Sharp-edged Orifice Research Articles

Theoretical analysis of pressure-drop type instabilities in an upflow boiling system with an exit restriction

In this work, two-phase flow pressure-drop type instabilities in an upflow boiling system are studied theoretically. Dynamic simulations of the pressure-drop type instabilities require the knowledge of the steady state characteristics of the system in terms of the pressure drop versus the mass flow rate. In a boiling system with an exit restriction at the outlet of the boiling channel, the pressure drop through the system concentrates at the exit restriction. Therefore, the correlation of the pressure drop of the two-phase mixture flowing through the exit restriction (i.e. a sharp-edged orifice) is essential in the calculation of the total pressure drop of the system. A model for the exit restriction is developed and compared with the experimental results covering a wide range of vapor quality with different heat inputs and inlet subcoolings. The drift-flux model is adopted to predict the steady state characteristics of the boiling system. The dynamic oscillations of the quasi-static pressure-drop type instabilities in the boiling system are simulated and good predictions of the system stability boundary and oscillatory characteristics are obtained when compared with the experimental results.

Mixing Characteristics of Axisymmetric Free Jets From a Contoured Nozzle, an Orifice Plate and a Pipe

The differences in mixing performance between axisymmetric turbulent jets issuing from three common types of nozzle, viz. a contoured (or smooth contraction) nozzle, a sharp-edged orifice and a long pipe, are investigated. The investigation is carried out using both qualitative flow visualizations and quantitative measurements of the centerline passive temperature. It is revealed that the jet issuing from an orifice plate provides the greatest rate of mixing with ambient fluid, while the pipe jet has the lowest rate. Physical insight into the differences is explored using a planar imaging technique and measurements of power spectra of the fluctuating velocity.

Slot jet impingement heat transfer from circular cylinders

The heat transfer characteristics of circular cylinders exposed to slot jet impingement of air has been studied experimentally. The study focused on Reynolds numbers (based on nozzle average exit velocity and cylinder diameter) in the range 600–8000. Both contoured orifice and sharp-edged orifice jet configurations were investigated for cylinder diameter-to-jet width spacings of 0.66, 1.0 and 2.0, and for jet exit-to-nozzle width spacings in the range 1< z/ w<11. Reference measurements were made with the same cylinder in infinite parallel flow in a wind tunnel. The results reveal that the slot jet yields considerably higher average heat transfer from the cylinder when compared to the infinite parallel flow case on the basis of identical average velocity in the slot jet and infinite flow configurations. As with slot jet impingement heat transfer from flat surfaces, there appears to be a nozzle-to-cylinder spacing, scaled by nozzle width, which exhibits a maximum in heat transfer. The average heat transfer characteristics of the cylinder are correlated empirically.

A method for determining orifice loss coefficients in strongly transient compressible liquid flows

The aim of the current work was to devise a method of establishing orifice loss coefficients in highly transient liquid flows. This was motivated by the fact that (i) many physical systems involve liquid transfer through narrow channels between cavities under unsteady conditions, and (ii) such data does not exist in the literature. A test facility was constructed, consisting of a drop-weight tester which operates in conjunction with a test cell comprising a vertically mounted thick-walled cylinder blanked off at the bottom, and containing upper and lower water-filled cavities separated by a plate with a small, sharp-edged orifice (thickness to diameter ratio of four). The upper cavity is enclosed at its top surface by a piston which protrudes beyond the upper section of the cylinder. When a weight is dropped onto the piston, a variation of pressure (p1) occurs in the upper cavity, approximating the shape of a half sinusoid with time, and with a typical half cycle (T) in the range 1.34–2.73 ms. Mass transfer takes place from the upper to the lower cavity, with a commensurate increase of pressure (p2) in the latter. At a certain time p1 and p2 become equal, at which the latter is at its maximum and the former is close to the end of its sinusoidal half cycle. Thereafter, p1 rapidly diminishes to ambient pressure and p2 approaches ambient pressure over a period of about 5T. During this latter phase, p2 exceeds p1, which is consistent with flow reversal. A comprehensive analysis of the system, in conjunction with pressure measurement, enabled experimental loss coefficients to be determined during that time when mass transfer was taking place between the upper and lower cavities (with p1&amp;gt;p2). Values of cd obtained were in the range 0.85–1.2, increasing for the smaller values of T. These data are viewed in the context of the expected steady flow value of 0.79 for this configuration of orifice, and confirm the hypothesis that flow unsteadiness of a sufficiently small time scale has a significant effect on loss coefficients.

Prediction of Single- and Two-Phase Flow Contraction through a Sharp-Edged Short Orifice

The predictions of a new model for the contraction coefficient of single- and two-phase flows through a sharp-edged short orifice are checked against data recently obtained with water, air, and air/water mixture flows. The model includes all relevant primary design parameters. The predictions are validated for a wide range of conditions and physical properties typically encountered in industrial fluid-dynamic systems. Calculations based on the new model are sufficiently accurate for engineering purposes. Reasonable extrapolations to other test conditions with an acceptable accuracy can be expected.

