High Pressure Nitrogen Gas Research Articles

Investigation on the pressure drop characteristics of ITER thermal shield cooling pipes

This paper presents the experimental results of the pressure drop through the cooling pipes of the ITER Thermal Shield (TS) panels. High pressure and room temperature nitrogen gas is selected for the experiment, which is equivalent operating condition with the 80 K helium gas from fluid mechanics point of view. Flow rate is set by a mass flow controller and pressure difference between the inlet and the outlet of the cooling pipe is measured by a differential pressure gauge. The experimental set-up is open loop type, which is connected to high pressure gas bottle. Flexible corrugated pipes are used to connect the TS cooling pipes with the measurement system line. The effect of the corrugated pipe is evaluated separately and excluded from the measurement results of the TS pipes. Test results of several TS panels are shown in this paper and are compared with the calculation using existing friction factor correlation and local loss coefficient of the pipe bends. The limitation of the calculation is discussed considering the hydrodynamic developing flow in the pipe routing.

Hypersonic flow study in a pneumatically operated academic shock tunnel.

A hypersonic shock tunnel is a primary tool used for basic experimental research and may be used in engineering and university courses to study compressible flows involving shock waves. In the present study, a pneumatically operated shock tunnel is demonstrated for hypersonic flow studies. The high-pressure nitrogen gas is used to drive a pneumatic cylinder, which is used to burst the thin metal diaphragms. Tunnel-free stream conditions are quantified using the measured pressure values and by applying shock tube relations. The free-stream Mach number of 5.5-7.2 is achieved by varying the bursting pressure and test gas pressure from 2.1 to 4.5 bars and 0.2 to 0.5bar, respectively. The simulation is performed and the shock standoff distance quantified, and the stagnation pressures measured. The results demonstrate that the pneumatically operated tunnel enhanced operation capacity compared to the manually operated tunnel and well suits the academic hypersonic research and developmental activities.

Experimental rice seed aging under elevated oxygen pressure: Methodology and mechanism.

Seed aging during storage results in loss of vigor and germination ability due to the accumulation of damage by oxidation reactions. Experimental aging tests, for instance to study genetic variation, aim to mimic natural aging in a shorter timeframe. As the oxidation rate is increased by elevating the temperature, moisture, and oxygen levels, this study aimed to (1) investigate the effect of experimental rice seed aging by an elevated partial pressure of oxygen (EPPO), (2) elucidate the mechanism of dry-EPPO aging and (3) compare aging under dry-EPPO conditions to aging under traditional moist-controlled deterioration (CD) conditions and to long-term ambient storage. Dry seeds from 20 diverse rice accessions were experimentally aged under EPPO (200 times higher oxygen levels), at 50% relative humidity (RH), along with storage under high-pressure nitrogen gas and ambient conditions as controls. While no decline in germination was observed with ambient storage, there was significant aging of the rice seeds under EPPO storage, with considerable variation in the aging rate among the accessions, with an average decline toward 50% survival obtained after around 21 days in EPPO storage and total loss of germination after 56 days. Storage under high-pressure nitrogen gas resulted in a small but significant decline, by an average of 5% germination after 56 days. In a second experiment, seven rice seed lots were stored under EPPO as compared to a moist-CD test and two different long-term ambient storage conditions, i.e., conditioned warehouse seed storage (CWSS) and traditional rice seed storage (TRSS). Untargeted metabolomics (with identification of lipid and volatile compounds profiles) showed a relatively high increase in levels of oxidized lipids and related volatiles under all four storage conditions. These compounds had a high negative correlation with seed viability, indicating oxidation as a main deteriorating process during seed aging. Correlation analysis indicated that EPPO storage at 50% RH is more related to aging under TRSS at 60% and CD-aging at 75% ERH rather than CWSS at 40% ERH. In conclusion, aging rice seeds under EPPO conditions is a suitable experimental aging method for analyzing variation among seed lots or genotypes for longevity under storage.

