Nozzle Geometry Research Articles

Optimization of Outer Diameter Bernoulli Gripper with Cylindrical Nozzle

Gripping and manipulating objects using non-contact and low-contact technologies is becoming increasingly necessary in manufacturing. One of the promising contactless gripping technologies is Bernoulli gripping devices for industrial robots. They have many advantages, but when changing the nozzle geometry, it is difficult to find the optimal parameters of the outer diameter of the gripper and its operating parameters. Therefore, the article presents a model for numerical simulation of the dynamics of airflow in the nozzle of the Bernoulli gripping device and in the radial gap between its active surface and the surface of the object of manipulation. Reynolds-averaged Navier–Stokes equations of viscous gas dynamics, SST-model of turbulence, and γ-model of laminar-turbulent transition were used for this purpose. The technical requirements for the design of the nozzle of Bernoulli jet gripping nozzles are determined and variants of their constructive improvement are offered. According to the results of numerical simulation in the Ansys-CFD software environment, the optimal diameter of the Bernoulli gripping device and the influence of the geometric parameters of the nozzle on the nature of the pressure distribution in the radial gap and its lifting force were determined. Determined the optimal parameters of the height of the gap between the object of manipulation and the Bernoulli gripping device using C—Factor, which will allow efficient operation of Bernoulli gripping devices during automated handling operations using industrial robots.

Numerical investigation of thermal and flow characteristics of impinging synthetic jet with different nozzle geometries at low nozzle-to-plate distances

Synthetic impinging jets are potentially useful techniques in electronic cooling. In this paper, the fluid and heat transfer characteristics of impinging synthetic jets were analyzed numerically by using circular, square, and rectangular shaped nozzles under short nozzle-to-plate spacing and actuation frequencies. A three-dimensional model was built to investigate dimensionless nozzle-to-plate distance (H/D = 0.10 – 1.00), Reynolds number (Re = 1810–4140), and excitation frequency (f = 250 – 500 Hz) effects on flow and heat transfer for a single jet. Firstly, the results were compared with experimental results from the literature, and a fair agreement has been obtained. Afterwards, instantaneous images of velocity contours and streamlines were presented to show the flow characteristics. By using simulation results, time-averaged Nu number and time and area-averaged Nu number (Nuavg) values were presented. Finally, a correlation was proposed for different cases to describe the variation in Nuavg. It was observed that a more homogenous temperature distribution on the impingement surface could be obtained by decreasing H/D and increasing Re number, whereas by increasing the nozzle-to-plate distance, lower temperature values could be obtained at the impingement region. Nuavg is almost unaffected from the nozzle geometry under the present investigated conditions. Higher local Nu number values were obtained for 0.50 = H/D around the impingement region. On the other hand, for 0.10 ≤ H/D < 0.50, a more uniform temperature distribution was obtained which leads to higher Nuavg. This study provides significant knowledge about the flow and heat transfer characteristics of synthetic impinging jets at low nozzle-to-plate distances, which could provide guidance in the thermal design procedure of electronic components.

Shock location effect on direct contact condensation stability

Direct contact condensation (DCC) is an efficient way of transferring heat between fluids’ vapor and liquid phases by mixing them directly rather than using a device like a heat exchanger. However, in the field, DCC may produce destructive and unwanted vibrations due to the instability of the gaseous plume condensing in the process fluid under certain conditions. Previous research on this topic has focused on correlating the flow conditions of the liquid and vapor phases to engineering quantities, such as the heat transfer coefficient, plume length, stability, and the dominant frequency exhibited by the DCC process. The present study investigates the impact of nozzle geometry on plume stability. It was motivated by the drastic difference observed experimentally between the stability of two identically designed nozzles with slightly different microfeatures. Tests were performed with several nozzle geometries, including converging/diverging, straight, and converging nozzles. The results from these experiments show that a nozzle with a supersonic flow at the exit plane is more likely to be stable than one with a subsonic exit flow. It is, therefore, possible to correlate the pressure ratio across the nozzle and nozzle geometry to the stability of the plume. This understanding allows a DCC nozzle geometry to be analyzed and designed for high stability with relatively simple one- and two-dimensional compressible flow modeling tools capable of resolving only the single-phase, compressible flow in the nozzle itself

