Gas Flow Rate Conditions Research Articles

Simulation of algae growth in a bench scale internal loop airlift reactor

The growth of red marine alga Porphyridium sp. cultivated in an internal loop airlift (ALR) photobioreactor was simulated. The model proposed integrates a dynamic formulation of the kinetics of photosynthesis, photoinhibition, and the fluid dynamics of the ALR, including shear stress effects on the kinetics of growth. The kinetic parameters obtained previously for a system under defined light/dark cycles were used, and satisfactory agreement was found. The maintenance term was modified to take into account the detrimental effects of shear stress in the bioreactor on the rate of growth. A hybrid method for approximate solution of the equations is proposed. The conditions of gas flow rate and illuminance required for positive growth were found. This is the first mathematical model that predicts the effect of gas flow rate, column height, column diameter, and cross-sectional areas on the productivity of a photosynthetic process in an airlift bioreactor. Extrapolations done using the model indicate the possibility of predicting the optimal diameter for an assembly of ALR photobioreactors.

Experimental study on mass transfer of a co-current gas–liquid contactor performing under high gas velocities

Two phase flow co-current horizontal spray column performing under high gas velocities (up to 14 m/s) is investigated in an air–water system. Experiments are carried out in order to characterize mass transfer between liquid and gas in the reactor under various conditions of liquid and gas flow rates. The mass transfer parameters studied are the interfacial area ( a), the liquid volumetric mass transfer coefficient ( k L a) and the liquid mass transfer coefficient ( k L). The method of gas/liquid absorption with chemical reaction using sodium sulphite was applied to determine the interfacial area and the volumetric mass transfer is determined experimentally by a ‘gasing out’ method.

Pilot-scale validation of the kinetics of SO 2 absorption into sulphuric acid solutions containing hydrogen peroxide

Sulphur dioxide removal efficiencies were measured in a pilot-scale column packed with Pall plastic rings, at 20 °C and atmospheric pressure, with sulphuric acid solutions (1.2–6.6 M) containing hydrogen peroxide (0.13–0.83 M) as the scrubbing liquid, for different sulphur dioxide partial pressures in the range of 100–500 Pa in the inlet air. A mathematical model previously developed to interpret laboratory experiments was adapted and used to treat the results of the pilot-scale runs for a wide range of operating conditions of gas and liquid flow rates, SO 2 partial pressures in the gas phase, H 2O 2 and H 2SO 4 concentrations of the solution. A quite satisfactory agreement was found between kinetic parameters deduced from the tests achieved in laboratory and pilot-scale contactors up to 5 M in H 2SO 4. It appears, therefore, that this model can provide good predictions of the absorption performances of industrial columns and be really helpful to design scrubbers for SO 2 abatement with hydrogen peroxide.

Microstructures and Magnetic Properties of Sm-Fe-N Thick Films Produced by the Aerosol Deposition Method

This paper describes magnetic properties and microstructures of Sm-Fe-N thick films prepared by the aerosol deposition (AD) method. The maximum thickness (d) of 77 μm was obtained in the AD conditions of gas flow rate (gfr) = 6 x 10 - 3 m 3 /min for 4 min. From this result, the deposition rate was estimated as 19 μm/min. The density (p) of Sm-Fe-N films were in the range of 4.9 × 10 3 -5.9 x 10 3 kg/m 3 , which were 64-77% of the X-ray density of the Sm 2 Fe 1 7 N 3 compound reported (7.67 x 10 3 kg/m 3 ). However, they were higher than the density of the green compact of Sm-Fe-N host powders (3.86 x 10 3 kg/m 3 ). The Sm-Fe-N AD films showed the remanences (B r ) of 0.36-0.42 T, which were 58-68% of that of hoxt powder (0.62 T). The coercivitics (μ 0 H c I ) increased irom 1.16 T to 1.69-1.86 T after the deposition because the average grain size decreased from 1.94 to 0.32 μm. XRD analysis revealed that the ratio of peak intensity of (006) to (033) in the Sm-Fe-N AD films was higher than that in the host powder. In addition, the remanence measured in perpendicular to the film plane was higher than that in parallel after the compensation of demagnetizing field. Therefore, it is considered that the c-axis in Sm-Fe-N AD films has a tendency to align in perpendicular to the film plane.

