Constant Gas Ratio Research Articles

CO2 foam structure and displacement dynamics in a Hele–Shaw cell

The substitution of CO2 gas with CO2 foam for improved mobility control has recently attracted research attentions in enhanced oil recovery (EOR) as well as aquifer and soil remediation. However, the interplay between CO2 foam properties and oil displacement remains less investigated. In this work, using clear visualizations, we systematically investigate the dynamic advection-dominated foam morphology, its corresponding viscosity, and the efficiency and dynamics of oil displacement process by CO2 foam in a Hele–Shaw cell under the effects of gas ratio (Rg), fluid injection rates (Qt), and surfactant type. Clear visualization enables particle image velocimetry to calculate actual, rather than nominal, foam velocity that significantly affects the estimated foam viscosity. Our results demonstrate that at elevated gas ratios under constant total injection rate, larger and more uniform bubbles with less number density and greater interfacial area are obtained. Increasing the injection rates leads to finer foam texture at a constant gas ratio. Different foam structures have an impact on the foam viscosity, with a general increasing trend of viscosity for larger bubbles as Rg increases from 0.5 to 0.85. The higher the foam viscosity, the more stable displacement interfaces with less viscous fingers are observed, leading to improved sweeping rates. The green surfactants (saponin + Cellulose NanoFibers) provide foams with higher viscosity and, thus, more stable displacement interfaces. These findings highlight the important effect of Rg–dependent foam structure on its viscosity, which in turn is crucial for controlling the mobility of CO2 foam to maximize oil recovery rate during EOR processes.

Influence of Coating Deposition Parameters on the Mechanical and Tribological Properties of TiCN Coatings

This paper is a continuation of our previous work. The article presents an investigation of the influence of coating deposition parameters, in particular a variation with 50% of both cathodic arc current and bias voltage, on the mechanical and tribological properties of TiCN coatings deposited by the cathodic arc evaporation of metals at a constant gas ratio. The thicknesses of the coatings are measured by the Calotest method using a 30-mm hard steel ball. The determined values are in the range of 734 – 1534 nm. Surface morphology and chemical composition are estimated by a Scanning Electron Microscope (SEM) and an Energy Dispersive Spectrometer (EDS) of SEM. The determined values of nanohardness are in the range of 10 - 23 GPa and adhesion values are in the range of 28 - 70 N. Tribology of the TiCN coatings is investigated with three different load forces (3N, 5N and 8N) by the CETR UMI Multi-Specimen Test System from Bruker with an Si3N4 ball counter-body. The friction coefficient is measured in the range of 0.19 - 0.23. Coating wear and wear of the counter-body are calculated, according to the standard EN1071-13:2010, wherein the values of the latter are in the range of (2.5 - 30) x 10-6 mm3.

Branched carbon fibres and other carbon nanomaterials grown directly from 304 stainless steel using a chemical vapour deposition process

The objective of this research is to examine and illustrate the effect of the preparation of temperatures for the direct synthesis of branched carbon fibres on 304 stainless steel sheeting without the addition of external metal catalysts and pretreatment by chemical vapour deposition. The effects of different temperatures (900, 1050 and 1200°C) at a constant gas ratio of hydrogen, acetylene and nitrogen (1:1:2) on the direct growth of branched carbon fibres were investigated. The morphology obtained and the quality of branched carbon fibres as well as other carbon nanomaterials were examined with transmission electron microscopy, field emission scanning electron microscopy, thermogravimetry analysis and Raman spectroscopy. It was found that the temperatures are necessary for the growth of branched carbon fibres, tree branched carbon fibres and X-branched carbon fibres, as well as other carbon nanomaterials. In addition, the nanostructures of 304 stainless steel surfaces were investigated by atomic force microscopy at each temperature to describe the growth mechanism of branched carbon fibres and other carbon materials on the surfaces.

