scholarly journals Influence of Thermoelastic Phenomena on the Energy Conservation in Non-contacting Face Seals

2020 ◽  
Author(s):  
Slawomir Blasiak
Keyword(s):  
Cross Sections ◽  
Thermal Stresses ◽  
Mechanical Energy ◽  
Fluid Film ◽  
Temperature Fields ◽  
Asymmetric Distribution ◽  
Displacement Potential ◽  
Thermal Deformations ◽  
Face Seals ◽  
Function Of Two Variables

The purpose of this study was to develop a mathematical model for non-contacting face seals to analyze how their performance is affected by thermoelastic phenomena. The model was used to solve thermal conductivity and thermoelasticity problems. The primary goal was to calculate the values of thermal deformations of the sealing rings in a non-contacting face seal with a flexibly mounted rotor (FMR) for a turbomachine. The model assumes conversion of mechanical energy into heat in the fluid film. The heat flux generated in the fluid film is transferred first to the sealing rings and then to the fluid surrounding them. An asymmetric distribution of temperature within the sealing rings leads to the occurrence of thermal stresses and, consequently, a change in the rings geometry. The model is solved analytically. The distributions of temperature fields for the sealing rings in the cross-sections are calculated using the Fourier-Bessel series as a superficial function of two variables (r,z). The thermoelasticity problems described by the Navier equations are solved by applying the Boussinesq harmonic functions and Goodier’s thermoelastic displacement potential function. The proposed method involves solving various theoretical and practical problems of thermoelasticity in FMR-type non-contacting face seals. The calculated thermal deformations of the sealing rings are used to determine the most important seal performance parameters such as the leakage rate and power loss.

scholarly journals Influence of Thermoelastic Phenomena on the Energy Conservation in Non-Contacting Face Seals

Energies ◽  
2020 ◽  
Vol 13 (20) ◽  
pp. 5283
Author(s):  
Slawomir Blasiak
Keyword(s):  
Mathematical Model ◽  
Cross Sections ◽  
Thermal Stresses ◽  
Mechanical Energy ◽  
Fluid Film ◽  
Temperature Fields ◽  
Graphical Form ◽  
Asymmetric Distribution ◽  
Thermal Deformations ◽  
Face Seals

The purpose of this study was to develop a mathematical model for non-contacting face seals to analyze how their performance is affected by thermoelastic phenomena. The model was used to solve thermal conductivity and thermoelasticity problems. The primary goal was to calculate the values of thermal deformations of the sealing rings in a non-contacting face seal with a flexibly mounted rotor (FMR) for a turbomachine. The model assumes the conversion of mechanical energy into heat in the fluid film. The heat flux generated in the fluid film is transferred first to the sealing rings and then to the fluid surrounding them. Asymmetric distribution of temperature within the sealing rings leads to the occurrence of thermal stresses and, consequently, a change in the geometry of the rings. The model is solved analytically. The distributions of temperature fields for the sealing rings in the cross-sections are calculated using the Fourier-Bessel series as a superficial function of two variables (r,z). The thermoelasticity problems described by the Navier equations are solved by applying the Boussinesq harmonic functions and Goodier’s thermoelastic displacement potential function. The proposed method involves solving various theoretical and practical problems of thermoelasticity in FMR-type non-contacting face seals. The solution of the mathematical model was made use of analytical methods, and the most important obtained results are presented in graphical form, such as the temperature distributions and axial thermal distortions in cross-sections of the rings. The calculated thermal deformations of the sealing rings are used to determine the most important seal performance parameters such as the leakage rate and power loss. The article also presents a multi-criteria analysis of seal rings materials and geometry, which makes it easier to choose the type of materials used for the sliding rings.

