Hydrodynamics and heat transfer in a plasma spouted bed reactor

The literature reveals very little intformation about plasma spouted bed hydrodynamics. Spouting of corindon particles with diameters ranging from 0.4 to 3.36 mm with argon plasma was conducted in a 90-mm-diameter column in the temperature range 300–1300°C. It was found that the maximum spoutable height (H_m) decreases with increasing particle diameter and decreasing mean bed temperature. A relation between the inlet plasma velocity and H_m is proposed. Concerning heat transport phenomena in the annulus, measurements and calculations indicate a large axial diffusivity but a poor radial mixing. Typical values of D_z and D_r are proposed on the basis of an identification procedure.Notation Ar Archimede number - Ar d ³ p (p — f) _f g ² - C_p specific heat - d_p particle diameter - d_e core diameter (or spout diameter) - D_i fluid inlet orifice diameter - D_e column diameter - D_r and D_z radial and axial diffusivity, respectively - g acceleration due to gravity - H packed static bed height - H_b bed height - H_m maximum spoutable bed height - P power     

Hydrodynamics and mixing in three-phase fluidized bed bioreactors

The effects of solid particles on hydrodynamics and mixing in a three-phase fluidized bed bioreactor were discussed. The gas holdup, bubble size, and liquid-phase axial dispersion coefficient were measured in a 0.25-m id bubble column bioreactors containing low-density particles. The presence of low-density solid particles slightly increased gas holdup. The decrease in average bubble diameter with solid presence was found. For the three-phase system, the liquid-phase axial dispersion coefficients were higher than for the two-phase system. We extended a model for a gas holdup developed for a gas-liquid two-phase bubble column bioreactor to a gas-liquid-solid three-phase fluidized bed bioreactor. Using the present data and available data in the literature, the predictions of the proposed model were examined. The proposed model agreed with a wide range of the experimental data. A theoretical correlation for liquid-phase axial dispersion coefficient was developed using Kolmogoroff's theory of isotropic turbulence. Reasonable agreement was obtained between the predicted and experimental values of axial dispersion coefficient.     

Vanadium separation with activated carbon and iron/activated carbon nanocomposites in fixed bed column: experimental and modelling study

In this work, iron nanoparticles were impregnated onto a commercial activated carbon surface to produce a novel adsorbent called iron-activated carbon nanocomposite (I-AC). Commercial activated carbon (CAC) and I-AC were used for vanadium separation in a fixed-bed column. The effects of various operating parameters such as inlet vanadium ion concentration, adsorbent dose and volumetric flow rate on vanadium separation performance of CAC were investigated. The performance of both adsorbents was compared in three adsorption/desorption cycles. The experimental breakthrough curves of vanadium ions in the fixed-bed column were modeled using the film-pore-surface diffusion model (FPSDM). The four mass transfer parameters characterizing this model, namely the external mass-transfer coefficient (k _f ), pore and surface diffusion coefficients (D _p and D _s ), and axial dispersion coefficient (D _L ) were evaluated through the model. Modelling and experimental results showed that the I-AC nanocomposite has a better performance for vanadium separation in comparison to AC. Sensitivity analysis on the FPSDM showed that the pore and surface diffusion, external mass transfer and axial dispersion play a significant role in vanadium separation using the I-AC. On the other hand, surface diffusion resulted to be relatively less important when CAC was used.     

Use of an automated tension cell to measure physical properties of colloidal systems

A tension cell device is described which is able to automatically collect outflow data and maintain constant loads (2 cm to 18 cm H₂O) for flow systems involving water saturated, deformable porous media. Using the theoretical apparatus presently available for analyzing such systems, various flow parameters are obtained:k, permeability;a, coefficient of bulk compressibility; andD _m, the material diffusivity. The flow parameters are a function of a variety of structural factors, which are controlled to a large extent by the nature of the forces operating between particles. Thus, the values fork, a andD _m are applied to the problem of understanding structure in relatively dilute colloidal systems. Two different aluminum hydroxycarbonate materials are examined, each having a pH dependent surface charge but different in surface area. Because of their particular properties, structural differences between cohesive particle networks (occurring at the point of zero charge (pzc)) and swelling type systems (at pH values much different than pzc) may be examined.     

