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In the modern aerospace industry, the importance of a lubrication system is self-evident for aero-engines, and the aero-engine bearing chamber return line is an even more challenging environment, as it involves a complex two-phase flow. The designer of the scavenge pipe needs to have an accurate understanding of the flow conditions in the scavenge pipe. This paper establishes a visual scavenge pipe test system. The flow direction was vertical flow, the test temperature was 370 k, and a high-speed camera was used to take high-definition flow photographs, which can observe the three main flow types: bubble flow, slug flow, and annular flow. Code program was created to analyze many pictures taken to obtain the apparent flow rate and perimeter of bubbles in the pipe under different flow conditions and to explore the gas–liquid two-phase flow in the scavenge pipe. A support vector machine (SVM) was used for data regression prediction, and the converted velocities of the gas–oil phases were inputted as eigenvalues to obtain the predicted values of bubble-flow velocity. The bubble-flow analysis prediction model established in this paper has a good prediction effect with root mean square error RMSE = 0.0172, which can more objectively and accurately describe the bubble-flow characteristics in the scavenge pipe. [ABSTRACT FROM AUTHOR]

Copyright of Atomic Energy Science & Technology is the property of Editorial Board of Atomic Energy Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper discusses the extension of an optical liquid film thickness measurement technique to characterize liquid film flow rate in wavy thin liquid film flow. The technique, based on laser refractometry, is used to measure wave height, shape, frequency, and velocity. A two-zone model to process the measured wave characteristics is used to estimate the liquid film flow rate. The method is validated in a falling film facility where easy optical access allows comparisons of the wave velocity measurements with high-speed videos and where the calculated liquid film mass flow rate can be compared with actual measurements. The paper provides a framework for analyzing time-resolved film thickness data using multizone models in more complex liquid film flows, such as in two-phase annular flow. [ABSTRACT FROM AUTHOR]

In this paper, the gas–liquid two-phase flow within a Tesla valve under zero-gravity conditions is numerically studied. Based on the VOF model and the inlet two-phase separation method, the forward and reverse flow patterns and pressure drop changes in a Tesla valve at different inlet velocities were analyzed. At an inlet velocity of 0.1–0.2 m/s, the flow pattern was slug flow, the bubbles were evenly distributed in different positions in the Tesla valve, and the velocity difference between the main pipe and the arc branch pipe was small. When the inlet velocity was 0.4 m/s, the main flow pattern was annular flow, and there was a phenomenon of gas–liquid phase separation through different flow channels, which was related to centrifugal force. At an inlet velocity of 0.6–0.8 m/s, bubbly flow and slug flow coexisted, which was related to the uneven velocity. In the study range, the difference in the forward and reverse pressure drops of two-phase flow was smaller than that of single-phase flow, and the two-phase diodicity decreased first and then increased with the change in inlet velocity, reaching minimum values of 0.78 at 0.2 m/s and 1.44 at 0.8 m/s. [ABSTRACT FROM AUTHOR]

Gas flexible pipes are critical multi-layered equipment for offshore oil and gas development. Under high pressure conditions, small molecular components of natural gas dissolve into the polymer inner liner of the flexible pipes and further diffuse into the annular space, incurring annular pressure build-up and/or production of acidic environment, which poses serious challenges to the structure and integrity of the flexible pipes. Gas permeation in pipes is a complex phenomenon governed by various factors such as internal pressure and temperature, annular structure, external temperature. In a long-distance gas flexible pipe, moreover, gas permeation exhibits non-uniform features, and the gas permeated into the annular space flows along the metal gap. To assess the complex gas transport behavior in long-distance gas flexible pipes, a mathematical model is established in this paper considering the multiphase flow phenomena inside the flexible pipes, the diffusion of gas in the inner liner, and the gas seepage in the annular space under varying permeable properties of the annulus. In addition, the effect of a variable temperature is accounted. A numerical calculation method is accordingly constructed to solve the coupling mathematical equations. The annular permeability was shown to significantly influence the distribution of annular pressure. As permeability increases, the annular pressure tends to become more uniform, and the annular pressure at the wellhead rises more rapidly. After annular pressure relief followed by shut-in, the pressure increase follows a convex function. By simulating the pressure recovery pattern after pressure relief and comparing it with test results, we deduce that the annular permeability lies between 123 and 512 mD. The results help shed light upon assessing the annular pressure in long distance gas flexible pipes and thus ensure the security of gas transport in the emerging development of offshore resources. [ABSTRACT FROM AUTHOR]

Understanding droplet sizes is crucial for modeling gas–liquid annular flow and has many applications across various industries. This paper presents a comprehensive review and analysis of experimental data on droplet-size characteristics in gas–liquid annular flow from the open-source literature. The existing models for droplet-size predictions are evaluated against experimental data. Based on the data analysis, we propose two new correlations to predict the maximum droplet diameter and Sauter mean droplet diameter. Model evaluation and parametric study show that the new correlations capture the effects of fluid properties and flowing conditions on the droplet diameters well, outperforming other existing models. The average absolute relative errors are reduced to 14.8% and 29% for the maximum droplet diameter and the Sauter mean droplet diameter, respectively. [ABSTRACT FROM AUTHOR]

Coalbed methane (CBM) is an increasingly important unconventional natural gas. Production logging can provide important information about the production status of each layer in a CBM well, which is crucial for developing and adjusting development plans. However, currently, only open-hole logging is done for CBM wells, and there is no mature technology for production testing of wells that produce low amounts of gas. To address this issue, a new method has been proposed in this paper for measuring the production profile of CBM wells. This method is based on the pressure difference method and measures the gas–liquid two-phase flow in a 125 mm vertical rising circular tube. The researchers established a simulation model of the CBM wellbore pressure difference method and obtained four flow patterns: bubble flow, slug flow, churn flow, and annular flow. We studied the relationship between the pressure difference and gas and water flow rates at different positions and spacing between measuring points in the wellbore. A differential pressure flowmeter without a throttling device was developed, and gas–liquid dynamic experiments were carried out through a simulation experiment platform to verify the feasibility of the flowmeter. Two well field tests were conducted in Shanxi CBM fields using differential pressure flowmeters, which accurately and quantitatively measured the stratified gas production of CBM wells. This technology can help improve the productivity and development efficiency of CBM wells. [ABSTRACT FROM AUTHOR]

