Investigation on gas-solids hydrodynamics and matching enhancement in feedstock injection zone of double-level nozzle riser

With the development of current energy economy, it is necessary to improve the product distribution of fluid catalytic cracking process, which is achieved by a riser reactor with double-level of nozzles. The new riser is constructed by adding a level of secondary nozzle 0.5 m below the main nozzle of traditional riser. This paper investigates the gas-solids flow and oil-catalyst matching feature based on the optical fiber and tracer technologies. According to the distribution of solids holdup, particle velocity and dimensionless jet concentration, the feedstock injection zone can be divided into the upstream flow control region, the main flow control region, and the secondary flow control region in the radial direction. The size of the regions is changed by the jet gas velocity and axial height. There is a poor match of secondary nozzle jet to particles below the main nozzle. The jet gas from secondary nozzles can improve the matching effect of oil-catalyst near the wall and reduce the probability of coking above the main nozzle.     

Mixing enhancement behind an oblique shock wave

The possibility of mixing enhancement when a design-condition cocurrent jet passes through a stationary oblique shock is investigated. In [4] the effect of such a shock on the mixing layer of flows with Mach numbers M = 3 and 5 was experimentally investigated and it was shown that behind the shock no turbulence is generated. However, irrespective of its effect on the turbulence characteristics, an oblique shock causes deformation of the jet, modifying its dimensions, and in the three-dimensional case the shape of the cross section. The effect of this deformation on mixing, which is shown to be fairly significant, has been investigated theoretically using a numerical method. An approximate relation describing the variation of the maximum admixture concentration in the jet behind the shock is proposed.Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No.2, pp. 61–68, March–April, 1992.The authors are grateful to V. A. Stepanov for useful discussions.     

Mixing enhancement in axisymmetric turbulent isothermal and buoyant jets

Measurements of the velocity and concentration in axisymmetric, turbulent, isothermal and buoyant jets have been performed with laser-Doppler velocimetry and planar and point laser-induced fluorescence to quantify the mixing enhancement achieved by periodic forcing when the jet exit has a fully-developed turbulent pipe flow, a situation less well-studied than the case of laminar initial conditions. It was found that forcing at Strouhal numbers around 0.6 enhances mixing in the developing region of the jet and this enhancement increased with increasing amplitude of excitation, consistent with results of initially-laminar jets. The initial turbulence intensity did not have any effect, but an increase in the initial lengthscale of the turbulence, controlled by a perforated plate inside the nozzle, caused faster mixing. In agreement with previous experiments, the initial conditions of the jet did not affect the far-field rate of decay, but the jet-fluid concentration there was significantly reduced by forcing due to the increased mixing during the early stages of development, an effect that can be described by a smaller virtual origin in decay laws of jet decay. These results are independent of the Froude number because the initial conditions have an influence only in the early stages where the flow is still momentum dominated.List of Symbols A normalised excitation amplitude, defined by A = u'/U ₀ - D nozzle diameter - f jet-fluid concentration - F mean f - f r.m.s. f - Fd Froude number, defined by Fd=U ₀ ² /(gDT ₀) - g acceleration of gravity - I fluorescent intensity - I _inc incident light intensity - I _ref light intensity of the reference flow - K decay constant - L _hf concentration halfwidth - M mixing enhancement, defined by U _cl/U _cl,st=0 at x/D=5 - r radial coordinate - Re Reynolds number, defined by Re=U ₀ D/v - [Rh] concentration of Rhodamine B - St Strouhal number, defined by St=D/U ₀ - T ₀ temperature of jet fluid - T temperature of outer fluid - T ₀ temperature difference (= T ₀–, T ) - u r.m.s. axial velocity - u r.m.s. of the sinusoidal velocity fluctuation due to forcing - U mean axial velocity - U _cl mean axial centreline velocity - U _cl,st=0 mean axial centreline velocity for an unforced jet - U _max U at the centre of the nozzle exit - U ₀ bulk velocity at nozzle exit - x streamwise coordinate - X ₀ virtual origin Greek coefficient of thermal expansion - kinematic viscosity of the jet fluid - forcing frequency The experiments described here have been performed together with Mr. J. Sakakibara. Acknowledgments are also due to Prof. H. Longmire, of the University of Minnesota, for helpful discussions on forcing. This work was done while E.M. visitied Keio University with the financial assistance of TEPCO.     

Mixing of gases due to injection of a low-pressure jet into a cross-flow

A gas jet injected into a channel is simulated numerically. The dependence of the mixing efficiency on the injection orifice aspect ratio, jet screening, and the ratio of the injected and channel gas densities is established. The mixing efficiency is estimated in terms of the mean concentration across the jet.Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 3, pp. 67–74, May–June, 1996.     

