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.

COBISS.SI-ID: 16562710

This paper presents new formulations of the radial integration boundary integral equation (RIBIE) and the radial integration boundary integro-differential equation (RIBIDE) methods for the numerical solution of two-dimensional diffusion problems with variable coefficients. The methods use either a specially constructed parametrix (Levi function) or the standard fundamental solution for the Laplace equation to reduce the boundary-value problem (BVP) to a boundary-domain integral equation (BDIE) or boundary-domain integro-differential equation (BDIDE). The radial integration method (RIM) is then employed to convert the domain integrals arising in both BDIE and BDIDE methods into equivalent boundary integrals. The resulting formulations lead to pure boundary integral and integro-differential equations with no domain integrals. Furthermore, a subdomain decomposition technique (SDBDIE) is proposed, which leads to a sparse system of linear equations, thus avoiding the need to calculate a large number of domain integrals. Numerical examples are presented for several simple problems, for which exact solutions are available, to demonstrate the efficiency of the proposed approaches.

COBISS.SI-ID: 16211990

The boundary element method was applied to study the motion of magnetic particles in fluid flow under the action of external nonuniform magnetic field. The derived formulation combines the velocity-vorticity resolved Navier-Stokes equations with the Lagrange based particle tracking model, where the one-way coupling with fluid phase was considered. The derived algorithm was used to test a possible design of high gradient magnetic separation in a narrow channel by computing particles trajectories in channel flow under the influence of hydrodynamic and magnetic forces. Magnetic field gradient was obtained by magnetization wires placed outside of the channel. Simulations with varying external magnetic field and flow rate were preformed in order to asses the collection efficiency of the proposed device. We found that the collection efficiency decreases linearly with increasing flow rate. Also, the collection efficiency was found to increase with magnetic field strength only up a saturation point. Furthermore, we found that high collection efficiently is not feasible at high flow velocity and/or at weak magnetic field. Recommendation for optimal choice of external magnetic field and flow rate is discussed.

COBISS.SI-ID: 16152342

This paper deals with the numerical analysis of the influence of bioethanol addition to diesel and biodiesel fuel on the injection process. It has been shown that the determined empirical expressions for density, sound velocity and bulk modulus enable satisfactory numerical modeling of the injection process for all tested fuels. The analysis of numerical results shows that for all operating regimens simulated, the addition of bioethanol to biodiesel and to diesel reduces fuelling, injection timing, injection duration, mean injection rate and maximum injection pressure.

COBISS.SI-ID: 15906582

This work investigated the possibilities of immobilizing incineration fly ash by applying different processing methods. Direct sintering of fly ash at 1050 °C produced material with increased resistance to leaching; however, the high content of halides prevented the achievement of appropriate strength. Fly ash melting and casting into metallic moulds resulted in the formation of glass with good chemical resistivity and mechanical properties, which were further improved by devitrification, and the formation of glass-ceramics. The most successful combination of strength and resistance to leaching was obtained by a process consisting of fly ash melting, by pouring the melt into water, then grinding, and sintering without additives at 850-950 °C. In this way, a material was produced that cannot only be landfilled as a stabilised and non-reactive waste in landfills for non-hazardous wastes, but can also be utilized as a valuable material for manufacturing useful products. This article provided valuable results for policy-makers in Slovenia, about the handling fly ash from incineration plants.

COBISS.SI-ID: 15970582