This paper considers the movement of an incompressible non-Newtonian Walters' B liquid within a rotating annulus. The flow lies within porous media and is magnetized by a uniform normal magnetic field. Mass transmission is included in the arrangements of homogeneous and heterogeneous chemical reactions (HHCR) with a thermal diffusion effect. Heat diffusion is exposed with a temperature- dependent heat source (THS) and an exponential radial-dependent heat source (ERHS), besides Joule heating and viscous dissipations. The mathematical construction is shown by momentum, energy and concentration of chemical materials equations along with time-periodic boundary conditions. The innovation of this study stems from considering mass transfer utilizing HHCR, with thermal diffusion effects in the flow within a rotating annulus, trying to understand the effect of these reactions on the flow and related applications. The principal regulating the structure of nonlinear partial differential equations is transferred by ordinary ones utilizing appropriate similarity analysis. These equations are analyzed by the homotopy perturbation method. Subsequently, the analytical solutions of the main profiles are obtained, and a graphical construction is established to clarify the effects of the relevant physical elements. It is observed that the velocity waves decrease with annulus width enlargement and increase with the wave phase amplitude. With an increase in all significant parameters, heat transmission gets better. Furthermore, as the strength of HHCR is increased, the concentration of molecules decreases. These outcomes are significant in several applications like cancer therapy, biochemical manufacturing purposes through reactors, where biochemical interactions can be regulated by accurate control of various parameters. [ABSTRACT FROM AUTHOR]

Modern laver fluffiness is achieved by applying high-speed gas to a laver, which is generated by the opening and closing of a laver fluffiness control valve in a fluffiness system. To address the problems of the slow response speed and poor stability of valves used in the laver processing industry at present, this paper proposes a novel principle of a high-speed switching control valve, which has the advantages of a fast response speed, high stability, and long service life. The structure and working principle of the control valve are introduced, and the calculation equation of the valve's flow area is established. The flow field inside the control valve with different openings was numerically calculated in this study using Fluent. The flow regulation characteristics and flow field performance of the control valve were also analyzed. The results show that, with an increase in the valve opening, the influence of the flow area at the valve throttle on the valve flow rate was weakened. When the valve was opened, a vortex appeared in both the upper and lower cavities, and jet flow occurred at the throttle of the middle flow channel. As the valve opening increased, the pressure in the upper cavity reduced, while the pressure in the lower cavity increased. The vortex in the flow field intensified, and the jet phenomenon at the valve throttle gradually disappeared. At the same time, the main stream in the lower cavity gradually changed from an annular flow to a direct flow toward the valve outlet. Furthermore, the impact, collision, and vortex formation of the fluid caused energy loss of the fluid, leading to a decrease in the outlet flow of the control valve. [ABSTRACT FROM AUTHOR]

Based on the differential quadrature procedure (DQP), the vibrational response of functionally graded (FG) sandwich annular plates enhanced with graphene platelets (GPLs) and with an FG porous core is illustrated in this paper. The current annular plate is assumed to deform axisymmetrically and expose to a radial magnetic field. The Lorentz magnetic body force is deduced via Maxwell's relations. The effective physical properties of the upper and lower layers of the sandwich plate are obtained by employing the Halpin–Tsai model. Our technique depends on a new four-unknown shear deformation theory to depict the displacements. In addition, the motion equations are established via Hamilton's principle. The motion equations are solved by employing the DQP. In order to study the convergence of the DQ method, the minimum number of grid points needed for a converged solution is ascertained. In addition, the current theory's outcomes are compared with those of previous higher-order theories. The effects of the porosity distribution type, porosity factor, GPLs distribution pattern, GPLs weight fraction, inner-to-outer radius ratio, outer radius-to-thickness ratio, magnetic field parameters, core thickness, and elastic substrate parameters on the nondimensional vibration frequencies are discussed. [ABSTRACT FROM AUTHOR]

This paper investigates non-invasive techniques for annular two-phase flow analysis, focusing on liquid film characterization to understand the interfacial phenomena that are crucial for heat and mass transfer. Limited methods allow the study of the temporal and spatial evolution of liquid film, such as Planar Laser-Induced Fluorescence (PLIF). However, this method possesses optical challenges, leading to the need for improved techniques to mitigate refraction and reflection, such as Refractive Index Matching (RIM). This study utilizes an experimental annular flow facility to analyze both RIM and non-RIM PLIF over a range of liquid Reynolds numbers from 4200 to 10,400. Three configurations—PLIF RIM90, PLIF RIM40, and PLIF nRIM40—are compared from both qualitative and quantitative perspectives. In the quantitative analysis, key variables of the liquid film are measured, namely mean film thickness, disturbance wave height, and frequency. Variations in the analyzed variables indicate minor deviations, which are not likely to be caused by the technique used. However, all three methodologies exhibited errors that are estimated to be within a maximum of 10%, with a mean value of approximately 8%. [ABSTRACT FROM AUTHOR]

A hydro-dynamic thermal fully developed forced convective heat transfer analysis of magneto-hydrodynamics fluid flow through an annular sector duct is presented in this paper. Two types of thermal boundary conditions i.e., axially uniform heat flux along with peripherally uniform temperature (known as H1-condition) and, axially and peripherally uniform temperature (known as T condition), have been considered to carry out the thermal analysis of fluid. The velocity components along r and θ direction are transformed into algebraic form by using power law discretized scheme, whereas cross-sectional pressure P (r , θ) is estimated with the help of well know technique S I M P L E R. The governing partial differential equations are solved by numerically with the help of M A T L A B code. Furthermore, simulated results have been compared with the existing results of literature to validate the results. From the results, it is noted that hydro-dynamically and thermally impacts relate directly by increasing the Hartman number, (M). It is further reported that the effect of magnetic field becomes insignificant for the higher number of fins, N. The findings of the present analysis will be applicable in various types of thermal systems. [ABSTRACT FROM AUTHOR]

It is of great significance to explore the flow velocity characteristics of piped cars when they are started under different loads. In this paper, the flow velocity characteristics of the water flow around a piped car when it is started in the straight pipe section are studied through physical experiments. The masses of the piped cars are 1.5 kg, 1.9 kg, and 2.3 kg, respectively. The results show that, with the increase in the load of the pipeline car, the axial flow velocity in the front section increases, the absolute values of radial flow velocity and circumferential flow velocity increase, and the gradient of flow velocity increases. The positive radial flow velocity and negative circumferential flow velocity regions increase, and the distribution of positive and negative radial flow velocities and circumferential flow velocities is obvious. The gradients of axial, radial, and circumferential flow velocities in the annular section all increase, and the contour spacing becomes smaller and more densely distributed. The absolute values of the radial and circumferential flow velocities increase. The regional demarcation of axial flow velocity in the rear section is more obvious, and the average value of axial flow velocity in the high-flow-velocity area behind the vehicle increases. Additionally, the gradient of flow velocity increases. The absolute values of radial velocity and circumferential velocity increase, the gradient of velocity increases, and the velocity distribution is obviously regional. This study supplements and improves the theoretical study of a piped car when it is started and has certain reference value for the research and application of the hydraulic transport technology of the barrel-loading pipeline. [ABSTRACT FROM AUTHOR]

