Function Of Gas Composition Research Articles

Application of Deep Neural Network-Artificial Neural Network Model for Prediction Of Dew Point Pressure in Gas Condensate Reservoirs from Field-X in the Niger Delta Region Nigeria

Reservoirs of natural gas and gas condensate have been proposed as a potential for providing affordable and cleaner energy sources to the global population growth and industrialization expansion simultaneously. This work evaluates reservoir simulation for production optimization using Deep Neural network - artificial neural network (DNN-ANN) model to predict the dew point pressure in gas condensate reservoirs from Field-X in the Niger Delta Region of Nigeria. The dew-point pressure (DPP) of gas condensate reservoirs was estimated as a function of gas composition, reservoir temperature, molecular weight and specific gravity of heptane plus percentage. Results obtained show that the mean relative error (MRE) and R-squared (R2) are 0.99965 and 3.35%, respectively, indicating that the model is excellent in predicting DPP values. The Deep Neural Network - Artificial Neural Network (DNN-ANN) model is also evaluated in comparison to earlier models created by previous authors. It was recommended that the DNN - ANN model developed in this study could be applied to reservoir simulation and modeling well performance analysis, reservoir engineering problems and production optimization.

Universal Map of Gas-Dependent Kinetic Selectivity in Carbon Nanotube Growth.

Single-walled carbon nanotubes have been a candidate for outperforming silicon in ultrascaled transistors, but the realization of nanotube-based integrated circuits requires dense arrays of purely semiconducting species. In order to directly grow such nanotube arrays on wafers, control over kinetics and thermodynamics in tube-catalyst systems plays a key role, and further progress requires a comprehensive understanding of seemingly contradictory reports on the growth kinetics. Here, we propose a universal kinetic model that decomposes the growth rates of nanotubes into the adsorption and removal of carbon atoms on the catalysts, and we provide its quantitative verification by ethanol-based isotope labeling experiments. While the removal of carbon from catalysts dominates the growth kinetics under a low supply of precursors, resulting in chirality-independent growth rates, our kinetic model and experiments demonstrate that chiral angle-dependent growth rates emerge when sufficient amounts of carbon and etching agents are cosupplied. The kinetic maps, as a product of generalizing the model, include five types of kinetic selectivity that emerge depending on the absolute quantities of gases with opposing effects. Our findings not only resolve discrepancies existing in the literature but also offer rational strategies to control the chirality, length, and density of nanotube arrays for practical applications.

Parameter estimation of a model describing respiration rate of dragon fruit as a function of gas composition and temperature

Parameter estimation of a model describing respiration rate of dragon fruit as a function of gas composition and temperature

Effect of Heat Input and Shielding Gas on the Performance of 316 Stainless Steel Gas Tungsten Arc Welding

The effect of nitrogen addition and heat input on weld metal microstructure and mechanical properties of alloy 316 is studied. Autogenous gas tungsten arc welding (GTAW) is employed by adding up to 2 vol‌.% N2 in Ar. Welding speed and heat input rate are measured as functions of gas composition. Weld defects are examined by radiographic testing, and weld metal microstructure is studied by optical microscopy. Mechanical properties of welds are determined by uniaxial testing, hardness measurements, and bending test. Weld dendritic structure is refined by increasing N2 content in Ar. The mechanical properties and cooling rate are lower with increasing heat input. Besides, adding nitrogen to argon shielding gas leads to higher values of the ultimate tensile strength and hardness. The tensile strength, yield stress and elongation percent of welds depends strongly on the heat input and nitrogen content of shielding gas. This is discussed on the basis of microstructural characterization. Moreover, the weld nugget area, cooling time and solidification time increase with increasing heat input and nitrogen content. Finally, after applying the bending test up to 180o no cracks, tearing or surface defects could be observed on welded samples.

A neural computing strategy to estimate dew-point pressure of gas condensate reservoirs

A novel multilayer perceptron artificial neural network (MLP-ANN) model is proposed to estimate the dew-point pressure (DPP) of gas condensate reservoirs as a function of gas composition, reservoir temperature and, molecular weight and specific gravity of C7+. For this purpose, a comprehensive database was prepared by reviewing literature and the results of MLP-ANN are graphically and statistically compared with these actual values. The R-squared (R2) and mean relative error are determined to be 0.9868 and 1.5%, respectively, which reveals that DPP values are well predicted by this model. Furthermore, the MLP-ANN model is compared with previous developed models.

