Nozzle Case Research Articles

INFLUENCE OF MODE PARAMETERS AND DESIGN OF THE EJECTION NOZZLE ON CHARACTERISTICS OF HIGHLY DISPERSED ALUMINUM POWDER. PART 2. INFLUENCE OF THE NOZZLE DESIGN

The influence of the design of an ejection nozzle on characteristics of highly dispersed aluminum powder in industrial conditions at the LLC «SUAL-PM» enterprise is performed. Measurements of dispersed characteristics of the spray product when spraying the aluminum melt by the ejection nozzle are performed for six variants of modified nozzles. The results of determining the median diameter of particles ( d ) and content of a highly dispersed phase ( z ) (with the particle diameter no larger than 10 μm) in the spray product are presented. It is shown that the most efficient method of modifying the spray nozzle is profiling the cone part of a protective bush and imposition of ultrasonic vibrations on a nozzle case (a decrease in d m by ~31,6 % and an increase in z by ~8,5 %).

Impinging cross-shaped submerged jet on a flat plate: a comparison of plane and hemispherical orifice nozzles

It is well known that the transfer of heat, mass and momentum to a wall by an impinging jet is partially linked to the way in which jet generation is realized. The organization of the vortices at the jet exit depends on the upstream conditions and on the geometry of the nozzle. Particle image velocimetry (PIV) and electrodiffusion techniques were used to investigate the characteristics of different impinging jets and the resulting wall shear rates and mass transfer. Two cross-shaped orifice jets, one produced by a plane orifice nozzle (i.e. a cross-shaped orifice made on a flat plate, CO/P) and the second by a hemispherical orifice nozzle (i.e. a cross-shaped orifice made on a hemisphere, CO/H), were compared to a reference round jet produced by a convergent nozzle. The distance between the jet exit and the target wall was equal to two nozzle equivalent diameters (D e ), based on the free orifice area. The Reynolds number, based on D e and on the exit bulk-velocity, was 5620 for each flow. PIV measurements give an overall view of the flow characteristics in their free and wall regions. The switching-over phenomena observed in the CO/P nozzle case, and already described in the literature with similar nozzles, did not occur in the jet from the CO/H nozzle. Electrodiffusion measurements showed differences in the shape and level of radial distribution of the wall shear rates and mass transfer. One of the most important observations is the large difference in wall shear stress between the three jets. For the same exit bulk-velocity, the maximum wall shear rate in the CO/P and CO/H nozzle jets was almost two and three times higher, respectively, than that of the reference convergent jet. This higher wall shear rate is accompanied by higher mass transfer rate. It is demonstrated that the cross-shaped orifices enhance the mass transfer not only locally but also globally

0801 超音速ジェットのせん断層速度分布とそこから発生する音響波の実験的研究

The effects of nozzle geometry on the acoustic waves from Mach 1.9 supersonic jet are experimentally investigated. PIV and microphone measurements are conducted to analyze the relationship between flows and acoustic waves. In this study, three different nozzles of conical nozzle, convergent-divergent nozzle (C-D) nozzle, and tab C-D nozzle in which tab is attached in nozzle inlet to generate disturbance are considered. Three noise sources are identified. Conical nozzle case shows screech and broad band shock noise spectra because of the existence of strong shock train in flow. For the other two cases (C-D nozzle and tab nozzle), there are not clear shock associated noise spectra due to nearly ideally expanded condition by the nozzle geometries so that turbulent mixing noise should be dominant. Tab nozzle case shows higher frequency acoustic spectra than that of C-D case. This is because inflow become turbulent flow from the very beginning by the existence of tab so that smaller scale turbulence is generated.

Excited-state kinetics and radiation transport in low-temperature plasmas

An advanced self-consistent plasma physics model including non-equilibrium vibrational kinetics, a collisional radiative model for atomic species, a Boltzmann solver for the electron energy distribution function, a radiation transport module coupled to a steady inviscid flow solver and, has been applied to study non-equilibrium in high enthalpy flows for Jupiter’s atmosphere. Two systems have been considered, a hypersonic shock tube and nozzle expansion, emphasizing the role of radiation reabsorption on macroscopic and microscopic flow properties. Large differences are found between thin and thick plasma conditions not only for the distributions, but also for the macroscopic quantities. In particular, in the nozzle expansion case, the electron energy distribution functions are characterized by a rich structure induced by superelastic collisions between excited species and cold electrons.

