Air-water Mixture Research Articles

A novel technology for optimizing dissolved air flotation unit efficiency via secondary saturation of the flotation cell with air bubbles and thin-layer settling

Specific ways to improve the technology for flotation (DAF) wastewater treatment have been determined. Prospects to increase functioning of DAF units via using thin-layer cells, and improving the hydraulic size of the emerging flotation aggregates have been shown. The latter is feasible due to secondary saturation of the flotation cell with air bubbles of 0.1–0.3 mm diameter floating in laminar flow regime and creating light turbulence thereof. The possibility of obtaining an air-water mixture with air bubbles during their breaking up in the annular space of the saturator-separator is experimentally proven. It is feasible to separate the air bubbles from the major fluid flow in the centrifugal field due to rotational and translational motion of the separated mixture. It is established that converting the Q-H vane pump characteristics, which provides for pumped flow circulation and useful flow selection for the two medium-pressure ejectors operating in series, allows to: ensure stable air ejection from the atmosphere; significantly increase the vane pump head H via reducing the supplied useful flow; exclude a compressor and replace an expensive high-pressure pump with a lower operating pressure one.

Study on the effect of air and argon assisted short electric arc machining on Ti6Al4V titanium alloy

The use of an argon–water medium rather than air–water medium is proposed to increase the material removal rate (MRR) and decrease surface oxide production for short electric arc machining. To provide a more stable discharge state during high-temperature processing, this approach uses argon to reduce the production of highly resistant refractory materials (e.g. titanium oxide). For short-arc machining of Ti6Al4V titanium alloy, the effects of the voltage, milling depth, electrode speed and gas flow rate on the MRR, relative electrode loss rate and surface roughness were compared for air–water and argon–water mixtures. It was discovered that the milling depth and voltage had the greatest impact on the MRR, voltage and electrode rotational speed had the greatest impact on the relative tool electrode wear rate (REWR), and voltage had the greatest impact on the surface roughness. In contrast to the air–water mixture, the MRR with the argon–water working medium was as high as 9391 mm3/min, with a 13% improvement in MRR, as well as a smooth and flat surface of the machined workpiece. Nevertheless, the REWR increased to 2.46% and the surface roughness was at least 432 μm with the argon–water medium, increasing by 59 μm compared with the air–water medium. Moreover, the addition of argon reduced the types of surface compound on the workpiece and decreased the residual stress defects, including the recast layer, microcracks and holes.

Experimental investigation of turbulent flow in a rectangular bonneted slide gate and eliminating random fluctuating loads

Bonneted slide gates are widely used in dam bottom outlets for flow regulation. High kinetic energy flow generates turbulence, which induces vibrations in bonneted slide gates under partially open conditions. Significant vibrations can indicate problems and cause damage or expedited deterioration of the gate if left unchecked. This experimental study focuses on two aspects: turbulent flow formation due to rectangular bonneted slide gates and elimination of random fluctuating loads on the gate using a turbulence inhibitor. Five reservoir heads were combined with nine gate openings (10%–90%) to produce 45 different discharges of 12–182 l/s. The different types of the gate flow create different turbulence and random loads based on the water–air mixture and the kinetic energy of the flow. Flow analysis indicates considerable random static pressure fluctuations under the slide gate. The results show the formation of swirling secondary flows in the gate's side guide slots, and their movement and collision with the gate are the leading cause of the turbulent multiphase flow and random fluctuations in static pressure. Also, the use of turbulence inhibitors on the gate can prevent the formation of secondary flows, which results in a 98.92% reduction in the amplitude of random static pressure fluctuations and the elimination of the random fluctuating loads on the slide gate. After removing the swirling secondary flows, a stable air boundary layer was formed under the gate. Finally, the gate flow changed from a turbulent two-phase flow to a steady single-phase jet of water.

