Injected Gas Bubbles Research Articles

The propagation of negative pulsed discharges facilitated by artificially injected gas bubble in water

Abstract The artificial injection of bubbles into the electrode gap can effectively enhance the performance of underwater pulsed spark discharge (UPSD). It is crucial to investigate the morphology and propagation characteristics of discharges for a comprehensive understanding of bubble-stimulated UPSD. This paper presented an extensive study of negative discharges facilitated by the injected large bubble (with a diameter of 3 mm) in UPSD. The bridging effect of the bubble and the morphology and propagation of discharges were observed through the shadowgraph images captured by a high-speed camera. A numerical model was built to analyse the influence of the bubble on the initial electric field distribution between the electrodes. The characteristics of discharges were notably influenced by bubble parameters and energization conditions. Not in all cases could the bubble play the bridging effect role. The effective range of the bubble was roughly confined to a small region near the HV electrode tip. The experimental results obtained in this paper have certain guiding significance for the practical application of UPSD.

Pressure in underwater spark discharge initiated with the help of bubble injection and its evaluation based on H-alpha line broadening

The pressure in an underwater discharge channel is the main parameter that influences all its applications. In this study, we investigate a relatively large gap with a plane-to-plane electrode geometry that uses the assistance of an injected gas bubble for breakdown. The delay in the application of high voltage following the injection of a gas bubble from a grounded electrode determines the initial dimensions of the bubble. We examined three types of discharge: (a) a large bubble with easy triggering, (b) a medium bubble, and (c) a small bubble with difficult triggering. The main diagnostic tool is H α line broadening. It is shown that (i) Doppler broadening plays no role; (ii) at pressure broadening, the resonance and van der Waals broadenings must be considered; (iii) the impact approximation is not applicable, and hence the quasi-static high-pressure (namely ‘nearest neighbour’) approximation must be used; and (iv) the Stark broadening plays the dominant role. Because a mixture of two gases (evaporated water vapour and nitrogen from bubble injection) is present in the discharge channel, simple thermodynamic considerations were applied to estimate the ratio of the contributions of resonance and van der Waals broadening. The larger the bubble, the smaller the pressure detected in the discharge channel. This is in agreement with the measurements of the pressure wave amplitude at a certain distance from the discharge channel using a piezoelectric pressure probe.

The guiding effect of artificially injected gas bubble on the underwater pulsed spark discharge and its electrical and acoustic parameters after breakdown

The presence of a low density area is beneficial to the facilitation of the underwater pulsed spark discharge, which can be achieved by artificially injecting gas bubble in between the inter-electrode gap. The generation of intensive acoustic waves by such gas-bubble-guided spark discharges makes them promising underwater acoustic sources in multiple practical applications. This paper is aimed at comprehensive investigation of the guiding effect of the injected bubble on the pre-breakdown process of underwater pulsed spark discharges and potential correlations between their subsequent electrical and acoustic parameters with the purpose of optimizing the acoustic emission. The breakdown probability and the pre-breakdown delay were used to evaluate the general facilitation effect brought by the injected bubble. Experimental and numerical works have been conducted and allow observation on the dynamics of the injected bubble under the influence of the applied voltage. Different guiding modes of the injected bubble for plasma streamers' propagation have been observed regarding its relative position. The characteristics of the electrical properties of gas-bubble-guided spark discharges, including the plasma resistance and the plasma energy density, were analyzed by relating them with the breakdown voltage. The dependency of the acoustic wave amplitude and the acoustic efficiency on these electrical parameters was verified, which provides solid regulation principles for the optimization of the plasma-acoustic system for target practical applications.

A Fundamental Investigation of Decarburization Reactions in the Argon–Oxygen Decarburization Converter Using Coupled Computational Fluid Dynamics and Thermodynamics Databases

Metallurgical converters such as the argon–oxygen decarburization (AOD) converter generally utilize gas blowing for the mixing and refinement of liquid steel. Due to the harsh environment of the complex and opaque system, it is common practice to study the stirring of the process through physical and numerical models. Effective mixing in the bath has an important role in refinement such as decarburization and has been vividly studied before. However, high‐temperature chemical reactions that also play a major role are sparsely investigated. With the help of modeling, a computational fluid dynamics model coupled with chemical reactions is developed, allowing the study of both dynamic fluid transport and chemical reactions. Herein, the chemical reactions for a single gas bubble in the AOD are investigated. The study shows that a 60 mm oxygen gas bubble rapidly reacts with the melt and is saturated with carbon in 0.2–0.25 s at low‐pressure levels. The saturation time is affected by the pressure and the composition of the injected gas bubble. The impact of ferrostatic pressure on the reactions is more significant at larger depth differences.

