Restricted Orifice Research Articles

Sensitivity analysis of influencing factors in large oscillation hydraulic transient process of pumped storage power station

Abstract The calculation of large oscillation transition process is of great significance for pumped storage power station, which is beneficial for ensuring the safe of the power station and extending the lifespan of the unit. Due to the presence of inertia in water and rotating components of the unit, as well as energy imbalance in the system, hydraulic transients will cause drastic changes in water pressure in the waterway system and unit speed, resulting in a sharp increase or decrease in pressure and a sharp change in unit speed, endangering the operational safety of the power plant and affecting the lifespan of the unit. It is necessary to optimize the layout of water conveyance system, basic parameters of units, and the closing law of guide vanes through calculation and analysis of large oscillation transition processes. Relying on a pumped storage power station in Guizhou, this paper analysis the sensitivity of the factors affecting the calculation results of the large oscillation transition process, such as runner characteristics, guide vane closing law, moment of inertia GD2, surge chamber diameter and restricted orifice size, to provide reference for similar projects.

Adaptive optimal control of pneumatic suspensions for comfort improvement of flexible railway vehicles using Monte Carlo simulations

ABSTRACT This paper presents an adaptive optimal control strategy focused on improving ride comfort by minimising the frequency-weighted acceleration measured at three locations on a flexible carbody floor. Front and rear suspensions adapt the restriction orifice, which connects each pneumatic spring to its auxiliary air reservoir, thus conferring different dynamic stiffness and damping depending on train speed and track quality. In this work, as opposed to previous publications by our group, the optimal control problem aims at the particular frequency range which affects passenger comfort in accordance to standard UNE-EN-12299. In addition, a rigorous statistical analysis based on Monte Carlo and Bootstrap sampling techniques has been used to deal with the stochastic nature of track irregularities. Results prove that focusing on the comfort frequency range improves the performance of the adaptive suspension, and that the proposed statistical analysis of optimisation results guarantees the appropriate selection of optimal diameters.

A regulating method for pressure drop of supercritical cracked-kerosene in cooling tube

Flow distribution of kerosene in actively cooling panel is an important factor that constraints the cooling efficiency of the thermal protection system of scramjet. However, the flow mal-distribution is a common phenomenon in the realistic thermal protection system. In order to investigate this problem, a way to regulate the pressure drop via restriction orifice is proposed. The flow, heat transfer and thermal cracking process in cooling tube are calculated using a three-dimensional fluid-solid conjugated simulation method for supercritical cracked-kerosene. The results indicate that with an appropriate restriction orifice, the pressure drop under a lower heat flux can match with that under correspondingly higher heat flux in a same tube, which verifies the feasibility of pressure drop regulating using the restriction orifice. Therefore, this research could provides a design method of flow distribution in actively cooling panel of scramjet.

불어내기식 감압시스템 유동해석 및 준 1차원 압축성 유동식을 이용한 설계 가이드 프로그램 개발

In this study, using LNG as a working gas, computational fluid dynamics(CFD) was performed on a blowdown depressuring system; then, a design guide program(DGP) which can be used in the initial design of the system was developed and validated. The physical phenomena occurring in the gas vessel, blowdown valve(BDV), restriction orifice(RO), diverging pipeline, and long pipeline, which are the main components of the system, were analyzed. Especially, it was confirmed that a supersonic flow was generated during the operation time of the system, and oblique shock waves and a terminal shock wave were generated inside the system. Therefore, in the DGP, the quasi-one-dimensional compressible flow formula that can reflect the physics of supersonic flow was used as the governing equation, and the Fanno flow equation was used to simulate the long pipeline flow. The DGP was validate by comparing with CFD results, and it is expected to shorten the initial design time by quickly deriving the pressure, temperature, and Mach number results of each major components.

