STATIC PRESSURE DROP IN A FIXED BED OF ROOT CROP CHIPS DURING DRYING AS AFFECTED BY AIRFLOW RATE AND MOISTURE CONTENT

Abstract

Pressure drop (mm H20/m depth) was generally higher in high-moisture chips than in low-moisture chips. Relationships were found to be normally linear for sweetpotato (Ipomoea batatas) and taro (Colocasia esculenta) and logarithmically linear for cassava (Manihot esculenta). Porosity also increased with moisture, but despite the presence of more void fraction, pressure drop remained high. This was primarily because interspaces in the bed were lined with starch granules and water molecules, thus suppressing the flow of air. When dried, chips decreased in volume and weight and exposed smooth surfaces, thereby causing less resistance to airflow. Among the empirical equations that had been evaluated, the Ramsin and Ergun equations fitted very well with the experimental data. The coefficient of determination, r² ranged through 0.94-0.99. The chip's particle diameter was twice larger than that of grains, resulting to lower pressure drop in chips compared to grains such as sorghum (Sorghum bicolor), rough rice (Oryza sativa), shelled corn (Zea mays), and soybean (Glycine max).