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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]

Research on hydrogen engines has been actively pursued to achieve carbon neutrality in the transportation sector. To optimize the combustion characteristics of hydrogen engines under various driving conditions, active and precise control of the hydrogen injection flow rate is crucial. Lightweight prediction for hydrogen injection rates from pintle-type injectors, which are widely used in hydrogen engines, is required for the control of the injection rate as well as the model-based engine development. However, lightweight injection rate prediction for gaseous fuel has been conducted solely for hole-type injectors and not for pintle-type injectors that have an annular internal flow path with complex configurations. In this study, a lightweight methodology is introduced to predict the hydrogen injection rate of pintle-type hydrogen injectors based on the compressible flow theory of converging-diverging nozzles with minimum mass flow rate data obtained with a safer surrogate gas. The validity of the method for various injection conditions and gases (nitrogen, helium, and hydrogen) is discussed. The methodology demonstrated prediction accuracy of over 92% for nitrogen and helium injection rates under different injection pressures (1.5–4 MPa) and ambient pressures (0.1–2 MPa). The versatility of the prediction methodology for various gases, including hydrogen, was also confirmed. The error sources were analyzed thoroughly based on the dynamic characteristics of the pintle behavior and differences in gas properties. • A lightweight method for predicting H 2 injection rates from pintle injectors is proposed. • Minimum mass flow rate data were obtained for calculating the nozzle throat area. • Safer surrogate gases can be used to predict H 2 injection rates. • The accuracy of the method showed over 92% for various gases and injection conditions. • Error analysis was conducted based on compressible flow theory and pintle dynamics. [ABSTRACT FROM AUTHOR]

We investigate the effect of pressure-dependent wall slip on the steady Newtonian annular Poiseuille flow employing Navier's slip law with a slip parameter that varies exponentially with pressure. The dimensionless governing equations and accompanying auxiliary conditions are solved analytically up to second order by implementing a regular perturbation scheme in terms of the small dimensionless pressure-dependence slip parameter. An explicit formula for the average pressure drop, required to maintain a constant volumetric flowrate, is also derived. This is suitably post-processed by applying a convergence acceleration technique to increase the accuracy of the original perturbation series. The effects of pressure-dependent wall slip are more pronounced when wall slip is weak. However, as the slip coefficient increases, these effects are moderated and eventually eliminated as the perfect slip case is approached. The results show that the average pressure drop remains practically constant until the Reynolds number becomes sufficiently large. It is worth noting that all phenomena associated with pressure-dependent wall slip are amplified as the annular gap is reduced. [ABSTRACT FROM AUTHOR]

Copyright of Lubrication Engineering (0254-0150) is the property of Editorial Office of LUBRICATION ENGINEERING and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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

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]

This study addresses the issue of unstable flow in large-scale annular linear induction pumps (ALIPs), with a focus on optimizing their design and enhancing performance. Utilizing the ALIP model developed by Toshiba Corporation as a reference, the design process employs the equivalent circuit method to improve the hydraulic performance of high-flow ALIP systems. A comparison of various hydraulic and excitation structure parameters facilitated the identification of an optimal design scheme. A numerical simulation of the ALIP's internal magneto-fluid coupling field was then conducted, based on magnetohydrodynamic (MHD) theory. The simulation results were validated against experimental data, confirming the model's accuracy. Further simulations under various operational conditions were performed to analyze the distribution and magnitude of the axial Lorentz force (FL) and the axial pressure gradient across different flow rates and currents. The analysis indicated that the unstable flow primarily results from inverse pressure gradients, which are caused by the uneven distribution of these forces. To mitigate this issue, the study proposes the addition of a regulating coil winding to the inner stator. This addition significantly reduces the uneven distribution of magnetic fields and pressure gradients. These coils generate a compensating magnetic field that enhances FL within the electromagnetic section, thereby improving the axial force on the magnetic fluid. The results demonstrate that this active regulation method markedly reduces unsteady flow phenomena, stabilizes fluid movement, and offers a novel design strategy for large-scale ALIP systems. The ratio of the area of the regulating coils to that of the driving coils is only 0.33, which minimally increases the pump dimension. Additionally, the energy conversion rate of different regulation currents between the inner and outer regulation coils was compared. It was found that variations in the regulation current alter the total efficiency of the ALIP by no more than 1%, indicating that the control coil winding consumes minimal energy and that the stability of the magnetic fluid can be effectively controlled, making this approach feasible for engineering applications. [ABSTRACT FROM AUTHOR]

