High Pressure Rheology Research Articles

High Pressure Rheology of Lubricants (Part 4)

High Pressure Rheology of Lubricants (Part 4)

Quantitative Elastohydrodynamic Lubrication—Seventeen Years In

Abstract Seventeen years have passed since the first full elastohydrodynamic lubrication (EHL) simulation employed the real pressure and shear dependence of viscosity measured in viscometers to accurately predict film thickness and friction. This is the appropriate time to enumerate the advances in understanding brought on by the application of high-pressure rheology to the EHL problem. The pressure dependence of the low-shear viscosity, which has been measured in viscometers for nearly a century, differs from the narratives taught to tribology students and often used to justify inaccurate models. The central film thickness often depends on the shear-thinning at low pressure and time–temperature–pressure superposition demands that the same shear dependence be active at the high pressure where friction is generated. In this article, some of the revelations resulting from quantitative EHL are reviewed. For example, it has been discovered that the minimum film thickness in point contacts depends upon the viscosity at the highest pressures of the contact. This explains the errors in the classical formulas, which were based upon the fictional narratives concerning piezoviscous response, and the assumption of film thickness governed by inlet conditions. Quantitative EHL provides quantitative predictions of contact behavior.

High Pressure Rheology of Lubricants (Part 7)

High Pressure Rheology of Lubricants (Part 7)

High Pressure Rheology of Lubricants (Part 2)

High Pressure Rheology of Lubricants (Part 2)

Rheological Characterization and Tribological Evaluation of Water-Based Lubricants in AISI 52100 Bearing Steel

This study explores the rheological and tribological behavior of water-based lubricants (WBLs) as potential alternatives for electric vehicle (EV) applications. As the transportation sector increasingly shifts towards EVs to reduce carbon emissions, the demand for efficient lubricants becomes critical. WBLs here are defined as fluids containing a minimum of 50 wt% water mixed with glycerol, ethylene glycol (MEG), polyethylene glycol (PEG), or one of two polyalkylene glycols (PAGs). Rheological properties were investigated and compared with traditional lubricating oils. Results demonstrate distinctive rheological characteristics in WBLs, with viscosity–temperature responses resembling traditional oils with lowered pressure–viscosity coefficients. Nevertheless, WBLs exhibit promising film-forming capabilities in highly loaded contacts. Additionally, in sliding contacts, WBLs generally display lower friction coefficients compared to traditional oils, with PEG exhibiting the lowest value near 0.1. These findings suggest that WBLs may offer advantages in reducing friction and energy loss in EV applications. Furthermore, sliding wear tests indicate low wear rates in WBLs such as PEG, PAG, and glycerol, supporting their potential as viable lubrication options. The study highlights the importance of high-pressure rheology and tribochemistry in wear mechanisms among the different lubricants.

The influence of alkyl ammonium modifiers on the microstructure and high-pressure rheology of sepiolite-vegetable oil dispersions

In the context of environmental sustainability, the drilling industry faces new challenges resulting in the study and development of new drilling fluids based on eco-friendlier components to replace harmful mineral oils. Organic modified sepiolite dispersed in oil is an excellent additive to provide suitable rheological properties at low concentrations. The present study investigates the effect of alkyl ammonium modifiers on the microstructure and rheological properties of sepiolite-vegetable oil dispersions under high-temperature (up to 140 °C) and high-pressure (up to 2000 bar) conditions. Organo-sepiolite, prepared using a high-shear processing method and containing surfactant with alkyl chains longer than 12 carbon atoms, exhibited a high degree of surface adsorption and thermal resistance. All modifiers developed a stable fibrous structure in the dispersion. This structure maintained the pseudoplastic behavior in a wide range of shear rate, temperature and pressure without reaching an apparent yield stress. These dispersions showed suitable rheological and thermal properties to develop sustainable drilling fluids.

