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Experimental study of the magnetic nanofluids forced convection in a constant magnetic field was carried out. Dependence study of the magnetic nanofluid heat transfer coefficient on the effect of a constant magnetic field was made. The effect of a constant magnetic field on the pressure drop during the magnetic nanofluid flow was shown.

In the present work, the regimes of the flow and mixing of fluids in a T-shaped micromixer in the range of the Reynolds numbers from 1 to 1000 are investigated systematically with the aid of numerical modeling. The flow and mixing regimes are shown to alter substantially with increasing Reynolds numbers. Five different flow regimes have been identified in the total. The dependencies of the friction coefficient and mixing efficiency on the Reynolds number are obtained. A sharp increase in the mixing efficiency at a flow transition from the symmetric to asymmetric steady regime is shown. On the other hand, the mixing efficiency slightly drops in the laminar-turbulent transition region. A substantial influence of the slip presence on walls on flow structure in the channel and mixing efficiency has been revealed.

We propose a numerical algorithm for simulating steady laminar flows of an incompressible fluid in annular channels with eccentricity and rotation of the inner cylinder. This algorithm enables us to describe this class of flows for wide ranges of the annular channel and flow parameters. We present the implementation details and the results of testing this numerical method. For a series of flows in an annular clearance, we compare the numerical results to available analytic solutions and experimental data. In all cases under consideration the simulated data agree well with the available experimental, analytical, and numerical solutions.

Saturated boiling of nanoliquids on a cylindrical heater is experimentally studied. The studied nanoliquids were prepared using distilled water and Fe3O4 iron oxide or diamond nanoparticles. The volume concentration of the nanoparticles was changed from 0.25 to 1%. It has been measured that the critical density of heat flow in nanoliquids is far higher than in water. Moreover, it depends on size of nanoparticles.

A method is proposed for modelling fluid flows in microchannels. The method is tested on the known experimental data on studying the flows in microchannels with the aid of the micro-PIV. The flow regimes in micromixers of the Y- and T-types are studied. The passive and active mixers are considered. The dependence of the mixing efficiency on the Reynolds and Peclet numbers as well as the possibility of using the hydrophobic and ultra-hydrophobic coatings are analysed. A T-mixer is proposed as an active technique of mixing, in which the flow rate in one of the inlet channels varied according to the harmonic law. The dependence of the mixing efficiency on the frequency of the variation of the flow rate and its amplitude is established.

The results of experimental studies of the microsuspensions filtration with silicon oxide nanoparticles additions through a porous medium with different permeability are presented. The particle concentration in fluids ranged from 0.25 to 4 wt.%. The microparticle size was 1.2 μm. The nanoparticle size was 5 nm. The nanoparticle concentration was 2 wt.%. Dependences of the filtration losses of microsuspensions on the microparticle concentration and the permeability of a porous medium were established.

A model is proposed, which describes the work of the viscometer sensor of the physical pendulum type. The model enables the obtaining of data on fluid viscosity directly from the measurement of the settling frequency of sensor oscillations or the amplitude of these oscillations. To describe the sensor operation a numerical computational algorithm is developed. This method enables the solution of a wide class of three-dimensional laminar fluid flow problems involving moving solids of arbitrary geometry. The results of testing the proposed numerical technique are presented.