Sm-Fe-N系エアロゾル·デポジション厚膜の磁気特性と組織

In this study, the relationship among magnetic properties, Aerosol Deposition (AD) conditions and microstructures in Sm-Fe-N AD films were investigated. The maximum thickness of 145 μm was obtained in the AD conditions of gas flow rate (gfr) = 6 L/min for 10 min. The density of Sm-Fe-N films were in the range of 5.43 - 6.24 g/cm3, which were 71 - 81 % of the X-ray density of the Sm2Fe17N3 compound reported (7.67 g/cm3). The Sm-Fe-N AD films showed remanence in the range of 0.38 - 0.42 T, which were 61 - 68 % of that of Sm-Fe-N host powder (0.62 T). The coercivities increased from 1.16 to 1.74 - 1.79 T after the deposition because the grain size decreased from 1.94 to 0.32 μm.

CFD Simulation of Reaction and Heat Transfer Near the Wall of a Fixed Bed

Modeling of fluid flow, heat transfer and reaction in fixed beds is an essential part of their design. This is especially critical for highly endothermic or exothermic reactions in low tube-to-particle diameter ratio (N) tubes, such as are used in steam reforming and partial oxidation. In the simulations a near-wall section of an entire bed is used to create a simulation geometry that can be handled in the available computational domain. A full bed model was also available for validation of the wall-segment model. In the wall-segment approach a section of the bed is modeled in more detail, allowing for a relatively smaller control volume size and a more detailed view of the flow and heat transfer patterns. A simple model of a steam reforming process is used in the CFD simulation to incorporate the effect of reaction rate on temperature profiles in the bed. Simulations were performed under realistic industrial conditions of high temperature, pressure and gas flow rate, with gas properties corresponding to those of steam reforming. A constant wall heat flux was imposed, and various shapes of particles studied with heat sinks on the surface to simulate the reforming endothermic reaction, which is mainly confined to the surface of the pellet. Results will be presented showing the existence and effect of temperature profiles on the catalyst particles, and the effect on the local heat transfer rates of different gas compositions, corresponding to conditions at different locations along the catalyst tube. Local deactivation of catalyst particles can also lead to wall hot spots, or 'giraffe-necking' which can be well-reproduced by the simulations.

Direct Simulation Monte Carlo Analysis of Rarefied Gas Flow Structures and Ventilation of Etching Gas in Magneto-Microwave Plasma Etching Reactors

Gas flows in plasma etching reactors for semiconductor fabrication became a chief consideration in designing second-generation reactors with higher etching rates. An axisymmetrical model based on the direct simulation Monte Carlo method has been developed for analyzing rarefied gas flows in a vacuum chamber with the conditions of downstream pressure and gas flow rate. By using this simulator, rarefied gas flows with radicals and etch-products were calculated for microwave-plasma etching reactors. The results showed that the flow patterns in the plasma chamber strongly depend on the Knudsen number and the gas-supply structure. The ventilation of the etch-products in the plasma chamber was found to be improved both for higher Knudsen numbers and for gas-supply structures of the downward-flow type, as compared with those of the radial-flow or upward-flow types.

A non-spherical model for bubble formation with liquid cross-flow

A non-spherical model for bubble formation at an orifice with liquid cross-flow has been developed. The interface element approach is applied to describe the dynamics of bubble formation. The effect of liquid cross-flow on the bubble formation process is modelled by a combination of tilting of the bubble axis and liquid pressure analysis of each element on the bubble interface. Model predictions compare well with the experimental results available in the literature for different conditions of gas flow rate, orifice diameter and liquid cross-flow velocity. Simulated bubble shapes are highly non-spherical, especially at high liquid velocities, and bear a striking resemblance with the experimental high-speed video sequences.

