Finite Element Analysis and MRI Validation of Intra-Kernel Moisture Migration of Single Rice
Date Issued
2007
Date
2007
Author(s)
Liou, Jhao-Huei
DOI
zh-TW
Abstract
In this study, we discuss the intra-kernel moisture migration of individual rice kernels by finite element method, and verify the simulated results with magnetic resonance imaging (MRI). Two kinds of rice kernel models were used in our study. The one is the prolate elliptical model and the other is the model based on real rice geometric structure. Functions provided by the COMSOL Multiphysics 3.2 software were used to obtain the real rice models from the MRI images of rice kernel. The simulation results show that the air temperature is the major parameter affecting the drying rate for rice drying. The moisture content on the surface of a rice kernel decreases rapidly and results in significant moisture gradient within the rice kernel when the air temperature for drying is high. The initial temperature of grain and the air velocity are less significant than the air temperature. The differences of moisture content between the bran and the central endosperm were only ±0.1% w.b. after 18 hours drying when the initial temperatures of grain were 25°C and 45°C. The average drying rate increases when the portion of drying time in a circulating drying is increased but the moisture gradient inside the rice kernel also increases at the same time. The moisture gradient can be reduced by increasing tempering time however, and then the fissuring of rice kernel can be improved. If we consider the energy consumption but not the total time of rice drying, the drying efficiency of circulating drying is better when it is implemented by the cyclic processes of short drying time followed by longer tempering time. For example, 20 minutes drying followed by 120 minutes tempering yields better drying efficiency. Beside simulations of drying and tempering process, we discuss the moisture migration of soaking process as well. From the simulating results of soaking of brown rice and rough rice, we found that the diffusion rate of the bran is higher than the hull. Hull layer provides a barrier to rapid absorption of water in rice soaking. The water absorption rate is 2.55% d.b./hr in the endosperm of a rough rice and 7.94% d.b./hr in the endosperm of a brown rice after 10-hour soaking.
Subjects
有限元素法
稻穀
水分遷移
磁共振影像
Finite Element Method (FEM)
Rice Kernel
Moisture Migration
Magnetic Resonance Imaging (MRI)
SDGs
Type
thesis
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