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Friction Factor Measurements in an Equally Spaced Triangular Tube Array

Description: Friction factor data for adiabatic cross-flow of water in a staggered tube array was obtained over a Reynolds number range (based on hydraulic diameter and gap velocity) of about 10,000 to 250,000. The tubes were 12.7mm (0.5 inch) outer diameter, in a uniformly spaced triangular arrangement with a pitch-to-diameter ratio of 1.5. The friction factor was compared to several literature correlations, and was found to be best matched by the Idelchik correlation. Other correlations were found to vary significantly from the test data. Based on the test data, a new correlation is proposed for this tube bundle geometry which covers the entire Reynolds number range tested.
Date: March 19, 2007
Creator: Vassallo P, Symolon P
Partner: UNT Libraries Government Documents Department

Separating Mechanical and Chemical Contributions to Molecular-Level Friction

Description: The authors use force-probe microscopy to study the friction force and the adhesive interaction for molecular monolayer self-assembled on both Au probe tips and substrate surfaces. By systematically varying the chemical nature of the end groups on these monolayers the authors have, for the first time, delineated the mechanical and chemical origins of molecular-level friction. They use chemically inert {double_bond}CH{sub 3} groups on both interracial surfaces to establish the purely mechanical component of the friction and contrast the results with the findings for chemically active {double_bond}COOH end-groups. In addition, by using odd or even numbers of methylene groups in the alkyl backbones of the molecules they are able to determine the levels of inter-film and intra-film hydrogen bonding.
Date: August 14, 2000
Partner: UNT Libraries Government Documents Department

Irrecoverable pressure loss coefficients for a short radius of curvature piping elbow at high Reynolds numbers

Description: Pressure drops in a piping elbow are experimentally determined for high Reynolds number flows. The testing described has been performed in order to reduce uncertainties in the currently used design values for predicting irrecoverable pressure losses. The earlier high Reynolds number correlations had been based on extrapolations over several orders of magnitude in Reynolds number from where the original database existed. The test data shows about a factor of two lower elbow pressure loss coefficient (at 40 {times} 10{sup 6} Reynolds number) than those current correlations.
Date: June 1, 1998
Creator: Coffield, R.D.; Hammond, R.B.; Koczko, J.P.; McKeown, P.T. & Zirpoli, P.J.
Partner: UNT Libraries Government Documents Department

One-dimensional, steady compressible flow with friction factor and uniform heat flux at the wall specified

Description: The purpose of this work is to present generalized graphical results to readily permit passage design for monatomic gases, the results including accommodation of any independently specified friction factor, heat transfer coefficient, and wall heat flux. Only constant area passages are considered, and the specified wall heat flux is taken to be uniform.
Date: October 27, 1997
Creator: Landram, C.S.
Partner: UNT Libraries Government Documents Department

Friction and wear performance of diamondlike carbon films grown in various source gas plasmas

Description: In this study, the authors investigated the effects of various source gases (methane, ethane, ethylene, and acetylene) on the friction and wear performance of diamondlike carbon (DLC) films prepared in a plasma enhanced chemical vapor deposition (PECVD) system. Films were deposited on AISI H13 steel substrates and tested in a pin-on-disk machine against DLC-coated M50 balls in dry nitrogen. They found a close correlation between friction coefficient and source gas composition. Specifically, films grown in source gases with higher hydrogen-to-carbon ratios exhibited lower friction coefficients and higher wear resistance than films grown in source gases with lower hydrogen-to-carbon (H/C) ratios. The lowest friction coefficient (0.014) was achieved with a film derived from methane with an WC ratio of 4, whereas the coefficient of films derived from acetylene (H/C = 1) was of 0.15. Similar correlations were observed for wear rates. Specifically, films derived from gases with lower H/C values were worn out and the substrate material was exposed, whereas films from methane and ethane remained intact and wore at rates that were nearly two orders of magnitude lower than films obtained from acetylene.
Date: January 18, 2000
Creator: Erdemir, A.; Nilufer, I. B.; Eryilmaz, O. L.; Beschliesser, M. & Fenske, G. R.
Partner: UNT Libraries Government Documents Department

A Low-Voltage Rotary Actuator Fabricated Using a Five-Level Polysilicon Surface Micromachining Technology

Description: The design, fabrication and characterization of a low-voltage rotary stepper motor are presented in this work. Using a five-level polysilicon MEMS technology, steps were taken to increase the capacitance over previous stepper motor designs to generate high torque at low voltages. A low-friction hub was developed to minimize frictional loads due to rubbing surfaces, producing an estimated resistive torque of about 6 pN-m. This design also allowed investigations into the potential benefit of using hard materials such as silicon nitride for lining of both the stationary and rotating hub components. The result is an electrostatic stepper motor capable of operation at less than six volts.
Date: September 22, 1999
Partner: UNT Libraries Government Documents Department

