High-velocity Nitrogen Research Articles

Quenching induced residue stress in M50 steel ring: a FEM simulation

A finite element method (FEM) combined with subroutines was established and used for tracing the evolution of stresses in M50 steel in quenching. The constitutive relation and thermal physical properties of M50 steel were tested and integrated into the modeling. The finite element analysis, taking into account of thermal stresses and martensitic phase transformation, predicts accurately the high-velocity nitrogen (HNQ) induced residual stresses in the M50 steel bulk. The simulation results suggested that the residual stresses in M50 steel is compressive at the surface while tensive at the center, along with very strong residual stresses at edges. The residual stress reaches to the high level of −810.3 MPa and −1436 MPa in the case of HNQ and water quenching, respectively. The evolution of stress is found to be jointly driven by the thermal stress and phase transformation stress. The thermal stress dominates the evolution at the initial stage while the phase transformation stress becomes dominating once the martensite transformation begins.

The thermal shock resistance of Y2O3 ceramics

Y2O3 ceramics samples with various grain size were tested in non-symmetric thermal shock conditions in two methods. In the first test the samples were heated in a furnace up to the predetermined temperature (530°C) and then the polished surfaces with Vickers indents were subjected to sudden temperature change using a high-velocity nitrogen jet at room temperature. The gas was channelled onto the disk centre for about 20s. In the second test samples were quickly inserted into a hot furnace (850°C). The polished surfaces with Vickers indents were sheltered by thick alumina disks. The length of surface cracks before and after thermal shocks were measured with an optical microscopy and then a parameter Rm (an indicator of thermal stress resistance) was obtained. Hence the thermal stress σT, which caused crack growth, was calculated using the value of fracture toughness KIc. These stresses were similar for both shock cases (about 50MPa) and they were not dependent on grain size of the ceramics.

Design, Fabrication, and Characterization of a Micro Vapor-Jet Vacuum Pump

A microelectromechanical system (MEMS) vapor-jet pump for vacuum generation in miniaturized analytical systems, e.g., micro-mass-spectrometers (Wapelhorst, E., Hauschild, J., and Mueller, J., 2005, “A Fully Integrated Micro Mass Spectrometer,” in Fifth Workshop on Harsh-Environment Mass Spectrometry;Hauschild, J., Wapelhorst, E., and Mueller, J., 2005, “A Fully Integrated Plasma Electron Source for Micro Mass Spectrometers,” in Ninth International Conference on Miniaturized Systems for Chemistry and Life Sciences (μTAS), pp. 476–478), is presented. A high velocity nitrogen or water vapor jet is used for vacuum generation. Starting from atmospheric pressure, a high throughput of more than 23ml∕min and an ultimate pressure of 495mbars were obtained with this new type of micropump. An approach for the full integration of all components of the pump is presented and validated by experimental results. The pump is fabricated from silicon and glass substrates using standard MEMS fabrication techniques including deep reactive ion etching, trichlorosilane molecular vapor deposition, and metal-assisted chemical etching for porous silicon fabrication. Micromachined pressure sensors based on the Pirani principle have been developed and integrated into the pump for monitoring.

Modeling of nonequilibrium effects in a high-velocity nitrogen-hydrogen plasma jet

A numerical simulation has been performed of a high-velocity nitrogen hydrogen plasma jet in air at atmospheric pressure including finite-rate chemical kinetics. Ions, electrons, and neutral atoms and molecules are treated as separate species in the plasma mixture. The chemical reactions considered are dissociation of molecular species, ionization of atomic species, charge exchange and dissociatioe recombination of nitrogen, and hydrogen-oxygen reactions. The calculational results show that strong departures from ionization and dissociation equilibrium develop in the downstream region as the chemical reactions freeze out at lower temperatures, in spite of the assumed chemical equilibrium at the nozzle exit. The calculations also show that ionized species are over-populated throughout the flow, while dissociated species in the core of the jet are underpopulated near the nozzle exit and become over-populated farther downstream. This initial underpopulation is due to diffusive depletion of dissociated species and enrichment of molecular species in the core of the jet.

