scholarly journals An Efficient Numerical Procedure for Thermohydrodynamic Analysis of Cavitating Bearings

1996 ◽  
Vol 118 (3) ◽  
pp. 555-563 ◽  
Author(s):  
D. Vijayaraghavan
Keyword(s):  
Experimental Data ◽  
Film Thickness ◽  
Boundary Conditions ◽  
Radial Direction ◽  
Heat Dissipation ◽  
Numerical Procedure ◽  
Hydrodynamic Performance ◽  
Numerical Examples ◽  
Thermal Boundary Conditions ◽  
Theoretical Predictions

In this paper, an efficient and accurate numerical procedure to determine the thermo-hydrodynamic performance of cavitating bearings is described. This procedure is based on the earlier development of Elrod for lubricating films, in which the properties across the film thickness are determined at Lobatto points and their distributions are expressed by collocated polynomials. The cavitated regions and their boundaries are rigorously treated. Thermal boundary conditions at the surfaces, including heat dissipation through the metal to the ambient, are incorporated. Numerical examples are presented comparing the predictions using this procedure with earlier theoretical predictions and experimental data. With a few points across the film thickness and across the journal and the bearing in the radial direction, the temperature profile is very well predicted.

Natural Convection of a Heat Generating Fluid in a Closed Vertical Cylinder: An Examination of Theoretical Predictions

1971 ◽  
Vol 13 (3) ◽  
pp. 151-156 ◽  
Author(s):  
A. Watson
Keyword(s):  
Experimental Data ◽  
Natural Convection ◽  
Boundary Conditions ◽  
Experimental Measurement ◽  
Analytical Method ◽  
Vertical Cylinder ◽  
Thermal Boundary Conditions ◽  
Integral Technique ◽  
Theoretical Predictions ◽  
Good Agreement

An analysis of the natural convection of a heat generating fluid in a semi-infinite vertical cylinder has been seen, in a previous publication, to give good agreement with experimental measurement. The analytical method used was that of solving the integrated equations of continuity, motion and energy, a technique which is frequently applied to internal natural convection problems and which has a reputation for being insensitive to thermal boundary conditions and the profile assumptions needed. The boundary conditions assumed for the analysis were not those of the experiment, and this paper is the result of an examination of the sensitivity of the prediction to the assumed conditions. A new analysis has been carried out with the boundary conditions of the experiment, and with profile assumptions closer to the experimental data. The new predictions show much less favourable agreement. It is concluded that the agreement obtained in the earlier analysis should not be used as a recommendation of the integral technique.

Thermohydrodynamic Analysis of Compliant Flexure Pivot Tilting Pad Gas Bearings

2008 ◽  
Vol 130 (3) ◽  
Author(s):  
Kyuho Sim ◽  
Daejong Kim
Keyword(s):  
Boundary Conditions ◽  
Energy Equation ◽  
Numerical Procedure ◽  
Computational Method ◽  
Temperature Fields ◽  
Linear Perturbation ◽  
Gas Bearings ◽  
Thermal Boundary Conditions ◽  
Thermal Growth ◽  
Tilting Pad

A new thermohydrodynamic (THD) analysis for compliant flexure pivot tilting pad gas bearings is presented. Unlike many previous THD analyses on oil-lubricated bearings and gas bearings, the new THD analysis solves the rotor and bearing pad temperatures as well as the gas film temperature simultaneously upon adequate thermal boundary conditions on the bearing shell and rotor ends are given. All the previous studies assume that the rotor and bearing temperatures are given as thermal boundary conditions to solve 2D or 3D energy equation in the bearing film. The developed computational method is unique because these boundary conditions are found internally through global energy balance around the bearing. A numerical procedure involves solving the generalized Reynolds equation, 3D energy equation, and heat flux equations around the bearings simultaneously through iterative process. Furthermore, rotor thermal and centrifugal expansions are also considered during the iteration. Parametric studies were performed for the various temperature fields, i.e., rotor temperature, gas film temperature, and pad temperature as a function of nominal clearance, external load, and various thermal boundary conditions. Nominal clearance showed the most significant influence on overall THD behavior. The analyses also show that the rotor-bearing system can go to thermal runaway if adequate cooling mechanism does not exist. Linear perturbation analysis was also performed to investigate the thermal effects on the rotordynamic performance. Rotor thermal growth and increased viscosity increased direct stiffness and damping coefficients compared to the isothermal case.

