bluuebunny/crossref_metadata_2025 huggingface dataset:
Scale Effects on Rarefied Supersonic Flows in Nanochannels
Authors: Gatsonis Nikolaos A. , Al Kouz Wael G. , Chamberlin Ryan E.
Published: June 2009

The supersonic flow of nitrogen into a nanochannel is investigated using a three dimensional unstructured Direct Simulation Monte Carlo (U3DSMC) method. The U3DSMC code is validated by comparisons with previous 2D DSMC simulations of flows in micron-scale channels. Rectangular nanochannels with heights between 100 nm to 1000 nm, and aspect ratios L/H of 1, 10, 100 are used in the U3DSMC investigation. The Mach 5.9 freestream has a pressure of 0. 1atm and Knudsen numbers of 0.481, 0.962 and 4.81. The nanochannel walls are assumed to be diffusively reflecting at the freestream temperature. The simulations show the development of a disturbance region upstream from the inlet that depends on the Knudsen number. For the L/H = 10 and L/H = 100 nanochannels considered the velocity decreases from its freestream value velocity decreases from its freestream value and becomes subsonic inside the nanochannel. The temperature shows an enhancement region near the inlet while the density shows an enhancement region inside the nanochannel.
Pressure Drop of Two-Phase Dry-Plug Flow in Round Mini-Channels
Authors: Lee Chi Young , Lee Sang Yong
Published: June 2009

As the fluid devices are being miniaturized, the flow channels inside the devices also become smaller, often down to about the size of 1 mm in hydraulic diameter. In such mini-channels, the interfacial tensions between solid and liquid (σSL) and solid and gas (σSG), as well as the surface tension between liquid and gas (σLG), play an important role in two-phase flows, which are determined by choice of tube materials. Among the various two-phase flow regimes, the plug flow appears more frequently in mini-channels than in macro-channels. The surface wettability affected the morphologies of two-phase plug flows, and eventually resulted in large difference in pressure drop. In the present experimental study, contribution of the moving contact lines to the pressure drop of air-water dry-plug flow (dry wall condition at the gas portions) in round mini-channels was investigated. The polyurethane and Teflon tubes were tested; the tube diameters were 2.16 and 1.62 mm, and the contact angles were about 75 and 110°, respectively. All the experiments were performed only in the dry-plug flow regime. The pressure drop became larger either by increasing the liquid superficial velocity or by decreasing the gas superficial velocity due to the increase of the number of the moving contact lines. It implies that the pressure drop by the energy dissipation of moving contact line is an important parameter to be considered in predicting the pressure drop in the dry-plug flow regime. Therefore, the total pressure drop of two-phase dry-plug flows consists of three parts: The frictional pressure drops at the gas- and liquid-plug portions and the pressure drop by energy dissipation at the moving contact lines. The void fraction and the number of liquid plugs could be determined from the superficial velocities of gas and liquid once the two-phase mixer is fixed. Also, the pressure drop by the energy dissipation at the moving contact lines was predicted through modification of the dynamic contact angle analysis. Finally, the simple model was proposed to predict the pressure drop of two-phase dry-plug flow in round mini-channels, which represents the experimental data within the mean deviation of 5.3%.
Numerical Study of Forced Convection of Nanofluids in a Microchannel Heat Sink
Authors: Vaziee Parisa , Abouali Omid
Published: June 2009

Effectiveness of the microchannel heat sink cooled by nanofluids with various particle volume fractions is investigated numerically using the latest theoretical models for conductivity and viscosity of the nanofluids. Both laminar and turbulent flows are considered in this research. The model of conductivity used in this research accounts for the fundamental role of Brownian motion of the nanoparticles which is in good agreement with the experimental data. The changes in viscosity of the nanofluid due to temperature variation are considered also. Final results are compared with the experimental measurements for heat transfer coefficient and pressure drop in microchannel. Enhancement in heat transfer is achieved for laminar flow with increasing of volume fraction of Al2O3 nanoparticles. But for turbulent flow an enhancement of heat removal was not seen and using higher volume fractions of nanoparticles increases the maximum substrate temperature. Pressure drop is increased with using nanofluids because of the augmentation in the viscosity and this increase is more noticeable in higher Reynolds numbers.
Heat and Mass Transfer and Wall Contact for Laminar Vortices in Microreactors
Authors: Dreher Simon , Kronsbein Matthias , Woias Peter
Published: June 2009

