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Thesis (PhD)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: The use of solar distillation as a means of desalination to provide potable water to communities in remote and arid regions has often been discarded on economic grounds mainly because of the inherent low efficiency of relatively expensive solar distillation units (solar stills). Closer analysis of this constraint showed that by following a mainly Physical Chemistry approach (rather than the traditional engineering one), the technology could be made more economically attractive through (1) lowering the construction cost of the solar still and / or (2) increasing its operational life and / or (3) increasing its efficiency. The study into different solar still designs showed that, despite its limitations, the basin solar still is preferred due to its simplicity, ease of operation and low maintenance. Given the solar distillation process as formulated in this study, substitute durable components could be identified and optimised for this design. A basin solar still that costs about 80% less than a reference unit without an apparent drop in performance was consequently developed and successfully tested up to full plant scale. An in-house experimental facility that simulates solar still behaviour under controlled environmental conditions was developed to simulate conditions of lower radiation intensity and productivity, which enabled research into performance enhancement and microbiological water quality. It was found that (a) absorption of the radiation by the water plays an important part in productivity and that a productivity decrease of up to 33% can be expected as the black interior lining becomes contaminated, (b) the simulated winter productivity of the basin still was about 25% of the summer value due to the lesser amount of solar radiation hours, the lower angles of radiation incidence onto the cover and the decrease in water area receiving direct radiation, (c) an annual productivity increase of about 10% can be obtained when a particular reflector configuration is fixed behind the basin, and (d) the microbiological pasteurisation temperature is less than the distillation onset temperature. This study played an important role in making solar still technology affordable for use by poor, rural communities, as was demonstrated by the successful use of the research product (basin solar still) in a pilot drinking water plant at a typical target community. This was made possible through the use of evaluation models developed as part of this research, which addressed relevant construction and performance factors influencing the economic viability of the specific solar still. The following outcomes of this study can be regarded as new contributions to the field of solar distillation technology, namely (a) a test matrix that can be used to screen solar still construction materials at component level, (b) an evaluation model that can be used to determine the economic viability of solar stills at a given location, (c) a laboratory testing facility to study solar still behaviour under controlled conditions and (d) a solar still design that has been optimised and tested for local field application. / AFRIKAANSE OPSOMMING: Die gebruik van son-energie om brakwater deur middel van distillasie te ontsout en sodoende drinkwater aan afgeleë gemeenskappe te verskaf, is herhaaldelik in die verlede as ekonomies nie-lewensvatbaar aangetoon. Dit is hoofsaaklik toeskryfbaar aan die inherente lae effektiwiteit van sodanige stelsels, asook die hoë kapitaalkoste daaraan verbonde. Die hoofsaaklike faktore wat die tegnologie bekostigbaar kan maak, is egter hieruit afgelei en volgens 'n Fisiese Chemie benadering geoptimeer, naamlik (1) vermindering van die konstruksiekoste van die sondistilleerder-eenhede, en / of (2) verlenging van die operasionele leeftyd daarvan, en / of (3) verhoging van effektiwiteit van die stelsel. Die literatuurstudie het aangetoon dat die pan-tipe sondistilleerder-eenheid verkieslik as navorsingsbasis is omdat dit eenvoudig en maklik bedryf- en onderhoudbaar is. Vanuit die geformuleerde beskrywing van die sondistillasie-proses kon plaasvervangende komponente vir die sondistilleerder-eenheid geïdentifiseer en getoets word, wat daartoe gelei het dat 'n eenheid met dieselfde funksioneringseienskappe vir sowat 80% goedkoper ontwikkel kon word. 'n Laboratoriumopstelling waarmee lae bestralingskondisies gesimuleer kan word, is ontwikkel om navorsing op produktiwiteitsverbetering en mikrobiologiese produkwaterkwaliteit te doen. Dit is aangetoon dat (a) absorpsie van die inkomende bestraling deur die water belangrik is en dat 'n sondistilleerder-eenheid tot 33% minder produktief kan wees indien die swart voering binne die eenheid besoedel sou word, (b) winterproduktiwiteit daal tot 25% van somerproduktiwiteit as gevolg van die verminderde sonlig-ure, die laer invalshoek van die bestraling op die glasdeksel, en die gepaardgaande verkleining van die blootgestelde water-oppervlakte, (c) 'n gemiddelde produktiwiteitsverhoging van 10% deur weerkaatsers agter die sondistilleerder-eenheid teweeggebring kan word, en (d) die distillasie-temperatuur die water-ontsmettingstemperatuur oorskry. Hierdie navorsmg het 'n belangrike rol gespeelom sondistilleerder-tegnologie bekostigbaar vir behoeftge gemeenskappe in landelike gebiede te maak. Dit is gedemonstreer deur die suksesvolle toepassing van die navorsingsproduk (sondistilleerder-eenheid) in 'n drinkwatervoorsieningsprojek by 'n tipiese teikengemeenskap. Dit is vermag deur die gebruikmaking van evaluasie-modelle wat gedurende hierdie studie ontwikkel is, en wat die toepaslike konstruksie- en funksioneringsfaktore wat die ekonomiese lewensvatbaarheid van die eenheid beïnvloed, aanspreek. Die volgende navorsingsprodukte kan beskou word as nuut in die veld van sondistillasie-tegnologie, naamlik (a) 'n toetsmatriks wat gebruik kan word om komponente vir sondistilleeerders te evalueer, (b) 'n ekonomiese evalueringsmodel wat gebruik kan word om die bekostigbaarheid van sondistilleerders in 'n bepaalde gebied te bepaal, (c) 'n laboratorium-toetsfasiliteit om die werking van sondistilleerders onder beheerde kondisies te ondersoek en (d) 'n sondistilleerdereenheid wat doelgeskik vir plaaslike omstandighede ontwikkel en getoets is.

