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Discrete element modeling and computational fluid dynamics approach to determination of tortuosity through packed bed of crushed rock particles
Thesis (MEng)--Stellenbosch University, 2023.
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| Format: | Thesis |
| Language: | en_ZA |
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Stellenbosch : Stellenbosch University
2023
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| _version_ | 1867614098205704192 |
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| access_status_str | Open Access |
| author | Piwang, Howard |
| author2 | Hoffmann, Jaap E. |
| author_browse | Hoffmann, Jaap E. Piwang, Howard |
| author_facet | Hoffmann, Jaap E. Piwang, Howard |
| author_sort | Piwang, Howard |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Thesis (MEng)--Stellenbosch University, 2023. |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/127381 |
| institution | Stellenbosch University (South Africa) |
| language | en_ZA |
| last_indexed | 2026-06-10T12:46:38.139Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2023 |
| publishDateRange | 2023 |
| publishDateSort | 2023 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/127381 Discrete element modeling and computational fluid dynamics approach to determination of tortuosity through packed bed of crushed rock particles Piwang, Howard Hoffmann, Jaap E. Sebitosi, Ben Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering. Computational fluid dynamics Solar thermal energy Renewable energy sources UCTD Thesis (MEng)--Stellenbosch University, 2023. ENGLISH SUMMARY: The use of packed beds of crushed rocks has been applied in thermal energy storage, as seen in the Stellenbosch University Solar Power Thermodynamic cycle (SUNSPOT). The SUNSPOT is a combined solar power cycle that uses the Brayton cycle which has been favorable in power plants for peak load duty during ramping. For CSP, integrating rock beds as thermal storage holds the potential to be a useful and fairly priced thermal storage technology. However, packed beds of rocks are irregular, with varying particle shapes and orientations. Previous works report that particle properties of shape, size, and roughness have a substantial impact on flow resistance in packed beds. In addition, the rocks are irregularly shaped, making it very difficult to formulate pressure drop correlations. Recent studies adopted the use of ellipsoids to mathematically represent crushed rocks to estimate the pressure drop. However, the use of an anisotropic resistance approach has been able to reasonably approximate pressure drop since it can consider multiphase flow simulations. Previous works used Discrete Element Modeling (DEM) and Computational Fluid Dynamics (CFD) to understand and analyze the physical conditions of packed beds while adopting various physical changes to predict the anisotropic nature of packed beds. However, the simulations of fluid flow underestimated the flow resistance across a packed bed. Therefore, this study, in an effort to reduce the deviation of pressure drop between real and simulated packed beds, introduces the tortuosity parameter tensor. The tortuosity parameter was determined by the use of DEM and CFD models. DEM model was used to generate a packed bed with minimum statistical uncertainty as the experimental packed bed of ellipsoids. The CFD was used to simulate fluid flow. DEM/CFD models can capture the physics in the porous media more than the plug flow resistance approach. The actual length taken by the fluid flowing through the porous media is generated as path lines. The lengths of these path lines are then utilized to determine the tortuosity of the porous material. Also, an easy local volumetric integral tortuosity is determined by extracting velocity magnitude and the velocity along the ydirection. The extracted local tortuosity averagely deviated by 6.06 % from the path line approach. However, as velocity increased from 0.04 m/s to 0.10 m/s, the deviation between the path line approach and the volumetric technique was very close. A satisfactory variation at a higher velocity greatly improved the tortuosity parameter between the two techniques. Therefore, the less cumbersome volumetric technique could be used for higher velocities to determine tortuosity. The results from the path line methods were validated with experimental diffusion tortuosity. The deviation between the path line approach and the experiment reported a maximum deviation of 16 % and a lowest of 14 %. The experiment deviated further from the volumetric approach than the path line technique. Accounting for uncertainty in the experiment, an R-squared greater than 0.95 of the modeled concentration was used to give confidence in the validation experiment. AFRIKAANSE OPSOMMING: Die gebruik van gepakte beddens van gebreekte klip is toegepas in termiese energieberging soos gesien