Methane decomposition properties of ZrNi alloy in flowing gas system

With the intention of developing the decomposition process of tritiated compounds, ZrNi alloy was taken up as one of proper materials and its methane decomposition properties were experimentally investigated in a laboratory-scale flowing gas system. Methane was selected as a typical tritiated compound because of being known to be hardly decomposed and little data. The performance tests of methane decomposition using ZrNi alloy under various process conditions of gas flow rates (20, 35, 70 and 100 cc min −1), granular sizes (70–200, 200–400 and <400 mesh) and reaction temperatures (823, 848 and 873 K), have been carried out. As a result, the methane and hydrogen concentrations after undergoing decomposition process showed qualitatively similar four-stage-time change profiles for all of the independent experimental conditions. However, the definite dependence of decomposition properties on the decomposition conditions was recognized by observing a duration time of a briskest decomposition rate of more than 70%, volumes of decomposed methane and generated hydrogen.

Observation of Molten Slag Surface under Gas Impingement by X-ray Computed Tomography.

Observation of molten slag at 1 673 K was carried out by X-ray Computed Tomography (X-ray CT) to make clear the shape of slag surface where gas was downward blown. X-ray CT scanning of molten slag heated in an electric furnace was conducted to take an image of its cross section. In order to examine the effects of gas momentum supplied on the surface shape, three kinds of inert gases, Ar, He and N 2 , were employed as the blowing gas under the several conditions of gas flow rate and gas pipe diameter. The obtained X-ray CT images successfully visualized the cross section of molten slag. The boundary line between gas and slag in the image was concave under the gas blowing, indicating a formation of depression on the slag surface by gas impingement. The concave boundary is completely different from the parabolic shape conventionally evaluated. The depression became larger, not only in depth but also in width, with increasing gas flow rate, whereas drastically smaller with increasing gas pipe diameter. In addition, larger depth was brought by impingement of larger molecular (atomic)-weight gas. These results were well explained by the conservation law of momentum between gas and slag. It was also revealed that the increment in the boundary line caused by formation of depression, which corresponds to an increase in the interfacial area, is in proportion to the depression depth in the range of more than 2 mm, and was independent of the pipe diameter and gas species.

Room Temperature Deposition of Silicon Nitride Films for Passivation of Organic Electroluminescence Device Using a Sputtering-Type Electron Cyclotron Resonance Plasma

Dense silicon nitride (SiN) films were deposited at room temperature by a sputtering technique using an electron cyclotron resonance (ECR) plasma. Film properties were studied using ellipsometry, chemical etching, Fourier transform infrared spectroscopy, and thermal desorption spectroscopy. A SiN film deposited under the optimum condition of nitrogen gas flow rate had a refractive index of 2.03 and showed a large Si–N bond number. The SiN film had a high barrier against moisture penetration relative to SiN films prepared by chemical vapor deposition at 900°C. This indicates that the film deposited using a sputtering-type ECR plasma has the potential to be utilized as a passivation layer of devices such as organic electroluminescence, which require low temperature processing.

Decomposition of inorganic gases in an atmospheric pressure non-equilibrium plasma

If various oxide powders were prepared by microwave heating under an argon gas flow for the purpose of improving catalysts' performance, we found that an atmospheric pressure non-equilibrium plasma was generated around some powders and that this phenomenon is peculiar to electrically conductive and heat-resistive materials. For industrial applications we tried to decompose inorganic gases by considering various utilizations. As a first step, nitric oxide which is one of the notorious atmospheric pollutants was treated. As a result nitric oxide gas could be decomposed by an atmospheric pressure plasma even under high gas flow rate conditions and under the presence of oxygen and water.

