Direct absorption solar collectors represent a promising direction for the green processing of light energy into heat, where nanofluids play a crucial role. The properties of the nanofluid are strongly dependent on the characteristics of the nanoparticles dispersed in the base liquid. Furthermore, both the morphology and composition of the nanoparticles are significantly influenced by the method of their production. This study examines the effects of arc-discharge synthesis of carbon nanoparticles on their morphology and composition, as well as on the optical properties, viscosity, and thermal conductivity of the resulting nanofluids. Numerical modeling indicated that helium pressure in the reactor chamber influences the spatial distribution of gas temperature and carbon concentration in nanoparticle formation zones, making pressure a key factor in synthesis control. Experimental studies provided novel insights into how reactor pressure influences the morphology and composition of the nanoparticles. In turn, these synthesized carbon nanoparticles proved effective in nanofluids for direct absorption solar collectors. Comprehensive studies revealed that nanoparticle dispersibility in water and nanofluid stability rely heavily on the presence of C=O and C–O–H bonds on their surfaces. The research demonstrated that carbon nanoparticles maintain effective thermal conductivity and viscosity in nanofluids, which are crucial for solar collector applications. Additionally, optical studies indicated that the high specific surface area and conjugated graphitized structure of carbon nanoparticles enhance photothermal energy conversion, enabling more efficient solar collector designs with smaller geometric dimensions.

In order to research the process of boiling occurring on a porous surface, a model of multiple blocks was developed. The mathematical basis of these blocks is the lattice Boltzmann method in combination with heat transfer equation. The reported complex allows one to obtain the boiling curves for various wall superheats and to find the optimal parameters of a porous heater in terms of heat transfer enhancement. The porous heater structure is specified as a skeleton of square metal heaters located in the lower part of the computational domain. The calculations were performed for the following parameters of the porous heater structure: different number and size of the metal heaters, different distances between them in horizontal and vertical directions, regular and asymmetric packing of the heaters. Using the developed numerical model, parametric studies of the boiling process on porous heaters with different parameters of the porous skeleton were carried out and phase pictures of such a process were obtained. It was shown that the heat transfer coefficient on a porous heater is 3–7 times greater than that on a smooth heater, and depends on the number of heater elements, their size, and location. The results showed a significant advantage of the porous heaters with greater critical heat flux at higher wall superheats compared to that on the smooth surface.

The paper presents the first experimental observation of an atypical phenomena during self-organization of dust particles into a one-dimensional chain structure levitated vertically in the plasma of a DC glow discharge. Using a laser, the third (middle) dust particle was removed from the chain of five particles so that the positions of the remaining particles did not significantly change, and a vacancy occurred in the place of the removed particle. This state of the chain turned out to be very stable, which is confirmed by the observation of the subsequent exchange of places of the fourth and the fifth particles of the chain upon the action of the laser on the forth particle. After the exchange process, vertical positions of all particles (first, second, fourth and fifth) in the chain remained almost the same as before the exchange, and the vacancy at the position of the third particle was preserved. The experimental data and the video record of the observed phenomena as well as the estimates of the plasma parameters are presented. An assumption has been made about the mechanism of the discovered phenomena that at present discharge conditions both the vacancy formation and the dust particles positions exchange are possible due to a strong ion wakes which are formed behind the upstream dust particles of the chain.

A phenomenon of spontaneous expansion of dielectric particles with a decrease in pressure in a vacuum chamber is experimentally studied. There is a certain range of ambient pressure and pressure decreasing rate at which the phenomenon is observed. The experiments show that the phenomenon relates weakly to gas dynamics, influence of wall material and particle surface desorption. It is established that the Coulomb repulsion of charged particles causes this effect.

Абстракт: To study the process of boiling on a solid heater surface, a hybrid model based on lattice Boltzmann method and heat transfer equation is presented. The process of formation and rise of a single bubble during boiling over a single lyophobic zone located on a smooth lyophilic surface was studied. Dependences of the bubble departure frequency and bubble departure diameter on the width of the lyophobic zone and the wall superheat were obtained. It is shown that the bubble departure diameter increases with the width of the lyophobic zone, and the frequency of bubble departure increases with the wall superheat. Based on the obtained data, the optimal size of the lyophobic zone on the lyophilic surface was determined from the point of view of heat transfer enhancement.

The process of boiling on spatially structured surfaces is simulated by a hybrid model based on Lattice Boltzmann Method and heat transfer equation. The model permits to study heat transfer at boiling in a wide range of surface superheats for different surface structural characteristics. The regimes of natural convection, nucleate boiling, and transition to film boiling are studied. The boiling curves for the surfaces with different structural and wetting properties are obtained. It was shown that the onset of nucleate boiling occurs at lower wall superheat on the structured surfaces than that on the smooth surface. However, at high wall superheats the heat flux and the critical heat flux at modified surfaces are lower. It was obtained that special modification of both structural and wetting properties of heat exchange surface permits to obtain higher removal heat flux as well as higher critical heat flux.

