Input Flow Rate Research Articles

Removal of Water Vapor in a Mist Singlet Oxygen Generator for Chemical Oxygen Iodine Laser

The mist singlet oxygen generator (Mist-SOG) for a chemical oxygen iodine laser (COIL) has been developed in order to increase basic hydrogen peroxide (BHP) utilization. It was clarified that the Mist-SOG generated much more water vapor than conventional SOGs because the heat capacity of BHP is small. The water vapor deactivates the excited iodine and depresses the laser power. Therefore, a jet-cold trap was developed in order to remove the water vapor while maintaining a minimum deactivation of singlet oxygen. In this method, a nozzle was used to spray chilled H2O2 at 238 K as a thin layer directly to the gas flow to achieve a large specific surface area for water vapor. As a result, the water vapor mole fraction was reduced to 7% from 18% with the BHP utilization of 21% at the Cl2 consumption rate of 3.5 mmol/s (Cl2 input flow rate of 8.0 mmol/s) for 65-µm-diameter BHP droplets.

HYDRODYNAMIC ASSESSMENT OF VARIOUS TYPES OF BAFFLES IN A SEDIMENT RETENTION POND

We assessed the relative improvement to the sediment trapping effectiveness of a permanent-pool sediment retentionpond due to the installation of baffles composed of different materials commonly used on construction sites. A suite ofexperiments was performed at the Sediment and Erosion Control Research and Education Facility (SECREF) at North CarolinaState University in which an acoustic Doppler velocimeter was used to record steady-state flow velocity and signal-to-noise ratio data. The data was gathered at 25 grid points at two depths within the pond for three different fixed input flowrates. The free flow maximum mean velocity in the pond, averaged over all input flow rates, was reduced by roughly 75% dueto the presence of baffles composed of jute germination biotextile backed by coir fiber. Baffles made from a standard tree-protection fence, folded and tied together into three layers to reduce pore size, reduced the free flow maximum mean velocityby 65%, while baffles made of standard silt fabric fence reduced the free flow maximum mean velocity by 55%. A similar trendin the reduction of the signal-to-noise ratio along the length of the pond confirmed that the jute/coir baffles most effectivelyreduced the concentration of turbulent density fronts over that of the tree-protection fence or silt fence baffles, or free flow.In addition, analysis of the transverse velocity variance and vertical velocity gradients for each experiment further demonstratedthat the jute/coir baffles most effectively diffused inflow momentum along the width and depth of the pond. The resultsof our analysis were used to calculate a sediment trapping efficiency based on Stokes settling. The minimum grain size capturedwould range from 30 to 42 microns with jute/coir baffles, compared to 68 to 86 microns for free flow.

Control mechanism of an organic self-regulating microfluidic system

The control mechanism and fluid dynamic properties of a previously developed organic pH regulation system are analyzed. The system regulates an output fluid stream to a pH of 6.7 with varying input flow rates. A pH sensitive hydrogel post acts as the feedback pH sensor and flow regulator. The control mechanism of the system is studied through numerical modeling of the regulator and the model is validated through experimentation. Analysis of the fluid dynamics at a T-channel junction, in which two buffer streams merge into one, is performed by solving the Navier-Stokes equation with commercial software. Various areas of a star-shaped orifice are occluded by a flexible membrane to throttle the rate that compensating buffer is fed back into the system. The relationship between orifice open area and volume of compensating buffer through the orifice was analyzed numerically. The axial and lateral visualization of the hydrogel post was obtained via optical microscopy. The model of the regulation system successfully predicts experimental results.

Automatic control of volatile fatty acids in anaerobic digestion using a fuzzy logic based approach

A control law based on fuzzy logic was developed and validated for an anaerobic wastewater treatment process. The controlled variable was the concentration of volatile fatty acids (VFA) in the reactor and the manipulated variable was the input flow rate. In order to use it as the input of the fuzzy sets, the controlled variable was treated using an algorithm of interpolation, extrapolation and filtering. The treatment of VFA values attempted to anticipate the behaviour of the variable and to avoid the inherent delay of the response, associated to the time constant of the system. Furthermore, the controlled variable derivative was used as a second input of the fuzzy sets to increase or decrease the speed of the control action. The control law was applied to a 0.948 m3 fixed-bed anaerobic reactor treating raw and diluted (1:2) industrial distillery vinasses. The validation was performed establishing different transient states between different set points in the range of 0.8 and 1.8 g VFA/l and different concentrations of the influent. The control law proved to be reliable supplying an adequate control action in terms of amplitude and velocity to achieve the desired set point for different types of perturbation and control purposes.

