Air Injection Rate Research Articles

Effects of surface air injection on the air stability of superhydrophobic surface under partial replenishment of plastron

Frictional drag reduction using a superhydrophobic (SHPo) surface has attracted great attention due to its potential for practical application. Air plastron (i.e., pockets) trapped between structures in a submerged SHPo surface serves a crucial role in the drag reduction effect. However, the air plastron on the SHPo surface can easily be depleted by various factors, resulting in the deterioration of the drag reduction performance. This study proposed a surface air injection method to resolve the depletion problem and explored its effect on the enhancement of the air stability of the SHPo surface as a controllable strategy under partial replenishment conditions in which the replenishment rate is less than the depletion rate. An air injection layer is added to a ridged multi-layered SHPo (ML-SHPo) surface to supply air through the surface. The dynamic behavior of air plastron on the surface is directly visualized by an x-ray imaging technique. The temporal evolution of depletion length on the ridged ML-SHPo surface is monitored under laminar flows to understand the underlying basic physics of the enhanced air stability caused by surface air injection. The depletion rate of air plastrons on SHPo surfaces depended on the nondimensional air injection rate (Cq). The dynamic behavior in the air depletion regime is closely associated with flow condition and Cq. The stability of air plastrons is enhanced by 12%–87% as the Cq value increases. In addition, a simple scaling relationship between the depletion rate and Cq is proposed to predict the depletion rate of air plastrons (longevity) on ridged SHPo surfaces.

Field performance and numerical simulation study on the toe to heel air injection (THAI) process in a heavy oil reservoir with bottom water

Extra-heavy oil and bitumen (EHOB) comprise 30 percent of the remaining recoverable fossil fuel resources on Earth. This means EHOB could play an important role in a secure transition towards net zero emissions (NZE) by 2050. Technological developments, such as toe to heel air injection (THAI), have been shown to efficiently recover heavy oil with reduced environmental footprint. The Kerrobert project was the first to utilise the THAI technology in presence of bottom water (BW) in the reservoir. The project demonstrated a good performance (with average oil rate of 10 m3/day per well) compared to the conventional ISC operations in a BW situation. Lessons taken from the Kerrobert operational experience can assist the forthcoming THAI operations explicitly in the presence of BW. Dynamic field data for one of the best performing THAI pilot well pairs (K2), were analysed in this work. It was found that the K2 pilot must have experienced interference from K5, which is the closest neighbouring THAI well pair to the K2. Previously developed THAI models have not been validated against actual field data. A new field-scale THAI model in the presence of BW was constructed and, for the first time, validated against the field data from the Kerrobert project in this work. In addition, the quasi-staggered line drive well arrangement, as used for the K2 pilot, was studied. The daily and cumulative oil production rates were predicted well (the final agreement with field data was within 3 percent). The history matched model was then used to investigate the effect of the variation in air injection rates on THAI performance in presence of BW. Major developed zones during the propagation of the combustion front were numerically examined. It was demonstrated that extra air ingress from the neighbouring THAI well pair has caused a reduction in oxygen utilisation throughout the process. As a result, the simulated temperature profile declined with the increasing combustion time. The oxygen profile around the horizontal producer (HP) well was studied via the new history-matched model. An inversely proportional relationship was detected between the coke concentration and the oxygen profile around the HP well. It was found that the size of the steam zone, ahead of the combustion front, differs with variation in air injection rates. It was observed that some of the mobilised oil sank into the BW, leaving a significant amount of oil trapped in the reservoir. To prevent such an event, the location of the HP well was altered as a potential strategy to optimise the THAI efficiency. Consequently, the oxygen utilisation was improved by 13%, resulting in 73% higher cumulative oil production in comparison with the history-matched model.

