Assisted Gas Research Articles

Parametric analysis and optimization of a solar assisted gas turbine

The objective of this study is to analyze and optimize a solar assisted gas turbine system. Parabolic trough collectors are used in order to supply a part of the demanded heat input, reducing the natural gas consumption and leading to an environmental friendly system. Emphasis is given in the pressure losses in the collector field loop which reduce the pressure level in the turbine inlet, leading to lower electricity production. In the first part of this study, the gas turbine and the collector field are investigated separately and in the second part, the solar assisted gas turbine is investigated parametrically and it is optimized. In the optimization part, a multi-objective optimization is performed by setting as goals the minimization of the collector area, of the fuel consumption and of the inversed electricity production. The final results proved that 1050 collector modules lead to 0.3389kg/s natural gas consumption and to electricity production equal to 14.81MWel. This optimum solution leads to 64% fuel savings with a 2.8% penalty on the produced electricity. The system is analyzed in steady state conditions with the Engineering Equator Solver (EES).

Characterization and comparison of key aroma-active compounds of cocoa liquors from five different areas

ABSTRACTThe volatile constituents of cocoa liquor and the differences between cocoa liquors from different origins were studied. Direct solvent extraction-solvent assisted flavor evaporation and gas chromatography-olfactrometry-mass spectrometry in conjunction with aroma extract dilution analysis were used to identify the key flavor compounds in five cocoa liquors. There were significant differences of specific compounds between cocoa liquor from different areas of origins. Then, the purge and trap method was used to gathering the aroma-active components of five cocoa liquors from different origins, and one internal standard was used during this process for the further quantitative analysis by gas chromatography-olfactrometry-mass spectrometry. The results indicated that 3-methylbutanal, acetic acid, tetramethylpyrazine, and 3-methylbutanoic acid were the components with high concentrations. The contents of most compounds in the five kinds of cocoa liquor were dramatically different. The content of odorants of cocoa liquors from Papua New Guinea was higher than that of the others and that from Indonesia was the lowest. For sensory evaluation, the overall odor outlines of the five cocoa liquors were very similar, the Papua New Guinea cocoa liquor had higher preference than those of the other four samples. Principal component analysis showed that the characteristics of cocoa liquor from Papua New Guinea, Indonesia, and Ivory Coast were very significant.

Evolution of Microstructure, Mechanical Properties and Corrosion Resistance of Ultrasonic Assisted Welded-Brazed Mg/Ti Joint

Ultrasonic vibration with different powers from 0 kW to 1.6 kW was applied during the tungsten inert gas welding-brazing of Mg/Ti. The microstructures, mechanical properties and corrosion resistance of the ultrasonic assisted tungsten inert gas (U-TIG) welded-brazed Mg/Ti joint were characterized. The results showed that, without being subjected to ultrasonic vibration, coarse columnar α-Mg grains occurred in the fusion zone of Mg/Ti joint. However, with ultrasonic power of 1.2 kW, the average grain size of columnar α-Mg grains was refined from 200 µm to about 50 µm and the tensile strength of joints increased ~18% up to 228 MPa. Besides, high fraction of grain boundaries was introduced by grain refinement, contributing to improve the corrosion resistance in two ways: (i) accelerating the formation of Mg(OH)2 protective layer and (ii) reducing the mismatch and disorder between Mg(OH)2 protective layer and Mg alloy surface.

Understanding the crystalline phase formation in Fe[sbnd]Ni and Al[sbnd]Ni binary alloy-nanoparticles produced by thermal plasma assisted gas phase condensation method

The paper addresses the issue of phase formation in the nano-crystalline binary alloys of FeNi and AlNi, synthesized by plasma assisted vapor phase condensation process. In depth experimental analysis of the crystal structure, for the alloy nanoparticles with different compositions, is presented. The observed crystalline phases of the products have been compared with those expected from the standard phase diagram of the respective alloys. Crystalline phases of FeNi system showed no deviation, whereas, those of AlNi showed considerable deviation. Differences in the thermo-physical properties of Al and Ni are shown to be responsible for such a deviation. The results are supported by a computational model, which accounts for the supersaturation of the species in gas phase, leading to nucleation and growth.

