Gas Injection Nozzle Research Articles

Durability Effects of Gas Nozzle Shape on Marine Two-Stroke Dual-Fuel Engines Using Numerical Analysis

To comply with rules on air pollutants released by ships, two-stroke dual-fuel engines with liquefied natural gas (LNG) as the primary fuel have been marketed and offered to the market. However, there are still reports of gas-injection nozzles being damaged after they have been put on the market. Damage to the nozzles might result in secondary accidents in addition to worsening engine combustion conditions from improper injection. This study aims to gather fundamental information regarding the impact of different types of gas-injection nozzles on durability and to pinpoint the prerequisites for an ideal nozzle design. The results of total deformation and equivalent stress were examined for 27 nozzles that each variable was applied to in order to compare and confirm the durability by changing the nozzle shape. The cause of the nozzle temperature change according to the change in nozzle length was found to have the biggest impact on the total deformation, and it was confirmed that the effect was increased at higher temperatures. As the nozzle length increased and decreased by 2 mm, the average temperature of the nozzle increased by 47% and decreased by 53%, but the total deformation increased by 100% and decreased by 70%. It was verified that the equivalent stress was determined by the complicated interplay between the pressure inside the nozzle and turbulent kinetic energy impacted by a change in the nozzle shape. The factor that has the largest influence on the equivalent stress is the adjustment of the nozzle hole pipe angle, and the difference in equivalent stress according to this factor was found to be up to 118% and at least 44%. As a result, it has been proven that shortening the nozzle length, increasing the hole pipe angle, and enlarging the hole diameter are the most effective and expected to be used as basic data for future nozzle development.

Angle-Resolved Time-of-Flight Electron Spectrometer Designed for Femtosecond Laser-Assisted Electron Scattering and Diffraction

We developed an apparatus for measuring kinetic energy and two-dimensional angular distributions of femtosecond laser-assisted electron scattering (LAES) signals with a high detection efficiency, consisting of a photocathode-type ultrashort pulsed electron gun, a gas injection nozzle, an angle-resolved time-of-flight analyzer, and a time-and-position sensitive electron detector. We also established an analysis method for obtaining the kinetic energy and two-dimensional angular distributions of scattered electrons from raw data of their flight times and the detected positions at the detector recorded using the newly developed apparatus. From the measurement of the LAES processes of Ar atoms in a femtosecond near-infrared intense laser field, we obtained a two-dimensional angular distribution image of the LAES signals and showed that the detection efficiency of the LAES signals was raised by a factor of 40 compared with that achieved before in 2010.

Reexamining Design of Gas Injection Nozzle for LNG Dual-fuel Engine

Reexamining Design of Gas Injection Nozzle for LNG Dual-fuel Engine

Small bubbles formation and contribution to the overall gas holdup in large diameter columns of very high viscosity oil

A limited number of studies are available in literature on the small bubbles which create from gas-very high viscosity oils interaction and its contribution to the gas holdup in the system. The rate of small bubble formation has an important impact on heat and mass transfer in many chemical and industrial processes. The work presented in the current paper provides unique information on the formation of bubbles of millimetre diameter in high viscosity oil. A column of 290 mm diameter and Silicon oil of 330 Pa.s viscosity, were employed besides Electrical Capacitance Tomography and a high-resolution camera to investigate the characteristics of the small bubbles. Mechanism of bubble generation, effect of gas injection time and flowrate were studied. The average void fraction, total gas-liquid height, overall Probability Density Function (PDF) profile, small bubbles volume fractions and diameter were measured. Small bubbles generate from the eruption of large bubbles, at gas injection nozzles, coalescence of large bubbles, and at liquid bridges at transition to churn flow regime. Properties and concentration of the small bubbles are controlled by the location of the bubble generation, gas flowrate, and gas injection time. Small bubbles contribute by 6.6- 30% to the total gas holdup. Bubble diameter increased from 0.68 mm to 0.75 mm and decreased from 1.1 mm to 0.75 mm at the top and the bottom sections of the column respectively after 60 minof gas injection.

