Effect Of Superficial Velocity Research Articles

Experimental study on gas uniformity at the inlets of six cyclones in a CFB with multi-tracer gas method

To investigate the non-uniform distribution of different gases passing through the parallel cyclones, experiments were conducted on a circulating fluidized bed (CFB) equipped with six asymmetrical cyclones. A multi-tracer gas method was used, with CO, O2, and CO2 chosen to represent gases with different properties in the flue gas at the inlets of the cyclones. The uniformity of multi-gas distribution was evaluated by measuring the concentration deviations of each tracer gas passing through individual cyclones. The results indicate that the concentrations of multi-tracer gases are higher in the middle cyclone among the three, which are located on the tracer gas injection side during the test of single-side secondary air (SA) tracing. The maximum concentration deviation of tracer gases is for CO2, while the minimum is for CO. At the three cyclone inlets on the opposite side, the tracer gas with higher density exhibits a more uniform distribution, and the gas uniformity decreases as the density decreases. The effects of superficial velocity, SA ratio, bed inventory, and tracer gas injection region on the uniformity of gas distribution were studied. The results show that superficial velocity and SA ratio primarily affect the uniformity of higher density gases, while bed inventory has a greater influence on lower density gases. The gas distributions are most non-uniform, especially for CO2, when the tracer gas injection region is near the rear wall closer to the induced draft fan during the test of regional SA tracing.

Dynamics of inclined simply supported piping system subjected to slug flow

In this paper, the linear and nonlinear dynamics of a simply supported inclined piping system conveying slug flow are investigated, by using a dimensionless approach. A method is proposed for constructing equivalent flow parameters in order to achieve a dimensionless model equation. The validity of this method has been verified through the literature data. The effects of superficial velocities and inclined angle on the stability of the system, as well as post-instability nonlinear dynamical behaviors, are investigated. The linear analysis results showed that the superficial gas velocity stabilized the system at lower values, but had a destabilizing effect at higher values. The main reason is the reduction in system mass resulting from the increase in superficial gas velocity. The superficial liquid velocity negatively impacted the system's stability, necessitating evaluation through the critical pipe length. The nonlinear analysis results showed that the inclined system, in the absence of modal coupling occurrence, may exhibit chaotic behavior due to its inherent nonlinearity. The system stability could be regained as the superficial gas velocity increased following self-weight instability under low superficial gas velocity conditions. This work is helpful for the design of operating parameters to ensure the safety of the piping system.

Investigation on solid dispersion in a CFB dense region with Bluetooth tracking method and MP-PIC simulation

Solid dispersion behavior in a dense region of a six-cyclone pant-leg CFB was investigated experimentally and numerically. The Bluetooth tracking technique was used to measure the solid dispersion characteristics. The numerical simulation was done by MP-PIC model and it was extended to study the influence of tracer particle size on solid dispersion characteristics after it was verified by the tests results. Effects of superficial velocity (Ug), initial bed inventory (Hm) and bed material particle size (dpi) were tested and compared. The results showed that wall constraint in width (x) direction is smaller than depth (y) direction and the dispersion coefficient Dx can be determined by analyzing X2 and dX2/2dt respect to time. The average particle displacement X/X0 increased with Ug, Hm and decreased with dpi. The Dx, in the range of 0.0021m2/s ∼ 0.0108 m2/s, has a linear relationship respect to Ug and Hm. A correlation formula for lateral dispersion coefficient was summarized and its results were compared with the present and literatures' work.

Pyrolyzed tannery sludge as adsorbent of volatile organic compounds from tannery air emissions

The tanning industry has a great impact on the environment for the large consumption of water, the huge amount of waste generated, and the high emissions of volatile organic compounds (VOCs), used in leather finishing operations. In this study, pyrolyzed tannery sludge (PTS) was investigated, after further pyrolysis at high temperature, as a sorbent of VOCs. Pyrolysis experiments were performed at various temperatures (750–850 °C) and times (6–60 min) to evaluate the optimal operating conditions in terms of developed BET specific surface area. Fixed bed adsorption experiments were performed to determine the breakthrough curves at room temperature using an air stream containing n-butyl acetate, a VOC largely used in leather finishing products. By pyrolysis at 850 °C for 6 min the BET of PTS increased from 72 to 127 m2/g, improving its sorption capacity. The effects of superficial velocity, inlet VOC concentration, and bed height on the sorption behaviour of PTS after further pyrolysis (PPTS) were investigated. Breakthrough curves were well fitted by the Bohart-Adams model (R2 = 0.92) and the adsorption isotherms with Freundlich equation (R2 = 0.97). Preliminary sorbent desorption tests were carried out by hot air in the temperature range 100–180 °C, demonstrating the feasibility of thermally regenerating this material. Multiple adsorption/desorption cycles on the PPTS will be performed on lab scale in a future study to investigate the real sorbent recyclability.