Study of an air bubble curtain along a wall in water and radiated noise mitigation

The injection of air bubbles into the liquid phase of a freestream flow has several impacts on the flow structure, which depends on the volume and size of the bubbles. This work experimentally investigates the characteristics of air bubble injection into freestream flow using three different injector models. The effects of the bubble curtain on the sound wave attention are studied. A wide range of air injection rates from 2 to 50 standard liters per minute is injected into the freestream water at Froude numbers (Fr) of 50.5, 70.7, and 90.9. The injector model is placed on the sidewall, which is where the bubble curtain is generated. High-speed cameras and an image processing technique are used to visualize and quantify the projected void fraction (PVF) of air bubbles. The sound measurement system consists of two hydrophones. The first hydrophone projects sound waves at discrete frequencies ranging from 17 to 50 kHz, and the second receives the transmitted sound waves. The bubble PVF is observed to increase with the air injection rate as the Froude number increases. There is no significant increment in the thickness of the bubbly curtain when the air injection rate or Froude number increases. The different air injector models produce various air bubble flow patterns, and model II provides the highest PVF. The bubble curtain greatly suppresses sound waves at all frequency ranges. However, the sound attenuation rate varies along the frequency range. The insertion loss increases depending on the PVF of the bubbles, freestream velocity, and frequency range. At a high Froude number of 90.9, the increased air injection rate does not affect the insertion loss. Model II has a relatively higher insertion loss rate at frequencies >26 kHz.

Numerical and experimental investigation of production performance of in-situ conversion of shale oil by air injection

In-situ conversion of oil shale process has been appealing from economic and energy security perspectives. Conventional in-situ upgrading techniques use electric heaters to heat oil shale, not shale oil. However, the efficiency of electrical heating method is very slow which requires preheating more than a year. Most conventional heating technologies focused on using different heat injection methods converting the shale oil reservoirs. As shale is a poor heat conductor, many of attempts are still in the laboratory stage. The shale oil matrix is very tight and the pore scale ranges from micro to nano-meter. In this paper, we propose to inject air into hydraulically fractured horizontal wells to create in-situ combustion of shale oil in ultra-low permeability formations. Heat is introduced into the formation through multistage fractured horizontal wells, which enhances the contact area of exposed kerogen. This process uses combustion reactants as fuel feed stock to generate perpetual heating. Firstly, we used the laboratory tube combustion of shale oil results to validate the simulation model. Then, we upscale the simulation model to investigate the well productivity performance by in-situ upgrading of shale oil by air injection.The main objective of this work is to determine the technical feasibility of recovering shale oil resources by air injection. It involves the application of hydraulic fracturing technology to enhance the kerogen exposure to oxygen. Heat flows from the fracture into shale oil formation, gradually converting the solid kerogen into mobile oil and gas which can be produced via fractures to the production wells. Our simulation results in this paper have shown the potential of in-situ combustion process to improved oil recovery in shale oil reservoirs. Simulation result indicates that the key parameters controlling the well productivity include air injection rate, injected gas composition and fracture spacing. The available literature provides limited studies on the applicability of in-situ combustion of shale oil in very low permeability formations. The paper provides a comprehensive model that allows kerogen to undergo thermal cracking and oxidation process. The results of this study indicate that the developed kinetic model is feasible to model the kerogen in-situ conversion process induced by air injection.

Publisher’s Note

In-situ conversion of oil shale process has been appealing from economic and energy security perspectives. Conventional in-situ upgrading techniques use electric heaters to heat oil shale, not shale oil. However, the efficiency of electrical heating method is very slow which requires preheating more than a year. Most conventional heating technologies focused on using different heat injection methods converting the shale oil reservoirs. As shale is a poor heat conductor, many of attempts are still in the laboratory stage. The shale oil matrix is very tight and the pore scale ranges from micro to nano-meter. In this paper, we propose to inject air into hydraulically fractured horizontal wells to create in-situ combustion of shale oil in ultra-low permeability formations. Heat is introduced into the formation through multistage fractured horizontal wells, which enhances the contact area of exposed kerogen. This process uses combustion reactants as fuel feed stock to generate perpetual heating. Firstly, we used the laboratory tube combustion of shale oil results to validate the simulation model. Then, we upscale the simulation model to investigate the well productivity performance by in-situ upgrading of shale oil by air injection. The main objective of this work is to determine the technical feasibility of recovering shale oil resources by air injection. It involves the application of hydraulic fracturing technology to enhance the kerogen exposure to oxygen. Heat flows from the fracture into shale oil formation, gradually converting the solid kerogen into mobile oil and gas which can be produced via fractures to the production wells. Our simulation results in this paper have shown the potential of in-situ combustion process to improved oil recovery in shale oil reservoirs. Simulation result indicates that the key parameters controlling the well productivity include air injection rate, injected gas composition and fracture spacing. The available literature provides limited studies on the applicability of in-situ combustion of shale oil in very low permeability formations. The paper provides a comprehensive model that allows kerogen to undergo thermal cracking and oxidation process. The results of this study indicate that the developed kinetic model is feasible to model the kerogen in-situ conversion process induced by air injection.

