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In this paper, an Artificial Neural Network soft matrix correlation to estimate the pressure drop of air-water two-phase flow is developed. The applicability of the model is extended by using dimensionless physical numbers as inputs (Air-Reynolds number, Water-Reynolds number, and the ratio of Air Inertial Forces to Water Inertial Forces), so the model can be implemented for vertical pipes with the proper combination of diameter-velocity-density-viscosity allowing estimations of dimensional numbers within the range of: Air-Reynolds numbers (430–6100), Water-Reynolds number (2400–7200), and Air-Water-Inertial forces ratio (1.6–1834), including the diameter range from 3 to 28 mm. Experimental measurements of frictional pressure drop of water-air mixtures are determined at different conditions. A search of the most suitable density, viscosity, and friction models was conducted and used in the model. The performance of the proposed ANN correlation is compared against published expressions showing good approximation to experimental data; results indicate that the most used correlations are within a mean relative error ( mre) of 23.9–30.7%, while the proposed ANN has a mre = 0.9%. Two additional features are discussed: i) the applicability and generality of the ANN using untrained data, ii) the applicability in laminar, transitional, and turbulent flow regimen. To take the approach beyond a robust performance mapping, the methodology to translate the ANN into a programmable equation is presented.

A computational analysis was carried out on the film cooling technique over the surfaces of eroded plates. The air–water mist coolant was injected through the slotted hole. A flat plate was patterned with various erosions. The loading fraction, f = 4–16%, and blowing ratio, M = 1–1.6, were simulated to understand their influence on the mist film cooling effectiveness. The coolant injection angle or the inclined angle of the secondary slot was kept at α = 35°. It can be observed that the increasing loading fraction raises the film cooling performance. Likewise, a higher blowing ratio can provide a better film cooling over the target surface. Again, it is found that the presence of erosion increases the cooling effectiveness at the particular surface of erosion. Simultaneously, a decrease in the effectiveness can also be noticed at the adjacent flat surfaces. Additionally, the erosions at the further downstream are more effective over the eroded surface compared to the upstream erosions. Considering the size of erosion as a crucial parameter, it was investigated for three different depth sizes. An increment in the mist film cooling performance is observed for the higher depth erosion.

The horizontal bubbly two-phase flow is preferably used in various industrial applications because it provides high interfacial areas which enhance the heat and mass transfer. In the present research, the phase distribution of controlled air-water flow in a horizontal acrylic round pipe with 60 mm inside diameter (D) has been investigated experimentally and modeled numerically. The modeled differential pressure and the mixture velocity profile at a distance of 33D from the mixing section (fully developed region) are computed numerically and compared with those obtained experimentally from the two-phase flow system established and maintained at the National Institute of Standards (NIS-Egypt). Furthermore, the numerical and the experimental data have been compared with previous correlations and models. Reasonable quantitative agreement between all data is found. An electronic device based on Arduino Uno board was designed and used with careful data manipulation for measuring the slug bubble velocity. The results point out that the air volume fraction has a maximum value at the upper pipe wall as the gas bubbles tend to migrate to the upper wall. A new correlation was obtained for bubble migration length to the upper pipe wall which is very important in chemical industrial processes and other engineering application.

Two-phase flow has been used in so many industrial processes, such as boilers, reactors, heat exchangers, geothermal and others. Some parameters which need to be studied include flow patterns, void fractions, and pressure changes. Research on void fractions aims to determine the composition of the gas and liquid phases that will affect the nature and value of the flow property. The purpose of this study is to find out the characteristics of the void fraction of various patterns that occurs and to determine the characteristics of the velocity, length, and frequency of bubbly and plug. Data acquisition was used to convert the data from analog to digital so that it can be recorded, stored, processed, and analyzed. High-speed camera Nikon type J4 was used to record the flow. The condition of the study was adiabatic with variation of superficial gas velocity (JG), superficial fluid velocity (JL), and also working fluid. To determine the void fraction by using the digital image processing method. The results of the study found that the flow patterns which occurred in this study were bubbly, plug, annular, slug-annular and churn flows. It also showed that the void fraction value is determined by the superficial velocity of the liquid and air. The higher the superficial velocity of the air, the lower the void fraction value.

본 연구는 공기-물 이젝터를 이용하여 수중에서 수평으로 주입되는 2상 분류의 유입 및 분류 거동에 대한 실험적 연구를 목적으로 한다. 이젝터의 구동 노즐 면적비를 변수로 유입율 및 유출 계수를 산출하였으며, 수조 내의 주유동 방향 속도 분포를 측정하여 분류의 정량적 거동을 분석하였다. 면적비가 커지면 유입률은 감소하였으며, 유출 계수는 약간 증가하였다. 구동 노즐 면적비가 작고 출구 속도가 감소하면 디퓨저 출구 부근을 제외하고 부력 분류의 특성이 나타나며, 면적비가 커지고 출구 속도가 증가하면 수평 분류에서 부력 분류로 천이되는 거리가 길어지고, 분류 중심선 부근의 주유동 방향 속도가 증가하였다.