Energy dissipation rate in a baffled vessel with pitched blade turbine impeller

1991 ◽  
Vol 56 (9) ◽  
pp. 1856-1867 ◽  
Author(s):  
Zdzisław Jaworski ◽  
Ivan Fořt
Keyword(s):  
Energy Dissipation ◽  
Cross Sections ◽  
Mechanical Energy ◽  
Vessel Diameter ◽  
Energy Dissipation Rate ◽  
Mean Velocity ◽  
Agitated Vessel ◽  
Radial Profiles ◽  
Pitched Blade Turbine ◽  
Turbine Impeller

Mechanical energy dissipation was investigated in a cylindrical, flat bottomed vessel with four radial baffles and the pitched blade turbine impeller of varied size. This study was based upon the experimental data on the hydrodynamics of the turbulent flow of water in an agitated vessel. They were gained by means of the three-holes Pitot tube technique for three impeller-to-vessel diameter ratio d/D = 1/3, 1/4 and 1/5. The experimental results obtained for two levels below and two levels above the impeller were used in the present study. Radial profiles of the mean velocity components, static and total pressures were presented for one of the levels. Local contribution to the axial transport of the agitated charge and energy was presented. Using the assumption of the axial symmetry of the flow field the volumetric flow rates were determined for the four horizontal cross-sections. Regions of positive and negative values of the total pressure of the liquid were indicated. Energy dissipation rates in various regions of the agitated vessel were estimated in the range from 0.2 to 6.0 of the average value for the whole vessel. Hydraulic impeller efficiency amounting to about 68% was obtained. The mechanical energy transferred by the impellers is dissipated in the following ways: 54% in the space below the impeller, 32% in the impeller region, 14% in the remaining part of the agitated liquid.

scholarly journals The use of a solution of the inverse heat conduction problem to monitor thermal stresses

2019 ◽  
Vol 108 ◽  
pp. 01003
Author(s):  
Jan Taler ◽  
Piotr Dzierwa ◽  
Magdalena Jaremkiewicz ◽  
Dawid Taler ◽  
Karol Kaczmarski ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Power Plants ◽  
Thermal Stresses ◽  
Thermal Power ◽  
Temperature Fields ◽  
Thick Wall ◽  
Fluid Temperature ◽  
Unsteady Temperature

Thick-wall components of the thermal power unit limit maximum heating and cooling rates during start-up or shut-down of the unit. A method of monitoring the thermal stresses in thick-walled components of thermal power plants is presented. The time variations of the local heat transfer coefficient on the inner surface of the pressure component are determined based on the measurement of the wall temperature at one or six points respectively for one- and three-dimensional unsteady temperature fields in the component. The temperature sensors are located close to the internal surface of the component. A technique for measuring the fastchanging fluid temperature was developed. Thermal stresses in pressure components with complicated shapes can be computed using FEM (Finite Element Method) based on experimentally estimated fluid temperature and heat transfer coefficient

Transient Elastic Thermal Stress Development During Laser Scribing of Ceramics

2000 ◽  
Vol 123 (1) ◽  
pp. 171-177 ◽  
Author(s):  
Michael F. Modest ◽  
Thomas M. Mallison
Keyword(s):  
Thermal Stresses ◽  
Continuous Wave ◽  
Elastic Stress ◽  
Three Dimensional ◽  
Thick Layer ◽  
Temperature Fields ◽  
Subsurface Cracks ◽  
Laser Scribing ◽  
Micro Cracks ◽  
Cutting Speeds

Lsaers are emerging as a valuable tool for shaping and cutting hard and brittle ceramics. Unfortunately, the large, concentrated heat flux rates that allow the laser to efficiently cut and shape the ceramic also result in large localized thermal stresses in a small heat-affected zone. These notable thermal stresses can lead to micro-cracks, a decrease in strength and fatigue life, and possibly catastrophic failure. In order to assess where, when, and what stresses occur during laser scribing, an elastic stress model has been incorporated into a three-dimensional scribing and cutting code. First, the code predicts the temporal temperature fields and the receding surface of the ceramic. Then, using the scribed geometry and temperature field, the elastic stress fields are calculated as they develop and decay during the laser scribing process. The analysis allows the prediction of stresses during continuous wave and pulsed laser operation, a variety of cutting speeds and directions, and various shapes and types of ceramic material. The results of the analysis show substantial tensile stresses develop over a thick layer below and parallel to the surface, which may be the cause of experimentally observed subsurface cracks.