Air entrainment and transport in a bottom outlet controlled by a cylindrical gate

This study deals with a bottom outlet that causes significant surges at both the inlet and exit. The bottom outlet comprises an intake, a vertical shaft and a tunnel underneath the rockfill dam and a submerged exit. In the intake tower, a cylinder gate controls hexagonal openings near the reservoir bottom. Operations during the dam construction show that discharges at a low reservoir water level result in upsurges of air-water mixture within the hollow gate cylinder and blowouts in the tailwater. To understand the flow behaviors, 3D CFD modeling is performed to examine air entrainment at the intake and transport down the waterway. Both low and high-water levels are simulated, and the air-water flow phenomenon is reproduced. In both cases, air pockets are generated, which undergo accumulation and breakup process. When moving downstream, they could cause severe surface fluctuations, even blowouts. Consequently, engineering solutions are required to address this issue. The aim of this study is to provide basis for risk assessment of outlet operations and potential rehabilitation measures.

Increasing the development of cone bits when drilling

When drilling blast wells in the technological process of mining magnetite quartzites, the cost of a cone bit is about 60% of the cost of the entire drilling tool. The work includes a literature review of modern methods of increasing the reliability of drilling tools. It has been established that the main directions for increasing the performance of cone bits are the use of wear-resistant materials and coatings for their production, improvement of drilling technology and the organization of repair and preventive maintenance. In the work, it is proposed to use MATEХ (Canada) drilling chemistry, which has found wide application in the oil and gas industry and in granite quarries during impact drilling. The research was carried out in a quarry for the extraction of magnetite quartzites on an Epiroc DM-75E drilling rig, drilling chemicals were fed into the water-air mixture using a MATEХ dispenser. The drilling chemical dispenser is completely self-contained and easy to install on the drilling machine, designed with only one moving part, which ensures low operating costs. Industrial studies with the use of MATEХ drilling chemistry (the consumption of chemistry was 1.5 liters per hour) showed a significant increase in the working hours of cone bits, on average, from 745 to 1488 linear meters. Conclusions were made regarding the use of MATEХ drilling chemistry in the conditions of iron ore quarries of the private joint-stock company «Northern Mining and Processing Plant» (Kryvyi Rih). Experimental studies showed the expediency of using drilling chemistry when drilling blast wells for the extraction of magnetite quartzites. Due to the increase in the working time of cone bits, a reduction in the cost of drilling 1 linear meter of blasting wells by 38.7% was achieved

INVESTIGATION OF WATER DISINFECTION PROCESSES USING PULSE ELECTRIC DISCHARGE

As a result of Russian military aggression in the south-eastern region of Ukraine, water supply pipes and structures of centralized water supply systems were destroyed, and therefore water supply was practically stopped. The solution to the problem can be the use of mobile water treatment stations which use local sources of water: canals, lakes, ponds, or underground water. A feature of water treatment technologies in the field is the need to reliably ensure the process of water disinfection. Existing water disinfection technologies have low efficiency, taking into account the growing number of chlorine-resistant microorganisms, therefore, the implementation of alternative methods of disinfection during water treatment is urgent. One of these methods is liquid disinfection by electric current discharge. The results of the research on disinfection of different types of surface water in Kyiv and water contaminated with E. coli (Escherichia coli (E. coli)) are described. The research was carried out on a laboratory setup with a circulation pump and an ejector-type reactor with integrated electrodes where a water-air mixture is formed through which an electric discharge passes. The discharges initiate the formation of various highly reactive chemicals such as radicals (OH•, H•, O•) and molecules (H2O2, H2, O2, O3). All physical and chemical processes that occur during discharge ensure the formation and action of short-term radicals and relatively long-term oxidants. The study of the influence of the concentration of microorganisms on the speed and completeness of water disinfection was carried out on technical (tap) water with the addition of washings from two tubes with test culture to the reaction tank, which provided the initial concentration of E. coli equal to 3.4∙106 CFU/cm3. Water treatment for 30 seconds reduced the number of microorganisms to 5.4∙104 CFU/cm3. After 1 minute of treatment this indicator decreased to 1.7∙102 and after 3 minutes the value of 5.2 CFU/cm3 was recorded in the samples, that is, the treated water had indicators of practically pure water. Experiments have proven the effectiveness of plasma disinfection for liquids with high concentration of microorganisms.