Experimental Determination of the Flow Coefficient for a Constrictor Nozzle with a Critical Outflow of Gas

Reduction of energy expenditures required for various technological processes is a pressing issue in today’s economy. One of the ways to solve this issue in regard to liquefied natural gas (LNG) storage is the recovery of its vapours from LNG tanks using an ejector system. In that respect, studies on the outflow of the real gas through the nozzle, the main element of the ejector, and identifying differences from the ideal gas outflow, are of high relevance. Particularly, this concerns the determination of the discharge coefficient µ as the ratio of the actual flowrate to the ideal one, taking into account the energy losses at gas outflow through the nozzle. The discharge coefficient values determined to date for various nozzle geometries are, as a rule, evaluated empirically and contradictory in some cases. The authors suggest determining the discharge coefficient by means of an experiment. This paper includes µ values determined using this method for the critical outflow of air to atmosphere through constrictor nozzles with different outlet diameters (0.003 m; 0.004 m; 0.005 m) in the pressure range at the nozzle inlet of 0.5–0.9 MPa. The obtained results may be used for the design of an ejector system for the recovery of the boil-off gas from LNG tanks, as well as in other fields of industry, for the design of technical and experimental devices with nozzles for various applications.

Study of Injector Geometry and Parcel Injection Location on Spray Simulation of the Engine Combustion Network Spray G Injector

Abstract Parcel-based simulations are the most common method to simulate fuel sprays, especially for reacting conditions, due to their lower computational cost compared to more highly resolved simulations. It is important, however, to understand how spray boundary conditions are used to initialize the parcels that represent the atomizing fluid affect downstream conditions and overall simulation performance. Traditionally, when parcel simulations are used, the injector tip geometry is either significantly simplified or removed altogether due to resolution limits. Recent advances in computational power and numerical methods, however, have made it possible to resolve flow through these features. Previous work has shown some potential effects of even simple injector tip geometries, and this study investigates the effect of very detailed nozzle geometries on parcel-based simulations that have typically ignored these details. Four different parameters were investigated: whether a simulation includes a detailed injector tip geometry or a flat surface; whether parcels are initialized at the counterbore exit, which is more common, or at the nozzle exit; the use of an experimentally derived rate of injection or one-way coupling with a separate internal nozzle volume of fluid (VOF) simulation; the use of nominal or measured injector geometry. Simulations were compared using both global penetrations as well as local data near the injector. Spray penetration and other global measures showed limited sensitivity to boundary conditions/initialization procedure, but local data such as the local liquid volume fraction showed greater variation between the conditions, which may have an impact on mixing and combustion predictions in engine applications.

AltPrint: new filling and slicing process planning based on deposited material with geometry variation

PurposeThis paper aims to address the development and implementation of “AltPrint,” a slicing algorithm based on a new filling process planning from a variation in the deposited material geometry. AltPrint enables changes in the extruded material flow toward local variations in stiffness. The technical feasibility evaluation was conducted experimentally by fused filament fabrication (FFF) process of snap-fit subjected to a mechanical cyclical test.Design/methodology/approachThe methodology is based on the estimation of the parameter E from the mathematical relationships among the variation of the material in the material flow, nozzle geometry and extrusion parameters. Calibration, validation and analysis of the printed specimens were divided into two moments, of which the first refers to the material responses (flexural and dynamic mechanical analysis) and the second involves the analysis of the printed components with localized flow properties (for estimating the response to cyclic loading). Finite element analysis assisted in the comparison of two snap-fit geometries, one traditional and one generated by AltPrint. Finally, three examples of compliant mechanisms were developed to demonstrate the potential of the algorithm in the generation of functional prototypes.FindingsThe contribution of AltPrint is the variable fill width integrated with the slicing software that varies the print parameters in different regions of the object. The alternative extrusion method based on material rate variation was conceived as an “open software” available in GitHub platform, hence, open manufacturing with initial focus on desktop 3D printer based on FFF. The slicing method provides deposited variable-width segments in an organized and replicable filling strategy, resulting in mechanical properties variations in specific regions of a part. It was implemented and evaluated experimentally and indicated potential applications in parts manufactured by the additive process based on extrusion, which requires local flexibilities.Originality/valueThis paper presents a new alternative method for application in an open additive manufacturing context, specifically for additive extrusion techniques that enable local variations in the material flow. Its potential for manufacturing functional parts, which require flexibility due to cyclic loading, was demonstrated by fabrication and experimental evaluations of parts made in acrylonitrile butadiene styrene filament. The changes proposed by AltPrint enable geometric modifications in the response of the printed parts. The proposed slicing and filling control of parameters is inserted in a context of design for additive manufacturing and shows great potential in the area of product design.

