Design, Development and Performance Evaluation of an Air Classifier for Decorticated Mass of Dried Water Chestnut (Trapa natans)

Abstract

The separation of dried and decorticated water chestnut kernels and peels is a critical step in post-harvest processing, as manual cleaning methods are labour-intensive, time-consuming and inefficient. To address this challenge, an air classifier was designed and developed; it consisted of a hopper, feed control mechanism, separation section (S-section), blowing unit, peel outlet, main outlet and power source. The experiment was conducted at three moisture contents (7, 14 and 21%), three blower RPM (1130, 1300 and 1450 RPM) and three feed rates (100, 200 and 300 kg/h) to evaluate the efficiency and capacity of the air classifier. Calculations of angular velocity, tangential velocity, terminal velocity, volumetric flow rate, mass flow rate and thrust force were carried out to analyse the air flow dynamics acting on kernels and peels. The results showed that the minimum air velocity required to separate the peels was 8.3 m/s, corresponding to the blower speed of 1130 RPM. The cleaning efficiency, separation efficiency and total efficiency were found to be 99.88%, 97.92% and 97.80% respectively with a throughput capacity of 500 kg/h and energy consumption 2.71 kWh/tonne. Hence the air classifier provides a practical, energy-efficient and scalable solution of the separation of dried and decorticated kernels and peels.