Air-water Mixture Research Articles

The Effect of Air–Water Mixture on the Dynamic Response of a Hydrodynamic Journal Bearing With Inclined Grooves

Abstract Water-lubricated hydrodynamic journal bearings with deep inclined grooves are often used to support radial loads and dampen pump vibrations in nuclear power plants. The inclined grooves increase the pumping effect of the lubricant thus reducing wear and friction during rotor startup and coast-down. The deep grooves also facilitate the removal of debris without damaging the bearing. The load capacity and the stability of this type of bearing are studied in the present work. A sensitivity study of the impact of the number of grooves on bearing performance underlined the superiority of the journal bearing with two inclined grooves. Moreover, these journal bearings may operate with a mixture of water and air. This compressible two-phase lubricant will modify the load capacity and the stability of the journal bearing. The impact of the ingested volume fraction of air is therefore investigated. A physical model of the homogeneous air–water mixture linking the local air volume fraction with the pressure was used in conjunction with the numerical solution of the compressible Reynolds equation on an unstructured grid. It was found that the air ingestion in the two-inclined grooves journal bearing decreases the load capacity but improves the stability for mild and low loads.

Oxidation of Airborne m-Xylene in Pulsed Corona Discharge: Impact of Water Sprinkling

Plasma from electric discharges can be used in the abatement of volatile organic compounds (VOCs). The application of gas-phase pulsed corona discharge (PCD) in air–water mixtures provides favorable conditions for the oxidation of VOCs at unsurpassed energy efficiency. This research investigates the impact of water sprinkling on PCD performance in the oxidation of m-xylene as a model compound. Experimental research into the plasma treatment of continuous air flow was undertaken using the PCD reactor in dry and water-sprinkled modes. Water sprinkling more than doubled the m-xylene oxidation rate, which can be attributed to abundant OH-radicals produced at the plasma–water interface. Water sprinkling substantially reduced the formation of nitrous oxide, which is considered to be a secondary pollutant in the outlet air. Ozone is considered a by-product helping the subsequent photocatalytic oxidation of potential residues and photocatalyst maintenance. The use of water-sprinkled PCD is a promising approach to energy-efficient abatement of VOCs.

Sensitized Reynolds stress modeling of a bubbly jet emerging into a water cross-flow

The present work is concerned with the computational study of an air–water mixture stream emanating from a nozzle submerged in a water cross-flow inside a rectangular open channel to form a curved, intensively dispersed, bubbly jet. The work focuses on evaluating the predictive performance of an eddy-resolving turbulence model applied to the described case of a multiphase gas-liquid flow system characterized by a variety of closely coupled phenomena, including: turbulence anisotropy-induced secondary motion, free surface flow, bubbly jet propagation, and the varying interaction dynamics of the carrier water flow with the air bubble dispersion. Correspondingly, an appropriately extended differential near-wall Reynolds stress model, which describes the dynamics of unresolved subscale structures within the Sensitized Reynolds-Averaged Navier–Stokes (RANS) computational framework, is currently used in conjunction with a two-way coupled Euler–Lagrange approach to simulate this gas-water bubbly flow, with the operating and boundary conditions following the experimental reference of Zhang and Zhu (2013). Accordingly, the conditions at the free surface are adequately derived for all components of the residual turbulence stress tensor and the corresponding length scale determining variable. It is shown that the statistics of the bubble phase can be accurately captured, and the proper-orthogonal-decomposition analysis of the dynamic properties of the flow reveals at least two large-scale transient effects associated with the bubbly jet. Furthermore, in the preliminary part of this work it is shown that the currently applied turbulence model can be successfully used to correctly capture the effects of Reynolds stress anisotropy in the single-phase open-channel configuration, representing the incoming flow field of the main two-phase flow configuration.