Nanofluids present a new type of dispersed fluids consisting of a carrier fluid and solid nanoparticles. Unusual properties of nanofluids, particularly high thermal conductivity, make them eminently suitable for many thermophysical applications, e.g., for cooling of equipment, designing of new heat energy transportation and production systems and so on. This requires a systematic study of heat exchange properties of nanofluids. The present paper contains the measurement results for the heat transfer coefficient of the laminar and turbulent flow of nanofluids on the basis of distilled water with silica, alumina and copper oxide particles in a minichannel with circular cross section. The maximum volume concentration of particles did not exceed 2%. The dependence of the heat transfer coefficient on the concentration and size of nanoparticles was studied. It is shown that the use of nanofluids allows a significant increase in the heat transfer coefficient as compared to that for water. However, the obtained result strongly depends on the regime of flow. The excess of the heat transfer coefficient in the laminar flow is only due to an increase in the thermal conductivity coefficient of nanofluid, while in the turbulent flow the obtained effect is due to the ratio between the viscosity and thermal conductivity of nanofluid. The viscosity and thermal conductivity of nanofluids depend on the volume concentration of nanoparticles as well as on their size and material and are not described by classical theories. That is why the literature data are diverse and contradictory; they do not actually take into account the influence of the mentioned factors (size and material of nanoparticles). It has been shown experimentally and by a molecular dynamics method that the nanofluid viscosity increases while the thermal conductivity decreases with the decreasing dispersed particle size. It is found experimentally for the first time that the nanofluid viscosity coefficient depends on the particle material. The higher is the density of particles, the higher is the thermal conductivity coefficient of nanofluid.

During the research we conducted an experimental study and numerical simulation of ferromagnetic nanoparticles transport behavior in a constant magnetic field. The growth dynamics of nanoparticle deposits on channel walls was studied depending on the Reynolds number and the intensity of the magnetic field. We obtained flow pattern, the concentration field and the trajectory of nanoparticles depending on the Reynolds number. The simulation results were compared with data from experiments. There was good qualitative and quantitative agreement between calculation and experiment.

Текст статьи не публикуется в открытом доступе в соответствии с политикой журнала. A complex mathematical model of aluminum casting and solidification in a variable electromagnetic field is constructed. The model is based on the solution of magnetohydrodynamic equations and the VOF method. Test results are presented for the model and the numerical algorithm proposed. The numerical results are compared with experimental data and computations of other authorsand are found to be in good agreement. The model is used to simulate aluminum solidification under an electromagnetic field. The physical processes influencing ingot formation are analyzed.

A new hybrid method is proposed for solving the problems of fluid dynamics and heat transfer in complex hydraulic systems. The peculiarity of the method consists in the idea that some elements of the model are represented as network elements, where the solving of the flow distribution problem is carried out on the basis of the hydraulic circuit theory, whereas the flow in the remaining elements is calculated by the spatial methods of computational fluid dynamics (CFD). The results are presented of testing the proposed hybrid method for the problems of fluid dynamics and heat transfer in microchannels. The test calculations demonstrate high efficiency of the method.

In this paper, the study of ferromagnetic nanoparticles behaviour in the constant magnetic field is carried out. For numerical simulation we have used Euler-Lagrange two-component approach. Using numerical simulation we have studied the growth of deposition of nanoparticles on the channel walls depending on the Reynolds number and the position of the magnet. The flow pattern, the concentration field and the trajectory of nanoparticles as a function of the Reynolds number were obtained. The good qualitative and quantitative agreement between numerical simulation and experiments was shown.

The paper presents numerical simulation of the flow in hydraulic turbine based on the experimental data of the II Francis-99 workshop. The calculation domain includes the wicket gate, runner and draft tube with rotating reference frame for the runner zone. Different turbulence models such as k-ω SST, ζ-f and RSM were considered. The calculations were performed by means of in-house CFD code SigmaFlow. The numerical simulation for part load, high load and best efficiency operation points were performed.

The free discharge through the turbine is applied in the course of construction of hydro power plant or in case of excessive water inflow during floods or emergency situations. The experimental and numerical investigation of flow-induced pressure pulsations in hydraulic turbine draft tube at free discharge was performed using a special setup for suppression of draft tube surge. Such special equipment in draft tube cone as fins and “spider”-like units was considered for reducing these pressure pulsations. The paper considers influence of these units on vortex structures and pressure pulsations in the draft tube in several regimes.

