Terms Of Contact Time Research Articles

A Numerical Study on Agglomeration in High Temperature Fluidized beds

Soft-sphere discrete element method (DEM) and Navier-Stokes equations were coupled with equations of energy for gas and solids to investigate the process of agglomeration in fluidized bed of polyethylene particles at high temperature. The Newton’s second law of motion was adapted for translational and rotational motion of particles and agglomerates. The cohesive force for polyethylene particles was calculated based on a time dependent model for solid bridging by the viscous flow mechanism. The motion of agglomerates was described by means of the multi-sphere method. By taking into account the cohesiveness of particles at high temperatures and considering real dynamic agglomerates, the fluidization behavior of a bed of polyethylene particles was successfully simulated in terms of increasing the size of agglomerates. Effect of the inlet gas temperature on mass and size of agglomerates was investigated. A mechanistic study in terms of contact time, cohesive force and repulsive force, which are the key parameters in the formation of agglomerates, were also carried out.

Investigating agglomeration phenomena in an air-polyethylene fluidized bed using DEM–CFD approach

Soft-sphere discrete element method and Navier–Stokes equations were coupled with the equations of energy to simulate the agglomeration process at high temperature in an air-polyethylene fluidized bed. The inter-particle cohesive force was calculated based on solid bridging by the viscous flow. The agglomerates were tracked as a real object with irregular shapes in which their translational and rotational motions were calculated according to the multi-sphere method. Fluidization behavior of an agglomerating bed was successfully simulated in terms of increasing the size of agglomerates as well as decreasing the bed height. The influence of gas velocity on the size of agglomerates was investigated and it was shown that the formation of massive agglomerates is postponed as the gas velocity is increased. Microscopic mechanistic studies in terms of contact time, cohesive force and repulsive force, which are the key parameters in the formation of agglomerates, were also carried out.

Adsorption of Zn(II) on dialdehyde m-phenylenediamine starch

A new chelating material dialdehyde m-phenylenediamine starch (DASMPA) was synthesized by reacting m-phenylenediamine with dialdehyde starch. The obtained material was characterized by element analysis and Fourier transform infrared (FT-IR) spectra. The FT-IR of DASMPA showed an absorption peak at 1605.95 cm(-1) indicating the formation of a Schiff base (C=N). Adsorption activity of DASMPA for Zn(2+) was also investigated in terms of contact time, pH, the initial Zn(II) concentration and temperature, the results revealed that pH = 5, t = 1 h were the optimal conditions. With the degree of substitution (DS) of the DASMPA increased, the adsorption capacity increased gradually. The adsorption equilibrium data correlated well with Freundlich isotherm. Moreover, lower temperature was preferable for the process as it was exothermic.

Increasing the large scale feasibility of a solid phase extraction procedure for the recovery of natural antioxidants from olive mill wastewaters

The present investigation was focused on improving the feasibility of large scale applications of a solid phase extraction (SPE) procedure dedicated to the recovery of polyphenols from olive mill wastewaters (OMWs). To this aim, a previously developed SPE procedure was optimized in terms of contact time without negatively affecting the overall process productivity. The possibility of regenerating and recycling both the solid phase (Amberlite XAD16 non-polar resin) and the extraction solvent (acidified ethanol) was also demonstrated. In particular, the resin was successfully reused in 10 consecutive SPE cycles (including washing and reactivation steps), allowing almost constant polyphenols adsorption and desorption ratios (81.44±0.91% and 52.69±5.57%, respectively). Up to 695mL of ethanol per liter of exhausted extraction solvent were recovered by means of a rotary evaporator. Furthermore, the solvent conventionally used for resin activation (i.e., methanol) was successfully substituted by a more biocompatible solvent (i.e., ethanol). An ORAC value corresponding to 6979μM of Trolox equivalents was observed for the concentrated polyphenolic solution, obtained as a result of rotary evaporator operations. Importantly, no substantial loss of radical scavenging and antioxidant activities occurred by means of the aforementioned operations dedicated to the recovery of ethanol from the obtained polyphenolic solution.

Efficacy of Colloidal Silver-Hydrogen Peroxide and 2-Bromo-2-nitroporopane-1,3-diol Compounds Against Different Serogroups of Legionella pneumophila Strains

Cooling towers are considered as amplifier and disseminator sources for Legionella spp. despite preventive treatments. Information which was obtained from biocidal tests could improve the effectiveness of treatments. Therefore, the choice of appropriate biocides and the applying of biocides in correct dosages and contact times are important. Various oxidizing and non-oxidizing biocides have been investigated in vitro for their effectiveness against legionellae. Colloidal silver-hydrogen peroxide (CSHP) and 2-bromo-2-nitroporopane-1,3-diol (BNPD) biocides were selected as an example for oxidizing and non-oxidizing agents, respectively, in view of bactericidal action against different serogroups of L. pneumophila strains [serogroup 1 (S1) and serogroup 2-14 (S2)] which are isolated different cooling towers in the vicinity of Istanbul, Turkey and reference strain. In the current study, oxidizing biocide was found more effective than non-oxidizing biocide in terms of contact times, log reductions and recommended dosages. At the recommended concentrations for cooling towers (100ppm), while CSHP compound killed all strains in 3h contact time, BNPD compound killed S2 and reference strain in the same contact time, S1 strain after 6h contact time. The results of the present study showed that effective biocide applications can be achieved by pre-determining minimum inhibitory concentration (MIC) and minimum contact time of different biocides to kill target bacteria.

