Surface Temperatures Generated With Ceramic Materials in Oscillating/Fretting Contact

1994 ◽  
Vol 116 (2) ◽  
pp. 260-267 ◽  
Author(s):  
B. L. Weick ◽  
M. J. Furey ◽  
B. Vick
Keyword(s):  
Surface Temperature ◽  
Tungsten Carbide ◽  
Heat Generation ◽  
Tribological Behavior ◽  
Ceramic Materials ◽  
Frictional Heat ◽  
Theoretical Treatment ◽  
Frictional Heat Generation ◽  
Surface Temperatures ◽  
Wide Range

This paper summarizes the results of a study of the tribological behavior of ceramic materials in unlubricated oscillating/fretting contact with particular emphasis on frictionally-generated surface temperatures. The study was carried out using an oscillating contact device coupled to an infrared microscope. The contact geometry consists of a stationary spherical specimen loaded against a thin sapphire optical flat driven by an electromagnetic shaker. With this system, measurements can be made of friction, wear, and surface temperature over a wide range of loads, frequencies, and vibration amplitudes. Four ceramic materials were investigated, namely zirconium oxide (zirconia), tungsten carbide, and two different forms of aluminum oxide (alumina and sapphire). The first important finding was that each material exhibited unique and characteristic tribological behavior. Instantaneous variations in friction and surface temperature occurring within a single cycle of oscillation (e.g., in less than 0.005 seconds) could readily be measured with this technique. By digitizing the surface temperature, friction, and velocity signals, comparisons are made in the time and frequency domains. Frequency content correlations are determined using Fourier transform techniques. In addition, instantaneous frictional heat generation rates are calculated using the digitized friction and velocity data. Based on a series of experiments at constant oscillation frequency and amplitude, a correlation appears to exist between wear and surface temperature for the ceramics studied. Sapphire-on-sapphire and zirconia-on-sapphire produced the highest wear and the highest surface temperature rises (ca. 130–140 K). Tungsten carbide-on-sapphire produced the lowest wear and lowest surface temperature rise, while alumina exhibited intermediate behavior. In all cases, the rate of frictional heat generation was relatively low. It may be that the rapid fluctuations in surface temperature under these conditions—with two major temperature peaks per cycle—could lead to a kind of thermal stress fatigue of the ceramics as a wear mechanism. The use of the IR microscope in the scanning mode, coupled with scanning electron microscopy of the wear scars and theoretical treatment of sub-divided areas, can shed light on the nature and distribution of real areas of contact.

An Investigation of Heat Generation Characteristics of Brush Seals

2007 ◽  
Author(s):  
Mehmet Demiroglu ◽  
John A. Tichy
Keyword(s):  
Contact Force ◽  
Heat Generation ◽  
Operating Conditions ◽  
Frictional Heat ◽  
Design Parameters ◽  
Frictional Heat Generation ◽  
Operation Conditions ◽  
Seal Design ◽  
Wide Range ◽  
Brush Seals

Brush seals are considered as a category of compliant seals, which tolerate a great high level of interference between the seal and the rotor or shaft. Their superior leakage characteristics have opened many application fields in the turbo-machinery world, ranging from industrial steam turbines to jet engines. However, brush seal designers have to find a trade-off between the lower parasitic leakage but higher heat generation properties of brush seals for given operation conditions. As brush seals can maintain contact with the rotor for a wide range of operating conditions, the contact force/pressure generated at the seal-rotor interface becomes an important design parameter for sustained seal performance and longevity of its service life. Furthermore, due to this contact force at the interface, frictional heat generation is inevitable and must be evaluated for various design and operating conditions. In this paper, frictional heat generation at the sealrotor interface is studied. To capture temperature rise at the interface, a thermal image of the seal and rotor is taken with an infrared camera under various operating conditions. The temperature map of the rotor is compared to results from thermal finite element analysis of the rotor to back calculate the heat flux to the rotor. A closed form equation for frictional heat generation is suggested as a function of seal design parameters, material properties, friction coefficient and empirical factors from testing.

scholarly journals Clausius–Clapeyron Scaling of CAPE from Analytical Solutions to RCE

2016 ◽  
Vol 73 (9) ◽  
pp. 3719-3737 ◽  
Author(s):  
David M. Romps
Keyword(s):  
Surface Temperature ◽  
Analytical Solutions ◽  
Convective Available Potential Energy ◽  
Specific Humidity ◽  
Tropopause Height ◽  
Surface Warming ◽  
Surface Temperatures ◽  
Humidity Change ◽  
Rate Of Increase ◽  
Wide Range

Abstract By deriving analytical solutions to radiative–convective equilibrium (RCE), it is shown mathematically that convective available potential energy (CAPE) exhibits Clausius–Clapeyron (CC) scaling over a wide range of surface temperatures up to 310 K. Above 310 K, CAPE deviates from CC scaling and even decreases with warming at very high surface temperatures. At the surface temperature of the current tropics, the analytical solutions predict that CAPE increases at a rate of about 6%–7% per kelvin of surface warming. The analytical solutions also provide insight on how the tropopause height and stratospheric humidity change with warming. Changes in the tropopause height exhibit CC scaling, with the tropopause rising by about 400 m per kelvin of surface warming at current tropical temperatures and by about 1–2 km K−1 at surface temperatures in the range of 320–340 K. The specific humidity of the stratosphere exhibits super-CC scaling at temperatures moderately warmer than the current tropics. With a surface temperature of the current tropics, the stratospheric specific humidity increases by about 6% per kelvin of surface warming, but the rate of increase is as high as 30% K−1 at warmer surface temperatures.

Brush Seal Temperature Distribution Analysis

2005 ◽  
Vol 128 (3) ◽  
pp. 599-609 ◽  
Author(s):  
Yahya Dogu ◽  
Mahmut F. Aksit
Keyword(s):  
Heat Flux ◽  
Temperature Distribution ◽  
Heat Generation ◽  
Operating Conditions ◽  
Frictional Heat ◽  
Distribution Analysis ◽  
Cfd Analysis ◽  
Oxidation Rates ◽  
Frictional Heat Generation ◽  
Brush Seal

Brush seals are designed to survive transient rotor rubs. Inherent brush seal flexibility reduces frictional heat generation. However, high surface speeds combined with thin rotor sections may result in local hot spots. Considering large surface area and accelerated oxidation rates, frictional heat at bristle tips is another major concern especially in challenging high-temperature applications. This study investigates temperature distribution in a brush seal as a function of frictional heat generation at bristle tips. The two-dimensional axisymmetric computational fluid dynamics (CFD) analysis includes the permeable bristle pack as a porous medium allowing fluid flow throughout the bristle matrix. In addition to effective flow resistance coefficients, isotropic effective thermal conductivity as a function of temperature is defined for the bristle pack. Employing a fin approach for a single bristle, a theoretical analysis has been developed after outlining the brush seal heat transfer mechanism. Theoretical and CFD analysis results are compared. To ensure coverage for various seal designs and operating conditions, several frictional heat input cases corresponding to different seal stiffness values have been studied. Frictional heat generation is outlined to introduce a practical heat flux input into the analysis model. Effect of seal stiffness on nominal bristle tip temperature has been evaluated. Analyses show a steep temperature rise close to bristle tips that diminishes further away. Heat flux conducted through the bristles dissipates into the flow by a strong convection at the fence-height region.

Sign in / Sign up

Export Citation Format

Share Document