This paper analyzes the developing adiabatic two-phase flow after an expansion valve in an air conditioning system. R245fa and POE 32 mixture is used as the working fluid. The developing two-phase flow patterns are visualized in an 8 mm straight tube after the expansion valve from 15 to 595 mm. To explore the effect of fluid properties on the developing two-phase flow, the experimental results from previous research by the same authors are compared with those of R245fa in this paper. An image analysis technique and a one-dimensional developing two-phase flow model proposed in a previous paper by the same authors (Yao & Hrnjak, 2023c) are applied to both R134a and R245fa. The flow patterns near the expansion valve exhibit some similarities when comparing the two refrigerants. However, a significant contrast emerges in the presence of a greater number of droplets suspended within the vapor phase in the case of R245fa flow. This disparity is primarily attributed to R245fa's higher vapor velocity. Furthermore, R245fa exhibits a shorter developing length than R134a. For fully developed flow, R245fa showcases a more pronounced turbulent behavior, and the transition to annular flow happens at a lower vapor quality in comparison to R134a. All of these distinctions can be adequately accounted for by the proposed model. The developed flow patterns of both refrigerants are compared with some existing flow pattern maps. At last, a new flow pattern map is proposed based on the observed flow patterns in this research. [ABSTRACT FROM AUTHOR]

Interactions of heat transfer enhancement and fouling can occur due the change in nature of the surface, operating condition, or the fluid itself. Interactions arising relating to higher clean heat transfer coefficients, and higher wall shear stresses of the enhanced surfaces are discussed in this paper. On the lab-scale, enhancement was often achieved by static elements, such as wire wrapping on a heated rod in an annular flow. Lab-scale tests of necessity suffered from effects of relatively short duration of runs, and re-circulation of a batch of liquid with the danger of changing the fluid composition during experiment. Nevertheless, initial fouling rate results consistent with expected trends could be achieved for hydrocarbon fouling, and particulate fouling. There is a continued need to better represent and compare performance of plain and enhanced surfaces over prolonged operating periods in industrial heat exchangers, using commercial enhancement technologies. Example case studies are discussed which demand different methods of comparing performances. A daily averaged cost analysis is identified as a possible systematic approach on the evaluation of the economic benefit of the use of enhancement devices. This is illustrated for a case study example where tube insert is used as an enhancement option. [ABSTRACT FROM AUTHOR]

The unsteady flow field in the aerostatic bearing always induces micro-vibrations, which are severely detrimental to the stability and precision of the bearing. Extensive research has been conducted on the mechanism of micro-vibration, but a consensus has not yet been reached. To this end, the large eddy simulation (LES) and proper orthogonal decomposition methods were employed to analyze the flow field of an annular aerostatic bearing in this paper. A mechanism for inducing micro-vibration and the identification of a novel flow behavior were ultimately revealed. First, the accuracy of our LES method has been validated through quantitative comparison with experimental data. Then, the mode decomposition has been conducted to analyze the flow field under various gas supply pressures. The results demonstrate that when the supply pressure Ps = 0.4 MPa, the micro-vibration is dominated by a pair of adjacent large-scale vortices with low frequencies in the recess. However, when Ps = 0.5 and 0.6 MPa, the convection and shearing processes near the orifice outlet and the rectangular recess inlet become intense, resulting in the displacement of large-scale vortices. Eventually, the small-scale high-frequency pressure fluctuation structures have been also observed, which are closely related to the convection process within recess. With the increase in gas supply pressure, the high-frequency pressure fluctuations at the circular recess outlet gradually diminish, while those at the orifice outlet emerge and gradually enlarge. Meanwhile, the mode dominant frequency is transferred from around 200 kHz to around 1000 kHz. The energy fraction of the high-frequency pressure fluctuations is also greatly increased. [ABSTRACT FROM AUTHOR]

The current paper presents a theoretical analysis of swirl flow stability, both inside a tube (vortex tube) and in a free annular swirl flow. The starting concept is the study of the evolution of velocity and temperature fluctuations. Methods of non-equilibrium thermodynamics are used to describe the magnitude of fluctuations and their properties. The important role of the total enthalpy follows from a variational analysis. Moreover, the thermodynamic criterion of the stability is formulated using the total enthalpy, and compared with experiments, numerical results and classical Rayleigh theory support its applicability. It was shown that the solid body vortex is at the margin of stability, which is experimentally observed. Analogously, the potential vortex is by the thermodynamic criterion stable; however, by the Rayleigh criteria it is on the onset of stability. The classical Taylor experiment of flow between two rotating cylinders is analysed from the point of view of this criterion. These results are underlined by swirl tube experiments at the Institute of Aerospace Thermodynamics at Stuttgart University and the annular nozzle experiments performed in the Institute of Thermomechanics CAS in Prague. Both independent experiments confirm the transformation of the initial annular vortex into a stable potential-type vortex. The results of this theory can also be used to explain the exceptional stability of tropical cyclones. [ABSTRACT FROM AUTHOR]

A horizontal smooth copper tube and two enhanced tubes (a dimpled tube and a diamond-shaped tube) with a length of 2 m and an outer diameter of 9.52 mm were studied in a two-phase condensation experiment using R410A and R32 as heat transfer working fluids. The condensation heat transfer performance of different heat transfer tubes at various mass fluxes ranging from 150 to 400 kg/(m²s) and different vapor qualities ranging from 0.8 to 0.2 was studied experimentally. For R410A, the heat transfer coefficients (HTCs) of the dimpled tube and the diamond-shaped tube were found to be 1.39-1.52 times and 1.30-1.35 times higher than those of the smooth tube, respectively. For R32, the HTCs were found to be 1.46-1.59 times higher for the dimpled tube and 1.26-1.35 times higher for the diamond-shaped tube than for the smooth tube. The diamond-shaped tube was found to be effective in directing the flow of the liquid phase and in thinning the liquid film thickness. The dimpled tube was found to promote droplet entrainment and disturbance. Both of those effects contributed to improving the HTCs in the two enhanced tubes investigated. The HTCs of R410A were found to be lower than those of R32 because of the smaller specific heat capacity, smaller latent heat of condensation, and relatively poorer thermal conductivity of R410A. Taking the combined effect of heat transfer and pressure drop into account, a performance enhancement factor (PEF) was computed and was found to range from 0.9 to 1.51. Based on the experimental data collected, a new empirical correlation equation has been proposed with a maximum error band of 10%. Flow pattern maps for the tested tubes have also been generated and are presented in the paper. Both of the two enhanced tubes were found to promote the development of annular flow. The HTCs were found to be highest when the flow pattern was of the annular flow type. [ABSTRACT FROM AUTHOR]

The aim of this paper is to propose an efficient numerical scheme to deal with heat transfer problems in pipe flow with a large length/diameter ratio. The generalized finite difference method (GFDM) is combined with a space stepping algorithm (SSA) for the solution. The SSA divides the solution domain into a number of overlapping sections in the length direction of the pipe. Due to the large Peclet number, the heat transport process is dominated by advection, which allows an approximate boundary condition to be applied at the downstream cross section. The problem is then solved section by section. Using the uniform distributed points, the solution matrix for each section does not change, and only the right hand side needs to be refreshed for the changing boundary conditions. This leads to a highly efficient scheme for problems with a large pipe length. To show the accuracy of the numerical scheme, a problem with available analytical solution is studied. Then the method is applied to problems of single pipe with different pipe wall temperature and flow Reynolds number, and concentric annular pipe. Numerical results confirm the stability and efficiency of the GFDM-SSA. The method can be applied to many real world transient heat transfer problems in which the pipe is heated or cooled along its length with arbitrary wall temperature for heat exchange and other purposes. [ABSTRACT FROM AUTHOR]

