Influence of surface morphology on electrophysical properties of PbTe: Sb films

The electrophysical properties of polycrystalline doped semiconductor thin films PbTe: Sb deposited on mica and sital (glass based ceramic) substrates are considered. The thickness dependencies of carrier mobility, of Hall coefficient and of Seebeck coefficient, and the correlations between these parameters for films deposited on different substrate materials were studied. The peculiarities of growth of thin films and their structural parameters are analyzed taking into account the features of the ‘substrate – film’ boundary section.

Influence of Fluid Film Boundary Migration on Dynamic Coefficients of Journal Bearings and Behavior of Rotor System

The position of fluid film in journal bearing will change while the journal moving in bearing, which can be named fluid film boundary migration (FFBM). It is usually ignored in the calculation of linear dynamic coefficients. While, the errors brought by this neglection was not ever investigated in detail. In this paper, the influence of FFBM on bearing dynamic coefficients and rotor system dynamic behaviors are investigated. A new perturbation-based model is proposed to take the FFBM into account by modifying the boundary conditions of governing equations. It is then verified by the experimental results and analytical results from previous research. Furthermore, the effects of FFBM on stiffness and damping in two typical journal bearings are investigated. The result indicates that the FFBM has a significant influence on dynamic coefficients of full circular journal bearing but little impact on journal bearing with axial grooves. Moreover, it affects the stiffness and damping more significantly in the cases of large length-to-diameter ratios or small eccentricity ratios in full circle bearing. Finally, the dynamical behavior of a rotor-bearing system with considering the FFBM is also investigated. The result shows that the FFBM of oil film has remarkable influences on the instability threshold and imbalance responses of the rotor system, which should not be ignored. The conclusions obtained in this research are expected to be helpful for the design of full circular journal bearings or rotor-bearing systems.

Detailed surface analysis of V-defects in GaN films on patterned silicon(111) substrates by metal–organic chemical vapour deposition

The growth mechanism of V-defects in GaN films was investigated. It was observed that the crystal faces of both the sidewall of a V-defect and the sidewall of the GaN film boundary belong to the same plane family of \{ {{{10\bar 11}}} \}, which suggests that the formation of the V-defect is a direct consequence of spontaneous growth like that of the boundary facet. However, the growth rate of the V-defect sidewall is much faster than that of the boundary facet when the V-defect is filling up, implying that lateral growth of \{ {{{10\bar 11}}} \} planes is not the direct cause of the change in size of V-defects. Since V-defects originate from dislocations, an idea was proposed to correlate the growth of V-defects with the presence of dislocations. Specifically, the change in size of the V-defect is determined by the growth rate around dislocations and the growth rate around dislocations is determined by the growth conditions.

Opto-thermally Excited Fabry-Perot Resonance Frequency Behaviors of Clamped Circular Graphene Membrane

An opto-thermally excited optical fiber Fabry-Perot (F-P) resonant probe with suspended clamped circular graphene diaphragm is presented in this paper. Then, the dependence of resonance frequency behaviors of graphene diaphragm upon opto-mechanical factors including membrane properties, laser excitation parameters and film boundary conditions are investigated via COMSOL Multiphysics simulation. The results show that the radius and thickness of membrane will linearly affect the optical fiber light-induced temperature distribution, thus resulting in rapidly decreasing resonance frequency changes with the radius-to-thickness ratio. Moreover, the prestress can be regulated in the range of 108 Pa to 109 Pa by altering the environmental temperature with a scale factor of 14.2 MPa/K. It is important to note that the availability of F-P resonant probe with a defective clamped circular graphene membrane can be improved notably by fabricating the defected circular membrane to a double-end clamped beam, which gives a broader perspective to characterize the resonance performance of opto-thermally excited F-P resonators.

A numerical analysis and experimental investigation of three oil grooves sleeve bearing performance

Purpose This paper aims to reveal the cavitation characteristics of three oil wedges sleeve bearing and set the theoretical and experimental basis for defining the oil film boundary condition. Design/methodology/approach Computational fluid dynamics model of three oil wedges sleeve bearings based on the Navier–Stokes equation is set using Fluent considering turbulent situation and two-phase flow theory. The cavitation characteristics of bearing is investigated by taking pictures of experiment. Findings The rupture region of oil film and the contours of air volume fraction increase distinctly with the increase of rotating speed and the decrease of input pressure. The critical rotating speed of cavitation occurrence and oil film pressure increases with the increase of input pressure. The change trend of experiment cavitation with the rotating speed and input pressure is consistent with theoretical cavitation in general. Originality/value The finite element model of three oil wedges sleeve bearings is established based on the Navier-Stokes calculation equation of the fluid, two-phase flow theory and turbulent model. Sleeve bearing is transparent, the pictures of cavitation can be easily taken by high-speed camera, the cavitation characteristics of bearing is studied by experiment. The cavitation performance of three oil wedges bearings is studied with the change of input pressure and rotating speed, the change trend is basically consistent for theory and experiment. The study on critical rotating speed of cavitation occurrence is benefit for defining the oil film boundary condition.

