Добірка наукової літератури з теми "Venturi´s nozzle"

The purpose of this investigation is to understand flow characteristics in mini/micro sonic nozzles, in order to precisely measure and control miniscule flowrates. Experimental and numerical simulation methods have been used to study critical flow Venturi nozzles. The results show that the nozzle?s size and shape influence gas flow characteristics which leading the boundary layer thickness to change, and then impact on the discharge coefficient. With the diameter of sonic nozzle throat decreasing, the discharge coefficient reduces. The maximum discharge coefficient exits in the condition of the inlet surface radius being double the throat diameter. The longer the diffuser section, the smaller the discharge coefficient becomes. Diffuser angle affects the discharge coefficient slightly.

AbstractThe introduction of 2,4-D–resistant soybean and cotton provided growers a new POST active ingredient to include in weed management programs. The technology raises concerns regarding potential 2,4-D off-target movement to sensitive vegetation, and spray droplet size is the primary management factor focused on to reduce spray particle drift. The objective of this study was to investigate the droplet size distribution, droplet velocity, and particle drift potential of glyphosate plus 2,4-D choline pre-mixture (Enlist Duo®) applications with two commonly used venturi nozzles in a low-speed wind tunnel. Applications with the TDXL11004 nozzle had larger DV0.1 (291 µm), DV0.5 (544 µm), and DV0.9 (825 µm) values compared with the AIXR11004 nozzle (250, 464, and 709 µm, respectively), and slower average droplet velocity (8.1 m s−1) compared with the AIXR11004 nozzle (9.1 m s−1). Nozzle type had no influence on drift deposition (P = 0.65), drift coverage (P = 0.84), and soybean biomass reduction (P = 0.76). Although the TDXL11004 nozzle had larger spray droplet size, the slower spray droplet velocity could have influenced the nozzle particle drift potential. As a result, both TDXL11004 and AIXR11004 nozzles had similar spray drift potential. Further studies are necessary to understand the impact of droplet velocity on drift potential at field scale and test how different tank solutions, sprayer configurations, and environmental conditions could influence the droplet size and velocity dynamics and consequent drift potential in pesticide applications.

A new structure is proposed for a DN25-type ultrasonic gas flow meter with a V-shape double sound channel arrangement. The flow field characteristics are analyzed including velocity curves for the four channel lines, velocity profiles for different cross-sections of the flow meter, and streamlines of the transducer channel sections. The metering characteristics of the flowmeter are measured using a Venturi nozzle device. When the pipeline flow rate is less than 2.26 m/s, the pipe installation does not have a significant effect on the velocity profile and the velocity in the channel lines. However, the error in the low-flow region is large, and the flow distortion directly affects the measurement accuracy. When an ultrasonic gas flow meter with an accuracy class of 1.5 is used with pipes containing a single or double bend upstream, the linear error doubles, low-flow error becomes a negative deviation, and reference error in the low-flow region becomes approximately 700%–949%. The installation structure of the first pair of transducers also affects the signal propagation of the transducers behind it. Therefore, it is critical to process the ultrasonic signal according to the flow field distribution and adopt different weighted algorithms to obtain accurate pipeline flow rates to improve the measurement accuracy of the ultrasonic flow meter.

This paper is a review of current techniques available for measuring the velocity and composition in multiphase streams, to obtain the mass flow rate of the individual phases. An extensive literature search was conducted on the topic and related areas of interest. The major difficulty in measuring both the velocity and composition of multiphase streams is in dealing with the wide variety of flow regimes which are possible in multiphase flow in pipes. A device which is suitable for accurate velocity measurement in multiphase flows is not commercially available. However, if the flow is well mixed, it should be possible to calibrate a simple device, such as a nozzle or a venturi, to provide accurate total volumetric flow rates. Several commercial in-line static mixing devices are suitable for low gas concentrations (≤ 10 percent) and with superficial gas velocities higher than 10 m/s. For lower gas velocities and high gas concentrations, the suitability of these in-line mixers will have to be further assessed experimentally. Other techniques such as cross-correlation are known for two-phase flow velocity measurements, and the results of these applications look promising. A multiphase compositional meter to monitor the concentration of oil, water, and gas phases flowing in a pipeline, used in combination with a suitable homogenizer and a velocity meter, would facilitate measurement of the mass flow rates of the individual phases. Further work must be done to develop this concept.

