Effect Of Superficial Liquid Velocity Research Articles

Experimental study on the addition of pulsating flow to enhance liquid-solid mass transfer in the circulating fluidized bed

The addition of pulsating flow in the conventional liquid-solid circulating fluidized bed (CLSCFB) to enhance liquid-solid mass transfer efficiency has been proposed. A pulsating continuous liquid-solid circulating fluidized bed (PCLSCFB) experimental system was designed and constructed. The liquid-solid mass transfer coefficient (kSL) in the PCLSCFB was measured by the experimental method of dissolving the insoluble benzoic acid particles. The effects of superficial liquid velocity, superficial solids velocity and pulsation property on the liquid-solid mass transfer coefficient (kSL) in the PCLSCFB were thus determined. It was concluded that the liquid-solid mass transfer coefficient (kSL) increases with the increasing pulsation amplitude and frequency in the experimental range. The addition of pulsating flow significantly strengthens the liquid-solid interphase transfer efficiency in comparison with the CLSCFB. The correlation of the mass transfer coefficient (kSL) for the PCLSCFB has been proposed based on experimental data and main parameters.

Experimental Study and Modeling of Slug Dissipation in a Horizontal Enlarged Impacting Tee-Junction

SummaryA novel experimental and theoretical study on slug dissipation in a horizontal enlarged impacting tee-junction (EIT) is carried out. Both flowing-slug injection and stationary-slug injection into the EIT are studied, and the effects of inlet slug length and liquid-phase fluid properties on the slug dissipation in the EIT are investigated.A total of 161 experimental data are acquired for air-water and air-oil flow. The flowing-slug data (with a horizontal inlet) show that the slug dissipation length increases with increasing mixture velocity, demonstrating a nonlinear trend with a steeper slope at lower mixture velocities. The effect of superficial gas velocity on the slug dissipation length is more pronounced compared with the effect of superficial liquid velocity. For stationary-slug injection into the EIT (with a 5° upward inclined inlet), the injected slug lengths vary between 40d to 100d (d is the inlet diameter). The data reveal that, when increasing the superficial gas velocity or the inlet slug size, the dissipation length in the EIT branches increases. For this case, the ratio of the slug dissipation length to the inlet slug length is higher for air-water compared with air-oil.A slug dissipation model is developed using the slug-tracking approach, which is based on the flow mechanisms of liquid shedding at the back of the slug and liquid drainage and penetration of bubble turning at the front of the slug. These phenomena result in different translational velocities at the back and the front of the slug, which result in the dissipation of the slug body. Evaluation of model predictions against the acquired experimental data shows an average absolute relative error of less than 11%.

Bubble characterization and gas–liquid interfacial area in two phase gas–liquid system in bubble column at low Reynolds number and high temperature and pressure

Bubbles hydrodynamic in gas–liquid contactor, including bubble size distribution, bubble size and gas–liquid interfacial area, was evaluated as a function of superficial gas velocity, superficial liquid velocity, temperature, pressure and different gases (N2 and He) and liquids (water and ethanol/water mixture) phases. The results showed that with the increase of superficial gas velocity, the bubble size distribution shifted from smaller- to larger-size bubble and the Sauter mean diameter, the gas holdup and the interfacial area generally increased due to the increase of coalescence. The effect of superficial liquid velocity on bubble characteristics was not significant. Pressure and temperature showed slight influence on gas holdup and interfacial area. The bubble characteristics were not significantly influenced by the type of gas phase, but mainly affected by the liquid composition. Correlations to predict Sauter mean bubble diameter and the gas holdup are developed using Kanaris correlation and in good agreement with experimental results.