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No description available.

Yes / The desalination of saltwater is a viable option to produce freshwater. All the desalination processes are energy-intensive and can be carried out on a large scale. Therefore, producing freshwater using renewable energy sources is the most desirable option considering the current energy crisis and the effect that fossil-fuel-based energy has on our carbon footprint. In this respect, the tray-type still, one of several solar power desalination still varieties, is popular owing to its straightforward design, economic materials of construction, and minimal maintenance requirements, especially in isolated island regions with restricted energy and natural water supplies. The traditional tray-type solar power has a few drawbacks, such as the inability to recover latent heat from condensation, reduced thermal convection, a large heat capacity, and comparatively minimal driving power through evaporation. Therefore, the improvement of heat and mass transfer capabilities in tray-type stills has been the subject of many studies. However, there is a lack of a comprehensive review in the open literature that covers the design and operational details of multistage solar stills. The purpose of this paper is to present a thorough overview of the past research on multistage solar stills, in terms of configurations, capabilities, and cutting-edge options. In comparison to a unit without a salt-blocking formation, the review indicates that a multistage distillation unit may run continuously at high radiation and generate pure water that is around 1.7 times higher than a unit without a salt-blocking formation. The most effective deign is found to be “V”-shaped solar still trays that attach to four-stage stills, since they are less expensive and more economical than the “floor” (Λ-shape) design, which requires two collectors. Additionally, it can be stated that the unit thermal efficiency, solar percentage, and collected solar energy (over the course of a year) increase by 23%, 18%, and 24%, respectively, when the solar collectors are increased by 26% (at the constant inflow velocity of the water).

Thesis (MTech (Mechanical Engineering))--Cape Peninsula University of Technology, 2015. / Access to adequate quantities of clean drinking water has become a serious issue on the worldwide level. This is particularly true in arid and rural areas where for the majority of people water is a limited and a vulnerable resource. These water sources which are often highly contaminated are potentially the cause for several diseases (waterborne diseases) and ultimately death especially in infants. Due to poverty and sometimes to the remote conditions of their regions, the population is unable to afford adequate water purification technologies, since they are relatively expensive and energy intensive. It is therefore vital to investigate appropriate water purification technology that people can afford or construct, operate and maintain themselves. A promising technology is solar distillation for the supply of drinking water on a small-scale level. It has proved to be a unique purification method as it can purify almost any type of water by using the high solar energy potential of the affected regions. The most basic form of solar distillation is the use of a single basin single slope solar still. However the downside of this technology is that it presents a low efficiency and productivity. To try to tackle this problem, many studies have been carried out to enhance productivity, effectiveness and efficiency of single-basin solar stills. In this present study, a solar distillation unit was designed, fabricated and experimentally tested. Its performance in terms of distillate output and energy efficiency was analysed under Cape Town conditions and compared to similar stills that have been reported in the literature. The main configuration of the solar still is a double glazed single basin solar still coupled to an external condenser. The study indicated that the performance of the solar still unit can be enhanced by increasing the evaporation rate which is a combined effect of solar radiation, ambient temperature, and the system components temperature. It was concluded that the applied techniques such as the external condenser, double glazing, good insulation and low level of water are effective. The unit was found to have an efficiency ranging between 21 and 29% over the test period and a mean distillate yield of about 2.5 litres per square meter was achieved per day.

