Pressure Viscosity Relationship Research Articles

The Mechanochemistry of Synthetic Phosphate Oil under High Pressure

The pressure-viscosity relationships of phosphate synthetic oil and other two kinds of similar atmospheric viscosity synthetic oils were studied using ultra-high pressure capillary viscometer. The pressure-viscosity relationship of phosphate synthetic oil is much better than the other two kinds of synthetic oils. The impact of pressure on viscosity is not limited to purely physical factors. The pressure can cause a variety of chemical reactions in some cases. The investigation results of mechanochemistry of phosphate synthetic oil at high pressure reveal that the physical state of phosphate synthetic oil changed from liquid into glassy amorphous state under high pressure, and the color varied from transparent into milky white. The mechanochemistry of phosphate synthetic oil was analyzed using the infrared spectroscopy and gel permeation chromatography, and the results indicate that under high pressure, the oxidation reaction of phosphate synthetic oil occurred, and the molecular weight distribution changed with the increase of the low molecular weight region. The reason of the mechanochemistry phenomena was that phosphate synthetic oil molecular chain disconnects to inform great radical. The great radical has strong activity, and reacts with other free radicals acceptor (oxygen, etc).

The Artificial Neural Network's Prediction of Crude Oil Viscosity for Pipeline Safety

Predicting crude oil viscosity is a challenge faced by reservoir engineers in production planning. Some early researchers have propounded some theories based on crude oil properties and have encountered various problems leading to errors in forecasted values. This article discusses work carried out with a model using an artificial neural network (ANN) for predicting crude oil viscosity of Nigerian crude oil. The model was started through adoption of a classical regression technique empirical method for dead oil viscosity as a function of American Institute for Petroleum (API) and reduced temperature. The Peng–Robinson equation of state and other thermodynamic properties are introduced, coupled with the Standing model for calculating bubble point pressure (Pb). The developed model was evaluated using existing measured real-life data collected from 10 oil fields within the Niger Delta region of Nigeria. Both the predicted and measured viscosities were plotted against each corresponding reservoir pressure to establish the model's level of reliability. The superimposition of the pressure-viscosity relationship shows that at each point, the viscosity model captures the physical behavior of viscosity variations with pressure. In each case, the ANN does not require a data relationship to predict the crude oil viscosity but rather relies on the field data obtained for training. For this reason, it is recommended that the ANN approach should be applied in oil fields for reduction in error, computational time, and cost of overproduction and underproduction.

High-pressure viscosity of used motor oil/vacuum residue blends

The overall objective of this work was to characterize and model the temperature–pressure–viscosity relationship for used motor oil, and its blends with heavy petroleum residue, in a wide range of pressure and temperature. With this aim, used motor oil, and a vacuum residue commonly used as bituminous base were used as components of the blends. Blends of used motor oil and vacuum residue were prepared by mixing both components in a batch tank with a four-blade impeller. Subsequently, the mixtures were stored at room temperature. The rheological study was performed using a controlled stress rheometer, using both a conventional coaxial cylinder geometry, and a coaxial cylinder-pressure cell. From the experimental results obtained it is apparent that whilst the used motor oil behaves as a Newtonian liquid, the blends behave as non-Newtonian fluids, showing a shear-thinning behaviour in most of the shear rate range studied, at atmospheric pressure, in a temperature range comprised between 0 and 60 °C. The viscous flow curves results obtained at different differential pressures prove that the influence of time-dependent phenomena on viscosity is not significant in most of the shear rate range studied (between 1 and 100 s −1). Pressure–temperature–viscosity relationship modelling, at constant shear rate, can be performed from pressure sweep data at constant temperature, temperature sweep data at constant pressure, or pressure–temperature sweep data. In this sense, the FMT predicts the above-mentioned relationship fairly well.

Traction in EHL Line Contacts Using Free-Volume Pressure-Viscosity Relationship With Thermal and Shear-Thinning Effects

Abstract This paper investigates the traction behavior in heavily loaded thermo-elastohydrodynamic lubrication (EHL) line contacts using the Doolittle free-volume equation, which closely represents the experimental viscosity-pressure-temperature relationship and has recently gained attention in the field of EHL, along with Tait’s equation of state for compressibility. The well-established Carreau viscosity model has been used to describe the simple shear-thinning encountered in EHL. The simulation results have been used to develop an approximate equation for traction coefficient as a function of operating conditions and material properties. This equation successfully captures the decreasing trend with increasing slide to roll ratio caused by the thermal effect. The traction-slip characteristics are expected to be influenced by the limiting shear stress and pressure dependence of lubricant thermal conductivity, which need to be incorporated in the future.

