Search Results (149)

In ultra-cold narrow-window drilling, pipe connection causes flow-path switching as the main circulation is interrupted and bypass circulation is established, breaking the initial relative pressure balance of the whole wellbore and inducing asymmetric transient variations in flow distribution, annular friction, and bottomhole pressure response, thereby increasing the risks of wellbore instability, lost circulation, and kicks. To address the poor pressure-control accuracy, long non-productive time, and inadequate low-temperature adaptability of conventional drilling technologies in the Irkutsk block of Russia, this study developed and field-tested an integrated all-electric managed pressure drilling (MPD) and cold-resistant continuous circulation system (CCS). Existing conventional technologies often suffer from high communication latency and hydraulic freezing in extreme cold environments, leading to uncoordinated pressure compensation. To overcome these limitations, the scientific novelty of this work lies in proposing a transient pressure rebalancing mechanism that effectively suppresses the asymmetric pressure disturbances induced by topological flow path switching. Methodologically, the proposed system was validated through a comprehensive industrial field test. An improved Herschel–Bulkley temperature–pressure coupled model was established to dynamically calculate full wellbore annular pressure loss. Furthermore, a dedicated hardware adapter module utilizing multi-protocol conversion was integrated to achieve a communication delay of less than 8 ms, enabling high frequency coordinated pressure regulation. Field results demonstrate that compared to the delayed responses of conventional systems, the proposed integrated approach successfully maintained a dynamic backpressure tracking error within ±0.069 MPa under extreme conditions of −38 °C and a narrow pressure window of 0.08 g/cm³. The rapid suppression of asymmetric transient responses prevented any lost circulation, kicks, or wellbore collapse. These findings highlight the significant advantages of the integrated system in maintaining pressure field stability, thereby providing a robust and innovative engineering solution for complex well interventions. Full article

This paper investigates flow resistance and heat transfer during flow boiling of HFE-649 in a vertical annular minigap formed between an outer glass tube and an inner copper tube heated by a centrally located cartridge heater. Two variants of the copper heating surface were examined: a smooth surface and an enhanced surface produced by threading. The experimental measurements included fluid temperature and pressure at the inlet and outlet of the minigap, wall temperature along the test section, and the electrical parameters of the heater. The total pressure drop was analyzed using the Lockhart–Martinelli approach, with the Fanning friction factor calculated from a correlation in the literature and from an empirical relation fitted to the present dataset. Because the available pressure drop dataset is limited, the latter relation is treated here as a preliminary, geometry-specific fitting used as an auxiliary input for the present calculations rather than as a generally validated correlation. The resulting pressure drop estimates were then used to determine an effective axial velocity profile in the minigap. The thermal analysis was based on a system of steady-state energy equations for the copper tube and the fluid. The coupled inverse problems were solved using the Trefftz method, which provided two-dimensional temperature distributions in both domains and enabled the calculation of local heat transfer coefficients at the solid–fluid interface. The wall temperature results obtained using the Trefftz method were cross-checked against the Fourier-transform-based solution, with both approaches giving similar results. For the dataset considered, the empirical friction factor relation provided lower mean relative differences in pressure drop prediction than the literature relation, particularly for the smooth surface. The reconstructed wall temperature field showed good agreement with the measurements, while validation of the fluid temperature field was limited to the inlet and outlet data. For the present operating conditions, the results indicate that the threaded surface modifies local heat transfer behaviour only moderately and does not produce a pronounced overall enhancement over the entire minigap length. Full article

Facing the harsh offshore environment characterized by severe space constraints and continuous platform motion, this study develops an optimized rotating packed bed (RPB) for compact and robust triethylene glycol dehydration. Through integrated experimental and computational investigation, the concentric-ring rotor was identified as superior among four configurations, consistently achieving dehydration equilibrium above 80% under lean TEG conditions. CFD analysis revealed its fundamental mechanism: synergistic matching between the centrifugal force field and annular flow paths yields the most uniform liquid distribution. This enabled the establishment of a strong predictive correlation (R² = 0.935) between simulated liquid uniformity and experimental dehydration performance. Guided by flow field diagnostics, targeted structural optimizations increased dehydration equilibrium from 86.1% to 92.25% while reducing system pressure drop by 73%. Parametric studies defined an optimal operating envelope at a gas-to-liquid ratio of 60:1 and system pressure of 2 MPa, achieving peak efficiency of 96.42% with robust performance across 50–150% load variations. This work demonstrates a simulation-guided pathway for intensifying separation processes, providing a validated framework for designing marine-adapted dehydration technology. Full article

