The paper considers the evaporation of droplets consisting of a mixture of liquids with different boiling points. The change in the component concentration in a solution over time is a process that takes place in many technological applications. This paper presents the results of direct measurements of the average concentration in suspended droplets using a capacitance method over a wide range of surrounding airflow temperatures and velocities. To measure the dielectric permittivity (and, consequently, the concentration) of a binary liquid, a coaxial capacitor probe connected to a high-frequency generator was used. A change in the droplet composition leads to a change in the capacitance of the probe and the frequency of the generator, which allows real-time registration of concentration. Drawing on the example of aqueous solutions of acetone, methanol, and ethanol, it is shown that under similar environmental conditions, the evaporation processes are identical and independent of their past history. The study has been conducted jointly with an analysis of the variation in droplet diameter, which has provided an opportunity to evaluate the mass loss from the droplet surface and to establish a criterial correlation dependent on the Nusselt number. To generalize experimental data with differing airflow temperatures, it is necessary to use a combination of dimensionless criteria including Reynolds, Prandtl, Fourier, and Kutateladze numbers. Within a wide range of temperature and airflow velocity parameters, sufficiently accurate generalizing correlations have been obtained, although different for acetone and the two types of alcohol. For complete data generalization, one must consider not only the environmental parameters but also the processes occurring inside the droplet. One of criterion, which determines the relative role of molecular momentum transfer and mass transfer of the impurity in the droplet volume under consideration, is the Schmidt number. The introduction of this number into the previously used complex has allowed reaching a good generalization of all experimental data.
Based on the theory of the thermodynamic equilibrium in a system of quantum vortices in superfluids in the presence of a counterflow, the influence of a vortex tangle on various thermodynamic phenomena in quantum liquids is studied. Using the early calculated partition function we study some of the properties of He II related to counterflow, such as the distribution of vortex loops in their length, the suppression of the superfluid density ρ _s and the shift T_λ. Good agreement with the early obtained results is a fairly strong argument in favor of the point of view that the gas of string-like topological excitations can indeed be considered as a additional kind of quasi-particles having the inner structure at high temperatures, especially near the phase transition. The application of the developed formalism to the theory of quantum turbulence is briefly discussed.
Flat surfaces with different patterns of hydrophobic spots were employed for experimental investigation of boiling heat transfer. In one case, hydrophobic spots were created on a smooth copper surface and on a surface coated with arrays of micrococoons from silicon oxide nanowires by vapor deposition of a fluoropolymer. In the second case, a hydrophobic coating was deposited on heater surfaces with cavity microstructures formed by laser ablation and chemisorption of fluorinated methoxysilane. Water under saturation conditions at atmospheric pressure was used as the working liquid. The temperature of the heating surface was varied from 100 to 125 °C, and the maximum value of the heat flux was 160 W/cm2. Boiling heat transfer on the test biphilic surfaces was significantly (up to 600%) higher than on non-biphilic surfaces. Surface texture, the shape of hydrophobic regions, and the method of their creation tested in this study did not show a significant effect on heat transfer. The boiling heat transfer rate was found to depend on the size of hydrophobic spots, the distance between them, and hence the number of spots. The highest heat transfer efficiency was detected for the surface with the largest number of hydrophobic spots. After long-term experiments (up to 3 years), the heat transfer coefficient on the obtained surfaces remained higher than on the smooth copper surface. Biphilic surfaces with arrays of cavities formed by laser ablation turned out to be the most stable during prolonged contact with boiling water.
The model of a DC glow discharge with metastable argon atoms and dust particles based on the Boltzmann equation for the electron energy distribution function (EEDF), dust particle charging, and balance equation for metastable argon atoms is presented. The processes of direct and stepwise electron impact ionization, metastable-metastable collisions, and recombination of electrons and ions on the dust particle surface and discharge tube wall are taken into account. The results show that the densities of metastable argon atoms and dust particles are in strong correlation, and both sufficiently influence gas discharge parameters.
The present paper aims to study the plug flow of immiscible liquids when the dispersed phase exhibits non-Newtonian properties. Plug formation regimes were studied both for the non-Newtonian dispersed phase case and three sets of Newtonian liquids with different viscosities. Plug length was measured and compared for various flow rates of the continuous and dispersed phases. It was shown that plug length could be dramatically increased by using non-Newtonian liquid as the dispersed phase.
