Temperature and Adhesion Influence on the Microbearings Operating Parameters

2013 ◽  
Vol 199 ◽  
pp. 176-181 ◽  
Author(s):  
Krzysztof Wierzcholski ◽  
Andrzej Miszczak
Keyword(s):  
Dynamic Viscosity ◽  
Hydrodynamic Pressure ◽  
Hydrodynamic Theory ◽  
Adhesion Forces ◽  
Oil Viscosity ◽  
Friction Forces ◽  
Oil Flow ◽  
Velocity Changes ◽  
Gap Height ◽  
Viscosity Changes

In presented paper are elaborated the preliminary problems of thermo-hydrodynamic theory of lubrication for dependences between temperature, adhesive forces, and oil dynamic viscosity, in micro-scale inside super thin cylindrical boundary layer arising between two cooperating grooved cylindrical surfaces. In cylindrical micro-bearings are visible the large gradients of temperature changes and adhesion changes in very thin gap height direction. Hence the oil dynamic viscosity changes significantly in gap height direction. This fact implies the visible oil flow velocity changes and friction forces and the hydrodynamic pressure changes during the micro-bearing exploitation. Up to now the influence of adhesion forces simultaneously with temperature on oil viscosity changes and next on hydrodynamic pressure and load carrying capacity changes in cylindrical micro-bearing gap were not considered in analytical and numerical way.

scholarly journals Electro-magneto-hydrodynamic lubrication

Open Physics ◽  
2018 ◽  
Vol 16 (1) ◽  
pp. 285-291 ◽  
Author(s):  
Krzysztof Wierzcholski ◽  
Andrzej Miszczak
Keyword(s):  
Thin Layer ◽  
Hydrodynamic Lubrication ◽  
Temperature Gradients ◽  
Hydrodynamic Theory ◽  
Oil Viscosity ◽  
Scientific Papers ◽  
Electro Magnetic ◽  
Gap Height ◽  
Viscosity Changes ◽  
Rotational Surfaces

Abstract The topic of the presented paper aims to demonstrate a new principle of hydrodynamic lubrication in mechanical, thermal and electro-magnetic fields. Up till now, when dealing with the hydrodynamic theory lubrication, many authors of scientific papers have assumed the constant oil dynamic viscosity value without variations caused by temperature crosswise the film thickness. Simultaneously, due to the numerous AFM measurements, it appears that oil temperature gradients and oil viscosity changes in the bearing gap height directions cannot be omitted. Therefore, in this paper, the problem of the viscosity changes across the lubricant thin layer was resolved as the main novelty in principles of mechanical thermal lubrication. The method of solving the mentioned problem was manifested by a general model of semi-analytical solutions of isothermal electro-magneto-elastohydro-dynamic and non-Newtonian, lubrication problem formulated for two deformable rotational surfaces in curvilinear, co-ordinates.

scholarly journals A New Progress in Random Hydrodynamic Lubrication for Movable Non-Rotational Curvilinear Biosurfaces with Phospholipid Bilayers

2020 ◽  
Vol 03 (02) ◽  
pp. 1-1
Author(s):  
Krzysztof Wierzcholski ◽  
Keyword(s):  
Dynamic Viscosity ◽  
Hydrodynamic Lubrication ◽  
Wrist Joint ◽  
Biological Fluid ◽  
Hydrodynamic Pressure ◽  
Superficial Layer ◽  
Estimation Methods ◽  
Friction Forces ◽  
Biological Surfaces ◽  
Gap Height

This paper aims to highlight the result of a new progression of mathematical estimation methods of stochastic bio-hydrodynamic lubrication parameters for arbitrary, curvilinear, non-rotational, co-operating, living biological surfaces coated with phospholipid bi-layers. Movable, non-rotational, co-operating surfaces occur in various biological friction nods like the collar bone, the blade bone, the jump joint, and the wrist joint. Specifically, the author presents a synthetic and comprehensive estimation of stochastic bio-hydrodynamic lubrication parameters for co-operating, rotational cartilage bio-surfaces with phospholipid bi-layers occurring in human spherical hip joints and cylindrical elbow joints. The method of research discussed in this paper focuses on a review of stochastic analytical considerations performed by the author. This research is based on the measurements of the gap height between two movable, non-rotational bio-surfaces. The gap is restricted between two co-operating biological surfaces. After several experiments, it could be inferred that there are symmetric as well as asymmetric random increments and decrements in the gap height. Such changes are applicable to the hydrodynamic pressure, load-carrying capacity, friction forces, and wear of the co-operating biological surfaces in human friction nods and contacts. The prime purpose of this paper is to demonstrate the influence of variations in the expected values and standard deviation of the gap height on the hydrodynamic lubrication parameters that occur during the friction process. It can thus be concluded that the apparent dynamic viscosity of biological lubricant varies in the ultra-thin gap height direction, depending on the susceptibility of the superficial layer of the lubricated bio-surface. The results presented in this paper are obtained considering the 3D variations in the dynamic viscosity of the biological fluid, particularly the random variations crosswise the film thickness in non-Newtonian biological fluid properties.

