Full Text Available
Note: Clicking the button above will open the full text document at the original institutional repository in a new window.
Oxygen transfer in cell-free and simulated alkane-based bioprocesses : Computational Fluid Dynamics (CFD) simulations and predictive modelling
Thesis (PhD)--Stellenbosch University, 2020.
Saved in:
| Main Author: | |
|---|---|
| Other Authors: | |
| Format: | Thesis |
| Language: | en_ZA |
| Published: |
Stellenbosch : Stellenbosch University
2020
|
| Subjects: | |
| Tags: |
No Tags, Be the first to tag this record!
|
| _version_ | 1867614136424202240 |
|---|---|
| access_status_str | Open Access |
| author | Gakingo, Godfrey Kabungo |
| author2 | Louw, Tobias M. |
| author_browse | Gakingo, Godfrey Kabungo Louw, Tobias M. |
| author_facet | Louw, Tobias M. Gakingo, Godfrey Kabungo |
| author_sort | Gakingo, Godfrey Kabungo |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Thesis (PhD)--Stellenbosch University, 2020. |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/109202 |
| institution | Stellenbosch University (South Africa) |
| language | en_ZA |
| last_indexed | 2026-06-10T12:47:14.760Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2020 |
| publishDateRange | 2020 |
| publishDateSort | 2020 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/109202 Oxygen transfer in cell-free and simulated alkane-based bioprocesses : Computational Fluid Dynamics (CFD) simulations and predictive modelling Gakingo, Godfrey Kabungo Louw, Tobias M. Clarke, Kim Gail Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering. Hydrodynamics UCTD Biocatalysis -- Alkanes Computational Fluid Dynamics (CFD) Mass transfer Thesis (PhD)--Stellenbosch University, 2020. ENGLISH ABSTRACT: Alkane activation using whole-cell biocatalysts is an attractive technology that can be employed in alkane valorisation. However, since metabolically active cells involved in this process require oxygen, a failure to effectively supply the same can limit the process. This recognition has created a need for a fundamental understanding of oxygen transfer in such systems. Additionally, there has been a need for predictive tools that can be used in bioreactor design and scale up. This study proposes a fundamental predictive model of oxygen transfer based on Computational Fluid Dynamics that is applicable to alkane-based bioreactors. The model was built using a step-wise approach that considered an increasing number of phases – aqueous, air-aqueous, air-aqueous-alkane and air-aqueous-alkane-yeast. Model validation was also done using flow and oxygen transfer parameters. For the latter, overall volumetric mass transfer coefficients were predicted using a framework proposed to incorporate effects of the alkane phase such as possible enhancement from new mass transfer pathways and longer saturation times of the aqueous-alkane mixture. For the aqueous and air-aqueous stirred tank reactor, model-predicted power and pumping numbers were observed to agree with established literature values. Additionally, predicted gas hold up values were accurate to within 22%. Transient variation in the mean flow (macro-instabilities) was also observed, this being a first in literature for simulations using the multiple reference frame technique. This finding implied that the latter technique can be employed in studies on macro-instabilities instead of the computationally intensive sliding mesh technique typically used. For the air-aqueous-alkane system, it was illustrated that the alkane phase influences the hydrodynamics through turbulence modification rather than through the effective fluid properties. An increase in turbulence due to interactions by the alkane droplets led to higher turbulence viscosity values and these served to dampen the mean flow velocities. Consequently, the gas phase experienced reduced drag/dispersion and it escaped the reactor quicker as evidenced by decreasing gas hold up values with increasing alkane concentration. This trend was similar to that observed experimentally (about 30% accurate) and was consistent irrespective of boundary condition treatment of the reactor’s top surface (velocity or pressure outlet boundary condition). Oxygen transfer was investigated using two models representing possible mass transfer pathways introduced by the alkane phase – series mass transfer with and without shuttling. Minimal differences were, however, observed for these models. The mass transfer coefficients were more sensitive to changes in the gas hold up and turbulence levels. Furthermore, the predicted values were accurate to within 11% at low agitation rates and alkane concentrations. Poor predictions at other conditions suggested that the model needed improvement through, for example, the incorporation of population balance modelling. For the air-aqueous-alkane-yeast system, the Computational Fluid Dynamics model provided a reasonable first approximation with gas hold up values predicted to within 40%. Possible mechanisms by which the yeast phase influences the hydrodynamics were highlighted. These included coalescence hindrance and the promotion of cluster formation. Oxygen transfer was poorly predicted and several factors were suggested to account for this observation. Nevertheless, further experimental investigations are required. AFRIKAANSE OPSOMMING: Alkaanaktivering deur heel-sel biokatalise is ’n