Investigation of two-phase flow distribution in the vertical annular distribution header of a variable refrigerant flow heat pump system

The characteristics of two-phase flow distribution from a vertically installed annular refrigerant distribution header to multiple branch ports are investigated, with a specific focus on simulating a real variable refrigerant flow heat pump (VRF HP) system. A test section is fabricated to replicate an actual distribution header for empirical investigation, utilizing an air–water mixture as the working fluid. A series of experiments are conducted to examine distribution characteristics, involving variations in the location of the main inlet port, operational mode, total mass flow rate, and void fraction. The experimental results indicate that the two-phase mixture exhibits a relatively uniform liquid phase distribution to the branch ports when the main inlet port is positioned at the bottom side. However, maldistribution to branch ports is intensified as the inlet void fraction increases and the flow rate of the two-phase mixture decreases. Furthermore, a series of computational fluid dynamics analyses is performed to investigate the distribution characteristics of R410A, the actual working fluid utilized in VRF HP systems. These analyses are conducted under the operational conditions typical of VRF HP systems. Despite identical Reynolds numbers for the two-phase R410A flow and air–water mixture flow, the former exhibits a notably uneven distribution to branch ports owing to the distinct thermophysical properties, particularly density and viscosity. The findings from this investigation enhance the comprehension of two-phase flow distribution characteristics in a vertically installed refrigerant distribution header under real VRF HP system conditions, offering valuable insights into mitigating the maldistribution of refrigerant flow to branch ports.

Numerical Analysis of the Submerged Horizontal Plate Device Subjected to Representative Regular and Realistic Irregular Waves of a Sea State

This study numerically analyzes a submerged horizontal plate (SHP) device subjected to both regular and irregular waves. This device can be used either as a breakwater or a wave energy converter (WEC). The WaveMIMO methodology was applied for the numerical generation and wave propagation of the sea state of the Rio Grande coast in southern Brazil. The finite volume method was employed to solve conservation equations for mass, momentum, and volume fraction transport. The volume of fluid model was employed to handle the water-air mixture. The SHP length (Lp) effects were carried out in five cases. Results indicate that relying solely on regular waves in numerical studies is insufficient for accurately determining the real hydrodynamic behavior. The efficiency of the SHP as a breakwater and WEC varied depending on the wave approach. Specifically, the SHP demonstrates its highest breakwater efficiency in reducing wave height at 2.5Lp for regular waves and 3Lp for irregular waves. As a WEC, it achieves its highest axial velocity at 3Lp for regular waves and 2Lp for irregular waves. Since the literature lacks studies on SHP devices under the incidence of realistic irregular waves, this study significantly contributes to the state of the art.

Pressure Drop Estimation of Two-Phase Adiabatic Flows in Smooth Tubes: Development of Machine Learning-Based Pipelines

The current study begins with an experimental investigation focused on measuring the pressure drop of a water–air mixture under different flow conditions in a setup consisting of horizontal smooth tubes. Machine learning (ML)-based pipelines are then implemented to provide estimations of the pressure drop values employing obtained dimensionless features. Subsequently, a feature selection methodology is employed to identify the key features, facilitating the interpretation of the underlying physical phenomena and enhancing model accuracy. In the next step, utilizing a genetic algorithm-based optimization approach, the preeminent machine learning algorithm, along with its associated optimal tuning parameters, is determined. Ultimately, the results of the optimal pipeline provide a Mean Absolute Percentage Error (MAPE) of 5.99% on the validation set and 7.03% on the test. As the employed dataset and the obtained optimal models will be opened to public access, the present approach provides superior reproducibility and user-friendliness in contrast to existing physical models reported in the literature, while achieving significantly higher accuracy.

Energy expenditure in the Z-type plate heat and mass exchanger based on the concept of heat-integrated distillation column

Thermal separation of substances typically involves the use of rectification columns equipped with condensers and reboilers. This conventional method is notably energy-intensive, necessitating substantial heat input to the reboiler and leading to significant waste heat discharge through the condenser into the environment. This paper presents our further study on an innovative alternative technology for thermal separation. The proposed approach involves conducting thermal separation within flow channels of a Heat and Mass Exchanger (HME), which are composed of plates with intricate geometries. In this system, heat distribution is maintained through the diaphragm, i.e., the channel walls, facilitating both heat exchange and simultaneous thermal separation of substances.This paper focuses on both laboratory and numerical investigations of two-phase flow within various channel geometries. Experimentally, four distinct channel designs were examined using an air–water mixture, aiming to identify a new geometry that facilitates countercurrent flow patterns in this challenging substance combination. The experimental phase led to the selection of a channel geometry that demonstrated the most effective countercurrent flow for intensive cases, then used for ethane-ethylene mixture. Subsequently, this selected geometry was subjected to numerical calculations using the mathematical model of the Heat and Mass Exchanger (HME). These calculations encompassed flow dynamics, thermal behavior, and the sizing of the HME, tailored specifically for the newly identified channel geometry.