Gas-liquid two-phase flow patterns in the wake of a submerged nozzle under co-flow condition

The present study aims to reveal gas-liquid flow patterns as gas is injected into co-flowing water. An experimental work was conducted in a loop in which pure water was circulated. The gas-injection nozzle was submerged in the flowing water. Effects of the water flow velocity and gas flow rate were jointly considered. Two-phase flow patterns were visualized using the high-speed photography and then analyzed statistically. The evolution of the cavity-water interface and collapse of cavity were explained. The results show that a sequential arrangement of a long attached cavity and dispersed bubbles in the streamwise direction constitutes a unique flow pattern. The cavity length is dependent of the contest between the gas velocity and water flow velocity. A single-valley distribution of pinch-off frequency as the gas/water velocity ratio varies is insensitive to the water flow velocity. At high water flow velocities, collapse of cavity follows the pattern of wake vortices. Distinct coalescence is evidenced at high gas/water velocity ratio as a large gas pocket is separated from the attached cavity. It is ascribed to the retarded motion of the gas pocket and high inertia of the subsequently detached small bubble.

Carbon dioxide conversion in an atmospheric pressure microwave plasma reactor: Improving efficiencies by enhancing afterglow quenching

Microwave plasma is effective for decomposing CO2, which is a major contributor to global warming. Atmospheric pressure microwave plasma is of particular interest due to its vacuum-free configuration. Here, we investigated the CO2 conversion performance of a microwave plasma system operating at atmospheric pressure. CO2 conversion efficiency and energy efficiency were measured for various CO2 flow rates and input power levels. Lower CO2 flow and higher power yielded an enhanced CO2 conversion efficiency and lower energy efficiency. The afterglow temperature in the reactor was also measured. At a specific energy input (SEI) of 7.25 eV/molecule, a temperature of 1342 K was observed 12 cm below the gas injection nozzle. To improve the efficiencies of the plasma system, we propose an afterglow quenching method with enhanced heat transfer characteristics. This was achieved using a water-cooled quenching rod inserted into the plasma reactor to cool the afterglow gas stream, thus limiting the recombination reaction of CO to form CO2. At a SEI of 7.22 eV/molecule, CO2 conversion increased from 30.1% to 36.1% with the quenching rod; at 2.46 eV/molecule, the increment of CO2 conversion efficiency was 29 %. An energy efficiency of 28.9 % was achieved using an SEI of 1.19 eV/molecule. By tracking down the heat loss to cooling water flowing through the applicator, exhaust port, and quenching rod, we determined the energy distribution from the plasma plume to the exit gas stream. The quenching rod increased the chemical enthalpy of the product gas by reducing CO recombination.

Impact of natural gas injection strategies on combustion and emissions of a dual fuel natural gas engine ignited with diesel at low loads

Previous studies have shown that diesel ignited natural gas dual fuel engine is multi-point ignition, so a more uniform mixture of natural gas and air is conducive to engine combustion and emissions. To improve engine combustion and emission by improving mixture uniformity, the effects of natural gas injection timing, direction and position on combustion and emissions were studied experimentally on a 6-cylinder turbocharged intercooled diesel/natural gas dual fuel heavy-duty engine at low loads. The natural gas injection timing changes from 220 °CA BTDC (before top dead center) to 420 °CA BTDC. Natural gas injection nozzle lengthened by 2 cm (changing position) and downward injection (changing direction) were studied. The experiments kept the total fuel quantity and diesel injection strategy unchanged. The results show that advanced natural gas injection timing can improve mixture uniformity and engine combustion and emission, but too early injection timing will involve a part of natural gas scavenging and a little part of natural gas is concentrated at the bottom of the combustion chamber, making engine combustion and emission performance worse. The optimum injection timing of this engine is about 300 °CA BTDC. Pmax (maximum of cylinder pressure) has good linear relationship with PHRR2 (the second heat release rate peak) under the change of injection timing. Natural gas injection nozzle lengthened by 2 cm (B strategy) makes the combustion and emissions worse. Natural gas downward injection (C strategy) can improve the combustion and emissions. When λ is 1.9 and compared with original injection strategy (A strategy), the Pmax of C strategy rises 5.3%, and CO and THC decrease 12.9% and 19.9% respectively. In addition, the effect of natural gas injection timing on mixture uniformity was carried out by simulation and there came similar conclusions with previous studies.

