【摘要】：高水分植物細(xì)胞物料的干燥過程中,物料失去的水分主要來源于封閉的細(xì)胞�，F(xiàn)有模型和理論對細(xì)胞封閉結(jié)構(gòu)在整個干燥過程中的變化以及細(xì)胞封閉結(jié)構(gòu)在這個過程中扮演的角色缺乏清晰完整的描述。本文從亞細(xì)胞水分傳輸出發(fā),建立了關(guān)于高水分植物細(xì)胞物料低溫對流干燥的等溫水分傳輸模型,模型中表觀水分傳輸參數(shù)由組織微觀參數(shù)算得。最后利用模型對干燥過程進(jìn)行了研究。通過對低溫對流干燥過程中細(xì)胞結(jié)構(gòu)變化的分析,認(rèn)為整個干燥過程中都可以把組織看成是由細(xì)胞構(gòu)成的,并提出了對整個干燥過程都適用的模型細(xì)胞,模型細(xì)胞保留了真實(shí)細(xì)胞中必要的、參數(shù)可測的亞細(xì)胞結(jié)構(gòu)。模型細(xì)胞構(gòu)成了植物細(xì)胞組織概念模型。利用場發(fā)射冷凍電鏡觀察得到了馬鈴薯細(xì)胞的幾何尺寸參數(shù)。給出了組織模型各部分水分狀態(tài)和水分傳輸規(guī)律。為獲得組織表觀傳輸參數(shù)與微觀參數(shù)之間的關(guān)系,建立了理想化立方體薄壁細(xì)胞串上細(xì)胞腔相和細(xì)胞壁相的水勢傳輸方程。假設(shè)細(xì)胞腔內(nèi)水勢分布為線性,得到了水分從細(xì)胞中心到細(xì)胞壁傳輸?shù)囊约皬募?xì)胞腔到細(xì)胞腔傳輸?shù)陌?xì)胞腔內(nèi)擴(kuò)散效應(yīng)的水導(dǎo)系數(shù)。通過兩相方程的尺度分析以及對細(xì)胞串上微觀水分傳輸?shù)哪M,得到了以下結(jié)論：薄壁細(xì)胞的結(jié)構(gòu)特點(diǎn)使得細(xì)胞腔和細(xì)胞壁之間水勢趨于平衡,干燥過程中細(xì)胞腔溶液水分?jǐn)U散系數(shù)的減小會破壞局部平衡；當(dāng)馬鈴薯細(xì)胞干基含水率不低于1時,細(xì)胞的細(xì)胞腔和細(xì)胞壁之間水勢平衡,存在細(xì)胞腔到細(xì)胞腔的水分傳輸；干基含水率從1至0.32的過程中,局部平衡狀態(tài)逐漸不再成立,細(xì)胞腔到細(xì)胞腔的水分傳輸終止。干燥過程中若細(xì)胞腔和細(xì)胞壁之間局部水勢平衡,則細(xì)胞間隙和細(xì)胞也保持局部水勢平衡。在局部平衡的條件下得到了組織表觀水導(dǎo)系數(shù)和組織微觀參數(shù)之間的關(guān)系模型。假設(shè)整個干燥過程中細(xì)胞腔、細(xì)胞壁和細(xì)胞間隙之間局部水勢平衡,利用上文得到的組織表觀水導(dǎo)系數(shù)模型建立了平板狀物料干燥的一維等溫水分傳輸和收縮模型。討論了組織一維收縮效應(yīng),認(rèn)為可以假設(shè)垂直于主流方向的截面上各相面積分?jǐn)?shù)在干燥過程中保持不變,并獲得了迂曲度系數(shù)和收縮系數(shù)的關(guān)系。把組織水分傳輸方程轉(zhuǎn)化為由參考坐標(biāo)描述的水分?jǐn)U散方程,得到了等效擴(kuò)散系數(shù)與組織收縮、組織水導(dǎo)系數(shù)以及組織水容的關(guān)系式。為驗(yàn)證組織水分傳輸模型的正確性,進(jìn)行了熱風(fēng)溫度為40℃的平板狀馬鈴薯組織的干燥實(shí)驗(yàn),并利用建立的擴(kuò)散方程對干燥過程進(jìn)行了模擬。模擬和實(shí)驗(yàn)結(jié)果表明：模型預(yù)測的干燥曲線在高水分段(平均含水率高于1)與實(shí)驗(yàn)吻合得較好,當(dāng)組織平均含水率小于1.5時,模型預(yù)測的干燥速率明顯比實(shí)驗(yàn)值要大。該結(jié)果表明假設(shè)整個干燥過程中細(xì)胞局部水勢平衡使得模型高估了細(xì)胞腔到細(xì)胞腔水分傳輸存在的時間,進(jìn)而高估了組織的干燥速率。模型預(yù)測表明：馬鈴薯干燥過程中物料內(nèi)部的水分傳輸主要是液態(tài)擴(kuò)散、跨膜傳輸和細(xì)胞壁中的毛細(xì)水分流動,細(xì)胞間隙中的蒸氣擴(kuò)散在高水分段可以忽略不計；影響干燥過程的主要微觀參數(shù)是細(xì)胞各部分的水分傳輸參數(shù),幾何尺寸的影響相對來說較小。因此正確測定細(xì)胞各部分水分傳輸參數(shù)對揭示干燥過程中組織內(nèi)水分傳輸機(jī)理至關(guān)重要。為完整描述整個干燥過程,需提出能考慮非局部平衡狀態(tài)下水分傳輸?shù)哪Ｐ汀?br/>[Abstract]:In the drying process of high-moisture plant cell materials, the loss of water mainly comes from the closed cells. The present models and theories lack a clear and complete description of the changes of the closed cell structure and the role of the closed cell structure in the whole drying process. An isothermal moisture transfer model for high moisture plant cell materials during low temperature convective drying was established. The apparent moisture transfer parameters in the model were calculated from the microstructure parameters. Finally, the drying process was studied by using the model. Tissue is considered to be composed of cells, and a model cell suitable for the whole drying process is proposed. The model cell retains the necessary and measurable subcellular structure of the real cell. The model cell constitutes the conceptual model of plant cell tissue. The geometric size parameters of potato cells are obtained by field emission freezing electron microscopy. In order to obtain the relationship between the apparent transport parameters and the microscopic parameters