基于OpenFOAM的精馏塔内气液两相流传热传质模拟

对于精馏塔内的多相传质过程,计算流体力学(Computational Fluid Dynamics,CFD)不仅可用于模拟流动现象,而且可以用于研究传热传质过程及其与流动的相互作用规律。基于之前精馏塔板气液流动模拟的研究工作,本研究应用OpenFOAM平台的多相流求解器,考虑了能量方程与组分输运方程,构建了精馏体系的传热传质模型,分别对环己烷-正庚烷理想体系与乙醇-水非理想体系进行了模拟,并分析了塔板上气液两相流动、组分浓度及温度等参数的分布规律。对于理想体系,理想溶液传质模型能够较准确地预测多层塔板上的温度及浓度场;对于非理想体系,需要在理想溶液传质模型的基础上引入活度系数模型,为此对比了UNIQUAC与NRTL两种活度系数模型的效果。在当前模拟框架下,引入活度系数模型有助于提升非理想体系温度场与浓度场的模拟精度,两种活度系数模型预测的整体趋势与文献结果基本一致,但在数值上UNIQUAC模型与文献结果吻合更好。此外,气液两相流场与浓度场分布的对比分析表明,液相的循环流动能够提升塔板的局部传质效率,导致液相入口与塔板堰处的效率高于塔板中心,但是循环区域内气液两相无法及时更新,将导致塔板整体传质效率下降。以上研究有望用于精馏塔板的设计与优化,为提高精馏塔传质效率、降低精馏能耗提供指导,对于其他气液两相流的CFD传热传质模拟也具有参考价值。

Energy budget of cold and hot gas-solid fluidized beds through CFD-DEM simulations

Direct energy budget is carried out for both cold and hot flow in gas–solid fluidization systems.First,the energy paths are proposed from thermodynamic viewpoints.Energy consumption means total power input to the specific system,and it can be decomposed into energy retention and energy dissipation.Energy retention is the variation of accumulated mechanical energy in the system,and energy dissipation is the energy converted to heat by irreversible processes.Then based on the Computational Fluid Dynamics-Discrete Element Method(CFD-DEM)framework,different energy terms are quantified from the specific flow elements of fluid cells and particles as well as their interactions with the wall.In order to clarify the energy budget,it is important to identify which system is studied:the particle-fluid system or the particle sub-system.For the cold flow,the total energy consumption of the particle sub-system can well indicate the onset of bubbling and turbulent,while the variation of local energy consumption terms can reflect the evolution of heterogeneous structures.For the hot flow,different heat transfer mechanisms are analyzed and the solver is modified to reproduce the experimental results.The impact of the heat transfer mechanisms and heat production on energy consumption is also investigated.The proposed budget method has proven to be energy-conservative and easy to conduct,and it is hopeful to be applied to other multiphase flow systems.

基于OpenFOAM模拟精馏塔板的气液流动

本研究对筛孔型精馏塔板上的空气-水两相流进行了模拟,模拟方法采用基于开源软件平台OpenFOAM的双流体模型框架。模拟体系选用Solari-Bell经典实验体系,研究了不同操作条件下的气液两相流动参数,包括清液层高度、气相速度、液相速度和塔板压降等,模拟结果与实验结果的变化趋势基本一致。基于CFD模拟结果,分析了不同工况下塔内气液两相速度场与气含率分布等流动参数,结果表明本工作可以较好地捕捉塔板上的气液流动特征。进一步地,讨论了应用OpenFOAM模拟精馏塔内气液两相流动的若干影响因素,在此基础上分析了气液错流体系相间曳力对模拟结果的影响,实现了与使用商业软件模拟结果相接近的预测效果,验证了使用OpenFOAM模拟精馏塔体系的可行性。