【作者】 张庆文；

【导师】 洪厚胜；

【作者基本信息】 南京工业大学 ， 生物化工， 2004， 硕士

【摘要】 气升式生物反应器以其优越的流体混合性能和广阔的应用前景而成为生物反应器领域的研究热点之一。但迄今为止,对其选型、设计及放大仍主要依赖实验验证和专家的经验,缺少理论指导,耗资巨大,投运周期长。而近年来发展起来的计算流体力学(Computational Fluid Dynamics, CFD)是一种可用于分析流体流动和混合传质的交叉学科。CFD 技术与具体工程问题相结合不仅可以节省大量的人力物力,提高实验效率,而且还可以得到实验无法得到的详细信息,CFD技术在反应器的设计和优化中越来越受到人们的重视。为了更微观更本质地研究气升式生物反应器内流体流动和传质,探索反应器的设计和放大的理论依据,本文研究工作的主要内容如下:(1)在对气升式生物反应器内部流动分析基础上,建立了能描述反应器内部复杂流动和相间传质的 CFD 数学模型。该数学模型从气液两相双流体κ ?ε 湍流模型出发,全面考虑了气升式生物反应器中气泡的并聚破碎、气液两相间相互作用和滑移等,并应用经典的双膜理论模型描述气液两相间的氧传递过程。(2)气体分布器部分采用编程增加源项的方法进行简化处理。在定义计算区域时只考虑气室而忽略喷嘴部分,采用子程序 USRINT 及 USRSRC 替换相关方程的源项内容,以此实现对反应器供气的数值模拟。(3)运用 CFX-4.4 对模型进行求解,通过求解得到了包括气液两相速度场、局部气含率分布、气泡并聚破碎后的直径分布及溶氧浓度分布等详尽信息,全面而定量地展示了气升式生物反应器内流体流动和传质状况。模拟结果显示气升式反应器具有宏观混合效果好、死区空间体积小以及剪切应力小而均匀等特点。(4)设计并制造了 30L 气升式生物反应器实验装置,采用粒子成像测速技术(Particle Image Velocity,PIV)和溶氧电极系统对反应器内液相流动速度及溶氧浓度进行实验测定。结果表明:CFD 数值模拟的结果与实验结果在数值上有一定的偏差,液相主体流动速度的偏差为 20.2～32.5%之间,溶氧浓度的偏差为35%左右,但两者总的变化趋势一致。生物反应器中多相流和混合传质属 CFD 技术应用中的复杂问题之一。尽管本文模拟结果与实验验证之间存在较大偏差,但偏差在目前的文献报道范围之 - I -<WP=5>摘 要内;较之经典反应器研究方法,本文给出了反应器中流动和传质的详细信息,对反应器的设计和放大有直观的指导意义,CFD 数值模拟方法用于气升式生物反应器研究是可行的,基于自然界质量、动量、能量三大守恒定律的 CFD 技术也是探索气升式生物反应器设计和放大理论依据的有效新手段。更多还原

【Abstract】 The airlift bioreactor has been being the focus of the bioreactor research for itspredominant fluid mixing performance and widely using foreground. While itsstructure choosing, designing and scale-up are still depended only on experimentalvalidation and expert experience, lacking in support of theories and consuming muchmoney and time. Being used to analyze the flow, mixing and mass transfer charactersof fluid, Computational Fluid Dynamics (CFD) can not only save a lot of resource,but also get some important local data that cannot be gathered in experiment. NowCFD technology is regarded more and more in the fields of the reactor designing andoptimization.For studying on fluid flow and mass transfer in the airlift bioreactor in detail andgroping after a theory of airlift reactor designing and scale-up, the major work of thispaper are summarized as follows:(1) Based on the analysis of fluid flow in airlift bioreactor, a turbulent two-fluidmodel was proposed. The model takes into account bubble break-up and coalescencein the reactor, velocity slip and interaction between gas and liquid. Besides, thenumerical model is combined with two-film model to describe the oxygen masstransfer process.(2) In order to simulate the gas input equipment of airlift bioreactor, FORTRANprograms were used to simulate the gas sparger and subroutine USRINT andUSRSRC were used to replace the source terms of model equations, while gas-roomwas simply excluded during defining computational space.(3) The established model equations were solved by means of CFX-4.4. Theprofiles of flow field, local gas holdup, bubble diameter and dissolved oxygenconcentration, etc. were gained, and the flow and mass transfer in reactor wereshowed roundly. The simulation results reveal that the airlift bioreactor hascharacteristics such as well macro-mixing, low dead-zone volume, and small shearstress.(4) An experimental system of 30L airlift internal loop bioreactor was designed - III -<WP=7>ABSTRACTand manufactured. The liquid velocity and dissolved oxygen concentration weremeasured by PIV system and dissolved oxygen probe respectively. The comparisonbetween experimental data and numerical results reveals that they have samedevelopment trends though there exist biggish warp.Multiple-phase flow and mass transfer in bioreactor is a complex question in theapplication of CFD technology. Although biggish warp exists between experiment andsimulation, the value is less than that of present reported. In contrast to conventionalstudy, this paper provided more information of flow and mass transfer in airliftbioreactor, which can be directly used to design and scale up airlift bioreactor. In aword, CFD technology is a kind of potentially valuable method for studying on theflow and mass transfer in airlift bioreactor.更多还原