scholarly journals CFD–DEM Simulation of Sand-Retention Mechanisms in Slurry Flow

Energies ◽  
2021 ◽  
Vol 14 (13) ◽  
pp. 3797
Author(s):  
Fatemeh Razavi ◽  
Alexandra Komrakova ◽  
Carlos F. Lange
Keyword(s):  
Fluid Dynamic ◽  
Size Exclusion ◽  
Mass Force ◽  
Slurry Flow ◽  
Sand Filters ◽  
Surface Deposition ◽  
Retention Mechanisms ◽  
Aspect Ratios ◽  
Refined Grid ◽  
Dem Model

The primary motivation of this paper is to investigate the sand-retention mechanisms that occur at the opening of sand filters. Various retention mechanisms under various conditions are explored that have a particulate flow with a low concentration of sand particles (called slurry flow) such as particle shape, size, and concentration. The computational fluid dynamic (CFD)–discrete element method (DEM) model is applied to predict the retention mechanisms under steady flow conditions of the well-bore. By using coupled CFD–DEM (CFD to model the fluid flow, and DEM to model the particle flow), the physics involved in the retention mechanisms is studied. The coarse grid unresolved and the smoothed unresolved (refined grid unresolved) coupling approaches implemented in STAR-CCM+ (SIEMENS PLM) are used to transfer data between the fluid and solid phases and calculate the forces. The filter slots under investigation have different geometries: straight, keystone, wire-wrapped screen (WWS) and seamed slot and the particles are considered with different shapes and different aspect ratios and size distributions. The flow regime is laminar in all simulations conducted. The CFD–DEM model is validated from the perspectives of particle–fluid, particle–particle, and particle–wall interactions. Verification of the CFD–DEM model is conducted by mesh sensitivity analysis to investigate the coupling resolution between the CFD and DEM. By simulation of numerous slurry flow scenarios, three retention mechanisms including surface deposition, size exclusion, and sequential arching of particles are observed. However, the concentration of particles is too diluted to result in multiparticle arch formation. In the simulations, various conditions are tested to give us an insight into the parameters and conditions that could affect the occurrence of the retention mechanisms. As an example, the importance of the gravity force and interaction forces on retention mechanisms are confirmed at the microscale in comparison with others forces involved in retention mechanisms such as the drag force, lift force, cohesive force, buoyancy force, and virtual mass force.

scholarly journals Particle Accumulation Structures in a 5 cSt Silicone Oil Liquid Bridge: New Data for the Preparation of the JEREMI Experiment

2021 ◽  
Vol 33 (2) ◽  
Author(s):  
Paolo Capobianchi ◽  
Marcello Lappa
Keyword(s):  
Liquid Bridge ◽  
Silicone Oil ◽  
Fluid Dynamic ◽  
Solid Particles ◽  
Critical Threshold ◽  
Marangoni Flow ◽  
Disk Radius ◽  
Carrier Fluid ◽  
Aspect Ratios ◽  
Time Periodic

AbstractSystems of solid particles in suspension driven by a time-periodic flow tend to create structures in the carrier fluid that are reminiscent of highly regular geometrical items. Within such a line of inquiry, the present study provides numerical results in support of the space experiments JEREMI (Japanese and European Research Experiment on Marangoni flow Instabilities) planned for execution onboard the International Space Station. The problem is tackled by solving the unsteady non-linear governing equations for the same conditions that will be established in space (microgravity, 5 cSt silicone oil and different aspect ratios of the liquid bridge). The results reveal that for a fixed supporting disk radius, the dynamics are deeply influenced by the height of the liquid column. In addition to its expected link with the critical threshold for the onset of instability (which makes Marangoni flow time-periodic), this geometrical parameter can have a significant impact on the emerging waveform and therefore the topology of particle structures. While for shallow liquid bridges, pulsating flows are the preferred mode of convection, for tall floating columns the dominant outcome is represented by rotating fluid-dynamic disturbance. In the former situation, particles self-organize in circular sectors bounded internally by regions of particle depletion, whereas in the latter case, particles are forced to accumulate in a spiral-like structure. The properties of some of these particle attractors have rarely been observed in earlier studies concerned with fluids characterized by smaller values of the Prandtl number.