A study of the effect of strain rate and temperature on the characteristics of quasi-unidirectional natural fibre-reinforced composites

The responses of quasi-unidirectional vegetable fibres (sisal and flax) – styrene polyester matrix composites under 6-J nominal strike energy at different sample temperatures and at higher impact energies of 9 and 12 J for samples at room temperature have been studied and indentation properties realized from static loading at different cross-head displacement speeds. The findings are explained in terms of the impact characteristics. At temperatures above ambient, there were changes in the impact characteristics. The drop impact tests were carried out on samples (70 × 70 × 5 mm3) at an ambient temperature of 18 °C and elevated temperatures of 40 °C, 60 °C, 80 °C, and 100 °C using an instrumented drop tester with a 12.1-mm diameter hemispheric tup and the load history and energy profile were obtained. The actual damage response depends on many intrinsic and extrinsic factors, including the thickness of the laminate, the exact stacking sequence, the shape and kinetic energy of the impactor, and the degree to which the laminate is supported against bending. The examination of the impact and post-impact characteristics at elevated temperatures revealed a plastic mode of failure and the performance was assessed in terms of contact time, post-impact displacement, and total energy. Composites are generally brittle in nature and respond elastically with little or no plastic deformation, but this is not the case for natural fibre – styrene polyester matrix composites, especially at high temperatures, as there exists some degree of plasticity seen in the after-impact state of the samples. Low energy impact (6 J) results in cracking of the matrix leading to reduction in the strength of the composite. However, higher energy impact strikes produce cracking of the matrix and splintering of the fibres. From the load–indentation curves, average power coefficients of 3.6 and 15.4 were obtained for sisal and flax composites, respectively, as against 1.5 for the special Hertz contact of two elastic bodies.

Predicting chromium (VI) adsorption rate in the treatment of liquid-phase oil-based drill cuttings

The adsorption rate of chromium (VI) on commercial activated carbon during the treatment of the flocculation effluent of liquid-phase oil-based drill-cuttings has been investigated in terms of contact time and initial chromium (VI) ion concentration. Homogenizing 1 g of the activated carbon with 100 ml of the flocculation effluent of known initial concentrations (1.25 → 6.25 mg/l, in turn) in a flask, at a constant stirring speed of 80 rpm at 25 o C for 180 min, the pseudo-second-order kinetics was observed to be more suitable in predicting the adsorption rate of chromium (VI) ion in the treatment process as experimental data fitted the model relatively better than the pseudo-first-order kinetics with R 2 = 0.9999. Adsorption took place in two steps: an initial high rate step before reaching a plateau at equilibrium in the low rate step. Equilibrium was attained in a contact time of 60 min and the equilibrium adsorption capacity of the activated carbon was 78.6%. Equilibrium adsorption data fitted the Freundlich isotherm well with R 2 = 0.981. The intensity of adsorption was 1.32, which indicates a strongly favourable adsorption. This showed that a large proportion of the chromium (VI) ion was adsorbed at low concentration of the adsorbate in solution. Key words : Carbon adsorption, kinetic models, drill cuttings, chromium removal.

Low temperature catalytic oxidation of aldehydes using wood fly ash and molecular oxygen

Aldehydes, such a 2-methylbutanal (2-MB) and 3-methylbutanal (3-MB), are odorous and regulated VOCs generated in the poultry rendering process that are ineffectively removed in chemical wet scrubbers. It was theorized that wood fly ash or selective crystalline phases in the ash could act to catalyze the oxidation of aldehydes at room temperature in the presence of ClO2, resulting in a low-cost/energy air pollution control method. Results indicate that wood fly ash catalyzed the oxidation (i.e., breakdown) of 2-MB and 3-MB both in the presence of ClO2 and with just O2 (i.e., air) itself, potentially via a free radical mechanism. Aldehyde oxidation did not occur at measurable rates without the wood fly ash or activated carbon. The presence of ClO2 did not increase the rate, but altered the end products of oxidation. Wood fly ash also catalyzed the oxidation of 2-MB in the presence of air, leading to the appearance of 2-butanone, compared to acetone from 3-MB. Contact times of 30s reduced 3-MB levels by ∼40% in bench scale, batch reactors. Similar results were found using activated charcoal (i.e., in terms of contact times), except that higher molecular weight compounds appeared to be formed. Continuous catalytic oxidation of 3-MB using wood fly ash was also demonstrated in a fixed-bed reactor at room temperature; the overall oxidation rate appeared to be first order with respect to 3-MB and a representative conversion of 20% at an inlet concentration of 67ppmv and 2s residence time (GHSV 18001/h, 25°C, 1atm) was measured. Results indicate the potential of using inexpensive solid waste materials to breakdown C5 aldehydes in rendering emissions to CO2, H2O, and less odor offensive compounds, but a carbon balance on the reaction and complete identification of end products are required for implementation.