Study on the effect of injection temperature and nozzle geometry on the flashing transition of liquid ammonia spray

Ammonia is a promising alternative fuel for carbon emission reduction in industry, transport, and power generation. For high-pressure combustion environment applications, direct injection of liquid ammonia (LNH3) is considered. Because of its thermophysical properties, and dependence on the injection and combustion environment conditions, the direct injection of ammonia in its liquid state can lead to flash-boiling, changing drastically the spray characteristics. In this study, we characterized the effect of injection temperature and nozzle geometry on the spray characteristics and transition to flashing using backlit imaging. Flow rates pressure curves and spray angles were obtained in a well-controlled environment and can be used as a database for simulation. Finally, some practical considerations on the design of nozzles are highlighted in the present work.

A Study on Converging-Diverging Nozzle Design for Supersonic Spraying of Liquid Droplets Toward Nanocoating Applications

Abstract Supersonic cold spray (CS) of functional nanomaterials from atomized droplets has attracted significant attention in advanced thin-film coating as it enables particle deposition with high-adhesion strength. In CS, optimum design of the supersonic nozzle (i.e., converging-diverging nozzle) is essential for accelerating particles to desired velocities. However, research on the nozzle design for supersonically spraying of “liquid droplets” for nanocoating applications is limited. To this end, we investigate the effect of nozzle geometrical parameters, including throat diameter, exit diameter, and divergent length on droplets impact velocity by numerical modeling and experimental validation, followed by a case study on nanocoating. The discrete-phase modeling was employed to study droplets’ flow behavior in continuous gas flow for various nozzle geometries. The results reveal that the nozzle expansion ratio, defined as a function of throat and exit diameters, has a significant influence on droplet velocity, followed by divergent length. Noteworthy, to correctly accelerate “low-inertia liquid microdroplets,” it was found that the optimum nozzle expansion ratio for axisymmetric convergent-divergent nozzles should be in a range of 1.5–2.5, which is different and way smaller than the recommended expansion ratio (i.e., 5–9) for CS of conventional micron-scale “metal” powders. Based on the simulation results, an optimum design of supersonic nozzle is established and prototyped for the experimental studies. Particle image velocimetry (PIV) was used to experimentally investigate the spray flow field and to validate the numerical modeling results. Moreover, coating experiments using the optimized nozzle confirmed the effective supersonic spraying of droplets containing nanoparticles, thereby showing the potential for advanced nanocoating applications.