Numerical study on the oscillation of a transient bubble near a confined free surface for droplet generation

In the present work, the oscillation of a spark-created bubble near a confined water–air interface and the ensuing droplet generation and ejection are studied numerically using the boundary element method. The interface is accorded by the top opening of either one of the following symmetrical configurations, which are distinguished by the value of angle between their vertical symmetry axis and lateral wall (i.e., θ): (i) a centrally perforated horizontal flat plate (θ = 90°) and (ii) vertically placed cylinder (θ = 0°), nozzle (θ > 0°) and diffuser (θ < 0°). Furthermore, the influences of the effective parameters such as the strength parameter (i.e., the intensity of local energy input), the bubble-free surface distance (standoff distance) and the nozzle size on the bubble dynamics and droplet formation and ejection processes are investigated. It was found that the moment at which the bubble attained its maximum volume was advanced as θ increased. In addition, by decreasing θ the attraction of the bubble toward the free surface during its expansion phase and its migration from the free surface during its contraction phase became stronger. Furthermore, for the nozzle case, by increasing θ, the volume of the droplet was increased. It was also found that by increasing the strength parameter, the volume of the droplet increased and its pinch-off happened earlier. Finally, as the standoff distance was increased, the volume of the droplet increased and its pinch-off was delayed.

Numerical Simulation and Optimization of Urea-SCR Catalyst for Diesel Engine

Numerical simulation of certain diesel engine Urea-SCR catalyst is carried out using computational fluid dynamics method. Injection and atomization of Urea solution, evaporation of water and thermolysis of Urea are taken into account, while the surface chemical reaction in the carrier is ignored. Through the study of ammonia concentration distribution index on the inlet cross-section of the carrier, performance of the catalyst under different situations is evaluated and compared, which can provide some guiding suggestion for further optimization, and the different situations are cases with or without a mixer, cases with different injection distances, cases with different nozzle numbers and cases with different nozzle diameters.

Twisted bundle heat exchangers performance evaluation by CFD (CJ12/5054)

Shell and tube heat exchanger with single twisted tube bundle in five different twist angles, are studied using computational fluid dynamics (CFD) and compared to the conventional shell and tube heat exchanger with single segmental baffles. Effect of shell-side nozzles configurations on heat exchanger performance is studied as well. Heat transfer rate and pressure drop are the main issues investigated in the paper. The results show that, for the same shell-side flow rate, the heat transfer coefficient of heat exchanger with twisted tube bundle is lower than that of the heat exchanger with segmental baffles while shell-side pressure drop of the former is even much lower than that of the latter. The comparison of heat transfer rate per unit pressure drop versus shell-side mass flow rate shows that heat exchanger with twisted tube bundle in both cases of perpendicular and tangential shell-side nozzles, has significant performance advantages over the segmental baffled heat exchanger. Optimum bundle twist angles for such exchangers are found to be 65 and 55° for all shell side flow rates.

Mathematical modelling of a compressible oxygen jet entering a hot environment using a pressure-based finite volume code

A procedure for solving compressible flow within a finite volume, pressure-correction-type scheme, has been devised and successfully implemented in two test cases: a de Laval nozzle and an oxygen jet entering a heated furnace. Both cases have been validated with the analytical solution for the nozzle case and experimental data for the oxygen jet case. The method was successful in predicting the axial variables of the jet, and used to develop a modified turbulence model for such jets.

Measurement on stages with 3D bladings and different relative width of stator blades

Two variants of a stage with modern 3D bladings were tested on a single-stage air turbine to determine the influence of relative width of stator blades (nozzles). The first case means a high-density nozzle row with t/Bax = 0.61; the second one represents a low-density row with t/Bax = 1.12. The 3D shaping of both nozzle cases is based on the same design features. Rotor blades (buckets) are kept the same (also 3D shaped). Comparisons of overall stage efficiency as well as measured flow fields data are presented in the paper.

