Vol 85, No 1 (2023)

The intensity of acoustic radiation and the characteristic widths (depending on the radii and charges of the drops) of the frequency ranges in which the radiation falls have been calculated for charged droplets of convective clouds and near-ground fogs, which are immobile in the superposition of gravitational and electric fields. The calculations have been carried out using the methods of classical mathematical physics taking into account two small parameters: the dimensionless oscillation amplitude and the equilibrium spheroidal deformation of a charged droplet in an external electrostatic field. All calculations have been performed using the model of an ideal incompressible electroconducting liquid. It has turned out that the acoustic radiation from clouds and fogs occurs in the ultrasonic frequency range, while the acoustic radiation of large rain-drops is in the acoustic range audible to the human ear. The boundary between the ultrasonic and sonic radiations is determined by droplet sizes, electric field strengths (in a small vicinity of the droplets), and the values of interfacial tension coefficient.

The properties of a mixed fullerenol (C60(OH)20)/bovine serum albumin film on a water surface depend on the method of film preparation. When the components are adsorbed from a solution of their mixture, the properties of such a film are mainly determined by the protein, which is more surface-active. At the same time, the compression isotherms of such films noticeably deviate from the results obtained for the films of the pure protein. When one of the components is adsorbed on a surface that contains a film of the other component, a synergistic effect is sometimes observed. In this case, the surface pressure and the dynamic surface elasticity modulus are markedly higher than their values for solutions of individual components due to strong interactions between the components and the formation of fullerenol/protein complexes in the surface layer.

A mathematical model has been presented for the formation of the conformational structure of chain units in a polyelectrolyte adsorbed on a flattened conducting charged nanospheroid polarized in an external electric field, which harmonically varies at a frequency much lower than the plasma frequency of the nanospheroid metal. Molecular dynamics has been employed to study the rearrangements in the conformational structure of uniformly charged polypeptides adsorbed on the surface of the oppositely charged flattened gold nanospheroid in an external alternating electric field, the strength vector of which varies along the rotation axis of the nanospheroid. One-dimensional density distributions along the rotation axis, as well as radial distributions, have been plotted for atoms of the polypeptides adsorbed on the nanospheroid surface. At a low temperature, a narrow ring-shaped polyelectrolyte fringe is formed in the equatorial region of the flattened metal nanospheroid, and the fringe density increases with the total charge of the nanospheroid and the number of charged units in polyelectrolyte macrochains. At a high temperature, the formed narrow macromolecular ring periodically shifts along the rotation axis of the nanospheroid with redirections of the polarizing electric field vector. The amplitude of the shifts increases with a decrease in the total charge of the nanospheroid and an increase in the fraction of charged units in a polyelectrolyte.

Abnormal changes have been found in the viscosity of aqueous poly(vinyl alcohol) solutions with different concentrations (1–8%) exposed to UV irradiation for 0–60 min. A molecular mechanism of this phenomenon has been proposed based on the assumption of a rearrangement in the hydration shells of the functional groups of poly(vinyl alcohol) as a result of changes in the environment under the influence of UV irradiation.

The article presents the results of experimental studying evaporation of water and nanofluid droplets on the surfaces of various materials. Plates made of materials with significantly different thermal conductivity coefficients have been used as substrates: copper (λ = 401 W/m °С), Teflon (λ = 0.25 W/m °С), and extruded foamed polystyrene (λ = 0.03 W/m °С). In the experiments, the evaporation of water and nanofluid droplets with a volume of 5 μL has been considered at a constant temperature and humidity of the ambient air. A nanofluid (a mixture of water with gold nanoparticles) has been prepared by laser ablation. The concentration of nanoparticles in the nanofluid is about 0.1 wt %. Infrared thermography has been employed to determine the average temperatures of evaporating droplet surfaces. The results obtained have shown that, for all studied materials, the surface temperature of evaporating water droplets is higher than the temperature of adiabatic evaporation. Therewith, the lower the thermal conductivity coefficient of a substrate material, the lower the surface temperature of the droplet and the longer the time of its evaporation. The performed experiments have shown that the minimum temperature of nanofluid droplets is lower than that of water droplets, and the evaporation time of nanofluid droplets is longer than that of water droplets on the corresponding surfaces.

This paper aims to analyze the thermal characteristics, entropy production, flow velocity and Bejan number profile for immiscible nature of micropolar and Newtonian viscous fluid within a channel. Here, the authors emphasize the influence of thermal radiation and oriented magnetic field on the thermal profile and entropy generation of two different types of non-miscible and incompressible micropolar and Newtonian fluids in a channel. The viscous dissipation and thermal radiation effect are also considered in the thermal energy equation. In this work, the entropy production is analyzed within a channel due to oriented magnetic field and thermal radiation. A constant pressure gradient acts on the entry zone of flow domain and static walls of the channel are isothermal. In this problem, we tried to simulate thermal radiation in energy equation by adopting the Rosseland’s diffusion approximation. According to geometrical configuration of the problem, the conditions of no-slip at the walls of the channel and continuity of thermal exchange, microrotation, shear stress, flow velocity and heat flux at the interface of immiscible fluids are used. The governing equations for the flow of immiscible fluids are solved by reliable technique and exact solution for thermal characteristics and flow field are evaluated. The mathematical results of thermal profile and flow characteristics are used to obtain the Bejan number profile as well as the entropy production number profile. The influence of various thermo-physical governing parameters such as radiation parameter, Reynolds number, inclination angle parameter, viscous dissipation parameter, micropolarity parameter and Hartmann number, which describe the physical significance of the present model, on the flow and thermal characteristics of the model are discussed graphically. The newly obtained results of this study are verified with previous published results.