Gas-liquid slug flow in horizontal pipes occurs frequently in industrial applications and its heat transfer characteristics are very important but complicated due to the intermittent flow structures. This paper aims at investigating the heat transfer mechanism of both air-oil and air-water slug flow in horizontal pipes. An experimental setup was fabricated to investigate the flow and heat transfer characteristics of air-oil and air-water slug flow under cooling conditions in horizontal pipes. The test section was made of a copper pipe with I.D. of 26 mm and a polyvinyl chloride pipe with I.D. of 63 mm using concentric geometry. The effect of flow parameters, such as liquid flow rate, gas flow rate, two-phase pressure drop multiplier, void fraction and slug frequency on heat transfer of gas-liquid slug flow was comprehensively investigated. The heat transfer coefficient of two-phase flow was significantly improved by the introduction of air and the maximum two-phase heat transfer enhancement ratio for air-water and air-oil flow were 150% and 300%, respectively. The circumferential temperature distribution and local heat transfer coefficient were also investigated. The local heat transfer coefficient at the bottom was around 25% higher than that at the top due to the uneven distribution of liquid and gas inside the pipe. Finally, a semi-empirical heat transfer correlation for gas-liquid slug flow was developed based on Reynolds and Chilton–Colburn analogies. The newly developed correlation predicts 96% of the present experimental two-phase heat transfer data within ±20% error and the mean relative deviations of the correlations are estimated to be -2.02% and +2.85% for Ref ≤ 2300 and Ref > 2300, respectively. This research helps researchers and engineers to better understand the heat transfer mechanism of gas-liquid slug flow.

Dialkyl dithiophosphates (DTP) are commonly used as primary or secondary collectors in base metal sulfide and platinum group mineral flotation. However, evidence in the literature suggests that, under basic conditions, DTP does not adsorb onto certain minerals. The purpose of this study was to investigate the interactions between DTP or xanthate collectors and frothers at the solid-liquid and air-liquid interfaces. Microflotation and contact time tests showed that DTP synergistically improved recoveries and attachment probabilities of galena and pyrite in the presence of frother. These improvements were not seen for any of the single reagents or, most importantly, for mixtures of a xanthate collector and frother. By measuring the residual collector concentration in solution, it was shown that no DTP adsorbed onto the galena surface and only minimal amounts onto the pyrite surface, either in the presence or absence of frother. In contrast, all of the xanthate collector adsorbed onto both pyrite and galena. Investigations at the air-water interface included surface tension and bubble size measurements. These showed that DTP, unlike xanthate, was weakly active at the air-water interface, but did not show evidence of synergistic interaction with frother. It was concluded that DTP can have an alternative mechanism of flotation enhancement to conventional collectors by adsorbing at the air-liquid interface and not the solid-liquid interface. Various theories of the detailed mechanism are discussed in the paper.

Low cost machining puts tremendous pressure on the research in machining hardened steel compared to traditional grinding. As environmental regulations are strict enough on application of cutting fluids, a novel method called spray impingement cooling (SIC) assisted hard turning has been studied. The current work explores the distinguish wear modes, surface characteristics, chip-tool interface temperature and chip morphology in turning of AISI D2 steel by coated carbide tools (TiN/TiCN/Al2O3/TiN). The results revealed the favorable chip tool interaction during machining in context to surface roughness, surface topology, flank wear, chip morphology, chip reduction coefficient and tool life. In the SIC, evaporation occurred due to atomization of water jet and sufficient to generate significant cooling as maximum temperature has been found as 200.6 0C. Modes of wear like abrasion, chipping and catastrophic breakage are noticed at tool-tip in hard turning. The optimal settings of parameters are founds as ap1-fn1-vc2 i.e. depth of cut-0.1 mm; feed-0.04 mm/rev; cutting speed-108 m/min. At these parametric conditions, the measured tool life is found as 20.3 minutes.

Considering the importance of two-phase flows in narrow rectangular channels and their use in various applications, the hydrodynamics of a co-current air-water two-phase flow in a vertical narrow rectangular channel has been studied. Experiments have been carried out and flow regime maps for vertical upward and vertical downward flows have been plotted based on measured data sets. Flow regimes were identified and classified based on visual observation and void fraction data. Flow visualization was performed using a high speed camera, while a void fraction analysis was done using the electrical impedance method and a digital image analysis. Four different flow patterns were identified for the vertical upward flow and seven flow patterns were identified for the vertical downward flow. The flow regime map for the vertical upward flow was compared with previous studies and also with the flow regime map obtained for the vertical downward flow in this study.

Novel air–water flow measurements were conducted in fully aerated hydraulic jumps with partially and fully developed supercritical inflow conditions. Irrespective of the inflow conditions, the hydraulic jumps resembled typical flow patterns with strong aeration and instabilities, albeit hydraulic jumps with fully developed inflow conditions had a more upward directed roller motion and a larger clear water core in the second half of the roller. Hydraulic jumps with fully developed inflow conditions had comparatively larger void fractions in the first half of the jump roller and larger bubble count rates throughout, while a comparatively larger number of smaller bubble sizes suggested a stronger break-up of bubbles. This was consistent with slightly larger interfacial velocities and turbulence intensities in the first half of the jump roller with fully developed inflow conditions. An assessment of the required sampling duration for air–water flow properties indicated the requirement to sample for at least five times longer than applied in previous studies. These results highlighted the need to carefully consider the inflow conditions and sampling parameters for aerated hydraulic jumps.

