Experimental study on secondary air mixing along the bed height in a circulating fluidized bed with a multitracer-gas method

A multitracer-gas method was proposed to study the secondary air(SA)mixing along the bed height in a circulating fluidized bed(CFB)using carbon monoxide(CO),oxygen(O_(2)),and carbon dioxide(CO_(2))as tracer gases.Experiments were carried out on a cold CFB test rig with a cross-section of 0.42 m×0.73 m and a height of 5.50 m.The effects of superficial velocity,SA ratio,bed inventory,and particle diameter on the SA mixing were investigated.The results indicate that there are some differences in the measurement results obtained using different tracer gases,wherein the deviation between CO and CO_(2) ranges from 42%to 66%and that between O_(2) and CO_(2) ranges from 45%to 71%in the lower part of the fluidized bed.However,these differences became less pronounced as the bed height increased.Besides,the high solid concentration and fine particle diameter in the CFB may weaken the difference.The measurement results of different tracer gases show the same trends under the variation of operating parameters.Increasing superficial velocity and SA ratio and decreasing particle diameter result in better mixing of the SA.The effect of bed inventory on SA mixing is not monotonic.

Different compression sutures combined with intracameral air injection for acute corneal hydrops

·AIM:To evaluate the efficacy and safety of full-thickness sutures combined with intracameral air injection(FTS-AI)versus pre-Descemet’s membrane sutures combined with intracameral air injection(PDS-AI)in the management of acute corneal hydrops in keratoconus.·METHODS:The research included 8 patients(8 eyes)suffering from acute corneal hydrops caused by keratoconus.Four patients were randomly assigned to FTS-AI.And the other four were randomly assigned to PDS-AI.Corneal oedema,visual acuity,corneal thickness were assessed during follow-up.·RESULTS:The demographics,preoperative duration of symptoms and severity of corneal hydrops between the two groups were not significantly different.The mean corneal oedema resolution time after FTS-AI and PDSAI were 11±1.15 and 15±1.41 d,respectively(P=0.005).The maximum corneal thickness of the scarred region decreased in both groups at one week postoperatively(P<0.05).No obvious difference was found in the mean maximal corneal thickness between the two groups postoperatively.The BCVA improved significantly after FTS-AI and PDS-AI at three months postoperatively.No obvious difference was found in the BCVA after FTS-AI and PDS-AI at three months postoperatively.·CONCLUSION:FTS-AI and PDS-AI are safe and effective therapies to accelerate the resolution of corneal oedema in acute corneal hydrops secondary to keratoconus.Despite faster resolution of corneal oedema in the FTS-AI group,we recommend PDS-AI to avoid potential endothelium cell damage.

Oil oxidation in the whole temperature regions during oil reservoir air injection and development methods

The oil oxidation characteristics of the whole temperature regions from 30 ℃ to 600 ℃ during oil reservoir air injection were revealed by experiments. The whole oil oxidation temperature regions were divided into four different parts: dissolving and inflation region, low temperature oxidation region, medium temperature oxidation region and high temperature oxidation region. The reaction mechanisms of different regions were explained. Based on the oil oxidation characteristics and filed tests results, light oil reservoirs air injection development methods were divided into two types: oxygen-reducing air flooding and air flooding;heavy oil reservoirs air injection in-situ combustion development methods were divided into two types: medium temperature in-situ combustion and high temperature in-situ combustion. When the reservoir temperature is lower than 120 ℃, oxygen-reducing air flooding should be used for light oil reservoir development. When the reservoir temperature is higher than 120 ℃, air flooding method should be used for light oil reservoir development. For a normal heavy oil reservoir, when the combustion front temperature is lower than 400 ℃, the development method is medium temperature in-situ combustion. For a heavy oil reservoir with high oil resin and asphalting contents, when the combustion front temperature is higher than 450 ℃, the development method at this condition is high temperature in-situ combustion. Ten years field tests of air injection carried out by PetroChina proved that air has advantages in technical, economical and gas source aspects compared with other gas agents for oilfield gas injection development. Air injection development can be used in low/super-low permeability light oil reservoirs, medium and high permeability light oil reservoirs and heavy oil reservoirs. Air is a very promising gas flooding agent.

