A stand-alone parabolic dish solar cooker for African conditions

Craig, Omotoyosi Onalapo (2015-12)

Thesis (MEng)--Stellenbosch University, 2015.

Thesis

ENGLISH ABSTRACT: The reduction in the availability and the ever-increasing prices of fossil fuels, as well as the expensive and insufficient electricity supply, are some of the reasons explaining why the public awareness of the use of alternative cooking methods has increased in recent years. In most rural areas of Africa, the use of wood is even more preferred for cooking than either fossil fuel or electricity, and this has led to deforestation in many areas. However, the time spent on wood collection by women, who often walk kilometres under scorching hot, sunny conditions, can be utilised better in more productive activities. Most of those lacking access to convenient cooking methods live in places with good solar resources and where solar cookers would thrive if developed. The study presented in this report considered a prototype solar cooking system that is relatively cheap and that can be modified to meet these challenges faced in African communities. A parabolic solar cooker, which uses a parabolic dish as concentrator, was designed and developed. The concentrator used was a television satellite dish of 2 m in diameter, in which the reflecting area was covered with reflective aluminium strips. The dish concentrates radiation from the sun onto a conical cavity receiver placed at its focal point. The system uses heat transfer fluid as its working fluid and a cuboid- shaped storage tank insulated with ceramic wool to enhance the sensible heat storage technique used. A specially modified automotive pump was used to circulate the heat transfer fluid throughout the system, while a cooking head in the form of a flat spiral copper tube put onto the storage tank was used as the cooking section. The cost of manufacturing the system was approximately R9 000, without considering the cost of the tracking system. However, this amount is expected to decrease if the system is mass produced. The solar cooker was tested under winter conditions in South Africa, and each cooking test was done according to international standard procedures for testing solar cooker performance. A utilisation efficiency of 47 % was achieved, the exergy efficiency was 0.05 %, while the average characteristic boiling time was around 13.32 min/kg. The solar cooker can be used indoors, thus eliminating the need for its user to stay in the sun. The reflecting dish was mounted on an automated dual tracking system stand, which eliminated the need for regular adjustment by the user. The cooking section of the system can be modified to be used for other high temperature-based development activities in African communities, such as, among other things, industrial baking.

AFRIKAANSE OPSOMMING: Die verlaging in die beskikbaarheid en ewig-stygende pryse van fossielbrandstowwe, sowel as duur en onvoldoende elektrisiteitsvoorsiening, is net van die redes hoekom openbare bewustheid van die gebruik van alternatiewe kookmetodes die afgelope paar jaar toegeneem het. In die meeste landelike gebiede in Afrika word die gebruik van hout bo fossielbrandstof en elektrisiteit verkies. Dit lei in baie gebiede tot ontbossing. Die tyd wat deur vrouens spandeer word om hout op te tel, soms etlike kilometers ver onder die skroeiende son, kan op meer produktiewe maniere benut word. Die meeste mense wat nie toegang het tot konvensionele kookmetodes nie, bly in areas met goeie sonblootstelling en waar sonkrag-kooktoestelle sal floreer indien dit daar ontwikkel word. Hierdie studie oorweeg ʼn prototipe kooktoestel wat aangepas kan word om die uitdagings in Afrika-gemeenskappe te oorkom. ʼn Paraboliese son-kooktoestel wat ʼn paraboliese skottel as konsentrator gebruik, is ontwerp en ontwikkel. Die konsentrator wat gebruik is, is ʼn televisie-satellietskottel, 2 m in deursnee, waarvan die weerkaatsende area met weerkaatsende aluminiumstroke bedek is. Die skottel konsentreer uitstraling van die son na ʼn ontvanger in die vorm van ’n koniese holte wat by die fokuspunt geplaas is. Die stelsel gebruik warmteoordrag vloeistof as sy werksvloeistof en ʼn kubusvormige bergingstenk wat met keramiekwol (ceramic wool) geïsoleer is om sodoende die hitte-bergingstegniek wat gebruik word, ten volle te benut. ʼn Spesiaal gewysigde pomp is gebruik om die warmteoordrag vloeistof deur die stelsel te sirkuleer, terwyl ʼn kookkop in die vorm van ʼn plat spiraal koperpyp op die bergingstenk as kookvlak gebruik is. Die vervaardigingskoste hiervan was ongeveer R9 000, hoewel hierdie bedrag moontlik sou verminder indien dit op ’n groot skaal geproduseer word. Die son-kooktoestel is tydens die winter in Suid-Afrika getoets en elke kooktoets is volgens internasionale standaardprosedures vir die toets van son-kooktoestelle se werkverrigting uitgevoer. Benuttingsdoeltreffendheid van 47 % is gemeet, die exergie-doeltreffendheid was 0.05 %, en die gemiddelde kenmerkende kooktyd was ongeveer 13.32 min/kg. Die son-kooktoestel kan ook binnenshuis gebruik word, wat beteken dat die gebruiker nie in die son hoef te staan nie. Die weerkaatsende skottel is op ʼn geoutomatiseerde dubbelbaan spoorstelsel wat die son volg, gemonteer, wat beteken dat die gebruiker nie self die skottel hoef te roteer nie. Die kookvlak van die stelsel kan vir ander hoë temperatuur-gebaseerde ontwikkelingsaktiwiteite in Afrika-gemeenskappe aangepas word , soos byvoorbeeld ʼn industriële bakkery.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/98096
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