Corrugated pipes (CP) have regularly shaped and spaced cavities on their internal walls that can induce dynamic changes in the flow, such as increased pressure drops. Offshore petroleum production pipelines are an example of an industrial application of CPs, known as flexible lines. Slug flow is the most challenging flow pattern in those lines due to its complex hydrodynamics. A number of previous studies proposed correlations to predict the two-phase flow pressure drops in smooth pipes (SPs). However, limited researches have evaluated the pressure drops associated with liquid–gas slug flow in CPs. In this work, experiments to analyze the pressure drops in horizontal air–water slug flow under different configurations of CPs were carried out. The tests were performed in three different CP internal diameters (IDs) (26, 40, and 50 mm) with different cavity widths (1.2, 1.6, and 2.0 mm). The effects of the internal diameters and the cavity widths on the pressure drops associated with slug flow were analyzed. Results demonstrated that the pressure drops increase with increasing cavity widths. The experimental data were fitted and a pressure drop correlation using the concept of multiplier factor was proposed. Comparisons between predictions and the experimental data proved to be within ±10% accuracy.

The surfactant effect on ESP boosting pressure under air–water flow is studied in this paper. A two-phase flow loop comprising a 7.62 cm diameter stainless steel liquid loop and 1.25 cm diameter gas loop is built up to conduct experimental measurements. A radial-type ESP with 14 stages assembled in series is installed on the testing bench. Pressure ports are drilled at inter-stage to measure the stage-by-stage pressure increment. The surfactant, isopropanol (IPA) is injected to change the interfacial properties of working fluids. Experiments are carried out with mapping and surging test schemes to evaluate pump behaviors at different operational conditions. ESP pressure increment under single-phase water flow agrees well with the catalog curves. For mapping tests without surfactant injection, ESP performance suffers from a severe degradation as gas flow rate increases. High gas entrainment rate causes oscillations of liquid flow rate and pump boosting pressure, featured by the instabilities of ESP operations. A sudden drop of ESP pressure increment, termed as pressure surging, occurs at the critical inlet gas volumetric fraction (GVF). For a larger rotational speed, the critical GVF is higher. With surfactant injection, ESP boosting pressure improves significantly. At different GVFs, only mild degradation is observed. Pressure surging phenomenon disappears. Further, liquid flow rate and pump boosting pressure are more stable at high GVFs compared to experimental data without surfactant injection.

In order to develop detailed model of the annular two-phase flow the average liquid film thickness is an important parameter. It can significantly affect the occurrence of dryout and post-dryout phenomenon on heater surfaces. Most research on film thickness has been focused on pipe flows. Data in rod bundle geometry are very limited. However data in rod bundle geometry is much more valuable for reactor safety modeling and calculations. Because of this, an experiment to measure liquid film thickness has been performed for the air-water annular flow in a 8 × 8 BWR rod bundle. Film thickness data were obtained both on the rods and on the channel wall. Data were recorded at four axial locations within the rod bundle. This included locations just before and just after a spacer grid. This allowed the spacer grids effect on the film thickness to be evaluated. The minimum film thickness was on the center rod. Also, the presence of the spacer grid resulted in reduced film thickness.

This study performs experimental investigation on two-phase bubbly flow through 90° vertical elbows going from vertical-upward to horizontal and horizontal to vertical-downward orientations. The elbows have an inner diameter of 50.8 mm and a radius of curvature of 152.4 mm. A detailed database for local and global two-phase flow parameters in different flow orientations and across vertical elbows is established with a state-of-the-art four-sensor conductivity probe, a pressure transducer, and a high-speed video camera. The evolution of void fraction, interfacial area concentration, bubble velocity, and two-phase pressure drop along the axial development length in different orientations and across elbows are presented. It is observed that elbows create secondary flow and cause redistribution of the bubbles, which significantly affect the development of two-phase flow parameters. The effects occur across the elbows and remain for a significant length downstream. The effects on the void fraction distribution downstream of the elbow are discussed in detail for both elbow orientations. Characteristic differences in the elbow effects due to the elbow orientation are observed. For the vertical-upward elbow, a similar trend in the evolution of the void fraction distribution is observed for all flow conditions investigated while two different trends are observed downstream of the vertical-downward elbow. It is found that the effects of the vertical-downward elbow dissipate faster than that of the vertical-upward elbow. The elbow effects on interfacial area concentration, bubble velocity, and two-phase pressure drop are also discussed. The evolution of the interfacial area concentration is similar to that of the void fraction evolution in the straight pipe sections. However, it increases significantly across both elbows due to the promotion of the bubble breakup induced by the secondary flow. The void-weighted area-averaged bubble velocity is subject to significant changes across and immediately downstream of the elbows due to the redistribution of the bubbles. Additionally, the two-phase pressure gradients across the vertical-upward and vertical-downward elbows are approximately 1.5 and 2 times of that in the straight pipe sections.

