| | SLO | ENG | Piškotki in zasebnost

Večja pisava | Manjša pisava

Iskanje po katalogu digitalne knjižnice Pomoč

Iskalni niz: išči po
išči po
išči po
išči po
* po starem in bolonjskem študiju

Opcije:
  Ponastavi


1 - 10 / 21
Na začetekNa prejšnjo stran123Na naslednjo stranNa konec
1.
High-Perssure process design for polymer treatment and heat transfer enhancement
Gregor Kravanja, 2018, doktorska disertacija

Opis: The doctoral thesis presents the design of several high-pressure processes involving »green solvents« so-called supercritical fluids for the eco-friendly and sustainable production of new products with special characteristics, fewer toxic residues, and low energy consumption. The thesis is divided into three main parts: polymer processing and formulation of active drugs, measurements of transport properties form pendant drop geometry, and study of heat transfer under supercritical conditions. In the first part, special attention is given to using biodegradable polymers in particle size reduction processes that are related to pharmaceutical applications for controlled drug release. The PGSSTM micronization process was applied to the biodegradable carrier materials polyoxyethylene stearyl ether (Brij 100 and Brij 50) and polyethylene glycol (PEG 4000) for the incorporation of the insoluble drugs nimodipine, fenofibrate, o-vanillin, and esomeprazole with the purpose of improving their bioavailability and dissolution rate. In order to optimize and design micronization process, preliminary transfer and thermodynamic experiments of water-soluble carriers (Brij and PEG)/ SCFs system were carried out. It was observed that a combination of process parameters, including particle size reduction and interactions between drugs and hydrophilic carriers, contributed to enhancing the dissolution rates of precipitated solid particles. In the second part, a new optimized experimental setup based on pendant drop tensiometry was developed and a mathematical model designed to fit the experimental data was used to determine the diffusion coefficients of binary systems at elevated pressures and temperatures. Droplet geometry was examined by using a precise computer algorithm that fits the Young–Laplace equation to the axisymmetric shape of a drop. The experimental procedure was validated by a comparison of the experimental data for the water-CO2 mixture with data from the literature. For the first time, interfacial tension of CO2 saturated solution with propylene glycol and diffusion coefficients of propylene glycol in supercritical CO2 at temperatures of 120°C and 150°C in a pressure range from 5 MPa, up to 17.5 MPa were measured. Additionally, the drop tensiometry method was applied for measuring systems that are of great importance in carbon sequestration related applications. The effect of argon as a co-contaminant in a CO2 stream on the interfacial tension, diffusion coefficients, and storage capacity was studied. In the third part, comprehensive investigation into the heat transfer performance of CO2, ethane and their azeotropic mixture at high pressures and temperatures was studied. A double pipe heat exchanger was developed and set up to study the effects of different operating parameters on heat transfer performance over a wide range of temperatures (25 °C to 90 °C) and pressures (5 MPa to 30 MPa). Heat flux of supercritical fluids was measured in the inner pipe in the counter-current with water in the outer pipe. For the first time, the heat transfer coefficients (HTC) of supercritical CO2, ethane and their azeotropic mixture in water loop have been measured and compared. A brief evaluation is provided of the effect of mass flux, heat flux, pressure, temperature and buoyancy force on heat transfer coefficients. Additionally, to properly evaluate the potential and the performance of azeotropic mixture CO2-ethane, the coefficients of performance (COP) were calculated for the heat pump working cycle and compared to a system containing exclusively CO2.
Ključne besede: supercritical fluids, PGSSTM, formulation of active drugs, biodegradable polymers, transport and thermodynamic data, pendant drop method, carbon sequestration, heat transfer coefficients
Objavljeno: 28.05.2018; Ogledov: 879; Prenosov: 133
.pdf Celotno besedilo (5,51 MB)

2.
HEAT TRANSFER IN UNIPORE CELLULAR STRUCTURE
Matevž Frajnkovič, 2017, magistrsko delo

Opis: This master’s thesis deals with heat transfer in a specific cellular structure, called UniPore cellular structure. Said structure has been developed at Japan’s Kumamoto university. The structure is manufactured using the technique of explosion welding. Due to longitudinal orientation of the pores and high thermal conductivity of materials, the thermal properties of the structure as a heat exchanger have been analysed. Influence of different boundary conditions on the effectiveness of heat transfer in the structure has been analysed. The results are compared and analysed. It has been concluded, that the structure itself might be suitable when dealing with dirty liquids. Usage of the structure in such systems would enable a quick and efficient cleaning process of the waste, that deposits on the walls over time.
Ključne besede: Heat transfer, cellular structure, porous materials, CFD
Objavljeno: 24.08.2017; Ogledov: 715; Prenosov: 152
.pdf Celotno besedilo (2,59 MB)

