Gas Flow Configuration Research Articles

Near-infrared laser based cavity ringdown spectroscopy for applications in petrochemical industry

A simple, economic diode laser based cavity ringdown system for trace-gas applications in the petrochemical industry is presented. As acetylene (C2H2) is sometimes present as an interfering contaminant in the gas flow of ethylene (ethene, C2H4) in a polyethylene production process, an on-line monitoring of such traces is essential. We investigated C2H2–C2H4 mixtures in a gas-flow configuration in real time. The experimental setup consists of a near-infrared external cavity diode laser with an output power of a few mW, standard telecommunication fibers and a home-made gas cell providing a user-friendly cavity alignment. A noise-equivalent detection sensitivity of 4.5×10-8 cm-1 Hz-1/2 was achieved, corresponding to a detection limit of 20 ppbV C2H2 in synthetic air at 100 mbar. In an actual C2H2–C2H4 gas-flow measurement the minimum detectable concentration of C2H2 added to the C2H4 gas stream (which may already contain an unknown C2H2 contamination) increased to 160 ppbV. Moreover, stepwise C2H2 concentration increments of 500 ppbV were resolved with a 1-min time resolution and an excellent linear relationship between the absorption coefficient and the concentration was found.

Development of wide area reaction system for Reel-to-Reel TFA-MOD process

The previously developed numerical simulation method for the TFA-MOD process, which calculated the YBCO growth kinetics, gas element diffusion and gas flow, was applied to study the suitable gas flow mode for a multi-turning Reel-to-Reel tape conveyance system of a long YBCO coated conductors. The high YBCO production rate with uniform Jc distribution among tape lines is desired in the system. It was found by the numerical simulation for the vertical gas flow onto the tape surface to realize the above demands even in a wider reaction area. We developed a new wide area reaction tube for the Reel-to-Reel TFA-MOD process according to the numerically designed gas flow configuration. The demand for the new tube was confirmed to be satisfied by experiments.

Quantitative Analysis of Mixture Preparation Processes in New Direct-Injection Spark Ignition Engines

Visualization plays an effective role in the establishment of a new combustion concept by helping to find the optimal results quickly among many different parameters and contributing to a shorter development period. Laser-induced fluorescence, Raman scattering and infrared absorption were used to measure the air/fuel ratio quantitatively in a third-generation direct-injection gasoline (DIG) engine with a spray-guided mixture formation process and comparisons were made with the mixture formation concepts of the first- and second-generation DIG engines. The optimum combination of fuel spray, gas flow and combustion chamber configuration was found to be different for the three generations of DIG engines. The characteristics of the stable combustion region for obtaining higher thermal efficiency and cleaner exhaust emissions differed among the three mixture formation concepts.

Visualization of the Membrane Temperature Field of a Polymer Electrolyte Fuel Cell

Membrane temperature field of a polymer electrolyte fuel cell (PEFC) has been visualized experimentally. PEFCs need further breakthrough for deployment in the market. One of the major issues is the temperature management of the polymer membrane and the whole cell that strongly govern system performance through electrochemical reactions, ion transport, water management, and gas supply. The temperature field of the membrane, however, had not been visualized due to the cell configuration. In our experiment, the thermography technique is applied to visualize an operating test cell. Despite the unique configuration, measured i-V characteristics guarantee the cell performance. The visualization results revealed several important characteristics that help us understanding the physics and suggest design knowledge. One major result is the existence of so called a hot spot. The membrane does have a temperature distribution, and a local temperature maximum may exceed the membrane design limitation. This trend, of course, is not favorable for design purposes. Also, the impact of the major operation parameters, such as current density, humidification, and gas flow configuration, have been clearly exhibited. The experimental results are examined by using the results of our previously developed numerical code. The code includes the conjugate nature of the electrochemical reaction and the heat and mass transport processes. By comparing the experiment and the calculation, the mechanisms of the hot-spot generation and the parameter dependence have been explained. The results revealed the physics and suggested essential design criteria.

Generalized model of planar SOFC repeat element for design optimization

A model for planar solid oxide fuel cell repeat elements and stacks has been developed. Distribution of concentrations, reaction rates and temperatures (both gases and solids) are computed as well as overall performance results. Specific experiments provide inputs to the model by a parameter estimation method. The modeling approach developed allows to compare several configurations. As the number of design parameters is large (from cell size, component thicknesses to gas flow configuration), the model is designed to change easily these parameters so as to explore as many cases as possible. This is particularly true for the flow configuration (inlet position, outlets) for which several options are considered. This model assists in choosing a configuration and allows to perform sensitivity studies in an efficient way (without having to produce a new mesh such as for CFD tools) or to be combined with an optimization tool. A first validation with experimental results, performed on a particular stack design, is presented. Issues of model accuracy and sensitivity to uncertain inputs are discussed.