Wax appearance temperature under shear in methane-saturated mineral oil + paraffin wax mixtures: Effects of concentration and pressure

Increasing oil production from cold environments, such as offshore deep-water, has resulted in flow assurance issues due to wax deposition and hydrate formation. Understanding of the high-pressure flow properties of waxy oils is important to minimize blockages and related issues. However, the effect of pressure on wax appearance temperature (WAT) and viscosity of waxy oils is not widely studied due to the challenges of high-pressure rheology experiments. Here, a model waxy oil system was investigated using a high-pressure rheology from 0 to 1400 psig at 100 s−1. The focus was on paraffin wax in heavy mineral oil, and we examined wax concentrations of 5, 10, 15, and 20 wt%. First, waxy oils were saturated in methane, and then, temperature was decreased until wax appearance occurred. The findings revealed that wax concentration has a larger effect on WAT than pressure. At a constant pressure of 0 psig, WAT increases up to 13 °C when wax concentration increases from 5 to 20 wt%. Increasing pressure from 0 to 1400 psig results in up to 6 °C depression in wax appearance temperature for 20 wt% wax. The findings of the current study contribute to addressing flow assurance challenges in cold environments by enhancing the understanding of waxy oil rheology under methane-saturated, high-pressure conditions.

High Pressure Rheology of Lubricants (Part 1)

High Pressure Rheology of Lubricants (Part 1)

High Pressure Rheology of Lubricants (Part 5)

High Pressure Rheology of Lubricants (Part 5)

A Proposed Pressure–Viscosity Coefficient Model Through Processing of Falling Body Viscometry Data for Di-(Ethylhexyl) Sebacate

Abstract The relative volume and falling body viscosity of a common high-pressure rheology reference lubricant, di-(2-ethylhexyl) sebacate (DEHS), are presented. Relative volume measurements up to 300 MPa are completed with a piezo-bellows relative volume cartridge. Viscosity measurements up to 1 GPa are completed with a pressurized falling body viscometer. Digital signal-processing routines used for viscosity and relative volume measurements are discussed. The viscosity data are then fit into the modified Yasutomi model. Integration of this fit, as well as that of other models found in the literature, is used to propose a pressure–viscosity coefficient model. Comparisons are first made to DEHS, followed by the application of the study results to 17 other well-documented fluids. The validity of this method is investigated using the integrated viscosity model of DEHS as well as other available datasets presented in literature. The authors perform a comparison between the calculated pressure–viscosity coefficient α* and those presented for the mentioned datasets created with the signal-processing routines. The analysis shows that the proposed pressure–viscosity coefficient model is able to accurately capture the inverse of the asymptotic isoviscous pressure response of the majority of data when compared to other calculation methods.

High Pressure Rheology of Lubricants (Part 5)

High Pressure Rheology of Lubricants (Part 5)

High Pressure Rheology of Lubricants (Part 8)

High Pressure Rheology of Lubricants (Part 8)

High Pressure Rheology of Lubricants (Part 7)

High Pressure Rheology of Lubricants (Part 7)

Native corn and potato starch as CO[formula omitted] gas bubble nucleation agent for low-temperature high-pressure foaming applications

Gas bubble nucleation and its control is one of the most important parameters in industrial foaming applications defining the physical and chemical properties of the end product. It is possible to enhance this process by adding gas bubble nucleation supporting agents. In this work, the potency of native corn and potato starch as bubble nucleating agents for low-temperature high pressure (HP) foaming applications have been evaluated at 30 barg. In a first work step, the physical properties of the starches were assessed using scanning electron microscopy (SEM), Washburn rise method, nitrogen adsorption, Hg porosimetry as well as light scattering and compared to those of talcum, a well know and widely used nucleating agent in non-food systems. Secondly, the effect of the addition of these starch particles on CO2 gas bubble nucleation in highly viscous watery hydroxy-methyl-propyl-cellulose dispersions was determined applying HP rheology. Results of the surface properties evaluation suggested that the investigated native starch particles are suitable natural nucleating agents for HP foaming applications but are less efficient than talcum particles. The critical supersaturation value of a 1 wt% HPMC dispersion was reduced from 2.9±0.4 to 1.1±0.7 and 1.3±0.6 after the addition of 1 wt% corn and potato starch particles, respectively. The applied HP rheology technique developed to measure the critical supersaturation revealed, that the starches can compete with the talcum. These findings also allowed to validate the suitability of HP rheology to investigate gas bubble nucleation under defined shear conditions thus, enabling new insights into the mechanism of this process for low-temperature foaming applications in food and pharmaceutical product systems.

