High Friction Losses Research Articles

A study on the influence of surface topography on the low-speed tribological performance of port plates in axial piston pumps

Axial piston pumps are widely used under severe conditions because they are able to operate highly efficiently at high pressure and various ranges of speed. However, pump efficiency is relatively low at low speed because of insufficient lubrication. The contact between the port plate and cylinder barrel is critically important because insufficient lubrication from this pair causes rapid wear and high friction loss which significantly reduces pump efficiency. Ring-on-disc testing was conducted to investigate the friction and wear behaviours of the port plate–cylinder barrel contact. Four types of surface finishing processes were used: coarse grinding, fine grinding, polishing, and laser texturing. A confocal laser scanning microscope and energy dispersive spectroscopy were used to examine the surface. Results indicate that the polished surfaces have the best tribological performance. Finely ground surfaces have lower wear but higher friction than coarsely ground surfaces. The number and size of the brass particles transferred to the steel surface are related to the surface topography. Laser textured surfaces have the highest friction and wear. Brass particles aggregate inside micro-dimples. Increasing contact pressure does not change the wear mechanism but increases abrasion.

Design Evolution: From Rolling Piston to Revolving Vane to Cross-Vane Expander-compressor unit

In this paper the design evolution from rolling piston compressor (RP) to revolving vane compressor (RV) and finally to cross-vane expander-compressor unit (CVEC) is presented and discussed. The details in the design philosophy which initiated this evolution will be presented and discussed.It is estimated that more than 90% of the room air-conditioners uses RP in its compressor. This is because of its advantages: it has the few parts, it is simple geometrically and it is reliable. However, it is with no weaknesses. RP's weaknesses lie in three parts:too many rubbing surfaces with high relative rubbing velocity with each other which give rise to high frictional losses;components (eccentric and roller) are not rotating at their centres and resulted in unnecessary inherent vibration;vane tip is constantly rubbing against the roller making it a weakest part in design.To overcome RP's weaknesses, RV is introduced. As compared to RP, RV has fewer rubbing surfaces, and the relative velocities among these surfaces are reduced Components in RV rotate at their own centres and there is no inherent vibration; the rubbing at the vane tip has been eliminated completely.However, like RP, RV also has a large rotor which occupied "useful" space and making the working chamber relatively small. To overcome this latter problem, CVEC is introduced. In this newly invented CVCE, not only parts are all concentric and rotate at their own centres, the unit also recovers expansion energy and hence significantly reduces energy required by the refrigeration systems. And, more importantly, all these are carried out not at the expense of the additional cost.In this paper, details on these three compressors are explained, compared and their respective uniqueness are shown and discussed.

Synthesis and Tribology of Micro-Carbon Sphere Additives for Enhanced Lubrication

Poor or inefficient lubrication often gives rise to high friction and wear losses in machine components, which adversely affect their performance, efficiency, and durability. Many approaches are being explored to enhance the antifriction and antiwear properties of sliding machine components. In this study, the antifriction and antiwear properties of carbon spheres, synthesized from plastic waste by an autogenic process, were investigated as an additive to a poly-alpha-olefin (PAO-4 grade) oil. When dispersed at 1 wt% concentration, the carbon spheres reduced both friction and wear under boundary-lubricated sliding conditions. In particular, the reduction in wear was quite dramatic and appeared to be enabled by the formation of a fairly thick (≈200 nm) carbon-rich boundary film, the formation of which is attributed to tribochemical interactions between the carbon particles and sliding contact surfaces.

To Investigate the Effect of Oil Film Thickness at the Entrance of the Infinitely Long Slider Bearing Using CFD Analysis

The oil film thickness between slider and shoe is a significant parameter and has a strong influence on the bearings performance. A CFD analysis has been carried out to find the effect of oil film thickness at the entrance of the slider using ANSYS workbench. Laminar viscous model with SIMPLE pressure-velocity coupling are used for the analysis. 2-D steady state, Navier-Stoke equations are discretized with finite volume approximations using structured grids. First the analysis has been carried out for the maximum load carrying capacity (i.e. m = 1.1889). For validation, CFD values are compared with the available analytical solution of Reynolds equation. CFD results showed good concord with the analytical values with a maximum error of 1%. After validation, the analysis has extended to four more 1m1 values such as 0.5, 1, 1.5 and 2. If bearing operate at below maximum load carrying capacity, the result shows that low load carrying capacity and high frictional losses. But for above, frictional forces reduces and blunt of the pressure profile at peak also decreases which will influence the action of extremely high load on a very small area of the shoe.

Experimental and computational investigation of double serpentine nozzle

Infrared radiation signatures of gas turbine engine exhaust are suppressed markedly when equipped with a serpentine nozzle compared to an axisymmetric nozzle. The aim of this paper is to research more detailed flow characteristics of the serpentine nozzle, and to this end a double serpentine nozzle cold fluid test was conducted in this paper, static pressures on the nozzle walls surface were measured, and schlieren flow visualizations downstream of the nozzle exit were observed. Then numerical simulations of the experimental model were carried out using CFD software with k-ɛ turbulence model adopted. And the effects of geometric design parameters (the length ratio of first S length to second S length and the centerline distributions) on serpentine nozzle performance were investigated numerically. Detailed flow characteristics were presented including the distributions of static pressure, Ma number (streamlines), wall shear stress (limited streamlines), and the total pressure. Results show good agreement between the experimental data and computation. Static pressure distributions on the upper and down walls surface of double serpentine nozzle are completely different compared to the traditional axisymmetric nozzle. The rapid turning and steep passage slope of the serpentine nozzle would result in high friction loss and strong secondary flow loss, hence the value of the length ratio of first S passage to second S passage is recommended to be chosen from 2:5 to 2:3. The centerline distributions are crucial to the nozzle design for its influence on air acceleration inside the nozzle. The centerlines with a rapid turning at the exit would result in a high Ma number, which brings on high friction loss and secondary loss at the turnings. For maximum efficiency of centerline distributions, it is recommended that curves with a gentle turning at each serpentine passage exit should be chosen.

