Air Injection Flow Research Articles

Investigation of cavitation with air injection using Eulerian-Lagrangian method

Abstract Air injection can be used to reduce the cavitation erosion in fluid machinery. However the inverse result that the injected air indeed increases the size of cavitation may be obtained. To find out the interaction between air injection and cavitation, the present work proposes a Eulerian-Lagrangian method to investigate the effect of air injection on the characteristics of cavitating flow. The Eulerian method is used to describe the liquid and vapor distribution, and the morphology of large cavities are tracked by the Volume of Fluid (VOF) method in the Eulerian frame. On the other side, the Lagrangian method is used to track both air and vapor bubbles in small scale. With the Eulerian-Lagrangian coupling, discrete micro bubbles in sub-grid scale as well as the large cavities can be well captured and simulated. This work takes two cavitation situations in different cavitation numbers of σ = 0.81 and 0.70 into account. The cavitation features in σ = 0.81 are mainly characterized by the intermittent shedding of small-scale cavities under re-entrant flow mechanism. For σ =0.70, the injected air flow plays an important part which enhances the scale of cavity. For both cases, simulated results of the cavity shapes and distribution of discrete bubbles anastomoses well with experimental results, which verifies the accuracy of the algorithm. The interaction between injected air and vapor is also analysed.

Next generation of flow analysis is based on flow programming

Concepts of air Segmented Flow Analysis (SFA) and Flow Injection Analysis (FIA) are discussed and compared with the performance of a new method based on comprehensive flow programming. The programmable Flow Injection (pFI), miniaturized on the lab-on-valve platform, can perform tasks that can not be done in any other way, such as Auto calibration by a single standard solution or analysis in a flow-batch mode that exactly simulates the traditional manual batch technique. Performance of pFI is documented by examples of nutrient determinations in sea water.

Study on the Effect of Hull Attitude on the Resistance Reduction of SWATH with Airflow Injection

With the development of the green ship concept in design and construction, how to reduce the resistance to reduce fuel consumption has become a focus of ship research. As an important drag reduction method, the air lubrication method has been applied to various ship types, but it is still a new method in the study of SWATH (small waterplane area twin hull) drag reduction. In this paper, the air lubrication method is applied to a SWATH model with an overall length of 2.5 m to numerically study the influence of the hull attitude on the air coverage and resistance reduction. The grid is verified by the grid independence and the experiment results. Then, the resistance of the SWATH model under different trim angles and drafts is calculated, and the air coverage on the surface is observed. The drag reduction rates of different areas, including the strut, underwater body, and fins, are analyzed, too. The results show that the slight trim by the head is more conducive to the resistance reduction of the SWATH model, and the resistance reduction rate can reach 39.11%. The draft mainly affects the resistance reduction of the strut, and the difference is more than 10%.

Investigation of synergistic integration and optimization in combining compressed-air energy storage and a gas turbine

It is very important to guarantee performance synergy when combining two sub-systems. This study investigated combinations of compressed air energy storage systems (CAESs) and a gas turbine (GT) while considering various design factors. These factors included the CAES type, CAES capacity, and air injection flow rate, which were not considered in previous studies. The feasibility of various integration scenarios was evaluated, and the best scenario with the highest synergistic effect was obtained through an optimization method. When using a conventional CAES (C-CAES), the combined system was undesirable. When using an adiabatic CAES (A-CAES) or regenerative A-CAES, the combined system outperformed the standalone operation. When the flow ratio of the GT and A-CAES was 1:1.33, the percentage increases in net power and generated energy were 31.5 % and 12.6 %, respectively, and the roundtrip efficiency increased by 3.4 %p. When the flow ratio of GT and regenerative A-CAES was 1:0.88, the percentage increases in net power and generated energy were 31.3 % and 20.6 %, respectively, and the roundtrip efficiency was improved by 2.2 %p. This study provides the best synergistic integration between a CAES and GT for the first time by fully considering various scenarios, including thermal and mass integrations.

