Studies on the hydrodynamic behavior and mass transfer in a down‐flow jet loop reactor with a coaxial draft tube

The effects of certain pertinent parameters such as gas and liquid flow rates and nozzle position on the behavior of a down‐flow jet loop reactor (DJR) have been studied. The mean residence times of gas and liquid phases and the gas holdup within the reactor have been measured. In addition, the overall volumetric mass transfer coefficient, and the influence of the gas flow rate and the position of the nozzle inside the draft tube on the latter has been determined. Correlations have been presented for the gas holdup and k_La which take into account the length of the draft tube and the nozzle immersion height. The k_La values obtained at different power per unit volume (P/V) values in the DJR used in the present study compare favorably with data presented for stirred tanks and bubble columns in the literature. The liquid residence time distribution (RTD) within the reactor has been studied by tracer analysis for various operating conditions and nozzle immersion height and the results are indicative of the high mixing intensities that can be obtained in such reactions. © 2001 Society of Chemical Industry     

CO2 absorption characteristics of a jet loop reactor with a two-fluid swirl nozzle in an alkaline solution

To investigate the performance of a jet loop reactor with the two-fluid swirl nozzle (TSN), CO₂ absorption experiments in an alkaline solution were performed. The experimental results obtained in the reactor were compared with those in a jet loop reactor with the two-fluid conventional nozzle (TCN). The neutralization time of alkaline solution and the CO₂ removal efficiency were used as the indices for a comparison of the reactor performance. Due to the swirling flow, the neutralization times of alkaline solutions by CO₂ in the reactor with the TSN were shortened compared with those in the reactor with the TCN. Also, the instantaneous and/or overall CO₂ removal efficiencies in the reactor with the TSN were higher than those in the reactor with the TCN at the same liquid circulation flow rate.     

Influence of geometry on gas holdups in a reversed flow jet loop reactor

The effects of ratio of draft tube to reactor diameter (D_d/D), liquid nozzle diameter (d_N), aeration tube diameter (d_G) and immersion height of the two-fluid nozzle into the draft tube (H_N) on overall and annulus gas holdups for the air-water system were evaluated experimentally in a reversed flow jet loop reactor over wide ranges of gas and liquid flow rates. Both the gas holdups increased with increasing gas and liquid flow rates and with decreasing d_N and H_N. The influence of d_G on gas holdups is found to vary with gas flow rates. Correlations are proposed to predict gas holdups.     

Hydrodynamics in a jet bubbling reactor: Experimental research and mathematical modeling

The radial distribution of liquid velocity in the axial direction of a jet bubbling reactor has been measured by experimentation. Three different typical flow structures controlled by liquid jet, gas bubbling, and liquid jet coupled with bubbling are observed. A tank in series model is established on this basis. Calculated values in each region are in good agreement with measured values in jet, bubbling, and wall effect controlled areas. Axial flow rate, radial exchange rate, and jet controlled volume η are analyzed from energy input aspect under different u_g and u_j. Simulation results indicate that under the synergetic action of the liquid jet and gas bubbling effect, jet controlled area exhibits a “spindle” structure, and its size decreases with the increase of u_g. When gas input power occupies about 67% of total energy consumption, the best synergy of liquid jet and gas bubbling is obtained. © 2017 American Institute of Chemical Engineers AIChE J, 64: 1814–1827, 2018     

Output Flow Determination of Reverse Flow Diverters in Reverse Flow Mode Based on Pressure Data

The key fluidic component of a pneumatic pulse jet pump is a reverse flow diverter (RFD), which consists of a driving nozzle and diffuser, with a suction gap separating the two. Because the suction gap is open to the storage tank, the mass flow through a RFD is not constant, and it is difficult to determine its pumping capacity in the reverse flow mode. For symmetrical RFDs, we experimentally investigated the effects of the driving nozzle exit diameter d₀, suction gap length d_c, liquid viscosity μ, and pipeline load impedance on the RFDs’ performance in the reverse flow mode. A dimensionless performance curve insensitive to d₀, d_c, μ, and the pipeline load impedance was found based on these experimental data. The output flows of RFDs with suction factors higher than 0.9 could be determined using this dimensionless performance curve.     