潤滑油の高圧物性（第5報） ―ファンデルワールス型粘性方程式の導出―

潤滑油の高圧物性（第5報） ―ファンデルワールス型粘性方程式の導出―

High Pressure Rheology of Lubricants (Part 6)

High Pressure Rheology of Lubricants (Part 6)

Is it possible to extract the pressure dependence of low-shear viscosity from EHL friction? Revised May, 2020

In the study of elastohydrodynamic lubrication the rheological properties of the liquid film are essential to understanding and predicting the friction and the film thickness in lubricated concentrated. There are two entirely different approaches to obtain these properties. In the quantitative approach, viscometers and rheometers are used at high pressure. In the classical approach, the same averaged properties are extracted from the contact itself. For more than 40 years the two methods have provided quite different pictures of high-pressure rheology. The claim has been made that the averaging technique provides viscosities that match those from this author's rheometer and viscometer. This claim can easily be shown to be false and the use of the contact as a viscometer must end.

High-Pressure Rheology of Methane Hydrate Sediment Slurry Using a Modified Couette Geometry

Information on the high pressure rheological properties of methane hydrate sediment slurry is an important precursor to understand their impact on the mechanical behaviour of host sediments during natural gas production from hydrate reservoirs. However, rheological analysis of gas hydrate slurries in the presence of natural sediments containing complex minerals and salts is not yet available in the open literature. The multiphase nature of hydrate systems is another challenge when it comes to the high pressure rheology study. Since, the conventional Couette geometry does not ensure proper mixing of solid, liquid and gas phases during hydrate formation and rheological measurements in a multiphase system, in this work, it has been modified to enhance the mixing capabilities. In this work, the rheological experiments on methane hydrate formation in sediment sample collected from Krishna Godavari Basin of offshore India have been performed. Rheological investigations were carried out using three different sed...

Enhancement of thermal stability of drilling fluid using laponite nanoparticles under extreme temperature conditions

Aiming to overcome the problem of polymer degradation in water based drilling fluids under high temperature, this letter examined the influence of laponite nanoparticles on the thermal stability of drilling fluids. Firstly, a terpolymer (AAD) was synthesized through radical polymerization of acrylamide, 2-acrylamido-2-methylpropane sulfonic acid, and diallyldimethylammonium chloride monomers. The presence of laponite nanoparticles significantly improved the onset decomposition temperature and viscosities of AAD terpolymer at high temperatures, according to thermogravimetric analysis (TGA) and high temperature high pressure (HTHP) rheology results, respectively. Thereafter, water based drilling fluids containing AAD and laponite were formulated and aged under different temperatures. The drilling fluids containing laponite had a substantially higher viscosity than that without laponite ascribing to strong interactions between laponite and functional groups of the ADD terpolymer. This letter provided us a novel strategy to develop high temperature resistant drilling fluids for deep reservoir excavation.

Fabrication of high-expansion microcellular PLA foams based on pre-isothermal cold crystallization and supercritical CO2 foaming

Poly(lactic acid) (PLA) is a kind of bio-based and biodegradable polymers. PLA foams with high expansion ratio have great application potential in heat insulation, adsorption and other areas. However, due to its low melt strength and slow crystallization rate, linear PLA has poor foaming ability, so it is hard to prepare PLA foams with high expansion ratio. Although chain branching, blending, and other methods have been utilized to improve PLA's melt strength and foaming ability, they easily destroy PLA's biodegradability, cause chemical pollution, and raise production costs. In this study, a new supercritical fluid foaming process, based on pre-isothermal cold crystallization, was proposed to prepare PLA foams with high expansion ratio. To improve PLA's melt strength and foaming ability, a pre-isothermal treatment was applied to induce sufficient cold crystallization. According to the SEM results, the cold crystallization of PLA becomes more sufficient and the crystal morphology becomes more perfect with the pre-isothermal treating. The DSC and WAXD results confirm that, the pre-isothermal treatment remarkably promotes the PLA's cold crystallization, and endows the PLA sample higher crystallinity and more perfect crystalline structure. Moreover, the high-pressure rheology testing results indicate that the pre-isothermal treatment improves the PLA's melt viscoelasticity significantly. Finally, the foaming results show that the pre-isothermal treatment significantly enhances the PLA's foaming ability. With the pre-isothermal treatment, the PLA's maximum expansion ratio increases from 6.40-fold to 17.7-fold, and the uniformity of cellular structure is also improved obviously. The new process provides a green, flexible, and low-cost way to prepare fully biodegradable PLA foams with high expansion ratio.