The effects of area ratio of the diffuser entrance to the nozzle exit, displacement vessel volume, and suction gap configuration on the performance of pumping systems with a Venturi-like reverse flow diverter are investigated experimentally. The performance of a pumping system with area ratio of 1.5 is greater than one with area ratio of 1.0, but when the jet outlet velocity ranges from 12–25 m/s, the performance of a suction gap in the shape of an axially-symmetric cylinder is the same as one with an arch-like configuration. The effective lifting factor should be more than 1.0, which means that the effective volume of the displacement vessel must be at least 1/(q-1) times the riser tube volume.

This thesis is focused on shape optimization of Venturi´s nozzle with optimization method called response surface method. The first part of this work is concerned with the description of this method as well as explaining the basic principle. Furthermore, there is an explanation of the application of this method in synchronicity with CFD and its operating algorithm. The second part of this thesis is then focused on simple example with plane wing and simplified optimization of Venturi´s nozzle in which this method was tested. In the third part there is described full multiparameter shape optimalization of the nozzle for two geometries.

In a gas turbine engine combustor, combustion performance is tied to the spatial distribution of the fuel injected into the dome. Swirl cup, as an air blast atomizer, is widely used to provide a uniform presentation of fuel droplets to the combustor dome. In this paper, two swirl cups with different venturi angle have been studied: case 1 (with narrow venturi angle) and case 2 (with wide venturi angle). Kerosene is injected to the test domain through a simplex nozzle. The spatial distribution of droplet characteristics produced by the two swirl cups were measured using dual-phase Doppler anemometry (PDA). A single cup combustor has been built in order to characterize the swirl cups’ ignition phenomena. Spark ignition test has been performed for ground condition, two swirl cups’ lean ignition limits are obtained, and ignition sequences have been recorded by a high-speed video camera. Comparing the two swirl cups’ small droplets velocity, case 1 swirl cup produces a different velocity profile from typical swirl cup. The air stream outflowing from case 1 swirl cup just ran into the side wall. The droplet size around the spark plug of case 2 is smaller than case 1. Ignition test results show that case 2 swirl cup’s lean ignition limit is wider than case 1’s. Record of the ignition process deepened the understanding of spark ignition of the swirl diffusion flame. It takes some time for the kernel to anchor in swirl cup. The results demonstrate that swirl cup’s venturi shape strongly influence the spray structure. Thereby affect the combustor ignition performance.

Adequate design engineering and maintenance of circuits with fast neutron reactors cooled with lead and lead-bismuth coolants require considering the peculiarities of hydrodynamics of these coolant flows. It is traditionally reputed that the hydrodynamic characteristics of heavy liquid-metal melts are analogous to the characteristics of water and primary sodium, which is practically valid for the conditions of part of the equipment and channels of a reactor circuit. The main peculiarities of heavy liquid-metal coolants compared to water and primary sodium, which affect the flow characteristics, are: - unwettability of channels with oxide protective coatings of reactor circuits by lead and lead-bismuth eutectic melts; - high boiling temperature exceeding the fusion temperature of steel; - high density exceeding by an order the densities of water and natrium; - low solubility of impurities in lead and lead-bismuth eutectic melts; - higher surface tension coefficient. The design value of saturated vapors of lead and its alloys at the temperatures 400–550 °C is 10−18–10−10 at (1 at = 0.1 MPa), which is essentially less than the values of natrium and water. Processes of traditional cavitation in the flow of heavy liquid-metal coolants cannot occur because of their specific character. The main circulation pumps are a basic element of reactor circuits. In fact, the flow sections of these pumps and those of other vane-type pumps operating in lead and its alloys cannot be calculated by traditional methods as far as cavitation characteristics are concerned; adequate calculation formulas are not available now. In a channel with walls unwettable by a flow of heavy liquid metal, this flow contacts with walls by means of the boundary layer having specific properties (surface energy, etc.) analogous to those of free surfaces of melts contacting with gas. Internal pressure in the flow forces liquid metal against walls, thus the liquid metal speed in the region of their contact is zero. As the pressure in the flow decreases due to growth of speed or other effects, the outer layer of the liquid metal flow can move away from the wall; in this case water appears on its surface. To study cavitation processes in a heavy liquid-metal coolant flow, the authors have carried out the following experiments: - determining the conditions of disconnection of liquid lead and lead-bismuth eutectic column; - determining the cavitation characteristics of the centrifugal pump pumping lead at the temperature 500 °C; - comparative investigation of the characteristics of Venturi nozzle in water and liquid metal. The experimental study of the characteristics of disconnection of heavy liquid-metal coolant column has shown that disconnection occurs at the boundary of liquid and cold metals; the reason of disconnection is leakage of gas from melt volume and, perhaps, from the near-wall region; disconnection occurs at negative voltages in the cross section of the column. The experimental study of the cavitation characteristics of the centrifugal pump at the temperature of pumped lead 500 °C and the circumferential speed of about 15 m/s has show that failure (cease) of pumping takes place at the pressure at the impeller inlet of about 19.6–24.5 kPa. Continuous operation of pump in the regime of pumping failure does not lead to destruction of the flow part surfaces of the pump. The character of the process corresponds to the so-called gas cavitation and is completely inconsistent with traditional cavitation. The experimental comparative study of the hydrodynamic characteristics of the same Venturi nozzle for water current at the temperature T = 20 °C and lead-bismuth eutectic at T = 350 °C without gas supply and with gas supply at the speeds 10–20 m/s has shown the following. The hydraulic resistance of the eutectic nozzle is more than an order higher than the analogous value for water under the same test conditions. This is, probably, due to flow disconnection and jet contraction in the narrow part of the nozzle with formation of water on its surface and backflows in the nozzle diffuser. Supply of relatively small amounts of gas into the narrow part slightly varies the characteristics of the processes. The consideration of specific character of heavy coolant flow hydrodynamics is required for adequate design engineering and maintenance of some elements of reactor circuit.