This study adopted nanosecond laser to conduct drilling research on nickel-based alloy with thermal barrier coatings (TBCs). The experiments of different processing environments on quality and efficiency of laser drilling were conducted. Through combination of high processing efficiency under air environment and good processing quality under water environment, temporal control of air/water environment on laser drilling is proposed. Since drilling efficiency was not significantly reduced, cold machining effect of water was used to improve processing quality. Research results proved that laser processing method with temporal control of air/water environment has advantages of traditional laser drilling under air and water. Laser drilling of temporal control of air/water environment was improved in quality in comparison with single environment.

Downward co-current air–water flow through a 12 mm diameter tube has been investigated in an indigenously developed test facility having a typical fluid injection and mixing section. The flow has been characterized and the different regimes of the flow have been identified based on extensive analysis of high speed images. Some unique methods have been proposed for processing the images to establish objective ways for identifying the flow regimes considering different scales of the spatial co-ordinates. Several new flow regimes with intermittent behaviour have been observed, while the absence of churn flow is noted. A unique flow regime map pertinent to the present study has also been proposed.

This paper experimentally studied the features of air-water flow during the emptying of a water-filled prismatic tank with a bottom orifice under different conditions. The experiments were conducted with both circular and elliptical orifices, with and without ventilation. The evolution of bubbles, water pressure variation, and water level change with time were recorded in the experiments and analyzed. Based on the results, the evolution of bubbles could be mainly divided into three stages of formation, deformation, and decomposition. Ventilation was found important to the emptying process, with which the drainage efficiency was much higher than that under the unventilated condition. Additionally, under the unventilated condition, the drainage efficiency with the circular orifice was slightly higher than that with the elliptical orifice.

Scaling of the lift reversal for a deformed bubble in the surface tension-inertial force dominant regime was discussed. Lift data of bubbles in water recently reported in literature were used. The negative lift component was well correlated in terms of the drag coefficient, which, in turn, implies that the vorticity produced at the bubble surface plays a key role in both drag and lift forces as is the case with the viscous force dominant regime. The scaling was confirmed to give good evaluations of the lift coefficients.

Experiments of air-water-oil three-phase flow pattern is investigated in a 20 mm diameter inclined pipe with a length of 6 m using a high speed digital camera. The superficial velocities are in the range of 0.25–3 m/s, 0.25–2.3 m/s, and 0.08–13 m/s for water, low viscosity oil and air, respectively. For describing flow patterns in three-phase flow, two parameters are considered: Interaction of gas and liquids mixture, and interaction of water and oil phases. The flow patterns for different pipe angles are discussed. Observed flow patterns are stratified-oil/water (or water/oil), wavy-stratified-o/w, bubbly-o/w, slug-o/w, plug-o/w, plug-stratified and annular-o/w. Major flow patterns for upward and downward pipe are slug-o/w and wavy-stratified-o/w, respectively. Also the effects of inclination angle varying from −45° to +45° and different oil cuts on flow patterns have been studied. The results show that by increasing the oil cut for different inclination angles, bubbly region extends and plug region becomes smaller.

Experiments on the total gas holdup, α G , in air–water cylindrical bubble columns were carried out to investigate effects of the column diameter, D H , and the initial liquid height, H 0 , on α G . Ranges of D H and H 0 were 160 ⩽ D H ⩽ 2000 mm and 400 ⩽ H 0 ⩽ 4000 mm, respectively. The superficial gas velocity, J G , was varied from 0.025 to 0.35 m/s. The characteristics of gas holdup showed that all the flows in the present experiments were pure heterogeneous. The following conclusions were obtained for α G in air–water bubble columns: (1) the effects of D H and H 0 on α G are negligible when scaling up from small to large bubble columns, provided that α G in the small columns are obtained for D H ⩾ 200 mm and H 0 ≳ 2200 mm. The height-to-diameter ratio is useless in evaluation of the critical height, above which α G does not depend on H 0 , (2) for the above ranges of D H and H 0 , Akita-Yoshida’s and Koide’s correlations can give good evaluations of α G for a wide range of J G by tuning the model constants, (3) for D H D H increases the population of large bubbles, which results in the decrease in α G , and (4) for H 0 ≲ 2200 mm and D H ⩾ 200 mm, α G at a constant J G decreases with increasing H 0 and approaches an asymptotic value, and the Froude number using J G and H 0 as the characteristic scales well correlates α G in this regime.

Self-propulsion of magneto-elastic composite microswimmers is demonstrated under a uniaxial field at both the air-water and the water-substrate interfaces. The microswimmers are made of elastically linked magnetically hard Co-Ni-P and soft Co ferromagnets, fabricated using standard photolithography and electrodeposition. Swimming speed and direction are dependent on the field frequency and amplitude, reaching a maximum of 95.1 μm/s on the substrate surface. Fastest motion occurs at low frequencies via a spinning (air-water interface) or tumbling (water-substrate interface) mode that induces transient inertial motion. Higher frequencies result in low Reynolds number propagation at both interfaces via a rocking mode. Therefore, the same microswimmer can be operated as either a high or a low Reynolds number swimmer. Swimmer pairs agglomerate to form a faster superstructure that propels via spinning and rocking modes analogous to those seen in isolated swimmers. Microswimmer propulsion is driven by a combination of dipolar interactions between the Co and Co-Ni-P magnets and rotational torque due to the applied field, combined with elastic deformation and hydrodynamic interactions between different parts of the swimmer, in agreement with previous models.