Modelling respiration rate of dragon fruit as a function of gas composition and temperature

The application of controlled atmosphere and modified atmosphere packaging to extend the shelf life of dragon fruit requires insight into the respiration behaviour of the fruit under different storage conditions. To this end, this study focused on characterising the respiration kinetics of dragon fruit using a dynamic closed depletion system. An integrated data analysis was performed using a Michaelis-Menten based respiration model extended with an Arrhenius equation to account for the effects of O2, CO2 and temperature. Iterative analysis of the data using different model versions eventually revealed that the classical Arrhenius equation did not suffice to explain the observed respiration behaviour over the whole temperature range (2 °C–35 °C). The experimental data consistently showed lower respiration at 35 °C as compared to what was predicted by the classical Arrhenius equation. To overcome this problem, a modified Arrhenius equation, incorporating the Boltzmann distribution function, was successfully introduced to account for this observed temperature effect, predicting a maximal respiration rate at 33.9 °C. The parameters of the final model were estimated with high precision, explaining 98 % the data variance. Additionally, it was shown that CO2 had an uncompetitive inhibition on oxidative respiration, while O2 concentration affected both oxidative respiration and fermentation. This is the first documented example of postharvest fruit respiration not following the classical Arrhenius’ law at what could still be considered near field temperatures.

Biopolymer Coatings as Alternative to Modified Atmosphere Packaging for Shelf Life Extension of Minimally Processed Apples

The effect of caseinate/chitosan blend on the shelf life of minimally processed apples was studied. In the first phase of the work, the effect of the biopolymer coating on the respiration rate of the minimally processed apples was studied as function of gas composition (5%, 10%, 21% of O2 with N2 as balance at 5 °C) and temperature (5 °C, 10 °C at 5% of O2 with N2 as balance). In the second phase, the shelf life of the packed product was studied during storage at 5 °C. The gas composition (O2%-CO2%) in the package headspace, relative humidity, pH, hardness, color and antioxidant capacity of the product were monitored after 0, 1, 4, 7, 11, and 14 days. The coating effectively reduced respiration rate of the product when oxygen was over 10%. In the presence of the coating, the reduction of oxygen did not affect the respiration rate. At 5% of O2, the respiration rate decreased by 50% by changing the temperature from 10 °C to 5 °C. Shelf life study showed that the chitosan—caseinate coating was able to preserve the mechanical properties and the antioxidant capacity of the product during storage by increasing the shelf life by 7 days to 11 days at 5 °C.

Study of pure and mixed clustered noble gas puffs irradiated with a high intensity (7 × 1019 W/cm2) sub-ps laser beam and achievement of a strong X-ray flash in a laser-generated debris-free X-ray source

AbstractWe present a broad study of linear, clustered, noble gas puffs irradiated with the frequency doubled (527 nm) Titan laser at Lawrence Livermore National Laboratory. Pure Ar, Kr, and Xe clustered gas puffs, as well as two mixed-gas puffs consisting of KrAr and XeKrAr gases, make up the targets. Characterization experiments to determine gas-puff density show that varying the experimental parameter gas-delay timing (the delay between gas puff initialization and laser-gas-puff interaction) provides a simple control over the gas-puff density. X-ray emission (>1.4 keV) is studied as a function of gas composition, density, and delay timing. Xe gas puffs produce the strongest peak radiation in the several keV spectral region. The emitted radiation was found to be anisotropic, with smaller X-ray flux observed in the direction perpendicular to both laser beam propagation and polarization directions. The degree of anisotropy is independent of gas target type but increases with photon energy. X-ray spectroscopic measurements estimate plasma parameters and highlight their difference with previous studies. Electron beams with energy in excess of 72 keV are present in the noble gas-puff plasmas and results indicate that Ar plays a key role in their production. A drastic increase in harder X-ray emissions (X-ray flash effect) and multi-MeV electron-beam generation from Xe gas-puff plasma occurred when the laser beam was focused on the front edge of the linear gas puff.

Evaluating the dielectric strength of helium-nitrogen gas mixtures by plasma parameter measurements

Plasma diagnostic experiments are used for understanding the dielectric strength of gaseous cooling media. Plasma measurements on helium-nitrogen gas mixtures with varying composition were conducted with a single-tip Langmuir probe. The data from the measurements were used to derive the electron temperature and electron density. The results suggest that the measured electron temperature is suitable for assessing the dielectric strength variation of the gaseous media as a function of gas composition. However, the results also confirmed that the measured electron density is substantially influenced by the effective wall area of the plasma chamber and thus is inappropriate for being used as the indicator of dielectric strength variation.

