Engineering properties of Roselle (Hibiscus sabdariffa) calyxes

Abstract

Physical, mechanical and thermal properties of dried and freshly harvested Roselle calyxes were determined using standard procedures based on literature. The obtained results showed that in terms of shape and size, the red variety was more slender with a pointed apex when compared to the dark red variety (Hibiscus sabdariffa. L). Porosity values were close for the dried calyxes and were 53.85% for fresh calyxes. A high percent (72.21%) of whole calyxes was obtained for the fresh calyxes when compared to that for the two varieties of dried calyxes studied. The value of angle of repose for the fresh calyxes was 51.530 while the dry calyxes had lower values (23.10 and 22.40o) for red and dark red calyxes, respectively. Results also showed that the coefficient of static friction on all surfaces used was highest for fresh Roselle calyxes while results obtained for the dry calyxes were similar. Thermal properties of the calyxes varied and were a function of the moisture content of the calyxes.
The results of this study are useful for further studies relating to processing, handling and storage of Roselle calyxes.