Numerical simulation for the characterization of operating conditions of RF-RF hybrid plasma torches

A two-dimensional (r, z) numerical code has been developed to investigate the prominent features of RF-RF hybrid plasma torches with two stages of different diameter. Flow and temperature fields have been calculated within the assumptions of laminar flow and local thermodynamic equilibrium for the optically thin argon plasma operated at atmospheric pressure, taking into full account the electromagnetic interaction between the primary and the secondary stage of the hybrid device. Results from a detailed parametric study for various geometric, gas flow and electric configurations aim at putting into evidence the wide range of operating conditions that can characterize the use of RF-RF hybrid plasma torches for industrial applications, showing also their possibility to give high enthalpy plasma jets with high torch efficiencies. The magnetofluidynamic modelling described in this work can be an effective tool for providing the theoretical framework for a deep understanding of RF-RF hybrid plasma torches and for designing them as suitable sources for chemical processing of materials, when utilized within an integrated approach that would match the induction plasma torch simulation with the RF generator operating conditions to evaluate the total source efficiency for each particular hybrid configuration.

Quantitative Analysis of Mixture Preparation Processes in New Direct-Injection Spark Ignition Engines(S.I. Engines, Stratified-Charge Combustion)

Visualization plays an effective role in the establishment of a new combustion concept by helping to find the optimal results quickly among many different parameters and contributing to a shorter development period. Laser-induced fluorescence, Raman scattering and infrared absorption were used to measure the air/fuel ratio quantitatively in a three generation direct-injection gasoline (DIG) engine including a spray-guided mixture formation process and comparisons were made with the mixture formation concepts of the first- and second-generation DIG engines. The optimum combination of fuel spray, gas flow and combustion chamber configuration was found to be different for the three generations of DIG engines. The characteristics of the stable combustion region for obtaining higher thermal efficiency and cleaner exhaust emissions differed among the three mixture formation concepts.

Characteristics of ultrathin Ta and TaN films

The electrical resistivity of thin films of Ta and TaN has been examined as a function of film thickness and other processing parameters. The films were deposited by magnetron sputtering of Ta cathodes with Ar, or mixtures of Ar and N2 for the case of TaN. Ta films deposited on silicon dioxide or Cu surfaces were always beta phase, and showed little resistance increase as the thickness was reduced. The TaN films were deposited in a broad range of compositions, depending on reactive gas flow and system configuration, and showed strong increases in resistivity as thickness was decreased. Ta films deposited on TaNx with x equal to or greater than 1, an electrical resistivity greater than 300 mΩ cm, and with thickness greater than 2 nm were alpha phase, and showed significant increases in resistivity as thickness was reduced. The application and electrical properties of these films as diffusion barriers in interconnect structures depends strongly on the thicknesses at the contact points at the bottoms of vias and only weakly on the phase of the Ta. The resistivity of the barrier films on via and trench sidewalls is high enough to be irrelevant to circuit performance.

A gas flow uniformity study in large-area showerhead reactorsfor RF plasma deposition

A simple one-dimensional model for plasma deposition in arectangular showerhead reactor with single side pumping has been developed inorder to explain the mechanisms which yield uniform deposition using this gasflow configuration. Although the flow velocity increases linearly withdistance towards the pumping side, the solution of the transport equations forthe neutral species shows that their number densities are constant throughoutthe reactor. Consequently, the plasma and surface deposition reactions areindependent of position in any arbitrarily-large-area showerhead reactor.

Practical aspects in the drawing of an optical fiber

The transport processes in the furnace for the continuous drawing of optical fibers have been studied numerically and analytically. Practical circumstances and operating conditions are considered. A peripheral gas flow configuration has been modeled, along with irises at the ends, as employed in practical furnaces. The neck-down profile of the fiber is not chosen, but has been generated on the basis of a surface force balance. The results obtained are validated by comparisons with earlier experimental results. A detailed analysis has been carried out to determine the relative contributions of different forces during the drawing process. Even though the internal viscous stress is shown to be the major contributor to the draw tension, it is found that under certain operating conditions, the force due to gravity is significant, especially at the beginning of the neck-down region. For a peripheral flow configuration, the effect of flow entrance is found to be very important in determining the necking shape. However, the effect of the iris size on the fiber temperature field is found to be negligible. It is found that for a given furnace temperature and fiber radius, there is an upper limit for draw-down speed at which a fiber can be drawn without rupture. Practical ranges of draw speeds and furnace temperature conditions are identified for the process to be feasible.

