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Performance and thermo-mechanical cost evaluation of API 661 air-cooled heat exchangersAckers, Mogamat Sadley 12 1900 (has links)
Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: The optimal design of a heat exchanger for a specified heat transfer, pressure drop
and set of ambient conditions entails minimising space, weight, material usage and
overall cost. However, the variables which influence the performance as well as the
overall cost of a heat exchanger are not related in a simple way and it is not obvious
which variables play the most important roles (Perry & Green, 1997:11-44).
Air cooled heat exchangers (ACHEs) are normally designed in three stages, by
different experts in the field, and with the aid of specially designed software. This
project combines these thermal, mechanical and cost estimation processes into a MS
Excel model which makes it easier to see the influence that design parameters have
on the overall cost of the heat exchanger.
A thermal model was created to design an API 661 (2006) ACHE. The results from
this model compared well with those of HTRI Xchanger Suite 6.0 software, with
HTRI being more conservative in its design mode.
A mechanical design model was then developed, which uses as inputs the outputs of
the thermal design. The output from this mechanical design model is the minimum
material thicknesses based on the stress criteria of Appendix 13 of ASME VIII div 1
(2007) Boiler and Pressure Vessel Code.
An experiment on a finned tube bundle was performed in a wind tunnel facility to
determine performance characteristics and compare these to existing correlations in
literature. The results showed that both the heat transfer coefficient (h) and loss
coefficient (Eu) correlations proposed by Ganguli et al. (1985) closely predict the
measured data, and were consequently used in the thermal design model. During this
experiment it was also shown that the tube bundle reached 8 % - 9 % of its allowable
internal fouling factor, due to rust build up inside the tubes, and in a testing period of
only nine days. The thermal and mechanical models were then combined with a cost estimation
process to perform both a thermal and mechanical parametric study. The thermal
study showed that to obtain an optimal solution, the design must attempt to maximise
the length, increase the width rather than the number of bays, make use of two
bundles per bay with fewer but larger fans and employ a large number of tube rows
with the least number of tube passes. These guidelines were used to create an initial
design; Excel Solver was then applied to locate the optimum combination of bundle
length and width that result in the minimum heat exchanger cost. Two mechanical considerations were investigated, both requiring additional welding
and thus increased welding cost. Firstly the use of stay plates result in reduced
required plate thicknesses according to the stress criteria since it provides additional
stiffness in the header box design. Secondly the use of more (but smaller) nozzles as
opposed to less (but larger) nozzles was also considered. The mechanical parametric
study showed no specific trends, but both considerations should still be checked as it
can be cost beneficial in a specific design. / AFRIKAANSE OPSOMMING: Optimale ontwerp van ’n warmteoordraer vir ’n gespesifiseerde warmteoordrag,
drukval en stel van omgewingstoestande behels die minimalisering van ruimte,
gewig, materiaalverbruik en algehele koste. Die veranderlikes wat egter die
werkverrigting, sowel as die algehele koste, van ’n warmteoordraer beïnvloed, hou
nie in ’n eenvoudige sin met mekaar verband nie, en dit is nie vanselfsprekend watter
veranderlikes die belangrikste rolle speel nie (Perry & Green, 1997:11-44).
Lugverkoelde warmteoordraers (air-cooled heat exchangers of ACHEs) word
normaalweg in drie fases ontwerp deur verskillende kundiges in die veld en met
behulp van spesiaal ontwerpte programmatuur. Hierdie studie kombineer dié
termiese, meganiese en kosteberamingsprosesse in ’n MS Excel-model, wat dit
makliker maak om van te stel wat die invloed wat ontwerpparameters op die algehele
koste van die hitteruiler is.
’n Termiese model is geskep om ’n “API 661 (2006) ACHE” te ontwerp. Die
resultate van hierdie model het goed vergelyk met dié van die HTRI Xchanger Suite
6.0-program, met HTRI meer konserwatiew in die ontwerp af.
Na die termiese model geskep is, is ’n meganieseontwerp-model ontwikkel, wat as
insette die uitsette van die termiese ontwerp gebruik het. Die uitset van hierdie
meganieseontwerp-model is die minimum materiaaldikte gebaseer op die
spanningskriteria van Bylae 13 van “ASME VIII div 1 (2007) Boiler and Pressure
Vessel Code.” Daar is ’n eksperiment op ’n vinbuisbundel in ’n windtonnelfasiliteit uitgevoer om
werkverrigtingskarakteristieke te bepaal en dit met bestaande korrelasies in die
literatuur te vergelyk. Die resultate het getoon dat sowel die
warmteoordragskoëffisiënt (h) en die verlieskoeffisient (Eu) korrelasies, voorgestel
deur Ganguli et al. (1985), die data wat gemeet is akkuraat voorspel, en gevolglik is
die korrelasies in die termieseontwerp-model gebruik. Gedurende die eksperiment is
ook getoon dat die buisbundel 8 % - 9 % van sy toelaatbare interne-aanpakkingfaktor
bereik het vanweë roesopbou binne-in die buise, en dit in ’n toetsingtydperk van slegs
nege dae.
Die termiese en meganiese modelle was toe gekombineer met ’n
kosteberamingsproses om ’n termiese sowel as ’n meganiese parametriese studie uit
te voer. Die termiese studie het getoon dat, om ’n optimale oplossing te verkry, die
ontwerp moet poog om die lengte te maksimeer; die wydte eerder as die aantal strate
(bays) te vermeerder; van twee bundels per straat gebruik te maak met minder, maar
groter waaiers; en ’n groot aantal buisrye met die kleinste hoeveelheid buisdeurvloeiweë in te span. Hierdie riglyne is gebruik in ’n aanvanklike ontwerp,
waarna die Excel Solver gebruik is om die optimale kombinasie van bundellengte en
–wydte vas te stel met die oog op die laagste moontlike warmteoordraerkoste.
Twee meganiese oorwegings is ondersoek wat albei addisionele sweiswerk sou vereis
en dus tot verhoogde sweiskoste sou lei. Eerstens lei die gebruik van ankerplate (stay
plates) tot ’n vermindering in die vereiste plaatdiktes volgens die spanningskriteria,
aangesien dit addisionele stewigheid in die spruitstukhouerontwerp bied. Tweedens is
die gebruik van meer (maar kleiner) spuitstukke teenoor minder (maar groter)
spuitstukke ook oorweeg. Die meganiese parametriese studie het geen spesifieke
voorkeurneigings getoon nie, maar altwee oorgewings moet nog getoets word want
dit kan koste voordelig word in 'n spesifieke ontwerp.
