【作者】 谷芳；

【导师】 袁希钢；

【作者基本信息】 天津大学 ， 化学工程， 2004， 博士

【摘要】 为精确描述规整填料塔气液传质过程中涉及的多尺度流动与传质现象,进而准确预测整塔传质效率,本文对规整填料塔气液传质过程的局部微观流动、气液两相传质机理、宏观气液分布及多尺度关联计算传质学方法进行了初步研究。建立描述规整填料塔传质过程的多尺度关联计算传质学模型涉及填料表面局部溪流液膜流动过程。为此,采用VOF法建立了二维气-液两相分层流动CFD模型;提出影响液膜流动的两个重要动量源项:表面张力动量源项和界面剪应力动量源项;根据模拟结果讨论了板面结构、液相物性及气液流速对液膜流动的影响。在流场模型基础上建立了二维气-液两相降膜解吸传质CFD模型,模拟结果显示,增强相界面波动(①增强气相流量;②采用波纹板面结构),能够有效提高降膜传质增强因子。在二维模型基础上,建立了三维溪流CFD模型和三维单片规整填料溪流CFD模型并进行求解。为验证相关理论,采用三维LDA技术测量了溪流液膜的流场和自由表面侧形;实验结果表明,本文提出的模型较现有文献发表的模型能更好地预测规整填料片表面的液体流动。通过精确测定Mallpak250X/Y、350X/Y四种填料在两片规整填料内的液相分布和持液量,本文建立了规整填料宏观液相分布的新模型。模型中考虑了壁效应、结点处液体混合再分配过程以及液体横向扩散过程;模型中用到了针对降膜溪流流动的部分CFD研究结果,即利用CFD模型求算局部溪流宽度,克服了传统经验关联式计算精度低的缺点;能方便获得规整填料内的局部流动信息。针对规整填料内气相宏观流动建立了相关的气相拟单相CFD模型并进行了求解。在上述研究基础上,初步建立了规整填料塔传质过程的多尺度关联计算传质学模型,提出了液相分布结点网络模型-气相拟单相流CFD模型-经典传质理论相耦合的规整填料塔传质效率计算方法,该方法属于一种由局部小尺度传质过程估算整体传质效率的多尺度计算传质学方法。利用所建立的耦合模型求得的HETP与常减压下的实验值吻合较好。本文所建立的方法不需输入实验数据,只需给定气、液相物性参数和填料结构参数,即可较为准确地估算填料塔的传质效率,对大规模填料塔的结构优化设计及整塔操作工艺优化设计提供了一种方法和途径。更多还原

【Abstract】 Better understanding of the multi-scale flow behavior and mass-transferphenomena that happened in structured packing columns is of great importance forpredicting their mass-transfer efficiency more accurately. In this thesis, the liquidfilm flow and mass-transfer mechanism at small scale, gas and liquid distributionpattern at large scale, and a multi-scale associated computational mass-transfermethod have been studied preliminary.The local rivulet film flow is the most popular behavior for distillation process instructured packing column. Using multi-scale coupled computational mass-transfermethod to predicting the column performance needs a better understanding of thiskind of flow. Therefore, a two-dimensional two-phase flow CFD model using thevolume of fluid (VOF) method is presented. Two important momentum source termsworking on the film flow, surface tension and interface stress shear, are considered.Based on the simulated results, the influences of the plate structures, liquid propertiesand gas and liquid velocities on the film flow are discussed. A mass-transfer CFDmodel for gas stripping is also presented based on the two-phase flow CFD model.The simulation results indicated that making the interfacial waves more violent is aneffective means to enhance the separation efficiency. Three-dimensional two-phaseflow CFD models for the single rivulet film flow and structured packing rivulet filmflow are also proposed based on the two-dimensional CFD flow model. For validatingthe corresponding theories, three-dimensional LDA technique is used to measure therivulet film flow. The experimental results of the free surface profile shows that themodel proposed here can predict the liquid flow on structured packing surface moreaccurately comparing with other literature models.A new macro liquid distribution model is established, where the wall effect,liquid mixing and allocation process at the crunodes and the liquid transversedispersion are taken into account. Some parameters of the model were regressedusing the experimental data obtained in a two-sheet testing rig for structured packingof Mellapak 250X/Y and 350X/Y. The experimental data include liquid flowdistribution and liquid holdup results for the four types of packings mentioned above.The local rivulet widths used in the model are calculated by the single rivulet flowCFD model, which improves the model precision greatly comparing with the modelsusing empiricism formulae. The local liquid flow characteristics can be obtainedconveniently by this liquid distribution model. A pseudo-single-phase gas flow CFDmodel is established for predicting the macro gas distribution in structured packing.A hybrid arithmetic which combined the gas CFD model, the macro liquiddistribution model and some classical mass-transfer theories has been proposed forpredicting the mass-transfer efficiency of structured packing. The hybrid arithmetic bylocal small-scale mass-transfer process estimating macro-scale mass-transferefficiency is a kind of multi-scale computational mass-transfer method. The simulatedHETP agreed with the experimental HETP very well under the conditions of normaland vacuum pressure. This hybrid arithmetic needn’t introduce any experimental data,gas-liquid properties and packing structural parameters are enough. The hybridarithmetic of mass-transfer process provides a new approach for the design of theequipment and optimization of the process of large-scale structured packing columns.更多还原