유동가시화 기법을 이용한 레이저가공의 보조가스 충돌특성에 관한 연구

Abstract: The characteristics of supersonic coaxial/off-axis jet impingements on a slanted kerf surface were experimentally studied, toinvestigate the role of the assist gas that removes molten materials from cut zone formed by laser machining. In this parametric study,hundreds of high-resolution schlieren images were obtained for various gas pressures, distances between nozzle exit and kerf surface,kerf widths, and alignments of off-axis nozzle. It was noticed that simply increasing the assist gas pressure was not effective ineliminating the flow separation that occurs downstream of the kerf surface. However, it was also observed that by increasing the kerfwidth and utilizing off-axis nozzles, the separation of the assist gas on the kerf surface can be weakened. The effect of the distancebetween the nozzle exit and the kerf surface on the characteristics of separation occurring on the kerf surface was found to be lower inthe case of supersonic nozzles than that in the case of sonic nozzles.†Corresponding Author, ylee@kau.ac.krⒸ2011 The Korean Society of Mechanical Engineers

Numerical study of the function of the slotting-tube in air-jet spinning

To study the functions of the slotting-tube, the realizable k-ϵ turbulence model is adopted to simulate the airflow patterns inside three different cases: first nozzle with slotting-tube (case 1), extended first nozzle (case 2), and normal first nozzle (case 3). Simulation results show that owing to the slotting-tube, the strengths of both the reverse flows near the injector upstream wall and the vortex breakdown in downstream of the injector increase. These help to produce more wrapper fibers and form larger twist difference. In addition, negative tangential velocity in the grooves can also help to loosen fiber strands. Therefore, high-quality yarn can be produced in case 1. The flatter pressure distribution also reveals that the existence of slotting-tube increases the flow steadiness. Consequently, the functions of the slotting-tube are demonstrated.

A gas jet superposition model for CFD modeling of group-hole nozzle sprays

In the present study, a jet superposition modeling approach is explored to model group-hole nozzle sprays, in which multiple spray jets interact with each other. An equation to estimate the merged jet velocity from each of the individual jets was derived based on momentum conservation for equivalent gas jets. Diverging and converging group-hole nozzles were also considered. The model was implemented as a sub-grid-scale submodel in a Lagrangian Drop–Eulerian Gas CFD model for spray predictions. Spray tip penetration predicted using the present superposition model was validated against experimental results for parallel, diverging and converging group-hole nozzles as a function of the angle between the two holes at various injection and ambient pressures. The results show that spray tip penetration decreases as the group hole diverging or converging angle increases. However, the spray penetration of the converging group-hole nozzle arrangement is more sensitive to the angle between the two holes compared to diverging nozzle because the radial momentum component is converted to axial momentum during the jet–jet impingement process in the converging group-hole nozzle case. The modeling results also indicate that for converging group-hole nozzles the merged sprays become ellipsoidal in cross-section far downstream of the nozzle exit with larger converging angles, indicating increased air entrainment.

End-burning 하이브리드 연소기 인젝터 분사각에 따른 연소 유동장의 수치적 연구

end-burning 연소실의 주요 설계인자들을 구축하기 위해 기존에 수행되었던 인젝터 배열 및 포트 직경 변화, O/F비 변화 외에 산화제 분사각 변화에 따른 연소 특성을 해석하였다. 연료면과 평행한 분사각(Case 1), 연료면을 향해 기울여진 분사각(Case 2)과 노즐을 향해 기울여진 분사각(Case 3)을 설정하여 모델을 구성하였다. 연료면을 향한 분사각의 경우 상류에서 가장 효율적인 혼합특성을 보였으나 상당량의 미연가스가 노즐 밖으로 배출됨을 알 수 있었다. 반면 Case 1과 Case 3은 낮은 혼합특성을 보였으나 연소효율은 연료면을 향한 경우보다 월등한 것으로 판명되었다. Case 1, Case 3 모두 유사한 경향을 나타내었으나 노즐을 향한 Case 3은 짧은 체류시간으로 인해 연료면과 평행한 Case 1에 비해 낮은 연소성능을 갖는 것으로 평가되었다. The effect of oxidizer injection angle on the combustion characteristics of end-burning hybrid combustor is numerically investigated. Besides the previously studied parameter(injector arrangement, port diameter and O/F ratio), three different injection angle are considered: parallel angle to fuel surface(Case 1), +30 degree inclined angle toward the fuel(Case 2) and 30 degree inclined angle toward the nozzle(Case 3). It is found that Case 2 has the best mixing pattern in the upstream area but has the worst combustion efficiency since non negligible amount of unburned fuel is expelled from the nozzle. In contrast, though Case 1 and Case 3 showed relatively low mixing effect than the Case 2, they had high combustion efficiency. The comparison of numerical results between Case 1 and Case 3 demonstrate that no major difference is encountered, however, Case 1 is expected to have the best combustion efficiency due to the low residence time of the Case 3 injector which heads toward the nozzle.

