Design considerations in mechanical face seals for improved performance. 2: Lubrication

The importance of sealing technology in our industrial, chemical-oriented society in regard to maintenance and environmental contamination is pointed out. It is stated that seal performance (leakage, life) is directly related to seal lubrication. Current thinking in regard to seal lubrication is reviewed; the effect of energy dissipation in the thin lubricating film separating the sealing faces is pointed out, and the results of vaporization due to heating are illustrated. Also, hydrodynamic lubrication is reviewed, and an inherent tendency for the seal to operate with angular misalignment is shown. Recent work on hydrostatic effects is summarized and the conditions for seal instability are discussed. Four different modes of seal lubrication are postulated with the mode type being a strong function of speed and pressure

Design considerations in mechanical face seals for improved performance. 1: Basic configurations

Basic assembly configurations of the mechanical face seal are described and some advantages associated with each are listed. The various forms of seal components are illustrated, and functions pointed out. The technique of seal pressure balancing and its application are described; and the concept of the PV factor, its different forms and limitations are discussed. Brief attention is given to seal lubrication since it is covered in detail in a companion paper. Finally, the operating conditions for various applications of low pressure seals (aircraft transmissions) are listed, and the seal failure mode of a particular application is discussed

The effects of numerical resolution on hydrodynamical surface convection simulations and spectral line formation

The computationally demanding nature of radiative-hydrodynamical simulations of stellar surface convection warrants an investigation of the sensitivity of the convective structure and spectral synthesis to the numerical resolution and dimension of the simulations, which is presented here. With too coarse a resolution the predicted spectral lines tend to be too narrow, reflecting insufficient Doppler broadening from the convective motions, while at the currently highest affordable resolution the line shapes have converged essentially perfectly to the observed profiles. Similar conclusions are drawn from the line asymmetries and shifts. In terms of abundances, weak FeI and FeII lines show a very small dependence (~0.02 dex) while for intermediate strong lines with significant non-thermal broadening the sensitivity increases (~0.10 dex). Problems arise when using 2D convection simulations to describe an inherent 3D phenomenon, which translates to inaccurate atmospheric velocity fields and temperature and pressure structures. In 2D the theoretical line profiles tend to be too shallow and broad compared with the 3D calculations and observations, in particular for intermediate strong lines. In terms of abundances, the 2D results are systematically about 0.1 dex lower than for the 3D case for FeI lines. Furthermore, the predicted line asymmetries and shifts are much inferior in 2D. Given these shortcomings and computing time considerations it is better to use 3D simulations of even modest resolution than high-resolution 2D simulations.Comment: Accepted for A&

Gas turbine ceramic-coated-vane concept with convection-cooled porous metal core

Analysis and flow experiments on a ceramic-coated-porous-metal vane concept indicated the feasibility, from a heat transfer standpoint, of operating in a high-temperature (2500 F) gas turbine cascade facility. The heat transfer and pressure drop calculations provided a basis for selecting the ceramic layer thickness (to 0.08 in.), which was found to be the dominant factor in the overall heat transfer coefficient. Also an approximate analysis of the heat transfer in the vane trailing edge revealed that with trailing-edge ejection the ceramic thickness could be reduced to (0.01 in.) in this portion of the vane

Full photon statistics of a light beam transmitted through an optomechanical system

In this paper, we study the full statistics of photons transmitted through an optical cavity coupled to nanomechanical motion. We analyze the entire temporal evolution of the photon correlations, the Fano factor, and the effects of strong laser driving, all of which show pronounced features connected to the mechanical backaction. In the regime of single-photon strong coupling, this allows us to predict a transition from sub-Poissonian to super-Poissonian statistics for larger observation time intervals. Furthermore, we predict cascades of transmitted photons triggered by multi-photon transitions. In this regime, we observe Fano factors that are drastically enhanced due to the mechanical motion.Comment: 8 pages, 7 figure

Numerical simulations of surface convection in a late M-dwarf

Based on detailed 2D and 3D numerical radiation-hydrodynamics (RHD) simulations of time-dependent compressible convection, we have studied the dynamics and thermal structure of the convective surface layers of a prototypical late-type M-dwarf (Teff~2800K log(g)=5.0, solar chemical composition). The RHD models predict stellar granulation qualitatively similar to the familiar solar pattern. Quantitatively, the granular cells show a convective turn-over time scale of ~100s, and a horizontal scale of 80km; the relative intensity contrast of the granular pattern amounts to 1.1%, and root-mean-square vertical velocities reach 240m/s at maximum. Deviations from radiative equilibrium in the higher, formally convectively stable atmospheric layers are found to be insignificant allowing a reliable modeling of the atmosphere with 1D standard model atmospheres. A mixing-length parameter of alpha=2.1 provides the best representation of the average thermal structure of the RHD model atmosphere while alternative values are found when fitting the asymptotic entropy encountered in deeper layers of the stellar envelope alpha=1.5, or when matching the vertical velocity field alpha=3.5. The close correspondence between RHD and standard model atmospheres implies that presently existing discrepancies between observed and predicted stellar colors in the M-dwarf regime cannot be traced back to an inadequate treatment of convection in the 1D standard models. The RHD models predict a modest extension of the convectively mixed region beyond the formal Schwarzschild stability boundary which provides hints for the distribution of dust grains in cooler (brown dwarf) atmospheres.Comment: 19 pages, 16 figures, accepted for publication in A&

Photometric colors of late-type giants: theory versus observations

To assess the current status in the theoretical modeling of the spectral properties of late-type giants, we provide a comparison of synthetic photometric colors of late-type giants (calculated with PHOENIX, MARCS and ATLAS model atmospheres) with observations, at [M/H]=0.0 and -2.0. Overall, there is a good agreement between observed and synthetic colors, and synthetic colors and published Teff-color relations, both at [M/H]=0.0 and -2.0. Deviations from the observed trends in Teff-color planes are generally within \pm 150K (or less) in the effective temperature range Teff=3500-4800K. Synthetic colors calculated with different stellar atmosphere models typically agree to ~100K, within a large range of effective temperatures and gravities. Some discrepancies are seen in the Teff-(B-V) plane below Teff~3800K at [M/H]=0.0, due to difficulties in reproducing the 'turn-off' to the bluer colors which is seen in the observed data at Teff~3600K. Note that at [M/H]=-2.0 effective temperatures given by the scale of Alonso et al. (1999) are generally lower than those resulting from other Teff-color relations based both on observed and synthetic colors.Comment: 2 pages, 1 figure. Proceedings of the IAU Symposium 232 "The Scientific Requirements for Extremely Large Telescopes", eds. P. Whitelock, B. Leibundgut, and M. Dennefel

On a generalization of Jacobi's elliptic functions and the Double Sine-Gordon kink chain

A generalization of Jacobi's elliptic functions is introduced as inversions of hyperelliptic integrals. We discuss the special properties of these functions, present addition theorems and give a list of indefinite integrals. As a physical application we show that periodic kink solutions (kink chains) of the double sine-Gordon model can be described in a canonical form in terms of generalized Jacobi functions.Comment: 18 pages, 9 figures, 3 table