Plexiglas Column Research Articles

Flow regimes and axial pressure profiles in a circulating fluidized bed

The hydrodynamics and flow regime in fast fluidized beds of FCC and silica sand particles were determined in a Plexiglas column (0.1 m i.d. × 5.3 m high). The transport velocity ( U tr) was determined by the emptying time and flooding point determination methods. At a given solid circulation rate, solid holdups in the upper dilute region exhibit their maximum values with variation of gas velocities, where a dense region forms at the bottom of the riser. The gas velocity at which solid holdup in the upper dilute region exhibits a maximum value is defined as the fast transition velocity ( U FT). The fast fluidization regime can be divided into the fast transition region and the fully developed fast fluidization region. A demarcation line between the two regions is proposed. The fast transition velocity and the transition velocity ( U FD) to pneumatic transport have been correlated. The transition velocity of the fast fluidization region can be predicted by the choking velocity, U FD and U FT.

Plexiglas column coatings for capillary electrophoresis of biomolecules

In this article, Plexiglas (primarily polymethylmethacrylate) was used to modify fused silica capillary columns for capillary electrophoresis (CE). The procedure was carried out using a dynamic coating method at room temperature. The whole process required only 20 min, and the resulting capillaries could be immediately used for the analysis of biomolecules. Greatly suppressed electroosmotic flow (EOF) was observed over a pH range of 3–10. Various biochemical standards including ribonucleotides, peptides, proteins, and DNA were successfully separated. More than 0.5×106 theoretical plates were obtained, and this efficiency changed little in more than 1 month of continuous use. Lower than ∼1.6% relative standard deviation in migration times (27 successive runs) was observed for model proteins. The simplicity of the modification process allows this method to be suitable for modifying miniaturized electrophoresis channels or devices. ©1999 John Wiley & Sons, Inc. J Micro Sep 11: 325–329, 1999

Plexiglas column coatings for capillary electrophoresis of biomolecules

In this article, Plexiglas (primarily polymethylmethacrylate) was used to modify fused silica capillary columns for capillary electrophoresis (CE). The procedure was carried out using a dynamic coating method at room temperature. The whole process required only 20 min, and the resulting capillaries could be immediately used for the analysis of biomolecules. Greatly suppressed electroosmotic flow (EOF) was observed over a pH range of 3–10. Various biochemical standards including ribonucleotides, peptides, proteins, and DNA were successfully separated. More than 0.5×106 theoretical plates were obtained, and this efficiency changed little in more than 1 month of continuous use. Lower than ∼1.6% relative standard deviation in migration times (27 successive runs) was observed for model proteins. The simplicity of the modification process allows this method to be suitable for modifying miniaturized electrophoresis channels or devices. ©1999 John Wiley & Sons, Inc. J Micro Sep 11: 325–329, 1999

Predictions on bubble and solids movement in laboratory polyethylene fluid beds as visualized by X‐ray computer assisted tomography (CAT) scanning

AbstractSolid and gas distributions are tomographically quantified as a function of position with high resolution in a series of laboratory fluid beds containing air and polyethylene particles. The resolution used is 0.4 mm by 0.4 mm by 3 mm. The laboratory models are Plexiglas columns of 10 cm in diameter and the settling bed L/D ratios vary between one and three. Large particles (up to 1.5 mm in diameter) of high density polyethylene and linear low density polyethylene are used. The superficial gas velocities vary from the minimum fluidization velocity to 50 cm/s. In this paper, the analysis of fluid bed CAT scanner images is extended to show bubble, emulsion and dense phase distribution. The analysis is also used to determine the bubble diameter and to predict the flow direction of solid particles as well as the velocity of descending solids. The voidage frequency distributions of a bed at different gas flow rates are compared to each other and the voidage threshold values corresponding to gas, emulsion and dense phases are determined. These threshold values are used to prepare ternary images that clearly show the parts of the bed cross‐section corresponding to bubble, emulsion and dense phases.