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Simulation of a syngas from coal production plant coupled to a high temperature nuclear reactor / Simulation of a cogeneration plant coupled to a high temperature reactorBotha, Frederick Johannes 12 1900 (has links)
Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: In light of the rapid depletion of the world’s oil reserves, concerns about energy
security prompted the exploration of alternative sources of liquid fuels for
transportation. One such alternative is the production of synthetic fuels with the
indirect coal liquefaction process or Coal-To-Liquids (CTL) process. In this
process, coal is burned in a gasifier in the presence of steam and oxygen to
produce a synthesis gas or syngas, consisting mainly of hydrogen and carbon
monoxide. The syngas is then converted to liquid fuels and a variety of useful
chemicals in a Fischer Tropsch synthesis reactor. However, the traditional
process for syngas production also produces substantial amounts of carbon
dioxide. In fact, only about one third of the carbon in the coal feedstock ends up
in the liquid fuel product using traditional CTL technology. If additional hydrogen
was available, the carbon utilisation of the process could be improved
significantly. The high temperature reactor (HTR) is a gas cooled Generation IV
nuclear reactor ideally suited to provide electrical power and high temperature
heat for the production of carbon neutral hydrogen via high temperature
electrolysis. The integration of an HTR into a CTL process therefore provides an
opportunity to improve the thermal and carbon efficiency of the CTL process
significantly. This thesis presents a possible process flow scheme for a nuclear
assisted CTL process. The system is evaluated in terms of its thermal or syngas
production efficiency (defined as the ratio of the heating value of the produced
syngas to the sum of the heating value of the coal plus the HTR heat input) as
well as its carbon utilisation. If the hydrogen production plant is sized to produce
only enough associated oxygen to supply in the needs of the gasification plant,
syngas is produced at about 63% thermal efficiency, while 71.5% of the carbon
is utilised in this process. It was found that the optimum HTR outlet temperature
to produce hydrogen with a high temperature steam electrolysis process is
850°C. If enough process heat and electrical power are available and process equipment capacities are sufficient, the carbon utilisation of the process could be
improved even further to values in excess of 90%. / AFRIKAANSE OPSOMMING: Die uitputting van die wêreld se olie-reserwes, asook kommer oor energiesekuriteit
het daartoe gelei dat alternatiewe bronne van vloeibare brandstowwe
vir vervoer ondersoek moes word. Een so 'n alternatief is die produksie van
sintetiese brandstof d.m.v. die indirekte steenkool vervloeiing proses of
sogenaamde Coal-To-Liquids (CTL) proses. In hierdie proses word steenkool in
die teenwoordigheid van stoom en suurstof in 'n vergasser gebrand om 'n
sintesegas of singas te produseer, wat hoofsaaklik uit waterstof en
koolstofmonoksied bestaan. Die sintesegas word daarna omgeskakel na
vloeibare brandstowwe en 'n verskeidenheid van nuttige chemikalieë in 'n
Fischer-Tropsch-sintese reaktor. Ongelukkig produseer die tradisionele proses vir
sintesegas produksie ook 'n beduidende hoeveelheid koolstofdioksied. Trouens,
slegs sowat een derde van die koolstof in die steenkool roumateriaal eindig in die
vloeibare brandstof produk indien van tradisionele CTL-tegnologie gebruik
gemaak word. Indien addisionele waterstof beskikbaar was, kon die koolstofbenutting
van die proses aansienlik verbeter word. Die hoë temperatuur reaktor
(HTR) is 'n gas-verkoelde Generasie IV kernreaktor wat by uitstek geskik is om
elektrisiteit en hoë temperatuur hitte te verskaf vir die produksie van koolstofneutrale
waterstof d.m.v. hoë temperatuur elektrolise. Die integrasie van 'n HTR
in 'n CTL-proses bied dus 'n geleentheid om die termiese- en koolstofdoeltreffendheid
van die CTL-proses aansienlik te verbeter. In hierdie ondersoek
word 'n moontlike proses vloeidiagram vir 'n kern-gesteunde CTL-proses
voorgestel. Die stelsel is geëvalueer in terme van sy termiese- of sintesegas
produksie doeltreffendheid (gedefinieer as die verhouding van die hittewaarde
van die geproduseerde sintesegas gedeel deur die som van die hittewaarde van
die steenkool en die HTR hitte-insette) sowel as sy koolstof-effektiwiteit. Indien
die waterstof produksie-aanleg ontwerp word om net genoeg geassosieerde
suurstof te voorsien om in die behoeftes van die vergassing-aanleg te voorsien, word sintesegas teen ongeveer 63% termiese doeltreffendheid vervaardig,
terwyl 71.5% van die koolstof in hierdie proses benut word. Daar is bevind dat
850°C die optimum HTR uitlaat temperatuur is om waterstof d.m.v. hoë
temperatuur stoom-elektrolise te vervaardig. Indien daar genoeg proses hitte en
elektrisiteit beskikbaar is en die proses toerusting kapasiteite voldoende is, sou
die koolstof-benutting van die proses tot meer as 90% verbeter kon word.
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Simultaneous measurement of air flow conditions and resultant blade and gearbox loading at large-scale cooling system fansMuiyser, Jacques 12 1900 (has links)
Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Axial flow fans used in large-scale air-cooled steam condensers (ACSCs) may operate
under distorted inflow conditions. These conditions occur due to the prevailing wind
conditions, the presence of buildings, and the location of the fan within the ACSC. Fans
located on the periphery of the ACSC are affected the most due to their exposure to
strong winds and the inner fans drawing in air past them. Distorted inflow conditions
cause varying fan blade and gearbox loading conditions.
The purpose of the investigation was to simultaneously measure the inlet air flow
and the resultant blade and gearbox loading conditions of a single fan located on the
periphery of a large-scale ACSC. Inlet and heat exchanger bundle outlet air flow velocities
were measured using a combination of ultrasonic and propeller anemometers while
blade loading was measured with strain gauges attached at the neck of the specific blade
being monitored. Strain gauges were also attached to the low-speed fan shaft to measure
gearbox loading.
Measurements were recorded over a period of 8 days where it was found that increased
wind resulted in increased air flow in the axial direction of the fan, which then
caused a reduction in average blade loading. This was due to a decreased static pressure
rise over the fan. The fan blade was found to vibrate at its own natural frequency of
6 Hz when excited by the variable aerodynamic loading. The aerodynamic loading was
extracted from the measured data and was found to correlate well with previous experimental
work performed by Bredell et al. (2006a). Shaft bending stresses and torque were
found to oscillate at the fan’s rotational frequency of 2Hz with a large torque exerted on
the shaft during fan start-up. / AFRIKAANSE OPSOMMING: Aksiaalvloeiwaaiers wat by groot lugverkoelde stoomkondensors gebruik word, werk
dikwels onder verwronge inlaat lugvloei toestande wat geskied as gevolg van heersende
winde, die teenwoordigheid van geboue en die posisie van die waaier in die kondensor.
Waaiers wat geleë is op die rand van die kondensor word die meeste beïnvloed as gevolg
van blootstelling aan die sterk winde en dwarsvloei wat deur die binneste waaiers geïnduseer
word. Verwronge inlaat lugvloei veroorsaak gevolglik variërende waaierlem en
ratkas belastingstoestande.