Incorporating bubble growth volume feedback to improve simulation of the response of a structure containing liquid and gas to sudden energy input

The SNS target module is a stainless-steel structure that contains and directs mercury. The mercury is struck with short, intense proton pulses to create neutrons. The pulses deposit energy and cause loads on the target structure and mercury cavitation. Helium bubbles are introduced into the mercury to reduce loads and cavitation. This gas complicates the prediction of the target module’s physical response. The current method used to simulate the structural response to the proton pulse incorporates a simple but effective approach to approximate mercury cavitation effects. This method cannot account for the changes from injected non-condensable gas. The ability to model the target vessel response is a prerequisite for estimating its life. Known approaches for simulating a bubbly fluid mixture’s response are computationally expensive and impractical for detailed engineering models. A constitutive model is proposed for target mercury with injected gas bubbles, with the intent of providing more accurate mercury–vessel response behavior without the computing costs required to track individual bubbles. The model’s assumptions and a computational model embodiment are described. The bubbly mercury computational model is subjected to test problems to assess its potential utility. The model was able to better predict the effect of gas on wave propagation.

Liquid Metals in Catalysis for Energy Applications

Summary To keep up with the fast-paced transitioning of the global energy sector, which is constantly thriving to enable reliable, economic, and sustainable energy production, catalysis research has been required to continuously evolve in response. The challenges in the existing systems are predominantly due to dependencies on heterogeneous solid catalysts that are susceptible to coking. In this respect, liquid-metal (LM) catalysts have been demonstrated to have a critical advantage over conventional catalysts. Recently, LMs acquired a place in catalysis, with a reputation often synonymous with interesting properties and a remarkable ability to break trade-offs between homogeneous and heterogeneous catalysis. This review bridges the fundamental principles of LM research and the recent advances in LM-based thermal and electrochemical catalysis for energy applications. Moreover, emerging approaches for the improved utilization of LMs are outlined, and the concepts requiring greater research attention that could enable the development of exciting energy solutions are highlighted.

Deformation, Cracking and Fracture Behavior of Dynamically-Formed Oxide Layers on Molten Metals

This study investigates the cracking behavior of oxide layers formed on molten metals and alloys including pure zinc, Zn–4 wt%Al (ZAMAK3) and Al–(0.5–2) wt%Ca in dynamic oxidation condition by injecting gas bubbles into the molten metal during the pouring process. The crack characteristics of the oxide layers were studied using a field emission scanning electron microscope. The results show that various stresses initiated from turbulence flow in the molten metal promote the deformation of the oxide layer, particularly at the initial stages of oxidation. Different coefficients of thermal expansion of the oxide layers and the metals can also result in deformation/cracking the oxide layers. Simultaneous aspiration of the molten metal and solidification phenomenon within the casting process may lead to various morphological changes, e.g. folded-, wrinkled- and cracked-oxide layers. In addition, a splitting and reforming phenomenon of multiple oxide layers is observed, called as strips of ‘ruffled tape’. An illustrative mechanism is suggested and discussed quantitatively for the formation of such phenomena. It is assumed that the unique appearance of these strips depends on the formation time and complex stress gradients on the oxide layers.

