bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamics of a Vaporizing Droplet in Laminar Entry Region of a Straight Channel
Authors: Bhatti M. S.
Published: November 2010

A theory is developed for two-phase flow wherein droplets suspended in a gas stream penetrate the hydrodynamic boundary layer in the laminar entry region of a straight channel with isothermal walls. A fraction of the droplets is captured by the boundary layer due to isotropic turbulence superimposed at the edge of the the boundary layer. Transverse motion of the droplet is under the influence of Stokes’ drag, buoyancy, gravity and inertia forces. Axial motion of the droplets is with the local gas velocity without slip. Droplet trajectories are determined by the numerical integration of the equations of motion employing the fourth order Runge-Kutta technique. Using these results, a two region model is developed for determining the convective heat transfer conductance augmented by droplet vaporization. Momentum and heat transfer results are presented for air/water-droplet system containing 10μ–50μ droplets under typical conditions encountered in dry cooling towers.
An Analysis of Deep Submerged Multiple-Port Buoyant Discharges
Authors: Kannberg L. D. , Davis L. R.
Published: November 2010

The results of an experimental study of deep submerged multiple-port thermal discharges are compared to the predictions of a theory treating the dilution of merging multiple-port buoyant jets discharge from a row of equally spaced ports. The paper summarizes the considerable alteration of the Hirst [11] model necessary to adequately treat merging multiple jets. The essential features of the analysis are: (1) the gradual transition of the profiles from simple axisymmetric profiles to merging profiles and finally to fully merged, pseudo-slot, two-dimensional profiles, and (2) an entrainment based on the available entrainment surface. Results indicate that the overprediction of plume characteristics associated with certain other models as compared to experimental data may be overcome using such an analysis and that suitable prediction may be obtained.
An Efficient Algorithm for Evaluating Arrays of Extended Surface
Authors: Kraus A. D. , Snider A. D. , Doty L. F.
Published: November 2010

In the consideration of single longitudinal fins of rectangular, trapezoidal, and triangular profile and in arrays of extended surface composed of these fins, it is shown that conditions of heat flow and temperature excess at the fin or array tip induce conditions of heat flow and temperature excess at the fin or array base. In particular, there is a linear transformation between the aforementioned data at the fin tip and the fin base. The conventional fin efficiency is abandoned and single fins or arrays of extended surface are instead characterized by a single important parameter, the heat flow to temperature excess ratio, which is a function only of fin geometry and heat transfer parameters. Algorithms are provided for combining the effects of individual fins in arrays of extended surface. A modification of the procedures developed leads to an exact solution for the double stack with unequal heat distribution at opposite ends, a problem which has heretofore required iterative solution procedures.
Heat Transfer From Arrays of Impinging Jets with Large Jet-to-Jet Spacing
Authors: Hollworth B. R. , Berry R. D.
Published: November 2010

Local and average convective heat transfer coefficients were measured for arrays of widely spaced impinging air jets and correlated in terms of system geometry, air flow, and fluid properties. The configurations were square arrays of circular turbulent jets (spaced from 10–25 diameters apart) incident upon a flat isothermal target surface. Independent parameters were varied over ranges generally corresponding to gas turbine cooling applications. Local heat transfer coefficients were influenced by interference from neighboring jets only when the target plate and the jet orifice plate were less than five jet diameters apart. Average heat transfer coefficients were nearly equal for all the arrays tested as long as the coolant flow per unit area of target surface was held constant. In fact, there was a tendency for the more widely spaced configurations to produce slightly higher average heat transfer under such conditions.
Turbulent Heat Transfer Downstream of an Unsymmetric Blockage in a Tube
Authors: Koram K. K. , Sparrow E. M.
Published: November 2010

Pipe flow experiments were performed to study the heat transfer in the separation, reattachment, and redevelopment regions downstream of a wall-attached blockage in the form of a segmental orifice plate. Water was the working fluid, and the Reynolds number encompassed the range from about 10,000–60,000. The extent of the flow blockage was varied from one-fourth to three-fourths of the tube cross section. Heat transfer coefficients were determined both around the circumference of the uniformly heated tube and along its length. The axial distributions of the circumferential average Nusselt numbers show an initial increase, then attain a maximum, and subsequently decrease toward the fully developed regime. These Nusselt numbers are much higher than those for a conventional thermal entrance region. The unsymmetric blockage induces variations of the Nusselt number around the circumference of the tube. Axial distributions of the Nusselt number at various fixed angular positions reveal the presence of two types of maxima. One of these is associated with the reattachment of the flow and the other occurs due to the impingement of flow deflected by the blockage onto the tube wall. The circumferential variations decay with increasing downstream distance, but the rate of decay for the case of the smallest blockage is remarkably slow. Although most of the tests were performed for Pr = 4, supplementary experiments for Pr = 8 showed that the results are valid for a range of Prandtl numbers.
Heat Transfer from a Cylinder Oscillating in a Cross-Flow
Authors: Saxena U. C. , Laird A. D. K.
Published: November 2010