A series of experiments are conducted to investigate the transition mechanisms and characteristics of six typical gas–liquid flow patterns in a horizontal–vertical elbow using electrical capacitance tomography and high-speed camera. The dominant modes and corresponding time coefficients are obtained by performing proper orthogonal decomposition on the pulsating gas holdup (GHU) distribution data to explore their physical mechanisms and correlations. Reduced-order descriptions for different flow patterns are discussed. The results show that after passing through the elbow, the horizontal slug or bubble flow turns into vertical bubble flow due to the small gas volume content and the mixing effect of secondary flow, accompanied by a swirl-switching phenomenon. A slug flow forms at the elbow outlet when there is a stratified flow comes from the horizontal pipe, and changes in flow conditions will affect the generation frequency and stability of Taylor bubbles. The horizontal annular or mist flow with high gas volume content will be transformed into churn flow in the vertical pipe. The modal decomposition analysis indicates that, for all the investigated conditions in the present study, mode 1 represents the mean distribution of GHU fluctuations, and there is a pair of modes representing the dominant swirling features. For the slug and churn flows, mode 2 characterizes the features of gas slug or large bubbles, the time coefficient of which is highly connected with that of mode 1. Meanwhile, it is also shown that the obtained low-dimensional descriptions of different flow patterns using the dominant modes are able to reconstruct most of the GHU distribution features in gas–liquid flows with the reconstructive loss less than 3%. [ABSTRACT FROM AUTHOR]

Pipeline transport serves as an effective means to alleviate traffic congestion and reduce carbon emissions from transportation. The hydraulic delivery system, which employs pipeline cars as carriers, addresses the limitations of existing systems. However, its transportation efficiency is affected by variations in the flow structure within the pipelines. During the acceleration of the pipeline car, the sudden contraction flow field from circular to annular gap formed in the vicinity of the end face under dynamic boundary conditions. This study utilized particle image velocimetry (PIV) to visualize and measure the sudden contraction flow field. Based on the obtained experimental results, it investigated the impact of dynamic boundary velocity on the flow structure, velocity characteristics, and energy dissipation of the annular gap. The acceleration process of the dynamic boundary is the conversion of flow energy into the kinetic energy of the annular gap flow and the kinetic energy of the pipeline car. This process is accompanied by phenomena of velocity slip and velocity overshoot. As the velocity of the pipeline car increases, the recirculating vortex within the annular gap dissipates and eventually disappears. The velocity slip gradually decreases, the location of the overshoot point shifts radially, and the magnitude of the overshoot diminishes before ultimately vanishing. From static to steady, the probability density distribution of the slipstream face transitions from a distribution with high skewness and low peak value to a normal distribution with high peak value and low skewness. The irreversible losses that arise in a sudden contraction flow field can be quantified by the increase in entropy. Due to the similarity of the solving processes of large Eddy simulation and PIV, a combined sub-grid stress model is used to solve the flow losses in the flow field. The turbulent dissipation occurs mainly in the recirculation region, shear layer, and high-speed shear regions near the wall. [ABSTRACT FROM AUTHOR]

To investigate the velocity distribution and atomization characteristics of gas–liquid swirl coaxial (GLSC) injectors, atomization experiments and simulations were conducted under atmospheric conditions. The velocity distribution and morphology of the spray from GLSC injectors at varying gas–liquid ratios were measured using particle image velocimetry. The gas–liquid interaction, breakup dynamics, and the velocity of liquid sheet were simulated based on the three-dimensional volume of fluid to discrete particle model (VOF-to-DPM) and octree adaptive mesh refinement. Additionally, a method for extracting droplet diameters from high-quality images has been developed and validated. The results indicate that the sprays maintain a stable cone when the gas–liquid ratio is low. As the gas–liquid ratio increases, particularly at larger recess ratios, self-pulsation phenomena occur. During self-pulsation, the spray cone angle is enlarged, and the breakup length shortens. In a stable spray field, the center exhibits a low velocity region (5–10 m/s), while the spray periphery shows a high velocity region (20–25 m/s). Self-pulsation is induced by the "Klystron effect," which arises from the Kelvin–Helmholtz (K–H) instability at the gas–liquid interface. The center of the self-pulsated spray transitions to a high velocity region due to the accelerated droplet motion driven by the annular gas flow through the spray's center. The radial distribution of mean droplet diameters for both stable and self-pulsated sprays has been summarized. As the gas–liquid ratios and recess ratios increase, the global droplet diameters gradually decrease, with a 75% of droplet diameters falling between 0 and 0.1 mm. [ABSTRACT FROM AUTHOR]

