Gas Inlet Position Research Articles

Physical simulation study on flow field characteristics of molten steel during argon blowing in shroud of tundish

In the current study, water models are used to study the effect of the flow control devices, the casting velocity, gas flow rate and gas inlet position in the shroud on the flotation of inclusions and molten steel transfer behaviour at the tundish. Microbubbles were generated by using a ladle shroud. The results show that the inclusion flotation efficiency decreases and the dead volume fraction increases as the casting velocity becomes faster. Meanwhile, with the installation of the flow control devices, the residence time of molten steel becomes longer and the inclusion flotation efficiency is getting higher. Bubble adhesion plays an important role in removing inclusions. Smaller bubbles are favourable for inclusion flotation. As the flow rate of gas becomes larger and the gas inlet position installs a topper in the shroud, the bubbles become small. In this experiment, the flotation rate of inclusions in the tundish can be improved to 95.28% by changing the blowing parameters.

Computational fluid dynamics predicts the nanoparticle transport in gas aggregation cluster sources

In a typical sputter-based gas aggregation cluster source (GAS), nanoparticles (NPs) are created from supersaturated vapours of the target material. The NPs then escape from the source with the expanding gas through an exit orifice. The carrier gas flow profile is one of the most critical parameters, which strongly affects the NP losses on the walls and determines the efficiency of the NP transport to the substrate. In this work, computational fluid dynamics (CFD) simulations are performed to understand the flow of the carrier gas inside the aggregation chamber. We focus on the impact of the inlet and outlet geometry on the carrier gas flow and, therefore, on the NP transportation. Two types of GAS with either a conventional planar magnetron or a cylindrical magnetron are considered. In the planar configuration, the working gas inlet is from behind the magnetron, and the gas flows around the target towards the orifice along the system axis, which may cause some vertices. The situation is even more critical for the cylindrical magnetron, where the gas inlet position and geometry have a drastic influence on the gas flow. Brownian diffusion is found to prevail for NPs smaller than 5 nm, regardless of the gas flow. This leads to their losses on the walls. Larger NPs experience a stronger drag force from the carrier gas flow, which should exceed 10 m s−1 to prevent loss of NPs on the walls and keep NP transport efficient. Therefore, the CFD simulations help to visualise the motion of the NPs and optimise the geometry of the GAS for future applications.

Effect of precursor gas inlet position relative to hot wire cells in HWC-IP-PECVD systems for low-temperature graphene growth

ABSTRACT Graphene growth at low temperatures was investigated by integrating a hot wire cell made from coil-shaped tungsten into a plasma-enhanced chemical vapour deposition (PECVD) system. It was found that the suitable position of the hot wire was such that the precursor gas comes out of the end of the gas pipeline and directly flows into the hot wire along its axis. This position puts the gas pipeline outside of plasma area, yielding uninterrupted plasma. The obtained films, which were grown at a low temperature between 290 °C to 300 °C, showed the presence of sharp G band in Raman spectra, indicating the presence of graphitic carbon structure and was confirmed by X-Ray Diffraction data. Also, sharp D band was detected in Raman spectra, which indicated that the film contains many defects. In addition to the nature of ion bombardment in the PECVD process, the defects were due to the addition of O-H functional groups and the formation of sp3 C-H in the samples, as shown in the FTIR spectra. Due to these defects, the Raman spectra obtained of the films showed very weak 2D bands, suggesting that our samples were in the form of graphene oxide.

Impact of the gas dynamics on the cluster flux in a magnetron cluster-source: Influence of the chamber shape and gas-inlet position.

Although producing clusters by physical methods offers many benefits, low deposition rates have prevented cluster-beam deposition techniques from being adopted more widely. The influence of the gas aerodynamics inside the condensation chamber of a magnetron cluster-source on the cluster throughput is reported, leading to an improved understanding of the influence of gas aerodynamics on cluster transport. In the first part of this paper, the influence of the carrier gas's inlet position on the cluster flux is studied. In particular, two inlet configurations were investigated, i.e., from the rear of the chamber and from within the magnetron sputtering source. It was found experimentally that the latter configuration can lead to an increased cluster flux, under the same conditions of gas pressure and power applied to the magnetron. This behavior is explained with the help of simulations. In the second part of this paper, the gas dynamics behavior inside four chamber shapes, namely, two cylindrical shapes with different cross-sectional diameters and two conical shapes with different apex angles, was simulated. The modeling showed that the fraction of clusters successfully leaving the aggregation zone can be increased by up to eight times from the worst to the best performing chamber geometries studied. Finally, the cluster throughput was determined experimentally using a quartz microbalance in two of the four chamber designs. It was found that the cluster flux increased up to one order of magnitude, reaching ∼20 mg/h for a condensation chamber with a smaller cross section and a conical exit.