scholarly journals Operating Parameters of a Slide Bearing with Parabolic-Shaped Slide Surfaces with Consideration of the Stochastic Changes in the Lubrication Gap Height

2019 ◽  
Vol 26 (4) ◽  
pp. 171-178
Author(s):  
Andrzej Miszczak ◽  
Krzysztof Wierzcholski
Keyword(s):  
Conservation Law ◽  
Hydrodynamic Pressure ◽  
Stochastic Equations ◽  
Hydrodynamic Theory ◽  
Lubricating Oil ◽  
Method Of Successive Approximations ◽  
Operating Parameters ◽  
Oil Viscosity ◽  
Slide Bearing ◽  
Gap Height

AbstractIn this article, the authors present the equations of the hydrodynamic theory for a slide bearing with parabolic-shaped slide surfaces. The lubricating oil is characterized by non-Newtonian properties, i.e. an oil for which, apart from the classic oil viscosity dependence on pressure and temperature, also an effect of the shear rate is taken into account. The first order constitutive equation was adopted for considerations, where the apparent viscosity was described by the Cross equation. The analytical solution uses stochastic equations of the momentum conservation law, the stream continuity and the energy conservation law. The solution takes into account the expected values of the hydrodynamic pressure EX[p(ϕ,ζ)], of the temperature EX[T(ϕ,y,ζ)], of the velocity value of lubricating oil EX[vi(ϕ,y,ζ)], of the viscosity of lubricating oil EX[ηT(ϕ,y,ζ)] and of the lubrication gap height EX[εT(ϕ,ζ)]. It was assumed, that the oil is incompressible and the changes in its density and thermal conductivity were omitted. A flow of lubricating oil was laminar and non-isothermal. The research concerned the parabolic slide bearing of finite length, with a smooth sleeve surface, with a full wrap angle. The aim of this work is to derive the stochastic equations, that allow to determine the temperature distribution, hydrodynamic pressure distribution, velocity vector components, load carrying capacity, friction force and friction coefficient, in the parabolic sliding bearing, lubricated with non-Newton (Cross) oil, including the stochastic changes in the lubrication gap height. The paper presents the results of analytical and numerical calculation of flow and operating parameters in parabolic sliding bearings, taking into account the stochastic height of the lubrication gap. Numerical calculations were performed using the method of successive approximations and finite differences, with own calculation procedures and the Mathcad 15 software.

THE PROBLEMS OF HYDRODYNAMIC NON-ISOTHERMAL LUBRICATION

Tribologia ◽  
2016 ◽  
Vol 268 (4) ◽  
pp. 211-223
Author(s):  
Krzysztof WIERZCHOLSKI
Keyword(s):  
Shear Rate ◽  
Temperature Gradient ◽  
Film Thickness ◽  
Flow Velocity ◽  
Dynamic Viscosity ◽  
Nano Particles ◽  
Hydrodynamic Theory ◽  
Oil Viscosity ◽  
Velocity Gradients ◽  
Gap Height

The classical hydrodynamic theory of slide bearing lubrication has been constituted on the assumption of constant pressure and viscosity perpendicular to the thin oil layer thickness. These fundamental assumptions are in contradiction to contemporary achievements connected with new devices such as micro-bearing, nano-bearing, magnetic bearings, artificial joints in humanoid robots, micro-motors. Therefore, new methods of measurements and calculations using AFM and a new mathematical computer programs are needed. Energy conservation equations after boundary layer simplifications confirm the fact that temperature gradient variations across the film thickness have the same order of magnitude as the variations in longitudinal or circumferential directions. The fact that temperature gradient variations across the bearing gap height can be significantly large are evident, despite the temperature differences across the film thickness that are negligibly small. This statement cannot be compliant with the assumption of a constant viscosity value in the gap height direction. It has been proven that hydrodynamic pressure is not constant across the film thickness for non-Newtonian oils with Rivlin Erickson constitutive equations. For pseudo-plastic non-Newtonian oils, the apparent dynamic viscosity significantly decreases with shear rate increases. However, for pseudo-plastic oils, the shear rate increments during the oil flow are strictly connected with the average flow velocity increments. Therefore, the apparent dynamic viscosity depends strongly on the oil velocity gradients. It is evident that flow velocity gradients across the film thickness have intensive variations, particularly in regions where gap height attains the least value. In these places, the dynamic viscosity attains the largest variations in gap height directions. If gap height in micro-bearing is smaller than one micrometre, than the largest oil dynamic viscosity increments caused by the velocity variations across the film thickness are located near the superficial layer of the movable journal surfaces in the case of the hydrodynamic lubrication by rotation, but in the neighbourhood where each of two come near lubricated surfaces during the squeezing. Hence, in these places, dynamic viscosity increases across the film thickness and attains the local maximum values. A gap height smaller than one micrometre has the largest oil dynamic viscosity increments caused by the adhesion force variations across the film thickness located near the motionless sleeve surfaces. In a similar manner, the influences on the viscosity variations caused by the cluster points of concentrations of nano particles as oil inhibitors or oil additives smaller than 5 nm occurring in micro-bearing gaps and the cluster concentration regions of collagen fibres occurring in human joint gap are observed. This paper describes and comments on the above-mentioned problem of oil viscosity changes in the gap height direction, and it presents the apparent dynamic viscosity functions for Newtonian and non-Newtonian oils as well indicates the largest viscosity variations in bearing gap height direction and gives examples of initial calculation results.