In microreactors, interactions between fluid and channel wall affect many chemical reactions. Due to a good heat and momentum transfer, highly exothermic reactions can be quenched and so combustion is inhibited. On the other hand, reactions on catalyst-coated walls call for a high mass transport to and from the walls which is one of the parameters determining the reaction rate for fast reactions. In this contribution, heat and mass transfer towards the walls are investigated in bent microchannels. Laminar flow in the Reynolds number range of 100 < Re < 1000 is studied, where Dean vortices are induced by bends. Optimized geometries of the bends are found with numerical fluid simulations and compared experimentally using chemical reactions. As characteristic parameter, the contact time distribution is calculated which is defined by the distribution of the residence time in regions near the wall. For the characterization of the reactors, also simulations of heat flux are performed. Various optimized reactors are fabricated and experimentally compared by a luminol reaction catalyzed at the copper-plated walls. In other experiments, heat transfer into the fluid is measured. The experimental results are compared to the simulated transport processes.
Application of Self-Control in Droplet-Based Microfluidics
Authors: Kielpinski Mark , Malsch Danie´ll , Gleichmann Nils , Mayer Gu¨nter , Henkel Thomas
Published: June 2009

Droplet-based microfluidics provide a powerful platform for high-throughput operations applied in micro analytics, micro reaction technology and live sciences. Todays research interests focus on the development of highly integrated fluidic networks for sample processing according to a microchemical or microanalytical protocol. Normally, fluidic networks with integrated fluidic loops and bypasses are very complicated systems that require a huge effort for external control and integration of actor components. In contrast, in droplet-based microfluidics interface generated forces can be used to temporarily seal bypasses or to generate well defined pressure gradients at strictures. This potential can be used to implement self-control and self-synchronization at functional nodes in order to minimize the effort for external control and actors integration. Here we report on progress in development of functional nodes for self-synchronized 1:1 coalescence of two independently generated droplet sequences at a Y-shaped junction and on approaches for droplet aliquotation at a Y-shaped bifurcation. The droplet connector automatically balances the time delay between two droplets arriving at the junction. On this account, strictures are integrated into the Y-junction and an additional bypass connects the arriving channels. The first arriving droplet stops at the stricture until its fusion partner arrives. The droplet splitter performs an 1:1 aliqoutation of all elements of a droplet sequence. The main challenges are the balancing of pressure differences at the outlets and the correct aliquotation of droplets independent of their volume at a wide range of flow rates. The splitter design is based on the rule that forces required for splitting are always lower than the forces required for complete droplet inflow into only one of the outlet channels without splitting.
Effects of Fluid and Interface Interaction on Droplet Internal Flow in All-Glass Micro Channels
Authors: Malsch Danie´ll , Gleichmann Nils , Kielpinski Mark , Mayer Gu¨nter , Henkel Thomas
Published: June 2009

Segmented flow of aqueous droplets transported by an immiscible separation medium in all-glass micro channels is characterized by an interplay of interface interaction and phase internal flow field formation. As a result, pressure drop, local shear rates and mixing performance are determined by this interplay. Yet, these effects are strongly influenced by the properties of the employed fluids, wettability of the channel walls and experimental conditions like flow rate and fluid phase ratio. We utilize micro Particle Imaging Velocimetry (μPIV) aside direct pressure measurements as a tool to measure and visualize these effects and show their dependency on fluidic properties and experimental conditions. All-glass micro channels have been prepared by wet etching of glass half channels and anodic bonding of two glass substrates. Micro channels have coplanar faces at top and bottom and sidewalls with a half circular shape. Wetting properties of the internal micro channel surfaces are adjusted by treatment with octadecyl-trichlorosilane. Sample droplets that fully seal the channel are embedded in a separation fluid that completely wets the channel. A permanent thin film of separation fluid prevents direct contact between sample fluid and micro channel walls. In contrast to micro channels with rectangular cross-section [1,2], we observe alternating flow circulation in separation medium and droplets under these conditions [3]. As a consequence, the total pressure drop is almost independent of droplet viscosity.
Dryout Incipience and Critical Heat Flux in Saturated Flow Boiling of Refrigerants in a Vertical Uniformly Heated Microchannel
Authors: Marti´n-Callizo Claudi , Ali Rashid , Palm Bjo¨rn
Published: June 2009

The prediction of dryout occurrence is crucial in the design and safety of compact heat exchangers. For this purpose, a series of experimental tests have been performed to investigate dryout incipience and critical heat flux (CHF) in a circular vertical microchannel with internal diameter of 640 μm and a uniformly heated length of 213 mm using refrigerants R-134a, R-22 and R-245fa as working fluids. The effects of mass flux, system pressure, and refrigerant on the dryout heat flux and vapour quality are explored in detail. Finally, the experimental CHF results are compared to existing correlations both specially developed for microchannels and for macroscale geometries. The comparison shows good agreement with the classical Katto and Ohno (1984) correlation, developed for conventional large tubes. On the other hand, none of the microchannel correlations predicts in agreement the experimental data.
Impact of Microchannel Boundary Conditions on Gas Diffusion Layer Saturation and Transport in Fuel Cells
Authors: Armijo Kenneth M. , Carey Van P.
Published: June 2009

