Pressure-viscosity Effect Research Articles

Electrokinetic energy conversion of high pressure-driven flow with pressure-viscosity effect at high zeta potential

In this study, the electrokinetic energy conversion efficiency is investigated theoretically in high pressure-driven flow with the pressure-viscosity effect. Calculations of the electrokinetic flow in a straight nanochannel are based on the Poisson-Boltzmann equation and modified fluid momentum equation. Once the viscosity of fluid is dependent on the pressure, the strongly non-linear governing equation should be solved simultaneously due to the unknown fluid viscosity. Thus, the domain perturbation method is used to solve the distributions of flow velocity and pressure. Based on obtained velocity and pressure, the maximum conversion efficiency is calculated by thermodynamic analysis. Results show the maximum efficiency increases with the decrease of salt concentration and the peak efficiency can be obtained at sufficiently low salt concentration. For a given salt concentration, the maximum efficiency decreases monotonously with the increase of pressure-viscosity coefficient. Besides, the maximum energy conversion efficiency of ignoring the pressure-viscosity effect is larger than that of considering the pressure-viscosity effect.

Analysis on micro-motion of cylinder block based on elasto-hydrodynamic lubrication

PurposeThe purpose of this paper is to analyze the micro-motion of the cylinder block.Design/methodology/approachBased on the elasto-hydrodynamic lubrication, a numerical model for the cylinder block/valve plate interface is proposed, with consideration of the elastic deformations, the pressure-viscosity effect and asperity contacts. The influence-function method is applied to calculating the actual deformations of the cylinder block and the valve plate. The asperity contact model simplified from Greenwood assumption is introduced into the numerical model. Furthermore, the relationship between the micro-motion and the operating condition, the sealing belt width is discussed, respectively.FindingsThe results show an increase in the discharge pressure causes the tilt state and the vibrating motion getting worse, which can be eased by improving the rotational speed, the sealing belt width and the ratio of external and internal sealing belt width.Originality/valueThe proposed research can provide a theoretical reference for the optimizing design of cylinder block/valve plate pair.

Numerical simulation of the roller hemming process based on pressure-viscosity effect

In the roller hemming process, the high-viscosity adhesive has affected the forming process of metal sheets, especially lightweight materials. However, the effect and mechanism are not clear. In this paper, the hemming adhesive is taken as a viscous Newtonian fluid. First of all, the pressure-viscosity effect in the model of parallel-panel squeeze is investigated, while the adhesive flow is simulated by smooth particle hydrodynamics (SPH) method, and the results are compared and verified by analytical solutions. Then, the roller hemming process of aluminum alloy sheet AA6106-T4 with adhesive is simulated by using the fluid-solid coupling method, while the adhesive is modeled by SPH and the aluminum alloy sheet is modeled by finite element method (FEM). The accuracy of the simulation model is verified by a comparison of roll-in/out in experiment and the effect and mechanism is studied based on the pressure-viscosity effect. The results show that adhesive thickness is the most important factor of the pressure-viscosity effect. The roll-in value of aluminum alloy sheet sample with 0.2-mm thick adhesive is relatively less than that without under the same conditions, and the roll-in of aluminum alloy sheet raises with an increase of the adhesive layer thickness. The evaluated roll-in/out of samples with different thickness of adhesive can obtain zero value theoretically after final hemming.

An Approach to Predict Wear Distribution of Valve Plate in Elasto-Hydrodynamic Lubrication

The leakage flow is the vital index judging axial piston pumps, which is strongly influenced by the wear resulting from the cylinder block tipping against the valve plate. In order to improve the energy efficiency and realize the reliable design of axial piston pumps, this paper presents an integrated model to predict the cylinder block/valve plate interface performance, numerically solving Reynolds equation coupled with the elasto-hydrodynamic deformations, the pressure–viscosity effect, and the asperity contacts. The film thickness distribution in steady state is numerically calculated, then the wear distribution under different kinds of operating conditions can be predicted based on the Archard wear equation. The analytical results indicate that the wear appears at both sides of the inner dead point, which is verified through measuring results. The proposed approach shows an essential prediction on the wear distribution.

Investigation on the radial micro-motion about piston of axial piston pump

The limit working parameters and service life of axial piston pump are determined by the carrying ability and lubrication characteristic of its key friction pairs. Therefore, the design and optimization of the key friction pairs are always a key and difficult problem in the research on axial piston pump. In the traditional research on piston/cylinder pair, the assembly relationship of piston and cylinder bore is simplified into ideal cylindrical pair, which can not be used to analyze the influences of radial micro-motion of piston on the distribution characteristics of oil-film thickness and pressure in details. In this paper, based on the lubrication theory of the oil film, a numerical simulation model is built, taking the influences of roughness, elastic deformation of piston and pressure-viscosity effect into consideration. With the simulation model, the dynamic characteristics of the radial micro-motion and pressure distribution are analyzed, and the relationships between radial micro-motion and carrying ability, lubrication condition, and abrasion are discussed. Furthermore, a model pump for pressure distribution measurement of oil film between piston and cylinder bore is designed. The comparison of simulation and experimental results of pressure distribution shows that the simulation model has high accuracy. The experiment and simulation results demonstrate that the pressure distribution has peak values that are much higher than the boundary pressure in the piston chamber due to the radial micro-motion, and the abrasion of piston takes place mainly on the hand close to piston ball. In addition, improvement of manufacturing roundness and straightness of piston and cylinder bore is helpful to improve the carrying ability of piston/cylinder pair. The proposed research provides references for designing piston/cylinder pair, and helps to prolong the service life of axial piston pump.