Increase in processing flue gas flow rate while maintaining the fluidization state and filtration performance in a low-temperature continuous regeneration filter using a fluidized bed

To increase the processing gas flow rate in a fluidized bed filter, the effects of superficial velocity and fluidization state on PM filtration and combustion were examined by experiments using large bed particles (710 μm). The fluidization state at 710 μm was measured by image analysis and recurrence plot, and the superficial velocities as experimental conditions were determined to obtain almost the same fluidization state and filtration efficiency as those for small bed particles (420 μm) in previous studies. The BET-surface area of 710 μm is slightly larger than that of 420 μm, and the amount of potassium catalyst doped on large bed particles is comparable to that at 420 μm. The gas phase velocity is increased by increasing the processing gas flow rate, and the contact probability between PM and oxidizer increases. The PM combustion reaction is significantly promoted owing to the effects of the potassium catalyst and the increase in the gas phase velocity, and the minimum continuous regeneration temperature is 30 °C lower than that at 420 μm. As a result, fluidized bed filters using large bed particles can be operated in continuous regeneration mode at a bed temperature of 320 °C while maintaining a filtration efficiency of 100%.

Experimental investigation on gas-liquid two-phase flow distribution characteristics in parallel multiple channels

The maldistribution in the parallel multiple channels commonly leads to a reduction in the efficiency of heat exchangers and even causes the equipment to suffer the risk of failure. The distribution of gas–liquid two-phase slug flow when moving through the parallel multiple channels is still an unresolved problem and limited by the lack of experimental data. This work presents an experimental study on the air–water two-phase flow in the parallel multiple channels characterized by a horizontal header and 2~4 vertically-upward branches under the slug flow pattern conditions and develops a new predictive model. The effects of inlet superficial velocities and branch number have been investigated in the ranges of inlet gas and liquid superficial velocities of 1.4~25.0 and 0.2~1.7 m·s−1, respectively. Results show that the distribution characteristics of two-phase slug flow highly depend on the inlet superficial velocities which manifest in that the peak value of liquid phase flow ratio shifts to the downstream branches sequentially as the inlet superficial velocities increase. Decreasing the branch number is beneficial for the uniform distribution of each phase. A predictive model is proposed for the distribution of air–water slug flow by considering the effects of superficial velocities and branch number. The new model achieves the agreement of 91.3% for prediction distribution within the range of ±25% when compares to present experimental data and shows good agreement with previously reported experimental results of both T-junction and parallel multiple channels. The acquired experimental data and predictive model are crucial for the development and optimal design of the heat exchangers.

Effect of superficial velocity on liquid injectivity in SAG foam EOR. Part 2: Modelling

Surfactant-alternating-gas (SAG) is a favored method of foam injection, which has been proved as an efficient way for enhancing oil recovery. However, foam flow is extremely complicated, and there are still unsolved problems for foam application. One is liquid injectivity. Our previous studies suggest that the injectivity in a SAG process is determined by propagation of several banks near the injection well that are not represented by current foam models. Uniform bank properties were assumed. However, in a companion paper, our experimental results show that the dimensionless propagation velocity and the total mobility of banks during the liquid-injection period depends on superficial velocity. Shearing-thinning behavior is observed. In radial flow, the superficial velocity varies with distance from the well. In this study, we scale-up the experimental results using a radial bank-propagation model. The comparison of liquid injectivity estimated from conventional foam simulators (Peaceman equation) and the bank-propagation model show that the conventional foam models cannot represent the effect of the superficial-velocity-dependent fluid properties during liquid injection in a SAG process. The shear-thinning behavior can lead to much better liquid injectivity than expected, which should be accounted for in a field application of a SAG foam process.

Design Strategy for CO2 Adsorption from Ambient Air Using a Supported Amine Based Sorbent in a Fixed Bed Reactor

In this work, a fixed bed reactor is evaluated for CO2 capture from ambient air using an amine based ion exchange resin. Using adsorption experiments, the effect of superficial velocity and bed length on process economics is investigated. It is shown that the optimal conditions are found at an adsorption duration of 0.5–1.5 times the stoichiometric time for sorbent loading. To reduce pressure drop during adsorption, a radial flow reactor is proposed and designed for capturing CO2 from ambient air.

