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The paper presents the results of experimental study of rheological behavior of nanofluids based from consideration of several tens of nanofluids based on water, ethylene glycol and engine oil, containing particles of different oxides and diamond. The sizes of nanoparticles ranged from 5 to 150 nm, while their volume concentration ranged from 0.25 to 8%. At that, no dispersants were used when preparing tested nanofluids. It is shown that in some cases, when increasing nanoparticle concentration, rheological behavior of nanofluids becomes non-Newtonian and is well described by power-law fluid models or Herschel–Bulkley fluids. The influence of nanoparticle size and material, as well as the nature of the base fluid on the rheological behavior of nanofluids have been studied.

This paper describes an experimental study of deformation of a droplet of an organic water—coal fuel in a gas flow. The experimental data obtained are used to develop a technique that serves as a basis for a numerical study of integral characteristics of deformation of the droplets of organic water—coal fuel 4.5 mm in diameter with a gas flow velocity of 2 m/s and a temperature of 298 K. The characteristic changes of the area of longitudinal and transverse sections of the droplets of the organic water—coal fuel during their gravitational deposition in time are revealed. It is shown that the theoretical and experimental data satisfactorily agree.

The effect of nanoparticles with different compositions and sizes on the rheological properties, filtration losses, and lubricating ability of drilling fluids has been experimentally studied. Nanoparticles of silicon, aluminum, and titanium oxides have been examined, while an aqueous bentonite suspension with a solid phase mass fraction of 5% has been used as a basic model of a drilling fluid. The concentrations and sizes of nanoparticles in the drilling fluids have been varied from 0.25 to 2 wt % and from 5 to 100 nm, respectively. It has been shown that the addition of nanoparticles substantially changes the properties of the drilling fluids. In contrast to suspensions of particles with macro- and microscopic sizes, the rheological parameters, filtration losses, and lubricating and sticking abilities of the suspensions containing nanoparticles depend on the size and nature of the latter and vary markedly already at low nanoparticle concentrations.

The flow and mixing modes of non-Newtonian fluids in a T-shaped micromixer were studied by numerical simulation in the range of Reynolds numbers 1–250. The non-Newtonian fluid was described using the power-law model. The exponent n was varied: 0.3, 0.5, and 0.8. The mixing efficiency and pressure drop in the channel were correlated with the exponent n and Reynolds number. The exponent n was shown to significantly affect the flow structure before and especially after the transition from symmetric to asymmetric flow modes.

The results of an experimental study of the rheological properties of clay-particle suspensions with additions of silicon-, aluminum-, and titanium-oxide nanoparticles are given. The concentration of particles in solutions ranges from 0.25 to 2 wt %. The particle sizes are in the range from 5 to 100 nm. The dependences of the effective viscosity and rheological parameters of these solutions on the concentration, size, and chemical nature of nanoparticles are established.

We report a new mechanism for the generation of membrane potential in polarizable nanoporous membranes separating electrolytes with different concentrations. The electric field generated by diffusion of ions with different mobilities induces a non–uniform surface charge, which results in charge separation inside the nanopore. The corresponding Donnan potentials appear at the pore entrance and exit leading to a dramatic enhancement of membrane potential in comparison with an uncharged non–polarizable membrane. At high concentration contrast, the interaction between electric field and uncompensated charge at a low concentration side results in the development of electrokinetic vortices. The theoretical predictions are based on the Space–Charge model, which is extended to nanopores with polarizable conductive surface for the first time. This model is validated against full Navier–Stokes, Nernst–Planck, and Poisson equations, which are solved in a high aspect ratio nanopore connecting two reservoirs. The experimental measurements of membrane potential of dielectric and conductive membranes in KCl and NaCl aqueous solutions confirm the theoretical results. The membranes are prepared from Nafen nanofibers with ∼ 10 nm in diameter and modified by depositing a conductive carbon layer. It is shown theoretically that the membrane potential enhancement becomes greater with decreasing the electrolyte concentration and pore radius. A high sensitivity of membrane potential to the ratio of ion diffusion coefficients is demonstrated. The described phenomenon may find applications in precise determination of ion mobilities, electrochemical and bio–sensing, as well as design of nanofluidic and bioelectronic devices.

