics equation in bubble clouds, the equation of bubble wall motion is linearly reduced, the expression of bubble resonance frequency in spherical bubble group is obtained and the correction coefficient of bubble resonance frequency and single bubble are given. Furthermore, the effects of the initial radius, the number of bubbles and the distance between bubbles on the resonance frequency are discussed. The results show that the phase of bubbles is taken into account. Considering the interaction between bubbles, the resonance frequency of bubbles in spherical bubble group is obviously less than that of single bubble. With the decrease of the number of bubbles in bubble group, the distance between bubbles increases, the interaction between bubbles in bubble group decreases, and the resonance frequency of bubbles returns to the resonance frequency of Minnaert single bubble. At the same time, the resonance frequency of bubbles in bubble group changes gradient with the increase of the distance between bubbles and the number of bubbles. However, when the number of bubbles increases a certain value, the resonant frequency of the bubble is almost constant. When the bubble group has a certain radius, the more the number of bubbles, the smaller the resonance frequency of the bubble is, but there exists a critical value. It is also found that a smaller correction coefficient is held by the bubble group with larger initial radius, which indicates the same number of bubble groups. Under the same bubble spacing, the interaction of small bubbles with smaller bubbles is more significant, and the resonance frequency of the bubble is obviously affected. Because the frequency and amplitude of driving sound pressure can only be given values in ultrasonic cavitation, the resonant frequency of cavitation bubbles will be reduced by properly injecting air bubbles into liquid, which makes most of cavitation bubbles undergo intense non-linear oscillating steady-state cavitation. Therefore, the occurrence of cavitation can be effectively suppressed.

A comprehensive second law analysis of coil side air injection in the shell and coiled tube heat exchanger: An experimental study

Recently, the use of air injection into heat exchangers to increase their thermal performance has attracted great attention. In the present study, air is injected into the coil side of a horizontal shell and coiled tube heat exchanger. An external unit for air bubbles injection is used. By means of this method, there is no need to modify the original design of the heat exchanger. The effect of various air volume fractions (VF) on the number of thermal units (NTU) and pressure drop is examined. Besides, the effect of air bubbles injection is analyzed from the viewpoints of the second law of thermodynamics, which has not been performed previously. The entropy generation, augmentation entropy generation number and Witte-Shamsundar efficiency as important criteria are analyzed for the developed system. The results revealed that air bubbles injection into the coil side improved the thermal characteristics of the heat exchanger. Also it was observed that for achieving the best performance the volume fraction should be optimized. Besides, according to the second law analysis, it is realized that air bubbles injection into the coil side is more effective method for the heat exchangers with high liquid flow rates.

Introduction to the Special Issue on High Frame Rate/Ultrafast Contrast-Enhanced Ultrasound Imaging

Since the first injection of air bubbles in blood to enhance the echoes backscattered from within the aorta (Gramick and Shah, 1968), contrast-enhanced ultrasound (CEUS) has seen the development of revolutionary methods for blood flow imaging, tissue perfusion quantification, and molecular targeting. The contrast agents, nowadays typically encapsulated microbubbles with a gas core, offer superb echogenicity from within the blood and can be deactivated by ultrasound at will, enabling quantification of tissue perfusion. Another exciting development in medical ultrasound is represented by high frame rate (HFR) imaging, also known as ultrafast ultrasound, which permits the formation of images at frame rates up to two orders of magnitude higher than the previous line-by-line scanning approach. Since their first introduction, both CEUS and HFR/ultrafast ultrasound have recently seen significant advancements with a substantial acceleration of their clinical application.

Acoustic impulses generated by air-bubble stimulated underwater spark discharges

Considerable research efforts have been expended in investigating and optimising the emission of acoustic pressure impulses by high power spark discharges in water. Several methods are typically used to generate transient underwater spark discharges, including breakdown of water by stressing electrode(s) with HV impulses, initiation of spark discharges with thin metallic wires placed between opposite electrodes and by injecting gas bubbles into the inter-electrode gap. This paper is aimed at the investigation of the acoustic, hydrodynamic and electrical characteristics of underwater spark discharges initiated by injected air-bubbles. At a constant applied voltage, the injection of air bubbles allows the inter-electrode gap to be increased thus producing stronger acoustic impulses. This paper reports on the impact of injected air bubbles on the characteristics of transient underwater plasma discharges and on the functional relationships between hydrodynamic and electrical parameters of such discharges, including breakdown voltage, plasma resistance, energy delivered into the plasma cavity and the period of gas/plasma cavity oscillation. An analytical model which relates the acoustic efficiency, plasma resistance and energy available in discharge has been developed which can be used for the optimisation and tailoring of underwater plasma-acoustic sources.