This review aims to contextualize the prospective integration of ferrofluid technologies into two critical oil macro-processes: recovery and transportation, both fundamental components of the oil supply chain. The initial section explores the research content and emerging trends associated with this technology by conducting a bibliometric analysis to highlight its advancements, drawbacks, and potential within the oil industry. The subsequent section discusses the most relevant theoretical aspects of ferrofluids, with a particular emphasis on stability, which is a pivotal yet insufficiently investigated aspect in the context of nanoparticle technologies in oil recovery and transportation. Furthermore, we present an overview of the magnetic properties, constitutive equations of ferrohydrodynamics, and magnetoviscous effects that elucidate the diverse rheological behaviors induced in ferrofluids by the action of uniform and oscillating magnetic field configurations. Against this background, subsequent sections summarize some selected experimental approaches conducted in systems that closely replicate real-world scenarios. These include the physiochemical interactions between ferrofluids and crude oils under the influence of external magnetic fields and thermodynamic flow conditions, such as those observed in reservoir environments. The review concludes with a section dedicated to the flow of ferrofluids in pipelines, highlighting experimental results under the influence of magnetic field configurations that induce reductions in viscosity, as well as alternative non-conventional applications associated with core annular flows. This comprehensive overview aims to provide an objective vision of the potential of ferrofluid technologies in enhancing the efficiency and effectiveness of multiple processes in the oil industry. [ABSTRACT FROM AUTHOR]

Due to the failure of string seals, gas can leak and result in the abnormal annulus pressure in gas wells, so it is necessary to relieve the pressure in gas wells. In the process of pressure relief, the leaked gas enters the annulus, causes a the great disturbance to the annulus flow field, and thus reduces the protection performance of the annular protection fluid in the string. In order to investigate the influence of gas leakage on the annular flow field, a VOF finite element model of the gas-liquid two-phase flow disturbed by gas leakage in a casing was established to simulate the transient flow field in the annular flow disturbed by gas leakage, and the influences of leakage pressure differences, leakage direction, and leakage time on annular flow field disturbance and wall shear force were analyzed. The analysis results showed that the larger leakage pressure difference corresponded to the faster diffusion rate of the leaked gas in the annulus, the faster the flushing rate of the leaked gas against the casing wall, and a larger shear force on the tubing wall was detrimental to the formation of the corrosion inhibitor film on the tubing wall and casing wall. Under the same conditions, the shear action on the outer wall of tubing in the leakage direction of 90° was stronger than that in the leakage directions of 135° and 45° and the diffusion range was also larger. With the increase in leakage time, leaked gas further moved upward in the annulus and the shear effect on the outer wall of tubing was gradually strengthened. The leaked acid gas flushed the outer wall of casing, thus increasing the peeling-off risk of the corrosion inhibitor film. The study results show that the disturbance law of gas leakage to annular protection fluid is clear, and it was suggested to reduce unnecessary pressure relief time in the annulus to ensure the safety and integrity of gas wells. [ABSTRACT FROM AUTHOR]

Parabolic Trough Collectors (PTCs) are a well-established technology for efficiently generating hot water and low-enthalpy steam. For instance, PTCs can be used in steam power systems to drive small Organic Rankine Cycles (ORCs). This study evaluated the thermal efficiency of a PTC equipped with a receiver tube featuring a concentric annular cross-section. This receiver design consists of a tube with a concentric rod inside, forming an annular gap through which the working fluid flows. A thermodynamic model was developed to assess the PTC's thermal efficiency in hot water and low-enthalpy steam applications. The evaluation considered the First and Second Laws of Thermodynamics, factoring in environmental losses. The model included a bare receiver tube with three-rod diameters—3/8, 1/2, and 3/4 inches—and a range of volumetric flow rates from 1 to 6 L per minute. The results showed improved heat transfer with the annular cross-section receiver compared to a conventional circular one, particularly at lower flow rates of 1 and 2 L per minute. The highest increase in thermal efficiency was observed with the 3/4-inch rod at a flow rate of 1 L per minute, where the maximum efficiency reached 40%. [ABSTRACT FROM AUTHOR]