Steady air injection flow control for increasing the surge margin of radial flow compressor

Steady air injection upstream of the leading edge was used to increase the surge margin of a centrifugal compressor.To reveal the mechanism,steady numerical simulations were performed on a high pressure ratio centrifugal compressor rotor operated with a rotor tip speed of 586 m/s.Eight different injection yaw angle with four different injection mass flow was performed to determine the configuration that provide the best results for the compression system studied in this work.The injection angle,α,was fifteen degree and the injectors were placed at short distance（ten percent of the inlet tip radius upstream of the compressor face） to achieve maximum control over the leading edge flow by varying individual injection parameters.The results show that at design speed（n=50 000 r/min） with injection flow rate more than 2% of the main flow rate and yaw angle between 20° and 30°,the mass flow rate at stall decreases for approximately 8%.But with higher injection rate,other compressor parameters were affected such as compressor efficiency and compressor total pressure ratio.

Lag times in toe-to-heel air injection(THAI)operations explain underlying heavy oil production mechanisms

From a time value of revenue point of view,it is preferred that the time between reservoir stimulation and oil production response is small.Heavy oil combustion processes have a lag time between air injection and liquid production,but the common practice in production data analysis uses simultaneous injection and production data when seeking a relationship between them.In this research,the time scales of production for the Kerrobert toe-to-heel air injection(THAI)heavy oil project in Saskatchewan,Canada,is analyzed by using cross correlation analysis,i.e.time delay analysis between air injection and oil production.The results reveal two time scales with respect to production response with two distinctive recovery mechanisms:(1)a short time scale response(nearly instantaneous)where oil production peaks right after air injection(directly after opening production well)reflecting cold heavy oil production mechanisms,and(2)a longer time scale(of order of 100-300 days)response where peak production occurs associated with the collective phenomena of air injection,heat generating reactions,heat transfer,and finally,heated mobilized heavy oil drainage to the production well.This understanding of the two time scales and associated production mechanisms provides a basis for improving the performance of THAI.

Resistance of Air Injection Transportation in a Cutter-suction Dredger

Cutter-suction dredger transports slurry through pipeline. But the pipeline is easy to be jammed and frayed because of huge resistance, resulting in limited exertion of dredger and high energy consumption. One of the solutions is air injection transporting, which can reduce the resistance in pipeline. This paper makes research on the relations between pipeline distance and other factors such as slurry concentration, pressure of air injection and transportation distance, by making use of Prof. Aluf Orell＇ s slug model. The test data prove that the key factors are slurry concentration and air volume fraction, and that high slurry concentration and low air volume fraction can reduce more resistance, and such reducing effect becomes weaker with the increase of transportation distance.

An analytical model to estimate the time delay to reach spontaneous ignition considering heat loss in oil reservoirs

During air injection into an oil reservoir,an oxidation reaction generates some heat to raise the reservoir temperature.When the reservoir temperature reaches an ignition temperature,spontaneous ignition occurs.There is a time delay from the injection to ignition.There are mixed results regarding the feasibility of spontaneous ignition in real-field projects and in laboratory experiments.No analytical model is available in the literature to estimate the oxidation time required to reach spontaneous ignition with heat loss.This paper discusses the feasibility of spontaneous ignition from theoretical points and experimental and field project observations.An analytical model considering heat loss is proposed.Analytical models with and without heat loss investigate the factors that affect spontaneous ignition.Based on the discussion and investigations,we find that it is more difficult for spontaneous ignition to occur in laboratory experiments than in oil reservoirs;spontaneous ignition is strongly affected by the initial reservoir temperature,oil activity,and heat loss;spontaneous ignition is only possible when the initial reservoir temperature is high,the oil oxidation rate is high,and the heat loss is low.

Experimental study on effects of air injection on cavitation pressure pulsation and vibration in a centrifugal pump with inducer

Cavitation commonly induces performance deterioration and system vibration in many engineering applications.This paper aims to investigate the effects of air injection on cavitation evolution,pressure pulsation and vibration in a centrifugal pump with inducer.In this paper,the high-speed camera is used to capture the gas flow pattern and cavitation evolution process in the inducer.The impacts of air injection on the inlet pressure pulsation and vibration are also investigated.The results show that the cavitation development in the inducer undergoes four patterns:incipient cavitation,sheet cavitation,cloud cavitation and super cavitation.During the development of cavitation,the main frequency of the pressure pulsation shifts to lower frequencies,and the amplitude of the vibration increases.In addition,air injection promotes the incipient cavitation but delays the cavitation development.A small amount of air can effectively decrease amplitudes of pressure pulsation and vibration.But as the air content increases,the fluctuations and amplitudes of pressure pulsation and vibration increase.

Enhancing Aerodynamic Performances of Highly Loaded Compressor Cascades via Air Injection

This article experimentally studies the effects of air injection near the blade trailing edge on flow separation and losses in a highly loaded linear compressor cascade. Aerodynamic parameters of eight cascades with different air injection slot configura- tions are measured by using a five-hole probe at the cascade outlets. Ink-trace flow visualization is performed to obtain the flow details around the air injection slots. The static pressure distribution is clarified with pressure taps on the endwalls. The...

