Rectangular Orifice Research Articles

Predicting the main geometrical features of horizontal rectangular source fuel jet fires

The main geometrical features of horizontal jet fire with rectangular source fuel have seldom been revealed in the past, especially the rectangular orifice with same area but different aspect ratios. In order to better understand the rectangular jet fire, a set of numerical simulations were carried out by rectangular source fuel with same rectangular orifice area S (4 cm2) but different aspect ratios (orifice length to orifice width: L/W = 1, 2, 4) to investigate the flame shape, flame length and flame width. The simulated flame lengths and flame widths were compared with previous experimental data and calculated values using the Thornton model. The non-dimensional flame length and flame width were defined, in which the flame geometrical features were found in relation to the orifice aspect ratio and fuel jet velocity. Results show that the flame length and flame width increases with fuel jet velocity, while the flame length decreases with aspect ratio n for same orifice area, but the flame width increases simultaneously. The simulated data agree well with previous experimental data, but the predictions by Thornton model are larger than simulated and previous experimental values. The modified Thornton model is proposed considering both orifice shape and aspect ratio to apply to rectangular jet fire.

Boundary layer suction through rectangular orifices: effects of aspect ratio and orientation

The flow field generated by suction through a rectangular orifice within a laminar boundary layer is investigated using stereoscopic particle image velocimetry. For orifice aspect ratios of 6, 12, and 18, the impact of suction on the surrounding flow field appears to be self-similar, scaling with aspect ratio and suction velocity. Changing the orifice pitch angle had almost no impact on the surrounding boundary layer, but, as expected, changing the skew angle significantly altered the extent of the suction impact on the flow field.

Discharge flow of granular media from silos with a lateral orifice and injection of air

Few studies concern the prediction of the mass flow rate of a granular media discharged from a silo with a lateral orifice. However, this situation can have pratical interest considering a tank of granular material with a leak on its side. We studied experimentally the discharge of a vertical silo filled by spherical glass beads. We consider rectangular silos with a rectangular orifice. The impact of size, aspect ratio and position of the orifice and the effect of an additional air flow were studied. The measured parameters are the mass flow rate and the pressure along the silo, whereas the controlled parameters are the size of particles, and the flow rate of air. We identified two regimes of discharge according to the aspect ratio (of width to height) of the rectangular orifice. Increasing the air flow rate induces an increase of the granular media flow rate. Using a simple physical model to describe the grains and gas flow, we put in evidence the role played by the air pressure gradient at the outlet. Then we compared the experimental results with continuum Navier-Stokes simulations with the granular μ (I)-rheology. We showed that the continuum μ (I)-rheology describes well our discharge flow of granular media from silos, taking into account the effect of the position of the orifice as well as the coupling with the gas flow.

Experimental study of synthetic jets with rectangular orifice for electronic cooling

Rapid evolution of technology has allowed electronic devices to become both more compact and with higher processing power, which also results in increased heat generation. Therefore, new cooling techniques are needed to replace conventional technology based on fans and heat sinks. Synthetic jets are still under development but these devices are considered an excellent alternative to replace or enhance fan-driven coolers due to their ability to generate turbulence and improve convective heat transfer. In this paper, a synthetic jet actuator was constructed with a speaker and acrylic plates to form the cavity and rectangular jet orifice. The device was subjected to several tests where different parameters were analyzed. Four different cavity sizes were tested (ranging from 2mm to 8mm), as well as three rectangular orifice shapes with two hydraulic diameters (4mm and 8mm) and two aspect ratios (4 and 8). Jet velocities were measured at distances of 2, 4, 6 and 8 orifice widths away from the exit plate. Variations in frequency and Reynolds number were performed in order to determine the combination which would yield the most heat transfer among the configurations tested. Results show that very shallow cavities have a detrimental effect on the jet velocity and should be avoided while best heat transfer results were obtained in orifices with a larger hydraulic diameter in conjunction with a smaller aspect ratio.

