Elastohydrodynamic Lubrication With O/W Emulsions

1994 ◽  
Vol 116 (2) ◽  
pp. 310-319 ◽  
Author(s):  
D. Zhu ◽  
G. Biresaw ◽  
S. J. Clark ◽  
T. J. Kasun
Keyword(s):  
Film Thickness ◽  
Transition Region ◽  
High Speed ◽  
Critical Speed ◽  
Two Phase ◽  
Ph Values ◽  
Wide Range ◽  
Oil Concentration ◽  
Oil Pool ◽  
Inlet Zone

This paper presents a set of experimental results of the EHL film thickness with oil-in-water (O/W) emulsions in a wide range of rolling speed for different oil concentrations and pH values. The O/W emulsions have wide applications in metal-forming and machining processes as well as hydraulic systems. However, their lubrication mechanisms are very complex and have not been fully understood. A newly developed high speed optical EHL rig was used to measure the film thickness and observe the two-phase flow around the EHL point and line contacts. Experimental observations indicate that phase inversion/oil pool formation mechanism around the inlet zone takes place only at very low speeds, which are most likely far below practical speed ranges for major industrial applications. When the speed is low, the lubricant film thickness is dominated by the bulk properties of oil phase, and can be estimated by the conventional EHL theory together with the consideration of starvation effect. After the speed exceeds a certain limit, called first critical speed, there is a transition region, where no stable oil pool is observed and the film thickness starts to decrease, or increases slightly then decreases. It is believed that in this transition region there is still a considerable amount of oil concentrated in the inlet zone, and this local oil concentration decreases as the speed increases. The film thickness appears to be dominated by the entrainment of oil-enriched two-phase lubricant in the inlet zone. The increase of film thickness is due to entraining effect and the decrease due to the increased oil phase starvation. If the speed is further increased exceeding a second critical speed, the film thickness will stop decreasing and start to increase again. In this high speed region the local oil concentration of entrained lubricant in the inlet zone is believed to become quite constant and close to that of the bulk lubricant supply. The film thickness, therefore, continuously increases for all of the tested line and point contact cases as the speed goes up, and is always significantly smaller than that of neat oil but larger than that of pure water. The destabilized emulsions with lower pH values can form more stable oil pools and considerably thicker films. This is because the oil droplets in these low pH emulsions can be more easily trapped and brought into the contact by the solid surfaces. However, for the tested emulsions, the oil pools still cannot survive reasonably high speeds.

Experimental and Numerical Study of Emulsion Lubricated Strip Rolling

2005 ◽  
Author(s):  
P. B. Kosasih ◽  
A. K. Tieu
Keyword(s):  
Film Thickness ◽  
Numerical Study ◽  
Rolling Process ◽  
Work Zone ◽  
Contact Ratio ◽  
Strip Rolling ◽  
Two Phase ◽  
Oil Concentration ◽  
Mixed Film ◽  
Inlet Zone

An experimental and numerical study of cold rolling lubricated by O/W emulsion has been carried out. The experimental measurements are compared to the computed results from the numerical scheme developed by the authors. The scheme, which is based on two-phase lubricant model, is able to calculate oil concentration at any point within the inlet zone and work zone, rolling pressure, film thickness, and fractional contact ratio associated with strip rolling under mixed film lubrication at different rolling speed. The study encompassed extensive mixed film regime for speed, S ranges from 10−5 to 10−1, and supply oil concentration level λds ranges from 1% to 10%, and oil droplet size ranges from Ds from 5 to 20. The numerical results show the occurrence of moderate oil concentration increase in the inlet zone followed by a sharp one at the beginning of the work zone. The effect of the concentration process is predominantly seen in the film thickness and the lubricant pressure whilst its effect on the total pressure is less pronounced. The analysis of the results suggests that it is possible to lower the emulsion oil concentration without detrimental effects on the rolling process and indeed use this principle to control the outlet lubricant film thickness.