LIQUID PHASE MIXING IN A SLURRY BUBBLE COLUMN WITH DRAFT TUBE

In this work we characterize liquid phase mixing in a 150 L bubble column with a draft tube (internal airlift configuration) for a water-air-sand system at high solid concentrations. Liquid mixing is assessed by measuring the evolution of sodium chloride concentration after a pulse of concentrated NaCl solution is injected. Tracer concentrations were measured by means of electrical conductivity probes. The experimental set up consists of a 0.29 m internal diameter, 3 m length Plexiglas column with a conical bottom (cone apex angle of 60°) and a concentric draft tube with 0.14 m internal diameter and 2 m length. The gas superficial velocity based on the cross section of the column vaired from 0.057 to 0.22 m/s. Sand particles of 280 μm in average size were used, with slurry concentrations ranging from 120 to 500 kg/m3. From the tracer outputs, circulation time (time between peaks of the response curve) and mixing time (time required to achieve a 95% homogeneous solution) were determined after the pulse had been injected. The experimental data were analyzed by means of a tank in series model with recirculation. The circulation and mixing times were found to increase with solids concentration, and to decrease as the riser gas velocity was increased. The circulation limes were larger in continuous operation than in semibatch mode. The results show that the system has equivalent dispersion coefficients that are one order of magnitude lower than those found in a conventional bubble column.

Gas holdup and liquid velocity in three-phase internal-loop airlift reactors

The liquid velocities and gas holdups in the riser and downcomer of three-phase internal-loop airlift reactors with Newtonian and non-Newtonian fluids were studied. The reactor was constructed of 19 cm ID Plexiglas column and 250 cm in height. The inside diameters of the draft tube were 9, 12, and 14 cm (wall thickness is 0.5 cm), which made the ratio of the cross-sectional area of the riser to the downcomer equal to 0.69, 1.33 and 3.22, respectively. The draft tube heights used in this study were 70, 110 and 150 cm. Water and various concentrations of carboxymethyl cellulose (CMC) aqueous solutions were employed as the liquid phases. Air and polystyrene particles were used as the gas and solid phases, respectively. The liquid velocities and gas holdups in the riser and downcomer were measured by tracer response and manometric techniques, respectively.It was found that the gas holdups and the liquid velocities generally decreased with an increase in the concentration of CMC or the solids loading. In addition, the gas holdup in the riser decreased but that in the downcomer increased with increasing draft tube length. The liquid velocities increased with increasing draft tube length. Furthermore, the gas holdup and the liquid velocity in the riser increased but those in the downcomer decreased with decreasing draft tube diameter. Based on the drift-flux model and energy balance, a hydrodynamic model was developed. It was shown that using a correlation equation for the gas holdup in the downcomer, the proposed model could predict satisfactorily the gas holdup in the riser and the liquid velocities in the riser and downcomer of the internal-loop airlift reactors with Newtonian and non-Newtonian fluids.

Axial and radial heat transfer studies in a circulating fluidized bed

The axial and radial variation of the heat transfer coefficient in a circulating fluidized bed riser column, and the effect of operating parameters thereon, are investigated. The experimental set-up consists of a riser column of 102 mm×102 mm in bed cross-section, 5·25 m in height with a return leg of the same dimensions. The unit is fabricated with plexiglass columns of 0·6 m in length which are interchangeable with one another. Two axial heat transfer test sections of 102 mm×102 mm in cross-section, 500 mm in height, and made of mild steel, are employed for the axial heat transfer study and one horizontal tube section of 22·5 mm OD made of mild steel is employed for the radial heat transfer study. The primary air velocity is varied between 4·21 and 7·30 m s−1. Local sand of mean size (dp) 248 μm is used as the bed material. One empirical model with the help of dimensional analysis has been proposed to predict the heat transfer coefficient to a bare horizontal tube in a CFB riser column and the model results are validated with the experimental data; good agreement has been observed. © 1997 John Wiley & Sons, Ltd.

Axial and radial heat transfer studies in a circulating fluidized bed

The axial and radial variation of the heat transfer coefficient in a circulating fluidized bed riser column, and the effect of operating parameters thereon, are investigated. The experimental set-up consists of a riser column of 102 mm×102 mm in bed cross-section, 5·25 m in height with a return leg of the same dimensions. The unit is fabricated with plexiglass columns of 0·6 m in length which are interchangeable with one another. Two axial heat transfer test sections of 102 mm×102 mm in cross-section, 500 mm in height, and made of mild steel, are employed for the axial heat transfer study and one horizontal tube section of 22·5 mm OD made of mild steel is employed for the radial heat transfer study. The primary air velocity is varied between 4·21 and 7·30 m s−1. Local sand of mean size (dp) 248 μm is used as the bed material. One empirical model with the help of dimensional analysis has been proposed to predict the heat transfer coefficient to a bare horizontal tube in a CFB riser column and the model results are validated with the experimental data; good agreement has been observed. © 1997 John Wiley & Sons, Ltd.

