Orifice Diameter Research Articles

Effects of structural parameters of active pre-chamber on the combustion process of methanol/gasoline TJI rotary engine

The application of Turbulent Jet Ignition (TJI) combustion mode in spark ignition engine can improve combustion efficiency and output power. This paper innovatively proposes the application of active pre-chamber (APC) in rotary engine (RE) to realize this mode. And blending a certain percentage of methanol in gasoline to achieve carbon reduction. A three-dimensional computational model of the APC-RE was developed, and the effects of three APC structural parameters including throat section diameter, throat section length and orifice diameter on the component flow and combustion characteristics were investigated. The results showed that the APC-RE exhibited higher sensitivity to the diameter of the throat section than the length variation under the fixed active fuel injection strategy. The low length or small diameter of the throat section causes insufficient energy in the APC jet, and too high values cause unstable combustion. The optimal APC volume is achieved at a throat length of 8 mm and a diameter of 6 mm, with the highest Indicated mean effective pressure (IMEP) and Indicated thermal efficiency (ITE). Next, The APC volume was fixed and the effect of jet orifice size on RE performance was discussed and the optimal size was determined 1.25 mm, which can further optimize the jet velocity and can continue to increase IMEP and ITE by 1.24 % and 1.46 % respectively.

Comparative study of turbulent round jet flows through direct numerical simulation at medium–high Reynolds numbers

This study examines a spatially evolving turbulent round jet at a Reynolds number of Re = 7000 based on the bulk velocity Ub and the orifice diameter D and a Prandtl number of Pr = 0.71 using direct numerical simulation (DNS). Statistical data are collected over 30 000D/Ub time units, including mean quantities, Reynolds stresses, heat fluxes, mixed moments, Reynolds stress and turbulent kinetic energy budgets, and probability density functions. Comparative analysis with a previous DNS at Re = 3500 (Nguyen and Oberlack, 2024a; 2024c) shows that the higher Reynolds number leads to a shift of the self-similarity to a greater distance from the orifice. A larger Reynolds number leads to higher magnitudes of different statistical moments, dissipation and production. In addition, a maximum visible in the near-field of the turbulence intensity components is smoothed at the larger Reynolds number. The probability density functions of the axial velocity and the passive scalar show Gaussian behavior on the centerline, but with larger standard deviations compared to the lower Reynolds number. The study highlights the significant impact of using a fully developed turbulent pipe flow profile as the inlet condition, which significantly reduces the size of the potential core by introducing initial turbulence intensities at the orifice.

Numerical investigation on the effect of an orifice plate on the flow-induced and acoustically induced vibration of a gas transmission pipe

In this paper, a numerical method is proposed for investigating the flow-induced vibration (FIV) and acoustically induced vibration (AIV) of a straight pipe with an orifice plate. First, the turbulent pressure (TP) and acoustic pressure (AP) signals on the pipe wall were obtained through the simulation of an unsteady flow field and the application of Mohring's analogy, respectively. Subsequently, the FIV and AIV of the pipe were calculated by means of one-way fluid-structure interaction and acoustic-structure interaction, respectively. The calculated pressures, flow velocities, and sound powers at the monitoring point were in good agreement with the experimental results reported in the literature. The numerical results revealed that the power spectral densities of the AP were significantly higher than those of the TP on the surface of the tested end pipe, particularly at the natural frequencies of the acoustic modes. In the low-frequency regime, FIV was the dominant factor, whereas in the medium-high frequency regime, particularly above the cutoff frequency of the plane wave, AIV was the dominant factor. The findings of the parametric studies demonstrated that the AP and AIV of the pipe exhibited a considerable increase with the Mach number. Conversely, the TP and FIV demonstrated a more pronounced rise when the Mach number increased from 0.1 to 0.2, followed by a less pronounced increase when the Mach number increased from 0.2 to 0.3. A reduction in the orifice diameter resulted in an increase in the AP and AIV. In contrast, the TP and FIV exhibited a comparatively minor increase.