Simulation of complex transient flows in geothermal wells

In a recent paper we discussed the development of a new transient geothermal wellbore simulator. In the present paper we discuss the application of this simulator to the modelling of challenging and interesting flows that occur in a geothermal wellbore. The first group of problems involve the opening and closing of hot geothermal wells with rapid transient flows. In some cases, this involves counter-flow with steam flowing upwards and liquid water flowing downwards. The final test case in this category is the simulation of a completion test which involves four stages: cold water injection, heating up of a shut-in well, discharge of the well to the atmosphere, connection of the well to a separator.Simulation of well stimulation by air-lifting and air-compression demonstrate the capability of the simulator for modelling flows of air-water mixtures with a moving interface between the phases.Finally, we demonstrate the ability of the simulator to model injection of water-carbon dioxide mixtures, with an increasing proportion of CO2. This is of particular importance as operators look to carbon sequestration as a way of mitigating green-house gas emissions from geothermal power plants.These are a selection of the more interesting problems of the many test cases that were used during the development of our simulator to ensure that it is robust and can simulate the full range of complex transient flows that can occur in a geothermal well.

Experimental and Prenemilary Numerical Evaluation of Pressure Drops under the Conditions of the Stratified Gas-Liquid Flow in a Horizontal Pipe Filled with Metal Foam

The paper reports the results of experimental tests and numerical simulations related to the pressure drop during two-phase air-water mixture flow through a pipe containing metal foam packing. Aluminium foam with 40 PPI open cells was used in the tests. A horizontal pipe with an internal diameter of 10 mm was used, and the foam only occupied a section of the pipe length equal to 240 mm. In the section of the pipe upwards of the foam, stratified flow pattern was generated, i.e., the most characteristic type for the gas-liquid flow. The results of the experimental research were compared with the values derived on the basis of the empirical method, which was developed for several different metal foams and two-phase systems. The values derived from measurements and calculations were subsequently applied to validate one numerical simulation method that is known to be particularly applicable for two-phase gas-liquid flow through metal foams. As a final result, the phenomena resulting from the presence of foam in the stratified flow through a gas-liquid system, the deficiencies of the methods applied in calculating pressure drops and modeling their values in accordance with the adopted numerical procedure were indicated. All research and modelling were carried out with the purpose of testing the potential of metal foam use in pipes dedicated to heat exchanger design, particularly ones intended to improve energy efficiency.

Improvement of entrainment model for horizontal flow in ATHLET and application to Mantilla experiment and TPTF

The entrainment correlations proposed by Al-Sarkhi & Sarica (2013) and the modified Pan & Hanratty (Lee, 2022) were newly implemented in ATHLET to improve the entrainment model for horizontal flows. In addition, the criterion for the onset of entrainment was adjusted with the model suggested by Ishii & Grolmes (1975). The implemented models were examined by simulating two horizontal two-phase flow experiments, the Mantilla experiment and TPTF, in the frame of a benchmark activity of FONESYS. The Mantilla experiment consisted of 2-inch and 6-inch diameter pipes, and it was conducted with air–water mixtures at ∼ 2 bar pressures and ∼ 20 °C temperatures. On the other hand, TPTF had 4-inch and 8-inch diameter test sections, and it was performed with highly pressurized steam-water mixtures in 30 – 86 bar. It turns out that the Al-Sarkhi & Sarica model could improve the prediction of entrainment for the 2-inch Mantilla test section, but it predicted much higher entrainment fractions for the 6-inch Mantilla test section and TPTF. On the other hand, the modified Pan & Hanratty correlation could achieve significant improvements for the entrainment prediction for both the Mantilla experiment and TPTF. Regarding the onset of entrainment, the Ishii & Grolmes criterion was able to yield a slightly better prediction than the ATHLET built-in model for high-pressure cases of TPTF.

