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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 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]

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]

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]

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]

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]

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]

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]

A steady Newtonian fluid flow through annular region in curved pipes is studied in this paper. The flow takes place due to an axial pressure gradient and it is three-dimensional in nature. The equations governing the flow are highly coupled and nonlinear. The solutions are obtained, analytically, using a regular perturbation method. The effects of curvature ratio (δ) , Reynolds number (Re) and the radius ratio (l) on the axial velocity and stream function are presented graphically. It is observed that, along with curvature ratio and Reynolds number, radius ratio highly affects the fluid flow in annular curved pipes. [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]

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]

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]

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]

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]

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]

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]

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]

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]

In this research paper, we numerically analyze the flow and heat transfer rate of non-Newtonian pseudo-plastic nanofluid with variable apparent viscosity and thermal conductivity effects, respectively, through annular sector duct. Concentric pipes annular sector duct of an apex angle, 2 β and ratio of radii, R ̂ , is filled with saturated porous media. For this purpose, we utilize the power law Darcy–Brinkman flow model along with Forchheimer term. Also, the contribution of nanoparticles is accounted in carboxy methyl cellulose (CMC)-water, which has been taken as base fluid. Finite volume method (FVM) is utilized to discretize the governing mathematical model, whereas algebraic equations are solved numerically by using strongly implicit procedure (SIP). With the help of graphs, the impacts of nanoparticles' contribution and porosity factor have been discussed by giving physical interpretation. Results are also found in the limiting sense and show the good agreement with already published data. At β = π / 3 , ϕ = 0. 1 0 , D a = 0. 0 1 and R ̂ = 0. 2 5 , we can observe down in f Re and Nu upto 5. 6 5 8 % and 1 0. 0 1 % , respectively, when n decreases from 1 to 0. 9 1 , whereas 1 3. 4 7 % and 2 3. 5 7 % , respectively, by decreasing the value of n from 1 to 0. 7 6. For both cases of nanoparticles' contribution, the downs in Nu have been observed same by decreasing the value of n. [ABSTRACT FROM AUTHOR]

To fully realize the advantages of the two-fluid model, accurate prediction of the interfacial area concentration (IAC) is indispensable. Since conventional flow regime-based IAC correlations are not capable of dynamically describing the evolution of interfacial structure, the interfacial area transport equation (IATE) was developed to close the two-fluid model. In the past 30 years, intensive efforts have been made to improve the prediction performance of IATE and extend the experimental database for the IATE benchmark. Recent efforts of the IATE development and benchmark conducted by the Thermal-hydraulics and Reactor Safety Laboratory at Purdue University are reviewed in this paper. This review covers (1) the development of IATE; (2) the experimental database for IATE modeling, including instrumentation development, local measurement data of adiabatic/diabatic two-phase flow, and annular flow characterization; and (3) implementation and evaluation of IATE in one-dimensional/three-dimensional scenarios. Significant progress has been achieved since 2009, and future works required to advance the modeling of IATE are also suggested. [ABSTRACT FROM AUTHOR]

The spacer represents an essential part in the nuclear fuel rod. Spacer grid with mixing vanes in fuel rod bundle of nuclear reactor core has a significant impact on heat transfer performance in downstream to grid spacer. Grid Spacers are located on the nuclear fuel rod assembly to hold suitable clearance among the rods in a bundle. The objective of this paper is to study the enhanced heat transfer performance of R134a at supercritical pressure 4.5 MPa near downstream to mixing vane spacer in a vertical channel of annular flow. A spacer of 0.38 blockage ratio with mixing vanes, situated at mid-span of an annular channel is used in the present work. Numerical simulations have been accomplished for spacer with mixing vane and spacer without mixing vane in an annular channel by using commercial CFD (Computational fluid dynamics) code ANSYS Fluent. The present investigation represents the comparative study for spacer with mixing vane and spacer without mixing vane effects on heat transfer and flow field characteristics in a downstream direction for mass flow-rate 0.41469 kg/s and heat flux 160 kW/m². The results indicate that spacer with mixing vane has notable influence on heat transfer performance and flow field characteristics downstream of mixing vane spacer as compared to spacer without mixing vane. Wall temperature fall and increase of coefficient of heat transfer are significantly greater adjacent to spacer downstream. Spacer influence in the improvement of the heat transfer is noted up to distance X/D = 40 downstream and then flow is found as fully developed. [ABSTRACT FROM AUTHOR]

