Air Injection Flow Research Articles

Experimental study of air injection effect on to the surface for preventing ice formation

In order to prevent the ice-accretion on the airfoil surface, an experimental study was conducted to investigate effect of injecting surrounding air from the surface into the main flow. For this purpose, holes were created at the leading edge of the airfoil. Five parameters of diameter, pitch, angle of position, holes arrangement, and velocity of the outlet flow from the holes were sought. Using principles of experimental design by two-level fractional factorial method, required tests were designed and determined. Conducting tests, the results indicated the injection method significantly reduces weight of ice accreted on the surface. The highest amount of ice mass reduction in experiments reached 85% of the ice mass accreted on the simple airfoil. The diameter and pitch of holes had greatest effect on reducing the mass of ice accreted on the surface, followed by the injection airflow rate and the angle of alignment. Therefore, the injection of air at lower temperature than freezing point is as effective for ice accretion and saves energy rather than using hot-air injection. Moreover, the injected air from holes created a protective layer around the surface, which enhanced the process.

Gas turbine efficiency and ramp rate improvement through compressed air injection

With the transition to more use of renewable forms of energy in Europe, grid instability that is linked to the intermittency in power generation is a concern, and thus, the fast response of on-demand power systems like gas turbines has become more important. This study focuses on the injection of compressed air to facilitate the improvement in the ramp-up rate of a heavy-duty gas turbine. The steady-state analysis of compressed airflow injection at part-load and full load indicates power augmentation of up to 25%, without infringing on the surge margin. The surge margin is also seen to be more limiting at part-load with maximum closing of the variable inlet guide vane than at high load with a maximum opening. Nevertheless, the percentage increase in the thermal efficiency of the former is slightly greater for the same amount of airflow injection. Part-load operations above 75% of power show higher thermal efficiencies with airflow injection when compared with other load variation approaches. The quasi-dynamic simulations performed using constant mass flow method show that the heavy-duty gas turbine ramp-up rate can be improved by 10% on average, for every 2% of compressor outlet airflow injected during ramp-up irrespective of the starting load. It also shows that the limitation of the ramp-up rate improvement is dominated by the rear stages and at lower variable inlet guide vane openings. The turbine entry temperature is found to be another restrictive factor at a high injection rate of up to 10%. However, the 2% injection rate is shown to be the safest, also offering considerable performance enhancements. It was also found that the ramp-up rate with air injection from the minimum environmental load to full load amounted to lower total fuel consumption than the design case.

Real-time controlling particle distribution in pneumatic conveyance by electrical capacitance tomography with airflow injection system (ECT-AIS)

Electrical capacitance tomography with airflow injection system (ECT-AIS) has been developed for controlling particle distribution in pneumatic conveyance in order to maintain homogeneous downstream particle distribution εndot+τ with a delay time τ even under inhomogeneous upstream particle distribution εnupt. ECT-AIS is composed of two ECT sensors for monitoring εnupt and for evaluating εndot+τ after injecting airflow. The airflow is injected to the conveyance pipe by activating a solenoid valve of airflow injection system (AIS) to control the homogeneous εndot+τ in the case that the spatial standard deviation of permittivity distribution at the upstream ECT sensor εSDupt which is calculated from εnupt and the spatial mean permittivity 〈εnup〉t is greater than the threshold value δ. With this developed ECT-AIS, three different experiments are performed under different particle loading ratios (ϕ = 0.25, 0.50 and 0.75) with air flow rate Qa = 0.75 kg/s, 0.50 kg/s and 0.25 kg/s. As εnupt is homogeneous, εndot+τ is also homogeneous. While εnupt was inhomogeneous, εndot+τ was homogeneously distributed due to airflow injection. To evaluate the homogeneity of εndot+τ, the spatial mean permittivity 〈εnup〉t in upstream sensor is compared with 〈εndo〉t+τ in downstream sensor and the two results were evaluated with the measured pressures pnupt and pndot. As a results, εSDdot+τ is less than or equal to δ so that 〈εndo〉t+τ is homogeneous after airflow injection. Based on Darcy–Weisbach equation, as the particles are homogeneous, the pressure is lower than that in inhomogeneous distribution. According to the relationship between mean permittivity and pressure, εndot+τ is successfully controlled in homogeneous conditions by ECT-AIS.