Experimental and finite element analysis of ultrasonic vibration−assisted continuous-wave laser surface drilling

ABSTRACTIn pulsed laser drilling with co-axial assisted gas, material removal mechanism (surface vaporization and melt expulsion) determines the machining/drilling rate and quality of the drilled holes. Incomplete melt expulsion is one of the major causes of laser drilling defects. To improve the drilling efficiency and quality of holes, a novel ultrasonic vibration−assisted continuous-wave laser drilling (UVLD) approach is proposed. The application of ultrasonic vibrations (of frequency of 20 kHz and vibration displacement of 23 µm) during laser surface melting facilitates the melt expulsion in the form of sideways melt flow and droplet ejection from the drilling front. A systematic experimental study on the ultrasonic vibration-assisted laser drilling of AISI 316 stainless steel is performed to investigate the effect of working distance on the geometric features and surface quality of the holes. The experimental results based on high-speed photography indicate that the melt expulsion under the influence of ultrasonic vibrations initiates after the laser melted pool reaches a critical size/volume. Based on this underlying mechanism, a simplified finite element analysis is performed for the UVLD process to predict the hole volumes for the investigated working distances.

Iridium single atom tips fabricated by field assisted reactive gas etching

We present a simple, reliable method to fabricate Ir single atom tips (SATs) from polycrystalline wire. An electrochemical etch in CaCl2 solution is followed by a field assisted reactive gas etch in vacuum at room temperature using oxygen as an etching gas and neon as an imaging gas. Once formed, SATs are cooled to liquid nitrogen temperatures and their underlying structure is examined through evaporation of the apex atoms. Furthermore, a method is developed to repair Ir SATs at liquid nitrogen temperatures when apex atoms evaporate. This method may be used to fabricate Ir SAT ion sources.

Prior sheet buckling leading to wrinkling formation in a gas forming a V-trough with wavy bottom

When the amount of stretching strain exceeds material's intrinsic capability in gas forming a complex shape metallic sheet, gas pressurization operation can fail due to sheet material's perforation. A hot-bent assisted gas forming method for shaping a long V-trough with deep bottom of longitudinal wavy shape is proposed for obtaining the product with harmless wrinkle and relatively uniform thickness. This method consists of three sequential actions—an instant hot V-shape bending together with die closing followed by controlled pressurized gas blowing for a period of time. For this method, the depth of hot bending is varied as a parameter to generate pre-forms bearing various contours which consequently determine wrinkling situation in the subsequent gas forming product. Two groups of specimens differing in sheet size are adopted. Regular AA5052 (coarsely grained) and superplastic grade AA5083 (fine grained) alloys are used for experimental works.

Deposition of Boron Nitride Films by Filament-Assisted CVD Using Tris(Bimethylamino)Borane Precursor

Boron nitride films were deposited on silicon substrate by a hot filament assisted chemical vapor deposition (HFCVD) system. The tris (dimethylamino) borane (B[N(CH3)2]3) was used as the single source precursor which has both the boron and nitrogen source, ammonia gas was used as the assisted gas to increase the nitrogen concentration in the films. The films deposited by different ratios of precursor to ammonia gas flow rate and filament temperatures were investigated. The boron-carbon-nitrogen (BCN) compound films were deposited under lower filament temperature. With increasing the ammonia gas flow rate, the carbon concentration in the films decreased. Fourier transform infrared spectroscopy (FT-IR) and transmission electron microscopy (TEM) image reveal that hexagonal boron nitride (hBN) films were deposited at the higher filament temperature of 2000°C. Moreover, the crystallization degree of the films became better with the filament temperature increased.

Development of Nanostructured Hybrid Materials for Electrocatalytic and Photoelectrocatalytic Reduction of Carbon Dioxide