Laser surface processing of Ti6Al4V alloy precoated with hard particles

Laser gas-assisting processing of preprepared Ti6Al4V alloy is carried out and resulting surface topology, wetting state, metallurgical changes, and hardness are examined. A thin carbon film accommodating TiC and B4C particles is developed over the surface in the preparation cycle. Laser surface treatment consisting of surface ablation and melting is performed at constant laser scanning speeds and high-pressure nitrogen gas jet. Laser treatment results in surface texture topology with hierarchically distributed micro/nanopillars having 5.6 μm average surface roughness (Ra). The texture of the surface demonstrates a hydrophobic state with a contact angle of about 109° ± 3° and hysteresis of 37° ± 4°. The treated surface free energy yields ∼132 mJ/m2, which is greater than that of TiC (∼120 mJ/m2). The high spreading rate of the molten alloy wets the surface of the hard particles while minimizing nano/mesopores around the particles in the treated layer. The presence of carbon film and TiC particles forms (Ti, Al)N, (Ti, Al)CxN1-x, TiN, TiNx, Ti2N, TiCxN1-x compounds on the surface, which contributes to microhardness enhancement in the treated zone. Surface microhardness of 1670 ± 50 HV is achieved, which remains higher than that of TiN coated, plasma nitrided, and laser nitrided surfaces.

Rehydration properties of regular and agglomerated milk protein concentrate powders produced using nitrogen gas injection prior to spray drying

This study evaluated the effect of high-pressure nitrogen (N2) gas injection prior to spray drying on the subsequent rehydration properties of regular and agglomerated milk protein concentrate (MPC) powders. Conductivity measurements demonstrated a slower release of ions for powders produced using N2 injection (NI) as they took longer to wet and sink due to their lower density. However, analysis of particle size distribution on reconstitution at both 23 and 50 °C showed an improvement in powder dispersion with NI. Powder solubility, when measured at 23 °C, was higher for the NI powders, while agglomeration negatively impacted solubility. Confocal laser scanning microscopy analysis showed a faster diffusion of dye into MPC powder particles produced using NI. The improvement in powder dissolution with NI was attributed to higher porosity and the presence of air voids which facilitated increased water transfer and accelerated the breakdown of primary powder particles.

Experimental investigation and numerical calculation of the cryogenic ejector in a liquid nitrogen system

A cryogenic ejector is designed, which can pump liquid from cold plates by high-pressure nitrogen gas. The pressure of primary flow ranges from 300 kPa to 700 kPa and the mass flow rate of jet flow is between 2 g/s and 8 g/s in the experiment. The ejector coefficient and exergy efficiency are calculated for different working conditions. Entrainment ratio reaches up to 1.8 and the maximum exergy efficiency is 0.7. The interdependence of the inlet pressure and flow rate ratio is theoretically evaluated. A model is built to obtain the thermal properties at different parts of the ejector. The errors of pressure, temperature and flow rate between computational results and experimental results are less than 3%, 1% and 15%, respectively. The cryogenic pump box systems are introduced. The exergy analyses are implemented to compare the efficiencies of traditional immersed pumps and the newly proposed cryogenic ejector. When the temperature of primary flow is less than 20 K, the exergy efficiency of the ejector pump is higher than the immersed pump, which is about 0.826. This research effectively settles the problems of the cryogenic liquid extraction and is also significant for the hydrogen energy regasification and utilization.