Aerodynamic influence of rim seal purge flow injection on the main flow in a 1.5-stage axial turbine with nonaxisymmetric end wall contouring

This paper presents an investigation of the aerodynamic influence of rim seal purge flow injection on the main flow in a 1.5-stage turbine with non-axisymmetric end walls and a bowed stator using experimental flow measurements and unsteady RANS simulations. The study focuses on the secondary vortex structures formed in the rotor passages of the 1.5-stage axial turbine rig. Through performance map measurements, it was found that the efficiency gain of the non-axisymmetric configuration is partially eliminated by the injection of purge flow. Numerical investigations, which are supported by detailed flow measurements with five-hole probes and hot-wire probes, revealed that the injection of purge air flow intensifies vortex structures near the hub, thereby generating additional losses. These resulting vortex structures are highly similar both in the axisymmetric baseline and the non-axisymmetric configuration and are the result of jet-like vortices emerging from the cavity. From these findings, it can be concluded that the non-axisymmetric contour and the bowed stator no longer provides any efficiency benefit near the hub. Only the near the casing, where the flow is not affected by the purge flow, the optimized configuration continues to improve the efficiency of the rig by homogenizing the stator outflow and thus reducing the secondary flow structures in the rotor passages.

Experimental Study on a Generic Side-View Mirror with Slotted Cylindrical Foot

A simple model consisting of a mirror-housing and its cylindrical foot is applied to represent the automobile side-view mirror that causes unwanted aerodynamic noise and wind drag during high-speed driving. An additional slot is made on the solid foot to modify the flow around the mirror and thus reduce the side wall pressure fluctuation and aerodynamic drag. Flow fields and wall pressure fluctuations of these side-view mirror models have been investigated experimentally in a wind tunnel. The airflow rate through the slot varies with the changing of the slot area. Wall surface pressure sensors, particle image velocimetry (PIV), and six-component balance were applied to measure the acoustic and flow characteristics. The results demonstrated that, with the increase of slot airflow rate to 30%, the side wall pressure fluctuations were reduced by 5.1 dB and the drag coefficient decreased by 10.2%. The PIV measurements showed that the vortex cluster center behind the mirror was moved upward from the wall surface due to the slot airflow injection into the wake. The turbulent kinetic energy in the side-view mirror wake near the wall decreased with the increment of the airflow rate, reducing the side wall pressure fluctuations and thereby suppressing the noise generation.

Экспериментально-теоретическое исследование обтекания сферы с учетом вдува газа с ее поверхности

The results of the experimental and theoretical studies of the gas flow around a solid sphere under conditions of mass outflow from its surface are presented. A new experimental setup and a method for studying the flow around a solid sphere during the gas injection from its surface are proposed with the aim of improving the accuracy of determining the drag coefficient. In the range of the Reynolds number (Re = 133÷667), experimental results show that the drag coefficient decreases at the gas injection from the surface of the sphere. Moreover, the drag coefficient decreases with an increase in the density of the injected air flow at the fixed Reynolds number. Numerical simulation of a two-phase flow around a sphere with the gas injection from its surface is carried out for two calculation cases: with a uniform gas outflow from the surface of a porous sphere and with gas injection from perforated holes on the sphere surface. The numerical calculation results for the case of gas injection from the holes of the sphere are in quantitative and qualitative agreement with the experimental data.

Frost protection of the mouth of the exhaust tower of the cooling tower with natural draft

The article presents the results of numerical simulation of the protection system of the mouth of the exhaust tower of a cooling tower with natural traction from freezing. To prevent the formation of ice, it is proposed to install an atmospheric air supply system at the mouth of the cooling tower, which ensures the creation of a protective boundary layer at the inner wall of the cooling tower and allows you to separate the warm moist air of the cooling tower from the cold walls. To test the possibility of using such a scheme, a numerical simulation of the process was performed using the k-SST turbulence model. The use of an additional air flow injection system makes it possible to increase the efficiency and reliability of a naturally aspirated cooling tower and a thermal power plant as a whole. Modeling of the cooling tower protection system from the formation of ice showed the possibility of using this scheme in all ranges of outdoor operating temperatures.

