On the liquid lining in fluid-conveying curved tubes

2011 ◽  
Vol 705 ◽  
pp. 213-233 ◽  
Author(s):  
Andrew L. Hazel ◽  
Matthias Heil ◽  
Sarah L. Waters ◽  
James M. Oliver
Keyword(s):  
Thin Film ◽  
Surface Tension ◽  
Film Thickness ◽  
Secondary Flows ◽  
Immiscible Fluid ◽  
Straight Tube ◽  
Core Flow ◽  
Film Model ◽  
Thin Film Model ◽  
Axial Pressure Gradient

AbstractWe consider axially uniform, two-phase flow through a rigid curved tube in which a fluid (air) core is surrounded by a film of a second, immiscible fluid (water): a simplified model for flow in a conducting airway of the lung. Jensen (1997) showed that, in the absence of a core flow, surface tension drives the system towards a configuration in which the film thickness tends to zero on the inner wall of the bend. In the present work, we demonstrate that the presence of a core flow, driven by a steady axial pressure gradient, allows the existence of steady states in which the film thickness remains finite, a consequence of the fact that the tangential stresses at the interface, imposed by secondary flows in the core, can oppose the surface-tension-driven flow. For sufficiently strong surface tension, the steady configurations are symmetric about the plane containing the tube’s centreline, but as the surface tension decreases the symmetry is lost through a pitchfork bifurcation, which is closely followed by a limit point on the symmetric solution branch. This solution structure is found both in simulations of the Navier–Stokes equations and a thin-film model appropriate for weakly curved tubes. Analysis of the thin-film model reveals that the bifurcation structure arises from a perturbation of the translational degeneracy of the interface location in a straight tube.

Modelling of Partially Wetting Liquid Film Using an Enhanced Thin Film Model for Aero-Engine Bearing Chamber Applications

2020 ◽  
Author(s):  
K. Singh ◽  
M. Sharabi ◽  
R. Jefferson-Loveday ◽  
S. Ambrose ◽  
C. Eastwick ◽  
...  
Keyword(s):  
Thin Film ◽  
Contact Angle ◽  
Film Thickness ◽  
Liquid Film ◽  
Flow Rate ◽  
Operating Conditions ◽  
Film Model ◽  
Thin Film Model ◽  
Wide Range ◽  
Aero Engine

Abstract In the case of aero-engine, thin lubricating film servers dual purpose of lubrication and cooling. Prediction of dry patches or lubricant starved region in bearing or bearing chambers are required for safe operation of these components. In the present work thin liquid film flow is numerically investigated using the framework of the Eulerian thin film model (ETFM) for conditions which exhibit partial wetting phenomenon. This model includes a parameter that requires adjustment to account for the dynamic contact angle. Two different experimental data sets have been used for comparisons against simulations, which cover a wide range of operating conditions including varying the flow rate, inclination angle, contact angle, and liquid-gas surface tension coefficient. A new expression for the model parameter has been proposed and calibrated based on the simulated cases. This is employed to predict film thickness on a bearing chamber which is subjected to a complex multiphase flow. From this study, it is observed that the proposed approach shows good quantitative comparisons of the film thickness of flow down an inclined plate and for the representative bearing chamber. A comparison of model predictions with and without wetting and drying capabilities is also presented on the bearing chamber for shaft speed in the range of 2,500 RPM to 10,000 RPM and flow rate in the range of 0.5 liter per minute (LPM) to 2.5 LPM.

scholarly journals Modeling of Partially Wetting Liquid Film Using an Enhanced Thin Film Model for Aero-Engine Bearing Chamber Applications

2021 ◽  
Vol 143 (4) ◽  
Author(s):  
Kuldeep Singh ◽  
Medhat Sharabi ◽  
Richard Jefferson-Loveday ◽  
Stephen Ambrose ◽  
Carol Eastwick ◽  
...  
Keyword(s):  
Thin Film ◽  
Contact Angle ◽  
Film Thickness ◽  
Liquid Film ◽  
Thin Liquid Film ◽  
Operating Conditions ◽  
Film Model ◽  
Thin Film Model ◽  
Wide Range ◽  
Aero Engine

Abstract In the case of aero-engine, thin lubricating film servers dual purpose of lubrication and cooling. Prediction of dry patches or lubricant starved region in bearing or bearing chambers are required for safe operation of these components. In this work, thin liquid film flow is numerically investigated using the framework of the Eulerian thin film model (ETFM) for conditions, which exhibit partial wetting phenomenon. This model includes a parameter that requires adjustment to account for the dynamic contact angle. Two different experimental data sets have been used for comparisons against simulations, which cover a wide range of operating conditions including varying the flowrate, inclination angle, contact angle, and liquid–gas surface tension coefficient. A new expression for the model parameter has been proposed and calibrated based on the simulated cases. This is employed to predict film thickness on a bearing chamber which is subjected to a complex multiphase flow. From this study, it is observed that the proposed approach shows good quantitative comparisons of the film thickness of flow down an inclined plate and for the representative bearing chamber. A comparison of model predictions with and without wetting and drying capabilities is also presented on the bearing chamber for shaft speed in the range of 2500 RPM to 10,000 RPM and flowrate in the range of 0.5 liter per minute (LPM) to 2.5 LPM.

scholarly journals Assessment of an Enhanced Thin Film Model to Capture Wetting and Drying Behavior in an Aero-Engine Bearing Chamber

2019 ◽  
Author(s):  
Kuldeep Singh ◽  
Medhat Sharabi ◽  
Stephen Ambrose ◽  
Carol Eastwick ◽  
Richard Jefferson-Loveday ◽  
...  
Keyword(s):  
Thin Film ◽  
Contact Angle ◽  
Film Thickness ◽  
Wetting And Drying ◽  
Film Model ◽  
Thin Film Model ◽  
Aero Engine ◽  
Thickness Prediction ◽  
Drying Behavior ◽  
Engine Bearing

