Fractional gas hold-up in gas inducing type of mechanically agitated contactors

Fractional gas hold up was measured in gas inducing type of mechanically agitated contactors (GIMAC) with single and multiple impellers. Three vessels of 0.57, 1.0 and 1.5 m i.d. were used. For the multiple impeller system, six different impeller designs were employed. The impeller speed was varied in the range of 0.30 to 15.45 s^?1. The ratio of impeller diameter to tank diameter (D/T), the submergence (S) of the upper impeller, the clearance of the lower impeller from the tank bottom (C₁) and the impeller spacing (C₃) were varied over a wide range. The design of the lower impeller was optimized in terms of diameter (D), blade width (W), blade angle (Bø), number of blades (n_b) and the blade thickness (t_b). An optimum design has been proposed for the multiple impeller system. Rational correlations have been proposed.     

Measuring gas hold-up in gas–liquid/gas–solid–liquid stirred tanks with an electrical resistance tomography linear probe

An electrical resistance tomography (ERT) linear probe was used to measure gas hold-up in a two-phase (gas–liquid) and three phase (gas–solid–liquid) stirred-tank system equipped with a Rushton turbine. The ERT linear probe was chosen rather than the more commonly used ring cage geometry to achieve higher resolution in the axial direction as well as its potential for use on manufacturing plant. Gas-phase distribution was measured as a function of flow regime by varying both impeller speed and gas flow rate. Global and local gas hold-up values were calculated using ERT data by applying Maxwell's equation for conduction through heterogeneous media. The results were compared with correlations, hard-field tomography data, and computational fluid dynamic simulations available in the literature, showing good agreement. This study thus demonstrates the capability of ERT using a linear probe to offer, besides qualitative tomographic images, reliable quantitative data regarding phase distribution in gas–liquid systems.     

Dispersion of liquid–liquid phase by a jet-induced gas–liquid–liquid mixing column developed for separation of organic pollutants

This article presents the gas and liquid entrainment and its dispersion in a gas–liquid–liquid mixing column. The variations in phase entrainment is observed with the change in the paraffin liquid and kerosene volume fraction from 5% to 35% due to the increase in the flow resistance with increase in the effective viscosity of the liquid–liquid mixture. The degree of dispersion is enunciated based on the axial dispersion model and the flow resistance of the phases in the column. A correlation is proposed to interpret the entrainment of phase as a function of operating variables within the range of experimental conditions.     

MULTI-PASS SOLAR HEATER WITH HEAT-EXCHANGING PASSES AND EXPOSED TO NON-UNIFORM RADIATION

This is an analytical treatment of the multi-pass solar fluid-heater when the received radiant energy is non-uniformly distributed in the cross direction, normal to the flow. Adjacent passes are allowed to exchange energy. Closed-form formulas are derived for the fluid and wall temperature distributions along different passes. Mathematical expressions are presented for two performance indices, the efficiency and the effectiveness.     

TURBULENT RANGE IMPELLER POWER NUMBERS IN CLOSED CYLINDRICAL AND SQUARE VESSELS

Impeller power numbers in closed square vessels with/or without baffles and in closed cylindrical vessels with baffles were studied for impeller Reynolds numbers in the range between 75000 and 300000. A flat vertical blade disk style, a vertical blade open style and a 45° pitched blade open style impellers were used. A substantial reduction of power number is observed for all three impellers inside the square vessels without baffles in comparison with baffled cylindrical and square ones reaching up to 61 %.     

Changes in intracellular sodium and potassium in chemostat-cultivated Escherichia coli

Escherichia coli was continuously cultivated at constant dilution rate for a range of agitation rates, and at constant agitation rate over a range of dilution rates. Mean cell volume increased linearly both with increase in agitation rate (as we have previously found) and with increase in dilution rate. In each case, measurement of intracellular sodium and potassium content after rapid separation of cells from the medium by centrifugation through silicone oil showed these to increase as the mean cell volume increased. In absolute terms, the increase in sodium or potassium per unit cell volume was significantly greater for changes in agitation rate than for changes in dilution rate.     

Which impeller should be chosen for efficient solid–liquid mixing in the laminar and transitional regime?

The vast majority of solid–liquid mixing studies have focused on high Reynolds number applications with configurations and impeller geometries adapted to this type of regime. However, the mixing of particles in a viscous fluid is an essential element of many contemporary industries. We used the computational fluid dynamics-discrete element method model previously developed in our group to investigate solid–liquid mixing with close-clearance impellers in the laminar regime of operation. We compared different geometries, that is, the double helical ribbon, anchor, Paravisc™, and Maxblend™ impellers. We investigated the impact of fluid viscosity and compared the results with those obtained with the pitched blade turbine, a more commonly used impeller, based on power consumption for equivalent mixing states. This study highlights that the higher the viscosity of the fluid, the more interesting it is to use close-clearance impellers for their ability to generate a strong shear stress and a strong bulk flow in the entire vessel.     