Gas entrainment rate and flow pattern of vertical plunging liquid jets

For a vertical plunging liquid jet system using various liquids, the effects of the operating conditions including the nozzle length-to-diameter ratio on the gas entrainment rate Q_g were evaluated experimentally. The differences in Q_g were related to the changes in the jet shape before plunging and the velocity of the plunging liquid jet at the point where the gas sheath breaks up. Empirical relationships were also presented to predict the maximum depth Z of bubbles entrained by the diffusing jet. The changes of Z were further discussed in terms of the downward liquid velocity distribution in the submerged two-phase region, which depends mainly on the size of entrained bubbles.     

Gas holdup and gas entrainment of a plunging water jet with a constant entrainment guide

The gas holdup and gas entrainment of a plunging liquid jet with a gas entrainment guide in an air-water system was investigated. The measurement of the gas holdup was performed using an over-flow method. The turbulent jet velocity calculated on an inside nozzle diameter in the range from 4.4-26.5 m/s for this system has been used in our correlations. The gas holdup has been well correlated in terms of 1/H(v₀² + 2gH₁), H₁ d₀ and the gas entrainment in terms of 1/H_w(v₀² + 2gH₁), H₁, d₀. The jet power requirement was also obtained from experimental data.     

The effect of geometrical parameters on the flow field of an opposed jet rim mix head: Equal flow and matched fluids

The effect of geometrical parameters on the flow field present in the mix head used in reaction injection molding (RIM) are presented for Re_d (Re_d = 4Q/πdv, nozzle diameter d, fluid kinematic viscosity v and the volumetric flow rate Q through the nozzle) representative of commercial practice. Quantitative velocity measurements of the flow field in a mix head have not been reported in the literature despite the extensive use of the mix head for reaction injection molding. Flow visualization and velocity measurements using a laser Doppler anemometer have been obtained for different values of geometrical parameters such as mix chamber diameter (D), distance from the nozzle inlet to the closed end of the chamber (H), and nozzle needle position (N). The ratio of the mix chamber to nozzle diameter (d) (D* = D/d) was a significant parameter affecting the flow field. The distance from the impingement point to the closed end of the chamber was found to have little effect on the observed flow field beyond the impingement area. A nozzle needle position that partially constricted the nozzle opening was found to decrease the axial distance to unidirectional flow within the mix chamber.     

Hydrodynamics of a rectangular liquid JET in an immiscible liquid–liquid system

Volume of fluid and continuum surface force methodologies were applied to two‐ and three‐dimensionally model the motion of a liquid jet injected vertically downward from a rectangular nozzle into another immiscible liquid. Grid independent solutions were obtained for a 10 mm² nozzle with aspect ratios in the range 1–10. It was found that unlike the 3D simulation, the 2D CFD model was not able to predict the necking and breakup features observed in the experimental system. The 3D model showed that upon exiting the rectangular nozzle the liquid jet underwent a transition before becoming circular in cross‐section and eventually reaching an equilibrium diameter prior to breakup into droplets. For a given nozzle geometry it was found that equilibrium jet diameter increased with increasing liquid volumetric flowrate, with good agreement between CFD simulations and experimental observations. The 3D model was applied to rectangular nozzles with different aspect ratios and it was found that for a given liquid flowrate there was an optimum aspect ratio for generating minimum‐sized droplets, which was approximately 30% less than for a circular nozzle with the same cross‐sectional area. © 2011 Canadian Society for Chemical Engineering     

Chemical hydrodynamics of a downward microbubble flow for intensification of gas‐fed bioreactors

Bioreactors are of interest for value‐upgrading of stranded or waste industrial gases. Reactor intensification requires development of low cost bioreactors with fast gas–liquid mass transfer rate. Here we assess published reactor technology in comparison with a novel downward bubble flow created by a micro‐jet array. Compared to known technology, the advanced design achieves higher volumetric gas transfer efficiency (k_La per power density) and can operate at higher k_La. We measure the effect of four reactor heights (height‐to‐diameter ratios of 12, 9, 6, and 3) on the gas transfer coefficient k_L, total interfacial area a, liquid residence time distribution, energy consumption, and turbulent hydrodynamics. Leading models for predicting k_L and a are appraised with experimental data. The results show k_L is governed by “entrance effects” due to Higbie penetration dominate at short distances below the micro‐jet array, while turbulence dominates at intermediate distances, and finally terminal rise velocity dominates at large distances. © 2017 American Institute of Chemical Engineers AIChE J, 64: 1399–1411, 2018     