The thermal conductivity of magnetic nanofluids in a constant magnetic field is investigated. The concentration dependence of the thermal conductivity coefficient of magnetic fluids based on water and iron oxide nanoparticles Fe3O4 in a constant magnetic field is obtained. The dependence of the thermal conductivity coefficient of nanofluid on the nanoparticles size in a magnetic field is obtained. The temperature effect on the thermal conductivity of magnetic nanofluid in a constant magnetic field is studied.

We performed numerical simulation of flow in a laboratory model of a Francis hydroturbine at startup regimes. Numerical technique for calculating of low frequency pressure pulsations in a water turbine is based on the use of DES (k-ω Shear Stress Transport) turbulence model and the approach of "frozen rotor". The structure of the flow behind the runner of turbine was analysed. Shows the effect of flow structure on the frequency and intensity of non-stationary processes in the flow path. Two version of the inlet boundary conditions were considered. The first one corresponded measured time dependence of the discharge. Comparison of the calculation results with the experimental data shows the considerable delay of the discharge in this calculation. Second version corresponded linear approximation of time dependence of the discharge. This calculation shows good agreement with experimental results.

We performed numerical simulation of flow in a laboratory model of a Francis hydroturbine at three regimes, using two eddy-viscosity- (EVM) and a Reynolds stress (RSM) RANS models (realizable k-, k-ω SST, LRR) and detached-eddy-simulations (DES), as well as large-eddy simulations (LES). Comparison of calculation results with the experimental data was carried out. Unlike the linear EVMs, the RSM, DES, and LES reproduced well the mean velocity components, and pressure pulsations in the diffusor draft tube. Despite relatively coarse meshes and insufficient resolution of the near-wall region, LES, DES also reproduced well the intrinsic flow unsteadiness and the dominant flow structures and the associated pressure pulsations in the draft tube.

Flow patterns and mixing of liquids with different densities in T-shaped micromixers are numerically investigated at Reynolds number range from 1 to 250. The density ratio of the mixing media varies from 1 to 2; its effect on the flow structure and the mixing is studied. The dependences of the mixing efficiency and the pressure difference in this mixer on the density ratio and the Reynolds number are obtained. It is shown that the density ratio has a considerable effect on the flow structure, especially before the transition from the symmetric to the asymmetric flow pattern.

Saturated boiling of nanofluid on a copper cylinder is experimentally studied. The studied nanofluid were prepared using distilled water and Al 2 O 3 nanoparticles. The volume concentration of the nanoparticles was equal 3 %. Cylinder diameter was equal 25 mm. The time dependence on the excess temperature at different boiling regimes were obtained. It shown increase of heat transfer coefficient under boiling of nanofluid.

The paper presents the results of experimental study of turbulent forced convection of water-based nanofluid with ZrO2 nanoparticles. Volumetric concentration of the nanoparticles in the experiments was equal to 4%. The average particle size was 105nm. The study was carried out for a smooth round tube and round tube with knurling ring. The effect of additives of ZrO2 nanoparticles on the average heat transfer coefficient and the pressure drop in the channel was investigated. Has been shown that the intensification of heat transfer by using nanofluid weakly dependent on the shape of the channel, and determined only by the properties nanofluid.

Several popular turbulent combustion models have been tested in a computational study of three experimentally well-documented non-swirling and swirling jet flames. Different combinations of turbulence, combustion and reaction mechanisms models were considered. It is shown that the eddy- dissipation concept (EDC) and the probability-density function (PDF) of flamelet combustion models with detailed kinetics mechanisms provide the best results for all flames examined. For some cases, a combination of RANS turbulence models and less costly combustion approaches (Hybrid or EDC with 4 reactions) also gives acceptable results.

The paper presents the results of systematic measurements of the thermal conductivity coefficient of nanofluids at room temperature. It is shown that the thermal conductivity of all considered nanofluids depend on concentration, nanopartical size, as well as the base fluid properties. It was revealed that thermal conductivity coefficient of nanofluids increases with increasing concentration and size of nanoparticles.

