Multiphase flow in the vascular system of wood: From microscopic exploration to 3-D Lattice Boltzmann experiments

This paper provides insights into liquid free water dynamics in wood vessels based on Lattice Boltzmann experiments. The anatomy of real wood samples was reconstructed from systematic 3-D analyses of the vessel contours derived from successive microscopic images. This virtual vascular system was then used to supply fluid-solid boundary conditions to a two-phase Lattice Boltzmann scheme and investigate capillary invasion of this hydrophilic porous medium. Behavior of the liquid phase was strongly dependent on anatomical features, especially vessel bifurcations and reconnections. Various parameters were examined in numerical experiments with ideal vessel bifurcations, to clarify our interpretation of these features. (c) 2010 Elsevier Ltd. All rights reserved.

Effect of processing induced particle alignment on the fracture toughness and fracture behavior of multiphase dental ceramics

Objective. To investigate the processing induced particle alignment on fracture behavior of four multiphase dental ceramics (one porcelain, two glass-ceramics and a glass-infiltrated-alumina composite). Methods. Disks (empty set12mm x 1.1 mm-thick) and bars (3 mm x 4 mm x 20 mm) of each material were processed according to manufacturer instructions, machined and polished. Fracture toughness (K(IC)) was determined by the indentation strength method using 3-point bending and biaxial flexure fixtures for the fracture of bars and disks, respectively. Microstructural and fractographic analyses were performed with scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. Results. The isotropic microstructure of the porcelain and the leucite-based glass-ceramic resulted in similar fracture toughness values regardless of the specimen geometry. On the other hand, materials containing second-phase particles with high aspect ratio (lithium disilicate glass-ceramic and glass-infiltrated-alumina composite) showed lower fracture toughness for disk specimens compared to bars. For the lithium disilicate glass-ceramic disks, it was demonstrated that the occurrence of particle alignment during the heat-pressing procedure resulted in an unfavorable pattern that created weak microstructural paths during the biaxial test. For the glass-infiltrated-alumina composite, the microstructural analysis showed that the large alumina platelets tended to align their large surfaces perpendicularly to the direction of particle deposition during slip casting of green preforms. Significance. The fracture toughness of dental ceramics with anisotropic microstructure should be determined by means of biaxial testing, since it results in lower values. (C) 2009 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Numerical methods for multiphase mixture conservation laws with phase transition

Magdeburg, Univ., Fak. für Mathematik, Diss., 2010

Error estimate and control in the MSFV method for multiphase flow in porous media

n this paper the iterative MSFV method is extended to include the sequential implicit simulation of time dependent problems involving the solution of a system of pressure-saturation equations. To control numerical errors in simulation results, an error estimate, based on the residual of the MSFV approximate pressure field, is introduced. In the initial time steps in simulation iterations are employed until a specified accuracy in pressure is achieved. This initial solution is then used to improve the localization assumption at later time steps. Additional iterations in pressure solution are employed only when the pressure residual becomes larger than a specified threshold value. Efficiency of the strategy and the error control criteria are numerically investigated. This paper also shows that it is possible to derive an a-priori estimate and control based on the allowed pressure-equation residual to guarantee the desired accuracy in saturation calculation.

Virtual autopsy with multiphase postmortem computed tomographic angiography versus traditional medical autopsy to investigate unexpected deaths of hospitalized patients: a cohort study.

BACKGROUND: "Virtual" autopsy by postmortem computed tomography (PMCT) can replace medical autopsy to a certain extent but has limitations for cardiovascular diseases. These limitations might be overcome by adding multiphase PMCT angiography. OBJECTIVE: To compare virtual autopsy by multiphase PMCT angiography with medical autopsy. DESIGN: Prospective cohort study. (ClinicalTrials.gov: NCT01541995) SETTING: Single-center study at the University Medical Center Hamburg-Eppendorf, Hamburg, Germany, between 1 April 2012 and 31 March 2013. PATIENTS: Hospitalized patients who died unexpectedly or within 48 hours of an event necessitating cardiopulmonary resuscitation. MEASUREMENTS: Diagnoses from clinical records were compared with findings from both types of autopsy. New diagnoses identified by autopsy were classified as major or minor, depending on whether they would have altered clinical management. RESULTS: Of 143 eligible patients, 50 (35%) had virtual and medical autopsy. Virtual autopsy confirmed 93% of all 336 diagnoses identified from antemortem medical records, and medical autopsy confirmed 80%. In addition, virtual and medical autopsy identified 16 new major and 238 new minor diagnoses. Seventy-three of the virtual autopsy diagnoses, including 32 cases of coronary artery stenosis, were identified solely by multiphase PMCT angiography. Of the 114 clinical diagnoses classified as cardiovascular, 110 were confirmed by virtual autopsy and 107 by medical autopsy. In 11 cases, multiphase PMCT angiography showed "unspecific filling defects," which were not reported by medical autopsy. LIMITATION: These results come from a single center with concerted interest and expertise in postmortem imaging; further studies are thus needed for generalization. CONCLUSION: In cases of unexpected death, the addition of multiphase PMCT angiography increases the value of virtual autopsy, making it a feasible alternative for quality control and identification of diagnoses traditionally made by medical autopsy. PRIMARY FUNDING SOURCE: University Medical Center Hamburg-Eppendorf.