Die doel van hierdie ondersoek was om terselfdetyd die inlaat lugvloei asook waaierlem
en ratkas belastingstoestande van ’n enkele waaier wat op die rand van ’n grootskaalse
lugverkoelde stoomkondensor geleë is, te meet. Waaier inlaat en warmteruiler
uitlaat lugvloei snelhede is gemeet met ’n kombinasie van ultrasoniese- en skroefwindsnelheidsmeters
terwyl die lem en ratkas belastings gemeet is met rekstrokies.
Metings is oor ’n tydperk van 8 dae geneem. Die bevindinge toon dat ’n toename
in windsnelheid ’n toename in aksiale lugvloei tempo, deur die waaier veroorsaak. ’n
Afname in die gemiddelde lembelasting is waargeneem as gevolg van ’n afname in die
waaier statiese druk. Daar is ontdek dat die waaierlem teen ’n natuurlike frekwensie van
6 Hz vibreer wanneer dit opgewek word deur die wisselende aerodinamiese belasting.
Die aerodinamiese belasting is verkry uit die gemete data en vergelyk goed met die numeriese
werk van Bredell et al. (2006a). Daar is ook bevind dat waaier-as buigspannings
en wringkragte ossileer teen die waaier se rotasiefrekwensie van 2Hz met ’n groot wringkrag
wat op die as uitgeoefen word wanneer die waaier aangeskakel word.
iii
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Impact response of a continuous fibre reinforced thermoplastic from a soft bodied projectileVan der Westhuizen, Artho Otto 03 1900 (has links)
Thesis (MScEng)--Stellenbosch University, 2013. / AFRIKAANSE OPSOMMING: Saamgestelde materiale het baie gewilde materiale in die lugvaart- en motor
industrië geword as gevolg van die gewigsbesparende voordele wat dit inhou.
Kostes en ander verwerkingsprobleme het tradisioneel die wydverspreide gebruik
van spesifiek termoplasties-versterkte vesels in hierdie areas verhinder. Baie van
die vervaardigingsprobleme (spesifiek lang siklusse) is aangespreek met die
aanvang van termoplastiese matriks materiaal soos Polyphenolien Sulfied (PPS).
Hierdie materiaal voldoen ook aan die lugvaart-industrie se brand-, rook- en
giftigheidstandaarde.
Termoplastiese saamgestelde materiale kan byvoorbeeld gevind word op
komponente in vliegtuie se binneruimtes en ook die voorste rand van die vlerke.
Hierdie komponente is hoogs vatbaar vir impakskade. Die hoë sterkte en styfheid
tot gewig verhoudings van saamgestelde materiale laat toe vir dun materiaal
dwarssnitte. Komponente is dus kwesbaar vir uit-vlakkige impak beladings.
Saamgestelde materiale kan ook intern deur hierdie beladings beskadig word en
kan nie met die blote oog waargeneem kan word nie. Dit is dus nodig om die
skade weens hierdie beladings tydens normale gebruik akkuraat te voorspel.
Verder sal dit nuttig wees om die struktuur se gedrag te bepaal in toepassings
waar byvoorbeeld passasier veiligheid krities is, soos op vliegtuig ruglenings
tydens noodlandings.
In hierdie studie is die potensiële vervaardigingsvoordele van termoplastiese
saamgestelde materiale gedemonstreer. Daarbenewens is 'n uit-vlakkige impak
deur 'n sagte liggaam herbou in 'n laboratorium omgewing. Die primêre doelwit
van hierdie studie was om die impak numeries te modelleer.
Vervaardigingsvoordele van `n vesel versterkte termoplastiese laminaat is
gedemonstreer deur die vervaardiging van 'n konkawe, agt laag laminaat uit 'n
vooraf gekonsolideerde geweefde doek. Die totale verwerkingstyd van die plat
laminaat na 'n konkawe laminaat was minder as vyf minute. 'n Eenvoudige plat
laminaat en 'n konkawe laminaat is onderwerp aan 'n lae snelheid impak deur 'n
sagte projektiel. Die impak is gemodelleer deur die evaluering van drie
modelleringsmetodes vir die saamgestelde paneel. Die evalueringskriteria het o.a.
ingesluit of laminaat se volle gedrag suksesvol gemodelleer kon word met behulp
van slegs 2D dop elemente.
Die reaksie van die saamgestelde paneel en gepaardgaande faling is met
wisselende vlakke van sukses deur die drie geëvalueerde modelle voorspel. Die
faling van tussen-laminêre bindings (verwys na as delaminasie) kon nie deur
enige van die modelle voorspel word nie. Twee van die modelle het egter in-vlak
faling met redelike akkuraatheid voorspel. / ENGLISH ABSTRACT: Due to weight saving advantages composite materials have become a highly
popular material in the aerospace and automotive industries. Traditionally
processing difficulties and costs have been a barrier to widespread composite
material use in these industries. With the advent of thermoplastic matrix materials
such as Polyphenoline Sulphide (PPS) the processing difficulties (especially long
cycle times) experienced with traditional thermosetting resins can be addressed
while maintaining aerospace Fire-Smoke and Toxicity (FST) approval.
Thermoplastic composites can for example be found on aircraft interior
components and leading edges of the wings. These areas are highly susceptible to
impact damage. The high strength- and stiffness to weight ratios of composites
allows for thin material cross sections. This leaves the components vulnerable to
out-of-plane impact loads. Composite materials may also be damaged internally
by these loads, leaving the damage undetectable through visual inspections. It
may therefore be necessary to predict the amount of damage a component would
sustain during normal operation. Additionally, it would be useful to predict
structural response of these materials in applications where passenger safety is
crucial, such as aircraft seat backrests during emergency landings.
In this study the potential processing benefits of thermoplastic composite
materials were demonstrated. Additionally an out-of-plane impact from a soft
bodied projectile was reconstructed in a laboratory environment. The primary
objective was to numerically model the impact event.
Processing benefits of thermoplastics were demonstrated by producing a single
curvature eight layered laminate from a pre-consolidated woven sheet. The total
processing time from flat panel to a single curvature panel was below five
minutes. A simple flat laminate and a single curvature laminate were subjected to
a low velocity drop weight impact load from a soft bodied projectile. These
impact events were modelled by evaluating three modelling methods for the
composite panel structural response and damage evolution. Part of the evaluation
criteria included whether laminate failure could be modelled successfully using
only 2D shell elements.
The response of the composite panel and accompanying failure were predicted
with varying levels of success by the three evaluated models. The failure of interlaminar
bonds (referred to as delamination) could not be predicted by either
model. However two of the models predicted in-plane failure with reasonable
accuracy.
