Search

A comprehensive interdisciplinary study is performed for 12 polymers promising for the fabrication of membranes for extracorporeal membrane oxygenation based on them by methods of gas permeability, wetting, piezoelectric microweighing, and direct biomedical methods for determining hemocompatibility of whole blood from healthy donors. It is found that trimethylsilyl-substituted polytricyclononene, polyhexafluoropropylene, and semicrystalline polyphenylene oxide are the best polymer materials for the diffusion membranes of oxygenators. It is shown that traditional approaches that associate the surface properties of polymers (water wettability, plasma protein adsorption, energy characteristics of surfaces) with their hemocompatibility do not provide precise correlations with the biomedical methods based on the analysis of the changes in the shape of blood cells as a result of adhesion on the surface of the polymer. The complexity of the mechanism of interaction of the surface of polymers with blood also does not allow for clear structure–property correlations traditional for membrane gas separation. The directions of further research in this area are defined.

Gas permeation properties of three highly permeable perfluorinated polymers (polyhexafluoropropylene (PHFP), amorphous Teflon AF2400, and polyperfluoro(2-methyl-2-ethyl-dioxole-1,3) (PPFMED)), which are promising materials for the dense thin layer of hollow fiber membranes for extracorporeal membrane oxygenation have been studied using nitrogen, oxygen, and carbon dioxide. Hemocompatibility of the polymeric films has also been investigated on whole blood from healthy donors. Gas permeation of the polymers increases in the order PHFP PPFMED > AF2400, with the most permeable polymer AF2400 exhibiting the worst hemocompatibility among the other polymers studied. Polyperfluoro(2-methyl-2-ethyl-dioxole-1,3) is shown to be the most appropriate polymer to fabricate hollow fiber membranes for blood oxygenation.

The results of numerical studies of energy separation of a helium-xenon gas mixture in a single Leontiev tube with a central cylindrical channel are presented. On the basis of the simulation data, a T-s diagram for energy separation is constructed. The changes in the total temperature depending on the entropy change in the central subsonic channel and in the annular supersonic nozzle are shown.

The results of numerical studies of heat and mass transfer during adiabatic evaporation of an aqueous solution of ethanol into an accelerated steam-air laminar boundary layer on a flat wetted plate are presented. The flow acceleration is realized due to the inclination of the upper channel wall, which ensures the constancy of the Kays acceleration parameter. The dependences of the evaporation intensity of the components of solutions of various compositions are obtained for the acceleration parameter 0 and 10-6 for the flow temperature from 20 to 50 °C. A significant effect of the accelerating pressure gradient on the evaporation intensity and its weak effect on the equilibrium wall temperature are shown.

We present results of the experimental study and numerical simulation of radiation-convective heat and mass transfer during the sublimation of spherical particles of metal β-diketonates in a high-temperature inert gas flow (argon or helium). The sublimation process is visualized, and experimental data on the temperature variation dynamics and particle size are obtained. It is shown that at stable transfer of the compound from the particle surface the sublimation proceeds with the formation of large pores in its structure. The effect of inert gas properties on the kinetics of the vaporization process of precursor particles with various initial diameters is analyzed in the temperature range from 200 °C to 330 °C. Due to a higher thermal conductivity and heat capacity of helium as compared with argon, the choice of helium as carrier gas causes an increase in the sublimation intensity.

Severe diseases of the anterior eye surface, such as ulcers and erosions of varied genesis, or the consequences of the cornea and conjunctiva burns are important topical issues of ophthalmology. Purpose: to assess the suitability of existing collagen substrates based on types I and II collagen for being used as a matrix for rabbit buccal epithelium cells. Material and methods. The study involved 12 rabbits (24 eyes), on whose intact cornea a contact lens was placed. The lens was covered with a variety of type I collagen which had been obtained from rabbit tendon by acid extraction. For control purposes, a contact lens covered with collagen gel based on type II collagen and designed for healing was placed on the cornea of the fellow eye. Biocompatibility and tolerability of collagen matrixes was assessed. Results. Type I collagen obtained from rabbit tendon had no toxic action on buccal epithelial cells. The types of collagen used were found to be an optimal medium for buccal epithelial cells, which adhere well and can be delivered to the site of corneal damage. Type I collagen, which was produced by acid extraction, had an irritating effect on the rabbit cornea, which is associated with high content of acetic acid. Therefore, the technique of producing type I collagen was modified to achieve an additional reduction of acidity. Conclusion. Type I collagen and collagen gel for corneal healing produced on the basis of type II collagen were shown to be safe and effective when used in bioengineering construction // Russian ophthalmological journal. 2017; 10 (2): 71-7. doi: 10.21516/2072-0076-2017-10-2-71-77.

The results of experimental and numerical investigations of the effect exerted by air flow rate and flow twist angle on the dynamics of an end-face boundary layer in a diaphragmed vortex chamber with a multislit lateral swirler are presented. Data on the hydraulic resistance of the chamber have been obtained. It is shown that gas injection through the slits of the lateral swirler leads to the formation of flow in the chamber of the same structure as that formed as a result of the injection uniformly distributed over the side wall with a smaller twist angle if the static pressure losses in the chamber in both cases are equal. Generalization of the dependence of the hydraulic resistance of the chamber on the effective flow twist angle is obtained for the investigated range of Reynolds numbers.

