Vol 52, No 5 (2018)

An exact solution of Navier–Stokes equations for laminar flows of a viscous incompressible liquid under constant pressure is presented. The solution describes the balance of nonlinear viscous forces and inert effects in a liquid. It shows that the exact solution is a linear superposition of the shear flow and vertical rotation of the liquid caused by the nonuniform boundary conditions on a free boundary. Accounting for the inertia forces allows studying the delamination of the velocity field (counterflows) by the vertical coordinate depending on the horizontal velocities and spatial acceleration. The corresponding sets of algebraic inequalities are presented.

The results of mathematical modeling of metal electrodeposition in reactors with three-dimensional flow-through electrodes in a limiting diffusion current mode taking into account the nonsteady-state state of electrode and electrolysis were presented. An algorithm was developed for calculating the overall density of the current that passes through the electrode, which supports the electrode work in the limiting diffusion current mode throughout the metal electrodeposition process. A numerical study was performed to investigate the changes in the main characteristics of the process and electrode with time for the model electrochemical system.

The use of the electromembrane method for the purification of chromium plating electrolytes from cationic impurities (iron, copper, etc.) by three approaches are described. The first variant is based on the removal of these ions during their migration from the solution to be purified into a catholyte through a cationexchange membrane. The second variant is a transfer of chromate anions from a contaminated solution into the anolyte through an anion-exchange membrane. In the third method for the recuperation of chromic acid, accumulated in a recovery bath, it is proposed to use the immersed electrochemical module, combining the processes of concentration and purification from impurities, instead of evaporation.

The problem of the minimal gain of the entropy of a system of heat transfer with a defined heat load and heat transfer surface during the change of the phase state of one of the contacting refrigerants is considered. The laws on the change of temperatures of hot and cold flows corresponding to the optimal solution are found. The possibilities of implementing the optimal heat transfer in a stationary system are considered.

A previously developed factorial analysis procedure is applied to one of the distributed models of the kinetics of bulk and suspension methyl methacrylate polymerization containing 15 empirical constants. It is shown that in the region of the initial conditions of carrying out the process, only six empirical constants are necessary for the complete empirical description of the process to an acceptable degree of accuracy. The consequences of this result are discussed.

In this paper, we have studied the patterns of the HCl absorption by calcium-containing sorbents under countercurrent gasification in the filtration combustion mode. Experiments have been performed in a vertical batch reactor at temperatures of up to 1200°C. The following sorbents have been employed: calcium oxide and calcium carbonate (in the form of chalk and marble). The efficiency of HCl absorption by sorbents has been estimated. The completeness of HCl uptake has been shown to be limited by partial hydrolysis of the calcium chloride formed in the high-temperature zone.

A new approach to calculation of the thermohydraulic efficiency of channels with different methods of intensification including small-size chaotic packings was considered, and the corresponding expressions were obtained. For this, the Kirpichev, Antufiev, and Spalding energy coefficients, thermal efficiency of the process in the channel, and cell model of the flow structure were used. Expressions were given for calculating the temperature profiles, thermal efficiency, hydraulic resistance of channels with chaotic elements, and average Nusselt number. The results of calculations agreed with the experimental data obtained on an experimental stand with a tube-in-tube heat exchanger and oil–water heat transfer agents. Examples of calculations were given for several types of metal packing, and conclusions were drawn about the most effective designs. It was recommended to use metal chaotic packing in channels for liquids with increased viscosity because the laminar flow of the heat transfer agent changes to the turbulent one, and the heat transfer coefficient substantially increases in this case.

Phase equilibria in sections of the phase diagram of the sodium-acetate—sodium-formate–water ternary system with component ratios of NaCH₃COO : NaHCOO varying from 3 : 1 to 1 : 3 are studied, and the anti-icing properties of the compositions based on these salts are investigated. Polythermal sections of ice crystallization and the ice-melting ability for each of the prepared compositions are calculated from the experimental data. The formulation with a 1 : 1 ratio of the considered salts has a eutectic temperature of‒22°C, which is 4–6°C lower than the eutectic temperatures of systems based on the individual salts. This formulation displays a high ice-melting ability and can be recommended for use as a de-icer in airports.