Investigation of nonlinear dynamic behaviors of vertical rotor system supported by aerostatic bearings

Abstract A common issue associated with gas bearing-rotor systems is the tendency to generate self-excited vibrations, leading to instability. To address this problem, the fluid-structure coupling model of an aerostatic bearing-rotor system is established in this paper. Then a hybrid method combining the finite difference method and direct integration method, is employed to solve the bearing lubrication equation and rotor motion equation simultaneously. Furthermore, based on the orbit of rotor center,frequency spectrum diagram, Poincaré map, waterfall diagram and bifurcation diagram, the effects of rotational speed, rotor mass, orifice diameter and nominal clearance on the nonlinear dynamic behaviors of the bearing-rotor system are investigated. The results indicate that the system exhibits rich nonlinear behaviors with increasing rotational speed and rotor mass, including the occurrence of typical half-speed whirl. However, the nonlinear vibrations of the system can be restricted by selecting appropriate bearing structural parameters, providing theoretical guidance for the design of aerostatic bearing-rotor systems.

Efficacy and Safety of Cardioband in Patients with Tricuspid Regurgitation: Systematic Review and Meta-Analysis of Single-Arm Trials and Observational Studies.

Background/Objectives: The incidence and prevalence of tricuspid regurgitation (TR) are increasing worldwide. "Traditional" drug therapy with diuretics is often ineffective and the identification of new strategies, including non-pharmacological ones, is an urgent need. The aim of this study was to summarize the results on the efficacy and safety of Cardioband, one of the few approved transcatheter tricuspid valve repair systems, in patients with TR. Methods: Three databases (Medline, Scopus, and CENTRAL) were searched to identify clinical trials and observational studies on the efficacy (primary outcome) and safety (secondary outcome) of Cardioband. A random-effects meta-analysis was performed with R software (version 4.3.3). Survival and freedom from heart failure (HF) hospitalization were estimated with the method of reconstructing individual patient data from Kaplan-Meier curves (IPDfromKM). Results: Eleven studies were included in this systematic review and meta-analysis. Cardioband significantly reduced annulus diameter (-9.31 mm [95% Confidence Interval, CI: -11.47; -7.15]), vena contracta (-6.41 mm [95% CI: -8.34; -4.49]), and effective regurgitant orifice area (EROA) (-0.50 cm2 [95% CI: -0.72; -0.28]) in patients with TR. Cardioband reduced the severity of TR and the extent of heart failure in 91% [95% CI: 85; 97] and 63% [95% CI: 52-75] of patients, respectively. Finally, Cardioband implantation was associated with prolonged survival and freedom from HF hospitalization (80.1% and 57.8% at 24 months, respectively). Conclusions: This study demonstrates that Cardioband implantation leads to cardiac remodeling and mechanical improvements, reduces the severity of TR, and improves quality of life. Therefore, Cardioband is an effective option for the non-pharmacological treatment of TR.

Left atrial appendage orifice morphology in sickness and in health.

The left atrial appendage (LAA) is the primary site of embolism in individuals with atrial fibrillation (AF). We aimed to evaluate the morphological features of the LAA orifice in patients with sinus rhythm, paroxysmal AF, and persistent AF using three-dimensional (3D) transesophageal echocardiography (TOE). We also intended to identify morphometric parameters of the LAA orifice that may be potentially associated with an increased risk of ischemic stroke. We prospectively enrolled 106 patients undergoing TOE. Patients were divided into three groups: group1 (sinus rhythm), group2 (persistent AF), and group3 (paroxysmal AF). All patients underwent acomprehensive evaluation through transthoracic echocardiography (TTE) and TOE. Off-line analyses were performed of the recorded images. The LAA minor orifice area and minimal orifice diameter were greater in patients with persistent AF compared with individuals in sinus rhythm. Patients with persistent AF also had deeper LAAs compared with those in sinus rhythm. None of the LAA orifice morphometric measures were related to ischemic stroke risk. The only independent predictors of ischemic stroke were heart rhythm and the CHA2DS2VASc score. Persistent AF is associated with LAA dilation, increased depth, and larger orifice size. To our knowledge, this is the first study to demonstrate LAA orifice structural remodeling in patients with AF using 3D TOE.

