Browsing by Author "Sibanda, Sipho."

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Development of a naturally-ventilated solar energy-assisted maize seed store.
(2018) Mdlalose, Siphiwe Nduduzo.; Workneh, Tilahun Seyoum.; Laing, Mark Delmege.; Sibanda, Sipho.
The seed industry continues to face losses during seed storage, especially in Africa. Moreover, there is high loss of seed viability during storage, mainly due to the poor ventilation in seed storage structures, which results in the development of storage fungi. In this study, the main objectives were to construct, to evaluate the solar energy assisted maize seed store. A 22-m3 room was converted to a seed storage room by retrofitting a chimney on its wall and a solar collector on its roof. Different chimney sizes were investigated in order to identify which size would be best for the construction of a naturally-ventilated seed storage room. The chimney sizes that were used included those with a diameter and a height of 200 mm x 3600 mm, 200 mm x 4800 mm, 300 mm x 3600 m and 300 mm x 4800 mm. The parameters, air velocity in the chimney duct, as well as the air temperature and relative humidity at the inlet, centre and outlet of the storage room, were recorded during the seed storage period. A naturally- ventilated seed storage room was developed based on the results obtained. A naturally-ventilated seed storage room was then evaluated in terms of its effectiveness to preserve the quality of the stored maize seeds. To compare the performance of the modified storage room, a room with similar storage capacity, but without the retrofitted components, was used as a control. Maize seeds were stored in each storage room for the duration of three months. Samples were taken every two weeks for germination, moisture content and seed vigour analyses. Both the diameter and height of the chimney were found to have a significant (P≤0.05) influence on the air ventilation rate inside the storage room. A seed storage was therefore developed using a 300 mm x 4.8 m chimney size, which performed better than the other chimney sizes that were explored in this study. The relative humidity in the control storage room was significantly (P≤0.05) higher (60.6 ± 5.87%) than the relative humidity in the modified storage room (40.1 ± 3.21%). The moisture content obtained in the control room was significantly (P≤0.05) higher (13.3%) than the moisture content obtained in the modified storage room (12.6%). The initial germination was 99%. The seed germination percentage obtained after three months of storage in the modified storage room was significantly higher (P≤0.05) (98.5 ± 0.85%) than the germinations percentage obtained in the control storage (96.8 ± 1.49%). The seed vigour obtained in the modified storage was significantly higher (P≤0.05) than the seed vigour obtained in the control room. Thus, a naturally-ventilated seed storage room was tested and was found to preserve the quality of the seeds over the duration of storage.
Development of a solar powered indirect air cooling combined with direct evaporative cooling system for storage of fruits and vegetables in Sub-Saharan Africa.
(2019) Sibanda, Sipho.; Workneh, Tilahun Seyoum.
Abstract available in PDF.
Drying of sweet potato tubers using a naturally-ventilated solar-venturi dryer and a hot-air dryer.
(2020) Gasa, Siyabonga Robern.; Workneh, Tilahun Seyoum.; Laing, Mark Delmege.; Kassim, Alaika.; Sibanda, Sipho.
Abstract available in PDF.
Evaluation of the effects of pre-drying treatments and drying methods on the drying kinetics and quality of Tommy Atkin mango slices.
(2017) Mugodo, Khuthadzo.; Workneh, Tilahun Seyoum.; Sibanda, Sipho.
Mango is a perishable fruit, harvested once a year during the summer season. Smallholder farmers growing mango experience relatively high post-harvest losses because they receive large volumes of produce at the same time. Drying is a preservation method proven second to cooling in performance. In South Africa, dried mango fetches higher returns compared to canned mango, and mango juice, atchar and jam. Open-Air solar Drying (OAD) is a popular drying method used for producing dried mango. However, this method of drying has setbacks resulting in produce quality loss. Convective Oven Drying (OVD) is a more efficient drying method, however, it has high-energy consumption. In South Africa, there is lack of research on hot-air drying methods, as well as their performance when drying mango fruit. With the current shift in use of renewable energy for drying operations, research is focusing on improving solar drying technologies. These include increasing the drying capacity and reducing the drying time through modifying a greenhouse. Considering the research gap in South Africa on drying technologies and the limitations of open-air solar drying, this study comparatively assessed the performance of three drying methods, namely, (a) Convective Oven Drying (OVD), (b) Open-Air solar drying (OAD) and (c) a Modified Ventilation Solar Drying (MVD). OVD was carried out at a set temperature of 70˚C, OAD and MVD at ambient temperature of 15.55˚C -36.77˚C, at an RH of 22.96%-79% and solar radiation of 317W.m-2- 1016 W.m-2. The MVD improved the ambient conditions to obtain an average maximum temperature of 64.26 ˚C and RH of 17.6%. The drying time was longer for mango slices dried in OAD, MVD and OVD, respectively. The lemon juice pre-treatment did not affect the drying time. The drying time was reduced for 3 mm, as compared to the 6 mm and 9 mm dried mango slices, due to the relatively high drying rates. Drying took place in the falling drying rate period for most mango samples, indicating that diffusion was the driving mechanism in the drying experiments. The effect of the drying methods on the drying kinetics of mango slices (3 mm, 6 mm and 9 mm) as well as the effect of lemon juice pre-treatment was investigated. Non-linear regression analysis was used to assess the empirical model that best fits the experimental moisture ratio data. The quality parameters that were evaluated included the colour, rehydration, sensory properties, changes in mango microstructure and microbial changes. The empirical model that was best fit for the drying data was that of the Midilli et al., followed by Page model because a higher R2, a lower root mean square (RMSE) and a lower chi-square (X2) was obtained from non-linear regression analysis. A quality analysis indicated that colour change (ΔE) was not significantly (P>0.05) affected by pre-treatment, although control samples that were dried in the OAD had a relatively higher colour change, resulting to browning. The rehydration ratio and electronic microscopy (SEM) showed structural changes in dried samples, with thicker mango slices having a relatively lower rehydration ratio, and the SEM scans dominated by cracks and pores, which were much more visible for 9 mm mango slices. Sensory evaluation results indicated that the panellists preferred the flavour and colour of pre-treated 3 mm mango slices compared to thicker control and pre-treated dried mango slices. In addition, the overall acceptability of dried mango was relatively higher for MVD-dried, than OVD- and OAD-dried mango slices, respectively. The fungi and anaerobic bacteria levels found in dried mango slices were higher than the recommended levels of 1x103; however, there were no pathogenic microbes detected in the fresh and dried samples. The study findings show that dried mango is an acceptable produce to consumers, especially in areas like Kwazulu-Natal, were mango is scarce. MVD is a drying method, which is practical and can solve the shortcomings of OAD. This method is a renewable energy alternative to OVD and further improvement is required to increase temperature and ventilation is necessary to reduce drying time.