scholarly journals Gravitational instabilities in binary granular materials

2019 ◽  
Vol 116 (19) ◽  
pp. 9263-9268 ◽  
Author(s):  
Christopher P. McLaren ◽  
Thomas M. Kovar ◽  
Alexander Penn ◽  
Christoph R. Müller ◽  
Christopher M. Boyce
Keyword(s):  
Carbon Capture ◽  
Granular Media ◽  
Gas Flow ◽  
Vertical Vibration ◽  
Contact Forces ◽  
Gravitational Instabilities ◽  
Granular Dynamics ◽  
Granular Mixtures ◽  
Granular Particle ◽  
Gas Channeling

The motion and mixing of granular media are observed in several contexts in nature, often displaying striking similarities to liquids. Granular dynamics occur in geological phenomena and also enable technologies ranging from pharmaceuticals production to carbon capture. Here, we report the discovery of a family of gravitational instabilities in granular particle mixtures subject to vertical vibration and upward gas flow, including a Rayleigh–Taylor (RT)-like instability in which lighter grains rise through heavier grains in the form of “fingers” and “granular bubbles.” We demonstrate that this RT-like instability arises due to a competition between upward drag force increased locally by gas channeling and downward contact forces, and thus the physical mechanism is entirely different from that found in liquids. This gas channeling mechanism also generates other gravitational instabilities: the rise of a granular bubble which leaves a trail of particles behind it and the cascading branching of a descending granular droplet. These instabilities suggest opportunities for patterning within granular mixtures.

A Novel Approach of Retrofitting a Combined Cycle With Post Combustion CO2 Capture

2010 ◽  
Vol 133 (1) ◽  
Author(s):  
Klas Jonshagen ◽  
Nikolett Sipöcz ◽  
Magnus Genrup
Keyword(s):  
Gas Turbine ◽  
Carbon Capture ◽  
Gas Flow ◽  
Carbon Capture And Storage ◽  
Main Tool ◽  
Pressure Level ◽  
Combined Cycle ◽  
Pressurized Water ◽  
Novel Approach ◽  
Gas Turbine Exhaust

Most state-of-the-art natural gas-fired combined cycle (NGCC) plants are triple-pressure reheat cycles with efficiencies close to 60%. However, with carbon capture and storage, the efficiency will be penalized by almost 10% units. To limit the energy consumption for a carbon capture NGCC plant, exhaust gas recirculation (EGR) is necessary. Utilizing EGR increases the CO2 content in the gas turbine exhaust while it reduces the flue gas flow to be treated in the capture plant. Nevertheless, due to EGR, the gas turbine will experience a different media with different properties compared with the design case. This study looks into how the turbomachinery reacts to EGR. The work also discusses the potential of further improvements by utilizing pressurized water rather than extraction steam as the heat source for the CO2 stripper. The results show that the required low-pressure level should be elevated to a point close to the intermediate-pressure to achieve optimum efficiency, hence, one pressure level can be omitted. The main tool used for this study is an in-house off-design model based on fully dimensionless groups programmed in the commercially available heat and mass balance program IPSEPRO. The model is based on a GE 109FB machine with a triple-pressure reheat steam cycle.

scholarly journals Design, Development, and Operation of an Integrated Fluidized Carbon Capture Unit Using Polyethylenimine Sorbents

2018 ◽  
Vol 140 (6) ◽  
Author(s):  
Ronald W. Breault ◽  
Lawrence J. Shadle
Keyword(s):  
Co2 Capture ◽  
Carbon Capture ◽  
Gas Flow ◽  
Gas Adsorption ◽  
Circulation Rate ◽  
Exponential Dependence ◽  
Design Development ◽  
Solid Sorbent ◽  
Process Step ◽  
Pressure Transducers

This paper presents the design, development, and operation of a reactor system for CO2 capture. Modifications were implemented to address differences in sorbent from 180 μm Geldart group B to 115 μm Geldart group A material; operational issues were discovered during experimental trials. The major obstacle in system operation was the ability to maintain a constant circulation of a solid sorbent stemming from this change in sorbent material. The system consisted of four fluid beds, through which a polyamine impregnated sorbent was circulated and adsorption, preheat, regeneration, and cooling processes occurred. Pressure transducers, thermocouples, gas flow meters, and gas composition instrumentation were used to characterize thermal, hydrodynamic, and gas adsorption performance in this integrated unit. A series of shakedown tests were performed and the configuration altered to meet the needs of the sorbent performance and achieve desired target capture efficiencies. Methods were identified, tested, and applied to continuously monitor critical operating parameters including solids circulation rate, adsorbed and desorbed CO2, solids inventories, and pressures. The working capacity and CO2 capture efficiency were used to assess sorbent performance while CO2 closure was used to define data quality and approach to steady-state. Testing demonstrated >90% capture efficiencies and identified the regenerator to be the process step limiting throughput. Sorbent performance was found to be related to the reactant stoichiometry. A stochastic model with an exponential dependence on the relative CO2/amine concentration was used to describe 90% of the variance in the data.