Evaluation of Efficiency of a Finned Corrugation Basin in Inclined Basin-Type Solar Stills in Regulating the Water Supply of the CaspiCement Plant

The need for fresh water production is especially high in hot dry climates without any sources of drinking water but with an abundance of sea and underground water. The solution is water desalination with efficient solar-powered water treatment plants. This article proposes a new modification of a basin made of thin-finned corrugation with 43°-angle-inclined sides, equal to the region’s latitude, which provide strong heating. The experiments were carried out in the hot climate of Aktau city (43°49′ N, 51°1′ E). The study’s outcomes can be useful for regions with drinking water scarcity. To define the level of the corrugated basin’s efficiency, two versions (SS-1, SS-2) of experiments were carried out on a two-slope distiller, complete with two basins. In SS-1, basin-2 was heated by air. By 15:00, basin-2 had heated up to 98.5 °C, and the acrylic cover above had heated up to 101.6 °C, which led to its “deformation”. By 12.00 p.m., the temperature differentials between the glass (40.7 °C), the air–water mixture (57.3 °C), and basin-1 (61.1 °C) were 16.6 °C and 20.4 °C. This resulted from the wind speed increasing up to 5.9 m/s. The large temperature differential contributed to the condensate yield increasing from 0.128 kg at 11 o’clock to 0.293 kg at 12 o’clock. The throughput capability of basin-1 per day was equal to 2.094 kg. Basin-2’s input to the performance in SS-1 was only the thermal effect. In SS-2, basin-2 was used as a regular basin. The plexiglass temperature was lower than the temperatures of the water and basin-2. The temperature differential between the glass and air–water mixture at 10:00 a.m. was 20 °C; at 12:00 p.m. it was 30.6 °C; and a value of 30.6 °C was recorded at 3:00 p.m. The thermal differential between the glass and the air-water mixture provided the highest condensate yield of 1.114 kg at 3.00 p.m. The condensate yield from the basins in SS-2 was 8.72 kg, including 3.5 kg from basin-1, which is 1.7 times more than from basin-1 in SS-1. The experimental results are consistent with the equations coming from the models of Clark J.A. and Dunkle R.V. Tcondensation ≠ Tevaporation is an irreversible process. When the basins are heated, the heat is consumed; when the glass cools down, the heat is given off. Heat losses are minimized due to the “gap” and positive energy is provided. The still’s throughput capability can be made larger by increasing the basin’s area, reducing the water layer thickness, and regulating the flowrate of the desalinated water.

Experimental investigation of storm sewer geyser using a large-scale setup

The storm sewer geyser is a process where an air–water mixture violently erupts from a manhole. Despite the low hydrostatic pressure, violent eruptions can achieve a height of tens of meters above the ground. This current study experimentally investigates large-scale violent geysers using a large air pocket inserted from a pressurized air tank. The total length of the pipe system is approximately 88 m with a 0.1572 m diameter pipe. This large-scale experiment facilitates the investigation of spontaneous geyser eruptions. This study identifies the role of air–water volume ratio and coefficient of pressure (ratio of absolute initial static pressure to initial dynamic pressure) on the geyser intensity using eruption images and pressure plots. A total of 116 cases are tested, in which the volume ratio is parametrically increased from 0 to 1.1 under various operating conditions. A geyser score is defined to quantify the geyser eruption nature based on visual observations. The key findings are as follows: first, a sharp transition in geyser intensity is observed at the critical volume ratio of 0.5, and pre-transition and post-transition intensity exhibit a linear relationship with the volume ratio; and second, the critical volume ratio linearly varies with the coefficient of pressure.