COMPARISON OF THREE PEDIATRIC AORTIC CANNULAE USING COMPUTATIONAL FLUID-DYNAMICS

The aortic cannula geometry is critically important during pediatric extracorporeal circulation, especially with pulsatile perfusion. Because of the small cross section area of the cannula tip, large hydraulic energy dissipation, high local shear stress, and a blood jet directed into the aorta take place. The objective of this study was to investigate these effects using computational fluid dynamics (CFD) for 3 cannulae with different geometries: the Argyle curved-tip (cannula A), the Surgimedics straight-tip (cannula B), and the DLP straight-tip (cannula C). A 3D, parametric model was developed to reproduce the inner conduit geometry of the different cannulae by simply varying geometrical parameters such as the tip length, curvature and bevel angle, the length and tapering of the conduit external to the aorta, etc. The models thus developed were inserted into a 3D-modeled, one-cm-ID aorta, featuring the aortic root cross clamping, aortic arch, and a tract of the thoracic aorta. CFD simulations were run with steady flow (centrifugal pump perfusion) and unsteady flow with experimental input flow rate tracings from a pulsatile roller pump or from a hydraulically driven physiologic pulsatile pump. The hydraulic power loss (δW), the maximum shear stress (τmax), and the exit force of the blood jet at the tip's outlet section (Fe) were extracted from simulations. Calculated δW was minimum for cannula C (9.9 mW) and maximum for A (14.9 mW); τmax was minimum for cannula C (10.3 Pa) and maximum for A (15.7 Pa); Fe was minimum for cannula A (5 X 10−3 N) and maximum for C (9 X 10−3 N).

농용 트랙터용 작업기 승.하강 제어시스템에 관한 연구

Rotary and plow implements are mainly utilized for the tillage operation in Korea, and a implement control system for agricultural tractors was designed and fabricated to improve the working accuracy and efficiency. The control system was composed of three units: 1) sensors fur detection of angle of liftarm, draft force, engine rpm, tillage depth and so on, 2) a controller, and 3) hydraulic circuits, which included solenoid valves and so on, for operation of three point linkage and implements. The control system can control the speed(high and low speed) of implements by adjusting input flow rates of the hydraulic cylinder which was controled by two speed valve, which was composed of a solenoid valve and a orifice. Indoor experiments were conducted to evaluate response characteristics of the designed implement control system under experimental conditions of various engine nm, two kinds of input flow rates of the cylinder and some input frequency. The results of experiments showed the response characteristics sufficient to use as the implement control system fur agricultural tractors.

High-rate chemical vapor deposition of nanocrystalline silicon carbide films by radio frequency thermal plasma

Silicon carbide films were deposited by radio frequency thermal plasma chemical vapor deposition (CVD) at rates up to several hundred micrometers per hour over a 40-mm diameter substrate. The films were primarily β-phase SiC. Film morphology was characterized by columnar growth terminating in hemispherical surfaces. The average crystallite size as determined by X-ray diffraction line broadening ranged from about 5 to 100 nm, and increased with increasing substrate temperature. The film growth rate varied linearly with the input flow rate of SiCl4 precursor, and appeared to be independent of substrate temperature over the range 680–1215 °C.

Particle−Liquid Mass Transfer Coefficient in Two-/Three-Phase Stirred Tank Reactors

Knowledge of particle−liquid mass transfer coefficient (kSL) is important for a rational design of a solid−liquid/solid−liquid−gas stirred tank reactor (STR). Considerable efforts have been made by different investigators to study and correlate the behavior of kSL in STRs for a variety of geometric and operating conditions. This review attempts to put together and analyze the information available in the literature on kSL in STRs systematically. Different approaches used by researchers to correlate kSL are critically discussed. The effect of system configurations (type of the impeller, D/T, and C/T), operating parameters (impeller speed/power input, particle loading, and gas flow rate), and physical properties (dP, Dm, μ, and Δρ) on kSL have been discussed elaborately. Some new data for six-bladed impellers have been generated to determine the optimum geometric configuration and operating conditions for particle−liquid mass transfer in three-phase STRs. It is concluded that kSL in two-/three-phase STRs ca...