In gas drilling, the local annular contraction caused by a drillpipe tool joint can markedly reduce cuttings’ carrying capacity and increase the risk of localized blockage and sand bridging near the tool-joint region, thereby threatening hole cleaning and drilling safety. To investigate this problem, a three-dimensional CFD–DEM two-way coupling model was established by considering the geometric features of the drillpipe tool joint and gas–solid interaction. The effects of gas mass flow rate, solids feed rate, and particle diameter on local cuttings’ transport states and annular pressure-drop responses near the tool joint were systematically analyzed. The results show that three typical local transport states can develop near the tool-joint region, namely continuous passage, fallback, and clogging accompanied by sand-bridge formation. Fallback cases occur only within a finite interval around the critical gas mass flow rate for cuttings’ transport. Under the geometric and operating conditions considered in this study, localized clogging first appears when the particle diameter reaches approximately 10.5 mm, and the proportion of clogging cases increases rapidly with a further increase in particle diameter. Increasing the solids feed rate intensifies particle retention, accumulation, and collision near the tool joint, promotes earlier clogging, and markedly narrows the operating range of continuous passage; stable clogging is difficult to form when the solids feed rate is below 8 kg/s. Distinct annular pressure-drop histories correspond to different local transport states, with low amplitude fluctuation for continuous passage, repeated pulsation for fallback, and sustained growth in pressure difference magnitude for developing clogging accompanied by sand bridge formation. These results demonstrate a clear correspondence between local transport states near the tool joint and annular pressure-drop responses under the investigated geometry and operating window. They provide a mechanism-level basis for interpreting localized blockage near the drillpipe tool joint, while quantitative field application requires calibration for the specific annular clearance, monitoring interval, gas-injection condition, and cuttings’ loading condition. Full article

Offshore high-water-rate gas wells can often sustain stable production for a considerable period after liquid first appears at the wellhead. Unlike conventional onshore gas wells with relatively low liquid production, these wells can remain in stable production during the middle and late production stages even when the gas velocity in the wellbore has fallen far below the critical value predicted by conventional liquid-carrying criteria. Under such conditions, the wellbore flow pattern commonly shifts from annular mist flow to churn flow and slug flow, and liquid transport becomes governed by a dynamic balance jointly controlled by pressure differential and gas entrainment. As a result, conventional critical liquid-carrying theory alone is no longer sufficient for accurate production state identification. To address this issue, this study proposes a production state identification method for offshore high-water-rate gas wells based on dynamic pressure profile calibration and nodal analysis. In this method, the wellbore pressure profile serves as the key link between outflow capacity and production state evaluation. Measured data from flowing pressure tests are used to calibrate the pressure profile within the selected multiphase flow correlation by introducing two calibration coefficients, namely the liquid holdup calibration coefficient and the two-phase friction calibration coefficient. Gaussian process regression is then applied to model the temporal evolution of the calibration coefficients, generate their fitted trajectories, and predict their values at the next time step. By using the predicted calibration coefficients to recalibrate the pressure profile, dynamic calibration of the wellbore pressure profile is achieved. Field applications to four offshore high-water-rate gas wells show that the calibrated pressure profiles are in closer agreement with the measured pressure points. The accuracy of production-state identification is also significantly improved, and the gas production rates calculated from calibrated nodal analysis are closer to the values reported in daily production records than those obtained before calibration. These results demonstrate that the proposed method effectively improves both wellbore pressure profile prediction and production-state identification for offshore high-water-rate gas wells. The study provides a practical method for production state evaluation and production management of offshore high-water-rate gas wells during the middle and late stages of field development. Full article

