bluuebunny/crossref_metadata_2025 huggingface dataset:
Transient Two-Dimensional Problems Utilizing The Least Squares Algorithm
Authors: Bruch J. C. , Lewis R. W.
Published: November 2010

The least squares time-stepping algorithm, which has previously been shown by the authors to be competitive for one-dimensional problems, is applied to the solution of several two-dimensional examples having constant material properties. The results are compared against answers obtained using recurrence relationships based on the finite element and finite difference methods. Analytical results for one of the examples are also used for comparison. The least squares algorithm proved to be more accurate for equal values of time step especially in the large time step cases. It, however, requires more computer time and storage than the other methods used. Several other limitations of the scheme are also presented.
Mechanical Augmentation of Convective Heat Transfer in Air
Authors: Hagge J. K. , Junkhan G. H.
Published: November 2010

An experimental investigation was conducted into augmentation of forced convection heat transfer in air by mechanical removal of the boundary layer. A rotating blade element passing in close proximity to a flat plate convective surface was found to increase the rate of convective heat transfer by up to eleven times in certain situations. The blade element effectively scrapes away the boundary layer, thus reducing the resistance to heat flow. Parameters investigated include scraping frequency, scraper clearance, and type of boundary layer. Increased coefficients were found for higher scraping frequencies. Significant augmentation was obtained with clearance as large as 0.15 in. (0.0038 m) between the moving blade element and the convective surface. The technique appears most useful for laminar and transitional boundary layers, although some improvement was obtained for the turbulent boundary layers investigated. The simple surface renewal theory developed for scraped surface augmentation in liquids was found to approximately predict the coefficients obtained. A new relation is proposed which gives a better prediction and includes the effect of scraper clearance.
Transient Melting of a Solid Heated by a Condensing Saturated Vapor—Case I: Negligible Interface Curvature
Authors: Contreras W. , Thorsen R. S.
Published: November 2010

A transient analysis has been performed to analytically determine the instantaneous dimensionless thickness of a vertically suspended solid at its melting temperature upon which a saturated vapor is condensing. The spatial variation and transient behavior of the melt-condensate liquid film, which is continuously drained, has also been obtained from the closed form analytical solution of the uncoupled equations for the solid-liquid and liquid-vapor interface motions under the condition of assumed negligible interface curvature. Classical boundary layer assumptions were applied to the convection process in the subcooled liquid film which was analyzed using integral techniques. From the analytic solution to the resultant interface motion equations in terms of characteristic curves, the functional dependence of the melting solid and the liquid layer thicknesses on the time and space variables was established. The liquid mass flux and heat transfer coefficient were then obtained analytically.
Transport-Reaction Mechanism of Mist Formation Based on the Critical Supersaturation Model
Authors: Hayashi Y. , Takimoto A. , Kanbe M.
Published: November 2010

The transport-reaction mechanism of mist formation in a convective field is discussed on the basis of a “critical supersaturation model”. Analyses are performed for mist formation conditions, mist region, and vaporization rate, and are verified experimentally by using a naphthalene sublimation technique.
Experimental Heat Transfer Behavior of a Turbulent Boundary Layer on a Rough Surface With Blowing
Authors: Moffat R. J. , Healzer J. M. , Kays W. M.
Published: November 2010

Heat transfer measurements were made with a turbulent boundary layer on a rough, permeable plate with and without blowing. The plate was an idealization of sand-grain roughness, comprised of 1.25 mm spherical elements arranged in a most-dense array with their crests coplanar. Five velocities were tested, between 9.6 and 73 m/s, and five values of the blowing fraction, vo/u∞, up to 0.008. These conditions were expected to produce values of the roughness Reynolds number (Reτ = uτks/ν) in the “transitional” and “fully rough” regimes (5 ≤ Reτ, ≤ 70, Reτ > 70). With no blowing, the measured Stanton numbers were substantially independent of velocity everywhere downstream of transition. The data lay within ±7 percent of the mean for all velocities even though the roughness Reynolds number became as low as 14. It is not possible to determine from the heal transfer data alone whether the boundary layer was in the fully rough state down to Re = 14, or whether the Stanton number in the transitionally rough state is simply less than 7 percent different from the fully rough value for this roughness geometry. The following empirical equations describe the data from the present experiments for no blowing: Cf2=0.0036θr−0.25St=0.0034Δr−0.25 In these equations, r is the radius of the spherical elements comprising the surface, θ is the momentum thickness, and Δ is the enthalpy thickness of the boundary layer. Blowing through the rough surface reduced the Stanton number and also the roughness Reynolds number. The Stanton number appears to have remained independent of free stream velocity even at high blowing; but experimental uncertainty (estimated to be ±0.0001 Stanton number units) makes it difficult to be certain. Roughness Reynolds numbers as low as nine were achieved. A correlating equation previously found useful for smooth walls with blowing was found to be applicable, with interpretation, to the rough wall case as well: StSt0Δ=ln(1+B)B1.25(1+B).25 Here, St is the value of Stanton number with blowing at a particular value of Δ (the enthalpy thickness). St0 is the value of Stanton number without blowing at the same enthalpy thickness. The symbol B denotes the blowing parameter, vo/u∞ St. The comparison must be made at constant Δ for rough walls, while for smooth walls it must be made at constant ReΔ.
Spatial Distribution of Active Sites and Bubble Flux Density
Authors: Sultan M. , Judd R. L.
Published: November 2010

