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Fractal geometry as an effective heat sink
Matjaž Ramšak, 2022, izvirni znanstveni članek

Opis: "How long is the coast of Britain?" was the question stated by Mandelbrot. Using smaller and smaller rulers the coast length limits to infinity. If this logic is applied to the fractal heat sink geometry, infinite cooling capacity should be obtained using fractals with mathematically infinite surface area. The aim of this article is to check this idea using Richardson extrapolation of numerical simulation results varying the fractal element length from one to zero. As expected, the extrapolated heat flux has a noninfinite limit. The presented fractal heat sink geometry is non-competitive to the straight fins.
Ključne besede: fractal heat sink, LED cooling, CPU cooling, conjugate heat transfer, laminar flow, boundary element method, Koch snowflake
Objavljeno v DKUM: 14.07.2023; Ogledov: 628; Prenosov: 14
.pdf Celotno besedilo (3,00 MB)
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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 v DKUM: 24.08.2017; Ogledov: 1555; Prenosov: 106
.pdf Celotno besedilo (354,14 KB)
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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 v DKUM: 07.07.2017; Ogledov: 1517; Prenosov: 381
.pdf Celotno besedilo (2,09 MB)
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Simulation of unsteady fluid flow and heat transfer by BEM
Jure Ravnik, Leopold Škerget, 2011, objavljeni znanstveni prispevek na konferenci

Opis: A boundary element method based solver for simulation of unsteady laminar viscous flow and heat transfer in three-dimensions has been developed. The algorithm solves the incompressible Navier- Stokes equations written in velocity-vorticity form and coupled with energy equation. Buoyancy is modelled within the Boussinesq approximation. The solver has recently been adapted for simulation of unsteady phenomena. The governing set of equations consists of the kinematics equation and transport equations for vorticity and temperature. Velocity and temperature boundary conditions are known, vorticity boundary conditions are calculated during the simulation by single domain BEM applied on the kinematics equation. The transport equations are solved by a domaindecomposition BEM approach, which yields sparse integral matrices and enables simulation using large computational grids. Rayleigh-Benard convection is used for a test case. In this case fluid is heated flow below, thus making it highly unstable. Already at low driving temperature of the bottom wall, the fluid becomes unstable. Vortices are formed above the hot bottom wall and travel up by buoyancy forces. Flow exhibits oscillatory behaviour, which at higher temperatures leads to chaotic and turbulent flow. The phenomenon was simulated using different driving temperatures of the bottom wall, observing the change of flow characteristics for steady to unsteady oscillatory regime and at even higher temperature to chaotic behaviour. Time series of heat flux and field functions were examined by phase portraits to determine the flow regime. A grid independence study and time step analysis was performed to asses the algorithms capability of simulation of unsteady behaviour.
Ključne besede: boundary element method, heat transfer, unsteady fluid flow, transport equations
Objavljeno v DKUM: 01.06.2012; Ogledov: 1982; Prenosov: 29
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Fast single domain-subdomain BEM algorithm for 3D incompressible fluid flow and heat transfer
Jure Ravnik, Leopold Škerget, Zoran Žunič, 2009, izvirni znanstveni članek

Opis: In this paper acceleration and computer memory reduction of an algorithm for the simulation of laminar viscous flows and heat transfer is presented. The algorithm solves the velocity-vorticity formulation of the incompressible Navier-Stokes equations in 3D. It is based on a combination of a subdomain boundary element method (BEM) and single domain BEM. The CPU time and storage requirements of the single domain BEM are reduced by implementing a fast multipole expansion method. The Laplace fundamental solution, which is used as a special weighting function in BEM, is expanded in terms of spherical harmonics. The computational domain and its boundary are recursively cut up forming a tree of clusters of boundary elements and domain cells. Data sparse representation is used in parts of the matrix, which correspond to boundary-domain clusters pairs that are admissible for expansion. Significant reduction of the complexity is achieved. The paper presents results of testing of the multipole expansion algorithm by exploring its effect on the accuracy of the solution and its influence on the non-linear convergence properties of the solver. Two 3D benchmark numerical examples are used: the lid-driven cavity and the onset of natural convection in a differentially heated enclosure.
Ključne besede: boundary element method, fast multipole method, fluid flow, heat transfer, velocity-vorticity fomulation
Objavljeno v DKUM: 31.05.2012; Ogledov: 2218; Prenosov: 98
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Boundary element method for thermal flows using k-[epsilon] turbulence models
Matjaž Ramšak, Leopold Škerget, 2008, objavljeni znanstveni prispevek na konferenci

Opis: Purpose - This paper aims to develop a multidomain boundary element method (BEM) for modeling 2D complex turbulent thermal flow using low Reynolds two-equation turbulence models. Design/methodology/approach - The integral boundary domain equations are discretised using mixed boundary elements and a multidomain method also known as a subdomain technique. The resulting system matrix is an overdetermined, sparse block banded and solved using a fast iterative linear least squares solver. Findings - The simulation of a turbulent flow over a backward step is in excellent agreement with the finite volume method using the same turbulent model. A grid consisting of over 100,000 elements could be solved in the order of a few minutes using a 3.0 GhzP4 and 1 GB memory indicating good efficiency. Originality/value - The paper shows, for the first time, that the BEM is applicable to thermal flows using k-▫$epsilon$▫.
Ključne besede: thermal flow, heat exchange, turbulence, boundary element method, simulation
Objavljeno v DKUM: 31.05.2012; Ogledov: 1793; Prenosov: 47
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Influence of water scale on thermal flow losses of domestic appliances
Danijela Urbancl, Darko Goričanec, 2007, izvirni znanstveni članek

Opis: Research results of how the precipitated water scale on heaters of small domestic appliances influences the consumption of electricity are presented. It shows that the majority of water scale samples are composed of aragonite, calcite and dolomite and that those components have an extraordinary low thermal conductivity. Also, the results show that at 2 mm thick deposit, depending on the chemical composition of water scale, the thermal flow is reduced for 10% to 40%; consequently, the consumption of electricity significantly increases.
Ključne besede: electricity, heat transfer, heat flow, heat exchanger, water scale
Objavljeno v DKUM: 31.05.2012; Ogledov: 2303; Prenosov: 68
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