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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]

Accurate prediction of the entrained liquid droplet fraction in an annular two-phase flow regime plays a crucial role for estimating the dryout type critical heat flux to identify the optimized flow characteristics in the thermal systems across different industries. Existing studies have provided different correlations based on the limited experimental data. However, these correlations are applicable to certain operating conditions. Therefore, the present study aims at applying a deep learning method, specifically an artificial neural network (ANN), to enhance the prediction of the entrained liquid droplet fraction. Experimental data from various works on annular flow, covering a wide spectrum of pressure and flow conditions, are utilized for training the ANN model. Eight input variables, viz, superficial gas velocity (J S G ), superficial liquid velocity (J S L ), gas viscosity (μ G), liquid viscosity (μ L), gas density (ρ G), liquid density (ρ L), pipe diameter (d) and liquid surface tension (σ L V ) are considered as input features. The entrained liquid droplet fraction is the single output feature. The present model employs the Bayesian regularization backpropagation algorithm for training. The present ANN model is compared against the performance of linear regression, decision tree and support vector machine algorithms, and found that the performance of the present Bayesian regularization neural network (BRNN) model is superior within ∼ 7.5 % deviation. Further, the BRNN model is coupled with the film mass flow rate model to obtain the axial variation of the liquid film mass flow rate and good agreement is noticed when compared against the experimental data. [ABSTRACT FROM AUTHOR]

An experimental campaign is conducted to investigate the pressure drop during the restart of a heavy oil-water core-annular flow (CAF) from a stratified configuration in a polyvinyl chloride (PVC) horizontal pipe. The evolution characteristic of restart pressure drop along time is explored, and the effects of various factors including oil holdup (0.26-0.76), oil viscosity (1.0553-3.02 Pa·s), standstill period (0.5 & 1.0 h) and water cleaning superficial velocity (0.25-1.01 m/s) on maximum restart pressure drop are emphatically investigated. The results demonstrate that the restart process can be divided into decay and steady two stages. The maximum restart pressure drop generally increases along with the increase of oil holdup, oil viscosity, standstill period and water cleaning superficial velocity. Moreover, of all the measured variables, oil holdup and water cleaning superficial velocity have a significant influence on maximum restart pressure drop. The results obtained can provide a theoretical reference and practical guidance for the development of appropriate restart schemes for on-site shutdown pipelines. [ABSTRACT FROM AUTHOR]

Hydrogen storage in porous geological formations can potentially provide large-scale, seasonal storage of energy. This study investigates the effect of relative permeability hysteresis on the storage processes, particularly addressing the effects on the dynamics of the hydrogen plume, on the two-phase flow regime in the wellbore, and on the storage operations. Numerical simulations of the underground hydrogen storage processes are conducted for scenarios which account for and which ignore hysteresis. The hysteretic constitutive relationships used are based on two independent, experimentally derived datasets from literature. In scenarios that account for hysteresis, the hydrogen plume is less mobile and the hydrogen mass is more dispersed than in scenarios without hysteresis. In addition, hysteresis leads to increased brine upconing and influx into the production borehole. A simple analysis of the two-phase flow regime in the borehole provides an estimate of the required minimum flow rate to ensure annular flow. Though different, both hysteretic constitutive relationships used in this study yield the same trend. All the effects of hysteresis mentioned above are detrimental for hydrogen recovery and tend to be more significant in the first few storage cycles. Operationally, these problems could be addressed by providing for a rest period between injection and production that is long enough to let the hydrogen plume accumulate near the well and potentially by the use of a cushion gas. • Analysed effects of relative permeability hysteresis in underground hydrogen storage. • Hysteresis reduces hydrogen recovery especially in initial storage cycles. • Hysteresis reduces mobility of the hydrogen plume and increases its spread and extent. • Hysteresis increases brine upconing and affects the wellbore flow regime. [ABSTRACT FROM AUTHOR]