The application of dynamic modelling technique on the pipeline drying operation during pre-commissioning

The objective of pipeline drying during pre-commissioning is to remove residual water left in the pipeline after dewatering and desalination operations. Removing the residual water mitigates corrosion and hydrate formation and aids quicker delivery of product to required dryness. The common pipeline drying methods are vacuum drying and convection drying. The convection drying method blows dry air through the pipeline to remove the residual water. Its disadvantages are an inability to adequately dry complex-shaped pipeline networks, significant equipment footprint and expelling air noise during the convection drying operation. The vacuum drying method can achieve low dewpoints particularly for complex-shaped pipeline networks and the equipment footprint can also be smaller than for the convection drying method. Therefore, it is advantageous when facing space restrictions for equipment. This paper introduces a dynamic integrated model to simulate the pipeline drying operation. This model considers vacuum pump performance and gas saturation condition in the pipeline during the drying operation. The modelling results can be used to determine the vacuum drying suitability, predict the drying operation duration and identify opportunities to improve the pipeline drying efficiency, such as vacuum pump performance, dry gas injection and convection dry air flow rate. It also demonstrates where vacuum drying is unlikely to be feasible, i.e. low ambient temperature conditions, and methods for identifying such. An optimisation case study is also presented. The drying duration can be reduced significantly by integrating vacuum drying with dry gas injection. This combined methodology can thus significantly improve the pipeline vacuum drying efficiency, which reduces the project cost and improves and de-risks scheduled and simultaneous operations.

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

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

Optimal control of turbulent premixed combustion instability with annular micropore air jets

This article experimentally investigates the suppressing of combustion instability in a model gas turbine combustor with annular air jets. Three parameters were optimized to find the control effectiveness—variations of the air injection flow rate, number, and diameter of jet nozzles. Results indicate that the suppression ratio of the self-excited oscillations can reach 95% with optimal control, the transition and saturation region of control effectiveness are identified, and the four jet nozzles design case can lead to the best effect of damping. Besides, mode shifting of flame heat release rate is observed, the amplitude of heat release rate increases to 2∼4 times than that of the uncontrolled flame, the main resonance frequency at 264.5 Hz was eliminated and triggered to a new oscillation frequency near 110 Hz. Moreover, after air injection control, the flame length and temperature changes inversely proportional to the air injection flow rate, as the air injection transforms the flow field and improves the turbulent combustion velocity. This study not only explored the mechanism behind combustion instability control under annular micropore air jets but also proposed the application of air injection as a practical tool for damping of combustion instability, which could contribute to the prevention of potential thermoacoustic instabilities in gas turbines.

Experimental investigation of bubble growth and detachment in stagnant liquid column using image – based analysis

An experimental study has been carried out to characterize bubble formation, growth, and detachment mechanisms in a stagnant liquid column. Both bubble frequency and bubble detachment size were measured in different gas flow rates, injector diameters and orientations, submergence height, and liquid properties. Experiments were performed for air injection flow rate ranges between 200 mlph and 1200 mlph using needle diameters of 1.6, 1.19, 1.07, and 0.84 mm submerged in liquids with viscosities of 0.001, 0.1, 0.35, and 1 Pa.s. The data for bubble formation was obtained using a high-speed imaging technique. The results show that the bubble diameter at the departure increases as the needle diameter, liquid viscosity, and gas flow rate increase. In addition, the decrease in the submergence height results in a larger bubble at the departure. In order to analyze the changes in bubble detachment characteristics, a force modelling on a growing bubble was proposed. The experimental data were utilized for training a feed-forward back propagation neural network system to estimate the bubble detachment diameter. They were also used to propose a correlation to predict bubble diameter at the departure. The proposed correlation is found to be in the range of ± 8% of the obtained experimental data.