Experimental study on head loss coefficients of tailrace surge tank for Baihetan hydropower station

The scale and hydraulic inertia of the tailrace surge tank of Baihetan hydropower station are huge. Its resistance characteristics are directly related to the accuracy of the calculation results of the hydraulic transient process, the stability of the unit operation, the economy and safety of the project. The influence of split ratio, cross-sectional area of the restricted orifice and unit operation on the head loss coefficient of Baihetan surge tank was studied by model experiment method. The results show that the head loss coefficient increases with the increase of split ratio and decreases with the increase of the cross-sectional area of the restricted orifice. Under the diffluence condition, the head loss coefficient of the restricted orifice in double unit operation is obviously larger than that in single unit operation. Under the confluence condition, the head loss coefficients of the restricted orifice in single and double unit operation are the same. The deviation will be large when using the recommended value in the specification, the experimental results are more reasonable. The research conclusions will provide technical support for the design and operation of Baihetan hydropower station as well as reference for similar projects.

A computational fluid dynamics assessment of 3D printed ventilator splitters and restrictors for differential multi-patient ventilation

BackgroundThe global pandemic of novel coronavirus (SARS-CoV-2) has led to global shortages of ventilators and accessories. One solution to this problem is to split ventilators between multiple patients, which poses the difficulty of treating two patients with dissimilar ventilation needs. A proposed solution to this problem is the use of 3D-printed flow splitters and restrictors. There is little data available on the reliability of such devices and how the use of different 3D printing methods might affect their performance.MethodsWe performed flow resistance measurements on 30 different 3D-printed restrictor designs produced using a range of fused deposition modelling and stereolithography printers and materials, from consumer grade printers using polylactic acid filament to professional printers using surgical resin. We compared their performance to novel computational fluid dynamics models driven by empirical ventilator flow rate data. This indicates the ideal performance of a part that matches the computer model.ResultsThe 3D-printed restrictors varied considerably between printers and materials to a sufficient degree that would make them unsafe for clinical use without individual testing. This occurs because the interior surface of the restrictor is rough and has a reduced nominal average diameter when compared to the computer model. However, we have also shown that with careful calibration it is possible to tune the end-inspiratory (tidal) volume by titrating the inspiratory time on the ventilator.ConclusionsComputer simulations of differential multi patient ventilation indicate that the use of 3D-printed flow splitters is viable. However, in situ testing indicates that using 3D printers to produce flow restricting orifices is not recommended, as the flow resistance can deviate significantly from expected values depending on the type of printer used.Trial registrationNot applicable.

Narrative review of Ebstein's anomaly beyond childhood: Imaging, surgery, and future perspectives.

Ebstein's anomaly is a rare congenital heart disease with malformation of the tricuspid valve and myopathy of the right ventricle. The septal and inferior leaflets adhere to the endocardium due to failure of delamination. This leads to apical displacement of their hinge points with a shift of the functional tricuspid valve annulus towards the right ventricular outflow tract with a possibly restrictive orifice. Frequently, a coaptation gap yields tricuspid valve regurgitation and over time the "atrialized" portion of the right ventricle may dilate. The highly variable anatomy determines the clinical presentation ranging from asymptomatic to very severe with need for early operation. Echocardiography and magnetic resonance imaging are the most important diagnostic modalities to assess the tricuspid valve as well as ventricular morphology and function. While medical management of asymptomatic patients can be effective for many years, surgical intervention is indicated before development of significant right ventricular dilatation or dysfunction. Onset of symptoms and arrhythmias are further indications for surgery. Modified cone reconstruction of the tricuspid valve is the state-of-the-art approach yielding the best results for most patients. Alternative procedures for select cases include tricuspid valve replacement and bidirectional cavopulmonary shunt depending on patient age and other individual characteristics. Long-term survival after surgery is favorable but rehospitalization and reoperation remain significant issues. Further studies are warranted to identify the optimal surgical strategy and timing before adverse right ventricular remodeling occurs. It is this article's objective to provide a comprehensive review of current literature and an overview on the management of Ebstein's Anomaly. It focuses on imaging, cardiac surgery, and outcome. Additionally, a brief insight into arrhythmias and their management is given. The "future perspectives" summarize open questions and fields of future research.

