Two-phase Turbulent Jet Research Articles

Modified k- ϵ model for two-phase turbulent jets

A modified k- ϵ model is proposed for two-phase turbulent jets which takes into account the additional dissipation of turbulent kinetic energy by the dispersed phase. Within the context of the two-phase averaged equation for the turbulent kinetic energy of the continuous phase, a constitutive relation is proposed for the additional dissipation of turbulence. The additional dissipation effect was modeled using a transfer function, which relates the fluctuations of the dispersed phase with the fluctuations of the continuous phase, integrating over the turbulence energy spectrum. A further improvement to the theory considers that dissipation only occurs when the eddies are bigger than the particles. Therefore a cutoff frequency is proposed and for big particles or bubbles dissipation may become negligible. The model is inserted in an Eulerian computational fluid dynamics code. The results are compared with data available in the literature for an air-particle jet. The results agree with the data within the range of experimental error. Comparisons were also made without including dissipation effects and it was concluded that the dissipation due to eddy-particle interactions is significant and should be included in a general two-phase k- ϵ model.

PARTICLE CONCENTRATION AND SIZE MEASUREMENTS IN TWO-PHASE TURBULENT COAXIAL JETS

Particle concentration and particle size distributions have been measured for two-phase (solid/air) turbulent coaxial jets using the Laser Diffraction Method (LDM) and a tomography data transform technique. Effects of velocity ratio, particle loading ratio, and particle size on the dispersions of gas and particles were determined. Experimental results show that the gas disperses much more rapidly than the particles and particle dispersion decreases with increasing in particle size. Increasing velocity ratio significantly increases gas dispersion, while effects of other variables are less significant. The mean particle size at the jet edge is about 15-20% smaller than that at the jet centerline. The turbulent Schmidt number Scp for two-phase turbulent coaxial jets ranges from 1.4 to 1.5.

Laser Diffraction Method Measurements of Particle-Gas Dispersion Effects in a Coaxial Jet

ABSTRACT Particle concentration and particle size distributions have been measured for two-phase (solid/air) turbulent coaxial jets using the laser diffraction method (LDM) and a tomography data transform technique. Effects of velocity ratio, particle loading ratio, and particle size on the dispersions of gas and particles were determined. Experimental results show that the gas disperses much more rapidly than the particles and particle dispersion decreases with increasing in particle size. Increasing velocity ratio significantly increases gas dispersion, while effects of other variables are less significant. The mean particle size at the jet edge is about 15–20% smaller than that at the jet centerline. The turbulent Schmidt number Scp for two-phase turbulent coaxial jets ranges from 1.4 to 1.5.

Two-phase multicomponent turbulent jet with phase transitions

Two-phase multicomponent turbulent jet with phase transitions

Two-phase multicomponent turbulent jet with phase transitions

Two-phase multicomponent turbulent jet with phase transitions

Two-phase multicomponent turbulent jet with phase transitions

A mathematical model of a gas-droplet nonisothermal multicomponent polydisperse turbulent jet is proposed. This model takes into account phase velocity and temperature nonequilibrium, gas and liquid phase inhomogeneity, the droplet coagulation and disintegration, and the possibility of the presence of vapor condensation or fluid evaporation, depending on the specific conditions in the jet. Certain results of calculating the parameters of both a nonisothermal two-component polydisperse gas-disperse jet with phase transitions and droplet coagulation and a three-component polydisperse gas-disperse jet without allowance for phase transitions are presented. The results obtained are analyzed.

Effect of particle size on a two-phase turbulent jet

The effect of particle size on two-phase turbulent jet flow structure is studied in the present experimental investigation. Polystyrene solid particles of 210, 460, and 780 μm were used. The particles' mass loading ratios ranged from 0 to 3.6. The flow Reynolds number was 2 ‘ 10 4 , which was based on the pipe nozzle diameter and the fluid-phase centerline velocity at the nozzle exit. A two-color laser-Doppler anemometer (LDA), combined with the amplitude discrimination method and the velocity filter method, was employed for measurement. The measurement range of the jet flow was from the initial pipe exit to 90D downstream. Results are presented for the mean velocities of particle and fluid phases, the flow's turbulent intensities and the flow's Reynolds stresses. The energy spectra and the correlation functions of the two-phase jet flow were also obtained by using another one-component He-Ne LDA system.

Dispersion of particles in anisotropic turbulent flows

A Lagrangian approach is used to simulate particle dispersion in anisotropic turbulent flows. Discrete particles are tracked in three dimensions, influenced by the fluid's turbulent velocity fluctuations. The fluctuations are temporally and directionally correlated through a statistical sampling method reflecting the anisotropy of the flow field. They are calculated at the discrete particle's position through a spatial correlation which takes into consideration the anisotropy of the Reynolds stresses. The method is first tested as to the performance of the temporal and directional correlation features and is then combined with a Eulerian scheme and an algebraic Reynolds stress model for the prediction of the carrier phase. The final form of the model is used to predict a two-phase turbulent round jet and a two-phase inert flow from a quarl burner, with swirl. In parallel to these, the method is compared to a previous particle-tracking method based on an isotropic hypothesis.

