搅拌槽内气液两相混沌混合及分散特性

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。     

穿流-柔性组合桨强化搅拌槽中流体混沌混合特性

刚性搅拌桨在搅拌混合过程中得到广泛的应用,在搅拌容器内容易形成两种不同的混合区域:混沌混合区和混合隔离区。强化流体混合的有效途径是合理设计搅拌桨,从而调控流体混沌混合行为。实验运用Labview和Matlab软件采集和处理流体内部压力脉动信号,并获取流体混沌特性参数Kolmogorov熵,对穿流-柔性组合桨体系的Kolmogorov熵随转速的变化规律进行了研究。结果表明,相比传统刚性桨,穿流桨对Kolmogorov熵影响不大。穿流-柔性组合桨通过穿流孔与柔性部分的共同作用调控流场结构,使流体混沌混合的效果最好,在转速为180 r·min^-1时流体的混沌混合达到最佳状态,穿流-柔性组合桨体系的Kolmogorov熵为0.285,而传统刚性桨体系的Kolmogorov熵只为0.125;穿流-柔性组合桨体系的混合时间明显低于传统刚性桨体系,当转速为120 r·min^-1时穿流-柔性组合桨体系的混合时间比传统刚性桨体系缩短了17%。     

穿流式刚-柔组合搅拌桨强化混合澄清槽内油-水两相混沌混合

运用LabView和Matlab软件分别采集和处理穿流式刚-柔组合搅拌桨扰动澄清槽中油-水两相流体内部的压力脉动信号,得出的最大Lyapunov指数（LLE）和多尺度熵（MSE）,反映流体内部的混沌程度;同时采用流场可视化技术观测流体混合状态。结果表明,相比于刚性组合桨,穿流式刚-柔组合搅拌桨通过穿流孔与柔性部分的共同作用改变流场的结构和能量耗散方式,使流体的混沌程度和混合状态都优于刚性组合桨。当转速为88 r·min^-1时,流体的混沌混合都达到最佳状态,各实验条件下的LLE均大于零,表明流场混合体系已进入混沌状态,且穿流式刚-柔组合搅拌桨体系的MSE明显高于刚性组合桨体系,说明穿流式刚-柔组合搅拌桨的混合效果优于刚性组合桨。另外,柔性片上穿流孔的数目和柔性桨叶的厚度对流场的混沌特性也有明显的影响。     

刚柔组合桨强化粉煤灰酸浸搅拌槽内固液混沌混合

传统粉煤灰提铝工艺中酸浸搅拌槽均采用刚性搅拌桨。因刚性桨卷吸能力有限，导致固体颗粒易沉槽、流体混沌混合效率低。提出刚柔组合桨强化酸浸搅拌槽中固液混沌混合行为。实验基于固含率为30%的粉煤灰-自来水体系，研究了刚柔组合酸浸搅拌槽内混沌混合特性及能量耗散规律。采用扭矩传感器采集扭矩时间序列信号，借助Matlab软件编译计算混合过程中最大Lyapunov指数和多尺度熵等混沌特性参数，以单位体积功耗表征搅拌反应器的功率特性。实验考察了搅拌桨安装离底高度、柔性片长度、柔性片宽度等因素对酸浸槽内粉煤灰混沌混合的影响，对比了刚性桨与刚柔组合桨体系的能耗差异。研究结果表明：刚柔组合桨通过柔性片的作用，能增大搅拌桨的卷吸力，进而减少固体颗粒沉槽现象，促进全槽混沌混合；在最优化条件（120 r/min，搅拌桨安装离底高度为T/4，柔性片长度为1.2H ₁、柔性片宽度为D/8）下，体系最大Lyapunov指数达到最大值0.0645，各尺度下的MSE均比其他条件更大，表明刚柔组合桨能够通过柔性片的多体运动，强化体系混沌混合，均化体系能量分布；刚性桨与刚柔组合桨的单位体积功耗随着转速的增加呈现指数规律增长。     