A numerical study with experimental validation of liquid-assisted fluidization of particle suspensions in a HydroFloat cell

Fluidization can assist in coarse particle flotation. Here the dynamic behaviors of three-dimensional flows of particle suspensions (without air bubbles) in the counter-gravity regime in a HydroFloat cell with a circular cross-section are numerically studied by using the Eulerian-Eulerian approach with the RNG k−ε turbulence model. The kinetic theory of granular flow is adapted to analyze the particle behaviors. Simulation results are validated by using a laboratory-scale HydroFloat cell. The effect of superficial liquid velocities on the fluidized beds of spherical and non-spherical particles is investigated. The predicted results are within 4% of experimental results of bed expansion. The pressure drop and bed expansion of non-spherical particles are higher than those of spherical particles. Distributions of time-averaged particle axial velocity, particle volume fraction, particle kinetic energy, liquid turbulent kinetic energy, and dispersion rate are examined. The simulation results show that the particle kinetic energy is high near the column wall and low in the central region. The energy flows and the efficiency of energy transfer from the liquid phase to the solid phase in the fluidized bed cell are calculated and examined. Finally, the obtained data are analyzed to develop a correlation for the overall particle volume fraction, which would be useful for further studies of three-phase bubble-particle fluidization in flotation.

Relationship between scouring efficiency and overall concentration of fluidized granular activated carbon (GAC) in microfiltration

The use of liquid–solid fluidization as a means of membrane fouling mitigation has aroused increasing attention especially in membrane bioreactors. Past studies have affirmed a relationship between the fluidized GAC media and fouling trends, and also shed light on the effects of superficial liquid velocity, power requirement, GAC particle diameter and foulant type on the effectiveness of fouling mitigation during microfiltration. In particular, the ratios of the local critical flux to the overall critical flux (Jc,local/Jc,overall) were shown to deviate from unity, owing to different expanded bed heights of the fluidized GAC and causes non-uniform fouling across the membrane. Accordingly, this study was aimed at understanding the impact of different overall GAC concentrations, which give different expanded bed heights, on the extent of fouling mitigation. Monodisperse millimeter-sized GAC were used as the fluidized media and the particulate foulants were micrometer-sized polystyrene and bentonite particles. The results indicate that the highest overall concentration was advantageous in terms of enabling (i) higher membrane fouling mitigation at a lower power required per unit permeate (Pp) for the polystyrene foulant but not bentonite foulant; and (ii) more similar Jc,local values over the three heights investigated, which implies more uniform fouling mitigation across the membrane. The relative benefits of adjusting overall GAC concentration versus the particle diameter of the GAC media were also critically assessed.

Gas–liquid flow mass transfer in a T-shape microreactor stimulated with 1.7 MHz ultrasound waves

Abstract This paper describes the application of ultrasound waves on hydrodynamics and mass transfer characteristics in the gas–liquid flow in a T-shape microreactor with a diameter of 800 μm. A 1.7 MHz piezoelectric transducer (PZT) was employed to induce the vibration in this microreactor. Liquid side volumetric mass transfer coefficients were measured by physical and chemical methods of CO2 absorption into water and NaOH solution. The approach of absorption of CO2 into a 1 mol·L− 1 NaOH solution was used for analysis of interfacial areas. With the help of a photography system, the fluid flow patterns inside the microreactor were analyzed. The effects of superficial liquid velocity, initial concentration of NaOH, superficial CO2 gas velocity and length of microreactor on the mass transfer rate were investigated. The comparison between sonicated and plain microreactors (microreactor with and without ultrasound) shows that the ultrasound wave irradiation has a significant effect on kLa and interfacial area at various operational conditions. For the microreactor length of 12 cm, ultrasound waves improved kLa and interfacial area about 21% and 22%, respectively. From this study, it can be concluded that ultrasound wave irradiation in microreactor has a great effect on the mass transfer rate. This study suggests a new enhancement technique to establish high interfacial area and kLa in microreactors.

Experimental Investigation on Disturbance Wave Velocity and Frequency in Air-Water Horizontal Annular Flow

The wave characteristics of horizontal air-water annular two-phase flow in 16 and 26-mm-diameter pipe were investigated experimentally using flush-mounted constant electric current method (CECM) sensors and visual observations. The air and water superficial velocities were varied from 12 to 40 m/s and 0.05 to 0.2 m/s, respectively. The flow morphology of annular flow such as the disturbance wave, ripple, wave coalescence, wave development, entrainment, and breakup could be observed. Using cross correlation and power spectral density functions of liquid holdup signals, the wave velocity and frequency were determined. The effect of superficial liquid velocity on the wave velocity and frequency was found to be less significant compared to that of superficial gas velocity. Simple correlations for wave velocity and frequency were also developed.

