Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: The feasibility of a closed loop thermosyphon for the Reactor Cavity Cooling
System of the Pebble Bed Modular Reactor has been the subject of many research
projects. Difficulties identified by previous studies include the hypothetical
inaccuracies of heat transfer coefficient correlations available in literature. The
aim of the research presented here is to develop inside-pipe heat transfer
correlations that are specific to the current design of the RCCS.
In order to achieve this, a literature review is performed which identifies reactors
which employ closed loop thermosyphons and natural circulation. The literature
review also explains the general one-dimensional two-fluid conservation
equations that form the basis for numerical modelling of natural circulation loops.
The literature review lastly discusses available heat transfer coefficient
correlations with the aim of identifying over which ranges and under which
circumstances these correlations are considered accurate. The review includes
correlations commonly used in natural circulation modelling in the nuclear
industry in aims of identifying correlations applicable to the modelling of the
proposed RCCS.
One of the objectives of this project is to design and build a one-third-height-scale
model of the RCCS. Shortcomings of previous experimental models were
assessed and, as far as possible, compensated for in the design of the model.
Copper piping is used, eliminating material and surface property uncertainties.
Several sight glasses are incorporated in the model, allowing for the visual
identification of two-phase flow regimes. An orifice plate is used allowing for bidirectional
flow measurement. The orifice plate, thermocouples and pipe-in-pipe
heat exchangers are calibrated in-situ to minimize experimental error and aid
repeatability.
Twelve experiments are performed with data logging occurring every ten seconds.
The results presented here are limited to selected single and two-phase flow
operating mode results. Error analyses and repeatability of experimental
measurements for single and two-phase operating modes as well as cooling water
mass flow rates are performed, to show repeatability of experimental results.
These results are used to mathematically determine the experimental inside-pipe
heat transfer coefficients for both the evaporator and condenser sections. Trends
in the heat transfer coefficient profiles are identified and the general behaviour of
the profiles is thoroughly explained.
The RCCS is modelled as a one-dimensional system. Correlations for the friction
factor, heat transfer coefficient, void fraction and two-phase frictional multiplier
are identified. The theoretical heat transfer coefficients are calculated using the
mathematical model and correlations identified in the literature review. Fluid
parameters are evaluated using experimentally determined temperatures and mass
flow rates. The resulting heat transfer coefficient profiles are compared to experimentally determined profiles, to confirm the hypothesis that existing
correlations do not accurately predict the inside-pipe heat transfer coefficients.
The experimentally determined coefficients are correlated to 99% confidence
intervals. These generated correlations, along with identified and established twophase
heat transfer coefficient correlations, are used in a mathematical model to
generate theoretical coefficient profiles. These are compared to the experimentally
determined coefficients to show prediction accuracy. / AFRIKAANSE OPSOMMING: Die haalbaarheid van ‘n natuurlike sirkulasie geslote lus vir die Reaktor Holte
Verkoeling Stelsel (RHVS) van die Korrelbed Modulêre Kern-Reaktor (KMKR)
is die onderwerp van talle navorsings projekte. Probleme geïdentifiseer in vorige
studies sluit in die hipotetiese onakkuraatheid van hitte-oordrag koëffisiënt
korrelasies beskikbaar in literatuur. Die doel van die navorsing aangebied is om
binne-pyp hitte-oordrag koëffisiënt korrelasies te ontwikkel spesifiek vir die
huidige ontwerp van die RHVS.
Ten einde dit te bereik, word ‘n literatuurstudie uitgevoer wat kern-reaktors
identifiseer wat gebruik maak van natuurlike sirkulasie lusse. Die literatuurstudie
verduidelik ook die algemene een-dimensionele twee-vloeistof behoud
vergelykings wat die basis vorm vir numeriese modellering van natuurlike
sirkulasie lusse. Die literatuurstudie bespreek laastens beskikbare hitte-oordrag
koëffisiënt korrelasies met die doel om te identifiseer vir welke massavloei tempo
waardes en onder watter omstandighede hierdie korrelasies as korrek beskou is.
Die ontleding sluit korrelasies in wat algemeen gebruik word in die modellering
van natuurlike sirkulasie in die kern industrie met die hoop om korrelasies vir
gebruik in die modellering van die voorgestelde RHVS te identifiseer.
Een van die doelwitte van die projek is om ‘n een-derde-hoogte-skaal model van
die RHVS te ontwerp en te bou. Tekortkominge van vorige eksperimentele
modelle is geidentifiseer en, so ver as moonlik, voor vergoed in die ontwerp van
die model. Koper pype word gebruik wat die onsekerhede van materiaal en
opperkvlak eindomme voorkom. Verkseie deursigtige polikarbonaat segmente is
ingesluit wat visuele identifikasie van twee-fase vloei regimes toelaat. ‘n Opening
plaat word gebruik om voorwaartse en terugwaartse vloeimeting toe te laat. Die
opening plaat, termokoppels en hitte uitruilers is gekalibreer in plek om
eksperimentele foute te verminder en om herhaalbaarheid te verseker.
Twaalf eksperimente word uitgevoer en data word elke tien sekondes aangeteken.
Die resultate wat hier aangebied word, is beperk tot geselekteerde enkel- en tweefase
vloei meganismes van werking. Fout ontleding en herhaalbaarheid van
eksperimentele metings, om die herhaalbaarheid van eksperimentele resultate te
toon. Hierdie is gebruik om wiskundig te bepaal wat die eksperimentele binne-pyp
hitte-oordrag koëffisiënte is vir beide die verdamper en kondenseerder afdelings.
Tendense in die hitte-oordrag koëffisiënt profiele word geïdentifiseer en die
algemene gedrag van die profiles is deeglik verduidelik.
Die RHVS is gemodelleer as 'n een-dimensionele stelsel. Korrelasies vir die
wrywing faktor, hitte-oordrag koëffisiënte, leegte-breuk en twee-fase wrywings
vermenigvuldiger word geïdentifiseer. Die teoretiese hitte-oordrag koëffisiënte
word bereken deur middle van die wiskundige model en korrelasies wat in
literatuur geidentifiseer is. Vloeistof parameters is geëvalueer met eksperimenteel
bepaalde temperature en massa-vloei tempos. Die gevolglike hitte-oordrag koëffisiënt profiles is vergelyk met eksperimentele profiele om die hipotese dat
die bestaande korrelasies nie die binne-pyp hitte-oordrag koëffisiënte akkuraat
voorspel nie, te bevestig.
Die eksperimenteel bepaalde koëffisiënte is gekorreleer en die gegenereerde
korrelasies, saam met geïdentifiseerde twee-fase hitte-oordrag koëffisiënt
korrelasies, word gebruik in 'n wiskundige model om teoretiese koëffisiënt
profiele te genereer. Dit word dan vergelyk met die eksperimenteel bepaalde hitteoordrag
koëffisiënte om die akkuraatheid van voorspelling te toon.
Tekortkominge in die teoretiese en eksperimentele model word geïdentifiseer en
aanbevelings gemaak om hulle aan te spreek in die toekoms.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/6708 |
| Date | 03 1900 |
| Creators | Sittmann, Ilse |
| Contributors | Dobson, R. T., University of Stellenbosch. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 1 v. (various pagings) : ill. |
| Rights | University of Stellenbosch |
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