刚柔组合桨强化粉煤灰酸浸搅拌槽内固液混沌混合

传统粉煤灰提铝工艺中酸浸搅拌槽均采用刚性搅拌桨。因刚性桨卷吸能力有限,导致固体颗粒易沉槽、流体混沌混合效率低。提出刚柔组合桨强化酸浸搅拌槽中固液混沌混合行为。实验基于固含率为30%的粉煤灰-自来水体系,研究了刚柔组合酸浸搅拌槽内混沌混合特性及能量耗散规律。采用扭矩传感器采集扭矩时间序列信号,借助Matlab软件编译计算混合过程中最大Lyapunov指数和多尺度熵等混沌特性参数,以单位体积功耗表征搅拌反应器的功率特性。实验考察了搅拌桨安装离底高度、柔性片长度、柔性片宽度等因素对酸浸槽内粉煤灰混沌混合的影响,对比了刚性桨与刚柔组合桨体系的能耗差异。研究结果表明:刚柔组合桨通过柔性片的作用,能增大搅拌桨的卷吸力,进而减少固体颗粒沉槽现象,促进全槽混沌混合;在最优化条件(120 r/min,搅拌桨安装离底高度为T/4,柔性片长度为1.2H1、柔性片宽度为D/8)下,体系最大Lyapunov指数达到最大值0.0645,各尺度下的MSE均比其他条件更大,表明刚柔组合桨能够通过柔性片的多体运动,强化体系混沌混合,均化体系能量分布;刚性桨与刚柔组合桨的单位体积功耗随着转速的增加呈现指数规律增长。     

双层刚柔组合搅拌桨调控流体宏观不稳定性行为

流体宏观不稳定性是搅拌槽内流体流动存在大尺度低频非稳态准周期现象,可以影响流体的能量﹑质量的传递行为。为揭示在双层组合桨作用下搅拌槽内流体的非稳态流动规律,实验采用频谱分析和流场可视化技术研究双层组合桨搅拌槽内自来水体系的宏观不稳定性,对比分析了双层刚性桨和双层组合桨对流体混合的影响。结果表明:直径为T的搅拌槽内流体宏观不稳定频率与转速呈线性增大趋势,在转速为180 r·min^-1时离底距离 0.25T刚柔组合桨体系的宏观不稳定性频率消失,出现谱带现象,流场呈现多尺度结构特征,而离底距离为0.33T和0.5T的刚柔组合桨体系的宏观不稳定性频率分别为0.5096 Hz和0.3459 Hz。双层组合桨体系分别使流体的混合时间缩短了22.5%和35%左右,减小离底距离,可使流场的规则区减小。双层刚柔组合桨调控流体宏观不稳定性,强化流体的能量传递行为,从而缩短混合时间,提高了流体的混合效率。     

搅拌槽内气液两相混沌混合及分散特性

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Lab VIEW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。     

刚柔组合搅拌桨强化流体混合的流固耦合行为

传统刚性搅拌桨通过对流体的剪切作用实现能量的传递,而刚柔组合搅拌桨可通过其多体运动行为强化能量传递。基于搅拌桨桨叶与流体之间的耦合运动作用,结合ANSYS Workbench仿真平台,采用双向流固耦合方法,模拟计算了刚性搅拌桨与刚柔组合搅拌桨桨叶的等效应力和总变形量,研究了流场的宏观结构;并通过测定混合时间和计算搅拌桨功耗对比分析了两种不同搅拌体系的混合行为。结果表明:刚柔组合搅拌桨使体系的混合时间缩短了近32%,搅拌桨功耗下降了7%,其桨叶尖端的变形量是刚性搅拌桨的10⁵倍,其应力比刚性搅拌桨增加了83%;与刚性搅拌桨相比,刚柔组合搅拌桨在流固耦合作用下对流体的作用力更大,能够更好地传递能量,增强流体运动,强化流体混合。     