In-line measurements and sample stream withdrawals for on-line and/or at-line measurements of slurries flowing in horizontal pipes can be complicated by nonuniform slurry profiles. More uniform profiles would improve measurements. Area contractions are a common means used to produce more uniform velocity fields for single phase flows. For example, contractions are used to condition the flow entering wind tunnel test sections and make velocity profiles more uniform at venturi throats. It was desired to determine whether area contractions could be used to make slurry concentration profiles more uniform in horizontal pipe flows. An ASME flow nozzle with a contraction diameter ratio of 0.5 was chosen as a well defined geometry to consider in a Computational Fluid Dynamic (CFD) study of the effects of a contraction on slurry concentration profiles. The pipe was 2.8 m long with a 50.8 mm diameter. The entrance of the contraction was placed at 35 pipe diameters from the inlet in fully developed flow. A length of 20 diameters followed the contraction. The slurry had a xylene liquid phase and an ADP solid phase with a density ratio of 1.7. The simulations were performed at primary phase velocities of 2 m/s and 4 m/s, corresponding to Reynolds numbers of 1.4E05 and 2.8E05. Spherical particle diameters of 38, 75, and 150 μm were used at concentrations of 0.05, 0.2, and 0.3. ANSYS FLUENT 12 software was used with the standard k-ε turbulence model and standard wall function. The mixture multi-phase model was used for the two-phase flow. An unstructured tetrahedral meshing scheme was used with 1.4 million elements. The grid was adjusted until the condition 30 < y+ <60 for the mesh point nearest the wall was satisfied. A grid refinement study was performed to insure grid independence. The computational scheme first was validated by comparing pipe flow velocity and concentration profiles to results in the literature. The computations performed with the contraction showed that in all cases the concentration profiles of the solid particles displayed greater uniformity than the profiles in the pipe upstream of the contraction. The effect of the contraction was more pronounced for the larger particles. As in the case of single phase flows, the contraction caused the axial turbulence intensity to decrease. The greater uniformity of the concentration profiles at the exit plane of the nozzle, suggest that the contraction can provide better conditions for performing measurements of a particle-laden slurry.

Adequate design solution and maintenance of circuits with fast reactors cooled by lead and lead-bismuth coolants require taking into account the peculiarities of hydrodynamics of these coolant flows. The design pressure of saturated vapors of lead and its alloys at temperatures of 400–550 °C is 10 −18−10 −10 atm, which is significantly less than that of sodium or water. Processes of traditional cavitation cannot occur in a flow of heavy liquid-metal coolants because of their specific character. The main circulation pumps of reactor circuits are one of their basic elements. In fact, the flow-type parts of these pumps and other vane pumps operating in lead and its alloys cannot be calculated by traditional methods in terms of cavitation characteristics; appropriate calculation formulas are not currently available. To study cavitation processes in a heavy liquid-metal coolant flow, the authors have carried out the experiments aimed at: - determining the conditions of disconnection of liquid lead and lead-bismuth eutectic column; - determining the cavitation characteristics of a centrifugal pump transferring lead at a temperature of 500 °C; - studying the characteristics of ejector (Venturi nozzle) in a liquid metal; - studying the cavitation erosion effect of the lead coolant on impeller vanes of an axial-flow pump in a limited volume in the FT-4-A stand at a lead flow rate of up to 1200 t/h; - studying the cavitation characteristics of an axial-flow pump in the FT-4 stand at shaft speeds of 13.34–25 Hz. These studies are performed with the lead coolant at temperatures of 450°−550°C, oxygen in lead from 10−4−10−5 to 100, flow rates from 20 to 1800 t/h, which corresponds to velocities of the lead coolant flow from 1.0 to 26 m/s. The experiments have shown that as distinct from water, traditional cavitation processes in a heavy liquid-metal coolant (HLMC) flow are not recorded. The probable cavitation mechanism is gas cavitation. The allowance for the specific character of hydrodynamics of HLMC flows is necessary for adequate design engineering and maintenance of some elements of the reactor circuit.

