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A 3D mathematical model combining the large eddy simulation turbulent model and discrete phase model is developed to investigate the influence of the stopper rod location on transient flow characteristics and the deposition of inclusions in a bifurcated submerged entry nozzle (SEN). Transient flow characteristics, including the instantaneous flow pattern, jet speed, vertical and horizontal jet angle, and the backflow zone speed and fraction, are quantitatively compared. Transient jet flow characteristics of the left and right SEN port are almost consistent when the stopper rod is ideally centered. When the stopper rod is offset 10 mm, the discrepancy of the jet speed, vertical jet angle, and backflow zone fraction is 0.12 m s−1, 4°, and 4%, respectively. The horizontal angle and backflow speed are primarily affected by the vortex swirling direction at the bottom region of the SEN well. A positive horizontal jet angle is observed under the counterclockwise vortex, resulting in a higher backflow speed. Conversely, a negative horizontal jet angle and a lower backflow speed are observed when the vortex swirling direction is clockwise. The deposition rate of inclusions on the upper SEN wall is much higher when stopper rod is offset. [ABSTRACT FROM AUTHOR]

The valve, armature, and armature pin are critical factors influencing the hydraulic pressure differences in diesel injectors, and are essential for injection and backflow quantity control. These components play crucial roles in enhancing energy efficiency and reducing engine emissions. This experimental study investigated the effects of clearance between the valve, armature, and armature pin guidance. Forty-nine 2000 bar common-rail injectors (Bosch) were tested in calibrated stations. Injection quantities were assessed at both minimum and maximum operational pressures. Backflow rates were specifically examined at maximum pressure. A correlation matrix was created using Python to analyze the relationship between inputs and outputs, identifying dominant characteristics that define injector behavior. Increased injector precision correlated with reduced fuel consumption and enhanced energy efficiency. The study found that the effect of clearance between the armature and armature pins was more significant than that between the valve and armature. Injection quantities were observed to increase with pressure, and no critical difference in injection quantities was noted among different diameter groups at the minimum pressure point. Backflow quantities were consistent within groups when the armature–armature pin and valve–armature clearances were minimized. [ABSTRACT FROM AUTHOR]

The flow in the draft tube of the water turbine is affected by the upstream flow and the inherent structure accompanied by various undesirable characteristics, affecting the efficient and stable operation of the water turbine. Changing the flow structure downstream of the runner is an important measure to reduce hydraulic loss in the draft tube and improve stability. In this study, three downstream structures of the runner, namely, the non-locking nut, small locking nut, and extended locking nut are numerically calculated and verified using experimental results. The unstable flow characteristics of the draft tube are analyzed using variations in swirling flow, backflow, pressure gradient, and vortex strip. The results show the non-negligible effect of the locking nut, which significantly reduces the rotational momentum flux at the draft tube inlet, accelerates the decay rate of the swirling flow, and suppresses the generation of axial low pressure. The small locking nut significantly reduces the pressure gradient, shortens the backflow zone, and decreases the backflow velocity. The extended locking nut reduces the backflow zone in some sections and reduces the vortex zone of the straight section but prolongs the backflow zone and increases the backflow velocity. [ABSTRACT FROM AUTHOR]

AbstractThe local injection of therapeutic drugs, including cells, oncolytic viruses and nucleic acids, into different organs is an administrative route used to achieve high drug exposure at the site of action. However, after local injection, material backflow and side effect reactions can occur. Hence, this study was carried out to investigate the effect of gelatin on backflow reduction in local injection. Gelatin particles (GPs) and hydrolyzed gelatin (HG) were injected into tissue models, including versatile training tissue (VTT), versatile training tissue tumor-in type (VTT-T), and broiler chicken muscles (BCM), using needle gauges between 23 G and 33 G. The backflow material fluid was collected with filter paper, and the backflow fluid rate was determined. The backflow rate was significantly reduced with 35 μm GPs (p value < .0001) at different concentrations up to 5% and with 75 μm GPs (p value < .01) up to 2% in the tissue models. The reduction in backflow with HG of different molecular weights showed that lower-molecular-weight HG required a higher-concentration dose (5% to 30%) and that higher-molecular-weight HG required a lower-concentration dose (7% to 8%). The backflow rate was significantly reduced with the gelatin-based formulation, in regard to the injection volumes, which varied from 10 μL to 100 μL with VTT or VTT-T and from 10 μL to 200 μL with BCM. The 35 μm GPs were injectable with needles of small gauges, which included 33 G, and the 75 μm GPs and HG were injectable with 27 G needles. The backflow rate was dependent on an optimal viscosity of the gelatin solutions. An optimal concentration of GPs or HG can prevent material backflow in local injection, and further studies with active drugs are necessary to investigate the applicability in tumor and organ injections.

Groundwater (GW)–surface water (SW) interactions profoundly impact aquatic systems. In karst regions characterized by the coexistence of various media, the hyporheic zone (HZ) remains poorly understood. This study explores the HZ by examining karst development and various hydrological, hydrochemical, and biological processes. The research reveals high development of karst and difference in water environment may suggest a diversity of water sources beyond GW, leading to the formation of a karst hyporheic zone (KHZ). Four common KHZ types are proposed based on karst development, with a focus on spring outlet and karst window types. Interactions in these zones are driven by river backflow and GW abstraction in high- and low-water periods, respectively. KHZs may have water quality purification capabilities, but further research on biogeochemical processes is needed. This study provides preliminary insight into KHZs in karst water systems and suggests key scientific questions for future research in South China. [ABSTRACT FROM AUTHOR]