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

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

Improvement of grinding technology with vortex cooling of steels that are liable to crack propagation

Abstract Complexity of grinding process and phenomena entailing it not always allow reaching required technological results, especially while machining surfaces of parts made of tough-to-machine steels, which are liable to crack propagation. Cracks can occur in these parts during grinding due to considerable temperature difference along the section, which can cause formation of high temporary internal tensile stress. Application of cooled air in grinding process exerts considerable influence over temperature decrease in cutting area. In addition, it depends not only on heat exchange, but also on properties of cold air flow. The greatest effect of temperature decrease can be reached by injection of cold air flow in cutting area with implementation of vortex effect, which occurs in swirl flow of compressed air originating in vortex tube. The study of heat generation during machining by tools with discontinuous cutting surface and vortex air cooling was carried out. Obtained thermophysical parameters of vortex air cooling (increase in speed of stream flowing, expansion degree, share of cold stream and decrease in humidity of air stream) allow reducing heat density due to growth of cooling effect in grinding zone. On the base of experimental studies we developed recommendations for choice of optimal grinding modes by tool with discontinuous cutting surface and vortex air cooling of flat parts made of steels being liable to cracking.

Numerical Simulation of Flow Field in Air-Jet Loom Main Nozzle

Abstract To improve airflow injection capacity of the main nozzle and decrease backflow phenomenon, a new main nozzle structure with two throats is designed. Negative pressure value and negative pressure zone length are first proposed evaluating the strength of backflow phenomenon. Commercial computational fluid dynamic (CFD) code “Fluent” is performed to simulate the flow field inside and outside the main nozzle. Exit velocity increases about 10 m/s in new main nozzle. Airflow core length of the new main nozzle is 35% higher than that of commonly used main nozzle. Smaller negative pressure value and shorter negative pressure zone length mean a weaker backflow phenomenon in the new main nozzle. Bigger air drag force indicates stronger weft insertion ability in the new main nozzle.

Experimental analysis of the operation of a small Francis turbine equipped with an innovative aeration device

Development of hydropower as renewable energy source is an actual trend within the worldwide energy strategy. Thus, the manufacturers and operators of hydraulic turbines are currently engaged in their ecological use. Some of the solutions tested for the development of environmentally-friendly turbines are the aeration devices. Their aim is to increase the dissolved oxygen level in the flow discharged from the turbines in order to improve the quality of the aquatic life downstream hydropower plants. The present paper presents the experimental analysis of an innovative air injection device influence over the main operation parameters of a small Francis hydraulic turbine. The aeration device is mounted downstream turbine runner, at the entrance of the turbine draft tube. The tests are focused on determining the operating parameters evolution of the turbine - generator assembly and the vibrations in the shaft bearings and in the casing of the unit during normal regime and with different injected air flow rates. The pressure in the elbow of the draft tube is recorded, in order to determine the influence of the air injection over the flow at the runner outlet. Six operating regimes of the turbine are analysed, between a minimum power output value and a maximum value. For each operating point various air flow rates are injected in hydraulic system, between 1% and 8% water flowrate. The results will present the influence of the air injection over the dynamic behaviour of the turbine-generator unit.

Treatment of Oily Wastewater by Electrocoagulation Process and Optimization of the Experimental Conditions Using Taguchi Method

In this study, electrocoagulation process was used for chemical oxygen demand (COD), total organic carbon (TOC) and turbidity removal from oily wastewaters and Taguchi experimental method was used to determine optimum operational conditions. For this purpose, 5 significant factors (initial pH, current, electrolysis time, air injection flow and electrode surface area) effective in COD, TOC and turbidity removal from the wastewaters were optimized. These experimental factors were handled in 4 levels and experimental conditions were optimized through performing L16 (54) tests with orthogonal series of Taguchi method. Optimum conditions were identified as: initial pH of 6 (pHi level 3), current of 1A (I level 2), electrolysis time of 20 min (ECtime level 4), air injection flow of 2 L/min (air flow level 3) and electrode surface area of 210 cm2 (electrode surface area level 2). Under these conditions, experimental and estimated pollutant removal efficiencies were respectively identified as 92.1-95.6% for COD, as 78.5-80.2% for TOC and as 96.2-95.7% for turbidity. Closer experimental and estimated values indicated the available use of Taguchi method for electrocoagulation process.

