自浮颗粒三相体系搅拌混合的临界转速

考察了釜径为386mm的搅拌釜内搅拌桨的类型、挡板和气体分布器等对自浮颗粒三相体系搅拌混合临界搅拌转速的影响 ,得到了回归的关联式:Ncr=CVSawbdcdSe,相对误差为3.34 %～11.58 %。该式可用于指导工业过程的设计和放大。     

影响下沉颗粒三相体系临界搅拌转速的因素

探讨了搅拌桨型、挡板和气体分布器等结构因素及气体流量、颗粒质量分数等工艺因素对下沉颗粒三相体系临界搅拌转速的影响。结果表明,底层桨对临界搅拌转速的影响最大,最佳的底层桨为3叶后掠桨。指型挡板对颗粒的悬浮非常有利,此外,给出了几种较好桨型-挡板-分布环组合的临界搅拌转速关联式。     

气液固三相搅拌的临界转速

考察了搅拌桨型、挡板和气体分布器对气液固三相搅拌混合的临界转速的影响 ,并回归了临界转速关联式 ,可用于指导工业过程的设计和放大。     

搅拌反应器中颗粒完全离底悬浮的临界转速

一、引言 工业搅拌釜广泛涉及液-固二相甚至气-液-固三相系统的反应过程。大部分反应的相际传递速率,特别是传质速率,决定了过程的总速率。在传质控制的固体颗粒作催化剂的快速反应过程中,催化剂在液相中的分散程度及外部质量传递,将对     

搅拌釜中自浮颗粒悬浮分散的临界搅拌转速

在釜径386 mm的搅拌釜内,考察了搅拌桨型、挡板和气体分布器等对自浮颗粒三相搅拌混合的临界搅拌转速的影响,并回归了实用的关联式,这对工业过程的设计和放大具有一定的指导意义.     

充气条件下多层桨悬浮颗粒的临界转速

在直径为386 mm 的通气多层桨搅拌釜中,实验考察了下层搅拌桨型、挡板和气体分布器等对颗粒悬浮临界搅拌转速的影响,这对工业过程的设计和放大具有一定的指导意义.     

气液固三相搅拌中的颗粒分布研究

考察了搅拌桨尤其是底层桨对液面附近颗粒质量浓度(S)的影响 ,发现底层桨采用3叶后掠桨时S最大 ,采用INTERMIG桨时S最小 ,顶层桨不宜采用上推式桨。     

搅拌轴临界转速分析

通过分析得到常用搅拌反应器中搅拌轴临界转 简化公式，为搅拌器的设计和校核提供了方便。     

搅拌轴临界转速近似计算方法的比较

阐述了搅拌轴临界转速的几种近似方法的特点,并与国内现行标准HG/T20569-94作了比较,并得出了相关结论。     

搅拌槽内液-固两相体系的数值研究(Ⅱ)临界搅拌转速的预测

The critical impeller speed, NJS, for complete suspension of solid particles in the agitated solid-liquid two-phase system in baffled stirred tanks with a standard Rushton impeller is predicted using the computational procedure proposed in Part Ⅰ. Three different numerical criteria are tested for determining the critical solid suspension. The predicted NJS is compared with those obtained from several empirical correlations. It is suggested the most reasonable criterion for determining the complete suspension of solid particles is the positive sign of simulated axial velocity of solid phase at the location where the solid particles are most difficult to be suspended.     

声波测量在搅拌釜中固体颗粒临界悬浮转速测定的应用

基于声发射测量技术,结合声信号的频谱分析、小波分解和R/S分析,获得了代表颗粒运动的特征信号频段（d₁、d₂频段）。同时,根据声波特征信号频段能量随搅拌转速的规律性变化,以固体颗粒碰撞壁面产生信号高频区域的声能量分率值为特征参数,提出了搅拌釜临界悬浮转速的测量判据,即声能量分率快速减少并开始趋于稳定时所对应的搅拌转速为临界悬浮转速。以水-玻璃珠体系为例,与目测法相比,声波法测量值的平均相对误差为3.51%,具有较高的精度。利用经典的Zweitering临界悬浮转速计算公式对声波法测得的实验数据进行拟合,计算值与测量值之间的平均相对误差为3.17%,表明公式对于临界悬浮转速的计算具有较高的准确性。由此获得了一种快速、准确、安全的搅拌釜反应器临界悬浮转速测量技术,有利于工业生产流程的优化和控制。     

基于Hilbert-Huang变换的搅拌釜临界悬浮转速的声发射测量

基于声发射测量技术,结合Hilbert-Huang变换（HHT）,分析搅拌釜壁声发射信号,获得了代表浆液运动的特征频段(20～230 kHz),以特征频段对声信号进行重构。同时,以重构信号能量为特征参数,根据其随搅拌转速的规律性变化,提出了搅拌釜临界悬浮转速的测量判据,即重构信号能量由上升转向平稳时所对应的搅拌转速为临界悬浮转速。与目测法相比,该方法平均相对误差为3.83%,具有较高的精度。进一步,发现外循环加强了搅拌釜内轴向流动,有利于固体悬浮,从而使临界分散转速变小,并建立了外循环搅拌釜临界悬浮转速的预测关联式,平均相对误差为5.78%。由此获得了一种快速、准确、安全的临界悬浮转速的测量技术,有利于工业生产流程的优化和控制。     

