高浓度水煤浆流变特性转变条件及其微观机理研究

发布时间：2018-06-05 06:39

本文选题：水煤浆 + 粘度　；参考：《中央民族大学》2017年硕士论文

【摘要】：浆体管道输送技术由于其节能环保、低成本、无污染、作业不受天气影响等优势成为了继水运、公路、铁路、空运之后的第五大运输方式。在管道输送中,如何在较小输送阻力下达到最大的输送效率以降低运行成本一直被普遍关注。固液两相流的流变特性与管道输送中流体的阻力特性密切相关,是管道输送系统参数设计和优化的基础依据。本研究将浆体和膏体作为一个有机整体,利用同心圆筒旋转式流变仪,探究不同浓度、不同粒径条件下水煤浆/膏的流变特性,并利用低场核磁共振技术检测浆体中水分的横向弛豫时间分布,区分和定量吸附水、间隙水和自由水,综合分析浆体的微观水分分布情况与宏观流变特性变化结果,分析固液两相流粘度变化的内在微观机理,从微观机理角度分析并确定不同条件下水煤浆的浆体向膏体转变临界条件。主要工作和结论如下:(1)探究了不同浓度、不同粒径条件下水煤浆的流变特性。随着剪切速率的增加,水煤浆切应力线性增加,符合宾汉塑性模型。水煤浆具有触变性,随着剪切速率的增加,表观黏度减小。流变参数随着浓度的增加而增加,变化趋势呈指数型。且存在一个临界浓度,在临界浓度前后,流变参数变化率相差30倍,这是由颗粒间距的变化导致的。在一定浓度下,粘度随着粒径的增加而减小,原因是颗粒的理化性能和浆体中水分含量的变化。(2)利用低场核磁共振技术区分并定量水煤浆中的三种状态水,分析了粒径和浓度对不同状态水分含量的影响。T2谱图显示三种水的加权平均弛豫时间存在1-2个数量级的差异。在一定粒径下,吸附水含量与浓度无关,.自由水和间隙水含量均随浓度的增加而增多。在一定浓度下,吸附水和间隙水量与粒径呈负相关,自由水量与粒径呈正相关,原因是颗粒间距的大小和吸附团聚作用的强弱。(3)分析了浆体中微观水分分布与宏观流变特性之间的相互作用关系,进一步从理论角度确定了浆体向膏体转变的临界条件。浆体中自由水含量的变化是决定其宏观流变特性的根本原因。提出了可以同时考虑颗粒间距、自由水含量及颗粒粒径大小等多因素的参数,即颗粒间距比L/d。0.05L/d0.10为不同浓度、不同粒径物料浆体向膏体转变的临界条件。通过数据拟合得到了不同粒径水煤浆物料浆体向膏体转变的临界浓度公式,为最佳输送条件的确定提供依据。
[Abstract]:Slurry pipeline transportation technology has become the fifth mode of transportation after waterway, road, railway and air transportation because of its advantages of energy saving, environmental protection, low cost, no pollution and operation without weather influence. In pipeline transportation, how to achieve the maximum transport efficiency and reduce the operation cost under the small transportation resistance has been widely concerned. The rheological characteristics of solid-liquid two-phase flow are closely related to the resistance characteristics of the fluid in pipeline transportation, which is the basis for the parameter design and optimization of pipeline transportation system. In this study, slurry and paste as an organic whole, using concentric cylinder rotary rheometer, the rheological characteristics of coal water slurry / paste under different concentration and different particle size were studied. The transverse relaxation time distribution of water in slurry was measured by low field nuclear magnetic resonance (LNMR) technique, and the absorption water, interstitial water and free water were distinguished and quantified. The microcosmic water distribution and the change of macroscopic rheological characteristics of slurry were analyzed synthetically. The internal microscopic mechanism of viscosity change of solid-liquid two-phase flow is analyzed and the critical conditions of slurry to paste transformation under different conditions are analyzed and determined from the angle of microscopic mechanism. The main work and conclusion are as follows: 1) the rheological characteristics of coal water slurry with different concentration and particle size are studied. With the increase of shear rate, the shear stress of coal water slurry increases linearly, which accords with the Bingham plastic model. Coal water slurry has thixotropy and the apparent viscosity decreases with the increase of shear rate. The rheological parameters increased with the increase of concentration, and the change trend was exponential. There is a critical concentration, and the change rate of rheological parameters varies by 30 times before and after the critical concentration, which is caused by the change of particle spacing. At a certain concentration, the viscosity decreases with the increase of particle size, because the physicochemical properties of the particles and the change of water content in the slurry. 2) the low field nuclear magnetic resonance technique is used to distinguish and quantify the three states of water in the coal water slurry. The effects of particle size and concentration on water content in different states were analyzed. T2 spectra showed that there were 1-2 orders of magnitude difference in the weighted mean relaxation time of the three kinds of water. Under certain particle size, the content of adsorbed water has nothing to do with the concentration. The contents of free water and interstitial water increased with the increase of concentration. At a certain concentration, adsorbed water and gap water were negatively correlated with particle size, and free water was positively correlated with particle size. The reason is that the size of particle spacing and the strength of adsorption and agglomeration are used to analyze the interaction between microscopic water distribution and macroscopic rheological properties in the slurry, and the critical conditions for the transition from slurry to paste are determined theoretically. The change of free water content in slurry is the fundamental reason for its macroscopic rheological characteristics. The parameters such as particle spacing, free water content and particle size can be considered at the same time, that is, the critical conditions for the transition from slurry to paste with different particle spacing ratio (L/d.0.05L/d0.10). The critical concentration formula for the transformation of coal water slurry with different particle sizes into paste is obtained by fitting the data, which provides the basis for determining the optimal transportation conditions.
【学位授予单位】：中央民族大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：U171

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