Multimode jetting unlocks a trade-off between nanostructure morphology and composition in focused electron beam induced deposition

An ability to accelerate the growth rate while simultaneously controlling shape and composition of deposits is fundamental to expanding the utility of electron beam assisted deposition for “direct write” nanostructure fabrication from gas phase precursors. We report on novel tunable mode of Focused Electron Beam Induced Deposition (FEBID) as enabled by the switchable use of reactive (O2) and inert (Ar) “assist” gases directed at high impingement energy and momentum to a deposition site concurrently with a supply of a precursor in a dual-nozzle FEBID arrangement. Organometallic molecules introduced into a deposition chamber in a free-molecular flow regime through a conventional gas injection nozzle, yielding a broad uniform substrate coverage by the precursor in a quasi-equilibrium adsorbed state. Simultaneously, a supersonic micro-jet from a micron-scale capillary placed in close proximity to a deposition site produces a low Knudsen number continuous flow impingement of energized “assist” gas, which perturbs the precursor state to facilitate different chemical reaction pathways. This process enables modulation of deposition outcomes, e.g., enhanced vertical growth rate (aspect ratio) of nanostructures when using argon micro-jet while locally removing parasitic carbonaceous by-products of organometallic precursor decomposition reaction by e-beam through interactions with oxygen micro-jet. Such in-situ/in operando (during growth and on-demand switchable) modulation of FEBID allows for rapid and precisely controllable deposition for a desired outcome, such as tuning metal-to-carbon composition and maintaining shape fidelity in fabricating high-aspect ratio composite nanostructures, which extends the capabilities of FEBID as a robust multi-dimensional, multi-purpose nanoscale 3D printing tool.

Thermal hydraulic characteristics of unstable bubbling of direct contact condensation of steam in subcooled water

The study of direct contact condensation (DCC) of steam is important owing to the diverse range of DCC applications, including uses in power plants, heat exchangers, and steam ejectors. In this study, an experimental investigation was performed to study the thermal hydraulic characteristics of the DCC of steam in an unstable condensation regime. Deionized water was used as the working fluid obtained with the use of a reverse osmosis method. The experiments were performed with pool temperatures in the range of 70 to 92 °C ± 2 °C, with different steam mixture mass fluxes in the range of 5 and 64 kg/m2 s, and with a gas injection nozzle with an inner diameter of 9.525 mm. The pool temperature was measured using thermocouples, and the surface area of the bubble and the volume flow rate were evaluated with high-speed camera image acquisitions. Subsequently, image processing was used to obtain the heat-transfer coefficient and other thermal hydraulic characteristics, such as the bubble condensing frequency and the bubble centroid velocity. The calculated condensation heat-transfer coefficients were found to be 24.57–179.78 kW/m2⋅K. According to the experimental results at various boundary conditions, a unified correlation of the heat-transfer coefficient was identified at the bubbling frequency in the unstable condensation regime, regardless of the pool subcooling temperature and steam mass flux. It was also found that the characteristic frequency of the steam bubble can be determined based on the boundary conditions to allow the determination of the heat-transfer coefficient with the given boundary conditions.

Effects of Nozzle Radial Position, Separation Angle, and Gas Flow Partitioning on the Mixing, Eye Area, and Wall Shear Stress in Ladles Fitted with Dual Plugs