Experimental investigation of forced flow regime transition in a dual bell nozzle by secondary fluidic injection

Experiments on an axisymmetric dual-bell nozzle were performed at EDITH nozzle test facility of CNRS in Orléans, France. The main purpose of the study was to explore the possibility of controlling the flow regime transition by a secondary fluidic injection in the dual bell nozzle. The main focus of the present paper is to investigate the impact of the secondary injection parameters on the flow regimes transition in such nozzles. Secondary injection has been found to effectively control the flow regime transition and consequently to increase the propulsive performance of the device. It has also been pointed out that even a very low injected secondary mass flow rate leads to the control of the transition and contributes to reducing the lateral loads which can exist, moreover, when transitions are operated without injection.     

Mass transport in a converging-diverging nozzle

The local concentration has been determined for a viscous liquid flowing through a converging-diverging tube with constant wall- and initial concentration. The liquid flow was considered as creeping flow and its velocity distribution was determined by solving the biharmonic differential equation of the stream function. The mass transport was presented in form of an infinite series of Legendre functions, which rendered with the Galerkin condition a determinant of finite order for the determination of the eigenvalues. The local concentration was evaluated numerically for differently diverging tubes, of which the case of mass transport for viscous (linearized) flow through an orifice of circular cross-section presented a special case.

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Stofftransport in einem konvergierenden-divergierenden Rohr

Znsammenfassung Es wird die lokale Konzentration eines in einer viskosen Strömung durch ein Venturirohr befindlichen Stoffes bei konstanter Wand-und Einlaßkonzentration bestimmt. Die viskose (kriechende) Strömungsgeschwindigkeit wurde aus der Lösung der biharmonischen Differentialgleichung der Stromfunktion bestimmt. Die Bestimmung des Massentransportes im Rohr wird mit einer Lösung in Form einer unendlichen Reihe von Legendrefunktionen bewältigt, wobei die Eigenwertgleichung eine Determinante unendlicher Ordnung ergibt. Die lokale Konzentration wurde für verschieden divergierende Rohre numerisch ausgewertet, wobei der Massentransport bei Strömung durch eine kreisförmige Öffnung als Sonderfall auftrat.

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Nomenclature a radius of throat area - c (, ) concentration - c _w wall concentration - c _i initial concentration - D diffusion coefficient - P _n ⁰ Legendre function - u (, ) flow velocity of liquid (in-direction) - flow volume per time unit - _n roots ofP ⁰ ( ₀)=0 - stream function - , , oblate spheroidal coordinates - ₀ wall of the nozzle     

Separated two-phase flow in a nozzle

This work was performed to extend and further test the method of handling separated two-phase flow by studying each phase separately and, particularly, by placing emphasis on the study of the gas phase with interface transport expressions showing the influence of the liquid phase on it. A one-dimensional flow model for accelerating flows was used in conjunction with experimental data to obtain the pressure distribution and velocity distribution in a converging nozzle for several values of flow quality and nozzle inlet stagnation pressure. The results tend to support the use of the model (which includes the assumption that the gas is in critical flow when the two-phase mixture is in critical flow) and give some insight regarding the nature of the liquid distribution near the nozzle throat.     

Map of regimes of pressure oscillations induced by absorption during gas jet injection through a submerged nozzle

Map of regimes of pressure oscillations induced by absorption during rapid injection of a soluble gas jet through a submerged nozzle into liquid, namely, oscillations during absorption, bubbling, internal chugging and small chugging, is suggested. Boundaries between various pressure oscillations regimes occurring when rapidly soluble gas is absorbed in water are investigated theoretically. It is showed that these boundaries are determined by four equations. It is showed that regime of high-frequency pressure oscillations during absorption occurs due to gas bubble oscillations, and other regimes of oscillations occur due to pressure oscillations in the whole system comprising the header, vent tubes and gas bubble. The conditions for excitation of high-frequency and low-frequency oscillations and boundaries between different regimes of pressure pulsations are determined. In a case when Henri's law for soluble gases is valid the developed model predicts that oscillations during absorption are not excited.     

Thrust of a contracting nozzle

A study is made of the influence of the nonuniformity of the parameters due to the two-dimensional nature of the flow on the specific thrust of a contracting nozzle. It is shown that for continuous flow of an ideal (inviscid and nonheat-conducting) gas the specific thrust in the supercritical regimes exceeds the value determined using the one-dimensional theory for the same stagnation parameters of the gas; in the subcritical regimes the specific thrust of the contracting nozzle is equal to the value found from the one—dimensional approximation.     

Nonequilibrium gas-condensate flow in a laval nozzle

A scheme is proposed which simplifies the algorithm and reduces the labor involved in solving the system of quasi-linear hyperbolic equations describing supersonic nonequilibrium two-phase flow in an axisymmetric nozzle.     