A self-consistent numerical model is presented in which a self-consistent spatial distribution of plasma potential is calculated near isolated dust particles whose shape represents an ellipsoid of revolution. In this model, self-consistent electric plasma potential is calculated with the help of Legendre polynomial expansion of a spatial space charge, while ion trajectories are calculated in the mean field approximation. This article demonstrates a large-scale study of self-consistent distributions of space charge density and plasma potential in the presence of an external electric field. The dependencies of “the ion cloud–dust particle” system on various dusty plasma parameters are calculated. The parameters are dust particles shapes and sizes, the external electrostatic field strength, and the ion mean free path. The dependencies of the dipole moment, wake local maximum, and position of the wake local maximum on these parameters are reduced to a simple analytical expression.

This paper describes a numerical study of the equilibrium parameters of a one-dimensional chain consisting of three dust particles levitating in the electric fields of a gas-discharge plasma. A numerical model is considered in which the movement of dust particles is simulated with account for the action of the Coulomb repulsion force, external electric field, gravity, electrostatic force induced by a plasma space charge, and ion drag described analytically. The spatial distributions of the plasma space charge are compared with a potential around dust particles and the equilibrium structural parameters of a dust chain, depending on the fact whether the ion drag is taken into account analytically or not. It is shown that, when the ion drag is taken into account analytically, the dust chain as a whole is displaced in the direction of the ion flow. In this case, the distances between the dust particles turn out to be smaller than in the case where the ion drag is neglected.

In the current paper a numerical study of the forces acting of a one-dimensional chain of three dust particles levitating in the near-electrode layer of a gas discharge plasma is presented. In the described model dust particle motion is calculated in consideration of the action of gravity, external electric field, the Coulomb repulsion and the force induced by plasma space charge. The dependences of the dust particles charges and their position in space on the mean value of external electric field were calculated. The investigation showed the effect of discharging dust particles in the chain due to ion focusing. The spatial distribution of forces acting on the dust particle chain has been studied. It is noted that the Coulomb repulsion force relative to the center of the chain loses its symmetry with an increase in the mean electrostatic field. It is shown that the displacement of a chain of dust particles is determined by the force induced by the plasma space charge.

A model of the polarization of dust particles with trapped ions in an external electric field is presented. It is based on the self-consistent solution of the integral balance equation for trapped ion density and Poisson equation for the electric potential. It is shown that, in a low collisional regime, trapped ions form a spread shell with a maximum located at some distance from thecharged dust particle proportional to the ion Debye length. The estimated polarizability of dusty "quasiatoms" is very high anddepends on the strength of the external electric field due to the field ionization of trapped ions. With increase in the electricfield, the dusty "quasiatom" loses their trapped ions from far orbits due to the field ionization. The radius of the dusty "quasiatom" ionic shell becomes smaller, and the coefficient of polarizability decreases.

This paper presents a numerical study of the structural parameters of a one-dimensional chain of three dust particles levitating in the near-electrode layer of an rf discharge or in the stratum of a dc discharge. The model considers the motion of dust particles under the action of gravity, external electric field, the Coulomb repulsion, and the electrostatic force from the space charge surrounding the dust particles. Particular attention is paid to the effect of plasma polarization around dust particles and the wake formation under the action of the external electric field. Calculations showed that the charge of the first dust particle in the chain and the total charge of the entire chain, as well as the length of the chain, grow linearly with the external electric field strength. Obtained data are in qualitative agreement with the experimental and numerical data presented in the literature. It was shown that for a certain large value of the external electric field, the charge of the third dust particle is the smallest of all the particles in the chain. It was found that with an increase in the mean value of the external electric field, the chain of dust particles is displaced as a whole in the direction opposite to the action of the electrostatic force on them.

To study the processes of boiling on a smooth surface with contrast wettability, a hybrid model was developed based on Lattice Boltzmann method and heat transfer equation. The model makes it possible to describe the phenomena of natural convection, nucleate boiling, and transition to film boiling, and, thus, to study heat transfer and the development of crisis phenomena in a wide range of surface superheats and surface wetting characteristics. To find the optimal configuration of the biphilic surface, at the first stage a numerical simulation was carried out for a single lyophobic zone on a lyophilic surface. The dependences of the bubble departure frequency and the departure diameter of the bubble on the width of the lyophobic zone were obtained, and its optimal size was determined. At the next stage, the boiling process on an extended surface was studied in the presence of several lyophobic zones of a given size with different distances between them. It is shown that in the region of moderate surface superheat, the intensity of heat transfer on biphilic surfaces can be several times (more than 4) higher compared to surfaces with homogeneous wettability. Based on numerical calculations, an optimal configuration of the biphilic surface with the ratios of the lyophobic zones’ width of the order of 0.16 and the distance between the lyophobic zones in the range of 0.9–1.3 to the bubble departure diameter was found.