Statistical analysis and hydrodynamic modeling of unsteady gas–liquid slug velocity behavior

Abstract Slug flow is the dominant two-phase flow pattern in horizontal and slightly inclined multiphase transport pipelines. Slugs generate and dissipate along pipelines due to the unsteady nature of slug flow, which gives rise to the time-dependent behavior, where the pressure, mass flow and velocity vary with time. The velocity of a newly initiated developing slug exhibits unsteady behavior downstream of the initiation point. The objective of this study is to experimentally investigate the unsteady velocity behavior of newly initiated slugs at a pipeline dip. A further objective is to develop a simple transient model to predict the development of slug velocity in time and space beyond the initiation point. Experimental observations show that pseudo-slugs initiated at the bottom elbow initially accelerate, then decelerate at a region near the uphill pipe section exit. Detailed analysis of the slug velocity distribution shows that the acceleration and deceleration phenomena are related to the slug growth and dissipation along the pipe. Furthermore, the maximum slug velocity is observed approximately at a dimensionless distance ( x / D ) of 110 from the pipeline dip where slugs are initiated. The investigation of operational and geometrical parameter effects showed that gas and liquid superficial velocities have a significant effect on slug velocity. However, the effect of superficial liquid velocity decreases as the flow develops along the pipeline. The experimental results show that an increase of 1° inclination angle promotes slug acceleration and deceleration trends significantly. A theoretical model based on a momentum balance and the equation of state for gases predicted the acceleration trend quite well close to the initiation point. The model error in predicting slug velocity increases as the pipe dimensionless distance increases due to the model's assumption of a single slug evolution. The developed model can be used as a predictive tool to estimate the distance required to accelerate a slug to its maximum velocity, and ultimately the location of flow related erosion/corrosion and produced sand accumulation and transportation.

The ozone mass transfer characteristics and ozonation of pentachlorophenol in a novel microchannel reactor

A “T” junction microchannel was employed to investigate the ozone mass transfer characteristics without chemical reaction taking place in the solution firstly. The correlations of the experimental kLα values with dimensionless numbers: ShL, Ret, ReL, Sc for Taylor, slug–annular and churn flow regimes were proposed through a least square regression method. The gas–liquid interfacial area was determined by chemical adsorption method in the present work. The results indicated that the effect of superficial liquid velocity on the interfacial area was insignificant compared with that of superficial gas velocity. And on the basis of the interfacial area determined above, the liquid side ozone mass transfer coefficient under varied superficial gas and liquid velocities was calculated. The mass transfer rate was accelerated in the presence of PCP in solution. The reaction rate between PCP and O3 was proved to fell in the instantaneous regime based on the experimental results of EO3 increasing with either liquid PCP concentration or the reciprocal interfacial ozone concentration, (CO3,L,i)−1. In addition, further studies indicated that dissociation of PCP and the elevation of the average mass transfer driving forces caused by increasing pH and gaseous ozone concentration, respectively, availed the degradation of PCP in the microchannel.

Two-dimensional volume of fluid simulation studies on single bubble formation and dynamics in bubble columns

In this paper, the volume of fluid (VOF) model in conjunction with continuum surface force (CSF) model was used to numerically investigate the single bubble formation and dynamics in the bubble columns on the software platform of Fluent 6.3. A set of transient conservation equations of mass and momentum taking surface tension and gravitational force effects into consideration were solved by pressure implicit splitting operator (PISO) algorithm and a piecewise linear interface calculation (PLIC) was applied to characterize the behavior of gas–liquid interface movement in the VOF method. The simulation results of bubble formation and dynamics compare well with available literature results. The effects of physical properties including surface tension, liquid viscosity and density, gas or liquid operation conditions and orifice size on the single bubble generation, detachment, rising and coaxial bubble coalescence were systematically analyzed, and the effect of superficial liquid velocity on single bubble behavior was especially discussed. It is found that non-zero superficial liquid velocity enhances the bubble detachment, decreases the bubble size, and delays the coaxial bubble coalescence obviously. Increasing superficial liquid velocity largely raises the velocity of the leading bubble and enlarging orifice gas velocity mainly accelerates the second bubble of two coalescence bubbles.