トリクロロエチレンの紫外線分解反応速度

A study has been made of obtaining the gas phase photooxidative decomposition rate of trichloroethylene (TCE) which was extracted from contaminated soil by evacuation. A cylindrical reactor which was equipped with a low pressure mercury lamp at the center axis (reactor I) was divided into several spaces with barriers. Conversion of TCE increased with increasing the number of divided spaces in the reactor under low gas flow rate, however, the conversion of TCE decreased with increasing the number of the spaces under high gas flow rate. Moreover, the conversion increased with increasing the initial concentration of TCE under the condition of the same gas flow rate. The photooxidative decomposition rate of TCE was obtained by using graphical method under the assumption of that the complete mixing flow was formed and the average photo intensity in each spaces in the reactor was same. The maximum decomposition rate was obtained at the conversion of c.a. 0.8 and the rate was proportional to the 1.2th power of the concentration of TCE. The photooxidative decomposition rate of TCE in a reactor with larger diameter (reactor II) was in passable agreement with the value expected from the data obtained in the reactor I.

Destruction of volatile organic compounds used in a semiconductor industry by a capillary tube discharge reactor

Nonthermal plasma technologies offer an innovative approach to the problem of decomposing various volatile organic compounds (VOCs). The authors focused on DC capillary tube discharge plasma reactors to study the decomposition/destruction efficiency for toluene, EGM, trichloroethane and trichloroethylene at 50-2300 ppm levels in dry air. The effects of gas flow rate, VOC concentration and reactor operating conditions on decomposition and analysis of reactant conversion for each VOC were investigated. The results show that VOC destruction efficiency as high as 90% can be achieved, even under a short residence time (3.8 ms) with a destruction energy efficiency of up to 95 g (VOC)/kWh. Laboratory-scale plasma technology was successfully demonstrated for its potential application for VOC control in the semiconductor clean-room environment.

Investigation of a flat sheet membrane desolvator for aqueous solvent removal with inductively coupled plasma atomic emission spectrometry

Results obtained from a preliminary investigation of the performance of a flat sheet membrane desolvator (FSMD) utilizing dual hydrophobic polypropylene membranes with an average pore size of 0.05 μm and a 50 ± 5 μm thickness are reported. The membranes have a desolvation area of 241 cm 2. The volume-to-surface area ratio is 0.3 cm. Using the FSMD with an ultrasonic nebulizer (USN), aqueous solvent desolvation efficiencies of greater than 99.9% were obtained at all nebulizer gas flow rates investigated (0.8, 1.2, and 1.8 l min −1). This efficient desolvation occurred when the countercurrent gas flow rate was equal to or slightly greater than the applied nebulizer gas flow rate. Under these conditions preconcentration factors of 18, 44, and 590 were observed with flows of 0.8, 1.2 and 1.8 l min −1, respectively. Operating with countercurrent gas flow rates much higher than the nebulizer gas flow rates leads to a significant reduction in analyte flux, thus increasing detection limits. Depending on the nebulizer and countercurrent gas flow rate conditions, the FSMD contributed between 10–40% to the overall analyte loss in the system. The lowest detection limit observed for aqueous copper with the USN-FSMD system is 0.4 ppb at nebulizer and countercurrent gas flow rates of 1.2 and 1.4 l min −1, respectively. At this nebulizer gas flow rate, replacing the FSMD in the system with a commercial tubular membrane desolvator, MDX100, gave a lowest Cu detection limit of 0.2 ppb at a countercurrent gas flow rate of 1.2 l min −1. These detection limits represents improvements over the 0.7 and 8 ppb obtained with USN and pneumatic nebulization, respectively.

Removal of Carbon Tetrachloride From Air Stream by A Corona Torch Plasma Reactor

Non-thermal plasma technologies offer an innovative approach to the problem of decomposing various volatile organic compounds (VOCs) in the paint and semiconductor industries. We focussed our attention on corona torch plasma reactors to study the decomposition destruction efficiency for carbon tetrachloride at 400 to 8600 ppm level in dry air. The effects of gas flow rate, concentration and reactor operating conditions on the decomposition and analysis of reactant conversion of carbon tetrachloride were investigated. Experimental results show that the destruction efficiencies of carbon tetrachloride depend nonmonotonically on discharge power or applied voltage and increase with decreasing gas flow rate. No significant O3, NOx , N2O and CO are observed as the by-products of discharge in air. CO2, H2O, Cl2 and HCl are observed to be the final products of carbon tetrachloride destruction.