Potential of integrating Solid Oxide Fuel Cell based on biomass in power generation in Malaysia: A feasibility study

Although many initiatives have been launched to achieve the ambitious Net Zero 2050 target, Malaysia is still struggling to control carbon emissions, particularly from electricity and heat generation. Fortunately, the potential to generate electricity from biomass in Malaysia reduces reliance on fossil fuels for power generation. Combining biomass gasification with a solid oxide fuel cell (SOFC) promises sustainable and more efficient performance than the traditional approach. To ensure optimal operation, the biomass-derived fuel should be compatible with the gasification system. A numerical simulation was carried out to gain insight into the feasibility of integrating hybrid gasification (GT) with SOFC based on selected biomass-derived fuels (i) palm oil mill effluent (POME) and (ii) refuse-derived fuel. A detailed anode-based planar SOFC model is developed and adopted into a gasification system that operates with an ideal gas under steady-state conditions. The other components considered in this study are a recuperator, combustor, and high-pressure turbine. A comprehensive energy balance for each stage was prepared to determine the overall performance of the system with higher accuracy. A detailed analysis shows that POME gave better results owing to its higher calorific value, resulting in higher thermal energy production. Reducing the required fuel flow rate has a positive effect on the overall performance compared with increasing the injected air flow rate. Furthermore, reducing the fuel flow rate tends to increase the combined efficiency. The study concludes that the fuel flow rate has a significant impact on the performance of the SOFC-GT hybrid system, particularly on combined efficiency and overall performance.

Structural optimization of disperser in polymer flooding distribution tank based on venturi pulse injection

ABSTRACT Polymer was carried by liquid in conventional polymer dispensing tank of polymer flooding in oilfield. Polymer particles often gather in the process of polymer blending, resulting in blockage of ground pipelines and formation. To reduce this phenomenon, finite element method was used. Optimization of polymer tank carrier based on venturi tube gas pulse injection. The polymer particles were carried into the liquid distribution tank by the injection method of pulse airflow to realize efficient carrying. Study on the effect of different pulse intensity and pulse waveform on cohesion. The results showed that the combined effect of strong pulse difference and pulse gap could make the airflow have strong carrying capacity for difficultly migrated polymer particles. Optimized the shortest pulse time and got the shortest time of triangle wave, sawtooth wave, square wave, and sine wave under simulated conditions. Time was 5.1 s, 6.3 s, 6.2 s, 6.2 s, respectively. The corresponding pulse frequencies were 20 times/s, 15 times/s, 10 times/s and 30 times/s, respectively. Properly increasing pulse intensity could enhance the carrying capacity of pulse airflow to polymer and reduced the carrying time of polymer. The optimal pulse parameters were triangular wave with pulse intensity of about 120 m/s and pulsed frequency of 20 times/s. Established the phenomenon and reason of indoor experiment. The viscosity of polymer solution after stirring was higher than that of liquid flow carried by gas phase pulse. This shows that the polymer system was more fully dissolved under the condition of gas phase pulse carrying. Pulsed airflow injection could effectively reduce polymer aggregation and shear action of agitator to protect polymer structure. Pulse airflow injection also plays an important role in safe operation of ground pipelines and stable seepage in porous media.

