Experimental Concentration Profiles Research Articles

An Interview with John H. Eichhorn

Anesthesiology, with its development of practice standards, helped create the patient safety movement, states Dr. Eichhorn, and "can continue to be the role model and to lead the way in patient safety for all of health care.

Structure of an atmospheric-pressure H2/O2/N2 flame doped with iron pentacarbonyl

This paper presents the measurement and simulation data on the thermal and chemical structure of an atmospheric-pressure premixed H2/O2/N2 flame doped with iron pentacarbonyl Fe(CO)5. Soft ionization molecular beam mass spectrometry was used to measure concentration profiles of the combustion products of iron pentacarbonyl: Fe, FeO2, FeOH, and Fe(OH)2. A comparison of experimental and simulated concentration profiles showed that they are in satisfactory agreement for FeO2 and Fe(OH)2 and differ significantly for Fe and FeOH. Thus, the previously proposed kinetic model for the oxidation of iron pentacarbonyl was tested and it was shown that the mechanism needs further elaboration.

Application of tritium imaging plate technique to examine tritium behaviors on the surface and in the bulk of plasma-exposed materials

We have applied a tritium imaging plate technique to measure the tritium distribution profile on surface and in bulk of various metal materials after exposure to a deuterium–tritium plasma in a linear plasma experimental apparatus. The experimental tritium concentration profiles in mm range are interpreted according to a simple hydrogen diffusion model in each metal. We found that a significant amount of tritium is localized in near surface regions and is clearly distinguishable from tritium diffused in the bulk. The amount of surface tritium is not likely correlated to bulk properties (diffusivity and solubility), but is related to trapping in surface defects or metal impurities such as oxide and carbide.

Identification of pollution sources in the Romanian Somes River using graphical analysis of concentration profiles

AbstractThe paper describes a method for the identification of pollution sources along a river, based on the analysis of graphical information obtained from long‐term monitoring data. Concentration profiles collected during 2004 at monthly resolution in the Romanian Somes River are employed. The graphical analysis method is based on the comparison of experimental concentration profiles against reference profiles showing concentration evolution along the river after pollutant release. Known nitrate and lead pollution sources along the river were used as reference in order to verify the applicability of the proposed method. Results show that the graphical analysis method enables detection of the majority of sources, and it could be used to investigate the seasonal existence of pollution sources. Moreover, the technique can help guide the definition of the structure of mathematical models for the transport of pollutants in rivers. Copyright © 2010 Curtin University of Technology and John Wiley & Sons, Ltd.

Auto-ignition and combustion characteristics in HCCI and JSR using 1-butanol/ n-heptane and ethanol/ n-heptane blends

In this study, the characteristics of homogeneous charge compression ignition combustion of 1-butanol/ n-heptane blend fuels are demonstrated. To evaluate the potential of this alcohol, a comparison with pure n-heptane and ethanol/ n-heptane mixtures was carried out. The experiments were conducted in a mono-cylinder Diesel engine fueled with alcohol/ n-heptane blends by varying the volume percentage of the alcohols (0%, 18%, 37%, and 57%) at constant equivalence ratio, intake temperature and engine speed (0.3, 80 °C, and 1500 rpm, respectively). New experiments were also performed in a jet-stirred reactor for the fuel-lean ( φ = 0.3) oxidation of mixtures 1-butanol/ n-heptane and ethanol/ n-heptane 1:1 in mole. The experimental concentration profiles vs. temperature obtained at 10 bars and at a residence time of 0.7 s were used to validate a detailed kinetic reaction mechanism. The modeling of constant volume combustion, at two pressures (20 and 40 bars), was performed with this chemical kinetic mechanism (1046 species and 4398 reactions) to interpret the engine results.

ChemInform Abstract: Kinetic Modeling of Propane Oxidation and Pyrolysis

Propane oxidation in jet-stirred reactor was modeled using a comprehensive kinetic reaction mechanism including the most recent findings concerning the kinetics of the reactions involved in the oxidation of C1C4 hydrocarbons. The present detailed mechanism is able to reproduce experimental species concentration profiles obtained in our high-pressure jet-stirred reactor (900 ⩽ T/K ⩽ 1200; 1 ⩽ P/atm ⩽ 10; 0.15 ⩽ ϕ ⩽ 4) and in a turbulent flow reactor at 1 atm; ignition delay times measured in shock tube (1200 ⩽ T/K ⩽ 1700; 2 ⩽ P/atm ⩽ 15; 0.125 ⩽ ϕ ⩽ 2); H-atoms concentrations measured in shock tube during the pyrolysis of propane and burning velocities of freely propagating premixed propane-air laminar flames. The computed results are discussed in terms of pressure and equivalence ratio (ϕ) effects on propane oxidation. The same detailed kinetic reaction mechanism can also be used to model the oxidation of methane, ethylene, ethane, and propene in similar conditions. © John Wiley & Sons, Inc.