Particula: A simulator tool for computational rock physics of granular media

Geophysics ◽  
2019 ◽  
Vol 84 (3) ◽  
pp. F85-F95 ◽  
Author(s):  
Mustafa A. Al Ibrahim ◽  
Abdulla Kerimov ◽  
Tapan Mukerji ◽  
Gary Mavko
Keyword(s):  
Granular Media ◽  
Rock Physics ◽  
Coherent Noise ◽  
Irregular Shapes ◽  
Granular Dynamics ◽  
Loose Sediments ◽  
Dynamics Simulations ◽  
Grain Surface ◽  
Spherical Grains

Granular dynamics simulations provide insights to the contact-scale physics of loose sediments. However, simulations using identical spherical grains do not reflect characteristics observed in natural sediments, such as pack sorting, grading, grain sphericity, and grain roundness. We have developed software to create 3D grain packs of a range of regular and irregular shapes with geologically realistic variations in sorting and grading. An efficient approach is used to create multiple realizations of nonspherical irregularly shaped grains using coherent noise modification of the spherical grain surface. The discrete-element method is used to assemble the grain pack with different depositional styles by letting grains fall under the influence of gravity. Characterization of various parameters of random loose and dense grain packs, and comparison with previous studies, helps to establish the validity, flexibility, and consistency of the simulator. The output of this software is a digital grain pack, including metadata such as contacts and coordinates, that can be studied further using other analysis tools, e.g., by conducting fluid flow, mechanical, or electrical simulations.

Effect of Interparticle Friction on the Micromechanical Strength Characteristics of Three Dimensional Granular Media

2015 ◽  
Vol 16 ◽  
pp. 79-89
Author(s):  
Karinate Valentine Okiy
Keyword(s):  
Shear Strength ◽  
Principal Stress ◽  
Coordination Number ◽  
Granular Media ◽  
Three Dimensional ◽  
Contact Forces ◽  
Strength Characteristics ◽  
Fabric Anisotropy ◽  
Granular Assemblies ◽  
Interparticle Friction

The role of interparticle friction on the micromechanical strength characteristics of granular assembly subjected to gradual shearing was analyzed. Three dimensional discrete element method (DEM) was applied in the simulation of quasi-static shearing of granular assemblies with varying interparticle frictional coefficients [µ= 0.10, 0.25, 0.50]. From the reported simulation results, analysis of the following was performed for varying interparticle frictional capacities.i. The normal and tangential stress contributions of weak and strong contacts to principal stress components.ii. Contribution of strong and weak contacts to principal and deviator stress.iii. Evolution of mechanical coordination number and fabric anisotropy of strong contact forces.From this analysis, it is safe to conclude that interparticle friction has a direct effect on the major and minor principal stress components in sheared granular assemblies. Consequently, increasing interparticle friction capacity enhances macroscopic shear strength in sheared granular assemblies. Likewise, at the peak shear strength of the sheared granular media, there exists a maximum fabric anisotropy of strong contact forces and this corresponds to a minimum value of mechanical coordination number (minimum possible number of load bearing contacts per particle).

scholarly journals Dynamic behaviors of supersonic granular media under vertical vibration

Ultrasonics ◽  
2006 ◽  
Vol 44 ◽  
pp. e1487-e1489 ◽  
Author(s):  
Kai Huang ◽  
Peng Zhang ◽  
Guoqing Miao ◽  
Rongjue Wei
Keyword(s):  
Granular Media ◽  
Vertical Vibration ◽  
Dynamic Behaviors

Optimal Combined Cycle for CO2 Capture With EGR

2010 ◽  
Author(s):  
Klas Jonshagen ◽  
Nikolett Sipo¨cz ◽  
Magnus Genrup
Keyword(s):  
Gas Turbine ◽  
Carbon Capture ◽  
Gas Flow ◽  
Carbon Capture And Storage ◽  
Main Tool ◽  
Pressure Level ◽  
Combined Cycle ◽  
Pressurized Water ◽  
Reheat Steam ◽  
Gas Turbine Exhaust

Most state-of-the-art natural gas fired combined cycle (NGCC) plants are triple-pressure reheat cycles with efficiencies close to 60 percent. However, with carbon capture and storage, the efficiency will be penalized by almost 10 percent units. To limit the energy consumption for a carbon capture NGCC plant, exhaust gas recirculation (EGR) is necessary. Utilizing EGR increases the CO2 content in the gas turbine exhaust while it reduces the flue gas flow to be treated in the capture plant. Nevertheless, due to EGR, the gas turbine will experience a different media with different properties compared to the design case. This study looks into how the turbo machinery reacts to EGR. The work also discusses the potential of further improvements by utilizing pressurized water rather than extraction steam as the heat source for the CO2 stripper. The results show that the required low-pressure level should be elevated to a point close to the intermediate-pressure to achieve optimum efficiency; hence one pressure level can be omitted. The main tool used for this study is an in-house off-design model based on fully dimensionless groups programmed in the commercially-available heat and mass balance program IPSEpro. The model is based on a GE 109FB machine with a triple-pressure reheat steam cycle.