A high-efficiency mini-hydrocyclone for microplastic separation from water via air flotation

A mini-hydrocyclone was designed to remove microplastics from water through air flotation. The hydrocyclone geometry parameters were optimized through the combination of the orthogonal design method and numerical simulation. The performance of the optimized mini-hydrocyclone was experimentally evaluated. The experimental and numerical underflow pressure drop results showed a consistent trend in the considered flow range. The separation efficiency increased with increasing inlet flow rate, but increased, and then decreased, with the flow split ratio. The separation performance of microplastic in the entire size range could be improved through the injection of air bubbles into the water. The separation efficiency enhancement ranged from 5 % to 15 % within a split ratio range of 0.04 to 0.23. The separation efficiency increased rapidly with a low flow rate of air injection and remained high (> 92 %) with a further increase in the air flow rate. The concentration ratios of the hydrocyclone were all >7.8 owing to low flow split ratios. The maximum concentration ratio reached 9.7 at a feed flow rate of 0.45 m3/h, a split ratio of 0.1 and an air holdup of 5.4 %. The results demonstrated that the designed hydrocyclone with injected microbubbles can achieve high separation efficiency and concentration rate at the same time. The air flotation-induced increase in grade efficiency was mainly due to the density reduction effect of MP–bubble agglomerates, and the volume expansion effect was relatively small. The cyclonic air flotation technology can be applied to small-scale water treatment, such as separating microplastics in a washing machine.

In-Situ Combustion: Myths and Facts

Summary In-situ combustion (ISC) involves compression and injection of air into heavy/extraheavy oil reservoirs for enhancing production and recovery. Initially, ISC was very popular due to its high theoretical thermal efficiency, though more failures than successes in the 1990s made this process unpopular. It is a fact that it is now widely considered archaic. However, Suplacu de Barcau (Romania) and Balol-Santhal (India) ISC projects have brought the process back into focus. Performance of the Balol-Santhal-Bechraji over the last 25 years provides clarity to answer the question “Failure to enhance oil production and recovery by ISC: Myth or fact?” The author appreciates the views, decisions, and efforts of all global scientists/engineers/operators associated with the ISC process in the laboratory/field. Opinions and views presented in this paper are solely based on the author’s experience, which may be in line or may differ. The discovery of heavy oil northwest of the Cambay Basin, India, in the 1970s led to the initiation of research and development in thermal processes. The depth, rock, and fluid characteristics, drive mechanism, and semi-arid area led to the testing of ISC over steamflood in Balol. Laboratory findings are key to understanding the reaction kinetics of oil and process manifestations. Upgrading of oil is the key manifestation of ISC in the laboratory, but it is not seen in the field due to blending in long-distance displacement methodology. The involvement of laboratory personnel in design and surveillance plays an important role in the success of the project. Over the last 25 years, the Balol-Santhal ISC projects demonstrate the rejuvenation of declining fields with sustained enhanced oil production and an increase in recovery. Lessons of the Bechraji field indicate that process does not succeed in all reservoir settings. It is particularly suited to relatively clean, mobile heavy oil reservoirs with structural relief. Long-distance displacement of oil (vertical injector-vertical/horizontal producer spaced apart) is effective in a mobile oil reservoir. With low mobility oils, a short-distance oil displacement process using a pair of vertical injector and horizontal producer (horizontal well placed below the air injector) can be the preferred way for exploitation. This methodology has also the potential to capture upgraded oil. The process attracts more value when it is designed as operator friendly and flexible, integrating with gravity. Appropriate ignition types, continuous surveillance, maintaining optimum air injection rates, and re-engineering are important for the success of ISC. Success depends on the fabric and architecture of the reservoir, the way it is designed and implemented, and by integration of knowledge gained in the journey from laboratory to field with the process. It can be concluded that the perception of the ineffectiveness of ISC to enhance oil production and recovery from mobile heavy/extraheavy oil reservoirs cannot be generalized as a fact.