Electron beam-generated Ar/N2 plasmas: The effect of nitrogen addition on the brightest argon emission lines

The effect of nitrogen addition on the emission intensities of the brightest argon lines produced in a low pressure argon/nitrogen electron beam-generated plasmas is characterized using optical emission spectroscopy. In particular, a decrease in the intensities of the 811.5 nm and 763.5 nm lines is observed, while the intensity of the 750.4 nm line remains unchanged as nitrogen is added. To explain this phenomenon, a non-equilibrium collisional-radiative model is developed and used to compute the population of argon excited states and line intensities as a function of gas composition. The results show that the addition of nitrogen to argon modifies the electron energy distribution function, reduces the electron temperature, and depopulates Ar metastables in exchange reactions with electrons and N2 molecules, all of which lead to changes in argon excited states population and thus the emission originating from the Ar 4p levels.

Evaluation of combustion models for determination of refinery furnaces efficiency

The efficiency of combustion in furnaces is the measure of heat released in the flame absorbed by the fluid to be heated and is considered one of the most important variables when conducting studies on processes that occur in continuous process industries. The furnace efficiency is calculated using various mathematical models proposed in the literature; these models vary in complexity depending on the analyzed variables. The models I and II are based on the amount of energy absorbed by the furnace using the heating value, the model III contains variables such as air excess, stack gas temperature and adiabatic flame temperature, meanwhile the model IV contains heating losses in furnace�s wall (2%), the stack gas temperature and excess air. In this paper was used computer simulation to evaluate fuel gas mixtures with Lower Heating Values (LHV) between 800 to 2500 Btu/ft3, and they were compared with natural gas and data process; the results show that the combustion characteristics might change by varying the fuel composition. It was also found decreased combustion efficiency due to high hydrogen concentration; on the other hand the adiabatic flame temperature was increased in function of gas composition. Model IV presented in this research allowed evaluating combustion process efficiency using only two variables: stack gas temperature and the excess air.

Behavior of Supported Palladium Oxide Nanoparticles under Reaction Conditions, Studied with near Ambient Pressure XPS.

Near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) is a promising method to close the "pressure gap", and thus, study the surface composition during heterogeneous reactions in situ. The specialized spectrometers necessary for this analytical technique have recently been adapted to operate with a conventional X-ray source, making it available for routine quantitative analysis in the laboratory. This is shown in the present in situ study of the partial oxidation of 2-propanol catalyzed with PdO nanoparticles supported on TiO2, which was investigated under reaction conditions as a function of gas composition (alcohol-to-oxygen ratio) and temperature. Exposure of the nanoparticles to 2-propanol at 30 °C leads to immediate partial reduction of the PdO, followed by a continuous reduction of the remaining PdO during heating. However, gaseous oxygen inhibits the reduction of PdO below 90 °C, and the oxidation of 2-propanol to carboxylates only occurs in the presence of oxygen above 90 °C. These results support the theory that metallic palladium is the active catalyst material, and they show that environmental conditions affect the nanoparticles and the reaction process significantly. The study also revealed challenges and limitations of this analytical method. Specifically, the intensity and fixed photon energy of a conventional X-ray source limit the spectral resolution and surface sensitivity of lab-based NAP-XPS, which affect precision and accuracy of the quantitative analysis.

Parameters Affecting the Rate and Product of Liquid Silicon Oxidation

The oxidation of liquid silicon resulting in silica fume has been the subject of previous investigation due to its importance to occupational health in the silicon alloy production industry. Small-scale experiments and industrial measurements have been carried out in order to understand the mechanisms and kinetics of liquid silicon oxidation. Key questions as to the main factors and conditions determining the rate of fume formation in the industry, still remain. In this work the rate of active oxidation of liquid silicon was studied by experimental investigations in a 75 kW induction furnace, where oxidizing gas was introduced via a lance above the liquid silicon surface. The silica formed as a result of the reaction was collected and the silica fuming rate determined as a function of gas composition and gas flow velocity. The system was also modeled using computational fluid dynamics (CFD) and kinetic modeling. The flux of silica increases with increased gas velocity above the liquid surface, and was found to correlate well with mass transfer rates calculated from impinging jet theory. The size of the silica particles was also found to be dependent on the gas flow rate; smaller average particle size was obtained at higher flow rates. It was found that the most important factor for the silicon oxidation reaction rate is the velocity of the gas in vicinity of the silicon surface (i.e. the boundary layer thickness). The velocity is more important than the actual amount of oxygen delivered to the system per unit time, indicating that oxygen “efficiency” is not a strong function of oxygen concentration in the gas. Thus, the gas velocity is the rate determining parameter in determining the mass transport of oxygen to the silicon surface. Results from computational fluid dynamics simulations show that the gas flow was laminar in all experiments and that oxidation takes place within 0.5 mm from the silicon surface. The results from the experiments and the CFD model were used to suggest a molecular mechanism of the active oxidation of liquid silicon.