Experimental Investigations of Micro Air Injection to Control Rotating Stall

Steady discrete micro air injection at the tip region in front of the first compressor rotor has been proved to be an effective method to delay the inception of rotating stall in a low speed axial compressor. Considering the practical application a new type of micro injector was designed and described in this paper, which was imbedded in the casing and could be moved along the chord. In order to verify its feasibility to other cases, such as high subsonic axial compressor or centrifugal compressor, some other cases have been studied. Experimental results of the same low speed axial compressor showed that the new injector could possess many other advantages besides successfully stabilizing the compressor. Experiments performed on a high subsonic axial compressor confirmed the effectiveness of micro air injection when the relative velocity at the blade tip is high subsonic. Meanwhile in order to explore its feasibility in centrifugal compressor, a similar micro injector was designed and tested on a low speed centrifugal compressor with vaned diffuser. The injected mass flow was a bit larger than that used in axial compressors and the results showed micro injection could also delay the onset of rotating stall in the centrifugal compressor.

The effects of step inclination and air injection on the water flow in a stepped spillway:A numerical study

In this work, we perform a numerical study of a water flow over a stepped spillway. This flow is described by the Reynolds averaged Navier-Stokes equation （RANS） associated with the turbulence k - model. These equations are solved using a commercial software based on the finite volume scheme and an unstructured mesh. The air-water flow was modeled using volume of fluid （VOF） and multiphasic methods. The characteristics of the profile, etc.. We analyze the effects on the flow structure of the flow were investigated including the total pressure, the velocity steps and countermarch inclination, the air injection through the countermarch into the water flow and the dynamics water discharges. Results show that the inclination of the countermarch relative to the vertical and the air injection into the water flow increase the total pressure in the neighbourhood of the steps.

Combustion enhancement in rearward step based scramjet combustor by air injection at step base

Numerical simulations were performed to model the non-reacting and reacting flow behind a rearward step flameholder in Mach 1.6 supersonic flow with fuel injection at the step base.The combustor geometry was based on the University of Florida scramjet experimental facility.Turbulence was modeled using k-u shear stress transport(SST),laminar flamelet was used for combustion modeling.Wall static pressure showed good agreement with experimental data for non-reacting and reacting flow.For non-reacting flow,dummy fuel helium mole fraction distribution in the recirculation region behind the step was validated with planar laser induced fluorescence(PLIF)images in experiments.To improve the combustion characteristics,air was injected in tandem with hydrogen at step base using various configurations.With all fuel injection as baseline,the case with 2 air jets around each fuel jet and air injected at 2 times the stagnation pressure of fuel showed the most improvement compared to other cases.It was most effective in reducing the local fuel richness,shortening the flame length and increasing combustion efficiency.

Simulation study of huff-n-puff air injection for enhanced oil recovery in shale oil reservoirs

This paper is the first attempt to evaluate huff-n-puff air injection in a shale oil reservoir using a simulation approach.Recovery mechanisms and physical processes of huff-n-puff air injection in a shale oil reservoir are investigated through investigating production performance,thermal behavior,reservoir pressure and fluid saturation features.Air flooding is used as the basic case for a comparative study.The simulation study suggests that thermal drive is the main recovery mechanism for huff-n-puff air injection in the shale oil reservoir,but not for simple air flooding.The synergic recovery mechanism of air flooding in conventional light oil reservoirs can be replicated in shale oil reservoirs by using air huff-npuff injection strategy.Reducing huff-n-puff time is better for performing the synergic recovery mechanism of air injection.O2 diffusion plays an important role in huff-n-puff air injection in shale oil reservoirs.Pressure transmissibility as well as reservoir pressure maintenance ability in huff-n-puff air injection is more pronounced than the simple air flooding after primary depletion stage.No obvious gas override is exhibited in both air flooding and air huff-n-puff injection scenarios in shale reservoirs.Huffn-puff air injection has great potential to develop shale oil reservoirs.The results from this work may stimulate further investigations.