EHL simulation using the free-volume viscosity model

The free-volume viscosity model can accurately predict the temperature–pressure–viscosity relationship of lubricants. However, it is seldom used in elastohydrodynamic lubrication (EHL) simulation. This paper presents the application of the free-volume viscosity model in a Newtonian EHL simulation of a squalane-lubricated circular contact. Good agreement is observed between available experimental data and simulation results. The pressure–viscosity coefficients fit from viscometer data are also discussed. A recently developed definition of the coefficient is used to compare the coefficient value extracted from EHL film thickness interference measurements. Results indicate that the coefficient values from the curve fitting and EHL film thickness extraction agree well which has not been previously observed. Two factors help achieve this agreement: the new coefficient definition and smaller prediction error when using the Hamrock–Dowson formula in the cases studied. The effects of different pressure–viscosity relationships, including the exponential model, the Roelands model and the free-volume model, are investigated through an example with bright stock mineral oil. It is found that the real pressure–viscosity behavior predicted by the free-volume model yields a higher viscosity at the low-pressure area which results in a larger central film thickness. Therefore, due to use of the free-volume model, the present results are more consistent with experimental observations than previously reported numerical results.

Pressure–temperature–viscosity relationship for heavy petroleum fractions

This paper deals with the influence that both pressure and temperature exert on the viscosity of heavy petroleum fractions, such as bitumen of different penetration grades, in temperature and pressure ranges comprised between 60 °C and 160 °C and 0–400 bars, respectively. From the viscous flow tests carried out, it is apparent that bitumen behaves as a Newtonian liquid in the above-mentioned range of temperature and pressure. The temperature–pressure–viscosity relationship for bitumen of different penetration grades, mainly used for paving applications, can be modelled using a modified WLF model, the FMT model. This model includes different physical parameters, such as material compressibility and expansivity, which have been obtained from pressure–volume–temperature (PVT) measurements.

An unconditional existence result for the quasi-variational elastohydrodynamic free boundary value problem

In this paper a two-dimensional quasi-variational inequality arising in elastohydrodynamic lubrication is studied for non-constant viscosity. So far, existence results for such piezo–viscous problems require an L ∞ property for an auxiliary problem. For the usual pressure–viscosity relations, this property needs small data assumptions which are not observed in experimental conditions. In the present work, such small data assumptions are proved unnecessary for existence results. Besides well-established monotonicity behavior for the viscosity–pressure relation, the only condition used here is on the asymptotic behavior for this law as the pressure tends to infinity. If the procedure used here, namely the introduction of a reduced pressure by Grubin transform followed by a regularization procedure, appears somewhat classical, the way in which an upper bound is obtained is completely new.

Validation of EHL Contact Predictions under Time Varying Load

In this paper, it is investigated how accurately current models predict the response of an elasto-hydrodynamically lubricated contact to time varying load conditions. For two patterns of time varying load, under conditions of pure rolling, the results obtained experimentally on a ball on disk interferometry apparatus by Sakamoto et al. (Behaviour of point contact EHL films under pulsating loads. Proceedings of the 30th Leeds-Lyon Symposium on Tribology, Elseviers Tribology Series, Vol. 43, pp. 391-399) are compared with the results of numerical simulations using the dynamic contact model of Wijnant (Contact dynamics in the field of elastohydro-dynamic lubrication. PhD Thesis, University of Twente, Enschede, The Netherlands, 1998 ISBN 90-36512239), Wijnant and Venner (Contact dynamics in starved elastohydrodynamic lubrication. Proceedings of the 25th Leeds-Lyon Symposium on Tribology, Elsevier Tribology Series, Vol. 36, pp. 705-716). The observed film changes are explained and related to the piezoviscous behaviour of the lubricant. Results for two different viscosity pressure relations are presented. It is shown that the details of the viscosity pressure relation have little effect on the local phenomena observed. The agreement between experimental and theoretical results is excellent in terms of the location and width of induced film thickness changes. The accuracy of the amplitude of the predicted changes is less. A amore accurate amplitude prediction requires more precise knowledge of the dynamic parameters, which describe the load system used in the experiments.

Erratum

The paper questions the accuracy of application of the Roelands equation in pressure viscosity relationships for lubricants. It shows that in the development of the equation Roelands discarded some measured data on high-pressure viscosity. The author suggests that conclusions based upon calculations using the Roelands equation should thus be re-examined.

