Martha Salcudean - Academia.edu (original) (raw)

Papers by Martha Salcudean

Chemical Engineering Science, 2009

... Pirooz Darabi a , Konstantin Pougatch a , Martha Salcudean Corresponding Author Contact Infor... more ... Pirooz Darabi a , Konstantin Pougatch a , Martha Salcudean Corresponding Author Contact Information , a , E-mail The Corresponding Author and Dana ... The viscous contribution has also been studied extensively ([Chan and Horn, 1985], [Ennis et al., 1990], [Ennis et al., 1991 ...

Volume 7: Fluid Flow, Heat Transfer and Thermal Systems, Parts A and B, 2010

ABSTRACT Numerical simulations of the governing Navier-Stokes equations are used to predict the r... more ABSTRACT Numerical simulations of the governing Navier-Stokes equations are used to predict the rupture and liquid distribution of stretching liquid bridges between two equal-sized solid spherical particles with different liquid-solid contact angles. A commercial computational fluid dynamics (CFD) tool — FLUENT — is used. The effects of the capillary number and contact angle on the rupture distance and liquid transfer fraction are studied. The simulation results show that for particles with different contact angles, the rupture distance increases as the capillary number is increased; this is similar to the case of particles with identical contact angles. Also, it is shown that for quasi-static conditions, the rupture distance decreases as the difference between the contact angles is increased. Plots of the variations of the liquid transfer fraction with respect to the capillary number show three zones: (1) for high capillary numbers, liquid is almost equally distributed (dynamic zone); (2) for low capillary numbers, the liquid transfer fraction depends on the contact angles and more liquid is transferred to the particle with the smaller contact angle (quasi-static zone); (3) at intermediate capillary numbers, the curve connecting the above limiting conditions resembles an S-shape (transition zone), showing the dependency of the liquid distribution on both capillary number and contact angles. The trends are consistent with the experimental findings published in the literature.

International Journal of Chemical Reactor Engineering, 2000

A simplified mathematical model is proposed to determine the agglomeration tendency of bitumen-co... more A simplified mathematical model is proposed to determine the agglomeration tendency of bitumen-coated coke particles in fluid cokers. The model calculates a theoretical critical velocity that depends on key parameters such as the particle size, bitumen viscosity, and bitumen thickness; it also accounts for the temperature-and reaction-dependent variations of the bitumen thickness and viscosity. A peak theoretical critical velocity at the intermediate reaction times for all coking temperatures is predicted. By comparing this peak critical velocity with the estimated inter-particle collision velocities within an industrial-scale reactor, the agglomeration tendency of coke particles is determined within fluid cokers. The results show that at low temperature regions (T=400 • C), there is no agglomeration tendency; however, at high coking temperatures (T=503 and 530 • C), substantial agglomeration tendency is expected. It is also found that the number of coke particles constituting an agglomerate could be as high as a few hundreds.

Powder Technology, 2011

ABSTRACT In this work, the impact of liquid coating on fluidized bed behavior is studied by perfo... more ABSTRACT In this work, the impact of liquid coating on fluidized bed behavior is studied by performing DEM investigations. A wet coefficient of restitution model, accounting for the viscous and capillary forces in addition to the inelasticity of particles, is implemented in an open-source numerical tool — MFIX-DEM. The modified numerical tool is used to study the effect of the coating thickness and viscosity on the operation of a bed consisting of mono-sized solid spherical particles pre-coated with the same film thickness. The simulation results show that as the coating viscosity is increased, particles tend to stay close together, hence the fluidization behavior changes and the air passes through the system in the form of slugs. It is also shown that as the coating viscosity is increased the time-average wet coefficient of restitution, normal relative collision velocities, and bed height decrease. The effect of increasing the coating thickness is similar to the above, i.e. it results in a reduction of the time-averaged wet coefficient of restitution and normal relative collision velocities.

International Journal of Multiphase Flow, 1983

Rupture characterization of a liquid bridge connecting wetted solid particles and the distributio... more Rupture characterization of a liquid bridge connecting wetted solid particles and the distribution of a liquid bridge between the particles plays a key role in many industrial particle processing systems. This work is aimed to provide a fundamental understanding of stretching liquid bridges. The work was applied to fluid cokers by investigating coke particle interaction with liquid bitumen; coating of particles and bridge formation. A simplified mathematical model and numerical simulation of Navier-Stokes equations have been used to predict the shape evolution, rupture distance, and liquid distribution of pendular liquid bridges between two spherical solid particles. In the simplified model, the problem has been modeled using a parabolic assumption for the bridge shape. It is also assumed that surface tension forces are dominant over viscous, inertia, and gravitational forces. For numerical simulations, a commercial computational fluid dynamics software FLUENT has been employed. Num...

