1. Calculation of the thermal conductivity of nanofluids containing nanoparticles and carbon nanotubesJurij Avsec, Maks Oblak, 2003, izvirni znanstveni članek Opis: A mathematical model for the calculation of thermal conductivity of nanofluids containing nanoparticles and nanotubes on the basis of statistical mechanics is presented. This appears to be the first such attempt published in the scientific literature. We focus on the influence of the liquid layer structure around nanoparticles as the reason for enhancement of the thermal conductivity of nanofluids. Analytical results of both the current analysis and statistical mechanics are compared with experimental data reported in the scientific literature, which show good agreement. Ključne besede: statistical thermodynamics, mathematical models, thermal conductivity, nanofluids, transport properties, statistical nano-mechanics Objavljeno: 31.05.2012; Ogledov: 861; Prenosov: 5 Celotno besedilo (0,00 KB) |
2. Analytical calculation of diffusion coefficients and other transport properties in binary mixturesJurij Avsec, Maks Oblak, 2006, izvirni znanstveni članek Opis: The note features the mathematical model of computing binary diffusion coefficient, thermal diffusion factor and viscosity in the real-gas region on the basis of nonequilibrium statistical mechanics. For the analytical calculation of transport properties, we have used the Kihara and Chapman-Cowling model up to the third order. In the presented note we calculated transport properties for mixtures between carbon monoxide and helium. We have developed the new mixing rules for the calculation of transport properties for mixtures. The analytical results obtained by statistical mechanics are compared with the experimental data and they show relatively good agreement. Ključne besede: thermodynamics, statistical thermodynamics, mathematical models, binary diffusion coefficient, thermal diffusivity, binary mixtures Objavljeno: 30.05.2012; Ogledov: 797; Prenosov: 6 Celotno besedilo (0,00 KB) |
3. The calculation of thermal conductivity, viscosity and thermodynamic properties for nanofluids on the basis of statistical nanomechanicsJurij 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: 999; Prenosov: 7 Celotno besedilo (0,00 KB) |
4. Statistical approach to calculate thermodynamic properties for propaneJurij Avsec, K. A... Watanabe, 2005, izvirni znanstveni članek Opis: The paper describes a mathematical model to compute equilibrium thermodynamic properties in the fluid phase of pure hydrocarbons with the aid of classical thermodynamics and statistical associating chain theories. In the present paper thermodynamic properties for propane, as an example of hydrocarbon substances, are calculated. To calculate the thermodynamic properties of real fluids, models based on the Lennard-Jones intermolecular potential were applied. To calculate the thermodynamic properties of real fluids with the aid of classical thermodynamics, Miyamoto-Watanabe (MW) equations, developed in terms of the Helmholtz energy were used. Analytical results obtained by statistical thermodynamics are compared with the MW model and show relatively good agreement. Ključne besede: statistical thermodynamics, propane, thermodynamic properties, SAFT model, chain theory Objavljeno: 01.06.2012; Ogledov: 655; Prenosov: 3 Celotno besedilo (0,00 KB) |
5. An approach to calculate thermodynamic properties of mixtures including Propane, n-Butane, and IsobutaneJurij Avsec, Koichi Watanabe, 2005, izvirni znanstveni članek Opis: This paper discusses a mathematical model for computing the thermodynamic properties of propane, n-butane, isobutane, and their mixtures, in the fluid phase using a method based upon statistical chain theory. The constants necessary for computations such as the characteristic temperatures of rotation, electronic state, etc. and the moments of inertia are obtained analytically applying a knowledge of the atomic structure of the molecule. The paper presents a procedure for calculating thermodynamic properties such aspressure, speed of sound, the Joule-Thomson coefficient, compressibility, enthalpy, and thermal expansion coefficient. This paper will discuss, for the first time, the application of statistical chain theory for accurate properties of binary and ternary mixtures including propane, n-butane, and isobutane, in their entire fluid phases. To calculate the thermodynamic properties of Lennard-Jones chains, the Liu-Li-Lu model has been used. The thermodynamic properties of the hydrocarbon mixtures are obtained using the one-fluid theory. Ključne besede: statistical thermodynamics, chain theory, mixtures, transport properties, hydrocarbons, isobutane, n-butane, propane, refrigerants Objavljeno: 01.06.2012; Ogledov: 792; Prenosov: 6 Celotno besedilo (0,00 KB) |