Laser sheet smoke visualization experiments were performed on vertical air/helium jets to quantify the effects of low density driven bursts on the jet structure and entrainment. The parameters of relative jet density, S, and jet exit Reynolds number, Re, are of most importance in determining the bursting. Previous research has shown that vertical jets of S ≤ 0.5, in a range of Rej = 1300 – 2500, display strong side ejections due to the baroclinic instability in the strained vorticity sheet between the primary torroidal vortices. The objective of this work was to determine if this phenomenon resulted in a significant increase in the mixing and jet entrainment compared to standard jets. The present study demonstrated that the strong and clearly visible burst phenomenon had a very minor impact on the time averaged spreading and mixing in the shear layer surrounding the potential core. Experiments were performed using laser sheet illumination with a YAG pulse laser and cylindrical lens with oil smoke droplet seeding. The images were acquired using a 12 bit CCD camera with a 1024 × 1280 pixel array. All images were acquired at a low enough frequency to ensure their statistical independence. The laser sheet was estimated to be 0.5 mm thick with a pulse duration of 6 ns. Planar instantaneous images both coplanar and normal to the jet centerline were obtained. The jet emerged into room air from an 11 mm diameter bicubic nozzle with a contraction ratio of 5.5. Mixed flows of air and helium were fed into a settling chamber and then passed through a flow straightening honeycomb upstream of the jet. Flow rates and Reynolds numbers were controlled using choked flow nozzles that fed the settling chamber. Oil droplet smoke was added to the air flow with an adiabatic venturi-jet oil atomizer. In the instantaneous images of the jets, the bursts were clearly visible in individual frames and qualitatively appeared to play a significant role in the downstream mixing of the jet. However, quantitative analysis of time averages of many sequential images revealed that the bursts are much less significant to the mixing and entrainment of the jet than they appear. Longitudinal images were acquired in sets of 100 or 200 and used to obtain averaged images of the plume from the source out to approximately 10 jet diameters. The pixel noise floor was subtracted from the mean images. These mean images were interpreted as an analogue for scalar concentration, and thus used to quantitatively estimate the plume spread. From these mean images, concentration profiles were obtained and plotted. The bursting phenomenon was shown to be insignificant on an engineering scale after analyzing the mean images. In fact, the mass in the region where the bursts occurred was only visible when a function which showed very small gradient differences was applied to the images. While the baroclinic instability bursting is interesting from a scientific point of view, it has been shown through the quantitative analysis of the means of instantaneous images that there is only a slight effect on the overall jet entrainment compared with regular jets.

Abstract Advancements in core compressor technologies are necessary for next generation, high Overall Pressure Ratio (OPR) turbofan engines. High pressure compressors (HPCs) for future engines are being designed with exit corrected mass flow rates less than 2.25 kg/s (5 lbm/s). In order to accurately measure the performance of these advanced designs, high accuracy measurements are needed in test facilities. The W7 High Speed Multistage Axial Compressor Facility at NASA Glenn Research Center has been used to acquire data for advanced compressor designs. This facility utilizes an advanced differential pressure flow meter called a V-Cone. The facility has historically tested components with physical mass flow rates in the range of 27 to 45 kg/s (60 to 100 lbm/s). As such, when the V-Cone was calibrated prior to installation, the calibrations focused on higher mass flow rates, and uncertainties in that regime range from 0.5% to 0.85%. However, for low mass flow rates under 9 kg/s (20 lbm/s), expected in tests of advanced high OPR HPCs rear stages, the uncertainties of the V-Cone exceed 2.5%. To address this, using a method similar to that utilized by the National Institute of Standards and Technology, an array of Critical Flow Venturi Nozzles (CFVs) was installed in the W7 test section and used to calibrate the V-Cone in 0.5 kg/s (1 lbm/s) increments up to 10.5 kg/s (23 lbm/s). This effort details the measurements and uncertainties associated with this calibration which resulted in a final uncertainty of the V-Cone measurements under 1%.