There has been growing interest in the electrochemical reduction of carbon dioxide (CO2), a potent greenhouse gas and a contributor to global climate change, and its conversion into useful carbon-based fuels or chemicals. Numerous homogeneous and heterogeneous catalytic systems have been proposed to induce the CO2 reduction and, depending on the reaction conditions various products that include carbon monoxide, oxalate, formate, carboxylic acids, formaldehyde, acetone or methanol, in addition to various hydrocarbons at different ratios. Given the fact that the CO2 molecule is very stable, its electroreduction processes are characterized by large overpotentials. To produce highly efficient and selective electrocatalysts, the transition-metal-based molecular materials are often considered. It is believed that, during electroreduction, the rate limiting step is the protonation of the adsorbed CO product to form the CHO adsorbate. Because reduction of CO2 can effectively occur by hydrogenation, to optimize the conventional electrocatalytic approach, we propose such a model catalytic system as nanostructured metallic palladium capable of absorbing reactive hydrogen in addition to the ability to adsorb monoatomic hydrogen at the interface. Under such conditions, the two-electron reduction of CO2 typically to CO is favored. To produce highly dispersed and reactive nanoparticles, we generate them by electrodeposition from N-coordination complexes of palladium(II). The resulting metallic Pd nanoparticles, rather than Pd cationic species, are stabilized and activated by nitrogen coordination centers from the macromolecular matrix. In the present research, we demonstrate that stabilization and activation of highly dispersed nanostructured metallic Pd centers with a supramolecular architecture of “privileged ligands” results in the electrocatalytic enhancement of the CO2 reduction. Reduction of carbon dioxide begins now at less negative potentials and is accompanied by significant enhancement of the CO2-reduction current densities. Among important issues are specific interactions between nitrogen coordinating centers and metallic palladium sites at the electrocatalytic interface. Another possibility to enhance electroreduction of carbon dioxide is to explore direct transformation of solar energy to chemical energy using transition metal oxide semiconductor materials. We show here that, by intentional and controlled combination of metal oxide semiconductors, we have been able to drive effectively photoelectrochemical reduction of carbon dioxide. The combination of titanium (IV) oxide (TiO2) and copper (I) oxide (Cu2O) has been explored toward the reduction of carbon (IV) oxide (CO2) before and after sunlight illumination. Application of the hybrid system composed of both above-mentioned oxides resulted in high current densities originating from photoelectrochemical reduction of carbon dioxide mostly to methanol (CH3OH), as demonstrated upon identification of final products using conventional and mass-spectrometry assisted gas chromatography. On mechanistic grounds, the role of TiO2 seems to be not only stabilizing: the oxide is also expected to prevent the recombination of charge carriers.

Biosynthesis of Gold Nanoparticles and Identification of Capping Agent Using Gas Chromatography-Mass Spectrometry and Matrix Assisted Laser Desorption Ionization-Mass Spectrometry.

In the present study, gold nanoparticles (AuNPs) were synthesized using leaf extract of Syzygium jambolanum and capping agent has been explored. The synthesized AuNPs have been characterized using UV-visible spectroscopy (UV-vis), Fourier transform infrared spectroscopy (FTIR), high resolution transmission electron microscopy (HRTEM) and atomic force microscopic (AFM) analysis. The AuNPs show intense surface plasmon resonance (SPR) band at 528 nm and were found to be spherical and hexagonal in shape with particle size ranging from 20-30 nm. Transmission electron microscopy and atomic force microscopy were used to analyze the surface morphology of synthesized AuNPs. The capping ligand has been evaluated using matrix assisted laser desorption ionization-mass spectrometry (MALDI-MS) and gas chromatography-mass spectrometry (GC-MS) analysis.

Superplastic forming process applied to aero-industrial strakelet: wrinkling, thickness, and microstructure analysis

Superplastic forming (SPF) of an aluminum sheet trough with a large depth to width ratio is challenging because of the difficulties in obtaining a satisfactory, uniform thickness distribution. To address this problem, two different SPF techniques, namely, two-stage gas forming (TSGF) and hot-bend assisted gas forming (HBAGF), were used to fabricate airplane strakelets. Undesirable wrinkling occurred in both cases, but the sites and causes of wrinkle formation were different. Thickness measurements around the edge of the circumference were relatively uniform, with a minimum thickness of ∼1.32 mm (∼34.0 % thinning percentage) for the HBAGF sample. This thickness significantly exceeded that of a sample processed by a previously developed TSGF method (∼0.8 mm, ∼60 % thinning percentage). Three-dimensional finite element analysis was implemented to accurately predict the shape and occurrence of wrinkling. Furthermore, experimental forming trials with the HBAGF die led to significant improvement of the thickness profile of superplastically formed parts.

Reinforcement of Mg/Ti joints using ultrasonic assisted tungsten inert gas welding–brazing technology

Ultrasonic assisted tungsten inert gas welding–brazing technology was developed to refine coarsening columnar α-Mg grains of Mg/Ti joints. In this study, ultrasonic vibration was introduced into molten pool of Mg/Ti joints with frequency of 20 kHz and maximum power of 1·6 kW. The results showed that, with ultrasonic power of 1·2 kW, the morphology of columnar α-Mg grains was refined to approximately equiaxed grains and the average grain size of columnar grains decreased from 200 to ∼50 μm. Moreover, the maximum joint strength of joints increased ∼18·1% to 228 N mm−1 over the joints welded without ultrasonic vibration (193 N mm−1). Furthermore, the optimised Mg/Ti joint fractured at base metal zone rather than fusion zone upon tensile–shear loading, indicating that efficient grain refinement was attained. However, welding voids occurred with the ultrasonic power further increased to 1·6 kW, which resulted in the decrease in mechanical properties.