Thermal Behavior and Friction in Journal Bearings

1970 ◽  
Vol 92 (3) ◽  
pp. 373-380 ◽  
Author(s):  
Al. Nica
Keyword(s):  
Experimental Data ◽  
Thermal Behavior ◽  
Heat Dissipation ◽  
Journal Bearings ◽  
Friction Torque ◽  
Operating Characteristics ◽  
Lubricant Flow ◽  
Theoretical Predictions ◽  
Theoretical Results ◽  
Good Agreement

This paper deals with friction and the field of temperature in the lubricant film of journal bearings. Theoretical results regarding the thermal behavior are checked with experimental data and good agreement is found. Emphasis is put on the variation of temperature and lubricant flow with the operating characteristics of the bearing and it is seen that theoretical predictions for minima of friction torque are backed by temperature measurements. Further on, the friction torque and the mechanism of heat dissipation in bearings are dealt with, in order to verify the assumptions used in the calculation schemes. The means of efficiently cooling the bearing are also discussed, as well as the part played by the divergent zone in this process.

scholarly journals Inhomogeneous Temperature Distribution Affecting the Cyclic Aging of Li-Ion Cells. Part I: Experimental Investigation

Batteries ◽  
2020 ◽  
Vol 6 (1) ◽  
pp. 13 ◽  
Author(s):  
Daniel Werner ◽  
Sabine Paarmann ◽  
Achim Wiebelt ◽  
Thomas Wetzel
Keyword(s):  
Boundary Conditions ◽  
Heat Dissipation ◽  
Single Cells ◽  
Internal Heat ◽  
Lithium Ion ◽  
Ambient Air ◽  
Substantial Impact ◽  
Temperature Changes ◽  
Thermal Boundary Conditions ◽  
Cyclic Degradation

Alongside electrical loads, it is known that temperature has a strong influence on battery behavior and lifetime. Investigations have mainly been performed at homogeneous temperatures and non-homogeneous conditions in single cells have at best been simulated. This publication presents the development of a methodology and experimental setup to investigate the influence of thermal boundary conditions during the operation of lithium-ion cells. In particular, spatially inhomogeneous and transient thermal boundary conditions and periodical electrical cycles were superimposed in different combinations. This required a thorough design of the thermal boundary conditions applied to the cells. Unlike in other contributions that rely on placing cells in a climatic chamber to control ambient air temperature, here the cell surfaces and tabs were directly connected to individual cooling and heating plates. This improves the control of the cells’ internal temperature, even with high currents accompanied by strong internal heat dissipation. The aging process over a large number of electrical cycles is presented by means of discharge capacity and impedance spectra determined in repeated intermediate characterizations. The influence of spatial temperature gradients and temporal temperature changes on the cyclic degradation is revealed. It appears that the overall temperature level is indeed a decisive parameter for capacity fade during cyclic aging, while the intensity of a temperature gradient is not as essential. Furthermore, temperature changes can have a substantial impact and potentially lead to stronger degradation than spatial inhomogeneities.

Analysis of Rewetting for Surface Tension Induced Flow

1992 ◽  
Vol 114 (3) ◽  
pp. 703-707 ◽  
Author(s):  
X. F. Peng ◽  
G. P. Peterson
Keyword(s):  
Experimental Data ◽  
Surface Tension ◽  
Heat Flux ◽  
Film Thickness ◽  
Liquid Films ◽  
Analytical Investigation ◽  
Liquid Front ◽  
Theoretical Predictions ◽  
Fluid Properties ◽  
Induced Flow

An analytical investigation was conducted to determine the rewetting characteristics of thin, surface tension driven liquid films over heated plates as a function of the fluid properties, the film thickness, and the applied heat flux. Analytical expressions for the maximum sustainable heat flux and the rewetting velocity were developed for both flat and grooved plates and were compared with data from previous investigations. The results indicated good agreement for low film velocities; however, at high velocities the experimental data deviated significantly from the theoretical predictions. It was hypothesized that this deviation was due to the presence of liquid sputtering near the liquid front. To compensate for this liquid sputtering, the expressions for maximum sustainable heat flux and rewetting velocity were modified using an empirical correction factor developed from the data of previous thin film thickness investigations. The resulting modified expressions were found to compare very favorably with available experimental data over a large range of flow conditions and velocities.