Characteristics of flow through small sharp-edged cylindrical orifices

The discharge coefficients for flow through small sharp-edged cylindrical orifices of diameters between 0.3 and 2 mm and aspect ratios between 1 and 50 are evaluated. The characteristics of flow in the separated, attached and cavitated flow regions are determined. It is shown that while the discharge coefficient scales with the Reynolds number and aspect ratio in the attached flow regions, the diameter influences the discharge coefficient in the separated flow region. The onset of cavitation in the orifice is also seen to be dependent on the diameter and aspect ratio. The hysteresis in the flow and the violent disintegration of the jet observed for an aspect ratio of about 5 are discussed.

An experimental study of viscous flows in contractions

The need to improve the methods used when designing emergency, pressure-relief systems on polymerisation reactors, has made the flow of highly viscous fluids in pipeline fittings highly topical. This paper investigates the flow processes involved in single-phase, viscous flows in nozzles and orifice plates. These fittings were chosen because they would give an insight into the behaviour of highly viscous flows in other geometries, such as the flow upstream of the seat in a pressure relief valve. Experimental data are presented for a pipe, two conical nozzles and a sharp-edged orifice plate for laminar flows in the Reynolds number range 50–400 and for turbulent flows. The volume flow rate—pressure drop characteristics are presented for both nozzles and the orifice plate. The discharge momentum flow rate for the pipe, a nozzle and the orifice plate are also given. Analysis of the data shows that nozzles and orifice plates that are geometrically similar have a similar resistance to flow. It is also shown that the contraction coefficient for an orifice plate tends to unity at low Reynolds numbers.

Experimental investigation of contraction in single- and two-phase flow through sharp-edged short orifice

The flow contraction through sharp-edged short orifices respectively the narrowest flow cross-section or the vena contracta has been measured for water, air and air/water mixture. The results demonstrate that the contraction in the case of subcritical single-phase flow is restricted to values between 0.62 and one, while in the two-phase flow it is limited to very narrow ranges of air mass flow qualities where the flow regime is specified as bubbly or spray.

Viscous flow through a sharp-edged orifice

A theoretical solution is proposed for the problem of flow through a thin orifice plate placed between chambers having large dimensions relative to the orifice diameter. Experimental results were obtained using molasses having a viscosity of the order of 1000 poise. These results confirmed the analysis, but flow was found to be 5–10% less than the theoretical value. This is attributed to the finite size of the chambers of the apparatus and the finite thickness of the orifice plate.

The Effect of Manifold Cross-Flow on the Discharge Coefficient of Sharp-Edged Orifices

Abstract : The objective of this study is to determine the effect of manifold cross-flow on the discharge coefficient and cavitation characteristics of sharp-edged orifices over a wide range of flow-rates, back-pressures and cross-flow velocities. The orifice geometries studied cover a range of orifice diameters, length to diameter ratios and orifice angles characteristic of impinging element liquid rocket injectors. Experimental results for an orifice angle of 900 with respect to the manifold are presented here. Along with the experimental effort, an analytical model is being developed. The model predicts the discharge coefficient for a sharp edged orifice over a wide range of flow regimes including cavitating and non-cavitating flow, and for a wide range of orifice geometries. The analytical model generally shows good agreement with the experimental data over the range of conditions studied here. The model also closely follows the experimental data for cavitating flow except when the orifice length to diameter ratio is small, in which case the model over-predicts the discharge coefficient.

励起された長方形噴流の拡散促進機構に関する研究

The diffusion mechanism of an excited rectangular jet was investigated by comparing the measured velocity profiles and the suggested vortical structures. Experiments were carried out using an air jet from a sharp-edged rectangular orifice of aspect ratio 4. The jet was excited in the interaction mode, in which the stable interaction of vortices occurred. The results reveal that the jet diffusion mechanism is closely related to the vortical structures in the rectangular jet : jet width in the major axis plane decreases due to inward flow induced by vortices bending downstream, and that in the minor axis plane increases significantly due to outward flow induced by stretched vortices and split small vortex rings.

Low Pressure Differential Discharge Characteristics of Saturated Liquids Passing Through Orifices

An experimental investigation has been performed to determine the effect of variation in the length-to-diameter ratios on the discharge characteristics of saturated liquids passing through square edge orifices subjected to low pressure differentials. Experiments were performed to confirm reported results for sharp edge orifices and for round edge orifices with appreciable ratios of inlet corner radius to orifice diameter.

Crossflow mixing of noncircular jets

An experimental investigation has been conducted of the isothermal mixing of a turbulent jet injected perpendicular to a uniform crossflow through several different types of sharp-edged orifices. Jet penetration and mixing was studied using planar Mie scattering to measure time-averaged mixture fraction distributions of circular, square, elliptical, and rectangular orifices of equal geometric area injected into a constant velocity crossflow. Hot-wire anemometry was also used to measure streamwise turbulence intensity distributions at several downstream planes. Mixing effectiveness was determined using 1) a spatial unmixedness parameter based on the variance of the mean jet concentration distributions and 2) by direct comparison of the planar distributions of concentration and of turbulence intensity. No significant difference in mixing performance was observed for the six configurations based on comparison of the mean properties.

