Computer Control for the Study of Reactor Dynamics

ABSTRACT

The key elements in the study of chemical reaction transients are generation of forcing functions, rapid measurement of process variables and reliable computer control system. A multicomponent reaction involving propene metathesis was studied under computer control. The real-time control of the inlet gas concentrations to a Berty reactor, reactor temperature measurement and control, and acquisition of reactor effluent composition via rapid analysis in a gas chromatograph are described. The time intervals for servicing the interfaced devices were generated by hardware interrupts. The multitasking computer control program with interrupt servicing was written in FORTH.     

Numerical study on the low density gas flows in a plasma etch reactor

The direct simulation Monte Carlo method is employed to predict the etch rate distribution on Al wafer for a chlorine feed gas flow. The etching process of an Al wafer in a plasma etch reactor is examined by simulating molecular collisions of reactant and product. The surface reaction on the Al wafer is simply modelled by one-step reaction: 3Cl₂+2Al → 2AlCl₃. The gas flow inside the reactor is compared for six different nozzle locations. The present numerical results show that the etch rate increases with the mass flow rate of source gas Cl₂. It is also shown that the flow field inside the reactor is significantly affected by the nozzle locations.     

Analysis of the combustion instability of a model gas turbine combustor by the transfer matrix method

Combustion instability is a major issue in design of gas turbine combustors for efficient operation with low emissions. A transfer matrix-based approach is developed in this work for the stability analysis of gas turbine combustors. By viewing the combustor cavity as a one-dimensional acoustic system with a side branch, the heat source located inside the cavity can be described as the input to the system. The combustion process is modeled as a closed-loop feedback system, which enables utilization of well-established classic control theories for the stability analysis. Due to the inherent advantage of the transfer matrix method and control system representation, modeling and analysis of the system becomes a straightforward task even for a combustor of the complex geometry. The approach is applied to the stability analysis of a simple combustion system to demonstrate its validity and effectiveness. This paper was recommended for publication in revised form by Associate Editor Ohchae Kwon Dong Jin Cha received his B.S. and M.S. degrees from Hanyang University in Seoul, Korea, in 1981 and 1983, respectively. He then received his Ph.D. in ME from the University of Illinois at Chicago in 1992, and worked at the US DOE NETL for the next three years as a National Research Council (NRC) Associate. Dr. Cha is currently a Professor at the Department of Building Services Engineering at Hanbat National University in Daejeon, Korea. His research interests include combustion instability of gas turbine for power generation and fluid flows in building services engineering. Jay H. Kim received his BSME from Seoul National University in 1977, MSME from KAIST in 1979 and Ph.D. in ME from Purdue University in 1988. He has joined the Mechanical Engineering faculty of the University of Cincinnati in 1990, and is currently a Professor. Before joining the University of Cincinnati, he worked in industry for six years in Korea and US. His research interests have been in broad areas of acoustics, vibrations and applied mechanics with recent focuses on human/bioacoustics and vibration, gas pulsations and elastic stability. Yong-Jin Joo received his BSME and MSME from Sung Kyun Kwan University in Seoul, Korea, in 1990 and 1992, respectively. Mr. Joo is currently a Project Leader for IGCC Operation Technologies at KEPRI (Korea Electric Power Research Institute) which is the central R&D center of KEPCO (Korea Electric Power Corporation). His research interests include the development of operation and maintenance simulator for power plants including IGCC.     

Computer Control and Data Acquisition for a Thermogravimetric Analyzer

ABSTRACT

A thermogravimetric analyzer (TGA) has been interfaced with a microprocessor to study solid/gas reaction kinetics. The TGA measures the change in weight of the solid as the reaction proceeds, thus serving as a microreactor. The TGA is controlled by the microprocessor, and the operating conditions are continuously displayed on the CRT. The system can send data obtained during the course of an experiment to tape storage or to a mainframe computer for further analysis. Software was developed to allow the microprocessor to communicate with two mainframe computers over ordinary telephone lines. This paper discusses the hardware and software which is used for data acquisition and control.     