机械搅拌反应器中挡板的结构设计

研究了内径为0．786m的搅拌釜中挡板尺寸及结构对圆盘透平桨RT和翼型桨k5及其组合在气液两相中的气体分散与混合特性的影响。对不同形式的挡板的搅拌功率、气含率及气液混合特性进行了对比分析。研究结果表明：挡板尺寸结构应根据搅拌特性需要进行优化设计;挡板系数为0．12时,组合浆的功率输入已与同一转速下的全挡板系数时的功率输入相近,它同时可改善微观混合、提高混合效率：采用开槽挡板可提高复杂快反应的选择性,混合效率提高20％～25％。     

Micromixing in a gas–liquid vortex reactor

The gas–liquid vortex reactor (GLVR) has substantial process intensification potential for multiphase processes. Essential in this respect is the micromixing efficiency, which is of great importance in fast reaction systems such as crystallization, polymerization, and synthesis of nanomaterials. By creating a vortex flow and taking advantage of the centrifugal force field, the liquid micromixing process can be intensified in the GLVR. Results show that introducing a liquid into a gas-only vortex unit results in suppression of primary and secondary gas flow. The Villermaux–Dushman protocol is applied to study the effects of the gas flow rate, liquid flow rate, and liquid viscosity based on a segregation index. Based on the incorporation model and reaction kinetics, the micromixing time of the GLVR is determined to be in the range of 10⁻⁴ ~ 10⁻³ s, which is comparable to the highly efficient rotating packed bed and substantially better than a static mixer.     

浅谈液相催化加氢反应器的形式

介绍了目前液相催化加氢反应中遇到的主要几种反应器的形式,并对各种反应器的结构、工作原理及优缺点进行了分析和互相对比,指出自吸式反应器是最适合应用于液相催化加氢反应场合,其中杭州原正化学工程技术装备有限公司是国内较早从事研究开发自吸式搅拌装置的单位,设计和生产制造的自吸式搅拌装置性能比较优越,技术在国内处于领先水平。     

Effect of cell volume on disintegration by ultrasonics

Wide variations in resistance to ultrasonic disintegration of continuously cultivated Bacillus cereus, Saccharomyces cerevisiae and Escherichia coli could be achieved by corresponding variations in fermenter impeller speed (agitation rate). In all cases examined, the relationship between disintegration constant and impeller speed was found to be linear. Although changes in relative strengths of E. coli were observed with changes in limiting nutrient (nitrogen-limited cells being weaker than carbon-limited cells for any one impeller speed), this was compensated for by the increased volumes of nitrogen-limited cells, and the relationship between disintegration constant and mean cell volume was linear, irrespective of nutrient limitation. Comparisons with other published data confirmed the view that for any one micro-organism, irrespective of cultural conditions, the principal determinand of susceptibility to ultrasonic disintegration was mean cell volume.     

A novel design for a gas-inducing impeller at the lowest critical speed

To disperse the unreacted overhead gas phase into the liquid in an agitated reactor without gas outlet, a gas-inducing impeller is usually employed. To determine the lowest critical rotating speed, the gas-induction mechanism was reconsidered by constituting a mechanical energy conservation equation between the gas inlet orifice in the gas phase and the gas outlet orifice in the liquid phase under a certain rotational speed. According to this model, the critical speed of the gas-inducing impeller could be basically determined by the submersion depth and the radial position of the gas outlet, and a novel design was proposed by introduction of six short pipes stretched radially from the axis of the impeller. The final design of the gas-inducing impeller was obtained by an optimal combination of the gas-inducing pipes, the blades of the impeller and the baffle dimension.     

具有双层桨结构的自吸式搅拌反应器的流体力学性能

在直径0.48 m的搅拌槽中以水?空气为介质,对具有双层桨结构的自吸式反应器的流体力学性能进行了实验研究,考察了自吸式桨浸没深度、底层桨结构和搅拌桨层间距对自吸式桨的临界吸气转速、吸气速率和气含率的影响。结果表明,临界吸气转速随自吸式桨浸没深度增加而增加,临界吸气转速几乎与下层桨的结构无关;吸气速率与气含率随浸没深度增加而减小,吸气速率与气含率受下层桨影响较大,层间距为自吸式桨直径(D)且采用上推式的四叶宽叶翼形轴流式桨作下层桨时,自吸式桨的吸气性能最佳。