The reliable design of multiphase micro‐structured apparatus requires a precise knowledge of the internal flow regime. Previous research indicated that classifiers based on artificial neural networks (ANN) are relatively simple to develop and provide a reasonable accuracy when trained with data for specific inlet designs. This paper introduces advanced ANN classifiers capable of predicting all relevant flow regimes regardless of the inlet design with a recall of 94 % and above for Taylor, churn, dispersed, rivulet, and parallel flows, between 89 % and 94 % for annular and bubbly flows, and 83 % for Taylor‐annular flow. These classifiers were trained and validated by using more than 13,000 experimental data points extracted from 97 flow maps. [ABSTRACT FROM AUTHOR]

Electrical Capacitance Tomography (ECT) is one of typical tomography technologies based on capacitance-sensitive fields, which can reconstruct the distribution images of permittivity distribution of different fluid in the measured field and is often used for realizing industrial detection in specific occasions. Landweber and homotopy perturbation regularization algorithms are used for image reconstruction in ECT system, but these algorithms are with many iteration steps, slow convergence speed, and relatively low quality of the reconstructed images. Aiming at these problems, this paper proposes an improved image reconstruction algorithm. Firstly, a regularization term is added to the target function by using the different dielectric constant distribution between the current moment and the previous moment. Then, using the homotopy perturbation to derive the second-order iterative formula to get the homotopy perturbation regularization algorithm, and finally the improved algorithm is obtained by combining the landweber algorithm based on weight factor. Furthermore, the improved homotopy perturbation regularization algorithm is applied for ECT image reconstruction. The numerical simulation experiment results show that the improved algorithm is with the highest comprehensive scores for the four flow patterns of laminar flow, annular flow, core flow and bubble flow, which is higher than the landweber algorithm and the improved homotopy perturbation regularization algorithm by 3% ~ 20%, and 18% ~ 31%, respectively. The relative error, correlation coefficient and subjective effect of the reconstructed image are significantly improved, and it has certain anti-noise performance. These reflect the improved algorithm is with practical value. [ABSTRACT FROM AUTHOR]

Air entrainment is a concern of paramount importance in the process industries, including nuclear power plant, hydraulic machines, water treatment plants, hydrocyclones, and power generation turbines. The ingression of the air into the equipment results in the reduction of the hydraulic efficiency. In the current paper, a combined experimental and numerical investigation has been performed using the commensurate high-speed photography and volume of fluid-based numerical simulations. The mitigation strategies for the reduction of the air ingression include the reduction of the critical height by increasing the number of intakes and changing the intake configuration. The viability of these solutions and the hydrodynamics behind the interfacial evolution leading to the air entrainment have been studied in detail. The air ingression progresses with the establishment of the flow patterns ranging from bubbly flow, slug flow, to the annular flow. The reduction of the critical height can be accomplished by increasing the number of intakes for the same cross-sectional area leading to the reduction in the Froude number F r = V down / g H local < 1 . Further increasing the number of intakes beyond four leads to the minimal reduction in the critical height in the tank. [ABSTRACT FROM AUTHOR]

In this paper, fully developed forced convective flow properties of hybrid nanofluid through annular sector duct are discussed. The studies of hybrid nanofluid, i.e. the combination of a nanofluid (nanoparticles plus water) with another nanoparticles' volume fraction, are considered. Hybrid nanofluids become most important due to enhancement in the heat transfer rate. Copper oxide (CuO)–water is taken as the nanofluid. The volume fraction of CuO nanoparticles in water is kept fixed at 4%, whereas the volume fractions of Cu nanoparticles are taken in the range of 0–4% in this study. Under the assumption of hydrodynamically and thermally fully developed flow, the deviation in the velocity components along the axial direction vanishes in the case of momentum equations; however, the deviation in the temperature becomes constant in the case of energy equation. After dimensionless analysis, the finite volume method is applied to find the numerical solutions for velocity, temperature, heat transfer rate and fanning friction factor. During physical analysis, it has been concluded that the percentage enhancement in heat transfer rate is comparably more than fanning friction factor when we increase the volume fraction of Cu nanoparticles in the CuO–water nanofluid. Furthermore, the same observation has been noticed in the case of heat transfer rate when the platelet shape factor of the nanoparticles has been used instead of brick and cylinder shape factors. Increase in fRe is 8.01% when we increase the Cu nanoparticles' volume fraction from 1% to 4%, whereas the increments in Nu are 15.09%, 18.56% and 20.81% for the brick-, cylinder- and platelet-shaped nanoparticles, respectively, for all values of the ratio of radii, R ̂ , and apex angle, 2 α , in both thermal cases. [ABSTRACT FROM AUTHOR]

• Experimentation on flow condensation inside newly fabricated micropillar tube is detailed. • Heat transfer coefficient and pressure drop for micropillar, microfin and smooth tubes are compared. • Fluidics behind enhancement of heat transfer using structures are described. • Prevailing flow regimes inside all the tube types are briefly dicsussed. • Performance analysis for all the enhanced tubes are reported. This paper presents an experimental investigation for evaluation of heat transfer coefficient, frictional pressure drops and flow regimes with their transitions during the condensation of R-134a inside a smooth, two microfins (MF1 and MF2) and a newly developed micropillar (MP) tubes. The experiments are carried out for a range of mass flux at an average saturation temperature of 35°C. Micropillar tube has produced the maximum heat transfer coefficient, while the microfin (MF1) tube resulted the highest frictional pressure gradient compared to other tubes. The experimental observations of microfin and micropillar tubes are plotted on the mass flux versus vapor quality flow map and Taitel and Duckler flow map to discuss the transitions within different flow patterns achieved. Visual inspection of the flow regimes with varying mass flux and vapor quality showed stratified-wavy, intermittent, and annular flow regimes. The occurrence of annular flow is found to be more in MF1 and MP tube. A performance evaluation factor (PEF) is defined to evaluate the thermal-hydraulic performance of the tubes. Using the same, it has been observed that the newly developed MP tube has a PEF value greater than unity which suggest augmentation of heat transfer coefficient at the expense of lesser pressure drop penalty. [ABSTRACT FROM AUTHOR]