Application of non-thermal atmospheric pressure ac plasmas to the carbon dioxide reforming of methane

Methane conversions of 11.9%, yields of hydrogen as high as 23.3% and energy yields of 1.0 mol H2/kWh have been achieved from CO2 reforming of CH4 in non-thermal, atmospheric pressure plasma reactors with Pt coated electrodes. Two reactors have been studied. A novel fan type reactor consisting of a movable rotor and immobile stator produced the highest yields in contrast to a tube type (silent discharge) reactor with a glass dielectric barrier. Conversions, yields of hydrogen and energy yields (expressed as mol H2/kWh) were studied for CO2/CH4 concentrations of 1.1% and 5.0% in He as a function of flow rate and input voltage. Hydrogen yields are observed to increase as the input voltage is increased from 411 V to 911 V and the flow rate is decreased from 100 cc/min to 30 cc/min. Energy yields vary only slightly with input voltage and flow rate. Hydrogen yields show little dependence on CO2/CH4 concentrations, but energy yields are approximately five times greater for the 5.0% mixture than the 1.1% mixture. Selectivities to H2, CO, coke, and low molecular weight hydrocarbons were also evaluated and compared to data obtained without CO2 in the feed. Hydrogen selectivities of nearly 100% were obtained, with small amounts of ethane and propane as the only observed side products and the selectivites were approximately the same whether CO2 was present or absent in the mixture. However, the reaction proceeds much more cleanly when CO2 is present, producing CO. The syngas product has an H2 : CO ratio of 1.5 with the fan type reactor and 0.67 with the tubular reactor. In the absence of CO2, coke is the main carbonaceous product. Under all conditions studied the fan type reactor demonstrated higher methane conversions (up to 11.9%) and selectivities to hydrogen.

Fuzzy logic observers for a biological wastewater treatment process

In order to monitor and control biological processes, on-line measurements of the living part of the system are necessary but difficult or too expensive to obtain. This paper presents fuzzy estimators for the concentration of the substrate at the input, the total and partial alkalinity in the influent and in the effluent and the volatile fatty acid concentration at the output of the reactor. Those observers are built on available on-line measurements like pH, temperature, input flow rate and output gaseous flow rate. The observers are tested on a pilot-scale anaerobic digestion reactor for the treatment of raw industrial wine distillery vinasses.

Large Amplitude pH Oscillations in the Hydrogen Peroxide−Dithionite Reaction in a Flow Reactor

The kinetics of the reaction between S2O4 2- and H2O2 is found to be very complex both in a closed reactor and in a continuous-flow stirred tank reactor (CSTR) in an unbuffered aqueous solution. The main products of the oxidation are SO4 2- and S2O6 2- in excess H2O2. The reaction is accompanied by acidification of the initially alkaline mixture. The measured pH-time traces show multiple inflection points in a closed reactor, suggesting that the reaction takes place in several distinct steps. Transient formation of SO 3 2- /HSO3 - buffer system is observed in the early stage of the reaction. Next, the sulfite ions are oxidized further to sulfate ions in an autocatalytic reaction. Simultaneously a small amount of dithionate ions is also formed. The pH exhibits very large amplitude relaxation oscillations in a CSTR in a narrow range of input concentrations, flow rate, and temperature. A simple empirical rate law model consisting of three redox reactions and three protonation equilibria is proposed. Numerical simulations based on this model agree well with the experimental results. The key to the pH-regulated oscillation is the H + -autocatalysis that results from the more rapid oxidation of the protonated than of the unprotonated sulfite intermediate.

The use of calorimetry for on-line optimisation of isothermal semi-batch reactors

This paper considers the maximisation of conversion by manipulating the input flowrate for an exothermic second-order esterification reaction (propionic anhydride + 2-butanol) performed in a semi-batch reactor. Safety considerations impose bounds on the heat release rate in normal operation and on the maximum attainable temperature in the case of cooling failure. The optimal time-varying input flowrate is calculated on-line using a heat balance over the reactor. Significant improvement over the best constant feed rate can be achieved.

Convective Instabilities in the Coextrusion Process

Abstract This paper is devoted to the numerical study of the stability of the plane flow for two immiscible fluids obeying Maxwell constitutive equation in a channel of aspect ratio 8. For fixed viscosity and flow rate ratios, the shape and non-linear behavior of interfacial waves induced by small perturbations of the input flow rate are studied using finite element simulations for various elasticity stratifications. The stationary flow, close to a Poiseuille flow and presenting a flat interface is first computed. Then the interfacial wave generated by a pulse-like disturbance on entry flow rates is computed by using time dependent computations. It takes the shape of a wave packet which is amplified or damped while moving towards the die exit. In unstable cases, the maximum deviation increases with elasticity (the Weissenberg number). Interestingly, the elastic stratification between the two layers can counteract unstable waves due to viscous stratification.

Estimation of the Methane Conversion in a Capacitively Coupled Radio-Frequency Plasma.