Mixing time, slag eye area, and wall shear stress in a ladle fitted with dual plugs have been studied as a function of operating variables, namely, gas flow rate, radial nozzle position, separation angle between nozzles and flow rate partitioning. While the mixing time and slag eye area have been experimentally investigated in a scaled water model (with and without a top slag layer), the shear stress on the vessel wall has been studied computationally via a RANS-based turbulent, three-dimensional coupled Eulerian–Lagrangian (VOF-DPM), multiphase flow model. Experimental and computational results have indicated that the mixing, eye area, and wall shear stress depend on the gas flow rate, i.e., while mixing efficiency increases with the increasing gas flow rate, the slag eye area, and wall shear stress, in contrast, become more pronounced with the increasing gas flow, leading to an undesirable operating regime. The radial nozzle position, separation angle between the nozzles and flow rate partitioning at any given flow rate also influence the ladle process performance, influencing the mixing, eye area, and wall shear stress, albeit to a varied degree. Within the range of operating conditions studied, an expected inverse correspondence between mixing time and shear behavior was observed. Experimental and computational results in conjunction have indicated that the best arrangement of porous plugs or gas injection nozzles for superior ladle process performance is dependent on the gas flow rate and is specific to the desired objective (i.e., decreasing the mixing time, or slag eye area and wall shear stress). Hence, a unique gas injection practice cannot and should not be suggested as the optimum for ladle metallurgy in steelmaking. Nevertheless, if the mixing time is the parameter of primary interest, a nozzle configuration with equal flow partitioning (1:1) between the nozzles and identical nozzle radial positions (0.7R/0.7R, 45 deg) should suffice for both low and high gas flow rates. In contrast, a nonidentical nozzle radial position (0.7R/0.5R, 90 deg) and an unequal gas flow rate per nozzle (1:3) appear preferable if both ladle eye and shear stresses, rather than mixing, are the issues of concern.

Influence of Obstruction at Gas-Injection Nozzles (Number and Position) in RH Degasser Process

One of the main problems that affects Ruhrstahl-Heraeus (RH) degasser circulation rate is the obstruction of the gas-injection nozzles. This study aims to elucidate the effects of obstructions in quantity and location using a physical model that depicts 16 injection nozzles on the up-leg distributed symmetrically in 2 rings (8 nozzles/ring). We simulated six, symmetric and nonsymmetric, obstruction conditions to gas flow. The gas-flow rate was varied from 30 to 130 NL/min. The results for symmetric obstructions when the gas-flow rate is kept constant, indicates that the circulation rate in the equipment does not significantly change. However, when these obstructions are non-symmetric, the circulation rate varies drastically, even when the gas-flow rate is kept constant. The analysis of the experimental data generated from this study allowed to determine an equation for the circulation rate that takes into consideration the number and distribution of blocked nozzles.

Critical Condition for Formation of Accretion at Gas-Injection Nozzle Tip and Cooling Capacity of Gas

Critical Condition for Formation of Accretion at Gas-Injection Nozzle Tip and Cooling Capacity of Gas

Measurements of water molecule density by tunable diode laser absorption spectroscopy in dielectric barrier discharges with gas–water interface

We measured water molecule (H2O) density by tunable diode-laser absorption spectroscopy (TDLAS) for applications in dielectric barrier discharges (DBDs) with a gas–water interface. First, the effects of water temperature and presence of gas flow were tested using a Petri dish filled with water and a gas injection nozzle. Second, the TDLAS system was applied to the measurements of H2O density in two types of DBDs; one was a normal (non-inverted) type with a dielectric-covered electrode above a water-filled counter electrode and the other was an inverted type with a water-suspending mesh electrode above a dielectric-covered counter electrode. The H2O density in the normal DBD was close to the density estimated from the saturated vapor pressure, whereas the density in the inverted DBD was about half of that in the former type. The difference is attributed to the upward gas flow in the latter type, that pushes the water molecules up towards the gas–water interface.

Experimental characterization of the gas injection nozzle for the ITER Neutral Beam Test Facility neutralizer

The gas supply for the neutralizer of the Heating Neutral Beam is designed to guarantee the establishment of the gas cloud needed to neutralize the negative ion beam, generated in the beam source, before it can be injected into the tokamak for plasma heating. To guarantee the proper function for optimal beam properties, an experimental validation of the analytical predictions of the gas flow behavior under the conditions of the test facility MITICA (Megavolt ITER Injector and Concept Advancement) was needed. Herewith the throughput properties of the designed gas injection nozzles had to be investigated as well as the behavior of the system in case of a sudden shutdown of the supply. These experiments have been performed at the modified TransFlow facility at KIT. Additionally, the experimental results have been compared with simulations and some effort was spent in order to find proper material and mounting options for the nozzles.