Facing an increasingly hostile ecological environment, the imperative for advancing hydrogen fuel cell vehicles has become more pronounced. This paper establishes a three-dimensional computational fluid dynamics model of a Roots-type hydrogen circulating pump by utilizing the generalized type line equation of the Roots rotor. Delving deep into the intricate interplay of backflow phenomena on the internal flow dynamics and operational efficiency of the Roots-type hydrogen circulation pump across various scenarios. The results reveal that mass flow rate and velocity vary continuously and with the same pulsation frequency as rotation angle or time during a complete rotation cycle. As the rotational speed increases, the number of backflow occurrences decreases, the frequency of backflow currents in the rotor basin decreases, and the temperature rise in both the suction and exhaust chambers decreases. It becomes evident that the rotational speed wields a more profound influence on the Roots pump's performance than temperature: the volumetric and isentropic efficiencies of the Roots-type hydrogen circulating pump decrease by 3.5% and 4.6%, respectively, with increasing temperature, while the volumetric and isentropic efficiencies of the pump increase by 32.6% and 24.0%, respectively, with increasing rotational speed. • The numerical simulation of hydrogen circulation pump using dynamic mesh technique. • Focus on the occurrence and impacts of backflow of hydrogen circulation pumps. • The influence of backflow on internal flow characteristics at different speeds and temperatures. • The general link between return frequency and flow pulsation is discussed in detail. [ABSTRACT FROM AUTHOR]

In this research article, the effect of rotating and second-grade fluid on an MHD Jeffery–Hamel flow (J–HF) has been investigated. Here, the MHD second-grade fluid theory has been used. The PDEs that represent this flow are transformed into ODEs, which are then solved using two separate methods: the 4th–5th-order Runge–Kutta Fehlberg technique with shooting methodology and the DTM technique. The impact of diverse physical factors, like rotational factor, Deborah, and Hartmann numbers, on the dimensionless rapidity F of the second-grade fluid and the wall frictional force factor is analyzed. Backflow is not detected in the lower part of the channel, according to the study. Additionally, the results show that the reverse flow disappears completely as the Hartmann number increases. Also, it is found that the Deborah quantity has less impact on the dimensionless velocity F of second-grade fluid nearby the down surface of the rotative diverging channel, but a significant increase in the thickener of the momentum boundary layer at the upper half of the channel is noticed with the rise in the magnitude of the Deborah number, hence signaling the beginning of the backflowing behavior. The current findings are contrasted to those of prior investigations and the HAM-built Mathematica package BVPh 2. The newly used analytical method shows high reliability, usefulness, and precision, as evidenced by the excellent agreement between DTM, HAM-BMP BVPh 2, and computational RKF45. [ABSTRACT FROM AUTHOR]

This contribution presents a novel wear dependent virtual flow rate sensor for single stage single lobe progressing cavity pumps. We study the wear-induced material loss of the pump components and the impact of this material loss on the volumetric efficiency. The results are combined with an established backflow model to implement a backflow calculation procedure that is adaptive to wear. We use a laboratory test setup with a highly abrasive fluid and operate a pump from new to worn condition to validate our approach. The obtained measurement data show that the presented virtual sensor is capable of calculating the flow rate of a pump being subject to wear during its regular operation. [ABSTRACT FROM AUTHOR]

The backflow and back-pressure propagation induced in a pulse detonation combustor (PDC) are the main factor in causing the thrust losses of a pulse detonation engine. In order to suppression the backflow propagation of a PDC, the aero-dynamic suppression strategy was implemented in this work. A total of ten isolators composed of different geometries were designed. A single-pulse detonation experiment was conducted by using the stoichiometric ethylene/enriched-oxygen mixture. It is shown that when the back-pressure has propagated about 0.86 the length of PDC, the propagation speeds and the pecks of the back-pressure in the isolator, which composed of the Venturi tube (V) and a long tube with 1.5 times diameter of the PDC, can be reduced by 10% and 20%, respectively, comparing with the base isolator. Comparing with the isolators that without the Tesla valve (T), the propagation speed of the back-pressure in the cases with the Tesla valve can be additionally reduced above 27.3%. Comparing with the isolators that without the slit (S), the peaks of the back-pressure in the cases with the slit can be decreased about 25%. The average decay rate of the back-pressure peaks can be highly increased if the cone (C) is introduced. It is found that the CVST-type isolator is the optimal. Comparing with the base isolator, the backpressure propagated in the CVST-type isolator can decrease about 50% and 40.5% of propagation speed and pressure peaks, respectively, and can increase the average decay rate of the back-pressure peaks by a factor of two.

Copyright of Journal of Drainage & Irrigation Machinery Engineering / Paiguan Jixie Gongcheng Xuebao is the property of Editorial Department of Drainage & Irrigation Machinery 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.)

This research delves into the complexities of backflow phenomena in finite-length and flat-walled fractures with elastic walls, specifically focusing on power-law fluids, whose shear-thinning behavior distinguishes them from Newtonian fluids. We model the backflow process under the lubrication approximation and by incorporating the linear Navier slip law. We numerically examine the influence of parameters such as slip length, fluid rheology, and external pressure on the backflow propagation of the carrier fluid. Our findings underscore the significant role played by the rheological index in determining the fracture closure rate. Additionally, our investigations highlight the marked effect of external pressure variations on pressure distribution within the fracture. Notably, the friction coefficient at the fracture walls, as denoted by a dimensionless slip number, exhibits limited influence on the fundamental dynamics of the problem. These insights advance our understanding of power-law fluid backflow and have wide-ranging applications across various engineering disciplines. [ABSTRACT FROM AUTHOR]

