本文關(guān)鍵詞： 土壤 多孔介質(zhì) 傳熱傳質(zhì) 孔道網(wǎng)絡(luò) 模擬與試驗(yàn)　出處：《陜西科技大學(xué)》2016年碩士論文　論文類(lèi)型：學(xué)位論文

【摘要】：隨著國(guó)民經(jīng)濟(jì)的提高,農(nóng)業(yè)生產(chǎn)和環(huán)境治理問(wèn)題受到了人們的高度重視,這些問(wèn)題的解決都離不開(kāi)對(duì)土壤多孔介質(zhì)熱質(zhì)傳遞過(guò)程的研究。目前所建立的傳統(tǒng)模型沒(méi)有充分考慮土壤物理結(jié)構(gòu)的影響,將其假設(shè)為連續(xù)性介質(zhì)考慮。在研究土壤熱質(zhì)傳輸過(guò)程中,不能真實(shí)反映多孔介質(zhì)內(nèi)部復(fù)雜的拓?fù)浣Y(jié)構(gòu),也不能合理解釋一些現(xiàn)象如優(yōu)勢(shì)流等。針對(duì)以上問(wèn)題本論文以砂土為典型代表,將孔道網(wǎng)絡(luò)理論引用到土壤多孔介質(zhì)熱質(zhì)傳遞的研究領(lǐng)域,進(jìn)行了以下研究：首先運(yùn)用孔道網(wǎng)絡(luò)理論對(duì)現(xiàn)實(shí)生活的中砂土堆進(jìn)行了網(wǎng)格提取并將網(wǎng)格規(guī)則化處理,構(gòu)建了土壤多孔介質(zhì)孔道網(wǎng)絡(luò)物理模型。對(duì)物理模型中常用的五個(gè)結(jié)構(gòu)參數(shù)：分布律、孔隙節(jié)點(diǎn)間距、空問(wèn)分布系數(shù)、模型規(guī)模數(shù)以及配位數(shù)進(jìn)行描述,并將這些參數(shù)與土壤多孔介質(zhì)的特征參數(shù)：孔隙率、粒徑分布、孔徑分布以及孔隙配位數(shù)進(jìn)行了一一對(duì)應(yīng),使孔道網(wǎng)絡(luò)理論可以應(yīng)用于實(shí)際土壤多孔介質(zhì)熱質(zhì)傳遞的理論分析中。在物理模型的基礎(chǔ)上,對(duì)熱質(zhì)傳遞過(guò)程機(jī)理進(jìn)行了分析,并對(duì)所建模型作了基本假設(shè)。構(gòu)建了土壤多孔介質(zhì)孔道網(wǎng)絡(luò)數(shù)學(xué)模型,建立了質(zhì)量、熱量傳遞過(guò)程控制方程,并給出了不同外界環(huán)境下(風(fēng)吹、日曬、雨淋)的邊界條件和初始條件。運(yùn)用有限元法對(duì)所建立的數(shù)學(xué)模型進(jìn)行了求解。采用VC++與Matlab語(yǔ)言聯(lián)合編程對(duì)所建立的模型進(jìn)行程序開(kāi)發(fā)及模擬。以砂土床為試驗(yàn)物料,使用自制的試驗(yàn)裝置模擬了不同大氣環(huán)境條件(日曬、風(fēng)吹、雨淋)下砂土床熱質(zhì)傳遞過(guò)程。確定了砂土床的各個(gè)結(jié)構(gòu)參數(shù),并通過(guò)試驗(yàn)得到了砂土床的平均濕含量分布曲線(xiàn)、溫度分布曲線(xiàn)。為與孔道網(wǎng)絡(luò)模型進(jìn)行對(duì)比,采用傳統(tǒng)連續(xù)性假設(shè)方法建立了連續(xù)性模型并采用ANSYS進(jìn)行模擬分析,得到了濕分場(chǎng)和溫度的變化曲線(xiàn)。通過(guò)模擬結(jié)果與試驗(yàn)結(jié)果的對(duì)比分析可以得出,所建立的模型能夠較好的描述實(shí)際土壤多孔介質(zhì)的傳熱傳質(zhì)過(guò)程。風(fēng)吹和日曬時(shí),初始階段土壤為濕飽和狀態(tài),水分梯度較小,導(dǎo)致毛細(xì)力較小,從而土壤濕含量變化較慢,隨著時(shí)間的推移,毛細(xì)力逐漸增大,濕含量變化逐漸加快。砂土溫度受太陽(yáng)輻射影響較大；雨淋時(shí),初始階段土壤為干飽和狀態(tài),重力作用引起的下滲使?jié)窈孔兓^快,隨著時(shí)間的推移,毛細(xì)力逐漸增大,濕含量變化趨于緩慢。多孔介質(zhì)的不同結(jié)構(gòu)參數(shù)對(duì)熱質(zhì)傳遞過(guò)程的影響為孔隙率、配位數(shù)越大則干燥速率越快,配位數(shù)減小導(dǎo)致了濕團(tuán)現(xiàn)象的產(chǎn)生。
[Abstract]:With the improvement of national economy, people attach great importance to the problems of agricultural production and environmental management. The solution of these problems is inseparable from the study of the heat and mass transfer process in porous soil media. The traditional models established at present do not fully consider the influence of soil physical structure. In the study of soil heat and mass transport, the complex topological structure of porous media can not be truly reflected. Some phenomena such as dominant flow can not be explained reasonably. Aiming at the above problems, this paper applies the theory of pore network to the research field of heat and mass transfer in porous soil. The following studies are carried out: firstly, the mesh extraction and regularization of the meshes are carried out by using the theory of pore network. In this paper, the physical model of porous soil pore network is constructed, and the five structural parameters commonly used in the physical model are described: distribution law, pore node spacing, spatial distribution coefficient, model size and coordination number. These parameters are correlated with the characteristic parameters of soil porous media, such as porosity, particle size distribution, pore size distribution and pore coordination number. The theory of pore network can be applied to the theoretical analysis of heat and mass transfer in soil porous media. Based on the physical model, the mechanism of heat and mass transfer is analyzed. The mathematical model of porous soil pore network was constructed, the control equations of mass and heat transfer were established, and the different external environment (wind and sun) were given. Rain). The finite element method is used to solve the established mathematical model. VC is used to solve the problem. The model was programmed and simulated with Matlab language. The sand bed was used as the test material. The heat and mass transfer process of sand bed under different atmospheric conditions (sun, wind, rain) was simulated by using self-made test device. The structure parameters of sand bed were determined. The average wet content distribution curve and temperature distribution curve of sand bed are obtained by experiments, which are compared with the pore network model. The continuity model is established by using the traditional continuity hypothesis method and simulated by ANSYS. The variation curves of the wet field and the temperature are obtained, which can be obtained by comparing the simulation results with the experimental results. The model can well describe the heat and mass transfer process of the actual soil porous media. When the wind and sunlight, the initial phase of the soil is wet saturated state, the water gradient is small, resulting in a small capillary force. As a result, soil moisture content changes slowly, with time, capillary force gradually increases, moisture content change gradually accelerate, sand temperature is greatly affected by solar radiation; In the initial stage of rain, the soil is dry saturated, the infiltration caused by gravity makes the moisture content change faster, and the capillary force increases gradually with the passage of time. The effect of different structure parameters of porous media on the heat and mass transfer process is porosity. The larger the coordination number is, the faster the drying rate is, and the smaller the coordination number is, the wet mass is produced.
【學(xué)位授予單位】：陜西科技大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2016
【分類(lèi)號(hào)】：TK124
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本文編號(hào)：1447541