Electrically-enhanced THAI in situ combustion technology for upgrading and production of heavy oil

Nearly 70% of the global oil reserves are made up of unconventional oils such as heavy oils, bitumen, and tar sand. However, they are yet to be fully exploited as a result of the capital-, energy-, water-, wastewater-, and carbon-intensive nature of their development. To be in consistent with the current goals of climate crisis mitigations, technologies that are more environmentally friendly with high efficiencies are needed. This is where the toe-to-heel air injection (THAI) in situ combustion process comes in. However, experiments and semi-commercial operations have shown that THAI is a low-oil-production-rate process where there was nonlinear relationship between air injection rate and oil production rate. Therefore, to find out about the feasibility of adding an extra source of heat in order to improve oil production rates and with the second aim of testing the possibility of heating an annular catalyst layer surrounding the horizontal producer (HP) well such as in the in situ catalytic upgrading process (CAPRI™), a first-of-a-kind study of electrically-enhanced THAI (i.e. eTHAI) process is presented in this paper. The eTHAI involves surrounding the HP well with the electrical heating coils in which induced current flows so that heat is generated and released in the reservoir. Through reservoir numerical simulations using CMG STARS, it is found that it is indeed possible to electrically heat the HP well whilst conducting pre-ignition steam injection and subsequently operating in situ combustion. Regardless of the rate of heating, it is found that the shape and the stability of the combustion front are not affected by the incorporation of the electrical heating around the HP wellbore. In the eTHAI process, addition of extra heat from the electrical heating coils resulted in increased cumulative oil production to 32,000 m3 compared to 25,000 m3 in the base case model over the 834 days of process time. This is an increase in oil recovery by 28% over the same period compared to in the base case model. It is concluded that the resulting acceleration in oil production rates and recoveries implies earlier realisations of returns on investment. Moreover, it is found that the higher the rate of electrical heating, the wider the length of the HP well used for mobilised oil production (i.e. the wider the thickness of the mobile oil zone (MOZ)). It is also discovered that the higher the electrical heating rate, the less the air cooling effect and in turn the higher the quantity of heat that is distributed inside the reservoir. As a result, it is concluded that the increased distribution of higher quantity of heat by the heated air coming from the outlet zone of the VI wells of the eTHAI models results in increased oil mobilisation and production rates. However, future work should investigate the limiting electrical heating rate beyond which no appreciable increase in oil production rates is achievable. Finally, it is shown that electrically-enhanced THAI process operates stably, efficiently, and selective sectional heating of catalyst-surrounded wellbore is indeed feasible.

Pore-scale study of coke combustion in a matrix-fracture system based on the micro-continuum approach

In situ combustion is an advanced recovery technique used to exploit heavy oil in the fractured reservoirs that make up approximately one-third of global heavy-oil resources. However, the mesoscopic mechanisms of coke combustion in the multiscale matrix-fracture system are not well understood because of the difficulty of performing pore-resolved simulations. In the present study, a pore-resolved micro-continuum approach was used to investigate fully coupled thermal and reactive flows through fractured media that contain nanometer-range coke pores, micrometer-range matrix pores, and sub-millimeter range natural fractures. Image-based simulations were implemented using synthetic geological models to mimic coke deposition patterns based on tomography images. The combustion regime diagram for the fractured media was mapped based on the ignition temperature and the air flux to exhibit three combustion regimes. The regime diagram was compared with that for unfractured media to address the impact of natural fractures on oxygen transport and the burning temperature. The oxygen diffusion mechanism dominated oxygen transport from the fracture into the matrix and led to a desirable smoldering combustion temperature regardless of the air injection rate. Effects of fracture geometries were quantified to demonstrate tortuous and discrete fractures, and matching air injection rates with fracture apertures can suppress air-channeling risk effectively. Possible discrepancies between lab measurements and field operations were demonstrated, and their potential to drive misinterpretation of experimental results was considered. The present pathway from tomography images to synthetic images and numerical simulations extends the “image and compute” technique to resolution of multiscale and nonlinear reactive transport.

Surface wave mitigation in a copper converter via H∞ mixed sensitivity control

In this paper, a robust control strategy for surface wave mitigation in copper converters is presented. In copper converters, the purification of copper is carried out by injection of air into the molten bath through lateral tuyeres. The constant rate of air injection produces undesirable oscillation and splashing of the bath in the surface diminishing the lifetime of the internal cover. An H∞ mixed sensitivity approach is proposed to robustly control the air injection rate in order to eliminate the modes of oscillation in the surface even in the case when uncertainty in the parameters of the model and noise in the measurements are present. The effectiveness of the proposed approach is shown by simulations and by comparison with a non-robust LQG control strategy.