This paper presents data on the effects of transverse oscillations on local heat transfer rates from a 7/8 in. (22 mm) diameter vertical circular cylinder, with an internal heater, subjected to cross-flow at a Reynolds number of 3500 in an open water channel during forced oscillations. The amplitude was varied from 0.89 to 1.99 times the diameter of the cylinder and the frequency from 0.4 to 1.2 Hz. The amplitude and frequency contributed about equally to the increases in local heat transfer coefficients. The increases in some cases were up to 60 percent, and were as much as 15 percent larger on the back than on the front of the cylinder. Motion pictures showed that the larger increases generally coincided with the larger flow disturbances that result from wake capture.
Selected Ordinates for Total Solar Radiant Property Evaluation from Spectral Data
Authors: Wiebelt J. A. , Henderson J. B.
Published: November 2010

Total radiant properties of materials at the earth’s surface are a function of the condition and type of atmosphere traversed by the sun’s energy. Therefore, the solar irradiation at the earth’s surface has been reexamined using the latest atmospheric data. Based on these calculations a new and expanded set of selected ordinates was calculated. These ordinates are used to evaluate the total solar transmittance, or other properties, for a wide variety of atmospheric conditions, from the spectral data.
The Structure of a Boundary Layer on a Rough Wall with Blowing and Heat Transfer
Authors: Pimenta M. M. , Moffat R. J. , Kays W. M.
Published: November 2010

A regular, deterministic, rough surface was tested at four velocities from 11 to 40 m/s, with and without blowing, to evaluate the Stanton number and friction factor characteristics. Hot-wire data were taken to document the turbulence components, the Reynolds stresses, and the turbulent heat flux. Data are presented concerning the streamwise development of the mean and fluctuating components, and the effect of blowing. Correlation coefficients and mixing lengths were deduced from the hot-wire data and are also presented. While the mean velocity data showed only two allowable states for the boundary layer (laminar and “fully rough”), the turbulence structure indicated a third: “transitionally rough”. Distributions of u′v′/uτ2 and v′t′/uτtτ are similar, except for high blowing (F = 0.004). The turbulent Prandtl number lies between 0.85 and 1.0 for the entire layer, and a mixing length constant of κ = 0.41 describes the data with good accuracy for all velocities and all values of blowing tested.
Structure of a Turbulent Thermal Plume Rising along an Isothermal Wall
Authors: Liburdy J. A. , Groff E. G. , Faeth G. M.
Published: November 2010

The weakly buoyant region of a turbulent thermal plume formed by a line heat source along the base of a vertical isothermal wall was investigated. The turbulence quantities: u′, v′, w′, t′, u′v′, u′t′, and v′t′ were measured, supplementing existing measurements of mean quantities in this flow. The plumes exhibited local similarity in terms of local plume thermal energy flux and height above the source. In the outer portions of the flow, the shear stress agreed with conventional mixing length models and the turbulent Prandtl number approached 0.5. Near the wall, however, turbulent stress and transport quantities do not approach zero when gradients in mean quantities are zero and eddy viscosity models do not properly represent the turbulence characteristics. Predictions of mean quantities were examined using a local similarity hypothesis and various eddy viscosity models. The theoretical results are in fair agreement with the measurements, in spite of the inaccurate representation of turbulence quantities near the wall. The theory indicates that local similarity for mean quantities is only approximately observed, and suggests the presence of systematic Grashof number effects that were not apparent in the measurements due to data scatter.
Velocity Measurements in Two Natural Convection Air Flows Using a Laser Velocimeter
Authors: Flack R. D. , Witt C. L.
Published: November 2010

Velocities in two laminar free convection air flow fields were measured using a laser velocimeter. Velocities were first measured in the boundary layer around a heated vertical flat plate and results compare within two percent of theoretical and previous experimental (streak photography) data. Second, velocities were measured throughout a two-dimensional triangular enclosure, which consisted of two isothermal side walls (one heated and one cooled), an insulated bottom, and glass end plates. Enclosure data are compared to simple inclined isothermal plate data and are also presented so that the flow patterns can be observed.
A Study of Penetrative Convection in Rotating Fluid
Authors: Quon C.
Published: November 2010

The effects of rotation on penetrative convection in an annulus of fluid are studied numerically by finite difference method. The axisymmetric flows for 14 sets of parameters are presented. It is found that rotation compresses the cell heights and increases the horizontal cell number in the r-z plane. The curvature of the container strongly affects the cell structure only at low rotation rate. The upper dynamical boundary conditions have virtually no effect on the flow fields if the upper temperature is sufficiently high.
Experimental Study of Two-Phase Propane Expanded through the Ranque-Hilsch Tube
Authors: Collins R. L. , Lovelace R. B.
Published: November 2010