Flooding within a Polymer Electrolyte Membrane (PEM) fuel cell occurs during operation as a result of product water vapor condensing near the surface of the cathode; this can be detrimental to fuel cell performance due to its role in reducing oxygen transport throughout the GDL. Previous Gas Diffusion Layer (GDL) transport models have made use of a zero-saturation boundary condition at the GDL/Oxygen (O2) gas channel (GC) interface. However, the physical correctness of this saturation boundary condition is still unclear. Further investigation of the saturation boundary condition could lead to a more robust model of the GDL saturation distribution and cathodic flooding. This exploration provides a one-dimensional two-phase transport model for saturation as well as liquid water and gaseous oxygen pressure distributions throughout the cathode-side gas diffusion layer (GDL) within a PEM fuel cell. The focus of this investigation is on the impact of non-zero saturation boundary conditions at the GDL / GC interface, and its impact on two-phase transport within the porous medium, with regard to fuel cell performance. Saturation boundary conditions at this location are determined based on GDL interfacial liquid coverage of water droplets that diffuse through the porous medium during operation and block oxygen transport paths. The results of this investigation suggest that non-zero saturation boundary conditions at the GDL/GC interface are evident when analyzing two-phase phenomena, which affect the overall saturation distribution throughout the GDL, and consequent performance of the fuel cell. In addition, GDL membranes with large porosities were found to improve gas and liquid transport by lowering the saturation at the GDL / Cathode interface that would otherwise impede oxygen transport.
Slippage and Wetting Transition of Water Flow in Superhydrophobic Micro-Channel
Authors: Byun Doyoung , Kim Jihoon , Hong Jongin
Published: June 2009

We investigate the slippage effect in a super-hydrophobic micro-channel. The micro-scale grooves are fabricated on the vertical wall to make the super-hydrophobic surfaces, which enable us visualize the flow fields near walls and directly measure the slip length. Velocity profiles are measured using micro-particle image velocimetry (PIV). The velocity profile near the wall shows larger slip length and, if the groove structure is high and wide, the liquid meniscus forms curves into the valley so that the wavy flow is created after the grooves. Also depending on the ratio of pitch to width of the groove structure, the water meniscus status can be either sustained between the valleys or collapsed to be wet. This Cassie to Wenzel transition is observed in the micro-channel. And we investigate the effects of grooves shape and the flow rate on the wetting transition.
Influence of Variable Heat Load on the Refrigerant Distribution of a Dual Cold-Plate System
Authors: Yang Kai-Shing , Yu Kun-Huang , Liu Chung-Che , Wang Chi-Chuan
Published: June 2009

This study examines the refrigerant distribution of a dual cold plate system subject to the influence of heating load using a R-134a based vapor compression system with a nominal capacity ranging from 50∼250 W. The cold plate is of identical configuration. Initially, test is performed under an equal heating load for each cold plate (70 W) which then gives rise to a uniform distribution and equal outlet superheat condition. For an unequal heating load, it is found that the distribution of mass flowrate subject to the influence of heating load is strongly related to the outlet states of the two cold plates. For the condition where one of the cold plate is in superheated state while the other is in saturated state, the mass flowrate for the fixed heating load is lower than that of smaller heating load, and the difference increases when the heating load gets smaller due to the influence of accelerational pressure drop. A maximum of 17% difference is seen at a loading ratio of 0.571 (40W/70W). For the condition where both outlet states of cold plate are at superheated states, the mass flowrate for the fixed heating load is marginally higher than that of the smaller heating load, and the difference is insensitive to the rise of heating load. For this situation, the effect of accelerational pressure is negligible, and it is mainly attributed to two-phase/single-phase distribution pertaining to the effect of heating load.
Numerical Simulation of Microscale Slot Jet Impingement Cooling of a Surface With Constant Wall Heat Flux Using DSMC-IP
Authors: Kursun U. , Kapat J.
Published: June 2009

The standard Direct Simulation Monte Carlo (DSMC) simulation is not capable of producing statistically meaningful results for low Re flows which are often encountered in micro-flows. Therefore, the non-isothermal Information Preservation (IP) algorithm is utilized in this study to predict the flow structure and the heat transfer characteristics of a microscale, slot, and confined jet impinging on a flat surface with uniform temperature boundary condition. The flow Knudsen number based on the slot width is in the slip flow and the lower transition regime. The jet is impinging at jet-to-target surface gaps normalized by slot width (H/W) of 0.25, 1 and 2 at a pressure ratio of 2.0. The effects of impingement gap (H/W) on flow structure and heat transfer are investigated. The velocity, pressure and Nusselt number distributions on the impingement target surface are presented. The results are compared to corresponding conventional large-scale values.
Numerical Simulation of an Array of Rectangular Cylinders in Cross Flow in a Microchannel Using DSMC-IP
Authors: Kursun U. , Kapat J.
Published: June 2009