Fractal dynamics of earthquakes

Description: Many objects in nature, from mountain landscapes to electrical breakdown and turbulence, have a self-similar fractal spatial structure. It seems obvious that to understand the origin of self-similar structures, one must understand the nature of the dynamical processes that created them: temporal and spatial properties must necessarily be completely interwoven. This is particularly true for earthquakes, which have a variety of fractal aspects. The distribution of energy released during earthquakes is given by the Gutenberg-Richter power law. The distribution of epicenters appears to be fractal with dimension D {approx} 1--1.3. The number of after shocks decay as a function of time according to the Omori power law. There have been several attempts to explain the Gutenberg-Richter law by starting from a fractal distribution of faults or stresses. But this is a hen-and-egg approach: to explain the Gutenberg-Richter law, one assumes the existence of another power-law--the fractal distribution. The authors present results of a simple stick slip model of earthquakes, which evolves to a self-organized critical state. Emphasis is on demonstrating that empirical power laws for earthquakes indicate that the Earth`s crust is at the critical state, with no typical time, space, or energy scale. Of course the model is tremendously oversimplified; however in analogy with equilibrium phenomena they do not expect criticality to depend on details of the model (universality).
Date: May 1, 1995
Creator: Bak, P. & Chen, K.
Partner: UNT Libraries Government Documents Department

Two-Phase Flow Pressure Drop of High Quality Steam

Description: Two-phase pressure drop across a straight test pipe was experimentally determined for high Reynolds (Re) number steam flow for a flow quality range of 0.995 to 1.0. The testing described has been performed in order to reduce uncertainties associated with the effects of two-phase flow on pressure drop. Two-phase flow develops in steam piping because a small fraction of the steam flow condenses due to heat loss to the surroundings. There has been very limited two-phase pressure drop data in open literature for the tested flow quality range. The two-phase pressure drop data obtained in this test has enabled development of a correlation between friction factor, Reynolds number, and flow quality.
Date: October 1, 2001
Creator: Curtis, J. M. & Coffield, R. D.
Partner: UNT Libraries Government Documents Department

Bending Effects in the Frictional Energy Dissipation in Lap Joints

Description: Frictional energy dissipation in joints is an issue of long-standing interest in the effort to predict damping of built up structures. Even obtaining a qualitative understanding of how energy dissipation depends on applied loads has not yet been accomplished. Goodman postulated that in harmonic loading, the energy dissipation per cycle would go as the cube of the amplitude of loading. Though experiment does support a power-law relationship, the exponent tends to be lower than Goodman predicted. Recent calculations discussed here suggest that the cause of that deviation has to do with reshaping of the contact patch over each loading period.
Date: January 1, 2002
Partner: UNT Libraries Government Documents Department

Preparation of ultralow-friction surface films on vanadium diboride.

Description: In this paper, we present a simple annealing procedure (which we refer to as ''flash-annealing'' because of short duration) that results in the formation of an ultralow friction surface film on vanadium diboride (VB{sub 2}) surfaces. This annealing is done in a box furnace at 800 C for a period of 5 min. During annealing, the exposed surface of the VB{sub 2} undergoes oxidation and forms a layer of boron oxide (B{sub 2}O{sub 3}). In open air, the B{sub 2}O{sub 3} layer reacts spontaneously with moisture and forms a boric acid (H{sub 3}BO{sub 3}) film. The friction coefficient of a 440C steel pin against this H{sub 3}BO{sub 3} film is {approx}0.05, compared to 0.8 against the as-received VB{sub 2}. Based on Raman spectroscopy and electron microscopy studies, we elucidate the ultralow friction mechanism of the flash-annealed VB{sub 2} surfaces.
Date: October 14, 1996
Creator: Erdemir, A.; Fenske, G. R. & Halter, M.
Partner: UNT Libraries Government Documents Department