Expansion and hydrodynamic properties of β-cyclodextrin polymer/tungsten carbide composite matrix in an expanded bed

The expansion and hydrodynamic properties of matrix are significant for expanded bed adsorption (EBA) processes. A series of new composite matrices CroCD-TuC are studied and estimated in an expanded bed. It is found that the heavier matrix is better suited for high operation fluid velocity than the lighters. Although the Richardson–Zaki equation can well correlate the bed voidage with fluid velocity for all CroCD-TuC matrices tested, the modifications are proposed to improve the accuracy of theoretical predictions of correlation parameters, including terminal settling velocity (U_t) and expansion index (n). Residence time distributions (RTDs) are determined, and the Bodenstein number (Bo) and axial dispersion coefficient (D_ax) are employed to analyze the liquid mixing in the expanded bed. It is found for CroCD-TuC matrices, both parameters notably changed with the variation of fluid velocity and viscosity. Furthermore, D_ax is an intuitive parameter estimating the bed stability on various operating conditions, and also a restriction on developing the matrix for high operation fluid velocity. The comparison of the hydrodynamic properties on different matrices reveals that CroCD-TuC 3 and CroCD-TuC 4 seem superior to other matrices in hydrodynamic properties, making them promising matrices for further use. The correlations as the functions of fluid velocity and viscosity have been established which may provide beneficial information for practical applications of CroCD-TuC matrices in EBA processes.     

Characterization and evaluation of a macroporous adsorbent for possible use in the expanded bed adsorption of flavonoids from Ginkgo biloba L.

The suitability of the use of macroporous adsorbent Amberlite XAD7HP in expanded bed adsorption processes for the isolation of flavonoids from crude extracts of Ginkgo biloba L. has been assessed. The expansion and hydrodynamic properties of expanded beds were investigated and analyzed. The bed expansion as a function of operational fluid velocity was measured and correlated with the Richardson–Zaki equation. Theoretical predictions of the correlation parameters (the terminal settling velocity u_t and exponent n) were improved by modifying equations in the literature. Residence time distributions (RTDs) were studied using acetone as a tracer. Three measures of liquid phase dispersion (the height equivalent of theoretical plate, Bodenstein number and axial distribution coefficient) were investigated and compared to values previously obtained with commercial EBA adsorbents developed for protein purification. A suitable bed expansion ratio was found to be 1.25 times the settled bed height, which occurred at a corresponding flow velocity of 183 cm/h. For an initial settled bed height of 42 cm, the mean residence time of liquid in the expanded bed was around 28 min. Under these flow conditions, the axial mixing coefficient D_ax was 7.54 × 10⁻⁶ m²/s and the Bodenstein number was 28; the number of theoretical plates (N) was 19 and the height equivalent of a theoretical plate (HETP) was 2.77 cm. Rutin trihydrate was used as a model flavonoid for the characterization of the adsorption properties of Amberlite XAD7HP. Adsorption was observed to reach equilibrium within 3 h with 70% of the adsorption capacity being achieved within 30 min. The estimated maximum equilibrium adsorption capacity for rutin was estimated to be 43.0 mg/(g resin) when the results were fitted to Langmuir isotherms. The adsorption performance was not seriously impaired by the physical presence of G. biloba leaf powders. Assessment of the kinetics of the adsorption of rutin revealed that the rate constant for adsorption was only reduced by 15% in the presence of leaf powders at a concentration of 50 mg/mL. The results demonstrated that Amberlite XAD7HP should be suitable for expanded bed adsorption of flavonoids from crude extracts of G. biloba L.     

