共查询到18条相似文献,搜索用时 78 毫秒
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搅拌槽反应器内宏观和微观混合及过程强化 总被引:1,自引:0,他引:1
搅拌槽反应器广泛应用于石油、化工、制药、冶金等过程工业中,这些过程大都涉及复杂快反应,往往属于混合传递控制的多相过程,反应收率、产品分布和质量等与搅拌槽内流体流动和混合状况密切相关。通过研究各因素对混合产生的影响规律,可以指导搅拌槽的实际生产操作,以达到强化混合的目的。因此,对搅拌槽内宏观和微观混合特性的研究,对反应器的优化设计、工程放大和过程强化具有重要的意义。本工作从实验研究和数值模拟两方面对搅拌槽反应器内的宏观、微观混合及其过程强化的研究进展进行了综述,依据目前的研究现状及存在的问题,对今后的研究方向进行了展望。 相似文献
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采用计算流体力学(CFD)方法对直径为0.476m双层涡轮桨搅拌反应器内的流动及混合进行了数值模拟,并实验测试了混合过程。利用大涡模拟(LES)及Smagorinsky-Lilly亚格子模型求解湍流流动与示踪剂传递过程,桨叶区域采用滑移网格技术。研究结果表明,大涡模拟得到的示踪剂响应曲线和混合时间与实验结果吻合良好,其预测精度明显优于基于雷诺平均(Reynolds-averaged Navier-Stokes,RANS)的标准k-ε模型的模拟结果。大涡模拟是研究搅拌反应器内非稳态及周期性湍流流动的有效方法。 相似文献
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<正> 1 引言 微观混合是指流体分子尺度上的混合,而化学反应过程又是反应物分子间相互有碰撞作用的过程,微观混合对搅拌槽内进行化学反应有直接影响,因此开展对间歇搅拌反应器微观混合状况的研究十分必要。但微观混合的机理和模型较复杂,测定方法较困难,过去20年来集中于机理与模型研究,实际应用报道较少。本文对乙酸乙酯不可逆二级皂化间歇反应器中搅拌转速、介质粘度对微观混合状况的影响进行研究。 2 微观混合状态的描述 2.1 微观混合模型概述 从Danckwerts提出一整套混合统计概念和微观混合的2种极限理想状态后,许多研究者力求把这2种状态结合起来描述实际的微观混合状态,并通过大量实验,从工程和机理角度提出了不少微观混合模型。但这些工程模型都是单参数模型,经湍流类比分析,其微观混合参数都与理想混合时间有关,具有共同的结构特征。 相似文献
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轴流式搅拌桨搅拌槽内混合时间的数值模拟 总被引:3,自引:0,他引:3
利用计算流体力学软件FLUENT 6.0程序计算了单层CBY搅拌槽内流体混合过程的速度场和浓度场,讨论了加料点位置和监测点位置对混合时间的影响。结果表明,拌槽内物料的混合过程主要由槽内的流体流动所控制;混合时间与加料点位置有关,在桨叶附近区域加料时混合时间比在液体表面加料时的混合时间短,应尽量在搅拌反应器的桨叶尖端处加料;不同的监测点位置对混合时间有很大的影响,在靠近槽底部进行监测所得到的混合时间最短。 相似文献
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本文对卧式双轴气相聚合搅拌床反应器的混合特性进行了实验研究。以三氧化二铝粉体和氯化钾粉体分别为主体物料和示踪物料,用电导法考察了搅拌转速、器内物料的装料高度及通气速率对该搅拌床反应器的混合特性的影响并获得了相应的关联式。结果表明,弗鲁德数、无因次装料高度及通气速率对混合特性有明显的影响。 相似文献
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An LIF technique was used to obtain unobtrusive measurements of scalar concentration as a function of time and mixing times in a fully baffled batch operated mixing vessel agitated by five forms of impeller (Rushton, ‘bucket’, six bladed 45°-and 60°-pitched blade, hyperboloid). The mixing time was comparable to the time required for the dye/scalar to be transported from the top of the vessel to the bottom part plus the time required for a further two rotations of the bulk flow in the circumferential direction. At constant power input the mixing times for similar impellers were similar, although different for different types. 相似文献
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Debmalya Mukherjee Nirvik Sen Krishna Kumar Singh Shilpi Saha Anuradha Mayya Kalsanka Trivikram Shenoy 《American Institute of Chemical Engineers》2023,69(3):e17966
Estimation of mixing time is an essential aspect in characterization of stirred tanks. In this work, we report a novel, non-invasive technique to estimate mixing time in an unbaffled stirred tank using a contact type ultrasonic sensor. Variation in speed of sound in stirred tank is measured by ultrasound and is used to determine the mixing time of solutions. A sensing time of 16.6 ms (~60 Hz) is achieved which leads to an estimation of the mixing process dynamics under forced vortex conditions. The method is validated against colorimetric technique using a dye. The technique is thereafter used to determine mixing time under different operating (impeller speed) and geometrical (impeller design, vessel diameter, and off-bottom clearance) conditions. Though the results presented are specific to unbaffled stirred tank, the method reported is general and can be used in any kind of stirred tank. 相似文献
