Thickness Of Fluids Research Articles

Perturbation method in gas-assisted power-law fluid displacement in a circular tube and a rectangular channel

In this paper the two dimensional flow of a power-law fluid is studied analytically using a singular perturbation method in order to determine the residual liquid film thickness of power-law fluids on the wall of a circular tube or a rectangular channel when displaced by another immiscible fluid. Inner and outer expansions are developed in terms of a small parameter C A 1/3 (modified capillary number). A differential equation for the shape of gas bubble is solved numerically in order to determine the inner solution. The method of matched asymptotic expansions is used to match the inner and outer solutions. This approach indicated that the residual liquid film thickness of non-Newtonian fluids increases with decreasing power-law index.

Effect of Viscosity Index Improvers on the Elastohydrodynamic Lubrication Characteristics of a Chlorotrifluoroethylene and a Polyalphaolefin Fluid

The film thickness characteristics and traction behavior, two of the more important elastohydrodynamic lubrication (EHL) properties, of two important classes of synthetic lubricants have been studied. The effect of viscosity index (VI) improvers on these properties has been determined for both hydrogenated polyalphaolefin (PAO) base fluids and chlorotrifluoroethylene oligomer (CTFE) base fluids. A polyalkylmethacrylate (PMM) VI improver was studied in PAO and a copolymer of vinylidine fluoride and chlorotrifluoroethylene was studied in CTFE. The VI improvers demonstrated insignificant improvement in the EHL film thickness of both the PAO and CTFE base fluids as determined by comparing the measured film thickness of the VI-improved fluids to the predicted film thickness based on measured pressure-viscosity characteristics and kinematic viscosities determined at low shear rates. Similarly, the traction behavior of VI-improved PAO and CTFE fluids was nearly equivalent to that of the respective base fluids, demonstrating very little effect of the VI improvers on these properties. The minimal contribution is attributed to the non-Newtonian behavior of the VI improved fluids under the high shear rates and stresses found in an EHL contact. Physical properties of the base oil determine the true behavior of a VI-improved fluid under EHL conditions; therefore, the properties of the base fluid should be used in theoretical predictions instead of the properties of the formulated fluid.

The Effect of Nonlinear Viscoelasticity of Lubricants on Piston Ring Lubrication.

In recent years, engine oils have contained various kinds of additives such as high molecular-weight polymers to improve their performance. Such lubricants exhibit viscoelastic behavior, but the lubricants were assumed to be Newtonian fluids in most of the previous investigations on piston ring lubrication. The objective of this paper is to theoretically clarify the effect of nonlinear viscoelasticity of lubricants on piston ring lubrication by introducing a nonlinear four-element viscoelastic model which consists of two nonlinear dashpots and two nonlinear springs. Numerical solutions show that the effect of viscoelasticity reduced the frictional force and the film thickness. In addition, the phase of the variations of the frictional force and the film thickness of viscoelastic fluids is delayed compared with that of Newtonian fluids.

On slip effect in free coating of non-Newtonian fluids

The failure of the current theories to predict the coating thickness of non-Newtonian fluids in free coating operations is shown to be a result of the effective slip at the moving rigid surface being coated. This slip phenomenon is a consequence of stress induced diffusion occurring in flow of structured liquids in non-homogeneous flow fields. Literature data have been analysed to substantiate the slip hypothesis proposed in this work. The experimentally observed coating thickness is shown to lie between an upper bound, which is estimated by a no-slip condition for homogeneous solution and a lower bound, which is estimated by using solvent properties. Some design considerations have been provided, which will serve as useful guidelines for estimating coating thickness in industrial practice.

Film Thickness and Effective Viscosity of Some Fire Resistant Fluids in Sliding Point Contacts

Optical film thickness measurements are performed in a pure sliding point contact apparatus for different fire resistant fluids: a water in oil emulsion, a water glycol and a chlorinated diphenyl. Good correlation between theoretical and experimental film thickness results is obtained in the elastohydrodynamic regime for a wide range of pressure viscosity coefficients. No relaxation effects are noted, but the viscosity of the water in oil emulsion is shown to exhibit essentially that of the base oil at high shear rates.

Closure to “Discussion of ‘Film Thickness and Effective Viscosity of Some Fire Resistant Fluids in Sliding Point Contacts’” (1978, ASME J. Lubr. Technol., 100, p. 307)

Closure to “Discussion of ‘Film Thickness and Effective Viscosity of Some Fire Resistant Fluids in Sliding Point Contacts’” (1978, ASME J. Lubr. Technol., 100, p. 307)

Piezoelectric method of determining viscosity at 40 kHz

The torsional composite oscillator enables the viscosity, shear modulus, strain rate, and fluid thickness of nonelasticoviscous and elasticoviscous fluids to be determined quickly and accurately, making it a powerful technique for measuring both static and transient phenomena. In this paper the equations relating the measured Q and period to the fluid viscous properties are derived and the resulting viscosity for four nonelasticoviscous fluids from 10−3 to 2 Pa s is confirmed to 1/2% and better by comparison with literature values. Experimental arrangements and procedures are described which indicate how this technique can be used for strain rates from as low as ∼10−5–10−3 s−1 to as high as ∼105–107 s−1.