Numerical investigation of the effect of primary nozzle geometries on flow structure and ejector performance for optimal design

Numerical investigation of the effect of primary nozzle geometries on flow structure and ejector performance for optimal design

Primary spray breakup from a nasal spray atomizer using volume of fluid to discrete phase model

Spray atomization process involves complex multi-phase phenomena. Abundant literature and validation of spray modeling for industrial applications like fuel injection in internal combustion and turbine jet engines are available. However, only a handful of studies, primarily limited to discrete phase modeling, of low-pressure applications, such as nasal spray exists. This study aims to provide insight into the external and near-nozzle spray characterization of a continuous spray and establishes good validation against the experiment. A three-dimensional (3D) x-ray scanner was used to extract the internal nasal spray nozzle geometry which was reconstructed to build a 3D computational model. A novel volume-of-fluid to discrete phase transition model was used to track the liquid phase and its transition to droplets, which was based on the shape and size of the liquid lumps. In this study, an early pre-stable and stable phase of spray plume development was investigated. Qualitative and quantitative analyses were carried out to validate the computational model. A liquid column exited a nozzle which distorted at its base with advancement in time and eventually formed a hollow-cone liquid sheet. It then disintegrated due to instability that produced fluctuations to form ligaments resulting in secondary breakup. This study provides in-depth understanding of liquid jet disintegration and droplet formation, which adds value to future nasal spray device designs and techniques to facilitate more effective targeted nasal drug delivery.

Analysis of the Effects of Nozzle Geometry on the Cavitation Water Jet Flow Field Using Orthogonal Decomposition

Analysis of the Effects of Nozzle Geometry on the Cavitation Water Jet Flow Field Using Orthogonal Decomposition

Computational fluid dynamics and experimental validation of aerosol jet printing with multi-stage flow focusing lenses

A 3D computational fluid dynamics (CFD) framework is presented to model and explain critical aerodynamic interactions occurring in the printhead during aerosol jet printing (AJP) with multi-stage flow focusing lenses. AJP has demonstrated great potential to fabricate complex circuits and conductive devices for numerous applications, including flexible electronics, medical diagnostic devices, and fuel cells. However, the devices manufactured by AJP are currently relegated to prototype roles due to poor repeatability of the deposited structures. The lack of process consistency in AJP arises from an incomplete understanding of causal aerodynamic interactions that influence the structure and repeatability of the printed features. Herein, a comprehensive CFD framework is presented to analyze the effects of gas flow rates, nozzle geometry, stand-off distance, printhead design, and aerosol droplet size on the resolution and morphology of printed features. Compressible Navier-Stokes equations with a k-ε turbulence model are solved to simulate flow conditions in the aerosol jet printhead. Additionally, a Lagrangian discrete phase model is used to simulate the transport of aerosolized ink droplets through the turbulent shear flow. The results highlight the crucial role of the design of the mist tube and the first aerodynamic lens, the density of the sheath gas, and the size of the droplets in the aerosol stream in determining print resolution and quality. A favorable comparison was found between numerically calculated results and experimental data obtained using the NanoJet™ system. CFD models presented in this work are expected to aid in identifying optimal process windows a priori, to improve process consistency.

Performance of elliptical nozzles on the spray dynamics of convergent and constant section nozzles by means of a [formula omitted] coupled model

In this paper, a computational study on the differences between a convergent and a constant section elliptical nozzle is performed. Coupled internal-external flow simulations were carried out by means of a Σ-Y model experimentally validated. The differences reported in terms of internal flow and spray parameters present the cavitation as an important effect in the elliptical nozzle geometries. The conclusions suggest a mixture improvement potential for the cavitating elliptical nozzles.

Influence of nozzle geometry on wall static pressure coefficient of the submerged turbulent jet impinging on a smooth flat surface

The experimental work is carried out to study the influence of nozzle geometry on the flow characteristics of the submerged turbulent jet impinging on a smooth flat surface. Three nozzle geometry configurations, viz. parabolic, conical and exponential, are considered. Depending upon the nozzle exit diameter, the Reynolds number of 12,000–23,500 and jet-to-plate distance of 0.5–6 is considered. At a higher jet-to-plate distance (z/d = 6), a secondary peak was observed at a radial distance around r/d = 0.4 from the stagnation point. It is due to the transition of fluid flow from laminar to turbulent on the impingement surface. At all Re and z/d, parabolic nozzle geometry resulted in maximum value as compared with other nozzle geometry configurations. This may be attributed to higher pressure losses in the conical nozzle and exponential nozzle than the parabola nozzle because of streamlined flow and this information can be used for local heat transfer phenomena for optimum conditions.