Performance evaluation and exergy analysis of a double pipe heat exchanger under air bubble injection

One of the most commonly used devices in thermal energy transfer is heat exchanger. Increasing the efficiency of heat exchangers by increasing its heat transfer rate has been the subject of study by many researchers. Heat transfer can be increased through two main kinds of methods, i.e. active methods and passive methods. The active methods require external power while in passive methods there is no need for external force to continue the durability of heat transfer enhancement mechanism. In this paper, an experimental study on the effect of air bubble injection as an active method in thermal performance of a double pipe heat exchanger is conducted. Air bubbles are injected into annulus side through different injectors. Experimental data are collected for different tube and annulus side flow rates. The effects of air flow rate and the angle of heat exchanger positioning on its thermal performance are investigated along with exergetic analysis. Obtained results show that the overall heat transfer coefficient can be improved through air bubble injection by 10.3% to 149.5%.

Study on performance of horizontal single pass shell and multi-tube heat exchanger with baffles by air bubble injection

ABSTRACTThe single pass shell and multi-tube heat exchanger with double segmental baffles'’ performance improvement were experimentally investigated by two methods of air injection into shell side when an increase in air bubble created an effect in the corresponding values of shell and tube heat exchanger such as the overall heat transfer coefficient, effectiveness, NTU and the pressure loss. In the first method, air bubble injection into shell side was parallel to the cold water flow; also in the second method, air bubble injection into shell side was cross flow to the cold water with different air flow rates to calculate approximately the most favourable performance conditions. 1–6 LPM of air flow rates and 10–20 LPM shell side water flow rates were transformed with constant tube side hot water flow rate.

Experimental investigation of air injection effect on the performance of horizontal shell and multi-tube heat exchanger with baffles

This paper presents a laboratory experiments for investigation of air injection into the shell side of shell-and-multi-tube heat exchanger aims to augment the thermal performance. The air has been injected inside the heat exchanger shell with two methods (cross injection from shell wall and parallel injection from the shell front side) and different air flow rates to estimate the optimum performance conditions. The air and shell side water flow rates were changed between 1 and 5 LPM and 12–21 LPM respectively with constant tube side water flow rate. Also, pressure loss between the shell side outlet and inlet caused by air bubble injection was measured to know the power loss in heat exchangers under enhancement technique. The results presented that the injected air flow rate and injection method have a significant impact on the heat exchanger performance enhancement. And also presented that, increase of air flow rate increases the overall heat transfer coefficient (U). The effect of air bubble injection on effectiveness (ε), U and NTU of heat exchanger in first method flow was more than the second method for all test conditions. The shell side pressure loss for the cross injection was higher than in the case of parallel injection from. The augmentation on the U caused by cross air injection into the heat exchanger shell was 131–176% depending on air and shell side water flow rates.

Numerical investigation of temperature increment effect on bubble dynamics in stagnant water and Al2O3 nanofluid column

ABSTRACTFormation, growth, and detachment of injected air bubble from a submerged needle in stagnant liquid at the different temperature of fluid, investigated numerically. Experiments have been done for validation of numerical simulation results. The injection flow rate of air was varied between 600 and 1200 mL/h in experimental study. Bubble formation, growth, and detachment information were obtained using high speed camera and visual photography technique. Young–Laplace equation that was derived from the force balance on the bubble, was utilized in numerical simulation. A novel method was used for solution of Young–Laplace equation. The bubble diameter, instantaneous contact angle, volume, and other characteristics of bubble were studied at different temperature of operating condition. Also, the enhancement of temperature in Al2O3 nanofluid with 0.01% volume concentration (φ = 0.01%) was compared with deionized water results. The results reveal that by increasing the Al2O3 nanofluid and the deionized water temperature, the diameter, volume, and center of gravity of bubble decrease; however, the instantaneous contact angle increases. Meanwhile, the size of bubble at Al2O3 nanofluid is larger than of that in deionized water at same temperature. Also, the bubble aspect ratio is almost senseless to temperature increment in both deionized water and Al2O3 nanofluid. Eventually, the variation of operating temperature and adding of nanoparticle to the deionized water have significant influence on behavior of growing bubble.