When air or other gases flow through the Ranque-Hilsch vortex tube, the well known temperature separation effect can be produced. This effect has been utilized for many purposes and is especially useful in providing cooling in applications not requiring the higher efficiencies of more sophisticated refrigeration systems. When the inlet fluid to the tube becomes a mixture of saturated liquid and vapor, one intuitively expects the temperature separation to diminish. Experimental data were obtained using propane to quantitatively determine the deterioration of temperature separation when the condition of the inlet fluid becomes a saturated mixture. Observations indicate that temperature separation diminishes rapidly for inlet qualities of less than 80 percent due largely to the decrease in “hot side” temperature. For qualities above 80 percent, significant temperature separation can be maintained.
Thermal and Hydrodynamic Phenomena Associated with Melting of a Horizontal Substrate Placed beneath a Heavier Immiscible Liquid
Authors: Taghavi-Tafreshi K. , Dhir V. K. , Catton I.
Published: November 2010

The melting of a horizontal slab of frozen olive oil placed beneath a pool of warm water has been studied experimentally. The interfacial heat flux data are taken in quasi-static mode by noting the time rate of change of enthalpy of the pool of water. Because of little agitation of the pool due to low melt volume flux (ρwater/ρolive oil ≃ 1.09; ΔT ≃ 5–45 K), the pool was found to stratify with time. Hence, heat transfer coefficient data have been based on the interfacial temperature rather than on the mean pool temperature. Visual observations show that melt removal is governed by Taylor instability and that melt releasing nodes lie about a Taylor wavelength apart. Predictions of the growth of the interface based on equilibrium between surface tension and buoyant forces have been made and found to compare well with the data obtained from the movies. The heat transfer coefficient data obtained at higher pool temperatures are found to correlate well with the predictions based on the proposed model.
Exact Solution for Freezing in Cylindrical Symmetry with Extended Freezing Temperature Range
Authors: O¨zis¸ik M. N. , Uzzell J. C.
Published: November 2010

The problem of solidification by a line heat sink in an infinite medium with cylindrical symmetry for a substance having an extended freezing temperature range between the solidus and liquidus temperatures is solved exactly for two different cases characterizing the distribution of the solid fraction within the two-phase zone. In one of the models, the solid fraction is assumed to vary linearly with the temperature and in the other solidification within the two-phase zone is assumed to have a linear relationship with the distance. The analysis is applicable for both eutectic and solid solution alloys.
Solids Circulation in Turbulent Fluidized Beds and Heat Transfer to Immersed Tube Banks
Authors: Staub F. W.
Published: November 2010

In gas fluidized beds of large particles, a change in flow regime from bubbling flow to turbulent flow has been observed as the superficial gas velocity is increased. Solids flow and heat transfer models based on the bubbling flow regime are not generally adequate in the turbulent flow regime. A turbulent flow model is given here that is supported by limited solids flow measurements. A simplified model of the heat transfer to tube banks immersed in fluidized beds, that employs the solids flow model, is also given and is shown to be supported by data over a wide gas pressure and temperature range with particles in the 350μm to 2600μm size range.
Heat Transfer by Forced and Free Convection in a Horizontal Channel with Differentially Heated Ends
Authors: Bejan A. , Imberger J.
Published: November 2010

The effect of net longitudinal flow on natural convection in a horizontal cavity with different end temperatures is discussed. The flow is studied using an asymptotic expansion in the aspect ratio A ≪ 1, the Grashof, Prandtl and Peclet numbers being arbitrary but fixed. It is shown that unlike the natural counterflow with zero longitudinal net flow [1] a net discharge leads to a nonparallel flow structure characterized also by a variable longitudinal temperature gradient. The influence of parameters A, Gr, Pr and Pe on the flow structure is discussed. An asymptotic expression for the Nusselt number for longitudinal heat transport through the cavity is derived in the limit A → 0 and Gr, Pr, Pe fixed.
Low Peclet Number Heat and Mass Transfer from a Drop in an Electric Field
Authors: Griffiths S. K. , Morrison F. A.
Published: November 2010

An electric field, when applied to a dielectric drop suspended in another such fluid, generates a circulating motion. The low Peclet number transport from the drop is investigated analytically using a regular perturbation expansion. A digital computer is used to obtain exact solutions to the resulting equations. These solutions yield accurate results up to a Peclet number of at least 60.
Optimal Fin-Side Design of Compact Tube-in-Fin Heat Exchangers with Rippled Fins
Authors: Mandel S. W. , Townsend M. A. , Parrish T. F.
Published: November 2010

The optimal design of rippled fins found in the common compact heat exchanger is addressed to maximize the heat transferred per unit pressure drop (pumping power). Ripples are common for structural integrity and to facilitate handling and manufacture. Typical designs operate at Reynolds numbers below about 1200. Because a complex flow with heat transfer-process is involved, the optimal design synthesis approach—modeling, objective function definition and optimization—coupled with the desire to efficiently verify the results leads to a highly effective hybrid design technique and substantially less experimentation than might be expected. The model uses a finite difference marching procedure and variable fluid properties. General results for ripple designs and spacings are obtained and corroborated experimentally. In general a short ripple of about 25 deg and height/fin spacing of 0.25 are optimum. Distance between ripples is shown to be a simple function of Reynolds numbers. The final discussion addresses aspects of this approach, its strengths and limitations.
On Prediction and Unified Correlation for Decay of Vertical Buoyant Jets
Authors: Chen C. J. , Chen C. H.
Published: November 2010