Experimental visualization and LES investigations on cloud cavitation shedding in a rectangular nozzle orifice

Shedding of cloud cavitation in a nozzle orifice is a common phenomenon of cavitation instability which has a great influence on erosion damage and spray atomization process, but it hasn't been studied in details and the mechanism remains unclear. In this paper, visualization experiments and Large Eddy Simulation (LES) were carried out to study the process of periodic cloud cavitation shedding and re-entrant jet happened in a 2mm-width nozzle with fuel of diesel. Numerical and experimental images provide a better insight into this physical mechanism. The results show that cavitation inception is formed at the edge of inlet and the recirculation zone which below the shear layer. Then the attached cavitation grows and shedding of cloud cavitation occurs due to the re-entrant jet located between cavity and wall. Moreover, the dynamic mechanism causing shedding of cloud cavitation is a combination of shedding vortex and pressure fluctuations. Cavitation shedding frequency can also be measured by experiment and numerical simulation. As a result, inception of cavitation, re-entrant jet and cavitation cloud shedding are accurately predicted by LES in accordance with the quantitative images observed in the experiment.

Effect of the Molten Metal Stream’s Shape on Particle Size Distribution of Water Atomized Metal Powder

The current knowledge indicated that water pressure, molten metal temperature, water flow rate and water jet configuration are very important factors which affect on the particle size distribution and shapes of atomized powder. This study aimed to investigate whether the shape of molten affects the particle size of atomized powder. The experiments were the production of copper powder with the fixed atomization process conditions, but varied the shape of molten metal by using two different shapes of tundish nozzle’s orifice to make the round and rectangular cross section of molten metal stream. There were three sizes for each orifice shape to determine the rate of production (metal flow rate) at 13 kg/min, 19 kg/min and 26 kg/min. The results showed that at the same flow rate of molten metal the production of flat metal stream from rectangular orifice made higher yield of finer particle, smaller median size (D50) and narrower range of size distribution than the production with the round cross section orifice for every production rates.

主流と干渉するシンセティックジェットにおける吹出し口形状の影響

A Synthetic jet device is a tool for generating a jet, and a useful tool for active flow control. Synthetic Jet actuators are low operating power, zero-net-mass-flux and very compact devices. Therefore, a synthetic jet is expected as a new method of boundary layer control. The orifice shape is an important parameter, which have an effect for boundary layer control. However, the effect of non-circular synthetic jets for boundary layer control is unknown. The purpose of this study is to investigate the effect of orifice shape for boundary layer control. In this experiment, circular orifice and two rectangular orifices were used. For the rectangular orifices with long side set in the spanwise direction, the boundary layer mixing is promoted and makes effective the separation control.

Local Multiphase Flow Characterization with Micro Particle Image Velocimetry Using Refractive Index Matching

AbstractAn accurate flow characterization is crucial for the understanding and optimization of emulsification processes. A method is presented to determine velocity fields of droplet‐containing phases flowing through an orifice by micro particle image velocimetry (µPIV). In order to overcome optical inaccessibility of emulsions, a recipe of a transparent emulsion system was developed using refractive index matching. Velocity fields could successfully be determined for an emulsion containing 30 vol % of droplets in a rectangular orifice channel with the narrowest gap being 200 µm. Emulsion flow was compared to a pure continuous phase and the influence of the dispersed phase was analyzed for each individual step of µPIV image processing. For the presented experimental conditions, one‐ and two‐phase flows exhibited no difference in flow characteristics.

Achieving a High-Speed and Momentum Synthetic Jet Actuator

A detailed analysis of a finite-span synthetic jet in a quiescent fluid is presented, with the goal of achieving a high speed and momentum synthetic jet, with a peak velocity exceeding 200 m/s. A total of two scales of actuator apparatuses having either 40- or 80-mm-diameter piezoelectric discs were used. A temperature-compensated hot wire, laser displacement sensor, and dynamic pressure transducers were used to quantify the performance of a given actuator. The synthetic jet generation process was divided into its main components, diaphragm displacement, cavity pressure, and orifice velocity, which were analyzed in detail in both their peak values and time responses. The phase shift between the disc displacement and velocity signals were found to be mainly attributed to compressibility effects. Doubling the diameter and thickness of the piezoelectric disc was found to double the output jet velocity and shift the operation frequency range of the system. In addition, a dual disc configuration was used, which yielded an approximately 40% higher jet velocity than its single disc configuration. Using the knowledge acquired from these experiments resulted in a synthetic jet having a peak velocity of 211 m/s out of a 12×1-mm rectangular orifice at 700 Hz, which is significantly stronger than any similar actuator reported in the literature.