The ecology of the aquatic environment in Poyang Lake, the largest fresh lake in China, is notably impacted by the backflow from the Yangtze River, which conveys a high flux of sediments. This study employs a widely recognized numerical model to replicate the backflow in 2007 (the strongest backflow after the operation initiation of the Three Gorges Dam) to investigate the contributions of wind and backflow to the sediment transport process. The results show that the influences of wind and backflow on flow patterns and sediment transport processes have significant spatial heterogeneity. In the narrow waterway leading to the central lake area, hydrodynamics is mainly driven by backflow. Conversely, the hydrodynamics of the open expanse of the lake is primarily influenced by wind forces. Dominant wind leads to the formation of gyres, which significantly alter flow paths and push sediment into the upstream areas. As a result, the suspended sediment area expands at an average rate of 20.1–21.3 km2 daily, marking a 75–85% surge compared to the no wind condition (11.5 km2). The study facilitates a deeper understanding of sediment transport processes in large lakes. HIGHLIGHTS Wind causes large gyres during the backflow period.; Wind-induced current could modify the lake mainstream direction.; Wind promotes sediment movement.;

A simple carrier phase based ultrafiltration technique that is akin to liquid chromatography and is suitable for medium-to-large volume sample preparation in the laboratory is discussed in this paper. A membrane module was integrated with a liquid chromatography system in a “plug and play” mode for ease of sample handling, and recovery of species retained by the membrane. The sample injector and pump were used for feed injection and for driving ultrafiltration, while the sensors and detectors were used for real-time monitoring of the separation process. The concentration of retained species was enriched by utilizing controlled concentration polarization. The recovery of the retained and enriched species was enhanced by backflow of carrier phase through the membrane using appropriate combination of valves. The backflow of carrier phase also cleaned the membrane and limited the extent of membrane fouling. Proof-of-concept of the proposed technique was provided by conducting different types of protein ultrafiltration experiments. The technique was shown to be suitable for carrying out protein fractionation, desalting, buffer exchange and concentration enrichment. Adoption of this approach is likely to make ultrafiltration easier to use for non-specialized users in biological research laboratories. Other advantages include enhanced product recovery, significant reduction in the number of diavolumes of buffer needed for conducting desalting and buffer exchange, minimal membrane fouling and the potential for repeated use of the same module for multiple separation cycles.

The valve, armature, and armature pin are critical factors influencing the hydraulic pressure differences in diesel injectors, and are essential for injection and backflow quantity control. These components play crucial roles in enhancing energy efficiency and reducing engine emissions. This experimental study investigated the effects of clearance between the valve, armature, and armature pin guidance. Forty-nine 2000 bar common-rail injectors (Bosch) were tested in calibrated stations. Injection quantities were assessed at both minimum and maximum operational pressures. Backflow rates were specifically examined at maximum pressure. A correlation matrix was created using Python to analyze the relationship between inputs and outputs, identifying dominant characteristics that define injector behavior. Increased injector precision correlated with reduced fuel consumption and enhanced energy efficiency. The study found that the effect of clearance between the armature and armature pins was more significant than that between the valve and armature. Injection quantities were observed to increase with pressure, and no critical difference in injection quantities was noted among different diameter groups at the minimum pressure point. Backflow quantities were consistent within groups when the armature–armature pin and valve–armature clearances were minimized.

The paper presents the results of the experimental research on the air grills designed to stop backflows in natural ventilation stacks. For each grill pressure drop was measured for different airflow rates, in both flow directions. Two ∅ 100 mm grills working on different principles were tested: one with moving flaps, and one shaped in a way that should greatly increase the hydraulic losses during backflow. For comparison, the ordinary air grill was also tested. The results show that the grill with moving flaps works as intended. With only slightly higher hydraulic losses in the forward direction compared to ordinary grill, it shuts off the backflows almost completely. The other, diffuser-shaped grill doesn’t work as intended. It has very high hydraulic losses in both directions, and the effect of changing the air resistance with the reverse flow is barely noticeable.

The flow in the draft tube of the water turbine is affected by the upstream flow and the inherent structure accompanied by various undesirable characteristics, affecting the efficient and stable operation of the water turbine. Changing the flow structure downstream of the runner is an important measure to reduce hydraulic loss in the draft tube and improve stability. In this study, three downstream structures of the runner, namely, the non-locking nut, small locking nut, and extended locking nut are numerically calculated and verified using experimental results. The unstable flow characteristics of the draft tube are analyzed using variations in swirling flow, backflow, pressure gradient, and vortex strip. The results show the non-negligible effect of the locking nut, which significantly reduces the rotational momentum flux at the draft tube inlet, accelerates the decay rate of the swirling flow, and suppresses the generation of axial low pressure. The small locking nut significantly reduces the pressure gradient, shortens the backflow zone, and decreases the backflow velocity. The extended locking nut reduces the backflow zone in some sections and reduces the vortex zone of the straight section but prolongs the backflow zone and increases the backflow velocity.

Most mixed-flow pumps obtain a saddle-like Q-P curve with a backflow, owing to the increased incidence angle at low flow rates. The backflow was developed near the shroud and followed downstream again at its end to form a recirculating flow. The rotating stall, which could be a part of the recirculating flow, followed the impeller’s rotational direction, and its properties affected the local stability. The reattaching flow became strong when the upstream flow from the blade leading edge deviated from the same circumferential degree as the dominant flow of the rotating stall heading downstream. The fluctuation in the total pressure rise decreased when the average incidence angle was smaller than that of the design flow rate. As a passive control to suppress the saddle and the above flow patterns, the impeller inlet diameter was reduced from the shroud, and the inlet blade angle was further adjusted to maintain the incidence angle. From the reduced inlet diameter, the backflow was mostly suppressed, and the saddle was improved with a wider operating range. Here, the performance near the design flow rate was almost maintained. The stability was evaluated using the fast Fourier transform, and the numerical method was validated through experimental tests.