Effect of operating parameters on heat transfer in the lean phase region of a CFB riser column

The radial variation of the heat transfer coefficient across the bed width, including the effect of fins and fin shapes (surface roughness), on the heat transfer characteristics in the lean phase region of a circulating fluidized bed riser column are investigated. Three test sections (bare horizontal tube, V-fin tube and square fin tube) are employed for the investigation. The experimental unit consists of a riser column of 102×102 mm in bed cross-section, 5·25 m in height with a return leg of the same dimensions, and both made up of plexiglas columns. For the same operating conditions, the provision of fins results in a drop in heat transfer coefficient, but increases total heat transfer owing to increased surface area. The present experimental data are compared with published literature and good agreement has been observed. The experimental data also corresponds to the two-zone hydrodynamics (i.e. the core–annulus structure) of a circulating fluidized bed. © 1997 John Wiley & Sons, Ltd.

Measurement of dynamic gas disengagement profile by using an analog output level gauge

The dynamic gas disengagement profile was measured in a 0.14 m diameter and 3.66 m high plexiglas column by using an analog output gauge, which was connected to a data acquisition system. This analog output gauge is a high accuracy continuous measurement level gauge. It is made up of a wave guide, a float, a motion or stress sensing device and a probe housing. The fluid level at any gas velocity is obtained by using the data acquisition system. The dynamic gas disengagement profile produced one slope in the bubble flow and two slopes in the churn turbulent flow representing unimodal and bimodal distributions of bubbles.

Influence of leaching with different amounts of water on desalinization and permeability behaviour of chloride and sulphate-dominated saline soils

Desalinization studies were carried out in Cl-dominated (Cl:S0 4 = 7:3) and SO 4-dominated (Cl:S0 4 = 3:7), saline (ECe = 9 dS m −1, ESP = 10) sandy loam soils, filled in plexiglass columns up to a height of 60 cm at uniform bulk density. Both soils were subjected to leaching with three amounts, i.e. 20, 40 and 60 cm of distilled water, 5 cm at a time until the three leaching cycles were completed. The S0 4 profiles had 20–75% faster percolation than their Cl counterparts, when 40 cm of water was leached. With higher amounts of leaching water, the differences in permeability between the two soils narrowed and became indistinguishable when 60 cm of water was leached. Desalinization of the Cl-profiles was more efficient than the S0 4-profiles, but the reverse was the case with desodification. When the depth of water (dW) leached was less than or equal to the depth of soil WS), desalinization was less efficient (10–25%) under S0 4 than under Cl-salinity. However, when dW was greater than dS, the differences in the magnitude of leaching of salts under the two salinities narrowed and became equal at a dW/dS ratio of 2. An increase in the soil ESP from 10 to 35 resulted in a 75% decrease in soil permeability under Cl compared with a 64% decrease in S0 4-salinity. At ESP of 10, application of farmyard manure (FYM) as an amendment increased soil permeability for both Cl- and S0 4-dominated soils. However, at higher ESP levels (30–35), FYM application decreased soil permeability under Cl-dominated soil, but increased it under S0 4-dominated soil.

5491968 Combustion system and method for power generation

The combined trapezoid spray tray (CTST) is a novel spray tray with unique trapezoid spatial structure. With gas-liquid co-current contact, the CTST has a lot of advantages, such as high capacity, efficiency and operation flexibility, low pressure drop, excellent anti-blockage performance, and foaming resistance. In the present work, the hydrodynamic and mass transfer performance of the CTST were investigated in a plexiglass column with air-water-carbon dioxide as an experimental system and were compared to a type of Glitsch V1 valve tray. Based on the result, the correlation equations of dry-plate and wet-plate pressure drop for the CTST were established. In terms of hydrodynamic and mass transfer performance, the CTST was superior than the Glistch V1 valve tray when the gas velocity is high. The industrial application case further validated the experiment result.

Distributions of flow regimes and phase holdups in three-phase fluidized beds

Pressure fluctuation characteristics at different axial and radial positions were investigated in a three-phase fluidized-bed Plexiglas column of 285 mm inside diameter and 4100 mm height operated with air, tap water and glass beads under different conditions. It was found that the whole column may display different flow regimes depending on the operating conditions, i.e. total homogeneous bubble regime, total transition regime, total turbulent bubble regime, while the two neighbouring or all three regimes may exist simultaneously at different heights of the column. Schemes of flow regime distribution, which changes with gas velocity, were given, and the criteria for flow regimes correlated with operating variables and axial distance above the gas distributor were established. It was also found that any flow regime was substantially identical at different radial positions across the column. Phase holdups at different heights of the column were measured by means of a combination of pressure drop and sampling methods. Correlations of gas and solid holdup in different flow regimes as a function of operating parameters and axial distance from the distributor were established.