Electrodialysis of groundwater with heavy metal and nitrate ions under low conductivity and effects of superficial velocities

AbstractThe efficiency of separation of lead, manganese, arsenic, and nitrate from groundwater with relatively low conductivity by electrodialysis (ED) was investigated. The effects of the superficial velocities in either the diluate or concentrate cell were also evaluated to understand the relative separation rate of the four ionic compounds by ED and to examine the possibility of reducing the energy for pumping. Significant removal (i.e. 92.8–99.2%) of manganese, arsenic, and nitrate from Ilgam (Seoul, Korea) groundwater was achieved, along with removal (61.3%) of lead comparable to that of Sungbuk (Seoul, Korea) water. The superficial velocity in the concentrate cell exerted no effects on either the conductivity or current reduction, or on the separation ratios. The superficial velocity in the diluate cell increased the operation time required to obtain the requisite conductivity reduction, but exerted little effect on the separation ratios. ED could be performed at reduced water velocity to treat grou...

Hydrodynamic studies on fluidization of Red mud: CFD simulation

Hydrodynamic studies are carried out for the fluidization process using fine i.e. Geldart-A particles. Effects of superficial velocity on bed pressure drop and bed expansion is studied in the present work. Commercial CFD software package, Fluent 13.0 is used for simulations. Red mud obtained as waste material from Aluminum industry having average particle size of 77 microns is used as the bed material. Eulerian–Eulerian model coupled with kinetic theory of granular flow is used for simulating unsteady gas–solid fluidization process. Momentum exchange coefficients are calculated using the Gidaspow drag functions. Standard k–ε model has been used to describe the turbulent pattern. Bed pressure drop and bed expansion studies are simulated by CFD which are explained with the help of contour and vector plots. CFD simulation results are compared with the experimental findings. The comparison shows that CFD modeling is capable of predicting the hydrodynamic behaviors of gas–solid fluidized bed for fine particles with reasonable accuracy.

Discrete Element Study of Solid Mixing Behavior with Temperature Difference in Three-Dimensional Bubbling Fluidized Bed

This work numerically evaluates the mixing behavior of a binary mixture with the same physical properties but different temperatures in a three-dimensional bubbling fluidized bed based on the coupling of computational fluid dynamics and discrete element method. General mixing procedure and mixing index are adopted to investigate the macroscopic mixing behavior of the solid phase. Moreover, the effects of superficial velocity and the initial temperature configuration of particle groups on the temperature evolution of the system are discussed. The results show that three mixing mechanisms induced by the bubbles can be identified. The time required for a system to reach the temperature dynamic equilibrium is different from that required for the spatial mixing. With an increase in the superficial velocity, the mixing procedure is enhanced, and the temperature of each particle group distributes more uniformly. In addition, the effect of temperature configurations of different particle groups appears at the initial stage of solid mixing. This initial effect weakens slowly and even disappears with time evolution.

Determination of Mass Transfer Coefficients for A Mixture of Compost, Sugarcane Bagasse, and Granulated Activated Carbon as Packing Medium in Biofilter

ABSTRACT A laboratory-scale biofilter unit packed with a mixture of compost, sugarcane bagasse, and granulated activated carbon (GAC) in the ratio of 55:30:15 by weight was used for a biofiltration study of air stream containing benzene, toluene, ethylbenzene, and o-xylene (BTEX). The effect of superficial velocity on mass transfer coefficient for the packing was studied by maintaining gas flow rates of 3, 4, 5, 6, and 8 L min−1 for inlet concentrations of 0.1, 0.4, and 0.8 g m−3 for each of benzene, toluene, ethylbenzene, and o-xylene. The maximum elimination capacity was found to be 20.92, 22.72, 20.73, and 18.94 g m−3 h−1 for BTEX, respectively, for stated flow rates. Removal efficiency of BTEX decreased from 99% to 71% for increasing inlet concentration from 0.1 to 0.8 g m−3. Gas film mass transfer coefficient predicted by modified Onda's equation was within ±10% of the experimental values.