Thermodynamic analysis of a combined chemical looping-based trigeneration system

Energy and exergy analyses of a newly developed three-reactor chemical looping hydrogen generation process are performed for trigeneration of power, hydrogen, and heating. The present integrated system consists of an (a) air separation unit (ASU), (b) gasification sub-system, (c) chemical looping hydrogen generation unit in connection with SOFC assisted gas turbine (CLHG-SOFC/GT), (d) an extended heat recovery steam generation unit (HRSG) to supply heat for Steam cycle, organic Rankine cycle and space heating, (e) a two stage steam Rankine cycle (SRC) for power generation with reheat and regeneration, and (f) an organic Rankine cycle (ORC) to produce power. The gasified coal is separated and purified in quench chamber and syngas cleaner; CO2 and H2 are generated from fuel and steam reactors of chemical looping unit, and both are then compressed after separated from water and ready for transportation. A specified amount of H2 produced from steam reactor is also used to produce electricity with SOFC/GT. A comprehensive parametric study is performed, and the effects of multi-generation and system integration, environmental conditions, and system parameter variations on overall efficiencies are investigated. Overall electrical, hydrogen, energy and exergy efficiencies are comparatively determined for different cases. Overall energy and exergy efficiencies of proposed system are found to be 56.9% and 45.05%, respectively, with a total exergy destruction rate of 15,421kW. The highest exergy destruction occurs in the gasifier and CLHG due to high temperature chemical processes.

Synthesis of Silicon Nanostructures Using DC-Arc Thermal Plasma: Effect of Ambient Hydrogen on Morphology

Silicon nanoparticles (Si-NPs) were synthesized using thermal plasma assisted gas phase condensation at different compositions of argon and hydrogen. The content of hydrogen in argon was varied from 0 to 15 mole percent. Synthesized nanoparticles were characterized by Transmission Electron Microscopy (TEM) and Fourier Transform Infrared spectroscopy (FTIR). Noticeable change in the morphology of nanostructures was observed with changing hydrogen content. Si-NPs synthesized in the presence of argon consisted of flake like structures, mostly amorphous. With increase in hydrogen concentration, flake like structures disappeared and prominent spherical structures and nanowires were observed. On further increasing hydrogen content spherical crystalline nanostructures with a tail of nanowire were formed and then nanoplatelets of SiC along with silicon nanostructures were observed. Different parameters that changed owing to different hydrogen concentration, were calculated and it is attempted to predict the cause of changing morphology.

Gas-Jet-Assisted Keyhole Laser Welding of Q235 Mild Steel

Increases in the penetration depth of laser welding has gained undoubted interest, especially in the aerospace, power station, ship building, and other heavy industries. Gas-jet-assisted keyhole laser welding is a prospective method for improving the penetration of conventional laser welding. A series of experiments using this method were conducted with different parameters of the assisted gas jet and the welding speed. The microstructures of weld joints were observed using optical microscopy, and microhardness was also measured. The investigation results showed that the penetration depth of this laser welding increased by more than 20%, with a maximum increase of approximately 26%, at different welding speeds, while the weld width was significantly reduced compared with that of conventional laser welding. The key factor affecting the penetration increase is the interaction between the assisted gas jet and the plasma. The penetration increase was determined by the distribution and amplitude of the assisted gas jet at the position of the keyhole orifice. The grain in the heat-affected zone (HAZ) and weld seam of gas-jet-assisted keyhole laser welding was finer, and the number of columnar grains was also significantly reduced. The microhardness of the HAZ for the assisted gas jet was much lower, and more pearlite and less martensite were observed this zone. This was caused by the reduced maximum temperature of the molten pool, reduced high-temperature residence time, increased cooling rate, and diminished temperature gradient with the introduction of the assisted gas jet.

Pyrometric Monitoring of Gas-Assisted Cutting of Steel Using Fiber Laser

Measurements of the temperature in zone of action of laser radiation on the molten metal have been performed. The results are reported for different speed of cutting of mild-steel plate of 3 mm-thick with high-power fiber laser; oxygen was used as an assisted gas. Researches demonstrate that fluctuations of local temperature are related to unequal radiation absorption that associates with local deformations of surface of melt. Thus noise spectrum of those fluctuations reflects turbulent surface deformation caused by gas jet and capillary waves. The standard temperature deviation does not exceed 10 K on the frequency of 7 KHz and above, and power law of spectrum of density of fluctuations of local temperature is about “-2.8” in range of capillary turbulence. Thus we can distinguish radiation pulsation due to laser cutting from other processes of radiation affection to the sample, including unwanted, degrading the quality of technological operations. The results of investigation can be useful for monitoring laser cutting process.