A study of the parameters affecting the particle velocity in cold-spray: Theoretical results and comparison with experimental data

Within coating applications, cold-spray is nowadays an extended technique commonly used in environments such as the additive manufacturing or repair industries. The differential factor that leads this approach to be chosen over others is its low deposition temperature. The need for ensuring the resistance and durability of the free-standing components has led to the development of models that can predict the kinetic energy of the particles, which is the main driving parameter affecting the deposit performance. In this study, an optimisation theoretical model, previously developed by the authors, is validated with the experimental exit particle velocity data taken from commercial geometries and using Fluent simulations available in literature. The aim of this work is to relate fundamental parameters in the cold-spray process such as the stagnation conditions, nozzle geometry, powder size or particle velocity. This objective is achieved by creating novel interdependent maps connecting these pivotal data by virtue of the model presented. Several graphs describing the final particle velocity depending on the stagnation pressure and temperature are obtained along with the optimal geometry for a wide range of materials (aluminium, titanium, steel, Inconel 625 and copper). In addition, the analytical model is able to hand over a deposition window of particle sizes and velocities that can be achieved using a specific cold-spray equipment. Both set of maps combined together can be a powerful tool which users and manufacturers can benefit from on the grounds that they do not only provide information about whether a deposition can be achieved or not with a cold-spray equipment but also about the stagnation conditions needed. The results obtained with this methodology reflect the limitations of low and medium-pressure equipment in terms of the maximum particle diameter that can be deposited and constitute a novel advance in the state of art of cold-spray. Moreover, the fundamental parameter regarding the geometry, namely the ratio between the nozzle exit and the nozzle throat diameters, is represented as a function of the above-mentioned parameters.

Detecting ultrafast turbulent oscillations in near-nozzle discharged liquid jet using x-ray phase-contrast imaging with MHz frequency

Characteristics of a discharged liquid jet in near-nozzle are determined by the in-flow turbulences generated by the evolution of inflow vortices and cavitation. High-fidelity simulations have indicated that such physical processes can generate ultrafast turbulent fluctuations (in the range of MHz) originating from the nature of turbulence by the interaction between the large and small-scale turbulence in the flow. Detecting ultrafast turbulent oscillations while resolving small-scale turbulences in the optically dense near-nozzle liquid jet has not been observed through experimental methods so far. In this study, therefore, ultrafast x-ray phase-contrast imaging, which can provide a clear image in the near-field using a high-energy x-ray source, was applied to observe the fluctuation of flow velocity in the near-field to obtain the ultrafast turbulent oscillations at the discharged jet. To capture the ultrafast variance of flow velocity originating from the nature of turbulence, the high imaging frequency was applied up to 1.2 MHz. With the implemented methodology, turbulence intensity distributions of discharged liquid jets were measured for various injection pressures and nozzle geometries. Such turbulence intensity results were also correlated with the initial dispersion angle of the spray. In addition, the turbulence length scales, which can be detected through the current methodology, were estimated and discussed considering standard-length scales. The results showed that the current experimental method introduced in this study can provide important insights into the turbulence characteristics of spray by resolving Taylor scale turbulences and can provide valuable validation data and boundary conditions for reliable spray simulations.

NIMOC: A design and analysis tool for supersonic nozzles under non-ideal compressible flow conditions