A Flow Time Model for Melt‐Cast Insensitive Explosive Process

Diphasic flows of concentrated suspensions of melt‐cast insensitive explosives exhibit specific rheological properties. In order to limit the handling of pyrotechnical products presenting a risk with respect to the mechanical and thermal shocks, a lot of work has been undertaken for many years in the civil engineering sector. The objective of this study is to propose a predictive model of the flow time of a concentrated suspension through a nozzle located at the bottom of a tank. Similar to our industrial process, the suspension is made out of insensitive energetic materials and flows under gravity. Experimental results are compared to three models (Quemada, Krieger‐Dougherty, and Mooney) predicting the viscosity μ of a suspension as a function of the solid volume fraction ϕ, the maximum packing density ϕ_m and the viscosity μ₀ of the interstitial liquid. De Larrard's model is used to calculate ϕ_m. The value of viscosity measured for the pure liquid is close to the one predicted by the Bernoulli theorem, where liquids are considered as incompressible and inviscid. Finally, it was found that the Quemada's model gives a fair agreement between predictions and experiments.     

三相下喷式环流反应器的传质性能

在三相非牛顿型流体体系中，对下喷式环流反应器传质特性进行了实验研究。讨论了表观气速、能量耗散速率、导流筒直径与反应器直径比、喷嘴直径、导流筒下端距反应器底部的距离、固体装填量、羧甲基纤维素钠（ＣＭＣ）溶液浓度及其流变特性对它的影响。实验结果表明，容积传质系数随表观气速和能量耗散速率的增加有所增加，在实验条件下，发现最优的导流筒直径与反应器直径比在０．４～０．４５这一范围、固体装填量大约为３％（体积百分比）、导流筒下端距反应器底部的距离为０．０８ｍ左右。同时提出了容积传质系数的经验关联式。     

Efficiency of a Gas‐Liquid Contactor for the Oxygenation of Activated Sludge: Assessment of Mass Transfer Coefficient

The aim of this work is to investigate a co‐current air‐liquid downward flow bubble column with air entrainment by liquid injection nozzle in order to use it as an aerator in activated sludge treatment plants. The study concerns the determination of mass transfer efficiency by measuring the mass transfer coefficient, k_La, both in clean water and in activated sludge. In clean water, this parameter is determined by three methods, i.e., gassing out method, absorption with chemical reaction and off‐gas method. In activated sludge medium, k_La values are measured by two methods, i.e., sludge reoxygenation and the hydrogen‐peroxide method. The values of k_La obtained in clean water are compared to those obtained in sludge, enabling the assessment of the α factor, i.e., ratio of oxygen transfer coefficient sludge/clean water. The results are in good agreement with those reported previously in the literature.     

Study of Hydrodynamics,Mixing and Gas‐Liquid Mass Transfer in a Split‐Rectangular Airlift Reactor

Global hydrodynamic characteristics, liquid mixing and gas‐liquid mass transfer for a 63 L split‐rectangular airlift reactor were studied. Correlations for gas holdup and overall liquid circulation velocity were derived for the air‐water system as a function of the specific power input; these were compared to data and correlations for reactor volumes between 4.7 L and 4600 L. A partial recirculation of small bubbles in the riser was observed when U_gr > 0.03 m/s, which was attributed to the use of a single‐orifice nozzle as the gas phase distributor. The dimensionless mixing time and the overall axial dispersion coefficient were nearly constant for the range of gas flow rates studied. However, values of K_L/d_B were greater than those reported in previous studies and this is caused by the partial recirculation of the gas phase in the riser. While scale effects remain slight, the use of a gas distributor favouring this partial recirculation seems adequate for mass transfer in split‐rectangular airlift reactors.     

喷射式环流反应器内流速分布的实验研究

主要研究了喷嘴位置和喷嘴出口速度对底部是圆锥台的喷射环流反应器(JLR)的影响,从而确定最优出口速度和喷嘴位置。对JLR内部流速进行测量,绘出JLR内的速度分布图,并从速度场和内外循环比2个方面进行分析,从而确定最优参数。结果表明:在实验室范围内,当喷嘴出口速度为2.1 m/s,喷嘴位置为40 mm时较优。导流筒内速度呈抛物线分布;喷嘴出口速度增加,环隙速度对应增大,内外循环比也增加;随着喷嘴位置逐渐靠近导流筒,内外循环比先增加,再减小。     

Gas-liquid mass transfer in bubble columns with a T-junction nozzle for gas dispersion