The static fluid-induced force and stiffness coefficient of the smooth annular seal directly affect the rotor system stability. In this paper, a computational fluid dynamics method is applied to investigate the flow characteristics of a smooth annular seal for various eccentricities, discharge/supply pressures and rotational speeds under different flow conditions (laminar, transition, and turbulent flow). The influence factors and formation mechanism of the static instability in the smooth annular liquid seal are analyzed. Results show that laminar flow dominates the flow state at a rotational speed of ω = 2000 rpm. As the rotational speeds increase, the transition flow (2000-7000 rpm) gradually transits to the turbulent regime (ω > 7000 rpm). The direct static stiffness decreases first and then increases from laminar to transition flow state, and the viscosity effect is the dominant factor. For transition and turbulent flow with high eccentricities (Ɛ = 80 %), the dominant viscous effect and inertial effect lead to the negative radial force and negative direct static stiffness coefficients. The smooth annular liquid seal shows best performance in the laminar flow and worst performance in the turbulent flow. [ABSTRACT FROM AUTHOR]

Supercritical water, known for its abrupt changes in fluid properties near the pseudocritical region, has always posed a design challenge, leading to enhancement or deterioration in heat transfer. Additionally, the lack of complete understanding of the thermodynamic behavior of supercritical water near the pseudocritical zone, unlike in the subcritical zone, highlights the necessity of a systematic study. Hence, this paper focuses on characterizing the convective upward flow and heat transfer characteristics inside a vertical smooth annular square channel. The numerical analysis uses a steady-state, pressure-based, compressible, Newtonian solver with body force term and two-equation turbulence model to study the influence of variation in pressure, heat flux, and heat-to-mass flux ratios. The flow characteristics and heat transfer behavior of deteriorated, normal, and enhanced heat transfer modes are studied. The heat transfer deterioration is suppressed with the increase in pressure; however, it increases with the increase in inlet bulk temperature. The supercritical boiling number that determines the heat transfer mode is calculated and analyzed for the square annulus section. The evolution of the flow in different heat transfer modes differs based on the effect of buoyancy on the velocity field and the turbulence. The calculated Nusselt numbers match the existing Jackson and Hall correlation well with a maximum absolute error of 9.91%. [ABSTRACT FROM AUTHOR]

Different techniques are used to analyze annular flow, but the more interesting ones are those techniques that do not perturb the flow and provide enough resolution to clearly distinguish the interfacial phenomena that take place at the interface, especially the disturbance waves (DW) and the ripple waves (DW). The understanding of these events is important because it influences the heat and mass transfer taking place through the thin film formed near the walls in this flow regime. The laser-induced fluorescence (LIF) and the three-electrode conductance probe are two commonly used techniques to study experimentally annular flow phenomena. In this paper, a set of experiments at different temperatures of 20 °C, 30 °C and 40 °C and different liquid Reynolds numbers have been performed in the annular flow regime, the characteristic of the DW and RW as average height and frequency of these waves has been measured by both techniques LIF and conductance probes. In addition, we also measured the mean film thickness. It was found that the mean film thickness and the DW height are practically the same when measured by both techniques; however, the height of the RW is smaller when measured by the conductance probe and this difference diminishes when the temperature increases. [ABSTRACT FROM AUTHOR]

Mass, energy, and momentum transfer processes between fluid-saturated porous media and the adjacent free flow occur in many natural and technical systems. The flow dynamics in the porous region and the adjacent free flow is strongly controlled by the mechanisms at the common interface and conditions on the outer surface of the free-flow. The present paper considers unsteady axisymmetric flows of viscous fluids through an annular domain with a porous layer covering a cylindrical solid core. Fluid flow in the domain filled with porous material and in transparent domain is described by Brinkman model and Navier Stokes equations, respectively. Analytical solutions for the dimensionless velocity fields in the Laplace domain are determined using Bessel functions, Laplace transform, and the appropriate interface and boundary conditions. The inversion of the Laplace transforms is done with the help of a numerical algorithm. In addition, the hydrodynamic permeability is determined. The dependence of the dimensionless velocity fields and of hydrodynamic permeability on characteristic parameters of the porous layer is numerically and graphically discussed. Since the velocity on the outer surface is given by an arbitrary function of time, the results in this paper could be used to study various filtration problems. [ABSTRACT FROM AUTHOR]