Thesis (Master of Engineering in Mechanical Engineering)--Cape Peninsula University of Technology, 2018. / The present study was centred on the design of a thermal multistage solar still desalination system. The design is a multistage with new configurations such as direct vapour input into each stage using vapour make-up tubes and the integration of a multistage with a basin type solar still. The incorporation of float a valve in the secondary seawater tank to regulate the seawater in the assembly eliminated the need of pumps to the system. The circulation of seawater between the evaporator and the evacuated tube solar collector (ETC) was through the pressure difference and the flow back was controlled through the incorporation of oneway flow valve. The ETC was used as a heat source to supply the thermal energy into the multistage system. The system had no electrical connections and therefore, no forced circulation as no pumps or any electrical components were used. The system consisted of six stages in total, the evaporator supplied the vapour to five of the six stages of the system. The system was tested on the roof of Mechanical Engineering Department and this location was chosen because of less sun’s intensity obstructions. The system was tested for nine (9) days but the distillate collection was not performed for the whole each day. This was due to the controlled access to the roof and the minor repairs that had to occur before the tests were conducted. The duration on which the tests were conducted varied in each day. The data was supposed to be logged from 08h00 am to 18h00 pm but this was not so due to the controlled access to where the tests were conducted. This data logging period was chosen based on the assumptions that the sun’s intensity would be at maximum within this period. The longest period of test was approximately 7 hours and the system managed to produce about 1500 ml and the maximum temperature for the day was 28oC. The system produced a minimum of 225 ml in the space of 3 hours and the temperature of the day was 26oC. The total amount of distillate produced was about 7600 ml and this amount was produced within the period of 49 hours. The 49 hours is equivalent to two days and 1 hour. It is anticipated that the system would have produced more should there be no repairs involved during the tests. The system produced a maximum of 48 ml at night and a minimum of 8ml in some nights. The night tests were not controlled and monitored due to limited access. It was noticed that the system was empty in each morning of the first few days of the tests. This emptiness contributed to the leakage occurred to the evaporator. The leakage of the evaporator was caused by unmonitored heat supplied by the ETC. The evaporator was constructed using unsuitable material and this was another factor which contributed towards the failure of the evaporator.

Thesis (MScEng)-- Stellenbosch University, 2013. / ENGLISH ABSTRACT: The objective of this research was to obtain clean drinkable water from treated sewage effluent by using a solar-powered distillation cycle. Technologies and concepts were borrowed from the solar desalination industry to propose a unique circular distillation cell design. From the design, a specific mathematical correlation was developed to predict the distillate mass flow rate by using only evaporation and condensation temperature as inputs. This model was incorporated into a simulation model built using Transient System Simulation software. Long-term simulations were carried out to determine the operating capabilities of the design. A prototype was successfully constructed and operated. Experimental results indicated good agreement with the mass flow rate mathematical correlation. Water quality levels were tested against the South African National Standard 241 national drinking water quality standard. Four quality parameters are outside acceptable levels. Evidence suggested that acceptable quality levels could be reached. The circular distillation cell design is a major contribution made by this research. Another contribution is the simulation model capable of predicting an output for different locations. Finally, the proposed prototype is potentially a very valuable device contributing towards the reduction of consumer demand in terms of water and energy as well as the household load on the wastewater treatment system. / AFRIKAANSE OPSOMMING: Die doel van hierdie tesis is om te beskryf hoe behandelde rioolwater deur middel van ’n son aangedrewe distillasiesisteem gesuiwer kan word om drinkbare water as eindproduk te lewer. Die nodige tegnologieë en konsepte is oorgeneem uit kommersiële sonaangedrewe ontsoutingsisteme om met ’n unieke ontwerp voorendag te kom wat uit ’n sirkelvormige natuurlike konveksie distillasiesel bestaan. Met behulp van hierdie ontwerp is ’n wiskundige korrelasie ontwikkel om die gesuiwerde water se massavloei te bepaal. Slegs die verdampings- en kondensasietemperature word as insetwaardes gebruik om die massavloei te bereken. ’n Simulasiemodel is met behulp van die Transient System Simulation programmatuur gebou. Die wiskundige korrelasie is by die simulasiemodel geïnkorporeer om langtermynsimulasies te kan uitvoer. Voorts is ’n demonstrasiemodel suksesvol gebou en aangedryf. Eksperimentele resultate toon goeie ooreenstemming met die simulasieresultate. Die gesuiwerde water se gehalte is met die nationale SANS 241 drinkwaterstandaard as maatstaf getoets. Slegs vier gehalteparameters val buite die aanvaarbare vlakke, hoewel dit blyk dat hierdie elemente wel tot aanvaarbare vlakke verlaag kan word. Hierdie navorsing se grootstet bydrae is die ontwerp van die unieke sirkelvormige distillasiesel. ’n Bykomende bydra is die aanpasbaarheid van die simulasiemodel sodat dit produksievermoë op verskillende plekke kan voorspel. Die demonstrasiemodel is ’n potensieel waardevolle ontwerp wat kan bydra tot die verlaging in verbruikersaanvraag na water en energie. ’n Ontwerp van hierdie aard kan die las wat huishoudings op suiweringaanlegte vir rioolwater plaas, verlig.