Dispersed phase hold-up in mechanically agitated gas–liquid contactors

In the present study, in mechanically agitated gas–liquid contactors (MAC), a generalized correlation for the direct estimation of dispersed gas phase hold-up is proposed. This present proposed new correlation in terms of fundamental operating variables, involving gas velocity, impeller speed in terms of Froude number, vessel geometry and the physical properties, is more accurate than those previously reported and also simpler to use. © 1998 SCI     

Behaviour of gas–liquid mixtures in an unbaffled reactor with unsteadily forward–reverse rotating impellers

The behaviour of gas–liquid mixtures in the vicinity of the blades of an unsteadily rotating impeller in an unbaffled agitated vessel was studied by observations made with a rotating camera. The impellers used were a disk turbine impeller with six flat blades (DT) and a novel cross‐type impeller with four delta blades (CD). The behaviour of gas–liquid mixtures near the blades of the forward–reverse rotating impeller was unsteady in terms of the formation of cavities behind the blades and their dispersion into gas bubbles, and differed from that near the blades of a unidirectionally, steadily rotating impeller. The differences in relative power consumption between the forward–reverse rotating impellers in the unbaffled vessel and the steadily rotating impellers in the baffled vessel are discussed in relation to the differences in the behaviour of gas–liquid mixtures near the blades of each rotating impeller. © 2002 Society of Chemical Industry     

气液旋流器内液相平均停留时间

旋流设备内伴有传热、传质或反应过程时,介质停留时间是其关键参数。在冷模实验装置上,采用持液量法,对气液旋流器内液相平均停留时间进行了研究。结果表明,液相停留时间随入口含液率增大明显降低,随入口气速增大降低较小。气液界面剪切力远小于液相重力是入口气速对液相停留时间影响较小的主要原因。基于液膜受力平衡,建立了气液旋流器内液相平均停留时间模型。模型预测停留时间与实测值总体吻合良好,在液膜Reynolds数Re_l< 1200范围内,模型预测停留时间偏大,讨论了模型预测偏差与液膜流型的关系。     

Progress in membrane gas–liquid reactors

Gas–liquid reactions are crucially important in chemical synthesis and industries. In recent years, membrane gas–liquid reactors have attracted great attentions due to their high selectivity, productivity and efficiency, and easy process control and scale‐up. Membrane gas–liquid reactors can be divided into three categories: dispersive membrane reactor, non‐dispersive membrane reactor and pore flowthrough reactor. The progress in membrane gas–liquid reactors, including features, applications, advantages and limits, is briefly reviewed. © 2012 Society of Chemical Industry     

Gas holdup for high gas velocities in a gas–liquid cocurrent upward‐flow system

Gas holdup has been measured in an 83‐mm diameter, 2.2‐m high column at high gas superficial velocities — 0.22 to 2.7 m/s — and at liquid (water) superficial velocities of 0 to 0.47 m/s, by means of a differential pressure transducer. The equation of Hills (1976) based on the slip velocity gives good predictions of the gas holdup for 0.1 ≤ E_g ≤ 0.4. However, the holdups predicted by this approach are considerably higher than the experimental values at gas velocities high enough that E_g > 0.4. Other equations from the literature are also shown to be inadequate. The new data and earlier data at high gas velocities are therefore correlated with a new dimensional equation for U_l ≤ 0.23 m/s.     

Gas hold-up behavior of mechanically agitated gas-liquid reactors using pitched blade downflow turbines

Fractional gas holdup was measured in 0.57, 1.0, and 1.5 m i.d. vessels. Pitched blade downflow turbines (PTD) were used as the impeller. Design details of the impeller, such as the impeller diameter (0.22 T to 0.5 T) and blade width (0.25 D to 0.4 D), were studied. The effect of sparger type, geometry and size on fractional gas hold-up has been investigated in detail. Four different types of spargers (pipe, conical, ring and concentric ring spargers) were used. Sparger location was varied for all the types studied. Further, design details of the ring sparger, which gave the highest hold-up were then studied in detail. These included ring diameter, number of holes and hole size. All the reported correlations for fractional gas hold-up in mechanically agitated gas-liquid reactors were tested and compared. A better correlation has been developed for pitched blade turbines.     