A Critical Assessment of the Role of Viscometers in Quantitative Elastohydrodynamics

Until very recently, viscometers have not had a significant role in the development of the field of elastohydrodynamic lubrication (EHL). Viscosity has generally been treated as an adjustable parameter that assumed the values at elevated pressure necessary to validate whatever model was proposed. The description of the pressure dependence of viscosity in EHL requires the choice of a model that reproduces the way that viscosity changes with pressure and requires values for the parameters of the chosen model. Viscometers are necessary for both requirements if a quantitative understanding of the mechanisms of film generation and friction is sought. Four types of pressurized viscometers, two based on Poiseuille flow and two on Couette flow, are investigated here. They yield remarkably similar pressure responses. There is therefore no ambiguity in the measurement of the pressure dependence of viscosity in pressurized viscometers. A significant challenge for engineers wishing to apply the results archived in the EHL literature is the assessment of the extent to which the results would be altered if an accurate viscosity had been employed. An important step toward establishing EHL as a quantitative science would be the designation of reference liquids for the pressure–viscosity effect and the use of these liquids in experimental and analytical investigations of EHL.

Study on the Hydrodynamic Lubrication Behavior in Cold Rolling Process

Partial lubrication in cold rolling process has been investigated. The average flow Reynolds equation for rolling lubrication is set. This equation considers the pressure-viscosity effect and the average flow effect. Lubricating factors such as inlet velocity, surface waviness, lubricant viscosity are studied in analyses. The results for lubrication equation show that inlet velocity and lubricant viscosity have some influence on the value of rolling friction. And the results also show that surface waviness has great influence on both rolling pressure and rolling friction.

An Elastohydrodynamic Lubrication Model for Coated Surfaces in Point Contacts

An elastohydrodynamic lubrication (EHL) model for coated surfaces in point contacts has been developed by combining the elastic deformation formulation for the coated surfaces with an EHL model. Inverse fast Fourier transform (IFFT) is employed first to obtain the influence coefficients (ICs) from the frequency response function (FRF). The subsequent calculation of elastic deformation is performed using the efficient algorithm of discrete convolution and fast Fourier transform (DC-FFT). The coating EHL model is verified by the comparison to available numerical results. The effects of coating on lubrication under various loads, speeds, rheological models, and pressure-viscosity behaviors are numerically investigated. Similar to the observations from dry contact, stiffer coatings in EHL tend to reduce the nominal contact radius but increase the maximum contact pressure, and vice versa for more compliant coatings. However, as coating thickness increases, the influence of coatings on film thickness, including the central and the minimum film thicknesses, does not follow a monotonic variation, and therefore, cannot be predicted by any simple film thickness equation. The reason for that is the pressure viscosity effect which tends to counterbalance the effect of coating. The average friction coefficient in lubricant film increases in stiff coating cases but decreases for compliant coating cases. Furthermore, two possible approaches to improving the minimum film thickness thus reducing friction and wear in mixed lubrication are indicated: a thin stiff coating for conventional EHL and a thick compliant coating for soft EHL.

Computer-aided Modelling of Pressure Balances

Pressure metrologists and other research workers have always aimed at the accurate determination of the distortion coefficient λ characterizing the effective area of a pressure balance. This paper presents a novel and unique treatment which incorporates both the elastic distortions of the piston and the cylinder, and the pressure-viscosity effect. The Finite Element method is used to calculate the elastic distortions, but an iterative solution is obtained for the pressure-viscosity effect. An extensive validation of the developed computer models have been carried out and one new finding is reported. It is concluded that for balances with complex geometries the distortion coefficient depends on the geometrical and material properties of a balance as well as on its operating pressure.

The Study of Hydrostatic Lubrication of the Slipper in a High-Pressure Plunger Pump

The lubrication condition between the slipper and the oblique plate of a high pressure pump affects its operating life. One of the studies in this paper is to analyze the oil film pressure distribution and load characteristics, considering the pressure-viscosity effect of the lubricant and the pressure-elasticity effect of the lubricating surface. In addition, a laser holographic photoelastic experimental verification is proposed. Another aspect of the study concerns the investigation of the dynamic stiffness properties of the oil film and its experimental verification. The conclusions obtained here provide a new theoretical basis for the design and parameter selection of a J high pressure plunger pump.

Pressure-viscosity effect on the solutions of a lubricated thick elastic bonded strip

Utilizing the numerical method developed by the author for isoviscous, fully flooded, elastohydrodynamic lubrication of a rigid cylinder rolling or sliding on an elastic strip (layer) which is attached to a rigid substrate (bonded strip), the influence on the pressure-viscosity coefficient, α, upon solutions is investigated. The present solutions are obtained for contacts operating in the transition region betweeen isoviscous-elastic and piezoviscous-elastic regimes where a pressure spike can be expected in some sense. New sets of results are presented for central and minimum film thicknesses in dimensionless form when the bonded strip is thick (0⪕γ⪕1, where γ = a/t is the ratio of the half contact width to strip thickness). It is shown that the film thickness depends not only on the values of α but also is influenced by Poisson's ratio, v.

The effect of pressure on viscosity in hydraulic lock

The solution of Reynolds' equation for hydraulic lock is given when the viscosity is a known function of pressure. This leads to the evaluation of an integral which is solved numerically on a digital computer. The results show that as a result of the pressure-viscosity effect the hydraulic-lock forces can be considerably increased.

The Pressure-Viscosity Effect: Background

Abstract Indications are that the pressure-viscosity effect is an important factor in certain cases of lubrication, notably heavily-loaded elements. How important it is in the lubrication of lightly-loaded elements we do not know, nor do we know what refinements in design may be possible by taking this factor into account. The three papers which follow this introduction are modern contributions to our knowledge in this area. Following them, the Research Proposal on the Machine Element Test program will be discussed. Hopefully, the result of this presentation and discussion will be a better understanding of the importance of this problem and the potential value to industry of a solution to it.