Effect of crossflow orientations in the impinging jet flow channel on flow and heat transfer enhancement under rotations

An experimental and numerical investigation was conducted to elucidate the flow and heat transfer characteristics of a row of impinging jets within a confined, rotating channel. The study focused on a jet Reynolds number (Rej) of 9,000, examining three distinct crossflow orientations: radially outward (ROCF), radially inward (RICF), and a combined radially outward and inward (ROICF) scheme. Jet-to-impingement surface distances (h/dj) of 2, 4, and 6 (where dj represents the jet orifice diameter) were considered, along with channel rotation speeds corresponding to Rotation numbers (Ro) from 0 to 0.0046. Heat transfer on the leading and trailing sides of the impinging jets was measured using a steady thermochromic liquid crystal (TLC) technique under constant heat flux conditions. Additionally, RANS simulations were employed to investigate the flow fields associated with the impinging jets. The results reveal that in both the ROCF and RICF schemes, heat transfer, characterized by the Nusselt number, decreases from upstream to downstream for each impinging jet. Increasing the rotation number (Ro) leads to enhanced heat transfer, with the trailing side exhibiting marginally higher values than the leading side. In the ROICF scheme, at h/dj = 2, a more uniform Nusselt number distribution is observed across all jet holes compared to the ROCF and RICF schemes, and this uniformity increases with higher Ro. However, for h/dj = 4 or 6, the heat transfer becomes non-uniform and can even deteriorate below the stationary case at high Ro numbers, attributed to the combined effects of Coriolis and centrifugal forces.

Experimental Analysis of Cavitation Erosion: Parameter Sensitivity and Testing Protocols

The scientific goal of this study was to investigate the effects of various parameters on cavitation-induced erosion, with the aim to enhance the understanding and assessment of cavitation resistance in hydraulic systems. Cavitation erosion poses significant challenges to the durability and efficiency of hydraulic components, such as those found in hydropower plants and pumping stations. Prompted by the need to improve the reliability of cavitation testing and material assessment, this research conducted a comprehensive sensitivity analysis of a cavitation jet apparatus (CJA). This study employed an experimental platform that consisted of a vertical cylindrical test tank, a submerged nozzle, and an aluminum sample. By examining a range of orifice diameters, this research identified that smaller diameters led to increased erosion intensity, with the most pronounced effects observed at a diameter of 2 mm. Furthermore, various standoff distances (SoDs) were tested, which revealed that shorter distances resulted in greater erosion, with the highest impact noted at an SoD of 5 cm. This study also evaluated different nozzle geometries, where it was found that a 132° conical sharped edges nozzle, combined with an orifice diameter of 2 mm and an SoD of 5 cm, produced the most severe erosion. Conversely, chamfered edges nozzles and a commercial nozzle (MEG2510) with an SoD of 10 cm or greater showed reduced erosion. These results highlight that by standardizing the testing duration to 1200 s, the CJA could reliably assess the cavitation resistance of materials. This study established a clear relationship between increased pressure and higher impact forces, which led to more severe erosion. The findings underscore the effectiveness of the CJA in evaluating material resistance under various cavitation conditions, thus addressing a critical need for reliable cavitation testing tools.

Numerical simulation and experimental study of the influence of disk groove structure optimization on the air film flow field signature of an air-cushion sandwich belt conveyor

A new type of disk groove mechanism was developed and manufactured. The effects of the structural and operating factors of the disk groove on the air film loading performance were examined using single factor and orthogonal experimental methods. The results of numerical simulation and experimental studies showed that the air film loading performance correlated positively with the orifice diameter and inlet pressure, with the orifice spacing and diameter having the most significant effects, and that the belt speed boosted the air film uniformity. Meanwhile, a comparative analysis of the corresponding level values showed that an air film thickness of 0.8 mm, orifice diameter of 5 mm, orifice spacing of 30 mm, inlet pressure of 8000 Pa, and conveyor speed of 5 m/s were the optimal parameter combinations for the maximum loading capacity. To verify the accuracy of the model, a field experiment was conducted at Jiangmen Southern Conveying Machinery Engineering Co., Ltd. The air film pressure at the experimental position matched the numerical simulation results. In addition, when the number of rows was one and the air volume was 10 m3/h, the smallest value of traction resistance was obtained under minimum power consumption.