An experimental investigation is presented concerning the boiling of water at atmospheric pressure on a single copper surface in which the spatial distribution of active nucleation sites was investigated at different levels of heat flux and subcooling. The results obtained indicated that the active sites were located randomly on the heating surface, since the distribution of active sites followed the Poisson relationship. Changes in heat flux and sub-cooling did not affect the distribution of active nucleation sites although additional active sites formed among the sites which had already been activated when heat flux was increased. The frequency of vapor bubble emission and the bubble flux density have been studied as well. The results obtained showed that the heat flux had a great effect on the vapor bubble emission frequency although the influence of subcooling was of lesser significance. However, the bubble flux density was found to be non-uniformly distributed over the heating surface contrary to what had been expected.
Effect of Circumferentially Nonuniform Heating on Laminar Combined Convection in a Horizontal Tube
Authors: Patankar S. V. , Ramadhyani S. , Sparrow E. M.
Published: November 2010

An analytical study has been made of how the circumferential distribution of the wall heat flux affects the forced/natural convection flow and heat transfer in a horizontal tube. Two heating conditions were investigated, one in which the tube was uniformly heated over the top half and insulated over the bottom, and the other in which the heated and insulated portions were reversed. The results were obtained numerically for a wide range of the governing buoyancy parameter and for Prandtl numbers of 0.7 and 5. It was found that bottom heating gives rise to a vigorous buoyancy-induced secondary flow, with the result that the average Nusselt numbers are much higher than those for pure forced convection, while the local Nusselt numbers are nearly circumferentially uniform. A less vigorous secondary flow is induced in the case of top heating because of temperature stratification, with average Nusselt numbers that are substantially lower than those for bottom heating and with large circumferential variations of the local Nusselt number. The friction factor is also increased by the secondary flow, but much less than the average heat transfer coefficient. It was also demonstrated that the buoyancy effects are governed solely by a modified Grashof number, without regard for the Reynolds number of the forced convection flow.
Combined Free and Forced Convection in Inclined Circular Tubes
Authors: Sabbagh J. A. , Aziz A. , El-Ariny A. S. , Hamad G.
Published: November 2010

The problem of combined free and forced convection in an inclined circular tube with uniform peripheral temperature and axial heat flux has been studied experimentally. For fixed Pr and Ra, experimental data showing the effect of tube inclination and Reynolds number on temperature and axial velocity profiles are reported and found to agree qualitatively with the theoretical predictions [7]. Also shown is the variation of Nusselt number with inclination angle for Ra Re = 30,000. No optimum angle for maximum Nusselt number was found.
Analysis of Large Dry Cooling Towers With Power-Law Heat Exchanger Performance
Authors: Moore F. K. , Ndubizu C. C.
Published: November 2010

An analysis is presented for heat exchanger area, tower exit area, and exchanger tube length and number, for heat exchangers in large dry cooling towers, having performance parameters given by powers of Reynolds number, but otherwise under very general cooling-cycle constraints. The calculation method is illustrated for a “spine-fin” heat exchanger which, in a tube size of about 3/8 in., seems capable of achieving low tower size in a practical device. Calculations, over ranges of water pumping power, approach, ITD, number of passes, tube size, tower shape (natural draft) or fan power (mechanical draft), and ambient pressure altitude are shown to be well represented by a chain of powers of these variables, and certain functions of the ratio of real to ideal tower exit area. This ratio is shown to have a best value, depending on the cost coefficients of heat exchange and exit areas, and it is pointed out that typical cost proportions lead to a fluid-mechanical “packaging” problem for the shallow heat exchangers which would be preferred.
Simultaneous Boiling and Forced Convection Heat Transfer From a Horizontal Cylinder to Water
Authors: Fand R. M. , Keswani K. K. , Jotwani M. M. , Ho R. C. C.
Published: November 2010

This paper presents the results of experiments involving simultaneous boiling and forced convection heat transfer from horizontal cylinders to water in crossflow. In these experiments all of the following primary variables were varied: heat flux, crossflow velocity, pressure, subcooling, and surface material. Based on these data an empirical correlation equation is developed which permits one to predict the performance of a cylindrical heater in the presence of crossflow and boiling, provided only that its performance in the absence of crossflow (pool boiling) is known. This correlation equation eliminates the need to perform experiments in the presence of crossflow to ascertain the performance of a “crossflow-plus-boiling” cylindrical heater.
Two-Dimensional Analysis of Conduction-Controlled Rewetting With Precursory Cooling
Authors: Dua S. S. , Tien C. L.
Published: November 2010

