Abstract

Winnowing called “Dhan Battaune” in Nepali is the process of separation of unwanted matters from paddy after threshing. In the conventional method; it requires at least four person to produce strong wind by bamboo basket (“Nanglo” in Nepali) to blow away straw, leaves of grasses and other unwanted matters; process starting with one of them pouring the sun dried grains from certain height. To perform MATLAB simulation for designing the screening chamber, a sample of 20 rice grains out of half kilogram was selected to measure its length, width and thickness. To locate the flow pattern, grains of highest weight 0.0324 mg and mean weight 0.0228 mg were considered and simulation was performed in MATLAB with drag coefficient 0.4 which indicated screening chamber as 0.4 m × 0.4 m. The rice-husk movement was also observed in ANSYS CFX which validate the result obtained from MATLAB as the recommended screening chamber design clearly separate them owing to their weight differences. Series of modification were done for better performance of the machine. This resulted in a final product having 0.16 m × 0.10 m grain outlet and 0.20 m × 0.20 m husk outlet in which 19 kg of rice grain were tested in average separation time of 70.8 s for five trails. The overall productivity of the machine was calculated to be 966.10 kg/h which is a promising result for the power consumption of 3.10 units per hour.

Key words: Cascade, drag force, grain regulator, iterative model, screening chamber, trajectory of rice grain.