An Experimental Study of Nanofluids Operated Shell and Tube Heat Exchanger with Air Bubble Injection

Shell and Tube heat exchangers are the heat exchangers that are most widely used in industries and for other commercial purposes. There are many techniques that have been utilized to enhance the heat transfer performance of the shell and tube heat exchangers. Air bubble injection is one of the promising and inexpensive techniques that can create turbulence in the fluids resulting in to enhancement of heat transfer characteristics of the shell and tube heat exchangers. In this paper, experimental study of heat transfer characteristics have been done by injecting air bubbles at tube inlet and throughout the tube for 0.1%v/v and 0.2%v/v Al2O3 nanoparticle concentration. Results obtained at two different injection points for both concentrations are compared with the case when no air bubble injection is done. The results showed the enhancement in the heat transfer characteristics with air bubble injection and volumetric concentration of nanoparticles. The maximum enhancement was found to be in the case where air bubbles are injected throughout the tube which is followed by the air bubble injection at the tube inlet and without air bubble injection. As the bubbles were injected throughout the tube, approximately 22-33% enhancement was observed. The overall heat transfer coefficient with injecting air bubbles throughout the tube showed an enhancement of about 12-23% and 14-25% for 0.1% and 0.2% of nanofluids.

Évaluation pratique de la prise en charge par DSAEK des décompensations endothéliales après kératoplasties transfixiantes

To report our anatomical and functional results as well as possible complications of the first six Descemet's stripping endothelial keratoplasties (DSAEK) performed in our department for endothelial decompensation after penetrating keratoplasty (PK) METHODS: This was a retrospective and observational monocentric study of six patients with DSAEK after prior PK between January 2015and July 2016. The data collected were: demographic characteristics (age, sex), ophthalmological comorbidities, initial indication for PK, delay between PK and DSAEK. Best corrected visual acuity (BCVA) preoperatively and at 1, 3and 6months postoperatively were collected in Monoyer's and Parinaud scale and converted to log MAR for statistical analysis. The central cornea and graft thickness measured on OCT as well as postoperative complications were also collected. Mean follow-up duration was 7.2months [3-10]. The average time after PK was 7.7years. The mean age of the patients was 67.5years [32-87]. The initial indication for PK was Fuchs dystrophy (3/6), pseudophakic bullous keratopathy (1/6), corneal laceration (1/6) and other corneal dystrophy (1/6). The authors report one case a combined phaco-DSAEK surgery. The complications observed were: an early graft detachment treated by an additional air bubble injection (1/6) and cystoid macular edema in one other case. The average central corneal thickness decreased from 780μm at day7postoperatively to 656μm at 6months. The average thickness of the graft decreased from 154μm at day7to 122μm at 6months. The mean preoperative BCVA was 1.52log MAR [1.0-1.7], compared to the mean postoperative BCVA which was 1.5log MAR [1.1-2.3] at 1month, 1.15log MAR [0.5-1.7] at 3months and 1.1log MAR [0.7-1.7] at 6months (data available for 4patients at 6months). The recovery of visual acuity was limited in 2cases, despite corneal clarity restored in all our patients. Our results can be compared to those described in literature. As more penetrating keratoplasty grafts reach the end of their lives, this will allow for more powerful studies. DSAEK on eyes previously treated with PK is a good alternative to a new PK in the case of endothelial decompensation of the graft. The possibility of a posterior lamellar graft allows for faster visual recovery, with preservation of the anterior corneal power and a lower rate of complications.

Optimization of drag reduction effect of air lubrication for a tanker model

The reduction of CO2 emissions has been a key target in the marine industry since the IMO's MEPC published its findings in 2009. Air lubrication method is one of the mature technologies for commercialization to reduce the frictional resistance and enhance fuel efficiency of ships. Air layer is formed by the coalescence of the injected air bubbles beyond a certain air flow rate. In this study, a model ship (λ = 33.33) of a 50,000 ton medium range tanker is equipped with an air lubrication system. The experiments were conducted in the 100 m long towing tank facility at the Pusan National University. By selecting optimal air injector configuration and distribution ratio between two injectors, the total resistance of model RTM was able to be reduced down to 18.1% in the model scale. Key issue was found to suppress the sideway leakage of injected air by appropriate injection parameters.