Recent operating experiences of the advanced ceramic tube filter (ACTF) for the Wakamatsu 71MW PFBC demonstration plant and design improvements for commercial plants

The ACTF installed in the 71-MW PFBC demonstration plant at Wakamatsu Power Station of Electric Power Development Co., Ltd (EPDC) is the first demonstration scale ceramic filter system for high-temperature, high-pressure application. The ACTF, developed by Asahi Glass Co. Ltd (AGC), is featured by inside to outside gas flow configuration with enhanced downward flow by a self circulation blowdown system, vertically arranged tubes in three compartments, backpulse system with regenerators and water or steam cooled tube sheets. Cordierite with micro-pore structure is used for filter tube material because of superior chemical stability and heat shock resistance. An extinguishing powder injection system is also provided to protect the filter tubes from abnormal boiler operation. This paper reviews the latest operating experiences of the ACTF at Wakamatsu and design improvements required to realize the ACTF system for the commercial PFBC plants.

Comparative evaluation of municipal solid waste incinerator designs by flow simulation

Flow simulations have been carried out to evaluate the effects of combustion chamber design and air/combustion gas flow configuration on the overall performance of municipal solid waste incinerators. Computational results show velocity and temperature fields in the entire region of flow passage. Local recirculations and uneven distributions of flow velocity and temperature should be minimized and mixing is to be enhanced. Two parameters are proposed to help quantify the overall flow condition. The degree of mixing of different species, which enter the incinerator from the air and combustion gas inlets, is represented by the mixing parameter α. Here, α is calculated on the nodal points. The probability distribution of α in the entire computational domain is used for comparative evaluation of incinerator designs. The thermal decomposition parameter β is calculated by integrating the kinetic rates along the trajectory of a fluid element. This parameter represents the portion of the unreacted materials among the total pollutants released from the bed. By employing these parameters, various incinerator design alternatives can be quantitatively analyzed from two principal viewpoints, i.e., the effectiveness in mixing and the thermal decomposition of pollutants.

Modeling of oxide breakdown from gate charging during resist ashing

Plasma damage was observed after exposing an antenna capacitor structure to an O/sub 2/ plasma in a single wafer resist asher. The observed early breakdown is well modeled by surface charging caused by plasma nonuniformity. Here, the plasma nonuniformity was induced by gas flow and electrode configuration. The present results agree well with our previous results where magnetic field leads to a nonuniform plasma. In this model, nonuniformity leads to a local imbalance of ion and electron currents which charge up the gate surface and degrade the gate oxide. Using SPICE, a circuit model for the test structure and plasma measurements, the Fowler-Nordheim current through the thin oxide regions at different points on the wafer was calculated and found to agree well with the observed damage. The important implication of this work on oxide reliability is that the modeling gives a clear picture to this breakdown mechanism. The charging model can also be applied to any ashing process in any nonuniform plasma. Moreover, this model provides a physical basis for design rules of device structures for the fabrication of reliable gate oxides in submicron MOS technology.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Modeling, simulation and model validation for an axial-radial ammonia synthesis reactor

This study is aimed at modeling axial-radial reactors and validating the model by comparing its prediction to experimental data. The axial-radial reactor is characterized by a gas-flow configuration which is an hybrid between the classical axial-flow and radial-flow configurations. The steady-state behavior of the reactor is found as solution to the Navier-Stokes equations describing the velocity field and pressure profile and to the mass and heat balance equations. A new solution approach is developed which decomposes the partial differential equation system into two subsystems, for each of which the most suited solution method can be applied.The Navier-Stokes equations are solved using two-dimensional collocation on finite elements while the mass and energy balance equations are solved using alternatively the collocation and the finite-difference methods together with an integration method.The solution to the Navier-Stokes equations is found to be very sensitive to the choice of boundary conditions. The mass and energy balance subsystem, on the other hand, is highly sensitive to the choice of the spatial coordinate that is integrated, the other being discretized. Since the two subsystems are coupled an appropriately devised iteration scheme is proposed to solve the complete system.Although rigorous parameter fitting was purposefully not attempted, satisfactory model prediction was obtained.