Development of a Surface Area Dependent Rate Expression for Soot Oxidation in Diesel Particulate Filters

We collected soot from diesel engine exhaust on miniature particulate filter samples and evaluated soot oxidation rates on an automated flow reactor system. A series of isothermal pulsed oxidation experiments quantified reaction rates as a function of gas composition, temperature, flow rate, and soot consumption. An O2 chemisorption method measured the soot active surface area as filter regeneration progressed. We developed a rate law with an explicit dependence on carbon surface area and estimated the associated kinetic parameters from the pulsed oxidation data. The resulting rate expression successfully captures the soot oxidation behavior over a wide range of operating conditions.

The electrical properties of NOx-storing carbonates during NOx exposure

In order to gain a deeper understanding of the different components in multi-component automotive catalyst systems and integrating type NOx-sensors, in-situ electrical methods are examined. The conductivity of BaCO3 and K2CO3, key components in automotive NOx storage catalysts, was examined as a function of gas composition and temperature. Impedance measurements performed on BaCO3, K2CO3, and equimolar mixtures of both, demonstrated that, in all cases, the resistance decreases in the presence of NO2 gas with progressive NOx sorption on the carbonate surface. Mixing the hygroscopic but low resistivity K2CO3 with the very highly resistive but stable BaCO3 resulted in greater stability than K2CO3 alone, as well as improved ability to measure resistivity changes. The resistance of the mixture recovered about 50% of its value after removing NO2 from the gas stream, believed to result from migration of sorbed NOx from K to Ba, instead of desorption alone. These results on NOx trap materials show that in-situ impedance spectroscopy measurements offer real-time characterization of NOx loading levels in lean NOx trap catalyst components.

Ion acceleration in Ar–Xe and Ar–He plasmas. II. Ion velocity distribution functions

Ion velocity distribution functions (ivdfs) are investigated by laser induced fluorescence in Ar–Xe and Ar–He expanding helicon plasmas as a function of gas composition. In the case of Ar–Xe plasma, it was found that in the helicon source, both the Ar+ and Xe+ vdfs are unimodal. Their parallel speeds are subsonic and unaffected by changes in gas composition. At the end of the source, the argon ivdf shows a bimodal structure indicative of an electric double layer upstream of the measurement location. The fast argon ion component parallel velocity increases with Xe fraction from 6.7 to 8 km/s as the Xe fraction increases from 0% to 4%. In the expansion region, the bimodal character of Ar ivdf is maintained with a supersonic fast component reaching parallel speeds of 10.5 km/s. For all the studied plasma conditions and different spatial locations, the Xe+ vdf exhibits a unimodal structure with a maximum parallel flow velocity of 2.2 km/s at the end of the source. For Ar–He plasma, the Ar ivdf is bimodal with the fast ion component parallel velocity increasing from 5.2 to 7.8 km/s as the He fraction increases from 0% to 30%. For the same He fraction range, the slow argon ion population distribution changes from a single Gaussian to a wide distribution extending all the way from the speed of the fast population to 0 m/s.

Studying the CO–CO 2 characteristics of SOFC anodes by means of patterned Ni anodes

The high potential of solid oxide fuel cells (SOFC) arises due to the high degree of efficiency and fuel flexibility. However, the elementary kinetic steps of the anodic processes taking place at the boundary of electrolyte–anode–gas are still largely unknown. Patterned Ni anodes on Y 2O 3-stabilized ZrO 2 are regarded as a promising method to determine these kinetics. In analogy to our previous study with patterned Ni anodes for the H 2–H 2O system, this study is systematically devoted to the elementary kinetics of the CO electrochemical oxidation in CO–CO 2 gas mixtures. Data analysis is backed by extensive knowledge on patterned anode stability and dynamics gained during previous studies. The electrochemical characterization is performed for a large parameter variation range ( pCO 2, pCO and T) by electrochemical impedance spectroscopy. Contrary to the characterization in H 2–H 2O atmosphere no slow relaxation processes were observed and the degradation rate is smaller. Changes in parameter dependency over the investigated parameter range indicate different reaction mechanisms as a function of gas composition. Only slightly higher polarization losses are observed for CO oxidation compared to H 2. The comparison of the results from patterned anodes to high-performance Ni/8YSZ cermet anodes employed in anode supported cells yields good agreement.

