Discussion: “Lubricant Limiting Shear Stress Effect on EHD Film Thickness” (Gecim, B., and Winer, W. O., 1980, ASME J. Lubr. Technol., 102, pp. 213–220)

1980 ◽  
Vol 102 (2) ◽  
pp. 220-221
Author(s):  
B. K. Daniels
Keyword(s):  
Shear Stress ◽  
Film Thickness ◽  
Stress Effect ◽  
Limiting Shear Stress

Lubricant Limiting Shear Stress Effect on EHD Film Thickness

1980 ◽  
Vol 102 (2) ◽  
pp. 213-220 ◽  
Author(s):  
B. Gecim ◽  
W. O. Winer
Keyword(s):  
Shear Stress ◽  
Film Thickness ◽  
Fluid Model ◽  
Operating Conditions ◽  
Stress Effect ◽  
Limiting Shear Stress ◽  
Viscous Fluid Model ◽  
Low Shear Stress ◽  
New Variables ◽  
Low Shear

A Grubin-like EHD inlet analysis utilizing a non-linear viscous fluid model with a limiting shear stress is reported. The shear rheological equation requires only a low shear stress viscosity and the limiting shear stress both functions of pressure. Values employed for these properties are taken from measurements on typical lubricants. Reductions of EHD film thickness are found to be up to 40 percent compared with the standard Grubin prediction for typical operating conditions. Slide-roll ratio, limiting shear stress dependence on pressure, and atmospheric pressure value of limiting shear stress are new variables required to determine film thickness with the first two being more important than the last. The EHD film thickness is reduced by increasing slide-roll ratio and/or decreasing the pressure dependence of the limiting shear stress.

Investigation of Parameters Affecting the Limiting Shear Stress-Pressure Coefficient: A New Model Incorporating Temperature

1994 ◽  
Vol 116 (3) ◽  
pp. 612-620 ◽  
Author(s):  
Victoria Wikstro¨m ◽  
Erik Ho¨glund
Keyword(s):  
Shear Stress ◽  
Film Thickness ◽  
Contact Pressure ◽  
Pressure Coefficient ◽  
Oil Viscosity ◽  
New Model ◽  
Lubricated Contacts ◽  
Limiting Shear Stress ◽  
Essential Parameter ◽  
Maximum Contact

When calculating film thickness and friction in elastohydrodynamically lubricated contacts, assuming a non-Newtonian fluid, the lubricant limiting shear stress is an essential parameter. It influences minimum film thickness and determines traction in the contact. The limiting shear stress is pressure dependent according to the Johnson and Tevaarwerk equation: τL=τ0+γp The limiting shear stress-pressure coefficient γ has in a previous screening investigation been shown to depend on several parameters: oil type, oil viscosity at + 40°C, maximum contact pressure and temperature. In the present investigation, the preliminary data is used together with response surface methodology. With these results in mind, further experiments are made and an empirical model is built. This paper presents a new model for γ which is valid for two types of oil (a polyalphaolefine with diester and a naphthenic oil) with different viscosities at +40°C. The model incorporates the influence of maximum contact pressure and oil temperature on γ. The measurements on which the model is based were carried out at temperatures ranging from −20 to + 110°C. The pressure range was 5.8–7 GPa and the shear rate was about 106 s−1.

An Anomalous Elastohydrodynamic Lubrication Film: Inlet Dimple

2005 ◽  
Vol 127 (2) ◽  
pp. 425-434 ◽  
Author(s):  
F. Guo ◽  
P. L. Wong
Keyword(s):  
Shear Stress ◽  
Film Thickness ◽  
Elastohydrodynamic Lubrication ◽  
Lubrication Film ◽  
Entrainment Velocity ◽  
Limiting Shear Stress ◽  
The Individual ◽  
Solid Liquid Interface ◽  
Solid Liquid ◽  
Wall Slippage