An Experimental Study of Liquid Film Thickness in Annular Air/Oil Flow in a Vertical Pipe Using a Laser Focus Displacement Meter

2001 ◽  
Author(s):  
S. Busam ◽  
J. Ebner ◽  
S. Wittig
Keyword(s):  
Experimental Study ◽  
Film Thickness ◽  
High Speed ◽  
Flow Direction ◽  
Oil Viscosity ◽  
Two Phase ◽  
Pressure Losses ◽  
Laser Focus ◽  
Wide Range ◽  
Oil Flow

The development of modern aero-engines is leading to increased pressure and temperature levels which makes increasing demands on the engines’ safety and reliability. In particular the vent-system of the bearing chambers located in the hot section of the engine represents a critical component in the design process due to the complex two-phase flow phenomena. The air/oil mixture that is discharged out of the bearing chambers has a strong influence on the overall pressure losses and it shows locally enhanced heat transfer where oil coking or oil fires with the risk of flashback into the bearing chamber can occur. In order to gain a deeper insight into the interacting flow of air and oil, a glass pipe test section with a inner tube diameter of 10 mm was integrated into the vent-line of the high speed bearing chamber test rig operated at the Institut für Thermische Strömungsmaschinen, University of Karlsruhe, Germany. Therewith, an experimental study of the oil film along the wall in vertical annular upflow was performed by use of a laser focus displacement meter. This instrument which was introduced by Takamasa et al. [1] allows accurate measurements of film thickness to be made in real time with a sensitivity of 2 microns and a datarate of 1.5 kilohertz. Comprehensive measurements were conducted at two locations of the pipe 320 mm apart in flow direction. A wide range of oil and air flow rates was examined to study their impact on the local film thickness. Both fluids were heated up to the same temperature of 70°C and 100 °C, respectively, to vary the oil viscosity by a factor of 2.

Observations of Liquid Droplet Behavior and Oil Film Formation in O/W Type Emulsion Lubrication

1988 ◽  
Vol 110 (2) ◽  
pp. 348-353 ◽  
Author(s):  
T. Nakahara ◽  
T. Makino ◽  
K. Kyogoku
Keyword(s):  
High Speed ◽  
Liquid Droplet ◽  
Film Formation ◽  
Flat Glass ◽  
Glass Plate ◽  
Rolling Speed ◽  
Liquid Droplets ◽  
Speed Range ◽  
Oil Concentration ◽  
Inlet Zone

The behavior of liquid droplets in O/W type emulsions flowing between a flat glass plate and a metal roller was observed by means of a microscope. The behavior of the droplets introduced into the EHL film was found to be related to the streamlines of the continuous water phase in the vicinity of the inlet zone. It was observed that the oil droplets which penetrated into the EHL zone formed an oily pool (an oily film zone) containing water droplets in the inlet zone close to the EHL zone. This oily pool was a W/O emulsion rich in oil caused by phase inversion. The effects of oil concentration, emulsifier content and rolling speed on the area of the oily pool were investigated, and it was found that the extent of the oily pool was influenced by the rolling speed as well as oil concentration. The EHD film thickness was measured by means of optical interferometry with use of two wavelengths, and the measured results were compared with the calculated ones employing the starvation theory of Wolveridge et al. and the empirical equation of Wymer and Cameron for the region of the oil pool. It was found that course droplets play an important role in film formation by causing the formation of the oily pool in the low speed range. In the high speed range, however, a fine O/W emulsion forms the film.

Numerical Analysis of Cavitation Instabilities Arising in the Three-Blade Cascade

2004 ◽  
Vol 126 (3) ◽  
pp. 419-429 ◽  
Author(s):  
Yuka Iga ◽  
Motohiko Nohml ◽  
Akira Goto ◽  
Toshiaki Ikohagi
Keyword(s):  
Numerical Method ◽  
High Speed ◽  
Homogeneous Model ◽  
Rotating Stall ◽  
Two Phase ◽  
Wide Range ◽  
Phase Medium ◽  
Long Time ◽  
Entire Flow ◽  
Locally Homogeneous

Three types of cavitation instabilities through flat plate cascades, which are similar to “forward rotating cavitation,” “rotating-stall cavitation” and “cavitation surge” occurring in high-speed rotating fluid machinery, are represented numerically under the three-blade cyclic condition. A numerical method employing a locally homogeneous model of compressible gas-liquid two-phase medium is applied to solve the above flow fields, because this permits the entire flow field inside and outside the cavity to be treated through only one system of governing equations. In addition, the numerical method suites to analyze unsteady cavitating flow with a long time evolution. From the calculated results of the present numerical simulation with wide range of cavitation number and flow rate, we obtain a cavitation performance curve of the present three-blade cyclic cascade, analyze the aspects of unsteady cavitation, and discuss the characteristics and mechanisms of cavitation.