Numerical Analysis of Spray Evaporation Process in Desuperheater

Abstract The cooling water is sprayed into the desuperheater to regulate the temperature of the superheated steam. Computational fluid dynamics (CFD) was applied to investigate the spray evaporation process in the desuperheater. Discrete phase model (DPM) was applied to describe the gas-liquid two-phase flow characteristics based on the Eulerian-Lagrangian approach. The Rosin-Rammler distribution and TAB model were used for the description of the primary and secondary droplet breakup, respectively. The coupling effect of gas-liquid two-phase, influence of temperature on latent heat, the stochastic collision and coalescence of droplets were considered in the CFD model. The numerical results show good agreement with the plant data. The hydrodynamics and temperature distribution characteristics were analysed. The influence of water mass flow rate and orifice dimensions on temperature distribution and temperature non-uniformity was further investigated. The results indicate that increasing the water flow rate can improve the desuperheating ability, but it will make the temperature uniformity worse. Under the same operating conditions, smaller orifice diameters are beneficial for production of droplets with smaller size, leading to better desuperheating ability.

Enhanced pointing and charge properties of electron beams from few-TW laser wakefield acceleration with an asymmetric density profile in a sub-millimeter nitrogen gas jet

This work demonstrates the feasibility of creating a sub-millimeter, subsonic nitrogen gas jet using a 178-μm diameter orifice to conduct laser wakefield acceleration (LWFA) with 1-TW, 40-fs laser pulses. More importantly, our findings reveal that using a blade to impede part of the gas flow and create an asymmetric density profile with a shortened down-ramp leads to a notable reduction in pointing fluctuations and an increase in the total charge of the output electron beams. As evidenced by the corresponding particle-in-cell simulation, the laser intensity is more effectively sustained toward the downstream end of the shaped gas jet, allowing for effective excitation of low-amplitude plasma waves that help preserve the accelerated electrons over the target rear side. In contrast, the pulse intensity drops significantly within the rear side of the unshaped gas jet, resulting in continuously diminishing plasma waves and decreased beam charge. The steeper gradient of the density down-ramp in the shaped gas jet also leads to a more rapid increase in the plasma wavelength over a reduced propagation distance, which helps mitigate the dephasing of accelerated electrons and increase the charge at the high-energy side of the spectrum. Our study paves the way for the future development of few-TW LWFA using a subsonic gas jet with sharp edges to further enhance the properties of output electron beams.

Influence of the flame jet on heat loss and thermal efficiency of lean burn pre-chamber natural gas engine with various geometrical combustion chambers

Due to relatively high thermal efficiency and low NOx emission, the pre-chamber type lean burn natural gas engine for cogeneration is expected to be spread rapidly in the near future. To offer a guidance for designing the pre-chamber natural gas engines, in the present study, the influence of the flame jets on combustion process and thermal efficiency of pre-chamber type lean burn natural gas engine was investigated with various pre-chamber orifice diameters and angles and piston bowl shapes by numerical simulation. The presented results showed that when the orifice diameter is smaller, it results in higher heat loss with the stronger gas flame jets impinging on piston top and cylinder liner walls, but the higher degree of constant volume heat release can be also obtained. Consequently, there is no significant difference in the thermal efficiency for these four orifice diameters. Increasing the angle of the orifice and the depth of the piston bowl can avoid the heat loss caused by the early impact of flame jets on the piston top wall. In addition, compared to the diameter of piston bowl, the depth of piston bowl, which is related to the distance from the orifice to the piston bowl, should have more effect on the combustion process and thermal efficiency. For wider orifice angle, the heat loss was also increased, particularly to cylinder head. Finally, the optimal thermal efficiency obtained by balancing heat loss and the degree of constant volume heat release is 44.73%.

Optimization of piezo pump and air impact cooling based on a synthetic jet

A synthetic jet piezo (PE) pump with an inlet channel structured akin to a diffuser/nozzle, featuring smoothed walls, was developed. The synthetic jet was characterized by analyzing the internal flow field of the PE pump. Furthermore, the flow performance of this novel PE pump was compared with that of a basic PE pump, thereby demonstrating the advantages of the proposed design. Utilizing regression equations and standardized effect plots derived from the response surface method, both the main and interaction effects of parameters on the flow rate were assessed. Subsequently, the flow performance of the optimized PE pump was evaluated through experimental testing. Additionally, air impact cooling experiments were conducted, focusing on the influence of the impact distance on cooling performance. The findings indicated that the PE pump's open cavity height, closed cavity height, outlet diameter, and orifice diameter were 1.3 mm, 0.5 mm, 1.5 mm, and 0.8 mm, respectively. The proposed synthetic jet PE pump achieved a flow rate of 1832.3 ml/min at 50 Vpp and 4.6 kHz. Furthermore, it was observed that the operation of the PE pump reduced the temperature of the heater by 63 % at an impact distance of 20 mm.