Axial Mixing in a Novel Perforated Plate Bubble Column

This investigation reports the experimental and theoretical results carried out to evaluate the axial dispersion number for an air-water system in a novel hybrid rotating and reciprocating perforated plate bubble column for single phase and two phase flow conditions. Axial dispersion studies are carried out using stimulus response technique. Sodium hydroxide solution is used as the tracer. Effects of superficial liquid velocity, agitation level and superficial gas velocity on axial dispersion number were analyzed and found to be significant. For the single phase (water) flow condition, it is found that the main variables affecting the axial dispersion number are the agitation level and superficial liquid velocity. When compared to the agitation level, the effect of superficial liquid velocity on axial dispersion number is more predominant. The increase in superficial liquid velocity decreases the axial dispersion number. The same trend is shown by agitation level but the effect is less. The rotational movement of the perforated plates enhances the radial mixing in the section; hence, axial dispersion number is reduced. For the two phase flow condition, the increase in superficial liquid velocity decreases the axial dispersion number, as reported in the single phase flow condition. The increase in agitation level decreases the axial dispersion number, but this decreasing trend is non-linear. An increase in superficial gas velocity increases the axial dispersion number. Correlations have been developed for axial dispersion number for single phase and two phase flow conditions. The correlation values are found to concur with the experimental values.

Enhanced liquid–solid mass transfer by carbon nanofibers on solid foam as catalyst support

This paper presents the liquid–solid mass transfer characteristics for Pd-catalyst on carbon nanofiber (CNF) covered reticulated vitreous carbon (RVC) foam (hairy foam). RVC foam was used with 20, 45, and 60 pores per linear inch (PPI), covered with CNFs synthesized at 773, 873, and 973 K. The effects of superficial liquid velocity ( u l = 4.3 × 10 - 3 to 77 × 10 - 3 m l 3 m r - 2 s - 1 ) and reaction temperature (323 and 343 K) are studied using the fast liquid phase oxidation of sodium formate. The overall reaction rate coefficient ( k ov ) increases with decreasing PPI number. k ov for 20 PPI CNF/RVC foam is significantly higher than for regular foam packings and random packings, ranging from 0.15 to 0.90 m l 3 m r - 3 s - 1 . k ov 's for 45 and 60 PPI CNF/RVC foams are higher than for regular foam packings and approximately equal to random packings, ranging from 0.075 to 0.36 m l 3 m r - 3 s - 1 . k ov 's for CNF/RVC foam with CNFs synthesized at 773 and 873 K are approximately equal, ranging from 0.07 to 0.4 m l 3 m r - 3 s - 1 . For CNFs synthesized at 973 K, k ov is significantly higher, ranging from 0.18 to 0.57 m l 3 m r - 3 s - 1 . The high liquid–solid mass transfer rates of CNFs on solid foam with respect to regular foam is attributed to the hydrodynamic accessibility of the CNFs. The pressure drop of the CNF/RVC foam ( < 4000 Pa m - 1 ) is significantly lower than for random packings ( 5.2 × 10 3 to 1.2 × 10 6 Pa m - 1 ). This shows that higher or at least equivalent mass transfer rates can be obtained, but at a considerably lower pressure drop than for random packings.