Surface Aggregates and Macropore Effects on Chemical Transport in Soil under Rainfall

AbstractSoil surface aggregates and macropores have the potential to greatly influence the transport of surface‐applied agricultural chemicals in soil and to surface and groundwater. We studied the effects of a 1.0‐cm layer of 4.5‐ to 12.5‐mm surface aggregates, a 3‐mm artificial macropore, and their combination on the transport of surface‐applied Br− and Sr2+ tracers (as SrBr2) under simulated rainfall, with the underlying soil initially dry or prewetted to a certain depth (about 7 cm). Air‐dried Kirkland soil (fine, mixed, thermic Udertic Paleustoll), <3.5‐mm size, was packed in duplicate 15‐cm‐diam., 30‐cm‐long, sectionable Plexiglas columns (Cole‐Parmer Instrument Co., Niles, IL) to a bulk density of 1.26 Mg m−3. During the rainfall, surface runoff or macropore flow out of the column bottom was measured and analyzed for Br− and Sr2+. After the rain, the column was sectioned in 1.15‐cm increments to determine soil water, Br−, and Sr2+ content distributions. Without a macropore, the surface aggregates reduced the overall movement of Br− in soil and increased Br− in runoff, the effects being much greater in prewetted columns than in nonprewetted columns. A macropore, by itself, also reduced the movement of the main Br− pulse as it allowed surface solution (runoff) to move down and infiltrate laterally below the main wetting front. Surface aggregates greatly increased Br− content of the macropore flow and of the wetted soil around the macropore below the main wetting front. Aggregates or the initial condition did not change the Sr2+ movement much but increased Sr2+ content of runoff or macropore flow.

Mass transfer in different flow regimes of three-phase fluidized beds

The volumetric gas-liquid mass transfer coefficient ( K L a) and axial dispersion coefficient ( D z ) of liquid phase have been studied in air-oxygen saturated water fluidized beds of 0.52 to 0.755 mm glass spheres in a plexiglass column. The effects of liquid velocity, gas velocity, particle size and loadings on K L a and D z were examined. According to the different correlations of mass transfer, three flow regimes of three-phase fluidized beds were distinguished. It was found that K L a and D z change with different regularities in these different flow regimes. The results have shown that the flow regimes distinguished by different correlations of mass transfer were substantially identical with those distinguished by gas holdup correlations as well as pressure fluctuation analysis as had been found in previous investigations.

Hydraulic conductivity of compacted municipal solid waste

Dry municipal solid waste (MSW) samples were compacted in Plexiglas columns to densities of 160, 320 and 480 kg m −3. The columns were set-up as constant head permeameters. Water flowed continuously through the columns under hydraulic gradients of 2–4·0 m m −1. Hydraulic conductivities were calculated according to Darcy's equation. Hydraulic conductivity was found to be time-dependent. The temporal variation was attributed to varying degrees of saturation due to gas formation and relative movement of fine particles in the columns. The average hydraulic conductivities at 160, 320 and 480 kg m −3 were 9·6 × 10 −2, 7·3 × 10 −4 and 4·7 × 10 −5 cm s −1, respectively.

Effect of different factors on movement of sulfate in soils of semiarid regions of India

Effects of soil texture, application rates of sulfate, initial water content, water application rates, and water management regimes on movement of sulfate were studied in a series of laboratory experiments in three soils. Soils in the plexiglass columns were compacted to 1.45 g cm‐3 bulk density in each column, and K2SO4 was applied as a source of sulfate. In a sulfate application rate experiment, 100, 200, and 400 μg, and in other experiments, 100 μg SO4 2‐ ‐S g‐1 soil was applied in the top 3‐cm soil layer. To 120‐cm‐long columns, 2.5, 5, and 10 cm of water was applied in a water application rate experiment, 10 cm of water in a water management regime experiment, and in the rest of the experiments, 5 cm of water was applied. Different rates of sulfate application did not change the leaching behavior, and sulfate moved to 27‐cm depth at all applied sulfate concentrations when 5 cm of water was used. The maximum depth of sulfate with 5 cm of water in initially dry soil was down to 15‐, 21‐, and 24‐cm and ...