6. Multifunctional composites by high-pressure spray processesEckhard Weidner, Marcus Petermann, Željko Knez, 2003, pregledni znanstveni članek Opis: A series of spraying processes designed to generate powders and composites using supercritical fluids have been proposed in the past 15 years. In this review, thermo- and fluid-dynamic aspects and engineering principles are discussed and advantages of such technologies are demonstrated. These new techniques display convincing advantages, producing competitive high-quality products with tailor-made properties. Initial industrial applications have been achieved in the production of food products and fine-chemicals. Ključne besede: chemical processing, high pressure technology, micronization, supercritical fluids, particles, powder generation, thermodynamics, fluid dynamics, PGSS Objavljeno: 01.06.2012; Ogledov: 1045; Prenosov: 3 Celotno besedilo (0,00 KB) |
7. Calculation of thermophysical and thermochemical properties during hydrocarbon combustionJurij Avsec, Franc Zgaga, Milan Marčič, 2002, izvirni znanstveni članek Opis: A mathematical model is presented for computing the chemical and thermophysical properties in the process of combustion of natural gas. To identify the parameters of state of combustion products, their composition hasto be known, which may be determined from chemical equilibrium. The computation is performed with the use of chemical potentials and statistical thermodynamics, featuring all important molecular contributions (translation, rotation, vibration, and intermolecular potential energy). A thermal equation of state with two virial terms is used. The real gas mixture is treated as consisting of four components: carbon dioxide, nitrogen, carbon monoxide, and water. Virial coefficients are dependent on temperature and mole fractions of the real components. Mixed terms are taken into account. The caloric equation of state is based on statistical thermodynamics for an ideal gas. Corrections are made in accordance with the second law of thermodynamics and the thermal equation of state. As the whole computation is based on matrix algebra, increasing the number of components presents no problems. We tested our model in the high-pressure region (100 bar) and the low-pressure region (1 bar), in the temperature range 500 - 6000°K. Our model is compared with other analytical models presented in the literature and shows relatively good agreement. At the same time we tested the influence of real conditions on the chemical and thermophysical properties of combustion products. Ključne besede: statistical thermodynamics, thermodynamical properties, combustion of natural gas, mathematical models, thermodynamic functions of state, equation of state, virial coefficients Objavljeno: 01.06.2012; Ogledov: 858; Prenosov: 4 Celotno besedilo (0,00 KB) |
8. Influence of vacuum energy on scatteringMilan Marčič, 1997, izvirni znanstveni članek Opis: We deal with photon-electron scattering which occurs between two uncharged conducting parallel plates moving away from each other at a constant velocity. The electromagnetic vacuum field between the two plates is defined by the configuration of space and also interacts with the electrons. We show the relevant operators for both the photon and the electron fields and the computation of the corresponding Feynman propagator, S-matrix and scattering cross section, taking into account the influence of the changeable vacuum field. Correction terms in the computed S-matrix and scattering cross section manifest the influence of the changeable vacuum field. We analyze an example for low-energy scattering of the influence of the changeable vacuum field uponthe scattering cross section. Ključne besede: physics, quantum electrodynamics, statistical thermodynamics Objavljeno: 01.06.2012; Ogledov: 812; Prenosov: 3 Celotno besedilo (0,00 KB) |
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10. Enzymatic fatty ester synthesisSimona Pečnik, Željko Knez, 1992, izvirni znanstveni članek Opis: Fatty ester synthesis with immobilized 1,3-specific lipase from Mucor Miehei is described. 1,2-Isopropylidene glycerol was peoduced by condensation of glycerol with acetone was esterified with oleic acid in the presence of a Mucor Miehei lipaze (Lipozyme TM) to obtain 1,2 isopropylidene- 3-oleoyl glycerol. The effects of various process parameters (temperature and pressure)and various ratios (enzyme/substrate) have been investigated to determine optimal conditions for the esterification process. The highest conversion of oleic acid (80% w/w) was obtained at 55 oC and 57.057 bar, while the optimal addition of lipase to substrate was determined to be 0,096 g per gram of reaction mixture. The esterification can be modelled successfully as a reverse second order reaction. Thermodynamic properties of the reaction system at 55 oC and 0.057 bar were also determined. Activation energy was 20.82 kJ/mole, entropy of activation -0,26 kJ/(Kmole) and free energy of activation was 103.32 kJ/mole. Ključne besede: chemical engineering, biotechnology, esterification, syntheses, esters, enzymes, lipase, Mucor miehei, reaction kinetics, reaction thermodynamics, 1, 2-isopropylidene-3-oleoyl glycerol Objavljeno: 06.06.2012; Ogledov: 1011; Prenosov: 10 Celotno besedilo (0,00 KB) |