Phase Doppler Particle Anemometer Research Articles

Force measurement of a gas-assisted atomization using an impulse probe

The main objective of this study was to develop further insight into the mass flux characterization of an effervescent atomization. The spray is injected through an industrial effervescent nozzle, and is measured using a newly developed coupled PDPA + IS method. Mass flux measurement of microscale droplets in multiphase atomization is a challenging task. The advanced laser diagnostics such as the phase Doppler particle anemometer (PDPA) are not capable of accurately measuring the droplet mass flux in a dense spray due to the high rejection of non-spherical droplets by the PDPA. A combined measurement of momentum rate data from the impulse sensor (IS) and velocity data from the PDPA provides a fairly reasonable estimate of mass flux data in effervescent atomization. Moreover, the mass flux data obtained by the coupled PDPA + IS will facilitate the estimation of the void fraction in multiphase dense spray, which will be very beneficial to the design of industrial multiphase nozzles.

Experimental and numerical study on the flow behavior in a jet-driven swirling flow

ABSTRACTIn order to understand the asphalt separation processes in a new technique of solvent deasphalting, the hydrodynamics of the jet-driven swirling flow within a spray granulation tower (SGT) was studied by using experimental and numerical methods. Mean velocity components were measured by use of the Phase Doppler Particle Anemometer (PDPA). Simulation with Reynolds Stress Model (RSM) was carried out to understand the flow information. Two different zones in the jet-driven swirling flow were observed in both experiment and simulation. A combined effect of jet, jet entrainment and jet interactions leads to complex flow behavior in the upper part. A double swirling flow was identified on the basis of the tangential and the axial velocity distribution in the lower part. The specific flow pattern was identified based on the experimental and computational flow field. An empirical formula was proposed to predict the percentage of the SGT occupied by the jet and the swirl zone.

Enhancement effects of methane/air explosion caused by water spraying in a sealed vessel

Experiments about the influence of ultrafine water mist on the methane/air explosion were carried out in a fully sealed visual vessel with methane concentrations of 8%, 9.5%, 11% and 12.5%. Water mists were generated by two nozzles and the droplets' Sauter Mean Diameters (SMD) were 28.2 μm and 43.3 μm respectively which were measured by Phase Doppler Particle Anemometer (PDPA). A high speed camera was used to record the flame propagation processes. The results show that the maximum explosion overpressure, pressure rising rate and flame propagation velocity of methane explosions in various concentrations increased significantly after spraying. Furthermore, the brightness of explosion flame got much higher after spraying. Besides, the mist with a larger diameter had a stronger turbulent effect and could lead to a more violent explosion reaction.

Cyclonic Separation Technology: Researches and Developments

Centered on the techniques and industrial applications of the reinforced cyclonic separation process, its principles and mechanism for separation of ions, molecules and their aggregates using polydisperse droplets are discussed generally; the characteristics and influential factors of fish-hook phenomenon of the grade efficiency curve in cyclonic separation for both gas and liquid are analyzed; and the influence of shear force on particle behavior (or that of particle swarm) is also summarized. A novel idea for cyclonic separation is presented here: enhancing the cyclonic separation process of ions, molecules and their aggregates with monodisperse microspheres and their surface grafting, rearranging the distribution of particles by size using centrifugal field, reinforcing the cyclonic separation performance with orderly arranged particle swarm. Also the investigation of the shortcut flow, recirculation flow, the asymmetric structure and non-linear characteristics of the cyclonic flow field with a combined method of Volumetric 3-component Velocimetry (V3V) and Phase-Doppler Particle Anemometer (PDPA) are elaborated. It is recommended to develop new systems for the separation of heterogeneous phases with cyclonic technology, in accordance with the capture and reuse of CO2, methanol to olefins (MTO) process, coal transfer, and the exploitation of oil shale.

Effects of the gas phase molecular weight and bubble size on effervescent atomization

The effervescent atomization from an industrial Coker feed nozzle is compared for two different gas densities (air and mixed gas of 81.4 vol.% helium/18.6 vol.% nitrogen) at equivalent operating temperatures. The application is to observe the similarity of lab tests using air at 20 °C to the industrial process using steam at 300–400 °C. The effects of operating conditions, such as gas to liquid mass ratio, mixing pressure and void fraction on the flow regime, bubble size, and droplet size distribution were also examined in this study. The experiments were performed using mixtures of water with air or mixed gas, which resulted in gas to liquid mass ratios ranging from 1% to 4%. Stroboscopic back scattered imagery (SBSI) indicates that the average bubble size inside the nozzle conduit is similar when air and water are used as the process fluids, when compared to the case when mixed gas and water are used as the process fluids. Under similar conditions, the Phase Doppler Particle Anemometer (PDPA) data indicate that the droplet size in the spray is similar when using either mixed gas or air as the atomization gas. Experimental results obtained by high-speed video shadowgraphy (HSVS) indicate that the flow pattern inside the nozzle feeding conduit was slug flow with a tendency to attain annular flow with increased air to liquid mass ratios. Thus, from the experimental results it is evident that the smaller molecular weight of the mixed gas versus air (8.4 versus 29) does not significantly reduce the bubble (<±10% difference) and droplet size (<±1.5% difference), indicating a weak dependence of the gas phase density on two-phase atomization. This confirms that laboratory experiments on effervescent nozzles using air have reliable similarity to systems that use high temperature steam for the gas phase.

