Thermal Effects in Thrust Washer Lubrication

2001 ◽  
Vol 124 (1) ◽  
pp. 166-177 ◽  
Author(s):  
To Him Yu ◽  
Farshid Sadeghi
Keyword(s):  
Heat Transfer ◽  
Numerical Model ◽  
Thermal Effects ◽  
Groove Depth ◽  
Operating Conditions ◽  
Temperature Fields ◽  
Frictional Torque ◽  
Time Step ◽  
Transfer Equations ◽  
Side Flow

A numerical model was developed to study the thermal effects on the lubrication mechanism of radially-grooved thrust washers. A mass-conserving transient thermohydrodynamic (THD) analysis was performed by solving the modified Reynolds and energy equations for the lubricant pressure and temperature distributions. The heat transfer equations were also solved simultaneously to obtain the temperature fields of the solids (thrust washers). Due to different thermal time responses of the lubricant film and the solids, heat transfer equations of the runner and the thrust washer pad were treated as in quasi-steady state at each time step in the transient solution. Elrod cavitation algorithm was implemented to include lubricant cavitation. The results show that thermal effects do not only reduce load carrying capacity and the frictional torque but also increase side flow rate. Moreover, the numerical model also demonstrates that the thermal effects have greater influence on the load support when the groove depth and groove numbers increase. Furthermore, the analytical results also show that there exists certain operating conditions before thermal effects become the dominating factors in influencing the thrust washer performance.

Numerical and Experimental Investigation of Interface Bonding Via Substrate Remelting of an Impinging Molten Metal Droplet

1996 ◽  
Vol 118 (1) ◽  
pp. 164-172 ◽  
Author(s):  
C. H. Amon ◽  
K. S. Schmaltz ◽  
R. Merz ◽  
F. B. Prinz
Keyword(s):  
Heat Transfer ◽  
Numerical Model ◽  
Molten Metal ◽  
Thermal Stresses ◽  
Initial Conditions ◽  
Metal Droplet ◽  
Solid Substrate ◽  
Numerical Results ◽  
Operating Conditions ◽  
Analytical Approaches

A molten metal droplet landing and bonding to a solid substrate is investigated with combined analytical, numerical, and experimental techniques. This research supports a novel, thermal spray shape deposition process, referred to as microcasting, capable of rapidly manufacturing near netshape, steel objects. Metallurgical bonding between the impacting droplet and the previous deposition layer improves the strength and material property continuity between the layers, producing high-quality metal objects. A thorough understanding of the interface heat transfer process is needed to optimize the microcast object properties by minimizing the impacting droplet temperature necessary for superficial substrate remelting, while controlling substrate and deposit material cooling rates, remelt depths, and residual thermal stresses. A mixed Lagrangian–Eulerian numerical model is developed to calculate substrate remelting and temperature histories for investigating the required deposition temperatures and the effect of operating conditions on remelting. Experimental and analytical approaches are used to determine initial conditions for the numerical simulations, to verify the numerical accuracy, and to identify the resultant microstructures. Numerical results indicate that droplet to substrate conduction is the dominant heat transfer mode during remelting and solidification. Furthermore, a highly time-dependent heat transfer coefficient at the droplet/substrate interface necessitates a combined numerical model of the droplet and substrate for accurate predictions of the substrate remelting. The remelting depth and cooling rate numerical results are also verified by optical metallography, and compare well with both the analytical solution for the initial deposition period and the temperature measurements during droplet solidification.

Unsteady Conjugate Heat Transfer Investigation of a Multistage Steam Turbine in Warm-Keeping Operation With Hot Air

2018 ◽  
Author(s):  
Piotr Łuczyński ◽  
Dennis Toebben ◽  
Manfred Wirsum ◽  
Wolfgang F. D. Mohr ◽  
Klaus Helbig
Keyword(s):  
Heat Transfer ◽  
Conjugate Heat Transfer ◽  
Flow Patterns ◽  
Operating Conditions ◽  
Angle Of Incidence ◽  
Time Step ◽  
Hot Air ◽  
Wide Range ◽  
Vortex Systems ◽  
Operating Points