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

This study investigates the droplet formation process in T-junction circular microchannels, emphasizing the influence of wetting properties and contact angles under various operating conditions. A coupled Volume-of-Fluid (VOF)/Level-set multiphase model is employed for Computational Fluid Dynamics (CFD) simulations to accurately capture the microscale phenomena. The effects of contact angles ranging from 125° to 145°, two-phase flow velocities (0.04–0.25 m/s), and interfacial tension (0.035–0.055 N/m) are systematically analyzed. The findings reveal that these parameters significantly impact the detachment length and flow patterns, with four distinct flow regimes identified: dripping, slug, jetting, and annular flow. New dimensionless correlations for slug and detachment lengths are developed and validated through experimental data, offering improved predictive capabilities. The comprehensive flow mapping provided in this study enhances the understanding of multiphase flows in microchannels, offering valuable insights for the optimization of microfluidic device design and practical applications such as extractive desulphurization. These contributions present a novel approach to integrating contact angle effects into microfluidic research, addressing previously overlooked aspects and providing robust guidelines for future studies. [ABSTRACT FROM AUTHOR]

Carrying out the experimental researches on the two-phase countercurrent behaviors in the flow unit of reactor core can provide sufficient theoretical supports for the smooth operation and emergency treatment of different forms of the reactor systems. In this research, the flooding phenomenon, the characteristics of flow parameters and formation mechanisms of parallel and countercurrent flooding instability of annular flow in rod bundle channel were analyzed, and the result indicates that one flooding cycle could be divided into the onset flooding region, the full flooding region and the whole liquid phase downstream region. The experimental conditions where the flow instability appeared in the rod bundle structure are in the flooding state according to the criterion from Wallis, but on the conversion line of flooding and not flooding state according to the criterion from Zapke and Alekseev. The experimental pressure drop changing with time was compared to the instability behaviors of annular flow, and the result shows that when the pressure drop reaches a local maximum, the high-speed photography captures the starting point of onset flooding region, and when the pressure difference reaches a local minimum, the starting point of whole liquid phase downstream region is seen in the field of view. According to the high-speed photographic image data processing, the parallel flow time, the countercurrent flow time and the overall cycle time were acquired and analyzed. When the liquid phase flow rate is lower than 0.1 m/s, the overall cycle time does not change significantly, and the parallel flow time is lower than the countercurrent flow time. When the liquid superficial velocity is within the range of 0.1-0.3 m/s, the overall cycle time decreases with the increasing gas superficial velocity, and the time ratio of the parallel and countercurrent flow time changes little. When the liquid superficial velocity is higher than 0.3 m/s, the time ratio increases with the increasing gas superficial velocity. The study on the micelle velocity for onset-flooding shows that when the liquid superficial velocity is lower than 0.2 m/s, the micelle velocity for onset-flooding is higher than the gas velocity. The value with which the micelle velocity for onset-flooding is higher than gas superficial velocity decreases gradually with the increasing liquid velocity. At some conditions with high gas velocity, the micelle velocity for onset-flooding is lower than the gas superficial velocity when the liquid superficial velocity is higher than 0.2 m/s. The formation mechanisms of parallel and countercurrent flooding instability depend upon the changing force of gas core and the effect of liquid gravity in different flooding regions.

Taylor-Couette-Poiseuille (TCP) flow, characterized by the flow through an inner rotating shaft and an outer stationary cylinder, is a fundamental flow system in many industrial applications, including ship stern tubes, turbomachinery, journal bearings, and offshore drilling. Understanding the hydrodynamics of the TCP flow offers significant benefits for ensuring the robust design and operational efficiency of such systems. This paper presents the numerical modeling of turbulent TCP flow to assess the combined effects of two key control parameters-axial Reynolds number (10000-30000) and Taylor number (2.2x107-3.1x109)-on the fluid dynamics within the system. Using Reynolds Stress Modeling, this study investigates the behavior of TCP flow at high Reynolds numbers, which is relevant to real-world rotating machinery. The results indicate that the interaction between rotation and axial flow is not linear, with high rotation rates showing distinct behavior from low rotation rates, especially in the throughflow effects. At low and moderate rotation numbers (N), both the mean and turbulent variables display strong dependence on the rotational velocity and axial flow rate. However, further increases in N lead the flow field to be increasingly dominated by the contribution of rotation, and mean flow variables become relatively independent of the imposed flow rate. Furthermore, systematic deviations from the log-law in the boundary layer velocity profiles further emphasize the need to account for the combined effects of rotation and axial flow in the TCP flow system design and operation.