Near-Field Characteristics of a Rectangular Jet and Its Effect on the Liftoff of Turbulent Methane Flame

Understanding the stability of turbulent flames is a key for the design of efficient combustion systems. The present paper reports an experimental study on the effect of the internal geometry of a rectangular orifice on the characteristics/stability of a turbulent methane flame. Three rectangular nozzles with different orifice lengths having an identical exit aspect ratio (AR) of 2 were used. The co-airflow strength was also varied to evaluate its effect on the jet flow emerging from the rectangular nozzle. The experimental data revealed that the jet initial conditions affect both the flow characteristics and the liftoff of turbulent diffusion methane flame. That is, increasing the orifice length of the rectangular nozzle resulted in delaying the occurrence of the axis-switching phenomenon, reducing the length of the jet potential core, and accelerating the liftoff transition of the attached flame. The co-airflow was found to reduce the velocity strain rate in the shear layer, displace the occurrence of axis-switching farther downstream of the jet, and delay flame detachment. The results revealed also that there is a clear interplay between the flame liftoff and the jet near-field molecular mixing and flow characteristics. That is, a rectangular jet which spreads faster and generates higher near-field velocity strain and turbulence intensity causes flame detachment at a lower fuel jet velocity. Based on this, a correlation was found between the flame liftoff velocity, the fuel molecular thermal diffusivity, the stoichiometric laminar flame speed, and the fuel jet strain rate at the nozzle exit. This relationship was shown to successfully predict the liftoff velocity of methane flame as well as other common gaseous hydrocarbons and hydrogen flames.

Joule heating in low-voltage electroosmotic with electrolyte containing nano-bubble mixtures through microchannel rectangular orifice

Joule heating effects on a rectangular orifice in microchannel filled with electrolyte containing nanobubbles are comprehensively investigated with emphasis on the thermal boundary conditions. Numerical studies are performed for the velocity and temperature fields to show the various aspects of fluid flow and thermal design in rectangular shaped microchannels. Furthermore the correlations for the maximum temperature increase were presented for several geometry parameters and thermal boundary conditions which gives us an insight to the best cooling scenario of microfluidic rectangular orifices. This study will provide useful information for the optimization of a bioMEMS device in thermal aspect and benefits of nano-bubble injection for temperature control. It is shown that the cooling from the side is superior in reducing the peak temperature of the micro-orifice.

Discharge prediction of circular and rectangular side orifices using artificial neural networks

A side orifice created in the side of a channel is a structure for diverting some of the flow from the main channel for different purposes. The prediction of the discharge through this side structure is very important in hydraulic and irrigation engineering. In the present study, three artificial neural network models including feed forward back propagation, radial basis function, and Generalized Regression neural networks as well as a multiple non-linear regression method were used to predict the discharge coefficient for flow through both square and circular shapes of sharp-crested side orifices. The discharge coefficient was modeled as a function of five input non-dimensional variables resulted from five dimensional variables, which were the type of orifice shape, the diameter or width of the orifice, crest height, depth and velocity of approach flow. The results obtained in this study indicated that all of the neural network models could successfully predict the discharge coefficient with adequate accuracy. However, according to different performance measures, the accuracy of radial basis function approach was a bit better than two other neural network models. The neural network models predicted the discharge coefficient more accurately than the non-linear regression relation.