Study on hydraulic transient process of K hydropower station with low head, large flow and complex long tail water system

K hydropower station is a hydraulic engineering with the main task of power generation, which is also a typical hydropower station with low head, large discharge and long tail water conveyance system. The hydraulic characteristics of these-type hydropower stations are of high water inertia, large amplitude of surge chamber water level fluctuation and poor stability of units. Therefore, due to the control requirements of the stability, the area of the horizontal section of the surge chamber is usually large, which leads to the long period of water level fluctuation of the surge chamber and the relatively long time of unit output oscillation in the transition process, and the regulating quality of the unit is often difficult to meet the control requirements due to the large inertia time constant of the water flow in the water conveyance system and the unique characteristic curve of unit. It is important to design appropriately to ensure the safe and stable operation of the hydropower station. In this paper, it is shown the process of hydraulic design of these-type stations. According to the design of K hydropower station, the simple surge chamber and restricted orifice surge chamber are compared in terms of hydraulic characteristics including the head loss of steady operation, the water level fluctuation of transition process and the stability of operation. Based on the optimized restricted orifice surge chamber, the overall calculation and analysis of the hydraulic transition process and the stability analysis of K hydropower station are carried out, it is concluded that the unit stability quality of the K power station is fine and the maximum pressure of pipe is in control, which provide strong support for the safe and stable operation of K station. The comprehensive and thorough analysis in this paper can provide reference for the design of the similar projects.

Comfort improvement in railway vehicles via optimal control of adaptive pneumatic suspensions

ABSTRACT This paper presents an adaptive optimal control strategy focused on improving ride comfort by minimising the root mean square of accelerations measured at seven locations on the carbody floor. It requires preview knowledge of both the train speed and the standard track quality (not the deterministic track disturbances) and differs from other works in considering pointwise constraints (upper and lower secondary suspension travel limits). Adaptive control is achieved by varying the diameter of the restriction orifice which connects the pneumatic spring to the auxiliary air reservoir, which confers different dynamic stiffness and damping to the front and rear secondary suspensions. Decision maps with the front and rear optimal diameters for five track irregularity levels and six different speeds were obtained using a Monte Carlo strategy based on solving the optimal control problem for 240 stochastic realisations of time-varying track irregularities of 300 s. Results show that the adaptive optimal control provides a successful compromise between comfort and safety which overshadows the conventional passive approach: it improves comfort up to 50% with respect to stiff passive configurations and it guarantees constraint fulfilment unlike compliant passive configurations.

Flow induced vibration of two-phase flow passing through orifices under slug pattern conditions

Flow restricting orifices are important components for flow and pressure control in the oil, gas, and power generation industries. In many situations, the piping systems are operating under two-phase flow conditions. These orifices affect the redistribution of the two phases and induce vibrations in the piping structures. These vibrations often occur during a slug flow pattern and can severely affect the integrity of a structure; therefore, in the present work, both the vibrations of the piping structure and the characteristics of the two-phase flow dynamics are experimentally investigated in the presence of an orifice. In this study, an air–water​ two-phase flow mixture was utilized at different superficial velocities ranging from 0.12 m/s to 1.7 m/s for air and 0.46 m/s to 1.3 m/s for water. Synchronized flow visualization images, along with local void fraction and vibration measurements, were used to evaluate the response of the structure as the slug flow passed through the orifices. Detailed instantaneous local void fraction measurements were carried out to understand the underlying physics of the phenomenon and their effect on the vibration response of the structure. The results showed that not all slug flow cases excited the piping at the slug frequency. The amplitude of vibration around the slug frequency was found to increase as the superficial velocity of the gas phase increased.

Complement receptor 3 mediates both sinking phagocytosis and phagocytic cup formation via distinct mechanisms.

