| Abstract: | Rough rice samples (400 grains per sample) were elevated to four moisture levels. Length, width and thickness measurements for each grain (25 grains per sample) were made on rough rice. The grains were then shelled and the same measurements were made on brown rice. Moisture elevated samples of 150 rough rice grains were dried for different durations with different air temperatures. After drying, similar dimensions of 25 dried grains (rough and brown) were measured. Similar work was done separately on milled rice. The dimensions of 100 grains each of rough, brown and milled rice from stock were measured before starting the experimental work. These measurements were considered as reference dimensions to those of the moisture elevated grains. Milled rice had the highest sensitivity to moisture change and rough rice had essentially no response except some in the thickness direction. In all forms of rice, the percent linear change was most in the thickness direction and least in the length direction. Adsorption produced more linear change than desorption. This phenomenon may be due to some type of hysteresis effect. The unequal percent changes in linear dimensions of rough, brown and milled rice was used as an essential input to continuously revise the finite element mesh for solution of differential equations relating moisture transfer in rice during drying. A two dimensional diffusion equation was solved by the finite element method to estimate transient moisture gradients in the endosperm of a rice grain during drying. Fissured grains were counted immediately after drying and at periodic intervals of 12 h. High initial moisture contents and high drying air temperatures caused the most fissured grains. Short drying periods caused grains to fissure soon after drying. The response was fast but the number of fissured grains was small. Long drying periods caused more grains to fissure but the time for these fissures to develop was longer... |
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