Three-Dimensional Vortical Structures in a Rectangular Jet.

The three-dimensional vortical structures in a rectangular jet were determined by measuring the phase-average fluctuating static pressure, and the characteristics of the structure were discussed. The experiments were carried out for an air jet issuing from a sharp-edged rectangular orifice. The jet was excited in the interaction mode, in which the stable interaction of vortices occurred. The phase-average pressure was measured over the flow field with a static pressure probe. The three dimensional contours of phase-average pressure provided useful information on complicated vortical structures. The structures were characterized by stretching, splitting and cut-and-connect of vortices. The results suggest that the direct measurements of fluctuating static pressure are very useful for detecting three-dimensional complicated vortical structures.

Impedance Characteristics of Hydraulic Orifices

The impedance characteristics of cylindrical and sharp-edged hydraulic orifices under non-zero mean flow conditions have been investigated through experimental measurement and computational fluid dynamics (CFD) simulation studies. Based upon these investigations a generic model of the impedance characteristics of orifices has been developed. This model can be adopted in computer simulations of pressure ripple in hydraulic systems. The results of this investigation also provide the basis for modelling more complex hydraulic components.

Two-phase modeling of cavitated flows

This paper describes a computational method for the treatment of viscous, time-dependent, cavitated flows. The method has been applied to the solution of the laminar, axisymmetric, Navier-Stokes equations using a two-phase model to account for cavitated regions. The two-phase treatment is accomplished through the addition of a pseudo-density which varies in magnitude between the vapor and liquid densities. A new treatment has been developed to provide the additional relationship required as a result of the inclusion of this new fluid variable. The model has been compared to experimental data for external flows over axisymmetric headforms. In addition, both steady and unsteady calculations of an internal flow in a sharp-edged orifice passage are also discussed.

Eduction of Vortical Structures in a Rectangular Jet by Fluctuating Pressure Measurements.

Vortical structures in a rectangular jet were educed by measurements of phase-average fluctuating pressure, and the results were discussed in comparison with those by visualization experiments. The measurements were carried out for the air jet issuing from a sharp-edged rectangular orifice. The jet was excited at the interaction mode where the stable interaction of vortical structures was generated. In the phase-average measurements, reference signals were detected by an I-type hot-wire probe fixed near the jet center, and the phase-average fluctuating pressure was measured over the flow field with a pressure probe. The contours of phase-average fluctuating pressure provided us with more information on the details of vortical structures than visualization experiments. The results suggest that direct measurements of fluctuating pressure are very useful to detect the complicated vortical structures occurring in the rectangular jet.

Experimental investigation of rarefied gas flow through rectangular slits and nozzles

The flow of a rarefied gas through rectangular configuratons of different geometries has been experimentally studied to determine their discharge coefficient characteristics. The configurations used are a set of sharp-edged slit orifices, a smooth converging nozzle and a tube. The range of the Reynolds number based on the throat conditions varied from 0.01 to 100. The equivalent Knudsen number range based on the upstream conditions and inlet diameter varied from 0.0521 to 2.521. The results for the smooth nozzle are compared with calculations using a numerical method with one-dimensional stream tube approximation based on integrated boundary layer equations. The slit and the tube results are compared with the experimental results of Sreekanth and Davis [1988].

Mixing between a sharp-edged rectangular jet and a transverse cross flow

The scalar mixing field of a turbulent rectangular jet issuing from a sharp-edged orifice with an aspect ratio of 10 into a cross stream flow in a square duct is investigated using marker nephelometry. Jet-to-cross stream velocity ratios of 2.0 and 3.4 are examined in this work. Results include contour plots and transverse profiles of the mean and concentration fluctuation intensity and jet trajectory paths and half concentration lengths expressed as a function of downstream position along the jet trajectory.

Nozzles for jet stabilization of rocks

The shape of the exit nozzles has great importance when developing the working part of a hydraulic jet monitor. All possible types of nozzles have already been investigated in certain experimental works of A. D. Al'tshul', I. E. Idel'chik, B. N. Siov, S. S. Shavlovskii, et al. [1, 2, 4]. In the present article the authors make an attempt to generalize collected data and to substantiate the type of nozzle which can be used in jet technology of rock stabilization. During discharge of a fluid through a round orifice without an extension (Fig. la), i.e., a sharp-edge orifice, the fluid particles smoothly round it. The extreme streams impart to the jet a conoidal shape and cause its contraction at the exit from the orifice. Contraction of the jet occurs also during discharge of a fluid through a cylindrical orifice having an extension (Fig. lb). But after that the discharge can flow differently. In the ftrst case, behind the smallest section of the jet its gradual expansion occurs. It reaches the inside walls of the orifice and flows out without contraction. An isolated annular cavity forms. This is that region which is filled with air and is located between the orifice walls and contracted section of the jet. The pressure in this region is Pc. In the second case the discharge differs in no way from discharge from a orifice without an extension, but the velocity in the contracted section can be described by the equation