Numerical simulation of wind loads on solar panels

2018 ◽  
Vol 32 (12n13) ◽  
pp. 1840009 ◽  
Author(s):  
Kao-Chun Su ◽  
Kung-Ming Chung ◽  
Shu-Tsung Hsu
Keyword(s):  
Fluid Dynamic ◽  
Pressure Coefficient ◽  
Solar Panel ◽  
Wind Loads ◽  
Strong Wind ◽  
Solar Panels ◽  
Wind Uplift ◽  
Aspect Ratios ◽  
Wind Tunnel Data ◽  
Inclined Angle

Solar panels mounted on the roof of a building or ground are often vulnerable to strong wind loads. This study aims to investigate wind loads on solar panels using computational fluid dynamic (CFD). The results show good agreement with wind tunnel data, e.g. the streamwise distribution of mean surface pressure coefficient of a solar panel. Wind uplift for solar panels with four aspect ratios is evaluated. The effect of inclined angle and clearance (or height) of a solar panel is addressed. It is found that wind uplift of a solar panel increases when there is an increase in inclined angle and the clearance above ground shows an opposite effect.

Hydrostatic Gas Journal Bearings for Micro-Turbomachinery

2004 ◽  
Vol 127 (2) ◽  
pp. 157-164 ◽  
Author(s):  
L. X. Liu ◽  
C. J. Teo ◽  
A. H. Epstein ◽  
Z. S. Spakovszky
Keyword(s):  
Natural Frequency ◽  
Analytical Model ◽  
High Speed ◽  
Experimental Testing ◽  
Fluid Dynamic ◽  
Damping Ratio ◽  
Journal Bearings ◽  
Fiber Optic Sensor ◽  
Gas Bearings ◽  
Aspect Ratios

Several years ago an effort was undertaken at MIT to develop high-speed rotating MEMS (Micro Electro-Mechanical Systems) using computer chip fabrication technology. To enable high-power density the micro-turbomachinery must be run at tip speeds of order 500m∕s, comparable to conventional scale turbomachinery. The high rotating speeds (of order 2 million rpm), the relatively low bearing aspect ratios (L∕D<0.1) due to fabrication constraints, and the laminar flow regime in the bearing gap place the micro-bearing designs to an exotic spot in the design space for hydrostatic gas bearings. This paper presents a new analytical model for axially fed gas journal bearings and reports the experimental testing of micro gas bearings to characterize and to investigate their rotordynamic behavior. The analytical model is capable of dealing with all the elements of, (1) micro-devices, (2) dynamic response characteristics of hydrostatic gas bearings, (3) evaluation of stiffness, natural frequency and damping, (4) evaluation of instability boundaries, and (5) evaluation of effects of imbalance and bearing anisotropy. First, a newly developed analytical model for hydrostatic gas journal bearings is introduced. The model consists of two parts, a fluid dynamic model for axially fed gas journal bearings and a rotordynamic model for micro-devices. Next, the model is used to predict the natural frequency, damping ratio and the instability boundary for the test devices. Experiments are conducted using a high-resolution fiber optic sensor to measure rotor speed, and a data reduction scheme is implemented to obtain imbalance-driven whirl response curves. The model predictions are validated against experimental data and show good agreement with the measured natural frequencies and damping ratios. Last, the new model is successfully used to establish bearing operating protocols and guidelines for high-speed operation.

scholarly journals Ultrathin ZSM-5 zeolite nanosheet laminated membrane for high-flux desalination of concentrated brines