In recent decades, the rising share of commonly subsidized renewable energy especially affects the operational strategy of conventional power plants. In pursuit of flexibility improvements, extension of life cycle, in addition to a reduction in start-up time, General Electric has developed a product to warm-keep high/intermediate pressure steam turbines using hot air. In order to optimize the warm-keeping operation and to gain knowledge about the dominant heat transfer phenomena and flow structures, detailed numerical investigations are required. Considering specific warm-keeping operating conditions characterized by high turbulent flows, it is required to conduct calculations based on time-consuming unsteady conjugate heat transfer (CHT) simulations. In order to investigate the warm-keeping process as found in the presented research, single and multistage numerical turbine models were developed. Furthermore, an innovative calculation approach called the Equalized Timescales Method (ET) was applied for the modeling of unsteady conjugate heat transfer (CHT). The unsteady approach improves the accuracy of the stationary simulations and enables the determination of the multistage turbine models. In the course of the research, two particular input variables of the ET approach — speed up factor (SF) and time step (TS) — have been additionally investigated with regard to their high impact on the calculation time and the quality of the results. Using the ET method, the mass flow rate and the rotational speed were varied to generate a database of warm-keeping operating points. The main goal of this work is to provide a comprehensive knowledge of the flow field and heat transfer in a wide range of turbine warm-keeping operations and to characterize the flow patterns observed at these operating points. For varying values of flow coefficient and angle of incidence, the secondary flow phenomena change from well-known vortex systems occurring in design operation (such as passage, horseshoe and corner vortices) to effects typical for windage, like patterns of alternating vortices and strong backflows. Furthermore, the identified flow patterns have been compared to vortex systems described in cited literature and summarized in the so-called blade vortex diagram. The comparison of heat transfer in the form of charts showing the variation of the Nusselt-numbers with respect to changes in angle of incidence and flow coefficients at specific operating points is additionally provided.

An Efficient Numerical Model of Pulsating Combustion and Its Experimental Validation

2009 ◽  
Author(s):  
Luca Casarsa ◽  
Pietro Giannattasio ◽  
Diego Micheli
Keyword(s):  
Numerical Model ◽  
Combustion Chamber ◽  
Second Order ◽  
Operating Conditions ◽  
Gas Dynamics Equations ◽  
Time Step ◽  
Flow Equations ◽  
Tail Pipe ◽  
Flux Difference ◽  
Pulse Jet

A simple and efficient numerical model is presented for the simulation of pulse combustors. It is based on the numerical solution of the quasi-1D unsteady flow equations and on phenomenological sub-models of turbulence and combustion. The gas dynamics equations are solved by using the Flux Difference Splitting (FDS) technique, a finite-volume upwind numerical scheme, and ENO reconstructions to obtain second-order accurate non-oscillatory solutions. The numerical fluxes computed at the cell interfaces are used to transport also the reacting species, their formation energy and the turbulent kinetic energy. The combustion progress in each cell is evaluated explicitly at the end of each time step according to a second-order overall reaction kinetics. In this way, the computations of gas dynamic evolution and heat release are decoupled, which makes the model particularly simple and efficient. A comprehensive set of measurements has been performed on a small Helmholtz type pulse-jet in order to validate the model. Air and fuel consumptions, wall temperatures, pressure cycles in both combustion chamber and tail-pipe, and instantaneous thrust have been recorded in different operating conditions of the device. The comparison between numerical and experimental results turns out to be satisfactory in all the working conditions of the pulse-jet. In particular, accurate predictions are obtained of the device operating frequency and of shape, amplitude and phase of the pressure waves in both combustion chamber and tail-pipe.

Experimental and Numerical Investigation of Heat Transfer Characteristics of Liquid Flow With Micro-Encapsulated Phase Change Material

2008 ◽  
Author(s):  
Rami Sabbah ◽  
Jamal Yagoobi ◽  
Said Al Hallaj
Keyword(s):  
Heat Transfer ◽  
Numerical Model ◽  
Pressure Drop ◽  
Phase Change ◽  
Phase Change Material ◽  
Operating Conditions ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Encapsulated Phase Change Material ◽  
Change Material

This experimental and numerical study investigates Micro-Encapsulated Phase Change Material (MEPCM) heat transfer characteristics and corresponding pressure drop. To conduct this study, an experimental setup consisting of a steel tube with an inner diameter of 4.3mm, outer diameter of 6.5mm and a length of 1,016mm is selected. A MEPCM mass concentration of 20% slurry with particle diameter ranging between 5–15μm is included in this study. Tube wall temperature profile, fluid inlet, outlet temperatures, the pressure drop across the tube are measured and corresponding Nusselt number are determined for various operating conditions. The experimental results are used to validate the numerical model predictions. The numerical model results show good agreement with the experimental data under various operating conditions. The controlling parameters are identified and their effects on the heat transfer characteristics of micro-channels with MEPCM slurries are evaluated.

scholarly journals Numerical Study of a Francis Turbine over Wide Operating Range: Some Practical Aspects of Verification

2020 ◽  
Vol 12 (10) ◽  
pp. 4301
Author(s):  
Chirag Trivedi ◽  
Igor Iliev ◽  
Ole Gunnar Dahlhaug
Keyword(s):  
Numerical Model ◽  
Transport Model ◽  
Numerical Study ◽  
Operating Conditions ◽  
Francis Turbine ◽  
Step Size ◽  
Time Step ◽  
Angular Rotation ◽  
Time Step Size ◽  
Automatic Optimization