Evolution of phase dimensions and interfacial morphology of polypropylene/polystyrene compatibilized blends during mixing

The morphology development of polypropylene/polystyrene (PP/PS) blends was studied by means of effective mathematics methods. Time resolved fracture morphology measurements on PP/PS (20/80) blends compatibilized with styrene-butadiene-styrene block copolymer (SBS) suggested that PP/SBS domains acted as a warehouse supplying compatibilizer (SBS) to the phase boundary in the initial stage of mixing and promoted the formation and development of the transition layer. The development of the transition layer leaded to a more complicated morphology of fracture surface and strengthened the adhesion between phases, which was quantitatively investigated using Brown fractal dimension D_Brown. In the early stage of the mixing (<2.0 min), the mean chord length Λ_m used to describe the domain size decreased; simultaneously, the distribution of Λ trended to uniform as the mixing proceeded. After 2.0 min, Λ_m fluctuated in a definite range. Further, a normalized distribution of dimensionless domain sizes Λ/Λ_m was independent of mixing time, indicating that the late stage of phase dispersion can be scaled with a time-depended single length parameter Λ_m. In other words, the morphology development shows a possible dynamic scaling behavior.     

Effective intraparticle diffusion coefficients of CoCl2 in mesoporous functionalized silica adsorbents

The scope of this work is to determine the effective intraparticle diffusion coefficient of CoCl₂ over mesoporous functionalized silica. Silica is selected as a carrier of the functionalized groups for its rigid structure which excludes troublesome swelling, often found in polymeric adsorbents. 2-(2-pyridyl)ethyl-functionalized silica is selected as a promising affinity adsorbent for the reversible adsorption of CoCl₂. The adsorption kinetics is investigated with the Zero Length Column (ZLC) method. Initially, experiments were performed at different flow rates to eliminate the effect of external mass transfer. The effect of pore size (60 Å and 90 Å), particle size (40?10^?6 m–1000?10^?6 m) and initial CoCl₂ concentration (1 mol/m³–2.0 mol/m³) on the mass transfer was investigated. A model was developed to determine the pore diffusion coefficient of CoCl₂ by fitting the experimental data to the model. The pore diffusion coefficients determined for two different pore sizes of silica are D _p (60 Å) =1.95?10^?10 [m²/s] and D _p (90 Å) =5.8?10^?10 [m²/s]. The particle size and the initial CoCl₂ concentration do not have an influence on the value of diffusion coefficient. However, particle size has an influence on the diffusion time constant. In comparison with polymer adsorbents, silica based adsorbents have higher values of diffusion coefficients, as well as a more uniform and stable pore structure.     

Kinetics of water sorption on a CaCl2-in-silica-gel-pores sorbent: The effects of the pellet size and temperature

Kinetics of water vapor sorption on the CaCl₂-in-KSK-pores composite (SWS-1L) have been studied at T = 33–69°C and vapor pressures of 8–70 mbar for pellet sizes of 2R _pel = 0.355–0.425, 0.71–0.85, and 1.2–1.4 mm. Sorption has been measured under isothermal conditions on a thermobalance by abruptly raising the vapor pressure in the measurement cell by a small value and then maintaining the new pressure. In the initial portion of the kinetic curves, the amount of sorbed water (Δm) increases in proportion to the sorption time (t) to the power 1/2. From the slope of the Δm versus t ^1/2 curve, it is possible to derive the sorption rate constant k _D = D _eff/R ² _pel and the effective diffusivity D _eff. The latter is independent of R _pel for 2R _pel ≥ 0.71 mm. The rate of water sorption on smaller (0.355-to 0.425-mm) pellets grows less rapidly, apparently because of the effect of the heat of sorption. The effective diffusivity is determined by the local slope of the water vapor sorption isotherm for SWS-1L. Applying an appropriate correction enables one to calculate the effective diffusivity for water vapor in the sorbent pores, which appears to be D _e = (0.35 ± 0.17) × 10^?6 m²/s. This value is approximately 10 times smaller than the Knudsen water diffusion coefficient calculated for a single cylindrical pore with a size equal to the average pore size of the composite. Two possible causes of this discrepancy are discussed, specifically, an increase in the pore tortuosity because of the presence of the salt and the interaction between water and the salt.     