2018 ◽  
Vol 4 (11) ◽  
pp. eaau8634 ◽  
Author(s):  
Zishu Cao ◽  
Shixuan Zeng ◽  
Zhi Xu ◽  
Antonios Arvanitis ◽  
Shaowei Yang ◽  
...  
Keyword(s):  
High Performance ◽  
Water Flux ◽  
Dip Coating ◽  
Size Exclusion ◽  
Zeolite Membranes ◽  
Scale Thickness ◽  
Thin Film Sensors ◽  
Aspect Ratios ◽  
Molecular Separation ◽  
Oriented Polycrystalline

The tremendous potential of zeolite membranes for efficient molecular separation via size-exclusion effects is highly desired by the energy and chemical industries, but its practical realization has been hindered by nonselective permeation through intercrystalline spaces and high resistance to intracrystalline diffusion in the conventional zeolite membranes of randomly oriented polycrystalline structures. Here, we report the synthesis of ZSM-5 zeolite nanosheets with very large aspect ratios and nanometer-scale thickness in the preferred straight channel direction. We used these ZSM-5 nanosheets to fabricate ultrathin (<500 nm) laminated membranes on macroporous alumina substrates by a simple dip-coating process and subsequent consolidation via vapor-phase crystallization. This ultrathinb-oriented ZSM-5 membrane has demonstrated extraordinary water flux combined with high salt rejection in pervaporation desalination for brines containing up to 24 weight % of dissolved NaCl. The ZSM-5 nanosheets may also offer opportunities to developing high-performance battery ion separators, catalysts, adsorbents, and thin-film sensors.

Effects of TSV (Through Silicon Via) Interposer/Chip on the Thermal Performances of 3D IC Packaging

2009 ◽  
Author(s):  
John H. Lau ◽  
Gong Yue Tang ◽  
Germaine Yen Yi Hoe ◽  
Xiao Wu Zhang ◽  
Tai Chong Chai ◽  
...  
Keyword(s):  
Fluid Dynamic ◽  
Junction Temperature ◽  
Engineering Practice ◽  
Equivalent Thermal Conductivity ◽  
Through Silicon Via ◽  
Aspect Ratios ◽  
3D Ic Packaging ◽  
Ic Packaging ◽  
Dynamic Analyses

Thermal performances of 3D SiP (system-in-package) with TSV (through silicon via) interposer/chip are investigated based on heat-transfer CFD (computational fluid dynamic) analyses. Emphases are placed on the determination of (1) the equivalent thermal conductivity of interposers/chips with various copper-filled, aluminum-filled, and polymer w/o filler filled TSV diameters, pitches, and aspect ratios, and (2) the junction temperature and thermal resistance of 3D SiP with various TSV parameters. Useful design charts and guidelines are provided for engineering practice convenient.

scholarly journals Tailored CNTs Buckypaper Membranes for the Removal of Humic Acid and Separation of Oil-In-Water Emulsions

Membranes ◽  
2020 ◽  
Vol 10 (5) ◽  
pp. 97
Author(s):  
Eman Elnabawy ◽  
Ibrahim M. A. Elsherbiny ◽  
Ahmed M. A. Abdelsamad ◽  
Badawi Anis ◽  
Abdelwahab Hassan ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Humic Acid ◽  
Membrane Surface ◽  
Pure Water ◽  
Size Exclusion ◽  
Organic Liquids ◽  
Separation Performance ◽  
Aspect Ratios ◽  
Oil In Water ◽  
Wide Range

Carbon nanotubes (CNTs) are a robust material and proven as a promising candidate for a wide range of electronic, optoelectronic and environmental applications. In this work, two different methods were utilized for the preparation of CNTs exhibiting different aspect ratios via chemical vapor deposition (CVD). The as-prepared CNTs were analyzed using scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2adsorption isotherms, thermogravimetric analysis and Raman spectroscopy in order to investigate their morphological and structural properties. Free-standing CNTs “buckypaper” membranes were fabricated, characterized and tailored to meet the requirements of two applications, i.e., (1) the removal of humic acid (HA) from water and (2) separation of oil-in-water emulsions. It was revealed that the hydrophobic buckypapers showed high separation performance for Shell oil-in-water emulsions filtration, with up to 98% through the accumulation of oil droplets onto the membrane surface. The absorption capacity of buckypaper membranes for various organic liquids (oil, chloroform and toluene) was evaluated over 10 absorption cycles to investigate their recyclability and robustness. Moreover, surface modification was introduced to the pristine CNTs to increase their surface hydrophilicity and improve the pure water permeability of buckypapers. These modified buckypapers showed high flux for HA solutions and excellent HA rejection efficiency up to 95%via size exclusion and electrostatic repulsion mechanisms.