Roelands' missing data

The author questions the accuracy of application of the Roelands equation in pressureviscosity relationships for lubricants. He contends that in the development of his equation when Roelands discarded some vital data on high-viscosity measurements that did not fit his claim of universal applicability. The author suggests that some conclusions based upon calculations using the Roelands equation should be reexamined.

Pressure-Viscosity Relationships for Elastohydrodynamics

The numerical simulation of elastohydrodynamic lubrication has evolved in terms of solution detail, speed and robustness. However, if EHL is to begin to solve practical quantitative problems involving differences among lubricants, practitioners must begin to utilize pressure-viscosity relationships in their numerical schemes that can describe real liquid response. The authors begin with the simple empiricisms that can be used to describe the pressure-viscosity response piecewise over the entire range from ambient to glass transition. Then various free volume formulations are introduced and compared. Finally, empirical expressions that can describe some essential features over the entire pressure range are presented. An example of the utility of one empirical equation is offered. Scheduled for Presentation at the 58th Annual Meeting in New York City April 28–May 1, 2003

A mixed-TEHD analysis and experiment of journal bearings under severe operating conditions

The increasingly high demands for compact design require journal bearings to work under severe operating conditions. A steady-state mixed-TEHD (thermo-elasto-hydrodynamic) model for journal bearings has been developed. The model considers the fluid flow in the gap formed by rough surfaces, asperity contact, surface thermoelastic deformations, and a temperature–pressure–viscosity relationship for the lubricant, as well as an angular misalignment between the journal and the bearing. The model is verified with experimentally measured temperature data. Numerical simulations of the operation of a typical journal bearing are conducted and the importance of several contributing factors in mixed lubrication is discussed. A bearing temperature transition has been experimentally identified and numerically analyzed.

Energy Efficiency of Industrial Oils

Lubricants influence energy efficiency mainly through reducing energy losses, which include churning losses and friction losses in hydrodynamic, elastohydrodynamic and boundary lubrication regimes. The total energy loss depends on lubricant viscosity and chemical composition. Different sources of lubricant-related power losses in industrial systems are described. The dependence of churning and friction losses on oil properties is analyzed. Viscosity shear-thinning and pressure-thickening effects and their dependence on base oil and viscosity index improver chemical composition are examined. The role of pressure-viscosity relationships is emphasized. Some aspects of oil compressibility and viscoelasticity are discussed in regard to oil energy efficiency. The mechanism and role of friction modifiers in industrial oil formulations are described. Significant savings in machinery energy consumption can be achieved by using energy-efficient lubricants. Methods for improving industrial lubricant energy efficiency are discussed and potential savings in energy consumption are estimated. Presented at the 54th Annual Meeting Las Vegas, Nevada May 23–27, 1999

The linear pressure dependence of the viscosity at high densities

Over the years, experimental data of the viscosity coefficient of simple dense fluids at high pressures have been obtained both in our laboratory and elsewhere. These data show that, at high densities, i.e. roughly in the last third of the density range from vacuum to the melting transition, for constant temperature the viscosity coefficient is a linear function of the pressure in a few different but neighbouring ranges, each with different slope and intersection with the pressure axis. The slope appears to be a time of picoseconds. The intersection with the pressure axis can be considered to be a value for the internal pressure. Thus, the viscosity coefficient is directly proportional to the thermal pressure, i.e. the combination of the experimental pressure and the internal pressure, in these ranges. It is shown that such a linear pressure dependence of the viscosity occurs in large ranges of the liquid state and at high densities in the fluid state of simple molecules. We subsequently call attention to old ideas of Maxwell on the equivalence of elasticity and viscosity and the modern basis of it given by Zwanzig and Mountain. This concept leads to Maxwell’s relaxation time. On account thereof, the slope of the linear viscosity–pressure relation is interpreted as the relaxation time, i.e. the time in which a disturbance to the Maxwellian equilibrium state decreases to 1/e of its original value, and as the ideal collision interval. The similarity of the present solution and the case of electrical conductivity in an n-type semiconductor is also pointed out. This leads to a simple view on the transport mechanism and gives reason to consider the temperature dependence of the relaxation times.

Numerical Analysis of Pressure Distribution in Piston-Cylinder Unit for Accurate Pressure Measurement

Precise and accurate pressure measurements are obtained using deadweight piston gauges. Pressure distribution and elastic distortion in the piston-cylinder unit are the leading factors in determination of effective area. The distortion depends upon the pressure distribution in the clearance between piston and cylinder and those are coupled each other. Considering the viscosity pressure relation of oil and governing flow equation in the clearance, a new numerical iterative algorithm is developed. The disagreement between the monotonous and sharp pressure profiles is an indication that the pressure profile will be different for each piston and cylinder unit due to material variances.