Vibration analysis of air-bearing work-stage under micro-scale effect

2018 ◽  
Vol 232 (4) ◽  
pp. 521-535
Author(s):  
Dongju Chen ◽  
Lihua Dong ◽  
Ri Pan ◽  
Jinwei Fan ◽  
Chenhui An
Keyword(s):  
Vibration Amplitude ◽  
Gas Flow ◽  
Maximum Amplitude ◽  
Velocity Slip ◽  
Vertical Vibration ◽  
Experimental Result ◽  
Machining Accuracy ◽  
Air Bearing ◽  
Micro Scale ◽  
Scale Factors

Vibration is one of the key factors that influences the ultra-precision machining. Taking the air-bearing work-stage for an example, the vertical vibration of the slide plate will directly affect the surface accuracy of machined parts. There are many factors that affect the vibration of precision machine tools, for example, the fluctuation of gas source, noise, environment, and so on. It will affect the machining accuracy and machining efficiency and cannot work in severe cases. Where the lubrication of the gas film in the air-bearing work-stage is in the micro scale category, its flow characteristics are different from the macroscopic gas flow, and it will also affect the stability of the sliding plate. This paper analyzed the vertical vibration characteristics of the air-bearing work-stage by considering the characteristics of gas film in micro scale when the velocity of the slide plate is 0. Based on the Reynolds equation and the characteristics of gas flow, the stiffness ( K) and the damping ( C) of the gas film are obtained by considering different micro factors. The gas film is assumed as the spring system. Then the stiffness and damping of the gas film are taken into the vibration equation of the slide plate. Through solving the vibration equations, the influence of the micro factor of the fluid on the vibration of the slide plate is researched. The results show that when considering the micro factors of the lubrication gas film, the vibration amplitude of slide plate and the frequency at the maximum amplitude are different from the one in macroscopic without considering any micro factors. At the same thickness of the gas film, the influence of the micro factors on the amplitude of slide plate is largest when three micro scale factors (the first order velocity slip, the flow factor Q and the effective viscosity) are considered. With the increase of the film thickness, the micro scale factors have the little effect on the frequency at the maximum amplitude. By analyzing the dimensionless parameters of the experimental signals and the different simulation signals, we found that when the micro-scale factors are considered at the same time, the vibration amplitude of the slide plate and the frequency at the maximum amplitude are closest to the experimental result. It is proved that combined with the micro scale factor, the analysis of dynamic characteristics of air-bearing work-stage is more accurate.

CORRELATION BETWEEN MICROSTRUCTURE AND YIELD STRESS IN MAGNETICALLY STABILIZED FLUIDIZED BEDS

2010 ◽  
Vol 02 (03n04) ◽  
pp. 185-198
Author(s):  
J. M. VALVERDE ◽  
M. J. ESPIN ◽  
M. A. S. QUINTANILLA ◽  
A. CASTELLANOS
Keyword(s):  
Magnetic Field ◽  
Tensile Strength ◽  
Gas Flow ◽  
Fine Particles ◽  
Contact Forces ◽  
Interparticle Contact ◽  
Gas Velocity ◽  
Jamming Transition ◽  
Interparticle Contacts ◽  
Different Response

A magnetofluidized bed consists of a bed of magnetizable particles subjected to a gas flow in the presence of an externally applied magnetic field. In the absence of magnetic field, there is a given gas velocity at which naturally cohesive fine particles can form a network of permanent interparticle contacts capable of sustaining small stresses. This gas velocity marks the jamming transition of the fluidized bed. For gas velocities above the jamming transition, the bed resembles a liquid. Below the jamming transition, the bed behaves as a weak solid and it has a nonvanishing tensile strength. In the absence of magnetic field, the tensile strength of the solidlike stabilized bed has its only origin in nonmagnetic attractive forces acting between particles. In the presence of a magnetic field, the gas velocity at the jamming transition and the tensile strength of the bed depend on the field strength as a consequence of the magnetostatic attraction induced between the magnetized particles. In this work we present experimental measurements on the jamming transition and tensile strength of magnetofluidized beds of linearly magnetizable fine powders. It is shown that powders with similar magnetic susceptibility but different strength of the nonmagnetic forces show a different response to the magnetic field. This finding can be explained by the influence of the nonmagnetic natural forces on the network of contacts. Thus, our experimental results reported in this paper reinforce the role of short-ranged interparticle contact forces on the behavior of the system, which contrasts with the usual modeling approach in which the magnetofluidized bed is viewed as a continuum medium and a fundamental assumption is that the fields can be averaged over large distances as compared with particle size.

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