International audience; A two-phase liquid pumping test ring is built to study the flow induced characteristics of centrifugal pump under the air-water flow working condition. Pump performances are measured under different flow rates and different inlet air void fraction (a). Pressure pulsation signal spectrums and their probability density maps are also recorded. The calculations, using URANS k-epsilon turbulence model combined with the Euler-Euler inhomogeneous two-phase model, are also performed to obtain inner flow structure inside the impeller and volute channels under different air-water conditions in order to understand the pump characteristic evolutions. The results show that the performance of centrifugal pump is more sensitive to air inlet injection at low flow rates. The maximum air void fraction of model pump could reach 10% when the pump operates at the highest efficiency point, and the performance drops sharply when the air void fraction is more than 8%. The dominant frequency of pump outlet pressure pulsation is still at the blade passing frequency even under two-phase condition. Frequency amplitude increases with the increase of a. The greater the a, the more low frequency appears in broadband characteristics. With the increase of a, the probability density amplitude of pressure pulsation decreases gradually, and its span becomes gradually wider as well. Comparisons between numerical local results, experimental unsteady pressure can explain part of the phenomena that are found in the present paper.

This paper focuses on liquid-phase turbulence measurements in air-water two-phase flows over a wide range of void fractions and flow regimes, spanning from bubbly, cap-bubbly, slug, to churn-turbulent flows. The measurements have been conducted in two test facilities, the first one with a circular test section and the second one with a rectangular test section. A particle image velocimetry-planar laser-induced fluorescence (PIV-PLIF) system was used to acquire local liquid-phase turbulence information, including the time-averaged velocity and velocity fluctuations in the streamwise and spanwise directions, and Reynolds stress. An optical phase separation method using fluorescent particles and optical filtration technique was adopted to extract the liquid-phase velocity information. An image pre-processing scheme was imposed on the raw PIV images acquired to remove noise due to the presence of bubble residuals and optically distorted particles in the raw PIV images. Four-sensor conductivity probes and high-speed images were also used to acquire the gas-phase information, which was aimed to understand the flow interfacial structure. The highest area-averaged void fraction covered in the measurements for the circular and rectangular test sections was about 40%.

The shape of elongated bubbles in upward inclined air-water slug flow was studied experimentally by quantitative measurements of the cross sectional distribution of the phases within the pipe, using a wire mesh sensor. Ensemble-averaged shapes of elongated bubbles were determined for a wide range of gas and liquid flow rates, as well as for different pipe inclination angles. The elongated bubble nose can be characterized by an annular domain where liquid is present above the gas. The effect of gas and liquid flow rates, as well as of the pipe inclination angle on the bubble shape (front and tail) is studied. A simplified theoretical model is proposed to determine the bubble front shape. The model predictions compare favorably with the experimental results.

为实现发动机的水空两用，提出了一种新型的多涵道水空两用发动机概念设计。在建立了初步的三维有限元模型的基础上，重点对水中模式的工作情况进行了分析计算，初选金属钠作为水反应燃料，得到了燃料流量、燃烧室压强、推力的变化关系及燃料流量和比冲的变化关系，初步确定了燃料流量的适宜范围，肯定了水中工作条件下的推进效果。使用CFD软件对金属水反应冲压发动机的参数设计进行了模拟分析，确定了最有利于金属水反应和水冲压发动机推进效果的参数选择。初步评定新型水空两用发动机达到了设计目的。 In order to realize the air-water engine, a new multi-bypass amphibious engine conceptual design is proposed. The situation of air mode is analyzed briefly based on the establishment of a three dimensional finite element model. The situation of water mode is analyzed and calculated, and determines the metal sodium as the fuel of the reaction of metal and water. The relationships of fuel flow, combustion chamber pressure, thrust, fuel flow rate and specific impulse are obtained. The suitable range of fuel flow rate is preliminarily determined and the effect of propulsion of water mode is affirmed. The simulation of the design parameters of the metal-water reaction engine is conducted with CFD software. The parameter which is the most advantageous to metal- water reaction and the propulsion effect of the metal-water reaction engine is determined. Preliminarily evaluating the design goal of the new air-water engine is achieved.