Ternary diffusion coefficients of diethylene glycol and lithium chloride in aqueous solutions containing diethylene glycol and lithium chloride

In this work, ternary diffusion coefficients of diethylene glycol and lithium chloride in aqueous solutions containing diethylene glycol and lithium chloride were reported for temperatures (303.2, 308.2, and 313.2 K) using the Taylor dispersion method. The investigated ternaries contained total glycol–salt concentrations of 10, 15, and 20 wt%. The main diffusion coefficients (D₁₁ and D₂₂) and the cross-diffusion coefficients (D₁₂ and D₂₁) were discussed as function of temperature and concentration. A modified equation originally proposed by Batchelor [1] for mixture of hard spheres in a continuum solvent was used to correlate the present diffusion coefficient data and the results are satisfactory.     

Measurement of diffusion and partition coefficients of ferrocyanide in protein-immobilized membranes

True diffusion (D_m) and partition (α) coefficients for the transport of potassium ferrocyanide through diaphorase (Dp)- and bovine serum albumin (BSA)-glutaraldehyde (GA) membranes with different cross-linking degrees of 1-8% GA concentrations immobilized on gold electrodes are investigated by using potential-step method and rotating-disk-electrode method. The thickness of dry and hydrated immobilized membranes is accurately measured by the focus-difference method with a reflection microscope. The thickness of hydrated Dp-GA and BSA-GA membranes are about 1.4 and 2.4 times that of dry membranes, respectively. In addition, the actual area of electrode surface is calculated by the charge amount of chemisorbed oxygen on gold electrode. Owing to the increase of swelling degree and net negative charge of the immobilized membranes, the values of D_m and α for both of Dp-GA and BSA-GA membranes enlarge and decrease with increase of GA concentration, respectively. Furthermore, BSA-GA membranes possess greater D_m and α than those of Dp-GA membranes due to the thinner thickness and the greater swelling degree of BSA-GA membranes.     

Numerical study of nitrogen desorption by rapid oxygen purge for a medical oxygen concentrator

Efficient desorption of selectively adsorbed N₂ from air in a packed column of LiX zeolite by rapidly purging the adsorbent with an O₂ enriched gas is an important element of a rapid cyclic pressure swing adsorption (RPSA) process used in the design of many medical oxygen concentrators (MOC). The amount of O₂ purge gas used in the desorption process is a sensitive variable in determining the overall separation performance of a MOC unit. Various resistances like (a) adsorption kinetics, (b) column pressure drop, (c) non-isothermal column operation, (d) gas phase mass and thermal axial dispersions, and (e) gas-solid heat transfer kinetics determine the amount of purge gas required for efficient desorption of N₂. The impacts of these variables on the purge efficiency were numerically simulated using a detailed mathematical model of non-isothermal, non-isobaric, and non-equilibrium desorption process in an adiabatic column. The purge gas quantity required for a specific desorption duty (fraction of total N₂ removed from a column) is minimum when the process is carried out under ideal, hypothetical conditions (isothermal, isobaric, and governed by local thermodynamic equilibrium). All above-listed non-idealities (a?Ce) can increase the purge gas quantity, thereby, lowering the efficiency of the desorption process compared to the ideal case. Items (a?Cc) are primarily responsible for inefficient desorption by purge, while gas phase mass and thermal axial dispersions do not affect the purge efficiency under the conditions of operation used in this study. Smaller adsorbent particles can be used to reduce the negative effects of adsorption kinetics, especially for a fast desorption process, but increased column pressure drop adds to purge inefficiency. A?particle size range of ??300?C500???m is found to require a?minimum purge gas amount for a given desorption duty. The purge gas requirement can be further reduced by employing a pancake column design (length to diameter ratio, L/D<0.2) which lowers the column pressure drop, but hydrodynamic inefficiencies (gas mal-distribution, particle agglomeration) may be introduced. Lower L/D also leads to a smaller fraction of the column volume that is free of N₂ at the purge inlet end, which is required for maintaining product gas purity. The simulated gas and solid temperature profiles inside the column at the end of the rapid desorption process show that a finite gas-solid heat transfer coefficient affects these profiles only in the purge gas entrance region of the column. The profiles in the balance of the column are nearly invariant to the values of that coefficient. Consequently, the gas-solid heat transfer resistance has a minimum influence on the overall integrated N₂ desorption efficiency by O₂ purge for the present application.     