Extraction and characteristic analysis of the nonlinear acoustic impedance of circular orifice in the presence of bias flow

The acoustic behavior of the circular orifice is influenced by the bias flow and high amplitude sound excitation. The present study proposes an approach based on the three-dimensional (3D) time-domain computational fluid dynamics (CFD) simulation to extract the nonlinear acoustic impedance of circular orifice. Impact coefficients of the bias flow on the acoustic impedance of circular orifice are defined as the ratio of the acoustic impedance difference between the cases in the presence and absence of bias flow under high amplitude sound excitation to that under low amplitude sound excitation. The effects of bias flow Mach number, orifice diameter, plate thickness, and porosity on the impact coefficients under different amplitude sound excitations are studied, and the impact coefficients could collapse all the predictions by using the non-dimensional sound particle velocity. The fitting formulas of nonlinear acoustic impedance of circular orifice are presented by using nonlinear regression analysis.

Cuboid obstacle influence on high-pressure jet dispersion: A CFD study

In the context of the process industry safety, one of the main accidental scenarios is the release of high-pressure gaseous material. Since natural gas is highly flammable, the likelihood of ignition increases as the jet develops, with a maximum area of effect related to its lower flammability limit (LFL). This work aims at simulating and evaluating the interaction between high-pressure natural gas jets and cuboid obstacles, which were selected due to their prevalence in the process industry as storage units or buildings present in industrial parks. The maximum extent of the cloud at the LFL of natural gas is often influenced by the jet-obstacle interactions, necessitating complex numerical methods like computational fluid dynamics (CFD) for accurate estimation. Therefore, this study provides pivotal insights that challenge traditional modelling approaches, like integral ones, offering cost-effective alternatives where needed without compromising on safety.The findings indicate that using a CFD approach is not always necessary, as it largely depends on the storage pressure, diameter size, and the release height of the jet. At storage pressures of 65–130 bar with an orifice diameter of 2.54 cm, and a release height above 2.75 m, simpler methods like integral models are applicable without any substantial reliability loss. This is especially true when the cuboid obstacle is farther away from the release source. At lower release heights, especially if coupled with a larger orifice diameter, the CFD approach should be utilised as jet-cuboid interactions become highly relevant to the development of the jet.

Modelling of air springs for metro vehicles and studies on the effect of orifice damping

With the metro vehicle as the subject, a mathematical model of the main chamber, the auxiliary chamber and the orifice of the air spring were established based on the thermodynamic theory. The lateral nonlinear model is obtained based on the analytical geometry. Establish the four-point levelling valve and differential valve models through theoretical analysis. A complete three-dimensional air spring model is established. The correctness of the model is verified by comparing it with the actual data. The impact of orifice diameters and secondary vertical dampers on the dynamic performance of the metro vehicle is investigated. The results show that the secondary vertical damping configuration has a greater effect on vertical stability and acceleration but a minor impact on operational stability. Metro vehicles equipped only with air springs in the smaller diameter orifice do not need to be configured with a vertical damper, resulting in excellent dynamic performance and savings in production costs.

Investigation of scaling-down experiments for accidental CO2 leakage dispersion risks in constant-pressure transportation pipelines within the CCUS process

Within the framework of strategies to prevent global warming, the safety of CO2 transportation pipelines requires thorough hazard analysis. Accidental leakage during long-distance CO2 transport, influenced by the size of the leakage opening, typically occurs under constant pressure conditions in the CCUS process. This paper introduces an innovative scaled experimental apparatus with an elliptical orifice, designed to simulate leakage due to free rupture in pipelines. The goal is to understand the risk characteristics of constant-pressure leakage in transportation pipelines. The results indicate that during leakage, the pressure drop in the source CO2 pipeline is less than 0.3013 MPa/s, which can be considered constant pressure leakage. The Mach disk size dm has a linear relationship with the elliptical leakage orifice ab. The scaled experiments also show that temperatures can drop to as low as −78°C, indicating significant low-temperature risks. This scaling experiment provides a new approach for predicting and mitigating diffusion risks in long-distance pipeline transportation by examining the relationship between pipeline length and orifice diameter. The research data and results contribute to a deeper understanding of the safety aspects of long-distance transportation of CO2 under constant pressure leakage conditions, providing a basis for risk assessment of leakage accidents and environmental protection measures.

