Microgravity investigations of instability and mixing flux in frontal displacement of fluids

The goal of the present study is to investigate analytically, numerically and experimentally the instability of the displacement of viscous fluid by a less viscous one in a two-dimensional channel, and to determine characteristic size of entrapment zones. Experiments on miscible displacement of fluids in Hele-Shaw cells were conducted under microgravity conditions. Extensive direct numerical simulations allowed to investigate the sensitivity of the displacement process to variation of values of the main governing parameters. Validation of the code was performed by comparing the results of model problems simulations with experiments and with the existing solutions published in literature. Taking into account non-linear effects in fluids displacement allowed to explain new experimental results on the pear-shape of fingers and periodical separation of their tip elements from the main body of displacing fluid. Those separated blobs of less viscous fluid move much faster than the mean flow of the displaced viscous fluid. The results of numerical simulations processed based on the dimensions analysis allow to introduce criteria characterizing the quality of displacement. The functional dependence of the dimensionless criteria on the values of governing parameters needs further investigations.     

Detonation combustion of lignite with titanium dioxide and water additives in air

The influence of mineral additives (6.2–70%) and water (15–54%) to lignite on the possibility of its burning in an air flow in a continuous detonation regime in a radial vortex combustor 500 mm in diameter is studied. A syngas with a composition CO + 3H₂ is used for transporting the coal mixture and for promoting the chemical reaction. It is shown that regimes of continuous spin detonation, conventional combustion, and pulsed combustion may occur depending on the amounts of the mineral (TiO₂) added to coal, water, and syngas. The boundaries between the domains of existence of detonation and combustion are determined in the coordinates of the ratio of the syngas flow rate to the rate of consumption of the combustible portion of coal and the mineral component of coal and water. It is seen that the continuous spin detonation regime persists if the mineral additive fraction in the lignite mixture is up to 65% and the water fraction is smaller than 30%. It is also demonstrated that the syngas flow rate should be increased with increasing mineral additive fraction and increasing coal humidity in order to ensure burning of the combustible component of syngas.     

Thermoelectric Properties of InSb Nanowires Over a Wide Temperature Range

The thermoelectric power and electrical conductance of bundles of indium antimonide nanowires with a diameter of about 5 nm have been measured over the temperature range of 80 K to 400 K. In the range from 80 K to 300 K, the temperature dependence of the conductance of nanowires is close to power law, while the thermopower increases linearly with temperature. The thermoelectric properties of the nanowires are discussed in terms of the Luttinger liquid theory, taking into account enhancement of the electron–electron interaction in one-dimensional conductors.     

Reactive thrust generated by continuous detonation in the air ejection mode

Processes of continuous spin detonation and pulsed detonation, as well as combustion of a hydrogen-air mixture in an annular combustor 306 mm in diameter in the regime of air ejection are studied experimentally. The specific flow rates of hydrogen are 0.6–9.8 kg/(s ·m²). It is found that the greatest specific impulses of thrust generated by the combustor are reached in the case of continuous spin detonation. On the average, they are greater than the corresponding values by a factor of 1.5 in the case of burning the mixture in streamwise detonation waves, by a factor of 2 in the case of conventional combustion (by a factor of 3 at the maximum thrust impulse of 2200 m/s), and by a factor of 10 in the case of exhaustion of cold hydrogen. A change in the specific flow rate of hydrogen beginning from ≈1.2 kg/(s·m²) corresponding to the maximum thrust impulse decreases its value, and this decrease is more profound as the detonation limits in terms of the specific flow rate of hydrogen are approached. The maximum reactive thrust (83 N) is developed in the examined detonation chamber near the upper limit at the specific flow rate of hydrogen equal to 3 kg/(s·m²).     

Continuous spin detonation of synthesis gas-air mixtures

Regimes of continuous detonation burning of synthesis gas-air mixtures in transverse (spinning) detonation waves are obtained for the first time in an annular cylindrical flow-type combustor. Carbon oxide-hydrogen mixtures with volume proportions of [CO]/[H₂] = 1/1, 1/2, and 1/3 are studied in a wide range of fuel-to-air equivalence ratios. The maximum detonation wave velocity equal to 1.57 km/s is observed for the mixture of CO + 3H₂ + air with a moderate (about 15%) excess of the fuel. The limits of existence of continuous detonation in terms of the equivalence ratio and the minimum specific flow rate of the mixture are determined. The range of detonation regimes obtained is constructed in the coordinates of the equivalence ratio-specific flow rate of the mixture.     

Crack resistance of plates in interaction of holes with a curved contour

The authors describe a solution of a problem of two symmetrically positioned holes of the triangular form whose curvilinear boundaries at the ends of the beam degenerate into slits, with the tip of one of the holes situated opposite the tip of the other hole. The results are presented of calculating the interaction of triangular and hexagonal holes forming doubly periodic systems.Translated from Problemy Prochnorti, No. 8, pp. 26–30, August, 1992.     

Use of X-Ray Thickness Gauges in Manufacturing Rolled Non-Ferrous Metals

A technique of taking into account modifications of the chemical composition of alloys in measuring the thickness of rolled non-ferrous metal products by X-ray thickness gauges is described. The possibilities and perspectives of using RIT10 X-ray thickness gauges in rolling mills with a wide assortment of treated non-ferrous metals and their alloys are demonstrated. The accuracy reached in measurements of tested objects of different thicknesses and chemical compositions is estimated and factors affecting the accuracy of device readings are indicated.     

On the influence of fatigue on machine part wear

The main aspects of the relationship between fatigue and machine part wear are considered and the relevant problem is formulated. The results of an investigation of the influence of the fatigue process on machine part wear are given for diesel engine piston rings. As the results show, the solution of the problem could open up new prospects in the development of the theory of machine part cyclic wear and the details of the technology of cyclic straining treatments for increasing fatigue wear resistance.