Diffusion of n-alkanes in mesoporous 5A zeolites by ZLC method

Diffusion properties of mesostructured zeolite 5A were investigated by employing n-alkanes as probe molecules using the zero length column (ZLC) method. The mesopores were found to enhance molecule diffusion. Moreover, the effective diffusion time constant (D _eff/R ²) increased with mesoporosity in the zeolites between 308 K and 393 K, whereas the activation energy decreased with increasing mesopore volume. The effective diffusivity values of n-alkanes in mesoporous zeolite 5A were generally higher than that the microporous zeolite 5A sample. This clearly implied the important role of the mesopore in zeolites crystals in facilitating the transport of reaction molecules due to shorter average diffusion path length and less steric hindrance.     

Axial dispersion coefficient in high-speed counter-current chromatography

Experimental measurements of axial dispersion coefficients in high-speed counter-current chromatography have been carried out in the single-phase and two-phase modes. Axial dispersion coefficients were calculated from the residence time distribution curve (or the elution profile). The experimental data obtained were used to develop a model involving Peclet number Pe, Reynolds number and the ratio of flow velocity u to linear angular velocity u_θ for predicting the axial dispersion coefficient. Furthermore, the models obtained from the single-phase and two-phase modes were compared, and a counterintuitive phenomenon was found in that the effects of the flow rate and the rotation speed on the axial dispersion coefficients are inconsistent: the axial dispersion coefficient decreases with the rotation speed and increases with the flow rate in the single-phase mode, but increases with rotation speed and decreases slightly with the flow rate in the two-phase mode.     

Determination of effective diffusion coefficients in calcium alginate gel plates with varying yeast cell content

Effective diffusion coefficients (D_e) have been determined for lactose, glucose, galactose, and ethanol in calcium alginate gel with varying yeast cell concentration. The measurements have been performed in a diffusion cell, and the results evaluated with the quasisteady-state method. An ultrasonic meter was used for gel thickness determination with an accuracy of 1.5% and a new method for the reproducible preparation of gel plates was developed. It was found thatD _e in pure alginate gel decreased to about 90% of the diffusivity in water and did not vary with alginate concentration.D _e decreased considerably with increasing yeast cell concentration. For the solutes studied, the effective diffusion coefficient can be estimated according to the equationD _e =D _eo (1 - ?)/[1+(?/2)], whereD _eo is the effective diffusivity in pure gel and ? is the volume fraction of yeast cells.     

Transport properties of annealed,drawn low-density polyethylene (LDPE)

The specific concentration c_a of methylene chloride, the zero-concentration diffusion coefficient D₀, and the concentration coefficient γ_D of the diffusivity in drawn and annealed LDPE were measured. The influence of the drawing rate, of annealing with the ends of the sample free and fixed and the effects of time of standing at room temperature after annealing were investigated. The observed transport properties are in good agreement with the microfibrillar model of fibrous structure, its relaxation during annealing, and the slow crystallization of relaxed tie-molecules upon standing at room temperature.     

