Abstract
The effect of the input flowrate ratio and the Reynolds numbers in range from 10 to 300 on the mixing of liquids in a T-type micromixer was examined. Linear trends of mixing efficiency ...change on the ratio of input flowrates and Reynolds number are approximated. The most effective mixing (the mixing coefficient reaches 0.86) was obtained at Reynolds numbers 186 and 300 and the input flowrate ratio
R
= 1. It is determined that with equal input flowrate ratio, as the Reynolds number increases from 10 to 300, the mixing efficiency rises sharply: from 0.2 to 0.8 (for 0.5 <
R
< 1). Variation of the ratio of input flowrates at low Reynolds numbers in the range from 10 to 120 can lead to a significant increase in the mixing of liquids (Re = 47, the growth mixing from 0.22 to 0.67). With Reynolds numbers 186 and 300, as the input flowrate ratio increases from 0.1 to 1, the mixing ratio rises from 0.25–0.30 to 0.85–0.90.
Abstract
Using digital processing of high-speed visualization data on a cavitation flow near NACA hydrofoil with critically low aspect ratio, the frequencies of the formation and separation of ...cavities in the flow are identified. It is shown that in the case of development of cloud cavitation the main dimensionless frequency varies within 0.4, which corresponds to the type of internal instability. The Strouhal number corresponds to the frequency of attached cavity occurrence and varies in range from 0.6 to 0.8. The Strouhal numbers calculated in third mode exceed 1. This mode corresponds to the forming of very small cavities near the leading edge of hydrofoil.
Abstract
The arising of the cavitation cavity behind the circular cylinder with aspect ratio 0.06 has been investigated using high-speed visualization. High-speed imaging at a sampling rate up to 200 ...kHz and even higher for the local areas allowed the spatial structure and dynamics of gas-vapor cavities thoroughly to be studied. The time dependence of the volume of the cavitation cavity on time was obtained for all investigated regimes. The vapor volume fraction, as expected, was found to increase with a decrease in cavitation number at higher flowrates. The feature of the separated cavitation cavity behind the cylinder is the complex structure consisting of the set of the flatted bubbles with a thin liquid interface between them. The collapse of the cavitation cavity proved to be always initiated only near one of the channel walls.
The Yamalo-Nenets Autonomous District is a stable, dynamically developing region, where a solid foundation for further socio-economic development is laid, which allows building large-scale plans for ...the future. In this article, the authors, based on published sources and the regulatory framework of the Russian Federation, consider the Yamalo-Nenets Autonomous District, as one of the largest regions of the Russian Arctic, and the strategy of its socio-economic development. Through a detailed SWOT analysis of strengths and weaknesses, identifying opportunities and threats, studying statistical data, measures are proposed to improve the socio-economic development strategy of the Yamalo-Nenets Autonomous District. The analysis revealed a number of problems in the socio-economic development of the Yamalo-Nenets Autonomous District, namely: a significant predominance of the extractive industry over the processing industry, poorly developed transport infrastructure, the outflow of young people and problems of higher education, lack of accessibility and low quality of health services in remote and hard-to-reach areas of the region. To solve the problems identified during the analysis and strengthen the strengths, as well as improve the existing strategy of the socio-economic development of the region, the authors developed a number of strategic measures that will improve the quality of life in the Yamalo-Nenets Autonomous District, its investment attractiveness, sufficient development not only in the production sector, but also the infrastructure of the region. The authors draw attention to the fact that all the identified problems and their solutions are interconnected. Consequently, the improvement of the proposed directions for the development of the YNAO must be comprehensive, which will make it possible to increase the effectiveness of the implementation of strategic measures for the socio-economic development of the YNAO.
