11 |
Design, build and test a passive thermal system for a loft : a roof solar chimney application for South African weather conditionsBeviss-Challinor, Lauren Margaret January 2007 (has links)
Thesis (MEng (Mechanical and Mechatronic Engineering))--Stellenbosch University, 2007. / ENGLISH: The design, construction and testing of a passive thermal system, a roof solar
chimney, for a loft is considered. Unlike conventional solar chimneys the solar
collector is constructed from corrugated iron roof sheets with the aim that it can be
integrated into existing buildings at a lower cost or used in low cost housing
developments. The main objective of the study was to determine the feasibility of
such low-cost design to regulate thermal conditions in a loft, that is heating the loft during winter and enhancing natural ventilation during summer, by carrying out an
experimental and analytical study. The results obtained from the experimental study showed that for winter the solar chimney, having a channel width, depth and length of 0.7 m, 0.1 m and 1.8 m respectively and with a peal solar radiation of 850 W/m², heated the room air 5°C higher than the ambient temperature during the hottest periods of the day, which is only marginally better than a loft with conventional roof insulation. At night, it was found that reverse airflow occurred through the chimney, cooling the loft down to
ambient temperature, due to radiation heat loss from the roof collector to the night
sky. For summer operation, the experimental data showed that the chimney was able
to maintain the loft at ambient temperature and the analytical study found that the
chimney was able to enhance natural ventilation effectively, reaching air exchange rate of 6.6 per hour for the 4.6 m³ volume space. It was also found that the chimney’s performance dropped rapidly and significantly during periods of low solar radiation and at night. A sensitivity analysis illustrated that for both summer and winter operation, the size, tilt angle and absorptivity of the roof collector greatly effected the efficiency and mass flow rates of the system, agreeing well with other literature. These results prove that this low cost solar chimney cooling design was feasible to enhance natural ventilation mainly during hot summer conditions with high solar radiation. Compared to a loft with only conventional roof insulation, the chimney did not perform effectively during the winter to heat the loft up, meaning that winter operation for this specific design is not feasible. Possible improvements to the design include using construction materials with higher thermal capacities to retain heat
energy and ensure continued operation during periods of low solar radiation, as well
as using selective absorber coatings on the collector surface. It is recommended that
further work on the project include the integration of these improvements into the
present design and to use the findings obtained from the sensitivity analysis to
improve system efficiencies. CFD analysis of the test-rig will be insightful as an
additional means to validate and compare with the analytical and experimental data
obtained in this report. With the continuation of these studies, this low-cost solar chimney design can be optimised, validated on a commercial scale and built into existing and new housing developments. Incorporating such a passive thermal device will aid homeowners in air regulation and thermal comfort of their living space as well as saving on energy requirements. / Sponsored by the Centre for Renewable and Sustainable Energy Studies, Stellenbosch University
|
12 |
A numerical analysis of the flow field surrounding a solar chimney power plantHarris, Rhydar Lee 04 1900 (has links)
Thesis (MScIng)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: This study investigated the flow field above a proposed solar chimney power plant, without
a cross wind, using a commercial numerical solver in the form of CFX 4-4 by AEA
Technology plc. The governing equations solved are for an incompressible steady state
solution. Variation in density due to buoyant effects is modelled with the Boussinesq
approximation, and turbulence is approximated by the k-ε model with modifications due to
buoyancy. The effect of different turbulence conditions at atmospheric inflows is also
investigated.
Modifications to the k-ε turbulence model in the context of atmospheric turbulence are
investigated and applied to the standard k-ε model. These modifications include the
addition of source terms in the turbulence kinetic energy and the turbulence dissipation rate
equations to allow for the production/destruction of turbulence due to buoyancy. Other
modifications include an additional source term in the turbulence dissipation rate equation
accounting for atmospheric stability and the specification of model constants relevant to
atmospheric flows.
Initial results for the flow field using the Boussinesq approximation show reasonable
correlation between the current study and the study by Thiart (2002) whereby the flow
field exhibits characteristics of the axially symmetric turbulent jet. One of the primary and
most noticeable differences between the current study and that of Thiart (2002) is the
difference in height at which air is drawn into the collector.