We present further arguments which show that the backflow has a universal character. It is not restricted to quantum theory and it appears in many theories (quantum or classical). It is a general property of waves propagating in any number of dimensions. [ABSTRACT FROM AUTHOR]

This research delves into the complexities of backflow phenomena in finite-length and flat-walled fractures with elastic walls, specifically focusing on power-law fluids, whose shear-thinning behavior distinguishes them from Newtonian fluids. We model the backflow process under the lubrication approximation and by incorporating the linear Navier slip law. We numerically examine the influence of parameters such as slip length, fluid rheology, and external pressure on the backflow propagation of the carrier fluid. Our findings underscore the significant role played by the rheological index in determining the fracture closure rate. Additionally, our investigations highlight the marked effect of external pressure variations on pressure distribution within the fracture. Notably, the friction coefficient at the fracture walls, as denoted by a dimensionless slip number, exhibits limited influence on the fundamental dynamics of the problem. These insights advance our understanding of power-law fluid backflow and have wide-ranging applications across various engineering disciplines.

Fractures are ubiquitous in Earth's upper crust and strongly affect its physical properties. Their visibility for elastic waves hinges on their stiffness, a measure of the relation between changes in fracture aperture and applied stress, which itself significantly increases with increasing stress according to laboratory data. We constrained normal stiffness (and its stress dependence) of two fractures intersecting a borehole in the research mine 'Reiche Zeche' in Freiberg, Saxony, Germany, from pressure-recovery behaviour observed when the pressure in a double-packer interval enclosing them was briefly released during shut-in sequences. For the evaluation of the pressure recovery, we developed a generic model that accounts for the inherent convolution of mechanical closing of the fracture, fluid flow in the fracture, fluid exchange between fracture and the surrounding rock, here addressed as fracture leakage, and effects associated with finite borehole storage. We address the hydraulic system by considering three different 'storage containers', described by non-dimensionless storage parameters: the wellbore with a fixed storage capacity, the fracture with storage capacities related to fluid compressibility and fracture stiffness, and the surrounding rock constituting a container with unlimited storage capacity. To examine the model's characteristics, we investigated pressure transients predicted for specific cases, such as negligible fracture leakage, and subsequently numerically determined the sensitivity of the model predictions to the involved model parameters. The model's application to the field data yield estimates of properties of the fractures (length, aperture and stiffness) and of the surrounding rock mass (product of permeability and specific storage capacity). The parameters derived from the modelling compare well with independent constraints. An analysis of currently available fracture-stiffness data shows that the lack of knowledge of the stress dependence of stiffness severely hampers firm conclusions on scale dependence and the bias between methods. [ABSTRACT FROM AUTHOR]

Most mixed-flow pumps obtain a saddle-like Q-P curve with a backflow, owing to the increased incidence angle at low flow rates. The backflow was developed near the shroud and followed downstream again at its end to form a recirculating flow. The rotating stall, which could be a part of the recirculating flow, followed the impeller's rotational direction, and its properties affected the local stability. The reattaching flow became strong when the upstream flow from the blade leading edge deviated from the same circumferential degree as the dominant flow of the rotating stall heading downstream. The fluctuation in the total pressure rise decreased when the average incidence angle was smaller than that of the design flow rate. As a passive control to suppress the saddle and the above flow patterns, the impeller inlet diameter was reduced from the shroud, and the inlet blade angle was further adjusted to maintain the incidence angle. From the reduced inlet diameter, the backflow was mostly suppressed, and the saddle was improved with a wider operating range. Here, the performance near the design flow rate was almost maintained. The stability was evaluated using the fast Fourier transform, and the numerical method was validated through experimental tests. [ABSTRACT FROM AUTHOR]

An axial fan in the general industry needs to secure stable characteristics in a wide operating range through an antistalling process, concerning its high demands, energy consumption, safety, and lifetime. As a "simple" and "original" method to control the stall of an axial fan, two-dimensional plates so-named anti-stall fin (ASF) were attached inside the casing and toward the shaft. The sensitivity analysis for design variables was conducted through the 2k full factorial design method, and the optimization was performed using the response surface method (RSM). In the case of an axial fan without the ASF, the backflow gradually increased in the spanwise direction toward the hub and the streamwise direction to the inlet passage (upstream), as the flowrate decreased, and the rotating stall was developed through the quickening-growing-setting period. However, an ASF-attached axial fan stably recovered performance degradation in the stalling flow rates and allowed to form a negative slope to 0.5Φd ⁠. This study was mainly based on numerical simulations, while the performance before/after application of the ASF was validated through experimental tests. [ABSTRACT FROM AUTHOR]

Copyright of Automobile Technology is the property of Automobile Technology Editorial Office 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.)

• Flow distribution in 58 parallel microchannel was compared using a facile method. • Backflow phenomena was observed experimentally as well as based on the CFD. • Increasing liquid film thickness along the channel length was correlated with backflow. • Deposition of thin titania layer improved wettability. • GLS contact angle and reactor inclination angle affect flow behavior. This work aims the experimental and numerical characterization of gas–liquid flow in an open multichannel falling film microreactor containing 64 coated microchannels, and a split & curve structure for the flow distribution. The operating flowrate range, the flow distribution, and the residence time of the liquid in the single channels were assessed via self-designed pulse input tracer experiments. 3D simulations based on Volume of Fluid (VoF) multiphase model were developed in ANSYS Fluent considering a representative section of a single microchannel. Simulation results indicate that backflow phenomena and an increase in film thickness along the channel length are the main reasons for the high film thickness observed experimentally. While the flow rate has only a marginal effect on both processes, the plate inclination angle has considerable contribution in overflow and flow stability. Finally, the numerically calculated transversal wetted area is mainly determined by the defined GLS contact angle at the sidewalls. [ABSTRACT FROM AUTHOR]