CFD and Thermal Analysis of Leaf Seals for Aero-Engine Application

2016 ◽  
Author(s):  
Vincenzo Fico ◽  
Michael J. Pekris ◽  
Christopher J. Barnes ◽  
Rakesh Kumar Jha ◽  
David Gillespie
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Thermal Analysis ◽  
Reynolds Number ◽  
Boundary Conditions ◽  
Frictional Heat ◽  
Analysis And Design ◽  
Thermal Boundary Conditions ◽  
Leaf Pack ◽  
Aero Engine

Aero-engine gas turbine performance and efficiency can be improved through the application of compliant shaft seal types to certain sealing locations within the secondary air system. Leaf seals offer better performance than traditional labyrinth seals, giving lower leakage flows at design duties. However, for aeroengine applications, seal designs must be able to cope with relatively large off-design seal closures and closure uncertainties. The two-way coupling between temperatures of seal components and seal closures, through the frictional heat generated at the leaf-rotor interface when in contact, represents an important challenge for leaf seal analysis and design. This coupling can lead to leaf wear and loss, rotor overheating, and possibly to unstable sealing system behaviour (thermal runaway). In this paper we use CFD, FE thermal analysis, and experimental data to characterise the thermal behaviour of leaf seals. This sets the basis for a study of the coupled thermo-mechanical behaviour. CFD is used to understand the fluid-mechanics of a leaf pack. The leaf seal tested at the Oxford Osney Laboratory is used for the study. Simulations for four seal axial Reynolds number are conducted; for each value of the Reynolds number, leaf tip-rotor contact and clearance are considered. Distribution of mass flow within the leaf pack, distribution of heat transfer coefficient at the leaf surface, and swirl velocity pick-up across the pack predicted using CFD are discussed. The experimental data obtained from the Oxford rig is used to develop a set of thermal boundary conditions for the leaf pack. An FE thermal model of the rig is devised, informed by the aforementioned CFD study. Four experiments are simulated; thermal boundary conditions are calibrated to match predicted metal temperatures to those measured on the rig. A sensitivity analysis of the rotor temperature predictions to the heat transfer assumptions is carried out. The calibrated set of thermal boundary conditions is shown to accurately predict the measured rotor temperatures.

Computational Fluid Dynamics and Thermal Analysis of Leaf Seals for Aero-engine Application

2017 ◽  
Vol 139 (7) ◽  
Author(s):  
Vincenzo Fico ◽  
Michael J. Pekris ◽  
Christopher J. Barnes ◽  
Rakesh Kumar Jha ◽  
David Gillespie
Keyword(s):  
Heat Transfer ◽  
Fluid Dynamics ◽  
Experimental Data ◽  
Thermal Analysis ◽  
Computational Fluid Dynamics ◽  
Reynolds Number ◽  
Boundary Conditions ◽  
Thermal Boundary Conditions ◽  
Leaf Pack ◽  
Aero Engine

Aero-engine gas turbine performance and efficiency can be improved through the application of compliant shaft seal types to certain sealing locations within the secondary air system. Leaf seals offer better performance than traditional labyrinth seals, giving lower leakage flows at design duties. However, for aero-engine applications, seal designs must be able to cope with relatively large off-design seal closures and closure uncertainties. The two-way coupling between temperatures of seal components and seal closures, through the frictional heat generated at the leaf–rotor interface when in contact, represents an important challenge for leaf seal analysis and design. This coupling can lead to leaf wear and loss, rotor overheating, and possibly to unstable sealing system behavior (thermal runaway). In this paper, we use computational fluid dynamics (CFD), finite element (FE) thermal analysis, and experimental data to characterize the thermal behavior of leaf seals. This sets the basis for a study of the coupled thermomechanical behavior. CFD is used to understand the fluid-mechanics of a leaf pack. The leaf seal tested at the Oxford Osney Laboratory is used for the study. Simulations for four seal axial Reynolds number are conducted; for each value of the Reynolds number, leaf tip-rotor contact, and clearance are considered. Distribution of mass flow within the leaf pack, distribution of heat transfer coefficient (HTC) at the leaf surface, and swirl velocity pick-up across the pack predicted using CFD are discussed. The experimental data obtained from the Oxford rig is used to develop a set of thermal boundary conditions for the leaf pack. An FE thermal model of the rig is devised, informed by the aforementioned CFD study. Four experiments are simulated; thermal boundary conditions are calibrated to match the predicted metal temperatures to those measured on the rig. A sensitivity analysis of the rotor temperature predictions to the heat transfer assumptions is carried out. The calibrated set of thermal boundary conditions is shown to accurately predict the measured rotor temperatures.

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