Accurate and efficient simulation of multiphase flow in a heterogeneous reservoir by using error estimate and control in the multiscale finite-volume framework

The multiscale finite-volume (MSFV) method is designed to reduce the computational cost of elliptic and parabolic problems with highly heterogeneous anisotropic coefficients. The reduction is achieved by splitting the original global problem into a set of local problems (with approximate local boundary conditions) coupled by a coarse global problem. It has been shown recently that the numerical errors in MSFV results can be reduced systematically with an iterative procedure that provides a conservative velocity field after any iteration step. The iterative MSFV (i-MSFV) method can be obtained with an improved (smoothed) multiscale solution to enhance the localization conditions, with a Krylov subspace method [e.g., the generalized-minimal-residual (GMRES) algorithm] preconditioned by the MSFV system, or with a combination of both. In a multiphase-flow system, a balance between accuracy and computational efficiency should be achieved by finding a minimum number of i-MSFV iterations (on pressure), which is necessary to achieve the desired accuracy in the saturation solution. In this work, we extend the i-MSFV method to sequential implicit simulation of time-dependent problems. To control the error of the coupled saturation/pressure system, we analyze the transport error caused by an approximate velocity field. We then propose an error-control strategy on the basis of the residual of the pressure equation. At the beginning of simulation, the pressure solution is iterated until a specified accuracy is achieved. To minimize the number of iterations in a multiphase-flow problem, the solution at the previous timestep is used to improve the localization assumption at the current timestep. Additional iterations are used only when the residual becomes larger than a specified threshold value. Numerical results show that only a few iterations on average are necessary to improve the MSFV results significantly, even for very challenging problems. Therefore, the proposed adaptive strategy yields efficient and accurate simulation of multiphase flow in heterogeneous porous media.

Multiphase Postmortem Computed Tomography Angiography in Pediatrics: A Case Report.

Postmortem imaging techniques, especially postmortem computed tomography, have become integral tools in forensic investigations. Multiphase postmortem computed tomography angiography (MPMCTA) visualizes the vascular system in detail and makes it possible to evaluate the perfusion of even the smallest vessels. Although the technique has been well described for adults, no pediatric cases have been reported and no pediatric protocol has been established for this type of investigation. We present the case a 7-year-old child for which we used a previously described MPMCTA protocol and adapted values of perfusion, with the same technical equipment as for adult cases. Our main objective was to propose a perfusion protocol adapted for the investigation of infants and children. Moreover, we discuss both the difficulties that we encountered and possible ways to further improve the investigation of pediatric cases by MPMCTA.

The impact of bioavailability limitations on microbial stable isotope fractionation in a multiphase system

Stable isotope fractionation analysis of contaminants is a promising method for assessing biodegradation of contaminants in natural systems. However, standard procedures to determine stable isotope fractionation factors, so far, neglect the influence of pollutant bioavailability on stable isotope fractionation. On a microscale, bioavailability may vary due to the spatio-temporal variability of local contaminant concentrations, limited effective diffusivities of the contaminants and cell densities, and thus, the pollutant supply might not meet the intrinsic degradation capacity of the microorganisms. The aim of this study was to demonstrate the effect of bioavailability on the apparent stable isotope fractionation, using a multiphase laboratory setup. The data gained show that the apparent isotope fractionation factors observed during biodegradation processes depend on the amount of biomass and/or the rate of toluene mass transfer from a second to the aqueous phase. They indicate that physico-chemical processes need to be taken into account when stable isotope fractionation analysis is used for the quantification of environmental contaminant degradation.