Fluid transportation is a critical element in the performance of fluid machinery devices. This paper proposes a ferrofluid linear pump in response to the demand for fluid control without mechanical moving parts inside tubes. The pump includes two rectangular permanent magnets, ferrofluid, tubes, four one-way valves, and a linear actuator. The ferrofluid is bound in the tube by a strong gradient magnetic field generated by two rectangular permanent magnets, forming a liquid plunger. Under the cooperation of four one-way valves on and off, the reciprocating motion of the permanent magnet makes the ferrofluid plunger drive fluid to flow directionally. The maximum backpressure of the ferrofluid plunger under static and dynamic conditions is thoroughly analyzed by theory and experiments. Experiments of the interface profile and backpressure are consistent with the theoretical results in the static condition. The maximum backpressure reaches 8.3kPa in the static condition when the volume of the ferrofluid plunger is 19ul. However, the dynamic test under a reciprocating speed of 10–50 mm/s has a significant backflow phenomenon, and the theory for calculating the backpressure is no longer applicable. The mechanism of the backflow is explored. There is a layer of water film between the ferrofluid plunger and the tube wall. With the increase of the backpressure and reciprocating speed, the thickness of the water film and the velocity gradient may enlarge, which increases the backflow and reduces the volume flow rate. Ultimately, failure occurs when the backpressure exceeds the sealing threshold during the ferrofluid plunger reciprocating process. The critical pressure difference for the pump failure fluctuates around 7.4 kPa. [Display omitted] • The pump consists of two rectangular magnets, a ferrofluid plunger, tubes, four one-way valves, and a linear actuator. • The interface of the ferrofluid plunger basically coincides with the isosurface of the magnetic field strength. • The backflow mainly depends on the volume, the backpressure, and the reciprocating speed of the ferrofluid plunger. [ABSTRACT FROM AUTHOR]

This article proposes a new type of subwavelength axicons for creating and focusing second-order vector cylindrical beams. It is also shown that using the proposed subwavelength axicons, it is possible to create focal spots with an energy backflow. The Comsol Multiphysics software is used to simulate the operation of subwavelength axicons with different twist angles. The dependence of the obtained intensity distributions on the angle of twist of the axicon spiral is investigated.

Pollutant emission standards and, in particular, those concerning particles from an internal combustion engine (ICE) are becoming increasingly restrictive. Thus, it is important to determine the main factors related to the production of particulate matter. In this article, the phenomenon of oil sweeping by the blowby gases between the rings/piston/cylinder is investigated. First, a blowby gas simulation model based on experimental results from a Turbocharged Gasoline Direct Injection (TGDI) is developed. From this model, it is possible to characterise the amount of oil swept by the blowby gases. This depends on the endgap position of both the compression and sealing rings. It also depends on the intensity of the blowby flow rate, which is highest at low rpm and high load. At 1500 rpm and full load, this flowrate exceeds 25 mg.cycle−1. From this result, it is possible to quantify the amount of oil swept by these gases as a function of the endgap position. For θ r i n g s = 180 ° ,   the quantity of oil swept rises to 20 µg.cycle−1 while for θ r i n g s = 30 ° , this decreases to 6 µg.cycle−1. The oil concentration of the blowby gas has a direct impact on the particulate emissions because the oil concentration of the backflow gas is inversely proportional to the blowby gas flowrate. As the backflow gases return to the cylinder, the oil oxidises and produces particles. Therefore, it is essential to control the oil concentration of the backflow gases. In addition, the simulation model shows the blowby flowrate becomes negative and decreases to −3.4 mg. cycle−1 in idle conditions. The amount of oil swept by the blowby is no longer directed towards the oil pan, but towards the piston crown. This phenomenon of oil storage of the piston crown in idle condition is proportional to the duration of the idle time. In order to confirm these results, experimental tests are carried out on a TGDI engine. It appears that when the idling time changes from 0 s to 7 s between two strictly identical accelerations, the level of particulate emissions is multiplied by 1.3. When the idling time changes from 0 s to 22 s between two strictly identical accelerations, the level of particulate emissions is multiplied by 3. These results confirm the mechanism of oil storage at idle highlighted by the simulation model. [ABSTRACT FROM AUTHOR]

Because the axial piston pump is often used in the aerospace and aviation fields, it is necessary to pay attention to its outlet pressure and flow characteristics. The parallel 2D piston pump proposed, based on the axial piston pump, has no structural flow ripple because it has a rail with a uniform acceleration and deceleration. Now, the pump is used in the special working conditions of the aerospace field, and it is required to meet the rated flow of 50 L/min, the rated load of 8 MPa, and an extremely low-pressure ripple. Based on CFD technology, this paper studies the pump's outlet flow and pressure ripples through numerical simulation. According to the causes of the outlet pressure ripple, an improved geometry is determined to further reduce the outlet pressure ripple. Using a high-frequency pressure sensor to measure the outlet pressure ripple of the optimized pump prototype, it was found that the outlet pressure ripple rate of the prototype was only 6%. The parallel 2D piston pump has been proved by the simulation and test that its outlet pressure ripple is extremely low. However, it is not effective to reduce the outlet flow ripple by increasing the pre-pressure and reducing the backflow. In parallel 2D piston pumps, it is still necessary to find a new method to further reduce outlet pressure and flow ripples. [ABSTRACT FROM AUTHOR]