Big Data Analysis from the worldwide field shows that lost circulation is a common phenomenon in drilling and the success ratio of remedial treatment for lost circulation is low. It is not only because of these complexities of the formation, but also because of the poor performances of the lost-circulation materials (LCM) and technologies. This paper proposes a new method in plugging, which is based on a particular physical method for lost circulation controlling and plugging while drilling. This method is different from these traditional treatments, which only use chemical methods. When pore-permeable and fractured leakage formations are encountered while drilling, We can use this new hydraulic tool, the drilling fluid will have a diffluence at a constant rate from the jet of the hydraulic tool which is installed on the drilling pipe and the fluid laden with particles can be injected into the natural or induced fractures of the borehole wall which may lead to lost circulation. Combined with the corresponding drilling fluids which have been tested in the laboratory, the additives such as ground marble, ground nutshells, and graphite in the drilling fluid are quickly pushed into the fractures because of the differential pressure provide by the hydraulic tool, then form a firm seal at the mouth of the fractures which could isolate fluid pressure in the wellbore and prevent effective pressure communication to interfere the extension of the fracture. What's more, according to the stress cage theory, when these sealing particles which prop the fracture open, act as wedges to compress the rock around the wellbore, the hoop stress could be increased, so that the wellbore pressure containment (WPC) could be improved. Since the annular flow may have some interference with the side nozzle jet, this paper also numerically simulates the flow field of the annular air section through the fluid simulation software Fluent, and the simulation results show that the interference of the annular flow on the jet is very weak and basically has no effect. In addition, through the oilfield field test, it is known that this new physical plugging method has good plugging effect, and it can obviously improve the pressure-bearing capacity of the formation, which has great popularization value. [ABSTRACT FROM AUTHOR]

AbstractIn cement engineering, the cement sheath is not only influenced by elevated temperatures, increased pressure, and the static load confining pressure within the formation but also encounters external impact loads. These loads can rupture the cement paste, compromising the cement sheath’s interlayer sealing capability. Consequently, this can give rise to an annular flow of oil, gas, and water. Hence, this study introduces wollastonite fiber (WF) into the cement slurry to modify the cement paste. The investigation explores the mechanical properties, energy evolution, and damage characteristics of the cement paste with WF under dynamic impact loads. This is achieved by simulating the dynamic impact loads experienced downhole using the separated Hopkinson pressure bar (SHPB) technique. A straightforward SHPB model is constructed using ABAQUS finite element simulation software, and its accuracy is confirmed through experimental validation. The impact test outcomes revealed a notable enhancement in the dynamic load peak strength of the cement paste cured for 14 days. Specifically, there was an increase of 136.75%, 202.10%, and 320.55% compared to the control group at impact speeds of 6 m/s, 8 m/s, and 10 m/s, respectively. The absorption energy increased remarkably, showing 356.03%, 388.61%, and 142.14%, respectively. The simulation findings confirm that the devised simple SHPB model effectively replicates electrical signals aligned with the observed experimental results. The dispersed fibers create a three-dimensional network within the cement paste. This network enhances the impact resistance of the cement paste by leveraging the mechanisms of crack deflection, fiber fracture, and energy dissipation through fiber pull-out. [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]

This study investigates countercurrent air-water two-phase flow in vertical pipes with inner diameters of 26 mm and 44 mm and a height of 2000 mm, under controlled conditions to eliminate heat and mass transfer. Cutting-edge techniques were employed to measure the liquid film thickness (δ) and entrainment (e) within the annular flow pattern. The methodology involved a systematic comparative analysis of experimental results against established models, identifying the most accurate methods for predicting flow behavior. Specifically, the Schubring et al. correlation was found to most accurately predict e in 26 mm pipes, while the Wallis correlation was more accurate for 44 mm pipes. Additionally, interfacial shear stress was analyzed, confirming the high precision of the δ and e parameters. This research enhances the understanding of countercurrent air-water two-phase flow by providing reliable estimation methods for different pipe diameters and emphasizes the significance of accurately determining interfacial shear stress. Key findings include the identification of the most accurate models for different pipe sizes and addressing challenges in measuring δ and e under controlled conditions. The study's novelty lies in its comprehensive comparative analysis of existing models, leading to improved predictions of flow dynamics in vertical pipes, thereby contributing valuable insights into two-phase flow behavior in geosciences and environmental engineering. [ABSTRACT FROM AUTHOR]