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Development aspects of a high temperature heat pipe heat exchanger for high temperature gas-cooled nuclear reactor systemsLaubscher, Ryno 03 1900 (has links)
Thesis (MScEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: High temperature heat sources are becoming an ever-increasing imperative in the
process industry for the production of plastics, ammonia and fertilisers, hydrogen, coal-toliquid
fuel and process heat. Currently, high temperature reactor (HTR) technology is
capable of producing helium temperatures in excess of 950°C; however, at these
temperatures, tritium, which is a radioactive contaminant found in the helium coolant
stream, is able to diffuse though the steel retaining wall of the helium-to-steam heat
exchanger. To circumvent this radioactivity problem, regulations require an intermediate
heat exchange loop between the helium and the process heat streams. In this paper, the
use of a uniquely designed sodium-charged heat pipe heat exchanger is considered, and
has the distinct advantage of having almost zero exergy loss as it eliminates the
intermediate heat exchange circuit.
In order to investigate this novel heat pipe heat exchanger concept, a special
intermediate-temperature (± 240°C) experimental heat pipe heat exchanger (HPHE) was
designed. This experimental HPHE uses Dowtherm A as working fluid and has two glass
windows to enable visual observation of the boiling and condensation two-phase flow
processes. A high temperature air-burner supply simulates the high temperature stream,
and the cold stream is provided by water from a constant-heat supply tank. This
experimental apparatus can be used to evaluate the validity of steady-state and start-up
transient theoretical models that have been developed.
This paper will highlight the special design aspects of this HPHE, the theoretical model
and the solution algorithm described. Experimental results will be compared with the
theoretically calculated results. The theoretical model will then be used to predict the
performance of a high temperature (sodium working fluid at 850°C) HPHE will be
undertaken and conclusions and recommendation made. / AFRIKAANSE OPSOMMING: Hoë temperatuur hitte bronne is besig om ‘n toenemende noodsaaklikheid te raak in die
proses industrie vir die vervaardiging van plastieke, ammoniak, kunsmis, waterstof,
steenkool-tot-vloeibare brandstof en proses hitte. Huidige hoë temperatuur reaktor
tegnologie is in staat om helium te verhit tot temperature hoër as 950°C, maar by sulke
hoë temperature is die vorming van tritium, wat ‘n radioaktiewe produk is, in die helium
verkoeling stroom wat deur die reaktor vloei, ‘n probleem. Die tritium is in staat om deur
die staal wand van ‘n enkel fase warmte uitruiler te diffundeer. Om hierdie radioaktiewe
probleem te uitoorlê, stel huidige regulasies voor dat ‘n oorgangs hitte uitruil lus gebruik
raak tussen die helium en proses strome van die reaktor stelsel. In hierdie tesis word ‘n
unieke natrium gevulde hitte pyp warmte uitruiler nagevors, hierdie ontwerp het die
voordeel dat dit geen “exergy” verlies het omdat dit nie ‘n oorgangs hitte uitruil lus
benodig nie.
Hierdie unieke konsep was nagevors deur ‘n spesiale oorgangs temperatuur (± 230°C)
eksperimentiële hitte pyp warmte uitruiler te ontwerp. Hierdie eksperimentiële hitte pyp
warmte uitruiler gebruik Dowtherm A as oordrags medium tussen die warm en koue
strome en het twee glas venters waardeur die kook en kondensasie van die oorgangs
medium dop gehou kan word. ‘n Hoë temperatuur verbrander simuleer die warm stroom
deur die reaktor en die koue stroom word gesimuleer deur koue water. Die
eksperimentiële opstelling sal gebruik word om die tyd afhangklike en tyd onafhangklike
teoretiese wiskundige modele te valideer.
Hierdie tesis sal die spesiale ontwerp aspekte van die hitte pyp warmte uitruiler,
teoretiese modelle en oplos algoritme te bespreek. Eksperimentiele resultate sal met die
teoretiese resultate vergelyk word en dan sal die teoretiese modelle gebruik word om ‘n
natrium gevulde warmte uitruiler te simuleer. Gevolgtrekkings en aanbevelings sal in die
lig van die resultate verskaf word.
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Solar assisted power generation (SAPG) : investigation of solar preheating of feedwaterPierce, Warrick Tait 03 1900 (has links)
Thesis (MEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Solar Assisted Power Generation (SAPG) can be seen as a synergy of solar and fossil
plants – combining the environmental benefits of the former and the scale, efficiency
and reliability of the latter. SAPG offers great potential for cost effective utilization
of solar energy on utility scale and could accelerate the adoption of solar thermal
energy technologies in the short and medium term, especially in countries with a
significant coal base and a good solar resource such as Australia, China, United
States, India and South Africa.
SAPG is the replacement of bled-off steam in a Regenerative Rankine power cycle.
Power plant simulations were performed using weather data for Lephalale, South
Africa (Matimba power station). With an increase in the solar field outlet
temperature, an increase in overall solar to electric efficiency was observed, superior
to a stand-alone Solar Thermal Power Plant(s) (STPP) at similar temperatures.
The performance of four solar collector technologies was compared: flat plate,
evacuated tube, Linear Fresnel (LF) and Parabolic Trough (PT). This comparison
was limited to the normal incidence angles of irradiation. For this application, nonconcentrating
technologies are not competitive.
For non-normal incidence angles, annual simulations were limited to PT and LF at
final feedwater heater temperatures. The actual aperture area of around 80 000 m2
was used (50 MW thermal based on LF). On an equal aperture area basis, PT
outperforms LF significantly. For the conventional North-South arrangement, LF
needs to be around 53% of the specific installation cost (in $/m2 aperture area) of PT
to be cost competitive. A SAPG plant at Lephalale was compared to a stand-alone Solar Thermal Power
Plant STPP in a good solar resource area, namely Upington, South Africa –
Parabolic Trough solar collector fields of equal size were considered for both
configurations. It was found that the annual electricity generated with a SAPG plant
is more than 25% greater than a stand-alone STPP. If the cost of SAPG is taken as
72% of the cost of a stand-alone STPP, this translates into SAPG being 1.8 times
more cost effective than stand-alone STPP. Furthermore, SAPG performs better in
high electricity demand months (South African winter – May to August).
Stand-alone STPP have been adopted in South Africa and are currently being built.
This was achieved by the government creating an attractive environment for
Independent Power Producers (IPP). Eskom, the national power supplier, is currently
investigating solar boosting at existing Eskom sites. This report argues that on a
national level, SAPG, specifically solar preheating of feedwater, is a more viable
solution for South Africa, with both its significant coal base and good solar resource. / AFRIKAANSE OPSOMMING: Son ondersteunde krag generasie (SOKG) kan gesien word as sinergie van sonkrag en
fossiele brandstof aanlegte – dit voeg die omgewings voordele van die eersgenoemde
en die grote, effektiwiteit en betroubaarheid van die laasgenoemde by mekaar. SOKG
opper groot potensiaal vir koste effektiewe gebruik van son energie op
nutsmaatskappyskaal en kan die aanvaarding van sontermiese energietegnologieë in
die kort en medium termyn versnel, veral in lande met beduidende kool reserwes en
goeie sonkrag voorkoms soos Australië, China, Verenigde State van Amerika, Indië
en Suid-Afrika.