This paper presents an experimental investigation of heat transfer coefficient and dryout inception during flow boiling of R134a in a circular channel with an internal diameter of 500 μ m for horizontal, 45° inclined, and vertical upward flows. The microchannel was heated by imposing the wall temperature by flowing hot water counter-currently to the test fluid through an annular region containing the test section. Experiments were performed for mass velocities ranging from 350 to 600 kg/(s·m2), heat fluxes up to 46 kW/m2, saturation temperature of 30 °C, and vapor qualities from 0 to 1. The experimental data were parametrically analyzed, and the effects of the experimental parameters (heating method, mass velocity, heat flux, and channel orientation) were identified. Almost similar heat transfer behaviors were found under conditions of imposing wall temperature and heat flux through the Joule effect. The effect of the flow orientation on the heat transfer coefficient prior to the dryout inception was negligible. The heat transfer coefficient increases with increasing vapor quality, heat flux, and mass velocity. The critical heat flux exhibited similar values independently of the flow orientation. Moreover, the critical heat fluxes increases as the dryout inception vapor quality reduces, regardless of the flow orientation. [ABSTRACT FROM AUTHOR]

Copyright of Atomic Energy Science & Technology is the property of Editorial Board of Atomic Energy Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this paper, an improved probability model is introduced to provide a more comprehensive prediction of annular flow. Unlike previous work, which did not consider atomization and deposition, as well as breakup and coalescence, simultaneously, the improved model integrates all four processes into its framework. The mechanisms of these processes are described in detail by the present model. When annular flow is fully developed, the four processes reach dynamic equilibrium. A numerical program is compiled based on the influence of the four processes on the droplets. Five important parameters, including the droplet-diameter probability density distribution, characteristic droplet diameters, entrainment ratio, liquid film thickness, and interfacial shear-stress coefficient, are calculated when the annular flow is in dynamic equilibrium. The validity and accuracy of the improved model are assessed by comparison with 377 cases from 12 experiments. For most cases used to validate the predicted droplet-diameter probability density distribution, the prediction curves closely match the experimental data. The mean absolute percentage errors (MAPEs) for the two experiments used to validate the predicted characteristic droplet diameters are 20.74% and 24.04%, respectively. Additionally, the mean MAPEs of the entrainment ratio, liquid film thickness, and interfacial shear-stress coefficient are found to be 34.11%, 20.60%, and 27.28%, respectively. This demonstrates the effectiveness and reliability of the improved probability model in predicting annular flow. [ABSTRACT FROM AUTHOR]

Recently, aortic valve stenosis has received more attention, and its pathophysiology may be connected to persistent inflammation caused by micro-organisms. This paper investigates the transient electroosmotic hybrid nanofluid (blood model) flow in the annular region between the axially symmetric mild stenosis and the catheter tube. The non-Newtonian Sutterby fluid has been considered as a blood model due to the migration of gyrotactic micro-organisms in the bloodstream. The hybrid nanofluid consists of the suspension of the solid nanoparticles of the (Ag–Al 2 O 3 ) in pure human blood. The problem is simplified using the mild stenosis procedure and solved numerically utilizing the finite difference technique. It is observed that more effort is required to pump the blood in the case of the suspended hybrid nanoparticles than with suspended nanoparticles. Moreover, the results demonstrate that hybrid nanoparticles have better thermal properties than nanoparticles. [ABSTRACT FROM AUTHOR]

This document is a special issue dedicated to Professor John Richard Thome on his 70th birthday. It contains nine articles written by his former colleagues and friends from various countries, covering topics such as green hydrogen energy systems, two-phase flows, and heat transfer. Professor Thome is a renowned expert in the field and has made significant contributions through his research, teaching, and engineering applications. He has published numerous papers and authored several books. The document also provides information about Professor Thome's background, career, and achievements. [Extracted from the article]

When the elongated bubbles and liquid slugs of slug flow alternately flow through a throttling element, the strong random fluctuations of pressure difference leads to low accuracy of online measurement of gas-liquid flow rates. In this paper, slug flow is converted into an annular flow before entering a venturi tube using a swirler, and the pressure fluctuation amplitude of the gas-liquid two-phase flow is greatly reduced, and the linear correlation between the pressure difference and the gas-liquid flow rates is more significant. The effects of gas-liquid flow rates on the axial pressure difference Δ P s across the swirler, the radial pressure difference Δ P r on a cross-section downstream of the swirler and the axial pressure difference Δ P o of the venturi tube were studied under the condition of 40%–82% gas volume fraction. The square root of the pressure difference increases linearly with the liquid/gas flow rate, and the empirical correlations between the square root of the pressure differences and the gas-liquid flow rates are established. By combining the empirical correlations in pairs, three flow rates measurement models of slug flow based on double pressure differences are established. When Δ P o and Δ P s are used as the measurement parameters of flow rates, the relative errors of liquid-phase flow rate and gas-phase flow rate are below ±2% and ±15%, respectively. When Δ P o and Δ P r are used as the measurement parameters of flow rates, the relative errors of liquid-phase flow rate and gas-phase flow rate are below ±3% and ±15%, respectively. It provides high-precision, low-cost and non-radioactive two-phase flow measurement technology for oil-gas gathering and transportation. • Gas-liquid flow rates are measured using a venturi tube with a swirler. • Linear correlations between pressure difference and flow rates are established. • Flow rates measurement models of slug flow are established. • Prediction accuracies of liquid and gas flow rates are below ±2% and ±15%. [ABSTRACT FROM AUTHOR]

• LN 2 flow boiling in a 10 mm horizontal tube at low pressure is studied. • Stratified and wavy flow and its transition to annular flow were observed. • Oscillations of parameters in plug and slug flow are studied. • Thermal oscillation shows a strong relationship with the flow patterns. Liquid nitrogen holds significant importance in high-temperature superconductivity. This study experimentally investigates the saturated flow boiling of liquid nitrogen in a horizontal macro-tube with an inner diameter of 10 mm. The experiments cover the following ranges: inlet gauge pressure from −31.0 to 2.5 kPa, mass flux from 27.0 to 71.3 kg/(m2·s), heat flux from 0 to 28.68 kW/m2, and vapor quality from 0 to 1. In the initial segment of the study, this paper concentrates on flow patterns, two-phase flow instability, and pressure drop. Flow patterns are identified by analyzing temperature distributions along the tube and oscillations of operating parameters. The two-phase flow patterns mainly comprise bubbly flow, plug and slug flow, stratified flow and wavy flow, annular flow, mist and vapor flow. Annular flow tends to occur under negative pressure due to the increased vapor velocity resulting from decreased vapor density. Oscillations are observed in plug and slug flow, with the pressure drop and wall temperature displaying a small period and a strong relationship. The oscillations in pressure drop and wall temperature are linked to the periodic formation and release of large bubbles in plug and slug flow. Thermal oscillation exhibits a strong correlation with flow patterns. For vapor quality less than 0.2, the amplitude of wall temperature oscillations is larger, attributed to the occurrence of plug and slug flow. The experimental data of the total pressure drop are compared with predicted values from the homogeneous and separated flow models. The separated flow model provides a more accurate prediction, with a Mean Relative Error (MRE) of 39 % within the present experimental range. [ABSTRACT FROM AUTHOR]

