Spray flow simulation

Keywords Binary drop colUsions Bouncing Coalescence Collision model Crossing separation Gaseous environment Immiscible liquids Lattice-Boltzmann simulation Miscible liquids Navier-Stokes simulation Reflexive separation Satellite droplets Spray flow simulation SPH simulation Stretching separation... 

Modeling of the complicated phenomena in binary droplet collisions occurring in spray flows is difficult due to the variety of potential outcomes from a collision [69-71]. The first necessity is to predict the stability against stretching or reflexive separation. Then, for unstable drop collisions, the resulting drop sizes need to be predicted. All predictions should follow from algebraic models without the need to solve additional transport equations in the spray flow code to account for the collisions. Needless to say that it is impossible to simulate the full detail of the processes in droplet collisions, as done in the simulations discussed in section Simulations of Droplet Collisions, in the course of a spray flow simulation [72-82]. 

The equation derived from cold-flow simulation naturally cannot account for deviations in penetration when the spray enters the high temperature and varied geometry ACR environment. However, the results permitted the design of an injection system suitable for the full-scale ACR high temperature flow tests which refined the cold-flow penetration equation to assure kinematic similarity in a commercial ACR reactor. 

In this work, direct interface tracking will be used to simulate the evolution of liquid jets and sheets into drops as shown in Fig. 5.1. The fundamental physics of spray flow without relying on assumptions about instabilities will be addressed. 

Abstract We put together the state of knowledge on binary colUsional interactions of droplets in a gaseous environment. Phenomena observed experimentally after drop collisions, such as coalescence, bouncing, reflexive separation and stretching separation, are discussed. Collisions of drops of the same liquid and of different -miscible or immiscible - liquids, as well as collisions of drops of equal and different size are addressed. Collisions of drops of immiscible liquids may lead to an unstable interaction which is not observed with drops of equal or miscible liquids. Regimes characterized by the various phenomena are depicted in nomograms of the Weber number and the non-dimensional impact parameter. The state-of-the-art in the simulation of binary droplet collisions is reviewed. Overall three different methods are represented in the literature on these simulations. We discuss models derived from numerical simulations and from experiments, which are presently in use for simulations of spray flows to account for the influence of coUisional interactions of the spray droplets on the drop size spectrum of the spray. 

The present chapter puts together the state of knowledge about the coUisional interaction of liquid droplets and gives an overview of the literature on experiments, as well as on simulation and modeling of binary liquid droplet collisions, both as an elementary phenomenon and also in the context of spray flows. 

The task of modeling binary droplet collisions in Euler-Lagrangian simulations of spray flows was first taken up by O Rourke and coworkers. Their model in [83] first estimates the coalescence efficiency, which is the probability that coalescence occurs after the collision, once it has taken place ... 

In order to obtain a correlation, the outflow of the effervescent spray was simulated by a numerical model based on the Navier-Stokes equations and the particle tracking method. The external gas flow was considered turbulent. In droplet phase modeling, Lagrangian approach was followed. Droplet primary and secondary breakup were considered in their model. Secondary breakup consisted of cascade atomization, droplet collision, and coalescence. The droplet mean diameter under different operating conditions and liquid properties were calculated for the spray SMD using the curve fitting technique [43] ... 

This approach is useful if the environment is well characterized and a few weeks or months have been allocated for the test examples include exposure to salt spray to simulate sea coastal areas, exposure to 3.5 wt% NaCl solution for submarine environment, Kesternich chamber test (humid SO2 and CO2 mixture) for industrial environment [6], and mixed flowing gas tests for a range of environments. 

Gopireddy, S. R., Humza, R. M., Wimmer, E., Brenn, G., Gutheil, E. (2014). Modelling and simulation of water and PVP/water evaporating spray flows using the direct quadrature method of moments. Atomization Sprays, 24, 403-429. 

To analyze the individual heat transfer kinetics of droplet clusters within the spray of twin-fluid atomizers, the local correlations between the droplet concentration and the heat and flow conditions are evaluated. Numerical simulations of the spray flow analyzed in this paper have been carried out with Large-Eddy-Simulation (LES) models with Lagrangian particle tracking (discrete particle method) for the droplet motion. A synthetic perturbation generator [30] for the inflow conditions for the gas flow and simple perturbations are added to the dispersed phase to induce realistic vortex patterns at the nozzle and in the consequent spray. 

The influence of the spray chamber boundaries on the mean spray flow is investigated with time-averaged simulations (RANS). By changing the shape and the size of the spray tower (Fig. 19.8), the effect on the entrainment has been analyzed. Here, a conical part and an orifice have been integrated into the spray chamber model. Variations of the spray tower width at different flow rates of the atomizer are also studied in Fig. 19.9. 