An Improved Correlation for Two-Phase Frictional Pressure Drop in Boiling and Adiabatic Downflow in the Annular Flow Regime

1991 ◽  
Vol 205 (5) ◽  
pp. 317-328 ◽  
Author(s):  
J F Klausner ◽  
B T Chao ◽  
S L Soo
Keyword(s):  
Pressure Drop ◽  
Film Thickness ◽  
Flow Regime ◽  
Annular Flow ◽  
Volume Fraction ◽  
Interfacial Shear Stress ◽  
Published Data ◽  
Two Phase ◽  
Frictional Pressure Drop ◽  
Wide Range

An improved correlation is presented for annular two-phase frictional pressure drop data for vertical downflow. An ideal dimensionless film thickness based on the vapour volume fraction, a characteristic friction factor based on the two-phase frictional pressure gradient and a Weber number relevant for the interfacial capillary wave structure are the correlating parameters. The proposed new correlating scheme is tested against a wide range of data obtained in this investigation for refrigerant R11 in forced convection boiling and in adiabatic test sections of 19 mm cylindrical cross-section as well as published data for air-water and air-glycerine solution mixtures in the annular flow regime. Over 80 per cent of the measured values fall within ±30 per cent of those predicted from the correlation. Due to the wide range of liquid film thickness covered, 0.05–2.9 mm, its validity extends past the range where previously reported downflow pressure drop correlations fail. A paradox connected with previously reported annular downflow pressure drop correlations based on the liquid-vapour interfacial shear stress is pointed out. Upflow frictional pressure drop data in the annular flow regime can also be correlated by the proposed scheme.

Gas-Expanded Lubricant Performance and Effects on Rotor Stability in Turbomachinery

2014 ◽  
Author(s):  
Brian K. Weaver ◽  
Timothy W. Dimond ◽  
Jason A. Kaplan ◽  
Alexandrina Untaroiu ◽  
Andres F. Clarens
Keyword(s):  
Film Thickness ◽  
Power Loss ◽  
High Speed ◽  
Turbine Generator ◽  
Generator System ◽  
Polyol Ester ◽  
Damping Coefficients ◽  
Wide Range ◽  
Bearing Stiffness ◽  
Stiffness And Damping

Gas-expanded lubricants (GELs) are tunable mixtures of synthetic oil and carbon dioxide that enable dynamic control of lubricant viscosity during bearing operation. This control can help reduce bearing power loss and operating temperatures while also providing direct control over bearing stiffness and damping, which can enhance rotordynamic performance. In this work, the bearing and rotordynamic performance of two representative high-speed machines was evaluated when different lubricants, including GELs, were supplied to the machine bearings. The machines chosen for this analysis, an 8-stage centrifugal compressor and a steam turbine-generator system, represent a wide range of speed and loading conditions encountered in modern turbomachinery. The fluids compared for machine performance were standard petroleum-based lubricants, polyol ester synthetic oils, and polyol ester based-GELs. The performance simulations were carried out using a thermoelastohydrodynamic bearing model, which provided bearing stiffness and damping coefficients as inputs to finite element rotordynamic models. Several bearing performance metrics were evaluated including power loss, operating temperature, film thickness, eccentricity, and stiffness and damping coefficients. The rotordynamic analysis included an evaluation of rotor critical speeds, unbalance response, and stability. Bearing performance results for the compressor showed a 40% reduction in power loss at operating speed when comparing the GEL to the petroleum-based lubricant. The GEL-lubricated compressor also exhibited lower operating temperatures with minimal effects on film thickness. GELs were also predicted to produce lower bearing stiffness when compared to standard fluids in the compressor. Rotordynamic results for the compressor showed that the fluid properties had only minor effects on the unbalance response, while GELs were found to increase the stability margin by 43% when compared with standard fluids. The results from the turbine-generator system also demonstrated increases in low-speed bearing efficiency with the use of GELs, though at higher speeds the onset of turbulent flow in the GEL case offset these efficiency gains. Rotordynamic results for this system showed a contrast with the compressor results, with the GELs producing lower stability margins for a majority of the modes predicted due to increased bearing stiffness in the high-speed turbine bearings and negative stiffness in the lightly loaded, low-speed pinion bearings. These results suggest that GELs could be beneficial in providing control over a wide range of machine designs and operating conditions and that some machines are especially well suited for the tunability that these fluids impart.

