Browsing by Author "Minja, Rwaichi"

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Analysis of Different Techniques for Improving Performance of Flat Plate Solar Collectors for Fruits Drying
(Tanzania Journal of Engineering and Technology (TJET), 2014-06) Bakari, Ramadhani; Minja, Rwaichi; Njau, Karoli
Fruits drying had become a broader technology in fruits and vegetables value addition. The technology is reported to be a promising way of dying without incurring higher cost but its adaptation has not been feasible in rural areas. Solar dryers have been developed but its poor performance limits its applicability. In this study, several techniques for modifications of traditional solar collector were addressed. It was observed that, varying collector designs in different techniques, a range of collector performances can be employing double duct counter flow, compared to conventional collectors. Likewise performance difference between conventional collectors and studied models were found to be 8%, 7.2%, 6.1% and 5.2% for model parked with charcoal 5 mm wire mesh, 4mm glass thickness and 8 baffles respectively. This study shows that, double duct counter flow system is the best option for improving the performance of the collectors, followed by charcoal and wire mesh. On the hand, using 4 mm glass thickness gave improved performance, however, it is recommended for collector size not exceeding 2 m in length.
Effect of Glass Thickness on Performance of Flat Plate Solar Collectors for Fruits Drying
(Hindawi Publishing Corporation, 2014) Bakari, Ramadhani; Minja, Rwaichi; Njau, Karoli
This study aimed at investigating the effect of thickness of glazing material on the performance of flat plate solar collectors. Performance of solar collector is affected by glaze transmittance, absorptance, and reflectance which results into major heat losses in the system. Four solar collector models with different glass thicknesses were designed, constructed, and experimentally tested for their performances. Collectors were both oriented to northsouth direction and tilted to an angle of 10° with the ground toward north direction. The area of each collector model was 0.72 m2 with a depth of 0.15 m. Low iron (extra clear) glass of thicknesses 3 mm, 4 mm, 5 mm, and 6 mm was used as glazing materials. As a control, all collector performances were analysed and compared using a glass of 5 mm thickness and then with glass of different thickness. The results showed that change in glass thickness results into variation in collector efficiency. Collector with 4 mm glass thick gave the best efficiency of 35.4% compared to 27.8% for 6 mm glass thick. However, the use of glass of 4 mm thick needs precautions in handling and during placement to the collector to avoid extra costs due to breakage.
Experimental analysis of air flow patterns in perfomance of flat plate solar collectors
(African Journal of Agricultural Research, 2015-02-05) Bakari, Ramadhani; Minja, Rwaichi; Njau, Karoli
Solar drying is one of the promising methods of reducing post-harvest losses in rural areas. Studies have shown that, heat transfer mechanisms in a solar collector influences the performance of solar dryers. This study aims at improving heat transfer in flat plate solar collectors by designing different air flow patterns inside the collector. Three flat plate solar collectors were constructed by using Pterocarpus timber (Mninga) and tested for their effect in heat transfer at various flow patterns. Three different flow patterns namely: single duct front pass, double duct parallel flow and double duct counter flow were designed and tested. Experimental results show that collector efficiency of single duct front pass, double duct front pass and double duct counter flow were 30.6, 36.1 and 38.2% respectively. It was found that, double duct flow gives improved performance compared to single duct flow due to the increased heat transfer area. In additional, double duct counter flow showed superior performance compared to double duct parallel flow due to extended heat transfer area and the advantage of air preheating at the inlet which reduces heat losses through glazing. Through this study, it was concluded that, solar collector designs with double duct counter flow can improve collector performance for up to 8.3% compared to single duct front pass.