A strong deflection of the gas flow (and thereby also of the particles) in the spray toward the wall is found for variant C showing that hot gas atomization demands tall spray towers. Here, the axial momentum flux of the spray flow is higher than for a conventional concurrent spray drying process. The entrainment flow in front of the orifice is increased because of the strong deflection of the gas, but close to the nozzle the entrainment flow is the same as for variant A and B. Variant D combines the effects of Variant B and C. In the measurements as well as in the simulations, the temperature distribution on the centerline is almost the same. 

The mean and rms velocities of the droplets are differing significantly for the different droplet sizes (Fig. 19.20a, b). The anisotropic character of the gas phase fluctuations is visible for both droplet sizes, but the droplets show lower velocity fluctuation intensities in the axial and radial direction for the intermediate droplets. The velocity profiles for the 30 pm droplet case are very similar to the profiles from the polydisperse simulation case. Despite the relatively high air-to-liquid ratio of the considered spray flow (ALR = 0.62), the impact of the dispersed phase on the mean gas flow in the core of the spray is low, indicated by similar profiles of the radial and axial rms velocity profiles of the gas phase for 10 and 30 pm droplets. 

As a result gas distributors were developed by flow simulation which significantly reduced gas-Weber numbers in the spray process with a LamRot. This ensures for a narrow particle distribution of the product. 

InsAument parameters (sheath and auxiliary gas flows, spray voltage, capillary temperature, collision cell gas flow and offset, etc.) should be optimized while infusing a standard of tebuconazole prior to the Arst attempt at analysis. Optimization should be performed at an HPLC Aow rate and composition simulating those present during elution of tebuconazole using each HPLC condition set employed... 

This review paper is restricted to stirred vessels operated in the turbulent-flow regime and exploited for various physical operations and chemical processes. The developments in the field of computational simulations of stirred vessels, however, are not separated from similar developments in the fields of, e.g., turbulent combustion, flames, jets and sprays, tubular reactors, and multiphase reactors and separators. Fortunately, there is a strong degree of synergy and mutual cross-fertilization between these various fields. This review paper focuses on aspects specific to stirred vessels (such as the revolving impeller, the resulting strong spatial variations in turbulence properties, and the macroinstabilities) and on the processes carried out in them. 

A spray is a turbulent, two-phase, particle-laden jet with droplet collision, coalescence, evaporation (solidification), and dispersion, as well as heat, mass and momentum exchanges between droplets and gas. In spray modeling, the flow of gas phase is simulated typically by solving a series of conservation equations coupled with the equations for spray process. The governing equations for the gas phase include the equations of mass, momentum and energy... 

Most current multidimensional spray simulations have adopted the thin or very thin spray assumptions,[55°1 i.e., the volume occupied by the dispersed phase is assumed to be small. This can be justified if a simulation starts some distance downstream of the nozzle exit, where the gas volume fraction is large enough, or if the computational cells are relatively large. Accordingly, two major classes of models have been used in spray modeling locally homogeneous flow (LHF) models and two-phase-flow or separated-flow (SF) models. 

Trapaga and Szekely 515 conducted a mathematical modeling study of the isothermal impingement of liquid droplets in spray processes using a commercial CFD code called FLOW-3D. Their model is similar to that of Harlow and Shannon 397 except that viscosity and surface tension were included and wetting was simulated with a contact angle of 10°. In a subsequent study, 371 heat transfer and solidification phenomena were also addressed. These studies provided detailed... 

COSILAB Combustion Simulation Software is a set of commercial software tools for simulating a variety of laminar flames including unstrained, premixed freely propagating flames, unstrained, premixed burner-stabilized flames, strained premixed flames, strained diffusion flames, strained partially premixed flames cylindrical and spherical symmetrical flames. The code can simulate transient spherically expanding and converging flames, droplets and streams of droplets in flames, sprays, tubular flames, combustion and/or evaporation of single spherical drops of liquid fuel, reactions in plug flow and perfectly stirred reactors, and problems of reactive boundary layers, such as open or enclosed jet flames, or flames in a wall boundary layer. The codes were developed from RUN-1DL, described below, and are now maintained and distributed by SoftPredict. Refer to the website http //www.softpredict.com/cms/ softpredict-home.html for more information. 

Fthenakis, V. M. and K. W. Schatz, 1991. Numerical Simulations of Turbulent Flow Fields Caused by Spraying of Water on Large Releases of Hydrogen Fluoride. In J.W. Hoyt and T.J. O Hern, Eds., Fluid Dynamics of Sprays, FED-131. Pp. 37-44. New York ASME (American Society of Mechanical Engineers). 

Simulation of free-surface and interfacial flows is a topic with many practical applications, e.g., the formation of droplet clouds or sprays from liquid jets,... 

S. V. Apte, M. Gorokhovski, and P. Moin. Large-eddy simulation of atomizing spray with stochastic modeling of secondary breakup. Int. J. Multiphase Flow, 29 1503-1522, 2003. 

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