Vibration induced segregation of single large particles

The vibration-induced segregation (e.g., rising of one large intruder - so called Brazil Nut Effect (BNE)) is studied by discrete element method. Vibration frequency and amplitude are two dominating factors in the occurrence of BNE and a phase diagram is constructed. For fixed vibration amplitude, segregation only occurs when vibration frequency is within a certain range. Larger vibration amplitude can expand the range of vibration frequency for BNE. Size ratio and the intruder shape are studied under certain vibration conditions. Larger size ratio can enlarge the segregation intensity. The shape of the intruder influences the segregation process by the intruder′s orientation. Standing-like initial orientation can increase the time required for the intruder to reach the top while lying-like initial orientation cannot significantly affect the vertical segregation.

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CYCLIC SEGREGATION STATE IN VERTICALLY VIBRATED BINARY GRANULAR MIXTURES

Modern Physics Letters B ◽

10.1142/s0217984914500201 ◽

2014 ◽

Vol 28 (03) ◽

pp. 1450020

Author(s):

QINGFAN SHI ◽

BEICHENG PAN ◽

CHANGHONG LU ◽

GANG SUN

Keyword(s):

Phase Diagram ◽

Atmospheric Pressure ◽

Air Flow ◽

Brazil Nut ◽

Positive Role ◽

Structure Changes ◽

Granular Mixtures ◽

Segregation Process ◽

Acceleration Amplitude ◽

Brazil Nut Effect

In this paper, the vertically vibrated binary granular mixtures at atmospheric pressure are studied experimentally. We find a nonstationary segregation state, of which the structure changes with time cyclically. The period of the cyclic segregation is measured and its variation with the vibration conditions is shown. The transition between the segregation states is also discussed, and a phase diagram on the plot of frequency against acceleration amplitude is given. In order to observe the effect of air flow in the segregation process, an alternative container with ventilated bottom is designed. Our experiments show that both regions of the Brazil nut segregation state and the cyclic segregation state shrink obviously by use of the latter container and disappear completely if the whole system is placed in vacuum. These results testify that the air pressure plays a positive role in both the Brazil nut effect and cyclic segregation.

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A modified calculation of particle buoyant forces in vibro-fluidized beds

EPJ Web of Conferences ◽

10.1051/epjconf/202124903047 ◽

2021 ◽

Vol 249 ◽

pp. 03047

Author(s):

Zhixiong Zhang ◽

Xihua Chu ◽

Yanran Wang

Keyword(s):

Large Particle ◽

Brazil Nut ◽

Flow Conditions ◽

Buoyant Force ◽

Segregation Behavior ◽

Particle Size Ratio ◽

Segregation Process ◽

Brazil Nut Effect ◽

Effect Of Particle Size ◽

The Difference

Segregation of granular materials under vibration or flow conditions such as the Brazil nut effect has been well known, however, there is yet no consensus mechanisms to explain this phenomenon. This study attempts to investigate particle buoyant forces in the segregation process. To explain the difference of the segregation behavior for the large particle with different size, a modified calculation method of particle buoyant force is suggested for considering the effect of particle size ratio. A simple verification illustrates its validity.

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Qualitative Observations of Dense Particle Motion in a Vibration-Excited Granular Bed

Volume 7: Engineering Education and Professional Development ◽

10.1115/imece2007-42306 ◽

2007 ◽

Cited By ~ 1

Author(s):

Timothy B. Morgan ◽

Theodore J. Heindel

Keyword(s):

Particle Motion ◽

Large Particle ◽

Granular Media ◽

Brazil Nut ◽

Dense Particle ◽

Brazil Nuts ◽

Bed Height ◽

X Ray Imaging ◽

Large Particles ◽

Brazil Nut Effect

The Brazil nut effect is a classic phenomenon in which larger objects typically migrate to the top of a bed of smaller granular media when exposed to vibration. An example of this phenomenon is finding Brazil nuts on the top of a can of mixed nuts. In this study, the Brazil nut problem is simulated by submerging a large particle in a bed of granular media and then subjecting the system to vibration. Stereoscopic X-ray imaging is used to visualize the large particle motion. These images are then compiled into movies where the particle motion may be tracked. Observations of the large particle motion are made under varying conditions of large particle material, vibration frequency, and bed height. Particle percolation, where smaller particles fill small voids beneath the large particles, is the dominate mechanism at higher vibration frequencies. However, as the frequency decreases, or as the disparity between the densities of the large and small particles decrease, the effects of convection become more pronounced.

