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Rheological properties of marine sediments from the port of Koper
Jasna Smolar, Matej Maček, Ana Petkovšek, 2016, izvirni znanstveni članek

Opis: Subaqueous, fine-grained, cohesive sediments are continuously fluidized by waves and other disturbances that cause their movement, which can be described with numerical models incorporating rheological parameters. The rheological behaviour depends on the soil (solid) type, the volume concentration, the salinity and the testing methods. In this study, rheological investigations of marine sediments from the Port of Koper were carried out by using two coaxial cylinder rheometers (DV3T HB, Brookfield and ConTec Viscometer 5). The influence of the specimen volume, the size of the gap and the type of measuring spindles were analysed and compared. The measured data were evaluated using the Bingham model. For each data set, the boundary between the sheared (“fluid”) and the un-sheared (“solid”) material was calculated and then the calculated boundary was used instead of the outer radius of the cylinder for the evaluation of the rheological parameters, where necessary. A good comparison of the results was found when using this approach. The results are also in agreement with the literature data. The ConTec Viscometer 5, primarily designed for mortars and concrete, was shown to be also suitable for the investigation of sediments.
Ključne besede: marine sediments, Bingham model, yield stress, plastic viscosity, coaxial cylinder rheometer, plug flow, Bay of Koper
Objavljeno: 18.06.2018; Ogledov: 486; Prenosov: 42
.pdf Celotno besedilo (709,57 KB)
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Rate-dependent extensions of the parametric magneto-dynamic model with magnetic hysteresis
Simon Steentjes, Martin Petrun, G. Glehn, Drago Dolinar, Kay Hameyer, 2017, izvirni znanstveni članek

Opis: This paper extends the parametric magneto-dynamic model of soft magnetic steel sheets to account for the phase shift between local magnetic flux density and magnetic field strength. This phase shift originates from the damped motion of domain walls and is strongly dependent on the microstructure of the material. In this regard, two different approaches to include the rate-dependent effects are investigated: a purely phenomenological, mathematical approach and a physical-based one.
Ključne besede: magnetic hysteresis, eddies, magnetic flux, viscosity, magnetic fields, magneto-dynamic models, parametric
Objavljeno: 03.08.2017; Ogledov: 608; Prenosov: 327
.pdf Celotno besedilo (567,72 KB)
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A theoretical and numerical study of an additional viscosity term in a modified elasto-plastic friction model for wet friction clutch simulations
Tomaž Petrun, Jože Flašker, Marko Kegl, 2013, izvirni znanstveni članek

Opis: This paper deals with a theoretical and numerical study of various viscosity terms in the modified elasto-plastic friction model and its influence on the resulting friction force-torque, transmitted through the contact of the friction clutch. Various simple viscous definitions for fluids considering shear rate dependent viscosity were investigated. As a basis for the research the Carreau fluid model was chosen, since it can describe Newtonian, dilatant and pseudo plastic fluids. Besides of theoretical investigations, numerical simulations at realistic friction clutch operation conditions were carried out. The results were compared to the results of a validation case for a dry friction clutch simulation with the modified elasto-plastic friction model. This research showed significant differences between various viscosity definitions and revealed the drawbacks of such a simplified approach. In addition to viscosity, a possibility to calculate the generated heat due to friction and its influence on the contact temperatures is discussed briefly. The basic theory and equations are given along with the directions for future work. The requirements for an accurate temperature calculation in the friction contact are outlined.
Ključne besede: friction model, friction clutch simulation, simple viscosity models, Carreau fluid
Objavljeno: 21.12.2015; Ogledov: 745; Prenosov: 59
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Determination of pressure losses in hydraulic pipeline systems by considering temperature and pressure
Vladimir Savić, Darko Knežević, Darko Lovrec, Mitar Jocanović, Velibor Karanović, 2009, izvirni znanstveni članek

Opis: Generally accepted methods for calculating pressure losses within flat pipelines, as presented in literature and used in praxis, are based on the Reynolds number, which considers the viscosity and density of fluid, internal pipe friction coefficient, pipe geometry, and oil circulation velocity. Such an approach contains serious inconsequentiality. Namely, only nominal values for viscosity and density are considered in the calculation, which differs substantially from real conditions. It often leads to inaccurate calculations of pressure losses. A numerical model has been developed within the work prescribed in the paper, which takes into account actual changes in density and viscosity under the current oil pressure and temperature in order to overcome the above weaknesses of standard calculation procedures. Such an approach is novel and provides new capacity for an accurate pressure drop analysis of advanced hydraulic systems.
Ključne besede: tlačne izgube, ravne cevi, viskoznost, gostota, temperatura, pressure loss, float pipelines, viscosity, density, temeprature
Objavljeno: 11.08.2015; Ogledov: 728; Prenosov: 53
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“Thermodynamic and physical properties for high pressure process design”
Maša Knez Marevci, 2014, doktorska disertacija

