Thesis (PhD)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: This dissertation is basically a summary, with some interpretation, of published research
by the author. The scope is limited to the fields of turbo-machinery, computational fluid
dynamics and solar chimney power plants.
The main contribution in the field of turbo-machinery in general is in the development
of a through-flow method that automatically satisfies mass conservation. Concerning
fan design, the contributions are the realization of the importance of the exit
kinetic energy in the determination of the efficiency of rotor-only axial flow fans, and
the quantification of the effect of off-axis inflow into cooling system fans on their performance.
In the field of centrifugal fans and compressors an original, unifying model
for the prediction of slip factor was developed. To investigate accident scenarios in
closed cycle gas turbine nuclear reactors, all possible operational modes of multi-stage
axial compressor operation caused by flow and rotation direction were investigated experimentally
and computationally. Spanning the fields of turbo-machinery and solar
chimneys, the basic theory of solar chimney turbines was developed, showing that high
turbine efficiency was possible.
In the field of solar chimneys, an original thermodynamic approach was developed
to predict the main relationships that govern solar chimney performance, and to solve
the through-flow equations for non-ideal systems with losses. Equations for the accurate
determination of all the thermodynamic variables in a solar chimney as dependent on
chimney height, wall friction, additional losses, internal drag and area change were
derived and solved. Coefficients of wall friction, bracing wheel loss and exit kinetic
energy were determined experimentally, and empirical equations were developed to
predict the loss coefficient of the collector to turbine transition section and and the
turbine inlet flow angle. A simple power law approach allowed the calculation of the
optimal turbine pressure drop in solar chimney power plants. A comparison of two sets
of equations used to calculate the heat fluxes into, inside and leaving the solar collector,
resulted in similar air temperature rises in the collector, and similar produced power.
It turned out however that the optimal flow for minimal turbine pressure drop was
dependent on the heat transfer models.
Investigation of the performance of various solar chimney turbo-generator layouts
using analytical models and optimisation techniques showed that the optimal number
of turbines varies with plant size, but the individual turbine size, the number of blades
and even the efficiency remains close to constant. It was found that the cost of a turbogenerator
system, however, varies significantly with size. A joint paper with several
German universities and institutions did a comparative cost analysis of solar chimney
power plants / AFRIKAANSE OPSOMMING: Hierdie verhandeling is basies ’n opsomming, met interpretasie, van gepubliseerde navorsing
deur die outeur. Die omvang is beperk tot die gebiede van turbomasjinerie,
berekeningsvloeidinamika en sonskoorsteenkragstasies.
Die hoof bydrae op die gebied van turbomasjinerie in die algemeen is in die ontwikkeling
van ’n deurvloeimetode wat outomaties massabehoud bevredig. Wat waaierontwerp
betref is die bydrae die besef van die belangrikheid van die uitlaat kinetiese
energie in die bepaling van waaierbenuttingsgraad, en die kwantifisering van die effek
van af-as invloei in verkoelingswaaiers op hulle gedrag. Op die gebied van sentrifugaalwaaiers
en -kompressors is ’n oorspronklike, samevattende model vir die voorspelling
van glipfaktor ontwikkel. Om ongeluk-scenario’s in geslote kringloop gasturbine kenreaktors
te ondersoek is al die moontlike werksmodusse veroorsaak deur vloei en rotasie
rigting van ’n multistadium aksiaalkompressor eksperimenteel en numeries ondersoek.
As brug tussen turbomasjinerie en sonskoorstene is die basiese teorie van sonskoorsteenturbines
ontwikkel met die aanduiding dat hoë turbine benuttingsgraad moontlik
is.
Op die gebied van sonskoorstene is ’n oorspronklike termodinamies benadering ontwikkel
om die hoofverwantskappe te voorspel wat sonskoorsteen gedrag bepaal, en
om die deurvloei vergelykings op te los vir nie-ideale stelsels met verliese. Vergelykings
vir die akkurate bepaling van al die termodinamiese veranderlikes in ’n sonskoorsteen
soos afhanklik van skoorsteenhoogte, wandwrywing, bykomstige verliese, interne
sleur en oppervlakte verandering is afgelei en opgelos. Koëffisiënte vir wandwrywing,
verstywingswiel-verlies en uitlaat kinetiese energie is eksperimenteel bepaal, en empiriese
vergelykings is ontwikkel om die verlieskoëffisiënt van die kollektor-tot-skoorsteen
oorgang en die turbine inlaatvloeihoek te bepaal. ’n Eenvoudige magswet benadering
het dit mootlik gemaak om die optimum turbine-drukval in sonskoorsteen aanlegte te
bepaal. ’n Verglyking van twee stelle vergelykings om warmtevloede in, binne en uit
die sonkollektor te bereken het gelei na soortgelyke temperatuurstygings en gelewerde
drywing. Die optimale vloei vir maksimum drywing was egter afhanklik van die warmteoordrag
modelle.
Ondersoek van die gedrag van verskeie turbo-generator uitlegte, deur gebruik van
analitiese modelle en optimeringstegnieke het getoon dat die optimale aantal turbines
wissel met aanleg grootte, maar die individuele turbine grootte, die aantal lemme en
selfs die benuttingsgraad bly feitlik konstant. Daar is egter gevind dat die koste van
’n turbogenerator stelsel beduidend wissel met grootte. ’n Gesamentlike artikel met
verskeie Duitse universiteite en instansies het ’n vergelykende koste analise van sonskoorstene
gedoen.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/71762 |
| Date | 12 1900 |
| Creators | Von Backstrom, Theodor W. |
| Contributors | Harms, T. M., Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | [550] p. : ill. |
| Rights | Stellenbosch University |
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