A numerical simulation is performed to study the characteristics of the gas cross flow over an array of rectangular cylinders in a two dimensional microchannel. Since Direct Simulation Monte Carlo (DSMC) suffers from the statistical noise for low Re flows which are often encountered in micro-flows, the non-isothermal Information Preservation (IP) method is employed. Pressure boundary conditions based on the characteristic theory are implemented at the inlet and outlet domain boundaries. The simulation results are presented. This study will form a base for our future particle-atomistic hybrid computations.
Formation of Temporary Separating Walls in Microfluidic Devices
Authors: Bazargan Vahid , Stoeber Boris
Published: June 2009

This work demonstrates a new mechanism for changing the architecture of microfluidic channels during device operation. This method uses an aqueous solution of a thermally responsive polymer (Pluronic), which undergoes reversible gel formation at elevated temperatures. This gelation temperature is lowered through the presence of sodium phosphate. A phase diagram for this material system is derived from rheometry experiments. Formation of a temporary gel wall in a microfluidic device occurs at the diffusive interface between a Pluronic solution and a sodium phosphate solution. The wall thickness increases along the channel, and it decreases at high flow rates. The wall thickness also increases with saline concentration. These observations are explained through scaling arguments for the diffusion problem and with the established phase diagram.
Structural Optimization of Microfluidic Gate Controlled Magnetic Bead System for DNA Sequencing-by-Synthesis
Authors: Esfandyarpour Hesaam , Davis Ronald W.
Published: June 2009

In this paper we present a structural and geometrical optimization of a microfluidic gate-controlled magnetic bead system for DNA Sequencing by Synthesis technology. To optimize the efficiency of the technology, we designed, fabricated and tested several structures of the GCMB platform. Different designs of the system were created to study the effects of the pressure, structure, geometry, materials, thickness of intermediate layer between flow and control lines; Toward optimization of the system for a better sensing and to concentrate signal (e.g. heat in Thermosequencing [4–9]) into specific regions for detection in the real system, we recommend an optimized modified gated structure for the microfluidic detection platform and show how this new platform could improve the detection efficiency.
Experimental and Analytical Studies on Frictional Pressure Drops of Gas-Liquid Two-Phase Flow at Vena Contract and Expansion
Authors: Ohtake Hiroyasu , Hagiwarai Masato , Koizumi Yasuo
Published: June 2009

The frictional pressure drops of gas-liquid two-phase flow in mini-micro pipes and at vena contract and expansion were investigated experimentally and analytically. Pressure drops of straight pipe, sudden enlargement and sudden contraction of gas-liquid two-phase flow in mini-pipes were measured. Test liquid was water at room temperature; test gas was argon. The diameter of the test mini-pipe was 1.0 and 0.5 mm, respectively. Each test tube was connected at both ends to small tanks. The diameter of the small tank was 15 mm for 1.0 mm diameter of test tube and 5 mm for 0.5 mm diameter of test tube, respectively. Thus, the cross-sectional ratio of the contraction was about 1000; the ratio of the enlargement was about 0.001. The pressure drop data were collected over 3.0 < UG < 130 m/s for the superficial gas velocity and 0.02 < UL < 6.0 m/s for the superficial liquid velocity. The present experimental results of sudden contraction pressure loss factor Kc and sudden enlargement pressure loss factor Ke of single-phase liquid flow in mini-pipes differed from the conventional values, Kc = 0.5 and Ke = 1.0. The calculated results by using a commercial code, STAR-CD, agreed with the present experimental results for mini-pipes. Assuming to homogenous flow and incompressible flow, sudden contraction pressure loss, sudden enlargement pressure loss and their factors Kc, Ke for gas-liquid two-phase flow were estimated by using momentum equation and energy equation. The contraction pressure losses by Hewitt’s correlation for conventional pipes were similar to the present experimental results of the contraction for mini-circular pipe. Collier’s correlation of the enlargement pressure loss for conventional pipes underpredicted the present experimental results of the enlargement for mini-tube. Based on the present experimental results, new correlations were obtained for the enlargement and the contraction pressure losses in mini-channel.
Friction Losses and Heat Transfer in Laminar Microchannel Single-Phase Liquid Flow
Authors: Silve´rio Vaˆnia , Moreira Anto´nio L. N.
Published: June 2009

Many studies addressed the validity of macroscale theories to describe momentum and heat transfer in single phase in microtubes, but the results are often inconsistent. It is suggested that the fluid flow and heat transfer in microchannels without phase change is substantially different from that in larger channels. However, these discrepancies may be attributed to experimental uncertainties mainly due to the use of conventional measurement apparatus that are too big to implement in the tested system. Other researchers explain the microfluidic behavior with the ratio of surface forces to body forces which evolve inversely to the hydraulic diameter. The present work considers the use of a dedicated experimental facility built to allow the use of optical diagnostic and flow visualization techniques in heated microtubes and addresses the potential microscale effects which may arise for single phase flow conditions. The experiments encompass measurements of the pressure drop and the longitudinal temperature distribution in the fully developed single phase liquid flow established in circular and square cross section of channels made of borosilicate glass with hydraulic diameters from 50μm up to 500μm. The flow conditions consider a range of Reynolds number from 10 up to around 2500 and the use of diverse fluids to account for the effects of liquid properties. Namely, three distinct fluids were used: distilled water, methoxy-nonafluorobutane and methanol. For heat transfer studies, the channels are heated with constant wall heat flux supplied by Joule effect by means of external wall rf-PERTE deposition of Indium Oxide thin film. The thin transparent film showed good chemical stability in the range of temperatures up to 70°C, therefore indicating that the thermal boundary condition approximates a constant wall heat flux condition. The mass flux is varied from 60 to 3300kg.m−2·s−1 and the heat flux was set between 4 and 6kW.m−2. Experimental uncertainties are estimated to be below 14% for the friction factor and below 24% for Nusselt number; the former is dominated by inaccuracies in the diameter, while the second is dominated by temperature measurements.
Critical Heat Flux of Butanol Aqueous Solution
Authors: Nishiguchi Shotaro , Ono Naoki , Shoji Masahiro
Published: June 2009