ChemInform Abstract: Kinetics of Liquid Phase Synthesis of Methyl tert-Butyl Ether from tert-Butyl Alcohol and Methanol Catalyzed by Ion Exchange Resin

Synthesis of methyl tert-butyl ether (abbreviated as MTBE) from methanol (MeOH) and tert-butyl alcohol (TBA) in the liquid phase was studied by using Amberlyst 15 in the H+ form as an acid catalyst. Experiments were carried out in a stirred batch reactor at different temperatures (313, 318, and 323 K) under atmospheric pressure. It was found that catalyst sizes and rotation speeds had no significant effects on reaction rates. Mechanism studies showed that three reactions took place simultaneously. It was also found that dehydration of TBA could not be neglected. The experimental concentration profiles with time could be simulated well by simple kinetics. Finally, rate constants could be expressed by Arrhenius equations. © 1993 John Wiley & Sons, Inc.

Diffusive Mixing of Polymers Investigated by Raman Microspectroscopy and Microrheology

Diffusive mixing in a model polymer blend of limited miscibility (i.e., the pair polydimethylsiloxane/polyisobutene) is investigated. The diffusion process is followed in the actual droplet-based microstructure of the polymer blend, as opposed to the ideal planar geometry used in previous studies (Brochard et al. Macromolecules 1983, 16, 1638; Composto et al. Nature 1987, 328, 234). In our experiments we combine Raman microspectroscopy and video particle-tracking microrheology. The first technique allows us to monitor local concentration of the two polymers with high spatial resolution both inside and outside a micrometer-size droplet of the dispersed phase. In addition, microrheology enables to follow how the local viscosity inside the droplet changes during the diffusion. The polymer viscosity inside the droplet is determined by video tracking the Brownian motion of a polystyrene bead microinjected into the droplet. The microspectroscopic and microrheological data are combined to estimate the concentration dependence of the monomer friction factor of the two species, which is a key parameter to calculate the interdiffusion coefficient D. Numerical calculations based on such concentration-dependent interdiffusion coefficient D and several alternative models of the polymer diffusion are compared to the experimental concentration profiles. A satisfactory agreement is found for the so-called "slow theory" (Brochard et al.). A phenomenological model improving the agreement of the model with the experimental data is also presented.

Interdiffusion behavior between Nb and MoSi 2 intermetallic compound

The interdiffusion behavior in Nb/MoSi 2 diffusion couples was studied in temperature interval 1250–1400 °C. The average binary interdiffusion coefficients in Nb 5Si 3 phase were determined from the interdiffusion fluxes calculated directly from experimental concentration profiles. The concentration dependence ternary interdiffusion coefficients in (Nb,Mo) 5Si 3 phase were calculated over the selected compositional ranges. Strong diffusional interaction between Nb and Mo in (Nb,Mo) 5Si 3 phase had been unfolded by the cross-interdiffusion coefficients D ˜ NbMo Si and D ˜ MoNb Si . The ternary interdiffusion coefficients were also examined to estimate binary interdiffusion coefficients and tracer diffusion coefficients of Nb and Mo in M 5Si 3 (M = Nb, Mo).

Comparison of theory and experiments for dispersion in homogeneous porous media

Modeling dispersion in homogeneous porous media with the convection–dispersion equation commonly requires computing effective transport coefficients. In this work, we investigate longitudinal and transverse dispersion coefficients arising from the method of volume averaging, for a variety of periodic, homogeneous porous media over a range of particle Péclet ( Pe p ) numbers. Our objective is to validate the upscaled transverse dispersion coefficients and concentration profiles by comparison to experimental data reported in the literature, and to compare the upscaling approach to the more common approach of inverse modeling, which relies on fitting the dispersion coefficients to measured data. This work is unique in that the exact microscale geometry is available; thus, no simplifying assumptions regarding the geometry are required to predict the effective dispersion coefficients directly from theory. Transport of both an inert tracer and non-chemotactic bacteria is investigated for an experimental system that was designed to promote transverse dispersion. We highlight the occurrence of transverse dispersion coefficients that (1) depart from power-law behavior at relatively low Pe p values and (2) are greater than their longitudinal counterparts for a specific range of Pe p values. The upscaling theory provides values for the transverse dispersion coefficient that are within the 98% confidence interval of the values obtained from inverse modeling. The mean absolute error between experimental and upscaled concentration profiles was very similar to that between the experiments and inverse modeling. In all cases the mean absolute error did not exceed 12%. Overall, this work suggests that volume averaging can potentially be used as an alternative to inverse modeling for dispersion in homogeneous porous media.