Numerical modeling of turbulent air-water mixture flows in spilling breaking waves

This paper presents a numerical study of turbulent air-water mixture flows under spilling breaking waves by using a mixture-flow model. The model is extended from the earlier 2D numerical framework NEWFLUME, which solves the Reynolds-averaged Navier-Stokes (RANS) equations for mean flow motions. The turbulence closure is accomplished by a modified k−ε two-equations model, in which the effect of entrained bubbles on turbulence production and dissipation is considered by incorporating additional buoyancy terms. A transient equation based on two-fluid formulation is solved for air bubble transport. The present model is validated by comparing the simulated free surface displacement, void fraction, mean velocity and turbulence kinetic energy against existing experimental data and the previous numerical results. The effects of the additional convective term in transient equation of void fraction and the bubble-induced turbulence term in turbulence transport equation are further explored. The results reveal that the additional convective term in the transient equation of void fraction plays an essential role of suppressing unphysical turbulence growth and bringing correct amount of air entrainment into water during wave breaking processes. The additional bubble-induced turbulence production and dissipation terms become effective after wave breaks when the void fraction has been appropriately modeled, and they can further reduce the simulated turbulence intensities in spilling breaking wave, rendering a better agreement with the experimental measurements.

Experimental investigation of limit parameters of direct contact condensation in the heat exchanger for waste heat recovery

In the present study, a suitable composition of parameters has been obtained to provide an efficient process of cooling flue gas with complete condensation of water vapour from air-water vapour mixture on a water film in co-current upward flow in the tube of the direct contact heat and mass exchanger. The results showed that the value of the irrigation density depends on the velocity of the air-water vapour mixture and the initial vapour content and should be calculated from an empirical equation. The active pipe height depends on the velocity of the air-water vapour mixture and the initial vapour content and should also be calculated from an empirical equation. For example, if the initial vapour content of the air-water vapour mixture is 11%, the velocity of the mixture is 20.8 m/s the height of the channel should not exceed 0.460 m. The value of the water heating limit temperature increases from 46◦C to 62◦C with a change in the initial vapour content from 11% to 30%. The present experimental results could be helpful in the design of direct contact heat and mass exchangers for waste heat recovery.

Flow pattern visualization and definition of transition criteria for two-phase flow in Chevron-type corrugated channels

This study aims to highlight the factors influencing flow patterns in Plate Heat Exchangers (PHEs) operated with two-phase flows. Our focus is on providing precise definitions of flow regimes and proposing transition boundaries by comparing diverse experimental datasets. To accomplish this, we designed an experimental apparatus for flow visualization through high-speed videos. The videos clarify flow patterns in an upward-flowing air-water mixture within a chevron-type plate heat exchanger. We introduce a new, clearly defined nomenclature and present the results in the form of a flow regime map. Moreover, we reclassify previously documented flow patterns in the literature using our established nomenclature, creating a unified and comparable database of visualization data. Subsequently, we explore semi-theoretical transition criteria and establish new transition boundaries based on the compiled experimental data. These newly determined transition lines are integrated into a comprehensive global flow regime map, advancing our understanding of two-phase flow behavior in PHEs.

Experimental Investigation of the Performance of a Novel Adiabatic Swirl-Flow Separation Apparatus in Air–Water Two-Phase Flow

Abstract Experiments were performed for determining the efficacy of a swirl-flow apparatus for phase separation of a premixed two-phase air–water mixture. In the experiments gas and liquid flow rates were parametrically varied. The goal of this study was to determine the ideal operating conditions for phase separation of an adiabatic mixture and to serve as a benchmark for future desalination experiments involving separation of vapor-saline water two-phase mixture generated by flash evaporation. The novel swirl-flow apparatus enables the formation of a stable air core (lighter fluid) in the middle of the separator tube due to centrifugal force induced by strategically injecting the two-phase mixture tangentially into the tubular test section. Separated air is removed by tapping into the air core using a retrieval tube that is mounted in the center of the test section. Conditions under which maximum phase-separation efficiency is obtained in the swirl-flow apparatus were identified and a correlation for the phase-separation efficiency is proposed for the range of experimental conditions explored in this study.

Experimental investigation of two-phase flow in Chevron-type compact plate heat exchangers: A Study on pressure drops and flow regimes visualization