Spectrum of temperature pulsations of the melt in gas-assisted cutting with fiber laser

Measurements of the temperature behavior in the zone of action of the laser-radiation on the molten metal have been performed using multichannel pyrometer. Measurements were carried out for test cutting of a 3-mm mild-steel plate with several values of cutting speed and pressure of assist gas (oxygen), using an 1800-watt Ytterbium fiber laser. It is shown that fluctuations of temperature are related to local melt's surface deformations due to unequal radiation absorption; thus the noise spectrum of temperature fluctuations reflects turbulent surface deformation caused by gas jet and capillary waves. The maximum density of turbulent energy dissipation ε depends on cutting conditions: its value rises with increasing cutting velocity and oxygen pressure in a described range of parameters. The maximum of ε is localized near depth of (1.2...1.5) mm along the cutting front. We can distinguish the specific radiation pulsation spectrum of laser cutting from other processes of radiation affection to the sample, including unwanted degrading of the quality of technological operations. The spectrum of capillary waves on the melt's surface is formed under the effect of assisted gas jet and has a function of ω −3 , ω is cycle frequency. The results of this investigation can be useful for the development of monitoring and quality-control systems for the laser-cutting process.

Fabrication of Al/Al2O3 composites by in-situ powder metallurgy (IPM)

Abstract Al6061/Al 2 O 3 composites containing 15–40 vol.% of different-sized (37–276 μm) alumina particles were produced by in-situ powder metallurgy (IPM). In this method, the stir casting and powder metallurgy (PM) synthesizing processes are combined into an integrated net shape forming process. For the preparation of each powder mixture, alumina particles were added to the molten aluminum alloy, and the resulting slurry was stirred at a specified temperature for a predetermined time. During the stirring process, alumina particles disintegrated into the molten alloy, and subsequent quenching resulted in a mixture of alumina and aluminum alloy powder particles. These powder mixtures were cold pressed and then sintered. The effects of stirring time and temperature, along with the alumina content and particle size on the size distribution, microstructure and morphology of the aluminum particles produced were investigated. It was found that the finer aluminum powder particles were produced by increasing the alumina content and by decreasing both the stirring temperature (from 780 to 710 °C) and alumina particle size (within the range of 37–150 μm). A comparison of optical and SEM micrographs of aluminum particles produced by IPM, solid assisted melt disintegration (SAMD) and gas atomization revealed that pore-free and more spherical particles were produced by the IPM and SAMD methods. Moreover, a microstructural investigation of the final products proved that consolidated composites with high contents of well-distributed reinforcing particles could be fabricated by the IPM method.

Analysis of volatile compounds from Curcuma by microwave assisted solid phase headspace-gas chromatography

A novel method of microwave assisted solid phase headspace gas chromatography (MASP-HSGC) was developed through online coupling of solvent-free microwave extraction (SFME) and headspace-gas chromatography via a six-way valve. The method can quickly and directly analyze the volatile compounds from solid samples with its ability of simultaneous extraction, separation and analysis without any pretreatment. The method was applied to analyze the volatile compounds of solid Curcuma. Some experimental parameters such as the chromatographic conditions, microwave power and irradiation time were studied. Curcumol was used as the standard to evaluate the recovery, the limit of detection and the contents of compounds in a Curcuma sample. The essential oils were prepared by hydrodistillation extraction (HD) and SFME separately, and analyzed by gas chromatography-mass spectrometry (GC-MS) to compare the results with those from the developed method. It showed that the numbers of compounds obtained by the three methods of HD-GC, SFME-GC and MASP-HSGC were 35, 33, 40 respectively. The contents of curcumol using the three methods were (0.294 +/- 0.015), (0.331 +/- 0.023), (0.297 +/- 0.009) mg/g respectively. The method was approved to be suitable for the rapid analysis of volatile components in Curcuma.

Research on short circuiting transfer mode of ultrasonic assisted GMAW method

Ultrasonic assisted gas metal arc welding (U-GMAW) has been recently developed to improve the metal transfer characteristics. The ultrasonic wave is applied on the metal transfer process by means of an acoustic field. Welding electrical signal measurement and high speed camera are employed to study the differences of short circuiting metal transfer between conventional GMAW and U-GMAW. Compared with the conventional GMAW, the short circuit frequencies of U-GMAW are obviously increased under the same welding parameters. Moreover, the voltage range of the stable short circuiting transfer is enlarged, and the weld appearances become more uniform with the action of the ultrasonic wave. The high speed video images indicate that the U-GMAW arc is compressed and the electrical field intensity is increased. The decrease in the arc length is the main reason for the increase in the short circuit frequency.