Aqueous solutions of some alcohols such as butanol show peculiar temperature dependence of surface tension. Contrary to ordinary liquids or solutions, the surface tension increases with temperature at the range of high liquid temperature. So at the triple-phase point on a heated surface, the thermo-capillary force acts for the liquid to wet the heated surface, so the solutions are sometimes called as “self-wetting liquids”. Self-wetting liquids may prohibit the dry-out of a heated surface so that the heat transfer performance would be enhanced. For this reason, applications of self-wetting liquids to heat transfer devices such as heat pipes are actively studied in recent years. However, the heat transfer characteristics of boiling of self-wetting liquids are not fully understood. In the present research, a boiling experiment of butanol aqueous solution was performed on a heated fine wire in order to make clear the fundamental heat transfer characteristics. A heated wire configuration is easy to observe the phenomena and easy to address the fundamental issues of boiling. In the present experiment, nucleate boiling heat transfer were investigated with special attention to critical heat flux (CHF), by changing solution concentration and temperature. Bubbling aspects were observed by high-speed video camera. It is found from the experiment that CHF is generally enhanced 20 to 50% when compared to the case of pure water. It is also found that at a certain concentration and at a certain liquid temperature, peculiar boiling takes place where very small bubbles are emitted from the heated wire and CHF enhancement becomes very large from 2 to 3 times higher than CHF of pure water. The temperature when the peculiar boiling takes place is close to boiling temperature of the solution. These results suggest the possibility of application of aqueous solution to high-performance cooling devices utilizing micro-scaled channels because generating bubbles are small enough so that the pressure loss of the flow passage is small and heat transfer rate is very large.
Photonics on a Silicon Chip
Authors: Lipson Michal , Manipatruni Sasikanth , Preston Kyle , Poitras Carl
Published: June 2009

Photonics on a silicon chip could enable a platform for monolithic integration of optics and microelectronics for applications of optical interconnects in which high data streams are required in a small footprint. In this talk I will review the challenges and achievement in the field of silicon photonics. Using highly confined photonic structures one can enhance the electro-optical and non-linearities properties of Silicon and enable ultra-compact and low power photonic components with very low loss. We have recently demonstrated several active components including GHz electro-optic low power switches and modulators, all-optical amplifiers and wavelength converters on silicon.
Cooling of Electronic Chips Using Microchannel and Micro-Pin Fin Heat Exchangers
Authors: Prasher Ravi , Chang Je-Young
Published: June 2009

The research community is experiencing a revolution in microscale and nanoscale heat transfer, with a focus on developing fundamental experiments and theoretical techniques. More recently, these advancements have begun to influence the design of electronic systems. A futuristic electronic cooling solution might include high efficiency thermoelectric devices made from nanomaterials for the cooling of hotspots on a chip, nano/micro particle laden thermal interface materials and micro-pin fin/microchannel based heat exchanger. Liquid cooling using integrated microscale heat exchangers is a promising future technology to address issues associated with integrated circuit thermal management. In this paper recent advances made by us on technology development of microchannel/micro-pin-fin heat exchangers is presented. Particular attention is given to the impact of hotspots on the performance of microchannel cooling.
A Safe Train State of Mind
Authors: Sarunac Radovan
Published: June 2009