Background: Infusion therapy is widely used in clinical settings, particularly in intensive care units., Aim: to explore the influence of simulated cardiac output on "bolus" or "backflow" events that can occur during syringe pump changeover, considering several factors that have been previously outlined in published research. Syringe infusion pumps are commonly used for precise continuous intravenous drug delivery. Syringe pump changeover can be a challenging procedure., Methods: Bench-top study in a laboratory setting. An extracorporeal circuit was used to simulate a cardiac output of 5 l/min. The following variables were used: three levels of vertical position of the syringe pump (-50 cm, 0, +50 cm), three levels of Central Venous Pressure (-5, 10, and 15 mmHg), presence/absence of carrier infusion (5 ml/h), and presence/absence of a needle-free connector between the syringe and extension line., Results: A total of 108 syringe pump changes were performed with different combinations of the investigated variables. The mean time for syringe pump changeover was equal to 9.48 ± 2.45 s and the overall fluid displacement was 8 ± 40 µL (microlitres) (range, -262-156 µL). The CVP level and vertical position of the pump always statistically affected the overall displacement during syringe pump changeover. When a second infusion with an equal velocity rate to that of a syringe pump infusion is present in the same lumen, the presence of a needle-free device reduces the overall volume of displacement., Conclusions: Syringe pump changeover can be a critical moment for patients when vasoactive drugs are administered., Implications for Clinical Practice: In a simulated environment with a cardiac output of 5 L/min, the CVP level and vertical position of the syringe pump generated bolus or backflow events during the syringe pump changeover. The application of carrier infusion appeared to intensify these phenomena. Employing a neutral, needle-free system can potentially aid in reducing the development of boluses or backflows., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

We show that, contrary to the statements made by many authors, the backflow is not a nonclassical effect. The backflow is a characteristic feature of solutions of the wave equations: quantum and classical. We present simple solutions of the Dirac equation, Maxwell equations and equations of linearized gravity where the backflow phenomenon is clearly seen. In this work we describe backflow in relativistic theories but this phenomenon can occur in the solutions of all kinds of wave equations: quantum and classical. [ABSTRACT FROM AUTHOR]

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The local injection of therapeutic drugs, including cells, oncolytic viruses and nucleic acids, into different organs is an administrative route used to achieve high drug exposure at the site of action. However, after local injection, material backflow and side effect reactions can occur. Hence, this study was carried out to investigate the effect of gelatin on backflow reduction in local injection. Gelatin particles (GPs) and hydrolyzed gelatin (HG) were injected into tissue models, including versatile training tissue (VTT), versatile training tissue tumor-in type (VTT-T), and broiler chicken muscles (BCM), using needle gauges between 23 G and 33 G. The backflow material fluid was collected with filter paper, and the backflow fluid rate was determined. The backflow rate was significantly reduced with 35 μm GPs ( p value < .0001) at different concentrations up to 5% and with 75 μm GPs ( p value < .01) up to 2% in the tissue models. The reduction in backflow with HG of different molecular weights showed that lower-molecular-weight HG required a higher-concentration dose (5% to 30%) and that higher-molecular-weight HG required a lower-concentration dose (7% to 8%). The backflow rate was significantly reduced with the gelatin-based formulation, in regard to the injection volumes, which varied from 10 μL to 100 μL with VTT or VTT-T and from 10 μL to 200 μL with BCM. The 35 μm GPs were injectable with needles of small gauges, which included 33 G, and the 75 μm GPs and HG were injectable with 27 G needles. The backflow rate was dependent on an optimal viscosity of the gelatin solutions. An optimal concentration of GPs or HG can prevent material backflow in local injection, and further studies with active drugs are necessary to investigate the applicability in tumor and organ injections.

We study, analytically and numerically, a simple P T -symmetric tight-binding ring with an onsite energy a at the gain and loss sites. We show that if a ≠0, the system generically exhibits an unbroken P T -symmetric phase. We study the nature of the spectrum in terms of the singularities in the complex parameter space as well as the behavior of the eigenstates at large values of the gain and loss strength. We find that in addition to the usual exceptional points (EPs), there are ‘diabolical points’, and inverse EPs at which complex eigenvalues reconvert into real eigenvalues. We also study the transport through the system. We calculate the total flux from the source to the drain, and how it splits along the branches of the ring. We find that while usually the density flows from the source to the drain, for certain eigenstates a stationary ‘backflow’ of density from the drain to the source along one of the branches can occur. We also identify two types of singular eigenstates, i.e. states that do not depend on the strength of the gain and loss, and classify them in terms of their transport properties. [ABSTRACT FROM AUTHOR]

This paper presents a three-dimensional fully hydro-mechanical coupled distinct element study on fault reactivation and induced seismicity due to hydraulic fracturing injection and subsequent backflow process, based on the geological data in Horn River Basin, Northeast British Columbia, Canada. The modeling results indicate that the maximum magnitude of seismic events appears at the fracturing stage. The increment of fluid volume in the fault determines the cumulative moment and maximum fault slippage, both of which are essentially proportional to the fluid volume. After backflow starts, the fluid near the joint intersection keeps flowing into the critically stressed fault, rather than backflows to the wellbore. Although fault slippage is affected by the changes of both pore pressure and ambient rock stress, their contributions are different at fracturing and backflow stages. At fracturing stage, pore pressure change shows a dominant effect on induced fault slippage. While at backflow stage, because the fault plane is under a critical stress state, any minor disturbance would trigger a fault slippage. The energy analysis indicates that aseismic deformation takes up a majority of the total deformation energy during hydraulic fracturing. A common regularity is found in both fracturing- and backflow-induced seismicity that the cumulative moment and maximum fault slippage are nearly proportional to the injected fluid volume. This study shows some novel insights into interpreting fracturing- and backflow-induced seismicity, and provides useful information for controlling and mitigating seismic hazards due to hydraulic fracturing.