Bubble Migration Velocity in a Uniform Pore Network

Gas bubbles can be generated naturally or introduced artificially in porous media. Gas bubble migration through porous media governs the rate of gas emission to the atmosphere as well as the hydraulic and mechanical properties of sediments. The migration of air bubbles through water-wet porous media of uniform geometry was studied using a glass micromodel. Experiments were conducted to measure the velocity of bubbles of various lengths rising in a glass micromodel saturated with different test liquids and varying elevation angles. The results showed a linear dependency of the average bubble velocity on the bubble length and the sine of inclination angle of the micromodel. Comparisons were made using experimental data for air bubbles rising in kerosene, Soltrol 170 and dyed white oil. The effective permeability of the micromodel for the gas bubble, Kg, was calculated for different systems at different inclination angles, assuming that the effective length for viscous dissipation is equal to the initial static bubble length. It was found that the calculated permeability of the medium for gas bubbles had an increasing trend with increasing the bubble length. To visualize the periodic nature of the flow of rising bubbles in a porous medium, the motion of the air bubbles in white oil was video recorded by a digital camera, reviewed and analyzed using PowerDVDTM11 software. The bubble shape, exact positions of the bubble front and bubble tail during motion and, hence, the dynamic bubble length were determined through image analysis. Numerical simulation was performed by modifying an existing simulation code for the rise velocity of a gas bubble and the induced pressure field while it migrates through the pore network. The results showed that the rise velocity of a gas bubble is affected by the grid size of the pore network in the direction perpendicular to the bubble migration. The findings of this study can have important implications for studies on the migration of injected gas bubbles in geoenvironmental applications, as well as fundamental studies on bubble transport and behavior in porous media.

Synthesis of a Polyaniline Nanoparticle Using a Solution Plasma Process with an Ar Gas Bubble Channel.

This work researched polymerization of liquid aniline monomer by solution plasma with a gas bubble channel and investigated characteristics of solution plasma and polyaniline (PANI). The injected gas bubble channel in the proposed solution plasma process (SPP) played a significant role in producing a stable discharge in liquid aniline monomer at a low voltage and furthermore enhancing the contact surface area between liquid aniline monomer and plasma, thereby achieving polymerization on the boundary of the liquid aniline monomer and plasma. Solution plasma properties were analyzed with voltage–current, optical emission spectroscopy, and high-speed camera. Conductivity, percentage yield, and firing voltage of PANI nanoparticle dispersed solution were measured. To investigate the characteristics of synthesized PANI nanoparticles, field emission scanning electron microscopy, dynamic light scattering, transmission electron microscopy, selective area electron diffraction (SAED) pattern, Fourier transform infrared spectroscopy (FTIR), gel permeation chromatography, 1H-nuclear magnetic resonance (1H-NMR), and X-ray photo spectroscopy (XPS) were examined. The FTIR, 1H-NMR, and XPS analysis showed the PANI characteristic peaks with evidence that some quinoid and benzene rings were broken by the solution plasma process with a gas bubble channel. The results indicate that PANI nanoparticles have a spherical shape with a size between 25 and 35 nm. The SAED pattern shows the amorphous pattern.

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.

Whole-field imaging of temperature and hydrodynamics in a gas fluidized bed with liquid injection

This work presents results of experiments on thermal effects and flow dynamics in a flat-bed geometry gas-fluidized bed at atmospheric pressure, with and without liquid injection. Whole-field measurements have been performed using a combination of thermography, particle image velocimetry and digital image analysis. A first series of experiments demonstrates the mixing of two layers of particles at initially different temperature for a sequence of injected gas bubbles. It is shown that the pulse duration strongly affects the solids mixing and that the influence of diffusion on thermal equilibration is limited without convective mixing. Subsequently liquid has been injected into the fluidizing bed, which has been carried out with water, isopentane and hexane. Owing to the use of a combination of infrared and visual cameras, under particular conditions liquid-solid conglomerates can be observed in situ. Under the conditions applied, the flow dynamics are not clearly affected by the liquid injection. The thermal behavior of the bed is not found to be strongly dependent on which of the model liquids is injected, but more on the cooling capacity obtained by evaporating the injected amount of liquid at the selected injection rate, and the mode of operation.

Continuous manufacture of polymeric cellular dosage forms

The most prevalent pharmaceutical dosage forms at present are granular solids in the form of oral tablets and capsules. While effective in releasing drug rapidly upon contact with gastrointestinal fluid, their manufacture, which relies on particulate processing, is fraught with difficulties associated with the unpredictable inter-particle interactions. Such difficulties, however, could be easily overcome by transitioning to a liquid-based process. Therefore, we have recently introduced melt‐processed polymeric cellular dosage forms. The drug release behavior of the cellular forms was tailored by altering the microstructure; yet their preparation relied on an inefficient batch method comprising gas dissolution, and nucleation and growth of microscopic gas bubbles in the melt. In this study, therefore, we present a continuous microfluidic melt extrusion and molding process. The cellular dosage forms are produced by injecting gas bubbles directly into the melt stream in a micro‐ or milli-fluidic channel, followed by molding and solidification of the cellular structure. A model is developed to illustrate the effects of the width, frequency, and pressure of the gas injection pulses, and the flow rate and viscosity of the melt, on the microstructural parameters of the dosage forms produced. Experimental results show that the size and volume fraction of gas-filled cells (or voids) are predictable. They also confirm that the dosage form disintegration rate and density can be tailored by altering the volume fraction of voids. It is thus demonstrated that polymeric cellular dosage forms with predictable drug release properties, and density, can be readily manufactured by a continuous process.

