IHTC14-22470 EFFECT OF RAIN ON EVOLUTION OF DISTRIBUTION OF SOLUBLE GASEOUS POLLUTANTS IN THE ATMOSPHERE

ABSTRACT We suggest a model of rain scavenging of soluble gaseous pollutants in the atmosphere. It is shown that below-cloud gas scavenging is determined by non-stationary convective diffusion equation with the effective Peclet number. The obtained equation was analyzed numerically in the case of lognormal droplet size distribution. Calculations of scavenging coefficient and the rates of precipitation scavenging are performed for wet removal of ammonia (NH 3 ) and sulfur dioxide (SO 2 ) from the atmosphere. It is shown that scavenging coefficient is non-stationary and height-dependent. It is found also that the scavenging coefficient strongly depends on initial concentration distribution of soluble gaseous pollutants in the atmosphere. It is shown that in the case of linear distribution of the initial concentration of gaseous pollutants whereby the initial concentration of gaseous pollutants decreases with altitude, the scavenging coefficient increases with height in the beginning of rainfall. At the later stage of the rain scavenging coefficient decreases with height in the upper below-cloud layers of the atmosphere

Combined multifluid‐population balance method for polydisperse multiphase flows

In the present work we analyse applicability of the adaptive multiple size-group (A-MuSiG) population balance method to modelling of multiphase flows. The dispersed phase is split into M size-groups, each one having its own mass- and momentum balance. An additional equation for the number density makes the method adaptive, that is, the groups sizes are not prescribed a priory, but calculated. A special attention is paid to the effect of the turbulent diffusion on size distribution. The method is implemented in the multiphase CFD code STAR-CCM+ of Siemens PLM Software

Progress in Applied CFD. Selected papers from 10th International Conference on Computational Fluid Dynamics in the Oil & Gas, Metallurgical and Process Industries

In the present work we analyse applicability of the adaptive multiple size-group (A-MuSiG) population balance method to modelling of multiphase flows. The dispersed phase is split into M size-groups, each one having its own mass- and momentum balance. An additional equation for the number density makes the method adaptive, that is, the groups sizes are not prescribed a priory, but calculated. A special attention is paid to the effect of the turbulent diffusion on size distribution. The method is implemented in the multiphase CFD code STAR-CCM+ of Siemens PLM Software.publishedVersio

Simulation of dispersion of immiscible fluids in a turbulent couette flow

Dispersion of immiscible fluids in a Couette device, in which the inner cylinder rotates whereas the outer one is immobile, is modelled. Two different modelling approaches are employed. The 1st approach is based on solving a one-dimensional Advection-Diffusion-Population Balance equation. An influence of upper and bottom Couette device covers (the so-called end effect) is ignored in this case. The Prandtl mixing length model of turbulence, employed for modelling of a Couette flow field, allows obtaining an analytical expression for calculation of the energy dissipation rate distribution across Couette device gap. Fixed Pivot method is employed for numerical solution of the population balance equation. The 2nd approach is based on the CFD-population balance AMuSiG method, recently implemented into the STAR-CCM+ code of Siemens PLM Software. The Reynolds stress turbulence model along with the Daly & Harlow transport model are employed for modelling two-dimensional axisymmetric flow field in a Couette device. In the present work, modelling is limited to only droplet breakup; i.e., only non-coalescing droplets are considered. A modified droplet breakup model of Coulaloglou and Tavlarides (1977) is employed for all the computations. Computed droplet size distributions are compared with those obtained in a laboratory Couette device of a relatively small height that is a cause of the significant end effect. Dispersion of water droplets in silicone oil is studied. Coalescence is suppressed by a surfactant. The experimental droplet size distributions are reasonably well fitted by both the models employed. The most significant advantage of the 3-D computations over the 1-D modelling is accounting for the end effect, that in its turn affects both velocity and energy dissipation rate distributions over the Couette device gap. Also, to better fit the experimental data, a weak coalescence was formally introduced into the 3-D computational code

Progress in Applied CFD. Selected papers from 10th International Conference on Computational Fluid Dynamics in the Oil & Gas, Metallurgical and Process Industries

Dispersion of immiscible fluids in a Couette device, in which the inner cylinder rotates whereas the outer one is immobile, is modelled. Two different modelling approaches are employed. The 1st approach is based on solving a one-dimensional Advection-Diffusion-Population Balance equation. An influence of upper and bottom Couette device covers (the so-called end effect) is ignored in this case. The Prandtl mixing length model of turbulence, employed for modelling of a Couette flow field, allows obtaining an analytical expression for calculation of the energy dissipation rate distribution across Couette device gap. Fixed Pivot method is employed for numerical solution of the population balance equation. The 2nd approach is based on the CFD-population balance AMuSiG method, recently implemented into the STAR-CCM+ code of Siemens PLM Software. The Reynolds stress turbulence model along with the Daly & Harlow transport model are employed for modelling two-dimensional axisymmetric flow field in a Couette device. In the present work, modelling is limited to only droplet breakup; i.e., only non-coalescing droplets are considered. A modified droplet breakup model of Coulaloglou and Tavlarides (1977) is employed for all the computations. Computed droplet size distributions are compared with those obtained in a laboratory Couette device of a relatively small height that is a cause of the significant end effect. Dispersion of water droplets in silicone oil is studied. Coalescence is suppressed by a surfactant. The experimental droplet size distributions are reasonably well fitted by both the models employed. The most significant advantage of the 3-D computations over the 1-D modelling is accounting for the end effect, that in its turn affects both velocity and energy dissipation rate distributions over the Couette device gap. Also, to better fit the experimental data, a weak coalescence was formally introduced into the 3-D computational code.publishedVersio

A computational study of an HCCI engine with direct injection during gas exchange

We present a new probability density function (PDF)-based computational model to simulate a homogeneous charge compression ignition (HCCI) engine with direct injection (DI) during gas exchange. This stochastic reactor model (SRM) accounts for the engine breathing process in addition to the closed-volume HCCI engine operation. A weighted-particle Monte Carlo method is used to solve the resulting PDF transport equation. While simulating the gas exchange, it is necessary to add a large number of stochastic particles to the ensemble due to the intake air and EGR streams as well as fuel injection, resulting in increased computational expense. Therefore, in this work we apply a down-sampling technique to reduce the number of stochastic particles, while conserving the statistical properties of the ensemble. In this method some of the most important statistical moments (e.g., concentration of the main chemical species and enthalpy) are conserved exactly, while other moments are conserved in a statistical sense. Detailed analysis demonstrates that the statistical error associated with the down-sampling algorithm is more sensitive to the number of particles than to the number of conserved species for the given operating conditions. For a full-cycle simulation this down-sampling procedure was observed to reduce the computational time by a factor of 8 as compared to the simulation without this strategy, while still maintaining the error within an acceptable limit. Following the detailed numerical investigation, the model, intended for volatile fuels only, is applied to simulate a two-stroke, naturally aspirated HCCI engine fueled with isooctane. The in-cylinder pressure and CO emissions predicted by the model agree reasonably well with the measured profiles. In addition, the new model is applied to estimate the influence of engine operating parameters such as the relative air-fuel ratio and early direct injection timing on HCCI combustion and emissions. The qualitative trends observed in the parametric variation study match well with experimental data in literature. (c) 2006 The Combustion Institute. Published by Elsevier Inc. All fights reserved