A simple carrier phase based ultrafiltration technique that is akin to liquid chromatography and is suitable for medium-to-large volume sample preparation in the laboratory is discussed in this paper. A membrane module was integrated with a liquid chromatography system in a "plug and play" mode for ease of sample handling, and recovery of species retained by the membrane. The sample injector and pump were used for feed injection and for driving ultrafiltration, while the sensors and detectors were used for real-time monitoring of the separation process. The concentration of retained species was enriched by utilizing controlled concentration polarization. The recovery of the retained and enriched species was enhanced by backflow of carrier phase through the membrane using appropriate combination of valves. The backflow of carrier phase also cleaned the membrane and limited the extent of membrane fouling. Proof-of-concept of the proposed technique was provided by conducting different types of protein ultrafiltration experiments. The technique was shown to be suitable for carrying out protein fractionation, desalting, buffer exchange and concentration enrichment. Adoption of this approach is likely to make ultrafiltration easier to use for non-specialized users in biological research laboratories. Other advantages include enhanced product recovery, significant reduction in the number of diavolumes of buffer needed for conducting desalting and buffer exchange, minimal membrane fouling and the potential for repeated use of the same module for multiple separation cycles.

The California-Nevada Section of the American Water Works Association (CA-NV AWWA) has received ISO/IEC 17024:2012 Standard accreditation for its Backflow Prevention Assembly Tester (BPAT) and Cross-Connection Control Specialist (CCCS) certification programs. This accreditation makes CA-NV AWWA the first organization in the United States to be accredited under this international standard. Backflow prevention and cross-connection control are crucial for protecting potable water distribution systems, and through certification programs, water professionals demonstrate their competence in these areas. CA-NV AWWA underwent a rigorous process to meet the ISO/IEC 17024 requirements and ensure the fairness and validity of its certification examinations. The organization may pursue accreditation for other certification programs in the future. [Extracted from the article]

The vortex gripper is a kind of pneumatic noncontact gripper that does not produce a magnetic field and heat. It can grip a workpiece without physical contact, which avoids any unintentional damage such as mechanical scratches, local stress concentrations, frictional static electricity, and surface stains. This study focused on the two-dimensional pressure distribution field on a workpiece surface under the vortex gripper. Theoretical, experimental, and computational fluid dynamics results were combined to study the backflow phenomenon in the annular skirt, which can decrease the gripper's suction force after the maximum value is reached. First, the pressure distribution in the annular skirt was theoretically modeled. A comparison with the experimental results showed that increasing the gap height between the gripper and workpiece generates a circumferentially asymmetrical flow field in the skirt. Based on this, it was hypothesized that an airflow in the circumferential direction may exist. The experimental data and simulation results were analyzed under large gap height conditions to observe the backflow in detail and it was found that an uneven pressure distribution with positive and negative pressure regions generated by the uneven flow is the root cause of the backflow. Finally, the effect of the backflow on the flow field in two different flow regions (in the annular skirt and inside the vortex chamber) was analyzed and the reason why the suction force of the vortex gripper has a maximum value was determined. [ABSTRACT FROM AUTHOR]

For rotating detonation engines, the high-pressure region behind the detonation causes backflow into the plenum, making it difficult to properly design injectors to achieve the target pressure balance due to blockage of a part of the injector area during engine operation. In this paper, we present the pressure and thrust measurement of a rotating detonation engine with two different triplet injectors (fuel injector diameters of 0.8 mm and 1.0 mm) using gaseous methane, gaseous ethylene, and gaseous oxygen. The detonation wave propagation velocity with the fuel injector diameter of 0.8 mm was approximately 200 m/s higher than that with the fuel injector diameter of 1.0 mm. Combustor pressures and specific impulses were almost identical for both fuel injector diameters in this study. For our evaluation of the extent to which the available injector area can be utilized during engine operation, the effective injector area ratio was defined as the ratio of the plenum pressure during burn time to the pre-ignition value. Regardless of fuel species and fuel injector orifice diameter, the effective injector area ratio decreased proportionally with the ratio of combustor pressure to pre-ignition plenum pressure. This result implies that the pressure balance between the upstream plenum pressure and the combustor pressure can be roughly determined taking the effect of backflow into consideration. [ABSTRACT FROM AUTHOR]

Pollutant emission standards and, in particular, those concerning particles from an internal combustion engine (ICE) are becoming increasingly restrictive. Thus, it is important to determine the main factors related to the production of particulate matter. In this article, the phenomenon of oil sweeping by the blowby gases between the rings/piston/cylinder is investigated. First, a blowby gas simulation model based on experimental results from a Turbocharged Gasoline Direct Injection (TGDI) is developed. From this model, it is possible to characterise the amount of oil swept by the blowby gases. This depends on the endgap position of both the compression and sealing rings. It also depends on the intensity of the blowby flow rate, which is highest at low rpm and high load. At 1500 rpm and full load, this flowrate exceeds 25 mg.cycle−1. From this result, it is possible to quantify the amount of oil swept by these gases as a function of the endgap position. For θrings=180°, the quantity of oil swept rises to 20 µg.cycle−1 while for θrings=30°, this decreases to 6 µg.cycle−1. The oil concentration of the blowby gas has a direct impact on the particulate emissions because the oil concentration of the backflow gas is inversely proportional to the blowby gas flowrate. As the backflow gases return to the cylinder, the oil oxidises and produces particles. Therefore, it is essential to control the oil concentration of the backflow gases. In addition, the simulation model shows the blowby flowrate becomes negative and decreases to −3.4 mg. cycle−1 in idle conditions. The amount of oil swept by the blowby is no longer directed towards the oil pan, but towards the piston crown. This phenomenon of oil storage of the piston crown in idle condition is proportional to the duration of the idle time. In order to confirm these results, experimental tests are carried out on a TGDI engine. It appears that when the idling time changes from 0 s to 7 s between two strictly identical accelerations, the level of particulate emissions is multiplied by 1.3. When the idling time changes from 0 s to 22 s between two strictly identical accelerations, the level of particulate emissions is multiplied by 3. These results confirm the mechanism of oil storage at idle highlighted by the simulation model.