Understanding the basic concepts of CO2 angiography

The diagnostic quality of carbon dioxide angiography depends both on optimal setting of radiological aspects (X-ray emission and image post-processing) and on the mechanical behavior of the injected gas bubbles. The gas behavior differs in large cavities (d > 12 mm), medium sized vessels (d > 6 mm), and small diameter vessels (d < 6 mm): to optimize the result the operator has to adapt his action to the physical rules governing the phenomenon in the particular situation. In most cases, it is impossible to fill a vessel completely with gas, and to obtain an adequate angiogram, the gas volume and injection pressure must be properly selected, patient's position must be adjusted and radiological image optimization algorithms, like Digital Subtraction Angiography (DSA) and stacking, must be applied. In this optimization process, the cultural and practical intervention of a medical physicist is fundamental. Obtaining a good quality CO2 angiogram is not only a matter of medical operator experience or radiological system performance, but involves matching a wide knowledge of medical physics to particular pathophysiological conditions and to unusual measurement tests. Most medical physicists are used to dealing mainly with radiological problems, and other physical aspects are considered beyond their interest. In CO2 angiography, non-radiological aspects strongly interfere with radiological issues and an optimal result can only be obtained by tackling the two simultaneously.

Experimental and analytical methods to determine minimum miscibility pressure (MMP) for Bakken formation crude oil

The Bakken is one of the shale reservoirs that has been discovered to hold a vast amount of resource and is contributing to the production boom in the US. This unconventional reservoir, like most others, displays favorable initial production rates due to stimulation by hydraulic fracturing, but production rates quickly decline after few months. Due to the extremely low permeability and low recoveries, miscible gas injection is considered for improving the recovery of oil in the Bakken formation. Feasibility of miscible gas injection in the Bakken would depend on the analysis of minimum miscibility pressure (MMP) experiments.The Rising Bubble Apparatus (RBA) has been chosen for the purpose of these experiments. The RBA provides results in a short amount of time using small amounts of fluid samples. The RBA consists of a cell gage containing a flat glass tube where oil samples are placed and an injection needle where gas is injected into the flat glass tube. To simulate reservoir conditions, the glass tube is pressurized using de-ionized water, and heating plates surrounding the cell are used to regulate temperature. Visual observation of the injected gas bubble behavior is captured by a camera as it rises and moves upward along the oil column. By observing the shape and dissolution behavior of the bubble, the MMP can be determined.MMP results from a Bakken crude sample are shown to range from 2100 to 3500psi at temperatures from 160 to 240°F using CO2 as the injection fluid. Other injection fluids such as nitrogen and hydrocarbon gases have been tested and also provided reasonable MMP values. MMP results from Bakken crude oil samples were compared to existing correlations, and the correlations were found to produce mostly unreliable MMP results for the Bakken oils evaluated in the study. On the other hand, an equation of state phase behavior program showed similarities with the RBA MMP results.The impact of different injection fluids, inclusive of CO2 and enriched hydrocarbon gases is the subject of this study. MMP results are influenced by the choice of injection fluids, providing valuable information for economic production and increased recovery in the Bakken formation. The results from this study provide a range of MMP data that can be used in planning pilot tests for miscible gas injection in the Bakken.

Note: On-chip multifunctional fluorescent-magnetic Janus helical microswimmers.