Inhibition of Pitting Corrosion Failure of Copper Tubes in Wet Sprinkler Systems

The inhibition of pitting corrosion failure of copper sprinkler tubes in wet sprinkler systems was studied. First, an apparatus and technology for removing air in the sprinkler tubes by vacuum pumping and then filling the tubes with water were developed. Using this apparatus and technology, three methods for inhibiting the pitting corrosion of the copper sprinkler tubes installed in several apartment complexes were tested. The first one was filling the sprinkler tubes with water bubbled by high-pressure nitrogen gas to reduce the dissolved oxygen concentration to lower than 2 ppm. In the second method, the dissolved oxygen concentration of water was further reduced to lower than 0.01 ppm by sodium sulfite. In the third method, the sprinkler tubes were filled with benzotriazole (BTAH) dissolved in water. The third method was the most effective, reducing the failure frequency of the sprinkler tubes due to pitting corrosion by more than 80%. X-ray photoelectron spectroscopy analyses confirmed that a Cu-BTA layer was well coated on the inside surface of the corrosion pit, protecting it from corrosion. A potentiodynamic polarization test showed that BTAH should be very effective in reducing the corrosion rate of copper in the acidic environment of the corrosion pit.

Femtosecond-laser-induced plasma spectroscopy for high-pressure gas sensing: Enhanced stability of spectroscopic signal

Gas composition detection and analysis in high-pressure environments, such as those encountered in combustors, power plants, and planetary bodies, are important for scientific and engineering research. Conventional laser-based sensing using nanosecond (ns)-laser-induced breakdown spectroscopy (ns-LIBS) remains unreliable at elevated pressures because of the relatively high measurement uncertainty. To circumvent this problem, we propose to employ femtosecond-laser-induced plasma spectroscopy (FLIPS) to achieve a stable and reliable gas sensing at elevated pressures. A comprehensive study on the differences in the measurement quality of FLIPS and ns-LIBS for high-pressure nitrogen gas is conducted. The results show that the signal level and stability of ns-LIBS significantly decrease with the increase in pressure. In contrast, the signal level of FLIPS increases with the increase in pressure while maintaining the stability in the pressure range of 1–40 bar. In addition to the superior measurement stability, the FLIPS measurement provides a longer probe length (∼3 times compared to ns-LIBS) with a higher data acquisition speed (100 times compared to 10-Hz ns-LIBS).

Cellular polypropylene foam films as DC voltage insulation and as piezoelectrets — A comparison

Polymer foams are in industrial use for several decades. More recently, non-polar polymer foams were found to be piezoelectric (so-called piezoelectrets) after internal electrical charging of the cavities. So far, few studies have been carried out on the electrical-insulation properties of polymer foams. Here, we compare the piezoelectric and the DC-voltage electrical-insulation properties of cellular polypropylene (PP) foams. Their cavity microstructure can be adjusted via inflation in high-pressure nitrogen gas in combination with a subsequent thermal treatment. While inflation is effective for improving the piezoelectricity, it is detrimental for the electrical-insulation properties. The original cellular PP foam shows a breakdown strength of approximately 230 MV/m, within the same range as that of solid PP. The breakdown strength decreases with increasing degree of inflation, and the dependence on the foam thickness follows an inverse power law with an exponent of 1.2. Nevertheless, up to a thickness of 140 μm (3.5 times the original thickness), the breakdown strength of cellular-foam PP films is at least 7 times that of an air gap with the same thickness. In addition, the influence of high temperatures and high humidities on the piezoelectricity and the breakdown strength of cellular PP was studied. It was found that the piezoelectric d33 coefficient decays rapidly already at 70 °C, while the breakdown strength slightly increases during storage at 70 or 90 °C. Under a relative humidity of 95%, the breakdown strength increases with storage time, while the piezoelectric d33 coefficient slightly decreases.

Influence of Atomizing Gas and Cooling Rate on Solidification Characterization of Nickel-based Superalloy Powders