This paper presents a two-dimensional analysis of the effect of precursory cooling on conduction-controlled rewetting of a vertical surface, whose initial temperature is higher than the sputtering temperature. Precursory cooling refers to the cooling caused by the droplet-vapor mixture in the region immediately ahead of the wet front, and is described mathematically by two dimensionless constants which characterize its magnitude and the region of influence. The physical model developed to account for precursory cooling consists of an infinitely extended vertical surface with the dry region ahead of the wet front characterized by an exponentially decaying heat flux and the wet region behind the moving film-front associated with a constant heat transfer coefficient. Apart from the two dimensionless constants describing the extent of precursory cooling, the physical problem is characterized by three dimensionless groups: the Peclet number or the dimensionless wetting velocity, the Biot number and a dimensionless temperature. Limiting solutions for large and small Peclet numbers have been obtained utilizing the Wiener-Hopf technique coupled with appropriate kernel substitutions. A semiempirical matching relation is then devised for the entire range of Peclet numbers. Existing experimental data with variable flow rates at atmospheric pressure are very closely correlated by the present model. Finally a comparison is drawn between the one-dimensional limit of the present analysis and the corresponding one-dimensional solution obtained by treating the dry region ahead of the wet front characterized by an exponentially decaying heat transfer coefficient.
Analysis of a Stefan-Like Problem in a Biological Tissue Around a Cryosurgical Probe
Authors: Rubinsky B. , Shitzer A.
Published: November 2010

Analysis of a Stefan-like problem in the in vivo freezing of a biological tissue is presented in cartesian coordinates. The analysis allows the inclusion of blood perfusion, metabolic heat and tissue heat capacity. Solutions are obtained for the temperature distributions in the frozen and unfrozen regions at different times. A constant freezing rate, in accordance with the optimal tissue destruction rate, is assumed. Results indicate the importance of the blood perfusion factor in the problem and allow the prediction of probe temperature and heat flux variations for optimal results in tissue destruction.
Effect of Density Change on Multidimensional Conduction Phase Change
Authors: Shamsundar N. , Sparrow E. M.
Published: November 2010

An analysis of transient multidimensional solidification in the presence of a growing shrinkage cavity has been performed. The enthalpy model, which had previously been applied only for cases with no density change, has been extended to accommodate substances which undergo a change of density upon phase change. The extended enthalpy model was implemented by an efficient, implicit finite difference scheme. A solidification model was adopted in which the shrinkage cavity is at the top of the container within which the phase change is taking place. Solutions were carried out for solidification of a liquid in a long, horizontal rectangular container with convectively cooled walls. Results are presented for the time variations of various heat transfer quantities and for the evolution of the shrinkage cavity and the solid-liquid interface, for parametric values of the Biot number, liquid-solid density ratio, and Stefan number. The influence of the density ratio and the Stefan number on the heat transfer results was most marked at times near the completion of solidification, whereas the Biot number had a major effect at all times.
Optimization of Radiating Fin Arrays With Respect to Weight
Authors: Schnurr N. M. , Shapiro A. B. , Townsend M. A.
Published: November 2010

A nonlinear optimization approach is used to determine the minimum weight design for radiating fin arrays used in space applications. Straight and circular fins of rectangular and triangular profile are considered for emissivities in the range of 0.8 to 1.0. The heat transfer analysis includes fin to fin and fin to base radiative interactions. The results, presented in graphical form, give the optimum geometries for the profiles considered in terms of dimensionless parameters. Thus, for specified values of heat transfer rate, base cylinder surface temperature and thermal properties of the fin material, these curves may be used to design minimum weight fin arrays. Two numerical examples are given.
Fully Developed Flow and Heat Transfer in Ducts Having Streamwise-Periodic Variations of Cross-Sectional Area
Authors: Patankar S. V. , Liu C. H. , Sparrow E. M.
Published: November 2010

The concepts of fully developed flow and heat transfer have been generalized to accommodate ducts whose cross-sectional area varies periodically in the streamwise direction. The identification of the periodicity characteristics of the velocity components and of a reduced pressure function enables the flow field analysis to be confined to a single isolated module, without involvement with the entrance region problem. A similar modular analysis can be made for the temperature field, but the periodicity conditions are of a different nature depending on the thermal boundary conditions. For uniform wall temperature, profiles of similar shape recur periodically. On the other band, for prescribed wall heat flux which is the same for all modules, the temperature field itself is periodic provided that a linear term related to the bulk temperature change is subtracted. The concepts and solution procedure for the periodic fully developed regime were applied to a heat exchanger configuration consisting of successive ranks of isothermal plate segments placed transverse to the mainflow direction. The computed laminar flow field was found to be characterized by strong blockage effects and massive recirculation zones. The fully developed Nusselt numbers are much higher than those for conventional laminar duct flows and show a marked dependence on the Reynolds number.
Effect of Molecular Gas Radiation on a Planar, Two-Dimensional, Turbulent-Jet-Diffusion Flame
Authors: James R. K. , Edwards D. K.
Published: November 2010