With the increasing demand for heavy oil, core annular flow (CAF) is an economical method to transport heavy oil, and many researchers have explored the energy-saving aspects of the CAF method. This paper presents a review of CAF energy saving and factors affecting CAF energy saving. Among them, the energy saving of CAF mainly concerns the changes in pressure drop and drag reduction efficiency; the factors affecting the energy saving of CAF mainly concern the problem of stability, the issue of restarting the pipeline system, the impact of a nozzle, the impact of fouling on the flow in the pipe, and the problem of oil–water accumulation. The aim of this paper is to provide a reference for the practical application of CAF in heavy oil transportation. [ABSTRACT FROM AUTHOR]

Compared with the traditional transportation of high-viscosity crude oil, water annular transportation has the advantages of low energy consumption and no change in crude oil composition. With the continuous development of marine heavy oil transportation, submarine oil pipelines are inevitably subjected to vibration and impact, affecting the annular flow in the pipeline. In this paper, the VOF model in Fluent software is used to simulate the stability of oil-water annular flow in a horizontal pipeline under different amplitudes and the interface characteristic parameters of annular flow. In addition, the influence of vibration on oil-water annular flow in the horizontal pipeline under different marine environments is studied. The results showed that the vibration parameters have an influence on the flow of oil-water annular flow in the horizontal pipeline. Under the condition of constant inlet velocity, the eccentricity degree of oil core is analyzed to reveal the law that the stability of annular flow decreases with the increase of amplitude. The relationship between the eccentricity of oil core and the vibrational parameters of pipes are explored in this paper. At the same time, the unit pressure drop under the condition of pipe vibration and its mechanism are studied. These results could provide references for parameters optimization of heavy oil-water annular flow transportation under vibration conditions. [Display omitted] • Oil-water annular flow under the impact of marine swell is numerically simulated. • Annular flow stability is described by pressure drop and flow characteristics. • Different vibration properties affect the stability of the oil-water annular flow. [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]

The paper investigated the benefits of having fins that induce swirling flow within an annular passage. The importance of the vortical structures produced using different fin angles and flow velocities in heat transfer was studied. The combination of swirling fluid with recirculation on heat transfer within an annular domain was not fully understood, and this paper aims to address that gap. The 10°, 20°, 30° and 40° angled fins were investigated to understand the changes in heat transfer performance as fluid recirculation becomes more dominant as angles become steeper. The usage of CGNP colloidal suspension was investigated for its potential benefits in heat transfer in a domain with angled fins. The CGNP concentrations of 0.025, 0.075 and 0.1 mass % were used as part of this investigation. Higher concentrations of CGNP increased the overall heat transfer coefficient. A more compact fin spacing improved heat transfer performance at the expense of increased pressure drop. Fin angles of 20° and 30° yielded poor heat transfer performance in the transitional flow regime (2000 < Re < 3000) due to the smaller swirling longitudinal vortices being insufficient in promoting fluid mixing from the thermal boundary layer into the freestream. [ABSTRACT FROM AUTHOR]

The stable transportation of pulverized coal in the vertical pipe is significant for the operation of the gasifier. There are few studies on the flow characteristics and flow pattern transition of particles in vertical pipes with small diameters. This paper has modeled and analyzed the flow characteristic of powder in dense-phase pneumatic conveying through 25 mm vertical pipe using CFD. Firstly, the grid independence is verified to determine the optimal mesh size. Then, the influences of different solid loading ratios (SLRs) and conveying velocities on particle flow characteristics, flow stability, and flow pattern transition are investigated. The results show that the flow pattern in the vertical pipe changes from annular flow to uniform flow at high SLR and low conveying velocity. Moreover, the evolution regulation of resistance characteristics under different conveying velocities is further revealed. Considering the conveying stability and economic benefit, the most suitable conveying velocity is 6 m/s. [ABSTRACT FROM AUTHOR]