The oil-based drilling fluids are widely used in well drilling. An experimental study on the effect of the addition of silicon oxide nanoparticles of various concentrations on the oil-based drilling fluids properties has been carried out. The range of nanoparticles concentration in drilling emulsions was taken from 0.25 to 2 wt%. The influence of nanosized particles on the viscosity and rheological properties, filtration and antifriction properties, as well as on the colloidal stability of oil-based drilling fluids is considered. This is the first time such a comprehensive study has been carried out. It is shown that the addition of nanoparticles to drilling fluids has a beneficial significant effect on their properties, and even a minute concentration of nanoparticles allowed to observe a change in all parameters. This indicates that the use of nanoparticles can become a promising direction in the field of further improvement of oil-based drilling fluids.

In the present paper, the regimes of flow and mixing of water and a nanofluid with aluminum oxide nanoparticles in a T-shaped microchannel have been studied numerically. The Reynolds number was varied from 10 to 400, and the volume concentration of nanoparticles was varied from 0 to 10%. Nanofluids with mean sizes of particles from 50 to 150 nm were considered. The viscosity coefficient of the nanofluid was taken from experimental data. In all cases, it exceeded the viscosity coefficient of water and depended on not only the concentration of nanoparticles, but also on their sizes, and the viscosity of the nanofluid with smaller particles was higher than the viscosity of the nanofluid with large particles. It has been established that there exist regimes of steady irrotational flow, steady vortex flow with two horseshoe vortices, and steady flow with two vortices in the mixing channel. It has been shown that when the flow goes from the regime with horseshoe vortices to the flow conditions with two single vortices, the mixing efficiency increases several times. It has been established that the flow conditions and the mixing efficiency largely depend on the volume concentration of particles and their sizes.

In the present study, we report on the results of an experimental study of pressure pulsations in the flow duct of a medium-scale hydrodynamic bench with Francis turbine. In various regimes, integral and pulsation characteristics of the turbine were measured. With the help of high-speed filming, the structure of the flow behind the turbine runner was analyzed, and the influence of this structure on the intensity and frequency of pressure pulsations in the flow duct was demonstrated.

Porous anodic alumina (PAA) membranes represent a widely used and extensively studied template for production of carbon nanotubes (CNT). The PAA–CNT membranes possess a number of unique properties, such as controllable nanotube geometry, size– and chemically–based selectivity as well as high water permeability. In this work, we first propose a combination of gas phase and surface reaction models to quantitatively describe the growth of carbon nanotubes in PAA membranes in a commercial CVD reactor. A complimentary experimental study of CNT formation from ethanol precursor with argon as a carrier gas is performed. A new method for characterizing carbon nanotubes geometry by SEM and TEM image processing of membrane cross–sections is proposed. The simulations show that the carbon growth rate (in nm/min) averaged over the membrane remains constant during the deposition process until the pore diameter becomes relatively small, and rapidly falls to zero after that. The carbon nanotube thickness near the membrane surface is slightly higher than that in the membrane center. The carbon growth rate increases with synthesis temperature and pressure, while it decreases with the argon flow rate. The dependence of carbon growth rate on the ethanol/water flow rate reaches maximum at some intermediate value. These results are supported by the experimental data obtained from SEM/TEM image processing. It is found that the SEM data provide overestimated values of nanotube diameter and thickness in comparison with the TEM data. The obtained results provide new insights into the CNT growth kinetics in nanoporous media, and develop quantitative guidelines for synthesis of CNT–PAA membranes with precisely controlled nanopore geometry. It also validates the combined homogenous / heterogeneous reaction model by comparison with carbon deposition kinetics on a nanometer scale.

