Packing spherical discrete elements for large scale simulations

2014

Powder Technology

Discrete element modelling of the packing of spheres and its application to the structure of porous metals made by infiltration of packed beds of NaCl beads. Powder Technology, Access from the University of Nottingham repository: http://eprints.nottingham.ac.uk/34443/7/DEM%20porous%20metals%20-%20Powder %20Technology.pdf Copyright and reuse:The Nottingham ePrints service makes this work by researchers of the University of Nottingham available open access under the following conditions. This article is made available under the Creative Commons Attribution Non-commercial No Derivatives licence and may be reused according to the conditions of the licence. For more details see: http://creativecommons.org/licenses/by-nc-nd/2.5/ A note on versions:The version presented here may differ from the published version or from the version of record. If you wish to cite this item you are advised to consult the publisher's version. Please see the repository url above for details on accessing the published version and note that access may require a subscription. AbstractA numerical model, using the discrete element method, has been developed to quantify specific parameters that are pertinent to the packing behaviour of relatively large, spherical NaCl beads and mixtures of beads of different sizes. These parameters have been compared with porosity and connectivity measurements made on porous aluminium castings made by molten metal infiltration into packed beds of such beads, after removal of the NaCl by dissolution. DEM has been found to accurately predict the packing fraction for salt beads with both monosized and binary size distributions and from this the pore fractions in castings made by infiltration into packed beds of beads could be predicted. Through simple development of the condition for contacting of neighbouring beads, the number of windows linking neighbouring pores, and their size, could also be predicted across a wide range of small bead additions. The model also enables an insight into the mixing quality and changes in connectivity introduced through the addition of small beads. This work presents significant progress towards the delivery of a 2 simulation-based approach to designing preform architectures in order to tailor the resulting porous structures to best suit specific applications. KeywordsDiscrete element method; particle packing; coordination number; porous metals; IntroductionPorous metals exhibit important characteristics which enable them to perform well in heat transfer applications. The high thermal conductivity of solid ligaments, the large surface area to volume ratios and their tortuous flow paths, which generate turbulence and high level-mixing in the cooling fluid, offer the potential for devices made from porous metals (for example high power electronic devices [1,2], heat shields, regenerators for thermal engines and thermal energy storage devices incorporating phase change materials [3]) to be compact, efficient and light weight.Experimental measurement and modelling [4][5][6][7] have sho...

Section: Overview Of Cast Porous Metal Structuressupporting

confidence: 90%

mentioning

confidence: 99%

Discrete element modelling of the packing of spheres and its application to the structure of porous metals made by infiltration of packed beds of NaCl beads

Langston

2014

Powder Technology

“…The "window" connections between pores are formed due to the inability of the PEEK powder (even after melting) to penetrate the regions between and in the vicinity of contacting salt beads. The number of connections is dictated by the coordination number for packing of the beads, which is between 5 and 6 for loose and dense random packing [27][28]. Typically 2 to 3 such windows can be seen in sectioned pores.…”

Section: Porous Structuresmentioning

confidence: 99%

“…Using spherical beads with a reasonably tight size range results in a homogenous network that is unlikely to have inaccessible areas of clustered porogen (as is likely to be the case for angular particles with a wide size distribution). The tapping process also pre-establishes the inter-particle contacts which are well-defined due to the repeatable and predictable loose or dense random packing characteristics for near-monosized spherical particles [27,28]. The level of interconnectivity achieved by tapping is sufficient, as measured by the connectivity density, to not require an additional sintering step.…”

Section: Benefits Of the Tapping Processmentioning

confidence: 99%

Porous poly-ether ether ketone (PEEK) manufactured by a novel powder route using near-spherical salt bead porogens: Characterisation and mechanical properties

Siddiq

Materials Science and Engineering: C

2015

Porous PEEK structures with approximately 85% open porosity have been made using PEEK-OPTIMA® powder and a particulate leaching technique using porous, near-spherical, sodium chloride beads. A novel manufacturing approach is presented and compared with a traditional dry mixing method. Irrespective of the method used, the use of near-spherical beads with a fairly narrow size range results in uniform pore structures. However the integration, by tapping, of fine PEEK into a pre-existing network salt beads, followed by compaction and "sintering", produces porous structures with excellent repeatability and homogeneity of density; more uniform pore and strut sizes; an improved and predictable level of connectivity via the formation of "windows" between the cells; faster salt removal rates and lower levels of residual salt. Although tapped samples show a compressive yield stress > 1 MPa and stiffness > 30 MPa for samples with 84% porosity, the presence of windows in the cell walls means that tapped structures show lower strengths and lower stiffnesses than equivalent structures made by mixing.

“…The coordination number and window radius are defined in separate equations, the coordination number as a function of the packing fraction (also shown in Eq 1), and the window radius in terms of the infiltration pressure and particle (pore) size. The model in [5] reduces to the same expression for permeability for the case of dense random particle packing if Nc = 6 (which is not atypical of this packing condition [7,8] Reasonable correlation between experimental measurements of permeability and the models was observed in both cases, with deviations attributed, in part, to the non-spherical nature of some of the salt particles used. Thus a strong dependence upon the size of the windows connecting the pores and the permeability is apparent and controlling the window size, through varying the infiltration pressure [6] has the capacity (for a given pore size) to vary the permeability by more than a factor of 10 and would be more convenient way to vary the permeability rather than by altering the packing (porosity) through additional and potentially costly processing steps.…”

mentioning

confidence: 92%

The permeability of virtual macroporous structures generated by sphere packing models: Comparison with analytical models

Otaru

2016

Scripta Materialia

The permeability of virtual macroporous structures generated by sphere packing models: comparison with analytical models. Scripta Materialia, 124 . pp. 30-33. ISSN 1359-6462 Access from the University of Nottingham repository: http://eprints.nottingham.ac.uk/34471/1/DEM%20CFD%20-%20scripta%20mat.pdf Copyright and reuse:The The version presented here may differ from the published version or from the version of record. If you wish to cite this item you are advised to consult the publisher's version. Please see the repository url above for details on accessing the published version and note that access may require a subscription. AbstractRealistic porous structures typical of those made by replication of packed beds of spherical particles have been produced by a novel modelling method. Fluid dynamics simulation of the permeability of these structures agrees well with experimental measurements and similar modelling of structures derived from X-ray tomographic images. By varying the model structures the "bottleneck" flow concept proposed by analytical models in the literature was substantiated, confirming the high dependence of permeability on the size of the windows connecting the pores but also highlighting the need for accurate determination of the connectivity of the pores for these models to be accurate.