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Measurement and modelling of flow and turbulence above a biomass boiler continuous ash discharge stoker grate
Du Plessis, J. 2025. Measurement and modelling of flow and turbulence above a biomass boiler continuous ash discharge stoker grate. Unpublished masters thesis. Stellenbosch: Stellenbosch University [online]. Available: https://scholar.sun.ac.za/items/ee223a58-b395-4ae1-a641-92d79017ab30
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Stellenbosch : Stellenbosch University
2025
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| _version_ | 1867614117548785664 |
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| access_status_str | Open Access |
| author | Du Plessis, Hennie |
| author2 | Laubscher, Ryno |
| author_browse | Du Plessis, Hennie Laubscher, Ryno |
| author_facet | Laubscher, Ryno Du Plessis, Hennie |
| author_sort | Du Plessis, Hennie |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Du Plessis, J. 2025. Measurement and modelling of flow and turbulence above a biomass boiler continuous ash discharge stoker grate. Unpublished masters thesis. Stellenbosch: Stellenbosch University [online]. Available: https://scholar.sun.ac.za/items/ee223a58-b395-4ae1-a641-92d79017ab30 |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/132147 |
| institution | Stellenbosch University (South Africa) |
| last_indexed | 2026-06-10T12:46:56.603Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2025 |
| publishDateRange | 2025 |
| publishDateSort | 2025 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/132147 Measurement and modelling of flow and turbulence above a biomass boiler continuous ash discharge stoker grate Du Plessis, Hennie Laubscher, Ryno Rousseau, Pieter Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering. Computational fluid dynamics Biomass -- Combustion Flow meters Turbulence UCTD Du Plessis, J. 2025. Measurement and modelling of flow and turbulence above a biomass boiler continuous ash discharge stoker grate. Unpublished masters thesis. Stellenbosch: Stellenbosch University [online]. Available: https://scholar.sun.ac.za/items/ee223a58-b395-4ae1-a641-92d79017ab30 Thesis (MEng)--Stellenbosch University, 2025. ENGLISH ABSTRACT: Computational fluid dynamics (CFD) plays an important role in the design and analysis of airflow and combustion in biomass boilers. The stoker grate bars, on which combustion of the solid fuel takes place, are responsible for generating high amounts of turbulence due to their intricate configuration. Typically, these complex geometries are omitted in boiler furnace CFD simulations, and in place of these grate bars, straightforward porous zone models are used that neglect any downstream turbulence effects. This study investigates airflow and turbulence downstream of biomass boiler grate bars using experimental and CFD methods. Velocity measurements were obtained through particle image velocimetry (PIV) and hot-wire anemometry at various locations and flow rates, with PIV data calibrated to hot-wire readings. In addition to experimental measurements, detailed simulations were performed using both the Realizable and SST turbulence models to simulate airflow through the grate bars. These simulation models yielded average errors of 20.1% and 17.4%, respectively, when compared to the experimental measurements. From the validated CFD data, a surrogate mixing model was developed, representing the grate bars as a porous zone and accurately predicting pressure drop with a normalized error of 0.327%. Mathematical functions derived from detailed CFD results were used to model turbulent kinetic energy and dissipation rate profiles, based on height above the grate and Reynolds number, with minimal errors of 0.37% and 0.07%. The integrated model predicts turbulent kinetic energy and dissipation rate with errors of 9.42% and 12.9%, and the turbulent mixing rate with a 6.15% error. The study highlights that neglecting turbulence underestimates mixing rates by 6 404%. The developed model enhances turbulence representation efficiently, making it practical for industrial applications. AFRIKAANSE OPSOMMING: Berekeningsvloeimeganika (CFD) speel ’n belangrike rol in die ontwerp en ontleding van lugvloei en verbranding in biomassaketels. Die roostertralie-stawe, waarop die verbranding van die vaste brandstof plaasvind, is verantwoordelik vir die opwekking van hoë vlakke van turbulensie as gevolg van hulle ingewikkelde konfigurasies. Tipies word hierdie komplekse geometrieë in CFD-simulasies van keteloonde weggelaat, en in plaas daarvan word eenvoudige poreuse sone-modelle gebruik wat enige turbulensie-effekte ignoreer. Hierdie studie ondersoek lugvloei en turbulensie bo die biomassaketel-roostertralie-stawe met behulp van eksperimentele en CFD-metodes. Snelheidsmetings is verkry deur deeltjiebeeld-velosimetrie (PIV) en warmdraad-anemometrie by verskeie liggings en vloeitempo’s, met PIV-data wat gekalibreer is met warmdraadlesings. Benewens eksperimentele meetings, is gedetailleerde simulasies uitgevoer met behulp van beide die Realiseerbare en SST-turbulensiemodelle om lugvloei deur die roostertralie-stawe te simuleer. Hierdie simulasie-modelle het gemiddelde foute van onderskeidelik 20.1% en 17.4% opgelewer, in vergelyking met die eksperimentele metings. Vanuit die gevalideerde CFD-data is ’n plaasvervanger-mengmodel ontwikkel wat die roostertralie-stawe as ’n poreuse sone voorstel en die drukval akkuraat voorspel met ’n genormaliseerde fout van 0.327%. Wiskundige funksies, afgelei van gedetailleerde CFD-resultate, is gebruik om die profiel van die turbulente kinetiese energie en dissipasiekoers te modelleer, gebaseer op die hoogte bo die stawe en die Reynolds-getal, met minimale foute van 0.37% en 0.07%. Die geïntegreerde model voorspel turbulente kinetiese energie en dissipasiekoers met foute van 9.42% en 12.9%, en die turbulente mengtempo met ’n fout van 6.15%. Die studie beklemtoon dat die verwaarlosing van turbulensie-eienskappe in die standaardbenadering, die turbulente mengtempo onderskat met 6,404%. Die ontwikkelde model verbeter die voorstelling van turbulensie doeltreffend, wat dit prakties maak vir industriële toepassings. Masters 2025-05-27T14:01:27Z 2025-05-27T14:01:27Z 2025-03 Thesis https://scholar.sun.ac.za/handle/10019.1/132147 Stellenbosch University xix, 117 pages : illustrations application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Computational fluid dynamics Biomass -- Combustion Flow meters Turbulence UCTD Du Plessis, Hennie Measurement and modelling of flow and turbulence above a biomass boiler continuous ash discharge stoker grate |
| title | Measurement and modelling of flow and turbulence above a biomass boiler continuous ash discharge stoker grate |
| title_full | Measurement and modelling of flow and turbulence above a biomass boiler continuous ash discharge stoker grate |
| title_fullStr | Measurement and modelling of flow and turbulence above a biomass boiler continuous ash discharge stoker grate |
| title_full_unstemmed | Measurement and modelling of flow and turbulence above a biomass boiler continuous ash discharge stoker grate |
| title_short | Measurement and modelling of flow and turbulence above a biomass boiler continuous ash discharge stoker grate |
| title_sort | measurement and modelling of flow and turbulence above a biomass boiler continuous ash discharge stoker grate |
| topic | Computational fluid dynamics Biomass -- Combustion Flow meters Turbulence UCTD |
| url | https://scholar.sun.ac.za/handle/10019.1/132147 |
| work_keys_str_mv | AT duplessishennie measurementandmodellingofflowandturbulenceaboveabiomassboilercontinuousashdischargestokergrate |