In order to investigate the recycling technology for efficiently recovering low-temperature wastewater waste heat from industrial production, we built an experimental device for forced boiling heat transfer in an annular tube. This paper takes a ring casing evaporator with an inner tube diameter of 30 mm, a length of 1450 mm, a wall thickness of 0.8 mm, and an outer tube diameter of 14.2 mm, which was used as the main object of study. We conducted experimental research on heat transfer in single-phase liquid flow and two-phase boiling phase change within annular tubes by varying the inlet circulating hot water temperature (60–85 °C), the mass flow rate of the circulating mass (0.85, 1.27, 1.69 kg m−2 s−1), and the inclination angle (0°–90°). The research results indicate that the heat transfer coefficient of boiling phase change within annular sleeves is significantly enhanced compared to convective heat transfer of single-phase liquid flow within annular tubes. This signifies that employing heat pipe technology for waste heat recovery can achieve highly efficient heat transfer processes. This study also reveals that with an increase in the inclination angle, the heat transfer coefficient on the boiling surface follows a trend of initial increase followed by a decrease. Near an inclination angle of 30° within the annular jacket tube, the heat transfer coefficient of two-phase boiling phase change reaches its maximum value. The findings of this study provide certain theoretical guidance for the application of heat pipe energy-saving technology in the field of medium- and low-temperature waste water recovery and utilization. [ABSTRACT FROM AUTHOR]

The paper presents the visualization results of the sudden contraction flow field with an annular gap downstream of the contraction cross section. The contraction ratio directly influences the flow phenomena. No stationary vortices were observed upstream of the contraction cross section, and flow separation divided the flow field within the annular gap into a recirculation zone, a shear layer, and a mainstream zone. Vena-contracta point and reattachment point occurred within the flow field of the annular gap. The production of Reynolds stress varied with the contraction ratio, and the momentum exchange mainly occurred in the recirculation zone and the shear layer, while the flow state in the mainstream zone tended to become isotropic. Rapid changes in turbulent kinetic energy primarily occurred in the shear layer, and the production term of turbulent kinetic energy contributed the most. Applying computational fluid dynamics and experimental results, this study has formulated an expression for the contraction coefficient of the proposed model. The axial positions of the vena-contracta point and reattachment point have a strong correlation with the contraction ratio, which can be represented by an exponential function. [ABSTRACT FROM AUTHOR]

Bubble dynamics are closely related to the electrochemical performance of a proton exchange membrane electrolyzer (PEMEC). However, tiny bubbles need to be clustered together to affect the electrochemical performance of PEMEC significantly. In this paper, the effect of microscopic bubbles on macroscopic electrochemical properties were assessed by bubble coverage. The bubble dynamics, two-phase flow, and electrochemical performance were captured under different conditions using a high-speed, microscopic visualization experimental system. The results show that various factors influence the two-phase flow pattern. At 60 °C, 1.5 A/cm2 and 5 mL/min, the annular flow occupied 76.8% of the gas phase area, and when the water flow increased to 80 mL/min, the annular flow ratio decreased substantially to 2.7%. The two-phase flow of bubbles in the flow channel showed different flow patterns over time. Under the experimental conditions (60 °C, 20 mL/min, 0.8 A/cm2), the bubble flow pattern experienced the emergence of bubbles, bubble flow, segmental plug flow, annular flow, and final steady state with the occurrence times of 0.15 s, 1.5 s, 5.0 s, 10.5 s, and 21.2 s, respectively. The bubble coverage increased with current density and temperature, while it decreased with the increase of water velocity. In addition, the effects of temperature and water velocity on bubble coverage and PEMEC performance vary in principle. Specifically, higher temperature mainly improves the bubble coverage by increasing the electrochemical performance of PEMEC. In contrast, higher water velocity mainly improves the electrochemical performance of PEMEC by decreasing the bubble coverage. This study elucidates the relationship between microscopic bubbles and macroscopic electrochemical performance, contributing to a better understanding of the processes and principles of bubble effects on the electrochemical performance of PEMEC. The results may provide a theoretical basis and experimental data for operating condition optimization, operating efficiency improvement, multiphase flow study, gas diffusion layer structure, and flow field design of PEMEC. • Two-phase flow experiments using a transparent visualization system. • Bubble flow is present under all conditions. • Annular flow occurs at high current density and low water velocity. • Two-phase flow shows different flow patterns with time. [ABSTRACT FROM AUTHOR]

Water production in the bottom hole is a frequent occurrence during gas drilling, posing a significant threat to the safety of the process. Obtaining the water flow rate quickly is critical to making further engineering decisions. This paper proposes a rapid calculation method of water flow rate based on the principle of pressure drop. The method can quickly identify the multiphase flow pattern and calculate the flow pressure drop, thereby establishing the relationship between the gas injection pressure and the water flow rate. At the gas drilling site, the gas injection pressure is continuously monitored in real-time, which enables rapid acquisition of the real-time water flow rate. The concept of ultimate water-carrying kinetic energy is introduced, which combined with the boundary of annular flow to other flow patterns, can determine the maximum water-carrying flow rate. The feasibility of this method is validated using the field-measured data of well X8-3. [ABSTRACT FROM AUTHOR]