Effect of dry density on 125I diffusion in GMZ bentonite

Gaomiaozi(GMZ) bentonite is regarded as the favorable candidate backfilling material for a potential repository in China.It is important to understand the diffusion behavior of 125 I in GMZ bentonite and compare the diffusion behavior in GMZ and other types of bentonite like MX-80,Avonlea,etc.Therefore,through-and out-diffusion experiments were conducted to obtain the effective diffusion coefficient(D e) and distribution coefficient(K d).A computer code named Fitting for diffusion coefficient(FDP) was used for the experimental data processing and theoretical modeling.At the dry density of GMZ bentonite from 1600-2000 kg/m 3,the D e values of 125 I were(2.4-20.4) × 10-12 m 2 /s and K d values were constants.At dry density above 1800 kg/m 3,the diffusion behaviors were almost the same,indicating that the anion exclusion was ineffective.Out-diffusion results showed that the species of 125 I may be changed during the diffusion processing.It was probably caused by some organic matters or reducing substances in GMZ bentonite.Since the main composition of bentonite is montmorillonite,similar diffusion parameters were obtained in GMZ and other types of bentonite.The relationship of D e and accessible porosity(acc) could be described by Archie’s law with exponent n = 1.2-2.8 for 125 I diffusion in bentonite,whereas n = 2.0 in GMZ bentonite.Furthermore,bentonite with the dry density of 1800 kg/m 3 was proposed as the backfilling materials used in the construction of high level radioactivity waste repository.     

Migration study of iodine in Beishan granite by a column method

The fate and migration behavior of radionuclides in environment are influenced by a series of physical and chemical processes such as advection, hydrodynamic dispersion (including mechanical dispersion and molecular diffusion), retention, chemical reaction and so on. In this study, the migration of ¹²⁵I^? in Beishan granite and the potential retention of iodine by silver halide additives were investigated by a pulse injection column method. All breakthrough curves were analyzed according to the analytical solution of transport equation and the dispersion coefficient (D), and first-order sorption constant (k) were obtained. For conservative nuclide, the dispersion behavior is only related to the dispersion medium. Silver halides were proved having sorption ability for ¹²⁵I^? in the order of AgCl > AgBr > AgI. The transport of iodine in the crushed granite column can be adequately described by the advection–dispersion equation with a first-order, irreversible sorption term. The pulse injection column method can be used as a fast method to evaluate the sorption or retention ability of solid phase.     

Validated, Stability-Indicating LC Method for Analysis of Pipenzolate Bromide and Its Hydrolysis Products

A liquid chromatographic method has been developed and validated for quantitative analysis of pipenzolate bromide (PP), its hydrolysis products, and phenobarbitone, sodium benzoate, and sodium saccharine. A 5-μm particle ODS column was used with acetonitrile–KH₂PO₄ (10 mm, pH 3.5) 40:60 (v/v), containing 5 mm heptanesulfonic acid sodium salt, as mobile phase. Quantitation was achieved by UV detection at 210 nm, on the basis of peak area. Forced degradation studies were performed on a bulk sample of PP using 0.1 M hydrochloric acid, 0.01 M sodium hydroxide, 0.33% hydrogen peroxide, heat (70 °C), and photolytic degradation. The proposed LC method was used to study the kinetics of acidic hydrolysis and pH-rate profiles of hydrolysis of PP in Britton–Robinson buffer solutions.     

Diffusion of levodopa in aqueous solutions of hydrochloric acid at 25 °C

Ternary mutual diffusion coefficients (D₁₁, D₂₂, D₁₂ and D₂₁) measured by the Taylor dispersion method are reported for aqueous solutions of {levodopa (l-dopa) + HCl} solutions at 25 °C and HCl concentrations up to 0.100 mol · dm⁻³. The coupled diffusion of l-dopa (1) and HCl (2) is significant, as indicated by large negative cross-diffusion coefficients. D₂₁, for example, reaches values that are larger than D₁₁, the main coefficient of l-dopa. Combined Fick and Nernst–Planck equations are used to analyze the proton coupled diffusion of l-dopa and HCl in terms of the binding of H⁺ ions to l-dopa and ion migration in the electric field generated by l-dopa and HCl concentration gradients.