Air-Water Bubbly Flow by Multiple Vents on a Hydrofoil in a Steady Free-Stream

Flow features, due to air injection through multiple vents on the surface of a hydrofoil inclined at an angle with respect to the free-stream in a cavitation tunnel, are presented here. The hydrofoil, with a chord length, c, is oriented at the angle of inclination, α = 3.5°. The Froude number, Fn, based on the free-stream velocity, V∞, and air injection vent diameter, dh, is 30.30, 50.51 and 70.71. Air is injected through multiple vents on the hydrofoil at the non-dimensional air injection coefficient, Cq∼16−8917. The air bubble packing per unit area is quantified using spatial density, SD, at various combinations of Fn,Cq based on a high-speed video from the side view. The time-averaged spatial density, <SD>, is observed to increase in a logarithmic manner with an increase in the air injection rate, Q, at various Froude numbers. There is an increase in the mean spatial density of the bubbles with the increase in Cq at all Fn. A power–law relation is shown to exist between the time-averaged spatial density, <SD>, and the non-dimensional flow variables, Reynolds number, Reair, Fn and Cq based on a regression analysis. By tracking individual finite volume bubbles flowing with the free-stream, the bubble dimensions in pixels are quantified using quantities such as the deformation rate, ϵ, and standardization, ϵS, from the side-view videos. It is observed that ϵ and ϵS change with time, even as they become advected with the free-stream. Through high-speed imaging from the top view, we characterize the bubbly flow features’ time-averaged thickness, t, at various combinations of Fn,Cq at α = 3.5°. We obtain a power-law relation between the non-dimensional time-averaged jet thickness, t/c, and the non-dimensional flow parameters such as, Reair, Fn,Cq and the non-dimensional streamwise distance, x/xref, based on a regression analysis, where xref is a reference distance. The results are relevant to engineering applications where the air–water bubbly flow in a free-stream is important.

Understanding the mobilised oil drainage dynamics inside laboratory-scale and field-scale reservoirs for more accurate THAI process design and operation procedures

The technical and economic validities of the toe-to-heel air injection (THAI) process for heavy oils upgrading and production are yet to be fully realised even though it has been operated at laboratory, pilot, and semi-commercial levels. The findings from Canadian Kerrobert THAI project suggested that there is no proportionality between oil production and air injection rates. However, this conclusion was reached without having to dig deeper into the dynamics of the transport processes inside the reservoir especially that efficient combustion was clearly taking place as the mol% oxygen in the produced gas was negligible. As a result, this study is conducted with aims of identifying the similarities and differences of the dynamics of the transport processes in lab-scale and field-scale reservoirs. For the first time, this study has found oil drainage dynamics inside the reservoir to be both scale-dependent and operation-dependent. For the laboratory-scale numerical model E, what is clearest is that all of the head of the oil flux vectors are either totally vertically directed or slightly inclined and pointing upward towards the heel. None of them is pointing backward towards the toe of the HP well. Thus, it is apparent that oil drainage pattern in this laboratory-scale model E is efficient as all the mobilised upgraded oil, including from the base of the combustion cell, is produced as the combustion front advances in the toe-to-heel manner. However, the combustion front has a backward-leaning shape which is an indicator that it is propagating even inside the HP well. This implies that the process is operating in an unstable, inefficient, and unsafe mode. These two opposing patterns at laboratory-scale must be resolved to ensure healthy combustion front propagation with efficient oil drainage and production rates are achieved. At the field scale (i.e. model F), this study has shown for the first time that there are actually two mobile oil zones: the one ahead of the combustion front with lower oil flux magnitude (i.e. MOZ) and the one containing large pool of mobilised partially upgraded oil at the base of the reservoir just behind the toe of the HP well. The above findings in model F show that there is conflicting dynamics about the goal of achieving large oil production rates downstream of the combustion front with the propagation of forward-tilting stable, safe, and efficient combustion front. If the combustion is to be optimally sustained, then most of the mobilised upgraded oil might be lost going in the wrong direction towards the region behind the toe of the HP well. In actual reservoir in the field, shale with very low permeability and porosity must be present behind the toe in order for the large pool of mobilised upgraded oil that is continuously draining from the vertical adjacent planes to be forced into the toe of the HP well. As a result, to balance these two conflicting dynamics of upward-tilted combustion front going longitudinally towards the heel of the HP well and the mobilised oil draining down at an angle towards the region behind the toe of the HP well, future studies are essentially required. These are proposed and also listed under the conclusion section in order to ensure thorough design and operation procedures for the THAI process are established.