Non-gray radiation described by the exponential model for molecular gas bands was added to the numerical solution of turbulent combustion of methane in a planar, enclosed, jet-diffusion flame. The planar jet of methane is injected with velocity ufuel into a stream of air flowing with velocity uair parallel to the fuel. Diffusion-controlled combustion occurs in the mixing region of the jet. Plane-parallel, isothermal, black walls symmetrically located above and below the jet form the combustion chamber. A soot-free flame is assumed to exist so that molecular gas bands determine the thermal radiative transfer to the walls. Velocity, composition, and temperature fields and heat flux at the wall are obtained numerically. Approximately 40 percent of the requisite computation time is expended on the radiation calculation. Solutions are obtained to show the effect of channel size, air preheat, and product recirculation. Also the effect of reaction zone thickness was examined by varying an effective first Damko¨hler or mixing number which parameterizes the mixing-controlled reaction rate. It is found that a given reduction in maximum combustion temperature to reduce nitric oxide formation can be accomplished with a much less detrimental reduction on heat transfer by recirculating exhaust product into the combustion air than by reducing air preheat.
Thermal Design of Pavement Structures in Seasonal Frost Areas
Authors: Frivik P. E. , Thorbergsen E. , Del Giudice S. , Comini G.
Published: November 2010

In many practical situations, adequate thermal design of pavement structures in seasonal frost areas can be done by utilizing a model based on heat conduction alone. In this paper we present a system of computer programs which allow the solution of practically any nonlinear heat conduction problem in soils, provided that a two-dimensional description, plane or axisymmetric, is possible. The finite element method, together with the empirical correlations for thermal properties and boundary conditions, is used in the simulations. Predictions of the thermal regime in different structures are favorably compared with the results of experimental measurements, both for long-term and short-term temperature variations.
An Experimental Investigation of the Plume Velocity Field Above a Horizontal Line Heat Source
Authors: Nawoj H. J. , Hickman R. S.
Published: November 2010

The vertical velocity field of a natural convection plume arising from a horizontal line heat source was investigated experimentally in detail. The measured vertical velocities were found to be 20–25 percent less than that predicted by analysis. Various causative factors for the discrepancy between analytical and experimental results were investigated, and shown to have a minimal effect. The power law relationship between the plume vertical velocity and energy input to the line source was found to be substantially greater than that predicted by analysis. A normalized similarity function did provide an excellent representation of the lateral diffusion of energy and momentum in the plume, indicating the validity of the boundary layer approximation for the velocity field. It was postulated that further refinement of the stream functions defined by existing analyses is required to accommodate the effects of the upstream flow field that exists in the physical representation of a line source and is omitted from consideration in the development of the analyses.
Heat Transfer Phenomenology of a Hydrodynamically Unstable Melting System
Authors: Farhadieh R. , Baker L.
Published: November 2010

An experimental study was conducted on a melting system consisting of a liquid layer overlying a solid substrate. The liquid and solid when molten were mutually miscible. To initiate melting, the liquid was heated by a heater grid suspended above the liquid-solid interface. Systems with the density of the liquid less than that of the molten solid were gravitationally stable, whereas those with the density of the liquid greater than that of the molten solid were gravitationally unstable. Total mixing of the melt layer and the liquid layer resulted in thermal mixing of the liquid. The heat transfer coefficient was found to be an increasing function of the density ratio of liquid and melted solid; this increase occurred in four stages. There was a marked enhancement of heat transfer in the system. The melting rate was also found to depend on temperature difference and conduction depth.
Assessment of Surface-Heating Problems in Laser-Fusion Reactors
Authors: Abdel-Khalik S. I. , Hunter T. O.
Published: November 2010

The surface-heating problems associated with the pulsed photon and ion irradiations of the first walls and liners of inertially-confined fusion reactor cavities are investigated. Analytical models for predicting the thermal response of these surfaces as a function of the different design and operational parameters of the system and the nature of the incident irradiations are developed. The effectiveness of residual gas as a means for protecting the wall from the ions and soft X-rays is assessed.
Thermal Properties of Tungsten SRM’S 730 and 799
Authors: Taylor R. E.
Published: November 2010

Samples of sintered and arc-cast tungsten are available from NBS as thermal conductivity (SRM 730) and electrical resistivity (SRM 799) standards for the temperature range from 4 to 3000K. NBS recommended values for these properties above room temperature are based on results of various researchers during a previous international program which included arc-cast and sintered tungsten. The sintered tungsten used in this program was found to be unsuited for use as a standard material due to inhomogeneity and high temperature instability. The present paper gives results at high temperatures for thermal conductivity, electrical resistivity, specific heat, thermal diffusivity and Wiedemann-Franz-Lorenz ratio for a sample of the NBS sintered tungsten using the Properties Research Laboratory’s multiproperty apparatus. These results are compared to values recommended by the Thermophysical Properties Research Center, NBS, and an international program.
Convection in a Porous Medium Heated from Below: The Effect of Temperature Dependent Viscosity and Thermal Expansion Coefficient
Authors: Horne R. N. , O’Sullivan M. J.
Published: November 2010