Effect of superficial velocity on the coking behavior of a nanozeolite-based Mo/HZSM-5 catalyst in the non-oxidative CH4 dehydroaromatization at 1073 K

The lifetime benzene and naphthalene productivity of a nanosized zeolite-based 5%Mo/HZSM-5 catalyst in the non-oxidative CH4 dehydroaromatization has been investigated at 1073 K and three different space velocities (4500, 10 000 and 30 000 mL g−1 h−1, corresponding to the superficial velocities 1.3, 3.0, and 9.0 cm s−1, respectively). The aim is to demonstrate that diffusion limitations do exist and have a strong influence on the coking behaviour and the lifetime aromatics productivity. The results showed that the catalyst deactivation rate increased with increasing CH4 superficial velocity, leading to decreased productivity. On the other hand, TPO and BET measurements of the spent samples revealed that the amount of coke accumulated in the spent samples decreased with increasing velocity, whereas their microporosity varied essentially depending upon the coke amount. Putting these observations together thus leads to a fact that less coke forms at a higher velocity but results in a more rapid deactivation and reduced productivity. As this may suggest the occurrence of non-uniform coke formation across catalyst particles, physical powdering of all spent samples and re-evaluation of the activity of all powdered samples were conducted to confirm this. It was found that the benzene formation activities of all powdered samples exhibited considerable but different degrees of recovery, and the most rapidly deactivated sample provided the greatest recovery. Thus, it is reasonably concluded that the preferential coke formation in the near-surface outer layers of catalyst particles and/or of crystal agglomerates inside the particles does occur in the nanozeolite-based catalyst at the test superficial velocities, particularly at 30 000 mL g−1 h−1. The essential cause for this occurrence is discussed in detail in the article.

The effect of flow pattern on split of two-phase flow through a micro-T-junction

An experiment has been carried out to study the phase split of water–nitrogen two-phase flow through a horizontal T-junction with a square cross section (500 μm × 500 μm), focusing on the effect of flow pattern. By comparing the results of slug, slug–annular and annular flows, it is shown that phase split characteristic of micro-T-junction highly depends on inlet flow pattern. When the inlet flow is a slug flow, it takes on gas rich in side branch. But when the inlet flow shifts to an annular flow, the side branch is rich in liquid. For an slug–annular flow, the curves show transitional characteristics. The effect of superficial velocities on the phase split of each flow pattern is considered as following: the liquid taken off decreases with an increase of liquid superficial velocity and increases with an increase of gas superficial velocity. The results have been compared to that of a 500 μm T-junction with a circular cross section. It is found that the square T-junction shows more liquid taken off at slug flow and slug–annular flow. While, at annular flow, the liquid taken off increases slower at high gas taken off in square T-junction due to cross section effect.

CFD and experimental studies of single phase axial dispersion coefficient in pulsed sieve plate column

This paper intends to study the single phase axial dispersion in pulsed sieve plate column using a combination of computational fluid dynamics (CFD) simulations and experimental measurements. Experiments and CFD simulations were conducted on 0.076 m diameter pilot scale column having standard geometry of 0.05 m plate spacing, 0.003 m hole diameter and 0.21 fractional free area. The effect of density of tracer solution and radial probe position on axial dispersion coefficient has been studied to ensure precision of the experimental measurement method. The effect of pulse velocity from 0.01 to 0.025 m/s and superficial velocity of water from 0.01 to 0.03 m/s has been studied. Simulations were carried out using commercial CFD software, FLUENT 6.2.16, with standard k– ɛ model for turbulence. An unsteady state tracer injection technique was used for axial dispersion measurement. The range of velocity ratio ( ψ = Re o / Re n ) employed in this work was 1–4 which is very low. Therefore the effect of superficial velocity, V c was found to be greater than pulse velocity. These results were critically compared with published data and it has been found that single phase axial dispersion coefficient is directly proportional to effective velocity ( Af + 0.5 V c ). The presented CFD predictions and validation with experimental data will provide useful basis for further work on single phase axial dispersion with various geometrical parameters and understanding the two phase flow patterns in pulsed sieve plate column.

Effect of scale-up of lower and middle splash region on heat transfer characteristics of circulating fluidized bed risers

In the present work, a comparative study of steady-state wall-to-bed heat transfer was conducted along the lower and middle splash region located in the riser of height 2.85 m of three different circulating fluidized beds (CFBs) with bed cross-sections of 0.15 m×0.15 m, 0.20 m×0.20 m, and 0.25 m×0.25 m. Experiments were conducted under similar operating conditions on above-mentioned three CFB set-ups using the same weight of sand per unit area of the distributor plate, non-dimensional superficial velocity ( U∗), heat flux, and sand particle size. Further, experiments were conducted on all the three CFB set-ups for five different non-dimensional air velocities ( U∗ = 5, 5.5, 6, 6.6, and 8) and two different weights of sand inventory per unit area of the distributor plate with average particle size of 460 μm. Bed temperature distributions across the lower and middle splash regions were measured and compared for the three bed cross-sections. Axial distributions of heat transfer coefficient along the height of lower and middle splash region of risers were evaluated and compared for the three bed cross-sections. The effect of superficial velocity, sand inventory, and bed cross-section on temperature and heat transfer coefficient was investigated. Based on the present study, correlations were developed for the bed Nusselt number as a function of various non-dimensional numbers for lower and middle splash regions of the riser. The non-dimensional area parameter ( A∗) was found to be a significant number. Predictions of these correlations are in agreement (±16 per cent) with experimental data.