Microswimmers integrated into microfluidic devices that are capable of self-illumination through fluorescence could revolutionize many aspects of technology, especially for biological applications. Few illumination and propulsion techniques of helical microswimmers inside microfluidic channels have been demonstrated. This paper presents the fabrication, detachment, and magnetic propulsions of multifunctional fluorescent-magnetic helical microswimmers integrated inside microfluidics. The fabrication process is based on two-photon laser lithography to pattern 3-D nanostructures from fluorescent photoresist coupled with conventional microfabrication techniques for magnetic thin film deposition by shadowing. After direct integration inside a microfluidic device, injected gas bubble allows gentle detachment of the integrated helical microswimmers whose magnetic propulsion can then be directly applied inside the microfluidic channel using external electromagnetic coil setup. With their small scale, fluorescence, excellent resistance to liquid/gas surface tension, and robust propulsion capability inside the microfluidic channel, the microswimmers can be used as high-resolution and large-range mobile micromanipulators inside microfluidic channels.

Thrust Enhancement Through Bubble Injection Into an Expanding-Contracting Nozzle With a Throat

This paper addresses the concept of thrust augmentation through bubble injection into an expanding-contracting nozzle with a throat. The presence of a throat in an expanding-contracting nozzle can result in flow transition from the subsonic regime to the supersonic regime (choked conditions) for a bubbly mixture flow, which may result in a substantial increase in jet thrust. This increase would primarily arise from the fact that the injected gas bubbles expand drastically in the supersonic region of the flow. In the current work, an analytical 1D model is developed to capture choked bubbly flow in an expanding-contracting nozzle with a throat. The study provides analytical and numerical support to analytical observations and serves as a design tool for nozzle geometries that can achieve efficient choked bubbly flows through nozzles. Starting from the 1D mixture continuity and momentum equations, along with an equation of state for the bubbly mixture, expressions for mixture velocity and gas volume fraction were derived. Starting with a fixed geometry and an imposed upstream pressure for a choked flow in the nozzle, the derived expressions were iteratively solved to obtain the exit pressures and velocities for different injected gas volume fractions. The variation of thrust enhancement with the injected gas volume fraction was also studied. Additionally, the geometric parameters were varied (area of the exit, area of the throat) to understand the influence of the nozzle geometry on the thrust enhancement and on the flow conditions at the inlet. This parametric study provides a performance map that can be used to design a bubble augmented waterjet propulsor, which can achieve and exploit supersonic flow. It was found that the optimum geometry for choked flows, unlike the optimum geometry under purely subsonic flows, had a dependence on the injected gas volume fraction. Furthermore, for the same injected gas volume fraction the optimum geometry for choked flows resulted in greater thrust enhancement compared to the optimum geometry for purely subsonic flows.

A boundary element study of the effect of surface dissolution on the evolution of immiscible viscous fingering within a Hele-Shaw cell

Abstract Fingering instabilities at the interface between two immiscible fluids can appear during the displacement of a fluid of higher viscosity by another one of lower viscosity. The evolution of the finger structures is determined by the interface kinematic and dynamic matching conditions, which describe mass and momentum conservation across the interface. In the case when the injected fluid is a gas and the resident one is a liquid, dissolution of the injected gas into the displaced liquid can occur at the interface between the two phases. In this case, the transfer velocity of the dissolved gas reduces the interface displacement velocity as described by the kinematic matching condition, delaying the evolution of the fingering. In addition, the momentum flux across the interface, due to the dissolution, modifies the dynamic matching condition with possible changes in the patterns of the fingers structures. This work studies the effects of gas dissolution on the evolution of fingering instabilities during the displacement of a viscous liquid by an immiscible injected gas in a Hele-Shaw cell. A boundary element numerical simulation of the growth of the injected gas bubble is developed and implemented. This numerical model takes into account the dissolution across a sharp interface between the two phases. Our numerical simulations suggest that the inclusion of gas dissolution can lead to the eventual breaking of the fingers. These “shed fingers” become individual bubbles, which move away from the injection source with the velocity of the surrounding fluid and eventually will dissolve into the ambient fluid. New fingers evolve, with their concurrent breaking, resulting in the possibility of a cascade of travelling and dissolving bubbles, instead of a continuous fingering structure.

Wetting phenomena in oil sand systems and their impact on the water-based bitumen extraction process

The highly efficient and economically feasible technology for bitumen recovery from U.S. oil sands using a water-extraction approach was developed at the end of the last century. This water-based bitumen extraction process has been optimized based on observations and analysis of microscopic mechanisms of bitumen release from oil sands and the bitumen transfer to a froth product as well as measurements of interfacial properties of bitumen. The wetting mechanisms that occur in the diluent-assisted water-based processing of U.S. oil sands include bitumen film rupture and recession on sand grains and bitumen transfer to nucleated and injected gas bubbles. These mechanisms are reviewed in this contribution.

