Variation of Local Void Fraction in Randomly Packed Beds of Equal Spheres

Thadani, M. C.; Peebles, F.N.

doi:10.1021/i260019a012

Cited by 64 publications

(17 citation statements)

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“…The damped oscillatory behavior starting from unity is common to the experimental results and the present ones. However, the experimental curves of porosity have alternate maxima and minima around several integral multiples of the particle radius from the cylindrical wall (4) ; the present simulations show that there are only a few or a little more of the maxima and minima for the case of wall effects (Fig. 4), while about a dozen maxima and minima appear for the case of the floor effects in Fig.…”

Section: Area Porositymentioning

confidence: 50%

“…Benenati and Brosilow (3) presented a similar wall effect for a number of cases with the ratio varying from 2.6 to infinity of the diameter of a cylindrical container to that of the spheres poured into it and concluded that the extent of the wall effect ranges from 4.5 to 5.0 diameters from the wall. For the safe operation of nuclear reactors, Thadani and Peebles (4) investigated the distribution of local void fraction in a bed of randomly packed uniform fuel spheres constructed in a typical model of pebble bed-type reactors.…”

Section: Introductionmentioning

confidence: 99%

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Effects of Cubic Container's Wall or Floor on Random Packing Structures of Spherical Particles

Taguchi

Kurashige²,

Imai³

2006

JSME Int. J., Ser. A

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By computer simulation, we examined how a wall or a floor of a container affects the random packing structure of a cubic aggregate of spherical particles. We constructed a model of the aggregate by sequential accumulation of spheres in a cubic box using (A) cyclic boundary conditions only in the y-direction together with random ups and downs of the box floor to estimate the wall effect and (B) the conditions in both of the horizontal directions to extract the floor effect. Using the obtained packing data, we estimated the "area porosities" and cumulative frequencies of the diameters of circles appearing on some cross sections created by cutting the aggregate at different levels, both as functions of distance from the wall/floor. From these results, we found that the surface effect seems to extend as deep as 2.5 particle diameters from the wall and approximately 4.5 diameters from the floor.

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Section: Area Porositymentioning

confidence: 50%

Section: Introductionmentioning

confidence: 99%

Effects of Cubic Container's Wall or Floor on Random Packing Structures of Spherical Particles

Taguchi

Kurashige²,

Imai³

2006

JSME Int. J., Ser. A

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“…Because of uneven CO 2 Uneven flow has been experimentally observed in packed beds operating with gases [111] and liquids [112,113], and can ruin chromatographic separations [112,113]. Even after correcting the negative effect of undesirable factors such as poor fluid distributor, and poor packing [93], uneven flow persists because of local variations in void fraction [114,115], particularly near the vessel wall;…”

Section: Perspectives and Future Directionsmentioning

confidence: 99%

Extraction of natural compounds using supercritical CO2: Going from the laboratory to the industrial application

Valle¹

2015

The Journal of Supercritical Fluids

108

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“…The void fraction ϵ, which ranges from 0 to 1 describes the packing of the beads inside the cylinder. For macroscopic cylindrical beds, ϵ stabilizes to 0.4 starting 5 D s from the wall (both through model and experiment [30][31][32]). Closer to the wall, the packing varies considerably, with ϵ oscillating between approximately 0.25 and 0.65.…”

Section: Capillary Emitter Designmentioning

confidence: 99%

Microfabricated electrospray emitter arrays with integrated extractor and accelerator electrodes for the propulsion of small spacecraft

Dandavino¹,

Ataman²,

Ryan³

et al. 2014

J. Micromech. Microeng.

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Microfabricated electrospray thrusters could revolutionize the spacecraft industry by providing efficient propulsion capabilities to micro and nano satellites (1–100 kg). We present the modeling, design, fabrication and characterization of a new generation of devices, for the first time integrating in the fabrication process individual accelerator electrodes capable of focusing and accelerating the emitted sprays. Integrating these electrodes is a key milestone in the development of this technology; in addition to increasing the critical performance metrics of thrust, specific impulse and propulsive efficiency, the accelerators enable a number of new system features such as power tuning and thrust vectoring and balancing. Through microfabrication, we produced high density arrays (213 emitters cm−2) of capillary emitters, assembling them at wafer-level with an extractor/accelerator electrode pair separated by micro-sandblasted glass. Through IV measurements, we could confirm that acceleration could be decoupled from the extraction of the spray—an important element towards the flexibility of this technology. We present the largest reported internally fed microfabricated arrays operation, with 127 emitters spraying in parallel, for a total beam of 10–30 µA composed by 95% of ions. Effective beam focusing was also demonstrated, with plume half-angles being reduced from approximately 30° to 15° with 2000 V acceleration. Based on these results, we predict, with 3000 V acceleration, thrust per emitter of 38.4 nN, specific impulse of 1103 s and a propulsive efficiency of 22% with <1 mW/emitter power consumption.

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Variation of Local Void Fraction in Randomly Packed Beds of Equal Spheres

Cited by 64 publications

References 0 publications

Effects of Cubic Container's Wall or Floor on Random Packing Structures of Spherical Particles

Effects of Cubic Container's Wall or Floor on Random Packing Structures of Spherical Particles

Extraction of natural compounds using supercritical CO2: Going from the laboratory to the industrial application

Microfabricated electrospray emitter arrays with integrated extractor and accelerator electrodes for the propulsion of small spacecraft

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