MASS TRANSFER AND PHASE HOLDUP CHARACTERISTICS IN THREE-PHASE FLUIDIZED BEDS

The effects of liquid surface tension (42.6 ∼ 72,4 mN/m) and viscosity (1 ∼214mPa • sn), liquid (0.01 ∼0.12m/s) and gas (0.01 ∼0.20m/s) velocities and particle sizes (1 — 8 mm) on phase holdup and mass transfer coefficient ( kLa) have been determined in a 0.142 m-I.D. × 2.0 m-high Plexiglas column. The gas phase holdup increases with liquid velocity, and the rate of increase in gas phase holdup sharply increases with gas velocity in the bed of surfactant solutions. In the beds of 1.0 and 1.7 mm glass beads, the bed contraction occurs whereas in the beds of 2.3 mm glass beads the bed contraction does not occur with an aqueous soltuion of ethanol (σ = 50.4 mN/m). The value of kLa increases with decreasing surface tension (σ ) but it decreases exponentially with increasing liquid viscosity in continuous bubble columns and three-phase fluidized beds. In three-phase fluidized beds with surfactant solutions, kLa increases with gas and liquid velocities and particle size. In three-phase fluidized beds of viscous or surfactant soltuions, kL,a can be estimated in terms of the energy dissipation rate based on the isotropic turbulence theory and a flow regime map is proposed based on the drift flux theory.

Glyphosate degradation by immobilized bacteria: laboratory studies showing feasibility for glyphosate removal from waste water.

To evaluate immobilized bacteria technology for the removal of low levels of glyphosate (N-phosphonomethylglycine) from aqueous industrial effluents, microorganisms with glyphosate-degrading activity obtained from a fill and draw enrichment reactor inoculated with activated sludge were first exposed to glyphosate production wastes containing 500-2000 mg glyphosate/L. The microorganisms were then immobilized by adsorption onto a diatomaceous earth biocarrier contained in upflow Plexiglas columns. The columns were aerated, maintained at pH 7.0-8.0, incubated at 25 degrees C, supplemented with NH4NO3 (50 mg/L), and exposed to glyphosate process wastes pumped upflow through the biocarrier. Glyphosate degradation to aminomethylphosphonic acid was initially > 96% for 21 days of operation at flows yielding hydraulic residence times (HRTs) as short as 42 min. Higher flow rate studies showed > 98% removal of 50 mg glyphosate/L from the waste stream could be achieved at a HRT of 23 min. Glyphosate removal of > 99% at a 37-min HRT was achieved under similar conditions with a column inoculated with a pure culture of Pseudomonas sp. strain LBr, a bacterium known to have high glyphosate-degrading activity. After acid shocking (pH 2.8 for 18 h) of a column of immobilized bacteria, glyphosate-degrading activity was regained within 4 days without reinoculation. Although microbial growth and glyphosate degradation were not maintained under low organic nutrient conditions in the laboratory, the low levels of degradable carbon (45-94 mg/L) in the industrial effluent were sufficient to support prolonged glyphosate-degrading activity. The results demonstrated that immobilized bacteria technology is effective in removing low levels of glyphosate in high-volume liquid waste streams.

Effect of sodium chloride on transport of bacteria in a saturated aquifer material

Determinations were made of the influence of NaCl concentration, cell density, and flow velocity on the transport of Pseudomonas sp. strain KL2 through columns of aquifer sand under saturated conditions. A pulse-type boundary condition was used. The experiments were conducted by using 0.3-m-long Plexiglas columns with an internal diameter of 0.05 m. When a 1-h pulse of a 0.01 M NaCl solution containing 10(8) cells per ml was added at a flow rate of 10(-4) m s-1, the bacterial density in the effluent never exceeded 2.2% of the density of cells added, and only 1.5% of the bacteria passed through the aquifer material. In contrast, when the bacteria were applied in distilled water, the relative cell density in the effluent approached 100%, and 60% of the bacteria were transported through the aquifer solids. Under these conditions, the breakthrough of Pseudomonas sp. strain KL2 was slower than chloride. When the flow rate was 2.0 x 10(-4) m s-1, the cell density in the effluent reached 7.3% of that added in 0.01 M NaCl solution, but only 3.9% of the bacteria were transported through the aquifer particles. On the other hand, the density in the effluent approached 100% of that added in deionized water, and 77% of the added bacteria were recovered. When the density of added cells was 10(9) cells per ml at a flow rate of 10(-4) m s-1, the densities in the effluent reached 70 and 100% of those added in salt solution and deionized water, respectively, and 44 and 57% of the bacteria were transported through the aquifer solids.(ABSTRACT TRUNCATED AT 250 WORDS)