Heat transfer and flow characteristics of a pair of adjacent impinging synthetic jets

The local convective heat transfer rate of an impinging synthetic jet has been shown to rival that of an impinging steady jet. Recent research has demonstrated a significant degree of interaction between adjacent synthetic jets, especially when generated from rectangular orifices. When operated in an impingement setup, adjacent jet interaction has been shown to enhance the convective heat transfer performance in some cases. This paper presents the findings of an experimental study to determine the effect of the orifice-to-impingement surface distance, H, and orifice-to-orifice centre separation distance, S, of a pair of synthetic air jets formed by two rectangular orifices with a span-to-width aspect ratio of 27:1 and a slot width D=1.65mm. The local convective heat transfer coefficient is determined on an electrically heated thin metal foil using infrared thermography. Particle image velocimetry (PIV) measurements of the flow field between the jet orifices and the impingement surface were performed. The jets are maintained at a constant Reynolds number and stroke length (Re=300, L0/D=29). For the parameter range considered (6<H/D<24, 3<S/D<12), an optimum configuration of H/D=24 and S/D=3 operated at a phase difference of 60°<Φ<120° gives the highest average cooling performance. For hot spot cooling, a configuration of H/D=6 and S/D=3 operated at a phase difference of 135°<Φ<180° gives the highest local maximum heat transfer. These results demonstrate the potential of this double impinging synthetic jet arrangement for actively controlled heat transfer applications.

An investigation into the effect of nozzle shape and jet pressure in profile creepfeed grinding

An experimental comparison of cutting fluid delivery nozzles was carried out with application to profile creepfeed grinding. A novel method of nozzle design and development involving rapid-prototyping enabled an exhaustive experimental approach. Circular, rectangular, and elliptical orifice nozzles were compared in terms of workpiece profile error, workpiece surface roughness, and grinding power over a variety of workpiece feedrates and cutting fluid jet pressures. For the grinding conditions used in this research, it was observed that, although the circular nozzle performed best, higher nozzle inlet pressures yielded smoother workpiece surface finishes.

Simulation of proton radiography terminal at the Institute of Modern Physics

AbstractProton radiography is used for advanced hydrotesting as a new type radiography technology due to its powerful penetration capability and high detection efficiency. A new proton radiography terminal will be developed to radiograph static samples at the Institute of Modern Physics of Chinese Academy of Science. The proton beam with the maximum energy of 2.6 GeV will be produced by Heavy Ion Research Facility in Lanzhou-Cooling Storage Ring. The proton radiography terminal consists of the matching magnetic lens and the Zumbro lens system. In this paper, the design scheme and all optic parameters of this beam terminal for 2.6 GeV proton energy are presented by simulating the beam optics using WINAGILE code. My-BOC code is used to test the particle tracking of proton radiography beam line. Geant4 and G4beamline codes are used for simulating the proton radiography system. The results show that the transmission efficiency of proton without target is 100%, and the effect of secondary particles can be neglected. To test this proton radiography system, the proton images for an aluminum plate sample with two rectangular orifices and a step brass plate sample are respectively simulated using Geant4 code. The results show that the best spatial resolution is about 36 μm, and the differences of the thickness are not &gt;10%.

21002 シンセティックジェットの噴出条件がパンタグラフ舟体の空力騒音低減効果に及ぼす影響

As the running speed of Shinkansen increases, the reduction of aerodynamic noise emitted from a pantograph head of Shinkansen becomes more important. This paper describes CFD analysis on the flow control around the pantograph head using synthetic jet actuator (SJA). In this study, spanwise and streamwise orientations of rectangular orifice are analyzed. In the case of streamwise oriented orifice, the cross-sectional area of orifice is also changed under the conditions of constant momentum coefficient or volume flow rate of SJA. The results of CFD analysis indicate that the streamwise oriented orifice is more effective than the spanwise one against the reduction of aeolian tone and that a dominant parameter which determines the reduction of aeolian tone is volume flow rate of SJA.