Hydropower plays an essential role in maintaining energy flexibility. Modern designs focus on sustainability and robustness using different numerical tools. Automatic optimization of the turbines is widely used, including low, mini and micro head turbines. The numerical techniques are not always foolproof in the absence of experimental data, and hence accurate verification is a key component of automatic optimization processes. This work aims to investigate the newly designed Francis runner for flexible operation. Unsteady simulations at 80 operating points of the turbine were conducted. The numerical model consisted of 16 million nodes of hexahedral mesh. A SAS-SST (scale adaptive simulation-shear stress transport) model was enabled for resolving/modeling the turbulent flow. The selected time-step size was equivalent to one-degree angular rotation of the runner. Global parameters, such as efficiency, torque, head and flow rate were considered for proper verification and validation. (1) A complete hill diagram of the turbine was prepared and verified with the reference case. (2) The relative error in hydraulic efficiency was computed and the over trend was studied. This allowed us to investigate the consistency of the numerical model under extreme operating conditions, far away from the best efficiency point. (3) Unsteady fluctuations of runner output torque were studied to identify unstable regions and magnitude of torque oscillations.

Portable pilot plant for evaluating marine biofouling growth and control in heat exchangers-condensers

2003 ◽  
Vol 47 (5) ◽  
pp. 99-104 ◽  
Author(s):  
J.F. Casanueva ◽  
J. Sánchez ◽  
J.L. García-Morales ◽  
T. Casanueva-Robles ◽  
J.A. López ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Exchangers ◽  
Pilot Plant ◽  
Economic Cost ◽  
Automatic Monitoring ◽  
Operating Conditions ◽  
Optimum Operating ◽  
Indirect Measure ◽  
Transfer Equations ◽  
And Control

Biofouling frequently involves a serious impediment to achieving optimum operating conditions in heat exchangers-condensers. The economic cost and energy losses associated with this phenomenon are significant and the environmental impact of biocides must satisfy stringent regulations. A portable pilot plant has been designed in order to carry out in-situ experimental study as biofilm is formed under thermal and hydrodynamically controlled conditions. The pilot plant has an automatic monitoring, control and data acquisition system, which automatically processes data from indirect measure of fouling in terms of increased fluid frictional and heat transfer resistances. A particular method is used and proposed for direct measuring and biofilm characterization. Once we know the actual film thickness, we can calculate the effective thermal conductivity of the layer by using the appropriate heat transfer equations.

scholarly journals The Effect of Heat Transfer and Polymer Concentration on Non-Newtonian Fluid from Pore-Scale Simulation of Rock X-Ray micro-CT

2017 ◽  
Author(s):  
Moussa Tembely ◽  
Ali M. AlSumaiti ◽  
Mohamed S. Jouini ◽  
Khurshed Rahimov
Keyword(s):  
Heat Transfer ◽  
Numerical Model ◽  
Newtonian Fluid ◽  
Polymer Concentration ◽  
Isothermal Condition ◽  
Operating Conditions ◽  
Flow Index ◽  
Micro Ct ◽  
Pore Scale ◽  
Fluid Rheology

Most of the pore-scale imaging and simulations of non-Newtonian fluid are based on the simplifying geometry of network modeling and overlook the fluid rheology and heat transfer. In the present paper, we developed a non-isothermal and non-Newtonian numerical model of the flow properties at pore-scale by direct simulation of the 3D micro-CT images using a Finite Volume Method (FVM). The numerical model is based on the resolution of the momentum and energy conservation equations. Owing to an adaptive meshing technique and appropriate boundary conditions, rock permeability and mobility are accurately computed. A temperature and concentration-dependent power-law viscosity model in line with the experimental measurement of the fluid rheology is adopted. The model is first applied at isothermal condition to 2 benchmark samples, namely Fontainebleau sandstone and Grosmont carbonate, and is found to be in good agreement with the Lattice Boltzmann method (LBM). Finally, at non-isothermal conditions, an effective mobility is introduced that enables to perform a numerical sensitivity study to fluid rheology, heat transfer, and operating conditions. While the mobility seems to evolve linearly with polymer concentration, the effect of the temperature seems negligible by comparison. However, a sharp contrast is found between carbonate and sandstone under the effect of a constant temperature gradient. Besides concerning the flow index and consistency factor, a good master curve is derived when normalizing the mobility for both the carbonate and the sandstone.

scholarly journals Turbulent Flow and Heat Transfer in Gas Turbine Blade Cooling Passages