Opis: The thesis is comprised of three main categories. The first part of dissertation covers investigations of phase equilibria of compounds from natural materials in conventional and also non conventional supercritical fluids. In details, the impact of pressure and/or temperature on the system behaviour (miscibility, solubility, phase inversion) is investigated, quantitative and qualitative analyses to evaluate and identify compounds contained after performing preliminary extraction experiments from different natural tissues are presented. The impact of operating parameters (pre-treatment of the raw material with SFE; different extraction solvents: propane, CO2, non conventional SCFs; different extraction temperatures and pressures) on extraction kinetics is observed. Following substances were taken into consideration: vanillins, caffeine, carnosoic acid extract and lecithin. Second part of dissertation covers studies of phase equilibria of the systems bio oil/gas, which is crucial in biorefinery process design. In this part of dissertation, which covers studies of phase equilibria of binary and ternary systems, the impact of pressure and/or temperature on the system behaviour (miscibility, solubility, phase inversion) for binary system bio oil/supercritical fluid (bio oil/CO2) and (bio oil/H2) was studied. Additionally, phase behaviour of ternary systems of (bio oil/diesel/CO2) and (bio oil/tail water/CO2) under the impact of pressure and/or temperature is observed. These data are of a high importance for bio refineries as an important part of necessary sustainable development. In recent years, studies on biodiesel synthesis have focused on development of process intensification technologies to resolve some of these issues. Fundamental data to design fractionation process of components of bio oil are crucial for an efficient hydrogenation process of bio oil. In the third part of dissertation observation of phase equilibria and determination of the parameters like diffusion coefficient, density and viscosity for the systems polymer/CO2 at elevated pressures is investigated. An overview of different methods applied to determine the parameters like diffusion coefficient, density and viscosity of the systems polymer (PEG)/CO2 at elevated pressures is offered. Observation of phase equilibria of the binary system PEG/CO2, determination of the impact of pressure and/or temperature on the system behaviour (miscibility, solubility, phase inversion), determination of thermodynamically and physically properties of the system with new applicative methods and finally, comparison of the results obtained by different methods is provided. The interfacial tension (IFT) at the (PEG)/CO2 interface has been determined by using an experimental technique developed to study the interfacial interactions of the liquids in equilibrium with gas in a glass-windowed equilibrium cell by the means of Capillary Rise (CR) method. Advantages and disadvantages of methods that were applied are exposed and discussed.
Ključne besede: phase equilibria, natural materials, conventional and non conventional supercritical fluids, extraction, bio oil, data for biorefinery process design, systems polymer (PEG)/CO2, diffusion coefficient, density, viscosity, surface tension, Capillary Rise (CR) method.
Objavljeno: 28.10.2014; Ogledov: 1827; Prenosov: 256
.pdf Celotno besedilo (4,46 MB)

The calculation of thermal conductivity, viscosity and thermodynamic properties for nanofluids on the basis of statistical nanomechanics
Jurij Avsec, Maks Oblak, 2007, izvirni znanstveni članek

Opis: The paper features the mathematical model of calculation of thermophysical properties for nanofluids on the basis of statistical nanomechanics. Calculation of properties for nanofluids for real substances is possible by the classical and statistical mechanics. Classical mechanics has no insight into the microstructure of the substance. Statistical mechanics, on the other hand, calculates the properties of state on the basis of molecular motions in a space, and on the basis of the intermolecular interactions. The equations obtained by means of classical thermomechanics are empirical and apply only in the region under observation. The main drawback of classical thermomechanicsis that it lacks the insight into the substance of microstructure. Contrary to classical mechanics, statistical mechanics calculates the thermomechanic properties of state on the basis of intermolecular and intramolecular interactions between particles in the same system of molecules. It deals with the systems composed of a very large number of particles. The results of the analysis are compared with experimental data and show a relatively good agreement. The analytical results obtained by statistical mechanics are compared with the experimental data and show relatively good agreement.
Ključne besede: statistical thermodynamics, thermophysical properties, viscosity, thermal conductivity, thermodynamic properties, mathematical model, nanofluids, statistical nanomechanics
Objavljeno: 31.05.2012; Ogledov: 1667; Prenosov: 116
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