Pareto genetic design of group method of data handling type neural network for prediction discharge coefficient in rectangular side orifices

The powerful method of Group Method of Data Handling (GMDH) was used for estimating the discharge coefficient of a rectangular side orifice. First, the existing equations for calculating the discharge coefficient were studied making use of experimental results. On the first hand, the factors affecting the discharge coefficient were determined, then five models were constructed in order to analyze the sensitivity in achieving accuracy by using different parameters. The results, obtained using statistical indexes (MARE=0.021 and RMSE=0.017), showed that one model out of the five models, on estimation using the dimensionless parameters of the ratio of depth of flow in main channel to width of rectangular orifice (Ym/L), Froude number (Fr), the ratio of sill height to width of rectangular orifice (W/L) and width of main channel to width of rectangular orifice (B/L), presented the best results.

Effect of noncircular orifice plates on the near flow field of turbulent free jets

In this paper, we experimentally investigate the near-field flow characteristics of turbulent free jets respectively issued from circular, triangular, diamond, rectangular, and notched-rectangular orifice plates into air surroundings. All the orifice plates have identical opening areas or equivalent diameters (De) and their aspect ratios (AR) range from 1 to 6.5. Planar particle image velocimetry (PIV) is used to measure the velocity field at the same Reynolds number of Re = 5 × 104, where Re = UeDe/v with Ue being the exit bulk velocity and v the kinematic viscosity of fluid. The mean and turbulent velocity fields of all the five jets are compared in detail. Results show that the noncircular jets can enhance the entrainment rate, reflected by the higher acceleration rates of mean velocity decay and spread, shorten the length of the unmixed core, expedite the increase of turbulent intensity compared with the circular counterpart shortened unmixed core, and increase turbulent intensity comparing to the circular counterpart. Among the five jets, the rectangular jet (AR = 6.5) produces the greatest decay rate of the near-field mean velocity, postpones the position at which the `axis-switching' phenomenon occurs. This supports that axis switching phenomenon strongly depends on jet initial conditions. In addition, the hump in the centerline variation of the turbulence intensity is observed in the rectangular and triangular jets, but not in the circular jet, nor in diamond jet nor in notched-rectangular jet.

Acoustic and heat transfer characteristics of an impinging elliptical synthetic jet generated by acoustic actuator

Abstract The acoustic aspects and average heat transfer characteristics of an elliptic synthetic jet impinging on a heated flat plate were experimentally investigated and compared with circular, rectangular and square orifices having same equivalent diameter. The aim of the study is to investigate the effect of orifice shape, aspect ratio and operating parameters of the synthetic jet at which optimum acoustic and heat transfer performance is obtained. It is found that irrespective of the shape of the orifice, the synthetic jet generates the minimum sound pressure level when operated at its resonance frequency, which is equal to the diaphragm frequency in the present case. The maximum heat transfer enhancement is obtained at the resonance frequency for elliptical orifice of aspect ratio 1.4 at the jet to plate spacing (z/de) of 3, where z is the axial distance and de is the equivalent diameter of the orifice. The aspect ratio of an orifice is a sensitive parameter as with increase in the aspect ratio, reduction in the Nusselt number is observed. For low jet to plate spacing ratios (z/de

Processing and Properties of Textured Potassium Sodium Niobate [K,Na]NbO3 Ceramic Ribbons by Alginate Gelation Method

Random and &lt;001&gt; textured potassium sodium niobate – [K,Na]NbO3 (KNN) ceramics with 1 mole% CuO sintering aid were fabricated in ribbon form through a combination of novel alginate gelation process and templated grain growth methods using platelike sodium niobate ‐ NaNbO3 (NN) template particles. The platelike NN template particles were prepared by a two‐step molten salt synthesis method. Ribbons were drawn from alginate‐based slurries without or with 10 wt% NN template particles using 50 mm long slit nozzle with a rectangular orifice of 10 mm × 1 mm. Development of crystallographic texture as a result of varying sintering time and temperature was evaluated through the calculation of the degree of orientation as measured by the Lotgering factor (ƒ(001)) and an ƒ(001) of 0.81 was achieved. The electrical properties of textured ribbons were evaluated with polarization and strain versus electric field measurements.