SOKG impliseer die vervanging van aftap stoom in die regeneratiewe Rankine krag
kringloop. Kragstasie simulasies was gedoen met die gebruik van weer data van
Lephalale, Suid-Afrika (Matimba kragstasie). Met die toename van die sonveld
uitlaat temperatuur kon oorhoofse son-na-elektrisiteit effektiwiteit vasgestel word,
wat hoër is as die van alleenstaande sontermiese krag stasie (STKS) by soortgelyke
temperature.
Die effektiwiteit van vier son kollekteerder tegnologieë was vergelyk: plat plaat,
vakuum buis, lineêre Fresnel (LF) en paraboliese trog (PT). Die vergelyking was
beperk tot normale inval van bestraling. Vir hierdie toepassing is nie-konsentreerende
tegnologie nie mededingend nie.
Vir nie-normale inval hoeke was jaarlange simulasies beperk tot PT en LF by finale
voedingswater temperatuur. Die werklike opening area van omtrent 80 000 m2 was
gebruik (50 MW termies gebaseer op LF). By gelyke opening area, uitpresteer PT LF
beduidend. Vir die gebruiklike Noord-Suid rankskikking benodig LF omtrent
53% van die spesifieke installasie kostes (in $/m2 opening area) van PT om kostes
mededingend te kan wees. ‘n SOKG aanleg by Lephalale was vergelyk met alleenstaande STKS in die goeie son
voorkoms gebied van Upington, Suid-Afrika – Paraboliese trog kollekteerder velde
van gelyke grote was oorweeg vir al twee konfigurasies. Dit was gevind dat die
jaarlikse elektrisiteit gegenereer vanaf SOKG meer as 25% is as die van alleenstaande
STKS. Indien SOKG oorweeg word met 72% van die kostes van alleenstaande STKS,
dan beteken dit dat SOKG 1.8 keer meer koste effektief is as alleenstade STKS.
Verder, SOKG presteer beter in die hoer elektrisiteitsnavraag maande (Suid-
Afrikaanse winter – May tot Augustus).
Alleenstaande STKS is gekies vir Suid-Afrika en word tans gebou. Dit is bereik deur
dat die regering ‘n aantreklike omgewing geskep het vir onafhanglike krag
produsente. Eskom ondersoek tans SOKG by bestaande Eskom persele. Hierdie
verslag beweer dat op nasionale/Eskom vlak, SOKG, besonders son voorverhitting
van voedingswater, meer haalbare oplossing is vir Suid-Afrika met sy beduidende
koolreserwes en goeie son voorkoms.
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The development of some rotationally invariant population based optimization methodsRas, Marthinus Nicolaas 03 1900 (has links)
Thesis (MScEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: In this study we consider the lack of rotational invariance of three different population based optimization
methods, namely the particle swarm optimization (PSO) algorithm, the differential evolution
(DE) algorithm and the continuous-parameter genetic algorithm (CPGA). We then propose
rotationally invariant versions of these algorithms.
We start with the PSO. The so-called classical PSO algorithmis known to be variant under rotation,
whereas the linear PSO is rotationally invariant. This invariance however, comes at the cost of lack
of diversity, which renders the linear PSO inferior to the classical PSO.
The previously proposed so-called diverse rotationally invariant (DRI) PSO is an algorithm that
aims to combine both diversity and invariance. This algorithm is rotationally invariant in a stochastic
sense only. What is more, the formulation depends on the introduction of a random rotation
matrix S, but invariance is only guaranteed for ‘small’ rotations in S. Herein, we propose a formulation
which is diverse and strictly invariant under rotation, if still in a stochastic sense only. To
do so, we depart with the linear PSO, and then we add a self-scaling random vector with a standard
normal distribution, sampled uniformly from the surface of a n-dimensional unit sphere.
For the DE algorithm, we show that the classic DE/rand/1/bin algorithm, which uses constant
mutation and standard crossover, is rotationally variant. We then study a previously proposed
rotationally invariant DE formulation in which the crossover operation takes place in an orthogonal
base constructed using Gramm-Schmidt orthogonalization.
We propose two new formulations by firstly considering a very simple rotationally invariant formulation
using constant mutation and whole arithmetic crossover. This rudimentary formulation
performs badly, due to lack of diversity. We then introduce diversity into the formulation using two
distinctly different strategies. The first adjusts the crossover step by perturbing the direction of the
linear combination between the target vector and the mutant vector. This formulation is invariant
in a stochastic sense only. We add a self-scaling random vector to the unaltered whole arithmetic
crossover vector. This formulation is strictly invariant, if still in a stochastic sense only. In this study we consider the lack of rotational invariance of three different population based optimization
methods, namely the particle swarm optimization (PSO) algorithm, the differential evolution
(DE) algorithm and the continuous-parameter genetic algorithm (CPGA). We then propose
rotationally invariant versions of these algorithms.
We start with the PSO. The so-called classical PSO algorithmis known to be variant under rotation,
whereas the linear PSO is rotationally invariant. This invariance however, comes at the cost of lack
of diversity, which renders the linear PSO inferior to the classical PSO.
The previously proposed so-called diverse rotationally invariant (DRI) PSO is an algorithm that
aims to combine both diversity and invariance. This algorithm is rotationally invariant in a stochastic
sense only. What is more, the formulation depends on the introduction of a random rotation
matrix S, but invariance is only guaranteed for ‘small’ rotations in S. Herein, we propose a formulation
which is diverse and strictly invariant under rotation, if still in a stochastic sense only. To
do so, we depart with the linear PSO, and then we add a self-scaling random vector with a standard
normal distribution, sampled uniformly from the surface of a n-dimensional unit sphere.
For the DE algorithm, we show that the classic DE/rand/1/bin algorithm, which uses constant
mutation and standard crossover, is rotationally variant. We then study a previously proposed
rotationally invariant DE formulation in which the crossover operation takes place in an orthogonal
base constructed using Gramm-Schmidt orthogonalization.
We propose two new formulations by firstly considering a very simple rotationally invariant formulation
using constant mutation and whole arithmetic crossover. This rudimentary formulation
performs badly, due to lack of diversity. We then introduce diversity into the formulation using two
distinctly different strategies. The first adjusts the crossover step by perturbing the direction of the
linear combination between the target vector and the mutant vector. This formulation is invariant
in a stochastic sense only. We add a self-scaling random vector to the unaltered whole arithmetic
crossover vector. This formulation is strictly invariant, if still in a stochastic sense only. For the CPGA we show that a standard CPGA using blend crossover and standard mutation, is rotationally
variant. To construct a rotationally invariant CPGA it is possible to modify the crossover
operation to be rotationally invariant. This however, again results in loss of diversity. We introduce
diversity in two ways: firstly using a modified mutation scheme, and secondly, following the same
approach as in the PSO and the DE, by adding a self-scaling random vector to the offspring vector.
