Partial Lubrication of Full Cylindrical Bearings

1983 ◽  
Vol 105 (1) ◽  
pp. 84-89 ◽  
Author(s):  
G. Capriz ◽  
G. Cimatti
Keyword(s):  
Pressure Gradient ◽  
Cavitation Bubble ◽  
Mass Conservation ◽  
Complete Analysis ◽  
Unknown Boundary ◽  
Boundary Relation

The phenomenon of cavitation in bearings is often studied under the assumption that the pressure and the pressure gradient both vanish along the unknown boundary of the cavitation bubble. However, such conditions (often named after Swift and Stieber) may be inconsistent with mass conservation. The discrepancy is particularly striking when the case of long bearings is studied within the so called Sommerfeld approximation. Therefore a complete analysis of the Sommerfeld case is carried out here again (in particular condition of starving feed are examined) under a hypothesis which allows mass-conservation and leads to a boundary relation of the Jakobson type.

scholarly journals Numerical Solution of Rare Metal Leaching Problem

2018 ◽  
Vol 7 (4.36) ◽  
pp. 5
Author(s):  
Oleg V. Galtsev ◽  
Oksana A. Galtseva ◽  
Vladimir A. Belenko ◽  
Alexander V. Mamatov ◽  
Alexander N. Nemtsev ◽  
...  
Keyword(s):  
Pore Space ◽  
Main Idea ◽  
Mass Conservation ◽  
Rare Metal ◽  
Unknown Boundary ◽  
Nickel Copper ◽  
The Mathematical Model ◽  
Liquid And Solid Phases ◽  
Boundary Dynamics

 It is well known that a lot of chemical and physical processes take place on the surfaces of interaction between solid and liquid substances. These processes include a very important technological process of uranium, nickel, copper, precious metal and other solid compound extraction - in-situ leaching. In this article we will rely on the mathematical description of these complex systems proposed by A.M. Meirmanov, where the main idea is the presence of new conditions on a free (unknown) boundary between liquid and solid phases (“pore space - solid skeleton”). These conditions express the usual laws of mass conservation of mass and the development of the mathematical model describing the processes at the macroscopic level. The method proposed in the book allows us to study numerically the dependence ways of free boundary dynamics on a heterogeneous solution distribution velocity and external parameters (reagent temperature, pressure and concentration).

scholarly journals Shale Gas Productivity Predicting Model and Analysis of Influence Factors

2015 ◽  
Vol 8 (1) ◽  
pp. 203-207 ◽  
Author(s):  
Yin Daiyin ◽  
Wang Dongqi ◽  
Zhang Chengli ◽  
Duan Yingjiao
Keyword(s):  
Mathematical Model ◽  
Pressure Gradient ◽  
Shale Gas ◽  
Diffusion Mechanism ◽  
Influence Factors ◽  
Mass Conservation ◽  
Isothermal Adsorption ◽  
Start Up ◽  
Gas Seepage ◽  
The Impact

In order to find the dynamic characteristics of shale gas reservoirs and improve shale gas well production, it is very important to research on shale gas seepage mechanism and production evaluation. Based on the shale gas seepage mechanism, adsorption and desorption characteristics, the diffusion mechanism and mass conservation theory in shale gas development, the dual pore medium shale gas reservoir mathematical model is set up. The mathematical model is built by the finite difference method based on start-up pressure gradient, slippage effect and the isothermal adsorption principle, and then programmed to solve it. Finally, this paper analyzed the impact of Langmuir volume, Langmuir pressure, start-up pressure gradient and slippage coefficient and other factors on shale gas wells production.

Pressure Gradient Variations During Reflux Condensation in a Closed Thermosyphon

2009 ◽  
Author(s):  
Siamak Moaveninejad ◽  
Mohammad Mahdi Heyhat
Keyword(s):  
Pressure Drop ◽  
Pressure Gradient ◽  
Integral Method ◽  
Species Conservation ◽  
Mass Conservation ◽  
Continuous Model ◽  
Mass Energy ◽  
Vapor Interface ◽  
Front Model ◽  
Thermodynamic Equilibrium Condition

The heat and mass transfer in the condenser region of a variable conductance thermosyphon, consisting of two components (R11 + R113) has been studied and special attention has been devoted to pressure drop during reflux condensation. The mass, energy, and species conservation equations in conjunction with the overall mass conservation and continuity of momentum at liquid-vapor interface constraints and the thermodynamic equilibrium condition have been solved numerically by use of the integral method. In contrast to the flat-front model which assumes a sharp interface between the active and shut-off portions in a variable conductance thermosyphon, in this paper a continuous model has been used. In this model a continuous variation of physical properties with condensation of both components along condenser is assumed. The results of the present study have been compared with available numerical and experimental results of other investigators and pressure gradient profiles have been achieved. A calculation of the frictional, accelerational and gravitational components of the pressure drop shows that the gravitational component has the greatest magnitude due to the relatively high density of the vapor.

