Development of an integrated multichannel inlet for improved particle classification in hydrocyclones

The effects of swirled inflows on the evaporation of dilute acetone droplets dispersed in turbulent jets are investigated by means of direct numerical simulation. The numerical framework is based on a hybrid Eulerian–Lagrangian approach and the point-droplet approximation. Phenomenological and statistical analyses of both phases are presented. An enhancement of the droplet vaporization rate with increasing swirl velocities is observed and discussed. The key physical drivers of this augmented evaporation, namely dry air entrainment and swirl-induced centrifugal forces acting on the droplets, are isolated with the aid of additional simulations in which the inertial properties of the droplets are neglected. The correlation between swirl and dry air entrainment rate is found to be responsible for the increase of the global evaporation rate and the spray penetration length reduction, while swirl-induced centrifugal forces are found to be effective only in the jet shear layer, close to the injection orifice, for the analyzed cases.

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Direct Numerical Simulations of the Evaporation of Dilute Sprays in Turbulent Swirling Jets

Low sensitivity to rheological properties of fluid and ability to produce fine sprays at low liquid pressure make airblast atomizers a preferred choice to process viscous liquids. Airblast atomizers essentially employ kinetic energy of coflowing gases to disintegrate a liquid sheet into fine spray. The present study employs the perturbation technique to carry out nonlinear investigation of the sinuous mode of instability in a thin planar viscous liquid sheet sandwiched between two inviscid gas streams moving at equal velocities. This paper analyzes temporal instability as well as droplet characteristics for a range of Reynolds numbers, Weber numbers, gas to liquid density ratios, and velocity ratios and reports the dual behavior of liquid viscosity at different operating conditions. For higher gas to liquid velocity ratios, this study identifies three regimes at all Weber numbers and gas to liquid density ratios: the first regime represents the stabilizing effect of viscosity at low Reynolds numbers, the second regime indicates the destabilizing effect of viscosity at intermediate Reynolds numbers, and the third regime further depicts the stabilizing effect of viscosity at high Reynolds numbers. However, for low gas to liquid velocity ratios, the third zone disappears at lower Weber numbers and gas to liquid density ratios, and the effect of viscosity is characterized by two regimes representing the weak stabilizing and destabilizing effect at low and relatively higher Reynolds numbers, respectively. Investigation of spray characteristics reveals that an increase in liquid viscosity produces relatively larger droplets at all flow conditions.Low sensitivity to rheological properties of fluid and ability to produce fine sprays at low liquid pressure make airblast atomizers a preferred choice to process viscous liquids. Airblast atomizers essentially employ kinetic energy of coflowing gases to disintegrate a liquid sheet into fine spray. The present study employs the perturbation technique to carry out nonlinear investigation of the sinuous mode of instability in a thin planar viscous liquid sheet sandwiched between two inviscid gas streams moving at equal velocities. This paper analyzes temporal instability as well as droplet characteristics for a range of Reynolds numbers, Weber numbers, gas to liquid density ratios, and velocity ratios and reports the dual behavior of liquid viscosity at different operating conditions. For higher gas to liquid velocity ratios, this study identifies three regimes at all Weber numbers and gas to liquid density ratios: the first regime represents the stabilizing effect of viscosity at low Reynolds numbers, the ...

A study on dual role of viscosity on the stability of a viscous planar liquid sheet surrounded by inviscid gas streams of equal velocities, and prediction of resulting droplet distribution using maximum entropy formulation