The annular flow payload is among the first batch of space science experimental projects carried out on the Fluid Physics Rack of the China Space Station. This paper provides a detailed introduction to the development of the payload, ground validation, and in orbit experiments. The payload, sized 320 mm × 200 mm × 220 mm, includes an annular flow model and supports supply (24 V, 12 V, and 5 V), communication, and data transmission. A multi-functional heating column in the annular flow model was designed, allowing for the column to operate in fixed, rotating, and lifting scenarios. In the first round, 96 sets of space experiments covering volume ratio ranges from 0.45 to 1.06 were carried out. The annular flow liquid surface state, temperature oscillation, and infrared temperature field evolution were obtained. Mode decomposition shows the oscillatory convection of the m = 4 travelling wave, and contains m = 3, m = 6, and m = 8 waves. [ABSTRACT FROM AUTHOR]

Spray drying is a widely used method for producing food powders in large quantities, but it also has a high energy demand. To address this, researchers have long aimed to increase the solid content of liquid feeds, which poses the challenge of atomizing high-viscosity liquids into fine droplets. The Air-Core-Liquid-Ring (ACLR) nozzle offers a potential solution by inducing an internal annular flow, though it faces its own limitations due to internal flow instabilities. This study investigates how the nozzle flow conditions impact spray performance under different process conditions and liquid viscosities. We found that internal lamella thickness and atomization uniformity vary with pressure, viscosity, and liquid volume flow. Nonetheless, pressure appears to be the real critical factor in that case. The Air-to-Liquid Ratio (ALR) might be more decisive for the droplet size distribution than liquid viscosity. Future research should explore higher viscosities and consider simulations to circumvent experimental limitations. [ABSTRACT FROM AUTHOR]

In the past decades, studies on a void fraction of gas–liquid two-phase flow have mainly focused on straight pipes, while voidage in pipeline-riser flows have been largely neglected. In this work, the void fraction of gas–liquid two-phase flow in pipeline-riser was investigated. The test loop consists of a 12 m horizontal pipe, followed by a 2 m downward inclined pipe, and ended at a riser. Both vertical riser and catenary riser were used in the experiment. Slip in severe slugging and annular flow was more pronounced than in bubbly flow. The transition from the mixed to the separated flow occurs at gas–liquid volumetric flow rate ratio equals to 0.8. However, the separated flow forms when the gas–liquid volumetric flow rate ratio is greater than 0.9 for catenary riser. A total of 28 correlations for predicting the void fractions were evaluated with the experimental data. The Mishima and Hibiki correlation was found to be the most accurate among the studied correlations, predicting 68.5% and 69.3% of the measured data within ±30% for vertical and catenary riser, respectively. A new correlation considering the effect of the elbow is still needed for more accurate prediction of void fraction in pipeline-riser. [ABSTRACT FROM AUTHOR]

Friction stir lap welding (FSLW) of dissimilar acrylonitrile butadiene styrene (ABS) and polycarbonate (PC) was conducted using a double-pin tool. The formation process of the weld and the influences of rotational speed on the microstructure and mechanical property were investigated. It was found that the weld was generated accompanying with the closure of old cavities in the front of the pins and the simultaneous regeneration of new cavities in the rear of the pins. Annular material flow on the vertical and horizontal directions occurred during FSLW. With the increase of the rotational speed, the PC anchors resulted from the upflow of plasticized PC layer and the shoulder affected zone both enlarged. Microstructure analysis of the weld nugget showed that PC was fragmented into lamellar, columnar, and spherical particles and their dimensions decreased when rotational speed increased. Lap-shear tensile tests showed that the weld strength increased with higher rotational speed and the maximum strength of the weld produced under 800 r/min reached 19.38 MPa, which was comparable to the ABS/PC welds produced by a tapered pin under the optimal parameters. Through the further optimization of such FSLW process, it was potential to join dissimilar polymeric components in future industrial manufacturing field. [ABSTRACT FROM AUTHOR]

Microchannel condensers play an essential role in cryogenic two-phase heat management systems due to their efficient heat transfer characteristics. Thus, it is worth conducting an in-depth study on microscale condensation characteristics of cryogenic fluids. This paper delves into the flow condensation process of methane in microchannels. A two-dimensional transient model with high accuracy for cryogenic fluids has been developed by combining a self-defined program for the source term of the phase transition model. The model fully considers the boundary layer thickness and accurately explores the mesh accuracy. The complete condensation flow patterns are captured for various vapor quality, mass flux, and wall subcooling degrees. The injection flow is a unique flow regime for condensation in microchannels. The decrease in wall subcooling degree and increase in mass flux leads to the separation point at the neck of the injected flow moving towards the exit, while the annular flow region is expanding and the flow pattern transition is lagging. The mass flux improves the heat transfer coefficient more significantly at high vapor quality. During injection and bubble flow, the wall shear stress and local heat transfer coefficient are subject to bouncing and oscillations, which may induce fluctuations in the upstream annular flow. The prediction performance of six classical heat transfer correlations is evaluated. The results indicate that the Nie et al. correlation has the highest comprehensive prediction accuracy with MRD and MARD of -5.00 % and 15.83 %, respectively. [ABSTRACT FROM AUTHOR]

