30F-12 |
Internal stress behavior of rice kernels during tempering by finite element analysis |
W. W. YANG1, X. Yang, C. Jia, T. J. Siebenmorgen, and M. H. Gordon5. (1) Department of Food Science, University of Arkansas, 2650 N. Young Ave., Fayetteville, AR 72704, (2) Department of Mechanical Engineering, University of Arkansas Tempering has been known to reduce rice fissures. Its effectiveness was related to reduced moisture content gradients (MCGs) and internal stresses. Quantitative relationship between head rice yield (HRY) and MCGs during tempering was studied through finite element analysis (FEA). No reports were made on internal stress behavior during rice tempering. In this study, internal stress behavior including strain distortion energy during tempering was examined by FEA. The results provided helpful insight on why tempering improves HRY. Our objective was to examine internal stress behavior during rice tempering by FEA. Axisymmetric linear triangular elements were used to mesh a half rough rice kernel in ANSYS. Fortran codes were developed to compute moisture and temperature profiles inside rice kernels during drying. Thin-layer drying was performed at 60 deg. C, 17% RH and 42 deg. C, 30% RH, respectively to develop drying curves for model verification. Simulation results were verified against the kernel temperatures and measured drying curves. The simulation results of moisture and temperature distributions at the final time step in drying were input as initial conditions in tempering for obtaining intra-kernel stress distribution during tempering. Both ANSYS and Fortran codes were written for simulating internal stress distribution of rice during tempering. Both the simulated temperature and moisture profiles agreed well with the measured values during drying. For tempering simulation, rough rice was dried for 20 min at 60 deg. C, 17% RH, followed by adiabatic tempering at 60 deg. C. Simulation results suggested that a tempering time around 40 min could eliminate about 90% of MCGs. The maximum strain distortion intensity was found to follow a decreasing trend during tempering, which helped understand why HRY is preserved after tempering. The tempering simulation results may provide useful information to understand the biomechanics of rice during tempering.
Session 30F, Food Engineering: Transport processes and kinetics
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