scholarly journals Estimation of Random Friction Forces on the Microbearing Cooperating Surfaces

2019 ◽  
Vol 26 (2) ◽  
pp. 167-174
Author(s):  
Krzysztof Wierzcholski ◽  
Andrzej Miszczak
Keyword(s):  
Dynamic Viscosity ◽  
Apparent Viscosity ◽  
Hydrodynamic Lubrication ◽  
Stochastic Theory ◽  
Superficial Layer ◽  
Mathematical Form ◽  
Friction Forces ◽  
Random Roughness ◽  
Load Carrying ◽  
Gap Height

Abstract Presented paper concerns a new mathematical form of stochastic theory of hydrodynamic friction forces occurring on the real cooperating surfaces in computer micro bearing fan and computer microbearing in hard disc driver HDD. This paper presents particularly a new-review of stochastic analytical considerations realized by the authors for friction forces estimation during hydrodynamic lubrication performed on the ground of the measurements of the gap height between two roughness surfaces. After numerous experimental measurements directly follows that the random unsymmetrical increments and decrements of the gap height of computer microbearings have important influence on the load carrying capacities and finally on the friction forces and wear of cooperating surfaces. The main topic demonstrates the influence of the variations of expectancy values and standard deviation of the computer microbearing gap height on the friction forces occurring in the HDD and microbearing fan. Moreover, it is observed the evident connection between the apparent dynamic viscosity and the features of the microbearing superficial surface. Hence after abovementioned remarks follows the corollary that the influence of the microbearing gap height stochastic variations connected with the surface roughness tend moreover indirect from the apparent viscosity into the friction forces variations. The synthetic, complex elaboration of obtained results indicates finally the influence of the random roughness in micro and nano level of microbearing surfaces on the friction forces distribution. A new results contained in this paper are obtained taking into account 3D variations of dynamic viscosity of the non-Newtonian lubricant, particularly variations crosswise the film thickness and influences of surface superficial layer features on the lubricant apparent viscosity.

ON RANDOM EXPECTED VALUES VARIATIONS OF TRIBOLOGY PARAMETERS IN HUMAN HIP JOINT SURFACES

Tribologia ◽  
2021 ◽  
Vol 297 (3) ◽  
pp. 45-56
Author(s):  
Krzysztof Wierzcholski ◽  
Jacek Gospodarczyk
Keyword(s):  
Friction Coefficient ◽  
Synovial Fluid ◽  
Carrying Capacity ◽  
Dynamic Viscosity ◽  
Fluid Dynamic ◽  
Load Carrying Capacity ◽  
Friction Forces ◽  
Load Carrying ◽  
Gap Height ◽  
Human Joint

This paper presents recent progress in the knowledge concerning the stochastic theory of bio- hydrodynamic lubrication with a phospholipids bilayer. On the basis of experimental measurements and analytical solutions, the research concerns the determination of the random expectancy values of load carrying capacity, the friction coefficient, and synovial fluid dynamic variations. After numerous measurements, it directly follows that the random density function of the gap height in the human joint usually indicates a disorderly increases and decreases in the height. Such irregular gap height variations have an important influence on the random synovial bio-fluid dynamic viscosity. This finally leads to the friction coefficient and cartilage wear changes of cooperating bio- surfaces. The main topic of this paper relates to the expectancy values of the tribology parameters localized inside the variable stochastic standard deviation intervals of the human joint gap height. The results obtained finally indicate the influence of the random roughness and growth of living biological cartilage surfaces on the expectancy values of the synovial fluid dynamic viscosity, load carrying capacity and friction forces in human hip joints.