The overall goal of each rail/transit Operator is to promote safety of the system. Concurrent effort of all stake holders is needed to achieve the best possible results. That should include as a minimum standard development groups and committees (FRA, APTA, FTA, ASME, IEEE, etc.), vehicle designers, train operators, train and infrastructure maintenance, quality assurance, safety and risk management, and engineering consulting companies. Recently, security of transit system has an increased impact. This paper is focused at specific topics of vehicle design and occupant protection, derailments, friction management, and fire safety. Most of these issues are interrelated; therefore any change in each category may impact all other categories as well. The objective was to evaluate specific impacts of each category, in order to improve passenger safety and underline most influential factors for future vehicle designs. The objective of a crashworthy design is to provide a vehicle capable of managing crash energy through the use of controlled crash zones. Secondary impact injuries can be controlled by limiting the maximum force required to initiate controlled deformation of carbody energy absorption zone, and by attention to interior design. While it is impossible to prevent all types of derailments, the probability of derailment may be reduced by appropriate systematic measures. Concurrent impact of various causal factors including friction management, vehicle design and contact geometry may adversely influence safety margin against low speed wheel climb derailments. Fire, smoke and toxic fumes present a considerable hazard to passengers. Materials used for vehicle design must provide assurance that this hazard is minimized. All combustible materials used in the construction of the car shall be minimized and shall satisfy standard requirements. Passenger evacuation is a key aspect of rail vehicle fire safety – the vehicle needs to remain “fire safe” until all passengers leave the train.
Review of Current Maintenance Practices Used on Commuter and Passenger Rail Cars
Authors: Ward Lamont B.
Published: June 2009

Commuter and passenger railroads invest large amounts of capital to purchase and maintain their rolling stock. Funding for maintenance is largely derived from operating budgets with some funds coming from other sources. Realizing maintenance is vital to the safety and operations of their rolling stock, railroads use maintenance methodologies found in other industries along with government regulations and in-house practices to determine the best maintenance practice for their fleet. By using Condition Based Maintenance, Life Cycle Maintenance, and Reliability Centered Maintenance, railroads have increased reliability by isolating unreliable parts and performing corrective actions when needed. This increases scheduled maintenance and reduces unscheduled maintenance. However, unscheduled maintenance still impacts operations and reliability for railroads. Rolling stock repair costs due to unscheduled maintenance are not captured or analyzed so further improvement can be made in this area.
Analysis of Energy Dissipation in an Electric Transit System
Authors: Renfrew Alasdair C. , Chymera Martyn , Barnes Mike
Published: June 2009

Reducing energy consumption in electrified transit systems is becoming increasingly important as energy prices rise and environmental concerns become more prominent. In electrified transit systems, significant savings can be accomplished by utilizing braking energy. Energy from regenerative braking can be used to power vehicles via the traction supply system, or stored on board vehicles using energy storage devices. The effectiveness and energy savings of regenerative braking or on board energy storage is dependent on the nature of the system, particularly the vehicle drive cycles and service frequency. The paper describes an analysis methodology developed to consider energy flows in an electrified transit system, hence enabling the potential benefits of regenerative braking and energy storage devices to be assessed.
Increase of Efficiency in Wireless Train Control Systems (ETCS Level 2) by the Use of Actual Packet-Oriented Transmission Concepts
Authors: Jobmann Klaus , Ruesche Simon F. , Steuer Jan
Published: June 2009

The European Rail Transport Management System (ERTMS) was introduced by the European Union (EU) to harmonize the nearly 18 different national train control systems which are currently in use, to accelerate the interoperability of the passenger- and freight-transport and, finally, to increase the utilization of tracks by dynamic train control. The essential components of ERTMS are the train-specific, cellular, professional mobile radio system GSM-R (GSM-Railway) and the so-called European Train Control System (ETCS) which provides, by its second expansion stage (ETCS Level 2), the control- and signalling-information between the train and the related control location via GSM-R in a connection-oriented and wireless way. This wireless and connection-oriented approach will be the bottleneck of the system, which considerably limits the possible number of voice- and data-connections in each cell at the same time and will cause a deadlock of the system, if the number of users will rapidly increase (e.g. accidents, freight depots, lines with a high and dynamic volume of traffic). Within this paper the first part of a packet-switched approach is presented to counteract this expected deadlock by taking into account that the GSM-R infrastructure, which is often already installed by the national railroad operators, also should be used to save the high capital investment of those companies.
Composite Coil Spring Development and Testing
Authors: Djomseu Patricia , Sardou Max A. , Berg Thomas R.
Published: June 2009

This paper will present the development of composite coil springs made from glass-fiber-epoxy materials. It will also review the results from prototype springs that have been manufactured and tested. Sardou S.A. has been developing and manufacturing composite structures and components of various designs for over 27 years. This experience, especially with composite torsion springs, has led to development, prototype production, and testing of several designs of composite coil springs. The design takes advantage of commercially available glass fiber and epoxy materials. The development process led to proprietary design methods and computer models to simulate unique configurations and material characteristics. The development process also allows design of composite springs for the same or smaller design volume as steel coil springs with comparable spring characteristics. The manufacturing methods that are used apply existing lost mold and winding processes in unique ways to produce prototype composite coils springs. These methods were also developed considering scaling-up and automation for volume production. Several generations of prototype composite coil springs have been produced and tested. Each generation has advanced the design and manufacturing methods. Several features of composite coil springs including light weight, dynamic response, flexibility of design, and fatigue resistance have been demonstrated through testing. Depending the steel counterpart considered, composite coils springs offer weight saving of about 75%, fatigue life improvement, no rust, no creep, and no notch sensitivity at a cost close to that of a steel spring.
Predicting Railway Wheel Wear Starting From Multi-Body Analysis: A Preliminary Study
Authors: Lewis Roger , Kuka Naim , Ariaudo Caterina , Dwyer-Joyce Rob , Tassini Nicola , Quost Xavier
Published: June 2009