刚柔组合搅拌桨增强混合澄清槽内流体宏观不稳定性

流体宏观不稳定性可以反映流体轴向能量和质量的传递行为。为揭示刚柔组合搅拌桨（简称柔性桨）作用下混合澄清槽中油水液-液两相非稳态流动规律,采用频谱分析和小波分析组合法研究混合澄清槽内宏观不稳定性,并进行模拟验证。研究表明,柔性桨在转速低于250 r·min^-1时,流体宏观不稳定频率与转速呈线性关系,而转速超过250 r·min^-1,流体因界面卷吸行为吸入空气,宏观不稳定频率谱图呈现功率谱带,流场结构呈多尺度结构特征,流体宏观不稳定频率消失,液-液混合体系出现明显的乳化现象。与刚性桨相比柔性桨能增强宏观不稳定性,提高流体混合效率,强化能量传递行为。计算模拟发现,柔性桨能明显提高桨叶的抽吸能力,增强流体轴向运动的行为,避免流体过度搅拌,有利于流体澄清。     

穿流式刚-柔组合搅拌桨强化混合澄清槽内油-水两相混沌混合

运用Lab View和Matlab软件分别采集和处理穿流式刚-柔组合搅拌桨扰动澄清槽中油-水两相流体内部的压力脉动信号,得出的最大Lyapunov指数(LLE)和多尺度熵(MSE),反映流体内部的混沌程度;同时采用流场可视化技术观测流体混合状态。结果表明,相比于刚性组合桨,穿流式刚-柔组合搅拌桨通过穿流孔与柔性部分的共同作用改变流场的结构和能量耗散方式,使流体的混沌程度和混合状态都优于刚性组合桨。当转速为88 r·min-1时,流体的混沌混合都达到最佳状态,各实验条件下的LLE均大于零,表明流场混合体系已进入混沌状态,且穿流式刚-柔组合搅拌桨体系的MSE明显高于刚性组合桨体系,说明穿流式刚-柔组合搅拌桨的混合效果优于刚性组合桨。另外,柔性片上穿流孔的数目和柔性桨叶的厚度对流场的混沌特性也有明显的影响。     

Enhancement of liquid–liquid mixing in a mixer-settler by a double rigid-flexible combination impeller

Mixing is crucial in the dispersion of two immiscible fluids. The rational design of an impeller is necessary to form suitable flow conditions and improve fluid mixing efficiency. A double rigid-flexible combination impeller was designed by connecting the upper and lower rigid impeller blades with flexible pieces. Experimental measurements were performed in a laboratory-scale mixer-settler under different impeller types. The largest Lyapunov exponent (LLE) and multi-scale entropy (MSE) were investigated using Matlab. Results showed that the double rigid-flexible combination impeller enhanced liquid–liquid mixing in the mixer-settler through the multiple-body motion behavior triggered by the swings of flexible pieces. At the optimum mixing point of each impeller, the LLEs of the double impeller, double rigid combination impeller, and double rigid-flexible combination impeller were 0.018, 0.055, and 0.057, respectively. At 75 rpm, the MSE of the combination impellers was obviously greater than that of the double impeller, and the rigid-flexible combination impeller had larger MSE than the double rigid combination impeller. The mixing efficiency of the rigid-flexible combination impeller increased with increasing width and quantity of the flexible piece. The quantity of rigid blade slice also influenced the enhancement of mixing ability. The double rigid-flexible combination impeller intensified the chaotic mixing of the two-phase fluid by changing the flow field structure and energy dissipation mode, ultimately achieving an efficient-mixing operation.     