Numerical modeling of cavitating flows for simple geometries using FLUENT V6.1

Cavitation is a phenomenon that can be present in several agro-forestry applications such as irrigation pressure-reducing valves, sprinkler orifices or even in the flow through xylem vessels inside plants. In the present research, numerical predictions of cavitation in a series of orifices, nozzles and venturis were compared to experimental measurements to show the possibilities and performances of the new cavitation model in the commercial Computational Fluid Dynamics (CFD) code FLUENT V6.1. A flashing study is also presented for the nozzle case. Model predictions for the orifice cases accurately capture cavitation inception and its influence on the orifice discharge coefficient. However, when an unsteady flow is modeled, the cavitation phenomenon is not simulated properly and leads to a steady situation. In general, the new cavitation model in FLUENT V6.1 provides very reliable simulation for easy geometries when steady flow is assumed.

An Electrospray Method Using a Multi‐Capillary Nozzle Emitter

AbstractA multi‐capillary nozzle emitter consisting of one metal plate with capillary nozzles and a ring type counter electrode was used as a multi‐electrospray atomizer. The number of capillary nozzles, flow rate of the liquid and the interval between the capillary nozzles were changed, and the droplet diameter and the voltage required for a steady cone‐jet mode were measured. For the multi‐capillary nozzle emitter, the interaction between the capillary nozzles is the important factor for obtaining fine droplets of uniform size. These fine droplets are obtained when there is only a small interaction between the capillary nozzles, and the equations obtained from the single capillary nozzle case are also applicable for the multi‐capillary nozzle emitter. When the number of capillary nozzles decreases (a situation which is not good for obtaining a large amount of droplets) or the interval between the capillary nozzles increases, the interaction between the capillary nozzles can be reduced. As the number of capillary nozzles increase, a higher voltage is required to obtain a fine droplet of uniform size.

Critical Point Analysis of Transonic Flow Profiles with Heat Conduction

Critical points arising in transonic flow profiles of the steady compressible Euler equations with heat conduction are investigated. Two examples of transonic flow profiles are studied, namely, radial outflow in a gravitational field, and flow in a quasi-one-dimensional nozzle. The stationary flow equations are reformulated in terms of a dynamical system that parametrizes the flow profiles. Adding the heat conduction term introduces a critical point that is of a type different from the well-known sonic critical point that occurs at the transition from subsonic to supersonic flow when there is no heat conduction. This thermal critical point takes over the saddle-point role of the sonic critical point in the flow profile. Both the sonic and the thermal critical points are present in radial outflow profiles, and the type of the sonic critical point is changed from a saddle point to a simple node by the addition of the heat conduction term. In the nozzle case, the sonic point is no longer a critical point of the dynamical system when heat conduction is added. It is illustrated how the results of this analysis can be used for efficient and accurate numerical calculation of transonic flow trajectories and boundary value problems with heat conduction that are of interest in applications like supersonic planetary escape and solar wind models, and in aerospace applications. The analysis also elucidates how many boundary conditions are required for a well-posed transonic boundary value problem with heat conduction and clarifies the mathematical structure of transonic flow profiles with heat conduction that have been calculated numerically in the literature for various applications.

Effect of Rounding-off Nozzle Hole Inlet on Fuel Injection and Combustion Characteristics under High-Temperature and High-Pressure

Fuel injection pressure of diesel engines has been increased to improve engine performance and to reduce emission year by year. The higher injection pressure causes a cavitation and leads to erosion in the nozzle hole. Deformation of nozzle hole may result deterioration in engine performance, especially when using heavy fuel oil. It is noted that rounding-offof nozzle hole inlet proves to be effective to maintain the nozzle hole shape and the injection characteristics. In the present paper, from a fundamental viewpoint, measurement of ignition delays of diesel sprays from single hole injection nozzles with and without rounding-off hole inlet were conducted in a high-pressure combustion chamber. Further, fuel flow patterns in the nozzle hole were numerically simulated by three dimensional highly precision nozzle flow model.When ambient pressure and fuel injection quantity are relatively low, sprays from nozzle without rounding-off hole inlet do not ignite at low ambient temperature. On the other hand, there is no difference in ignition delay under high ambient temperature. In cases where an ambient pressure is high enough and a large amount of fuel is injected, ignition delays of nozzle with rounding-off and without rounding-off show almost the same values even at low ambient temperature. The computed results of numerical simulations show that cavitation level decreases significantly for all cases of rounding-off nozzles.