Generation and Propagation Characteristics of an Auto-Ignition Flame Kernel Caused by the Oblique Shock in a Supersonic Flow Regime

The auto-ignition caused by oblique shocks was investigated experimentally in a supersonic flow regime, with the incoming flow at a Mach number of 2.5. The transient characteristics of the auto-ignition caused by shock evolvements were recorded with a schlieren photography system, and the initial flame kernel generation and subsequent propagation were recorded using a high-speed camera. The fuel mixing characteristics were captured using NPLS (nanoparticle-based planar laser scattering method). This work aimed to reveal the flame spread mechanism in a supersonic flow regime. The effects of airflow total temperature, fuel injection pressure, and cavity length in the process of auto-ignition and on the auto-ignitable boundary were investigated and analyzed. From this work, it was found that the initial occurrence of auto-ignition is first induced by oblique shocks and then propagated upstream to the recirculation region, to establish a sustained flame. The auto-ignition performance can be improved by increasing the injection pressure and airflow total temperature. In addition, a cavity with a long length has benefits in controlling the flame spread from the induced state to a sustained state. The low-speed recirculating region created in the cavity is beneficial for the flame spread, which has the function of flame-holding and prevents the flame from being blown away.

Simultaneous degradation of phenol-Cr(VI) wastewater on air injection plasma electrolysis using titanium anode

Phenol and Cr(VI) are dangerous wastewater were degraded simultaneously by reactive chemical species on plasma electrolysis reactor where direct air injection into plasma zone which titanium as the working electrode. Air injection contributes to increasing the formation of the radical species, such as radical ·OH, ·H, O2·−, and H2O2 molecules, even reducing the energy consumption. The effects of various air injection flow rates, pH, and voltages on phenol–Cr(VI) degradation were observed. The removal efficiency on the binary system was achieved 66% for phenol and 91% for Cr(VI) within 30 min, where the optimum condition of air injection flow rate is 0.2 L min−1 and pH 3.7. The energy efficiency of degradation was compared with that in other competitive processes. Increasing the voltage at constant power decreases the number of ·OH and ·H and increases the number of H2O2 molecules, indicating the formation of new reactive species. This study validated the synergistic effect on the simultaneous oxidation and reduction processes in wastewater.

Thrust Vectoring of a Fixed Axisymmetric Supersonic Nozzle Using the Shock-Vector Control Method

The application of the Shock Vector Control (SVC) approach to an axysimmetric supersonic nozzle is studied numerically. SVC is a Fluidic Thrust Vectoring (FTV) strategy that is applied to fixed nozzles in order to realize jet-vectoring effects normally obtained by deflecting movable nozzles. In the SVC method, a secondary air flow injection close to the nozzle exit generates an asymmetry in the wall pressure distribution and side-loads on the nozzle, which are also lateral components of the thrust vector. SVC forcing of the axisymmetric nozzle generates fully three-dimensional flows with very complex structures that interact with the external flow. In the present work, the experimental data on a nozzle designed and tested for a supersonic cruise aircraft are used for validating the numerical tool at different flight Mach numbers and nozzle pressure ratios. Then, an optimal position for the slot is sought and the fully 3D flow at flight Mach number M∞=0.9 is investigated numerically for different values of the SVC forcing.

Improvement of Thermal Performance of Coiled Tube Heat Exchanger Utilizing Air Bubble Injection Technique

The heat transfer enhancement in terms of temperature of a vertical helically coiled tube heat exchanger is carried out experimentally. The experiments were achieved in a heat exchanger with a 50 cm height and 15 cm internal diameter under four different cold and three hot water mass flow rates and four different airflow rates. At the same time, the temperature difference was taken invariant (ΔT=20°C). To avoid some uncertainties, the hot side temperature of the heat exchanger was measured via k-type thermocouples. The results showed that the increase of air injection flow rate improved heat transfer from the hot stream flowing in the coil to the shell’s cold stream. An intimate thermal mixing when air injected is clearly observed, which could be responsible for the heat exchanger’s thermal enhancement. Finally, the injected air pressure was noticed to be having only a minor effect on thermal performance improvement.