One of the key-elements of train design is the wheelset lifetime, which is strongly dependent on the levels of wheel wear. In order to reduce costs and increase safety, wheel wear needs to be predicted with increasing precision. In the past few years specific tools have been introduced to combine the predicted dynamic data from multi-body models, with the analytical computation of the wheel-rail contact parameters, to achieve an improved wear prediction. The aim of the present work is to consider the different methodologies for wear prediction and to create a wear prediction tool which is based on available railway dynamics codes enhanced by improved rolling contact analysis, combined with recent research on wear.
Dynamic Analysis of Pitch Plane Railway Vehicle-Track Interactions Due to Single and Multiple Wheel Flats
Authors: Uzzal Rajib Ul Alam , Rakheja Subhash , Ahmed Waiz
Published: June 2009

The dynamic impact forces due to the wheel defect such as a flat is a main concern for a heavy freight train operating at high speed. The present investigation employs a pitch plane vehicle model coupled with a comprehensive three-layer track system model to study the impact force generated in the wheel-rail interface due to the presence of wheel flats. The wheel-rail contact is modeled using nonlinear Hertzian contact theory. Responses in terms of wheel-rail impact load and forces transmitted to bearings, pad and ballast are evaluated in an attempt to identify desirable design and operating factors. Wheel-rail impact loads due to the presence of multiple flats either in single or different wheels in-phase or out-of-phase conditions are evaluated and analyzed. A detailed parametric study is carried out that includes the variations in selected vehicle, track, operational as well as flat parameters. The results show that the effect of multiple flats is insignificant if they are more than 45° apart. The impact due to single wheel flat can be larger than in-phase flats at each wheel due to the presence of pitch dynamics. The parametric study shows that other than speed, depth and length of the flats are most sensitive parameters, and there exists a critical length at each flat depth that leads to the largest impact load.
A Metallurgical and Experimental Investigation Into Sources of Warm Bearing Trending
Authors: Cole Kevin D. , Reed Martin , Tarawneh Constantine M. , Wilson Brent M.
Published: June 2009

In the railroad industry, bearing hot-box detectors are the primary tools utilized for the removal of distressed bearings from service. Current technology has expanded the role of these detectors to monitor bearings that appear to “warm trend” relative to the average temperatures of the remainder of bearings on the train. Several bearings set-out for trending and classified as non-verified revealed that a common feature was discoloration of rollers within a cone assembly. A number of laboratory tests were performed to determine a minimum temperature and environment needed to reproduce these discolorations. In addition, a metallurgical examination concluded that microhardness profiles from discolored rollers exhibited evidence of heating, which lead to softening of the case microstructure, and a reduction in case depth. In order to determine a cause for the internal heat leading to the discoloration of rollers, selected laboratory experiments were carried out in a simulated service environment. Testing focused on exploring certain defects or hypothetical scenarios that may raise the bearing cup temperature above that of normal operating conditions. None of the examined cases resulted in similar roller discolorations to those observed in the trended set-outs. The studies presented in this paper comprise the initial work aimed at determining the root cause of warm bearing trending that some tapered roller bearings experience during service.
The Effect of Friction Modifiers on Wheel/Rail Isolation
Authors: Gallardo Hernandez E. A. , Cotter J. , Lewis R. , Eadie D. T.
Published: June 2009

Train detection, for signalling purposes, is often by means of track circuits. Signalling block occupancy is triggered by the wheelset of the train ‘shorting out’ the track circuit, i.e. the wheels and axle act as a shunt. Contamination on the track such as ballast dust, rust, oil, or leaves as well as substances designed to improve train operation such as friction modifiers or sand may cause the contact between the wheelsets and the track to be compromised, inhibiting train identification. In previous work a twin disc approach has been used to study the effect of sand (used to improve adhesion) and leaves on wheel/rail isolation. Friction modifiers are of significant current interest in wheel/rail research. Introducing a new material into the tread/top of rail interface can raise questions about the impact on signalling systems. Although no significant effects have been observed in practical operation on a range of railway systems, the intention in this work was to evaluate conductance between wheel and rail in a more controlled and systematic fashion using the previously established methodology. Using the twin disc technique, friction modifier, in the form of a solid stick, was applied using a spring loaded device to the rotating wheel disc to generate a visible film. Tests were run to measure contact impedance at typical loads and slips. Static tests were also carried out using discs pre-conditioned with a friction modifier film. The electrical circuit used was a modified simplified simulation of audio frequency track circuit. No significant difference was observed in the measured impedance for dry conditions with no friction modifier, versus tests where friction modifier was applied, regardless of percentage slip or input voltage. The analysis suggests that the introduction of friction modifier into the existing wheel/rail interfacial film does not result in increased impedance with all other factors being equal.
Brake Rigging Analysis and the Development of Link Brake Stabilizers
Authors: Malachowski Jerry , Cline Dave
Published: June 2009

