本文選題：多孔介質　切入點：格子Boltzmann方法　出處：《大連理工大學》2015年碩士論文　論文類型：學位論文

【摘要】：地熱源熱泵技術由于其良好的環(huán)境和經(jīng)濟效益,近年來發(fā)展迅速。在地埋管換熱器與土壤換熱過程中,地下水滲流影響不可忽視,且熱滲耦合機制也較為復雜。在以往研究中,大多針對宏觀方面開展相關的實驗和數(shù)值模擬分析。本文嘗試從微觀角度出發(fā),采用數(shù)值模擬計算的方法以揭示土壤內部結構演化及其熱滲耦合規(guī)律。本文首先引入了不可壓耦合雙分布函數(shù)格子Boltzmann模型,介紹了其基本原理和邊界處理格式,同時借助封閉方腔自然對流驗證了選取模型和邊界處理的可行性和準確性。其次本文通過隨機四參數(shù)生成法(QSGS)重構得到了與真實土壤形態(tài)相近的二維飽和多孔介質模型,通過調整模型參數(shù)之間的關系可以表征出多孔介質更多細節(jié)信息。在此基礎上,從孔隙尺度角度出發(fā),在無滲流純導熱情況下對有效導熱系數(shù)同多孔介質結構之間的關系作了探討。最后對飽和土壤滲流與傳熱開展了相關數(shù)值模擬研究。在模擬中分別針對不同滲流壓差、孔隙率、土壤固相顆粒尺寸分布、溫度梯度方向對熱滲耦合特性影響進行了詳細的討論,同時對土壤相關的水力學參數(shù)進行了計算分析。數(shù)值模擬結果表明：(1)無滲流影響時,土壤有效導熱系數(shù)隨著孔隙率增加而近似呈指數(shù)形式遞減,且關于土壤固相顆粒導熱系數(shù)呈冪函數(shù)關系；對于同一孔隙率,土壤固相顆粒尺寸越小,有效導熱系數(shù)越大。(2)在有滲流時,土壤滲流速度與滲流壓差呈線性遞增關系,且隨著速度增加,土壤內部傳熱機制逐漸由固液熱傳導占優(yōu)轉變?yōu)閷α鲹Q熱為主,整個土壤內部平均溫度上升速率減緩。(3)隨著土壤孔隙率的增加,土壤內部孔隙間連通性變好,滲流速度隨之增大；由于孔隙水與周圍固體骨架形成的液橋增加,接觸熱阻減小,加之滲流速度大幅度增加,滲流方向與導熱方向一致,對流換熱作用得到強化,導致土壤內部溫度呈明顯上升趨勢。(4)在同一孔隙率和滲流壓差下,土壤固相顆粒尺寸較大時,多孔介質內部會出現(xiàn)局部流速突增情況,形成典型的優(yōu)先流效應。隨著顆粒尺寸的減小,顆粒之間接觸更加緊密,生成隨機多孔介質有效導熱系數(shù)增大,對流換熱系數(shù)減小,會造成傳熱過程中熱擴散阻力增加,土壤內溫度變化逐漸趨于平緩,平均溫度下降。(5)對于熱源相同作用位置,流動與傳熱兩者驅動勢同向比反向時土壤內平均溫度要高,且隨著孔隙率增加,溫度差距也隨之加大。
[Abstract]:The geothermal source heat pump technology has developed rapidly in recent years because of its good environment and economic benefits. In the process of heat transfer between ground heat exchanger and soil, the influence of groundwater seepage can not be ignored, and the mechanism of heat and permeability coupling is more complicated. Most of the experiments and numerical simulation are carried out on the macro aspect. This paper tries to start from the micro point of view. In this paper, the incompressible coupled double distribution function lattice Boltzmann model is introduced, and its basic principle and boundary treatment scheme are introduced. At the same time, the feasibility and accuracy of the selection model and boundary treatment are verified by natural convection of closed square cavity. Secondly, a two-dimensional saturated porous media model similar to the real soil morphology is obtained by the stochastic four-parameter generation method (QSGS) reconstruction. By adjusting the relationship between the parameters of the model, more detailed information of porous media can be expressed. On this basis, from the point of view of pore scale, The relationship between effective thermal conductivity and porous media structure is discussed in the case of pure thermal conductivity without seepage. Finally, the numerical simulation of seepage and heat transfer in saturated soil is carried out. The effects of particle size distribution and temperature gradient direction on the thermo-osmotic coupling characteristics were discussed in detail, and the soil hydraulic parameters were calculated and analyzed. The effective thermal conductivity of soil decreases exponentially with the increase of porosity, and the thermal conductivity of soil solid particles is a power function, and for the same porosity, the smaller the size of soil solid particles is, The larger the effective thermal conductivity is, the more the seepage velocity increases linearly with the seepage pressure difference when there is seepage, and with the increase of the velocity, the heat transfer mechanism in the soil gradually changes from solid-liquid heat conduction to convection heat transfer. With the increase of soil porosity, the connectivity between pores in soil becomes better and the seepage velocity increases, and the contact thermal resistance decreases due to the increase of liquid bridge between pore water and surrounding solid skeleton. In addition, the seepage velocity is greatly increased, the direction of seepage flow is consistent with the direction of heat conduction, and the convection heat transfer is strengthened, which results in an obvious upward trend of soil internal temperature. (4) under the same porosity and seepage pressure difference, the particle size of soil solid phase is larger. With the decrease of particle size, the contact between particles becomes closer, the effective thermal conductivity of random porous media increases, and the convection heat transfer coefficient decreases. During heat transfer, the resistance of thermal diffusion increases, the variation of temperature in soil tends to be gentle, and the average temperature drops at the same position of heat source, and the driving potential of both flow and heat transfer is higher than that of the reverse, and the average temperature in soil is higher when the driving potential of flow and heat transfer is the same as that in reverse. With the increase of porosity, the temperature gap also increases.
【學位授予單位】：大連理工大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：S152

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本文編號：1611507