Nickel-based superalloy powders have been produced by high pressure argon gas and nitrogen gas atomization, separately. The microstructural characterization of nickel-based alloy powders has been performed by a scanning electron microscope equipped with an EDS microanalysis unit. Based on a Newtonian cooling model, the flight speed and the cooling rate of two kinds of alloy droplets were calculated. The results show that the droplet cooling rate, which depends on atomization medium and droplet size, has an effect on the solidification microstructure. For argon-gas atomized powders, the developed dendrite structure is predominant at a lower cooling rate and a mixed microstructure composed of dendrite structure and cellular structure is observed at a higher cooling rate. For nitrogen-gas atomized powders, the dendrite structure is predominant at a lower cooling rate and a full cellular structure can be observed at a higher cooling rate. According to calculation, the cooling rate of argon-gas atomized droplets is in a range from 1.0×105 K·s−1 to 4.24×106 K·s−1, while the cooling rate of nitrogen-gas atomized droplets is from 1.0×105 K·s−1 to 4.8×106 K·s−1. The cooling rate increases with decreasing of droplets diameter. Two kinds of atomizing gases have a slight influence on the cooling rate of droplets. The dendrite axis is rich in elements such as Cr, Co, W, Ni and Al while the inter-dendrite region is rich in Ti element.

Effect of environmental dust particles on laser textured yttria-stabilized zirconia surface in humid air ambient

Zirconium nitride is used as a selective surface for concentrated solar heating applications and one of the methods to form a zirconium nitride is texturing of zirconia surface by a high intensity laser beam under high pressure nitrogen gas environment. Laser texturing also provides hydrophobic surface characteristics via forming micro/nano pillars at the surface; however, environmental dust settlement on textured surface influences the surface characteristics significantly. In the present study, laser texturing of zirconia surface and effects of the dust particles on the textured surface in a humid air ambient are investigated. Analytical tools are used to assess the morphological changes on the laser textured surface prior and after the dust settlement in the humid air ambient. It is found that laser textured surface has hydrophobic characteristics. The mud formed during condensate of water on the dust particles alters the characteristics of the laser textured surface. The tangential force required to remove the dry mud from the textured surface remains high; in which case, the dried liquid solution at the mud-textured surface interface is responsible for the strong adhesion of the dry mud on the textured surface. The textured surface becomes hydrophilic after the dry mud was removed from the surface by a desalinated water jet.

Mechanical behavior and fracture spatial propagation of coal injected with liquid nitrogen under triaxial stress applied for coalbed methane recovery

Fracturing technology through liquid nitrogen (LN2) injection alters the physical properties of coal and rock masses because of the thermal and pressure effects. In order to investigate heat transfer and fracture propagation behaviors under in situ geological condition with LN2 injections, experimental work was conducted to study the LN2 induced rock/coal failures under true triaxial stress conditions. During the experiments, the temperature, ultrasonic waves, and acoustic emission location detection were monitored to determine the intensity and complexity of specimen failure under singular or cyclic LN2 injections. The results show that a single LN2 injection mainly transfers heat through the solid skeleton and only damages areas adjacent to the injection tube. However, cyclic injections formed a propagated fracture network and the heat can sequentially transfer further along the induced fractures. Moreover, plastic deformation occurred in the entire volume of the sample and the main fractures coalesced until the sample failed. Based on the spatial locations of the acoustic emission sources, the dynamic fracturing within the sample progressed after LN2 injection was clarified. The experimental results can provide evidences for the proposed crack propagation model for the coal masses. The research revealed that high-pressure nitrogen gas transferring liquid water to the tips of new fractures is essential for cyclic LN2 injection to form effective frost-heaving forces and fracturing. Therefore, the fracturing efficiency of the cyclic LN2 injection is far higher than that of singular LN2 injections.