Chemical Engineering Science, 2015

ABSTRACT A comparative study has been carried out to determine the ability of computational fluid... more ABSTRACT A comparative study has been carried out to determine the ability of computational fluid dynamics (CFD) and computational particle fluid dynamics (CPFD) codes to predict the hydrodynamics of FCC particles in a bubbling fluidized bed. Simulations were conducted in both 2-dimensional (2-D) and 3-dimensional (3-D) CFD configuration and in a 3-D CPFD model. The new structure based force-balance (FB) model of Ahmadi Motlagh et al. (2014. Chem. Eng. Sci. 120, 22–36.) was incorporated in CFD to simulate the behavior of FCC in the bubbling fluidization regime. This model modifies the conventional drag correlation by considering the effect of interparticle forces on the formation of agglomerates inside the bed, updating the drag calculations by replacing the particle diameter in the Wen and Yu correlation by an agglomerate diameter. The effects of superficial gas velocity, particle diameter, particle-particle restitution coefficient and specularity coefficient on voidage are examined. The sensitivity of different gas–solid drag closures in CFD are tested and compared. Experimental time-average axial and radial voidage profiles were simulated with varying degrees of agreement with experimental data obtained using different advanced experimental techniques in the “Traveling fluidized bed” (Dubrawski et al., 2013. Powder Technol. 235, 203–220; Tebianian et al., 2014. Extending the comparison of voidage measurement and modeling techniques in fluidized beds. In: Proc. 11th International Conference on Fluidized Bed Technology, (Eds.), J. Li, X.J. Bao and W. Wang. Chemical Industry Press, Beijing 137–142.). Both the FB and CPFD models were successful in resolving key issues in 3-D, whereas 2-D models tended to seriously underpredict particle volume fraction, especially near the wall.

Chemical Engineering Science, 2014

ABSTRACT The well-documented inaccuracy of conventional two-fluid modeling of hydrodynamics in fl... more ABSTRACT The well-documented inaccuracy of conventional two-fluid modeling of hydrodynamics in fluidized beds of Geldart Group A particles is revisited. A new force-balance (FB) sub-grid-scale model, applied to the conventional Wen–Yu drag correlation, analyzes the balance of van der Waals, drag, gravity and buoyancy forces. It predicts formation of agglomerates inside the bed, updating the drag calculations by applying a correction factor to the conventional drag models to account for agglomerate formation. Good predictions were obtained of fluidization regimes and bed expansion, and there was promising agreement with experimental time-average radial voidage profiles reported by Dubrawski et al. (2013). Good quantitative agreement between DEM and two-fluid predictions of minimum bubbling velocity was also observed when the model was used to predict minimum bubbling velocity, in contrast to the predictions from a non-cohesive, Wen–Yu model. Further evaluation studies are required to test the ability of the new model to predict the properties of larger-scale fluidized beds.

Metallurgical Transactions B, 1978

ABSTRACT The fluid flow patterns generated during the course of tapping operations from Basic Oxy... more ABSTRACT The fluid flow patterns generated during the course of tapping operations from Basic Oxygen Furnaces have been analyzed using two mathematical models of the filling process. The present work is mainly concerned with the application of the κ — ∈ turbulent flow model to describe recirculatory flow in filling ladles. Predicted velocity fields were quite similar to those based on the laminar flow model and both models provided predictions which checked reasonably closely with experimental values using a one tenth scale model. Based on the full scale predictions, it is suggested that the magnitude of flow velocities are technologically significant in terms of their effect on ferro-alloy immersion times.

This project was initiated in October 1990, with the objective of developing and validating a new... more This project was initiated in October 1990, with the objective of developing and validating a new computer model of a recovery boiler furnace using a computational fluid dynamics (CFD) code specifically tailored to the requirements for solving recovery boiler flows, and using improved submodels for black liquor combustion based on continued laboratory fundamental studies. The key tasks to be accomplished were as follows: (1) Complete the development of enhanced furnace models that have the capability to accurately predict carryover, emissions behavior, dust concentrations, gas temperatures, and wall heat fluxes. (2) Validate the enhanced furnace models, so that users can have confidence in the predicted results. (3) Obtain fundamental information on aerosol formation, deposition, and hardening so as to develop the knowledge base needed to relate furnace model outputs to plugging and fouling in the convective sections of the boiler. (4) Facilitate the transfer of codes, black liquid submodels, and fundamental knowledge to the US kraft pulp industry. Volume 5 contains model validation simulations and comparison with data.

Volume 3: Pipeline and Riser Technology; CFD and VIV, 2007

ABSTRACT In order to improve the understanding of the air-lift process a Computational Fluid Dyna... more ABSTRACT In order to improve the understanding of the air-lift process a Computational Fluid Dynamics (CFD) model has been developed. A multi-fluid Eulerian approach is used in the modeling. Three independent interpenetrating phases are considered: a continuous liquid phase (water) and two discrete phases (air bubbles and solid particles). The simulations are conducted two-dimensionally. After the transient computational results have been obtained for a sufficiently long time period, averaging is done to obtain mean values of the flow rates for all the phases. The model has been verified by comparison with published experimental results for the air-lift pipes in the range of 300–450 m in height. Good agreement between experiment and computations has been obtained. The solution process proves to be sufficiently robust for a fairly wide range of particle sizes, densities, flow rates, pipe and injection depths, and inlet volume fractions. Flow analysis reveals the distribution of velocities and volume fractions for all phases inside the airlift pipe that improves our understanding of the process. The computational results highlight some interesting transient behavior of the multiphase flow in the pipe. The numerical model can be utilized during various stages of the design of the air-lift pumps to help answer fundamental questions on the process, and during their operation to select optimal process parameters and to address possible problems.