Experimental study of forced turbulent convection of water-based nanofluids with nanoparticles of zirconium oxide (ZrO 2 ) was carried out in smooth tubes and channels with wall heat transfer enhancers. Nanopowders with average particle size of 44 and 105 nm were used in the experiments. The Reynolds number ranged from 3000 to 8000. It is revealed that the increments in the heat transfer coefficient and the pressure drop when using nanofluids depend on the surface shape of the channel. It is shown that nanofluids allow reaching thermal-hydraulic efficiency comparable to that of the channels with artificial heat transfer enhancers.

The paper deals with the experimental study of nanofluids boiling on cylindrical heater. The studied nanofluids were prepared on the basis of distilled water and nanoparticles of silicon, aluminum and iron oxides as well as diamond. The volume concentration of nanoparticles varied from 0.05 to 1%. The nanoparticles diameter ranged from 10 to 100 nm, the diameter of the heater was varied from 0.1 to 0.3 mm. It is revealed that the use of nanofluids provides a several-fold increase of the critical heat flux. However, critical heat flux in nanofluids depends on the material and size of nanoparticles as well as on the diameter of used cylindrical heater. It is shown that the critical heat flux increases with increasing the nanoparticles size, while it decreases with increasing the heater diameter. It was revealed for the first time that the critical heat flux depends on the boiling process duration.

We report on the examination of several approaches to simulate computationally the unstable regime of a model Kaplan turbine operating at off-design load. Numerical simulations complemented by laboratory experiments have been performed for a 60:1 scaled-down laboratory turbine model using two Reynolds-averaged Navier–Stokes (RANS) models (linear eddy viscosity model (LEVM), and a Reynolds stress model (RSM), including realizable , k-ω SST, and LRR), detached eddy simulation model (DES), and large eddy simulation model (LES). Unlike the LEVM, the RSM, DES, and LES reproduced the mean velocity components and the intensities of their fluctuations and pressure pulsations well. The underperformance of the LEVM is attributed to the high eddy viscosity as a consequence of an excessive production of the turbulent kinetic energy due to the models’ inability to account for the turbulent stress anisotropy and the stress-stain phase lag, both naturally accounted for by the RSM. This led to a much larger model...

Experimental data have been presented on the influence of silver on the viscosity and thermal conductivity of a dispersion of diamond nanoparticles. A stable dispersion (5 wt %) of detonation nanodiamond particles has been used in the experiments. Silver ions have been introduced electrolytically into the dispersion of diamond nanoparticles. Silver concentration was not higher than 0.05 wt %. It has been shown that the introduction of silver ions significantly affects the thermal conductivity and viscosity of the dispersion.

A computational study of the micromixer form influence on the mixing efficiency and pressure drop in a wide range of Reynolds numbers 1 ≤ Re ≤ 300 was carried out. It was found that as the number of segments increases, the pressure drop and mixing efficiency also increase in the whole range of Reynolds numbers. The obtained results were compared with the similar in the formulation of the problem and the initial conditions one for the T-type micromixer with a direct mixing channel of the corresponding length. The dependence of the relative reduced mixing efficiency on the Reynolds numbers was obtained. It is revealed that the use of micromixers with a complex geometric shape allows the mixing processes to intensify, especially at low Reynolds numbers.

We have experimentally studied the filtration of microsuspensions with added silica (Aerosil) nanoparticles via porous media of variable permeability. The concentration of added nanoparticles in solution was changed from 0.25 to 4 mass % and their average size was varied from 5 to 100 nm. Dependences of the filtration losses of microsuspension on the concentration and size of nanoparticles and the permeability of porous medium variable have been determined.