Numerical study on the performance of the thermoelectric generator with different air-water mixtures

Thermoelectric generators (TEGs) have been widely used to convert thermal energy into electrical energy directly. Nowadays, the most popular TEG applications, such as vehicle heat recovery and geothermal power generation, typically utilize water as the cooling working fluid. Water sources, however, may not be available or extremely limited in some cases. Therefore, in this study, we proposed a new method of mixing water and air as the working fluid to save water. It is necessary to find out the suitable ratio of water to air, under which the performance loss could be minimized. A numerical model of TEG was built utilizing COMSOL Multiphysics to investigate the effect of water mole fraction (WMF, representing water to air ratio) on the performance of TEG, where the properties of the air-water mixture (AWM) could vary with WMF. In this study, 5 cases were considered at different flow velocities, different WMFs, and different combinations of air, water, and AWMs. The effects of these parameters on the voltage and the output power of TEGs were studied and analyzed. The TEG module could generate higher voltage and power output with increasing velocity and WMF. When air fixed on one side, only 0.2 of WMF on the other side could boost over 1.5 times of voltage and 3 times of power generation than only using air. Based on the simulation results, TEGs reach the best performance when the value of WMF is equal to 0.5 on both sides.

Numerical analysis of evaporation from a falling film in a vertical parallel plate channel

A detailed numerical analysis is performed of evaporation from a laminar falling liquid film with a co-current laminar gas-vapour mixture flow in a vertical parallel plate channel. A finite volume method is used to obtain a fully coupled implicit solution of a complete set of parabolic two-phase two-dimensional governing equations. Comparisons with the previous numerical and experimental studies are made to demonstrate the accuracy and capability of the present numerical model. Water-air and ethanol-air mixtures are used to examine the effects of buoyancy forces on the flow and the thermal characteristics of the evaporation process. The effects on the heat and mass transfer of the system of the wall heat flux, the relative humidity, and the inlet pressure are investigated.

Investigation of the formation of service properties of parts made from forgings of microalloyed steels after controlled cooling from stamping temperatures

The use of microalloyed dispersion-hardening steels allows not only to save expensive alloying elements, but also leads to significant energy savings due to the possibility of using controlled cooling of steel semi-finished products directly after hot forming. The purpose of the research carried out in this work was to determine the rational modes of controlled cooling of forgings made of dispersion-hardening steels that provide the properties and microstructure required by the standard. For this purpose, a simulation simulation of the cooling of the forgings of the connecting rod of the KAMAZ car engine with the temperatures of the stamping end in various media (compressed air, water-air mixture, water, oil) was carried out, which made it possible to determine the composition of the medium (ratio) of water and air in the water-air environment and its supply modes providing cooling of forgings with speeds above critical, that is, without the formation of a ferritic mesh along grain boundaries during the decay of austenite. Subsequently, these modes were reproduced in laboratory and experimental-industrial conditions with the determination of the mechanical properties and microstructure of the steel of the connecting rod forgings. For 38MnVS6 steel, it has been established that controlled cooling from the stamping end temperatures not lower than 950 °C and the cooling rate not lower than 10 °C/sec, the properties and microstructure of forgings meet the requirements of the standard for connecting rods. This makes it possible to abandon the energy-intensive heat treatment (thermal improvement) of forgings provided for by the production technology.

Efficiency of an Inverted-Shroud Gravitational Gas Separator: Effect of the Liquid Viscosity and Inclination