A differential turbulence model is used to predict the decay behavior of turbulent buoyant jets in a uniform environment at rest. The turbulent stresses and heat fluxes are modeled by the algebraic expressions while the differential transport equations are solved for the kinetic energy of turbulence, k, the rate of dissipation of turbulence kinetic energy, ε, and the fluctuating temperature T′2. The numerical result correlated with a unified scaling law was shown to fall into a single curve for the flows beyond the zone of flow establishment. The flow characteristics are then classified into a non-buoyant region, an intermediate region and a plume region. The predicted results show that the buoyant jets is accelerated in the zone of flow establishment. Equations for decay of velocity, density, and turbulent quantities are given from the non-buoyant region to the plume region for both plane and round buoyant jets.
Freezing Controlled by Natural Convection
Authors: Sparrow E. M. , Ramsey J. W. , Kemink R. G.
Published: November 2010

Experiments were performed for freezing under conditions where the liquid phase is either above or at the fusion temperature (i.e., superheated or nonsuperheated liquid). The liquid was housed in a cylindrical containment vessel whose surface was maintained at a uniform, time-invariant temperature during a data run, and the freezing occurred on a cooled vertical tube positioned along the axis of the vessel. The phase change medium was n-eicosane, a paraffin which freezes at about 36°C (97°F). In the presence of liquid superheating, the freezing process is drastically slowed and ultimately terminated by the natural convection in the liquid. The terminal size of the frozen layer and the time at which freezing terminates can be controlled by setting the temperature parameters which govern the intensity of the natural convection. The stronger the natural convection, the thinner the frozen layer and the shorter the freezing time. In the absence of liquid superheating, a cylindrical frozen layer grows continuously as predicted by theory, but the growth rate is higher than the predictions because of the presence of whisker-like dendrites on the freezing surface.
Local Nonsimilarity Solution of Free Convection Flow and Heat Transfer from an Inclined Isothermal Plate
Authors: Hasan M. M. , Eichhorn R.
Published: November 2010

The effect of the angle of inclination on free convection flow and heat transfer from an isothermal surface is analyzed by the local nonsimilarity method of solution. An inclination parameter ξ as obtained from the analysis is tan γ/4 (Grx/4)1/4, where γ is the angle of inclination measured from the vertical and Grx is the local Grashof number, based on the component of the gravity vector along the surface. Numerical solutions of the equations are obtained for Prandtl numbers of 0.1, 0.7, 6 and 275. Results show an appreciable effect of ξ on the velocity field, and practically none on the temperature field, except for very large angles of inclination from the vertical or for very small values of the Prandtl number. In the limiting case of very large Prandtl number, ξ has no effect either on the velocity or the temperature field.
Vortex Instability in Buoyancy-Induced Flow over Inclined Heated Surfaces in Porous Media
Authors: Hsu C. T. , Cheng Ping
Published: November 2010

A linear stability analysis is performed for the study of the onset of vortex instability in free convective flow over an inclined heated surface in a porous medium. The undisturbed state is assumed to be the steady two-dimensional buoyancy-induced boundary layer flow which is characterized by a non-linear temperature profile. By a scaling argument, it is shown that the length scales of disturbances are smaller than those for the undisturbed boundary layer flow, thus, confirming the so-called “bottling effects” whereby the disturbances are confined within the boundary layer. By neglecting the lowest order terms in the three-dimensional disturbances equations, the simplified equations are solved based on the local similarity approximations, wherein the disturbances are assumed to have a weak dependence in the streamwise direction. The resulting eigenvalue problem is solved numerically. The critical parameter and the critical wave number of disturbances at the onset of vortex instability are computed for different prescribed wall temperature distribution of the inclined surface. It is found that the larger the inclination angle with respect to the vertical, the more susceptible is the flow for the vortex mode of disturbances; and in the limit of zero inclination angle (i.e., a vertical heated plate) the flow is stable for this form of disturbances.
An Iterative Solution for Anisotropic Radiative Transfer in a Slab
Authors: Sutton W. H. , O¨zis¸ik M. N.
Published: November 2010

An iterative method is applied to solve the integral form of the equation of radiative transfer for the cases of isotropic scattering, highly forward, and backward anisotropic scattering in plane-parallel slab with reflecting boundaries. Calculations are performed for the values of single scattering albedo from ω = 0.7 to 1.0 where the convergence was previously reported to be poor. It is found that the convergence is significantly improved for most cases if the P-1 approximation of the spherical harmonics method is used for the initial guess. Results are presented for the hemispherical reflectivity and transmissivity of the slab over a wide range of parameters.
A General Method for Predicting the Influence of Structural Support Upon Rolling Element Bearing Performance
Authors: Filetti E. G. , Rumbarger J. H.
Published: November 2010