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DEM Study on the Segregation of a Non-Spherical Intruder in a Vibrated Granular Bed

Processes ◽

10.3390/pr9030448 ◽

2021 ◽

Vol 9 (3) ◽

pp. 448

Author(s):

Jinpeng Qiao ◽

Kejun Dong ◽

Chenlong Duan

Keyword(s):

Aspect Ratio ◽

Vibration Frequency ◽

Vibration Amplitude ◽

Granular Temperature ◽

Equivalent Diameter ◽

Granular Bed ◽

Small Particles ◽

Porosity Variation ◽

Segregation Process ◽

Prolate Shape

The segregation process of a single large intruder in a vibrated bed of small particles has been widely studied, but most previous studies focused on spherical intruders. In this work, the discrete element method was used to study the effects of vibration conditions and intruder shape on the dimensionless ascending velocity (va) of the intruder. The intruder was in a prolate shape with aspect ratio varied but its equivalent diameter fixed. Three equivalent diameters, namely volume-equivalent diameter, surface-area-equivalent diameter, and Sauter diameter, were used. It was found that va increases and then decreases with the rise of the dimensionless vibration amplitude (Ad) and the dimensionless vibration frequency (fd), and va increases with the decrease of the sphericity of the intruder (Φ). Moreover, the porosity variation in the vibrated bed and the granular temperature were analyzed, which can be linked to the change of va. It was further found that va can be uniformly correlated to Ad‧f 0.5 d, while the critical change of the response of va to Ad and fd occurs at Γ = 4.83, where Γ is the vibration intensity. Based on these findings, a piecewise equation was proposed to predict va as a function of Ad, fd, and Φ.

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Effect of Number of Bars and Reciprocation Speed on Residence Time of Particles on a Moving Grate

2013 21st Annual North American Waste-to-Energy Conference ◽

10.1115/nawtec21-2735 ◽

2013 ◽

Author(s):

Masato R. Nakamura ◽

Jason Singh

Keyword(s):

Diffusion Coefficient ◽

Residence Time ◽

Waste To Energy ◽

Particle Sizes ◽

Brazil Nut ◽

Combustion Chambers ◽

Particle Mixing ◽

Large Particles ◽

Brazil Nut Effect ◽

The Mean

The moving grate systems of waste-to-energy (WTE) mass-burn combustion chambers are designed for providing efficient flow and mixing of the municipal solid waste (MSW) over the length of the grade. This study presents results from a numerical analysis of the effect of number of reciprocating bars and reciprocation speed on the degree of mixing and residence time of MSW particles on the grate. A particle-based bed model of MSW and a physical model of reverse-acting grate were used in order to quantify the mixing diffusion coefficient of MSW particles. We analyzed the particle mixing with different parameters: particle size (d = 6–22cm diameter), reciprocation speed of moving bars (Rr = 0–90recip./h), and number of moving bars (Nb = 0 to 16 bars). This combination of mathematical modeling and experimental work has shown that: (1) different particle sizes result in different residence times, according to the Brazil Nut Effect (BNE) (2) The number of moving bars (from 0 to 16 bars) of a reverse-acting grate has the net effect of increasing the mean residence time of small and medium sized particles, while decreasing that of large particles. (3) The bar height, h, was found to be one of the major geometric parameters influencing mixing diffusion coefficient, D, and residence time.

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The water-enhanced Brazil nut effect

EPL (Europhysics Letters) ◽

10.1209/0295-5075/91/54001 ◽

2010 ◽

Vol 91 (5) ◽

pp. 54001 ◽

Cited By ~ 24

Author(s):

C. P. Clement ◽

H. A. Pacheco-Martinez ◽

M. R. Swift ◽

P. J. King

Keyword(s):

Brazil Nut ◽

Brazil Nut Effect

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A Horizontal Brazil-Nut Effect and Its Reverse

Physical Review Letters ◽

10.1103/physrevlett.95.028001 ◽

2005 ◽

Vol 95 (2) ◽

Cited By ~ 41

Author(s):

T. Schnautz ◽

R. Brito ◽

C. A. Kruelle ◽

I. Rehberg

Keyword(s):

Brazil Nut ◽

Brazil Nut Effect

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Microbial Brazil nut effect

Soft Matter ◽

10.1039/d1sm01327k ◽

2021 ◽

Author(s):

Atul Srivastava ◽

Kenji Kikuchi ◽

Takuji Ishikawa

Keyword(s):

Granular Medium ◽

Brazil Nut ◽

Large Object ◽

Intuitive Process ◽

Brazil Nut Effect

The Brazil nut effect (BNE) is a counter-intuitive process of segregation of a large object inside a vibrated granular medium (GM), which has been studied widely by subjecting GMs to...

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