Specification of Surface Roughness for Hydraulic Flow Test Plates

Description: A study was performed to determine the surface roughness of the corrosion layer on aluminum clad booster fuel plates for the proposed Gas Test Loop (GTL) system to be incorporated into the Advanced Test Reactor (ATR) at the Idaho National Laboratory. A layer of boehmite (a crystalline, non-porous gamma-alumina hydrate) is typically pre-formed on the surface of the fuel cladding prior to exposure to reactor operation to prevent the uncontrolled buildup of corrosion product on the surface. A representative sample coupon autoclaved with the ATR driver fuel to produce the boehmite layer was analyzed using optical profilometry to determine the mean surface roughness, a parameter that can have significant impact on the coolant flow past the fuel plates. This information was used to specify the surface finish of mockup fuel plates for a hydraulic flow test model. The purpose of the flow test is to obtain loss coefficients describing the resistance of the coolant flow paths, which are necessary for accurate thermal hydraulic analyses of the water-cooled booster fuel assembly. It is recommended that the surface roughness of the boehmite layer on the fuel cladding be replicated for the flow test. While it is very important to know the order of magnitude of the surface roughness, this value does not need to be matched exactly. Maintaining a reasonable dimensional tolerance for the surface finish on each side of the 12 mockup fuel plates would ensure relative uniformity in the flow among the four coolant channels. Results obtained from thermal hydraulic analyses indicate that ±15% deviation from a surface finish (i.e., Ra) of 0.53 ìm would have a minimal effect on coolant temperature, coolant flow rate, and fuel temperature.
Date: May 1, 2006
Creator: Guillen, Donna Post & Yoder, Timothy S.
Partner: UNT Libraries Government Documents Department

Interfacial Friction in Gas-Liquid Annular Flow: Analogies to Full and Transition Roughness

Description: New film thickness and pressure gradient data were obtained in a 5.08 by 101.6 mm duct for nitrogen and water in annular flow. Pressures of 3.4 and 17 atm and temperatures of 38 and 93 C were used to vary the gas density and liquid viscosity. These data are used to compute interfacial shear stresses and interfacial friction factors for comparison with several accepted literature correlations. These comparisons are reasonable for small values of the relative film thickness. However, the new data cover conditions not approached by the data used to construct those correlations. By combining the current data with the results of two other comprehensive modern experimental studies, a new correlation for the interfacial friction factor has been developed. This correlation adds elements of transition roughness to Wallis' fully-rough analogy to better predict interfacial friction factors over a wide range of gas Reynolds numbers and liquid film thicknesses.
Date: March 1, 1999
Creator: Bauer, R.C.; Beus, S.G. & Fore, L.B.
Partner: UNT Libraries Government Documents Department

Microstructure of bulk and electro-formed Ni implanted with Ti and C

Description: The microstructure of high-purity Ni implanted with overlapping concentration profiles of Ti and C was examined with transmission electron microscopy. An amorphous phase forms at concentrations of 15--18 at.% Ti and 22 at.% C, while a two-phase alloy (amorphous + fcc Ni) forms for {le} 16 at.% C. Electroformed layers with sub-micron fcc grains of Ni or Ni{sub 80}Fe{sub 20} were also found to be amorphized by Ti + C implantation, a key requirement for applying this treatment to Ni-based micro-electromechanical systems to reduce their friction and wear.
Date: October 13, 1997
Creator: Follstaedt, D.M.; Myers, S.M.; Knapp, J.A.; Dugger, M.T. & Christenson, T.A.
Partner: UNT Libraries Government Documents Department

Mitigation of sub-surface crack propagation in railroad rails by laser surface modification

Description: The authors address the mitigation of sub-surface crack propagation in railroad rails via laser surface modification. The goal is to reduce the shear forces from rail-wheel friction, which contribute significantly to the nucleation and propagation of cracks in the sub-surface region at rail gage corners. Microhardness scans and tensile tests were performed on samples from cross-sections of unused and heavily used rail heads. The results of these tests indicate that the severe cyclic plastic deformation that occurs at the gage corners, during service, significantly hardens the sub-surface region there, which leads to cracking. Laser glazing, the rapid melting and rapid solidification of a thin surface layer, was used to reduce the friction coefficient of rail steel. The advantages of this process are that specific regions of the rail surface can be targeted; the treatment does not wash away as the currently used liquid lubricants do; it is more environmentally sound than liquid lubricants; and it can be applied in service, during re-work or during rail fabrication. A number of laser treatments were conducted on AISI 1080 steel plates, similar to rail steel, from which friction samples were extracted. Static block-on-ring friction experiments performed on a variety of laser treated surfaces showed reductions in the friction coefficient by about 25% relative to untreated surfaces at loads corresponding to prototypic rail service loads. The authors laser-glazed two areas on the top surface of a 6-ft length of rail with multiple pass treatments, one with adjacent passes overlapping, and one with adjacent passes separated by 1 mm. Friction measurements were made after they were subjected to 20,000 run-in cycles. The laser treatments remained intact after these cycles. Reductions of friction coefficient of ca. 40%, relative to untreated surfaces, were observed, corresponding to a reduction in the calculated mixed mode crack propagation rate by ...
Date: October 1, 1997
Creator: DiMelfi, R.J.; Sanders, P.G.; Hunter, B.; Eastman, J.A.; Leong, K.; Kramer, J.M. et al.
Partner: UNT Libraries Government Documents Department