错位刚柔桨强化搅拌槽内流体混合实验及数值模拟

为消除搅拌反应器中混合隔离区，对标准刚性桨（R-RT）、错位刚性桨（PR-RT）和错位刚柔桨（PRF-RT）三种桨叶体系的流体混沌特性参数、流场结构以及流体运动速度进行了探讨。采用Matlab软件编程计算最大Lyapunov指数（LLE）和多尺度熵（MSE），通过计算流体力学研究了三种桨叶体系流场结构和流体运动速度的差异。实验及计算结果表明，错位刚柔桨通过柔性桨叶的随机扰动破坏了隔离区介稳态流场边界，较大程度地消除了混合隔离区。PRF-RT的LLE相比于R-RT和PR-RT分别提高了13.29%和7.25%，MSE也较PR-RT和R-RT大；PRF-RT增强了流场不稳定性，形成了不对称性流场结构，减少了隔离区分布范围；PRF-RT强化桨叶能量耗散，提高了搅拌槽底部、顶部液面以及搅拌槽壁区域流体运动速度，减小了流体混合时间。     

Experiment and numerical simulation of chaotic mixing performance enhanced by perturbed rigid-flexible impeller in stirred tank

To eliminate the isolated mixing regions in the stirred tank, factors associated with chaotic mixing performance were studied, including flow field structure and fluid velocity of rigid RT impeller (R-RT), perturbed rigid RT impeller (PR-RT) and perturbed rigid-flexible RT impeller (PRF-RT). The maximum Lyapunov exponent (LLE) and multi-scale entropy (MSE) were calculated by using Matlab software programming, and the differences in flow field structure and fluid velocity of the three blade systems were studied through computational fluid mechanics. The experimental and computational results showed that perturbed rigid-flexible RT impeller could destroy the boundary of the mesostatic flow field in the isolated mixing regions and the symmetry flow in the process of fluid mixing through the random disturbance of the flexible blade, eliminating the isolated mixing regions. At 90 r/min, the LLE of the perturbed rigid-flexible RT impeller is larger than that of rigid RT impeller and perturbed rigid RT impeller. The LLE of the rigid-flexible RT impeller compared with the rigid RT impeller and perturbed rigid RT impeller increases 13.29% and 7.25% respectively and the MSE of the perturbed rigid-flexible RT impeller is also larger than that of rigid RT impeller and perturbed rigid RT impeller. The perturbed rigid-flexible RT impeller enhances the flow field instability, forms an asymmetric flow field structure, and reduces the distribution range of isolated mixing regions. The perturbed rigid-flexible RT impeller enhances the energy dissipation of the blade, improves the fluid velocity at the bottom and top of the tank and the wall of the tank, and reduces the mixing time.     

Chaotic mixing performance and mass transfer enhanced by rigid-flexible impeller with pulse jet

Conventional stirred reactors generally use rigid impeller for mechanical stirring, which leads to the easy creation of isolation mixing regions in the reactor and reduces the efficiency of fluid mixing. The use of multi-flow field coupling to induce chaos and promote more fluids into a chaotic state is one of the effective ways to improve fluid mixing efficiency. In this work, the largest Lyapunov exponent(LLE) and multi-scale entropy(MSE) are investigated with the Matlab compile pressure pulsation signals. The effects of duty ratio, paddle type, flexible paddle thickness, paddle height from the bottom and pulsed air jet flow rate on the chaotic mixing of fluids in a stirred reactor under different pulse periods are explored. In addition, the effects of different impeller types, jet types and air jet flow rate on the volume oxygen mass transfer coefficient K_La are compared and analyzed. When T=0.4 s and D=80%, the results show that the LLE of the rigid-flexible RT impeller compared with the rigid RT impeller increases 11.58% and the MSE of the rigid-flexible RT impeller is also larger than that of rigid RT impeller. It was showed that the pulsed jet rigid-flexible impeller system can better enhance fluid chaos, increase the fluid mixing efficiency and homogenize the system energy distribution. In addition, pulse jet coupling RF-RT impeller system enhances the turbulent characteristics of the fluid, promotes the reduction of the thickness of the liquid film, strengthens the mass transfer and increases the K_La value of the system. When power consumption per unit volume is 360 W/m³, the K_La of the PJ-RF-RT system compared with the PT-R-RT system increases 13.46%, and the K_La of the PJ-R-RT system compared with the SJ-R-RT system increases 11.86%.     