A Computer Interfaced,Time-Of-Flight Mass Spectrometer for Studies of Rapid,Gas-Phase Reactions.

ABSTRACT

A gas-phase reactor, consisting of a reaction tube with nine gas reagent injection jets placed axially along its length, has been connected to the ion source of a time-of-flight mass spectrometer. Provision has been made for purifying, and mixing several gases and exciting this mixture by microwave discharge prior to entry into the reaction tube. The mass spectrometer has been interfaced to a dedicated mini-computer system which is capable of simultaneous monitoring of five different masses and on-line control of the setting of one of these mass values. Performance of the system is illustrated by observation of the titration of active nitrogen with nitric oxide.     

In situ analysis of gas composition by electron energy-loss spectroscopy for environmental transmission electron microscopy

We have developed methods for using in situ electron energy-loss spectroscopy (EELS) to perform quantitative analysis of gas in an environmental transmission electron microscope. Inner-shell EELS was able to successfully determine the composition of gas mixtures with an accuracy of about 15% or better provided that some precautions are taken during the acquisition to account for the extended gas path lengths associated with the reaction cell. The unique valence-loss spectrum associated with many gases allowed simple methodologies to be developed to determine gas composition from the low-loss region of the spectrum from a gas mixture. The advantage of the valence loss approach is that it allows hydrogen to be detected and quantified. EELS allows real-time analysis of the volume of gas inside the reaction cell and can be performed rapidly with typical acquisition times of a few seconds or less. This in situ gas analysis can also be useful for revealing mass transport issues associated with the differential gas diffusion through the system.     

Clearance Regulation of Mechanical Gas Face Seals: Part II—Analysis and Control

This article presents the analysis and control of noncontacting mechanical gas face seals based on the state space model developed in Part I. Methods to analyze the controllability and observability of axial and tilt modes are described. The controllability analysis determines to what extent the dynamic response of the seal system modes can be shaped in a closed-loop feedback system, and the observability analysis determines if the seal system modes can be reconstructed from specific state measurements of the axial clearance and stator tilts. The error state-space method is employed to design a tracking controller to regulate the seal at a prescribed axial clearance. The control law is a function of all axial states; therefore, reduced order linear observers are designed to observe the unmeasured axial and tilt seal states. The axial clearance and tilt state estimates are used to reconstruct the gas film axial force and moments, which cannot be directly measured, for design and analysis. The analysis and control techniques are applied to the illustrative example presented in Part I. The results demonstrate that the gas film forces and moments can be estimated well and the seal system can be satisfactorily regulated with a sufficiently damped response that is within the bandwidth of today's electropneumatic actuators.     

A Microcontroller Based,Low Cost Oxygen Gas Controller for Medical Purposes

Abstract

In this work, an oxygen gas concentration controller circuit is designed and implemented for use in medical applications such as incubator environments. Since the air of the incubator environment is dried during the control processes, oxygen gas flow is humidified by the designed ultrasonic nebulizer. A polarographic type oxygen gas sensor was used. A signal conditioning circuit was developed to capture the required voltage levels. Control processes have been performed by a high speed PIC microcontroller. Set values can be entered either via an embedded control circuit or via a keyboard. The system is linear, sensitive, and relative error is only about ?1 O₂%. All of the parts of the system are renewable. As a result, a low cost and effective microcontroller based circuit, modular in structure, has been provided.     

A Microprocessor Based Energy Dispersive X-Ray Diffractometer

ABSTRACT

A microprocessor based Energy Dispersive X-ray Diffraction system is described. The system is built around three 8085 microprocessors and is suitable for performing rapid structural analysis. It can acquire four spectra in programmable memory banks and can do online data analysis. The software includes a nonlinear least square fitting program, which can fit the complete diffraction pattern at a time. To highlight the data processing capabilities of this system, we have presented the results for a simple solid.     