scholarly journals Numerical Investigation of the Pressure Drop Characteristics of Isothermal Ice Slurry Flow under Variable Ice Particle Diameter

2020 ◽  
Vol 2020 ◽  
pp. 1-13
Author(s):  
Shehnaz Akhtar ◽  
Taqi Ahmad Cheema ◽  
Haider Ali ◽  
Moon Kyu Kwak ◽  
Cheol Woo Park
Keyword(s):  
Pressure Drop ◽  
Flow Velocity ◽  
Mass Fraction ◽  
Fluid Dynamic ◽  
Particle Diameter ◽  
Ice Slurry ◽  
Slurry Flow ◽  
Two Phase ◽  
Wide Range ◽  
Volumetric Loading

Ice slurry is an advanced secondary refrigerant that has been attracting considerable attention for the past decade due to the growing concerns regarding energy shortage and environmental protection. To stimulate the potential applications of ice slurry, the corresponding pressure drop of this refrigerant must be comprehensively investigated. The flow of ice slurry is a complex phenomenon that is affected by various parameters, including flow velocity, ice particle size, and ice mass fraction. To predict the pressure drop of ice slurry flow in pipes, a mixture computational fluid dynamic model was adopted to simulate a two-phase flow without considering ice melting. The numerical calculations were performed on a wide range of six ice particle sizes (0.1, 0.3, 0.5, 0.75, 1, and 1.2 mm) and ice mass fraction ranging within 5%–20% in the laminar range of ice slurry flow. The numerical model was validated using experimental data. Results showed that the ice volumetric loading and flow velocity have a direct effect on pressure drop; it increases with the increase in volumetric concentration and flow velocity. The findings also confirmed that for constant ice mass fraction and flow velocity, the pressure drop is directly and inversely related to the particle and pipe diameters, respectively. Moreover, the rise in pressure drop is more significant for large ice particle diameter in comparison to smaller size ice particles at high values of ice concentration and flow velocity.

scholarly journals Numerical Simulation of Slurry flow in horizontal pipe based on CFD-DEM

2020 ◽  
Vol 306 ◽  
pp. 01007
Author(s):  
Jinchao Fan ◽  
Benchun Yao ◽  
Yi Hao ◽  
Shimin Zhang ◽  
Xiaoxiao Zhu
Keyword(s):  
Numerical Simulation ◽  
Particle Size ◽  
Pressure Loss ◽  
Pipe Wall ◽  
Flow Characteristics ◽  
Cleaning Process ◽  
Slurry Flow ◽  
Horizontal Pipe ◽  
Particle Accumulation ◽  
Dem Model

In this paper, we propose a novel pipeline cleaning method utilizing slurry. The reason why slurry can be used for pipeline cleaning is that the collisions between the particles and the contaminant in the pipe wall can enhance the cleaning effect. A slurry with polypropylene particles embedded in water is used to cleaning a horizontal pipe is conducted to realize this method. Because the flow characteristics of the slurry is crucial for the cleaning process, it is valuable to conduct a simulation and investigate the influence of several different factors including the convey velocity and the particle size. A 3D CFD-DEM model has been established. The indicators including pressure loss, particle accumulation level at the top of the pipe are choses to characterize the slurry flow and the influence of convey velocity and particle size has been investigated accordingly. In addition, an effective method is proposed to determine the critical convey velocity for each size of the particle.