3.
Multiple-effect evaporation in aluminosilicate technology
Dušan Klinar, Janvit Golob, 2001, strokovni članek

Opis: The article presents an engineering approach to the development of an alternative production with the existing equipment. Zeolite production is becoming an alternative to the old »Bayer« process for aluminum hydrate production. By applying appropriate know-how old equipment was used for an economically as well as ecologically acceptable production. In this equipment adaptation among other production steps the multistage evaporation battery was the most critical part of the process. We applied semi empirical approach on the basis of Z. Rant ideas to find heat transfer coefficients and to determine which equipment elements are more relevant for efficient performance and need serious maintenance.
Ključne besede: chemical engineering, evaporation in silicate technology, bauxite alumina production, evaporators, process optimization, heat transfer, heat flow, empirical equations, heat transfer coefficients, zeolites
Objavljeno: 24.08.2017; Ogledov: 661; Prenosov: 68
.pdf Celotno besedilo (354,14 KB)
Gradivo ima več datotek! Več...

4.
Cooling analysis of a light emitting diode automotive fog lamp
Matej Zadravec, Matjaž Ramšak, Jure Ravnik, Matjaž Hriberšek, Jernej Slanovec, 2017, izvirni znanstveni članek

Opis: Efficiency of cooling fins inside of a light emitting diode fog lamp is studied using computational fluid dynamics. Diffusion in heat sink, natural convection and radiation are the main principles of the simulated heat transfer. The Navier-Stokes equations were solved by the computational fluid dynamics code, including Monte Carlo radiation model and no additional turbulence model was needed. The numerical simulation is tested using the existing lamp geometry and temperature measurements. The agreement is excellent inside of few degrees at all measured points. The main objective of the article is to determine the cooling effect of various heat sink parts. Based on performed simulations, some heat sink parts are found to be very ineffective. The geometry and heat sink modifications are proposed. While radiation influence is significant, compressible effects are found to be minor.
Ključne besede: heat transfer, cooling of electronic devices, cooling fins, light emitting diode automotive lamp, compressible flow
Objavljeno: 07.07.2017; Ogledov: 758; Prenosov: 306
.pdf Celotno besedilo (2,09 MB)
Gradivo ima več datotek! Več...

5.
Conduction and convection heat transfer characteristics of water-based Au nanofluids in a square cavity with differentially heated side walls subjected to constant temperatures
Primož Ternik, Rebeka Rudolf, 2014, izvirni znanstveni članek

Opis: The present work deals with the natural convection in a square cavity filled with the water-based Au nanofluid. The cavity is heated on the vertical and cooled from the adjacent wall, while the other two horizontal walls are adiabatic. The governing differential equations have been solved by the standard finite volume method and the hydrodynamic and thermal fields were coupled together using the Boussinesq approximation. The main objective of this study is to investigate the influence of the nanoparticles' volume fraction on the heat transfer characteristics of Au nanofluids at the given base fluid's (i.e. water) Rayleigh number. Accurate results are presented over a wide range of the base fluid Rayleigh number and the volume fraction of Au nanoparticles. It is shown that adding nanoparticles in a base fluid delays the onset of convection. Contrary to what is argued by many authors, we show by numerical simulations that the use of nanofluids can reduce the heat transfer rate instead of increasing it.
Ključne besede: natural convection, heat transfer, nanofluid, Nusselt number
Objavljeno: 07.07.2017; Ogledov: 603; Prenosov: 287
.pdf Celotno besedilo (834,69 KB)
Gradivo ima več datotek! Več...

6.
Heat-transfer characteristics of a non-newtonian Au nanofluid in a cubical enclosure with differentially heated side walls
Primož Ternik, Rebeka Rudolf, Zoran Žunič, 2015, izvirni znanstveni članek

Opis: The present work deals with the laminar natural convection in a cubical cavity filled with a homogenous aqueous solution of carboxymethyl cellulose (CMC) based gold (Au) nanofluid obeying the power-law rheological model. The cavity is heated on the vertical and cooled from the adjacent wall, while the other walls are adiabatic. The governing differential equations were solved with the standard finite-volume method and the hydrodynamic and thermal fields are coupled using the Boussinesq approximation. The main objective of this study is to investigate the influence of the nanoparticle volume fraction on the heat-transfer characteristics of CMC-based Au nanofluid over a wide range of the base-fluid Rayleigh number. Accurate numerical results are presented in the form of dimensionless temperature and velocity variations, the mean Nusselt number and the heat-transfer rate. It is shown that adding nanoparticles to the base fluid delays the onset of natural convection. In addition, numerical simulations showed that, just after the onset of natural convection, adding nanoparticles reduces the mean Nusselt number value for any given base-fluid Rayleigh number.
Ključne besede: natural convection, CMC-Au nanofluid, heat transfer, Nusslet number
Objavljeno: 16.03.2017; Ogledov: 683; Prenosov: 69
.pdf Celotno besedilo (736,13 KB)
Gradivo ima več datotek! Več...

