ENERGY AND EXERGY ANALYSIS DURING THE DEHYDRATION OF PRETREATED SWEET POTATO VIA A CONVENTIONAL AIR DRYER

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2017-12-02

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The energy and exergy analysis during the dehydration of pretreated sweet potato via a conventional air dryer (Model: DHG-9023A, England) was investigated. Sweet potatoes were sliced and divided into three lots; first lot was pretreated in 0.5% sodium metabisulphite (SMB), second lot was water blanched (WAB) and the last lot was untreated (UNT). The samples were dried at varying drying temperatures (60oC, 70oC and 80oC) and constant air velocity of 1.5 ms-1. Energy utilization (EU), Energy utilization ratio (EUR), heat transfer rate (Qevap), exergy loss and exergy efficiency were estimated using standard equations. The results showed that the higher the temperature, the shorter the drying time irrespective of the treatment. However, WAB sweet potato slices takes longer time to dehydrate than SMB and UNT. The energy analysis showed that EU, EUR and Qevap increases as temperature increased. WAB slices has the highest EU, EUR and Qevap next to it was SMB and UNT had the least values. For exergy analysis, exergy loss and exergy efficiency increases with increased in drying temperatures. Comparing the drying temperatures, the highest and lowest exergy loss was obtained at 80oC and 60oC. The least exergy efficiency was obtained at 60oC, thus, drying at 70oC and pretreatment with SMB gave the most acceptable processing conditions base on effective moderate exergy loss (8.69 KJ/s) and exergy efficiency (0.38). However, it is recommended that process optimization should be done in further studies.

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energy, exergy, sweet potato, dehydration, conventional air dryer

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