自吸式气液搅拌槽气液分散性能的实验研究

本研究在CFD数值模拟基础上,对双层桨自吸式搅拌槽有定子(自吸分散)和无定子(表面充气分散)两种情况进行性能研究.深入研究了不同桨型组合的气体吸入临界转速、功率准数、气含率和氧传递等性能.结果表明,在搅拌介质中,六直叶圆盘桨和六叶上斜叶桨在自吸分散时具有较好的吸气量和气液两相之间的传质性能.     

新型最大叶片式搅拌器用于工业规模反应器气液混合特性的数值模拟

以1.0%质量分数黄原胶溶液为研究体系,运用计算流体力学(CFD)方法对10 m~3工业规模搅拌釜内新型最大叶片式搅拌桨的气液混合性能进行了数值模拟,重点研究了新型最大叶片式搅拌桨在搅拌转速为42 r/min,五种通气量(0.27~0.35 vvm)下气液混合特性。结果表明:流体在新型最大叶片式搅拌桨作用下呈现一个整体大循环;在相同转速下,增加通气量,搅拌器单位体积功耗减小,气含率、气泡尺寸及气液传质系数呈不同增加趋势。     

多层新型桨搅拌槽内气-液两相流动的实验与数值模拟

对三层新型组合桨气-液两相搅拌槽内的流体流动进行了实验研究,并采用计算流体力学(CFD)的方法对气-液两相搅拌槽的通气搅拌功率、流场、局部气含率及总体气含率进行了数值模拟,数值模拟采用了欧拉-欧拉方法,数值模拟结果与实验值吻合良好,同时考察了通气流量和搅拌转速对通气搅拌功率和气含率的影响规律. 研究结果表明,欧拉-欧拉方法能较好地模拟搅拌槽内气-液两相流的流动状况.     

生物反应器内不同桨叶组合计算流体力学模拟

运用计算流体力学(CFD)数值模拟方法研究在相同工况下(搅拌桨转速为400 r/min、通气速度为0.86 vvm和操作温度为15 ℃),4种不同桨叶组合方式对5 L气液生物反应器流场、氧传质系数kLα、空气体积分数、气含率(体积分数)和功率的影响,评判各桨叶组合综合性能.计算结果表明:1号方案上下档均为径向桨,具有最...     

双层桨气液搅拌反应槽气液分散特性

采用搅拌功率与氧传质系数方法,对一双层桨搅拌反应槽的自吸分散和表面充气分散性能进行研究.比较了两种桨叶组合在两种分散方式下的气相分散临界转速、搅拌功率及两种桨叶组合自吸分散时的气含率和气液传质系数.结果表明,六叶圆盘直叶桨和六叶圆盘斜叶桨的组合在自吸分散时具有较优的分散性能.     

双层桨自吸式搅拌槽气-液分散性能

对一双层桨自吸式搅拌槽内气液分散性能进行了研究,在有无定子两种情况下,对比了不同桨型组合的搅拌功率、相对功率消耗、气含率和容积传氧系数。结果表明:自吸式搅拌槽可以有效降低功率消耗;6P-6PDTU(抛物线型桨与六叶上斜叶桨)组合的功率消耗小于6DT-6PDTU(六直叶圆盘桨与六叶上斜叶桨)组合,相对功率消耗更接近于1;气含率和容积传氧系数小于6DT-6PDTU组合。研究表明,虽然6DT-6PDTU组合的搅拌功率较大,且不利于气液分散和混合,但吸气量和气液两相之间的传质效果较好。     

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

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%。     

环流反应器和搅拌槽传质特性的分析

本文测定了提升管为单段和提升管分为三段的气升式环流反应器中的液相体积氧传质系数，在螺带式搅拌桨区应器中测定了液相体积氧传质系数和功率消耗，实验体系为模拟生物发酵液非牛顿流体特性的核甲基纤维素水溶液，本文还从液相体积氧传质系数及单位液相体积的功耗所产生的氧传质效果方面对提升管不分段和提升管分为三段的气升式环流反应器与螺带式搅拌反应器进行了比较。     

偏氟乙烯乳液聚合的气液传质效果影响因素研究

推导了表征气液传质效果的K值计算方法,并研究了聚合釜装填量、搅拌桨型和转速等因素对气液传质效果的影响。结果表明,随着聚合釜装填量和搅拌转速的增大,K值增大,气液传质效果提高;在搅拌转速大于500r/min的情况下,桨型采用上层二叶平桨、下层二叶斜桨的方式明显比单层的二叶斜桨或二叶平桨的K值大,气液传质效果好。确定了5L釜偏氟乙烯(VDF)乳液聚合必需的良好搅拌效果的条件:装填量3L,搅拌转速700r/min,桨型采用上层二叶平桨和下层二叶斜桨;VDF聚合速率达到115g/(L·h),合成出固体质量分数20%、粒径分布窄、稳定性好的聚偏氟乙烯(PVDF)乳液。     

偏氟乙烯乳液聚合的气液传质效果影响因素的研究

首先推导出表征气液传质效果的K值计算方法,借此研究了聚合釜装填量、搅拌桨型和转速等因素对气液传质效果的影响,结果表明:随着聚合釜装填量和搅拌转速的增大,K值增大,气液传质效果提高;在搅拌转速大于500r/min情况下,桨型采用上层二叶平桨、下层二叶斜桨的方式明显比单层的二叶斜桨或二叶平桨的K值大,气液传质效果好。确定了5L釜偏氟乙烯(VDF)乳液聚合必需的良好搅拌效果的条件:装填量为3L、搅拌转速700r/min、桨型采用上层二叶平桨和下层二叶斜桨;VDF聚合速度达到了115gPVDF/L·h,合成出含固体质量分数为20%、粒径分布窄、稳定性好的聚偏氟乙烯(PVDF)乳液。     

Application of KHX Impeller in a Low-shear Stirred Bioreactor☆

In our previous work, a low-shear stirred bioreactor was explored. With a pitched blade turbine impeller downflow (PBTD) used, the shear stress generated is high compared with that in some low shear ax...     