Summary Gas-liquid separation is a typical process in many applications. For instance, gas separation is critical for the proper operation of electrical submergible pumps in the oil and gas industry as the pumps’ performance and lifetime are severely reduced when working with high gas/oil ratios. Gas-liquid separators are installed in oil production wells to reduce the void fraction at the pump inlet. The inverted-shroud gravitational separator stands out due to its efficiencies higher than 97%. This separator performs the gas separation process in two stages. The first is a segregation process related to inversion from liquid to gas continuous flow, whereas the second stage is related to gas entrainment associated with kinetic-energy dissipation process. The latter is more complex to model in the vertical than in the inclined separator’s position. Previous studies revealed that the liquid flow rate and separator’s inclination are relevant parameters for the gas separation efficiency (GSE). However, studies regarding the effect of the liquid viscosity on GSE are scanty. We evaluate the influence of the liquid viscosity and separator’s inclination on the GSE of an inverted-shroud separator (IS-separator) with water-air and oil-air mixtures. Efficiency maps for each inclination and empirical correlations to predict the GSE in the vertical inclination are proposed. New experimental data collected for several liquid flow rates and separator inclinations are offered in this study as a starting point to develop universal GSE maps. Different gas separation phenomena are observed depending on the flow pattern at the inner annular channel (IAC) of the separator and its inclination. The experiments conducted with the water-air mixture indicated turbulent flow, while the oil-air mixture revealed laminar flow for both inclined and vertical positions. The results suggest that the greater the liquid viscosity, the higher the GSE. The efficiency maps indicate that it is possible to reach total gas separation (TGS) for many experimental conditions. In practice, our approach proposes an alternative technology where the variables that influence the production well’s dynamic fluid level are actively controlled. Therefore, the IS-separator can operate under operational field conditions similar to those tested on a laboratory scale. This fact makes the IS-separator a promising tool for industrial applications.

The use of PIV methods in the study of two-phase flows in small diameter channels

The PIV (Particle Image Velocimetry) method is one of the optical, non-invasive measurement methods for measuring fluid velocity and can be used in the study of two-phase gas-liquid flows to determine velocity fields. The velocity distribution of the liquid and gas phases influences the formation of two-phase flow structures and, consequently, the mechanisms of energy and moment exchange in the two-phase flow. The article concerns the application of the PIV method to the assessment of hydrodynamic phenomena occurring during two-phase flow realized in pipe minichannels with an internal diameter d > 2 mm. Fluorescent marker particles with a density close to that of water were used in the research. The preliminary tests were carried out on the adiabatic water-air mixture. The research aimed to check the applicability of PIV methods also in non-adiabatic flows. As a result of preliminary studies, velocity maps of the liquid phase, histograms and velocity profiles in the vertical section of the tested minichannel were obtained.

Intensification of oil production using water-air mixture

The inhibitors based on nano-containing compositions (NCC) have been developed for hardness deposition. A method for developing an inhibitor for saline deposits involves the interaction of amino alcohols with orthophosphoric acid by adding nanoparticles and further diluting them with water to form a 2% solution. It was found out that the inhibitors developed by NSC for saline deposits at a flow rate of 20-30 mg/l are highly effective for controlling the deposits of calcium and magnesium sulfate in the produced water model. The controlling effect of inhibition in these cases is 86.3-99.4%. Keywords: oil saturation; permeability; formation; polymer; water-air mixture; viscosity.

Alleviating mass transfer limitations in industrial external-loop syngas-to-ethanol fermentation

Mass transfer limitations in syngas fermentation processes are mostly attributed to poor solubility of CO and H2 in water. Despite these assumed limitations, a syngas fermentation process has recently been commercialized. Using large-sale external-loop gas-lift reactors (EL-GLR), CO-rich off-gases are converted into ethanol, with high mass transfer performance (7–8.5 g.L-1.h−1). However, when applying established mass transfer correlations, a much poorer performance is predicted (0.3–2.7 g.L-1.h−1). We developed a CFD model, validated on pilot-scale data, to provide detailed insights on hydrodynamics and mass transfer in a large-scale EL-GLR. As produced ethanol could increase gas hold-up (+30%) and decrease the bubble diameter (≤2 mm) compared to air–water mixtures, we found with our model that a high volumetric mass transfer coefficient (650–750 h−1) and mass transfer capacity (7.5–8 g.L-1.h−1) for CO are feasible. Thus, the typical mass transfer limitations encountered in air–water systems can be alleviated in the syngas-to-ethanol fermentation process.