An experimental and theoretical study of multiphase flow in a circulating fluidized bed

A systematic averaging procedure has been derived in order to obtain an integral form of conservation equations for dispersed multiphase flow, especially applicable to fluidized beds. A similar averaging method is applied further to formulate macroscopic integral equations, which can be used in one-dimensional and macroscopic multi dimensional models. Circulating fluid bed hydrodynamics has been studied experimentally and both macroscopic and microscopic flow profiles have been measured in a cold model. As an application of the theory, the one dimensional model has been used to study mass and momentum conservation of gas and solid in a circulating fluid bed. Axial solid mixing has also been modelled by the one dimensional model and mixing parameters have been evaluated.

Concentrated Winding Multiphase Permanent Magnet Machine Design and Electromagnetic Properties – Case Axial Flux Machine

Concentrated winding permanent magnet machines and their electromagnetic properties are studied in this doctoral thesis. The thesis includes a number of main tasks related to the application of permanent magnets in concentrated winding open slot machines. Suitable analytical methods are required for the first design calculations of a new machine. Concentrated winding machines differ from conventional integral slot winding machines in such a way that adapted analytical calculation methods are needed. A simple analytical model for calculating the concentrated winding axial flux machines is provided. The next three main design tasks are discussed in more detail in the thesis. The magnetic length of the rotor surface magnet machines is studied, and it is shown that the traditional methods have to be modified also in this respect. An important topic in this study has been to evaluate and minimize the rotor permanent magnet Joule losses by using segmented magnets in the calculations and experiments. Determination of the magnetizing and leakage inductances for a concentrated winding machine and the torque production capability of concentrated winding machines with different pole pair numbers are studied, and the results are compared with the corresponding properties of integral slot winding machines. The thesis introduces a new practical permanent magnet motor type for industrial use. The special features of the machine are based on the option of using concentrated winding open slot constructions of permanent magnet synchronous machines in the normal speed ranges of industrial motors, for instance up to 3000 min-1, without excessive rotor losses. By applying the analytical equations and methods introduced in the thesis, a 37 kW 2400 min-1 12-slot 10-pole axial flux machine with rotor-surfacemounted magnets is designed. The performance of the designed motor is determined by experimental measurements and finite element calculations.

A high frequency electronic transducer for multiphase flow measurements

This paper describes an electronic transducer for multiphase flow measurement. Its high sensitivity, good signal to noise ratio and accuracy are achieved through an electrical impedance sensor with a special guard technique. The transducer consists of a wide bandwidth and high slew rate differentiator where the lead inductance and stray capacitance effects are compensated. The sensor edge effect is eliminated by using a guard electrode based on the virtual ground potential of the operational amplifier. A theoretical modeling and a calibration method are also presented. The results obtained seem to confirm the validity of the proposed technique.

CFD Simulation of Multiphase Reactors

Regional Research Laboratory

Investigation of Multiphase Power Converter using Integrated Coupled Inductor Regarding Electric Vehicle Application

The challenge of reducing carbon emission and achieving emission target until 2050, has become a key development strategy of energy distribution for each country. The automotive industries, as the important portion of implementing energy requirements, are making some related researches to meet energy requirements and customer requirements. For modern energy requirements, it should be clean, green and renewable. For customer requirements, it should be economic, reliable and long life time. Regarding increasing requirements on the market and enlarged customer quantity, EVs and PHEV are more and more important for automotive manufactures. Normally for EVs and PHEV there are two important key parts, which are battery package and power electronics composing of critical components. A rechargeable battery is a quite important element for achieving cost competitiveness, which is mainly used to story energy and provide continue energy to drive an electric motor. In order to recharge battery and drive the electric motor, power electronics group is an essential bridge to convert different energy types for both of them. In modern power electronics there are many different topologies such as non-isolated and isolated power converters which can be used to implement for charging battery. One of most used converter topology is multiphase interleaved power converter, pri- marily due to its prominent advantages, which is frequently employed to obtain optimal dynamic response, high effciency and compact converter size. Concerning its usage, many detailed investigations regarding topology, control strategy and devices have been done. In this thesis, the core research is to investigate some branched contents in term of issues analysis and optimization approaches of building magnetic component. This work starts with an introduction of reasons of developing EVs and PEHV and an overview of different possible topologies regarding specific application requirements. Because of less components, high reliability, high effciency and also no special safety requirement, non-isolated multiphase interleaved converter is selected as the basic research topology of founded W-charge project for investigating its advantages and potential branches on using optimized magnetic components. Following, all those proposed aspects and approaches are investigated and analyzed in details in order to verify constrains and advantages through using integrated coupled inductors. Furthermore, digital controller concept and a novel tapped-inductor topology is proposed for multiphase power converter and electric vehicle application.