Compact plate heat exchangers are a very promising technology and lately they are being considered for potential use as steam generators in Small Modular Reactors. However, there is a lack of scientific literature on their operation with two-phase flows, especially with non-refrigerant fluids. In this study, we conducted experiments to visualize and measure the pressure drop of a two-phase flow in a Chevron-type Plate Heat Exchanger. An air–water mixture was used in adiabatic conditions as the operating fluid in upward-flow configuration. Visualization was achieved through high-framerate videos. This study covers a wide range of operating conditions, surpassing those documented in existing literature by specifically analyzing also the region of very low mass flux for both phases. The tested conditions ranged from 6 to 365 kg/m2s of water and from 0.02 to 5 kg/m2s of air. Single-phase pressure drops were measured to establish a correlation for the Darcy friction factor. Instead, measurements of the pressure drop in two-phase conditions were processed and presented using a non-dimensional form referred to as the two-phase multiplier. The adoption of a void-fraction model played a crucial role in accurately extrapolating the frictional component of the pressure drop from the measurements, resulting in less scattered data on the Lockhart–Martinelli plot. In addition, the observed flow structures were categorized into distinct regimes (fine-coarse bubbly, Taylor-like bubbly, heterogeneous, partial film, and film flow) based on visual observation and were represented on a flow map. Finally, these data were used to develop new criteria for predicting flow pattern transitions.

АНАЛІЗ ЯКОСТІ ФУНКЦІОНУВАННЯ СИСТЕМИ НЕЧІТКОГО УПРАВЛІННЯ ЗАСПОКОЮВАЧЕМ ХИТАВИЦІ РЕАКТИВНОЇ ДІЇ

systems to stabilize its position and reduce the negative impact of various types of rocking on the crew and equipment. The corresponding devices, ship stabilizers, have many design options based on the use of different physical principles. Thus, this work considers a type of water-jet ship stabilizer, which stabilizes the ship's hull by creating mechanical moments from the reactive action of jets of a water-air mixture, which are ejected from the stabilizer in the appropriate direction. All ship stabilizers can be divided into passive ones, which do not require the supply of energy for their operation, and active ones, which usually use part of the power of the ship's power plant. It should be noted that active stabilizers make up a significant share of all their types and significantly reduce ship oscillations, although they cause significant energy costs. Accordingly, active ship stabilizers require effective control of their work, which should ensure good values of the stabilization parameters of the ship's hull at acceptable energy costs. It should be noted that the process of control the operation of a complex design stabilizer (which, in particular, is the mentioned reactive water-jet ship stabilizer) is quite complex: it includes many input and output variables of different nature, as well as dependencies between them, which are difficult to formalize during construction deterministic control system, which also cannot take into account the uncertainty of the specified values. Taking this into account, it is advisable to implement a control system for a water-jet ship stabilizer based on the principles of artificial intelligence, one of which is the theory of fuzzy sets. In this work, the implementation of a fuzzy controller for controlling a water-jet-type ship stabilizer was carried out, and its effectiveness was also studied using the Matlab Simulink model. The obtained results showed that the proposed fuzzy control system has satisfactory performance and can be recommended for implementation within the framework of the development of a ship stabilizer of the corresponding design.

Two- and three-body attachment, electron transport and ionisation in water-air mixtures

Three-body electron attachment in the mixtures of H2O and dry air have been measured over a wide range of the density-reduced electric field, E/N, from 3–130 Td and gas pressures, for mixture combinations ranging from 1% to 50% of H2O. We have measured the regions of three-body attachment (3–30 Td) and two-body dissociative attachment (40–130 Td). Besides, the increasing amount of H2O in the mixture causes an increase in the three-body reaction rates of up to two orders of magnitude in comparison with that measured for dry air. On the other hand, the three-body attachment coefficients exceed the two-body ones (dissociative attachment) at high pressures. Good agreement has been found with previous measurements of H2O-dry air mixtures with H2O concentrations of up to 2%. We know of no previous work for higher H2O concentrations. Values of the effective ionisation coefficients and longitudinal diffusion coefficients derived from the same measurements are also presented.

Vertically downward gas-liquid flow: Void fraction and pressure drop

Using an air-water mixture and 34 mm ID pipe, a series of pressure drop and void fraction measurements were collected. The observed flow regimes were falling film, annular, bubbly, cap bubble, slug, and churn flows. The temporal fluctuations of void fraction and pressure drop measurements were firstly studied using signals visualization and PDF. It was revealed that both signals can be used to identify the flow regimes. A new flow pattern map is proposed based on the Froude number, calculated using the mixture velocity of the two phases, and the ratio of gas-to-liquid superficial velocities. The behaviors of the total and frictional pressure drops were studied and the influence of the superficial velocities as well as the flow regimes were identified. The experimental results were compared to four existing vertically downward frictional pressure drop models, none of which provided accurate predictions.