This paper focuses on investigating the dynamic behaviour of foam flows, including flow regimes, their transitions and pressure profiles in relation to foam characteristics (foam holdup and wetness) at different surfactant concentrations (0–500 ppm). The experiments cover a wide range of gas and water flowrates in a 4.3 m long vertical acrylic pipe with 44 mm internal diameter. Flow regimes and their underlying mechanisms are characterised through Power Spectral Density analysis of the associated pressure fluctuation signals, collected at 100 Hz frequency. A flow map is developed for foam flow in a vertical pipe based on the gas and liquid Webber numbers, representing different flow regimes. The results from this study reveal that, even at small concentrations, the surfactant attenuates flow fluctuations, as observed in the pressure data, resulting a relatively uniform flow compared with air-water flows. The results also indicate the promoting effect of surfactant on the flow transition from churn to annular flow at much lower gas velocities compared to air-water flows. The flow transition from slug to churn and churn to annular in foam flows is shown to be associated with an increase in foam wetness. The lowering effect of surfactant on the pressure gradient is most pronounced at lower gas rates. Increasing the gas rate in the foam flow encourages bubble breakup, leading to the formation of a denser foam, composed of smaller bubbles carrying more liquid in the lamella of the foam network. This therefore leads to a higher pressure gradient at higher gas rates.

The paper presents the study of experimental as well as the numerical study of air-water mist jet impingement cooling over a heated cylinder in the non-boiling region. The studies are conducted for various mist loading fraction, f = 0.0025, 0.0050, 0.0075 and 0.01; Reynolds number, Remix.=8000, 10,500, 13,000 and 15,500; and surface-to-nozzle spacing, H/d = 30, 40, 50 and 60. Enhancement in the heat transfer (η) for mist jet impingement as compared to air jet impingement is obtained from experimental and numerical analysis. The numerical study also helped in understanding the distribution and tracking of droplets in the computational domain. High enhancement in the heat transfer is observed with high mist loading fraction. Also, the lowest Reynolds number yielded the highest enhancement in heat transfer with comparison to the higher Reynolds number. At various surface-to-nozzle spacing, the enhancement in heat transfer is high for low surface-to-nozzle spacing near the stagnation zone to a certain point, after which point the enhancement reverses as higher enhancement in heat transfer is observed for high surface-to-nozzle spacing. As high as 408% and 775% enhancement in the heat transfer at the stagnation point is observed for f = 0.01, Remix.= 8000and H/d = 30 during experimental and numerical analysis respectively. The correlation has been proposed to estimate the enhancement in heat transfer at the stagnation point.

Annular flow with swirl induced by a swirler has been widely used in industry. Swirl decay which closely related to working performance and length of the flow is significantly important for its application in industry. Axial development of annular flow with and without swirl has been investigated in this work by means of experimentation and modelling. A vertical pipe system with 11 m long and 62 mm inner diameter was carried out to investigate axial development of flow pattern, void fraction and pressure drop in the annular flow with and without swirl. The experimental results show that a swirling annular flow with swirling streak and less disturbed waves is observed downstream of the swirler. Void fraction decreases, total pressure drop increases and the PDF (probability density function) of pressure drop becomes more concentrated in the annular flow with swirl, compared with these in the annular flow without swirl. However, swirling annular flow is gradually transformed to annular flow without swirl along the streamwise direction. To qualitatively predict the decay in an annular flow with swirl, a simplified theoretical model was developed here. The results calculated with the theoretical model were in agreements with experimental results. The obtained results can be used in predicting working performance and length of devices, such as separators and heat exchangers.

Stratified gas–liquid flow is a flow regime typically encountered in multiphase pipelines. The understanding and modeling of this regime is of engineering importance especially for the oil and gas industry. In this work, simulations have been conducted for stratified air–water flow in pipes. We solved the Reynolds-averaged Navier–Stokes (RANS) equations with the volume of fluid (VOF) method. The aim of this work was to evaluate the performance of the k–ω shear stress transport (SST) turbulence model with and without damping of the turbulence at the gas–liquid interface. Simulation results were compared with some of the latest experimental results found in the literature. A comparison between the simulated velocity and kinetic energy profiles and the experimental results obtained with the particle image velocimetry (PIV) technique was conducted. The characteristics of the interfacial waves were also extracted and compared with the experiments. It is shown that a proper damping of the turbulence close to the interface is needed to obtain agreement with the experimental pressure drop and liquid hold-up. In its current form, however, RANS with the k–ω turbulence model is still not able to give an accurate prediction of the velocity profiles and of the interface waves.

Hydraulic jumps are characterized by strong flow turbulence, flow aeration, and three-dimensional flow motions. Whereas comprehensive research into hydraulic jumps on smooth bed has improve...

Although chute aerators have been investigated experimentally by many researchers, only a few studies have been conducted on the comprehensive air–water flow properties of the lower jet dow...

For the previous experiments of entrainment at T-junction, the air–cold water two-phase flow is always selected as working medium, and the theoretical models of liquid entrainment are established mainly based on the experimental data of air–water entrainment through a small break. The saturated steam–water entrainment experiments are gravely insufficient, especially the steam–water experiments of entrainment through a large size branch are even fewer. Hence, a scale-down experiment of steam–water entrainment at T-junction has been conducted referring to liquid entrainment through ADS-4 (Fourth Stage Automatic Depressurization System) in AP1000 nuclear plant. The steam–water experimental results are comprehensively compared with the results of the previous similar air–water experiment: The visualization research shows that the same entrainment phenomena can be observed including intermittent flow entrainment, stratified flow entrainment and annular flow entrainment; The transition conditions between the two entrainment phenomena have a little difference but can be negligible; The comparison of experimental data of entrainment onset and stable entrainment indicates that the experimental data of steam–water and air–water have the same change tendency, and the air–water correlation can agree well with the steam–water data. Hence, we can make a conclusion that effect of different working mediums on liquid entrainment is negligible. In addition, based on the analysis of model formation, we suppose that effect of the system pressure on entrainment can be neglected under 0.22 MPa.