Numerical simulation on dense phase pneumatic conveying of pulverized coal in horizontal pipe at high pressure

A kinetic–frictional model, which treats the kinetic and frictional stresses in an additive manner, was incorporated into the two fluid model based on the kinetic theory of granular flow to simulate three dimensional flow behaviors of dense phase pneumatic conveying of pulverized coal in horizontal pipe. The kinetic stress was modeled by the kinetic theory of granular flow, while the friction stress is from the combination of the normal frictional stress model proposed by Johnson and Jackson [1987. Frictional–collisional constitutive relations for granular materials, with application to plane shearing. Journal of Fluid Mechanics 176, 67–93] and the modeled frictional shear viscosity model proposed by Syamlal et al. [1993. MFIX documentation and theory guide, DOE/METC94/1004, NTIS/DE94000087. Electronically available from http://www.mfix.org], which was modified to fit experimental data. For the solid concentration and gas phase Reynolds number was high, the gas phase and particle phase were all treated as turbulent flow. The experiment was carried out to validate the prediction results by three kinds of measurement methods. The predicted pressure gradients were in good agreement with experimental data. The predicted solid concentration distribution at cross section agreed well with electrical capacitance tomography (ECT) image, and the effects of superficial velocity on solid concentration distribution were discussed. The formation and motion process of slug flow was demonstrated, which is similar to the visualization photographs by high speed video camera.

Experimental Study on Adsorption of Carbon Dioxide by 5A Molecular Sieve for Helium Purification of High-Temperature Gas-Cooled Reactor

A fixed-bed apparatus with the dynamic two-route proportional gas mixing system was designed to investigate the adsorption behavior of carbon dioxide on 5A molecular sieve for designing the helium purification system of high-temperature gas-cooled reactors (HTGR). Experiments were performed at near atmospheric pressure, and the dynamic column breakthrough method was used to derive the single-component adsorption equilibrium of carbon dioxide with helium as the carrier gas. The breakthrough curves and the desorption curves were measured at low carbon dioxide partial pressure of 10−150 Pa and temperatures of 5−35 °C. By analyzing the breakthrough curve, both the equilibrium adsorption capacity and the kinetic adsorption capacity at the breakthrough point were determined. The effects of superficial velocity, temperature, gas feed concentration, adsorption pressure, and regeneration temperature on the adsorption capability were studied. The CO2 single-component adsorption isotherm at 10 °C was obtained and fi...

Effects of non-Newtonian liquid properties on pressure drop during horizontal gas-liquid flow

An experimental study was performed on two-phase pressure drop of gas/non-Newtonian liquid systems in co-current horizontal flow. The effects of superficial velocities and polymer concentrations on two-phase pressure drop were investigated. A total of 180 experimental tests were conducted for the following conditions: superficial liquid velocity from 0.18 m/s to 1.42 m/s, and superficial gas velocity from 0.13 m/s to 2.59 m/s. The results show that the drag reduction will occur when the value of flow behavior index, n, is smaller than 0.6, and the lower the value of n is, the greater the effect of drag reduction will be.

In Vitro Evaluation of Biospecific and Pseudobiospecific Ligands Aimed at Extracorporeal Treatment for Immunoglobulin E Removal

This work investigated the potential use of an alternative adsorbent to anti-immunoglobulin E (IgE)-agarose for IgE selective adsorption therapy. A screening of several commercially available adsorbents (Concanavalin A, Lens culinaris[Lc], d-tryptophan, poly-l-lysine, and aminohexyl immobilized on agarose) was done through batch system assays, considering some criteria, such as adsorption capacity, selectivity, and biocompatibility. In the Lc-agarose adsorbent, total IgE, and specific IgE--for the airborne allergens Dermatophagoides pteronyssinus and Blomia tropicalis--were significantly better removed (63, 58, and 59%, respectively) than immunoglobulin G (19%), immunoglobulin A (33%), immunoglobulin M (9%), and albumin (18%). This adsorbent was packed into a column and the effect of superficial velocity, ratio of plasma volume to bed volume, number of perfusions, and temperature on IgE adsorption were evaluated. In vitro simulation of therapeutic adsorption (single perfusion) indicated that about 50% of total IgE could be eliminated.