Comparison of natural convection heat exchangers for solar water heating systems

Description: Thermosyphon heat exchangers are used in indirect solar water heating systems to avoid using a pump to circulate water from the storage tank to the heat exchanger. In this study, the authors consider the effect of heat exchanger design on system performance. They also compare performance of a system with thermosyphon flow to the same system with a 40W pump in the water loop. In the first part of the study, the authors consider the impact of heat exchanger design on the thermal performance of both one- and two-collector solar water heaters. The comparison is based on Solar Rating and Certification Corporation (SRCC) OG300 simulations. The thermosyphon heat exchangers considered are (1) a one-pass, double wall, 0.22 m{sup 2}, four tube-in-shell heat exchanger manufactured by AAA Service and Supply, Inc., (the Quad-Rod); (2) a two-pass, double wall, 0.2 m{sup 2}, tube-in-shell made by Heliodyne, Inc., but not intended for commercial development; (3) a one-pass, single wall, 0.28 m{sup 2}, 31 tube-in-shell heat exchanger from Young Radiator Company, and (4) a one-pass single-wall, 0.61 m{sup 2}, four coil-in-shell heat exchanger made by ThermoDynamics Ltd. The authors compare performance of the systems with thermosyphon heat exchangers to a system with a 40 W pump used with the Quad-Rod heat exchanger. In the second part of the study, the effects of reducing frictional losses through the heat exchanger and/or the pipes connecting the heat exchanger to the storage tank, and increasing heat transfer area are evaluated in terms of OG300 ratings.
Date: September 15, 1998
Creator: Davidson, J. & Liu, W.
Partner: UNT Libraries Government Documents Department

Tribological performance of NFC coatings under oil lubrication[Near Frictionless Carbon]

Description: An increase in engine and vehicle efficiency usually requires an increase in the severity of contact at the interfaces of many critical components. Examples of such components include piston rings and cylinder liners in the engine, gears in the transmission and axle, bearings, etc. These components are oil-lubricated and require enhancement of their tribological performance. Argonne National Laboratory (ANL) recently developed a carbon-based coating with very low friction and wear properties. These near-frictionless-carbon (NFC) coatings have potential for application in various engine components for performance enhancement. This paper presents the study of the tribological performance of NFC-coated steel surfaces when lubricated with fully formulated and basestock synthetic oils. The NFC coatings reduced both the friction and wear of lubricated steel surfaces. The effect of the coating was much more pronounced in tests with basestock oil. This suggests that NFC-coated parts may not require heavily formulated lubricant oils to perform satisfactorily in terms of reliability and durability.
Date: January 20, 2000
Creator: Ajayi, O. O.; Alzoubi, M.; Erdemir, A.; Fenske, G. R.; Eryilmaz, O. L. & Zimmerman, S.
Partner: UNT Libraries Government Documents Department

Integrated modeling and testing of a micro hinged structure for sliding friction measurement

Description: This paper summarizes the design, modeling, and initial evaluation of a hinged structure for friction measurement in surface micromachining technology. While the area requirements are small, the present structure allows a much larger velocity and pressure range to be evaluated as compared to comb drive structures. The device consists of a cantilevered driver beam connected to a friction pad through a strategically located hinge. AC excitation of the beam flexure forces axial sliding of the friction pad due to beam foreshortening. Normal force is controlled by DC voltage on wings adjacent to the friction pad. While the achievable slip is small (10--30 nm), it is sufficient to disengage contacting asperities and engage new points of contact, and thus should be representative of frictional processes. Furthermore, the design enables the friction pad contact area to remain relatively constant over the excitation cycle. Computer simulation results are provided to mimic on-going experimental work. Increased friction forces are shown to enhance the size of hysteresis loops relating beam deflection to driver voltage.
Date: August 1, 1998
Creator: Redmond, J.M.; Boer, M.P. de & Michalske, T.A.
Partner: UNT Libraries Government Documents Department