The natural convection of water through permeable formations is an important phenomenon governing the behavior of geothermal aquifers. In such situations the temperature of the fluid can vary by amounts of the order of 250 K, over which range the viscosity of the water may decrease by as much as a factor of 10, and the coefficient of thermal expansion may increase by an even greater factor. Although previous studies have examined the effect of this behavior on the onset conditions at which natural convective flow in the medium first occurs, the actual flow patterns that will result from the convection of a fluid with such widely varying properties has not been reported. To this end, numerical methods of solution are applied to this problem and a visualization of the flows obtained. By solving in terms of both pressure and stream function instead of stream function alone, it was possible to maintain semiconservative properties of the numerical scheme. The convective motion is unstable (in two dimensions) at even moderate values of the Rayleigh number and exhibits a fluctuating convective state analogous to the case of a fluid with constant viscosity and coefficient of thermal expansion. In some cases the acceleration of the flow in certain areas due to the decrease in viscosity causes localized thermal instabilities.
On the Influence of Surface Conditions in Nucleate Boiling—the Concept of Bubble Flux Density
Authors: Shoukri M. , Judd R. L.
Published: November 2010

A study of the influence of surface conditions in nucleate pool boiling is presented. The surface conditions are represented by the number and distribution of the active nucleation sites as well as the size and size distribution of the cavities that constitute the nucleation sites. The heat transfer rate during nucleate boiling is shown to be influenced by the surface condition through its effect on the number and distribution of the active nucleation sites as well as the frequency of bubble departure from each of these different size cavities. The concept of bubble flux density, which is a function of both the active site density and the frequency of bubble departure, is introduced. A method of evaluating the bubble flux density is proposed and a uniform correlation between the boiling heat flux and the bubble flux density is found to exist for a particular solid-liquid combination irrespective of the surface finish within the region of isolated bubbles.
Three-Dimensional Numerical Analysis of Transient Natural Convection in Rectangular Enclosures
Authors: Chan A. M. C. , Banerjee S.
Published: November 2010

A simple numerical technique of considerable practical utility for the solution of transient multidimensional natural convection problems is described. It is based on the solution of the conservation equations in primitive form. The technique can be extended to calculation of natural convection problems in porous media and in turbulent flows where the eddy viscosities and conductivities can be predicted. It has been applied to the solution of several two and three-dimensional natural convection problems. The solutions compare well with the numerical and experimental results published by other investigators.
The Thermal-Hydraulic Phenomena Resulting in Early Critical Heat Flux and Rewet in the Semiscale Core
Authors: Snider D. M.
Published: November 2010

Analysis was performed to determine the thermal-hydraulic behavior in the electrically heated core simulator of the Semiscale Mod-1 system during the early stage of a simulated LOCA initiated by a large cold leg break. The calculated incore hydraulic behavior was used to obtain a better understanding of early CHF (480 to 700 ms after rupture) and the occurrence of rewet in some locations after CHF. Analysis indicated that shortly after rupture the flow in the upper core stagnated for 600 ms, and the core rapidly voided of coolant. In the center and lower regions of the core, the calculated fluid qualities were between 30 and 70 percent at the time of measured CHF. The high fluid qualities in the flow channels about the heater rods indicated that the mechanism of CHF was dryout of the heater rod surfaces. Critical heat flux did not happen at the location of instantaneous flow stagnation associated with the flow reversal; nor did CHF occur in the region of the prolonged flow stagnation. At about 700 ms after rupture the core flow completely reversed direction, and the influx of coolant from above the heated core was responsible for the measured rewets.
Prediction of Radiation Absorption and Scattering in Turbid Water Bodies
Authors: Daniel K. J. , Laurendeau N. M. , Incropera F. P.
Published: November 2010

In this study four methods of solving the radiative transfer equation applied to shallow ponds have been compared. The methods include a simple version of Beer’s law, a representative two-flux model, a six-flux model and the method of discrete ordinates. Calculations have been performed for a wide range of representative conditions typical to natural water. It was found that scattering was unimportant when the scattering albedo is small (ω ≲ 0.5) and the phase function is highly forward peaked. Consequently, even the simple Beer’s law expression yielded accurate predictions. However, in general only the six-flux method provided a suitable compromise between accuracy and operational convenience for all the conditions considered. The two-flux method was found to be the least accurate primarily due to its inability to account for refraction.
Characteristics of Transition Boiling in Sodium-Heated Steam Generator Tubes
Authors: France D. M. , Carlson R. D. , Chiang T. , Priemer R.
Published: November 2010

