Computational investigation of liquid-solid slurry flow through an expansion in a rectangular duct

The flow of a mixture of liquid and solid particles at medium and high volume fraction through an expansion in a rectangular duct is considered. In order to improve the modelling of the phenomenon with respect to a previous investigation (Messa and Malavasi, 2013), use is made of a two-fluid model specifically derived for dense flows that we developed and implemented in the PHOENICS code via user-defined subroutines. Due to the lack of experimental data, the two-fluid model was validated in the horizontal pipe case, reporting good agreement with measurements from different authors for fully-suspended flows. A 3D system is simulated in order to account for the effect of side walls. A wider range of the parameters characterizing the mixture (particle size, particle density, and delivered solids volume fraction) is considered. A parametric analysis is performed to investigate the role played by the key physical mechanisms on the development of the two-phase flow for different compositions of the mixture. The main focuses are the distribution of the particles in the system and the pressure recovery

A combined CFD-experimental method for abrasive erosion testing of concrete

Serious damage may occur to concrete hydraulic structures, such as water galleries, spillways, and stilling basins, due to the abrasive erosion caused by the presence of solid particles in the flow. This underlines the importance of being capable in providing characterization of the concrete from the point of view of its vulnerability to abrasive erosion, in order to improve the design of the structure and the material selection. Nevertheless, the existing apparatus for concrete abrasive erosion testing are either far from allowing realistic simulation of the actual environment in which this phenomenon occurs, or show a large degree of complexity and cost. An alternative method has been developed with the aid of Computational Fluid Dynamics (CFD). CFD was first employed to verify the effectiveness of a new laboratory equipment. Afterwards, a parameter has been introduced which, by successful comparison against preliminary experiments, proved suitable to quantify the effect of the fluid dynamic conditions on the concrete abrasive erosion, thereby opening the way to CFD-based customization of the apparatus. In the future, the synergy of numerical and physical modelling will allow developing predictive models for concrete erosion, making it possible to reliably simulate real structures

Numerical Prediction of Particle Distribution of Solid-Liquid Slurries in Straight Pipes and Bends

Turbulent solid-liquid slurry flows in pipes are encountered in many engineering fields, such as mining. In particular, the distribution of the solids is a serious concern to engineers, but its determination involves considerable technical and economic difficulties. A two-fluid model for the numerical prediction of this parameter is presented. The model is robust and numerically stable, and requires relatively low computer time to provide converged steady-state solution. The novelty of the proposed model and its better performance compared to similar ones resides in the method of accounting for some key physical mechanisms governing these flows, namely turbulent dispersion, interphase friction, and viscous and mechanical contributions to friction. The model is first validated by comparison with many experimental data available in literature regarding the horizontal pipe case over a wide range of operating conditions: delivered solid volume fraction between 9 and 40%; slurry velocity between 1 m/s and 5.5 m/s; and pipe diameter between 50 and 160 mm. A further comparison was performed with respect to recent experiments concerning a horizontal 90° bend

Computational Fluid Dynamics Modelling of Liquid–Solid Slurry Flows in Pipelines: State-of-the-Art and Future Perspectives

Slurry pipe transport has directed the efforts of researchers for decades, not only for the practical impact of this problem, but also for the challenges in understanding and modelling the complex phenomena involved. The increase in computer power and the diffusion of multipurpose codes based on Computational Fluid Dynamics (CFD) have opened up the opportunity to gather information on slurry pipe flows at the local level, in contrast with the traditional approaches of simplified theoretical modelling which are mainly based on a macroscopic description of the flow. This review paper discusses the potential of CFD for simulating slurry pipe flows. A comprehensive description of the modelling methods will be presented, followed by an overview of significant publications on the topic. However, the main focus will be the assessment of the potential and the challenges of the CFD approach, underlying the essential interplay between CFD simulations and experiments, discussing the main sources of uncertainty of CFD models, and evaluating existing models based on their interpretative or predictive capacity. This work aims at providing a solid ground for students, academics, and professional engineers dealing with slurry pipe transport, but it will also provide a methodological approach that goes beyond the specific application

A CFD-based method for slurry erosion prediction

The numerical prediction of the impact erosion produced by slurries is particularly challenging from the modeling point of view, not only due to the complex interactions between the phases, but also because self-induced geometry changes can influence the course of the wear process. The usual methodology for impact erosion estimation, which is based on the Eulerian-Lagrangian description of the slurry flow followed by the application of a single-particle erosion model to each particle-wall impingement, may be able to reproduce the complex physics underlying slurry erosion only at the price of complex algorithms and heavy computation, which is unaffordable in practical applications. In order to overcome these difficulties, an alternative approach was proposed, which involved the steady-state simulation of the slurry flow by an Euler-Euler model followed by the repeated calculation of individual particle trajectories in the proximity of the solid walls and the continuous update of the wear profile. The improved accuracy obtained in the simulation of several abrasive jet impingement experiments reported in the literature make the application of this method to more complex flows very promising

Improvements in the numerical prediction of fully-suspended slurry flow in horizontal pipes