Green hydrogen, produced using renewable energy sources, represents a critical component in the transition to sustainable energy systems due to its clean and versatile nature. This research investigates the dynamic behavior of bubbles within the serpentine flow field of a Proton Exchange Membrane Water Electrolysis (PEMWE) cell, aiming to enhance the understanding of two-phase flow dynamics and improve the efficiency of green hydrogen production. Utilizing the Volume of Fluid (VOF) method, a three-dimensional unsteady model was developed to simulate the flow dynamics at the anode of a PEMWE system. The study explores the transition of bubbles from bubbly flow to slug and annular flow, highlighting the significant impact of bubble formation on mass transport and overall cell performance. The results demonstrate that larger bubbles impede liquid water delivery to reaction sites and cause unstable pressure drops. The investigation also examines the influence of wall contact angles on bubble behavior, revealing that hydrophobic surfaces lead to increased gas coverage and more oxygen accumulation inside the channel, which hinders mass transport. These findings underscore the necessity for optimized flow channel designs and enhanced surface treatments to mitigate bubble coalescence and improve PEMWE performance. [Display omitted] • 3D VOF model simulates two-phase flow in PEMWE anode channels. • Flow patterns affect oxygen distribution and pressure drop in channels. • Annular flow reduces water supply to electrodes, impacting efficiency. • Wall wettability is crucial for bubble dynamics and PEMWE mass transport. • Hydrophilic surfaces aid bubble removal, hydrophobic surfaces cause flow hindering. [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]

Air-assisted nozzles are widely used in many industrial fields. For example, in artificial snowmaking systems, air-assisted nozzles can provide a key promoting role for the nucleation and crystallization of snow. To reveal how spray behavior depends on the internal flow patterns of air-assisted nozzles, we designed an experimental platform to observe the two-phase flow inside the nozzle. The results show that the internal flow pattern of the nozzle exhibits an annular flow pattern, forming a continuous hollow conical spray. As the gas–liquid pressure ratio (GLRP) increases, the interfacial disturbance waves gradually disappear at the gas–liquid interface of the internal flow, indicating a transition from a more turbulent to a more stable flow regime. As the gas core expands, the liquid film thickness gradually decreases, promoting finer atomization and a more uniform droplet distribution. This transition from a disturbed wave pattern to a stable annular flow enhances the uniformity of the droplet distribution and the stability of the spray. When GLRP increases from 20% to 67%, the uniformity of droplet distribution improves by 17%, and the stability is enhanced by 60%. Additionally, this study examines the link between internal flow patterns and atomization, providing a dimensionless formula that correlates nozzle flow dynamics with spray quality based on experimental and simulation data. This contributes valuable insights for optimizing air-assisted nozzle design for superior spray performance. [ABSTRACT FROM AUTHOR]

This paper provides a detailed description of the development and experimental results of the supercritical flow experiment payload carried on the TZ-6 cargo spacecraft, as well as a systematic verification of the out-of-cabin deployment experiment. The technical and engineering indicators of the payload deployment experiment are analyzed, and the functional modules of the payload are shown. The paper provides a detailed description of the design, installation location, size, weight, temperature, illumination, pressure, radiation, control, command reception, telemetry data, downlink data, and experimental procedures for the out-of-cabin payload in the extreme conditions of space. The paper presents the annular liquid surface state and temperature oscillation signals obtained from the space experiment and conducts ground matching experiments to verify the results, providing scientific references for the design and condition setting of space experiments and comparisons for the experimental results to obtain the flow field structure under supercritical conditions. The paper provides a specific summary and discussion of the space fluid science experiment project, providing useful references for future long-term in-orbit scientific research using cargo spacecraft. [ABSTRACT FROM AUTHOR]