Influence of precursor layer ablation on laser doping of silicon

AbstractThis paper presents a numerical model, which quantitatively demonstrates that ablation and partial recondensation of the dopant precursor layer are some of the dominating physical processes in laser doping (LD) of crystalline silicon. Our pulsed LD process uses a line focused laser beam, enabling the creation of solar cell emitters without the generation of dislocations, if the width w of the short axis of the line focus is w < 10 μm. The concentration profiles of the dopant atoms strongly depend on the pulse energy density Ep, the pulse to pulse separation Δx and the number of laser scans Ns. By comparing measured with modeled concentration profiles, we are able to evaluate the ablation width as well as the amount of the ablated precursor layer. In case of a sputtered phosphorus precursor layer, the ablation width wa is wa = 6 μm, whereas the width of the molten silicon layer wm is wm = 5 μm. The model also explains the dependence of experimental dopant concentration profiles on the number of subsequent laser scans Ns and pulse to pulse separation Δx. Copyright © 2010 John Wiley & Sons, Ltd.

Shrinking Core Model in characterizing aqueous phase dye adsorption

The fluid–solid non-catalytic reactive system is characterized by the widely accepted Shrinking Core Model. In the present investigation the same model has been applied to characterize the adsorption of Methylene Blue (MB) and Congo Red (CR) dyes in the aqueous phase onto Rice Husk Ash (RHA). The effective pore diffusivities of different dye molecules in RHA are determined by a suitable global optimization technique. The depth of penetration has also been estimated for various initial concentrations of dyes. The values predicted by the model are compared with experimental concentration profiles at different initial concentrations of these dyes. The theory–experiment comparison has revealed that predicted values are in excellent agreement with the experimental values.

Site Preference and Diffusion in Ni<sub>3</sub>Al Alloyed with Ir, Ta or Re at 1200°C

Diffusion in L12-Ni3Al with ternary alloying additions of Ir, Ta and Re was investigated at 1200°C using solid-to-solid diffusion couples, and examined with respect to site preference in ordered intermetallic compound. In addition to determination of average ternary interdiffusion coefficients [1-3], average effective interdiffusion coefficients were determined directly from the experimental concentration profiles. Ni has the largest magnitude of average effective interdiffusion coefficient, followed by Al, Ir, Re and Ta. The average effective interdiffusion coefficients for Ir, Re and Ta are much smaller than those for Ni and Al. Tracer diffusion coefficients determined by extrapolation technique, and available literature also followed the same trend. The relative tendency of Ni, Al, Ir, Re and Ta to occupy the -Ni and -Al sites are correlated to these diffusion coefficients, with due consideration for diffusion mechanisms and coordination of atoms.

A revisit to the one form kinetic model of prothrombinase

Thrombin is generated enzymatically from prothrombin by two pathways with the intermediates of meizothrombin and prethrombin-2. Experimental concentration profiles from two independent groups for these two pathways have been re-analyzed. By rationally combining the independent data sets, a simple mechanism can be established and rate constants determined. A structural model is consistent with the data-derived finding that mechanisms that feature channeling or ratcheting are not necessary to describe thrombin production.

A general kinetic law for heavy metal vaporization during municipal solid waste incineration

Metal emissions from waste incineration plants become a great environmental concern because of their toxicity for both human health and environment. Metals are not destroyed by high-temperature thermal treatment and some vaporized metals may be emitted. It is thus essential to understand the release mechanism of metals during high-temperature waste treatment, in order to improve the understanding of their behavior and the control of their emission. The objective of this study is to identify the kinetic law for metal release from realistic artificial waste. The vaporization of three metals of most concern (Cd, Pb and Zn) during municipal waste incineration was studied. The vaporization rate at the particle level was determined from the experimental concentration profile in the outlet gas of a fluidized bed reactor, by using the inverse method that was previously developed and validated by our team. As a first step, the kinetic parameters were determined thanks to experiments carried out at several temperatures. Specific laws, for each studied metal, were thus obtained as a function of temperature. Nevertheless, it is very useful to identify all the experimental kinetic curves (all studied metals at all temperatures) to one single mathematical law. Therefore, a general kinetic law, expressing the solid matrix influence on the metal vaporization dynamic, was determined as a second step. It permits to predict the vaporization characteristic time and the time course of the metal concentration in the waste.

