高含水稻穀前期乾燥數學模型

Abstract

夏、秋兩季是台灣一期稻作收穫期，期間時常遭遇豪雨及颱風侵襲，已經結穗成熟的稻作很容易就會因豪雨及強風而倒伏，倒伏的稻作因堆疊在一起不利通風，這些富含大量水分的稻穀繼續擺在田裡很容易就會開始發芽或是長霉，因此只要雨季或颱風到來，農民皆紛紛搶收濕穀送至各乾燥中心進行乾燥，但由於乾燥中心採用的循環式乾燥機在處理高含水率稻穀上的效率較差，除了增加能源成本外，也拖慢了整個乾燥流程，導致乾燥機使用壅塞。為解決此問題，必須探討高含水稻穀的乾燥現象並以此設計針對高含水稻穀的預乾燥機。 本研究利用有限元素分析軟體COMSOL Multiphysics 5.0電腦模擬軟體，建立一維球對稱熱、質傳數學模型來模擬單粒厚度稻穀在乾燥過程中的含水率及溫度變化，並進行薄層乾燥實驗。在通風量0.1CMM、0.3CMM、0.5CMM、0.7CMM，通風溫度50度的比較試驗中，各條件之間的含水率變化並無顯著變化，只有在開始的1分鐘，高通風量的乾燥速率顯得稍快一些；而在40℃、50℃、60℃、70℃，通風量0.3CMM的比較試驗中，較高溫的兩組的乾燥速率明顯比較低溫兩組快，且待在恆率乾燥的時間也比低溫的多出將近6分鐘，可以說通風溫度越高對乾燥效率的提升越有幫助。 本研究以乾燥條件60℃，0.3CMM來對照實驗數據與數學模型之吻合度，對照含水率變化和乾燥速率變化在趨勢上都大致吻合。

The 1st paddy harvest in summer and fall always suffer from typhoons and torrential rain in Taiwan. The ripe paddies could be easily beaten down by heavy rain and strong wind. These paddies were difficult to ventilate and could bud or mold in the wet stack. Therefore, farmers would rush in the harvest when the typhoon or rainy season comes, and deliver the wet paddies to drying center for drying. But the recirculating dryer with poor efficiency for the high moisture content paddies. Increase the energy cost, prolong the drying process and decrease the operation capacity. To solve the problem, it is necessary to investigate the drying phenomenon of high moisture content paddies, and design a specific pre-dryer for the high moisture content paddy. The study using the FEM analysis software COMSOL Multiphysics5.0. Establish a 1-dimension sphere symmetry geometry with heat and mass transfer model to simulate the changes of moisture content and paddy temperature during the thin layer drying process. Comparing with the flow rate at 0.1CMM, 0.3CMM, 0.5CMM and 0.7CMM at 50℃, the changes of moisture content almost identical. The drying rate show higher at higher flow rate at the initial 1 minutes. On the other hand, Comparing with the drying temperature at 40℃, 50℃, 60℃ and 70℃ at 0.3CMM, Condition at higher temperature with higher drying rate, and with 6 minutes more than the low temperature in the constant rate period. In the other word, higher the drying temperature, higher the drying efficiency. The study compared the experimental and the mathematical data in the condition of 60℃，0.3CMM, and the changes of moisture content and drying rate roughly identical between the experiment and model.