Frequency domain analysis of acoustic wave propagation in heterogeneous media considering iterative coupling procedures between the method of fundamental solutions and Kansa's method

Acoustic wave propagation in heterogeneous media is a topic of significant interest in many areas of science and engineering, including aeroacoustics and sound propagation in oceans. In the present work, numerical frequency domain models based on the joint use of the method of fundamental solutions and of the radial basis function collocation method (also known as Kansa's method) are discussed. In this context, the method of fundamental solutions is used to model the homogeneous part of the propagation domain, while Kansa's method is employed to model the presence of heterogeneities. The coupling between the two parts of the propagation domain is performed iteratively, allowing independent spatial discretization between the different subdomains of the model (i.e. matching collocation points at common surfaces are not necessary). Additionally, an optimised algorithm, based on the use of a varying relaxation parameter, is employed to speed up and/or to ensure the convergence of the iterative coupling process. At the end of the paper, numerical results illustrate the applicability and potentialities of the proposed formulations. Copyright © 2011 John Wiley & Sons, Ltd.     

Production of hydrogen via methane reforming using atmospheric pressure microwave plasma

In this paper, results of hydrogen production via methane reforming in the atmospheric pressure microwave plasma are presented. A waveguide-based nozzleless cylinder-type microwave plasma source (MPS) was used to convert methane into hydrogen. Important advantages of the presented waveguide-based nozzleless cylinder-type MPS are: stable operation in various gases (including air) at high flow rates, no need for a cooling system, and impedance matching. The plasma generation was stabilized by an additional swirled nitrogen flow (50 or 100 l min⁻¹). The methane flow rate was up to 175 l min⁻¹. The absorbed microwave power could be changed from 3000 to 5000 W. The hydrogen production rate and the corresponding energy efficiency in the presented methane reforming by the waveguide-based nozzleless cylinder-type MPS were up to 255 g[H₂] h⁻¹ and 85 g[H₂] kWh⁻¹, respectively. These parameters are better than those typical of the conventional methods of hydrogen production (steam reforming of methane and water electrolysis).     

Hybrid modelling of yeast production processes – combination of a priori knowledge on different levels of sophistication

Process models are used to formulate knowledge about process behaviour. They are applied, e.g., to predict the process' future behaviour and for state estimation when reliable on-line measuring techniques to monitor the key variables of the process are not available. There are different sources of information available for modelling, which provide process knowledge in different representations. Some elements or aspects may be described by physically based mathematical models and others by heuristically obtained rules of thumb, while some information may still be hidden in the process data recorded during previous runs of the process. Heuristic rules are conveniently processed with fuzzy expert systems, while artificial neural networks present themselves as a powerful tool for uncovering the information within the process data without the need to transform the information into one of the other representations. Artificial neural networks and fuzzy technology are increasingly being employed for modelling biotechnological processes, thus extending the traditional way of process modelling by mathematical equations. However, a sufficiently comprehensive combination of all these techniques has not yet been put forward. Here, we present a simple way of combining all the available knowledge relating to a given process. In a case study, we demonstrate the development of a hybrid model for state estimation and prediction on the example of a yeast production process. The model was validated during a cultivation performed in a standard pilot-scale fermenter.     

Atmospheric pressure microwave plasma source for hydrogen production

Nowadays hydrogen is considered as a clean energy carrier and fuel of the future. That is why the interest in production and storage of hydrogen is still increasing. One of the promising technology is using microwave plasma for hydrogen production. In this study we propose two types of an atmospheric pressure microwave plasma source (MPS) for hydrogen production via methane conversion. The first one was a nozzleless waveguide-supplied coaxial-line-based. The second one was a nozzleless waveguide-supplied metal-cylinder-based. They can be operated with microwave frequency of 2.45 GHz and power up to a few kW with a high gas flow rates (up to several thousands l/h). We present experimental results concerning electrical properties of the MPS, plasma visualization, spectroscopic diagnostics and hydrogen production. The experiment was carried out with methane flow rate up to 12,000 l/h. An additional nitrogen or carbon dioxide swirl flow was used. The absorbed microwave power was up to 5000 W. Our experiments show that MPSs presented in this paper have a high potential for hydrogen production via hydrocarbon conversion.     

Hydrogen production by direct injection of ethanol microdroplets into nitrogen microwave plasma flame

Liquid ethanol introduced as microdroplets into the tip of microwave nitrogen plasma, operating at 2.45 GHz under atmospheric pressure, has been investigated. Injection of ethanol outside the region of plasma generation eliminated a problem of soot formation at that region, which was responsible for short reactor lifetime. Using liquid ethanol allows to save energy needed for vaporization. Hydrogen, carbon monoxide and solid carbon were the main outlet products. Other products detected with gas chromatography were CH₄, C₂H₄ and C₂H₂. The best results concerning hydrogen production were as follows: concentration in the outlet gas up to 28%, production rate up to 1043 L/h, energy yield up to 209 L per kWh of microwave power, and were obtained for liquid C₂H₅OH flow rate of 3.7 L/h. A numerical 0D model was used to determine contributions of chemical reactions in formation of measured gaseous products. Simplified model involving only radical reactions without any ions and electrons predicts final concentrations of main compounds quite well for microwave power up to 4 kW.     