Thermal fluctuations were measured in the tube wall in the transition boiling zone of a full-scale LMFBR sodium-heated steam generator tube. The tube had an inside diameter = 10 mm, wall thickness = 2.90 mm, heated length = 13.1 m, and material = 2 1/4 Cr-1 Mo steel. Water flowed vertically upwards inside the straight tube, and sodium flowed counter-currently in a surrounding annulus. Results of thermal, spectral, and thermal stress analyses are presented for a test within the normal operating range of LMFBR steam generators. Results of other tests are presented that show the effects and sensitivity of sodium temperature and water pressure on the severity of the thermal fluctuations.
On Predicting Boiling Burnout with the Mechanical Energy Stability Criterion
Authors: Lienhard John H. , Hasan Md. Mojibul
Published: November 2010

The mechanical energy stability criterion has been used in the past to predict burnout in flow boiling and is extended here to describe pool boiling burnout. Its use replaces the need for a knowledge of the Helmholtz wavelengths, which is needed in the conventional hydrodynamic theory, with a need to know the surface area of departing bubbles. The hitherto unpublished data of Sun are used to predict the latter. The geometries investigated include the infinite horizontal flat plate, the cylinder, and the sphere.
Transient Freezing of Liquids in Turbulent Flow inside Tubes
Authors: Cho Chul , O¨zis¸ik M. N.
Published: November 2010

The problem of freezing of a liquid in turbulent flow inside a circular tube whose wall is kept at a uniform temperature lower than the freezing temperature of the liquid is solved. The radius of the solid-liquid interface and the local wall heat flux are determined as a function of time and position along the tube for several different values of the Prandtl number and the freezing parameter.
A Three-Flux Method for Predicting Radiative Transfer in Aqueous Suspensions
Authors: Incropera F. P. , Houf W. G.
Published: November 2010

A three-flux method is formulated for predicting radiative transfer in aqueous suspensions. The radiation field is resolved into three components, and the physical effects which are considered include refraction at the air-water interface, highly anisotropic scattering in the suspension, and diffuse reflection at the bottom. Calculations are performed for wide ranges of the scattering albedo, bottom reflectance, optical depth and irradiation, and results obtained for the local radiation flux and volumetric absorption, as well as for the overall suspension absorptance and the reflectance of the suspension-bottom complex, are in good agreement with those obtained from the more detailed method of discrete ordinates. Excellent agreement is also obtained between predictions of the net radiative flux in the suspension and measurements obtained for a suspension of unicellular algae.
Forced-Convection Heat Transfer from Irregular Melting Wavy Boundaries
Authors: Hsu K.-S. , Locher F. A. , Kennedy J. F.
Published: November 2010

The problem of turbulent flow past freezing or melting ice is formulated for the case of random boundary waves, with particular attention to the distribution of heat-transfer rate along wavy surfaces. Relations are obtained for the celerity and unsteady spectrum of the boundary waves. The results of 21 laboratory experiments are reported and used to establish the values of certain quantities appearing in the heat-transfer relation adopted. The velocity Reynolds number of the phase shift between the boundary waves and heat-transfer variation is found to have a nearly constant value of 4 × 104.
Ultrasonic Temperature Profiling System for Detecting Critical Heat Flux in Non-Uniformly Heated Tube Bundles
Authors: Barber A. R. , Kneidel K. E. , Fitzgerald C. S. , Lynnworth L. C.
Published: November 2010

A new ultrasonic instrumentation system was developed and applied to the problem of detecting critical heat flux (CHF) in experiments that simulate a nuclear reactor fuel assembly. This instrumentation system used the principles of ultrasonic thermometry to detect and locate CHF in a tube bundle with non-uniform axial heat generation. The technique consists of measuring the time between pairs of ultrasonic echoes that reflect from a sequence of evenly spaced discontinuities along a sensor. Each measurement of time is directly related to the temperature of a specific segment of a sensor. The system was designed to handle many 16-zone sensors at a high rate of data acquisition so that CHF could be rapidly detected and accurately located. This paper includes a description of the sensor and the signal processing techniques as well as examples of the system’s response to CHF.
Determination of the Integration Constant for Squeeze Films in Infinitely Long Journal Bearings
Authors: Kuzma D. C.
Published: November 2010

The complete film solution for the squeeze film in an infinitely long journal bearing contains an arbitrary constant. When only positive pressure regions are retained, this constant influences the load capacity. Several different values have been used for this constant. Its value is determined here so that the infinitely long journal bearing is the limiting case of the finite journal bearing.
Lubrication Review—A Digest of the Literature for
1968
Authors: Rumbarger J. H. , Liu J. Y. , Adams M. L. , Colsher R. J. , Poplawski J. V. , Galate J. W. , Schroeder R. J. , Roberts W. L. , Myers H. , Devine M. J.
Published: November 2010

The volume of lubrication literature continued to expand, reflecting the increased experimental and theoretical attention being focused upon this discipline. Eight categories of lubrication technology are summarized by authorities in each particular field. 481 reference publications are included in the review.
An Analytical Study of the Stress Concentration Around a Furrow
Shaped Surface Defect in Rolling Contact
Authors: Chiu Y. P. , Liu J. Y.
Published: November 2010