Influence of Endwall Air Injection with Discrete Holes on Corner Separation of a Compressor Cascade

The aim of this study is to reveal the influence mechanism of endwall air injection with distributed holes on the corner separation of a highly loaded compressor cascade,so as to promote the application of injection in aero-engines.Single-hole and double-hole endwall injection schemes featuring different axial locations,pitchwise locations,injection mass rates and injection directions,were designed and investigated.Results showed that the corner separation was eliminated by endwall injection;the optimal single-hole injection scheme achieved an endwall loss coefficient reduction of 29.7%,with injection coefficient as low as 0.48%.The optimal axial location of single-hole endwall injection was at 82%axial chord,being the center of corner separation.However,as injection hole was located at upstream of it,endwall injection resulted in severer corner separation.The mid-span flow field was deteriorated after endwall injection,which was due to 3D flow effects,i.e.,AVDR(axial velocity density ratio)effect and low-momentum fluid spanwise migration effect.The optimal injection was achieved at low injection angle and from close to the suction surface on pitchwise.Double-hole injection exhibited inferior performance compared with single-hole,which was due to the interaction of the two injection streams and mixing of injection streams with the bulk stream.

Effect of reservoir heterogeneity on air injection performance in a light oil reservoir

Air injection is a good option to development light oil reservoir.As well-known that,reservoir heterogeneity has great effect for various EOR processes.This also applies to air injection.However,oil recovery mechanisms and physical processes for air injection in heterogeneous reservoir with dip angle are still not well understood.The reported setting of reservoir heterogeneous for physical model or simulation model of air injection only simply uses different-layer permeability of porous media.In practice,reservoir heterogeneity follows the principle of geostatistics.How much of contrast in permeability actually challenges the air injection in light oil reservoir?This should be investigated by using layered porous medial settings of the classical Dykstra-Parsons style.Unfortunately,there has been no work addressing this issue for air injection in light oil reservoir.In this paper,Reservoir heterogeneity is quantified based on the use of different reservoir permeability distribution according to classical Dykstra-Parsons coefficients method.The aim of this work is to investigate the effect of reservoir heterogeneity on physical process and production performance of air injection in light oil reservoir through numerical reservoir simulation approach.The basic model is calibrated based on previous study.Total eleven pseudo compounders are included in this model and ten complexity of reactions are proposed to achieve the reaction scheme.Results show that oil recovery factor is decreased with the increasing of reservoir heterogeneity both for air and N2 injection from updip location,which is against the working behavior of air injection from updip location.Reservoir heterogeneity sometimes can act as positive effect to improve sweep efficiency as well as enhance production performance for air injection.High O2 content air injection can benefit oil recovery factor,also lead to early O2 breakthrough in heterogeneous reservoir.Well-type does not show great effect on production performance for air injection in extreme heterogeneous reservoir.While adopting horizontal producer is favourable to promote production performance for air injection in homogenous reservoir.

ALKALINE PRETREATMENT AND AIR MIXING FOR IMPROVEMENT OF METHANE PRODUCTION FROM ANAEROBIC CO-DIGESTION OF POULTRY LITTER WITH WHEAT STRAW

Alkaline pretreatment(AL)and air mixing(air)both have the potential to improve anaerobic co-digestion(Co-AD)of poultry litter with wheat straw for methane production.In this study,the effects of the combination of AL(pH 12 for 12 h)and air mixing(12 mL·d^(−1))on the Co-AD process were investigated.The substrate hydrolysis was enhanced by AL,with soluble chemical oxygen demand increased by 4.59 times and volatile fatty acids increased by 5.04 times.The cumulative methane yield in the group of Co-AD by AL integrated with air(Co-(AL+air)),being 287 mL·(g VS_(added))^(−1),was improved by 46.7%compared to the control.The cone model was found the best in simulating the methane yield kinetics with R^(2)≥0.9979 and root mean square prediction error(rMSPE)≤3.50.Co-(AL+air)had a larger hydrolysis constant k(0.14 d^(−1))and a shorter lag phaseλ(0.99 d)than the control(k=0.12 d^(−1),λ=2.06 d).The digestate improved the removal of total solids and total volatile solids by 2.0 and 2.3 times,respectively.AL facilitated substrate degradation,while air can enrich the microbial activity,together enhancing the methane generation.The results show that AL+air can be applied as an effective method to improve methane production from the Co-AD process.

Adaptive feedback control of stability in an axial compressor with circumferential inlet distortion

The adaptive feedback control of stability with circumferential inlet distortion has been experimentally investigated in a low-speed,axial compressor.The flat-baffles with different span heights are used to simulate different distorted inflow cases.Compared with auto-correlation and root-mean-square analysis,cross-correlation analysis used to predict early stall warning does not depend on the distortion position.Hence,the cross-correlation coefficient was used to monitor the stable status of the compressor and provide the feedback signal in the active control strategy when suffering from different distortions.Based on the stall margin improvement of tip air injection obtained under different distorted inflow cases and the sensitivity analysis of cross-correlation coefficients to injected momentum ratios,tip air injection was adopted as the actuator for adaptive feedback control.The digital signal processing controller was designed and applied to achieve adaptive feedback control in distorted inflow conditions.The results show that the adaptive feedback control of air injection nearly achieves the same stall margin improvement as steady air injection under different distortion intensities with a reduced injection mass flow.Thus,the proposed adaptive feedback control method is ideal for the engine operation with circumferential distorted inflow,which frequently occurs in flight.

