Experiment and Modeling of Rice Winnowing: Granular Segregation Method in Ancient Traditions

TL;DR

This study investigates the ancient rice winnowing process, modeling the physical mechanisms behind grain segregation by air flow, and provides insights for designing improved grain separation methods based on size and density differences.

Contribution

It develops a physical model of rice winnowing, revealing the influence of vortex dynamics on grain segregation, which was previously undocumented in traditional practices.

Findings

Segregation effectiveness depends on grain size differences.

Initial grain position influences separation outcome.

A phase diagram predicts final grain distribution.

Abstract

Rice winnowing is a process of separation of small and large rice grains by air flow practiced since the ancient human history especially in societies where rice is the main source of carbohydrate (in Asia, Africa, and Latin America). Indeed, this process contains rich of scientific rule but has never been documented by the old society. We report here experimental investigation of the rice winnowing and develop a physical model to explain the process of segregation of rice grains having different size or density. Flapping the tray in the winnowing process, generates a vortex centered at position around the tray free end. We demonstrated numerically that the effectiveness of segregation is strongly depended on the different in grain sizes (for grain from the same material), the initial position of the grain, and the angular velocity of the vortex generated by flapping the tray. We obtained a phase diagram describing different final conditions of winnowing process (either the small grains move towards the tray fee end or move toward the inner end of the tray, able or unable to leave the tray at the free end). The result can be useful to design a new method in separating grains based on size or density.