L–S mass transfer in G–L–S countercurrent magnetically stabilized bed with amorphous alloy SRNA-4 catalyst

Liquid–solid (L–S) mass transfer coefficients ( K s) were characterized in a gas–liquid–solid (G–L–S) three-phase countercurrent magnetically stabilized bed (MSB) using amorphous alloy SRNA-4 as the solid phase. Effects of superficial liquid velocity, superficial gas velocity, magnetic field strength, liquid viscosity and surface tension were investigated. Experimental results indicated that the external magnetic field increased K s in three-phase MSB, as compared to those in conventional G–L–S fluidized beds; that K s increased with magnetic field strength, superficial gas and liquid velocities and decreased with liquid viscosity and surface tension; and that K s showed uniform axial and radial distributions except for small increases close to the wall. Dimensionless correlations were established to estimate K s of the G–L–S countercurrent MSB using SRNA-4 catalyst, with an average error of 3.6%.

Minimum Fluidization Velocity in a Three Phase Inverse Fluidized Bed Reactor with Newtonian and Non-Newtonian Fluids

The influence of operational parameters and the effect of viscosity on minimum fluidization velocity, Ulmf (minimum fluidization liquid velocity) and Ugmf (minimum fluidization gas velocity) were investigated in a three-phase inverse fluidized bed reactor using low-density polyethylene (LDPE) and polypropylene (PP) particles. The Ulmf showed an increasing trend with an increase in particle diameter. The effect of superficial gas velocity, Ug on Ulmf and the effect of superficial liquid velocity, Ul on Ugmf for water, glycerol and carboxy methyl cellulose (CMC) as the liquid phase were studied. With an increase in Ug, the Ulmf decreased and with an increase in Ul, the Ugmf also decreased. With an increase in the viscosity (concentration) of glycerol and CMC, Ulmf decreased. Correlations for the prediction of Ulmf in Newtonian and non-Newtonian systems are proposed.

Mass transfer from the wall of a column to the fluid in a fluidized bed of inert spherical particles

Mass transfer in fluidized beds is an important operation for separation processes. Two effects can be achieved by using fluidized beds in mass transfer processes increasing interface area and relative movement between the phases. These effects are both desirable because they lead to greater process rates. This paper presents an experimental investigation regarding mass transfer from the wall of a column to the fluid in a fluidized bed of inert spherical particles. The experiments were conducted in column 40 mm in diameter with spherical particles 0,8-3 mm in diameter and water as one fluidizing fluid. The method of dissolution of benzoic acid was used to provide very low mass flux. The average wall-to-fluid mass transfer coefficients were determined for two systems: single-phase fluid flow and a fluidized bed of inert particles The measurements encompassed a Reynolds number range from 100-4000 for single-phase flow and 600-4000 in fluidized beds. The mass transfer coefficients for both systems were calculated from weight loss of benzoic acid. The effects of superficial liquid velocity and particle diameter on the mass transfer coefficient were investigated. It was found that mass transfer was more intensive in the fluidized bed in comparison with single phase flow. The best conditions for mass transfer were reached at a minimum fluidization velocity, when the mass transfer coefficient had the greatest value. The experimental data were correlated in the form: jd = f(Re), where jd is the dimensionless mass transfer factor and Re the Reynolds number.

Fixed-bed study for lanthanide (La, Eu, Yb) ions removal from aqueous solutions by immobilized Pseudomonas aeruginosa: experimental data and modelization

A fixed-bed study was carried out by using cells of Pseudomonas aeruginosa immobilized in polyacrylamide gel as a biosorbent for the removal of lanthanide (La, Eu, Yb) ions from aqueous solutions. The effects of superficial liquid velocity based on empty column, particle size, influent concentration and bed depth on the lanthanum breakthrough curves were investigated. Immobilized biomass effectively removed lanthanum from a 6 mM solution with a maximum adsorption capacity of 342 μmol g −1 (±10%) corresponding closely to that observed in earlier batch studies with free bacterial cells. The Bohart and Adams sorption model was employed to determine characteristic parameters useful for process design. Results indicated that the immobilized cells of P. aeruginosa enable removal of lanthanum, europium and ytterbium ions from aqueous effluents with significant and similar maximum adsorption capacities. Experiments with a mixed cation solution showed that the sequence of preferential biosorption was Eu 3+⩾Yb 3+>La 3+. Around 96±4% of the bound lanthanum was desorbed from the column and concentrated by eluting with a 0.1 M EDTA solution. The feasibility of regenerating and reusing the biomass through three adsorption/desorption cycles was suggested. Neural networks were used to model breakthrough curves performed in the dynamic process. The ability of this statistical tool to predict the breakthrough times was discussed.