7.
Numerical study of heat-transfer enhancement of homogeneous water-Au nanofluid under natural convection
Primož Ternik, Rebeka Rudolf, Zoran Žunič, 2012, izvirni znanstveni članek

Opis: A numerical analysis is performed to examine the heat transfer of colloidal dispersions of Au nanoparticles in water (Au nanofluids). The analysis used a two-dimensional enclosure under natural convection heat-transfer conditions and has been carried out for the Rayleigh number in the range of 103 < Ra < 105, and for the Au nanoparticles' volume-fraction range of 0 < j < 0.10. We report highly accurate numerical results indicating clearly that the mean Nusselt number is an increasing function of both Rayleigh number and volume fraction of Au nanoparticles. The results also indicate that a heat-transfer enhancement is possible using nanofluids in comparison to conventional fluids. However, low Rayleigh numbers show more enhancement compared to high Rayleigh numbers.
Ključne besede: natural convection, nanofluid, heat transfer, numerical modelling
Objavljeno: 10.07.2015; Ogledov: 750; Prenosov: 92
URL Povezava na celotno besedilo
Gradivo ima več datotek! Več...

8.
Numerical study of Rayleigh-Bénard natural-convection heat-transfer characteristics of water-based Au nanofluids
Primož Ternik, Rebeka Rudolf, Zoran Žunič, 2013, izvirni znanstveni članek

Opis: The present work deals with the natural convection in a square cavity filled with a water-based Au nanofluid. The cavity is heated from the lower and cooled from the adjacent wall, while the other two walls are adiabatic. Theg overning differential equations have been solved with the standard finite volume method and the hydrodynamic and thermal fields have been coupled using the Boussinesq approximation. The main objective of this study is to investigate the influence of the nanoparticlesć volume fraction on the heat-transfer characteristics of Au nanofluids at a given base-fluid (i.e., water) Rayleigh number Rabf. Accurate results are presented over a wide range of the base-fluid Rayleigh numbers (102 £ Rabf £ 105) and the volume fraction of Au nanoparticles (0 % £ j £ 10 %). It is shown that adding nanoparticles to the base fluid delays the onset of convection. Contrary to what is argued by many authors, we show, with numerical simulations, that the use of nanofluids can reduce the heat transfer instead of increasing it.
Ključne besede: Rayleigh-Bénard natural convection, water-Au nanofluid, heat transfer, numerical modelling
Objavljeno: 10.07.2015; Ogledov: 693; Prenosov: 80
.pdf Celotno besedilo (282,00 KB)
Gradivo ima več datotek! Več...

9.
Distortion of the substructure of a 20-ft shipping container exposed to zinc hot-dip galvanizing
Ivana Ivanović, Aleksandar Sedmak, Rebeka Rudolf, Leo Gusel, Biljana Grujić, 2013, izvirni znanstveni članek

Opis: The main goal of this study was to build a model for a numerical simulation of hot-dip galvanizing of a 20-ft ISO shipping container. For that purpose, the basic transient thermo-mechanical problem of a steel structure under the influence of the temperature characteristic for a zinc hot-dip galvanizing bath was analyzed. Numerical calculations were performed for a simple part and for the complex substructure of the container. Calculations were carried out on the Salome-Meca platform using a Netgen mesh generator and a Code_Asterfinite-element solver.
Ključne besede: shipping container, structural steel, zinc hot-dip galvanizing, transient heat transfer, distortion
Objavljeno: 10.07.2015; Ogledov: 609; Prenosov: 63
.pdf Celotno besedilo (703,73 KB)
Gradivo ima več datotek! Več...

10.
Heat diffusion in fractal geometry cooling surface
Matjaž Ramšak, Leopold Škerget, 2012, izvirni znanstveni članek

Opis: In the paper the numerical simulation of heat diffusion in the fractal geometry of och snowflake is presented using multidomain mixed Boundary Element Method. he idea and motivation of work is to improve the cooling of small electronic devices sing fractal geometry of surface similar to cooling ribs. The heat diffusion is ssumed as the only principle of heat transfer. The results are compared to the heat lux of a flat surface. The limiting case of infinite small fractal element is computed sing Richardson extrapolation.
Ključne besede: heat transfer, cooling of electronic devices, boundary element method, fractals
Objavljeno: 10.07.2015; Ogledov: 1022; Prenosov: 254
.pdf Celotno besedilo (313,63 KB)
Gradivo ima več datotek! Več...

Iskanje izvedeno v 0.29 sek.
Na vrh
Logotipi partnerjev Univerza v Mariboru Univerza v Ljubljani Univerza na Primorskem Univerza v Novi Gorici