scholarly journals Experimental Investigation Into Droplet Impingement Upon Moving Films Using High Speed Video and Thermal Imaging

2015 ◽  
Author(s):  
Antony J. Mitchell ◽  
Kathy Simmons ◽  
David Hann
Keyword(s):  
Film Thickness ◽  
Parameter Space ◽  
High Speed ◽  
A Priori ◽  
Experimental Parameter ◽  
Infrared Camera ◽  
High Speed Imaging ◽  
Two Phase ◽  
Jet Breakup ◽  
Crater Shape

Aeroengine bearing chambers are geometrically complex, typically containing shafts, bearings, seals and stationary components. Oil is supplied for lubrication and cooling and so the chamber contains a highly rotating two-phase (oil/air) flow where the oil is typically present as droplets, ligaments, mist and films. These films may be thick or thin and film speed varies with chamber location. It is desirable to know a priori the outcome of a droplet-film impact event in terms of mass, momentum and energy transfer. There is a significant body of research on the interaction between droplets and static films. The experimental parameter space has been characterised on the basis of film thickness and impact parameter to predict the outcome of an impingement. The impingement of droplets on moving films has only begun to be investigated over the last decade and consequently models have not yet been developed and the parameter space has barely begun to be characterised. Within this paper results are presented from an experimental study in which water droplets of 3 mm and 3.8 mm at 20°C falling under the influence of gravity impinged onto water films flowing down an inclined plane. Film temperature was 30°C and film thicknesses were between 2.3 mm and 4.2 mm. High speed imaging was used to determine the impingement outcomes and cavity morphology. A high speed infrared camera was used to determine the extent of the thermally affected region and its temperature behaviour. We find that by using the resultant droplet velocity (combining droplet and film velocities) the film impingement outcomes can be characterised into regions very similar to those for static films. The data is presented as a function of splashing parameter and non-dimensional film thickness. It was observed that for these impacts on supercritical films (Fr > 1) there is less propensity for secondary droplet formation through jet breakup than on static and subcritical films (Fr < 1). Data was obtained for extent of the thermally affected region. It was found that the cooler droplet liquid spreads over the inside of the crater before heating up to film temperature. Development of crater shape and size was also studied and data compared to established models for droplet impact on deep static films. During the initial stages of an impact crater area increases similarly to that for static films although the crater shape itself is less similar and is asymmetrical due to the film motion.

Gas-Expanded Lubricant Performance and Effects on Rotor Stability in Turbomachinery

2015 ◽  
Vol 137 (7) ◽  
Author(s):  
Brian K. Weaver ◽  
Timothy W. Dimond ◽  
Jason A. Kaplan ◽  
Alexandrina Untaroiu ◽  
Andres F. Clarens
Keyword(s):  
Film Thickness ◽  
Power Loss ◽  
High Speed ◽  
Turbine Generator ◽  
Generator System ◽  
Low Speed ◽  
Damping Coefficients ◽  
Wide Range ◽  
Bearing Stiffness ◽  
Stiffness And Damping

