【摘要】：傳統(tǒng)水文地質(zhì)學(xué)理論是以地下水的水頭壓力作為地下水流的唯一驅(qū)動力來建立地下水水流模型,并將地下水水流模型應(yīng)用到描述溶質(zhì)遷移規(guī)律的對流-彌散方程中,得到溶質(zhì)遷移的規(guī)律。而對于具有半透膜特性的粘性土弱透水層中溶質(zhì)遷移問題研究中,需要考慮粘性土半透膜效應(yīng)對溶質(zhì)遷移影響,由于弱透水層兩側(cè)存有濃度差,弱透水層中水流驅(qū)動力不僅只有水頭壓力,還應(yīng)包含滲透壓,因此,傳統(tǒng)水文地質(zhì)理論是難以適用此情況。本文主要研究內(nèi)容是:在前人研究基礎(chǔ)上,推導(dǎo)了粘性土中溶質(zhì)遷移的簡化模型,并利用簡化模型對反滲透系統(tǒng)在給定流速和滲入端定濃度條件的室內(nèi)試驗進行模擬和計算。本文先從非平衡熱力學(xué)角度,確定溶質(zhì)的質(zhì)量通量表達式,在粘性土中選取典型單元體,根據(jù)質(zhì)量守恒原理,推導(dǎo)出溶質(zhì)遷移模型。對溶質(zhì)遷移模型的簡化分別從化學(xué)滲透與反滲透方面進行討論:化學(xué)滲透的室內(nèi)試驗可控制滲透條件,使得滲透系統(tǒng)近似無流狀態(tài),可得到粘土中溶質(zhì)的濃度隨時間變化率主要取決于分子擴散項,忽略由流體流速所引起的濃度的變化情況;反滲透的簡化模型是基于粘土層對溶劑主要起通道作用所建立,將粘土中流體流速視為與時間有關(guān)而與位置無關(guān)的函數(shù),使用時要求反滲透系統(tǒng)中越流量遠(yuǎn)遠(yuǎn)大于粘土層同時段所"儲存"的水量或者粘土層厚度能符合要求。隨后,設(shè)計了給定流速和滲入端定濃度的反滲透室內(nèi)試驗,利用反滲透的簡化模型推導(dǎo)出試驗條件下的解析解去計算粘土膜效率系數(shù),并對這種計算方法的可靠性進行分析。結(jié)果發(fā)現(xiàn),試驗條件下重塑粘土膜效率系數(shù)為0.9010～0.9064,表明粘土的膜性能好,但120 d后計算的滲出濃度達到0.0998 mol·L-1,接近于滲入濃度0.1 mol·L-1,說明粘土膜攔截鹽的能力隨時間下降。此外,在擬穩(wěn)定狀態(tài)下的敏感性分析表明,流速假定值在偏離原有值的±10%范圍內(nèi),對膜效率系數(shù)的影響不超過±1.25%,擬穩(wěn)定時長變化對膜效應(yīng)系數(shù)的影響不超過0.71%,說明計算方法可靠性高。最后,討論滲入濃度對粘性土的膜效率系數(shù)影響。調(diào)試膜效率系數(shù)值,同時考慮到有效分子擴散系數(shù)與膜效率系數(shù)的關(guān)系,對應(yīng)調(diào)整有效分子擴散系數(shù)值,利用有限元數(shù)值模擬軟件comsol對第二次反滲透試驗的滲出濃度數(shù)據(jù)進行模擬計算,結(jié)果發(fā)現(xiàn),當(dāng)滲入濃度增大時,第二次反滲透試驗的膜效率系數(shù)值取值比第一次反滲透試驗值要小時,計算的結(jié)果更吻合試驗結(jié)果,表明粘性土的膜效率系數(shù)是隨滲入溶液的濃度增大而減少。
[Abstract]:The traditional hydrogeological theory takes the head pressure of groundwater as the only driving force of groundwater flow to establish the groundwater flow model, and applies the groundwater flow model to the convective dispersion equation describing the solute migration law, and obtains the solute transport law. In the study of solute transport in weak permeable layer of clayey soil with semi-permeable film characteristics, it is necessary to consider the effect of semi-permeable film effect on solute transport. Because of the concentration difference between the two sides of weak permeable layer, the driving force of flow in weak permeable layer is not only water head pressure, but also osmotic pressure. Therefore, the traditional hydrogeological theory is difficult to apply to this situation. The main contents of this paper are as follows: on the basis of previous studies, a simplified model of solute migration in clay is derived, and the laboratory tests of reverse osmosis system at a given velocity and at the end of infiltration are simulated and calculated by using the simplified model. In this paper, the mass flux expression of solute is determined from the point of view of non-equilibrium thermodynamics, and the typical unit body is selected in clay. According to the principle of mass conservation, the solute transport model is derived. The simplification of solute transport model is discussed from the aspects of chemical infiltration and reverse osmosis respectively: the laboratory test of chemical osmosis can control the infiltration conditions, so that the infiltration system can approximate the flow-free state, and it can be obtained that the change rate of solute concentration in clay with time mainly depends on the molecular diffusion term, neglecting the change of concentration caused by fluid velocity; The simplified model of reverse osmosis is based on the channel effect of clay layer on solvent. The fluid velocity in clay is regarded as a time-dependent and position-independent function. When used, the flow rate in reverse osmosis system is much larger than the amount of water stored in clay layer or the thickness of clay layer in the same period. Then, the laboratory test of reverse osmosis with given flow rate and fixed concentration at the end of infiltration is designed, and the analytical solution under the test conditions is derived by using the simplified model of reverse osmosis to calculate the efficiency coefficient of clay membrane, and the reliability of this calculation method is analyzed. The results show that the efficiency coefficient of remolded clay film is 0.9010 鈮，

本文編號：2500818