Measurement and simulation of the two-phase velocity correlation in sudden-expansion gas-particle flows

In this paper the present authors measured the gas-particle two-phase velocity correlation in sudden expansion gas-particle flows with a phase Doppler particle anemometer (PDPA) and simulated the system behavior by using both a Reynolds-averaged Navier-Stokes (RANS) model and a large-eddy simulation (LES). The results of the measurements yield the axial and radial time-averaged velocities as well as the fluctuation velocities of gas and three particle-size groups (30 µm, 50 µm, and 95 µm) and the gas-particle velocity correlation for 30 µm and 50 µm particles. From the measurements, theoretical analysis, and simulation, it is found that the two-phase velocity correlation of sudden-expansion flows, like that of jet flows, is less than the gas and particle Reynolds stresses. What distinguishes the two-phase velocity correlations of sudden-expansion flow from those of jet and channel flows is the absence of a clear relationship between the two-phase velocity correlation and particle size in sudden-expansion flows. The measurements, theoretical analysis, and numerical simulation all lead to the above-stated conclusions. Quantitatively, the results of the LES are better than those of the RANS model.

EXPERIMENTAL INVESTIGATION OF GEOMETRIC SCALING ON ATOMIZATION IN A TWO-PHASE GAS/LIQUID SPRAY

In this study the atomization performance of a full-scale industrial air-liquid nozzle is compared to a one-quarter model. The objective is to establish a global Sauter mean diameter D32(gb) correlation as a function of nozzle size (D) in a two-phase gas/liquid (TPGL) spray atomization. This information is to be used in the design and development of nozzles for heavy oil upgrading industry. Compressed air was used as the gas phase; the liquids were water, canola oil, and glycerine solutions all at room temperature. The liquid flow rates were varied from 0.095 to 0.195 L/s, and the gas-to-liquid-ratio (β), by mass, was fixed at 1%, similar to commercial fluid coker nozzles. Fluid mixing pressures in the test were between 516 and 1000 kPa. The D32 within the spray was measured using a Dantec 2-D phase-Doppler particle anemometer (PDPA) with measurements performed at axial distances of 100, 202, and 405 mm from the nozzle exit and within spray widths of +50 to -50 mm in the horizontal plane. Experimental results show that if the D is increased from 3.1 to 4.1 mm (1.3 times), D does not show a change on D32 and equates to the power of 0.1 (glycerine solution sprays at μL = 67 mPa s) to 0.9 (water sprays at μL = 1 mPa s). Finally, the D32(gb) correlation as a function of geometric scaling estimated drop size within a 17% maximum deviation between the experimental and curve fit data.

Studies of the effect of a coal concentrator on NO formation in swirling coal combustion

To develop low-pollution burners, the effect of a coal concentrator on NO formation in swirling coal combustion is studied using both numerical simulation and experiments. The isothermal gas–particle two-phase velocities and particle concentration in a cold model of swirl burners with and without coal concentrators were measured using the phase Doppler particle anemometer (PDPA). A full two-fluid model of reacting gas–particle flows and coal combustion with an algebraic unified second-order moment (AUSM) turbulence-chemistry model for the turbulent reaction rate of NO formation are used to simulate swirling coal combustion and NO formation with different coal concentrators. The results give the turbulent kinetic energy, particle concentration, temperature and NO concentration in cases of with and without coal concentrators. The predicted results for cold two-phase flows are in good agreement with the PDPA measurement results, showing that the coal concentrator increases the turbulence and particle concentration in the recirculation zone. The combustion modeling results indicate that although the coal concentrator increases the turbulence and combustion temperature, but still can remarkably reduce the NO formation due to creating high coal concentration in the recirculation zone.