As the important component to guide the airflow in the classifier, installation position of the guide vane determines the width of the classification annular region and influences the flow field distribution. The influence of the guide vane positioning on the flow field in the annular region is analyzed through numerical simulation. The simulation results show the tangential velocities near the inner edge of the guide vanes increase, and the tangential velocity gradient decreases with decrease of the width of the annular region. The increases of turbulent dissipation rate near the guide vanes are beneficial to powder dispersion. However, the increases of turbulent dissipation rate near the rotor cage aren′t conducive to uniformity of the flow field. In case of the narrow annular region, the cut size gradually increases when the width of the annular region increases. However, when the width of the annular region continues to increase, the particle′s residence time become long, and the solid concentration increases significantly to increase the probability of particle aggregation. The reasonable range of the installation diameter of the guide vane in the classifier is between 504 mm and 524 mm. [ABSTRACT FROM AUTHOR]

As an efficient heat transfer enhancement device, a helical tube is widely used in various industrial applications and its composite heat transfer enhancement technique has also elicited widespread attention. This study proposes an innovative technique that combines sinusoidal pulsating flow with annular corrugation and then applies it to a helical tube. Numerical simulation is performed to investigate the effects of pulsation flow parameters on the structure of the flow field and the efficiency of heat transfer. Then, the mechanism of heat transfer improvement is revealed. Results show that the collaborative effects of pulsating flow and annular corrugation can enhance the turbulent intensity of the mainstream fluid. In addition, the structure of the secondary flow field is changed and synergy between the velocity field and the temperature field is enhanced further. Within the studied range, the average Nusselt number (Nu) of sinusoidal pulsating flow in a helical tube with an annular corrugated wall structure is enhanced by 16.05 % and 10.52 % compared with that of steady flow in a smooth helical tube and an annular corrugated helical tube, respectively. With an increase in the dimensionless pulsation frequency (Wo), Nu initially increases and then decreases, while the friction resistance coefficient (fD) gradually increases. As the dimensionless pulsation amplitude (A0) increases, Nu and fD gradually increase. The comprehensive thermal performance evaluation index exhibits a maximum observed value of 1.241 when Dean number = 7709, Wo = 25, and A0 = 0.25 within the studied range. [ABSTRACT FROM AUTHOR]

Objective: To evaluate the efficacy, safety, and improvement of symptoms by ultrasound-guided microwave ablation (MWA) for patients with large benign thyroid nodules (BTNs). Methods: Eighty-seven patients with 87 BTNs (≥ 4 cm) treated with MWA between April 2015 and March 2021 were enrolled in this retrospective multicenter study, with clinical and ultrasound examinations performed at the 1st, 3rd, 6th, and 12th months. A multivariable linear mixed effects model was employed to explore the alterations in volume and volume reduction ratio (VRR), as well as the potential factors associated with VRR. Results: The mean age of the 87 patients was 45.69 ± 14.21 years (range 18–76 years), and the ratio of men to women was 1:4.8. The mean volumes were much decreased at the 12th month after ablation compared to the initial volumes (p <.001). The mean VRR was 76.09% at the 12th month. The technique efficacy (VRR > 50%) was 90.80% at the 12th month. A multivariate analysis revealed that VRR was related to the initial volume (p =.015), annular flow (p =.010), and nodule composition (p =.024). The mean symptomatic score decreased from 4.40 ± 0.28 to 0.26 ± 0.06 at the 12th month (p <.001). At the same time, the mean cosmetic score decreased from 3.22 ± 0.10 to 1.31 ± 0.08 (p <.001). Conclusion: MWA could serve as a safe and effective therapy for large BTNs, significantly reducing the volume of BTNs and significantly improving compressive symptoms and appearance problems. Clinical relevance statement: Microwave ablation could serve as a safe and effective therapy for large benign thyroid nodules, leading to significant volume reduction and satisfied symptom and cosmetic alleviation period. Key Points: • This multicenter study investigated the feasibility and safety of microwave ablation for large benign thyroid nodules. • After ablation, the nodule volume was significantly reduced, and patients' symptoms and appearance problems were significantly improved. • Microwave ablation is feasible for large benign thyroid nodules and has been a supplement treatment. [ABSTRACT FROM AUTHOR]