Novel Device and Strategy for Growing Large, High-Quality Protein Crystals by Controlling Crystallization Conditions

Neutron diffraction experiments are informative for determining the locations of hydrogen atoms in protein molecules; however, much larger crystals are needed than those required for X-ray diffraction. Thus, additional techniques are required to grow larger crystals. Here, a unique crystallization device and strategy for growing large protein crystals are introduced. The device uses two micropumps to control crystal growth by altering the precipitant concentration and regulating the pinpoint injection of dry air flow to the crystallization cell. Furthermore, the crystal growth can be observed in real time. Preliminary microbatch crystallization experiments at various concentration ranges of polyethylene glycol (PEG) 4000 and sodium chloride were first performed to elucidate optimized crystallization conditions. Based on these results, a device to precisely control the sodium chloride and PEG concentrations and the supply of dry air to the crystallization cell was used, and 1.8 mm lysozyme and 1.5 mm alpha-amylase crystals with good reproducibility were obtained. X-ray data sets of both crystals were collected at room temperature at BL2S1 of the Aichi Synchrotron Radiation Center and confirmed that these crystals were of high quality. Therefore, this crystallization device and strategy were effective for growing large, high-quality protein crystals.

Leading Edge Blowing to Mimic and Enhance the Serration Effects for Aerofoil

Leading edge serration is now a well-established and effective passive control device for the reduction of turbulence–leading edge interaction noise, and for the suppression of boundary layer separation at high angle of attack. It is envisaged that leading edge blowing could produce the same mechanisms as those produced by a serrated leading edge to enhance the aeroacoustics and aerodynamic performances of aerofoil. Aeroacoustically, injection of mass airflow from the leading edge (against the incoming turbulent flow) can be an effective mechanism to decrease the turbulence intensity, and/or alter the stagnation point. According to classical theory on the aerofoil leading edge noise, there is a potential for the leading edge blowing to reduce the level of turbulence–leading edge interaction noise radiation. Aerodynamically, after the mixing between the injected air and the incoming flow, a shear instability is likely to be triggered owing to the different flow directions. The resulting vortical flow will then propagate along the main flow direction across the aerofoil surface. These vortical flows generated indirectly owing to the leading edge blowing could also be effective to mitigate boundary layer separation at high angle of attack. The objectives of this paper are to validate these hypotheses, and combine the serration and blowing together on the leading edge to harvest further improvement on the aeroacoustics and aerodynamic performances. Results presented in this paper strongly indicate that leading edge blowing, which is an active flow control method, can indeed mimic and even enhance the bio-inspired leading edge serration effectively.

Dewaterability and degradability of municipal wastewater sludge by electrooxidation/electrocoagulation (EOx/EC) and ultrasound-assisted electrooxidation/electrocoagulation(US/EOx/EC) processes: Determination of operational conditions

In this study, the potential use of electrooxidation-electrocoagulation and ultrasound-assisted electrooxidation-electrocoagulation processes with hybrid electrodes to improve the dewaterability and degradability of active sludge was investigated. Effects of electrode type, current density, electrode connection mode, air injection flow rate, and electrode distance on sludge dewaterability and degradability were determined through measuring specific resistance to filtration (SRF), filtration time (s), degree of degradation (DD, %) and sludge moisture content (Mc, %). To determine the effects of the ultrasound-assisted electrochemical process, experiments were conducted in a different reactor under optimum conditions of the electrochemical process, constant frequency (40 kHz), and varying ultrasound powers (60–240 W). The experiments results showed that for all electrode materials, at high values of current density, the dewaterability of the sludge decreased while the degradability of the sludge increased. Besides, both filtration times and degree of degradation decreased with increasing air injection flow rates. Under the optimum operational conditions (TiPbO2-Fe-SS-SS hybrid electrode type, 100 A/m2 current density, MP-P connection mode, 1 L/min air injection flow rate, 1 cm electrode distance, and 20 min operation time), SRF value decreased from 50 × 1012 m/kg to 2.02 × 1012 m/kg, filtration times decreased from 132 s to 9 s, DD value was observed as 20.2% and Mc value was observed as 42.3%. Under the optimum operational conditions of electrooxidation-electrocoagulation process, sludge DD values in the ultrasound-assisted electrooxidation-electrocoagulation process increased, but SFR values decreased. The structural change in the sludge after each process was determined by SEM analysis.