Chemical Vapour Deposition Rate of Mo Film in Horizontal Tubular Reactor

A gas mixture consisting of Mocl s , H 2 and Ar (carrier and dilute gas) was fed into an externally heated horizontal quartz tube (tubular reactor). Mo film was deposited on the inner wall of the reactor by atmospheric thermal CVD under different conditions of gas flow rate, wall (substrate) temperature and gas compositions. Film growth rate increased with the deposition temperature and the apparent activation energy was determined to be 83.5 kJ/mol in the range between 923 and 1123 K. Above 1223 K, deposits were composed of fine particles. Distribution of the film growth rate along the axial direction in the reactor was dependent on the composition of gas mixture. At high P H2 , the deposition rate was high, and a peak was formed at the inlet region in the distribution. On the other hand, a flat distribution was obtained at low P H2 . Deposition experiments were conducted using a tubular reactor with a shorter length and the output gas was condensed into powder, which was composed of MoCl 4 , and MoCl 2 The fractional conversion from MoCl 5 into Mo and into the condensed powder were obtained at different gas compositions. It turned out that the effect of P H2 change on the fractional conversion was larger than that of P MoCl5 . Considering the compounds of the deposited powder and the variation in the growth rate distribution with the gas compositions, the role of the gas phase reaction was discussed.

Flooding in Gas-Liquid Countercurrent Two-Phase Flow in Parallel Vertical Pipes.

Flow regime transition and pressure drop in gas-liquid countercurrent two-phase flow was studied in three vertical parallel channels. The conditions for flooding initiation in parallel-channel systems could be predicted well using Imura's correlation for a single channel. After flooding, the flow patterns were different in each channel. Aflow pattern classification diagram for the three-channel system was developed based on the flow patterns observed under various conditions of gas and liquid flow rates. It was seen from the results of pressure measurement in the three-channel system that the maximum pressure developed in each channel had a serious effect on the average pressure in the lower plenum, and that the frictional loss coefficient, estimated from the time-averaged pressure in the lower plenum, could be correlated to the relative gas Reynolds number.

Influence of the power and pressure on the growth rate and refractive index of a-C:H thin films deposited by r.f. plasma-enhanced chemical vapour deposition

Thin films of hydrogenated amorphous carbon (a-C:H) were prepared from a mixture of 10% methane and 90% hydrogen by the plasma-enhanced chemical vapour deposition (PECVD) technique at an r.f. frequency of 13.56 MHz. Different conditions of pressure, power and gas flow rate were employed. The films were characterized by a variety of surface analytical techniques, and ellipsometry was used to characterize the optical properties of the films. The films obtained were uniform, soft, transparent, non-conducting and chemically inert, with good thermal conductivity and high stability. In this paper, we report and discuss some of the parameters that influence the optical properties of the films and the rate at which they are deposited.

Flooding in Gas-Liquid Countercurrent Two-Phase Flow in Parallel Vertical Pipes.

Flow regime transition and pressure drop in gas-liquid countercurrent two-phase flow was studied in three vertical parallel channels. The conditions for flooding initiation in parallel-channel systems could be predicted well using Imura's correlation for a single channel. After flooding, the flow patterns were different in each channel. Aflow pattern classification diagram for the three-channel system was developed based on the flow patterns observed under various conditions of gas and liquid flow rates. It was seen from the results of pressure measurement in the three-channel system that the maximum pressure developed in each channel had a serious effect on the average pressure in the lower plenum, and that the frictional loss coefficient, estimated from the time-averaged pressure in the lower plenum, could be correlated to the relative gas Reynolds number.