Bubbly drag reduction investigated by time-resolved ultrasonic pulse echography for liquid films creeping inside a turbulent boundary layer

Frictional drag reduction due to bubble lubrication was investigated by measuring liquid films creeping along a wall within a two-phase turbulent boundary layer. We developed noninvasive time-resolved ultrasonic pulse echography for imaging a liquid film at a profiling rate of 3 kHz and a spatial resolution of 50 μm. Various film patterns were obtained for a 4-m-long flat-bottom model ship towed in a 100-m-long water tank, where a drag reduction rate of 30% was recorded for maximum air injection. We found that the liquid-film thickness ranged from 50 to 150 wall units of the single-phase turbulent boundary layer; this film was thicker than the buffer layer depth. With an increase in the air injection flow rate, the average thickness decreased close to the buffer layer limit while the skewness and kurtosis of the probability density function of the film thickness increased. A sudden transition of the film form was detected according to the kurtosis, allowing the monitoring of the criteria of the coalescence of dispersed bubbles into large elongated bubbles via ultrasonic pulse echography.

Modeling an Airlift Reactor for the Growing of Microalgae

Objective: The flow dynamics of an airlift reactor for the growing of microalgae is modeled using Computational Fluid Dynamics (CFD). The model is applied to the operation and optimization of the reactor, giving a valuable picture of the liquid movement and carbon dioxide trajectory at different air injection flow rates. Methods: A novel aspect of the model is that air and carbon dioxide are injected at separated locations. Air is injected at the bottom of the reactor and CO2 injection takes place in the downcomer region of the reactor to obtain longer CO2 paths, improving its transference. Results: The results show modeling is a useful tool in the control of the reactor operation; for example, in avoiding the sedimentation of microalgae or for detecting the existence of zones with extremely low CO2 concentrations.

Effects of operating parameters and injection method on the performance of an artificial upwelling by using airlift pump

Artificial upwelling by using airlift pump is considered a sustainable way in actualizing ocean fertilization, which could potentially alleviate the pressures on the fish stocks and human-driven climate change. However, few experimental data about the effects of operating parameters and injection method on the performance of the airlift artificial upwelling were found in the literature. In this paper, an airlift pump for artificial upwelling was investigated through three field experiments, in which airlift pumps of pipe length ranges from 20 to 28.3 m and pipe diameter ranges from 0.4 to 2 m, were designed and tested. Pumped water flow rate and injected air flow rate were measured to study the effects of different factors on the performance of airlift pump. The experiment results show that airlift pump efficiency is closely related to pipe diameter, submerged depth, submergence ratio and nozzle designs. There is no best nozzle for all the range of air flow rate, and the recommended nozzles are double-ring-shaped or star-shaped nozzles when the air flow rate is less or more than 220 L/min, respectively. Moreover, the lift effectiveness increases when the hole size of nozzle is enlarged, which indicates a relatively large bubble size will enhance the lift effectiveness.

Gas and liquid backwash for flux restoration in latex paint effluent ultrafiltration

Abstract The main objective of this study was to evaluate the effectiveness of various backwash scenarios on fouling cleaning for flux restoration in ultra filtration of simulated latex effluent. The effects of water and injected air flow rates, backwash duration, and transmembrane pressure on the flux restoration were examined. Polycarbonate and Polysulfone flat membranes with uniform pore sizes of 0.05 μm and molecular weight cut of 60,000 were used under a constant feed flow rate and a cross-flow mode in ultrafiltration of the latex paint effluent. The cross flow water backwash could restore 60% and 52% of the permeate flux for Polycarbonate and Polysulfone membranes, respectively. Alternatively, cross flow air backwash restored the flux by 28% and 19% for the two membranes, respectively. These results reflect that the shear force created by air removes fouling materials on the membrane’s surface, but does little to reduce the fouling within the membrane’s pores. On the other hand, the combination of gas and liquid backwash was very effective, with optimum performance occurring at 4 LPM of water (cross-flow velocity of 41.6 cm/s), concurrent gas at 1 m/s and 15 psi for 5 min. This combination restored the permeate flux by75% and 63% for Polycarbonate and Polysulfone membranes, respectively.

