共查询到18条相似文献,搜索用时 72 毫秒
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新型搅拌桨用于黄原胶溶液气液传质的计算流体力学模拟 总被引:1,自引:0,他引:1
采用计算流体力学(CFD)方法对高黏度非牛顿流体黄原胶水溶液(质量分数2%)中对称锯齿双斜叶涡轮搅拌桨(SPT)的搅拌效果进行模拟,并与传统的圆盘涡轮搅拌桨(DT)进行对比。通过多重参考系方法解决搅拌桨区域的运动问题,采用Eulerian-Eulerian模型模拟气液二相流动,气泡聚并和破裂过程通过群落平衡方程计算。结果发现,在高黏度体系中SPT气液传质混合性能优于DT。与DT相比,在考察的转速和表观气速下,SPT搅拌功率消耗降低35%左右,氧传质效率提高超过24%。 相似文献
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The mixing process in a stirred tank of 0.476m diameter with single, dual and triple 3-narrow blade hydrofoil CBY impellers was numerically simulated by using computational fluid dynamics (CFD) package FLU-ENT6.1. The multi-reference frame (MRF) and standard k-ε turbulent model were used in the simulation. The shaft power and the mixing time predicted by CFD were in good agreement with the experiment. The effects of tracer feeding and detecting positions on mixing time were investigated. The results are of importance to the optimum design of industrial stirred tank/reactors. 相似文献
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对一种自吸式反应器的气液分散性能进行了实验研究,并采用计算流体力学(CFD)ANSYS CFX中对自吸式反应器在600,800,1 000,1 200 r/min 4种转速条件下气液二相流的流场、局部气含率及整体气含率进行了数值模拟,并采用Higbie溶质渗透模型模拟研究了反应器的容积传质系数。研究结果表明:气液二相流场与高速摄像机拍摄的结果相同,成对称分布;自吸式反应器的局部气含率分布均匀,上下分布良好,整体气含率的模拟结果与实验结果一致,实验值和模拟值误差为5.1%;局部容积传质系数分布良好,气体出口附近较好,容积传质系数模拟值与实验值变化趋势一致。 相似文献
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双层组合桨搅拌槽内气液微观分散特性 总被引:1,自引:0,他引:1
采用双电导电极探针法对双层组合桨搅拌槽内气液相界面积特性进行了实验研究,考察了通气量、搅拌转速和桨组合对槽内相界面积的影响。结果表明:对于上层桨为上翻斜叶桨和下层桨为凹叶桨的组合,随着通气量的增加,搅拌槽内大部分区域的相界面积增大,但在槽底区域减小。随着搅拌转速的增加,在叶轮区域的相界面积增加明显,而在槽底和液面区域基本不变化。上下层桨的分散能力和气体分布器结构和操作条件密切相关。对于近壁管式气体分布器搅拌槽,在较低通气量下,上层桨对气液分散起着主要作用,而在高通气量下,下层桨的作用增强,起主要作用。带圆盘的搅拌桨对气体具有良好的阻缓作用,不同气速下均具有优异的气液分散能力。 相似文献
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翼形桨搅拌槽内混合过程的数值模拟 总被引:8,自引:0,他引:8
采用FLUENT软件的多重参考系(MRF)及标准k-ε模型,将速度场与浓度场方程分开进行求解,对单层轴流式三叶CBY翼形桨搅拌槽内的混合过程进行了数值模拟,所得的混合时间的模拟结果与实验值相吻合。同时采用数值模拟的方法研究了不同的示踪剂加料点、监测点位置及操作条件对混合时间的影响规律;模拟结果表明,混合过程主要由搅拌槽内的流体流动所控制,混合时间与示踪剂加料点及监测点位置密切相关。上述的研究结果对于工业搅拌反应器的优化具有一定的参考意义。 相似文献
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多层组合桨搅拌槽内气-液分散特性的研究 总被引:17,自引:4,他引:17
在直径为0,476m的椭圆底搅拌槽中,采用由六叶半椭圆管叶盘式涡轮桨(HEDT)及四叶宽叶翼型桨的上提(WHU)及下压(WHD)操作组合的六种不同的三层桨,研究了气-液两相体系中的通气功率变化及气含率特性,获得不同桨型的通气搅拌功率及气含率的关联式;结果表明,底桨为HEDT的组合桨通气功率下降幅度最小,相同输入功率时气含率最高,其次为WHD,WHU为底桨时气液分散性能最差。因此,适用于气液两相操作的优化组合桨应以HEDT为底桨。此研究结果可为工业用多层组合桨气液搅拌反应器的设计提供参考。 相似文献
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采用欧拉-欧拉模型对搅拌釜内气液两相流进行了三维CFD模拟,重点研究了采用不同曳力模型时CFD模拟对搅拌桨附近排出流区两相流动的预测能力。模拟结果表明CFD能准确地预测排出流区的液相速度分布,但采用传统的Schiller-Naumann曳力一定程度上低估了排出流区的气液相间曳力,导致在完全扩散区CFD预测的分布器和桨叶下方区域气含率偏小,而基于气液非均匀结构和能量最小多尺度(EMMS)方法得到的DBS-Global曳力模型能更准确地描述完全扩散区气液搅拌釜内流动情况。与传统曳力模型相比,采用DBS-Global曳力模型能显著提高对气含率的预测。 相似文献
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Both the numerical and experimental approaches were used to study the effects of the gas recirculation and non‐uniform gas loading on the mass transfer rate for each impeller in a multiple impeller system. By combining the calculated gas velocity and local gas holdup, the gas recirculation rate around each impeller was estimated. The local mass transfer coefficients for systems equipped with various combinations of the Rushton turbine impeller (R) and pitched blade impeller (P) were determined by using the dynamic gassing out method. It is found that the Rushton turbine impeller has to be served as the lowest impeller in order to have a better gas dispersion and to give a higher overall KLa for a multiple impeller gas‐liquid contactor. The upper pitched blade impeller always enforces the circulating flow around the Rushton turbine impeller just beneath it and gives a higher overall average mass transfer rate. However, the system equipped with only the pitched blade impellers results in a much lower mass transfer rate than the other systems owing to the poor gas dispersion performance of the pitched blade impeller. 相似文献