Absract This work aims to study experimentally the rheology and viscosity of nanofluids based on ethylene glycol, water, and isopropyl alcohol containing single-walled carbon particles (SWCNT). The weight concentration of SWCNTs varied from 0.05 to 1%, the temperature varied within the range from 10 to 50 °C. Sodium dodecylbenzene sulfonate, polyvinylpyrrolidone, and sodium dodecyl sulfate were used as dispersants. All the studied nanofluids were characterized by non-Newtonian rheology, if only the concentration of SWCNTs was not too low. The nanofluids were either pseudoplastic or viscoplastic fluids. With the increasing concentration of SWCNTs, the fluid index decreased, while the consistency factor increased. Moreover, as the CNT concentration increased, pseudoplastic fluids could become viscoplastic. In the general case, the rheology of nanofluids also changed with increasing temperature. An important fact is that the viscosity of the studied nanofluids depends actually on the effective size of the SWCNTs. The greater their effective size, the greater the viscosity. Indirectly, the answer to the question about the reason for this behavior is given by studying the microrheology of these nanofluids. They demonstrate viscoelastic properties of the nanofluids. This behavior is associated with the formation of a solid spatial lattice of nanotubes in the bulk of nanofluid.

In this work, a numerical study of the combustion of pulverized coal in a gas flame is carried out on the basis of the proposed mathematical model of combustion processes, using a nonstationary method for modeling turbulence, complex heat transfer and a reduced mechanism for chemical kinetics. The calculation results show acceptable agreement with the experimental data on the main characteristics of the flame, make it possible to qualitatively correctly determine the structure of the dust and gas flow and derive such parameters as the gas composition, the temperature of particles and gas, the degree of carbon burnout, etc.

The paper presents the results of systematic experimental studies of interfacial tension (IFT) and oil wettability of three different types of rock (dolomite, metabasalt, and sandstone) in nanosuspensions. Nanoparticles of silicon and aluminum oxides were used at the concentration ranged from 0.01 to 1 wt%. It is shown that with increasing NP concentration, the contact angle of an oil droplet resting on a rock in a nanosuspension increases quite essentially (from 33 to 153°). The nanoparticle size and compositional effects on interfacial tension coefficient and contact angle (CA) within a wide range of particle concentrations were systematically studied for the first time. The contact angle oil/dolomite/nanofluid increased from 92 to 151° with decrease in the SiO2 nanoparticle size 50 nm to 5 nm. With an increase in the NP size from 5 to 50 nm, there was a decrease in interfacial tension of about 30%. The first-ever experiments were conducted to study the influence of nanoparticles in water on the oil wettability of various types of hydrophilic and hydrophobic rocks. It is shown that the wettability characteristics of various types of rocks can be controlled by adding minor amounts of nanoparticles of different sizes and compositions to influence the parameters that play a key role in the problems related to oil recovery enhancement during reservoir flooding.

The paper presents the results of systematic measurements of the thermal conductivity coefficient of nanofluids at room temperature. In total, more than fifty various nanofluids based on water, ethylene glycol, and engine oil containing particles of SiO2, Al2O3, TiO2, ZrO2, CuO, and diamond were studied. The nanoparticles volume concentration ranged from 0.25 to 8% and the particles size ranged from 10 to 150 nm. It is shown that the thermal conductivity of nanofluids is not described by the classical theories (Maxwell’s and so forth). The nanofluid thermal conductivity coefficient is a complicated function not only of the particle concentration, but also the particles size, their material, and type of base fluid. Measured thermal conductivity coefficients almost always exceed the values calculated by the Maxwell’s formula, though nanofluids with sufficiently small particles may have thermal conductivity coefficients even lower than those predicted by the Maxwell theory. However, in all cases, the nanofluid thermal conductivity coefficient enhances with increasing particle size. It is convincingly shown that there is no direct correlation between the thermal conductivity of the nanoparticle material and the thermal conductivity of nanofluid containing these particles. The base liquid also significantly influences the effective thermal conductivity of the nanofluid. It has been confirmed that the lower the thermal conductivity of the base fluid, the higher the relative thermal conductivity coefficient of the nanofluid.

We have experimentally studied how the Prandtl number (Pr) of a nanofluid depends on the concentration, size, and material of nanoparticles. The nanofluids were prepared using distilled water and nanoparticles of silica, alumina, titania, and zirconia. The volume concentration of particles was varied from 1 to 8% and their diameters changed from 10 to 150 nm. It is established that Pr values of nanofluids increase with the concentration of nanoparticles. The Prandtl number also significantly depends on the size of nanoparticles and decreases with increasing particle diameter.