A Study on Heat Loss in DI Disel Engines by Using a Rapid Compression and Expansion Machine (2nd Report, The Effects of Spray Flow and Swirl on Heat Loss)

In order to clarify the mechanism of heat loss in DI diesel engines, total amount of heat loss to the combustion chamber and local heat flux at various locations on the piston head were measured by using a rapid compression and expansion machine. High-speed direct photography of spray flame was carried out and flame temperature was obtained by two-color method. In order to investigate the effects of the flow induced by the spray and its impingement on the chamber wall on heat loss, swirl ratio was varied from 0 to 5 and two different fuel injection nozzles (φ0.15 mm ×4 and φ0.10mm × 10) were used. The measured local heat flux exhibited more uniform distribution with theφ0.10mm×10 nozzle than with the φ0.15 mm ×4 nozzle, and at higher swirl ratio. The heat loss amount during the single cycle increased with the increase in swirl ratio due to the increased heat loss after the combustion period. The heat loss amount during the combustion period was almost constant regardless of the swirl ratio. The heat loss amount during the single cycle and the combustion period were not very different between the two different nozzle cases. The magnitude of heat flux at flame impinging point did not significantly vary with the nozzle orifice diameter. This is because the effect of the reduced impinging velocity is cancelled out by the effect of the increased flame temperature in the case of smaller orifice diameter on the heat flux.

An over-pressure correction to the slug model for vortex ring circulation

The slug model provides a formula for the circulation of vortex rings formed by starting jets ejected from a nozzle or orifice in terms of the time history of the jet velocity. For rapidly initiated jets, however, the model under-predicts circulation by an amount that remains nearly constant as circulation increases. To remedy this shortcoming, the present study derives an equation for circulation directly from the governing equations for the flow, illustrating that the circulation can be expressed as the sum of a flux term, $\Gamma_U$, determined by the jet centreline velocity and a ‘source’ term, $\Gamma_p$, determined by over-pressure at the jet centreline during vortex ring formation. For impulsively or nearly impulsively initiated jets, $\Gamma_p$ is modelled using potential flow analysis since over-pressure is significant primarily during the rapid jet initiation in these cases. The effects of the jet initiation and boundary-layer growth on the jet centreline velocity are also considered to provide a realistic model for $\Gamma_U$. Models for nozzle and orifice configurations are developed. In the case of a nozzle-type generator, the need to model the jet centreline velocity leads to an approximate solution for starting flow near the exit of an infinitely long pipe. For the nozzle case, the model results agree with available circulation measurements to within ${\pm}$6.2% for a wide range of conditions, except for jet velocity programs that are nearly triangular. In the orifice case, the model agrees with available results to within ${-}$13%. Both cases show substantial improvement over the slug model, which is in error by ${-}$21% to ${-}$67% for the data considered.

Starting flow through nozzles with temporally variable exit diameter

Starting flow through a nozzle or orifice typically results in the transient formation of a leading vortex ring and trailing jet. Experiments are conducted to investigate the dynamics of this process in the case of a temporally variable nozzle exit diameter, with the aim of understanding these flows as they occur in Nature and emerging technologies. By kinematically decoupling the source flow from the nozzle motion, comparison across several classes of exit diameter temporal variation is facilitated. Kinematic models of the starting flows are used to accurately predict the fluid circulation produced by the vortex generators, and to emphasize the special role of the nozzle boundary layer in dictating the nature of the global flow patterns. A dimensionless temporal parameter is derived in order to track the vortex formation process for the various classes of nozzle motion. Dynamics of vortex ring disconnection from the source flow are studied in this new dimensionless framework. We show that temporally increasing the nozzle exit diameter as the starting flow develops results in higher-energy vortex ring structures with peak vorticity located further from the axis of symmetry relative to a static nozzle case. In addition, the normalized energy supplied by the vortex generator is increased in this process. We do not observe a delay in the onset of vortex ring disconnection from the trailing jet, as predicted by previous numerical simulations. In contrast, growth of the leading vortex ring is substantially augmented by temporally decreasing the nozzle exit diameter during fluid ejection, as noted in a previous experiment. Normalized vortex ring circulation is increased 35% in these cases, and the normalized energy of the generated vortex rings is equivalent to that of Hill's spherical vortex. These observed effects are explained by considering the measured vorticity distribution and energy of the starting flows. Strategies are suggested to exploit the discovered dynamics for various pulsed-jet applications.