A HUMBLE TRIBUTE TO CHURCHILL-SENSEI

The performance of pitched blade turbines in a gas-liquid dispersion has been studied. The two-phase hydrodynamics, gassed power consumption and mass transfer properties have been examined using six blade open turbines with blade angles from 30 to 60 degrees to the horizontal, mounted for down flow.

There are two distinct regimes by which gas leaving the sparger reaches the impeller: at low gas rates this is indirect via the recirculation loops, while at higher gas flow rates the flow is direct.

The transition between these regimes is reflected in power consumption and mass transfer characteristics and is related to the formation of large cavities behind the blades. It was also concluded that, with respect to mass transfer efficiency, a pitched blade turbine is at least as good as a Rushton turbine.     

GAS-LIQUID DISPERSION WITH PITCHED BLADE TURBINES

The performance of pitched blade turbines in a gas-liquid dispersion has been studied. The two-phase hydrodynamics, gassed power consumption and mass transfer properties have been examined using six blade open turbines with blade angles from 30 to 60 degrees to the horizontal, mounted for down flow.

There are two distinct regimes by which gas leaving the sparger reaches the impeller: at low gas rates this is indirect via the recirculation loops, while at higher gas flow rates the flow is direct.

The transition between these regimes is reflected in power consumption and mass transfer characteristics and is related to the formation of large cavities behind the blades. It was also concluded that, with respect to mass transfer efficiency, a pitched blade turbine is at least as good as a Rushton turbine.     

精对苯二甲酸氧化反应器中气体停留时间分布

对苯二甲酸的工业生产多采用对二甲苯液相催化氧化方法,因此,氧化气体的混合特性就成为氧化反应器设计、放大的重要参数。文中针对工业中采用的涡轮桨和斜叶桨组合搅拌反应器型式,以氢气为示踪剂,采用阶跃激发响应技术测定了不同气量、搅拌转速下气体停留时间分布,同时开展了对二甲苯氧化试验,了解了气体混合对氧化中间产物含量影响。研究结果表明,只有当搅拌桨叶尖速度高于一个临界值,使气体接近全混的状态,才能实现单釜氧化目的产物的高收率。     

搅拌反应器内三种桨型的气、液分散与相际传质特性研究

本文以改进搅拌发酵罐的桨型为目的,对空气-水、空气-亚硫酸钠溶液系统就六平叶、弯叶、箭叶三种圆盘透平桨产生的气泡平均直径、气含率及容量传质系数的变化规律作了较为系统的研究。实验发现:相同单位体积功率、表观气速条件下,三种桨型各自产生的气泡平均直径相差不大;箭叶桨的气含率较低;六平叶圆盘透平桨具有最大的容量传质系数。     

Hydrodynamics and volumetric gas-liquid mass transfer coefficient of a stirred vessel equipped with a gas-inducing impeller

Hydrodynamic and mass transfer characteristics of a gas-liquid stirred tank provided with a radial gas-inducing turbine were studied. The effect of the rotation speed and the liquid submergence on global hydrodynamic and mass transfer parameters such as the critical impeller speed, the induced gas flow rate, the gas holdup, the power consumption and the volumetric gas-liquid mass transfer coefficient were investigated. The experiments are mainly conducted with air-water system. In the case of critical impeller speed determination, two liquid viscosities have been used. The volumetric gas-liquid mass transfer coefficient k_La has been obtained by two different techniques. The gas holdup, the induced gas rate and the volumetric gas-liquid mass transfer coefficient are increasing functions with the rotation speed and decreasing ones with the liquid submergence. The effects of these operating parameters on the measured global parameters have been taken into account by introducing the dimensionless modified Froude number and correlations have been proposed for this type of impeller.     

Scale up criteria for dual stirred gas-liquid unbaffled tank with concave blade impeller

Experimental investigation has been done in unbaffled gas-liquid stirred tanks using dual concave blade impeller to analyze the mass transfer, power consumption and gas holdup. Optimal impeller clearance has been suggested for lower and upper impeller based on maximum mass transfer rate. Numerical modeling has been done to analyze the flow pattern for different combinations of impeller clearance. The lower impeller positioned at 0.3 of tank diameter and clearance between lower and upper impeller at 0.4 of tank diameter gave the maximum mass transfer coefficient. Scale-up criteria for mass transfer rate, power and gas holdup have been developed for optimal geometrical similar systems of unbaffled stirred tanks with dual concave impeller.     

Gas recirculation rate and its influences on mass transfer in multiple impeller systems with various impeller combinations

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 K_La 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.     

气泡大小对反应器内氧传递系数的影响

在气液反应过程中,气泡的大小对结果往往起了决定性的作用。通过减小气泡的尺寸,可以促进气液传递,加快反应的进程。在气液搅拌式反应器上安装了一种特殊的气体分布器,通过搅拌产生离心场,从而诱导生成泰勒涡柱,使大量进入反应器的空气气泡保持在泰勒涡柱的内部。由于减少了气泡间的凝并作用,气泡尺寸减小,与对照组相比,反应器中最小的气泡尺寸减小了近50%,气泡的比表面积增加近80%。通过对不同通气流量和搅拌速度下气液反应器内氧传递系数的测量,与对照实验比较,使用特殊气体分布器的反应器中,氧的传递系数增加了10%~40%,证明这种气体分布器确实可以增加气液间氧的传递。