Simulation of automotive NH 3 oxidation catalysts based on pre-computed rate data from mechanistic surface kinetics

This paper demonstrates how pre-computed rate data can be used to enable the numerically efficient implementation of mechanistic kinetics in a reactor model for an automotive ammonia slip catalyst. In a pre-processing step the source terms for the gas species are mapped as a function of gas composition and temperature. From this map (80,000 data points), a spline interpolation function is constructed. The spline function approximates the numerical steady state solution of the kinetic model with an average error of less than 1%. Application of the rate mapping procedure results in a speedup of about two orders of magnitude. The spline approximation is implemented in a 2-dimensional model of a monolith reactor channel that includes diffusion in the washcoat layer. Depending on the channel diameter and the washcoat thickness, diffusion limitations in the open channel and in the washcoat can have a significant influence on the NH 3 conversion. Surprisingly, the selectivity for the products N 2, N 2O and NO is not sensitive to diffusion effects in the gas phase or in the washcoat.

Short-Time Oxidation Behavior of Low-Carbon, Low-Silicon Steel in Air at 850–1180 °C: II. Linear to Parabolic Transition Determined Using Existing Gas-Phase Transport and Solid-Phase Diffusion Theories

Existing gas-phase transport and solid-phase diffusion theories are used to calculate the oxidation kinetics of low carbon and low silicon steel in flowing air at 850–1180 °C. The linear-to-parabolic transition scale thickness derived is proportional to the parabolic rate constant and inversely proportional to the linear rate constant. Calculated parabolic rate constants are consistent with experimental results, whereas calculated linear rate constants are 40% smaller and calculated linear-to-parabolic transition scale thicknesses are 20–40% greater than the experimental results. Introduction of a correction factor cannot simultaneously resolve the discrepancies. Various sources causing the discrepancies are discussed. One important issue identified is that the conditions for deriving the equation for calculating the linear rate constant are different from those in laboratory furnaces. The linear-to-parabolic transition scale thickness derived is also a function of gas composition, gas velocity and sample length. An intrinsic gas-phase mass-transfer factor, independent of gas velocity and sample size, is recommended to express the gas-phase mass-transfer coefficient for calculating the linear rate constant.

Combustion of Boron-Titanium Nanocomposite Powders in Different Environments

Combustion of nanocomposite powders with the bulk composition 2B+Ti was compared with combustion of blended boron and titanium powders with the same bulk composition and with combustion of aluminum in wet and dry gas environments. Nanocomposite powders were prepared by Arrested Reactive Milling. The gas environments were N2/O 2/CH 4 mixtures with oxygen concentration fixed at 22.5 % and methane concentration varied from 0 to 12 %. The experiments were conducted in a constant volume explosion vessel. The mass loads of metallic fuel were determined from thermodynamic calculations to ensure the maximum flame temperature for each metal fuel – gas mixture combination. The calculations showed that despite the higher adiabatic flame temperatures for Al than for 2B+Ti, a greater energy per unit mass of metal fuel was released to produce heated gaseous combustion products in combustion of 2B+Ti as compared to Al. Experiments with Al powders showed that the flame temperature did not change noticeably as a function of gas composition and remained close to 2560 K. The combustion temperature for the nanocomposite 2B+Ti increased from about 2180 to 2370 K as the methane concentration increased from 0 to 12 %. The bulk burn rates inferred from the rates of pressure rise were consistently higher for the nanocomposite 2B+Ti powder, followed by Al and then by the blended 2B+Ti powder. The efficiency of combustion for all the fuels was assessed by comparing the predicted and experimental portions of the combustion energy used to produce the heated gaseous products. Based on this assessment, nanocomposite boron-based fuels outperformed Al for all environments, with the difference increasing at the increased methane concentrations. Nearly complete combustion was observed for both 2B+Ti fuels (nanocomposite and blended powders) at high methane concentration, when the highest rates of combustion were also observed. Thus, the effect of kinetic trap associated with formation of HOBO could not be detected. It was concluded that nanocomposite 2B+Ti powders enable one to achieve rapid and highly efficient combustion in both dry and wet gaseous environments.