偏心射流-刚柔组合桨搅拌器内混沌混合行为研究

搅拌反应器内普遍存在混合隔离区,是实现高效混合的一大障碍。流场耦合诱发流体的混沌现象,可减少混合隔离区,提高流体混合效率。结合Matlab软件,探究偏心空气射流-单层刚柔组合桨体系的混合行为演变规律,对比分析了不同偏心率下桨叶类型、桨叶离底高度、空气射流量以及转速对流体混沌混合的影响。结果表明,刚柔组合桨通过其自身刚-柔-流的多体运动与偏心空气射流的流场耦合,破坏了流体混合过程中出现的对称性流场,使更多的流体进入混沌状态。刚-柔组合桨（RF-RDT、RF-IRDT）比刚性桨（RDT、IRDT）的LLE值大,其中RF-RDT相比于其他3种类型的搅拌桨（IRDT、RDT、RF-IRDT）,其LLE值分别提高了约42.8%,27.0%、6.9%;空气射流的偏心率等于0.6时,其最大LLE值相比于其他偏心率（0.8、0.4、0.2、0）,依次提高了6.5%、2.4%、17.6%、25.1%。该研究结果可为刚柔组合桨的优化设计提供理论依据。     

Chaotic mixing performance enhanced by rigid-flexible impeller with long-short blades in stirred tank

The presence of a mixing isolation regions in a stirred reactor is a major obstacle to enhancing fluid mixing. Breaking the symmetrical flow field structure in the stirred tank and destroying the mixing isolation area can improve the fluid mixing efficiency. The Matlab software was used to calculate the maximum Lyapunov exponent (LLE) and multi-scale entropy (MSE). The effects of different blade types, flexible blade length, flexible blade number, blade height from bottom and rotation speed on fluid mixing were compared. The results show that the rigid-flexible impeller with long-short blades (RF-LSB) can enhance the flow field structure more unstable and asymmetric with deformation and random vibration of flexible pieces, destroy the symmetry flow in the process of fluid mixing, induce the asymmetric flow field, and make more fluid into the chaotic state. When at 90 r/min and three pieces of flexible, the LLE of the RF-LSB is larger than that of rigid impeller and rigid-flexible impeller RF-LSB with increase of 20.22% and 7.98% respectively. The mixing time (θ_m) of the three systems [RF-LSB (three pieces), rigid impeller, rigid-flexible impeller] has an exponential relationship with the power consumption per unit volume (P_v). When P_v is constant, θ_m of the RF-LSB system is the smallest. Results showed that the RF-LSB (three pieces) is superior to rigid impeller and rigid-flexible impeller, which is more conducive to fluid chaotic mixing.     

长短叶片复合型刚柔桨强化搅拌槽内流体混沌混合行为

搅拌反应器中混合隔离区的存在是强化流体混合的主要障碍。打破搅拌槽中的对称性流场结构，破坏混合隔离区，可以提高流体混合效率。采用Matlab软件编程计算最大Lyapunov指数（LLE）和多尺度熵（MSE），比较了不同桨叶类型、柔性片长度、柔性片数量和桨叶离底高度以及转速对流体混合的影响。结果表明，长短叶片复合型刚柔桨（RF-LSB）桨叶通过刚柔耦合错位连接，柔性片的形变与随机振动对流体的非稳态扰动，使流场结构不稳定性和不对称性增强，强化了流体混合效果。当柔性片数量为3，搅拌转速为90 r/min时，RF-LSB体系比刚性桨和刚柔桨体系的LLE值分别提高了20.22%和7.98%；三种体系[RF-LSB（柔性片数量为3）、刚性桨和刚柔桨体系]的混合时间（θ_m）与单位体积功耗（P_v）呈指数型关系，当P_v相同时，RF-LSB（柔性片数量为3）的θ_m最小，表明RF-LSB（柔性片数量为3）更有利于流体混沌混合。