This formulation is strictly invariant, albeit still in a stochastic sense only.
Numerical results are presented for the variant and invariant versions of the respective algorithms.
The intention of this study is not the contribution of yet another competitive and/or superior population based algorithm, but rather to present formulations that are both diverse and invariant, in the
hope that this will stimulate additional future contributions, since rotational invariance in general
is a desirable, salient feature for an optimization algorithm. / AFRIKAANSE OPSOMMING: In hierdie studie bestudeer ons die gebrek aan rotasionele invariansie van drie verskillende populasiegebaseerde
optimeringsmetodes, met name die partikel-swerm optimerings (PSO) algoritme, die
differensi¨ele evolusie (DE) algoritme en die kontinue-parameter genetiese algoritme (KPGA). Ons
stel dan rotasionele invariante weergawes van hierdie algoritmes voor.
Ons beginmet die PSO. Die sogenaamde klassieke PSO algoritme is bekend dat dit variant is onder
rotasie, terwyl die lineˆere PSO rotasioneel invariant is. Hierdie invariansie lei tot ’n gebrek aan
diversiteit in die algoritme, wat beteken dat die lineˆere PSO minder goed presteer as die klassieke
PSO.
Die voorheen voorgestelde sogenaamde diverse rotasionele invariante (DRI) PSO is ’n algoritme
wat beoog om beide diversiteit en invariansie te kombineer. Hierdie algoritme is slegs rotasioneel
invariant in ’n stogastiese sin. Boonop is die formulering afhanklik van ’n willekeurige rotasie
matriks S, maar invariansie is net gewaarborg vir ’klein’ rotasies in S. In hierdie studie stel
ons ’n formulering voor wat divers is en streng invariant onder rotasie, selfs al is dit steeds net
in ’n stogastiese sin. In hierdie formulering, vertrek ons met die lineˆere PSO, en voeg dan ’n
self-skalerende ewekansige vektor met ’n standaard normaalverdeling by, wat eenvormig van die
oppervlakte van ’n n-dimensionele eenheid sfeer geneem word.
Vir die DE algoritme toon ons aan dat die klassieke DE/rand/1/bin algoritme, wat gebruik maak
van konstante mutasie en standaard kruising rotasioneel variant is. Ons bestudeer dan ’n voorheen
voorgestelde rotasionele invarianteDE formulering waarin die kruisingsoperasie plaasvind in ’n ortogonale
basis wat gekonstrueer wordmet behulp van die Gramm-Schmidt ortogonalieseringsproses.
Verder stel ons dan twee nuwe formulerings voor deur eerstens ’n baie eenvoudige rotasionele
invariante formulering te oorweeg, wat konstante mutasie en volledige rekenkundige kruising gebruik.
Hierdie elementˆere formulering onderpresteer as gevolg van die afwesigheid van diversiteit.
Ons voeg dan diversiteit by die formulering toe, deur gebruik te maak van twee afsonderlike strategie
¨e. Die eerste verander die kruisings stap deur die rigting van die lineˆere kombinasie tussen die
teiken vektor en die mutasie vektor te perturbeer. Hierdie formulering is slegs invariant in ’n
stogastiese sin. In die ander formulering, soos met die nuwe rotasionele invariante PSO, voeg ons bloot ’n self-skalerende ewekansige vektor by die onveranderde volledige rekenkundige kruisingsvektor.
Hierdie formulering is streng invariant onder rotasie, selfs al is dit steeds net in ’n
stogastiese sin.
Vir die KPGA wys ons dat die standaard KPGA wat gemengde kruising en standaard mutasies
gebruik, rotasioneel variant is. Om ’n rotasionele invariante KPGA te konstrueer is dit moontlik
om die kruisingsoperasie aan te pas. Dit veroorsaak weereens ’n verlies aan diversiteit. Ons maak die algoritmes divers op twee verskillende maniere: eerstens deur gebruik te maak van ’n
gewysigde mutasie skema, en tweedens deur die selfde aanslag te gebruik as in die PSO en die DE,
deur ’n self-skalerende ewekansige vektor by die nageslag vektor te voeg. Hierdie formulering is
streng invariant onder rotasie, selfs al is dit steeds net in ’n stogastiese sin.
Numeriese resultate word vir die variante en invariante weergawe van die onderskeie algoritmes
verskaf.
Die doel van hierdie studie is nie die bydrae van bloot nog ’n kompeterend en/of beter populasiegebaseerde
optimeringsmetode nie, maar eerder om formulerings voor te lê wat beide divers en invariant
is, met die hoop dat dit in die toekoms bykomende bydraes sal stimuleer, omdat rotasionele
invariansie in die algemeen ’n aantreklike, belangrike kenmerk is vir ’n optimerings algoritme.
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Modelling and verification of the dynamics of an ocean current energy converterGraaff, Simon 12 1900 (has links)
Thesis (MScEng) -- Stellenbosch University, 2014. / ENGLISH ABSTRACT: South Africa has a signi cant potential resource for electrical power generation
in the Agulhas Current on the southeast coast. The Ocean Current
Energy Convertor studied in this project was designed to generate power from
this current. The feasibility of this device was investigated by analysing the
dynamic stability and controllability of the convertor, when acted upon by
hydrodynamic forces while harvesting energy from the current. A simulation
model was developed to predict the dynamic behaviour using the Simulink
software suite. A scale model of the prototype was built and tested in the
Towing Tank at Stellenbosch University, and the experimental results were
compared against the simulation results. A control algorithm was designed,
using the mathematical model, to control the roll angle and deployment depth.
The control algorithm was tested in simulation.
The results indicated that the simulation model accurately predicted the
behaviour of the prototype in testing, and results showed that the device
is both stable and controllable. It was concluded that this OCEC design
concept warrants further investigation. The recommendations are that the
experimental model be improved to ensure reliable experimental results, that
further complexity be added to the simulation model, and that the control
algorithm be tested on the improved prototype in the towing tank. / AFRIKAANSE OPSOMMING: Die Agulhas-seestroom aan die suidooskus van Suid-Afrika bied 'n aansienlike
potensiële hulpbron vir elektriese kragopwekking. Die seestroomenergieomsetter
(SEO) wat in hierdie projek bestudeer is was ontwikkel om krag uit
hierdie seestroom te genereer. Die doenlikheid van hierdie toestel is ondersoek
deur die dinamiese stabiliteit en beheerbaarheid van die omsetter onder die invloed
van hidrodinamiese kragte te analiseer terwyl dit energie van die stroom
inwin. 'n Simulasiemodel is met behulp van Simulink-sagteware ontwikkel om
die dinamiese gedrag te voorspel. 'n Skaalmodel van die prototipe was gebou
en in die sleeptenk by Universiteit Stellenbosch getoets en die eksperimentele
resultate met die simulasie se resultate vergelyk. 'n Beheer-algoritme is
daarna ontwerp, deur middel van die wiskundige model, om die rolhoek en
diepte van ontplooiing te beheer.Hierdie algoritme is tydens simulasie getoets.