CFD simulations of gas-liquid-solid stirred reactor: Prediction of critical impeller speed for solid suspension

In this work, simulations have been performed for three phase stirred dispersions using computational fluid dynamics model (CFD). The effects of tank diameter, impeller diameter, impeller design, impeller location, impeller speed, particle size, solid loading and superficial gas velocity have been investigated over a wide range. The Eulerian multi-fluid model has been employed along with the standard k-ε turbulence model to simulate the gas-liquid, solid-liquid and gas-liquid-solid flows in a stirred tank. A multiple reference frame (MRF) approach was used to model the impeller rotation and for this purpose a commercial CFD code, FLUENT 6.2. Prior to the simulation of three phase dispersions, simulations were performed for the two extreme cases of gas-liquid and solid-liquid dispersions and the predictions have been compared with the experimental velocity and hold-up profiles. The three phase CFD predictions have been compared with the experimental data of Chapman et al. [1983. Particle-gas-liquid mixing in stirred vessels, part III: three phase mixing. Chemical Engineering Research and Design 60, 167-181], Rewatkar et al. [1991. Critical impeller speed for solid suspension in mechanical agitated three-phase reactors. 1. Experimental part. Industrial and Engineering Chemistry Research 30, 1770-1784] and Zhu and Wu [2002. Critical impeller speed for suspending solids in aerated agitation tanks. The Canadian Journal of Chemical Engineering 80, 1-6] to understand the distribution of solids over a wide range of solid loading (0.34-15 wt%), for different impeller designs (Rushton turbine (RT), pitched blade down and upflow turbines (PBT45)), solid particle sizes (120-) and for various superficial gas velocities (0-10 mm/s). It has been observed that the CFD model could well predict the critical impeller speed over these design and operating conditions.     

Expansion of fluidized solids' layer at the critical impeller speed marking the onset of a complete suspension

Experimental measurements of the expansion of suspended solids' layer at the critical suspension state have been done in using two representatives of axial-type turbines differing in blades inclination. Results obtained have been correlated by means of theoretical equations which are derived from turbulent mechanical balances. Experimental results have been exploited for the estimation of turbulence intensity near the slurry-pure liquid interface.     

Gas dispersion and solid suspension in a three-phase stirred tank with triple impellers

The hydrodynamics is still not fully understood in the three-phase stirred tank equipped with multi-impeller due to the intensive interaction between phases. In this work, the solid critical suspension speed(NJSG), relative power demand(RPD) and overall gas holdup(ε_G) were measured in an air–water–glass beads stirred tank equipped with multi-impeller, which consists of a parabolic blade disk turbine below two down-pumping hydrofoils. Results show that either the NJSGor the specific power consumption increases when increasing the volumetric solid concentration or superficial gas velocity. RPD changes less than 10% when solid volumetric concentration ranges from 0 to 15%. ε_G decreases with the increase of solid concentration, and increases with the increase of both superficial gas velocity and the total specific power consumption. The quantitative correlations of NJSG,RPD and εGwere regressed as the function of superficial gas velocity, specific power consumption, Froude number and gas flow number, in order to provide the reference in the design of such three-phase stirred tank with similar multi-impellers.     

搅拌固液悬浮研究进展

固液悬浮是典型的单元操作,对其进行研究具有重要意义。回顾了60年来搅拌容器内固液悬浮的研究历程,介绍了常见的搅拌悬浮设备结构,对比分析了有挡板和无挡板时的临界悬浮转速,阐述了固液悬浮的各种实验测试及数值模拟方法,论述了自由液面变形对搅拌固液悬浮的影响及研究现状,并展望了未来在数值研究方面的发展方向。     

Phase hold-up and critical fluidization velocity in a three-phase inverse fluidized bed

We studied the hydrodynamic characteristics of a three-phase inverse fluidized bed made of a transparent acrylic column of 0.115 m inner diameter and 2 m heights. Air, water and polyethylene particles were used as the gas, liquid and solid phase, respectively. We used both hydrophobic low density polyethylene (LDPE) and hydrophilic LDPE as solid phase, and distilled water as liquid phase, and filtered air as gas phase. The LDPE was chemically treated by chlorosulfonic acid to change the surface property from hydrophobic to hydrophilic. We tried to solely investigate the effect of the surface hydrophilicity of polymeric particles on the phase holdup and the critical fluidization velocity of three-phase inverse fluidization. Thus, we measured the static pressure and eventually observed critical fluidization velocity. Critical fluidization velocity became smaller in case of using MDPE hydrophobic particles than LDPE hydrophilic particles. This was thought to be due to the retardation of rising bubbles near hydrophobic particles and, subsequently, the increase of gas hold-up.     

悬浮液体系错流微滤过程研究

对悬浮液体系的错流微滤（ＣＦＭＦ）过程进行理论分析和实验研究，探讨了料液类别、浓度、循环流速及操作时间、压力等参数对ＣＦＭＦ性能的影响。建立了稳态ＣＦＭＦ过程的简化组合模型，对过程的计算具有现实意义。