Study of Properties of AlN Thin Films Deposited by Reactive Magnetron Sputtering

Study of Aluminum nitride (AlN) thin film deposited on silicon wafer and glass substrates by DC magnetron sputtering technique at different power variation. The X-ray diffraction and Fourier transform infrared spectroscopy (FTIR) study revealed the formation of the AlN phase. The optical characteristics of films, such as refractiveindex, extinction coefficient, and average thickness, were calculated by Swanepoel's method using transmittance measurements. The refractiveindex and average roughness values of the films increased with film thickness. At lower power (100W) and constant gas ratio the film surface roughness was 1.7 nm. It was observed that films coated at lower power were 75% transparent in the visible spectral region.

Influence of ignition condition on the growth of silicon thin films using plasma enhanced chemical vapour deposition

The influences of the plasma ignition condition in plasma enhanced chemical vapour deposition (PECVD) on the interfaces and the microstructures of hydrogenated microcrystalline Si (μc-Si:H) thin films are investigated. The plasma ignition condition is modified by varying the ratio of SiH4 to H2 (RH). For plasma ignited with a constant gas ratio, the time-resolved optical emission spectroscopy presents a low value of the emission intensity ratio of Hα to SiH* (IHα/ISiH*) at the initial stage, which leads to a thick amorphous incubation layer. For the ignition condition with a profiling RH, the higher IHα/ISiH* values are realized. By optimizing the RH modulation, a uniform crystallinity along the growth direction and a denser μc-Si:H film can be obtained. However, an excessively high IHα/ISiH* may damage the interface properties, which is indicated by capacitance—voltage (C−V) measurements. Well controlling the ignition condition is critically important for the applications of Si thin films.

Influence of RF power on the electrical and mechanical properties of nano-structured carbon nitride thin films deposited by RF magnetron sputtering

Nano structured carbon nitride thin films were deposited at different RF powers in the range of 50 W to 225 W and constant gas ratio of (argon: nitrogen) Ar:N 2 by RF magnetron sputtering. The atomic percentage of Nitrogen: Carbon (N/C) content and impedance of the films increased from 14.36% to 22.31% and 9 × 10 − 1 Ω to 7 × 10 5 Ω respectively with increase in RF power. The hardness of the deposited films increased from 3.12 GPa to 13.12 GPa. The increase in sp 3 hybridized C–N sites and decrease of grain size with increase in RF power is responsible for such variation of observed mechanical and electrical properties.

Reaction Rates in the Synthesis of Ammonia. I. Dependence upon Reaction Pressure and Hydrogen-Nitrogen Ratio

Abstract This series of experiments presents the well known fact about the different concentration increases as well as the different decreases of the conversion efficiency with the increasing pressure depending upon the kinds of catalysts in greater detail. At extremely high space velocities, the ammonia concentration remains constant independent of the change of the total pressure when the mixture of a constant gas ratio (H2: N2=3: 1) is used; however, it increases with increasing nitrogen pressure when the mixtures of different initial compositions are used at a constant pressure. As predicted by Temkin’s equation, the nitrogen percentage or hydrogen percentage, at which a maximum ammonia concentration or a minimum conversion efficiency is observed, shifts towards the higher percentage with the increasing space velocity; however, the nitrogen percentage corresponding to the maximum shifts further through the critical value predicted by Temkin. The shifting is-more or less rapid depending on the kind of catalyst. To the extent that the space velocity is very high and the total pressure remains constant the equation by S. L. Kiperman can represent the shifting in a better agreement together with the observed proportionality between the ammonia concentration and the reciprocal space velocity. The rate equations of M. I. Temkin and M. Shindo, which are based on different concepts, have been compared with the present results, and neither M. I. Temkin’s nor M-Shindo’s (unimproved) is in satisfactory agreement with the results. An equation based on the concept by M. I. Temkin and provided with another factor characteristic of the kind of catalyst has been proposed. The equation is in better agreement with the experimental results concerning the ammonia concentration expressed as functions of the space velocity and the pressure. The maximum of the ammonia concentration or the minimum of the conversion efficiency related to the ratio of hydrogen to nitrogen is represented in a somewhat better agreement with the singly promoted catalyst, while yet unsatisfactorily with the triply promoted.