Flow Statistics and Visualization of Multirow Film Cooling Boundary Layers Emanating From Cylindrical and Diffuser Shaped Holes

The research presented in this paper strives to exploit the benefits of near-wall measurement capabilities using hotwire anemometry and flowfield measurement capabilities using particle image velocimetry (PIV) for analysis of the injection of a staggered array of film cooling jets into a turbulent cross-flow. It also serves to give insight into the turbulence generation, jet structure, and flow physics pertaining to film cooling for various flow conditions. Such information and analysis will be applied to both cylindrical and diffuser shaped holes, to further understand the impacts manifesting from hole geometry. Spatially resolved PIV measurements were taken at the array centerline of the holes and detailed temporally resolved hotwire velocity and turbulence measurements were taken at the trailing edge of each row of jets in the array centerline corresponding to the PIV measurement plane. Flowfields of jets emanating from eight staggered rows, of both cylindrical and diffuser shaped holes inclined at 20 deg to the main-flow, are studied over blowing ratios in the range of 0.3–1.5. To allow for deeper interpretation, companion local adiabatic film cooling effectiveness results will also be presented for the geometric test specimen from related in-house work. Results show “rising” shear layers for lower blowing ratios, inferring boundary layer growth for low blowing ratio cases. Detachment of film cooling jets is seen from a concavity shift in the u′rms line plots at the trailing edge of film cooling holes. Former rows of jets are observed to disrupt the approaching boundary layer and enhance the spreading and propagation of subsequent downstream jets. Behavior of the film boundary layer in the near-field region directly following the first row of injection, as compared to the near-field behavior after the final row of injection (recovery region), is also measured and discussed. The impact of the hole geometry on the resulting film boundary layer, as in this case of cylindrical verses diffuser shaped holes, is ascertained in the form of mean axial velocity, turbulence level (u′rms), and length scales profiles.

A Model for Surface-Film Lubricated Cold Rolling Incorporating Interdependence of Mechanics, Heat Transfer, and Surface-Film Lubrication

This paper aims to establish a theoretical feasibility of metal cold rolling with only surface-film boundary lubrication. To this end, a mathematical model for surface-film lubricated cold rolling is developed. It is formulated to factor in the interdependence of mechanics, heat transfer, and surface-film lubrication with three submodels: the lubrication-friction model, the stress-deformation model, and the thermal model. Governing equations are obtained based on fundamental physics of the rolling process and tribochemistry of the surface-film lubrication. The equations are solved simultaneously with full numerical methods of solutions. Sample results are presented to evaluate the model and to show the theoretical potential of the surface-film lubrication for cold rolling. The model may be used as a theoretical tool to aid the research and development of surface-film lubrication technology for cold rolling. It may be further developed in conjunction with precision experiments.

Flow Statistics and Visualization of Multi-Row Film Cooling Boundary Layers Emanating From Cylindrical and Diffuser Shaped Holes

The research presented in this paper strives to exploit the benefits of near-wall measurement capabilities using hotwire anemometry and flowfield measurement capabilities using particle image velocimetry (PIV) for analysis of the injection of a staggered array of film cooling jets into a turbulent cross-flow. It also serves to give insight into the turbulence generation, jet structure, and flow physics pertaining to film cooling for various flow conditions. Such information and analysis will be applied to both cylindrical and diffuser shaped holes, to further understand the impacts manifesting from hole geometry. Spatially-resolved PIV measurements were taken at the array centerline of the holes and detailed temporally resolved hotwire velocity and turbulence measurements were taken at the trailing edge of each row of jets in the array centerline corresponding to the PIV measurement plane. Flowfields of jets emanating from eight staggered rows, of both cylindrical and diffuser shaped holes inclined at 20 degrees to the main-flow, are studied over blowing ratios in the range of 0.3–1.5. To allow for deeper interpretation, companion local adiabatic film cooling effectiveness results will also be presented for the geometric test specimen from related in-house work. Results show “rising” shear layers for lower blowing ratios, inferring boundary layer growth for low blowing ratio cases. Detachment of film cooling jets is seen from a concavity shift in the u’rms line plots at the trailing edge of film cooling holes. Former rows of jets are observed to disrupt the approaching boundary layer and enhance the spreading and propagation of subsequent downstream jets. Behavior of the film boundary layer in the near-field region directly following the first row of injection, as compared to the near-field behavior after the final row of injection (recovery region), is also measured and discussed. The impact of the hole geometry on the resulting film boundary layer, as in this case of cylindrical verses diffuser shaped holes, is ascertained in the form of mean axial velocity, turbulence level (u’rms), and length scales profiles.

Oil film boundary analysis of spiral oil wedge sleeve bearing based on the dynamic loading conditions

The area and location of cavitation change with time in the condition of dynamic loading. The cavitation location of sleeve bearing not only depends on axis location and velocity at a certain moment but also is affected by cavitation history, so the boundary condition need to be defined in the solution of lubrication equation. Based on the balance of axial inertia force, oil film force, and dynamic loading, the motion equation, generalized Reynolds equation and oil film thickness equation of spiral oil wedge sleeve bearing are established. The results show that the cavitation location and carrying capacity vary periodically with the change in time. The effect of dynamic loading and rotational speed on the oil film cavitation and carrying capacity is studied.