Flow around Ship Spoiler.(Dept.M)

To control the roll, pitch motion and speed of the ship, a proposed system of spoilers is mounted at the bottom of the ship. The bow spoilers consist of an even number of sections arranged port and starboard forward of the center of mass of me ship. The stem spoilers consist of an even number of sections arranged port and starboard attached to the ship's transom or transom plate. Injecting exhaust gas stabilizes cavities behind spoilers. The forces and moments acting on the ship's bottom depend on its inclination, spoiler extensions and positions of the spoilers relative to the ship's center of mass. To improve the understanding of the parameters affecting the flow field around such spoiler, we computed the flow field with different spoiler position, and inclination angle with air flow injection. We used a three-dimensional Navier-Stokes code (CFDRC, 2000) to model the two-phase (low field around a ship spoiler with the Free Surface simulation In Piecewise Linear Interface Construction (PUC) method. The governing equations are discretized on a structured grid using an upwind difference scheme. For different conditions, we detemline the bubbles shape, the two-dimensional flowfield around the spoiler body and the pressure variation on the wake of the spoiler body. Higher spoiler inclination angle gives higher pressure difference between front and back of the spoiler. Spoiler with injection at a distance L from ship spoiler gives higher pressure difference between front and back of the spoiler than injection just beside the spoiler In spoiler with 45o inclination angle the cavity has high stability with long bubble foot shape. The bubble shape depends on the spoiler position and inclination. These parameters affect the roll, pitch and speed of the ship.

Phenol degradation by fenton reaction in air injection using plasma electrolysis method

Phenolic compounds are pollutants which have high toxicity and could be harmful to the environment even at low concentrations. The degradation of phenolic has been conducted by various methods including photocatalytic and ozonation. However, these methods require high costs and large energy. Therefore, plasma electrolysis by the Fenton reaction may be an alternative method for phenol degradation. The purpose of this study is to determine the optimum conditions for phenol degradation by adding Fe2+ ions. The result shows that the most effective phenol degradation was obtained by using an optimum power of 700 watts with an air injection flow rate of 0.2 L/min and addition Fe2+ 20 ppm ions for 30 min experiments. Based on these conditions, the concentration of phenol in waste was reduced to 0.425 mg/L and the highest percentage of phenol degradation (99.58%) was observed. The final phenol concentrations obtained in this study met the quality standards for clean water at a concentration of 1 mg/L as well as the quality standards for drinking water treatment at a concentration of 0.5 mg/L.

Quantifying vulnerability to embolism in tropical trees and lianas using five methods: can discrepancies be explained by xylem structural traits?

Vulnerability curves (VCs) describe the loss of hydraulic conductance against increasing xylem tension, providing valuable insights about the response of plant water transport to water stress. Techniques to construct VCs have been developed and modified continuously, but controversies continue. We compared VCs constructed using the bench-top dehydration (BD), air-injection-flow (AI), pneumatic-air-discharge (PAD), optical (OP) and X-ray-computed microtomography (MicroCT) methods for tropical trees and lianas with contrasting vessel lengths. The PAD method generated highly vulnerable VCs, the AI method intermediate VCs, whereas the BD, OP and MicroCT methods produced comparable and more resistant VCs. Vessel-length and diameter accounted for the overestimation ratio of vulnerability estimated using the AI but not the PAD method. Compared with directly measured midday embolism levels, the PAD and AI methods substantially overestimated embolism, whereas the BD, MicroCT and OP methods provided more reasonable estimations. Cut-open vessels, uncertainties in maximum air volume estimations, sample-length effects, tissue cracks and shrinkage together may impede the reliability of the PAD method. In conclusion, we validate the BD, OP and MicroCT methods for tropical plants, whereas the PAD and AI need further mechanistic testing. Therefore, applications of VCs in estimating plant responses to drought need to be cautious.