The pressure–driven electrolyte transport through nanofiltration membrane pores with constant surface potential or charge density is investigated theoretically. Two approaches are employed in the study. The first one is based on one–dimensional Nernst–Planck equation coupled with electroneutrality, zero current, and Donnan equilibrium conditions. This model is extended to account for interfacial effects by using a smooth approximation of step function for the volume charge density. The second approach is based on two–dimensional Nernst–Planck, Poisson, and Navier–Stokes equations, which are solved in a high aspect ratio nanopore connecting two reservoirs with much larger diameter. The modification of equations on the basis of Slotboom transformation is employed to speed up the convergence rate. The distributions of potential, pressure, ion concentrations and fluxes due to convection, diffusion, and migration in the nanopore and reservoirs are discussed and analyzed. It is found that for constant surface charge density, the convective flux of counter–ions in the nanopore is almost completely balanced by the opposite migration flux, while for constant surface potential, the convective flux is balanced by the opposite diffusion and migration fluxes. The co–ions in the nanopore are mainly transported by diffusion. A particular attention is focused on describing the interfacial effects at the nanopore entrance/exit. Detailed comparison between one– and two–dimensional models is performed in terms of rejection, pressure drop, and membrane potential dependence on the surface potential/charge density, volume flux, ion concentration, and pore radius. A good agreement between these models is found when the Debye length is smaller than the pore radius and the surface potential or charge density are sufficiently low.

The article presents a procedure to calculate fluid pressure losses in hole drilling with units equipped with replaceable core tubes and using non-Newtonian mud fluids. It is found that main hydraulic loss takes place when mud fluid flows in clearing between a drill string and drill hole walls. Numerical modeling has shown that it is possible to reduce hydraulic pressure loss by 76.5–89.0% by increasing drill string diameter by 2 mm. Based on the analytical research results, diamond drill bits and underreamers with the outer diameters of 78.0 and 78.4 mm, respectively, are manufactured for drilling operations in Talnakh ore field.

The experiment investigation of turbulent forced convection of nanofluids with SiO 2 and Al 2 O 3 nanoparticles was carried out. Nanoparticle concentration varied in the range from 0.5 to 2 vol.% in the experiments. The nanoparticle size ranged from 10 to 100 nm. The dependence of heat transfer coefficient and pressure drop from the concentration, size, material of the nanoparticles and temperature was studied. It was shown that adding nanoparticles to the coolant significantly influences the heat transfer coefficient in the turbulent flow regime. It is shown that with increasing nanoparticles concentration, the local and average heat transfer coefficients at a fixed Reynolds number increase. Decrease in heat transfer coefficient with increasing particles concentration may take place at a fixed flow rate. It is shown that, the heat transfer coefficient of the nanofluid in turbulent regime increases with increasing nanoparticles size at a fixed flow rate, while has a certain maximum at a fixed Reynolds number. The effect of nanoparticles material on the heat transfer coefficient and pressure loss has been also demonstrated. It is found that the inlet temperature is another factor having a significant effect on turbulent heat transfer performance of nanofluids.

The paper presents experimental data on the laminar-turbulent transition in the nanofluid flow in the pipe. The transition in the flows of such fluids is shown to have lower Reynolds numbers than in the base fluid. The degree of the flow destabilization increases with an increase in concentration of nanoparticles and a decrease in their size. On the other hand, in the turbulent flow regime, the presence of particles in the flow leads to the suppression of smallscale turbulent fluctuations. The correlation of the measured viscosity coefficient of considered nanofluids is presented.

Flow patterns and mixing of liquids with different viscosities in T-type micromixers are numerically investigated on the Reynolds number range from 1 to 250. The viscosity ratio of the mixing media varied 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 the channel on the viscosity ratio and the Reynolds number are obtained. It is shown that the viscosity ratio has a considerable effect on the flow structure before and after transition from the symmetric to the asymmetric flow pattern. The self-similar behavior of the asymmetric flow pattern is established.

