【作者】 孙博；

【导师】 刘春江；

【作者基本信息】 天津大学 ， 化学工程， 2013， 博士

【摘要】 本文的研究内容分为两部分，第一部分为第二至第四章，主要对气液两相传热及传质过程进行模拟与实验研究，包括液膜蒸发、冷凝过程以及新型换热板结构对降膜传热的影响；第二部分为第五至第七章，采用多尺度计算理论预测填料塔内部的液相分布行为，并建立了完善的液相分布模型。在降膜蒸发器以及海水淡化等设备中，气液两相流动过程以及传热传质过程一直是人们关注的焦点。为此，本文首先采用VOF方法建立了二维气液两相分层流动的CFD模型，引入影响液膜流动的表面张力源相和气液界面剪应力源相，并考虑相界面处由于发生蒸发或冷凝所导致的水蒸气浓度变化和传热量的变化。根据模拟结果讨论了气液相温度、流率、气相水蒸气浓度以及壁面热通量对传热系数以及相界面处显热、潜热的影响。模拟结果显示，液膜传热系数在进口附近显著减小，在相界面处潜热为主要的传热方式，冷凝过程由于冷凝放热的影响进一步限制了显热传热过程。液相流动行为能够显著地影响传热及传质过程。为此，本文提出了一种新型换热板结构，并通过实验对比研究了翅片板、平板和粗糙板三种结构对降膜传热过程的影响。实验结果表明，翅片板能够显著改善液膜分布，同时翅片板上的翅片和小孔结构增大了液相再混合以及湍流程度，进一步提高其传热性能。本文第二部分采用微观CFD模拟和宏观计算相结合的多尺度研究方法，分析并预测规整填料塔内的液相分布行为。首先根据规整填料片的结构特征，提炼出具有代表性并重复出现的填料最小特征单元，通过对液相在特征单元模型的流动行为进行CFD模拟分析，建立了新型规整填料宏观液相分布模型，并利用微观模拟结果统计得到其模型参数，进而预测得到了整个填料塔的液相分布行为。此外，本文又进一步完善了该液相分布模型，考虑填料表面开孔的影响，使该模型能够适用于开孔填料上液相流动行为的计算，并考虑了逆流气相对模型参数的影响。该多尺度方法摒弃了前人需要通过实验回归模型参数的做法，并且计算量较小，这为今后大规模填料塔的结构优化设计提供了一种较好的方法和途径，具有广泛的工业应用前景。更多还原

【Abstract】 The thesis is composed by two parts. Theoretical simulation and experiments onthe falling film heat and mass transfer process are discussed in chapter2-4, whichincludes the evaporation, condensation and the effects of plate structure on liquid filmflow. In chapter5-7, A novel liquid distribution model is established and multi-scaletheory is applied to predict the liquid distribution in packed column.The gas-liquid two phases flow behavior and heat and mass transfercharacteristics have always been the focus of attention in falling-film evaporators anddesalting plates. Therefore, a two-dimensional two-phase flow CFD model using thevolume of fluid (VOF) method is presented to investigate the transport phenomena.Two important momentum source terms, surface tension and interface stress shear，areconsidered. Moreover, the change of water vapor concentration and heat transfercapacity around the interface have also been described by adding the heat and masstransfer source term in the model. Based on the simulated results, the influence of twophase temperatures, flow rates, water vapor concentration and wall flux on heattransfer coefficients, latent and sensible heat have been discussed. The simulationresults show that the heat transfer coefficients near the inlet decrease rapidly, and thelatent heat is the major mode of heat transfer in the interface. Moreover, the heatreleased from condensation process further restricts the increase of sensible heat.The heat and mass transfer process is significantly influenced by liquid film flowbehavior. For this, a novel heat transfer plate structure is proposed, and the heattransfer coefficients on three different plates have been investigated, the structures ofwhich are flat, coarse and oriented baffled plate, respectively. The experimentalresults indicate better liquid distribution and increased remixed and turbulence degreeon oriented baffled plate, which improve the heat transfer performance.In section2, multi-scale method which consists of microcosmic CFD simulationand macrocosmic calculation is applied to predict the liquid distribution in structuredpacking column. The minimum representative units reappearing in structured packingis proposed and liquid film flow on the units is also been simulated to obtain themodel parameters. Based on the parameters and established liquid distribution model,the fluid mechanics behavior in packed column is obtained. Furthermore, a refinedmodel is developed to take the condition of liquid film flowing on structured packing with holes into consideration, as well as the influence of counter-current flow of gasphase. This multi-scale method doesn’t need complex computation and anyexperimental data to regress model parameters. Therefore, it provides a new approachfor the design and optimization of the large-scale packing column, and has broadfuture in industrial applications.更多还原