Effect of graphene film on laser textured alumina surface characteristics

Laser gas assisted texturing of alumina surface is considered and the effects of graphene film on the properties of the textured surface are examined. Since laser texturing under the high pressure nitrogen gas jet environments results in formation of aluminum nitride compounds, free energy of the textured surface reduces considerably. The mismatch between the surface free energies of the graphene film and the laser textured surface makes it difficult to transfer the graphene film on the textured surface without rippling and edge defects. A graphene oxide film is formed at the textured surface prior to transferring of the graphene film. The characteristics of the laser textured and the graphene transferred surfaces are assessed using the analytical tools including electron and atomic force microscopes, Raman spectroscopy, X-ray diffraction, and UV visible absorbance spectroscopy. Surface hydrophobicity of the graphene transferred and laser textured surfaces is determined incorporating the water droplet contact angle measurement technique. Friction coefficient of the graphene transferred and laser textured surfaces are measured using the scratch tester. It is found that laser texturing results in hydrophobic characteristics because of the micro/nano size pillars formed at the surface and reduced surface energy due to aluminum nitride compounds. Transferring of the graphene film on to the laser textured surface reduces both the water droplet contact angle and the contact angle hysteresis. The presence of the graphene film reduces the friction coefficient and it does not alter notably the absorption characteristics of the laser textured surface.

Experimental and numerical investigation of the transverse impact damage and deformation of 3-D circular braided composite tubes from meso-structure approach

The transverse impact deformation and damage of 3-D circular braided composite tubes were studied both in experimental and numerical approaches. A meso-structure geometrical model based on the braided architecture was established to analyze the impact damage and morphology. The transverse impact tests were conducted on a modified split Hopkinson pressure bar (SHPB) apparatus driven with high pressure Nitrogen gas under different pressures. The load-time histories and deformations of the 3-D circular braided composite tubes under transverse impact were obtained from experimental and compared with those in finite element analysis (FEA). The FEA results show satisfactory agreements with experimental data and demonstrate the validity of the model. Based on the finite element results, the deformation process and stress propagation were obtained to analyze the failure mechanism. The stress distribution on the composite tubes showed that the 3-D circular braided reinforcement was the main load-carrying component and absorbed most of the impact energy. The impact region was dented along the impact direction and a clear shear band was found around the impacted region.

Laser gas assisted texturing of alumina surfaces and effects of environmental dry mud solution on surface characteristics

High pressure nitrogen gas assisted laser texturing of alumina surface is carried out and the effects of dust accumulation and mud formation on the surface characteristics are examined. The dust accumulation and mud formation is simulated in the laboratory environments in line with the local environmental conditions. Morphological and metallurgical changes in the laser treated region are examined using scanning electron and atomic force microscopes, energy dispersive spectroscopy, and X-ray diffraction. Surface microhardness is measured and residual stress formed in the surface region is determined from the X-ray diffraction data. Surface hydrophobicity is assessed through the contact angle measurements. Scratch tests are incorporated to measure the friction coefficient of the laser treated and as received workpiece surfaces. It is found that laser texturing results in superhyrophobic surface and the formation of AlN compounds at the textured surface lowers the surface energy while contributing to the surface hydrophobicity enhancement. The mud solution modifies the surface texture characteristics of the laser treated workpieces; in which case, surface hydrophobicity reduces significantly. Surface hardness increases considerably after the laser treatment process because of grain refinement under high cooling rates and volume shrinkage due to AlN compound formation in the surface region. Residual stress is compressive in the surface region of the laser textured workpiece and the mud solution increases slightly surface hardness and residual stress in the surface region.

In-water injection of high-pressure pulsed gas jet: A simple analytical tool for direct injection of gaseous fuels in automotive engine

Visualizing high pressure pulsed gas jet can be challenging due to its weak scattering of light which requires reliable flow tracer. Complex and costly laser source and high speed camera settings using shadowgraph, Schlieren and Laser Induced Fluorescent (LIF) techniques with seeding of flow tracers such as acetone have been used. In the spirit of simplification, this paper presents a technique to visualize high pressure pulsed gas jet in liquid ambient. It can be used as predictive tool to investigate the structure, dynamic and interaction of gas jet with the environment [1]. A gas injector with square-shaped nozzle was used. High pressure nitrogen gas at 5 and 6MPa with 12ms injection pulse exits the injector through a 1mm2 square nozzle into quiescent water. The injector tip is immersed below water surface in an optically-accessed container and placed inside an extremely low illuminated square chamber. Two small windows on opposite walls of the chamber allow image capturing with injection-flash light synchronization. Images of the gas jets formed from nozzle at various time after the start of the injection (SOI) were captured by a digital camera. During exposure, the flash light was triggered for 1ms at some times after SOI, thus images captured correspond to the flash timing.Results showed that the shape of the gas jet was in agreement with the vortex ball model but with difference in the magnitude of penetration with respect to previous works. Some similarities in the gas injection behavior are found in the liquid and gas ambient. The tip penetration and gas width in water environment are about half of the magnitude in the gas environment. A dimensionless gas dynamic analysis shows a good agreement in the trend of jet development between the gas environment using Planar Laser Induced Fluorescent (PLIF) imaging and in-water imaging techniques. Results indicate that both gas jet length and width are very sensitive to injection pressure.