Effect of System Pressure on Frictional Pressure Gradient in Vertical Upward Gas-Liquid Two-Phase Flow. Experimental Results on Pressure Drop for System Pressure from 0.3 to 20 MPa.

In order to clarify the pressure effects on frictional pressure gradients in vertical upward gas-liquid two-phase flow, measurements of pressure gradients were made for a pressure range of 0.3∼20 MPa. Frictional pressure gradients for each system pressure were presented and it was revealed that the effects of superficial liquid velocity on the frictional pressure gradient gets smaller with increasing system pressure. Furthermore, the characteristic is clarified that there exist minimum values with increasing superficial gas velocity in the pressure range of 10∼20 MPa. Comparison of measured values of frictional pressure gradients with the correlations proposed by Lockhart-Martinelli and Chisholm were made and these correlations were found not to be valid for the data at high pressure conditions. A new correlation to predict friction pressure gradients was proposed.

Radial nonuniformity of flow structure in a liquid-solid circulating fluidized bed

Electrical conductivity probes were used to measure the radial distributions of solids holdup and liquid velocity in a liquid-solid circulating fluidized bed. These distributions are found to be non-uniform, unlike those in a non-circulating bed. The effects of superficial liquid velocity and particle circulation rate on the radial distributions of bed voidage and liquid velocity are studied. Based on the experimental results, a qualitative explanation is given for the difference between the dispersed fluidization and the circulating fluidization. The effect of the radial nonuniformity of the flow structure on the reactions in the liquid-solid circulating fluidized bed reactor is also discussed.

Modelling of three-phase sparged reactor: Non-uniform solid concentration profile

Models have been developed in order to obtain the non-uniform concentration profiles and the exit age distribution of the solid phase in three-phase sparged reactors. The constant-size particles as well as the dissolving particles have been considered. Procedures have been developed for the estimation of solid-phase residence time even though the net particle velocity is in the backward direction. The effects of superficial liquid velocity, particle size and solid-phase dispersion coefficient on solid-phase residence time have been investigated. Using the exit age distribution and the conversion—time relationships for single particles, performance charts have been constructed for when the rate-controlling step is associated with the solid phase. Several reaction mechanisms have been considered for the construction of performance charts. It has been shown that the design of reactor outlet is very important and governs the solid-phase concentration profile within the reactor. An attempt has been made to propose a theoretical boundary condition at the reactor outlet for a non-uniform solid concentration profile of constant-size particles. The relationship between the design of the outlet and the concentration jump at the outlet has been analysed.

GAS HOLD-UP AND BACKMIXING IN A BUBBLE-COLUMN REACTOR UNDER COAL-HYDROLIQUEFACTION CONDITIONS

Abstract Gas hold-up and the extent of liquid-phase backmixing have been investigated experimentally at room temperature and under coal hydroliquefaction conditions (viz. temperature 164 to 384°C and pressure between 4.5 to 15 MPa) using a continuous tubular bubble-column reactor of small diameter (1.9 cm) and large length to diameter ratio. Gas hold-up is affected by superficial gas velocity and temperature particularly above 300°C. The effects of superficial liquid velocity, gas molecular weight and pressure are negligible. Liquid-phase dispersion coefficient and Peclet number are strongly dependent on superficial gas velocity. The modified correlation of Hikita et al. (1980) for the fractional gas hold-up is found to fit the experimental data at high temperatures after corrections have been applied for dissolution of gas and liquid vaporization. Literature correlations derived from two- and three-phase systems are found to be inapplicable under coal hydroliquefaction conditions for [vcirc]G < 1 cm/s. E...