Methane decomposition was investigated experimentally with the capacitively coupled rf discharge. Glow discharge was generated from the low temperature capacitively coupled radio frequency (rf) plasma and was used for activating methane to make free radicals without catalysts. Operating variables in the experiment were reaction pressure, feed flow rate, and total input power. The gaseous reaction products were mainly hydrogen, ethane, propane and ethylene. When the input power increased, the density of hydrogen increased and the unsaturated groups of C2 and C3 began to form. The surface-phase polymerization reactions occurred inside the discharge tube wall. A mathematical model was derived using collision theory and diffusion effect of reaction products. From the result of the mathematical modeling, the simple mathematical relation of the methane conversion was obtained, and it was the function of specific input energy only. As the results of sensitivity analysis, the conversion of methane could be determined from the input flow rate and the electrical input power without measuring reaction temperature.

Vaporizing liquid microthruster

MEMS technology is expanding into increasingly diverse applications. As part of a micropropulsion system, microthruster attitude controls have been micromachined in silicon. This paper presents the microthruster design, fabrication, and test results. Fluid injected into a microchamber is vaporized by resistive silicon heaters. The exiting vapor generates the thruster force as it exits a silicon micro-nozzle. The vaporization chamber, inlet and exit nozzles were fabricated using anisotropic wet etching of silicon. With a 5 W heater input, injected water could be vaporized for input flow rates up to a maximum of 0.09 cc/s. Experimental testing produced thruster force magnitudes ranging from 0.15 mN to a maximum force output of 0.46 mN depending on fabrication parameters: chamber length, nozzle geometries, heater power, and liquid flow rates.

Effect of gas-phase nucleation on chemical vapor deposition of silicon carbide

An advanced model taking into account formation of silicon clusters in the gas phase is employed for modeling analysis of CVD of SiC in commercial vertical rotating disc reactor. It has been found that two main parameters have significant influence on the nucleation and transport of the clusters in the gas phase: input flow rate of silane and the temperature gradient near the growing surface determining the thermophoretic force. The results of modeling the deposition are in good agreement with experimental data. The silicon-to-carbon ratio in the gas phase over the SiC wafer is analyzed.

Modeling of gas phase nucleation during silicon carbide chemical vapor deposition

Abstract An advanced model taking into account silicon cluster formation in the gas phase is suggested. 2D simulation is carried out at the growth parameters typical for chemical vapor deposition (CVD) of SiC in a vertical reactor. It is found that two main parameters have a significant effect on the nucleation and transport of the clusters in the gas phase: the input flow rate of silane and the thermophoretic force. Using a special criterion, the growth conditions favorable for parasitic graphite and silicon phases formation are determined. The obtained results are in good agreement with experimental data.

Ultrasound process tomography system for hydrocyclones

The implementation of a laboratory-based ultrasound tomography system to an industrial process application is not straightforward. In the present work, a tomography system with 16 transducers has been applied to an industrial 50 mm hydrocyclone to visualize its air-core size and position. Hydrocyclones are used to separate fine particles from a slurry. The efficiency of the separation process depends on the size of the air core within the cyclone. If the core is too large due to spigot wear, there will be a detrimental effect on the slurry throughput. Conversely, if the throughput is increased to an extent where the air core becomes unstable or disappears, the particle separation will no longer take place, and the processed batches may become contaminated. Ultrasound tomography presents a very good tool with which to visualize the size, position and movement of the air core and monitor its behaviour under varying input parameters. Ultimately, it could be used within this application both to control the input flow rate depending on the air core size and to detect spigot wear. This paper describes the development of an ultrasonic tomography system applied to an instrumented hydrocyclone. Time-of-flight data are captured by a dedicated acquisition system that pre-processes the information using a DSP and transfers the results to a PC via a fast serial link. The hardware of the tomography system is described, and cursory results are presented in the form of reconstructed images of the air core within the hydrocyclone.

A mathematical model of the edge-defined film-fed growth process

A model is presented to simulate the steady-state growth of a fiber produced by the edge-defined film-fed growth (EFG) process. Equations describing the axisymmetric transport of heat in the melt and fiber are discussed. Heat transfer between the system and the surrounding environment is assumed to take place via convection and radiation. Given the fiber translation velocity, the external temperature profile, the die temperature, and the input flow rate or the pressure, asymptotic solutions for the temperature profiles in the melt and fiber, and the melt/gas and solidifying interfacial shapes are developed in the limit of a small melt slenderness ratio (fiber radius/approximate melt height). The effect of process parameters on the shape of the fiber system is investigated.

Instability of magma flow from volatile-dependent viscosity

Volatiles dissolved in silicic magma at depth exsolve as the magma nears the surface and cause an increase in viscosity of the magma. A model of a volcanic conduit within an elastic medium and a viscosity dependent on the volatile content of the magma produces oscillatory magma flow for a critical range of steady input flow rates. Oscillatory flow is recognized as a fundamental mode of behavior at silicic volcanoes, and understanding it allows improved short-term forecasting of timing and eruption style.