We introduce a notion of stability for non-autonomous Hamiltonian flows on two-dimensional annular surfaces. This notion of stability is designed to capture the sustained twisting of particle trajectories. The main Theorem is applied to establish a number of results that reveal a form of irreversibility in the Euler equations governing the motion of an incompressible and inviscid fluid. In particular, we show that nearby general stable steady states (i) all fluid flows exhibit indefinite twisting (ii) vorticity generically exhibits gradient growth and wandering. We also give examples of infinite time gradient growth for smooth solutions to the SQG equation and of smooth vortex patches that entangle and develop unbounded perimeter in infinite time. [ABSTRACT FROM AUTHOR]

This article discusses a focused study on visualizing the flow patterns in a two-phase pulsating heat pipe (PHP) using Fe3O4/water as the working fluid at 3 V/V% concentration. The research also aims to meticulously examine phase change phenomena in the heating section, particularly focusing on bubble formation and expansion processes. A high-speed video camera was utilized to capture dynamic insights into the behavior of the Fe3O4/water mixture. Based on the findings, a straightforward model was developed to explain bubble generation and growth in the mixture, serving as a useful reference for future PHP designs and optimizations. Visual observations also noted the stable nature of the Fe3O4/water nanofluid over a 4-day period, confirming its consistency throughout the experiments. Moreover, the impact of heat load variation on the evaporator section was assessed using controlled heat inputs ranging from 10 to 80 W. Observations on the arrangement of slugs and plugs at a 50% filling ratio revealed interesting self-adjusting flow patterns in response to increasing heat inputs, providing valuable insights into PHP operational dynamics. Notably, the oscillatory flow behavior of Fe3O4/water, the chosen working fluid, exhibited greater activity in comparison to water. This distinctive flow behavior contributed to achieving heightened thermal performance efficiency for the Fe3O4/water system, attributed to its faster attainment of the annular flow condition. [ABSTRACT FROM AUTHOR]

As a three-dimensional flow channel, the laminated filter has a complex structure, and it is easy to appear phenomena such as too short blocking time and increasing head loss caused by sand interception in the operation process. According to the relationship between head loss and cross-sectional area, an annular flow channel laminated filter was proposed. The circumferential flow channel was added on the lamination surface, which increased the flow direction of the flow channel and played the role of dividing the radial flow channel, achieving the purpose of hierarchical multi-layer filtration in the lamination and improving the number of available flow channels. In order to explore the advantages and disadvantages of the linear flow channel and annular flow channel laminated filter for irrigation water filtration capacity. Through indoor comparative experiments, 120 mesh laminated filter, namely the filter particle size of 125 μm was used to test the head loss and filtration performance of the two filters under four kinds of sand grading median particle size (106, 121, 126 and 165 μm), three kinds of sediment content (0.10, 0.15 and 0.2 g/L) and five kinds of inlet flow (1.5, 2.0, 2.5, 3.0 and 3.5m3 /h), a total of 60 groups of tests. The dependent variables were the head loss, the sediment retention capacity and the median particle size of the interception, and the independent variables were the inlet flow, the sediment concentration and the median particle size of the inlet. The evaluation indexes were the head loss, the plugging uniformity, the sediment retention capacity and the particle size distribution of the interception sediment. The multiple regression equation was established to verify the correlation between the head loss and the filtration capacity. The entropy weight method was used to determine the optimal lamination of the head loss and the filtration capacity. The results show that: under the condition of clear water, the maximum flow head loss of the annular flow laminated filter is 9.1% lower than that of the trapezoidal linear filter. Under the condition of sandy water, the time for the head loss to reach 8m is 1.5～10 times longer than that of the trapezoidal linear filter, and the maximum head loss is reduced by 52.5%. The total sediment retention capacity is increased by 0.5%～6.3%, and the average sand removal rate is increased by 0.22% for the sand with the median particle size greater than 110μm. The siltation channels of the trapezoidal linear filter account for 25%～ 86% of the total number of channels of the trapezoidal lamination, while no siltation phenomenon is observed in the operation cycle of the annular lamination. The head loss of the two kinds of laminated filters was positively correlated with the sediment concentration, inlet flow and inlet median particle size, the sediment retention was positively correlated with the sediment concentration, inlet flow and inlet median particle size, and the interception median particle size was positively correlated with the sediment concentration and inlet median particle size. The annular flow channel laminated filter was more suitable for irrigation water with high sediment concentration and high median particle size distribution than the trapezoidal linear laminated filter. Therefore, the optimal laminated filter can be designed by considering the change of the geometric distribution of the flow channel of the laminated filter, which can reduce the filter head loss and extend its backwashing cycle without reducing the filtration capacity. [ABSTRACT FROM AUTHOR]