A general analytical technique is presented for the evaluation of rolling element bearings when their structural support significantly influences the equilibrium solution. A cylindrical roller bearing supported by an elastic outer housing with two stiff leg supports is analyzed to illustrate the application of this computer oriented method. Experimental determination of the roller load distribution by “footprint” measurement techniques shows excellent agreement with the analytical predictions. The method of solution is outlined with sufficient detail to enable the cooperation of structural and bearing analysis in the solution of a class of problems requiring both disciplines.
Effects of Combined Shearing and Stretching in Viscoelastic
Lubrication
Authors: Williams G. , Tanner R. I.
Published: November 2010

It is argued theoretically that in normal bearing and squeeze film geometries, when using a nonlinear Maxwell constitutive relation, that elongation and normal stress effects are of minor importance.
Thermodynamics, Adhesion, and Sliding Friction
Authors: Bikerman J. J.
Published: November 2010

The belief that the roughness theory of friction cannot explain frictional heat is shown by a thermodynamic reasoning to be incorrect. The adhesion theory of friction contradicts the modern science of adhesive joints and, hence, is erroneous.
Wear Behavior of Polybenzimidazole Bonded Solid-Film
Lubricants
Authors: Hubbell R. D. , McConnell B. D.
Published: November 2010

A new thermally stable organic resin is described. Results are presented for the development of polybenzimidazole (PBI) resin-bonded solid-film lubricants. These solid-film lubricants are composed of molybdenum disulfide, antimony trioxide, and the PBI resins. Steps followed for mixing, applying, and curing these films are presented. The test equipment and procedures used to test the film formulations are described. Wear-life comparisons to conventional commercially available resin-bonded films qualified under MIL-L-8937 are presented.
Experimental Measurement of Forces During Extrusion and Correlation With Theory
Authors: DePierre Vincent
Published: November 2010

A summary is furnished of Air Force Materials Laboratory efforts in the application of analytical and experimental methods for the determination of forces required for extrusion of metals and alloys. The analyses yield mathematical equations correlating extrusion pressures with process variables such as friction, die geometry, and materials resistance to deformation under processing conditions. The following two equations are used for extrusion force studies: Pt=Pd+4kL/DandPd=Y(a+blnR)+ScotαlnR where Pt = total pressure, Pd = die pressure, L = billet length in container, D = container diameter, Y = material flow strength at processing temperature and strain rate, R = reduction ratio, α = half die angle, a and b = constants for each die angle, and S and k = interface friction sheer stress in die and liner, respectively. These formulas plus an instrumented high speed extrusion press are utilized for quantitative evaluation of the effectiveness of lubrication systems in reducing total extrusion forces.
The Hybrid Boost Bearing—A Method of Obtaining Long Life in Rolling
Contact Bearing Applications
Authors: Wilcock D. F. , Winn L. W.
Published: November 2010

A new bearing concept is described which offers the almost unlimited life of the fluid film bearing combined with the free starting, stopping, and oil system failure characteristics of the rolling element bearing. This new bearing type is termed the Hybrid Boost Bearing. It is envisioned as having application in jet engines to extend bearing life, and in land turbine equipment as a means of providing high overload capacity.
Design Charts for Optimum Bearing Configurations: 2—The Pivoted-Pad Thrust Bearing
Authors: Bosma R. , Moes H.
Published: November 2010

As a followup to an earlier paper in which a new type of design chart for full journal bearings was given a complete set of design charts for pivoted-pad thrust bearings (Michell bearings) shall now be presented. The dimensionless groups of parameters representing minimum film thickness and bearing traction for one single pad, respectively, have been plotted in a new design chart. Some illustrative examples demonstrating how to use the chart for optimization of pivoted-pad thrust bearings have been included. Some attention has also been paid to the stiffness of the film of lubricant. A design chart for film stiffness has been added to this purpose.
Inertial Considerations in Parallel Circular Squeeze Film Bearings
Authors: Tichy J. A. , Winer W. O.
Published: November 2010

A second order regular perturbation solution for squeeze film flow of a Newtonian fluid between circular parallel surfaces is presented. All the inertial terms are included in the momentum equation. Experimental measurements of pressure in a squeeze film at high squeeze rates are shown to be in good agreement with the solution. The solution is particularly useful in assessing the extent to which fluid inertial effects would cause the classical lubrication theory to be in error for any particular squeeze film. The inertial effects are shown to be functions of two readily determined dimensionless parameters, the squeeze Reynold’s number Res and the squeeze acceleration number A.
The Effect of Misalignment on the Life of High Speed Cylindrical Roller Bearings
Authors: Liu J. Y.
Published: November 2010

This paper describes an analytical investigation of the effects of misalignment and shaft speed on cylindrical roller bearing performance. Numerical results are presented for the contact load distributions and bearing fatigue lives under various amounts of misalignment for an NU308-type bearing operating under the load and speed conditions of a mainshaft bearing or a gearbox bearing in a helicopter gas turbine engine. The analysis is of use in bearing selection and in comparing different bearing designs for specific applications.
The Influence of a Gas Atmosphere and Its Moisture on Sliding Wear in PTFE Compositions
Authors: Schubert R.
Published: November 2010