A long-standing hypothesis is that complement receptors (CRs), especially CR3, mediate sinking phagocytosis, but evidence is lacking. Alternatively, CRs have been reported to induce membrane ruffles or phagocytic cups, akin to those induced by Fcγ receptors (FcγRs), but the details of these events are unclear. Here we used real-time 3D imaging and knockout mouse models to clarify how particles (human red blood cells) are internalized by resident peritoneal F4/80+ cells (macrophages) via CRs and/or FcγRs. We first show that FcγRs mediate highly efficient, rapid (2-3 min) phagocytic cup formation, which is completely abolished by deletion or mutation of the FcR γ-chain or conditional deletion of the signal transducer Syk. FcγR-mediated phagocytic cups robustly arise from any point of cell-particle contact, including filopodia. In the absence of CR3, FcγR-mediated phagocytic cups exhibit delayed closure and become aberrantly elongated. Independent of FcgRs, CR3 mediates sporadic ingestion of complement-opsonized particles by rapid phagocytic cup-like structures, typically emanating from membrane ruffles and largely prevented by deletion of the immunoreceptor tyrosine-based activation motif (ITAM) adaptors FcR γ-chain and DAP12 or Syk. Deletion of ITAM adaptors or Syk clearly revealed that there is a slow (10-25 min) sinking mode of phagocytosis via a restricted orifice. In summary, we show that (1) CR3 indeed mediates a slow sinking mode of phagocytosis, which is accentuated by deletion of ITAM adaptors or Syk, (2) CR3 induces phagocytic cup-like structures, driven by ITAM adaptors and Syk, and (3) CR3 is involved in forming and closing FcγR-mediated phagocytic cups.

Complement receptor 3 mediates both sinking phagocytosis and phagocytic cup formation via distinct mechanisms

A long-standing hypothesis is that complement receptors (CRs), especially CR3, mediate sinking phagocytosis, but evidence is lacking. Alternatively, CRs have been reported to induce membrane ruffles or phagocytic cups, akin to those induced by Fcγ receptors (FcγRs), but the details of these events are unclear. Here we used real-time 3D imaging and KO mouse models to clarify how particles (human red blood cells) are internalized by resident peritoneal F4/80+ cells (macrophages) via CRs and/or FcγRs. We first show that FcγRs mediate highly efficient, rapid (2–3 min) phagocytic cup formation, which is completely abolished by deletion or mutation of the FcR γ chain or conditional deletion of the signal transducer Syk. FcγR-mediated phagocytic cups robustly arise from any point of cell-particle contact, including filopodia. In the absence of CR3, FcγR-mediated phagocytic cups exhibit delayed closure and become aberrantly elongated. Independent of FcγRs, CR3 mediates sporadic ingestion of complement-opsonized particles by rapid phagocytic cup-like structures, typically emanating from membrane ruffles and largely prevented by deletion of the immunoreceptor tyrosine-based activation motif (ITAM) adaptors FcR γ chain and DAP12 or Syk. Deletion of ITAM adaptors or Syk clearly revealed that there is a slow (10–25 min) sinking mode of phagocytosis via a restricted orifice. In summary, we show that (1) CR3 indeed mediates a slow sinking mode of phagocytosis, which is accentuated by deletion of ITAM adaptors or Syk, (2) CR3 induces phagocytic cup-like structures, driven by ITAM adaptors and Syk, and (3) CR3 is involved in forming and closing FcγR-mediated phagocytic cups.

Abstract 14534: In vitro Assessment of Transvalvular Peak Velocity Measurement for Various Orifice Shapes: Comparison Between 4D Flow MRI vs. Doppler Echocardiography