Effect of back pressure on the separation performance of a hydrocyclone

This PhD is a joint venture between VINCI Technologies and the CNRS Laboratory CORIA. For its application, VINCI Technologies, developed mainly oil-related equipments and in particular injection/atomization systems. Some of these injectors are characterized by a very big geometrical dimensions (several meters long), that leads to very high Reynolds and Weber number. In addition, many injectors incorporate an internal mixing zone, in which liquid and gas phases are both present in a significant proportion. Consequently, this zone belongs to the dense two-phase flow category. To simulate the liquid dispersion and to characterize the spray formation special from these injectors, appropriate models are required. On its side, the CORIA team, has developed a suitable approach, so-called ELSA, based on the pioneering work of Borghi and Vallet [1, 2]. Key points of this approach are the liquid dispersion that can be associated to the turbulent liquid flux and the amount of liquid-gas surface that can be used to determine eventually the Sauter mean diameter (SMD) of the spray. During this PhD, the applications proposed by V INCI Technologies, have promoted a review of a large part of the multiphase flow approaches to find the more appropriate for each case. This has been the opportunity to clarify the range of application of each approach, and therefore stress the necessity to develop coupled approaches, in order to cover the proposed application in the most suitable way. In particular, this manuscript reports, in one hand, the theoretical development of the ELSA family models, and on the other hand, the corresponding industrial approximations. Since ELSA approaches are originally developed for RANS simulation of the dense zone, it has been extended to LES description. The link of this approach to the DNSi ICM approach, has been studied with a special care. The resulting proposed solver, switches dynamically from ICM to subgrid spray, through the ELSA concept, and thanks to resolution based indicator (IRQ). On the opposite side, once the dispersed spray is formed, the ELSA approach is coupled to multiphase flow method, that aims to determine the spray distribution through the WBE equation. This later equation, is solved with an original hybrid Euler-Lagrange method. The purpose is to solve the WBE equation with a Lagrange stochastic approach, and at the same time, preserving the compatibility to the Euler description of two-phase flow, based on ELSA, to benefit from both approaches. This coupled approach has been tested against academic experimental data coming from ECN research initiative, a combined DNS and experimental measurement of dispersed spray on a Diesel jet, and under an air-blast atomizer numerical test case, for which the mean liquid volume fraction has been measured. Eventually, these developed approaches have been applied to industrial application showing there robustness and their capacity to help in the process of design development of new injectors.

Modeling an oil injector for a FCC reactor

Effect of particle concentration on turbulent modulation inside hydrocyclone using coupled MPPIC-VOF method

High fidelity simulations offer a promising way to study primary breakup of liquid sheets. The present work aims at simulating liquid sheet breakup under the assumption of a 2D planar prefilming gas blast atomization. An in-house finite volume method based solver has been used in the study. Interface tracking is done using volume of fluid (VOF) methodology. The study analyzes the effect of parameters such as inner core gas velocity, outer gas velocity, and liquid sheet thickness on the atomization process. The spray is characterized in terms of liquid sheet breakup length, spray cone angle, and droplet size distribution. The obtained droplet size distribution closely represents lognormal distribution. The inner core gas velocity was found to have significant impact on liquid sheet breakup length and droplet mean diameter within the parametric range of this study. Additionally, increase in liquid sheet thickness has shown an increase in the sheet breakup length.

Direct simulations of liquid sheet breakup in planar gas blast atomization


 Primary breakup of a liquid jet emanating from a simplex swirl atomizer is numerically studied in this work. The liquid-gas interface is tracked using a coupled Level-Set VOF method. In order to improve the curvature calculation, a dual grid approach is used. Level set function is solved on a grid that is finer than the grid used to solve the rest of the variables. This solver is developed using OpenFOAM libraries and is validated by estimating the pressure profile and spurious velocities across the interface of a static bubble. The validation test shows significant improvement in the performance of curvature estimation without significant increase in the computational cost. Additionally, it is found that curvature calculation improves with increase in grid refinement index. A parametric study to understand the effects of grid refinement index on the flow features of the simplex swirl atomizer primary jet is reported here.

Rajesh Reddy

Papers

Effect of particle concentration on turbulent modulation inside hydrocyclone using coupled MPPIC-VOF method

Direct simulations of liquid sheet breakup in planar gas blast atomization

Numerical Study of Primary Jet Breakup in a Simplex Swirl Atomizer Using Dual Grid Coupled Level Set VOF Method