Die resultate het aangedui dat die simulasiemodel akkuraat die gedrag van
die prototipe tydens toetse voorspel het, en die resultate het gewys dat die
toestel beide stabiel en beheerbaar is. Die gevolgtrekking is gemaak dat die
SEO se ontwerpkonsep verdere studie regverdig. Die aanbevelings is dat die
eksperimentele model verbeter word om betroubare eksperimentele resultate
te verseker, dat verdere kompleksiteit by die simulasiemodel gevoeg word,
en dat die beheer-algoritme op die verbeterde model in die sleeptenk getoets
word.
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Perimeter fan performance in forced draught air-cooled steam condensersVan der Spuy, Sybrand Johannes 12 1900 (has links)
Thesis (PhD)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Axial flow fan arrays form part of air-cooled steam condensers in direct drycooled
power plants. This dissertation investigates the performance of axial flow
fans when located at the perimeter of a fan array. The perimeter (or edge) fans
may experience a reduction in air flow through the fan due to the prevalence of
distorted inlet conditions upstream of the fan. The reduction in air flow leads to a
reduction in the heat transfer capability of the steam condenser and a consequent
reduction in the electricity output of the power plant.
Due to the physical size of an air-cooled condenser, full-scale experiments are
often impractical and computational fluid dynamics (CFD) is used to model its
performance under various conditions. To limit the size of the CFD model the
axial flow fans in the CFD analysis are represented by means of simplified
methods. Three different simplified methods are presented and applied to a CFD
model of a single axial flow fan, namely the pressure jump method (PJM),
actuator disc method (ADM) and extended actuator disc method (EADM). The
results are compared to experimental values. The comparison highlights the
limitations of the models: The ADM fails to model fan performance correctly at
low flow rates, while the PJM ignores the variation in fan blade properties at
different locations within the fan rotor. The EADM is presented as an
improvement on both the other two models.
A multiple fan test facility is constructed, consisting of three 630 mm diameter
fans extracting air from a common inlet chamber. The inlet chamber is
constructed in such a way that one of the three fans act as the perimeter (edge)
fan. The floor of the inlet chamber can be adjusted to increase or reduce the inlet
flow distortion experienced by the edge fan. Six different fan configurations are
tested in the position of the edge fan and an empirical method is derived by which
the volumetric effectiveness of an edge fan can be predicted. The experimental
results are compared to CFD results for the same facility using the three different
simplified simulation methods investigated previously. Particle image velocimetry
(PIV) measurements are also performed upstream of the edge fan and the velocity
profiles at the inlet of the fan are compared to the profiles obtained numerically.
The comparisons show that the EADM predicts the performance of the edge fan
more accurately than the ADM en PJM.
The effect of adding a walkway and removing the bell mouth upstream of the
edge fan was investigated using the EADM. The results are used to show the
location of the loss mechanisms upstream of the edge fan. The addition of a
walkway moves the location of the pressure loss away from the edge fan bell
mouth towards the edge of the walkway. Consequently the distortion directly
upstream of the edge fan is reduced and its volumetric effectiveness increased.
The effect of removing the edge fan’s bell mouth is similar to the effect of adding
a walkway upstream of the edge fan. / AFRIKAANSE OPSOMMING: Aksiaalwaaiermatrikse vorm deel van lugverkoelde kondensors in direk droëverkoelde
kragstasies. Hierdie verhandeling ondersoek die werkverrigting van
aksiaalwaaiers wat geleë is op die rand van ‘n groot waaiermatriks. Die
randwaaiers kan ’n vermindering in deurvloei ondervind as gevolg van versteurde
inlaattoestande stroom-op vanaf die waaier. Die vermindering in lugvloei lei tot ’n
vermindering in die warmetoordagvermoë van die stoomkondensor en ’n
gepaardgaande afname in die elektrisiteitslewering van die kragstasie.
As gevolg van die fisiese grootte van die lugverkoelde kondensor is volskaalse
eksperimente gewoonlik onprakties en word berekeningsvloeimeganika (BVM)
gebruik om die werking van die aanleg onder verskeie toestande te modelleer. Ten
einde die grootte van die BVM model te beperk, word die aksiaalwaaiers in so ‘n
BVM analiese voorgestel met behulp van vereenvoudigde metodes. Drie
verskillende vereenvoudigde metodes word aangebied en toegepas op ‘n BVM
model van ‘n enkelwaaier, naamlik die druksprongmetode, die aksieskyfmetode
en die verlengde aksieskyfmetode. Die resultate word vergelyk met
eksperimentele waardes. Die vergelyking benadruk die beperkings van die
modelle: Die aksieskyfmetode kan nie die werking van die waaier akkuraat
voorspel by lae vloeie nie en die druksprongmetode ignoreer die variasie in
lemeienskappe op verskillende liggings binne-in die waaierrotor. Die verlengde
aksieskyfmetode word voorgestel as ‘n verbetering op die ander twee metodes.
‘n Veelvuldige waaiertoetsfasiliteit is saamgestel, bestaande uit drie 630 mm
deursnee waaiers wat lug uit ’n gemeenskaplike inlaatkamer suig. Die inlaatkamer
is so saamgestel dat een van die waaiers in die fasiliteit ‘n randwaaier
verteenwoordig. Die vloerhoogte van die inlaatkamer kan aangepas word om die
inlaatversteuring wat deur die raandwaaier ondervind word te vermeerder of te
verminder. Ses verskillende waaierkonfigurasies is getoets in die
randwaaierposisie. ‘n Empiriese metode waarmee die volumetriese effektiwiteit
van ‘n randwaaier voorspel kan word is afgelei. Die eksperimentele resultate word
vergelyk met ooreenstemmende BVM resultate vir dieselfde fasiliteit deur gebruik
te maak van die drie verskillende vereenvoudigde metodes wat vroeër ondersoek
is. Partikelbeeld snelheidsmetings word ook stroom-op vanaf die randwaaier
uitgevoer en die snelheidsprofiele by die inlaat van die waaier word vergelyk met
profiele wat numeries bereken word. Die vergelykings wys dat die verlengde
aksieskyfmetode die werkverrigting van ’n aksiaalwaaier meer akkuraat voorspel
as die aksieskyf- of druksprongmetodes.