Spouted bed design considerations for coated nuclear fuel particles

High Temperature Gas Cooled Reactors (HTGRs) are fueled with tristructural isotropic (TRISO) coated nuclear fuel particles embedded in a carbon-graphite fuel body. TRISO coatings consist of four layers of pyrolytic carbon and silicon carbide that are deposited on uranium ceramic fuel kernels (350μm – 500μm diameters) in a concatenated series of batch depositions. Each layer has dedicated functions such that the finished fuel particle has its own integral containment to minimize and control the release of fission products into the fuel body and reactor core. The TRISO coatings are the primary containment structure in the HTGR reactor and must have very high uniformity and integrity.To ensure high quality TRISO coatings, the four layers are deposited by chemical vapor deposition (CVD) using high purity precursors and are applied in a concatenated succession of batch operations before the finished product is unloaded from the coating furnace. These depositions take place at temperatures ranging from 1230°C to 1550°C and use three different gas compositions, while the fuel particle diameters double, their density drops from11.1g/cm3 to 3.0g/cm3, and the bed volume increases more than 8-fold. All this is accomplished without the aid of sight ports or internal instrumentation that could cause chemical contamination within the layers or mechanical damage to thin layers in the early stages of each layer deposition.The converging section of the furnace retort was specifically designed to prevent bed stagnation that would lead to unacceptably high defect fractions and facilitate bed circulation to avoid large variability in coating layer dimensions and properties. The gas injection nozzle was designed to protect precursor gases from becoming overheated prior to injection, to induce bed spouting and preclude bed stagnation in the bottom of the retort. Furthermore, the retort and injection nozzle designs minimize buildup of pyrocarbon and silicon carbide on the retort wall and manage nozzle orifice accretions. The equipment and operating methods have yielded very good reliability of equipment and product reproducibility in the TRISO coated particles batches.

Experimental detection of bubble-wall interactions in a vertical gas–liquid flow

Abstract Bubble motions and bubble-wall interactions in stagnant liquid were experimentally investigated by high-speed CCD and PIV technique with the main feature parameters such as Eotvos numbers Eo = 0.98–1.10, Morton number Mo = 3.21 × 10 − 9 and Reynolds numbers Re = 180 ~ 190. The effect of bubble injecting frequency and the distance S between the gas injection nozzle and the wall on the statistical trajectory of bubbles, average velocity distribution of flow field and Reynolds shear stress were studied in detail. It was shown that the combination of bubble injecting frequency and the distance S caused different bubble motion forms and hydrodynamic characteristics. When the normalized initial distance was very little, like S ⁎ ≈ 1.2 (here S ⁎ = 2 S / d e , and d e is the bubble equivalent diameter), bubbles ascended in a zigzag trajectory with alternant structure of high and low speed flow field around the bubbles, and the distribution of positive and negative Reynolds shear stress looked like a blob. With the increase of distance S ⁎ , bubbles' trajectory would tend to be smooth and straight from the zigzag curve. Meanwhile, with the increase of bubble injecting frequency, the camber of bubble trajectory at 20 y S ⁎ ≈ 3.6, the low-frequency bubbles gradually moved away from the vertical plane wall in a straight trajectory and the high-frequency bubbles gradually moved close to the vertical wall in a similar straight trajectory after an unstable camber motion. Under the circumstances, high-speed fluid was mainly distributed in the region between the wall and the bubbles, while the relative large Reynolds shear stress mainly existed in the region far away from the wall.