Optimization of Secondary Air Injection in a Wood-Burning Cookstove: An Experimental Study.

Nearly 40% of the world's population regularly cooks on inefficient biomass stoves that emit harmful airborne pollutants, such as particulate matter (PM). Secondary air injection can significantly reduce PM mass emissions to mitigate the health and climate impacts associated with biomass cookstoves. However, secondary air injection can also increase the number of ultrafine particles emitted, which may be more harmful to health. This research investigates the effect of secondary air injection on the mass and size distribution of PM emitted during solid biomass combustion. An experimental wood-burning cookstove platform and parametric testing approach are presented to identify and optimize secondary air injection parameters that reduce PM and other harmful pollutants. Size-resolved measurements of PM emissions were collected and analyzed as a function of parametric stove design settings. The results show that PM emissions are highly sensitive to secondary air injection flow rate and velocity. Although increasing turbulent mixing (through increased velocity) can promote more complete combustion, increasing the total flow rate of secondary air may cause localized flame quenching that increases particle emissions. Therefore, biomass cookstoves that implement secondary air injection should be carefully optimized and validated to ensure that PM emission reductions are achieved throughout the particle size range.

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

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

Experimental study of microbubble drag reduction on an axisymmetric body

Microbubble drag reduction on the axisymmetric body is experimentally investigated in the turbulent water tunnel. Microbubbles are created by injecting compressed air through the porous medium with various average pore sizes. The morphology of microbubble flow and the size distribution of microbubble are observed by the high-speed visualization system. Drag measurements are obtained by the balance which is presented as the function of void ratio. The results show that when the air injection flow rate is high, uniformly dispersed microbubble flow is coalesced into an air layer with the larger increment rate of drag reduction ratio. The diameter distributions of microbubble under various conditions are submitted to normal distribution. Microbubble drag reduction can be divided into three distinguishable regions in which the drag reduction ratio experiences increase stage, rapid increase stage and stability stage, respectively, corresponding to the various morphologies of microbubble flow. Moreover, drag reduction ratio increases with the decreasing pore sizes of porous medium at the identical void ratio in the area of low speeds, while the effect of pore sizes on drag reduction is reduced gradually until it disappears with the increasing free stream speeds, which indicates that smaller microbubbles have better efficiency in drag reduction. This research results help to improve the understanding of microbubble drag reduction and provides helpful references for practical applications.

Remazol Brilliant Blue Degradation Using Contact Glow Discharge Electrolysis Reactor with Air Injection and NaCl Solution

Remazol Brilliant Blue dye waste is one of the liquid waste produced from the textile industry and harmful to the environment. Contact Glow Discharge Electrolysis (CGDE) method is an effective method to degrade dye waste by producing OH radicals which will be used in liquid waste degradation process. This study aims to determine the effect of anode depth, temperature, and flow rate of air injection on the production of hydroxyl radicals and dye degradation of Remazol Brilliant Blue. This research was conducted in batch reactor with electrolyte NaCl 0,03 M. Variation which done is anode depth which is 0,5 cm; 2 cm; 4 cm, temperature of 40°C; 50°C; 60°C, and air injection flow rate of 0 lpm and 2.5 lpm. The research was conducted by voltage - current characteristic test, hydroxyl radical production test, and dye degradation test. Remazol Brilliant Blue degradation reached 96.15% within 30 minutes where the tension was 750 V, 0.03 M NaCl solution concentration, Fe2+ 40 ppm, 2 cm anode depth, 50°C temperature, and 2.5 lpm air injection flow rate.