Influence of Air Dissolved in Hydraulic Oil on Cavitation Erosion

This article gives experimentally evidence that cavitation erosion in hydraulic components like valves and pumps is caused by vapour cavitation not gas or pseudo cavitation. In fact, the free air content which is released by vapour and gas cavitation reduces the erosion significantly. In order to clearly separate the different cavitation types, a test rig with a specially designed reservoir with integrated degassing capability is presented. As flow geometry a valve model with realistic dimensions and under realistic operating conditions was used, which ensures very high transferability of the results to the reality of hydraulic components in practical applications and typical operating conditions. A total of 4 five-hour long tests are performed and analysed. The quantification of the cavitation erosion is determined by the mass loss of the copper samples. The experimental results show a 4.4–5.1 times higher mass loss in tests with air-free oil compared to tests with air-saturated or oversaturated hydraulic oil. The experimental fact that air-free hydraulic oil causes significantly more cavitation erosion than normal (saturated) hydraulic oil, and its implications are discussed. The conclusion can be drawn, that further developments of hydraulic components and systems towards the use of air-free oil or increasing power densities will be disproportionately challenged by cavitation erosion.

SOLUTION OF THE PROBLEM OF FREE FLOW OF ROUGH TWO-DIMENSIONAL WATER FLOW WHEN FLOWING OUT OF A PRESSURE-FREE PIPE

The authors improved the solution of the problem of free spreading of two-dimensional in terms of turbulent potential uniform flows obtained by I.A. Sherenkov. To obtain an analytical solution, the concept of a general flow is used. The conjugation of the solution in the physical plane and in the plane of the velocity hodograph (virtual plane) is used. This made it possible to determine the coordinates of the points of the extreme current line and determine the current parameters leading to an unambiguous analytical solution of the flow geometry.

U-turn capacity at signalized intersections

The article presents the results of a study of the intersections capacity, at which the U-turn lane is organized, depending on the traffic flow volume and its organization. Signalized intersection capacity depends on traffic flow, geometry, traffic organization type, driver’s behaviour and headways between drivers in each traffic lane. To analyse signalized intersection capacity it is necessary to determine traffic lanes saturation flow. The study presents field observation analyses of headways between drivers and saturation flow on U-turn lanes at signalised intersections in Moscow. To conduct research and identify patterns, intersections in Moscow were chosen with different conditions and different organization of the U-turns.

Microfluidic on-chip Production of Alginate Hydrogels Using Double Co-flow Geometry

Microfluidic on-chip production of microgels employing external gelation has numerous biological and pharmaceutical applications, particularly for the encapsulation of delicate cargos, however, the on-chip production of microgels in microfluidic devices can be challenging due to problems such as clogging caused by accelerated progress in precursor solution viscosity. Here, we introduce a novel microfluidic design incorporating two consecutive co-flow geometries for microfluidic droplet generation. A shielding oil phase is employed to avoid emulsification and gelation stages from occurring simultaneously, thereby preventing clogging. The results revealed that the microfluidic device could generate highly monodispersed spherical droplets (coefficient of variation < 3%) with an average diameter in the range of 60–200 μm. Additionally, it was demonstrated that the device could appropriately create a shelter of the oil phase around the inner aqueous phase regardless of the droplet formation regime and flow conditions. The ability of the proposed microfluidic device in the generation of microgels was validated by producing alginate microgels utilizing an aqueous solution of calcium chloride as the continuous phase.

Changing Accretion Geometry of Seyfert 1 Mrk 335 with NuSTAR: A Comparative Study

We present a detailed spectral study of the narrow-line Seyfert 1 galaxy, Markarian 335, using eight epoch observations made between 2013 and 2020 with the Nuclear Spectroscopic Telescope Array. The source was variable during this period both in spectral flux and flow geometry. We estimated the height of the Compton cloud from the model fitted parameters for the whole observation period. This allowed us to investigate the underlying physical processes that drive the variability in X-rays. Our model fitted mass varies in a narrow range, between (2.44±0.45−3.04±0.56)×107M⊙, however, given the large error bars, it is consistent with being constant and is in agreement with that known from optical reverberation mapping observations. The disk mass accretion rate reached a maximum of 10% of the Eddington rate during June 2013. Our study sheds light on mass outflows from the system and also compares different aspects of accretion with X-ray binaries.

Constructing AdS2 flow geometries

We consider two-dimensional geometries flowing away from an asymptotically AdS2 spacetime. Macroscopically, flow geometries and their thermodynamic properties are studied from the perspective of dilaton-gravity models. We present a precise map constructing the fixed background metric from the boundary two-point function of a nearly massless matter field. We analyse constraints on flow geometries, viewed as solutions of dimensionally reduced theories, stemming from energy conditions. Microscopically, we construct computationally tractable RG flows in SYK-type models at vanishing and non-vanishing temperature. For certain regimes of parameter space, the flow geometry holographically encoding the microscopic RG flow is argued to interpolate between two (near) AdS2 spacetimes. The coupling between matter fields and the dilaton in the putative bulk is also discussed. We speculate on microscopic flows interpolating between an asymptotically AdS2 spacetime and a portion of a dS2 world.