PTFE materials with various types of filler are required to operate in nonlubricated piston compressors for increasingly long periods. This is not merely a matter of the material used but also of careful design calculation. In order to be able to meet certain frequently encountered requirements various filled PTFE compositions were tested in a wear lest rig and the effects of the gas and its moisture on the wear characteristics have been worked out. A different effect of the gases was sometimes stated on the wear factor of the PTFE compositions formed with different fillers so that specific application might be recognized. Finally the success is shown with results from some field compressors which were also equipped with piston rings totally pressure balanced in a new efficient method running for almost two years without ever having to replace a set of rings.
Experimental Load Capacity and Power Loss of Herringbone Grooved Gas Lubricated Journal Bearings
Authors: Cunningham R. E. , Fleming D. P. , Anderson W. J.
Published: November 2010

Load capacity, attitude angle, and power loss were determined for 1 1/2-in-dia herringbone grooved journal bearings operating in air to speeds of 60,000 rpm. Results showed that groove-to-ridge-clearance ratios of 2.0 to 2.4 give a greater load capacity than do ratios outside this optimum range. Agreement with a small-eccentricity pressure perturbation theory was good for groove-to-ridge-clearance ratios in the optimum range. Power loss, relative to that calculated for a plain bearing of the same dimensions, did not vary widely for the range of geometric variables used. Relative power loss generally increased with speed and was generally comparable to that for a plain bearing.
Effect of Velocity Slip on Porous-Walled Squeeze Films
Authors: Sparrow E. M. , Beavers G. S. , Hwang I. T.
Published: November 2010

The fluid flow processes in a squeeze film having one porous bounding wall are analyzed. The analysis takes account of velocity slip at the surface of the porous medium as well as of the coupled flows in the squeeze film and the porous material. Results are presented for the load-carrying capacity of the squeeze film and its thickness–time relation. The results show that porous media are effective in diminishing the response times of squeeze films. In particular, substantially faster response can be attained by the use of porous materials which accentuate velocity slip.
An Elasto-Plasto-Hydrodynamic Lubrication Analysis of the Hydrostatic Extrusion Process
Authors: Snidle R. W. , Dowson D. , Parsons B.
Published: November 2010

The authors describe a numerical procedure for the solution of the problem of hydro-dynamic lubrication in the hydrostatic extrusion process. The lubricant is assumed to be a Newtonian fluid and in this preliminary analysis it is assumed that the yield strength of the worked material remains constant. Elastic deformation of the billet as it enters and leaves the die is considered but this effect is found to have only a small influence upon the thickness of the lubricant film which is generated. Thermal effects arising from plastic deformation of the billet and viscous dissipation in the lubricant film are also considered. Theoretical results are presented showing the influence of die angle and reduction ratio upon values of film thickness and extrusion pressure for two materials.
The Pressure and Deformation Profiles Between Two Normally Approaching Lubricated Cylinders
Authors: Lee K. M. , Cheng H. S.
Published: November 2010

The pressure and deformation profiles between two colliding lubricated cylinders are obtained by solving the coupled, time-dependent elastohydrodynamic equations with an iterative procedure. The analysis includes several effects which were not considered in a previous solution by Christensen [4], namely, the effect of surface velocities due to local deformation, the effect of the lubricant compressibility, and the effect of a lubricant with composite pressure-viscosity coefficients. It is found that the local approach velocity plays an important role during final stages of normal approach. It causes the lubricant to be entrapped within the contact region, and both the pressure and deformation profiles appear to converge to the Hertzian profile. The use of a smaller pressure-viscosity coefficient at high pressures reduces the sharp pressure gradient at the center of the contact, and produces a much milder variation of load with respect to the film thickness. The effect of compressibility of the lubricant is found to be relatively small.
Solution of the Elastohydrodynamic Finite Journal Bearing Problem
Authors: Oh K. P. , Huebner K. H.
Published: November 2010

Finite-element techniques are applied to solve the elastohydrodynamic finite journal bearing problem. Reynolds’ equation for the fluid film and the three-dimensional elasticity equations for the bearing housing are solved simultaneously using a unique iteration scheme. The analysis yields the pressure distribution and the displacement distribution which satisfy the elastohydrodynamic requirements of realistic three-dimensional bearing geometries. From these distributions, important information such as the stresses in the bearing material and the minimum film thickness in the lubricant can be calculated. In the calculations it is assumed that the bearing operates with a constant-property lubricant and a linearly elastic bearing material. The solution procedure is applied to a typical problem and numerical results are presented.
Hydromagnetic Squeeze Films Between Porous Rectangular Plates
Authors: Sinha P. C. , Gupta J. L.
Published: November 2010

A theoretical study is made of the squeeze film behavior between two rectangular plates, one with a porous facing, in the presence of a uniform transverse magnetic field. Results are presented for pressure distribution, load capacity, and film thickness as functions of time. It is shown that the application of a magnetic field improves the squeeze-film action.
An Analytical and Experimental Investigation of Turbulent Flow in Bearing Films Including Convective Fluid Inertia Forces
Authors: Smalley A. J. , Vohr J. H. , Castelli V. , Wachmann C.
Published: November 2010