TEMPERATURE CONTROL IN FERMENTERS: APPLICATION OF NEURAL NETS AND FEEDBACK CONTROL IN BREWERIES

The main objective of on-line quality control in fermentation is to perform the production processes as reproducible as possible. Since temperature is the main control parameter in the fermentation process of beer breweries, it is of primary interest to keep it close to the predefined set point. Here, we report on a model-supported temperature controller for large production-scale beer fermenters. The dynamic response of the temperature in the tank on temperature changes in the cooling elements has been modeled by means of a difference equation. The heat production within the tank is taken into account by means of a model for the substrate degradation. Any optimization requires a model to predict the consequences of actions. Instead of using a conventional mathematical model of the fermentation kinetics, an artificial neural network approach has been used. The set point profiles for the temperature control have been dynamically optimized in order to minimize the production cost while meeting the constraints posed by the product quality requirements.     

Migration of mycotoxins into rice starchy endosperm during the parboiling process

Considering the occurrence of rice contamination by mycotoxins and the increase in rice consumption, the present work had the objective of assessing the migration of mycotoxins into the starchy endosperm during the parboiling process, as to propose conditions that provide lower contamination levels. The newly harvested rice grain sample was examined for the natural occurrence of mycotoxins (aflatoxin B₁, aflatoxin B₂, deoxynivalenol, ochratoxin A, and zearalenone); only the presence of aflatoxin B₁ was found (17 ng/g). The samples were then artificially contaminated with deoxynivalenol and zearalenone, and the parboiling process was conducted according to a 2³ factorial planning with central point, having as variables the contamination level deoxynivalenol 720, 1440, and 2160 ng/g, and zearalenone 476, 952, and 1428 ng/g the soaking time (4, 5, and 6 h) and autoclave time (15, 22.5, and 30 min). Mycotoxins aflatoxin B₁ (AFA B₁), deoxynivalenol (DON), and zearalenone (ZEA) were confirmed and determined through gas chromatography. Findings showed a lower migration trend for AFA B₁ under 6 h of soaking and 30 min of autoclaving, for DON under 6 h of soaking regardless of the autoclaving time, and for ZEA under 4 h of soaking and 15 min of autoclaving. This information can contribute to the choice of process parameters that limit the migration of these mycotoxins if they happen in the raw material.     

Efficient numerical models for the prediction of acoustic wave propagation in the vicinity of a wedge coastal region

In this paper, numerical frequency domain formulations are developed to simulate the 2D acoustic wave propagation in the vicinity of an underwater configuration which combines two sub-regions: the first one consists of a wedge with rigid seabed and free surface, and the second one is assumed to have a rigid flat bottom and a free flat surface.The problem is solved using two different numerical methods: the Boundary Element Method (BEM) and the Method of Fundamental Solutions (MFS). Two models are developed by using a sub-region technique, where only the vertical interface between sub-regions of different geometries has to be discretized. These formulations incorporate Green's functions that take into account the presence of flat rigid and free surfaces and of a wedge. Green's functions are defined using two approaches: the image source method is used to model the rigid flat bottom and free flat interface, whereas the response provided by the wedge sub-region is based on a normal mode solution. Additionally, a MFS and a BEM model are also implemented which require the discretization of the sloping rigid seabed of the wedge, therefore making use of Green's functions for a rigid flat bottom and a free surface (using the image source method).A detailed discussion on the performance of these formulations is performed, with the aim of finding an efficient formulation to solve the problem. It is found that the model based on the MFS and on the sub-region technique has a significantly lower computational cost and is stable, therefore being the most suitable for the analysis of acoustic wave propagation in the studied configurations.     

Application of atmospheric pressure microwave plasma source for hydrogen production from ethanol

In contrast to conventional technologies of hydrogen production like water electrolysis or coal gasification we propose a method based on the atmospheric pressure microwave plasma. In this paper we present results of the experimental investigations of the hydrogen production from ethanol in the atmospheric pressure plasma generated in waveguide-supplied cylindrical type nozzleless microwave (915 MHz and 2.45 GHz) plasma source (MPS). Argon, nitrogen and carbon dioxide were used as a working gas. All experimental tests were performed with the working gas flow rate Q ranged from 1500 to 3900 NL/h and absorbed microwave power P_A up to 6 kW. Ethanol was introduced into the plasma as vapours carried with the working gas. The process resulted in the ethanol conversion rate greater than 99%. The hydrogen production rate was up to 210 NL[H₂]/h and the energy efficiency was 77 NL[H₂] per kWh of absorbed microwave energy.     

Computational fluid-dynamic model of laser-induced breakdown in air

Temperature and pressure profiles are computed by the use of a two-dimensional, axially symmetric, time-accurate computational fluid-dynamic model for nominal 10-ns optical breakdown laser pulses. The computational model includes a kinetics mechanism that implements plasma equilibrium kinetics in ionized regions and nonequilibrium, multistep, finite-rate reactions in nonionized regions. Fluid-physics phenomena following laser-induced breakdown are recorded with high-speed shadowgraph techniques. The predicted fluid phenomena are shown by direct comparison with experimental records to agree with the flow patterns that are characteristic of laser spark decay.