Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: The focus of this project was on the potential application of waste heat recovery and utilisation
(WHR&U) systems in pebble bed modular reactor (PBMR) technology. The background theory
provided in the literature survey showed that WHR&U systems have attracted the attention of
many researchers over the past two decades, as using waste heat improves the system
overall efficiency, notwithstanding the cost of extra plant. PBMR waste heat streams were
identified and investigated based on the amount of heat rejected to the environment.
WHR&U systems require specially designed heat recovery equipment, and as such the used
and/or spent PBMR fuel tanks were considered by the way of example. An appropriately
scaled system was designed, built and tested, to demonstrate the functioning of such a
cooling system. Two separate and independent cooling lines, using natural circulation flow in a
particular form of heat pipes called thermosyphon loops were used to ensure that the fuel tank
is cooled when the power conversion unit has to be switched off for maintenance, or if it fails.
A theoretical model that simulates the heat transfer process in the as-designed WHR&U
system was developed. It is a one-dimensional flow model assuming quasi-static and
incompressible liquid and vapour flow. An experimental investigation of the WHR&U system
was performed in order to validate the theoretical model results. The experimental results
were then used to modify the theoretical heat transfer coefficients so that they simulate the
experiments more accurately.
Three energy conversion devices, the dual-function absorption cycle (DFAC), the organic
Rankine cycle (ORC) and the Stirling engine (SE), were identified as suitable for transforming
the recovered heat into a useful form, depending on the source temperatures from 60 ºC to
800 ºC. This project focuses on a free-piston SE with emphasis on the thermo-dynamic
performance of a SE heat exchanger. It was found that a heat exchanger with a copper woven
wire mesh configuration has a relatively large gas-to-metal and metal-to-liquid heat transfer
area. Tube-in-shell heat exchanger configurations were tested, with the working fluid flowing in
ten copper inner pipes, while a coolant flows through the shell tube.
A lumped parameter model was used to describe the thermo-fluid dynamic behaviour of the
SE heat exchanger. In order to validate the theoretical results, a uni-directional flow
experimental investigation was performed. The theoretical model was adjusted so that it
simulated the SE heat exchanger. It was found that after this correction the theoretical model
accurately predicts the experiment. Finally, a dynamic analysis of the SE heat exchanger
experimental set-up was undertaken to show that, although vibrating, the heat exchanger setup
assembly was indeed acceptable from a vibrational and fatigue point of view. / AFRIKAANSE OPSOMMING: Die hoofoogmerk met hierdie projek was die moontlike aanwending van afvalhitteherwinningen-
benutting-(WHR&U-) stelsels in modulêre-gruisbedreaktor-(PBMR-) tegnologie.
Agtergrondteorie in die literatuurondersoek toon dat WHR&U-stelsels al menige navorser se
belangstelling geprikkel het, hetsy vanweë die moontlike ekonomiese voordele wat dit inhou óf
vir besoedelingsvoorkoming, bo-en-behalwe die koste van bykomende toerusting. Die PBMRafvalhittestrome
is ondersoek en bepaal op grond van die hoeveelheid hitte wat dit na die
omgewing vrystel.
Om in die prosesbehoeftes van WHR&U-stelsels te voorsien, moet goed ontwerpte,
doelgemaakte hitteherwinningstoerusting in ʼn verkoelings- en/of verhittingsproses gebruik
word, dus is die PBMR as voorbeeld gebruik vir die konsep. ʼn Toepaslik geskaleerde
WHR&U-stelsel is dus ontwerp, gebou en getoets om die geldigheid van die stelselontwerp te
toon. Twee onafhanklike verkoelingslyne, wat van natuurlike konveksie gebruik maak, in die
vorm van hitte-pype of termoheuwel lusse, was gebruik om te verseker dat verkoeling verskaf
word wanneer die hoof lus breek of instandhouding nodig hê.
ʼn Teoretiese model is ontwikkel wat die hitteoordragproses in die ontwerpte WHR&U-stelsel
simuleer. Dié model was ʼn eendimensionele vloeimodel wat kwasistatiese en
onsamedrukbare vloeistof- en dampvloei in die WHR&U-stelsel-lusse veronderstel. ʼn
Eksperimentele ondersoek is op die WHR&U-stelsel uitgevoer ten einde die teoretiese model
se resultate te bevestig. Die eksperimentele resultate was dus geneem om die teoretiese
hitteoordragkoëffisiënte aan te pas sodat dit die eksperimente kon simuleer.
Drie energieomsettingstoestelle, naamlik die dubbel funksie absorpsie siklus (DFAC), die
organiese Rankine siklus (ORC) en die Stirling enjin (SE), is as geskikte toestelle uitgewys om
die herwonne hitte op grond van brontemperature tussen 60 ºC en 800 ºC in ʼn bruikbare vorm
om te sit. Hierdie tesis het op vryesuier-SE’s gekonsentreer, met klem op die hitteruiler. Meer
bepaald is die termodinamiese werkverrigting van ʼn SE-hitteruiler ondersoek. Daar is bevind
dat ʼn hitteruiler met ʼn geweefde koperdraadmaas-samestelling oor ʼn betreklik groot gas-totmetaal-
en metaal-tot-vloeistof-oordragoppervlakte beskik. Die verhitter en verkoeler is in ʼn
buis-in-mantel-vorm ontwerp, met die werksvloeistof wat deur tien koperbinnepype vloei en ʼn
koelmiddel deur die mantelbuis. ʼn Saamgevoegde-parameter-model is gebruik om die termodinamiese gedrag van die SEhitteruiler
te beskryf. Ten einde die teoretiese resultate te bevestig, is ʼn eenrigtingvloeiproefondersoek
uitgevoer. Die teoretiese model is aangepas sodat dit die SE-hitteruiler kon
simuleer. Ná die nodige verstellings is daar bevind dat die teoretiese model die proefneming
akkuraat voorspel. Laastens was ʼn dinamiese ontleding van die SE-hitteruiler ook onderneem
om te toon dat, hoewel dit vibreer, die hitteruiler proef samestel inderdaad veilig is.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/19957 |
| Date | 03 1900 |
| Creators | Senda, Franck Mulumba |
| Contributors | Dobson, R. T., Stellenbosch University. Faculty of Engineering. Dept. of Mechanical & Mechatronic Engineering. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 1 v. (various pagings) : ill. |
| Rights | Stellenbosch University |
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