This paper presents a simple model for the stress concentration around a furrow shaped surface defect in rolling contact. An idealized two-dimensional defect profile, consisting of two curved shoulders smoothly connected to the remaining surface of an elastic half space under compression, is considered. The “undisturbed” stress state in the contacting cross section plane is assumed to be hydrostatic compression, corresponding to the “localized” stress state near the surface in the contact zone of two cylinders in contact. Numerical results are obtained for the contact pressure distribution and subsurface stress (octahedral shear stress). In this solution, which corresponds to the particular undisturbed stress state, the maximum value of the octahedral yield stress occurs underneath the curved “shoulders” of the defect.
Gyroscope Bearing Cross-Torque
Authors: Kingsbury E.
Published: November 2010

Ball bearing cross-torques (which appear at right angles to the spin axis) are described, demonstrated, and analyzed. Several methods for their control are described.
Critical Gas Bearing Slew Test Evaluation With a Varmeter
Authors: Lynch A. J. , Steranka P.
Published: November 2010

In the Pendulous Integrating Gyro Accelerometer (PIGA) used in inertial guidance systems, the gas bearing wheel is operated in a slewing mode at high slew rates. The high performance criteria of the guidance system require that the gas bearing operate without degradation and without loss of synchronous spin velocity at high slew rates. Size and weight restrictions limit the available support area, requiring that the gas bearing be operated near its maximum capability under high slew rates. An MIT-designed varmeter has been a proven tool to critically evaluate gas bearing performance under high slew rates. The varmeter is sensitive to slightest contact between the rotating member and a stationary member and can detect the slightest loss of synchronous speed.
Analysis and Selection of Fluid-Film Bearings for Spool-Shaft Gas Turbines
Authors: Shapiro W. , Colsher R. , Decker O.
Published: November 2010

The mechanical simplicity and damping qualities of fluid-film bearings makes them attractive possibilities for spool-shaft bearings of gas turbines. The simultaneous high-speed rotation of journal and bearing, however, causes whirl stability to be a major problem. Computerized analysis was utilized to screen a spectrum of practical candidate configurations. Stability threshold plots were expeditiously generated using accurately determined cross-coupled spring and damping coefficients to represent the bearings. Performance of each bearing type was determined as a function of configuration, ambient pressure, and machined clearance. The selected three-lobe design was further tested with a “time-transient” analysis that accurately traced a complete time history of the motions of the system in its various degrees of freedom.
The Dynamic Characteristics of a Turborotor Simulator Supported on Gas-Lubricated Foil Bearings—Part 1: Response to Rotating Imbalance and Unidirectional Excitation
Authors: Licht L.
Published: November 2010

A 16-in-long rotor, weighing approximately 21 lb, was supported by air-lubricated foil bearings. In physical size and in mass distribution, the rotor was closely matched with that of an experimental Brayton cycle turboalternator unit. The rotor was stable in both the vertical and horizontal attitudes at speeds up to 50,000 rpm. A detailed description of the experimental apparatus and of the foil bearing design are given. The paper contains data of response of the rotor to rotating imbalance, symmetric and asymmetric, and to excitation by means of a vibrator (shake table). It is concluded that the gas-lubricated foil-bearing suspension is free from fractional-frequency whirl and suffers no loss of load capacity when excited at frequency equal half the rotational speed. On contrast with rigid gas bearings, the foil bearing imposes no stringent requirements with respect to dimensional tolerances, cleanliness, or limitations of journal motion within the narrow confines of bearing clearance.
Variable Viscosity Effects in Hydrostatic Films: The Adiabatic Transformation
Authors: Donaldson R. R.
Published: November 2010

A transformation is presented whereby a hydrostatic film pressure distribution p(x, y) for constant viscosity ν is transformed into a solution assuming ν = ν(p, T) in which T(x, y) satisfies the adiabatic energy equation. The effects of variable viscosity on film pressure profiles and load capacities are demonstrated by applying the transformation to simple hydrostatic bearing film geometries.
The Elastohydrodynamic Problem With a Viscoelastic Fluid
Authors: Chow T. S. , Saibel Edward
Published: November 2010

Film thickness and pressure distribution are calculated analytically for a heavily loaded line contact of rollers in the presence of a viscoelastic (Maxwell) lubricant. The overall film shape is flattened for a given exit film thickness. A reduction in the film thickness from its Newtonian value is predicted. An extension to the case of variable viscosity is also included and a comparison with the situation for a Newtonian fluid is indicated.
Analysis of Pumping Rings
Authors: Kuzma D. C.
Published: November 2010

A slightly tapered ring riding on a reciprocating shaft can be used as a pump. The pumping capacity of these rings is analyzed.
The Effects of Temperature and Inertia on Hydrostatic Thrust Bearing Performance
Authors: Ting L. L. , Mayer J. E.
Published: November 2010