Turbulent Diffusion of Heavy-Particles in Turbulent Jets

The turbulent dispersion of heavy suspended particles in turbulent shear flows is analyzed when crossing trajectory effects are important. A semiempirical expression for particle diffusion coefficient is developed via a comparison with experimental data of two-phase turbulent jet flows. This expression gives the particle momentum diffusion coefficient in terms of the gas diffusion coefficient, mean relatively velocity, and root mean square of the fluctuating fluid velocity. The proposed expression is used in a two-phase flow mathematical model to predict different particle-laden jet flows. The good agreement between the predictions and data suggests that the developed expression for particle diffusion coefficient is reasonably accurate in predicting particle dispersion in turbulent free shear flows.

An experimental study of two-phase turbulent coaxial jets

The effect of solid particles on the flow structure of axisymmetric turbulent coaxial jets has been studied. A laser-Doppler anemometer was used to measure the mean and fluctuation velocities of both phases, and a Malvern laser diffraction instrument was applied to measure particle size and concentration. A series of velocity ratios and particle loading ratios were investigated, and the results were analysed for the effects of these ratios on the mixing characteristic and the similarity behavior of the jet. The effects of particle diameter and its distribution were also studied as well as their influence on the coaxial jet behavior.

Measurement of bubble size distribution: an acoustic technique

This paper reports the successful correlation of the bubble size distribution in a bubbly two-phase flow with the sound spectrum as measured by a hydrophone and spectrum analyser. Two types of bubbly flow were considered: (i) horizontal two-phase flow in a pipeline and (ii) a two-phase turbulent axisymmetric jet. The scientific basis of this technique of measurement lies in the well-established relationship between the bubble size and the frequency of the sound emitted by a gas bubble when it is suitably stimulated; the frequency of the sound increases as the bubble size diminishes. The development of the simple idea into a potentially useful experimental technique is discussed. The advantages of this technique, as compared to alternative methods, e.g. photographic measurements, include the suitability of the technique for use in existing opaque pipework without requiring major modifications and minimal disturbance of the flow. Results from the acoustic technique are compared with those from a photographic technique; agreement between the two methods is good. The technique was also used to predict successfully the gas-liquid mass transfer coefficient in horizontal pipelines.

Numerical analysis of transient two-phase turbulent flame jets

Numerical analysis of transient two-phase turbulent flame jets

Particle lagrangian simulation in turbulent flows

A Lagrangian approach is used to describe particle dispersion in turbulent flows. Fluid particle trajectories are simulated with the aid of a correlation matrix evolving along the particle trajectory. Discrete particles are tracked in a given turbulent field taking into account crossing-trajectory effects, and the influence of the particles on the flow characteristics is deduced from momentum and energy exchanges between both phases. Comparisons of the simulations are given for both experimental and theoretical results for fluid particle diffusion problems. Particle dispersion predictions are presented for grid turbulence experiments, and for three two-phase turbulent round jets, from different authors. Predictions compared favourably with experimental results.

Analysis of a two-dimensional, two-phase turbulent jet along a circular cylinder. (Concentration of the solid particles).

Analysis of a two-dimensional, two-phase turbulent jet along a circular cylinder. (Concentration of the solid particles).

Model of a two-phase turbulent jet with heterogeneous particle combustion taken into account

Model of a two-phase turbulent jet with heterogeneous particle combustion taken into account

Experimental and numerical investigation of a gas-droplet polydisperse turbulent jet

The mathematical model of an axisymmetric two-phase turbulent jet proposed in [i] makes it possible to calculate polydisperse jet flows with allowance for the phase velocity disequilibrium and the polydispersity of the droplets of the discrete phase in the presence of coalescence and fission and for an arbitrary form of the phase parameter fields. The system of differential equations describing the two-phase jet includes the equation of momentum of the discrete phase in projection on the radius of the jet, which makes it possible to calculate the transverse particle velocity, previously assumed equal eo the transverse gas velocity. The system of averaged equations is closed using a model of the particle-turbulent gas interaction based on Prandtl mixing length theory and representing a development of the ideas put forward in [2]. The advantages of this model are its relative simplicity and the fact that the two-phase jet is calculated using a single constant known from the theory of single-phase jets. In the course of the calculations the entire range of droplet sizes is divided into classes and the parameters of each class are calculated.

Two-component LDA measurement in a two-phase turbulent jet

Two-component LDA measurement in a two-phase turbulent jet

Explanation of the ?anomalous? dispersal of the discrete particles in a two-phase turbulent jet with allowance for their inertia

The “anomalous” dispersal of the discrete particles in a two-phase turbulent jet (growth of their concentration in the region of the axis, rapid damping of the concentration in the initial sections of the jet, and “wavelike” axial distribution) is studied with allowance for the initial conditions and the Magnus effect.

Mathematical model of a two-phase turbulent jet

Mathematical model of a two-phase turbulent jet

A model of the two-phase turbulent jet

A model of the two-phase turbulent jet is presented. Consideration is given to cases in which the primary fluid phase contains a secondary phase of rigid particles. The mass fraction of the secondary phase is at most of order unity while its volume fraction is much less than unity. A set of model differential equations is developed for cases in which the mean velocities of the phases are sensibly equal. A first-order closure scheme for the axisymmetric jet is devised and the resulting equations solved numerically. This scheme accounts for momentum transfer between the phases and the imperfect response of the particles to the fluid turbulence. Satisfactory agreement with published experimental data is obtained for computed values of the mean velocity, and the mean mass flux of the particles.