The results of studies of heat and mass transfer during adiabatic evaporation of binary liquids of water/ethanol and water/acetone into a turbulent boundary layer of a vapor-air mixture from a flat wetted plate are presented. The dependences are obtained for the evaporation intensity of solutions of various compositions on the temperature of the air flow or the equilibrium superheated steam into which the liquids evaporate. The inversion temperature values for liquids with different concentration of the volatile component are determined. The effect of flow turbulence on the evaporation rate and inversion temperature is analyzed.

The redistribution of the total temperature between the parts of the gas stream flowing through the Leontiev tube depends not only on the temperature recovery factor (Prandtl number) and the ratio of flows through the supersonic and subsonic channels of the tube (Mach numbers), but also on the thermal resistance of the separation wall. Earlier it has been shown that the reduction of thermal resistance due to the separation wall finning on the side of the subsonic flow leads to an increase in the efficiency of energy separation. It may be assumed that the intensification of heat exchange between channels, due to finning, reduces the length of the tube, which at the same intensity of heat exchange leads to a decrease in pressure losses and an additional increase in efficiency. This paper presents the results of numerical simulation of energy separation in Leontiev tubes with a finned separation wall and different lengths of supersonic nozzle. It is shown that the adiabatic efficiency of the energy separation in a short Leontiev tube with a finned wall increases when the outlet pressure decreases, while it does not change for smooth tubes.

The results of the analysis of the problem of wetting the microstructured flat wall surface during adiabatic liquid evaporation into a boundary layer of air flowing at right angles are presented. The basic conservation laws are formulated in the form of differential equations that allow calculating the velocity and height of liquid rise in capillaries, wetting dynamics, depth and mass of the liquid in capillaries, and the evaporation surface area.

Results of numerical simulation of heat and mass transfer in a laminar flow of three-component gas at adiabatic evaporation of binary solutions from a flat plate are presented. The studies were carried out for the perfect solution of ethanol/methanol and zeotrope solutions of water/acetone, benzene/acetone, and ethanol/acetone. The liquid-vapor equilibrium is described by the Raoult law for the ideal solution and Carlson–Colburn model for real solutions. The effect of gas temperature and liquid composition on the heat and diffusion flows, and temperature of vapor-gas mixture at the interface is analyzed. The formula for calculating the temperature of the evaporation surface for the binary liquid mixtures using the similarity of heat and mass transfer was proposed. Data of numerical simulations are in a good agreement with the results of calculations based on the proposed dependence for all examined liquid mixtures in the considered range of temperatures and pressures.

The paper presents results of numerical simulation of energy separation (temperature stratification) of helium-xenon gas mixture with low-Prandtl number, flowing in the finned single Leontiev tube. Only the inner surface of the central channel for subsonic part of the flow was finned by longitudinal fins. The influence of the flow rate of the cooling gas, flowing through the central channel, on the energy separation efficiency was analyzed in comparison with the efficiency of Leontiev tube with smooth walls. The method of efficiency enhancement by insulating the low-temperature area at the tube outlet was suggested.

A stationary flow of three-component gas in a laminar boundary layer on a flat plate is considered at adiabatic evaporation of a two-component liquid film. Numerical modelling were carried out at atmospheric pressure, air flow velocity of 2 m/s and temperature from 20 to 500 °C in the whole range of concentrations of a low-boiling component of binary solutions: ethanol/water, acetone/water, and acetone/ethanol. Data on the local specific evaporation rate of ethanol/water and acetone/water solutions into dry air and superheated mixture of ethanol, acetone and water vapors were obtained depending on the temperature of the inlet flow. Composition of superheated vapor mixture was taken to be equilibrium relative to the liquid solution. With an increase in the molar fraction of ethanol or acetone in the water solution, the evaporation rate increases, and when evaporated into superheated vapor, the growth of evaporation rate with increasing vapor temperature is significantly higher than at evaporation into air. With an increase in ethanol or acetone concentration in the liquid solution, the inversion temperature decreases from down to 155…165°C.

The paper presents the results of numerical simulation of nonstationary sublimation of spherical particles of Cr(acac)3, floating in the volume of a binary mixture (argonsuperheated vapor of precursor) in a reactor with hot walls. The influence of the vapor content, reactor wall temperature and radiative heat transfer on the kinetics of sublimation/desublimation are analyzed. The characteristic times of induction and total sublimation, as well as the intensity of mass entrainment from the surface of particles of different sizes are determined. The influence of radiation from the hot walls of the sublimator on these parameters is determined.

The method of energy separation in a high-speed flow proposed by A.I. Leontyev is investigated numerically. The adiabatic compressible gas flow (of a helium-xenon mixture) with a low Prandtl number in a planar narrow duct and a flow with heat exchange in a duct partitioned by a heat-conducting wall are analysed. The temperature recovery factor on the adiabatic wall, degree of cooling the low-speed flow part, temperature efficiency, and the adiabatic efficiency in a duct with heat exchange are estimated. The data are obtained for the first time, which make it possible to compare the efficiency of energy separation in a high-speed flow with the efficiency of similar processes in vortex tubes and other setups of gas-dynamic energy separation.

The authors analyze the parameters involved in the mixing of fiber-reinforced plastics and their binders and use this analysis to arrive at the design of a mixer which utilizes the specific flow characteristics of the constituent materials in order to optimize its capacity and energy efficiency.The performance as well as the mathematical justification for the design of the mixer are given.