Turbulent flow of nanofluids based on the distilled water with aluminum and silicon oxide particles of different sizes in a cylindrical channel is studied. The results of the measurements of the heat transfer coefficient and the pressure difference are presented. The maximum volume concentration of the particles was not greater than two percents. The dependence of the heat transfer coefficient on the nanoparticle concentration and their sizes and material is studied. It is shown that a considerable increase in the nanofluid heat transfer coefficient, compared with the corresponding value for water, may generally be expected. At the same time, the heat transfer coefficient of a nanofluid depends on the nanoparticle size and material; because of this, under certain conditions the nanofluid heat transfer coefficient can turn out to be lower than that of the baseline fluid. Situations, when this can occur, are established. It is for the first time experimentally shown that the nanofluid viscosity coefficient depends not only on the nanoparticle size but also on its material.

Some results of experimental studies of the vortex-core reconnection phenomenon in the flowthrough duct of a combined-flow turbine were presented. The studies were performed on a medium-scale hydrodynamic test bench, the design of which was maximally similar to real hydroturbines. Using high-speed recording in a regime with a 75% load in a suction-pipe diffuser, the reconnection of a precessing vortex-core with detachment of vortex rings was observed. Aperiodic pressure surges due to the reconnection of a vortex and the formation of vortex rings were experimentally detected.

The slow-flug regime in a mixture of castor and paraffin oils in a T-type microchannel with crosssectional dimensions of 200 × 400 μm has been studied by numerical and experimental methods. The domain of existence of the slow-flug regime in this system has been determined. Dependence of the paraffin-oil slug length on the ratio of flow rates of the mixture components is established. Comparison of the calculated and experimental data shows their good agreement.

A superhydrophobic phenomenon during fluids flow through microchannel due to the presence of the textures on the walls of the channels was considered. A numerical study of fluids flow and mixing in the microchannel at different Reynolds numbers and average roughness sizes has been carried out. The shift in the critical Reynolds number of the transition from the vortex symmetric flow regime to the vortex asymmetric (engulfment) regime towards lower values in the T-shaped microchannels with textured walls was found. The substantially unsteady structures in the straight microchannels with textured walls at Reynolds numbers of about 1000 were obtained.

A spatial mathematical model of the evaporation system using film flows has been developed. A numerical study of several modes of film flow in an evaporation cell at a heater temperature below the boiling point has been carried out. The characteristics of the film flow and the features of the coupled heat and mass transfer processes in the gas-film-metal substrate system have been studied. Good agreement between the calculation and the experiment on the main parameters of the wave motion of the film and the heat transfer characteristics has been obtained.

A mathematical model of heat and mass transfer processes in the combustion chamber of diesel generator sets with valve-inductor generators has been developed. The main characteristics of a diesel generator have been analysed within a wide range of operating modes.

The paper presents the results of an experimental study of oil displacement by distilled water and an aqueous suspension of aluminum oxide nanoparticles. The correlation of extracted oil volume on the flow rate of the displacing fluid is obtained, and the pressure drop during the pumping of the displacing fluid through the rock sample is measured. It has been revealed that the suspension of nanoparticles can significantly improve the extraction of oil from sandstone.

The calculated study of the flow regimes of two-phase oil and water mixture in straight microchannels simulating a pore or crack in the rock formation was carried out. It was shown as a result of the literature survey that all modern, industrially developed methods of the oil recovery from the oil reservoirs is considered as unsatisfactory in all oil-producing countries. The average value of the final oil recovery is varied from 25% to 45%, so, it is easy to count, that residual or unrecoverable oil reserves in the subsoil reach an average of 55-75% of their initial values. Also, it was found, that the use of micro and nanotechnologies in a broad sense is one of the possible and promising ways to solve these problems. A numerical method called «Volume of Fluid» (VOF) was used to simulate the two-phase flows of oil and displacing agents in the considered microchannels. It was proposed to use the dimensionless number, called Regime number, to describe the different flow regimes of oil/water mixture and transitions between these regimes. The plug flow, the slug flow, the parallel flow and the emulsion flow regimes were observed.