Experimental investigations on the characteristics of air–water two-phase flow in the vertical helical rectangular channel are performed using the high speed flow visualization. The flow pattern map and the transition in the helical rectangular channel are presented. The flow pattern evolution in different positions of the helical rectangular channel is illustrated. The discussion on the coalescence of the bubble and slug is presented. The slug velocity, slug length distribution, liquid slug frequency, falling liquid film velocity and falling film thickness along the slug are investigated. The dimensionless liquid film thickness of the annular flow on the outer side of the channel is measured using the digital image processing algorithm.

To obtain the phase fraction and velocity of vertical air-water two-phase flows, an electromagnetic flowmeter with two arc-shaped electrodes is proposed. The electromagnetic flowmeter is operated in two measuring modes: electrical measurement mode and electromagnetic measurement mode. The geometry of the electromagnetic flowmeter for dual-parameter measurement is optimized based on the numerical finite element analysis. The electric field and sensitivity distribution of the electromagnetic flowmeter is investigated to ensure an accurate measurement of volume fraction under the mode of the electrical measurement. Weight function of the electromagnetic flowmeter operated under the mode of the electromagnetic measurement is also analyzed for the velocity measurement. Preliminary experiments are conducted to calibrate the optimized electromagnetic flowmeter in simulated air-water flows. It is noted that the proposed electromagnetic flowmeter with arc-shaped electrodes can be adopted to obtain the phase fraction and velocity of vertical air-water two-phase flows.

In this work, the influence of surfactants on air–water flow was studied by performing experiments in a 12 metre long, 50 mm inner diameter, vertical pipe at ambient conditions. High-speed visualisation of the flow shows that the morphology of the air–water interface determines the formation of foam. The foam subsequently alters the flow morphology significantly. In annular flow, the foam suppresses the roll waves, and a foamy crest is formed on the ripple waves. In the churn flow regime, the flooding waves and the downwards motion of the liquid film are suppressed by the foam. The foam is transported in foam waves moving upwards superposed on an almost stagnant foam substrate at the pipe wall. Foam thus effectively reduces the superficial gas velocity at which the transition from annular to churn flow occurs. These experiments make more clear how surfactants can postpone liquid loading in vertical pipes, such as in gas wells.

Air–water adiabatic upward flows were measured in seven parallel microchannels. The total mass velocity was adjusted to 50, 100, 200 and 300 kg/m 2 s. Superficial air velocities ranging from 0.16 to 41.70 m/s were applied for each mass velocity. The superficial water velocity ranged from 0.005 to 0.30 m/s in order to maintain the mass velocity constant. A gas quality of up to 0.90 was obtained. The visualizations showed different flow configurations in each microchannel, although approximately homogeneous conditions were verified in the inlet manifold for single-phase flows. For the same time step, single-phase regimes (only liquid or only gas) were simultaneously obtained together with two-phase flow patterns (annular, bubbly, slug and churn, and their transitions) at each microchannel. The variety of single-phase and two-phase flow configurations was also observed for different time steps at the same microchannel. The Mishima and Ishii (1984) flow pattern map for single microchannels was reassessed with parallel flows. For quality over 0.08 and mass velocity over 100 kg/m 2 s annular flow patterns are predominant. This corresponds approximately to superficial gas and liquid velocities over 10 and 0.1 m/s, respectively, at the inlet manifold. For other inlet conditions there are miscellaneous flow configurations. Similarities to results of Nino (2002) indicate that the current analysis can be extended to air–water horizontal flows or to microchannels with other cross-sectional geometries if the hydraulic diameter is kept at around 1 mm.

This work concerns the modelling of stratified two-phase turbulent flows with interfaces. We consider an equation for an intermittency function α ( x , t ) which denotes the probability of finding an interface at a given time t and a given point x . In Waclawczyk and Oberlack (2011) a model for the unclosed terms in this equation was proposed. Here, we investigate the performance of this model by a priori tests, and finally, based on the a priori data discuss its possible modification and improvements.

International audience; We study how confinement affects the viscous spatio-temporal instability of a two-phase mixing layer. We show that the absolute instability triggered by the inclusion of finite liquid and gas thicknesses leads to a good prediction of experimental data. In addition, this new mechanism provides a justification for the relevance of both simplified inviscid scaling laws and more sophisticated viscous approaches.