The paper presents the numerical simulation method of three-dimensional turbulent flows in the hydraulic turbine. This technique was verified by means of experimental data obtained on a water model of the Francis turbines. An aerodynamic stand, which is a miniature copy of the real hydraulic turbine, was designed. A series of experiments have been carried out on this stand and the corresponding calculations were performed. The dependence of the velocity and pressure pulsations profiles for different operation regimes are presented.

Application of DES method for swirling flows was considered. Swirling flow in a diffuser and vortex breakdown past an abrupt expansion were considered to test the application of detached eddy simulation method for swirling flows. Calculations of unsteady flows in draft tube of Kaplan turbine Holleforsen and in draft tube of high head Francis turbine were provided to investigate vortex rope precession in hydro turbine.

The experimental study of influence of adding high-molecular weight polymers on heat transfer characteristics of water-based nanofluids with Al 2 O 3 nanoparticles. Volumetric concentration of particles was very low, 10-3 %. The volumetric particle concentration was equal to 2%. We investigated the dependence of heat transfer coefficient and pressure drop on the concentration of additives high polymers.

Saturated boiling of nanofluids on a cylindrical heater with different diameters is experimentally studied. Studied nanofluids were prepared using distilled water and different metal oxides nanoparticles. The volume concentration of the nanoparticles was changed from 0.05 to 1%. It has been measured that the critical heat flux for nanofluids was much higher than for water. A strong dependence of CHF on the material and size of the nanoparticles and duration of boiling and size of heater was shown.

The paper presents numerical simulation of flow in Francis-99 water turbine under three operation modes: part load, best efficiency point and high load. Calculations were performed by means of Reynolds stress model and detached eddy simulation based on k-omega SST model. The paper focuses on the flows in the draft tube. The calculated mean velocity components in the draft tube are in close agreement with experimental results. Calculated r.m.s velocity components agree with experimental pulsations qualitatively.

This article investigates electrolyte filtration in the bottom of the aluminum electrolyzer cathode device using the mathematical modeling. Penetration of molten electrolyte in the heat insulation part of the lining is one of the main reasons of electrolyzer premature shutdown, because it leads to bottom destruction and excessive heat loss. This problem is considered a two-phase filtration of incompressible immiscible liquids in an inhomogeneous non-deformable porous body. The verification of the model on the problem of water filtration pin a porous medium has confirmed its adequacy. With the help of the developed mathematical model the dynamics of the impregnation of the lining of the cathode and electrolyte device defined thermal balance baths. Research has identified the speed of penetration of the melt in the bottom of the bath during service of the electrolyzer.

Results of testing methodology for calculating two-phase flows based on the method of fluid in the cells (VOF method), and the procedure for CSF accounting of surface tension forces in the microchannel are considered in the work. Mathematical modeling of two-component flow fluid -fluid in the T- microchannel conducted using this methodology. The following flow regimes studied slug flow, rivulet flow, parallel flow, dispersed (droplet) flow, plug flow. Comparison of numerical results with experimental data done. Satisfactory agreement between the calculated values with the experimental data obtained.

Free discharge through the units is applied in the course of construction of hydro power plant or in case of excessive water inflow during floods or emergency situation. Free discharges throw the hydro units at 80 m head and more are unknown. Possibility of high velocity swirling flow discharged through the whole hydro unit consisting of penstock, turbine (with Francis runner and distributor or without them) and draft tube is being analyzed in the present paper. Investigation method is based on mathematical simulation of unsteady flow through the hydro unit under the following conditions: with the free running or locked runner and with removed runner. Physical researches of the swirling flow behavior in the model bent penstocks and model turbine water passages have been performed. Based on the results of calculations and model tests the following extensive data have been obtained: pressure fluctuation in the whole hydro unit, fluctuation of hydrodynamic forces acting on guide vanes, torque fluctuation on the runner and discharge fluctuation. Thus, based on this data preferable designs of free discharge are proposed.