In order to account for variation in density with height, a modification on the Boussinesq
approximation, the Deep Boussinesq model, Montavon (1998), is applied to a simplified
100 m by 100 m rectangular geometry. The results obtained are compared to a similar
model using the Boussinesq approximation and it is seen that the average velocities
reached in the deep Boussinesq model are significantly larger than those obtained in the
Boussinesq approximation. / AFRIKAANSE OPSOMMING: Hierdie studie ondersoek die vloeiveld bo 'n aangewese son-skoorsteen kragstasie, deur
die gebruik van 'n kommersiële numeriese oplosser in die vorm van CFX 4-4; van AEA
Technology plc. Die heersende vergelykings wat opgelos moet word, is vir 'n niesaampersbare,
tyd-onafhanklike oplossing. Die wisseling in digtheid as gevolg van
saamdrukbaarheids effekte, word gemodelleer met die Boussinesq benadering en
turbulensie-skatting deur die k-ε model met aanpassings as gevolg van dryfkrag. Die effek
van die verskillende turbulensie-toestande teen atmosferiese invloeing word ook
ondersoek.
Aanpassings op die k-ε turbulensie-model in die konteks van atmosferies turbulensie word
ondersoek en toegepas op die standaard k-ε model. Hierdie veranderinge sluit die
byvoeging van bron terme in die turbulente kinetiese energie en die turbulensieverspillings
vergelykings om ruimte te laat vir die produksie/afbreking van turbulensie as
gevolg van dryfkrag in. Ander aanpassings sluit in 'n bykomende bron term in die
turbulensie-verspillings vergelyking wat rekenskap gee vir atmosferiese stabiliteit en die
spesifikasie van model onveranderlikes met betrekking tot atmosferiese vloei.
Aanvanklike resultate vir die vloeiveld met die gebruik van die Boussinesq benadering dui
op geredelike ooreenstemming tussen de huidige studie en die studie van Thiart (2002),
waar die vloeiveld eienskappe toon van 'n simmetriese turbulente spilpunt. Een van die
mees primêre en duidelikste verskille tussen die huidige studie en diè van Thiart (2002) is
die verskil in die hoogte waarteen die lug in die samesteller ingesuig word.
Om rekenskep te kan gee vir die verskil in digtheid met betrekking tot hoogte is 'n
aanpassing van die Boussinesq benadering, die Diep Bussinesq model, Montavon (1998),
aangebring. Hierdie aanpassing word toegepas op ‘n vereenvoudigde 100 m by 100 m
reghoek. Die resultate wat verkry word, word vergelyk met 'n soortgelyke model waar die
algemene snelheid wat met die diep Boussinesq model bereik word merkbaar groter is as
die in die Boussinesq benadering.
|
13 |
Performance evaluation of a solar chimney power plantHedderwick, Richard Anthony 12 1900 (has links)
Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2000. / A solar chimney power plant consists of a central chimney that is surrounded by a
transparent canopy located a few meters above ground level. The ground beneath
this canopy or collector as it is known is heated by the solar radiation that is
effectively trapped by the collector. This in turn heats the air in the collector, which
flows radially inwards towards the chimney. This movement is driven by the
difference between the hydrostatic pressure of the air inside- and outside the solar
chimney system. The energy is extracted from the air by a turbine driven generator
situated at the base of the chimney.
The performance of such a solar chimney power plant is evaluated in this study
making use of a detailed mathematical model. In this model the relevant discretised
energy and draught equations are deduced and solved to determine the performance
of a specific plant referred to as the "reference plant". This plant is to be located at a
site near Sishen in the Northern Cape in South Africa where meteorological data is
available.
The performance characteristics of this plant are presented using values from the
21 st of December as an example. These characteristics include the instantaneous
and integrated power output, as well as the absorption of the solar radiation of each
of the parts of the collector. The air temperatures throughout the plant and the
convective heat transfer coefficients in the collector in the region of developing and
fully developed flow are presented. The pressure of the air throughout the system is
presented as well as the pressure drop over the turbine. Temperature distributions in
the ground below the collector are also presented and discussed.