This paper presents the results of laboratory tests and numerical simulation of polymer drilling fluids. The influence of the rotation speed on the values of the pressure ratio and cutting transport is studied. The influence of rheological parameters on the efficiency of cuttings transport is investigated.

The work is devoted to experimental and computational studies of the behavior of water drop in a flow behind incident shock wave and verification of calculations on this basis. High-Speed visualization of the water drop interaction with the flow behind incident shock wave was obtained in the experiments at shock wave Mach numbers Ms=1.109–1.34 and Weber numbers We = 208–2260. Conditions consistent with the experiments are simulated in the calculations. The numerical approach is based on the use of the volume of fluid (VOF) method to resolve the phase interface, large eddy simulation (LES) model to describe turbulence, and adapted dynamic grid technology. The structure of the flow near and in the wake of a drop, the features of the flow around a drop, the type of the shape evolution, and the character of the mass entrainment were studied. Comparison of simulation results with experimental data indicates good agreement with the main integral characteristics of the process, i.e. morphology, dynamics, and induction time of droplet breakup.

It was experimentally investigated the nanofluids evaporation rate in this study. The nanofluids were prepared using the distilled water and different nanoparticles. The nanoparticles of aluminium oxide, silicium and zirconium dioxides, as well as the nanodiamonds were used. The average diameters of the particles were as follows: SiO2 – 25 nm, ZrO2 – 105 nm, Al2O3 particles – 43 nm and nanodiamonds – 5 nm. The Simultaneous Thermal Analyzer STA 449 C Jupiter (NETZSCH) was used to carried out the study of the evaporation rates of fluids. The dependence of the evaporation rate on the material of the nanoparticles was investigated. It was found in that study that the evaporation rate significantly depends on the nanoparticles material. Moreover, based on the obtained results it was shown, that the evaporation rate of nanofluids monotonically increases with an increase of nanoparticles volume concentration.

The study of suspensions with aluminum nanoparticles was carried out. Ethylene glycol was used as the base fluid. The mass concentration of Al nanoparticles varied from 2.5 to 20%. The viscosity coefficient of the suspension at different shear rates was measured. The dependence of the viscosity on the concentration of Al nanoparticles in ethylene glycol was obtained. The attenuation of the suspensions was measured. The dependence of the sound speed in suspension on the nanoparticle concentration was obtained. The acoustic parameters of the suspension, such as adiabatic compressibility, acoustic impedance, intermolecular free length, viscous relaxation time, are calculated.

The research presents the numerical modeling findings of the secondary breakup of droplets of coal water slurries containing petrochemicals (CWSP) droplet with the filter cake content of 50 % for different Weber number values. The modeling method of the secondary droplet breakup is based on the VOF method for interface resolution, LES model for describing turbulence, and the technology of adapted dynamic grids. This technology enables the grid to be automatically concentrated in the region of large solution gradients during the calculation. The implementation of such a highly detailed grid allowed resolving secondary droplets with the dimensions down to 15 μm. We established the droplet breakup modes depending on the Weber number ranging from 36 to 342. The structure of the stream behind droplets was studied in detail and the numerical method was tested. The results are in good agreement with the results of known experiments.

Intensification of heat transfer processes is an important and relevant task, and one way to solve it is the use of liquids with various nanoparticles, called “nanofluids.” Therefore, an experimental study of the convective heat transfer of nanodiamonds suspensions in a circular straight pipe was carried out in this paper. Ethylene glycol was used as the base liquid. The concentration of nanoparticles ranged from 0.25 vol.% to 2 vol.%. The Reynolds numbers varied from 5 to 100. The values of the viscosity and the thermal conductivity coefficients of the resulting nanofluids were also measured experimentally. It was found as a result of these measurements, that the dependence of the thermal conductivity on the concentration of nanoparticles is described by the Maxwell equation. The dependence of the nanofluids viscosity coefficient on the nanoparticles concentration was significantly differ from the Einstein equation, it was much higher. It was found as a result of experimental studies of convective heat transfer, that as the concentration of nanoparticles increases, the heat transfer coefficient also increases, and for a maximum concentration, it was 15% higher then for the base fluid.