The article presents the results of an experimental study of the cavitation flow around the NACA 0012 series foil in a slit channel with a width of 1.2 mm. The aspect ratio of the streamlined body ...was 0.02. To identify the main features of the two-phase flow, high-speed visualization was performed using the Photron FASTCAM NOVA S12 camera with a sampling frequency of 20 kHz. The internal structure of cavities was detected. The main frequencies of cavities formation in the flow were determined using digital processing of visualization data. The close location of the channel walls was shown to significantly affect the return flow propagation under the cavity and its separation.
Numerical modeling and experimental investigation of hydrodynamic cavitation on a microcylinder located in a microchannel were carried out. The Zwart–Gerber–Belamri cavitation model was employed to ...simulate cavitation processes, and turbulence was simulated using the LES model. Experimental studies were performed by visualization with a shooting frequency of 960 Hz. Fluid pressure at the channel inlet ranged from 2 to 30 bar. Time dependences of pressure, velocity and vapor volume fraction, as well as their average values, were obtained at five points. Stable developed cavitation was found to exist for inlet pressures above 18 bar; no cavitation at all was observed for inlet pressures below 8 bar as confirmed by experimental studies. A fairly good agreement was revealed between the calculated and experimental data. The cavitation pulsation frequency (480–2200 Hz) and hydrodynamic pulsation frequency values (26–96 kHz) were obtained. The presence of cavitation was shown to shift the frequency of hydrodynamic pulsations towards larger values. Dependence of the relative drag coefficient on the inlet pressure, well approximated by a correlation ζr = (2Δp)0.5, was obtained.
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The effect of the ratio of inlet flow rates on the flow structure and efficiency of liquid mixing in a T-shaped micromixer was studied at low Reynolds numbers using the method of particle image ...velocimetry and laser-induced fluorescence techniques. It was found that under the stationary flow regimes, the maximum efficiency of liquid mixing is 0.86 at Re = 186 and inlet flow ratio (R) of 1. The maximum dimensionless value of the longitudinal component of the mean flow velocity (up to 2.0) is achieved for the cases with the smallest and largest inlet flow ratio, that is, at R = 0.03 and R = 1.
Accelerators are used in many areas of modern science and technology (FCC-ee, CEPC, ILC, ESS, MYRRHA, etc.). One of the main elements of accelerators is the superconducting cavity based on ...high-purity niobium sheets. In addition to RRR requirements (over 300) niobium sheets for the SRF cavities should meet rather tough requirements for the grain size, recrystallization degree and mechanical properties. Development of the manufacture regimes of the niobium sheets with the required characteristics for the SRF cavities is a promising and relevant task. The paper presents the study results of the deformation route, true strain value, recrystallization heat treatment regimes influence on the structural and mechanical characteristics of the high-purity niobium sheets.
The analysis of the engineering process of reforming dead catalysts for the extraction of platinum group metals has been carried out. Fully-dead catalyst, having passed several cycles of regeneration ...and entitled to utilization, has the considerable carbonaceous deposits, both on external and internal surfaces. Their content averages 5.0% of the mass of the catalyst. The research objectively consisted in selection of the sweet roasting modes, promoting the fullest removal of the dense carbonaceous deposits from the surface of the dead platinum-rhenium catalysts. The kinetics research of carbonaceous removal deposits from the surface of the catalyst was carried out in a pipe-still heater; oxygen content, duration and temperature of sweet roasting being varied. The maximum temperature during the research reached 950°C, the maximum duration of isothermal holding didn't exceed 6 hours. The extent of carbonaceous deposits removal was calculated by changing sample weight. The kinetic curves were approximated by high-order polynomials, which made it possible to obtain a diagram, illustrating the degree of organic deposits removal, depending on temperature and firing time. It is shown that in the environment enriched to 30-35 vol. % oxygen, the engineering process of catalysts for regeneration is possible to be carried out at 650 °C, with holding for 2 hours at a specified temperature. The alternative of sweet roasting is the air blowing of dead catalysts at temperature of 800 °C within an hour. Both modes guarantee the complete removal of the dense carbonaceous deposits from the surface of the dead catalyst.
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