A means of handling both fluid film turbulence and the effects of fluid convective inertia in bearing films has been developed. The analysis employs a number of simplifying assumptions but has proved quite successful in the prediction of experimentally measured pressures. In this analysis turbulence is treated by means of turbulent viscosity correction factors. Convective inertia is accounted for by convective derivatives of mean fluid velocities averaged over the bearing film. Direct numerical solution of simultaneous equations representing conservation of momentum and fluid continuity is employed. The analysis developed is applied to pad bearings of arbitrary surface geometry, and has been incorporated in a computer program to calculate the film pressures developed in such bearings. Results from this program are compared with experimental pressure profile measurements made on a 12-in. dia, four pad, shrouded step journal bearing with silicone fluids as test lubricants. Good agreement is obtained for both concentric and eccentric operation.
Turbulent Lubrication—Its Genesis and Role in Modern Design
Authors: Wilcock D. F.
Published: November 2010

Turbulence, a phenomenon well known in fluid flow, was first reported in journal bearings and thrust bearings in 1949. The observations were of higher torques and greater temperature rises than were expected from lower speed data. The transition from laminar behavior occurred at a Reynolds’ number corresponding to the predicted occurrence of Taylor vortices. This was the starting point for efforts to understand the phenomenon and to establish rules of behavior useful for predicting turbulent bearing performance. From an engineering point-of-view, good results in design have been achieved by treating turbulence as an increase in lubricant viscosity, the percent of increase being a function of the ratio of inertia forces to viscous forces, the Reynolds’ number. The effective result is greater film thickness and larger power losses in turbulent lubrication than would be anticipated from laminar theory. Where will the designer of the future encounter turbulence, and how will he treat its effects? Large turbogenerators have already reached a size where turbulent operation is experienced. The gradually increasing use of process-fluid-lubricated machinery, often involving low viscosity fluids such as water, liquid metal, and liquified gases, offers the designer fresh opportunities to understand and take advantage of turbulence in both hydrodynamic and hydrostatic designs.
Reduction of Air Films in Magnetic Recording by External Air Pressure
Authors: Eshel A.
Published: November 2010

The effect of external pressure exerted on foil bearings is studied. Analysis and numerical results are provided for its influence on the bearing gap. It is shown that a substantial reduction in film thickness can be achieved by applying small pressures in the inlet zone. The effect of several pertinent parameters is presented and discussed.
Hydrodynamic Porous Journal Bearings. Part I—Finite Full Bearings
Authors: Rouleau W. T. , Steiner L. I.
Published: November 2010

The Reynolds condition is shown to correctly describe the film termination in hydrodynamic porous journal bearings. A practical and accurate numerical method for calculating bearing performance is developed, which permits the use of realistic boundary conditions, including the Reynolds condition. It also accounts for slip at the film-bearing interface by means of Darcy’s law. Results show that performance predicted on the basis of the Reynolds condition is closely approximated when the Gumbel and Everting condition is used, but that the Sommerfeld condition yields a substantial difference. For practical bearings, it is found that (a) slip at the interface is negligible, (b) the “thin wall” assumption is valid, (c) sealing the axial ends of the bearing produces only a small increase in load capacity, and (d) axial flow in the film is significant.
The Stress Field Generated in an Elastic Layer by Normally Loaded, Periodically Spaced Circular Contacts
Authors: Johns T. G.
Published: November 2010

The stress field generated in an elastic layer by normally loaded, periodically spaced circular contacts is analyzed. It is intended that this model represent a pair of rough, plated contact surfaces whose plating is much more compliant than the substrate material. The effect of plating thickness and spacing of load-bearing asperities upon the state of stress within the layer is studied. It is shown that there exist values of layer thickness and contact-spot spacing such that the octahedral shear stress within the layer is maximized. Further, for very thin layers, the maximum octahedral shear occurs at the surface of the layer as in tangentially loaded contacts.
Some Experimental Results From Compliant Air Lubricated Thrust Bearings
Authors: Lowe I. R. G.
Published: November 2010

Experimental results are presented from a series of tests on axisymmetric, inherently compensated, air thrust bearings which had one compliant surface. The results demonstrate that in general compliant surface bearings have greater load capacities than equivalent rigid surface bearings. The dependence of load, flow, and stability on the nature of the compliant layer is also shown. Comparisons with the load capacities predicted theoretically by Pirvics and Castelli show agreement in the range of most practical interest, that is when the load advantage vis-a`-vis rigid bearings is greatest.
The Wear Process Between Normally Impacting Elastic Bodies
Authors: Engel P. A. , Bayer R. G.
Published: November 2010