Liquid flow in a simplex swirl nozzle

Pressure-swirl nozzles are widely used in applications such as combustion, painting, air-conditioning, and fire suppression. Understanding the effects of nozzle geometry and inlet flow conditions on liquid film thickness, discharge coefficient and spray angle is very important in nozzle design. The nozzle-internal flow is two-phase with a secondary flow which makes its detailed analysis rather complex. In the current work, the flow field inside a pressure-swirl nozzle is studied theoretically. Using the integral momentum method, the growth of the boundary layer from the nozzle entry to the orifice exit is investigated and the velocity through the boundary layer and the main body of the swirling liquid is calculated. A numerical modeling and a series of experiments have also been performed to validate the theoretical results. The effect of various geometrical parameters is studied and results are compared for viscous and inviscid cases. In addition, the condition in which the centrifugal force of the swirling flow overcomes the viscous force and induces an air core is predicted. The theoretical analysis discussed in this paper provides better criteria for the design and the performance analysis of nozzles.     

Hysteresis phenomena in a plane rotatable nozzle

The flow in a rotatable nozzle is calculated within the framework of the Reynolds equations and the Spalart-Allmaras turbulence model on the pressure difference range 1.1 < π < 5 for four configurations of the nozzle with the area ratio ε = 1.52 and two angles of the nozzle axis rotation. The flow structure is determined and the thrust characteristics and the angles of the thrust vector rotation are obtained. It was found that in the overexpansion regime the flows in plane symmetric and rotatable nozzles involve hysteresis phenomena due the Coanda effect and the interaction between the boundary layer and a shock generated within the nozzle on its supersonic walls. The hysteresis phenomena detected provide an up-to-4% divergence in the thrust coefficient for the same problem parameters. The results of the numerical modeling are compared with the experimental data and the results of calculations in accordance with Sekundov’s model.     

Slowly mixing cylinder in a cone-shaped nozzle

We report on a surprising phenomenon in a turbulent jet setup which uses a cone-shaped nozzle with an excentric inlet. Inside the nozzle a slowly mixing, rotating cylinder surface was observed. The speed of mixing on this cylinder surface is reduced by approximately a factor of 8 compared to the remaining flow field of the nozzle. The phenomenon seems to be independent of the Reynolds number and the pressure distribution inside the nozzle.     

Flow of a two-phase medium in a laval nozzle

The back reaction of particles on a gas flow in Laval nozzles was investigated experimentally. Experimental data were obtained that characterize the change produced by the particles of a solid phase in the shape of the sonic line, the pressure distribution on the nozzle profile, and the configuration of the shock waves in the jet. Flow rate coefficients are given for different nozzle profiles and mass fraction and sizes of the particles in the flow.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 1, pp. 107–111, January–February, 1981.     

Shock unsteadiness in a thrust optimized parabolic nozzle

This paper discusses the nature of shock unsteadiness, in an overexpanded thrust optimized parabolic nozzle, prevalent in various flow separation modes experienced during start up and shut down sequences. The results are based on simultaneously acquired data from real-time wall pressure measurements using Kulite pressure transducers, high-speed schlieren (2 kHz) of the exhaust flow-field and from strain-gauges installed on the nozzle bending tube. Shock unsteadiness in the separation region is seen to increase significantly just before the onset of each flow transition, even during steady nozzle operation. The intensity of this measure (rms level) is seen to be strongly influenced by relative locations of normal and overexpansion shock, the decrease in radial size of re-circulation zone in the back-flow region, and finally, the local nozzle wall contour. During restricted shock separation, the pressure fluctuations in separation region exhibit periodic characteristics rather than the usually observed characteristics of intermittent separation. The possible physical mechanisms responsible for the generation of flow unsteadiness in various separation modes are discussed. The results are from an experimental study conducted in P6.2 cold-gas subscale test facility using a thrust optimized parabolic nozzle of area-ratio 30.

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Heat transfer enhancement for laminar natural convection along a vertical plate due to sub-millimeter-bubble injection

Sub-millimeter-bubble injection is one of the most promising techniques for enhancing heat transfer for the laminar natural convection of liquids. However, flow and heat transfer characteristics for laminar natural convection of water with sub-millimeter bubbles have not yet been fully understood. The purpose of this study is to experimentally clarify the effects of sub-millimeter-bubble injection on the laminar natural convection of water along a heated vertical plate. The use of thermocouples and a particle tracking velocimetry (PTV) technique are applied to temperature and velocity measurements, respectively. The temperature measurement shows that the ratio of the heat transfer coefficient with sub-millimeter-bubble injection to that without injection increases with an increase in the bubble flow rate or a decrease in the wall heat flux and that the ratio ranges from 1.35 to 1.85. Moreover, it is concluded from simultaneous measurement of temperature and velocity that the heat transfer enhancement is directly affected by flow modification due to bubbles rising near the heated vertical plate.