This study investigates the flow boiling heat transfer characteristics of refrigerants R134a and R407c in horizontal micro-fin tubes. We conducted experiments across a range of heat flux (15–35 kW·m−2), mass flux (50–250 kg·m−2 s−1), and saturation temperature (15 °C-25°C) conditions. Our findings reveal that R134a consistently exhibits a higher heat transfer coefficient (HTC) compared to R407c, making it advantageous for applications requiring efficient heat transfer. However, R134a also shows a tendency towards premature dry-out flow patterns at higher heat fluxes, which could limit its effectiveness under certain conditions. In contrast, R407c demonstrates more stable flow regimes, maintaining wavy-annular and annular flows without early dry-out, which highlights its robustness at higher heat fluxes. Flow pattern maps indicate that higher heat fluxes promote the formation of wavy and annular flow patterns in both refrigerants, with R134a transitioning to dry-out flows more readily than R407c. The influence of saturation temperature on HTC was also significant, with lower temperatures resulting in higher HTCs for both refrigerants. This can be attributed to the increased thermodynamic driving force for phase change at lower temperatures. Our study aligns with previous research, corroborating the critical role of micro-fin tubes in enhancing HTC. The findings have practical implications for the design and optimization of refrigeration systems, emphasizing the need to carefully select refrigerants and operating conditions to achieve efficient and stable heat transfer performance. [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]

In this study, three types of flow channels including single serpentine, double serpentine, and parallel were compared to investigate the relationship between two-phase flows and the cell performance in the proton exchange membrane water electrolyzer. Pressure drop between the inlet and outlet was measured at the anode channel, and flow patterns affecting the cell performance were investigated using high-speed optical imaging. The single serpentine channel exhibited the best performance among the flow channels used in the experiment because an annular flow with a thin liquid film continuously provided water, preventing performance degradation. The parallel channel performed the worst owing to the slug flow accompanied by Taylor bubbles, which interrupted the water supply. [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]

The flow mechanism of internal two-phase flow atomization remains unclear despite its widespread applications. A newly outside-in-liquid (OIL) atomizer is designed to investigate the two-phase flow mechanism inside the effervescent atomizer in this work. Numerical simulation is used to study the internal flow characteristics of the OIL atomizer under different gas–liquid mass flow ratios (GLRs). The findings indicate that the volume-of-fluid (VOF) model and compressible Euler method effectively capture the intricate evolution of the internal flow. The cavitation phenomenon occurs before the gas phase reaching the orifice. Subsequently, the cavitation phenomenon disappears as the gas phase flows downstream into the orifice. At different GLRs, the gas phase before reaching the mixing chamber is a single separated bubble. However, the final flow patterns are mainly annular flow, which is most obvious at high GLR. Increasing the GLR can increase the gas void fraction in the orifice. Furthermore, the gas void fraction will reach the peak faster and then remain stable. The two phases are accelerated after entering the orifice. Among them, the flow velocity of gas phase is much higher than that of liquid phase. This research demonstrates the notable impact of GLR on the internal flow. Furthermore, it addresses the existing research gap in this aspect of internal flow. [ABSTRACT FROM AUTHOR]