A new two-fluid model is presented for the simulation of fully-suspended liquid-solid slurry flows in horizontal pipes. The model is a significant upgrade of an earlier one [G.V. Messa, M. Malin, S. Malavasi, Powder Technol. 256 (2014), 61???70], and the main improvements concern the use of: (1) a new wall boundary condition for the solid phase (2) a more general correlation for the viscosity of the mixture, which allows accounting for particle shape; (3) a different solution algorithm, which reduces significantly the already low computational burden. By comparison with experimental data available in the literature regarding sand???water slurries, the model showed wider applicability compared to the earlier one. In particular, the validation was carried out for the following flow conditions: pipe diameter between 50 and 200 mm; particle size between 90 and 640 ??m; mean delivered solid concentration up to 40% by volume; and slurry superficial velocity up to 9 m/s. Slurries in which the dispersed phase consists of spherical glass beads have been briefly explored too. The improvements considerably increase the accuracy of the pressure gradient predictions, without affecting the model's capability in reproducing the other features of these flows of most engineering interest, namely solid volume fraction distribution and velocity distribution

Numerical investigation of solid-liquid slurry flow through an upward-facing step

The flow of a solid-water mixture through an upward-facing step in a channel is numerically investigated. The effect of expansion ratio, mean solids volume fraction and particle diameter on the velocity field, pressure distribution and solid volume fraction field is studied. Expansion ratios of 0.50 and 0.67, particle diameter of 125 mu m and 440 mu m and mean solid volume fraction between 0.05 and 0.20 are considered. Particle density is 2465 kg m(-3). An Eulerian two-fluid model is used to simulate the flow. Due to the lack of experimental data, the model was validated by comparison to other numerical investigations and to experimental data about the horizontal pipe case. Afterwards, it is studied the effect of the above mentioned parameters upon the degree of coupling between the phases and the extension of the disturbance region in the pressure and solid volume fraction fields downstream the step. Parameters of engineering interest, such as the reattachment length and the pressure recovery downstream the enlargement, are investigated

Computational investigation of liquid-solid slurry flow through an expansion in a rectangular duct

The flow of a mixture of liquid and solid particles at medium and high volume fraction through an expansion in a rectangular duct is considered. In order to improve the modelling of the phenomenon with respect to a previous investigation (Messa and Malavasi, 2013), use is made of a two-fluid model specifically derived for dense flows that we developed and implemented in the PHOENICS code via user-defined subroutines. Due to the lack of experimental data, the two-fluid model was validated in the horizontal pipe case, reporting good agreement with measurements from different authors for fully-suspended flows. A 3D system is simulated in order to account for the effect of side walls. A wider range of the parameters characterizing the mixture (particle size, particle density, and delivered solid volume fraction) is considered. A parametric analysis is performed to investigate the role played by the key physical mechanisms on the development of the two-phase flow for different compositions of the mixture. The main focuses are the distribution of the particles in the system and the pressure recover

A numerical strategy to account for the effect of self-induced geometry changes in wear estimation

The erosion of a surface impinged by solid particles dragged by a liquid is a serious concern in the oil&gas industry. Recent experiments indicate that the changes in the geometry produced by the erosion may significantly alter the evolution of the erosion process itself. This typically happens when a surface is exposed to aggressive flow condition for a prolonged period, and it becomes a significant issue for complex devices such as valves. However, none of the predictive techniques available at present, which mainly involve the use of algebraic erosion correlations in conjunction with an Eulerian-Lagrangian model, appears capable in handling this phenomenon. In this study, we propose a numerical strategy that allows accounting for the effect of the self-induced geometry changes on the wear estimates. The evolution of the erosion process is estimated by an effective post-processing technique applied to the solution of a steady-state Eulerian-Lagrangian simulation. The good agreement between our predictions and experimental data available in the literature regarding an abrasive jet impingement test makes the application of this strategy to more complex flows very promising

Analysis and discussion of two fluid modelling of pipe flow of fully suspended slurry

Thanks to the advancements in computer power and capability of Computational Fluid Dynamics codes, the amount of research work on the numerical simulation of slurry flows in pipelines has increased exponentially in few years, opening the way to the use of this approach for engineering purposes. The Two Fluid Model (TFM), in which both phases are interpreted as interpenetrating continua and solved in the Eulerian, cell-based framework, allows the best compromise considering the engineering requirements of computational efficiency, applicability, and accuracy. However, the solution of this model is affected by several numerical and modelling factors, and, even if good agreement is achieved between simulation results and experimental measurements, it might be difficult to trust the predictions outside the validation conditions, thereby limiting the engineering potential of the two-fluid approach. The fully-suspended slurry flow in horizontal pipes was numerically simulated using the TFM recently developed by one of the authors of this paper, and the computational results were compared to experimental data reported in the literature. It has been clearly demonstrated that, even in this simple geometry, many possible sources of inaccuracy and uncertainty come into play. Whilst assessing their role, best practice guidelines and consistency checks were proposed to improve the accuracy of the estimates and increase the reliability of the TFM solution. Afterwards, pipe size-up scaling tests and a careful specification of the applicability conditions provided further confidence to the use of the TFM as a tool for engineering design