A computational tool for non-ideal supersonic nozzle flows is developed to perform direct design of nozzle geometries and flow analysis of shock-free off-design conditions. So-called non-ideal flows are characterized by the departure of the fluid thermodynamics from the ideal-gas law, which is the case of supersonic expansions close to the critical point, either in the superheated vapour or in the supercritical region. Deviations from the ideal-gas model of remarkable significance are observed in connection with, but not limited to, fluids made of complex molecules. NIMOC (Non-Ideal Method Of Characteristics) implements a formulation of the Method Of Characteristics (MOC) valid for non-ideal flows: the classical formulation of the MOC is complemented with state-of-the-art nonlinear multiparameter Equations of State (EoS) implemented in external thermodynamic libraries. NIMOC implements a two-dimensional and axisymmetric formulation of the MOC, which is applied to the solution of the isentropic expansion through nozzles of different geometrical configurations: straight-axis symmetric and axisymmetric conventional wind-tunnel nozzles, straight-axis symmetric and axisymmetric minimum-length nozzles, and asymmetric nozzles with curved meanline. Results are presented, which demonstrate nozzle design and flow analysis in the presence of paradigmatic non-ideal flow phenomena. Verification of MOC computations is performed by means of inviscid Computational Fluid Dynamics (CFD) simulations and experimental data. Results are presented for selected geometrical configurations.

Experimental study of dripping, jetting and drop-off from thin film flows on inclined fibers

Gravity driven film flows on vertical fibers are known to exhibit a variety of flow dynamics including the formation of droplet trains induced by the hydrodynamic (Kapitza) and Plateau–Rayleigh instability mechanisms. Through an experimental study, it is shown how inclination of the fiber from the vertical influences these dynamics. The formation of waves, regime transitions from dripping to jetting regimes, as well as the onset of drop-off in the form of droplet detachment from the fiber are illustrated and described in dependence of the fiber inclination angle and the liquid mass flow rate. Additionally, the influence of fiber diameter and nozzle geometry on regime transitions and the onset of drop-off from the substrate are examined. It is shown that the onset of drop-off is strongly related to the transition from a regime characterized by a regular wave pattern to a regime characterized by an irregular wave pattern. It is also demonstrated that this regime transition depends not only on flow rate and fiber geometry, but also strongly on the inclination angle. Interestingly, a stabilizing effect of increasing the fiber inclination is detected for constant fiber geometry and film flow rate.

Direct ink writing of textured piezoelectric ceramics

Textured ceramics are often formed via tape casting in order to align platelet particles in the preferred direction, allowing the ceramic to have properties approaching those of single crystals without the complexities of growing such a crystal. However, tape casting produces significant waste material, as flat plates are machined to produce the desired geometries, e.g., rings. Additive manufacturing reduces these issues by allowing the complex geometries to be formed in the green state, thus reducing waste and improving design freedom. This presentation will discuss progress to-date on direct ink writing (DIW) of textured PMN-PZT. The focus will be on the methodology used to develop a suitable paste for printing. Development of a stable, shear thinning paste with a quick recovery time is critical. Zeta potential and rheological data were collected as a function of pH and other relevant slurry parameters such as percent solids loading and binder content. Sintered filaments and bulk parts were characterized to evaluate the efficacy of template alignment in the process as a function of slurry rheology, nozzle geometry, and print parameters.

Improving Homogeneity of 3D-Printed Cementitious Material Distribution for Radial Toolpath

The 3D cementitious material printing method is an extrusion-based additive manufacturing strategy in which cementitious materials are extruded through a dynamic nozzle system to form filaments. Despite its ability to fabricate structures with high complexity and efficiency, the uneven material distribution during the extrusion and deposition process is often encountered when a radial toolpath is introduced. This limits the design freedom and printing parameters that can be utilized during radial toolpath printing. Here, we report a facile strategy to overcome the existing challenges of cementitious material non-homogeneity by rationally developing new nozzle geometries that passively compensate the differential deposition rate encountered in conventional rectangular nozzles. Using two-phase numerical study, we showed that our strategy has the potential of achieving a homogeneous mass distribution even when the nozzle travel speed is unfavorably high, while filament from a rectangular nozzle remains highly non-homogenous. The material distribution unevenness can be reduced from 1.35 to 1.23 and to 0.98 after adopting trapezoid and gaussian nozzles, indicating improvements of 34.3% and 94.2%, respectively. This work not only outlines the methodology for improving the quality of corner/curved features in 3DCMP, but also introduces a new strategy which can be adopted for other extrusion-based fabrication techniques with high material inertia.