Introduction: 4D flow MRI can assess transvalvular velocity, but validation against continuous wave (CW) Doppler echo is limited in high-velocity regurgitation and stenosis situations. We sought to compare 4D flow MRI and echo peak velocity using a pulsatile echo-MRI flow phantom. Materials and Methods: An MRI-compatible flow phantom with restrictive orifice situated was driven by a left ventricular assist device at 50 bpm (figure 1A). Three orifice shapes were tested: circular, elliptical and 3D-printed patient-specific mitral regurgitant orifice model of prolapse with areas of 0.5, 0.41 and 0.35 cm 2 , respectively. CW Doppler was acquired with peak velocity extracted from the profile. Retrospectively-gated 4D flow MRI was performed (spatial resolution = 2 mm isotropic, temporal resolution = 36 ms, encoding velocity = 400 cm/s). Maximal velocity magnitude was extracted volumetrically (figure 1B). An echo-mimicking profile was also obtained with a “virtual” ultrasound beam in the 4D flow data to simulate CW Doppler (figure 1C). Bland-Altman analysis was used to assess the agreement of temporal peak velocities. Results: 4D flow MRI demonstrated a centrally directed jet for the circular and elliptical orifices and an oblique jet for the prolapse orifice (figure 1B). Peak velocities were in excellent agreement between 4D flow MRI vs. echo for the circular (peak: 5.13 vs. 5.08 m/s, bias = 0.06 ± 0.66 m/s, figure 1D) and the elliptical orifice (peak: 4.95 vs. 4.79 m/s, bias = 0.07 ± 0.87 m/s, figure 1E). The prolapse orifice velocity was underestimated somewhat by MRI by ~10% (peak: 4.41 vs. 4.90 m/s, bias=0.26±1.18, figure 1F). Conclusion: 4D flow MRI can quantify high velocities like echo for simple geometries while underestimating for more complex geometry, likely due to partial volume effects. Further investigation is warranted to systematically investigate the effects of 4D flow MRI spatial and temporal resolution as well as the jet angle on velocity quantification accuracy.

Evaluating the two-phase flow development through orifices using a synchronised multi-channel void fraction sensor

Understating two-phase flow through flow restricting orifices is critical in evaluating the piping degradation mechanisms in nuclear power generation systems. Characterizing the instantaneous changes of the two-phase local parameters across flow restricting orifices is critical in evaluating the piping structure dynamics. A multi-channel void fraction sensor was developed to investigate the effect of flow restricting orifices on flow pattern development in a 25.4 mm horizontal pipe. Instantaneous void fraction measurements were obtained at multiple locations upstream and downstream of the flow restricting orifices with area ratios of 0.062, 0.14, 0.25, and 0.56. Additionally, pressure measurements and flow visualizations were carried out to investigate the dynamics flow characteristics through the orifice. A liquid superficial velocity of 0.526, and 1.08 m/s and a gas superficial velocity ranging from 0.164 to 2.795 m/s were selected to represent the intermittent flow pattern. The results revealed that as the gas superficial velocity increased, the flow pattern downstream of the restriction changed to dispersed bubbly, or liquid jet and annular-dispersed liquid for an intermittent flow upstream of the orifice. The flow pattern development along the test section was affected significantly in the region close to the orifice, especially at a lower area ratio. Analysis of statistical characteristics of the slug flow pattern such as slug velocity, elongated bubble length and slug frequency were determined from the void fraction data and presented. The slug velocity upstream of the orifice decreased non-linearly as the area of the flow restriction decreased for the same flow condition upstream. The pressure variations along the pipe for different two-phase flow conditions across the orifices were obtained and different correlations to predict pressure drop across the orifices were evaluated. The Simpson et al. [1] correlation was the best as it predicted 93% of the experimental data with a 25% error.

원뿔형 오리피스 경사각이 유동 형태에 미치는 영향에 관한 수치적 연구

Flow through the orifice can result in flow separation, reattachment, and recirculation. Cavitation, which occurs together with a sudden drop in pressure, can cause fluid-induced vibrations and noise, along with friction in the inner wall of the pipe. Many pieces of research have been conducted on these issues, and various methods have been proposed to solve the problems. Conical-shaped restriction orifices have been proposed and used in some applications as a way to solve the related issues, but the number of published studies on the flow characteristics through conical-shaped orifices is very small compared to flat orifices. In this study, the characteristics of conical orifice flow and the effect of conical orifice cone angle on the fluid behavior using single-phase flow were investigated by using the commercial computational fluid dynamics software ANSYS fluent 18.0.