Thermoacoustic instability remains an important challenge in gas turbines. In can-annular combustors, cross-talk effects can lead to complex collective dynamics. This paper investigates the in-phase synchronization of low-frequency thermoacoustic oscillations in a can-annular combustor, focusing on the upstream cross-talk mechanism mediated by the compressor combustion casing. Dynamic pressure data from the full-scale engine reveal a transition from independent, low-amplitude pressure dynamics to a state of high-amplitude, in-phase synchronized oscillation in the combustor system. To quantify the upstream cross-talk effect, the multi-port acoustic scattering matrix of the casing is computed by solving the Helmholtz equation based on a mean-flow field obtained from Reynolds-Averaged Navier–Stokes simulations. Analysis of the matrix shows that the casing provides a coupling path between cans, with strength and phase being insensitive to the relative azimuthal position of the cans. Based on this physical insight, a star-network model of coupled Van der Pol oscillators is developed. The model, with parameters identified from experimental data and inferred from the scattering matrix, successfully reproduces the synchronization phenomenon observed in the experiment. A subsequent parametric study based on the validated model shows that in-phase synchronization occurs within periodic windows of the time delay and that the range of these windows expands with increasing coupling strengths. For $\tau =0.1T$, $0.85T$ and $1.1T$, synchronization is achieved with moderate coupling strengths. For $\tau =0.35T$ and $0.6T$, the interaction between the two coupling mechanisms suppresses synchronization even at strong coupling strengths. This study shows that the upstream cross-talk effect is an important mechanism for in-phase synchronization and provides a validated, physics-based model for analyzing and predicting the collective thermoacoustic behavior of can-annular combustors. Full article

This study utilizes computational fluid dynamics (CFD), numerical simulation of particle separation characteristics enhanced by synergistic extraction–shearing is performed, and the two-phase flow in a liquid–solid stirred tank is simulated using the Eulerian–Eulerian two-fluid model and the standard $k-\epsilon$ model. The effects of impeller speed, the hole arrangement pattern of the annular shroud, and the hole area on the multiphase fluid dynamics behavior and stirring power inside the tank are systematically studied. The results show that stirring speed is a key operating parameter affecting turbulence intensity and particle mixing uniformity. When the stirring speed increases from 2000 r/min to 4000 r/min, the overall tank turbulence increases significantly, but the stirring power increases from 4.69 kW to 36.57 kW. The annular cover at the bottom is arranged with vertical openings, which enables full energy transfer within the tank and effectively enhances the turbulence intensity in the middle and lower sections of the flow field; the horizontal opening form is more conducive to the radial diffusion of particles in the middle layer. Reducing the hole area by half increases the fluid jet velocity and local shear stress, effectively improving particle distribution uniformity, while the stirring power decreases by 43.75%, thereby achieving the collaborative optimization of mixing efficiency and energy consumption. Full article

Nine sets of fin parameter combinations, including a plain tube control group, were modeled. Simulations were performed under steady-state conditions using the EWT Realizable k-ε turbulence model, with benzene and water as working fluids, while accounting for temperature-dependent thermophysical properties. Flow field distribution, temperature profile, Nusselt number, and pressure drop in the shell side of the heat exchanger were analyzed. Response surface methodology was employed to systematically evaluate the coupled effects of fin height and fin spacing on thermal performance. The results indicate that annular fins significantly enhance heat transfer by inducing secondary flow and disrupting the thermal boundary layer. Compared to the smooth tube, the finned tubes increased the Nusselt number (Nu) by up to 28.6% and the total heat transfer rate by 13.55%, while the pressure drop (ΔP) increased by approximately 9.81% to 16.5%. The analysis revealed that fin height is the dominant factor affecting performance, whereas fin spacing plays a regulatory role. As the fins became taller or denser, the temperature field evolved from stable stratification to intense mixing and eventually to local disorder. The study identified an optimal parameter range for engineering applications. A fin height of 2–3 mm combined with a spacing of 10–15 mm achieves the best balance between heat transfer enhancement and flow resistance. Specifically, the combination of h = 3 mm and s = 10 mm yielded the highest Energy Efficiency Coefficient (EEC) of 1.567. This configuration is recommended for large-flow, pressure-drop-sensitive systems, such as those found in petrochemical plants or long-distance heat transmission applications. Full article