Abstract In the present work, a wetting and drying model is coupled with Eulerian Thin-Film model (ETFM) to analyze the wetting and drying behavior inside the bearing chamber. In the enhanced model, an additional source term is included to account for the contact angle effect. These models were coupled with volume-of-fluid (VOF) such that the core region is resolved by VOF and region close to the chamber walls, where a thin film is expected is resolved by either ETFM or enhanced ETFM model. Numerical studies are conducted for a shaft speed of 5,000 rpm, lubricant and air flow rates of 100 1/hr and 10 g/s respectively, at a scavenging ratio of 4. In the case of enhanced ETFM model lubricant to surface contact angle was varied from 10° to 45°. The performance of enhanced ETFM model is evaluated to capture drying and wetting behavior on a flat plate and found to be satisfactory. Film thickness prediction of enhanced ETFM model is found to be comparable with the VOF predictions reported in the literature. The effect of contact angle on the spreading of oil and film thickness is found to be small for the investigated conditions on an aero-engine bearing chamber.

scholarly journals Prediction of Film Thickness of an Aero-Engine Bearing Chamber Using Coupled VOF and Thin Film Model

2019 ◽  
Author(s):  
Kuldeep Singh ◽  
Medhat Sharabi ◽  
Stephen Ambrose ◽  
Carol Eastwick ◽  
Richard Jefferson-Loveday
Keyword(s):  
Thin Film ◽  
Film Thickness ◽  
Air Flow ◽  
Shaft Speed ◽  
Oil Film ◽  
Film Model ◽  
Thin Film Model ◽  
Wide Range ◽  
Aero Engine ◽  
Engine Bearing

Abstract In the present work, a coupled volume-of-fluid (VOF) model with Eulerian thin-film model (ETFM) approach is used to predict the film thickness in an aero-engine bearing chamber. Numerical studies are conducted for a wide range of shaft speeds with lubricant and air flow rates of 100 1/hr and 10 g/s respectively, at a scavenge ratio of 4 on a simplified bearing chamber test rig. Air-flow analysis inside the bearing chamber is also assessed. Primary and secondary airflow predictions are found to be in good agreement with the experimental results. The coupled ETFM+VOF approach is found to be sensitive enough to capture the qualitative trend of oil film formation and distribution over the chamber wall. Oil collection near the sump at a low shaft speed and a rotating oil film at a higher shaft speed are well captured.

scholarly journals Two-layer modeling of thermally induced Bénard convection in thin liquid films: Volume of fluid approach vs thin-film model

AIP Advances ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 045317
Author(s):  
Ali Mohammadtabar ◽  
Hadi Nazaripoor ◽  
Adham Riad ◽  
Arman Hemmati ◽  
Mohtada Sadrzadeh
Keyword(s):  
Thin Film ◽  
Volume Of Fluid ◽  
Liquid Films ◽  
Thin Liquid Films ◽  
Thermally Induced ◽  
Film Model ◽  
Bénard Convection ◽  
Thin Film Model ◽  
Benard Convection

scholarly journals Nanostructured, mesoporous Au/TiO2 model catalysts – structure, stability and catalytic properties

2011 ◽  
Vol 2 ◽  
pp. 593-606 ◽  
Author(s):  
Matthias Roos ◽  
Dominique Böcking ◽  
Kwabena Offeh Gyimah ◽  
Gabriela Kucerova ◽  
Joachim Bansmann ◽  
...  
Keyword(s):  
Thin Film ◽  
Photoelectron Spectroscopy ◽  
Catalytic Properties ◽  
Model Catalysts ◽  
Model Systems ◽  
Structure Stability ◽  
Titanium Tetraisopropoxide ◽  
X Ray ◽  
Film Model ◽  
Thin Film Model

Aiming at model systems with close-to-realistic transport properties, we have prepared and studied planar Au/TiO2 thin-film model catalysts consisting of a thin mesoporous TiO2 film of 200–400 nm thickness with Au nanoparticles, with a mean particle size of ~2 nm diameter, homogeneously distributed therein. The systems were prepared by spin-coating of a mesoporous TiO2 film from solutions of ethanolic titanium tetraisopropoxide and Pluronic P123 on planar Si(100) substrates, calcination at 350 °C and subsequent Au loading by a deposition–precipitation procedure, followed by a final calcination step for catalyst activation. The structural and chemical properties of these model systems were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), N2 adsorption, inductively coupled plasma ionization spectroscopy (ICP–OES) and X-ray photoelectron spectroscopy (XPS). The catalytic properties were evaluated through the oxidation of CO as a test reaction, and reactivities were measured directly above the film with a scanning mass spectrometer. We can demonstrate that the thin-film model catalysts closely resemble dispersed Au/TiO2 supported catalysts in their characteristic structural and catalytic properties, and hence can be considered as suitable for catalytic model studies. The linear increase of the catalytic activity with film thickness indicates that transport limitations inside the Au/TiO2 film catalyst are negligible, i.e., below the detection limit.

Detrimental MnPO4F and MnF2 formation on LiMn2O4 in the 3 V region

2021 ◽  
Author(s):  
Louis L. De Taeye ◽  
Philippe M. Vereecken
Keyword(s):  
Thin Film ◽  
Direct Interaction ◽  
Film Model ◽  
Thin Film Model ◽  
V Region

The 3 V region of LMO is inhibited when using LiPF6 based electrolytes, due to the formation of a LiF/MnF2 decomposition layer. This layer is formed by direct interaction between LiPF6 and Li2Mn2O4, as demonstrated using a thin-film model electrode.

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