How gas flow design can influence the performance of a DBD plasma reactor for dry reforming of methane

DBD plasma reactors are commonly used in a static ‘one inlet – one outlet’ design that goes against reactor design principles for multi-component reactions, such as dry reforming of methane (DRM). Therefore, in this paper we have developed a novel reactor design, and investigated how the shape and size of the reaction zone, as well as gradual gas addition, and the method of mixing CO2 and CH4 can influence the conversion and product composition of DRM. Even in the standard ‘one inlet – one outlet’ design, the direction of the gas flow (i.e. short or long path through the reactor, which defines the gas velocity at fixed residence time), as well as the dimensions of the reaction zone and the power delivery to the reactor, largely affect the performance. Using gradual gas addition and separate plasma activation zones for the individual gases give increased conversions within the same operational parameters, by optimising mixing ratios and kinetics. The choice of the main (pre-activated) gas and the direction of gas flow largely affect the conversion and energy cost, while the gas inlet position during separate addition only influences the product distribution.

Tunable composition and properties of Al-O-N films prepared by reactive deep oscillation magnetron sputtering

We report a low-temperature deposition of Al-O-N films in a wide range of compositions. We use and explain the advantages of reactive deep oscillation magnetron sputtering (leading to suppressed arcing on the Al target) with a pulsed reactive gas flow control and optimized reactive gas inlet position (leading to a very smooth composition control, despite the different reactivities of O2 and N2). Next, we focus on the relationships between film composition, structure and functional properties. We demonstrate a smoothly controlled refractive index at a very low extinction coefficient, and identify the Al-O-N composition leading to the highest hardness, elastic recovery and elastic strain to failure. We discuss some of the technological applications which these properties are useful for.

The Impact of the Gas Inlet Position, Flow Rate, and Strip Velocity on the Temperature Distribution of a Stainless-Steel Strips during the Hardening Process

A non-uniform temperature across the width of martensitic stainless-steel strips is considered to be one of the main reasons why the strip exhibits un-flatness defects during the hardening process. Therefore, the effect of the gas inlet position in this process, on the temperature distribution of the steel strip was investigated numerically. Furthermore, an infrared thermal imaging camera was used to compare the model predictions and the actual process data. The results showed that the temperature difference across the width of the strip decreased by 9% and 14% relative to the calculated temperature and measured values, respectively, when the gas inlet position was changed. This temperature investigation was performed at a position about 63 mm from the bath interface. Moreover, a more symmetrical temperature distribution was observed across the width of the strip. In addition, this study showed that by increasing the amount of the hydrogen flow rate by 2 Nm3/h, a 20% reduction of temperature difference across the width of strip was predicted. Meanwhile, the results show that the effect of the strip velocity on the strip temperature is very small.

Three Dimensional Temperature Distribution Analysis in Directly Internal Reforming SOFC Fuelled by Methane

High SOFC operating temperature allows direct internal reforming (DIR) of methane within the SOFC anode, which is expected to be load-following simple dispersed power system. However, temperature decrease by endothermic reforming reaction leads to carbon formation and increase of thermal stress which cause decrease in the performance and durability of SOFC cells. We have developed a reactor model coupled with computer fluid dynamics and reactions to predict three dimensional temperature distributions. Calculated temperature distributions along flow direction agree with experimentally measured ones in both cases of homogeneous and functionally-graded paper structure catalysts. Detailed three dimensional analyses of temperature distributions tell us the importance of cell structures, gas inlet position, and catalyst thickness. Then, we have extended the analysis tool to more practical model where three SOFC cells are stacked. Temperature distribution in an upstream cell has steeper gradient than that in a downstream cell. Better temperature distribution was obtained by designing functionally-graded paper structure catalysts in two dimensions, along the stacking direction and the gas flow in a cell.