Analytical Standards

ABSTRACT

A simple system for recovering the helium (He) gas from the gas mixtures used in the CO₂ laser is discussed. Separation of the gases CO₂, N₂ and H₂ from He gas is accomplished by various chemical and physical processes. An example, including the dimension of the system and the quantity of the chemicals needed, is given for a Molectron Corporation model T250 CO₂ gas laser, based on an hour of operation. The cost and the efficiency of the system as well as the purity of the recovered He gas are analyzed.     

Moving bed reactor setup to study complex gas-solid reactions

A moving bed scale reactor setup for studying complex gas-solid reactions has been designed in order to obtain kinetic data for scale-up purpose. In this bench scale reactor setup, gas and solid reactants can be contacted in a cocurrent and countercurrent manner at high temperatures. Gas and solid sampling can be performed through the reactor bed with their composition profiles determined at steady state. The reactor setup can be used to evaluate and corroborate model parameters accounting for intrinsic reaction rates in both simple and complex gas-solid reaction systems. The moving bed design allows experimentation over a variety of gas and solid compositions in a single experiment unlike differential bed reactors where the gas composition is usually fixed. The data obtained from the reactor can also be used for direct scale-up of designs for moving bed reactors.     

Analysis of performance deterioration of a micro gas turbine and the use of neural network for predicting deteriorated component characteristics

Deteriorated performance data of a micro gas turbine were generated and the artificial neural network was applied to predict the deteriorated component characteristics. A program to simulate operation of a micro gas turbine was set up and deterioration of each component (compressor, turbine and recuperator) was modeled by changes in the component characteristic parameters such as compressor and turbine efficiency, their flow capacities and recuperator effectiveness and pressure drop. Single and double faults (degradation of single and two parameters) were simulated. The neural network was trained with a majority of the generated deterioration data. Then, the remaining data were used to check the predictability of the neural network. Given measurable performance parameters as inputs to the neural network, characteristic parameters of each component were predicted and compared with original data. The neural network produced sufficiently accurate prediction. Using a smaller number of input parameters decreased prediction accuracy. However, an acceptable accuracy was observed even without information on several input parameters. This paper was recommended for publication in revised form by Associate Editor Ohchae Kwon Mr. J. E. Yoon received his MS degree from Dept. of Mechanical Engineering, Inha University in 2008. His thesis topic was test and simulation of micro gas turbines. He has been working at LG Digital Appliance Company. Mr. J.J. Lee received his MS degree from Dept. of Mechanical Engineering, Inha University in 2006, and is now Doctoral student at the same department. His research topics include simulation and diagnosis of gas turbines. Prof. T.S. Kim received his PhD degree from Dept. of Mechanical Engineering, Seoul Na-tional University in 1995. He has been with Dept of Mechanical Engineering, Inha Univeristy since 2000, and is Associate Professor as of Oct. 2008. His research area is aero-thermodynamc simulation and test of gas turbine systems including microturbine and their components. His recent research concern also includes analysis on fuel cells and fuel cell/gas turbine hybrid systems. Prof. J.L. Shon received his PhD degree from Dept. of Mechanical Engineering, The University of Alabama in Huntsville in 1986. He has been with School of Mechanical & Aerospace Engineering, Seoul National University since 2000, and is BK Associate Professor as of Oct. 2008. His research area is design, simulation and test of gas turbine system and components. He is also interested in researches on fuel cells and fuel cell/gas turbine hybrid systems.     

Oxy-fuel combustion boiler for CO2 capturing: 50 kW-class model test and numerical simulation

A novel oxy-fuel burner was devised and integrated into a 50 kW-class furnace-type boiler system. A series of experiments was conducted to verify its feasibility for industrial applications. Additionally, numerical simulations were performed and the results validated against experimental data on the detailed physics inside the conventional-design combustion chamber. The oxy-fuel burner, with the help of gas radiation, could effectively heat the combustion chamber. The composition of the exhaust gas revealed that the sealing of the system is crucial to the achievement of high CO₂ concentrations and low NOx emissions.     