The wear process between two elastic bodies, repeatedly impacting in an axially symmetric configuration is investigated analytically and experimentally. The mechanism initiating wear is that of surface fatigue, and the paper aims to explain the geometric process of wear formation beyond the “zero wear limit.” In doing so, an engineering, predictive model is sought, whereby the depth of a worn crater is related to the stresses arising during impact and to the number of loading cycles on the specimen. Four major accomplishments are embodied in the paper: (1) the quasi-static analysis of impact on a medium of nonuniform (cratered) surface geometry, (2) a heuristic derivation of the optimum wearpath, (3) derivation of the partial differential equation of normal impact wear, and (4) computation of the impact wear process for two discrete impact wear configurations and comparison of experimental work with the analytical results. The resulting conclusion is that impact wear proceeds at continuously varying curvature until the soft body conforms to the shape of the hard indenter. By equating the hysteretic wear energy with a fraction of the peak strain energy, quantitative wear history predictions are made for discrete geometries, such as a hard sphere impacting against a soft plane. Some experimental results are given between steel and aluminum specimens, confirming the analytical predictions.
Effects of Cyclic Squeeze on Externally Pressurized Gas Journal Bearings
Authors: Majumdar B. C.
Published: November 2010

Theoretical investigation on the performance characteristics of externally pressurized gas bearings with several supply holes is made. The solution is obtained for finite bearings using pressure perturbation method. The results are compared with an approximate solution assuming quasi-steady film. It has been shown that quasi-steady solution overestimates the squeeze film force.
Solutions of Finite Journal Bearings With Incomplete Films
Authors: Etsion I. , Pinkus O.
Published: November 2010

The Reynolds equation is here solved for journal bearings using new upstream boundary conditions which reflect the fact that starting films in these bearings are often incomplete. The work is an extension of previously published results for short bearings to the case of finite bearings of arbitrary width and arbitrary extent of inlet film. An expression is also derived relating the width of the inlet film with the lubricant feed pressure and the bearing operating parameters, when the lubricant is fed through a hole. The results provide an explanation for the profound lack of agreement between previous theory and experiment with regard to side leakage in journal bearings.
Partial Journal Bearing Performance in the Laminar Regime
Authors: Yu T. S. , Szevi A. Z.
Published: November 2010

In this approximate analysis of laminar journal bearing operations both the momentum and the energy equations are two dimensional, the shaft operates at a constant temperature and the bearing conducts heat in the radial direction only. Via the last of these assumptions, the equation of heat conduction is eliminated from consideration. The remaining equations are solved by a numerical iteration method. A parametric study of therohydrodynamic journal bearing operations is performed and design charts are given for a 100 deg arc bearing.
Traction and Film Thickness Measurements Under Starved Elastohydrodynamic Conditions
Authors: Wedeven L. D.
Published: November 2010

Traction measurements under starved elastohydrodynamic conditions have been obtained for a point contact geometry. Simultaneous measurements of the film thickness and the location of the inlet lubricant boundary were made optically. The thickness of a starved film for combination rolling and sliding conditions varies with the location of the inlet boundary in the same way found previously for pure rolling. A starved film was observed to possess greater traction than a flooded film for the same slide roll ratio. For a given slide roll ratio a starved film simply increases the shear rate in the Hertz region. The maximum shear rate depends on the degree of starvation and has no theoretical limit. The relative increase in traction due to starvation is influenced by thermal and fluid rheological conditions within the Hertz region. This makes the prediction of traction under starved conditions difficult. Traction measurements under starved conditions were compared with flooded conditions under equivalent shear rates in the Hertz region. When the shear rates in the Hertz region were low and the film severely starved, the measured tractions were found to be much lower than expected.
Friction and Wear Studies of Articular Cartilage: A Scanning Electron Microscope Study
Authors: Clarke I. C. , Contini R. , Kenedi R. M.
Published: November 2010

The friction and wear characteristics of human hip joints were investigated using a pendulum-device and the Scanning Electron Microscope (SEM). The frictional phenomena of the joints oscillating under a variety of conditions were integrated with published data to provide a composite picture. As an accelerated “wear” model, joints were run “dry”, i.e., no fluid environment. This “wear” model was less severe than anticipated and subsequent damage involved only the superficial regions of the cartilage bearing material. The disruption occurred at sites where osteoarthritic damage has been detected clinically and progressed along the orientated fibrillar layers and was therefore oriented predominantly perpendicularly to joint motion.
Performance Tests on Six-Inch Tilting Pad Thrust Bearings
Authors: Gardner W. W.
Published: November 2010

Laboratory tests were conducted on six-in-dia tilting pad thrust bearings to compare operating characteristics of several pad facing and backing material combinations and also to study the effects of different oil feed and discharge arrangements. Tests were conducted at various speeds and loadings, including a series of failure tests. Results of these tests are presented.
Large Disturbance Solutions for Initally Flat, Frictionally Heated Thermoelastically Deformed Surfaces
Authors: Burton R. A. , Nerlikar V.
Published: November 2010

When to semi-infinite plates contact edge to edge, with sliding parallel to the line of contact, frictional heating can cause deformations which lead to the initial uniform-pressure contact changing to a periodic sequence of loaded patches separated by regions where the surfaces part from one another. This condition will appear near the speed at which small-disturbance instabilities occur. When it does appear there are two solutions or two configurations which satisfy the boundary conditions. One of these solutions is shown to be stable, and the other is shown to be unstable. The derivations may be applied to seals where a thermally conductive material slides on a material of significantly lower conductivity.