Thermal, efficiency and power output evaluation of pyramid, hexagonal and conical forms as solar panel

Through the present investigation, the thermal and power output of novel-shaped solar panels are evaluated. For the cooling of the mentioned forms, forced air flow was utilized. Three novel shapes, of Pyramid, Hexagonal, and Conical which had the equal lateral surface were considered. For the simulation, an open source CFD software was utilized. The lateral surfaces were put under identical amount of heat flux. Air as the coolant fluid was injected with constant inlet temperature from the trapdoors at the bottom of different shaped structures. Three different values of heat flux and air injection rate were evaluated for each shape. The outcomes presented that the conical shaped solar panel exhibits better thermal performance than other geometries. Furthermore, conical form finds the least temperature that was about 10.5 °C less than that of the pyramid-shaped panel. Furthermore, it was revealed that the corners of pyramid and hexagonal-shaped solar panels have higher temperature. Also, it was found that the efficiency of conical shaped panel was up to 8.4% more than that of pyramid-shaped panel.

공기 주입에 따른 프란시스 수차 모델의 흡출관 내 유동 특성

Undesirable pressure fluctuations in Francis turbines are caused by precession of the vortex rope in the draft tube under conditions of low flow rate. These pressure fluctuations can cause a resonance that seriously undermines the stability of the turbine system. In the previous study, the effects of anti-swirl fins in the draft tube were investigated to suppress the vortex rope. However, despite the installation of anti-swirl fins, the precession of vortex rope is occurred near the draft tube cone, and an additional suppression factor for vortex rope is required. Therefore, this preliminary study investigates the effect of air-injection to select flow rate of the air-injection for suppressing the vortex rope in the draft tube cone. Three-dimensional steady-state Reynolds-averaged Navier-Stokes analyses were conducted with a shear stress transport turbulence model to investigate the performance and internal flow characteristics according to the flow rate of air-injection. The efficiencies were decreased by the air-injection into the draft tube, however, the effect of vortex rope suppression was exhibited when the flow rate of air-injection was above 0.5%Q.

A novel air plasma electrolysis with direct air injection in plasma zone to produce nitrate in degradation of organic textile dye

AbstractNitrogen is one of the essential nutrients for plants. Even though its availability in the air is abundant, it cannot be utilized yet due to its structure. Plasma electrolysis by air injection is effectively degrade organic textile dyes waste. In this study we propose a novel air plasma electrolysis (APE) where direct air injection into plasma zone inside electrolysis plasma can converts air into nitrate, while simultaneously the degradation of dyes waste produces organic nitrogen. Degradation of organic textile dye by APE can also transform nitrogen‐rich organic wastewater into nitrogen fertilizers. In this experiment, Remazol red as a compound in the azo dye group was used as a model for organic textile dye wastewater. Air plasma electrolysis reactor equipped with a stainless‐steel cathode, a tungsten anode, with various air injection rates and electric power. The results show 99.82% Remazol red degradation and 41.41 mmol of nitrate production. Preliminary efficacy tests on tomato plants showed that the nitrogen fertilizers produced from Remazol red produce the best plant growth. This study shows that APE simultaneously reduces organic textile dye waste, transforms them into potential organic fertilizer, and at the same time, synthesizes nitrates.

Experimental investigation on ship’s model in carrying out energy economics of BDR/ALS methodology

ABSTRACT For vessels moving at slower speeds, the frictional resistance contributes up to 80% of the total resistance, demanding a reduction in it. In the BDR/ALS technique, to reduce frictional resistance, the air is injected below the moving body, which is one of the active and interesting research topics. In this work, to reduce the total resistance and the energy required to run a ship, experimental investigations were performed on a 1:23 scaled model of 8000 Tonnes Deadweight Bulk Carrier for a Froude number range of 0.06 to 0.18. For each speed of operation, consequences of different air injection rates of 0.5 to 3.0 CFM, and different sizes of injection holes were thoroughly investigated. With the injection holes of 2mm and 1mm in diameter, the maximum savings in the energy of 29.2% and 25.1% were observed at the Froude numbers of 0.09 and 0.11, respectively.