Investigating the liquid film characteristics of gas–liquid swirling flow using ultrasound doppler velocimetry

A novel gas–liquid two‐phase flow metering method was proposed. A spiral vane mounted in the inner pipe was used to transform inlet flow patterns into gas–liquid swirling annular flow. The thickness and velocity profile of liquid film were measured by ultrasound Doppler velocimetry. The liquid flow rates were obtained by integrating of velocity profile during the liquid film zone. Experiments were carried out in an air–water two‐phase flow loop and an ultrasonic transducer was installed under the bottom of the test section with the Doppler angle of 70°. The flow patterns included stratified wavy, annular, and slug flows. Compared with non‐swirling flow, the liquid film thickness at the bottom reduces greatly. The measurement accuracy of liquid flow rate was independent of inlet flow patterns, gas and liquid velocities. © 2016 American Institute of Chemical Engineers AIChE J, 63: 2348–2357, 2017     

Bubble shape,gas flow and gas–liquid mass transfer in pulp fibre suspensions

Gas–liquid mass transfer in pulp fibre suspensions in a batch‐operated bubble column is explained by observations of bubble size and shape made in a 2D column. Two pulp fibre suspensions (hardwood and softwood kraft) were studied over a range of suspension mass concentrations and gas flow rates. For a given gas flow rate, bubble size was found to increase as suspension concentration increased, moving from smaller spherical/elliptical bubbles to larger spherical‐capped/dimpled‐elliptical bubbles. At relatively low mass concentrations (C_m = 2–3% for the softwood and C_m ? 7% for the hardwood pulp) distinct bubbles were no longer observed in the suspension. Instead, a network of channels formed through which gas flowed. In the bubble column, the volumetric gas–liquid mass transfer rate, k_La, decreased with increasing suspension concentration. From the 2D studies, this occurred as bubble size and rise velocity increased, which would decrease overall bubble surface area and gas holdup in the column. A minimum in k_La occurred between C_m = 2% and 4% which depended on pulp type and was reached near the mass concentration where the flow channels first formed.     

Hydrodynamics and mass transfer of gas–liquid flow in a falling film microreactor

In this article, flow pattern of liquid film and flooding phenomena of a falling film microreactor (FFMR) were investigated using high‐speed CCD camera. Three flow regimes were identified as “corner rivulet flow,” “falling film flow with dry patches,” and “complete falling film flow” when liquid flow rate increased gradually. Besides liquid film flow in microchannels, a flooding presented as the flow of liquid along the side wall of gas chamber in FFMR was found at high liquid flow rate. Moreover, the flooding could be initiated at lower flow rate with the reduction of the depth of the gas chamber. CO₂ absorption was then investigated under the complete falling flow regime in FFMR, where the effects of liquid viscosity and surface tension on mass transfer were demonstrated. The experimental results indicate that k_L is in the range of 5.83 to 13.4 × 10^?5 m s^?1 and an empirical correlation was proposed to predict k_L in FFMR. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Sensor‐based flow pattern detection—gas–liquid–liquid upflow through a vertical pipe

Flow distribution during gas–liquid–liquid upflow through a vertical pipe is investigated. The optical probe technique has been adopted for an objective identification of flow patterns. The probability density function (PDF) analysis of the probe signals has been used to identify the range of existence of the different patterns. Dispersed and slug flow have been identified from the nature of the PDF, which is bimodal for slug flow and unimodal for dispersed flow. The water continuous, oil continuous, and emulsion type flow distributions are distinguished on the basis of the PDF moments. The method is particularly useful at high flow rates where visualization techniques fail. Based on this, a flow pattern detection algorithm has been presented. Two different representations of flow pattern maps have been suggested for gas–liquid–liquid three phase flow. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3362–3375, 2014     

A multi‐scale theoretical model for gas–Liquid interface mass transfer based on the wide spectrum eddy contact concept