Oxidative Removal of Boron from Molten Silicon by CaO-based Flux Treatment with Oxygen Gas Injection

Oxidative removal of boron from molten silicon has been investigated at 1773 K (1500 °C) by CaO-based flux treatment with oxygen gas injection. Since oxygen gas is injected into the silicon melt after adding CaO- or CaCO3-CaF2 flux onto the melt, high oxygen partial pressure is maintained at the flux-O2-Si interface and the removal of boron proceeds under nonequilibrium conditions. The experimental results clarified that the behavior of boron removal from molten silicon depends on the competition between the oxidation reactions of boron and silicon. On the basis of the results obtained, optimum operating conditions for boron removal by the flux treatment were examined from the viewpoints of initial flux composition, reaction time, oxygen gas flow rate, and orifice size of gas injection nozzle. By repeating the batch operation for 120 seconds three times under the optimum conditions determined in the present study, boron concentration in metallurgical-grade silicon could be reduced from 14 to 7.6 mass ppm efficiently.

Particle attrition with supersonic nozzles in a fluidized bed at high temperature

Fluidized beds are used for a variety of processes such as food, pharmaceutical, petrochemical and energy production. Supersonic gas injection nozzles are used to grind particles in fluidized beds. For example, in the Fluid Coking process, which uses thermal cracking reactions to upgrade heavy oil, supersonic nozzles inject steam to control coke particle size. Maintaining a high attrition rate with a lower steam flowrate would reduce energy consumption, increase reactor throughput, and reduce sour wastewater production. The purpose of the present research is to study particle attrition with supersonic convergent–divergent nozzles in a fluidized bed at high temperatures, under conditions such as those encountered in the Fluid Coking process. According to the experimental results, the grinding efficiency is significantly improved by increasing fluidized bed temperature, attrition gas properties, or nozzle size. The experimental data further suggest that particle fragmentation is the dominant attrition process when using supersonic nozzles in a hot fluidized bed.

Comparison of the performance of liquid–gas injection nozzles in a gas–solid fluidized bed

It is often necessary to inject a liquid in fluidized bed reactors, such as fluid cokers, fluid catalytic crackers and gas-phase polymerization reactors. A more uniform dispersion of the injected liquid over the bed solids minimizes agglomeration, and prevents mass and heat transfer limitations, resulting in improved reactor operability and increased yields of desired products. The quality of the injection can be significantly affected by nozzle design and by several operating parameters. The goal of the current study was to compare several gas-assisted liquid injection nozzles under a variety of operating conditions. The nozzles sprayed water atomized with air into a bed of silica sand particles fluidized with air. The quality of the jet-bed interaction associated with each experiment was characterized using a conductive probe method, which uses the measured electrical conductance of the bed. It has been found that the bed conductance increases as the liquid becomes more uniformly dispersed throughout the fluidized bed. The droplet size of the injected spray was also measured in open air using a laser scattering system. In all tests, the liquid flowrate was held constant, while the atomization gas flowrate was varied. It was found that different nozzles displayed their best performance at different gas flowrates. Large droplets tended to negatively impact the spread of liquid throughout the bed, especially when they were larger than the fluidized particles. Large fluctuations in the water flowrate tended to decrease the performance of the nozzles. Multi-linear regression was used to correlate the nozzle performance to various nozzle parameters.

In situ TEM observation of solid-gas reactions

Under a gaseous atmosphere at high temperatures, almost all the materials (metal, catalysts, etc.) change their structures and properties. For the research and development of materials, it is of vital importance to clarify mechanisms of solid-gas and liquid-gas reactions. Recently an in situ TEM system combined with an environmental holder, which has a gas injection nozzle close to a specimen-heating element, has been developed. The gas injection nozzle permits gas to flow around the specimens sitting on the heating element made of a fine W filament. The newly developed in situ TEM has a differential pumping system; therefore, the pressure in the specimen chamber is maintained in the range of higher than 1 Pa, while the pressure in the electron gun chamber can be kept in the range of 10-5 Pa. This system was applied to in situ observation of chemical reactions of metals with gases: Observation of oxidation and reduction under a gas pressure ranging from 10-5 Pa to 1 Pa at high temperatures (room temperature to ∼1473 K) were successfully carried out on pure metal and rare metal catalysts at near-atomic resolution. This in situ environmental TEM system is promising for clarifying mechanisms of many solid-gas and liquid-gas reactions that take place at high temperatures under a gas atmosphere.