The paper presents new numerical results on the behavior of plasma parameters around an isolated chargeddust particle under the action of the external electric field. For the first time, the model takes into account thedependence of mean electron energy on the reduced electric field strength. As a result of the calculations, thedependencies of self-consistent spatial distributions of the electron and ion densities and electric potentialaround the dust particle on reduced external electric field strength were obtained. These distributions wereanalyzed through the expansion into Legendre polynomials. The processes of ion focusing wakeformation behind the dust particle were studied. The dust particle charge and the dipole moment of the“ion cloud - dust particle” are calculated for different values of the reduced electric field and ion mean freepaths. It is shown that in the determination of electron density spatial profile and the dust particle charge thedependence of electron temperature on electric field strength plays a significant role. Key words: dusty plasma, dust particle charging, dipole moment, wake, plasma polarization.

The formation of a 1D chain-like structure of dust particles in a low-temperature argon plasma was studied. A new numerical model for calculation of the self-consistent spatial distribution of plasma parameters around a chain of dust particles was presented. The model described the motion of positively charged ions in the electric potential of several negatively charged dust particles, taking into account the action of an external electric field. The main advantage of the model was that the charges of the dust particles and the interparticle distances were determined self-consistently. As a result of numerical simulations, the dependencies of the spatial distributions of the plasma parameters (the densities of electrons and ions and the self-consistent electric potential) near the dust particles chain on the strength of the external electric field, an external force acted on the last particle, and the mean free path of the ions was determined. The obtained results made it possible to describe the process of the formation of chain-like structures of dust particles in discharge plasma.

The nonlocal self-consistent model for the low temperature plasma parameters in a glow discharge positive column is presented. The model implies relaxation method for the solving of the nonlocal Boltzmann equation for electron energy distribution function, continuity equation for ions distribution and Poisson equation for radial electric field. Calculations are provided for a cylindrical discharge tube used in the Plasma Kristall-4 experiments for neon as a plasma forming gas for the gas pressures of 30-70 Pa and discharge currents of 0.5-2.5 mA. Axial electric field strength, electron temperature and electron density are calculated as functions of the discharge current and the gas pressure. The results are in good agreement with the data provided by other authors.

A low frequency (100 kHz) ferromagnetic enhanced inductively coupled plasma (FMICP) source has been developed to obtain a large volume of dense Cl2/Ar plasma. The influence of chlorine addition on the FMICP parameters was investigated both experimentally and numerically using a global (volume averaged) model of Ar/Cl2 discharge. Radial distributions of the positive ions flux as well as the values of FMICP voltage were measured at a fixed FMICP current of 10 A for molecular chlorine concentrations of 0–4 vol%. Plasma species densities were calculated for various values of chlorine content of 0–4 vol% and absorbed power of 500–2000 W. The calculations showed that chlorine ion density exceeds argon ion density even at low chlorine content of about 0.5 vol%. While experimentally measured discharge voltage and power increased almost linearly up to 3 times with chlorine addition, the experimental and numerical data on plasma density demonstrated only a weak dependence on the discharge power. Thereby, at a fixed FMICP current the discharge power adjusts itself to keep plasma density at the same level even despite a significant change in plasma composition.

Low-frequency inductive discharges with enhanced magnetic coupling are considered to be a promising solution for large-scale plasma processing. Here we present the results of experimental and numerical investigation of a distributed ferromagnetic enhanced inductive discharge in argon/chlorine mixture, performed for a large discharge chamber with a volume of about 200 liters in the pressure range of 0.1-10 Pa at the driving frequency of 100 kHz.

A ferromagnetic-enhanced inductively coupled plasma source consisting of a narrow U-shaped gas discharge tube and a large chamber has been investigated. The effect of chlorine admixture with argon on the discharge properties was studied both experimentally and numerically. The discharge electric field strength and gas temperature were measured in chlorine concentrations of 0%–4% and discharge current densities of 0.2–1.5 A cm−2. The appearance of discharge instabilities was noticed at current densities below 1 A cm−2. A global model of Cl2/Ar discharge was modified and used to describe basic features of plasma in the U-shaped tube. The plasma composition, energy balance terms and electric field strength values were calculated, and satisfactory agreement between the experimental and numerical data was found. A possible approach to decrease the U-shaped tube's power losses and the mechanism of the instabilities' formation are discussed.

Pool boiling on a solid surface is simulated with a hybrid model based on lattice Boltzmann method and heat conduction equation developed for modeling of multiphase flows with phase transitions. Special attention is paid to the effect of the surface wettability with the liquid-solid contact angles in the range from 67 degrees to 110 degrees. The evolution of the vapor phase and heat transfer during boiling were analyzed for different values of the wall superheat and the contact angles. It was shown that the model permits one to reproduce the basic features and characteristics of the boiling including nucleation, bubble dynamics, and transition of nucleate boiling mode to film boiling regime. Moreover, the simulation results are in a good qualitative agreement with experimental observations of the influence of the lyophobic surfaces on the local boiling characteristics, heat transfer, and critical heat fluxes. In particular, the calculated boiling curves show that at low wall superheat the heat transfer rate increases with an increase of lyophobicity. At the same time, in the region of high wall superheat the heat transfer rate and the critical heat fluxes increase with the decrease of the wetting contact angle.