During the drilling of ultra-deep wells, gas kick often occurs, influenced by the complex void pressure profile. The accurate description of particle settling behavior in the gas–liquid mixture is of great significance to effectively deal with gas kicks and ensure drilling safety. In this study, the gas–liquid two-phase annulus flow with different gas volume fractions is created through the transparent annular pipe, constant pressure air pump, and gas flowmeter. High-speed photography is used to record and analyze the sedimentation of particles in gas–liquid mixtures. This study is based on 288 tests. The main parameters in this experiment include the particle Reynolds number, the gas fraction, and liquid viscosity. The effects of wall and gas fraction on the drag coefficient were analyzed. The correlation of particle terminal settling velocity was established. The results obtained show a correlation with average absolute errors (AAE) of 10.7%. This study reveals the settling characteristics of particles in the annular gas–liquid mixed flow, provides an accurate terminal settling velocity prediction explicit formula, and provides guidance for the calculation of bottom hole pressure under the condition of gas kick. [ABSTRACT FROM AUTHOR]

This study investigates the electro-osmotic flow of a biological fluid (blood with varying cholesterol levels) in annular flow to simulate a first approximation to arterial occlusion. The fluid´s rheology is characterized by amulti-modal convectedMaxwell model equation. The charge density follows the Boltzmann distribution, governing the electrical field. Mathematically, this scenario can be modeled by the Poisson–Boltzmann partial differential equation. Assuming a small zeta potential (less than 25mV) using the Debye–Huckel approximation and considering a pulsatile electrical field, analytical solutions are derived using the Fourier transform formalism. These solutions, expressed in terms of the modified Bessel function, provide transfer functions for axial velocity and volumetric flow as functions of material parameters represented by characteristic dimensionless numbers. This study further analyzes thermal, electric, inertial, viscoelastic, and various interactions within the plasma, hematocrit, hematocrit–cholesterol, and cholesterol–cholesterol as well as weight concentration through numerical simulations. Finally, the flow and rheology predictions are validated using experimental data on human blood with varying cholesterol levels. The obtained transfer functions reveal that the electric–thermal–viscoelastic effects and the multiple geometric relationships contribute to the dynamic response of the interactions between the input electrical field and output volumetric flow and shear stress functions, leading to and evolution of resonance curves. It is noteworthy that electro-osmotic flow in blood with pathologies associated with low and high cholesterol has been scarcely reported in the literature on rheology. Thus, this work represents a significant contribution to the field. [ABSTRACT FROM AUTHOR]

In horizontal annular flow, the high gas velocity leads to the strong randomness, rapidity and complexity of the structure and dynamic characteristics of gas-liquid interfacial wave. As one of the important parameters to describe the interfacial wave, the liquid film thickness is significant to study the hydrodynamic characteristics of the gas-liquid two-phase flow. In this paper, the ultrasonic echo resonance main frequency (UERMF) method and the ultrasonic reference signal elimination (URSE) method are compared by numerical simulation method. The minimum liquid film thickness measured by these two methods are 0.3 mm and 0.01 mm, respectively. Experiments are conducted on a stainless steel test section with an inner diameter of 50.0 mm to study annular air-water flow under five different pressure conditions (from 0.1 MPa to 0.7 MPa). The experimental data is processed using the URSE method to analyze the characteristics of the liquid film under different operating conditions. In addition, based on the aforementioned experimental dataset, a comparison is made regarding the performance of existing predictive correlations. It is found that the existing correlations have certain limitations in capturing the variations of liquid film thickness in annular flow, particularly at high pressures and for different pipe diameters. Therefore, a new liquid film thickness correlation suitable for different system pressures and pipe diameters is proposed. By expanding the range of fitted data points (220 data points), the 95 % relative error of improved model is within ±25 % error band for all available data (authors' and literature). The mean absolute percentage error (MAPE) is 11.08 %. The improved correlation has the applicability and extrapolation for different system pressure and pipe diameter conditions. • Numerical simulations confirm higher accuracy of URSE method. • Experiments under different pressures are conducted in horizontal annular flow. • Experimental results are compared and analyzed with existing predicted correlation. • A liquid film thickness correlation under different pressure and diameter is proposed. • The new model is validated by comparing with real flow experimental data. [ABSTRACT FROM AUTHOR]

Slug flow is widely existed in power engineering, petrochemical industry, nuclear engineering and other fields, and the study of two-phase flow gas slug parameters plays a key role in the precise control of industrial processes. According to the electromagnetic wave propagation theory, considering the cross-correlation algorithm and power spectral density (PSD) principle, a new double embedded U-tube electromagnetic wave phase sensor is designed to build a gas slug parameter measurement system for gas-liquid slug flow. A phase difference model is proposed to measure the velocity of the gas slug, and the mean absolute percent error (MAPE) of the model is 5.35%, with the 87% relative error are within ±10% error band. Experiments are conducted at 70 operating points for the gas-liquid slug flow pattern to predict the gas slug frequency. The PSD function is used to solve for the peak gas slug frequency to obtain the gas slug frequency prediction model for the gas-liquid slug flow. Laboratory results indicate that the MAPE of the model is 14.07%, the 85% relative error are within ±20% error band. In this paper, three literature data are selected to compare with the prediction results of this model, and the MAPE of the Strouhal-Froude (St-Fr) predictive model is 35.51%, 4.78%, and 19.16%, respectively, with a total MAPE of 19.87%, and 90.91% of the literature data are within ±30% error band. The results indicate that the St-Fr model based on gas/liquid superficial velocity has wide applicability in predicting gas slug frequency within the selected data range. And further research is needed on the applicability of the Strouhal-Froude model to other pipeline diameters, gas superficial velocities, and liquid superficial velocities. • A new double embedded U-tube electromagnetic wave phase sensor is designed. • The parameters are calculated according to the cross-correlation and power spectral density principle. • Based on the Strouhal-Froude model, a gas slug frequency prediction model is proposed. • The mean absolute percent error of the model is 14.07%. [ABSTRACT FROM AUTHOR]

Conventional conductivity methods for measuring the void fraction in gas-liquid multiphase systems are typically affected by accuracy problems due to the presence of fluid flow and salinity. This study presents a novel approach for determining the void fraction based on a reciprocating dynamic conductivity probe used to measure the liquid film thickness under forced annular-flow conditions. The measurement system comprises a cyclone, a conductivity probe, a probe reciprocating device, and a data acquisition and processing system. This method ensures that the flow pattern is adjusted to a forced annular flow, thereby minimizing the influence of complex and variable gas-liquid flow patterns on the measurement results; Moreover, it determines the liquid film thickness solely according to circuit connectivity rather than specific conductivity values, thereby mitigating the impact of salinity. The reliability of the measurement system is demonstrated through laboratory experiments. The experimental results indicate that, in a range of gas phase superficial velocities 5–20 m/s and liquid phase superficial velocities 0.079–0.48 m/s, the maximum measurement deviation for the void fraction is 4.23%. [ABSTRACT FROM AUTHOR]