Determination of mechanical properties of FFF 3D printed material by assessing void volume fraction, cooling rate and residual thermal stresses

2019 ◽  
Vol 25 (10) ◽  
pp. 1661-1683 ◽  
Author(s):  
Rafael Quelho de Macedo ◽  
Rafael Thiago Luiz Ferreira ◽  
Kuzhichalil Jayachandran
Keyword(s):  
Mechanical Properties ◽  
Cooling Rate ◽  
Young’S Modulus ◽  
Thermal Stresses ◽  
Volume Fraction ◽  
Young's Modulus ◽  
Void Volume Fraction ◽  
Void Volume ◽  
Temperature Fields ◽  
Content Type

Purpose This paper aims to present experimental and numerical analyses of fused filament fabrication (FFF) printed parts and show how mechanical characteristics of printed ABS-MG94 (acrylonitrile butadiene styrene) are influenced by the void volume fraction, cooling rate and residual thermal stresses. Design/methodology/approach Printed specimens were experimentally tested to evaluate the mechanical properties for different printing speeds, and micrographs were taken. A thermo-mechanical finite element model, able to simulate the FFF process, was developed to calculate the temperature fields in time, cooling rate and residual thermal stresses. Finally, the experimental mechanical properties and the microstructure distribution could be explained by the temperature fields in time, cooling rate and residual thermal stresses. Findings Micrographs revealed the increase of void volume fraction with the printing speed. The variations on voids were associated to the temperature fields in time: when the temperatures remained high for longer periods, less voids were generated. The Young's Modulus of the deposited filament varied according to the cooling rate: it decreased when the cooling rate increased. The influence of the residual thermal stresses and void volume fraction on the printed parts failure was also investigated: in the worst scenarios evaluated, the void volume fraction reduced the strength in 9 per cent, while the residual thermal stresses reduced it in 3.8 per cent. Originality/value This work explains how the temperature fields can affect the void volume fraction, Young's Modulus and failure of printed parts. Experimental and numerical results are shown. The presented research can be used to choose printing parameters to achieve desired mechanical properties of FFF printed parts.

Transient Thermal Stresses in a Sphere by Local Heating

1974 ◽  
Vol 41 (4) ◽  
pp. 930-934 ◽  
Author(s):  
J. B. Cheung ◽  
T. S. Chen ◽  
K. Thirumalai
Keyword(s):  
Thermal Stresses ◽  
Numerical Solutions ◽  
Integral Transformation ◽  
Separation Of Variables ◽  
Local Heating ◽  
Local Surface ◽  
Displacement Potential ◽  
Heated Zone ◽  
Localized Heating ◽  
Transient Thermal

The problem of transient thermal stresses in a solid, elastic, homogeneous, and isotropic sphere is solved for uniform and nonuniform, local surface heating. The temperature solutions are obtained by using separation of variables and integral transformation. The corresponding thermal stresses are derived by superposing a particular displacement potential function on Boussinesq solutions. Numerical solutions for two particular cases of localized heating of a typical brittle spherical solid have been obtained and presented. The results indicate a tensile stress concentration in the interior of the solid below the heated zone.

The study of thermal stresses and parameters of refractory structures for the formation of the temperature field when changing the heating rate of the working surface of products

2020 ◽  
pp. 34-38
Author(s):  
A. Kh. Akishev ◽  
S. M. Fomenko ◽  
S. Tolendiuly
Keyword(s):  
Temperature Field ◽  
Specific Heat ◽  
Heating Rate ◽  
Thermal Stresses ◽  
Thermomechanical Properties ◽  
Heat Fluxes ◽  
Temperature Fields ◽  
Experimental Setup ◽  
Working Surface ◽  
Refractory Structures

An experimental setup for micro- and macro-studies of specific heat fluxes and thermomechanical properties of refractories has been developed. The influence on the heat resistance of refractory structures of thermal stresses, temperature field, shape and size of products under various heating conditions of their working surface is studied. It is shown that reducing the width of the side of the working surface of the refractory allows you to increase the speed and specific heat flux without violating the integrity of the structure of the refractory material. The distribution of the temperature fields of the refractory with a change in the heating rate of its working surface, as well as its shape, is studied. Ill. 5. Ref. 11.