In this paper, the transient ignition process of an annular combustor with 16 centrally staged swirling burners is experimentally investigated to study the mechanism of burner–burner flame propagation. The flame propagation patterns are studied by high-speed imaging. Three typical patterns of the burner–burner flame propagation are identified: the kindled-swirling pattern, entrained-swirling pattern, and sweeping pattern. The patterns are featured with different flame paths of motion. For fixed flow rates, the paths of motion are mainly determined by the overall equivalence ratio Φ. Furthermore, during the burner–burner flame propagation, the effect of the flow field on the local flame fronts is analyzed by Mie scattering and particle image velocimetry (PIV) methods. The PIV results show that the flame paths of motion are greatly influenced by the flow structure of the annular combustor. The optical diagnosis of the flame–flow interaction provides new insights into the ignition dynamics of the centrally staged annular combustor. [ABSTRACT FROM AUTHOR]

The efficiency of annular-nozzle ejectors serving as components of complex technical systems interacting with high-temperature media in engines and in the field of energy technologies is not linearly related to the gas-dynamic characteristics of the flows formed in the device. In this paper, we have analyzed the results of numerical and experimental studies of gas jets in an annular-nozzle air ejector. The regression equations built according to the circumscribed central composite design described the relationship between a pressure drop and the structural parameters of the nozzle with the speed and mass flow rates of the airflows, including error rates of no more than 15 percent. A two-factor optimization based on Harington's generalized desirability function was performed to obtain a relatively accurate estimate of the ejector efficiency under the influence of the structural and operating parameters. An optimization method based on the combination of response surface methodology and the desirability function approach, allowing simultaneous consideration of all responses, made it possible to simultaneously optimize multiple conflicting objectives. [ABSTRACT FROM AUTHOR]

• Application of porous materials to heat dissipation of LFR-PV system. • A new metal foam porous-wall mini-channel is proposed. • The MFP-channel increases the heat transfer coefficient by 35%. A metal foam porous-wall mini-channels heat sink is proposed to solve the heat dissipation problem of linear Fresnel reflection photovoltaic (LFR-PV) system. This paper compares the heat transfer performance of the metal foam porous-wall mini-channels heat sink and the rectangular mini-channels heat sink under different working conditions by method of experimental investigation. The research results show that metal foam porous wall mini-channels heat sink performs larger annular flow area so that the heat transfer performance is better. Compared with rectangular mini-channels of the same size, the heat transfer coefficient is improved by 135% in the same size. Due to the addition of metal foam, the local heat flow distribution in the heat sink changes, and the wall temperature distribution of the heat sink is more uniform. [ABSTRACT FROM AUTHOR]

As an advanced flexible dynamic sealing technology, the leakage characteristics of a finger seal (FS) is one of the key research areas in this technology field. Based on the fractal theory, this paper establishes a mathematical model of the FS main leakage rate considering the fractal wear effect by taking into account the influence of the wear height on the basis of the eccentric annular gap flow equation. Based on the Hagen-Poiseuille law and the fractal geometry theory of porous media, a mathematical model of the FS side leakage rate considering the fractal porous media seepage effect is developed. Then, a mathematical model of the FS total leakage rate is established. The results show that the mathematical model of the FS total leakage rate is verified with the test results, the maximum error rate is less than 5%, and the mathematical model of the FS total leakage rate is feasible. With the gradual increase in working conditions and eccentricity, the FS main leakage rate gradually increases. In addition, the effects of the fractal dimension, fractal roughness parameters and porosity after loading on the FS main leakage rate are negligible. As the fractal dimension of tortuosity after loading gradually decreases, the fractal dimension of porosity after loading gradually increases, and the FS side leakage rate gradually increases. As the porosity after loading gradually increases, the FS side leakage rate gradually increases. Under different working conditions, different fractal characteristic parameters and different porosities after loading, the weight of the FS main leakage rate is much greater than that of the FS side leakage rate by more than 95%. [ABSTRACT FROM AUTHOR]