The effective determination of pressure losses depends on accurate knowledge of the drilling fluid rheology. As the fluid circulates deeper around the wellbore, its rheological behavior undergoes significant alterations due to the variations in downhole conditions encountered. The present study investigates the effects of the rheological properties of Yield-power law fluid at various pressures and temperatures on annular pressure losses and velocity profiles. Simulations were performed using Computational Fluid Dynamics to examine the fluid flow in turbulent and laminar regimes. Comparison between numerical, experimental and slot approximation model results showed a good agreement. Results indicated that pressure losses have reduced in both regimes with increasing temperature, at a constant pressure. However the pressure has the opposite effect at a constant temperature. For a drilling fluid flow velocity of 1 m/s, the elevation of temperature from 25 °C to 90 °C, decreases the pressure drop gradient by (31% to 48%) at low and high- pressure conditions respectively. Whereas, the influence of increasing pressure on pressure losses is more apparent at 25 °C. Earlier transition from laminar to turbulent is observed with temperature rise. Therefore, the temperature effect on pressure losses in the turbulent region; is shown for different Generalized Reynolds numbers. [ABSTRACT FROM AUTHOR]

A high-speed backlight system was adopted to investigate the evolution process of the inside-out-gas (IOG) effervescent atomizer and subsequent influence on spray morphology. The results show that bubble flow and annular flow are the most obvious flow patterns when the liquid flow rate is 20 g/s. During the transition from bubble to annular flow, slug flow occurred at gas–liquid mass ratio (GLR) of 3.2%. The annular flow was observed when the GLR further increased to 6.4%. In particular, when the mixing chamber is in a large bubble flow, an annular flow can still be formed at the orifice for the small exit diameter. For the annular flow, a relatively stable spray cone angle was observed. On the contrary, the slug flow has a greater oscillation for the spray cone angle. It was found that bubble flow in the orifice has little effect on atomization effect. For the spray cone angle, the oscillation in the slug flow is larger. Furthermore, the effects of GLR and liquid injection pressure drop are carefully considered in the empirical formula fitting compared to the widely used empirical formula. The empirical formula of the discharge coefficient of the effervescent atomizer is fitted, which provides fast data support for engineering applications. [ABSTRACT FROM AUTHOR]

The aim of this article is to introduce a novel approach to identifying flow regimes and void fractions in microchannel flow boiling, which is based on binary image segmentation using digital image processing and deep learning. The proposed image processing pipeline uses adaptive thresholding, blurring, gamma correction, contour detection, and histogram comparison to separate vapor from liquid areas, while the deep learning method uses a customized version of a convolutional neural network (CNN) called U-net to extract meaningful features from video frames. Both approaches enabled the automatic detection of flow boiling conditions, such as bubbly, slug, and annular flow, as well as automatic void fraction calculation. Especially CNN demonstrated its ability to deliver fast and dependable results, presenting an appealing substitute to manual feature extraction. The U-net-based CNN was able to segment flow boiling images with a Dice score of 99.1% and classify the above flow regimes with an overall classification accuracy of 91%. In addition, the neural network was able to predict resistance sensor readings from image data and assign them to a flow state with a mean squared error (MSE) < 10−6. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of the present study is to develop a new numerical framework that can predict the supersonic base flow more accurately, including the development of axisymmetrically separated shear layer and recompression shock. To this end, two aspects are improved and combined, i.e. a newly self-adaptive turbulence eddy simulation (SATES) turbulence modeling method and a high-order discretization numerical scheme. Furthermore, the performance of the new numerical framework within a general-purpose PHengLEI software is assessed in detail. Design/methodology/approach: Satisfactory prediction of the supersonic separated shear layer with unsteady wake flow is quite challenging. By using a unified turbulence model called SATES combining high-order accurate discretization numerical schemes, the present study first assesses the performance of newly developed SATES for supersonic axisymmetric separation flows. A high-order finite differencing-based compressible computational fluid dynamics (CFD) code called PHengLEI is developed and several different numerical schemes are used to investigate the effects on shock-turbulence interactions, which include the monotonic upstream-centered scheme for conservation laws (MUSCL), weighted compact nonlinear scheme (WCNS) and hybrid cell-edge and cell-node dissipative compact scheme (HDCS). Findings: Compared with the available experimental data and the numerical predictions, the results of SATES by using high-order accurate WCNS or HDCS schemes agree better with the experiments than the results by using the MUSCL scheme. The WCNS and HDCS can also significantly improve the prediction of flow physics in terms of the instability of the annular shear layer and the evolution of the turbulent wake. Research limitations/implications: The small deviations in the recirculation region can be found between the present numerical results and experimental data, which could be caused by the inaccurate incoming boundary layer condition and compressible effects. Therefore, a proper incoming boundary layer condition with turbulent fluctuations and compressibility effects need to be considered to further improve the accuracy of simulations. Practical implications: The present study evaluates a high-order discretization-based SATES turbulence model for supersonic separation flows, which is quite valuable for improving the calculation accuracy of aeronautics applications, especially in supersonic conditions. Originality/value: For the first time, the newly developed SATES turbulence modeling method combining the high-order accurate WCNS or HDCS numerical schemes is implemented on the PHengLEI software and successfully applied for the simulations of supersonic separation flows, and satisfactory results are obtained. The unsteady evolutions of the supersonic annular shear layer are analyzed, and the hairpin vortex structures are found in the simulation. [ABSTRACT FROM AUTHOR]

A ship is affected by the transient ocean motion during navigation, and the two-phase flow is often in a transient motion state. The two-phase flow pattern may be different from the land-based conditions, which may affect the flow and heat transfer characteristics. Therefore, it is significant to accurately distinguish the two-phase flow pattern under transient motion conditions for the calculation of two-phase resistance and heat transfer. In this paper, by using a separated flow model, the momentum equations for the liquid film and gas core of annular flow were listed separately. Meanwhile, based on introducing the transient external force field generated by the motion under two typical ocean motion conditions of rolling and heaving and considering the effects of buoyancy and additional inertial forces, a transition criterion which was suitable for churn flow to annular flow under transient motion conditions was also proposed. This criterion can also be applied to vertical upward and inclined flows. The calculation results of the transition criterion model were verified through experimental data under static and transient motion conditions, and there is good agreement with the experimental results. The results show that when the superficial liquid velocity is less than 0.35 m/s, the transition curve approximates a vertical curve, while the superficial liquid velocity is larger than 0.35 m/s, the thickness of the liquid film increases, and the axial motion of the liquid phase plays a major role in the flow pattern transformation. Similarly, by comparing the calculation results of the transition from churn flow to annular flow under different motion conditions with experimental data, it can be found that within the existing parameter range, the additional force introduced by rolling motion has little effect on the continuous gas phase at the center of the channel. Therefore, although the thickness distribution of the liquid film on the wall is uneven due to the influence of rolling motion, the annular flow structure will not be damaged, and the transition curve between churn flow and annular flow is basically consistent with the vertical upward direction. Moreover, with the increase of the heaving amplitude and the decrease of the heaving period, the transition boundary curve of the churn flow towards the annular flow shifts to the right. This is because the additional acceleration introduced by the heaving increases, and the liquid film is subjected to instantaneous volume force in the vertical direction and oscillates periodically, making it easier to fall. Therefore, a larger gas phase apparent velocity is required to maintain a stable annular flow, so the transition boundary shifts to the right. By analyzing the transition criteria, a churn flow to annular flow transition curve is given, and the influence of motion parameters on the transition boundary is obtained.