This article discusses a focused study on visualizing the flow patterns in a two-phase pulsating heat pipe (PHP) using Fe3O4/water as the working fluid at 3 V/V% concentration. The research also aims to meticulously examine phase change phenomena in the heating section, particularly focusing on bubble formation and expansion processes. A high-speed video camera was utilized to capture dynamic insights into the behavior of the Fe3O4/water mixture. Based on the findings, a straightforward model was developed to explain bubble generation and growth in the mixture, serving as a useful reference for future PHP designs and optimizations. Visual observations also noted the stable nature of the Fe3O4/water nanofluid over a 4-day period, confirming its consistency throughout the experiments. Moreover, the impact of heat load variation on the evaporator section was assessed using controlled heat inputs ranging from 10 to 80 W. Observations on the arrangement of slugs and plugs at a 50% filling ratio revealed interesting self-adjusting flow patterns in response to increasing heat inputs, providing valuable insights into PHP operational dynamics. Notably, the oscillatory flow behavior of Fe3O4/water, the chosen working fluid, exhibited greater activity in comparison to water. This distinctive flow behavior contributed to achieving heightened thermal performance efficiency for the Fe3O4/water system, attributed to its faster attainment of the annular flow condition. [ABSTRACT FROM AUTHOR]

VOF model and user-defined function were applied to simulate the flow boiling process of water in microchannel with V-cavities. The effects of V-cavity asymmetry (ε) and distribution on the bubble growth and detachment and the transition of gas-liquid two-phase flow in microchannel were analyzed. The results show that the magnitude of the V-cavity asymmetry can change the bubble detachment diameter and detachment time. The bubble detachment diameter of the V-cavity with asymmetry ε of 1.0 is 0.063 mm and 0.025 mm smaller than that of the V-cavity with ε of 0 and ε of 0.5, and the bubble detachment time is shortened by 5.20 ms and 2.40 ms, respectively. The transition of gas-liquid two-phase flow from bubbly flow to confined bubble flow is 2.7 mm backward along the flow direction, and the occupied area of the segment annular flow in microchannel is reduced slightly. When the V-cavity with ε of 1.0 has different distribution along the flow direction, the gas-liquid two-phase flow in microchannel presents different characteristics. The V-cavity with increasingly dense distribution can better inhibit the coalescence of bubbles in microchannel without segment annular flow, which can ensure the existence of liquid film near the wall to avoid the local drying for improving the stability and reliability of flow boiling heat transfer in microchannel. [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]

AbstractIn the present work, air-water two-phase flow pattern and pressure drop in vertical upward annular channel with different diameters are experimentally studied. Two concentric annular test sections with the same hydraulic diameter of 4.6 mm are used in the experiments. The outer diameter and inner diameter corresponding to the two test sections are 18.60 and 12.30, and 86.75 and 80.45, respectively. Bubble flow, cap-slug flow, cap-churn flow, and annular flow were found in both the test sections and the flow pattern map is developed. It is found that the superficial gas velocity has an important effect on the transition of the flow patterns. Pressure drop correlations are reviewed and a total of 12 correlations are collected, including 4 homogeneous flow model (HFM)-based correlations and 8 separated flow model-based correlations. The existing correlations for estimating pressure drop were tested against the measured data. The comparisons show that no correlation studied here provides satisfactory agreement with the whole database. The Chisholm correlation provides the best accuracy with 20.9% for the small test section and 21.5% for large test section. It is also found that the existing models based on separated flow method predict frictional pressure drop with higher accuracy than those based on HFM. The result of this study highlights the requirement of a new method for calculating the frictional pressure drop in annular channels. [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]

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]

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]

This current work evaluates the efficacy of a co-flow nozzle for cold spray applications with the aim of mitigating nozzle clogging issues, which can occur during long-duration operations, by replacing the solid wall of a divergent nozzle section with an annular co-flow fluid boundary. Simulations were conducted on high-pressure nitrogen flowing through convergent–divergent (C–D) axisymmetric nozzles, with a stagnation pressure of 6 MPa and a stagnation temperature of 1273 K. In these simulations, Inconel 718 particles of varying sizes (15 µm to 35 µm) were modeled using a 2-way Lagrangian technique, and the model's accuracy was confirmed through validation against experimental results. An annular co-flow nozzle with a circular cross section and straight passage covering the primary C–D nozzle has been designed and modeled for cold spray application. Co-flow was introduced to the reduced nozzle length to compensate for particle velocity loss at higher operating conditions. It was found that co-flow facilitates momentum preservation for primary flow by providing an annular gas boundary, resulting in increased particle speed for a longer axial distance beyond the nozzle exit of the reduced divergent length nozzle. The particle acceleration performance of the reduced divergent section nozzle, when combined with co-flow, is comparable to the original length nozzle. [ABSTRACT FROM AUTHOR]

