AIRFLOW RESISTANCE THROUGH BULK SWEET POTATO ROOTS

Abstract

Storage of sweet potato roots in bulk is common in tropical and subtropical countries. Hot spots and mold damage may occur during storage, especially if the roots are not ventilated. Airflow resistance data are therefore required to predict the uniformity of airflow and to design optimum ventilation systems. This study presents the resistance to airflow through unwashed and clean sweet potato roots over a superficial velocity range of 0.08 to 1.70 m s-1. The results were correlated by a physically meaningful modified Ergun model and compared with the modified Shedd’s model. In the modified Ergun model, the physical properties of the roots, such as porosity, shape factor, and surface roughness, were explicitly incorporated into the model. The modified Ergun model exhibited higher values for coefficient of determination, lower root mean square error, and lower percentage error and therefore provided the best fit when compared with the modified Shedd’s model. The model can therefore be used to predict resistance to airflow through bulk sweet potato roots realistically. The differences in the pressure drop between sweet potato roots arranged differently to airflow and with or without soil fraction on the surfaces of the roots were further explained by the contribution of particle drag and surface friction. The pressure drop through unwashed and clean sweet potato roots was observed to increase with higher airflow, bed depth, root grade composition, and presence of soil fraction. The results for the effect of soil fraction stress the importance of cleaning sweet potato roots before storage. Airflow was the most significant factor affecting pressure drop of unwashed and clean sweet potato roots compared with root grade composition and presence of soil fraction for all batches studied. The results obtained from this study are comparable to those reported by other researchers, particularly for other agricultural roots.