Three Dimensional Temperature Distribution Analysis in Directly Internal Reforming SOFC Fuelled by Methane

High SOFC operating temperature allows direct internal reforming (DIR) of methane within the SOFC anode, which is expected to be load-following simple dispersed power system. However, temperature decrease by endothermic reforming reaction leads to carbon formation and increase of thermal stress which cause decrease in the performance and durability of SOFC cells. We have developed a reactor model coupled with computer fluid dynamics and reactions to predict three dimensional temperature distributions. Calculated temperature distributions along flow direction agree with experimentally measured ones in both cases of homogeneous and functionally-graded paper structure catalysts. Detailed three dimensional analyses of temperature distributions tell us the importance of cell structures, gas inlet position, and catalyst thickness. Then, we have extended the analysis tool to more practical model where three SOFC cells are stacked. Temperature distribution in an upstream cell has steeper gradient than that in a downstream cell. Better temperature distribution was obtained by designing functionally-graded paper structure catalysts in two dimensions, along the stacking direction and the gas flow in a cell.

Numerical Modeling of an Inductively Coupled Plasma Based Remote Source for a Low Damage Etch Back System

Fluid model based numerical analysis is done to simulate a low damage etch back system for 20 nm scale semiconductor fabrication. Etch back should be done conformally with very high material selectivity. One possible mechanism is three steps: reactive radical generation, adsorption and thermal desorption. In this study, plasma generation and transport steps are analyzed by a commercial plasma modeling software package, CFD-ACE+. Ar + <TEX>$CF_4$</TEX> ICP was used as a model and the effect of reactive gas inlet position was investigated in 2D and 3D. At 200~300 mTorr of gas pressure, separated gas inlet scheme is analyzed to work well and generated higher density of F and <TEX>$F_2$</TEX> radicals in the lower chamber region while suppressing ions reach to the wafer by a double layer conducting barrier.

Effect of switching gas inlet position on the performance of a polyurethane biofilter under transient loading for the removal of benzene, toluene and xylene mixtures

The performance of a polyurethane (PU) biofilter was evaluated using different operating modes (unidirectional flow (UF) and flow-directional switching (FDS) operations) under transient loading conditions (intermittent and shutdown). Gas mixtures containing benzene, toluene and xylene (BTX) were employed as model gases. Quantitative real-time PCR methods were used for targeting the tmoA gene responsible for BTX degradation and estimating density of the BTX-degraders in the PU filter bed. Although the overall BTX Removal efficiencies at the outlet (50 h−1 of space velocity) were similar between the UF and FDS biofilters, the removability of BTX in the FDS biofilter was higher than that in the UF biofilter until the 3rd sampling position (68 h−1 of space velocity). The BTX removal potentials and tmoA gene copy numbers of the FDS biofilter remained constant, irrespective of the distances from the inlet, but those of the UF biofilter increased with increasing distance from the inlet position. These results indicate that an even distribution of BTX degraders in the FDS filter bed contributed to better BTX removal performance. After a 10 day-shutdown, the performances of the UF and SDF biofilters were rapidly restored within 1 day.

The Monomer Inlet Position Effect on the Fluorocarbon Film Deposited Using RF Plasma

The octafluorotoluene (C7F8) monomer was used to deposit fluorocarbon (a-C:F) film with an aromatic ring structure in an RF plasma reactor. While keeping the argon gas inlet position fixed, the inlet position effect of the C7F8 monomer on the deposited a-C:F film characteristics was investigated. It was found that, when C7F8 entered upstream of the plasma, the deposited film possessed no aromatic structure and the F/C atomic ratio of the film was higher than 1.4. Whereas for film deposited as C7F8 entered from the afterglow region (the so-called 'downstream' process), copious amount of the aromatic structure were preserved and the F/C ratio of the film was lower than 1.0. Higher deposition rate and rougher surface were also found in films deposited in the downstream process. A simplified reaction mechanism is proposed based on these results.

排気速度測定用テストドーム内壁の気体分子流束分布

A new solution has been obtained on the distribution of the moleclular flux density striking the wall of a test dome for measuring the speed of a high vacuum pump. The calculation was carried out based on sloving Clausing's integral equations by using iterative approximation method. It is found that the exact position of the wall of the tube where flux denisty shows the same value as exhaust end of the tube (≅0.5D, where D is tube diameter) is little affected by the gas inlet position nor the angular distribtion of inlet gas.

Cold Model Study on Inclusion Removal from Liquid Steel Using Fine Gas Bubbles.