scholarly journals Dynamics and acoustics of cavitation bubble in adverse external pressure gradient

2020 ◽  
Author(s):  
К.В. Рождественский
Keyword(s):  
Pressure Gradient ◽  
Cavitation Bubble ◽  
Acoustic Pressure ◽  
Bubble Radius ◽  
Pressure Rise ◽  
Leading Edge ◽  
External Pressure ◽  
Gas Content ◽  
Bubble Collapse ◽  
Spectral Parameters

В статье приводятся аналитические и численные результаты по динамике и акустике кавитационного пузырька при повышении внешнего давления. В начале рассматривается модельная задача о сжатии пузырька вплоть до коллапса при мгновенном повышении давления. При этом уравнение Рэлея-Плессета рассматривается с учетом газосодержания, поверхностного натяжения и вязкости. Акустическое давление, вызванное сжатием пузырька, записанное в безразмерном виде, определяется как с привлечением формул, так и численным путем. Показано, что если наряду с паром, внутри пузырька имеется некоторое количество газа, скорость его сжатия и акустическое давление оказываются конечными вплоть до полного схлопывания. Кроме того, возможно многократное повторение цикла расширения-сжатия с затуханием амплитуды колебаний. На каждом периоде колебаний вблизи момента времени коллапса (достижения минимального радиуса) наблюдается импульсное возрастание давления. Во второй части аналогичное исследование проводится для случая, когда кавитационный пузырек возникает в закругленной носовой части подводного крылового профиля. При этом демонстрируется зависимость динамического поведения пузырька и вызываемого им в заданной точке контура профиля акустического давления от типа профиля, его толщины и угла атаки. По периоду первого цикла схлопывания спектральные параметры акустического импульса определяются как у эквивалентного треугольного импульса. Presented in this paper are analytical and numerical results on dynamics and acoustics of a cavitation bubble in adverse external pressure gradient. First considered is a model problem of bubble collapse due to instantaneous increase of pressure. Therewith, the Rayleigh-Plesset equation is treated with account of gas content, surface tension and viscosity. Non-dimensional acoustic pressure caused by the compression of the bubble, is determined both with use of relevant formulae and numerically. It is shown that if together with vapor the bubble contains some quantity of gas, than its collapse rate and acoustic pressure during compression turn out to be finite. In addition, multiple expansion compression cycles are possible. For each period of bubble radius variation there occurs near the moment of collapse (moment of reaching a minimum radius) an impulse acoustic pressure rise. In the second part of the paper a similar investigation is carried out for the case when the bubble occurs near the rounded leading edge of a hydrofoil. Demonstrated therewith is the dependence of the bubble dynamic behavior and accompanying acoustic pressure pulses upon the foil type, thickness and angle of attack. Based on the period of the first bubble collapse cycle the spectral parameters of the induced acoustic pressure impulse are determined as for an equivalent triangular impulse.

Cavitation Bubble Collapse Observations in a Venturi

1966 ◽  
Vol 88 (3) ◽  
pp. 649-657 ◽  
Author(s):  
R. D. Ivany ◽  
F. G. Hammitt ◽  
T. M. Mitchell
Keyword(s):  
Pressure Gradient ◽  
Cavitation Bubble ◽  
Small Bubble ◽  
Bubble Collapse ◽  
Cavitating Flows ◽  
Spherical Bubble ◽  
Slowing Down ◽  
Large Pressure ◽  
Large Pressure Gradient ◽  
The Asymmetry

Bubbles collapsing in water in a cavitating venturi are photographically observed. The large pressure gradient in the venturi causes the bubbles to collapse by flattening in the direction of flow. In many cases a torus is formed, implying the existence of a central jet which, as has been suggested by other investigators, may well be the primary damaging mechanism in cavitating flows. The effect of adjacent bubbles upon each other is visually observed. Numerous bubble rebounds, even in relatively degassed water, are noted. A comparison of observed collapse rates with incompressible theory for a spherical bubble indicates that the slowing down of collapse herein observed at small bubble radii probably results primarily from the asymmetry of the collapse and perhaps also from metastable compression of vapor within the bubble.