The present work aims to focus on the heat transfer analysis of the peristaltic flow of biviscosity fluid in an annular region between two coaxial flexible tubes with different amplitudes and phases under the influence of a radially varying magnetic field and constant rotation. In this model, the non‐Newtonian biviscosity fluid is flowing through the annulus region between the two concentric inclined tubes. The outer flexible tube is permeable and supposed to satisfy the Saffman slip condition. The governing equations for the considered problem are simplified under the assumptions of a creeping flow and long‐wavelength approximations. Semi‐analytical expressions for the axial velocity and temperature profile are obtained using the homotopy perturbation method. Here, the expressions for shear stress and stream function are also obtained. In this work, the authors discussed the impact of various flow parameters like the Hartmann number, rotation of the frame, permeability parameter, phase difference, amplitude ratios of inner and outer tubes, radius ratio, and inclination angle on the above flow variables. The streamline contour plots are also drawn for the realization of the fluid flow inside the annular endoscopic region. A noticeable result which is drawn from the present study is that phase difference ξ$\xi$ and amplitude ratio ϕ1$\phi _1$ are responsible for reduction and enhancement in temperature and axial velocity of the moving fluid, respectively. It is also found from the present examination that the rise in the strength of the applied magnetic field enhances the transverse fluctuations of peristaltically propagating waves. The comparison of the sinusoidal waveform with the various types of waveforms, such as triangular, trapezoidal, and square waveforms, in the case of a peristaltic endoscope is also discussed. The proposed model may give insights into designing a novel endoscope and decide whether such types of peristaltic endoscopes have exemplary implementations for surgical and mechanical purposes. [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]

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]

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]

A conductance-based sensor to measure liquid film thickness during annular two-phase flows in microchannels has been developed in the present study. The liquid film plays an important role on the characterization of two-phase annular flows. The mean thickness and the presence of interfacial waves influence the heat transfer rate, critical heat flux and pressure drop. The proposed sensor has a ring-shaped design and targets the measurement of films thinner than 50 µm in order to provide detailed information on the liquid film behavior during wall dryout events. It is fabricated on a TEMPAX wafer with micro-electro-mechanical systems (MEMS) technologies. The performance of the prototype device is assessed by using aqueous solutions of known conductivity and imposing liquid films with prescribed thicknesses above the sensor. The effects of the geometrical parameters on the sensor behavior are discussed with the aid of numerical simulation and experimental results. It is found that increasing the size of the electrodes increases the measured electrical signals, while increasing the spacing between the electrodes decreases the measured signal. [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]

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]

Experiments were conducted on the pressure drop fluctuations of R245fa boiling through a horizontal microchannel with a diameter of 0.94 mm and a heated length of 170 mm at various gravity levels. The visualization results show that under inlet saturation conditions, three typical periodic oscillation modes are observed: continuous two-phase flow, bubbly/annular alternating flow, and churn/annular alternating flow. The flow oscillation characteristics within the channel are closely related to bubble dynamics, the vapor–liquid interface evolution, and the upstream compressible vapor volume. It has also been found that increasing the mass flux or decreasing the heat flux can enhance the suppression effect on pressure drop oscillation. In addition, under inlet subcooling conditions, although the total pressure drop increases with the increase in gravity level (1–2.78 g), and the amplitude of pressure drop fluctuation first increases and then decreases with the increase in gravity level, with the transition point occurring approximately at an = 1.10 g. The impact of gravity level on the amplitude of pressure drop fluctuation is primarily determined by the relative dominance of bubbly flow and annular flow within the channel. [ABSTRACT FROM AUTHOR]

