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Experimental simulation of cross-flow rice drying: moisture content and milling yield profiles
S. MUKHOPADHYAY (1), T. Siebenmorgen (1) (1) University of Arkansas, Fayetteville, AR, U.S.A..

After harvest, rough rice is generally dried to ~ 12% MC (wb) for safe storage. Drying is often conducted in cross-flow (CF) dryers using heated air. The objectives for this study were to experimentally simulate a CF drying column so as to measure MC and milling yield profiles throughout the column, as well as to quantify the impact of air-flow rate (Q) on these profiles. These data are intended to also serve to validate a mathematical model describing CF dryer operation. Drying runs were conducted using air at 60°C/12% RH, three Qs (0.36, 0.46, and 0.56 (m3/s)/m2) for three drying durations (Ds) (30, 60, and 90 min). The 39-cm tall bed of rice comprised an assembly of ten, fiber-mesh, hand-woven cylindrical baskets that were placed inside a Plexiglass® column to facilitate sampling at various distances from the hot-air plenum (HAP). After a drying run, the baskets were taken out from the column, each basket was placed into individual sealed bags and then the bags were tempered at 60°C for 4 h. After tempering, MC of rice in each basket was measured. Then, all samples were conditioned to ~ 12% MC, milled and separated, to determine milled rice yield (MRY) and head rice yield (HRY). Moisture content and milling yield profiles throughout the drying column were reported. Across all Qs and Ds, both MC and HRY increased with increasing distance from the HAP. Increasing either Q or D resulted in reduced final MCs and HRYs, with D having a greater impact than Q. HRY reduction (HRYR) was more prominent in baskets closer to the HAP, especially at greater Qs and Ds. There were negligible HRYRs in the upper layers of the column. These profiles confirmed that rice near the HAP may often become over-dried and consequently, incur severe HRYRs, which ultimately may lower the economic value of the rice lot. These findings could be used to optimize the rice CF drying process.

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