ВПЛИВ ПАРАМЕТРІВ РУХУ ВОДИ НА ЕНЕРГОЕФЕКТИВНІСТЬ ЇЇ ОБРОБКИ ІМПУЛЬСНИМ БАР’ЄРНИМ РОЗРЯДОМ

A study of the energy efficiency of the pulsed barrier discharge during water treatment in the aerosol state depending on the energy of the pulses (21-72 mJ), their repetition rate (50-300 Hz), the concentration of organic impurities in water (50-100 mg / l) and water content (1.6−3.2%) in the water-air mixture. The discharge was generated by unipolar short pulses (~ 100 ns) in an electrode system with vertically arranged cylindrical electrodes with a diameter of 2 mm, the distance between which was 2 mm. The highest energy yield, which was obtained by decomposing the impurity by 90%, was 32 g / kWh. In order to determine the influence of water movement parameters on the energy efficiency of a pulsed barrier discharge under similar conditions, the energy efficiency of this type of discharge during water movement in film, drip and aerosol states was compared. It is concluded that water treatment should be carried out in the drip state on the submillimeter size of the drops. In the case of such water movement, the energy efficiency of the pulsed barrier discharge is ≈30% higher than in aerosol. References 15, figures 6, table 1.

Understanding the effect of surfactants on two-phase flow using computer vision

The effect of surfactants on vertical gas-liquid flow is experimentally investigated in a 12.7 mm diameter tube at conditions relevant to an ammonia-water bubble absorber. The characteristics of two-phase flow are studied using an air-water mixture, both with and without the addition of 1-octanol as the surfactant. High-speed videography is used to study the flow patterns and quantify interfacial areas and bubble velocities. Novel computer vision-based methods are used to analyze and quantify these flow parameters. The addition of 1-octanol results in enhancement in interfacial area due to the prevention of bubble coalescence leading to many small diameter bubbles. Measured values of interfacial area are compared with predictions from correlations in the literature, and agreement and differences are interpreted and discussed. The bubble velocity is measured by object tracking using the optical flow method. Surfactants lead to a decrease in bubble velocity and increase in the residence time. These are surmised to be due to the shear stresses caused by the non-uniform concentration distribution of surfactant along the bubble surface. Overall, the addition of surfactants can lead to appreciable enhancement in heat and mass transfer rates due to their effect on interfacial areas and residence times.

Modeling spark-plug discharge in humid air

Detailed knowledge of the species involved in the oxidation steps during combustion is of interest for technological applications. Using a formerly developed numerical model for a spark-plug discharge in dry air at atmospheric pressure, we studied here the influence of air humidity in the evolution of the densities of neutral and charged species and the gas temperature. The reduced electric field, electronic density, and temperature previously obtained from experimental measurements are parametrically introduced in the model. The effect of relative humidity with the values of 25%, 50%, 75%, and 100% is studied considering the water–air mixture formed by 63 species and coupled by 738 physical and chemical processes. The source term of the chemical reactions is calculated with the ZDPlaskin tool coupled to the numerical model. The analysis of the predominant pathways in the production and consumption of selected species is also carried out. Highly reactive species originated from the inclusion of water in the plasmochemical cycle reach relatively large density values and might play a significant role when considering an air–fuel mixture.

The Flow-Structure Couplings of Fluidelastic Instability and the Effect of Frequency Detuning in Triangular Tube Bundles Subjected to a Two-Phase Flow

Abstract For decades, fluidelastic instability (FEI) has been known to cause dramatic mechanical failures in tube bundles. Therefore, it has been extensively studied to mitigate its catastrophic consequences. Most of these studies were conducted in controlled experiments where significant simplifications to the geometry and flow conditions were utilized. One of these simplifications is the assumption that all tubes have the same dynamic characteristics. However, in steam generators with U-bend tube configuration, the natural frequencies of tubes are nonuniform due to manufacturing tolerances and tubes' curvature in the U-bend region. Thus, this investigation aims to understand the rule of frequency variation (detuning) on FEI in two-phase flow. This includes investigating the effect of detuning on transverse and streamwise FEI for air–water mixture flow. The role of FEI damping and stiffness couplings was investigated over the entire range of air void fraction, or equivalently, the mass-damping parameter. It was found that frequency detuning could elevate the stability threshold caused by either coupling at high air void fraction in the case of transverse FEI. Furthermore, the frequency detuning had a marginal effect on the stability threshold for water flow. It was observed that the mass-damping parameter has a critical impact on FEI under detuning conditions.