Investigations of hydraulic operating conditions of air lift pump with three types of air-water mixers. The paper presents the analysis of results of the investigations concerning the influence of various constructive solutions of the air-water mixers on hydraulic operating conditions of the air lift pump. The scope of the investigations encompassed the determination of characteristics of delivery head and delivery rate for three types of air-water mixers applied in the constructed air lift pump. Using the obtained results, the efficiency of the three types of air-water mixers applied in this air lift pump was determined. The analysis was carried out and there was checked whether the improved analytical Stenning-Martin model can be used to design air lift pumps with the air-water mixers of these types. The highest capacity in the water transport was reached by the air lift pump with the 1st type air-water mixer, the lowest one – with the 3rd type air-water mixer. The water flow in the air lift pump increases along with the rise in the air flow. The lower are the hydraulic losses generated during flow of the air flux by the air-water mixer, the higher is the air lift pump capacity. Along with the rise in the water delivery head, the capacity of the air lift pump decreases. The highest efficiency is reached by the air lift pump with the 1st type air-water mixer, the lowest – with the 3st type air-water mixer. The efficiency of the air lift pump for the three investigated types of air-water mixers decreases along with the rise in air flow rate and water delivery head. The values of submergence ratio (h/L) of the delivery pipe, calculated with the use of the improved analytical Stenning-Martin model, coincide quite well with the values of h/L determined from the measurements.

In this study a methodology is applied to quantify the effect of evaporator maldistribution on operating costs of air–water heat pumps. The approach is used to investigate the cost-effectiveness of two technologies enabling to counteract maldistribution: a flash gas bypass setup and the individual superheat control in parallel evaporator channels. In the total cost of ownership analysis, different scenarios for climatic conditions, severity of maldistribution, and economic framework are considered. Results show that the flash gas bypass system is cost-effective only in a few conditions, namely severe maldistribution, high electricity prices, and colder climate. Investment in the individual superheat control technology, however, can be quickly amortized in many scenarios. For the warmer climate zone with a small number of operating hours counteracting of maldistribution does not pay off under the used economic assumptions.

The hazard of oil contamination in sewage detection has drawn great attention and gives rise to some technical difficulties for pipe inspection applications using robots. In the attempt to face this challenge, a magnetically controlled micro-robot model was designed to allow it to move directionally on oil-contaminated water. In this design, magnetically responsive mesh supports were used; moreover, these were required to float at air/water and oil/water interfaces. Optimal analysis of force shows the importance of superhydrophobicity for the floatability of mesh supports at these two interfaces. Accordingly, mesh surfaces were decorated to produce superhydrophobicity by a simple fluorination process. A superhydrophobic mesh was experimentally verified to freely float at both interfaces, providing a large supporting force to improve its floating stability. Guided by a magnetic field, the micro-robot model with mesh supports could float, move and rotate at air/water and oil/water interfaces in a closed system. Therefore, our findings could offer guidance for the design of aquatic micro-devices to detect sewage in bent or small-sized pipes.

Two-phase flows across tube bundles are very commonly found in industrial heat exchange equipment such as shell and tube heat exchangers. However, recent studies published in the literature are generally performed on devices where the flow crosses the tube bundle in only a vertical or horizontal direction, lacking geometrical fidelity with industrial models, and the majority of them use air and water as the working fluids. Also, currently, experimental approaches and simulations are based on very simplified models. This paper reports the simulation of a laboratory full-scale tube bundle with a combination of vertical and horizontal flows and with two different baffle configurations. Also, it presents a similarity analysis to evaluate the influence of changing the fluids to hydrogen and diesel in the operational conditions of the hydrotreating. The volume of fluid (VOF) approach is used as the interface phenomena are very important. The air/water simulations show good agreement with classical correlations and are able to show the stratified behavior of the flow in the horizontal regions and the intermittent flow in the vertical regions. Also, the two baffle configurations are compared in terms of volume fraction and streamlines. When dealing with hydrogen/diesel flow using correlations and maps made for air/water, superficial velocity is recommended as similarity variable when a better prediction of the pressure drop is needed, and the modified superficial velocity is recommended for prediction of the volume-average void fraction and the outlet superficial void fraction.

Several simple ways of improving the accuracy of Spalding model predictions over common textbook conventions for air/water evaporation/condensation problems are illustrated using open-literature examples. First is the choice of thermodynamic reference state for enthalpy evaluation. The common practice of choosing the steam table reference point (0.01 °C) with water-vapor enthalpy of hfg (2501 kJ/kg) and air enthalpy of zero introduces an enthalpy mismatch between air and water vapor that unnecessarily compromises accuracy. Choosing the air/water interface temperature as the reference point and setting both air and water-vapor enthalpies at this point to the same numerical value gives the most accurate results of several methods tried. Second is judicious choice of the blowing factor in high-rate mass transfer situations. The laminar boundary layer blowing factor is more accurate than the common stagnant-film (Couette flow) blowing factor for flat-plate flow and may be more accurate for a cylinder in crossflow under laminar conditions, as illustrated by the example of air leak effect on steam condenser tube performance. Third is radiation modeling, often a problematic or ignored feature in this type of problem. Two common, but opposite, assumptions about radiation participation in water—transparent interface and opaque interface—are shown to be equivalent for most purposes. A methodology is introduced for modeling true interfacial absorption/emission associated with phase change if/when the amount of this effect becomes known well enough to justify its inclusion. The importance of including radiation is illustrated by several examples: cloud droplet evaporation–condensation, sweat cooling, and the wet-bulb psychrometer. Fourth is inaccuracy introduced by unnecessarily setting Lewis number to unity.