Analysis of a Bow-Free Prestressed Test Specimen

2014 ◽  
Vol 81 (11) ◽  
Author(s):  
E. Suhir ◽  
J. Nicolics
Keyword(s):  
Cross Sections ◽  
Test Specimen ◽  
Thermal Loading ◽  
Thermal Stresses ◽  
Effective Means ◽  
Physical Nature ◽  
Accelerated Testing ◽  
Mode Shift ◽  
Temperature Range ◽  
Operation Conditions

Broadening the temperature range in accelerated testing of electronic products is a typical measure to assure that the product of interest is sufficiently robust. At the same time, a too broad temperature range can lead to the shift in the modes and mechanisms of failure, i.e., result in failures that will not occur in actual operation conditions. Application of mechanical prestressing of the test specimen could be an effective means for narrowing the temperature range during accelerated testing and thereby achieving trustworthy and failure-mode-shift-free accelerated test information. Accordingly, simple engineering predictive models are developed for the evaluation of the magnitude and the distribution of thermal and mechanical stresses in a prestressed bow-free test specimen. A design, in which an electronic or a photonic package is bonded between two identical substrates, is considered. Such a design is often employed in some today's packaging systems, in which the “inner,” functional, component containing active and/or passive devices and interconnects is placed between two identical “outer” components (substrates). The addressed stresses include normal stresses acting in the component cross sections and the interfacial shearing and peeling stresses. Although the specimen as a whole remains bow-free, the peeling stresses might be nevertheless appreciable, since the outer components, if thin enough, deflect to a greater or lesser extent with respect to the inner component. The numerical example has indicated that the maxima of the interfacial thermal shearing and peeling stresses are indeed comparable and that these maxima are on the same order of magnitude as the normal thermal stresses acting in the components' cross sections. It is shown that since the thermal and the prestressing mechanical loads are of different physical nature, the stresses caused by these two load categories are distributed differently over the specimen's length. It is shown also that although it is possible and even advisable to apply mechanical prestressing for a lower temperature range, it is impossible to reproduce the same stress distribution as in the case of thermal loading. The obtained results enable one to shed light on the physics of the state of stress in prestressed bow-free test specimens in electronics and photonics engineering.

Transient Elastic and Viscoelastic Thermal Stresses During Laser Drilling of Ceramics

1998 ◽  
Vol 120 (4) ◽  
pp. 892-898 ◽  
Author(s):  
M. F. Modest
Keyword(s):  
Solid Surface ◽  
Thermal Stresses ◽  
Bending Strength ◽  
Pulsed Laser ◽  
Laser Drilling ◽  
Heat Fluxes ◽  
Temperature Fields ◽  
Drilling Process ◽  
Elastic Stresses ◽  
Viscoelastic Effects

Lasers appear to be particularly well suited to drill and shape hard and brittle ceramics, which are almost impossible to netshape to tight tolerances, and are presently machined in industry only by diamond grinding. Unfortunately, the large, focussed heat fluxes that allow the ready melting and ablation of material, also result in large localized thermal stresses within the narrow heat-affected zone, which can lead to microcracks, significant decrease in bending strength, and even catastrophic failure. In order to assess the where, when, and what stresses occur during laser drilling, that are responsible for cracks and decrease in strength, elastic and viscoelastic stress models have been incorporated into our two-dimensional drilling code. The code is able to predict temporal temperature fields as well as the receding solid surface during CW or pulsed laser drilling. Using the resulting drill geometry and temperature fields as well as the receding solid surface during CW of pulsed laser drilling. Using the resulting drill geometry and temperature field, elastic stresses as well as viscoelastic stresses are calculated as they develop and decay during the drilling process. The viscosity of the ceramic is treated as temperature-dependent, limiting viscoelastic effects to a thin layer near the ablation front where the ceramic has softened.

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