|
14 |
Flow through a solar chimney power plant collector-to-chimney transition sectionKirstein, Carl 12 1900 (has links)
Thesis (MScIng)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: One of the areas of the fluid dynamic design of solar chimney power plants that has
not been investigated sufficiently is the collector-to-chimney transition section of a
single turbine layout. The transition section contains the turbine inlet guide vanes
(IGVs) that support the whole chimney and guide the flow entering the turbine. The
primary objective of the study was to determine the dependence of the loss coefficient
of the section on inlet guide vane stagger angle and collector roof height. Experiments
were done on a nominal 900 mm chimney diameter rig, with four combinations of
two collector roof heights and two IGV stagger angles. Velocity components and
pressures in the transition section were measured in three conical planes, respectively
at the IGV exit and midway to, and just below the turbine position, using a five-hole
pneumatic pressure probe. Very good agreement was found between experimental
values and commercial CFD code predictions of flow angles, velocity components
and internal and wall static pressures. The agreement between measured and predicted
total pressure loss coefficient was reasonable when considering that most of the loss
occurred in the weak wakes of the IGVs and in the very thin transition section wall
boundary layers. The CFD code served to extend the predictions to a proposed full
scale geometry. The losses are less than previously assumed. The study led to
correlations between respectively loss and turning angle as dependent variables, and
collector roof height and IGV stagger angle as independent variables. / AFRIKAANSE OPSOMMING: Een van die gebiede van vloeidinamiese ontwerp van sonskoorsteen kragstasies wat
nog nie voldoende navorsing geniet het nie is die kollektor-tot-skoorsteen oorgangs
gedeelte van `n enkel turbine opstelling. Die oorgangs gedeelte bevat die turbine se
inlaat lei lemme (ILL) wat die hele skoorsteen dra en die vloei lei wat by die turbine
ingaan. Die hoof doel van hierdie studie was om die verlies koëffisiënt van hierdie
oorgangs gedeelte te bepaal as afhanklike van die ILL stel hoek en die hoogte van die
kollektor se dak hoogte. Die eksperimente het op `n nominale 900mm deursnee
skoorsteen skaal model geskied, met vier kombinasies van twee dak hoogtes en twee
ILL stel hoeke. Snelheidskomponente en drukke is met `n pneumatiese 5-punt buis in
drie koniese vlakke in die oorgangs gedeelte gemeet. Die vlakke was by die ILL se
stert, halfpad deur die oorgangs gedeelte en by die turbine se inlaat. Baie goeie
ooreenstemming is gevind met die eksperimentele waardes en `n kommersiële CFD
kode se voorspellings van vloei hoeke, snelheidskomponente en interne- en wand
statiese drukke. Die ooreenstemming tussen die gemete waardes en die berekende
waardes vir die totale druk verlies koëffisiënt was redelik siende dat die meeste
verliese van die klein versteurings van die ILL en die oorgangs gedeelte se dun-wand
grenslae kom. Die CFD kode is toe ingespan om verdere voorspellings te maak vir `n
voorgestelde volskaal geometrie. Die verliese is minder as wat daar van te vore
voorspel is. Hierdie studie het gelei tot korrelasies tussen onderskeidelik verlies en
draai hoeke as afhanklike veranderlikes, en kollektor dak hoogte en ILL plasings hoek
as onafhanklike veranderlikes.
|
15 |
Automatic positioner and control system for a motorized parabolic solar reflectorPrinsloo, Gerhardus Johannes 12 1900 (has links)
Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Most rural African villages enjoy high levels of sunlight, but rolling out solar
power generation technology to tap into this renewable energy resource at remote
rural sites in Africa pose a number of design challenges. To meet these
challenges, a project has been initiated to design, build and test/evaluate a
knock down 3 kW peak electrical stand-alone self-tracking dual-axis concentrating
solar power system.
This study focusses on the mechatronic engineering aspects in the design
and development of a dynamic mechatronic platform and digital electronic
control system for the stand-alone concentrating solar power system. Design
specifications require an accurate automatic positioner and control system for
a motorized parabolic solar reflector with an optical solar harnessing capacity
of 12 kWt at solar noon. It must be suitable for stand-alone rural power generation.
This study presents a conceptual design and engineering prototype
of a balanced cantilever tilt-and-swing dual-axis slew drive actuation means
as mechatronic solar tracking mobility platform for a ∼12 m2 lightweight
parabolic solar concentrator. Digital automation of the concentrated solar
platform is implemented using an industrial Siemens S7-1200 programmable
logic controller (PLC) with digital remote control interfacing, pulse width modulated
direct current driving, and electronic open loop/closed loop solar tracking
control. The design and prototype incorporates off-the-shelf components
to support local manufacturing at reduced cost and generally meets the goal
of delivering a dynamic mechatronic platform for a concentrating solar power
system that is easy to transport, assemble and install at remote rural sites
in Africa. Real-time experiments, conducted in the summer of South Africa,
validated and established the accuracy of the engineering prototype positioning
system. It shows that the as-designed and -built continuous solar tracking
performs to an optical accuracy of better than 1.0◦ on both the azimuth and
elevation tracking axes; and which is also in compliance with the pre-defined
design specifications.