This study investigates the backflow of a Newtonian fluid in a two-dimensional flat-walled fracture with Navier slip boundary conditions. The fracture has a uniform aperture and two rigid pre-strained plates as walls; their elastic deformations are described by the Winkler model. Under the lubrication assumption, the governing nonlinear ordinary differential equation and the time-dependent velocity profile are derived; in turn, this yields the time and space evolution of the pressure distribution inside the fracture, numerically. In addition, the condition when the external pressure becomes zero, is discussed, and a parametric study is performed to highlight the influence of the slip length.

Because the axial piston pump is often used in the aerospace and aviation fields, it is necessary to pay attention to its outlet pressure and flow characteristics. The parallel 2D piston pump proposed, based on the axial piston pump, has no structural flow ripple because it has a rail with a uniform acceleration and deceleration. Now, the pump is used in the special working conditions of the aerospace field, and it is required to meet the rated flow of 50 L/min, the rated load of 8 MPa, and an extremely low-pressure ripple. Based on CFD technology, this paper studies the pump’s outlet flow and pressure ripples through numerical simulation. According to the causes of the outlet pressure ripple, an improved geometry is determined to further reduce the outlet pressure ripple. Using a high-frequency pressure sensor to measure the outlet pressure ripple of the optimized pump prototype, it was found that the outlet pressure ripple rate of the prototype was only 6%. The parallel 2D piston pump has been proved by the simulation and test that its outlet pressure ripple is extremely low. However, it is not effective to reduce the outlet flow ripple by increasing the pre-pressure and reducing the backflow. In parallel 2D piston pumps, it is still necessary to find a new method to further reduce outlet pressure and flow ripples.

The tip leakage flow formed by the tip clearance of a semi-open centrifugal pump adversely affects the energy performance and the energy waste. A T-shaped blade is proposed to be used to improve the energy characteristics. The internal flow field is simulated via the shear stress transport turbulence model to analyze the influence of the T-shaped blade on the performance of a centrifugal pump. It is shown that with the T-shaped blade, the hydraulic loss can be reduced, the Euler head can be increased, and the external characteristics can be improved. The maximum head and efficiency improvements are 3% and 1.6%, respectively. The relative flow angle near the tip clearance of the T-shaped blade decreases, and the strength of the backflow region is remarkably weakened. The area of the high entropy production region decreases, and the trend of the upstream diffusion is restrained under the design condition. The T-shaped blade can help to inhibit the diffusion of the high entropy production region to the hub under the low flow rate condition, but the entropy production and the mixing losses at the tip clearance are slightly increased. This research provides a new method for improving the energy performance of the semi-open centrifugal pump. [ABSTRACT FROM AUTHOR]

Convection-enhanced delivery (CED) is a technique to bypass the blood-brain barrier and deliver therapeutic agents into the brain. However, animal studies and preliminary clinical trials have reported reduced efficacy to transport drugs in specific regions, attributed mainly to backflow, in which an annular zone is formed outside the catheter and the fluid preferentially flows toward the surface of the brain rather than through the tissue toward the targeted area. In this study, a finite element model of backflow was updated by implementing the pre-stress generated during needle insertion, which allows considering the effect of needle insertion velocity during CED infusions in agarose gel. The nonlinear mechanical properties of the agarose solutions were obtained by fitting experimental data from stress-relaxation tests. Additional experimental measurements of backflow lengths were used to adjust the pre-stress model. The developed model was able to reproduce changes of backflow length under different insertions velocities and flow rates. These findings reveal the relevance of considering the pre-stress in the tissue located around the needle surface during CED infusions into the brain. • A numerical model was developed to include the pre-stress during CED infusions. • In-vitro infusion experiments were performed to measure the backflow lengths. • Mechanical properties of agarose gel were obtained based on compression experiments. • The numerical model reproduced backflow lengths for different insertion velocities. [ABSTRACT FROM AUTHOR]

Potentially favourable conditions for overflows of water between the Vistula and Curonian lagoons via two branches of the Pregolya River were studied using water level data (2002-2007) at the hydrological stations located in lagoons and the river. The episodes (of two days and longer) of the 'reversed slope', when the water level in the Vistula Lagoon (7 cases) and the Curonian Lagoon (41 cases) was higher than in the river streams connecting them, were found. This confirms the theoretical possibility of water overflow between the Vistula and Curonian lagoons, back and forth. Some unusual cases (of two days and longer) when the 'reverse slope' of water level existed simultaneously in both recipient bodies (Vistula and Curonian lagoons) were also found. The analysis showed that wind conditions were not the single determining factor. Direct measurements of near-bottom currents showed that backward water flow appeared in both branches. Backward water flow developed mainly in the low parts of river branches, i.e. closer to the lagoons. Time delay in water flow variations and the appearance of backward water flow between downstream and upstream points was 2-7 hours, or about 4 hours on average. The signal of backward current in one branch penetrated upstream not only the other branch (correlation coefficient was about 0.64 and 0.71 for 1-h and 12-h running averaged series, respectively) but further upstream the mainstream of the Pregolya River. [ABSTRACT FROM AUTHOR]