A water model study was undertaken to investigate inclusion removal from liquid steel using fine gas bubbles, which were created by injecting air into a shroud nozzle just underneath the slide gate. The water flow rate was varied in the range of 2.0-3.2 m 3 hr -1 which is equivalent to 1.77-2.83 m s -1 of the linear velocity at the exit of the shroud nozzle. The ratio of gas to liquid flow rates was varied in the range of 0-12 % by volume. Polyethylene, PVC and ABS particles were used to imitate the inclusion. The characteristics of the bubble formation varied with the gas inlet position along the shroud: the closer the slide gate, the better the mixing between the gas and liquid phases. This was dependent on the slide gate opening: the smaller the opening, the more turbulence and hence the better mixing of the gas and the liquid. The relative removal efficiency was fairly independent of such variables as liquid flow rate, i.e., linear velocity, the slide gate opening (up to 58 % by area), and inclusion concentration. However, this was greatly affected by the wettability, i.e., contact angle of the inclusion with the liquid: the larger the contact angle, the higher the efficiency. It is concluded that the governing factor which determines the removal efficiency of the inclusion from liquid steel is the wettability of the inclusion with the steel, and the idea proposed in the present study should be an effective means for production of clean steels.

Development of a steady-state microwave ion source with large spherical electrodes for geometrical focusing

A steady-state electron cyclotron resonance ion source with large spherical electrodes has been developed to study the plasma wall interaction, erosion mechanism, and hydrogen retention of first wall materials in a nuclear fusion reactor. Discharge characteristics of the ion source were studied in terms of microwave power, magnetic field configuration, and gas (H2) pressure. Ion saturation current density Jis of about 21 mA/cm2 near the electrodes (target value is 20 mA/cm2) was achieved with microwave power of 3.0 kW and magnetic field of 2.3 kG at an optimal gas pressure. The measurement of Jis was made by a Langmuir probe. It was found that the dependence of ion saturation current density on the magnetic field was different between high (&amp;gt;5 mTorr) and low (&amp;lt;5 mTorr) pressure. The change of the gas inlet position from the center of the plasma production chamber to near the microwave input window gave higher ion saturation current density.

Computational Fluid Dynamics Evaluation of Good Combustion Performance in Waste Incinerators

ABSTRACT Combustion control techniques have become a legal requirement to minimize pollution in municipal solid waste incinerators. In-furnace destruction of pollutants is achieved when 2-second gas residence time at 850 oC and 6% O2 are guaranteed. Incinerator performance is analyzed numerically to validate good combustion performance. Computational Fluid Dynamics (CFD) modeling of gas flow inside the furnace chamber provides three-dimensional temperature, concentration, and velocity vectors. General flow patterns and the presence of recirculation pockets are traditionally observed. Local temperature and oxygen concentration can also be checked. The CFD results are analyzed further in terms of residence time, mixing, and thermal decomposition of potential pollutants. The residence time needs to be carefully determined based on the gas inlet position. The statistical variation requires evaluation of the average and minimum (or shortest) residence time. Mixing is quantified by defining a local mixedness parameter, a, with which the effects of secondary air jets are interpreted. Thermal decomposition parameter B integrates the temperature and oxygen availability over the residence time, which may be directly related to good combustion.

Effect of gas inlet positions on plasma carburizing of AISI 1020 steel

Samples of 1020 grade steel were carburized for 30 min at 1000 °C in a d.c. plasma system enclosed in a tube furnace. A gas mixture consisting of methane (CH 4) and hydrogen was bled into the system using one of two inlet positions located at the top and the bottom of the reactor. The latter position was close to the vacuum pump outlet. It was found that the carburizing results obtained with each gas inlet position differ significantly even though all other parameters (temperature, pressure, current density, flow rate and treatment time) were identical. The carburizing results are discussed in view of different mass transfer rates of carbon species in the plasma in the two different positions. It is concluded that when the gas inlet is located at the bottom of the reactor a large proportion of the methane molecules are not reaching the plasma reaction zone efficiently as their concentration in the stream is depleted faster than with flow from the opposite position, and this affects the active carburizing capacity of the plasma.

Inaccurate ventimetry by fresh gas inlet position.

A new position is described for the fresh gas inlet on Boyle Anaesthesia Machines (Model M 222) with CO2 absorber Mark III. The location of this inlet between the valves directly in the breathing circuit leads to inaccurate measurement of the expiratory volume when using a Wright ventimeter on the expiratory limb of the circuit. Correction is made by the manufacturer on request.