Components of truck brake rigging, especially brake beam supports and guides have always presented wearing and maintenance problems. The high contact stresses between the brake beam ends and the supporting/ guiding wear liners in non-stabilized truck brake rigging cause an accelerating progression of wear in the areas of contact. This wear invariably results in reduced braking output and unacceptable alignment between the brake shoes and wheels. The Link Brake Stabilizer has been developed to greatly minimize these contact stresses and resulting wear. This is accomplished by replacing the typical reactive supporting torque at the brake beam end guides with additional brake beam sustaining forces at the brake beam strut and simple support forces at the brake beam end guides. Mathematical analysis, lab and service testing and interpretation of observed data have led to insights into the influences of the various components of the brake rigging under different operating conditions. These insights can be used to make operational and economic decisions about brake system features.
In-Situ Test Measurement Techniques Within Railway Track Structures
Authors: Anderson Justin S. , Rose Jerry G.
Published: June 2009

Recent changes in national transportation needs have placed increased burden on railroad infrastructure. To meet the increased demand for efficient freight transport, the railroad industry has increased traffic volume and maximized axle loadings. Increased axle loads have forced railroads to reevaluate existing infrastructure to ensure their ability to accommodate the additional traffic loads. It is imperative to design and maintain tracks such that they can withstand high volume and increasing axle loads over an extended service life, considering the track structure is the most significant capital expense for railroad companies. It has been desirable for years to develop non-intrusive procedures to directly measure pressures and stresses at various levels and interfaces in the railroad track structure in order to optimize track designs and improve subsequent track performance. Methods for measuring both pressures and deflections have been presented in recent research focusing on assessing the performance of trackbeds with increased track modulus, primarily through the addition of asphalt underlayment. These studies involve instrumenting HMA trackbeds with earth pressure cells and displacement transducers to measure pressure levels and distributions within the track structure and rail deflections under moving trains. Additional test methodologies have been developed to include pressure readings at interfaces like the rail/tieplate interface and the tieplate/tie interface using very thin pressure sensitive Tekscan sensors. The Tekscan Measurement System uses a piezoelectric film sensor composed of a matrix-based array of force sensitive cells, similar to mini strain gauges, to obtain accurate pressure distributions between two surfaces in the track. The procedure appears applicable for a wide variety of specific track related measurements to include: 1) analyzing pressure distribution patterns at the rail base/tie plate/tie interfaces to minimize wear and eliminate pressure points, 2) validating and optimizing horizontal curve geometric design criteria relative to superelevation, 3) assessing crossing diamond, other special trackwork, and bridge approach impact pressures, and 4) evaluating the advantages/disadvantages of various types of tie plates, fastenings, and tie compositions with the objective of equalizing pressure distributions over the interface areas. Results of testing are presented in detail for test installations on CSX Transportation heavy tonnage mainlines and at the Transportation Technology Center (Pueblo) low track modulus heavy tonnage test track.
Investigating Friction Modification and Potential Wear Reduction in the Railroad Wheel to Rail Contact
Authors: Blasko Daniel S. , Cogdell J. David , Lonsdale Cameron P.
Published: June 2009

Reduced friction with top of the rail friction modifiers continues to be investigated for improved energy efficiency and reduction in lateral forces between railroad car wheels and the rail. Another benefit often not considered is the potential reduction in wear of both the wheel and the rail surfaces. This paper details the results of fundamental laboratory test work to compare dry contact condition with one where a “friction modifier” has been applied, to define the difference in the surface deterioration and wear. The basics of this wear testing are described, along with information on the materials used for the testing. The results show a very significant difference in friction coefficients and the wear characteristics, suggesting substantial benefit potential in both reduced rail wear and wheel tread wear. Selected wheel wear tests are discussed and historical wheel wear information is provided. Wheel life data for two North American coal freight car fleets are reviewed to point out the average mileage of wheels in service. The potential for increasing wheel wear life, and therefore potential cost savings, is highlighted. Finally, recommendations for future work are offered.
Supercapacitors On-Board Light Rail Vehicles: Enhanced Energy Storage Systems for Improved Vehicle Efficiency
Authors: Van Mierlo Joeri , Barrero Ricardo , Tackoen Xavier
Published: June 2009

This article will propose different energy storage systems, ranging from 0.91 kWh to 1.56 kWh, suitable for a 30 m long tram. To configure the system regarding energy content, voltage variation, maximum current and power losses, a model of the tram, network and substations power flow has been developed in a Matlab/Simulink environment. Results obtained in energy savings at substation level vary from 24% to 27, 6% under the same driving profile and auxiliaries load; while at the end-of-life of supercapacitors, the range varies from 18, 1% to 25, 1% depending on the supercapacitor module used and vehicle load.