Thermal enhancement remains a critical requirement in different engineering applications. Many factors can affect the efficiency of the techniques used for this aim. The purpose of this study is to investigate the impact of particle‐fluid suspensions with heat transfer through porous annular‐sector duct on enhancement techniques and address the potential application of deep learning to suspension problems. The analysis is focused on the fully developed region of the forced convection flow. Thermal and rheological properties of particle‐fluid suspensions were studied using physics‐informed neural networks exploiting transfer learning capabilities for making parameter analysis. Another finite element solution was introduced as a measure of accuracy and to support our findings. Results were prepared in a comparative manner for both solvers including contour plots, tabular, and two dimensional figures. The average Nusselt number and friction factors were calculated for different cases to investigate the value of the thermal performance factor. Our results indicate the downside of suspensions on thermal enhancement and their negative impact on other techniques. [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]

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]

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 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]

As a transitional flow pattern, slug–annular flow occurs over a wide range of operating conditions in micro-channels while its distribution in parallel micro-channels has not been well characterized. Herein, we conducted an experiment to study the phase distribution of slug–annular flow in parallel micro-channels. The test section consists of a header with a diameter of 0.48 mm and six branch channels with a diameter of 0.40 mm. Nitrogen and 0.03 wt% sodium dodecyl sulfate (SDS) solution were used as the test fluids. It was found that the phase distribution of the slug–annular flow was unstable and the duration of the varying process showed regularity with different inlet conditions. Increasing the liquid superficial velocity facilitated the liquid phase to flow into channels at the fore part of the header, while the channels at the rear part of the header were more supplied with liquid as the gas superficial velocity, volume fraction of gas, and volume flow rate increased. Furthermore, the results indicated that the channels located at the rear part of the header experienced a pronounced enhancement in the supply of both the liquid and gas phases, with the spacing between the branches increasing. A predictive correlation was formulated to ascertain the distribution of the liquid phase within slug–annular flow across parallel micro-channels. [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]

Multiphase flow entrainment in natural gas engineering significantly influences the safety and efficiency of oil companies since it affects both the flow and the heat transfer process, but its mechanisms are not fully understood. Additionally, current computational fluid dynamics (CFD) methodologies seldom consider entrainment behavioral changes in pipe elbows. In this article, a verified CFD method is used to study the entrainment behavior, mechanism, and changes in an elbow. The results show that droplet diameter in a developed annular flow follows a negative skewness distribution; as the radial distance (from the wall) increases, the fluctuation in the droplets becomes stronger, and the velocity difference between the gas and the droplets increases linearly. Turbulence bursts and vortices sucking near the wall jointly contribute to droplet entrainment. As the annular flow enters the elbow, the secondary flow promotes the film expansion to the upper and lower parts of the pipe. Droplets re-occur near the elbow exit intrados, and their size is much smaller than those in the upstream pipe. Vortices sucking under low gas velocity play an important role in this process. These findings provide guidelines for safety and flow assurance issues in natural gas production and transportation and bridge the gap between multiphase flow theory and natural gas engineering. [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]

In the work, the annular liquid film and flow condensation heat transfer of R134a inside four horizontal micro-fin tubes were experimentally studied under mass fluxes of 500–1100 kg m -2 s -1. The biggest difference of the tested tubes in geometry is essentially tube diameter and fin helical angle. The influencing mechanisms of mass flux, vapor quality, saturation temperature, fin helical angle, tube diameter, etc., on the heat transfer property were firstly revealed through the liquid film variation. In other words, the transformation rules of the heat transfer coefficient with the experimental variable can be further explained by the liquid film thickness and flow variations. The measured heat transfer coefficients, subsequently, were compared with the calculated values of some existing correlations. After verification, all correlations reported in the researches underestimate the heat transfer coefficient at high mass flux, and the experimental variables, particularly mass flux and vapor quality, have a great effect on the correlation prediction accuracy. To achieve a high-accuracy prediction for the heat transfer coefficient, therefore, on the basis of the theoretical analysis of the continuity, momentum and energy processes in the liquid film, a new correlation was proposed and it can predict the experimental data with an average deviation of 1.61 %. [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]