This study experimentally investigated, using a water-model hydrodynamic analogue, the effects of crystallizer rotational speed and baffle configuration on the flow-field structure, mass transfer, and mixing behavior inside the crucible of a rotational segregation model system relevant to silicon processing. Three configurations were examined: no baffle, straight baffles, and inclined baffles. Flow visualization and stimulus–response tracer experiments were conducted at 200 and 300 rpm to compare their effects on the main flow pattern and mixing characteristics. The results showed that, without baffles, a complete annular main flow formed, and the fluid moved downward spirally along the crystallizer wall. Mixing was relatively fast, indicating limited potential for local tracer retention. With straight baffles, the main flow was strongly obstructed and redistributed, and the mixing time in local bottom regions, especially in front of the 90° baffle, was markedly prolonged. This behavior suggested a more favorable hydrodynamic environment for local retention and accumulation in the model system, and the effect was most evident at 200 rpm. With inclined baffles, transport in the upper region was enhanced, whereas bottom flow was weakened. Although the tracer could move downward along the baffle surface, it was rapidly swept away after reaching the bottom, indicating reduced stability of local accumulation. Increasing the rotational speed from 200 to 300 rpm strengthened the overall flow and shortened the mixing time under all conditions. Overall, straight baffles, particularly at 200 rpm, produced the strongest tendency for local retention in the present model system. These results provide preliminary hydrodynamic insight into flow regulation and transport behavior in rotational segregation systems. Full article

To address the issues of sealing leakage and airflow-induced vibration in high-speed turbomachinery, a conical straight-tooth annular clearance sealed hybrid aerostatic/aerodynamic bearing is investigated. A three-dimensional CFD model is established to study the effects of radial clearance height, inlet pressure, rotor speed, and eccentricity on pressure distribution, velocity distribution, and leakage rate. The results show that leakage exhibits a strong positive nonlinear correlation with clearance height and inlet pressure, following a power-law or polynomial relationship, while rotor speed and eccentricity exert negligible effects (less than 5%). The underlying mechanisms are identified as the kinetic energy diversion caused by circumferential shear and the mutual cancelation of throttling and backflow effects. Increasing the gap height enhances leakage by expanding the hydraulic diameter and strengthening vortex disturbance; increasing inlet pressure promotes leakage by elevating the driving force and intensifying local flow separation. Full article

This study investigates the factors influencing the performance characteristics of annular jet pumps (AJPs) conveying non-Newtonian fluids, to enhance their suction capability for marine organisms such as jellyfish, which exhibit properties close to non-Newtonian fluids. Based on the power-law fluid model, realizable k-ε model, and volume of fluid (VOF) model, shear-thinning carboxymethyl cellulose (CMC) was selected to simulate marine organisms like jellyfish. Fluent software was employed to numerically simulate the performance characteristics and internal flow field of the annular jet pumps. The results demonstrate that the shear-thinning effect of non-Newtonian fluids reduces the maximum efficiency point of annular jet pumps and decreases the flow rate ratio corresponding to this efficiency point. As the concentration of CMC solution increased to 0.5%, the maximum efficiency point decreased by 5.5%, and the flow rate ratio corresponding to this efficiency point dropped from 1 to 0.8. These findings provide reference and insights for analyzing the full flow field of annular jet pumps pumping shear-thinning non-Newtonian fluids and for structural design of such pumps. Full article

To address the issues of easy leakage and low sand-flushing efficiency of coiled tubing working fluid in shale gas horizontal wells, this study investigates the flow behavior of foam fluid in both the coiled tubing and the annulus during foam sand-flushing operations, and optimizes operational parameters to enhance sand-flushing efficiency. Considering the dynamic variations in foam fluid properties with temperature and pressure, secondary flow effects in the spiral section, annular eccentricity, wellbore trajectory, and the solid phase in sand-carrying fluid, a one-dimensional steady-state hydraulic model incorporating flow and heat transfer is developed for the entire wellbore. This model covers the spiral, straight, jet, and annular sections of coiled tubing. Using field data from an example well, simulations yield the pressure distribution along the foam circulation path, the total circulation time, and key operational parameters. The feasibility of coiled tubing foam sand-flushing in shale gas horizontal wells is demonstrated, and the optimization of operational parameters to improve sand-flushing efficiency is analyzed. The findings provide important guidance for parameter design and equipment selection for safe and efficient sand-flushing operations in shale gas horizontal wells. Full article