Visualization of the two-phase flow in micro-scale helps to reveal the thermophysical behavior of the fluids. This paper presents and discusses the flow patterns of two-phase R1234yf, R1233zd(E), and R1336mzz(Z) in a 0.643 mm microchannel tube. The condition covers mass flux from about 25 to 250 kg-m−2 s−1. The inlet saturation temperature is 30 °C for R1234yf and R1233zd(E), and 40–60 °C for R1336mzz(Z). As vapor quality increases, the flow is firstly in plug/slug flow, then transitional flow, and finally annular flow at high quality. When mass flux is 50 kg-m−2 s−1, no transitional flow is observed. The annular flow starts at high quality. The transitional flow in the low mass flux was absent. When mass flux is 100 kg-m−2 s−1, the transitional flow covers quality from 0.8 to 0.9. The superficial velocities follow a power function for flow pattern transitioning. The velocity is measured by a video processing method proposed in this paper. The vapor plug velocity is calculated by measuring the velocity of the vapor plug head in the frames and corrected by the video information (frame per second and meter per pixel). The velocity is slightly higher than the velocity calculated based on the homogeneous assumption when it is higher than 1 m-s−1. A new correlation for predicting the vapor plug velocity is proposed. The new correlation has a small MAE (5.42%) compared to the results and can be used for Capillary number less than 0.14. [ABSTRACT FROM AUTHOR]

This paper describes an experimental study on shear-based spray formation. A laminar liquid jet was ejected inside co-annular non-swirling and swirling air streams. The aerodynamic Weber numbers (WeA) and swirl numbers (S) of the flow cases ranged from 4 to 1426 and from 0 to 3.9, respectively. High-speed shadowgraphy was utilized to obtain data on the first droplet locations, breakup lengths of the liquid jets, and two-dimensional wave spatiotemporal spectra for the jets. In order to detect the large-scale instabilities of the central liquid jet, proper orthogonal decomposition (POD) was performed on the high-speed shadowgraphic images. Stereo particle image velocimetry was utilized to investigate the annular air flow fields with S in the range of 0–2.5. It was found that air swirl promotes the morphological development of the jets with S in the range of 1.2–2.5. Both the breakup length and axial distance between the first droplet separation and the nozzle exit reduce as WeA and S increase. Scaling of the first droplet locations and breakup lengths is also evaluated in this paper. In terms of the air flow fields, radial expansion of the annular swirling air jets was observed, and the annular swirling jets expand radially further as S goes up. Central reversal air flows appear near the nozzle exit when S ≥ 1.2 , and some small droplets are blown upward to the nozzle exit by these central reversal air flows. In terms of large-scale instabilities, flapping is the dominant instability across most of the flow cases (as revealed by the first POD mode). Wavy and explosive breakup appear as the secondary breakup modes when WeA is low (≤ 110). In the absence of the central reversal air flows, the temporal frequencies of the instabilities of the air–water interfaces increase as S goes up. It was found that the central reversal air flows tend to stabilize the air–water interfaces. The spatial frequencies of the instabilities of the air–water interfaces remain low (≤ 0.06 mm−1) across all the flow cases, which produce long-wave structures. [ABSTRACT FROM AUTHOR]

• Boiling of ammonia in a vertical dimpled tube bundle: bare tubes, full length round PVC inserts and 33% cut inserts. • Study of wide range of experimental parameters. • Heat transfer comparison. This paper is the last leg of the previous three papers of the same series with experimental study carried on a vertical shell and tube heat exchanger comprising of seven dimpled enhanced tubes. Three different tube configurations were tested. (1) bare tube (2) with full length solid PVC nonconductive round rod insert (12.7 mm diameter) and (3) 33% cut insert. For the same flow, tubes with rods developed annular flow within the annular portion between the tube and the rod. Source of heat was hot ethylene glycol/water solution flowing on the shell side. Saturation temperature of ammonia was -20 °C ≤ T sat ≤ -2 °C, heat flux range 5 kW m−2 ≤ q ˙ ≤ 45 kW m−2 and mass flow rate of 0.008 and 0.015 kg s−1. Tests were conducted for each mass flow rate at four saturation temperature. Two-phase heat transfer coefficient increased with saturation temperature and heat flux for all cases with initial increase and then a drop at the onset of partial dry out. The tube with 33% cut rod exhibited better overall performance. Results were also compared with plate type evaporator data. [ABSTRACT FROM AUTHOR]