On the basis of the wide spectrum eddy contact concept and the isotropic turbulence theory, a multi‐scale theoretical model for the prediction of liquid‐side mass transfer coefficient in gas–liquid system was developed. The model was derived from an unsteady‐state convection and diffusion equation and considered the contributions of eddies with different sizes to the overall mass transfer coefficient. The proper contact time distribution at the surface is need to be determined to obtain satisfactory results with this model. Moreover, a simplified model was also proposed based on the assumption of steady‐state mass transfer mechanism for single eddy. The results predicted by this model showed a very good agreement with the available experimental data in a comparatively wide range of turbulence intensities. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

CFD simulation of solid–liquid flow in a two impinging streams cyclone reactor: Prediction of mean residence time and holdup of solid particles

The hydrodynamic behavior of a two impinging streams cyclone reactor (TISCR) was simulated using the computational fluid dynamics (CFD) technique. An Eulerian multiphase model has been used to compute the unsteady flow of a solid–liquid suspension in a 3D geometric configuration. The mean residence time (t_m) and holdup of solid particles were calculated from a number of simulated results obtained at different solid and liquid flow rates. The CFD simulation results were compared with the experimental data available in the literature and a fairly well agreement was observed. Such a correlation was gradually improved with increasing solid flow rate.     

Gas–liquid chromatographic study of polystyrene–n‐alkane interactions

Gas–liquid chromatography is used to study the thermodynamic interactions between polystyrene and n‐alkanes (C₆–C₁₀). Polystyrene is used as a stationary phase with n‐alkanes as the probe molecules. Retention times and specific retention volumes are measured over the temperature interval of 60 to 170°C. Partial molar free energy of mixing, polymer–solvent interaction parameter, glass‐transition temperature, and solubility parameter of polystyrene at infinite dilution are calculated. Experimental results are discussed in terms of the theoretical calculations and size of the probe molecules. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1291–1298, 2001     

Trajectory modeling of gas–liquid flow in microchannels with stochastic differential equation and optical measurement

The numbering‐up of microchannel reactors definitely faces great challenge in uniformly distributing fluid flow in every channel, especially for multiphase systems. A model of stochastic differential equations (SDEs) is proposed based on the experimental data recorded by a long‐term optical measurement to well quantify the stochastic trajectories of gas bubbles and liquid slugs in parallel microchannels interconnected with two dichotomic distributors. The expectation and variance of each subflow rate are derived explicitly from the SDEs associated with the Fokker–Planck equation and solved numerically. A bifurcation in the trajectory is found using the original model, then a modification on interactions of feedback and crosstalk is introduced, the evolutions of subflow rates calculated by the modified model match well with experimental results. The established methodology is helpful for characterizing the flow uniformity and numbering‐up the microchannel reactors of multiphase system. © 2015 American Institute of Chemical Engineers AIChE J, 61: 4028–4034, 2015     

Dispersed phase holdup and bubble size distributions in gas–liquid cocurrent upflow and countercurrent flow in reciprocating plate column

Dispersed phase holdup and the bubble size distribution were measured in a reciprocating plate column under cocurrent upflow and countercurrent flow of gas and liquid phases. The response of the system to a variation in design and operating conditions was found similar to that for liquid–liquid contacting; the magnitude of response, however, differed significantly between them. Taking into consideration the dominant forces encountered in gas–liquid dispersions, the experimental data are satis–factorily correlated in terms of Froude, Weber and Gallileo numbers.     

Liquid‐bridge flow in the channel of helical string and its application to gas–liquid contacting process

To solve the problems of the traditional packings, such as high pressure drop, mal‐distribution and short liquid residence time, a helical flow structured packings was proposed. Two different flow patterns, liquid‐bridge flow and liquid‐drop flow were identified when the width of the channel of the helical string was adjusted. Moreover, the characteristics of the helical liquid‐bridge flow including maximum liquid loading, mean thickness of liquid film, mean residence time and effective specific surface area, were examined. And the separation efficiency was studied by the lab‐scale distillation column. In comparison, the effective specific surface area of the helical flow type packings is almost as large as the traditional B1‐350Y structured packings, but with thinner liquid film, longer liquid residence time and finally higher separation efficiency. © 2018 American Institute of Chemical Engineers AIChE J, 64: 3360–3368, 2018