Diet form is increasingly recognized as a welfare-relevant factor in intensive aquaculture, yet the effects of feed cooking on fish behavioral and physiological welfare remain poorly characterized. Juvenile southern catfish (Silurus meridionalis; 6.18 ± 0.52 g) were reared for 6 weeks in an indoor recirculating aquaculture system and fed either raw grass carp (Ctenopharyngodon idella) muscle (fish fed raw muscle, FR) or cooked grass carp muscle (fish fed cooked muscle, FC; 15 min ramp to ~100 °C followed by 2–3 min at ~100 °C). Locomotor activity and anxiety-like behavior were assessed using the open-field test and an annular light–dark preference assay, respectively. Flow-through respirometry further revealed a significantly lower standard metabolic rate (SMR) in FC fish than in FR fish, decreasing from 10.30 to 6.83, which represents a 33.7% reduction. Endocrine and biochemical analyses showed that cooking significantly decreased serum total triiodothyronine (T3) by 23.8%, whereas routine serum biochemical indices remained unchanged. In brain tissue, dopamine (DA) was significantly reduced by 7.2% in the FC group, and RT-qPCR analysis of dopamine-related genes further showed a significant downregulation of the rate-limiting synthesis gene th. These results indicate that cooking primarily downshifts the activity-energy axis in southern catfish and is accompanied by coordinated thyroid and dopaminergic changes. To our knowledge, this is the first integrated study to evaluate the behavioral, metabolic, and neuroendocrine effects of cooked feed in S. meridionalis, providing a short-term phenotypic baseline for assessing welfare-relevant feeding scenarios in aquaculture. Full article

In fire emergency ventilation systems, EC (Electronically Commutated) internal-rotor axial fans are critical devices, but their high-speed operation generates aerodynamic noise often exceeding 90 dB (A). While struts are core structural components regulating flow field stability, their specific geometric impact on trailing-edge vortex shedding and noise generation mechanisms remains unclear. This study investigates three strut configurations: a hexagonal annular type, a hexagonal double-ring type, and a three-pronged type. A coupled numerical model was established using Large Eddy Simulation (LES) and the Ffowcs Williams and Hawkings (FW-H) acoustic analogy. The Q-criterion was employed to analyze vortical structures, with numerical predictions validated against experimental measurements in a semi-anechoic chamber. The results quantitatively demonstrate that optimizing the strut geometry significantly mitigates unsteady flow separation. The three-pronged strut (Model C) effectively dispersed high-velocity airflow, reducing the peak turbulent kinetic energy (TKE) at the inlet by 30% compared to the original design (Model a). Furthermore, Model C achieved a 6.7 dB reduction in the sound pressure level at the blade-passing frequency (BPF), alongside a 14.1% reduction in pressure pulsation amplitude near the blade tip. Structural optimization of struts enables synergistic control over turbulence distribution and pressure fluctuations. By disrupting the phase coherence of shed vortices, the optimized design fundamentally suppresses aerodynamic noise, advancing axial fan design toward precise quantitative aeroacoustic optimization. Full article

Ammonium bisulfate (ABS) fouling in air preheaters has become a critical challenge restricting the safe and efficient operation of coal-fired units. Optimizing the flow field of the outlet of the upstream SCR system is a potentially effective path to mitigate ABS fouling. In this work, CFD simulations were conducted on the SCR De-NO_x system and its succeeding flue ducts connected to the air preheater. The simulation results of the original design show that a significant velocity deviation exists at the inlet of the air preheater (with the CV₁ up to 53.2%), with a portion of the flue gas adhering to the walls, which could induce ABS fouling in the low-temperature region. By adding flow guide plates into the flue duct, the flow uniformity before the air preheater was expected to be effectively improved. Notably, considering the deposition characteristics of ABS and the operating characteristics of the rotary air preheater, this study proposed a novel evaluation indicator, radial variance coefficient (CV₂), which focuses on the velocity uniformity based on the annular sector unit, to indicate the risk of ABS deposition. The influence on velocity uniformity of different flow guide plate layouts was analyzed. Based on the multiple evaluation metrics including pressure drop and flow uniformity, the optimal layout scheme was then selected. After optimization, the radial variance coefficient decreased from 30.7% to 11.7%, with the pressure drop slightly increased from 50 Pa to 80 Pa. This study could help to reduce unit failure frequency and support efficient operation of coal-fired power plants. Full article