Experimental simulation of phosphites additives tribochemical reactions by gas phase lubrication

Abstract

Tribochemical reactions of phosphites additives on steel surface have been simulated by gas phase lubrication. Trimethylphosphite (TMPi), P(OCH₃)₃, has been used as model molecule for phosphites additives. It has been introduced under gas phase up to 5 hPa in a new tribometer dedicated to gas phase lubrication. Friction tests have been carried out at ambient temperature and 100°C. Chemical analyses by X-ray photoelectron spectroscopy and by Auger electron spectroscopy have been conducted inside and outside of the track. Two kinds of analysis have been carried out: ex situ and in situ surface analyses after tribological test. Indeed, a new environmentally controlled tribometer allows friction test then accurate analyses without air exposure of the formed tribofilm. Tribotests conducted under TMPi gas phase show a reduction of friction coefficient until 0˙2 instead of 1˙4 under high vacuum. Jointly, formation of tribofilm has been confirmed by optical microscopy and ex situ chemical analysis. Comparison between analyses performed inside and outside of the wear scar indicates that the friction induces the formation of phosphide compound that could reduce friction. Moreover analyses show the formation of methoxy group (CH₃O) and carbonate originally from the decomposition of TMPi under friction into H₂ and CO. In situ analyses clearly show the importance to investigate an uncontaminated tribofilm in order to obtain a better characterisation of it and then a better comprehension of the tribochemical mechanisms.     

Natural convection heat transfer estimation from a longitudinally finned vertical pipe using CFD

In this study, CFD analysis of air-heating vaporizers was conducted. A longitudinally finned vertical pipe was used to represent the air-heating vaporizer in the CFD model. Nitrogen gas was used as the working fluid inside the vertical pipe, and it was made to flow upward. Ambient air, which was the heat source, was assumed to contain no water vapor. To validate the CFD results, the convective heat transfer coefficients inside the pipe, h_i-c, derived from the CFD results were first compared with the heat transfer coefficients inside the pipe, h_i-p, which were derived from the Perkins correlation. Second, the convection heat transfer coefficients outside the pipe, h_o-c, derived from the CFD results were compared with the convection heat transfer coefficients, h_o-a, which were derived from an analytical solution of the energy equation. Third, the CFD results of both the ambient-air flow pattern and temperature were observed to determine whether they were their reasonability. It was found that all validations showed good results. Subsequently, the heat transfer coefficients for natural convection outside the pipe, h_o-c, were used to determine the Nusselt number outside the pipe, Nu_o.. This was then correlated with the Rayleigh number, R_a. The results show that R_a and Nu_o have a proportional relationship in the range of 2.7414×10¹² ≤ Ra ≤ 2.8263×10¹³. Based on this result, a relation for the Nusselt number outside the pipe, Nu_o, was proposed. This paper was recommended for publication in revised form by Associate Editor Man Yeong Ha Hyomin Jeong is currently a professor of Mechanical and Precision Engineering at Gyeongsang Nation University. He received his ph.D. in mechanical engineering from the University of Tokyo in 1992 and he joined Arizona State University as a visiting professor from 2008 to 2009. His research interests are in fluid engineering, CFD, cryogenic system, cascade refrigeration system and ejector system, mechanical vapor compression Hanshik Chung is a professor of Mechanical and Precision Engineering at Gyeongsang National University. He obtianed his Ph.D. in Mechanical Engineering from Donga University. He joined Changwon Master’s College and Tongyeong Fisher National College as an assistant Professor in 1988 and 1993, respectively. His research fields extend into the thermal engineering, heat transfer, solar heating & cooling system, LNG vaporizer optimum, solar cell, hydrogen compressor for fuel cell and making fresh water system from sea water     