The experiment-calculated investigation of forced convection of nanofluids based on CuO nanoparticles was carried out. Nanoparticle concentration varied in the range from 0.25 to 2 vol.% in the experiments. The considerable heat transfer intensification was obtained. The power applied to the pump for pumping the nanofluid was measured. A strong influence of the polymer used to stabilize the transport properties of nanofluids was shown. The Newtonian behavior for 0.25%-nanofluid, and non-Newtonian behavior, that described well with power-law model, for all other cases, were obtained. The hydrodynamic description and the model of homogeneous nanofluids are used for modelling. As is shown by the results, such a model satisfactorily describes in some cases the data of full-scale experiment of nanofluids forced convection in laminar flow regimes.

Текст статьи не публикуется в открытом доступе в соответствии с политикой журнала. The results of the modeling of unsteady three-dimensional flows in the hydroturbine ducts of two high-head hydroelectric stations are presented. The flow structure behind the turbine wheel is analyzed and its effect on the frequency and the intensity of unsteady processes in the duct is shown. The individual features and the general tendencies in the behavior of the fluctuation characteristics of both turbines are established.

Anumerical procedure is presented for analysis of pressure pulsations in hydraulic turbines. Results of its use for description of unsteady turbulent flow in the continuous run of a hydraulic turbine are presented. The numerical method is adapted for results of modeling of turbulent unsteady flow in the continuous rune of a high-head HPP. The structure of the flow beyond the impeller and its effect on the intensity of unsteady processes are examined. Results of the analysis are compared with full-scale data. Good agreement is obtained between the computed and experimental results.

The paper presents results of numerical simulation of unsteady three-dimensional flow in the two high-head hydraulic turbines. The numerical technique for calculating of low-frequency pressure pulsations in a hydraulic turbine is based on the DES turbulence model and the approach of rotated reference frame. The paper also presents the analysis of the flow structure behind the runner of the turbines, as well as shows the effect of the flow structure on the frequency and intensity of non-stationary processes in the turbines. Besides, the behavior of the pulsations in the hydraulic turbines was defined. Comparison of the calculation results with the experimental data has shown close agreement between theory and experiment.

Numerical technique for calculating pressure pulsations in the high-head hydro turbines is presented in the paper. The numerical technique is based on the use of DES turbulence model and the approach of “frozen rotor”. This technique is applied for simulating unsteady turbulent flow in a flow path of a high head hydropower plant. The flow structure downstream the runner and its influence on the intensity of non-stationary processes is analyzed. It is shown that the low-frequency pressure pulsations in water turbines are mainly caused by the precessing vortex rope downstream the runner. The vortex dynamics basically determines the pulsational characteristics of turbine operation. It is found that the averaged velocity components of flow downstream the runner can serve as indicators, which characterize the intensity of transient phenomena in the draft tube of water turbine. The comparison of simulation results with the experimental data shows reasonable agreement in the integral characteristics (efficiency, flow rate, power) as well as pulsational characteristics (intensity and frequency) of the flow and turbine operation.

The heat transfer coefficient of a nanofluid in a cylindrical channel under constant heat flux density at the walls is measured experimentally. The studied fluid was prepared based on distilled water and CuO nanoparticles with an average size of 55 nm. To stabilize the nanofluid, a biopolymer was used. The volume concentration of nanoparticles was in the range from 0.25 to 2%. It is shown that the nanofluid is Newtonian at the lowest concentration of nanoparticles, and in all other cases, its rheology is described well by the model of a power-law fluid. A correlation of the dependence of the parameters of this model on the concentration of nanoparticles is obtained. It is found that the presence of nanoparticles greatly intensifies the heat transfer.