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传统Rushton刚性桨常应用于过程工业中搅拌反应器内的气液分散过程,但由于桨叶背后易形成较大的气穴,气液混合效果较差。为了提高搅拌槽内气液两相的混合效果,提出了一种刚柔组合桨强化气液两相的分散过程。利用LabVIEW软件处理刚性桨和刚柔组合桨体系中气液混合过程的压力脉动信号,通过Matlab软件编程计算最大Lyapunov指数(LLE),分析气液混合体系的混沌混合行为,同时,对刚性桨和刚柔组合桨体系中的相对搅拌功耗、整体气含率、局部气含率进行测量。结果表明,在功耗为170 W,通气量为10 m3·h-1条件下,与刚性桨相比,刚柔组合桨能够通过刚-柔-流的耦合作用促进桨叶能量的传递过程,提高搅拌体系的混沌混合程度,刚柔组合桨体系的LLE提高了8.89%。同时,在相同操作条件下,与刚性桨相比,刚柔组合桨能够有效提高相对搅拌功耗以及搅拌槽内的整体气含率和局部气含率,且搅拌槽内气体分散更为均匀。 相似文献
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Power consumption, gas holdup and oxygen mass transfer in agitated gas-liquid columns have been studied for an air-water system. Measurements have been carried out in a reciprocating plate reactor using five different types of perforated plates and in a stirred tank reactor with one, two and three Rushton turbines, a helical ribbon impeller with and without surface baffles. Each mixing vessel had an identical geometry with a working volume of 17 L. For reciprocating plate stacks, the gas holdup is a complex function of the perforation diameter, the frequency of agitation and the gas superficial velocity. For radial-type mixing devices, the gas holdup increases more rapidly with the speed of rotation for the helical ribbon. The power imparted to the fluid by the mixing device is independent of the gas superficial velocity for the plate stacks and the helical ribbon impeller for a given frequency or speed of agitation whereas it decreases for Rushton turbines. The correlation of the power consumption obtained for all mixing devices plotted against the reciprocating frequency or speed of rotation to the third power shows a linear fit. KLa values were correlated very well with the power input per unit volume and superficial gas velocity for all mixing devices. At lower power input per unit volume, KLa is a function of only the gas superficial velocity. At higher input power per unit volume, KLa increases rapidly with an increase in the intensity of agitation. Reciprocating plates with larger diameter perforations led to higher KLa values whereas the lowest KLa were obtained with the helical ribbon impeller. Correlations for one and three Rushton impeller assemblies were almost identical whereas measured KLa were much higher for the two-impeller assembly due to the presence of a highly mixed zone in the vicinity of the dissolved oxygen probe. 相似文献
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Two experimentally determined sets of impeller boundary conditions were used to simulate the flow generated by a pitched blade turbine in a cylindrical baffled tank. Use of these two sets of boundary conditions in simulations with two different off bottom clearances led to the conclusion that the flow generated by a pitched blade impeller cannot be successfully predicted without considering the impeller location. Correct prediction of velocity fields in the tank required the correct specification of velocity boundary conditions. Successful prediction of the turbulent energy distribution required proper specification of the turbulence boundary conditions. There was almost no interaction between the velocity and turbulence fields. The turbulet kinetic energy dissipation rate was at a maximum close to the impeller in both geometries. Within this region the average dissipation rate was five and a half times greater that the average dissipation rate in the tank. 相似文献