Bubble characteristics from injected air sheet through slots in a water cross-flow

While air injection has already been widely studied for stagnant water at low air injection rates for circular injectors, limited data is available on gas in liquid cross-flows injected through slots at high air flow rates. The key purpose of this work is to observe the evolution of bubble swarm characteristics for simple geometries such that, by correlation rules, these characteristics can be projected for more complicated geometries and environment. To that effect, an experimental water loop with both controllable water and air flow rates is used to generate bubble clouds with cross-flow air injection.Measurements with an optical probe allow the void fraction, the size and velocity of bubbles to be measured. The findings show that the general size of bubbles increases with an increase in the air flow rate for a constant water flow rate. Furthermore, bubbles pick up speed while moving away from the injection slot. Bigger bubbles travel faster than small ones ; they also tend to rise to the top of bubble plumes while small bubbles stay in the lower portion. Finally, the maps of void fraction indicate that its local values drop while heading away from the injection slot.

마이크로 급 펠톤 터빈의 설계와 공기주입에 따른 성능 분석

In this study, a new efficiency improvement method by means of air injection into Pelton turbine jet is presented. In order to analyze air injected jet performance, firstly, micro size 5kW Pelton turbine was designed and analyzed. Similarly the analysis was carried out on a small size 100kW turbine. For the 100kW Pelton turbine, 5kW model was scaled up based on the jet diameter and rotational speed. 5kW performance analysis was performed under several rotational speed. After achieving optimized rotational speed. Air injected jet analysis was performed for rated rotational speed condition. Air injection rate was 1%, 5%, 10%, 15% of the water volume flow rate. Efficiency increase rate was reliable. The 100kW turbine was designed in two types, one jet and two jets systems. Air injection rate was made same and also found to have a reliable increase in efficiency.

Experimental investigation of bubbly flow by air injection on an inclined hydrofoil

Flow features resulting from air injection through a hole on an inclined hydrofoil in a free stream flow are characterized in this work. The experiments were carried out in a cavitation tunnel at the Chungnam National University. The hydrofoil was oriented at angles of inclination, α=±3.5° and 0°, in the test section with water flowing at the free stream velocity, V∞= 3, 5, and 7 m/s (Froude number, Fn∼ 30–70). The air jet emanating from the hole on the inclined hydrofoil along the streamwise direction [Reynolds number of air, Reair∼O(103)], at various air injection rates, Cq, was characterized by high-speed imaging. Geometric features of the air jet, such as jet width, w, jet angle, β, jet effective diameter, deff, and jet thickness, t, are measured from the high-speed images. A power-law relation is shown to exist between the non-dimensional geometric features of the jet and the non-dimensional parameters, Reair,Fn,Cq. Depending on the Froude number, Fn, and non-dimensional air injection rate, Cq, several jet domains such as unstable jet, cloudy puff, buoyant-bifurcating jet, and stable-buoyant jet domains were observed upon air injection at Reair∼O(103) for various hydrofoil inclinations.

Numerical study of building pressure cycling to generate sub-foundation aerobic barrier for mitigating petroleum vapor intrusion.

In this study, the role of building pressure cycling (BPC) method in generating a subslab aerobic barrier at petroleum contaminated sites was examined numerically. The numerical model was first validated with field observations and then used to simulate BPC applications in petroleum vapor intrusion scenarios. The results indicated that, after a long-term BPC operation (60days), a subslab aerobic barrier could be generated with an adequate air injection rate (10L/min in this study). The effects on hydrocarbon soil gas concentration profiles are expected to last for weeks even after the BPC system is turned off. Moreover, our investigations showed that the performances of the BPC application are virtually independent of hydrocarbon's reaction rate constant. The simulated sub-foundation aerobic conditions expected during BPC were comparable to those observed in a field study where a subsurface pipe system at the same air injection rate was used to create a subslab aerobic barrier. Thus, BPC application can represent an interesting alternative approach to the subsurface delivery systems as it is expected to achieve similar performance but with lower installation costs.