Intermetallic alloys based on Ti₃Al with strengthening additives of refractory compounds and MAX phases of various compositions have been obtained by the powder metallurgy method. Their structure and microhardness were studied. Optimum conditions were determined (sintering temperature was 1400°C, sintering time was 1 h, B₄C additive was 15 wt %), which made it possible to obtain a composite material with the best mechanical properties.

The processes of obtaining fine-grained corundum with a given crystal size and habit are considered. It is shown that thermocouple treatment in aqueous supercritical fluid allows one to obtain corundum from various precursors in a wide range of crystal sizes (0.01–500 μm). Powders with a crystal size in the range 20–500 μm can be obtained directly from hydrargillite prepared in the course of the Bayer Process. The size and habit of the crystals are determined by the parameters of the thermocouple treatment and properties of the process activators used. Powders with a crystal size falling in the range 30–1000 nm can be obtained by using synthesized or commercially available boehmite as a precursor for the thermocouple treatment. The crystal habit is determined by the habit of the boehmite crystals used. New methods of boehmite synthesis have been developed that allow one to obtain nonaggregated crystals with a size of 10 nm with a narrow distribution curve.

We propose creating a solar cell on the basis of a nanocomposite medium consisting of am electrochemically fabricated porous silicon matrix with copper embedded into its pores and oxidized to Cu₂O and a conductive transparent ITO film deposited by an extraction-pyrolytic method. The obtained structure with two electron–hole junctions represents, according the ratio between semiconductor band gaps, a cascade version of the solar cell with a nonconcentrated sunlight photoconversion efficiency of 7.12%.

Issues of application of “green chemistry” principles to the extraction and separation of components of liquid mixtures have been discussed. In particular, quantitative characteristics of the interphase distribution of a number of aromatic acids in extraction systems based on polyethylene glycol and sodium sulfate have been determined. It has been shown that these systems, which do not contain components that are toxic or pose a fire hazard, are promising for the effective extraction of aromatic acids from natural and technogenic products.

The possibility of using a catalyst system based on hydrogen peroxide and formic acid for the oxidative desulfurization of nonhydrotreated vacuum gas oil has been explored. Conditions for the effective extraction of oxidized sulfur compounds from nonhydrotreated vacuum gas oil have been selected. The effect of oxidation and thermolysis conditions on the oxidative desulfurization process has been studied, and a 44% decrease in the total sulfur content in nonhydrotreated vacuum gas oil has been achieved.

The effect of machining conditions on the scandium leaching effectiveness from the wastes of wet magnetic separation of iron–titanium magnetites in sulfuric acid solution has been studied. It has been shown that the degree of recovery of scandium into sulfuric acid solution linearly increases with an increase in the degree of amorphization of specimens of wastes of wet magnetic separation.

The problem of treatment of the dump of Khovu-Aksy with conversion of arsenic into a storable nontoxic sulfide form was studied. The optimum conditions were developed: annealing of sludge in a mixture with sodium carbonate, water leaching from the cake stub, and precipitation of arsenic in sulfide form from solution.

We studied the conditions for separating rhenium and polyanions (molybdenum and tungsten) by selective extraction of rhenium from the phase of saturated gel-type strongly basic anion exchanger by tertiary amine solution. Rhenium passes quantitatively into the organic phase under both dynamic and static conditions. The optimal parameters of this method of extractive desorption of rhenium are designed, which ensure complete removal of polyanions and other accompanying impurities. In order to make rhenium further pass into the aqueous phase, the extractant is treated with ammonia solution. Ammonia–salt mixtures are recommended to be used for desorption of molybdenum or tungsten polyanions from the strongly basic anion exchangers.