Comparisons of experimental topside electron concentration profiles with IRI and NeQuick models

A critical part of the vertical ionospheric electron concentration profile is the region above its maximum (topside ionosphere) and many attempts have been made to model this region because of the limited experimental data available. Recently, many topside electron concentration profiles obtained with the Intercosmos-19 satellite became accessible through the Internet. The period analyzed corresponds to March 1979 - December 1980, a time interval of high solar activity. The present work describes the comparison of these profiles with the IRI and NeQuick model profiles obtained by driving the models with the values of the maximum electron concentration and its height given by the satellite.

Mathematical modeling and simulation of hexane degradation in fungal and bacterial biofilters: effective diffusivity and partition aspectsThis article is one of a selection of papers published in this Special Issue on Biological Air Treatment.

Mathematical modeling in the biofiltration of volatile organic compounds is a valuable tool for performance prediction and in scaling up. Majority of the published models include parameters obtained from fitting experimental data, thus masking their real influence as they are lumped generally. The present work aims to evaluate experimentally some of the most relevant parameters including kinetic constant, partition coefficient in the biofilm, biofilm thickness, superficial area, and effective diffusivity. For the fungal biofilm, all the parameters mentioned above were obtained experimentally; and for the bacterial biofilm, the biofilm thickness and some intrinsic parameters used to obtain the first-order kinetic constant were taken from the literature. These parameters were then incorporated in a mathematical model to describe the steady-state degradation of hexane in bacterial and fungal biofilters operating under continuous mode. Experimentally, the dimensionless partition coefficients (mG) indicated that hexane was 4 and 35 times more soluble in the bacterial (mG = 9.14) and fungal (mG = 0.88) biofilters, respectively, than in water (mG = 30.4). Comparison of model estimates with experimental concentration profiles of the pollutant along the height of the biofilters proves that the first-order limited by reaction model was appropriate to interpret the experimental results with a small error of ∼1%.

Copper Removal from Aqueous Media Using a Cylindrical Flow Electrochemical Reactor

The construction and application of an electrochemical cylindrical flow reactor packed with copper wires, was used to eliminate Cu2+ ions from dilute aqueous CuSO4 solutions. The cathode of reactor was constructed with a series copper wire cylindrical hanks, piled up one on top of the other. The anode consisted of a graphite road electrode surrounded with a drilled PVC tube wrapped with Celgard® that serves to separate both the cathode and anode electrodes. Current and potential are supplied by an external power source. Results for Cu2+ ion concentration profile for dilute aqueous solutions applying an 8 V potential and a 0.17 cm3/s flow are reported. Copper removal efficiency ranges from 35 to 70% for all the samples examined. The experimental concentration profile fits an exponential decay along the axial reactor coordinate, in agreement with the theory for porous tubular flow reactors. A decrease in both solution conductivity and pH due to the reduction of copper ion concentration and water oxidation was observed.

Experimental and Simulation Study of Uphill Diffusion of Al in a Pt-Coated γ-Ni-Al Model Alloy

An experimental study of diffusion of Al, Ni, and Pt in a Pt-coated binary Ni-Al alloy has been made and compared with a computer simulation. Assessed thermodynamic and kinetic descriptions have been used. Starting from the measured experimental concentration profiles after 1 h heat treatment at 1173 K the simulation is compared to the experimentally determined profiles after 11 h continuous heat treatment. The experimental finding that Al will diffuse against its concentration gradient is explained by the strong lowering of the chemical potential by Pt. The simulation predicts that Al will reach a concentration maximum at the surface, larger than its bulk composition.

Catalytic reforming of gasoline to hydrogen: Kinetic investigation of deactivation processes

Abstract Catalytic reforming of gasoline to a hydrogen-rich gas is a possible route to feed a fuel cell for electricity production on-board a vehicle. To properly design a fuel processor system, knowledge about the kinetics of the different reactions involved in the reforming is needed. Kinetic studies are hampered by the fact that sulfur compounds present in commercial gasoline may lead to a progressive deactivation of the catalyst. We have undertaken such a study with an optically accessible catalytic channel flow reactor enabling concentration profiles and catalyst surface temperatures to be measured. The concentration profiles measured at different times on stream revealed a progressive deactivation of the catalyst. Isothermal reaction rate constants, depending on the time on stream, were derived by fitting a Langmuir–Hinshelwood kinetic model to the experimental species concentration profiles. The modeling results indicated that the steam reforming of higher hydrocarbons was more strongly affected by the presence of sulfur in the feed than the water gas shift reaction and the steam reforming of methane. Carbon formation was inferred from changes in surface emissivity during the experiments. It is suggested that the primary reason for the observed deactivation is due to the presence of sulfur compounds in the feed. The deactivated catalyst would then promote the formation of coke at the surface, i.e. coke formation is probably a consequence of the deactivation and not a cause for it. Although the variability in preparing the coated catalytic plates affected the measured kinetic rate parameters, the observed trends were in general consistent for all runs.