Generation of microbubbles at high gas concentrations via cavitation

A novel method of continuous microbubble generation is proposed in which an air–water mixture is pressurized in a chamber (up to 47 atm), leading to complete gas dissolution, before being expelled through a restriction to induce bubble nucleation. This approach differs from existing methods for small-scale bubble generation due to the high pressure gas–liquid mixture, nucleation approach, and large gas concentrations, which range from saturation ratios of 2.85 to 9.56 at normal temperature and pressure. The flow of bubbles produced by the system is characterized through optical microscopy to determine the influence of various operating parameters on the volumetric bubble size distributions (VBSDs) at a fixed flow rate. In particular, the gas concentration, compressor pressure, restriction diameter, and restriction length are varied for two classes of restrictions: capillaries with large length-to-diameter ratios, and orifices with comparatively low ratios. VBSDs are modestly polydisperse under all conditions, but with tunable distributions in the 10–70 μm diameter range. The VBSDs for each configuration collapse when non-dimensionalized by the Sauter mean diameter, which provides an opportunity to describe bubble size distributions using a predictor model for this reduced order quantity. The coefficients from the predictor model reveal a low sensitivity of the Sauter mean diameter to the gas concentration and a reduction of bubble diameters when the residence time of solution in the restriction is decreased. Analysis of the technique of bubble generation yields an energy balance to quantify the relative energy ratio of the bubble generation process, which is presently less than 0.2%. Insight from the energy balance suggests that the process could be optimized to generate smaller bubbles.

Comparing the productivity of potato plants when growing mini-tubers in the conditions of air hydroponics and in the pots with soil substrate

The article provides the results of comparative tests on growing mini-tubers of potato in greenhouse culture using the pots with soil substrate and in the conditions of air hydroponics without hard substrates by treatment of root system with water-air nutrient mixture. The results of field testing of seed qualities of mini-tubers obtained by various methods are given. The experiments were carried out in Moscow region in potato varieties Fioletovy and Severnoe siyanie. On the basis of the research, it has been established that using the method of obtaining mini-tubers in the conditions of air hydroponics it is possible to increase the seed reproduction coefficient raising the quantitative characteristics of the yield. When growing in the conditions of air hydroponics in the Severnoe siyanie variety there was recorded two time increase of reproduction coefficient and obtained 19.2 mini-tubers per plant. At the same time, in greenhouse culture the average yield was 9.2 mini-tubers per plant. In Fioletovy variety, the reproduction coefficient in air hydroponic plants was 1.8 times higher than in greenhouse culture, 29.1 and 16.1 mini-tubers per plant, respectively. In the yield of greenhouse mini-tubers there were no seeds of small fractions, while in air hydroponic parts there were 25 % of them in Severnoe siyanie variety and 19 % in Fioletovy one. The number of fractions of large seeds more than 30 mm in size was much higher in greenhouse parts than in air hydroponic ones, 49.9 % against 1.82 % in Severnoe siyanie variety and 38.5 % against 1.3 % in Fioletovy variety. By comparative field tests of plants obtained from seed greenhouse and air hydroponic mini-tubers there has not been established significant differences in their yield and reproduction coefficient.

Effect of Air-Liquid Homogeneous Mixture on the Linear Dynamic Characteristics of a Hydrostatic Journal Bearing

Abstract Water lubricated hydrostatic journal bearings are widely used to support radial load of pumps in nuclear power plants. In some situations, these pumps may be required to operate with a mixture of water and air. This compressible air–water mixture will alter the dynamic characteristics of the hydrostatic journal bearings and can have a significant impact on the vibration behavior of the entire pump shaft line. This work is a parametrical investigation of the rotordynamic characteristics of these bearings relative to the volume fraction of the ingested air. The compressibility, the density, and the viscosity of the air–water mixture depend on this volume fraction. In order to evaluate this influence, a homogeneous air-liquid mixture model were developed. Moreover, for low viscosity lubricants, inertia effects can also have an important impact on bearing rotordynamic coefficients. Therefore, the flow is modeled first with the Reynolds equation and then with the bulk flow system of equations to evaluate this impact. The results show the variation of the direct and cross-coupling stiffness and of the direct damping with the evolution of inertial effects and of the level of air contamination.