Hydrostatic Gas Journal Bearings for Micro-Turbomachinery

2003 ◽  
Author(s):  
L. X. Liu ◽  
C. J. Teo ◽  
A. H. Epstein ◽  
Z. S. Spakovszky
Keyword(s):  
Natural Frequency ◽  
Analytical Model ◽  
High Speed ◽  
Experimental Testing ◽  
Fluid Dynamic ◽  
Damping Ratio ◽  
Journal Bearings ◽  
Fiber Optic Sensor ◽  
Gas Bearings ◽  
Aspect Ratios

Several years ago an effort was undertaken at MIT to develop high-speed rotating MEMS (Micro Electro-Mechanical Systems) using computer chip fabrication technology. To enable high-power density the micro-turbomachinery must be run at tip speeds of order 500 m/s, comparable to conventional scale turbomachinery. The high rotating speeds (of order 2 million rpm), the relatively low bearing aspect ratios (L/D &lt; 0.1) due to fabrication constraints, and the laminar flow regime in the bearing gap place the micro-bearing designs to an exotic spot in the design space for hydrostatic gas bearings. This paper presents a new analytical model for axially fed gas journal bearings and reports the experimental testing of micro gas bearings to characterize and to investigate their rotordynamic behavior. The analytical model is capable of dealing with all the elements of, (1) micro-devices, (2) dynamic response characteristics of hydrostatic gas bearings, (3) evaluation of stiffness, natural frequency and damping, (4) evaluation of instability boundaries, and (5) evaluation of effects of imbalance and bearing anisotropy. First, a newly developed analytical model for hydrostatic gas journal bearings is introduced. The model consists of two parts, a fluid dynamic model for axially fed gas journal bearings and a rotordynamic model for micro-devices. Next, the model is used to predict the natural frequency, damping ratio and the instability boundary for the test devices. Experiments are conducted using a high-resolution fiber optic sensor to measure rotor speed, and a data reduction scheme is implemented to obtain imbalance-driven whirl response curves. The model predictions are validated against experimental data and show good agreement with the measured natural frequencies and damping ratios. Last, the new model is successfully used to establish bearing operating protocols and guidelines for high-speed operation.

Evaluation of the Proximal Flow Field to Circular and Noncircular Orifices of Different Aspect Ratios

1997 ◽  
Vol 119 (3) ◽  
pp. 349-356 ◽  
Author(s):  
J. G. Myers ◽  
J. F. Fox ◽  
A. M. Elmahdi ◽  
G. J. Perry ◽  
A. S. Anayiotos
Keyword(s):  
Flow Field ◽  
Evaluation Method ◽  
Fluid Dynamic ◽  
Color Doppler ◽  
Flow Fields ◽  
Approximation Technique ◽  
Valvular Regurgitation ◽  
Aspect Ratios ◽  
Flow Field Characteristics

Investigations of valvular regurgitation attempt to specify flow field characteristics and apply them to the proximal isovelocity surface area (PISA) method for quantifying regurgitant flow. Most investigators assume a hemispherical shape to these equivelocity shells proximal to an axisymmetric (circular) orifice. However, in vivo flow fields are viscous and regurgitant openings vary in shape and size. By using centerline profiles and isovelocity surfaces, this investigation describes the flow field proximal to circular and elliptical orifices. Steady, proximal flow fields are obtained with two- and three-dimensional computational fluid dynamic (CFD) simulations. These simulations are verified by in vitro, laser-Doppler velocimetry (LDV) experiments. The data show that a unique, normalized proximal flow field results for each orifice shape independent of orifice flow or size. The distinct differences in flow field characteristics with orifice shape may provide a mechanism for evaluating orifice characteristics and regurgitant flows. Instead of the hemispherical approximation technique, this study attempts to show the potential to define a universal flow evaluation method based on the details of the flowfield according to orifice shape. Preliminary results indicate that Magnetic Resonance (MR) and Color Doppler (CD) may reproduce these flow details and allow such a procedure in vivo.

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