Gas-expanded lubricants (GELs) are tunable mixtures of synthetic oil and carbon dioxide that enable dynamic control of lubricant viscosity during bearing operation. This control can help reduce bearing power loss and operating temperatures while also providing direct control over bearing stiffness and damping, which can enhance rotordynamic performance. In this work, the bearing and rotordynamic performance of two representative high-speed machines was evaluated when different lubricants, including GELs, were supplied to the machine bearings. The machines chosen for this analysis, an eight-stage centrifugal compressor and a steam turbine-generator system, represent a wide range of speed and loading conditions encountered in modern turbomachinery. The fluids compared for machine performance were standard petroleum-based lubricants, polyol ester (POE) synthetic oils, and POE-based GELs. The performance simulations were carried out using a thermoelastohydrodynamic bearing model, which provided bearing stiffness and damping coefficients as inputs to finite element rotordynamic models. Several bearing performance metrics were evaluated including power loss, operating temperature, film thickness, eccentricity, and stiffness and damping coefficients. The rotordynamic analysis included an evaluation of rotor critical speeds, unbalance response, and stability. Bearing performance results for the compressor showed a 40% reduction in power loss at operating speed when comparing the GEL to the petroleum-based lubricant. The GEL-lubricated compressor also exhibited lower operating temperatures with minimal effects on film thickness. GELs were also predicted to produce lower bearing stiffness when compared to standard fluids in the compressor. Rotordynamic results for the compressor showed that the fluid properties had only minor effects on the unbalance response, while GELs were found to increase the stability margin by 43% when compared with standard fluids. The results from the turbine-generator system also demonstrated increases in low-speed bearing efficiency with the use of GELs, though at higher speeds the onset of turbulent flow in the GEL case offset these efficiency gains. Rotordynamic results for this system showed a contrast with the compressor results, with the GELs producing lower stability margins for a majority of the modes predicted due to increased bearing stiffness in the high-speed turbine bearings and negative stiffness in the lightly loaded, low-speed pinion bearings. These results suggest that GELs could be beneficial in providing control over a wide range of machine designs and operating conditions and that some machines are especially well suited for the tunability that these fluids impart.

Measurement of Void Fraction and Pressure Drop of Air-Oil Two-Phase Flow in Horizontal Pipes

2004 ◽  
Vol 126 (1) ◽  
pp. 107-118 ◽  
Author(s):  
J. L. Pawloski ◽  
C. Y. Ching ◽  
M. Shoukri
Keyword(s):  
Pressure Drop ◽  
Flow Regime ◽  
Void Fraction ◽  
High Speed ◽  
Two Phase Flow ◽  
Flow Regimes ◽  
Phase Flow ◽  
Two Phase ◽  
Wide Range ◽  
Flow Regime Maps

The void fractions, flow regimes, and pressure drop of air-oil two-phase flow in a half-inch diameter pipe over a wide range of test conditions have been investigated. The flow regimes were identified with the aid of a 1000 frames per second high-speed camera. A capacitance sensor for instantaneous void fraction measurements was developed. The mean and probability density function of the instantaneous void fraction signal can be used to effectively identify the different flow regimes. The current flow regime data show significant differences in the transitional boundaries of the existing flow regime maps. Property correction factors for the flow regime maps are recommended. The pressure drop measurements were compared to the predictions from four existing two-phase flow pressure drop models. Though some of the models performed better for certain flow regimes, none of the models were found to give accurate results over the entire range of flow regimes.

scholarly journals Synchronized Multiple Drop Impacts into a Deep Pool

Fluids ◽  
2019 ◽  
Vol 4 (3) ◽  
pp. 141 ◽  
Author(s):  
Manfredo Guilizzoni ◽  
Maurizio Santini ◽  
Stephanie Fest-Santini
Keyword(s):  
Fluid Dynamics ◽  
High Speed ◽  
Laboratory Experiments ◽  
Distilled Water ◽  
Single Drop ◽  
Two Phase ◽  
Wide Range ◽  
Computational Fluid Dynamics Cfd ◽  
Drop Impacts ◽  
The Impact

Drop impacts (onto dry or wet surfaces or into deep pools) are important in a wide range of applications, and, consequently, many studies, both experimental and numerical, are available in the literature. However, such works are focused either on statistical analyses of drop populations or on single drops. The literature is heavily lacking in information about the mutual interactions between a few drops during the impact. This work describes a computational fluid dynamics (CFD) study on the impact of two, three, and four synchronized drops into a deep pool. The two-phase finite-volume solver interFoam of the open source CFD package OpenFOAM® was used. After validation with respect to high speed videos, to confirm the performance of the solver in this field, impact conditions and aspects that would have been difficult to obtain and to study in experiments were investigated: namely, the energy conversion during the crater evolution, the effect of varying drop interspace and surface tension, and multiple drop impacts. The results show the very significant effect of these aspects. This implies that an extension of the results of single-drop, distilled-water laboratory experiments to real applications may not be reliable.

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