USDOE Top-of-Rail Lubricant Project

Description: Lubrication of wheel/rail systems has been recognized for the last two decades as a very important issue for railroads. Energy savings and less friction and wear can be realized if a lubricant can be used at the wheel/rail interface. On the other hand, adverse influences are seen in operating and wear conditions if improper or excessive lubrication is used. Also, inefficiencies in lubrication need to be avoided for economic and environmental reasons. The top-of-rail (TOR) lubricant concept was developed by Texaco Corporation to lubricate wheels and rails effectively and efficiently. Tranergy Corporation has been developing its SENTRAEN 2000{trademark} lubrication system for the last ten years, and this revolutionary new high-tech on-board rail lubrication system promises to dramatically improve the energy efficiency, performance, safety, and track environment of railroads. The system is fully computer-controlled and ensures that all of the lubricant is consumed as the end of the train passes. Lubricant quantity dispensed is a function of grade, speed, curve, and axle load. Tranergy also has its LA4000{trademark} wheel and rail simulator, a lubrication and traction testing apparatus. The primary task of this project was collecting and analyzing the volatile and semivolatile compounds produced as the lubricant was used. The volatile organic compounds were collected by Carbotrap cartridges and analyzed by adsorption and gas chromatography/mass spectrometry (GC/MS). The semivolatile fraction was obtained by collecting liquid that dripped from the test wheel. The collected material was also analyzed by GC/MS. Both of these analyses were qualitative. The results indicated that in the volatile fraction, the only compounds on the Environmental Protection Agency's (EPA) Superfund List of Analytes detected were contaminants either in the room air or from other potential contamination sources in the laboratory. Similarly, in the semivolatile fraction none of the detected compounds are on the EPA's Superfund List of Analytes. ...
Date: February 1, 2002
Creator: Alzoubi, Mohumad F.; Fenske, George R.; Erck, Robert A. & Boparai, Amrit S.
Partner: UNT Libraries Government Documents Department

Maglift Monorail

Description: In the 1990s, significant experience has been gained with high-speed passenger rail technologies. On the one hand, high speed versions of conventional-configuration trains, such as the French TGV, have proven themselves in service; on the other hand, magnetic levitation (maglev) trains such as the German Transrapid, which some expected to supplant conventional trains in some high speed applications, have not yet proven themselves and face a problematic future. This is because of maglev's high capital cost, the magnetic drag which it introduces, and the high development risks associated with this complex technology. This paper examines a new form of high-speed train expected to be capable of speeds of 300 mph, the Maglift Monorail. The Maglift Monorail was developed by simplifying and improving two well-understood technologies--wheelsets and LIMs--and then integrating them. The solution is a vehicle with flangeless wheels mounted in two axes, powered by a high-efficiency and light-weight LIM, positioned to give magnetic lift (maglift), i.e., electromagnetic force in the vertical direction which reduces the vehicle weight on the suspension, and thereby reduces static and rolling drag. Maglift can be considered a form of maglev as it uses the same electromagnetic forces to lift and propel the vehicle. This solution is presented in a Spanish-designed monorail system which has a unique suspension designed to minimize friction while giving great stability and turning capability. This monorail vehicle is propelled by the Seraphim motor (Segmented Rail Phased Induction Motor) which virtually eliminates magnetic drag and provides significant maglift. The Maglift Monorail achieves lower operating costs and a greater overall reduction in drag than conventional noncontact maglev does, and it does so without incurring maglev's high capital costs or its technology development risks.
Date: June 10, 1999
Creator: Hopkins, Tom; Kelley, Bruce; Marder, Barry; Silva, Julio Pinto & Turman, Bob
Partner: UNT Libraries Government Documents Department

Factors affecting characterization of bulk high-temperature superconductors

Description: Three major factors affect the characterization of bulk high-temperature superconductors in terms of their levitation properties during interaction with permanent magnets. First, the appropriate parameter for the permanent magnet is internal magnetization, not the value of the magnetic field measured at the magnet`s surface. Second, although levitation force grows with superconductor thickness and surface area, for a given permanent magnet size, comparison of levitation force between samples is meaningful when minimum values are assigned to the superconductor size parameters. Finally, the effect of force creep must be considered when time-averaging the force measurements. In addition to levitational force, the coefficient of friction of a levitated rotating permanent magnet may be used to characterize the superconductor.
Date: November 1, 1997
Creator: Hull, J.R.
Partner: UNT Libraries Government Documents Department

Two-phase flow in horizontal pipes

Description: A method is developed in this paper which calculates the two-phase flow friction factor at any state of the fluid in the pipe. The mixing-length theory was employed for the calculation of the Reynolds stresses in turbulent two-phase flow. The friction factors obtained this way are in good agreement with experimental data. It is clear that the choice of the parameter m, or the density distribution, is rather arbitrary. Careful experimentation is required to refine the analysis given in this study, and in particular to provide guidance in the proper selection of the parameter m.
Date: September 1, 1981
Creator: Maeder, P.F.; Michaelides, E.E. & DiPippo, R.
Partner: UNT Libraries Government Documents Department