1992 ◽  
Author(s):  
F. J. Cunha
Keyword(s):  
Heat Transfer ◽  
Turbulent Flow ◽  
Gas Turbine ◽  
Turbine Blades ◽  
Operating Conditions ◽  
Temperature Fields ◽  
Air Cooling ◽  
Turbine Blade Cooling ◽  
Gas Turbine Blades ◽  
Analysis Methodology

A numerical analysis methodology has been created to predict the heat transfer within the air cooling passages of gas turbine blades. In this paper, the turbulent flow heat convection with developed velocity and temperature fields is studied for cavities with turbulators. The influence of Coriolis forces and rotational buoyancy effects were also included. The k-equation turbulence model was employed over most of the cross section while a modified Van Driest’s version of the mixing length hypothesis is used in the near-wall sublayer. This methodology was successfully benchmarked against experimental results for air cooling passages of turbine blades. Analytical results are presented in terms of the Reynolds, Rossby and rotational Rayleigh numbers for realistic operating conditions.

scholarly journals Conjugate Heat Transfer of an Internally Air-Cooled Nozzle Guide Vane and Shrouds

2014 ◽  
Vol 6 ◽  
pp. 146523 ◽  
Author(s):  
Leiyong Jiang ◽  
Xijia Wu ◽  
Zhong Zhang
Keyword(s):  
Heat Transfer ◽  
Gas Turbine ◽  
Conjugate Heat Transfer ◽  
Guide Vane ◽  
Operating Conditions ◽  
Temperature Fields ◽  
Pressure Side ◽  
Cooling Flow ◽  
Nozzle Guide Vane ◽  
Nozzle Guide

In order to assess the life of gas turbine critical components, it is essential to adequately specify their aerothermodynamic working environments. Steady-state analyses of the flow field and conjugate heat transfer of an internally air-cooled nozzle guide vane (NGV) and shrouds of a gas turbine engine at baseline operating conditions are numerically investigated. A high-fidelity CFD model is generated and the simulations are carried out with properly defined boundary conditions. The features of the complicated flow and temperature fields are revealed. In general, the Mach number is lower and the temperature is higher on the NGV pressure side than those on the suction side. There are two high temperature regions on the pressure side, and the temperature across the middle section is relatively low. These findings are closely related to the locations of the holes and outlets of the cooling flow passage, and consistent with the field observations of damaged NGVs. As a technology demonstration, the results provide required information for the life analysis of the NGV/shrouds assembly and improvement of the cooling flow arrangement.

Analysis of Thermal Effects in a Cavitating Orifice Using Rayleigh Equation and Experiments

2010 ◽  
Vol 132 (9) ◽  
Author(s):  
Maria Grazia De Giorgi ◽  
Daniela Bello ◽  
Antonio Ficarella
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Thermal Effects ◽  
Internal Combustion Engines ◽  
Operating Conditions ◽  
Rayleigh Equation ◽  
Liquid Temperature ◽  
Dimensional Model ◽  
Cloud Cavitation ◽  
One Dimensional

The cavitation phenomenon interests a wide range of machines, from internal combustion engines to turbines and pumps of all sizes. It affects negatively the hydraulic machines’ performance and may cause materials’ erosion. The cavitation, in most cases, is a phenomenon that develops at a constant temperature, and only a relatively small amount of heat is required for the formation of a significant volume of vapor, and the flow is assumed isothermal. However, in some cases, such as thermosensible fluids and cryogenic liquid, the heat transfer needed for the vaporization is such that phase change occurs at a temperature lower than the ambient liquid temperature. The focus of this research is the experimental and analytical studies of the cavitation phenomena in internal flows in the presence of thermal effects. Experiments have been done on water and nitrogen cavitating flows in orifices at different operating conditions. Transient growth process of the cloud cavitation induced by flow through the throat is observed using high-speed video images and analyzed by pressure signals. The experiments show different cavitating behaviors at different temperatures and different fluids; this is related to the bubble dynamics inside the flow. So to investigate possible explanations for the influence of fluid temperature and of heat transfer during the phase change, initially, a steady, quasi-one-dimensional model has been implemented to study an internal cavitating flow. The nonlinear dynamics of the bubbles has been modeled by Rayleigh–Plesset equation. In the case of nitrogen, thermal effects in the Rayleigh equation are taken into account by considering the vapor pressure at the actual bubble temperature, which is different from the liquid temperature far from the bubble. A convective approach has been used to estimate the bubble temperature. The quasisteady one-dimensional model can be extensively used to conduct parametric studies useful for fast estimation of the overall performance of any geometric design. For complex geometry, three-dimensional computational fluid dynamic (CFD) codes are necessary. In the present work good agreements have been found between numerical predictions by the CFD FLUENT code, in which a simplified form of the Rayleigh equation taking into account thermal effects has been implemented by external user routines and some experimental observations.

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