The effects of the lubricant rotational inertia and the temperature on the performance of parallel stepped hydrostatic thrust bearings have been investigated. Expressions for pressure and temperature distributions and load carrying capacities are obtained under adiabatic flow conditions. Satisfactory correlation between theory and experiment has been observed especially when the bearing speed is high. In order to insure the increase of load capacity as speed increases, the ratio of step location to bearing radius must be chosen no less than a limiting value which depends on the other geometry and operating conditions of the bearing. Since the bearing performance estimation by adiabatic theory is conservative, the design criteria provided will be practical and useful if long bearing life is essential.
The Minimum Gauge Problem in Thin Strip Rolling
Authors: Kuhn H. A. , Weinstein A. S.
Published: November 2010

All previous analyses of the minimum gauge problem either fail to arrive at a criterion for determination of the minimum gauge or result in predictions which are grossly in error. The basic assumptions utilized in these analyses are investigated in the present work with a view toward improving the existing theories. Those assumptions whose validity appears questionable are considered in detail through appropriate analysis. In particular, these assumptions are: (i) the strip and rolls deform uniformly across the width of the strip; (ii) Coulomb (sliding) friction occurs between the rolls and strip. Theoretical treatment of the complex three-dimensional behavior of the rolls and strip is made tenable through simplifications to suitable two-dimensional problems. The primary result of the investigation indicates that the assumption of sliding friction is completely without justification in rolling at the limiting conditions. A new shear traction distribution is postulated which is consistent with the fundamental laws of friction and results in sticking friction (zero slip) over most of the contact region. Incorporating this shear distribution, limiting rolling conditions can be shown to exist theoretically and the minimum gauge can be predicted. It is also found that the Poisson’s ratio must be one-half in the regions of incipient plastic yielding in the strip if a minimum gauge is to be predicted.
Interpretations of the Thickness of Lubricant Films in Rolling Contact. 1. Examination of Measurements Obtained by X-Rays
Authors: Kannel J. W. , Bell J. C.
Published: November 2010

The thickness of the film formed by each of five lubricants between a pair of disks in rolling contact has been measured by an X-ray technique for a range of loads (80,000 to 225,000 psi maximum Hertz stress), two temperatures (178 F and 250 F), and three speeds (4300 fpm to 9100 fpm). An empirical formula fitted to the X-ray data shows a much higher sensitivity of film thickness to load than is normally predicted. In order to judge whether the measurements themselves are at fault, the X-ray measuring process has been reexamined for accuracy, especially where load-dependent errors might arise. Some weaknesses are noted, such as in the amount of X-ray absorption, but these should not affect load sensitivity greatly. New experiments designed to find effects of imperfect collimation of X-rays indicate that reflection of X-rays may be significant, but these effects too do not seem to account for the anomalies of the film thickness measurements.
Statistical Analysis of Mechanical Interaction of Rough Surfaces
Authors: Gupta P. K. , Cook N. H.
Published: November 2010

The contact problem of a pair of mating rough surfaces has been investigated. The problem is formulated analytically, in terms of junction deformation models and surface topography described by statistical distribution of heights and curvatures of the peaks. Statistical analysis of a surface profile was possible by suitable analog to digital conversion. For most surfaces the distribution of all heights and peak heights closely approach a Gaussian distribution. The data on distribution of radius of curvature at the peaks are best fitted by a log-normal function. Statistical correlation between peak heights and radii is found to be very low and hence heights and radii are considered to be independent. With suitable junction deformation models for a pair of asperities in sliding interaction, friction behavior of a pair of mating rough surfaces is estimated. It is shown that surface roughness does not appreciably change the friction behavior under conditions of insignificant adhesion. In cases of strong adhesion, the analytical results show that an improvement in surface finish can substantially reduce the friction coefficient.
The Performance of Hydrodynamic Lubricating Films With Viscosity Variations Perpendicular to the Direction of Motion
Authors: Qvale E. B. , Wiltshire F. R.
Published: November 2010

The effects of prescribed viscosity variations across a hydrodynamic lubricating film are studied. The film is strictly one dimensional and end effects are neglected. The viscosity variations are given by three families of curves. The considerable decreases (in the limit 100 percent) and occasional increases in the coefficient of friction that can occur for constant film thickness and load-carrying capacity are evaluated and the results are presented in terms of parametric curves. Important physical situations where these viscosity variations may be observed or produced are described.
Static Properties of Hydrostatic Thrust Gas Bearings With Curved Surfaces
Authors: Rehsteiner F. H. , Cannon R. H.
Published: November 2010

The classical treatment of circular, hydrostatic, orifice-regulated thrust gas bearings, in which perfectly plane bearing plates are assumed, is extended to include axisymmetric, but otherwise arbitrary, plate profiles. Plate curvature has a strong influence on bearing load capability, static stiffness, tilting stiffness, and side force per unit misalignment angle. By a suitable combination of gas inlet impedance and concave plate profile, the static stiffness can be made almost constant over a wide load range, and to remain positive at the closure load. Extensive measurements performed with convex and concave plates agree with theory to within the experimental error throughout and demonstrate the practical feasibility of using curved plates.