林達德臺灣大學：生物產業機電工程學研究所劉昭慧Liou, Jhao-HueiJhao-HueiLiou2007-11-262018-07-102007-11-262018-07-102007http://ntur.lib.ntu.edu.tw//handle/246246/52845本研究探討單粒稻穀內部的水分遷移情形，使用有限元素分析的方法進行模擬，並且利用磁共振影像進行模擬結果的驗證。模擬過程使用了兩種不同的稻穀模型，其中一種是扁橢圓模型，而另一種則是真實稻穀模型。所使用的真實稻穀模型是以高解析度的磁共振影像經COMSOL Multiphysics 3.2軟體內附加的程式指令在MATLAB 6.5上運算後取得。模擬結果顯示稻穀使用熱風乾燥時，熱風的溫度是一個影響乾燥速率的重要因子，使用較高的溫度進行稻穀乾燥時，稻穀表面的水分會快速地被帶走，而使穀粒內水分的分佈呈現不均勻的現象，位於穀粒表面的稻殼與穀皮水分明顯比胚乳處的水分低。稻穀乾燥前的初始溫度對於單粒稻穀乾燥的結果影響不顯著，不同初始溫度的稻穀分別置於熱風中經過18小時的乾燥，初始溫度為25°C與45°C之稻穀內部的長軸穀皮外緣、短軸穀皮外緣與胚乳中心的含水率的差異皆在±0.1% w.b.之內。若使用間歇式乾燥，即乾燥一段時間、均化一段時間的方式，隨著乾燥時間的加長，稻穀的平均乾燥率可明顯的提升，但相對地快速乾燥會造成穀粒內水分梯度的累積，但是若將均化時間拉長，即可減少穀粒內的水分梯度，降低稻穀產生胴裂的情況。因此，若不考慮完成乾燥所須的總時間長短，而僅考慮耗費能源多寡的情況下，使用較短的乾燥時間搭配稍長的均化時間，如乾燥20分鐘—均化120分鐘此一方式來進行間歇式乾燥將可得到較高的乾燥效率，且可減少穀粒因水分梯度過大導致大量胴裂使得整米率下降的情況發生。除了乾燥與均化之外，本研究也探討浸泡時稻穀內水分遷移的情形，分別對帶殼稻穀與去殼稻穀進行浸泡模擬後，分析模擬結果得知在相同溫度下將稻穀浸泡於水中，水分在稻殼的擴散速率比在穀皮慢，稻殼會阻礙穀粒快速地吸附水分，當穀粒經過10小時的浸泡後，帶殼稻穀胚乳中心的水分吸附率為2.55%d.b./hr，去殼稻穀胚乳中心的水分吸附率為7.94% d.b./hr。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.誌謝 i 摘要 ii Abstract iii 目錄 v 表目錄 ix 第一章 緒論 1 1.1前言 1 1.2研究目的 3 第二章 文獻探討 4 2.1稻穀的結構 4 2.2稻穀含水率 6 2.2.1稻穀水分含量表示方法 6 2.2.2稻穀含水率測定方式 6 2.2.3稻穀乾燥 8 2.3磁共振成像 10 2.3.1磁共振成像基礎原理 10 2.3.2穀物磁共振成像相關研究 13 2.4有限元素模擬 17 2.4.1有限元素法簡介 17 2.4.2 COMSOL Multiphysics 3.2軟體介紹 17 2.5穀物內部水分遷移模擬相關研究 19 第三章 材料與方法 22 3.1稻穀磁共振影像之取得 22 3.1.1磁共振成像實驗設備 22 3.1.2磁共振影像資料處理方法 22 3.2單粒稻穀水分遷移數學模型 24 3.2.1乾燥過程 24 3.2.2均化過程 25 3.2.3浸泡過程 26 3.3有限元素分析架構與流程 29 3.3.1二維有限元素分析模型 29 3.3.2水分擴散模擬 34 3.4稻穀含水率量測 37 3.5有限元素模擬之個案整理 38 第四章 結果與討論 40 4.1稻穀乾燥過程模擬 40 4.2稻穀均化過程模擬與驗證 49 4.2.1磁共振影像之驗證 51 4.2.2非理想均化 55 4.2.3間歇式乾燥 60 4.3稻穀浸泡過程模擬與驗證 65 4.4稻穀各部位含水率量測 72 4.5討論 73 第五章 結論與建議 74 5.1結論 74 5.2建議 76 參考文獻 77 附錄A 網格參數設定 82 附錄B 程式碼節錄 830 bytesapplication/pdfen-US有限元素法稻穀水分遷移磁共振影像Finite Element Method (FEM)Rice KernelMoisture MigrationMagnetic Resonance Imaging (MRI)[SDGs]SDG7thesishttp://ntur.lib.ntu.edu.tw/bitstream/246246/52845/1/ntu-96-R94631037-1.pdf