in die Universiteit Stellenbosch Sonkrag Termodinamiese siklus (SUNSPOT). Die SUNSPOT is 'n gekombineerde sonkrag kringloop wat ‘n Brayton-siklus gebruik wat gunstig was in kragsentrales vir piekvragdiens tydens sonlig ure. Vir CSP hou die integrasie van rotsbeddens en termiese berging die potensiaal in om 'n nuttige en billike geprysde termiese bergingstegnologie te wees. Gebreekte klip is egter onreelmatig, met verskillende partikelvorms en -orientasies. Vorige werke meld dat deeltjie-eienskappe van vorm, grootte en grofheid 'n wesenlike impak op die drukval oor gepakte beddens het. Boonop is die klippe onreelmatig gevorm, wat dit baie moeilik maak om drukvalkorrelasies te formuleer. Onlangse studies het die gebruik van ellipsoiede aangeneem om gebreekte rotse wiskundig voor te stel om die drukval te skat. Die gebruik van 'n anisotropiese-weerstandsbenadering kon egter drukval redelik benader, aangesien dit meerfasevloeisimulasies kan oorweeg. Vorige werke het Diskrete Element Modellering (DEM) en Berekeningsvloeidinamika (CFD) gebruik om die fisiese toestande van gepakte beddens te verstaan en te ontleed, terwyl verskeie fisiese veranderinge aangeneem is om die anisotropiese aard van gepakte beddens te voorspel. Die simulasies van die vloei het egter die vloeiweerstand oor 'n gepakte bed onderskat. Daarom stel hierdie studie 'n poging voor om die afwyking van drukval tussen werklike en gesimuleerde gepakte beddens te verminder deur die tortuositeit tensor as ʼn parameter van die oplossing in te bring. Die tortuositeit is bepaal deur die gebruik van DEM en CFD modelle. DEM model is gebruik om 'n gepakte bed met minimum statistiese onsekerheid te genereer as die eksperimentele gepakte bed van ellipsoiede. CFD is gebruik om vloeistofvloei te simuleer. DEM/CFD-modelle kan die fisika in die porieuse media beter vasvang as die propvloei weerstandsbenadering. Die padlyne vir die vloei deur die bed is uit die CFD data onttrek. Die gemiddelde lengte van die padlyne gedeel deur die bed lengte wat deur deeltjies beset word, is een benadering vir tortuositeit. 'n Tweede, en makliker benadering is om die volume-integraal van die grootte van die snelheidsvektor gedeel deur sy ykomponent te onttrek. Die volume-intergaal metode en die padlyn benadering gee antwoorde binne 6.06 % van mekaar. Die verskil is onsensitief vir die snelheid tussen 0.04 m/s en 0.10 m/s. 'n Bevredigende variasie teen 'n hoer snelheid het die tortuositeitsparameter tussen die twee tegnieke aansienlik verbeter. Daarom kan die minder omslagtige volumetriese tegniek gebruik word vir hoer snelhede om tortuositeit te bepaal. Die resultate van die padlynmetodes is met eksperimente, wat van ʼn derde metode om tortuositeit te meet, naamlik diffusie, gevalideer. Die afwyking tussen die padlynbenadering en die eksperiment het 'n maksimum afwyking van 16 % en 'n laagste van 14 % gerapporteer. Die eksperiment het selfs verder afgewyk van die volumetriese benadering as die padlyntegniek. Met inagneming van onsekerheid in die eksperiment, is 'n R-kwadraat groter as 0.95 van die gemodelleerde konsentrasie gebruik om vertroue in die bekragtigingseksperiment te gee. Masters 2023-03-02T10:12:11Z 2023-05-18T07:19:14Z 2023-03-02T10:12:11Z 2023-05-18T07:19:14Z 2023-03 Thesis http://hdl.handle.net/10019.1/127381 en_ZA Stellenbosch University xv, 93 pages : illustrations, includes annexures application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Computational fluid dynamics Solar thermal energy Renewable energy sources UCTD Piwang, Howard Discrete element modeling and computational fluid dynamics approach to determination of tortuosity through packed bed of crushed rock particles |
| title | Discrete element modeling and computational fluid dynamics approach to determination of tortuosity through packed bed of crushed rock particles |
| title_full | Discrete element modeling and computational fluid dynamics approach to determination of tortuosity through packed bed of crushed rock particles |
| title_fullStr | Discrete element modeling and computational fluid dynamics approach to determination of tortuosity through packed bed of crushed rock particles |
| title_full_unstemmed | Discrete element modeling and computational fluid dynamics approach to determination of tortuosity through packed bed of crushed rock particles |
| title_short | Discrete element modeling and computational fluid dynamics approach to determination of tortuosity through packed bed of crushed rock particles |
| title_sort | discrete element modeling and computational fluid dynamics approach to determination of tortuosity through packed bed of crushed rock particles |
| topic | Computational fluid dynamics Solar thermal energy Renewable energy sources UCTD |
| url | http://hdl.handle.net/10019.1/127381 |
| work_keys_str_mv | AT piwanghoward discreteelementmodelingandcomputationalfluiddynamicsapproachtodeterminationoftortuositythroughpackedbedofcrushedrockparticles |