aantreklike tegnologie wat gebruik kan word in alkaan valorisasie. Maar, siende dat die metaboliese aktiewe selle wat by die proses betrokke is, suurstof benodig, kan oneffektiewe voorsiening daarvan die proses beperk. Hierdie erkenning het ’n behoefte geskep vir ’n fundamentele verstaan van suurstofoordrag in sulke stelsels. Boonop is daar ’n behoefte vir voorspellende gereedskap wat gebruik kan word in bioreaktorontwerp en skaal vergroting. In hierdie studie is ’n fundamentele voorspellende model van suurstofoordrag toepaslik op alkaan-gebaseerde bioreaktors ontwikkel deur berekeningsvloeidinamika te gebruik. Die model is gebou deur ʼn stap-gewyse benadering wat ’n toenemende aantal fases beskou – waterig, lug-waterig, lug-waterig-alkaan en lug-waterig-alkaan-gis. Model validasie is ook gedoen deur vloei- en suurstofoordrag parameters te assesseer. Vir die laasgenoemde, was algehele volumetriese massa-oordragkoëffisiënte voorspel deur gebruik te maak van ’n raamwerk voorgestel om moontlike effekte van die alkaanfase te inkorporeer, soos verbetering deur nuwe massaoordrag meganismes en langer deurwekingstye van die waterige-alkaan mengsel. Vir die waterige en lug-waterige stelsels het modelvoorspelde krag-en-pompsyfers ooreengestem met gevestigde literatuurwaardes. Boonop, voorgestelde gasvertragingswaardes was akkuraat tot binne 22%. Verbygaande variasie in die gemiddelde vloei (makro-onstabiliteite) is ook waargeneem, met hierdie ’n eerste in literatuur vir simulasies gebaseer op die veelvoudige verwysingsraam tegniek. Hierdie bevinding impliseer dat die laasgenoemde tegniek gebruik kan word vir toekomstige studies op makro-onstabiliteite in plaas van die berekenings intensiewe skuiwende netwerk tegniek wat gewoonlik gebruik word. Vir die lug-waterige-alkaanstelsel, was dit gewys dat die alkaanfase die hidrodinamika deur turbulensie aanpassing eerder as deur die effektiewe vloei-eienskappe, beïnvloed. ʼn Verhoging in turbulensie agv interaksies met die alkaan druppels het gelei tot groter turbulensieviskositeit waardes wat gedien het om die gemiddelde vloeisnelhede te smoor. Gevolglik het die gasfase verminderde weerstand/verspreiding ervaar en kon vinniger uit die reaktor ontsnap, soos bewys deur die verminderde gasvertragingswaardes met toenemende alkaan konsentrasie. Hierdie verloop was soortgelyk aan dit wat eksperimenteel waargeneem is (omtrent 30% akkuraat) en was konsekwent ongeag van die grenskondisies op die reaktor se boonste oppervlakte (snelheid of drukuitlaat grenskondisie). Suurstofoordrag was ondersoek deur twee modelle wat moontlike massaoordrag meganismes voorgestel het deur die alkaan fase – serie massaoordrag met en sonder spoeling. Minimale verskille was egter waargeneem vir die modelle. Die massaoordrag koëffisiënte was meer sensitief tot veranderinge in die gasvertragingswaardes en turbulensie vlakke. Verder, die voorspelde waardes was akkuraat binne 11% van die lae roertempos en alkaan konsentrasies. Swak voorspellings by ander toestande stel voor dat die model verbetering benodig deur, byvoorbeeld, die inkorporasie van populasie balans modelle. Vir die lug-waterige-alkaan-gis stelsel, het die berekeningsvloeidinamika model ʼn redelike eerste benadering vir die gasvertragingswaardes voorspel, binne 40%. Moontlike meganismes waardeur die gisfase die hidrodinamika kan beïnvloed is uitgelig. Hierdie sluit in samesmeltingshindernis en die vordering van groepsformasie. Suurstofoordrag was swak voorspel en verskeie faktore was voorgestel om verantwoording te doen vir die observasie. Nietemin, word verdere eksperimentele studies vereis. Doctoral 2020-11-19T07:27:11Z 2021-01-31T19:39:30Z 2020-11-19T07:27:11Z 2021-01-31T19:39:30Z 2020-12 Thesis http://hdl.handle.net/10019.1/109202 en_ZA Stellenbosch University 157 pages application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Hydrodynamics UCTD Biocatalysis -- Alkanes Computational Fluid Dynamics (CFD) Mass transfer Gakingo, Godfrey Kabungo Oxygen transfer in cell-free and simulated alkane-based bioprocesses : Computational Fluid Dynamics (CFD) simulations and predictive modelling |
| title | Oxygen transfer in cell-free and simulated alkane-based bioprocesses : Computational Fluid Dynamics (CFD) simulations and predictive modelling |
| title_full | Oxygen transfer in cell-free and simulated alkane-based bioprocesses : Computational Fluid Dynamics (CFD) simulations and predictive modelling |
| title_fullStr | Oxygen transfer in cell-free and simulated alkane-based bioprocesses : Computational Fluid Dynamics (CFD) simulations and predictive modelling |
| title_full_unstemmed | Oxygen transfer in cell-free and simulated alkane-based bioprocesses : Computational Fluid Dynamics (CFD) simulations and predictive modelling |
| title_short | Oxygen transfer in cell-free and simulated alkane-based bioprocesses : Computational Fluid Dynamics (CFD) simulations and predictive modelling |
| title_sort | oxygen transfer in cell free and simulated alkane based bioprocesses computational fluid dynamics cfd simulations and predictive modelling |
| topic | Hydrodynamics UCTD Biocatalysis -- Alkanes Computational Fluid Dynamics (CFD) Mass transfer |
| url | http://hdl.handle.net/10019.1/109202 |
| work_keys_str_mv | AT gakingogodfreykabungo oxygentransferincellfreeandsimulatedalkanebasedbioprocessescomputationalfluiddynamicscfdsimulationsandpredictivemodelling |