In this experimental study, we demonstrate that settling polymethyl methacrylate (PMMA) microparticles with diameters ranging from 6 to 60 µm segregate into distinct bands according to their size when subjected to a rotating laminar annular gap flow with a diverging gap width in the axial direction. Different gap widths ranging from 130 to 1200 µm have been investigated in the fully laminar flow regime. Distinct, spatially separated particle bands of different particle sizes have been observed for nine different geometric configurations, including non-conical, conical, double conical, and variously inclined conical inner cylinder shapes. The study considers different rotation rates, geometric combinations, particle volume fractions, and particle size combinations. Particle size separation was achieved at volume fractions ranging from 2.2% to 11% for rotating inner cylinders. In contrast, no separation occurs during the experimental run when both the outer and inner cylinders are perfectly cylindrical, with no significant variation in the annular gap height. Our experiments also show that rotation of the inner cylinder results in more pronounced particle separation than rotation of the outer cylinder. Microscopic particle image velocimetry (µPIV) measurements show that the presence of particles induces an axial velocity component, which acts as a key transport mechanism. In addition, a significant variation in shear rate is observed across particle bands, which may explain size segregation by shear-induced migration. Furthermore, single particle simulations show that particle trajectories and velocities vary significantly with particle size. [ABSTRACT FROM AUTHOR]

In order to improve the accuracy and efficiency of flow pattern recognition and to solve the problem of the real-time monitoring of flow patterns, which is difficult to achieve with traditional visual recognition methods, this study introduced a flow pattern recognition method based on a convolutional neural network (CNN), which can recognize the flow pattern under different pressure and flow conditions. Firstly, the complex gas–liquid distribution and its velocity field in the annulus were investigated using a computational fluid dynamics (CFDs) simulation, and the gas–liquid distribution and velocity vectors in the annulus were obtained to clarify the complexity of the flow patterns in the annulus. Subsequently, a sequence model containing three convolutional layers and two fully connected layers was developed, which employed a CNN architecture, and the model was compiled using the Adam optimizer and the sparse classification cross entropy as a loss function. A total of 450 images of different flow patterns were utilized for training, and the trained model recognized slug and annular flows with probabilities of 0.93 and 0.99, respectively, confirming the high accuracy of the model in recognizing annulus flow patterns, and providing an effective method for flow pattern recognition. [ABSTRACT FROM AUTHOR]

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

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]

Based on a diesel hydrogenation unit in Middle East, INPLANT software is for hydraulic calculations of the two-phase flow pipeline in the reaction system. The effects of pipeline diameter, gas-liquid ratio and fluid load on the transition of two-phase flow patterns in horizontal pipelines are analyzed. The results show that the unsteady slug flow can be transformed into stable annular flow by increasing the gas-liquid ratio of the fluid; changing the pipe diameter and fluid load cannot transform the two-phase flow pattern of the pipeline studied in this paper from slug flow to annular flow; however, when the liquid phase velocity is reduced to a sufficiently low, the flow pattern can be transformed into wavy flow. The calculation results are used to guide the operation adjustment of the unit, improving the gas-liquid ratio of the fluid can eliminate the pressure fluctuations of the reaction system. It shows that the flow pattern transformation trend simulated by the software is close to the actual production, and the accuracy is high. [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]

The mode of a supersonic flow around a cavity depends on the parameters of the incoming flow and the geometry of the cavity. In a certain range of ratios between the length and depth of the cavity, both open and closed flow modes in the cavity are possible. An important practical problem is to find ways to control the flow modes in the cavity, and in particular, ways to expand the region of favorable open flow modes. This paper presents the results of an experimental study of a supersonic flow around an annular cavity formed by a coaxial conical tip and a cylindrical body connected by a cylindrical rod. A perforated interceptor is used to control the flow mode in the cavity at different angles of the tip cone. With a continuous change in the length of the cavity in the flow, the boundaries of the regions of the single-mode and multimode cavity flow are determined. The data obtained show the possibility of significantly expanding the region of the fopen flow mode in the cavity. [ABSTRACT FROM AUTHOR]

This paper presents experimental studies of a supersonic flow around axisymmetric annular cavities on pointed cylindrical bodies at angles of attack. A single- and multimode flow around the cavity is observed in a wide range of determining parameters (relative length of the cavity L/h and angle of attack α). Reversible and irreversible switching of flow modes in the cavity occurs with a continuous change in the determining parameters. In a closed cavity, with an increase in the angle of attack, a local pressure increase is recorded on the leeward side of the rear step, exceeding the pressure on the windward side of the same step. [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]

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]

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]

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]

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]

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]

Copyright of Environmental & Social Management Journal / Revista de Gestão Social e Ambiental is the property of Environmental & Social Management Journal and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This 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]

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]