Dimensionless numbers for the analysis of air sparging aimed to reduce fouling in tubular membranes of a membrane bioreactor

Membrane bioreactors (MBR) combine conventional wastewater treatment and membrane filtration to create a system that uses very efficient, specialized microbes, produces a high quality effluent, and leaves small footprint. Fouling remains the major drawback of membrane processes, including MBR systems. Recently, one of the more frequent strategies employed to combat fouling and its consequent reduction in production is air sparging, in which injecting gas bubbles to the membrane generates high shear stress and scours cake layers from the membrane surface. This study mainly focused on permeate flux enhancement by air sparging. The results showed that air sparging over several weeks significantly increased permeate flux. In interpreting the findings, the dimensionless fouling and shear stress numbers are utilized. The fouling number is the ratio of the Peclet number for mass transfer and the Sherwood number. It was found that fouling resistance significantly decreased with air injection ratios between 0.4 and 0.5. This paper introduces a new approach: dividing the fouling number by the Reynolds number, which basically corresponds to the ratio of the Schmidt and Sherwood numbers. That dimensionless number, subsequently called the viscous fouling number shows qualitatively the same graph as the fouling number if viscosity remains constant. If viscosity changes during the filtration process, the fouling number and the viscous fouling number diverge from each other. Using the viscous fouling number instead of the fouling number may be especially useful for processes where fluctuations in viscosity are significant, as they are in MBR.

Anaesthetic management in vitreo-retinal surgery

EDITOR: We read about the analgesic effects of sub-Tenon's block in vitreo-retinal surgery under general anaesthesia by Farmery and colleagues with great interest [1]. Their study reported that all the patients scheduled for vitreo-retinal surgery under general anaesthesia received a standardized general anaesthetic technique consisting of propofol infusion and 50% oxygen in nitrous oxide. The duration of administration of nitrous oxide was not mentioned. Among the 43 patients, 16 had already been treated by injection of gas/oil. The movement of nitrous oxide into gascontaining spaces in the body has been known for a long time. The use of nitrous oxide during vitreous surgical procedures in which gas bubble injection is used will lead the bubble to increase in size and elevate the intraocular pressure. Stinson and Donlon, in 1982, conducted a study to predict the effect of 70% nitrous oxide anaesthesia on the volume of the intravitreal bubble by using a mathematical method. They suggested that nitrous oxide, independent of the duration it is used, causes an increase in volume of the injected gas bubbles in varying sizes, with the risk of occlusion of the central retinal artery [2]. In addition, after vitreous surgery in which a gas bubble was used for retinal re-attachment, subsequent administration of nitrous oxide should be avoided until the bubble is absorbed. Re-administration of nitrous oxide may cause occlusion of the central retinal artery by moving into the pre-existing intravitreal bubbles, leading to blindness [3,4]. To avoid these complications, we have been using remifentanil infusion (0.05 μg kg−1 min−1) for its analgesic effect instead of nitrous oxide due to the fact that nitrous oxide is 35 times more soluble in blood than nitrogen (the major component of air). We use 50% oxygen in air with volatile anaesthetics [5]. We have administered a remifentanil infusion to 50 patients undergoing vitreous surgery. At the end of surgery, 15 min before anaesthesia was stopped, a single dose of metoclopramide and metamizol were administered intravenously. During surgery, we did not observe any large swings in arterial pressure or increase in postoperative opioid requirement leading to nausea and vomiting, as reported by Farmery and colleagues. We have been able to provide smooth intraoperative haemodynamic conditions by using a remifentanil infusion with volatile anaesthetic agents. We recommend our technique of anaesthesia including remifentanil infusion instead of nitrous oxide in vitreo-retinal surgery in order to avoid the undesirable effects of nitrous oxide on intraocular pressure. It is important to know of the existence of a residual intravitreal gas bubble injected in recent vitreal surgery, so that nitrous oxide can be avoided. D. Dal T. Aykut F. Demirtaş Department of Anesthesiology and Reanimation; Hacettepe University; Ankara, Turkey