• The visualization of nitrogen-based capillary PHP is studied. • Bubbly flow, slug flow, churn flow, and annular flow are observed in nitrogen PHP. • Cryogenic PHPs are easy to form annular flow and circulation flow. • The coupling relationship between heat transfer and flow is investigated. This paper presents the results of a visualization study of a cryogenic pulsating heat pipe (PHP). The impact of radiation heat leakage was reduced by minimizing optical windows. Visual images of the adiabatic section of a 2-turn PHP with nitrogen as working fluid were obtained at a filling ratio of 50 % and an inclination angle of 90°. The lengths of the evaporator, adiabatic section, and condenser were 50 mm, 100 mm, and 50 mm, respectively. The adiabatic section was made of quartz, whereas the evaporator and condenser were made of stainless-steel capillaries soldered onto copper plates. The flow channel of PHP was 1 mm. The fluid characteristics of the PHP under quasi-steady state conditions at different heat inputs were captured using a high-speed camera. Based on the experimental results, the evolution of flow patterns and fluid motion characteristics, and the coupling relationship between flow and heat transfer were illustrated and discussed. [ABSTRACT FROM AUTHOR]

• A novel in-focus criterion with gray-level gradient for droplets image extraction. • Simultaneous acquisition of droplet size, velocity, and concentration with vortex. • The coupling mechanism between droplets and vortex has been discussed. • When φ l < 0.03, droplet velocity PDF shows double peaks downstream the bluff body. • The increase in φ l from 0.03 to 0.041 deteriorated the vortex signal quality. Annular mist flow widely exists in natural gas and other engineering fields. Vortex flowmeter has gradually become an effective means of wet gas measurement. However, the droplets in the flow field will influence the stability of the vortex. In this paper, the interaction between droplets and vortex was studied by experiments. A novel in-focus criterion was proposed to improve the accuracy of droplet measurement. Simultaneous acquisition of droplet size, velocity, and concentration was achieved. The spatial evolution of droplet parameters was obtained to determine the position where the droplets were evenly distributed. The bidirectional coupling mechanism between droplets and vortex was studied. Firstly, the influence of the vortex flow field on droplets was reflected by the characteristics of droplet distribution around the bluff body. Secondly, the effect of droplets on the vortex signal in the flow field was analyzed based on Stokes number St p and liquid-phase load φ l. When φ l < 0.03, the probability distribution of droplet velocity downstream of the bluff body presents double peaks. The exchange momentum between the small droplets and the vortex is stronger, and vice versa for the larger droplets. Finally, the quality factor of vortex signals decreases from −2.09 to −2.18 with the increase in the volume concentration of droplets. It is further demonstrated that the increase in volume concentration of droplets will destroy the vortex structure and degrade the quality of the vortex signal. [ABSTRACT FROM AUTHOR]

• Development of average velocity and film thickness in a free-falling annular flow. • Good agreement with previous experimental data and empirical predictions. • Extended flow range up to Re = 30000. • Droplet entrainment along the free-falling annular flow. • Impact of the 'T' junction of the building drainage system on drop entrainment. Annular flow is the primary characteristic of unsteady wastewater flow, which initiates entrained air and sets up the air pressure regime within the system - an important design consideration. This paper reports on an experimental investigation of free-falling annular flow in a vertical pipe with different inlets at extended flow ranges up to Re = 3 × 104, similar to those in Building Drainage Systems (BDS). In the experimental setup, a vertical pipe system (5 m) was used to record velocity profiles and film thickness in the developing region through Particle Image Velocimetry (PIV) measurements. Entrained droplets were collected through a separator, and the entrainment fraction was calculated at different flow conditions. The study reports on the development process of the film velocity and thickness along the vertical pipe, which agrees well with empirical predictions. The results of the droplet entrainment of a vertical annular flow show the development process to the steady state. Additionally, a Tee-junction inlet in drainage system generates a higher and different entrainment profile. [ABSTRACT FROM AUTHOR]

Gas–liquid annular flow occurs frequently in industrial production processes, and the accurate measurement of film thickness is essential for applying its mass and heat transfer properties. The non-invasive planar laser-induced fluorescence (PLIF) method is widely employed in annular flow investigation. However, both methods of PLIF90 and PLIF70 (the measurement angles between laser and camera are set to 90°and 70°) suffer from total reflection. In this paper, the effect of measurement angle on total reflection, measurement accuracy, and robustness are quantitatively investigated. Accordingly, a PLIF40 method is proposed, which minimizes the influence of total reflection by reducing the measurement angle to 40°. Sub-pixel-based edge detection and liquid film smoothing algorithms are developed to accurately identify liquid films with missing edge details, resulting in a measurement error of 0.09 mm. The flow structure is qualitatively diagnosed by waveform reconstruction and wave height extraction combined with the film thickness distribution. Furthermore, the prediction models for average film thickness are established and compared with the classical prediction models to demonstrate the accuracy and reliability of PLIF40. • The effect of measurement angle is quantitatively investigated. • A PLIF40 method is proposed to minimize the influence of total reflection. • A measurement angle calibration method is designed. • A sub-pixel-based liquid film extraction algorithm is proposed. [ABSTRACT FROM AUTHOR]

• The characteristics of gas-liquid phase-isolation caused by different swirlers. • Five flow patterns after evolution in phase distribution caused by swirler. • Flow pattern maps representing phase-isolation characteristics. • The relationship between phase-isolation characteristics and pressure drops. The characteristics of phase-isolation of annular flow caused by axial flow swirler are very critical for separation efficiency of axial inlet separator and accuracy of phase-isolation based measurement method. However, there are lack of comparative study among different types of swirlers and research focusing on characteristics of phase-isolation. In this paper, the phase-isolation characteristics caused by four different classic axial flow swirlers with the same main structural parameters were firstly experimentally studied in upward vertical gas-liquid two-phase flow. Five flow patterns were proposed after obvious evolution in phase distribution at downstream of the swirler, including gas-column flow, swirling annular flow , central bubble flow , central bubble-column flow , and variable diameter gas-column flow. According to the different phase-isolation characteristics, flow patterns downstream of the swirler were divided into stable phase-isolation, quasi-phase-isolation, and non-effective phase-isolation. The corresponding flow pattern maps were also obtained respectively. The experimental results also show that the swirler with good phase-isolation performance generally requires a larger pressure drop as the cost. Finally, the flow in the swirlers was studied numerically. It is found that although the outlet angle of the swirlers is the same, different types of swirlers will result in flow with different deflection angle, and eventually cause the different phase-isolation performance. [ABSTRACT FROM AUTHOR]