A comparative simulation analysis of propane dehydrogenation in composite and microporous membrane reactors

Propane dehydrogenation has been simulated for a composite membrane reactor and a microporous membrane reactor using plug-flow reactor models, in which both were packed with Pt/Al2O3 catalyst in the tube-side. The reaction kinetics employed in the analysis were obtained from experimental data produced in an integral fixed bed reactor with the same catalyst. Comparative studies were carried out to analyse the performances of reactors containing the different membranes in terms of contact time, flow pattern and flow rate of sweep gas, and pressure. In general, the composite membrane reactors gave the better performance for all cases investigated. © 2002 Society of Chemical Industry

Biomechanics of heading a soccer ball: implications for player safety.

To better understand the risk and safety of heading a soccer ball, the author created a set of simple mathematical models based upon Newton's second law of motion to describe the physics of heading. These models describe the player, the ball, the flight of the ball before impact, the motion of the head and ball during impact, and the effects of all of these upon the intensity and the duration of acceleration of the head. The calculated head accelerations were compared to those during presumably safe daily activities of jumping, dancing, and head nodding and also were related to established criteria for serious head injury from the motor vehicle crash literature. The results suggest heading is usually safe but occasionally dangerous, depending on key characteristics of both the player and the ball. Safety is greatly improved when players head the ball with greater effective body mass, which is determined by a player's size, strength, and technique. Smaller youth players, because of their lesser body mass, are more at risk of potentially dangerous headers than are adults, even when using current youth size balls. Lower ball inflation pressure reduces risk of dangerous head accelerations. Lower pressure balls also have greater “touch” and “playability”, measured in terms of contact time and contact area between foot and ball during a kick. Focus on teaching proper technique, the re-design of age-appropriate balls for young players with reduced weight and inflation pressure, and avoidance of head contact with fast, rising balls kicked at close range can substantially reduce risk of subtle brain injury in players who head soccer balls.

Analysis and Optimization of Cross-Flow Reactors for Oxidative Coupling of Methane

A cross-flow reactor model with distributed feed of oxygen and product removal for the oxidative coupling of methane (OCM) was developed, and comparison studies were carried out to analyze the different performances of reactors with different configurations in terms of contact time, temperature, pressure, dilution ratio, and permeability. For each of the reactor configurations considered, the overall methane to oxygen feed ratio was optimized such that the C2 yield at the reactor outlet was maximized. Modeling results showed that distributed feed oxygen could give rise to much higher C2 yields than the cofeed reactor, as long as the ratio of catalyst loading to initial methane flow rate was sufficiently high. Although reactors with optimally distributed oxygen feed give higher C2 yields than evenly distributed ones, the improvement is not significant. In the case of a two-membrane reactor, where one membrane is used for oxygen feed and the other for C2 product removal, higher C2 yields could be obtained t...

PARTICLE-WALL INTERACTIONS AS RELATED TO SLIP VELOCITIES

Particle-wall interaction responses have been analyzed by use of a gamma distribution function in terms of contact times. The slip velocity behavior with varying loadings was shown to have the same format as the coefficients of the gamma distribution. This points to the direct dependence of the slip velocity on the particle-wall interaction phenomena. The basic structure of the particle and wall interactions can thus be the direct cause of the slip velocities measured experimentally over the loading ranges probed.

Fretting Corrosion of Cu-Ni–Al against Plain Carbon Steel

Fretting corrosion of a Cu-Ni-Al alloy against plain carbon steel has been studied in air with 60 per cent relative humidity, nitrogen with 100 p.p.m. oxygen, and silicone oil. As was to be expected on the basis of already existing evidence, the wear in air exceeded that in nitrogen or silicone oil by a factor of 3 to 5. However, contrary to the generally accepted opinion, the high rate of wear in air is not ascribed to the formation of hard abrasive oxides. Instead, the influence of the environment is explained by assuming that in nitrogen with 100 p.p.m. oxygen, and under silicone oil containing dissolved air, an iron oxide with adhesion-reducing properties is formed. The influence of amplitude and frequency has been studied extensively. The observed effects are explained in terms of contact time and deformation of the microwelds.