This paper presents a deliberately designed elastohydrodynamical lubrication (EHL) experiment for the study of the individual effect of the limiting shear stress and wall slippage. Very slow entrainment speeds were employed to avoid influential shear heating and oils of high viscosities were chosen to ensure that the conjunction was under typical EHL. An anomalous EHL film, characterized by a dimple at the inlet region, was obtained. Literature revealed that this inlet dimple was reported in some numerical studies taking into consideration the limiting-shear-stress characteristics of the lubricant and wall slippage. It was found that even under the same kinematic conditions, different types of film shape would be generated by simple disc sliding and simple ball sliding. Simple disc sliding produces an inlet dimple with a comparatively thick inlet film thickness, which droops rapidly toward the outlet region. For simple ball sliding, there is also an inlet dimple but the central film thickness is rather uniform. However, by prerunning the conjunction at a zero entrainment velocity (at the same linear speeds but in opposite directions) before the sliding experiment, the slope of the central film of simple disc sliding becomes smaller. It is probably due to the modification of solid-liquid interface, i.e., the slippage level, by the highly pressurized and stressed prerunning conditions. With a prescribed prerunning, which can produce very similar films at simple disc sliding and simple ball sliding, variation of film thickness was studied and it was found that the inlet dimple film has obvious dependence on entrainment speeds, but was not sensitive to loads. The present experimental results can be considered as direct evidence for those numerical findings of the inlet dimple. Tentatively, an effective viscosity wedge is proposed to account for the formation of the inlet dimple.

A Film Thickness Analysis for Line Contacts Under Pure Rolling Conditions With a Non-Newtonian Rheological Model

1981 ◽  
Vol 103 (2) ◽  
pp. 305-313 ◽  
Author(s):  
B. Gecim ◽  
W. O. Winer
Keyword(s):  
Shear Stress ◽  
Film Thickness ◽  
High Viscosity ◽  
Low Viscosity ◽  
Limiting Shear Stress ◽  
Lubrication Regime ◽  
Pure Rolling ◽  
Reasonable Range ◽  
Line Contacts ◽  
Rolling Elements

The non-Newtonian constitutive equation proposed by Winer and Bair [1] is applied in a conventional isothermal film thickness analysis of line contact lubrication of rolling elements. The present analysis provides four different dimensionless film thickness equations for four different regimes of lubrication. Due to the formulation technique used in deriving the governing pressure-gradient equation, the present study is recommended for high viscosity, high rolling speed, and low limiting shear stress cases where Newtonian models fail to match the experimental data. Comparison of the present film thickness equations with the Newtonian correspondences in each lubrication regime shows a considerable difference, but the analysis suffers from the fact that the limiting shear stress parameters of these high viscosity lubricants need to be determined experimentally. The present analysis assumes a reasonable range of limiting shear stress which is smaller than the corresponding values for low viscosity lubricants which are predominantly Newtonian in behavior (unless severe rolling and/or sliding with high loads is applied).

EHL Film Thickness Limitation Theory Under a Limiting Shear Stress

2002 ◽  
Vol 45 (4) ◽  
pp. 531-539 ◽  
Author(s):  
Yongbin Zhang ◽  
Shizhu Wen
Keyword(s):  
Shear Stress ◽  
Film Thickness ◽  
Limiting Shear Stress

Shear Loss Characteristics of an Aerobic Biofilm

1992 ◽  
Vol 26 (3-4) ◽  
pp. 595-600 ◽  
Author(s):  
S. M. Rao Bhamidimarri ◽  
T. T. See
Keyword(s):  
Growth Rate ◽  
Shear Stress ◽  
Film Thickness ◽  
Removal Rate ◽  
Surface Growth ◽  
Phenol Removal ◽  
Concentric Cylinder ◽  
Substrate Utilisation ◽  
Utilisation Rate ◽  
Net Growth Rate