An experimental and numerical investigation into the dispersion of powder from a pipe

This paper presents the results of the experimental and numerical investigation of the dispersion of spherical particles from a pipe. The experimental study is based on the use of the phase Doppler particle anemometer (PDPA) technique to measure the diameter and velocity of the particles as well as the intensity of the particle flow signal. The PDPA software measured the concentration levels of the particles by converting the particle flow signal intensities into particle mass concentration measurements. The PDPA software also converted the particle mass concentration measurements into local particle mass flux measurements. This study of the dispersion characteristics of the spherical particles was carried out in a domain that extends from the exit position of the nozzle to 10 nozzle diameters downstream. The particulate jet was measured in five sections X/ D=0.5, 2.5, 5.0, 7.5 and 10. Numerical simulations for the experiment were performed by using an in-house CFD code, AFLOW and using two coefficient values of the standard k– ε turbulence model and the RNG k– ε model based on Yakhot’s coefficients. Comparisons between the numerical and experimental results were therefore performed. Pressure drop predictions and measurements are presented for this work.

Simulation of swirling gas–particle flows using a nonlinear k– ε– kp two-phase turbulence model

The linear k– ε– k p two-phase turbulence model is rather simple, but it cannot predict the anisotropic turbulence of strongly swirling gas–particle flows. The second-order moment, two-phase turbulence model can better predict strongly swirling flows, but it is rather complex. Hence, the algebraic Reynolds stress expressions are derived based on two-phase Reynolds stress equations, and then the nonlinear relationships of two-phase Reynolds stresses and two-phase velocity correlation with the strain rates are obtained. These relationships, together with the transport equations of gas and particle turbulent kinetic energy and the two-phase correlation turbulent kinetic energy constitute the nonlinear k– ε– k p turbulence model. The proposed model is applied to simulate swirling gas–particle flows. Predictions give the two-phase time-averaged velocities and Reynolds stresses. The prediction results are compared with phase Doppler particle anemometer (PDPA) measurements and those predicted using the second-order moment model. The results indicate that the nonlinear k– ε– k p model has modeling capability nearly equal to that of the second-order moment model, but the former can save much computation time.

Simulation of 3-D gas-particle flows and coal combustion in a tangentially fired furnace using a two-fluid-trajectory model

A two-fluid-trajectory (TFT) model is used to simulate three-dimensional (3-D) gas-particle flows and coal combustion in a tangentially fired furnace. A grid system, rotated by an angle, is proposed to reduce the numerical diffusion caused by non-orthogonal crossing of the burner jets with the grid lines. The predictions of cold two-phase flows using the two-fluid (TF) model are compared with those using the stochastic trajectory model (ST model of particle phase) and the phase Doppler particle anemometer (PDPA) measurements. The predicted particle concentration distribution using the TF model is in agreement with PDPA measurements, while the ST model gives too high particle concentration in the near-wall region, not observed in experiments. The 3-D coal combustion predictions give the hot-flow field, coal concentration, gas temperature, species concentration, and heat fluxes on the walls. The prediction results for coal combustion show a local high-temperature zone near the exit of the furnace.

Studies on the effect of swirl numbers on strongly swirling turbulent gas-particle flows using a phase-Doppler particle anemometer

The effect of swirl numbers on the flow behavior of strongly swirling turbulent gas-particle flows with swirl numbers of s=0.47, 1.0, 1.5 and 2.1 in sudden-expansion and cyclone chambers is studied using a 2-D and a 3-D phase Doppler particle anemometers (PDPA). The axial and tangential time-averaged and the root mean square (RMS) fluctuation velocities of gas and particle phases and particle concentration are measured. The result shows that the swirl number has an obvious effect on the axial velocity profiles, the Rankine vortex structure of tangential velocity profiles, the relationship between two-phase velocities, the turbulence intensity level and the anisotropy of turbulence.

Strongly swirling gas-particle flows and coal combustion in a cyclone combustor

Strongly swirling gas-particle flows with swirl numbers 1.5 and 1.0 in a cyclone combustor are measured using a 3-D phase Doppler particle anemometer system (PDPA), and the case of swirl number 1.5 is simulated using a unified second-order moment (USM) model of anisotropic two-phase turbulence. The prediction results using the USM model are then compared with those obtained using the isotropic k-epsilon-kp two-phase turbulence model and the PDPA measurements. The measurements and predictions show that for strongly swirling flows with axial and tangential inlets there is no recirculation zone in axial velocity profiles: the gas and particle tangential velocity profiles have the Rankine-vortex structure, but the solid-body rotation zone is much larger than that for weakly swirling flows: the axial gas and particle fluctuations are at first stronger than, then near to, and finally slightly smaller than the tangential ones: both axial and tangential particle time-averaged and fluctuation velocities lag behind the gas one: and the USM model can better predict the Rankine-vortex structure of tangential velocity profiles and the anisotropy of two-phase turbulence in strongly swirling flows than the k-ε-kp model. The research results of two-phase flows are used for optimum design of the coal-fired cyclone combustor burning 3- to 5-mm coal particles, which finally gives higher combustion efficiency and lower NO x formation, and for developing the combustion modeling.