Activated Prominences; Mechanisms for Activation and Eruption

1979 ◽  
Vol 44 ◽  
pp. 307-313
Author(s):  
D.S. Spicer
Keyword(s):  
Pressure Gradient ◽  
Density Gradient ◽  
Current Density ◽  
Convective Instability ◽  
Tearing Mode ◽  
Magnetic Shear ◽  
Long Wavelength ◽  
Ideal Mhd ◽  
Gradient Change ◽  
Accelerated Particles

A possible relationship between the hot prominence transition sheath, increased internal turbulent and/or helical motion prior to prominence eruption and the prominence eruption (“disparition brusque”) is discussed. The associated darkening of the filament or brightening of the prominence is interpreted as a change in the prominence’s internal pressure gradient which, if of the correct sign, can lead to short wavelength turbulent convection within the prominence. Associated with such a pressure gradient change may be the alteration of the current density gradient within the prominence. Such a change in the current density gradient may also be due to the relative motion of the neighbouring plages thereby increasing the magnetic shear within the prominence, i.e., steepening the current density gradient. Depending on the magnitude of the current density gradient, i.e., magnetic shear, disruption of the prominence can occur by either a long wavelength ideal MHD helical (“kink”) convective instability and/or a long wavelength resistive helical (“kink”) convective instability (tearing mode). The long wavelength ideal MHD helical instability will lead to helical rotation and thus unwinding due to diamagnetic effects and plasma ejections due to convection. The long wavelength resistive helical instability will lead to both unwinding and plasma ejections, but also to accelerated plasma flow, long wavelength magnetic field filamentation, accelerated particles and long wavelength heating internal to the prominence.

An Attack on the Contamination Problem in the Electron Microscope

1967 ◽  
Vol 25 ◽  
pp. 368-368
Author(s):  
J. J. Kelsch ◽  
A. Holtz
Keyword(s):  
Electron Microscope ◽  
Pressure Gradient ◽  
Ionization Potential ◽  
Simple Solution ◽  
Specimen Surface ◽  
Contamination Rate ◽  
Local Pressure ◽  
High Ionization ◽  
Hydrocarbon Molecules ◽  
Contamination Problem

A simple solution to the serious problem of specimen contamination in the electron microscope is presented. This is accomplished by the introduction of clean helium into the vacuum exactly at the specimen position. The local pressure gradient thus established inhibits the migration of hydrocarbon molecules to the specimen surface. The high ionization potential of He permits the use of relatively large volumes of the gas, without interfering with gun stability. The contamination rate is reduced on metal samples by a factor of 10.

Hydration Chamber for Jeolco 200 Kv Microscope

1970 ◽  
Vol 28 ◽  
pp. 542-543
Author(s):  
V. R. Matricardi ◽  
G. G. Hausner ◽  
D. F. Parsons
Keyword(s):  
Electron Microscope ◽  
Water Vapor ◽  
Vapor Pressure ◽  
Pressure Gradient ◽  
Room Temperature ◽  
List Type ◽  
Type Number ◽  
Equilibrium Vapor Pressure

In order to observe room temperature hydrated specimens in an electron microscope, the following conditions should be satisfied: The specimen should be surrounded by water vapor as close as possible to the equilibrium vapor pressure corresponding to the temperature of the specimen.The specimen grid should be inserted, focused and photo graphed in the shortest possible time in order to minimize dehydration.The full area of the specimen grid should be visible in order to minimize the number of changes of specimen required.There should be no pressure gradient across the grid so that specimens can be straddled across holes.Leakage of water vapor to the column should be minimized.

TOURIST BUSINESS DEVELOPMENT IN UKRAINE

2019 ◽  
pp. 39-46
Author(s):  
Stefania Mosiuk ◽  
Igor Mosiuk ◽  
Vladimir Mosiuk
Keyword(s):  
National Economy ◽  
Methodological Approach ◽  
Business Development ◽  
Tourism Industry ◽  
The State ◽  
Complete Analysis ◽  
Resource Potential ◽  
The World ◽  
Potential Resource ◽  
Favorable Conditions

The purpose of the article is to analyze and substantiate the development of tourism business in Ukraine as a priority component of the national economy. The methodology of this study is to use analytical, spatial, geographical, cultural and other methods. This methodological approach provided an opportunity to carry out a complete analysis of the state of the tourism industry of the state and to draw some conclusions.The scientific novelty lies in the coverage of the real and potential resource potential for the development of the recreational and tourism sphere in Ukraine, detailing the measures for the country ‘s entry into the world tourist market. Conclusions. Analyzing the state and prospects of tourism business development in Ukraine, it should be noted that this industry is one of the priority areas for improving the economy of the country. Historical, cultural – ethnographic, gastronomic, sanatorium and resort potentials of the country will lead the country into world leaders of the tourism industry when creating favorable conditions for investment and proper marketing.

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