Electric Control of Friction on Silicon Studied by Atomic Force Microscope

NANO ◽  
2015 ◽  
Vol 10 (03) ◽  
pp. 1550038 ◽  
Author(s):  
Yan Jiang ◽  
Lili Yue ◽  
Boshen Yan ◽  
Xi Liu ◽  
Xiaofei Yang ◽  
...  
Keyword(s):  
Atomic Force Microscope ◽  
Bias Voltage ◽  
Electrostatic Force ◽  
Adhesion Forces ◽  
Friction Forces ◽  
Type Silicon ◽  
Atomic Force ◽  
Electric Control ◽  
Before And After ◽  
Track Line

We investigated friction on an n-type silicon surface using an atomic force microscope when a bias voltage was applied to the sample. Friction forces on the same track line were measured before and after the bias voltages were applied and it was found that the friction forces in n-type silicon can be tuned reversibly with the bias voltage. The dependence of adhesion forces between the silicon nitride tip and Si sample on the bias voltages approximately follows a parabolic law due to electrostatic force, which results in a significant increase in the friction force at an applied electric field.

Experimental Characterization of Oil-Refrigerant Two-Phase Flow

2000 ◽  
Author(s):  
V. T. Lacerda ◽  
A. T. Prata ◽  
F. Fagotti
Keyword(s):  
Flow Visualization ◽  
Two Phase Flow ◽  
Working Fluid ◽  
Phase Flow ◽  
Oil Viscosity ◽  
Two Phase ◽  
Mixture Flow ◽  
Horizontal Tubes ◽  
Constant Diameter ◽  
Oil Flow

Abstract Several phenomena occurring inside refrigerating systems depend on the interaction between the refrigeration oil and the refrigerant working fluid. Regarding the refrigeration cycle, good miscibility of oil and refrigerant assure easy return of circulating oil to the compressor through the reduction of the oil viscosity. Inside the compressor the lubricant is mainly used for leakage sealing, cooling of hot elements and lubrication of sliding parts. In the compressor bearing systems the presence of refrigerant dissolved in the oil greatly influences the performance and reliability of the compressor due to the outgassing experienced by sudden changes in temperature and pressure resulting in a two-phase mixture with density and viscosity strongly affecting the lubricant characteristics. A general understanding of the oil-refrigerant mixture flow is crucial in developing lubrication models to be used in analysis and simulation of fluid mechanics problems inside the compressor. In the present investigation the refrigeration oil flow with refrigerant outgassing is explored experimentally. A mixture of oil saturated with refrigerant is forced to flow in two straight horizontal tubes of constant diameter. One tube is used for flow visualization and the other is instrumented for pressure and temperature measurements. At the tubes inlet liquid state prevails and as flow proceeds the pressure drop reduces the gas solubility in the oil and outgassing occurs. Initially small bubbles are observed and eventually the bubble population reaches a stage where foaming flow is observed. The flow visualization allowed identification of the two-phase flow regimes experienced by the mixture. Pressure and temperature distributions are measured along the flow and from that mixture quality and void fraction were estimated.

Influence of the Powder Particle Size on the Denudated Zone Width at Selective Laser Melting

2020 ◽  
Vol 989 ◽  
pp. 816-820
Author(s):  
Roman Sergeevich Khmyrov ◽  
R.R. Ableyeva ◽  
Tatiana Vasilievna Tarasova ◽  
A.V. Gusarov
Keyword(s):  
Particle Size ◽  
Selective Laser Melting ◽  
Powder Particle ◽  
Powder Particle Size ◽  
Adhesion Forces ◽  
Laser Melting ◽  
Friction Forces ◽  
Single Bead ◽  
Powder Particles

Mass transfer in the laser-interaction zone at selective laser melting influences the quality of the obtained material. Powder particles displacement during the formation of the single bead is experimentally studied. The so-called denudated zone was visualized by metallography. It was determined that increasing the powder particle size leads to widening the denudated zone. This can signify that the adhesion forces between powder particles prevail over the friction forces.

Temperature-induced switchable interfacial interactions on slippery surfaces for controllable liquid manipulation

2019 ◽  
Vol 7 (31) ◽  
pp. 18510-18518 ◽  
Author(s):  
Zubin Wang ◽  
Quan Xu ◽  
Lili Wang ◽  
Liping Heng ◽  
Lei Jiang
Keyword(s):  
Interfacial Friction ◽  
Adhesion Forces ◽  
Interfacial Interactions ◽  
Friction Forces ◽  
Temperature Responsive ◽  
Slippery Surface

The interfacial friction forces and adhesion forces are directly detected and controllable liquid sliding is achieved on a temperature-responsive slippery surface.

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