Numerical simulation investigations of the applicability of THAI in situ combustion process in heavy oil reservoirs underlain by bottom water

The presence of a bottom water(BW)layer in heavy oil reservoirs can present substantial problems for efficient oil recovery for all recovery techniques.Hence,it is necessary to know how particular production processes are affected by different BW layer thicknesses,and how standard production procedures can be adapted to handle such reservoirs.Toe-to-heel air injection(THAI)is a thermally efficient process,generating in situ energy in the reservoir by burning a fraction of the oil-in-place as coke and has the potential to economically and environmentally friendly work in reservoirs with BW layer.However,to ascertain that,studies are needed first.These are conducted via numerical simulations using commercial reservoir thermal simulator,CMG STARS.This work has shown that the shape of the combustion zone in THAI remains forward-leaning even in the presence of a BW layer,indicating that the process is stable,and that there is no oxygen bypassing of the combustion front.However,the oil recovery rate is highly negatively affected by how large the thickness of the BWzone is,and the severity of such effect is determined to be proportional to the thickness of the BW layer.This study also shows that there is a period of low oil production rate which corresponds to mobilised oil displacement into the BW zone which in turn causes a surge in water production rate.The practical implication of this is that prolonged period of low oil production rates will expose companies and/or investors to higher risk due to the oil market volatility.In this study,it is also revealed that the height of the mobilised oil that is displaced into the BW zone equates to that of the displaced and replaced water thereby implying that when the BW layer thickness is 50%that of the oil layer(OL),less than 50%of the mobilised oil will be recovered when the entire reservoir is swept by the combustion front.Therefore,conclusively,applying the THAI process in its conventional form in reservoirs containing bottom water is not recommended,and as a result,a new strategy is needed to enhance process economics by improving the oil production and hence recovery rates.

Comparison of aerodynamic characteristics between a novel highly loaded injected blade with curvature induced pressure-recovery concept and one with conventional design

This paper introduces a novel design method of highly loaded compressor blades with air injection.CFD methods were firstly validated with existing data and then used to develop and investigate the new method based on a compressor cascade.A compressor blade is designed with a curvature induced pressure-recovery concept.A rapid drop of the local curvature on the blade suction surface results in a sudden increase in the local pressure,which is referred to as a curvature induced ‘Shock＇.An injection slot downstream from the ‘Shock＇ is used to prevent ‘Shock＇ induced separation,thus reducing the loss.As a result,the compressor blade achieves high loading with acceptable loss.First,the design concept based on a 2D compressor blade profile is introduced.Then,a 3D cascade model is investigated with uniform air injection along the span.The effects of the incidence are also investigated on emphasis in the current study.The mid-span flow field of the 3D injected cascade shows excellent agreement with the 2D designed flow field.For the highly loaded cascade without injection,the flow separates immediately downstream from the ‘Shock＇;the initial location of separation shows little change in a large incidence range.Thus air injection with the same injection configuration effectively removes the flow separation downstream from the curvature induced ‘Shock＇ and reduces the size of the separation zone at different incidences.Near the endwall,the flow within the incoming passage vortex mixes with the injected flow.As a result,the size of the passage vortex reduces significantly downstream from the injection slot.After air injection,the loss coefficient along spanwise reduces significantly and the flow turning angle increases.

Effect of blowing ratio on the relaminarization phenomenon over convex curved wall

Relaminarization is a reverse transition from turbulent state to laminar or laminar-like state as the turbulent boundary layer is accelerated,which cause the boundary layer easy to separate under the adverse pressure gradient.To investigate the mechanism of relaminarization flow control with air injection,large eddy simulations were performed for a turbulent flow over a convex curved wall at Mach number 3.0 under different blowing ratios.The results show that the acceleration has markedly reduced the turbulent characteristics including the number of large-scale turbulent structures and the turbulence kinetic energy values in the boundary layer for the baseline case.As the air injection is excited,the relaminarization is effectively suppressed.Meanwhile,the simulation reveals that the blowing ratio plays an important role in controlling the turbulence.The air injection with higher blowing ratio is more effective in suppressing the relaminarization under the condition that the jet-to-cross flow momentum flux ratio and static pressure of injected air are kept unchanged.