Bubble break-up, gas holdup, and the gas-liquid volumetric mass transfer coefficient are studied in a bubble column reactor with simultaneous injection of a gas and liquid through a T-junction nozzle. The theoretical dependence of bubble break-up and the volumetric mass transfer coefficient on liquid velocity in the nozzle is developed on the basis of isotropic turbulence theory. It is shown that correlations which are developed based on liquid jet kinetic power per nozzle volume explain average gas holdup and the volumetric mass transfer coefficient within an error of 15% for all gas and liquid flow rates and nozzle diameters used. Experiments with a larger scale column, height 4.64 m and diameter 0.98 m, show a transition from homogeneous to heterogeneous flow at a certain liquid flow rate through the nozzle. Liquid composition was found to have a significant effect on gas-liquid mass transfer. A phenol concentration of 10–30 mg/l in water increases the volumetric mass transfer coefficient of oxygen by 100%. This phenomenon may have significance in the chemical oxidation of wastewater.     

Classification and identification of gas–liquid dispersion states in a jet bubbling reactor

Three gas–liquid dispersion states including flooding, loading, and complete dispersion are observed sequentially in a jet bubbling reactor with an increase of the liquid jet velocity at the nozzle outlet (u_j). The gas–liquid dispersion states are identified through the slope (k) of the curve of fluctuation distribution index (FI) versus u_j as follows: (a) under the flooding, k = 0; (b) under the loading, k > 0; (c) under the complete dispersion, k < 0. In particular, the u_j at the transition points from flooding to loading and from loading to complete dispersion are referred to flooding jet velocity (u_jf, the transition point between k = 0 and k > 0) and complete dispersion jet velocity (u_jcd, the transition point from k > 0 to k < 0), respectively. The average relative deviations of the u_j at the transition points obtained through the acoustic emission measurement and visual observation are less than 5%.     

Flow characteristics of gas–liquid two phase plunging jet absorber–gas holdup and bubble penetration depth

A gas-liquid two phase plunging jet is formed through a gas sucking type multi-jet ejector nozzle. In this study, the effects of various conditions in the multi-jet ejector nozzle, the column diameter, and the liquid jet length on penetration depth of air bubblesl _B and gas holdup h_G in a gas-liquid two phase plunging jet absorber were studied experimentally. Consequently, empirical equations concerningl _B and h_G were obtained, respectively. These equations agree with the experimental data with an accuracy of ±20% forl _B and ±25% for h_G.     

Comparison of Overall Gas‐Phase Mass Transfer Coefficient for CO2 Absorption between Tertiary Amines in a Randomly Packed Column

The mass transfer performance of CO₂ absorption into an innovative tertiary amine solvent, 1‐dimethylamino‐2‐propanol (1DMA2P), was investigated and compared with that of methyldiethanolamine (MDEA) in a packed column with random Dixon‐ring packing. All experiments were conducted under atmospheric pressure. The effects of inert gas flow rate, amine concentration, liquid flow rate, CO₂ loading, and liquid temperature on mass transfer performance were analyzed and the results presented in terms of the volumetric overall mass transfer coefficient (K_Ga_v). The experimental findings clearly indicate that 1DMA2P provided better mass transfer performance than MDEA. For both 1DMA2P and MDEA solutions, the K_Ga_v increased with rising amine concentration and liquid flow rate, but decreased with higher CO₂ loading. The inert gas flow rate only slightly affected the K_Ga_v. A satisfactory correlation of K_Ga_v was developed for the 1DMA2P‐CO₂ system.     

Mass transfer behaviour of gas-liquid jet loop reactors

A special type of jet loop reactor (JLR), designed for continuous operation and short residence times was investigated with regard to its mass transfer behaviour, described by the volumetric mass transfer coefficient k_La. The jet stream and superficial gas velocities are varied in two JLRs of different sizes, equipped with different nozzles. Fully desalinated water, 0.08 molar NaCI solution and solutions of different concentration of carboxymethyl cellulose (CMC) are used as the liquid phase. A steady-state physical method is employed to determine k_La: air oxygen is purged from the liquid phase by gaseous nitrogen. The measurements show that the reactor is characterized by high power density and high mass transfer performance. No limit of mass transfer capacity was observed in the chosen ranges of volumetric gas and liquid flow rates, i.e. at a given jet stream velocity, the relationship between k_La and the superficial gas velocity is nearly linear. The investigations show that the mass transfer contributed by the jet stream largely depends on liquid phase composition.