Structural aspects of the prototype parabolic dish are evaluated and optimized
by other researchers while the Stirling and power handling units are under
development in parallel projects. Ultimately, these joint research projects
aim to produce a locally manufactured knock down do-it-yourself concentrated
solar power generation kit, suitable for deployment into Africa. / AFRIKAANSE OPSOMMING: Landelike gebiede in Afrika geniet hoë vlakke van sonskyn, maar die ontwerp
van betroubare sonkrag tegnologie vir die benutting van hierdie hernubare
energie hulpbron by afgeleë gebiede in Afrika bied verskeie uitdagings. Om
hierdie uitdagings te oorkom, is ’n projek van stapel gestuur om ’n afbreekbare
3 kW piek elektriese alleenstaande selfaangedrewe dubbel-as son-konsentreeder
te ontwerp, bou en te toets.
Hierdie studies fokus op die megatroniese ingenieurs-aspekte in die ontwerp
en ontwikkeling van ’n dinamiese megatroniese platform en ’n digitale
elektroniese beheerstelsel vir die alleenstaande gekonsentreerde sonkrag stelsel.
Ontwerp spesifikasies vereis ’n akkurate outomatiese posisionering en beheer
stelsel vir ’n motor aangedrewe paraboliese son reflekteerder met ’n optiesekollekteer-
kapasiteit van 12 kWt by maksimum sonhoogte, en veral geskik wees
vir afgeleë sonkrag opwekking. Hierdie studie lewer ’n konsepsuele ontwerp en
ingenieurs-prototipe van ’n gebalanseerde dubbelas swaai-en-kantel swenkrat
aandrywingsmeganisme as megatroniese sonvolg platform vir ’n ∼12 m2 liggewig
paraboliese son konsentreerder. Digitale outomatisering van die son konsentreerder
platform is geimplementeer op ’n industriële Siemens S7-1200 programmeerbare
logiese beheerder (PLB) met ’n digitale afstandbeheer koppelvlak,
puls-wydte-gemoduleerde gelykstroom aandrywing en elektroniese ooplus
en geslote-lus sonvolg beheer. Die ontwerp en prototipe maak gebruik van
beskikbare komponente om lae-koste plaaslike vervaardiging te ondersteun en
slaag in die algemeen in die doel om ’n dinamiese megatroniese platform vir ’n
gekonsentreerde sonkrag stelsel te lewer wat maklik vervoer, gebou en opgerig
kan word op afgeleë persele in Afrika. Intydse eksperimente is gedurende die
somer uitgevoer om die akkuraatheid van die prototipe posisionering sisteem
te evalueer. Dit toon dat die sisteem die son deurlopend volg met ’n akkuraatheid
beter as 1.0◦ op beide die azimut en elevasie sonvolg asse, wat voldoen
aan die ontwerp spesifikasies.
Strukturele aspekte van die prototipe paraboliese skottel word deur ander
navorsers geëvalueer en verbeter terwyl die Stirling-eenheid en elektriese sisteme
in parallelle projekte ontwikkel word. Die uiteindelike doel met hierdie
groepnavorsing is om ’n plaaslik vervaardigde doen-dit-self sonkrag eenheid te
ontwikkel wat in Afrika ontplooi kan word.
|
16 |
Dynamic evaluation of the solar chimneyRousseau, Jean-Pierre 12 1900 (has links)
Thesis (MEng (Civil Engineering))--University of Stellenbosch, 2005. / Previous studies on the solar chimney have shown that its structural integrity might be
compromised by the occurrence of resonance. A structure may displace excessively when a load of
the same frequency as a structural eigen-frequency is applied. The wind gust spectrum peaks near
the solar chimney’s fundamental resonance frequency. This phenomenon poses a reliability threat,
not only to the solar chimney, but also to all high-rise, slender structures.