of the tissue, the water potential transfer equations of the cell lumen and cell wall phases on the idealized cubic parenchyma cell string are established. Assuming the water potential distribution in the cell lumen is linear, the water flow from the cell center to the cell wall is obtained. The water conductivity of cell wall transport and that of cell wall transport from cell cavity to cell cavity including intracellular diffusion effect. Through the scale analysis of two-phase equation and the simulation of micro-water transport on cell string, the following conclusions are obtained: the structural characteristics of parenchyma cells make the water potential between cell cavity and cell wall tend to balance, and the drying process. When the water content in the cell lumen is not less than 1, the water potential between the cell lumen and cell wall is balanced and there is water transfer from the cell lumen to the cell lumen. The water transport in the cell lumen terminates. If the local water potential between the cell lumen and cell wall is balanced during drying, the cell gap and cell also maintain the local water potential equilibrium. A one-dimensional isothermal water transport and shrinkage model for plate material drying is established by using the model of apparent water conductivity obtained above. The effect of one-dimensional shrinkage of tissue is discussed. It is assumed that the area fraction of each phase on the cross-section perpendicular to the main direction remains unchanged during drying. The relationship between tissue water transfer equation and tissue shrinkage, tissue water conductivity coefficient and tissue water capacity was obtained by transforming tissue water transfer equation into water diffusion equation described by reference coordinates. The results of simulation and experiment show that the drying curve predicted by the model is in good agreement with the experiment in the high moisture section (the average moisture content is higher than 1). When the average moisture content of the tissue is less than 1.5, the drying rate predicted by the model is obviously higher than the actual drying rate. The results show that the model overestimates the time of water transport from the cell cavity to the cell cavity, and then overestimates the drying rate of the tissue. The model predicts that the water transport in the material during potato drying is mainly liquid diffusion, transmembrane transport and fineness. The capillary water flow in the cell wall and the vapor diffusion in the intercellular space can be neglected in the high water section; the main microscopic parameters affecting the drying process are the water transport parameters of the cell parts, and the geometric size has relatively small influence. In order to describe the whole drying process completely, it is necessary to propose a model which can consider the moisture transfer in non-local equilibrium state.
【學(xué)位授予單位】：中國農(nóng)業(yè)大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2016
【分類號】：S375

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