Experiment and modeling of the rice winnowing process: granular segregation method from an ancient era

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.

Kite festival: the physics behind the oscillations of a kite’s long tail

“…We see that equation ( 26) is similar to equations (10) or (13) just by shifting the oscillation amplitude in equations (10) or (13) with a small factor in the second term in the square bracket. Since J 1 (γ 0 n s/L) s/L increases with s, the correction factor increases with s. The deviation of the tail displacement from the true Bessel function increases as we approach the tail top end.…”

“…The general expression becomes: It is clear from equation (25) that when the tail top end does not oscillate, P (ν) = 0; equation (25) returns to equations (10) or (13). It is also clear from equation (25) that the oscillation of the kite does not change the oscillation frequency of the tail and only produces a different response on the tail deviation.…”

“…Based on such approaches, we obtain simple equations that can be solved analytically or computed using simple numerical procedures, for example, by using an excel spreadsheet. We report similar approaches by developing physical models underlying some common phenomena in our daily lives [11][12][13][14].…”

A Sarong rolled around a body demonstrates that the force for separating two sheets joined by folding and rolling is very large

“…Goldberg and O'Reilly described the geometry evolution of cooking spaghetti [13]. The present author has also investigated simple common phenomena such as bending of fireworks [14], wringing of wet cloth [15], rolling of a cylinder containing granules [16,17], sand tunnel collapse [18], rice winnowing [19], measuring the atmospheric temperature in an aircraft cabin [20], and bending of vertical sheets that lead to a phase transition [21].…”

The stable and unstable oscillations of a rod attached to many springs

“…One of our goals in this paper is to demonstrate that many existing societal practices may contain challenging scientific aspects [12][13][14][15][16][17]. Indeed, there are several practices from ancient societies that have found applications in modern technology after extensive research.…”