Structural dynamics describe the response of a structure to a varying load. The dynamic equation
incorporates four terms that bind the factors responsible for resonance: kinetic energy, dissipated
energy (damping), stiffness energy and input energy (loading). After a brief literature study on
classical chimney design procedures, the study scrutinises each of these terms individually in the
context of the solar chimney as designed to date.
A dynamic analysis is undertaken with all the above-mentioned parameters as defined and
estimated by the study. The results from the analysis show amplifications of approximately three
times the static displacements. In load cases where the wind direction inverts along the height,
higher eigen-modes are excited. However, the most severe dynamic amplification occurs at the
fundamental eigen-mode. In the context of solar chimney research, this study brings valuable new
insights regarding the dynamic behaviour of the chimney structure to the fore.
|
17 |
Solar chimney turbine performanceGannon, Anthony John 03 1900 (has links)
Thesis (PhD (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2002. / This project investigates the performance of solar chimney power plant turbines. A solar chimney
power plant consists of a tall chimney surrounded by a transparent deck or solar collector. The sun
heats the air in the collector through the greenhouse effect. A turbine extracts energy from the hot
air rising up the chimney. An investigation of the requirements and operation of such turbines is
needed.
Correct matching of the turbine to the plant requires the determination of the turbine operational
range and other requirements. An air-standard cycle analysis is extended to include component and
system losses. Simple steady-state and transient collector models are added to take into account the
coupling effect of the collector air temperature rise and mass flow rate on the turbine operation. The
predicted turbine operational range for a representative day shows that the expected pressure drop
in a full-scale solar chimney turbine is significantly higher than has previously been predicted.
A turbine design method is developed and used to design a turbine for the representative day. The
methods can easily be extended to include more operating points for a full year of operation. A
turbine layout is suggested that uses the chimney support pillars as inlet guide vanes (IGVs). These
introduce pre-whirl to the turbine and reduce the amount of exit whirl thus decreasing the kinetic
energy at the turbine exit. Non-radial inlet guide vanes add to the torsional stiffness of the chimney
base. A matrix throughflow method is used to design the radial to axial duct between the IGVs and
rotor. The turbine blade profiles are simulated using a surface-vortex method. This is coupled to an
optimisation scheme that minimises both the chord length and maximum flow velocity of the
profile to reduce blade drag.
An experimental program investigates the performance of the turbine. Volume flow, pressure drop,
torque and speed are measured on a scale model turbine to map the turbine performance over a
wide range. The velocity and pressure profiles are measured at two design points to investigate the
flow through the turbine in more detail. These are compared to the design predictions and used to
improve the design method. The experiments show that the design of a solar chimney turbine with
a total-to-total efficiency of 85 % - 90 % and total-to-static efficiency of 75 % - 80 % is possible.
Analysis of the experimental results shows that the turbine efficiency can be improved.
|
18 |
Solar energy technology road map developing a local supply chain in South Africa for concentrated solar power plant16 September 2015 (has links)
M.Ing. / The necessity for deployment of Concentrated Solar Power (CSP) technology in the South African energy sector is examined in this dissertation. A background is given on the different technologies that exist in the solar power sector with specific reference to Concentrated Solar Thermal Power (CSTP). The economic, social and environmental benefits that this technology embodies in the near-, medium-, and long-term is discussed in detail. It highlights the local market potential for the establishment and large-scale roll out of CSP technology in a South African context and the economic value-chain that could subsequently be created...
|
19 |
Combining of renewable energy plants to improve energy production stabilityBroders, Adam C. January 2008 (has links)
Thesis (M.S.)--Worcester Polytechnic Institute. / Keywords: wind energy, solar energy, stability analysis, renewable. Includes bibliographical references (leaves 99-100).
|
20 |
Optimalizace využití elektrické energie vyrobené domácí solární elektrárnou / Optimization of the electrical energy production of the domestic solar power plantCICHRA, Karel January 2013 (has links)
The subject of this thesis is to design, construct and test the control system based on single-chip microcomputer Atmel AVR for a small solar power plant. The proposed system will enable to optimize the use of electricity generated by solar power installed at the family house. The objective is to minimize the amount of power sent to the distribution network and maximize the reduction of purchase of electricity. The first section provides an overview and analysis of several possible solutions and their economic comparison. The next section describes basic characteristic of the hardware components and the source code of programs with additonal comments. The final section presents the results of test operation a futher potential improvements of the system for future expansion and better operation efficiency.
|
Page generated in 0.0643 seconds