Laser assisted nitriding of nickel–chromium-based superalloy surface: Heating and diffusion analysis

Inconel 718 is a nickel–chromium-based superalloy, and it is widely used in power industry because of its resistance to high-temperature environments. Treatment of the alloy becomes essential to prevent niobium segregation at the surface. Laser controlled melting and gas assisted nitriding is one of the methods to minimize changes in the elemental composition of the alloy surface. In general, high pressure nitrogen assisting gas is used coaxially with the laser beam to form a nitride layer and avoiding high-temperature exothermic oxidation reactions in the laser-irradiated region. The present study is carried out to model and simulate sequentially coupled thermal-diffusion process during laser assisted surface nitriding of nickel–chromium-based superalloy in line with experimental conditions. High pressure nitrogen gas jet is considered to impinge onto a workpiece surface coaxially with the laser beam during the treatment process. Finite element model is incorporated to predict the nitrogen concentration and temperature in the laser treated layer. It is found that the predictions of surface temperature and nitriding are found to be in close agreement with the experimental data. The study is extended to include the effect of laser intensity on the nitriding behavior.

Crack growth of throughwall flaw in Alloy 600 tube during leak testing

We examined the issue of whether crack growth in a full thickness material can occur in a leaking crack. A series of leak tests was conducted at a room temperature and constant pressure (17.3MPa) with Alloy 600 tube specimens containing a tight rectangular throughwall axial fatigue crack. To exclude a potential pulsation effect by a high pressure pump, the test water was pressurized by using high pressure nitrogen gas. Fractography showed that crack growth in the full thickness material can occur in the leaking crack by two mechanisms: time-dependent plasticity at the crack tip and fatigue induced by jet/structure interaction. The threshold leak rate at which the jet/structure interaction was triggered was between 1.3 and 3.3L/min for the specific heat of the Alloy 600 tube tested.

Laser Texturing of Plasma Electrolytically Oxidized Aluminum 6061 Surfaces for Improved Hydrophobicity

Laser surface texturing of plasma electrolytically oxidized aluminum 6061 alloy has been carried out through a controlled surface ablation under a high pressure nitrogen gas assistance. Morphological and metallurgical changes in the laser-treated region were examined using optical, scanning electron, and atomic force microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction phase analysis. The hydrophobicity of the textured surface was assessed through water droplet contact angle measurements. It was found that a dense layer with a nanotexture/microtexture is developed at the surface after the laser treatment process. The assessment of the surface characteristics reveals that a superhydrophobic surface results from the laser treatment process; in which case, high water droplet contact angles are measured over the treated surface, which can be explained by known models of texture-induced superhydrophobicity.

Design and Optimization of the Flywheel Compressor Based on SolidWorks and Fluent

To deal with the problem of energy waste in High-pressure gas relief of pulverized coal injection in the blast furnace, designed a flywheel compressor which consists of an energy storage mechanism and a power mechanism. It is used for recycling and reusing the energy released by the high-pressure nitrogen gas in pulverized coal mixing. It is a safe and an energy saving equipment without motor driving. In this paper, the model of the flywheel compressor was established in Solidworks and Fluent to simulate the flow field, then basic dimensions of the compressor was conducted, and structural design and optimization were completed at last.