Thin CdTe Layers Deposited by a Chamberless Inline Process using MOCVD, Simulation and Experiment

The deposition of thin Cadmium Telluride (CdTe) layers was performed by a chamberless metalorganic chemical vapour deposition process, and trends in growth rates were compared with computational fluid dynamics numerical modelling. Dimethylcadmium and diisopropyltelluride were used as the reactants, released from a recently developed coating head orientated above the glass substrate (of area 15 × 15 cm2). Depositions were performed in static mode and dynamic mode (i.e., over a moving substrate). The deposited CdTe film weights were compared against the calculated theoretical value of the molar supply of the precursors, in order to estimate material utilisation. The numerical simulation gave insight into the effect that the exhaust’s restricted flow orifice configuration had on the deposition uniformity observed in the static experiments. It was shown that > 59% of material utilisation could be achieved under favourable deposition conditions. The activation energy determined from the Arrhenius plot of growth rate was ~ 60 kJ/mol and was in good agreement with previously reported CdTe growth using metalorganic chemical vapour deposition (MOCVD). Process requirements for using a chamberless environment for the inline deposition of compound semiconductor layers were presented.

Two-phase flow induced vibration of piping structure with flow restricting orifices

In this paper, two-phase flow-induced vibration in a horizontal piping structure with flow restricting orifices has been experimentally investigated. The effect of flow patterns, void fraction, mass quality and orifice area ratio on vibration response is evaluated in detail. The two-phase flow measurements and vibration signals were analyzed simultaneously in order to understand the effect of two-phase flow behaviour on the governing factors responsible for flow-induced vibration mechanisms. The results show that the dynamic vibration response of the structure increased with the increase in the liquid mass flux and upstream void fraction in the case of intermittent flow patterns. The flow pattern change across the orifice is found to strongly affect the magnitude of the resulting vibrations. The maximum response was found in the region where a transition to slug flow occurred. Also, the RMS amplitude of vibration increased with an increase in the gas flux for both stratified and annular flows. Flow pattern maps were therefore created for both horizontal and vertical dynamic responses. These maps can be used in evaluating the dynamic response of piping structures with flow restrictions which are commonly found in the power generation industry. This will allow for a better design and safe operation of systems suffering from multiphase flow-induced vibration.

Mathematical procedure for predicting tube metal temperature in the second stage reheater of the operating flexibly steam boiler

Deployment of renewables introduces new regimes of large scale boiler operation. The units are required to operate at flexible rather than baseload mode. One of the requirements is to reduce the minimum load of the existing boilers which adds thermal stress to pressure parts. Significant operational issue is the local overheating of the heat exchangers material due to lower steam flow rates and poor heat dissipation conditions. The problem is particularly intensified in low-pressure reheaters. The current paper demonstrates a novel computational method of predicting tube metal temperature of specific reheater platens. The proposed numerical procedure incorporates coupling of CFD simulations of the boiler fire side with 1-D pipe flow model in the heat exchanger. Simulation results are compared to measurement data. The numerical method can be used to make decision on the modification strategy of the reheater design to achieve uniform temperatures of the tube metal in each platen by restriction orifices adjustment.

Fabrication of an implant-supported fixed complete denture using multiple digital technologies for a patient with a perioral burn: A clinical report

This clinical report describes the prosthetic and surgical management of a patient with a restricted oral orifice due to a perioral burn. Complete oral rehabilitation was achieved with maxillary and mandibular implant-supported fixed prostheses using a combination of digital and conventional impressions, design, and processing techniques.

Influence of the geometry on the riser gas holdup in an external-loop airlift reactor: empirical and neural network modelling

Experimental studies on the effect of geometrical characteristics (restriction orifice free area and sparger configuration) on the riser gas holdup of an external-loop airlift reactor have been conducted in this paper. The impact of the addition of non-coalescing media, such as n-butanol, was also investigated. In general, the decrease in the restriction orifice free area led to a substantial increase (up to 90%) in the riser gas holdup. The addition of n-butanol effected gas holdup to a lesser extent, as it increased the gas holdup in the range of 4-15%, depending on the restriction orifice free area. On the other hand, the impact of the sparger type was observed only at lower gas velocities, for which the sinter plate increased the gas holdup up to 20% in comparison to the single orifice. The paper also presents an empirical correlation for the estimation of the riser gas holdup with an average relative error of 7%. Finally, a neural network model with an average relative error of 2.4% was proposed.