On the volume dependence of viscosity of some magmatic silicate melts

Density and viscosity measurements of three melts of volcanic rock composition (basalt and andesite) at low temperatures were carried out to understand the role of free volume in the viscous behavior of a magma and to estimate the flow unit in the melts. The data combined with literature data suggest the following conclusion: free-volume theory is not applicable to these silicate melts; the relation between viscosity and the inverse of free volume does not yield a straight line in a wide temperature range from the glass-transion temperature to 1550°C. However, two depolymerized melts, diopside and Oki-Dozen alkali basalt (OAB), yield almost linear relationships. Thus, the free-volume theory should hold to a fairly good approximation for these two melts. Based on this approximation, the radius of flow unit for diopside melt was calculated to be about 4.7 A, and that for Oki-Dozen alkali basalt to be about 4.2 A. The three-dimensional silicate anions which may correspond to the flow unit are Si14O3514− and Si16O4016− for diopside melt, and Si10O2510− and Si12O3012− for OAB melt. The temperature effect on the initial slope of the viscosity-pressure relation has also been examined in the frame of free-volume theory. It was concluded that the relative increase of the initial slope of the relation with increasing temperature might be caused by the increase of free volume.

Delay of pitting by hydrogen chloride dissolved in a lubricating oil

Using a simplified rolling-four-ball method, the influence of gaseous hydrogen chloride dissolved in a Polish lubricating oil “Komprenol-32” on pitting was tested and the results were compared with those for pure oil. The hydrogen chloride dissolved in the oil increased the time to appearance of the first pit under the test conditions, despite its corrosive static action on the test balls. The pressure-viscosity relationship of the lubricant, and its hydrogen chloride and iron contents were measured. This paper offers a hypothesis to explain the observed improvement in pitting performance seen with the oil with dissolved HCl. So-called corrosion-tribopolishing is suggested as an explanation.

Effect of Surface Roughness on the Point Contact EHL

In this paper a full numerical solution for the partial elastohydrodynamic lubrication in elliptical contacts is presented, and the procedure of computation is briefly described. The average Reynolds equation developed by Patir and Cheng, the elasticity equation, and the pressure-viscosity relationship are solved simultaneously. The asperity contacts are also taken into account by using the model contributed by Greenwood and Tripp. The distribution of surface irregularities is assumed to be Gaussian. The effects of various roughness parameters on the film thickness are investigated. Special attention is given to the surface pattern parameter and hydrodynamic roughness parameter.

Piezoviscous Effects in Nonconformal Contacts Lubricated Hydrodynamically

The analysis is concerned with the piezoviscous-rigid regime of lubrication for the general case of elliptical contacts. In this regime several formulas of the lubricant film thickness have been proposed by Hamrock and Dowson, by Dowson et al., and more recently by Houpert. However, either they do not include the load parameter W, which has a strong effect on film thickness, or they overestimate the film thickness by using the Barus formula for pressure-viscosity characteristics. The Roelands formula was used for the pressure-viscosity relationship. The effects of the dimensionless load, speed, and materials parameters, the radius ratio, and the lubricant entrainment direction were investigated. The dimensionless load parameter was varied over a range of one order of magnitude. The dimensionless speed parameter was varied by 5.6 times the lowest value. Conditions corresponding to the use of solid materials of steel, bronze, and silicon nitride and lubricants of paraffinic and naphthenic mineral oil were considered in obtaining the exponent in the dimensionless materials parameter. The radius ratio was varied from 0.2 to 64 (a configuration approaching a line contact). Forty-one cases were used in obtaining a minimum film thickness formula. Contour plots indicate in detail the pressure developed between the contacting solids.

Pressure-Viscosity Coefficients of Liquid Lubricants

The Barus equation relating viscosity to pressure includes a pressure-viscosity coefficient used widely by investigators even though that coefficient is grossly inaccurate at elevated pressures. A new empirical equation was developed relating viscosity to pressure. The equation is mathematically simple and provides two coefficients that are satisfactory over a wide pressure range. These coefficients are temperature dependent and produce a pressure-viscosity relationship with a maximum error of only about 8 percent at a temperature of 37.8°C over a pressure range to 0.60 GPa for a number of fluids. One of the coefficients in this new equation directly reflects the chemical nature of the lubricants investigated. It distinguishes between paraffinic and naphthenic petroleum oils and relates to their degree of aromaticity. Presented as an American Society of Lubrication Engineers paper at the ASLE/ASME Lubrication Conference in New Orleans, Louisiana, October 5–7, 1981