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Suspensions of nanoscale particles and fluids have been recently subject of intense research, since it was proved that they considerably improve heat transfer capabilities of the fluid which can be crucial in several technological processes. Several applications can be found in the field of porous media flow, such as oil recovery systems, thermal and geothermal energy, nuclear reactors cooling. Since nanofluids are a mixture of a solid and fluid phase, in general, the two phase mathematical model would be the most appropriate to use. However, due to very small size of nanoparticles (1-100 nm) can be assumed, that they behave as a water molecule and a single phase model along with empirical correlations for nanofluid properties can be used. In the present study a convective flow through porous cavity fully saturated with nanofluid is analyzed in detail using the single phase mathematical model based on the Navier-Stokes equations taking into account the non-Darcy parameters. The mathematical model is written at a macroscopic level enabling the simulation of the porous media flow. The solutions are obtained with the in house numerical code based on the Boundary Element Method, which was already proved to have some unique advantages when considering fluid flow problems in different configurations. The effects of the presence of different types of nanoparticles as well as the porous matrix were investigated in detail for different values of governing parameters in order to examine the improved heat transfer characteristics of added nanoparticles.

In this chapter, the boundary element method (BEM) is introduced for solving problems of transport phenomena in porous media domains, which is an important topic in many engineering and scientific branches as well as in fields of practical interest. The main objective of the present work is to find a numerical solution of the governing set of equations written for fluid flow in porous media domains, representing conservation of mass, momentum, and energy. The momentum equation is based on the macroscopic Navier-Stokes equations and is coupled with the energy equation. In order to use BEM for the solution of the obtained set, the governing equations are transformed by the velocity-vorticity formulation, which separates the computational scheme into kinematic and kinetic computational parts. A combination of single-and sub-domain BEM is used to solve the obtained set of partial differential equations. Solution to a problem of natural convection in porous media saturated with pure fluid and nanofluid, respectively, for examples of 2D and 3D geometries, is shown. Results are compared to published work in order to estimate the accuracy of developed numerical algorithm. Based on the results, the applicability of the BEM for solving wide range of various problems is stated.

In the present paper a three-dimensional numerical code for simulation of porous media flow is presented which is based on the Boundary Element Method (BEM). The most general mathematical model is used to describe momentum, energy and solute transport in porous media which are based upon the general Navier-Stokes equations valid for the pure fluid flow. The developed numerical algorithm enables detailed investigation of the fluid flow together with heat and solute transfer under various conditions given with different governing parameters, e.g. thermal and solutal Rayleigh numbers, Darcy number, Lewis number, buoyancy coefficient. In the paper the effect of different governing parameters on the rate of heat, solute and momentum transfer are investigated. Under a certain range of parameters, complex flow patterns occur which exhibits the importance for us to investigate the problem in three dimensions.

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The problem of sedimentation in surface waters has considerable implications for environmental protection, but also for the use of hydropower on the watercourse and for long-term planning of flood risk management and water management. For an efficient management of suspended sediments, it is necessary to carry out appropriate measurements in order to maintain the quantity and dynamics of sediment movement as a function of changing hydraulic conditions. The data collected on site are the input for the development of a suitable model that can be used to establish a long-term plan for sediment management and to calibrate the numerical models. The paper presents an analysis of suspended sediment measurements in a Slovenian river. A correlation between concentration and discharge was investigated, especially during flood event. The suspended sediment dynamics depends on energy conditions, i.e. material is transported during high discharge events and deposited during low flow. The model of the suspended sediment concentration is a function of the water runoff and the amount of sediment deposition. Different models should be used at low discharge and at high discharge to correctly predict the amount of transported sediment concentrations. When modelling flood events, an additional sediment supply term should be added to the rating curve.

Managing sediment transport in streams is crucial to the surface water resource development strategy and has several implications for flood risk and water management, hydropower use, and balancing river morphology. This paper summarises the movement and behaviour of suspended sediment within the Slovenian portion of the River Drava, covering a span of thirteen years from 2005 to 2018. An analysis of relevant data collected during this period is also presented. Suspended-sediment dynamics strongly depend on flow velocity, seasonal variations in sediment sources, and human interventions in the riverbed. The transportation of material in the River Drava results in the accumulation of sediments in reservoirs and riverbeds, consequently impeding the natural hydrological cycle by reducing the outflow into aquifers. The 2018 high-water event is analysed in terms of the dependence of concentration of suspended sediments on discharge, where counterclockwise hysteresis was observed, providing an essential clue to the origin of sediment. Sediments from the River Drava in Slovenia are managed with some conventional processes and are mainly deposited or reintegrated into rivers and aquatic ecosystems. Some additional sediment management strategies with long-term solutions for efficient and comprehensive water management, hydropower, and ecological problems are proposed.