Characterization of gas flow configurations for phosphoric acid fuel cells

The cell performance and polarization distribution in the horizontal plane of a phosphoric acid fuel cell (PAFC) were studied for thirteen different types of gas flow. In all cases, the potentials of the anode and cathode in the fuel outlet area shifted to positive directions. At 90% utilization of fuel, the potential shift and the cell voltage changed significantly from one type to another. Experimental results show that the cell voltage increased, and the potential shift decreased in the following order; CROSS-FLOW < RETURN-FLOW = CO-FLOW < COUNTER-FLOW < type E2. The extent of the change between various types depended on the following three conditions. (1) The fuel gas has an opportunity to be used twice in the horizontal plane of a cell. (2) The fuel gas flow is in parallel with the air flow. (3) The fuel gas flow is opposite to the air flow. These are requirements for obtaining good and stable performance of a fuel cell. The CROSS-FLOW case has none of these three conditions, the RETURN-FLOW case has the first condition, the CO-FLOW case has the second, the COUNTER-FLOW case has the second and the third conditions, and the best gas flow type (type E2) has all.

Fluid flow through lances with constant and variable pitch swirled inserts

Sirosmelt-type gas injection systems for submerged combustion in metallurgical baths use tubular lances with single or multistart-type helical vane swirlers in the annular region. These inserts not only promote heat transfer from the tube wall to the gas flowing through the tube but also increase pressure drop across the lance. The total pressure loss across such inserts is due to entrance effects and fully developed flow losses. These losses can be quite substantial depending upon the gas flow rate and configuration of inserts. In this paper, a comparison has been made between fixed and variable pitch inserts as far as pressure drop is concerned. A simple flow model has been proposed to describe the flow characteristics of both types of insert. An understanding of these flow characteristics forms a basis for improved lance designs.

Heat and mass transfer in a molten carbonate fuel cell. 2nd Report, Analysis investigation of performance and temperature distribution in a cell stack.

A large-scale stack model of a molten carbonate fuel cell was developed for evaluating the variation of cell performance and temperature in the cell stacking direction. A numerical method for the solution of the performance and the three-dimensional temperature distribution in a stack was proposed and examined. For the temperature distribution, calculated results, taking the heat transfer at the end plate surface into account, have been compared with the measured temperature distribution of the cell stack, and the comparison showed good accordance. For several stacks which were composed of 12 cells with different gas flow configurations, the total stack performance and the temperature distribution were investigated analytically. As a result, it was shown that the temperature distribution of a cell becomes more uniform by the effect of heat exchange in the stacking direction.

RF-pumped infrared laser using transverse gas flow

A transverse gas flow configuration has been developed utilizing RF discharge waveguide technology for several infrared lasers. Two potential applications have been identified: pulsed chemical laser and CW CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> laser. In the 3.8 μm DF laser, the flowing gas device provides rapid gas replenishment to maintain high electrical efficiency at high repetition rates. An average power of 0.6 W was achieved at 1 kHz. An order of magnitude power improvement can potentially be developed in a closed cycle system. In the CW CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> laser, the flowing gas provides efficient cooling so that high output power per unit gain length can be achieved. A 16 W output in a 20 cm gain length device, corresponding to a record 0.8 W/cm output has been demonstrated. This system can be developed into a 20-60 W laser with a 20-50 cm gain length.

A Unified Analysis of Concurrent Modes of Flame Spread

A theoretical study is conducted of the spread of flames in gas flows moving in the direction of flame propagation. The study draws on the fact that concurrent flame spread configurations have common general characteristics, thus allowing a unified treatment of the problem. The analysis, although approximate, provides an analytic expression for the rate of flame spread over the surface of thermally thick fuels in laminar gas flow configurations that accept a similarity solution. The predicted flame spread rates for these particular flows provide limits for the rates of spread in other non-similar gas flow configurations.

Optical gain measurements at 10.6 µm in an 80 µm hollow-core slab waveguide

N <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> , when externally excited in a gas discharge and mixed with CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> +He in a planar metallic waveguide with plate separation less than 80μm, has produced an active laser medium with gain in excess of 17 dB/m. These results demonstrate that an active medium capable of sustaining oscillation can be produced in a waveguide with core dimensions suitable for distributed feedback at 10.6μm. Results are reported for both longitudinal and transverse gas flow configurations.