ABSTRACT This project was initiated in October 1990 with the objective of developing and validati... more ABSTRACT This project was initiated in October 1990 with the objective of developing and validating a new computer model of a recovery boiler furnace using a computational fluid dynamics (CFD) code specifically tailored to the requirements for solving recovery boiler flows, and using improved submodels for black liquor combustion based on continued laboratory fundamental studies. Many of these objectives were accomplished at the end of the first five years and documented in a comprehensive report on that work (DOE/CE/40936-T3, 1996). A critical review of recovery boiler modeling, carried out in 1995, concluded that further enhancements of the model were needed to make reliable predictions of key output variables. In addition, there was a need for sufficient understanding of fouling and plugging processes to allow model outputs to be interpreted in terms of the effect on plugging and fouling. As a result, the project was restructured and reinitiated at the end of October 1995, and was completed in June 1997. The entire project is now complete and this report summarizes all of the work done on the project since it was restructured. The key tasks to be accomplished under the restructured project were to (1) Complete the development of enhanced furnace models that have the capability to accurately predict carryover, emissions behavior, dust concentrations, gas temperatures, and wall heat fluxes; (2) Validate the enhanced furnace models, so that users can have confidence in the results; (3) Obtain fundamental information on aerosol formation, deposition, and hardening so as to develop the knowledge base needed to relate furnace model outputs to plugging and fouling in the convective sections of the boiler; and (4) Facilitate the transfer of codes, black liquor submodels, and fundamental knowledge to the U.S. kraft pulp industry.

One of the tasks in the project was to obtain data from operating recovery boilers for the purpos... more One of the tasks in the project was to obtain data from operating recovery boilers for the purpose of model validation. Another task was to obtain water model data and computer output from University of British Columbia for purposes of benchmarking the UBC model against other codes. In the course of discussions on recovery boiler modeling over the course of

Experimental work and mathematical modeling is carried out to investigate the motion of gas bubbl... more Experimental work and mathematical modeling is carried out to investigate the motion of gas bubbles in moving liquids in low gravity environments typically found in aircraft flying Keplerian parabolas. Experiments are carried out on board the NASA KC-135 and the NAE T-33 in which an aqueous solution of glycerine is stirred in a plexiglass test cell. Air is injected into

Journal of Turbomachinery, 1997

ABSTRACT The fluid mechanics and heat transfer characteristics of film cooling are three-dimensio... more ABSTRACT The fluid mechanics and heat transfer characteristics of film cooling are three-dimensional and highly complex. To understand this problem better, an experimental study was conducted in a low-speed wind tunnel on a row of six rectangular jets injected at 90 deg to the crossflow (mainstream flow). The jet-to-crossflow velocity ratios (blowing ratios) examined were 0.5, 1.0, and 1.5, and the jet spacing-to-jet width ratio was 3.0. No significant temperature difference between jet and crossflow air was introduced. Mean velocities and six flow stresses were measured using a three-component laser-Doppler velocimeter operating in coincidence mode. Seeding of both jet and cross-stream air was achieved with a commercially available smoke generator. Flow statistics are reported in the form of vector plots, contours, and x-y graphs, showing velocity, turbulence intensity, and Reynolds stresses. To complement the detailed measurements, flow visualization was accomplished by transmitting the laser beam through a cylindrical lens, thereby generating a narrow, intense sheet of light. Jet air only was seeded with smoke, which was illuminated in the plane of the light sheet. Therefore, it was possible to record on video tape the trajectory and penetration of the jets in the crossflow. Selected still images from the recordings are presented. Numerical simulations of the observed flow field were made by using a multigrid, segmented, k-∈ CFD code. Special near-wall treatment included a nonisotropic formulation for the effective viscosity, a low-Re model for k, and an algebraic model for the length scale. Comparisons between the measured and computed velocities show good agreement for the nonuniform mean flow at the jet exit plane. Velocities and stresses on the jet centerline downstream of the orifice are less well predicted, probably because of inadequate turbulence modeling, while values off the centerline match those of the experiments much more closely.

Computational Technologies for Fluid/Thermal/Structural/Chemical Systems With Industrial Applications, Volume 2, 2002

ABSTRACT Country-Specific Mortality and Growth Failure in Infancy and Yound Children and Associat... more ABSTRACT Country-Specific Mortality and Growth Failure in Infancy and Yound Children and Association With Material Stature Use interactive graphics and maps to view and sort country-specific infant and early dhildhood mortality and growth failure data and their association with maternal