Experimental and theoretical effects of nitrogen gas flow rate on liquid-jet atomization

Two-phase flows were investigated by using high-velocity nitrogen gas streams to atomize small-diameter liquid jets. Tests were conducted primarily in the acceleration-wave regime for liquid-jet atomization, where it was found that the loss of droplets due to vaporization had a marked effect on drop-size measurements. In addition, four identically designed two-fluid atomizers were fabricated and tested for similarity of spray profiles. A scattered-light scanning instrument was used to measure the following characteristic drop diameters: volume median A.s, Sauter mean D32, and volume-linear mean Am and it was found that each one of the three characteristic drop diameters varied inversely with nitrogen gas flow rate raised to the 1.33 power. The exponent 1.33 power is identical to that predicted by atomization theory for liquied-jet breakup in the acceleration-wave regime, and it is somewhat higher than the value of 1.2 that was previously obtained at a sampling distance of 4.4 cm downstream of the atomizer. The difference is attributed to the fact that drop-size measurements obtained at the 2.2 cm sampling distance are less affected by vaporization and dispersion of small droplets and, therefore, should have better agreement with atomization theory.

Nitrogen Gas and Sand: A New Technique for Stimulation of Devonian Shale

Summary A process has been developed and demonstrated in 17 field tests in which sand proppant is added to a nitrogen gas stimulation treatment. Excepting minor problems with five treatments, all recent applications have been operationally successful. The early production results from two offset wells show decline curve improvement from the nitrogen-gas/sand treatment. Theories based on observed data from well treatments have been developed. Displacement of proppant without the use of water or other liquids is a significant advantage both environmentally and economically. Additionally, the process causes no formation damage, and the well cleanup is rapid. The current major disadvantage is the small amounts of proppant displaced, although improved process design already has shown an increase in sand quantities. A wide variety of stimulation conditions involving flow rates, total nitrogen, number of perforations, and well depths have been tried. Introduction The use of nitrogen gas alone as a stimulation treatment has been practiced since 1978. Preliminary investigations into the specifics of this process have been published by several authors. Nitrogen gas has been the most widely used stimulation treatment on the Devonian shale for several reasons. The advantages of using nitrogen gas on the shale are as follows.Nitrogen gas, being inert, is nondamaging to the shale. Problems with clay swelling, clay migration, or oil and water emulsions are eliminated.Nitrogen gas stimulated wells will clean up quickly in most cases. Controlled cleanup will cause minimal permeability damage from fractured formation fines moving to the wellbore.There is no liquid invasion of the microfractures in the shale, thus preventing possible reduction of the long-term productivity of the well.The cost for a nitrogen gas treatment is usually less than for other stimulation methods, which allows a quicker return on invested capital. These advantages provide a strong case for nitrogen gas stimulation; however, there is one disadvantage that has caused limited acceptance of the technique by some. The lack of any type proppant being used with a nitrogen gas stimulation treatment has provided the strongest argument against it. provided the strongest argument against it. The contention that fracture conductivity cannot be maintained without proppant is well known. Production results showing rapid decline curves Production results showing rapid decline curves are given as corroboration to the lack of fracture conductivity after the nitrogen gas fracture. It has been demonstrated that some natural propping does occur under certain conditions. However, any additional placement of a proppant would improve the expected results from a nitrogen gas fracture. This placement of proppant and the process description thereof are the main concerns of this paper. The three main considerations when adding proppant to a nitrogen gas fracture are (1) proppant proppant to a nitrogen gas fracture are (1) proppant transport capability of nitrogen gas; (2) created fracture geometry capacity to accept proppant; and (3) a method to add proppant to a high-velocity nitrogen gas stream under pressure. The approach selected to investigate these considerations was to perform an experimental treatment on a gas well completed in a shale interval. Before this treatment, preliminary testing was used to determine proppant transport ability of nitrogen gas. The test was set up as shown in Fig. 1. Nitrogen gas was pumped down the 2 3/8-in. [6.0-cm] tubing at velocities ranging from 27 to 120 ft/sec [8.23 to 36.58 m/s] and out the three perforations. Then, 20/40-mesh sand was added to the nitrogen gas stream at the various nitrogen rates. The sand was transported out the perforations at all rates. At 27 ft/sec [8.23 m/s], sand was transported out the bottom perforation only. At 120 ft/sec [36.58 m/s], sand was carried out all three perforations. Visual inspection inside the tubing after pumping stopped showed minimal sand left inside the tubing below the bottom perforation. From this test, it was concluded perforation. From this test, it was concluded that nitrogen gas could be used to transport proppant and, if a created fracture was wide proppant and, if a created fracture was wide enough, the proppant could be displaced into it. The test to determine the creation of adequate fracture width was designed to be an experimental treatment on a well completed in a gas-bearing shale. The treatment was simply to pump a pad of nitrogen gas followed by more nitrogen gas carrying 20/40-mesh sand. Total job size was 1,700 bbl [270.3 m3], with 60% being pad and 40% carrying sand at an average concentration of 0.3 lbm/gal [0.14 kg/m3]. Maximum rate achieved was 20 bbl/min [3.2 m3/s]. JPT p. 901