Control of a pulse combustion reactor with thermoacoustic phenomena

We have developed a novel way of controlling parameters in reactors using flue gases from pulse combustion as a direct source of heat and as a means of transport of particulate materials synthesized in a slightly reductive environment or oxidative environment. The reactor is used for a spray pyrolysis synthesis of materials or the sintering of different ceramic powders. The reactor is heated directly, which means reduced energy losses, and the enhanced drying reported using pulse combustion is implemented for faster reaction. A slightly reductive atmosphere is maintained by combusting a stoichiometric fuel and air mixture and adding acetylene to the flue gas flow. Reaction conditions must be carefully controlled; this is achieved by influencing the characteristic times of the pulse combustion and changing the frequency of combustion and with it the temperature and flue gas composition in the reactor. The frequency is changed by nitrogen dilution of burning gas, influencing the mixing of the combustible mixture with hot flue gases and damping of frequencies with a secondary Helmholtz resonator. The frequency of pressure oscillations in the combustor should be the same as one of the harmonic frequencies of the reactor pipe to reach an acoustic resonance. In this work, the frequency of pulse combustion was altered in such a way that resonance was established with the reactor pipe and that a suitable reaction environment was obtained. With good control over all parameters, we were able to synthesize different Li-ion cathode materials, such as LiFePO₄ and Li(Ni_xMn_yCo_z)O_2.     

Relatively Simple Modification of an AEI MS-902 High-Resolution Mass Spectrometer to Permit Chemical Ionization Studies

ABSTRACT

Relatively inexpensive and simple modifications to an AEI MS-902 double focusing high-resolution mass spectrometer allow chemical ionization studies to be undertaken without compromising the instrument's high resolving power or sensitivity. A standard AEI source block was made gas tight except for a 0.013 to 0.020 in. diameter ion exit and an 0.013-in. electron entrance hole. A specially designed direct insertion probe was utilized to introduce both the sample and reagent gas. The reagent gas itself was supplied via a system utilizing both the manufacturers cold inlet system and Matheson lecture bottles. An additional pumping system was added in parallel to the existing pumping system to handle the increased gas flow.     

LASER PHOTOACOUSTIC TRACE GAS DETECTION,AN EXTREMELY SENSITIVE TECHNIQUE APPLIED IN BIOLOGICAL RESEARCH

Abstract

The use of infrared laser based photo-acoustic trace gas detection equipment in biological research is discussed on the basis of two examples. A CO₂ laser based photo-acoustic trace gas detection system is employed to follow the time-dependent pattern of the nitrogen fixation process by the cyanobacteria Nodularia Spumigena on a one-minute time scale. Due to the high sensitivity of the detection system for ethylene (detection limit 6 part per trillion; 6:10¹²), the fixation process can be followed on-line in a flow-through system. Following a 50 h dark incubation period, the bacteria show nitrogen fixation only after a certain illumination period, indicating lack of carbohydrates needed to start the nitrogen fixation.

Another, CO laser based, system allowed to monitor acetaldehyde emission (detection limit 0.1 part per billion) of Docks Rumex palustris during the change from anoxic environment to O₂ levels of air. An almost immediate emission is found, indicating that acetaldehyde plays an important role for post-anoxic injury in Rumex palustris.     

A gas mixture regeneration system for a position-sensitive thermal neutron detector with a 3He-based gas converter

A gas mixture regeneration system is designed for a two-dimensional position-sensitive thermal neutron detector based on a multiwire proportional chamber with a ³He-based converter. The basic characteristics of the system are given, and processing steps aimed at decreasing the gas liberation from the detector structure are described. The influence of the electronegative impurity accumulation on the detector characteristics and operation of the gas regeneration system are studied. The system is designed on request of the Laboratory of Neutron Physics, JINR (Dubna), for modernizing the ДH-2 diffractometer operating on beams of the ИБP-2 reactor.