Vol 55, No 3 (2017)

A numerical study of a laminar mixed convection problem in a ventilated square cavity partially heated from bellow is carried out. The fluid in the cavity is a water-based nanofluid containing Cu nanoparticles. The effects of monitoring parameters, namely, Richardson number, Reynolds number, and solid volume fraction on the streamline and isotherm contours as well as average Nusselt number along the two heat sources are analyzed. The computation is performed for Richardson number ranging from 0.1 to 10, Reynolds number from 10 to 500, and the solid volume fraction from 0 to 0.1. The results show that by adding nanoparticles to the base fluid and increasing both Reynolds and Richardson numbers the heat transfer rate is enhanced. It is also found, regardless of the Richardson and Reynolds numbers, and the volume fraction of nanoparticles, the highest heat transfer enhancement occurs at the left heat source surface.

The work is devoted to numerical simulation of the flow around blunt bodies in supersonic streams containing solid polydisperse particles. We consider a widespread variant of two-parameter gamma function for the particle size distribution. To account for interparticle collisions and interactions of particles with a streamlined surface, the direct numerical simulation of collisional dynamics for the dispersed phase was used. The local particle size distribution near the streamlined surface is studied. The screening effect due to the interaction of the incident and reflected from the surface particles is analyzed. It is noted that the energy flux from a polydisperse admixture to the streamlined surface can be represented with sufficient accuracy by equivalent impact of monodisperse admixture.

Stationary nonisothermal flow of viscous Newtonian liquid in a flat channel filled with porous material is studied. The Brinkman equation is used as a motion equation. It is assumed that viscosity depends on temperature. The energy equation is denoted using a single-temperature model. Dissipative heat emissions are accounted. The problem is solved for temperature first-order boundary conditions.

With the kinetic equation, the phenomenon of convection of electron gas in metals is described and the drag force, undergone by the convective flow of electrons, is calculated. As a result of the theory, the coefficient of volume expansion of the gas of free electrons, β_e, is numerically estimated.

A model is developed of a flat wall probe, accounting for all the transition processes: convective motion, diffusion, and mobility. Computer modeling is performed and the current distributions over the probe surface obtained. The influence of the border and edge effects on probe current are investigated. A set of current–voltage characteristics within the ranges of the characteristic parameter variation sufficient for the practice is obtained.

For the first time, the ion distribution function over energies and directions of the motion for He+ in He and Ar+ in Ar is measured at the arbitrary value of the electric field by the method of the plane onesided probe. The experiment is carried out under conditions when the ion velocity acquired at the mean free path is on the order of and larger than the average thermal velocity of atoms and resonance recharging is the dominating process in plasma. The obtained results make it possible to conclude that, in independent gas discharge plasma, even at moderate fields where E/P = 10–20 V (cm Torr), the ion distribution function can have noticeable anisotropy and can strongly differ from the Maxwellian distribution.

Power-law and exponential asymptotics of distribution functions are analyzed based on the Ornstein–Zernike equation. The correlation length at the critical point is shown to remain finite and, therefore, the partition function has no singularity at this point.

The embedded atom model (EAM) potentials are proposed, enabling the description of liquid lead and bismuth under conditions typical of shock compression. The potentials reported earlier to describe metals under pressures close to normal and experimental data on shock compression are used. The contributions of collective electrons to energy and pressure are taken into account. Series of models are constructed of 2048 or 2000 atoms in a basic cube at compression ratios Z down to 0.5 of the initial volume under pressures up to 280 GPa and temperatures up to 24 850 K. These potentials give an adequate description of liquid lead and bismuth in these conditions. The thermodynamic properties of the metals at Z = 1.0–0.5 and temperatures up to 20000 K are calculated and presented in tables. The cold pressures for states at a temperature of 298 K are evaluated. Using the embedded atom potential of lead, the shock adiabat going from any initial state can be calculated. These calculations are performed for initially liquid and porous lead and bismuth.

A novel effective method of distinguishing between phonon and magnetic contributions into the total resistivity of 3d metals is presented. The method allows for the nonlinear character of interatomic forces and their change with temperature. Obtained results are important for quantitative estimates of the magnetic properties of ferromagnetic materials, including the nanostructured. This is illustrated by a calculation of the temperature behavior of s–d exchange interaction energy in 3d metals and by description of the temperature dependence of the resistivity of a one-threaded ferromagnetic nanowire made of Ni.

Specific features of the heat transfer in nanostructures and methods of their investigation are discussed. Phonon heat conduction that is characteristic of semiconductors and insulators is considered. In nanostructures, the Fourier law is violated and the methods of classical theory of heat conduction are inapplicable. Analysis of the physics of heat-transfer processes has shown that the heat conduction of nanostructures depends on the shape and size of the sample, properties of its surface, and direction of the heat flow with respect to the nanostructure geometry. This fact has led to the development of radically new approaches to the determination of thermal conductivity of solids on the nano- and micrometer scales. Therefore, main attention is paid to the review of existing methods for finding thermal conductivity of nanostructures and the results of its theoretical and experimental determination. Various models of heat transfer in nanostructures are presented. The knowledge of statistical thermodynamics, kinetic theory, and solid-state physics is fundamental for this field of thermal physics.

The results from studies of an electric discharge between a metal cathode and liquid anode at atmospheric pressure are presented. We investigate the discharge shape, the plasma emission spectrum, the electron concentration and temperature, and the molecule temperature; we analyze the continuous emission in the plasma spectrum and perform infrared thermography.

By means of the calorimetric method, we investigate the LaM₂NiMnO₅ (M—Li, Na, K) nickelitemanganite heat capacities within the range of 298.15–673 K. For the studied compounds, within the stated temperature range, we reveal the λ-like effects respective to the second kind phase transition at 323 and 498 K for compounds containing Li, 323 K and 523 K for compounds containing Na, and 448 K for those containing K. Taking into consideration the phase transition temperatures, we derive the equations of the temperature dependence of the compound heat capacity. On the basis of the experimental values of the heat capacities as well as of the calculation data on the nickelite-manganite standard entropy, we calculate the temperature dependences of the heat capacity, the entropy, the enthalpy, and the reduced thermodynamic potential.