Effect of orientation angle for needle-free jet injection

In this paper, we report on the delivery efficiency of needle-free jet injections using injectors with typical jet speed vj≈140m/s, orifice diameter do=157μm, and volume V=0.1 mL. The target substrates were either hydrogel tissue phantoms or porcine tissues combined with excised human skin. The novelty of this study is two-fold: First, we investigate the influence of injection angle relative to the skin surface, and second, we also study the influence of the jet path relative to the orientation of muscle fibers. While most commercial jet injectors employ a fitting that would render the device normal to the skin surface, recent studies have proposed oblique injections, which may be beneficial for intradermal or subcutaneous tissue injection. Furthermore, for deeper intramuscular injections, we propose that an angled jet path taking the muscle fiber orientation into account may result in a bolus or dispersion zone that is conducive to increased cellular uptake of the drug.

Study on volumetric heat and mass transfer coefficient in a spray drying process utilizing pressure swirl nozzle: A numerical and experimental approach

This paper applies a sectional and cumulative approach to estimate the volumetric heat and mass transfer coefficients (hV and kV) to characterize the behaviour of the spray drying process. The investigation utilizes a tailor-made spray dryer equipped with a pressure swirl nozzle with a 0.2 mm orifice diameter, utilizing Mannitol solution as the precursor and air as the carrier gas. A comprehensive numerical analysis is conducted using the Adaptive Mesh Refinement (AMR) technique alongside selective experiments. The study considers precursor mass flow rates of 1 g/s, 1.2 g/s, and 1.5 g/s, along with carrier gas velocities of 0.88 m/s and 1.19 m/s at a temperature of 250 °C. Comparisons between predicted and estimated hV and kV are performed, leading to the proposal of a method for identifying constant rate and falling rate periods. The analyses contribute to delineating the solvent evaporation zone, solid particles heating zone, spray penetration length, and drying length. Additionally, experimental temperature measurements in both axial and radial directions at 12 grid points in the chamber are conducted to validate the numerical results, showing acceptable deviation.

Influence of mass flux ratio and phase difference on impingement heat transfer characteristics of coaxial synthetic jet

The aim of the present study is to introduce and investigate the performance of a novel independently controlled coaxial synthetic jet (CSJ) designed for enhancing impinging heat transfer applications. The CSJ features a unique configuration with two coaxial cavities, each featuring inner and annular orifices of the same hydraulic diameter, all aligned at 0∘ The independently controlled CSJ allows precise manipulation of jet conditions and phase differences between its inner and outer cavities, offering a versatile platform for optimizing heat transfer performance under varying operational scenarios. This capability not only enhances our understanding of the heat transfer characteristics of the CSJ but also underscores its potential as an innovative tool for advancing thermal management in engineering systems. Here, the actuators are operated at a Reynolds number (Re) of 1260 to perform the jet impingement experiment. The study explores mass flux ratios, including 0.5, 1, and 2, to understand how these ratios affect impinging heat transfer characteristics. The investigation also explores the influence of different phase differences (∅) between the inner and outer diaphragms, ranging from 0∘ to 180∘ for different mass flux ratios. It has been observed that the percentage enhancement of the peak stagnation Nusselt number (Nustag) for Mr=0.5 is approximately 30.36░% and 53.68░% compared to Mr=1 and Mr=2, respectively. The peak Nustag enhancement of CSJ operated at Mr=0.5 is approximately 63.9░% and 58.6░% compared to the inner jet and annular jet operated separately. In the far field, when a phase difference of ∅=135∘ is provided, the peak Nustag is enhanced by approximately 17.29░% compared to ∅=0∘ for Mr=0.5. Based on the present study, it is recommended to operate the CSJ at a lower mass flux ratio (Mr=0.5) and a higher phase difference between the actuators (∅=135∘) to achieve maximum cooling effect from the heated plate.