Growth and shear loss characteristics of phenol utilizing biofilm were studied in a concentric cylinder bioreactor. The net accumulation of the biofilm and the substrate utilisation were measured as a function of torque. Uniform biofilms were obtained up to a thickness of around 300 microns, beyond which the surface growth was non-uniform. The substrate utilisation rate, however, reached a constant value beyond film thickness of 50 to 100 microns depending on the operational torque. The maximum phenol removal rate was achieved at a shear stress of 3.5 Nm-2. The effect of shear stress on net growth rate was found to be described byand a zero net growth was obtained at a shear stress of 18.7 Nm-2.

scholarly journals The Effect of Wall Shear Stress on Two Phase Fluctuating Flow of Dusty Fluids by Using Light Hill Technique

Water ◽  
2021 ◽  
Vol 13 (11) ◽  
pp. 1587
Author(s):  
Dolat Khan ◽  
Ata ur Rahman ◽  
Gohar Ali ◽  
Poom Kumam ◽  
Attapol Kaewkhao ◽  
...  
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Base Fluid ◽  
Perturbation Technique ◽  
Fluid Velocity ◽  
Dust Particles ◽  
Stress Effect ◽  
Parallel Plates ◽  
Dusty Fluid ◽  
Wall Shear

Due to the importance of wall shear stress effect and dust fluid in daily life fluid problems. This paper aims to discover the influence of wall shear stress on dust fluids of fluctuating flow. The flow is considered between two parallel plates that are non-conducting. Due to the transformation of heat, the fluid flow is generated. We consider every dust particle having spherical uniformly disperse in the base fluid. The perturb solution is obtained by applying the Poincare-Lighthill perturbation technique (PLPT). The fluid velocity and shear stress are discussed for the different parameters like Grashof number, magnetic parameter, radiation parameter, and dusty fluid parameter. Graphical results for fluid and dust particles are plotted through Mathcad-15. The behavior of base fluid and dusty fluid is matching for different embedded parameters.

scholarly journals Rapid Fabrication of Microfluidic Devices for Biological Mimicking: A Survey of Materials and Biocompatibility

Micromachines ◽  
2021 ◽  
Vol 12 (3) ◽  
pp. 346
Author(s):  
Hui Ling Ma ◽  
Ana Carolina Urbaczek ◽  
Fayene Zeferino Ribeiro de Souza ◽  
Paulo Augusto Gomes Garrido Carneiro Leão ◽  
Janice Rodrigues Perussi ◽  
...  
Keyword(s):  
Shear Stress ◽  
Cell Viability ◽  
Cellular Response ◽  
Fluid Shear Stress ◽  
Umbilical Vein ◽  
Microfluidic Devices ◽  
In Vitro Assays ◽  
Stress Effect

Microfluidics is an essential technique used in the development of in vitro models for mimicking complex biological systems. The microchip with microfluidic flows offers the precise control of the microenvironment where the cells can grow and structure inside channels to resemble in vivo conditions allowing a proper cellular response investigation. Hence, this study aimed to develop low-cost, simple microchips to simulate the shear stress effect on the human umbilical vein endothelial cells (HUVEC). Differentially from other biological microfluidic devices described in the literature, we used readily available tools like heat-lamination, toner printer, laser cutter and biocompatible double-sided adhesive tapes to bind different layers of materials together, forming a designed composite with a microchannel. In addition, we screened alternative substrates, including polyester-toner, polyester-vinyl, glass, Permanox® and polystyrene to compose the microchips for optimizing cell adhesion, then enabling these microdevices when coupled to a syringe pump, the cells can withstand the fluid shear stress range from 1 to 4 dyne cm2. The cell viability was monitored by acridine orange/ethidium bromide (AO/EB) staining to detect live and dead cells. As a result, our fabrication processes were cost-effective and straightforward. The materials investigated in the assembling of the microchips exhibited good cell viability and biocompatibility, providing a dynamic microenvironment for cell proliferation. Therefore, we suggest that these microchips could be available everywhere, allowing in vitro assays for daily laboratory experiments and further developing the organ-on-a-chip concept.

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