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Agitated tanks are used in several industrial processes to achieve complete drawdown of floating solids in liquids. The design requirements for this process are not completely defined, and are currently limited to heuristics regarding the use of a surface vortex and the effect of wettability on the difficulty of mixing, along with several initial studies in the literature. In this study, the effect of the type of impeller, particle size and shape, solids concentration, impeller submergence, and baffle configuration on the minimum drawdown speed (Njd) are investigated. It was found that the formation of a large surface vortex acts to hold particles close to the surface. Suppression of the surface vortex is recommended. In baffled tanks where the formation of a large surface vortex is suppressed, the intensity of turbulence and mean circulation velocity of the liquid are responsible for solids drawdown and distribution in the tank. The submergence of the impeller relative to the liquid surface and the pumping mode of the pitched blade turbine (PBT) were found to be the controlling parameters. CFD simulations were carried out to obtain a better understanding and interpretation of the flow patterns and drawdown mechanisms for the different baffle configurations. 相似文献
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Tomasz Płusa Jan Talaga Andrzej Duda Piotr Duda 《American Institute of Chemical Engineers》2021,67(9):e17322
This paper presents results of measurements performed in uncovered baffled and unbaffled stirred tanks. The Laser Doppler Anemometry (LDA) set consists of a 300 mW argon-ion laser generating two pairs of blue and green beams. Additionally, three turbulence models are verified to simulate mixing dynamics in uncovered baffled and unbaffled stirred tanks. Simulations are performed using both the steady- and the transient-state approach. The unbaffled tank was modeled using both the single- and the multiphase approaches. The cited correlations of the central vortex depth are used to verify the multiphase calculations. In order to reduce the computational time, a simplified numerical model is proposed. It assumes a single-phase simulation without the central vortex. The flow fields below the central vortex level are compared between the single- and the multiphase approach. The simplified model can be used both to design and optimize the mixing process. 相似文献
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研究了在搅拌釜内利用溶析沉淀法制备姜黄素纳米颗粒的过程,分别探讨了搅拌釜尺寸、搅拌形式、初始浓度以及搅拌转速对制备结果的影响。通过平面激光诱导荧光技术定量测量釜内液液混合行为,揭示了流体混合环境的控制是决定溶析沉淀产品过程的关键因素。实验表明,搅拌速度过低无法保证流体混合效率,将导致颗粒黏结;搅拌速度过高带来颗粒与流场的强剪切作用,引起颗粒破碎;局部过饱和度过大,引起颗粒的生长和聚团。搅拌釜内纳米颗粒制备需提供适度强化的流体混合环境。 相似文献