Die effek van die installering van ‘n loopvlak en die verwydering van die
randwaaier se inlaatmondstuk word ondersoek met behulp van BVM deur gebruik
te maak van die verlengde aksieskyfmetode. Die resultate word spesifiek gebruik
om die ligging van die verliesmeganismes stroom-op vanaf die randwaaier aan te
dui. Die resultate wys dat die installering van ‘n loopvlak die ligging van die
drukverlies wegneem vanaf die rand van die waaierinlaat na die rand van die
loopvlak. Dit verminder die inlaatversteuring stroom-op vanaf die randwaaier en die volumetriese effektiwiteit word verhoog. Die verwydering van die randwaaier
se inlaatmondstuk het ‘n soortgelyke effek as die installering van ‘n loopvlak
stroom-op vanaf die randwaaier.
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Three-dimensional modelling of simultaneous saccharification and fermentation of cellulose to ethanolVan Zyl, Josebus Maree 03 1900 (has links)
Thesis (PhD)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Second-generation bioethanol is an alternative transportation fuel currently being
investigated whereby cellulose, specifically lignocellulosic (woody) portions, of
any plant mass can be converted to ethanol. To date, the technology had only been
successfully implemented with demonstration scale facilities. Despite intensive
research efforts at laboratory scale, no-one is certain what the secondary effects of
scale-up to large systems are. The objective of this project was to develop threedimensional
numerical models of a laboratory scale fermenter which could predict
the effects of particulate mixing and reaction kinetics for future scale-up
investigations.
A numerical model of the reaction kinetics for simultaneous saccharification and
fermentation of Avicel (microcrystalline cellulose) particles to ethanol is
presented. The novelty of this model is the separation of the two primary
cellulase enzyme-kinetics, which generated the capability to predict the
heterogeneous behaviour of the enzyme-substrate interactions. This model
improves the understanding of these systems while maintaining sufficient
simplicity for implementation alongside a commercial computational fluid
dynamics environment.
Effects of the various fermentation medium constituents and the influence of each
on the dynamic viscosity of the medium were also investigated. Results indicated
that particle volume fraction had the dominant effect on the apparent dynamic
viscosity resulting in further research of the particle properties. Due to the
irregular shapes of Avicel particles, tests were conducted to determine drag and
settling behaviour, which led to the development and modification of models to
account for these phenomena. This investigation is unique as it allows a more
accurate calculation of particle transportation through a three-dimensional
environment including the effects of natural packing density. At lower particle
volume fraction the concentration of ethanol and glycerol had the greatest effect
on the apparent dynamic viscosity and was calculated from models obtained from
literature.
Validation of the physics and the incorporation thereof in the simulations resulted
in the modification of various generic models which either improved numerical
stability or accuracy, or both. Contributions included a modified form of the
pressure force model, which proved significantly more stable and accurate than
previous models proposed in literature. The models developed for capturing the
effects of particles on the apparent dynamic viscosity proved effective for this
specific substrate.
Results from cross-coupling the reaction models with computational fluid
dynamic simulations provide a novel approach to capturing the secondary effect
of substrate conversion and particle distribution on the performance of the
fermentation vessels. This is the first time where that biological reactions were successfully combined with particle dynamics and fluid flow fields to investigate
the secondary effects which occur in fermenters.
This work served as a foundation for future research and development within the
bioethanol field with significant potential for expansion into other biochemical
disciplines. / AFRIKAANSE OPSOMMING: Tweede-generasie bioetanol is ’n alternatiewe vervoerbrandstof wat tans
ondersoek word waar sellulose, spesifiek lignosellulosiese (houtagtige) gedeeltes,
van enige plantmassa na etanol omgesit kan word. Tot op hede was die
tegnologie slegs suksesvol geïmplimenteer in demonstrasieskaal fasiliteite. Ten
spyte van intensiewe navorsingpogings op laboratoriumskaal, is niemand seker
wat die sekondêre effekte van die opskaal tot groot stelsels sal wees nie. Die
doelwit van die projek was om drie-dimensionele modelle te ontwikkel van ’n
laboratoriumskaal fermentor wat die effekte van partikulêre vermenging en
reaksiekinetika kan voorspel vir toekomstige opskaal navorsing.
’n Numeriese model van die reaksiekinetika vir gelyktydige versuikering en
fermentasie van Avicel (mikrokristallyne sellulose) partikels tot etanol word
aangebied. Die oorspronklikheid van die model is geleë in die skeiding van die
twee primêre sellulase ensiemkinetika, wat lei tot die vermoë om die heterogene
gedrag van die ensiem-substraat interaksies te voorspel. Hierdie model verbeter
die kennis van die stelsels, terwyl voldoende eenvoud behoue bly vir
implementering parallel aan kommersiële berekeningsvloeidinamika sagteware.
Effekte van die verskillende bestanddele van die fermentasiemedium en die
invloed van elk op die dinamiese viskositeit van die medium is ook ondersoek.
Resultate dui aan dat partikel volume fraksie die dominante invloed op die
skynbare dinamiese viskositeit het, wat gelei het tot verdere ondersoek van die
partikel eienskappe. As gevolg van die onreëlmatige vorms van Avicel partikels,
is toetse gedoen om die sleur-en uitsakkingsgedrag te bepaal, wat gelei het tot die
ontwikkeling en aanpassing van modelle om hierdie verskynsels in ag te neem.
Hierdie ondersoek is uniek, want dit laat meer akkurate berekening van
partikelvervoer deur ’n drie-dimensionele omgewing toe, insluitend die effekte
van natuurlike verpakkingsdigtheid. By laer partikel volume fraksie het die
konsentrasie van etanol en gliserol die grootste effek op die skynbare dinamiese
viskositeit gehad en was bereken vanaf modelle in die literatuur.
Bevestiging van die fisika en die insluiting daarvan in die simulasies het gelei tot
die aanpasing van verskillende generiese modelle wat óf numeriese stabiliteit óf
akkuraatheid óf beide verbeter. Bydraes gemaak sluit ’n aangepaste vorm van die
drukkragmodel in, wat heelwat meer stabiel en akkuraat was as die vorige modelle
voorgestel in die literatuur. Die modelle wat ontwikkel is om die effek van
partikels op die skynbare viskositeit vas te vang, was effektief bewys vir hierdie
spesifieke substraat.
Resultate van die kruiskoppeling van inligting vanaf die reaksiemodelle met
berekeningsvloeidinamika simulasies lewer ’n nuwe benadering tot die bepaling
van die sekondêre effek van substraatomskakeling en partikeldistribusie op die
uitvoering van die fermentasie toestel. Hierdie is die eerste poging om biologiese reaksies met partikel dinamika en vloeivelde te kombineer om die sekondêre
effekte wat in fermenter plaasvind, te ondersoek.
Hierdie werk dien as ’n grondslag vir toekomstige navorsing en ontwikkeling
binne die bioetanolveld, met beduidende potensiaal vir uitbreiding na ander
biochemiese dissiplines.
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