Effect of tribochemistry on lubricity of DLC films in hydrogen

This paper presents the results of a systematic study demonstrating how controlled or targeted tribochemistry can lead to super-low friction and wear in diamond-like carbon (DLC) films. Specifically, how hydrogen can lead to dramatic reductions in the friction and wear of hydrogen-free DLC films which otherwise experience high friction and severe wear losses. When sliding tests are performed with a hydrogen-free DLC film in an inert gas (like Ar), the friction coefficients were in the range of 0.4 to 0.7 and it wore out rather quickly. However, when the same tests were run under the 1333Pa partial pressure of hydrogen, the friction coefficients were reduced by factors of more than 10 and the wear damage became very difficult to quantify. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) analyses provided strong chemical evidence that the sliding contact surfaces of these films underwent tribochemical reactions with hydrogen effectively passivating dangling bonds of surface carbon atoms, which is believed to be responsible for ultralow friction and wear. In an effort to rule out the possibility of contamination and confirm the pivotal role of hydrogen in lubricity of DLC films, we ran similar tests with the same hydrogen-free DLC in deuterium (an isotope of hydrogen) and achieved essentially the same level of reduction in friction. TOF-SIMS clearly confirmed the formation of a deuterium-rich tribofilm on rubbing surfaces thus confirming the critical role of tribochemistry in super-low friction and wear of DLC.

Technology Focus: Multilateral/Extended Reach (May 2014)

Technology Focus The oil industry has always been innovative, even under adverse and challenging conditions imposed by the nature of upstream projects. In the past, drilling and completion activities have faced the complexity of the wells and tougher operational and environmental regulations with ingenuity and efficiency. Some prospects considered not feasible 5 years ago are delivering an attractive rate of return to shareholders after the implementation of new techniques. On a day-by- day basis, deepwater, extended-reach, slimhole, and environmentally sensitive drilling projects are reaching the limit of industry capability and pushing for faster evolution in terms of technology, equipment, and procedures. It is not rare anymore to deal with prospects that require pressure ratings of 20,000 psi, temperatures greater than 350°F, and measured depths to 40,000 ft. These challenging project characteristics are leading to a review of conventional techniques and the use of innovative technology for wellbore positioning in a thin oil column, long horizontal drilling and completion legs, extremely low fracture margin in deepwater wells, and downhole tool telemetry. In the case of extended-reach wells (ERWs), the extension of horizontal legs aligned with low gradient fracture in deepwater projects requires an appropriate pressure-management system to mitigate the effect of friction losses at bottomhole conditions. The horizontal legs of multilaterals and ERWs are reaching lengths of 11,000 to 12,000 ft, with corresponding high friction losses that preclude the setting of casing shoes at planned depth in conventional drilling methods because of the equivalent circulating density (ECD). This challenge becomes even more critical when dealing with deepwater environments. Techniques such as the Reelwell drilling method (RDM) and managed-pressure drilling (MPD) have advanced considerably in recent years and are now feasible alternatives to mitigate the ECD and, consequently, are helping the execution of ERWs onshore and offshore. For example, RDM has a unique flow architecture that uses a conventional drillstring combined with an inner string to form a dual-conduit drillstring. This arrangement allows the return fluid containing cuttings to be transported back through the inside of the drillstring, thus eliminating the ECD. RDM also has the advantage of increasing the drilling envelope for ERWs because of torque and drag reduction and optional hydraulic weight on bit caused by a piston-type arrangement at the drillstring. It is difficult to comment about all the new available technologies in this summary, but the following papers address other advancements that are making possible the continuity of drilling and completion activities in a responsible, safe, and feasible way. JPT Recommended additional reading at OnePetro: www.onepetro.org. SPE 166143 Multilateral Wells in the Urucu Field of Western Brazil: Reducing Environmental Impact in the Amazon by Sandro Mendes, Petrobras, et al. OTC 23985 Combining Contemporary and Tested Technologies To Achieve Successful Deepwater Extended-Reach Completions by Ray Brister, Chevron, et al. SPE/IADC 168049 New Rotary- Shouldered Connection Expands the Capability of World-Record ERD Operation by S.R. Sanford, ExxonMobil, et al.

Design optimization of cam and roller follower for improving efficiency of an I.C engine

The existing cams used in internal combustion engines are made in a variety of forms which have a line contact with follower. As line contact between current cam and follower mechanism results in high frictional losses which results in low mechanical efficiency. Hence in this work an attempt is made to change the flat face of follower by using optimization technique, so that the required length of contact is reduced near about to point contact can be achieved to minimize frictional losses and the efficiency of the cam and roller follower will be improve.

A CFD (computational fluid dynamics) based heat transfer and fluid flow analysis of a solar air heater provided with circular transverse wire rib roughness on the absorber plate

This article presents the study of heat transfer and fluid flow processes in an artificially roughened solar air heater by using computational fluid dynamics (CFD). The effects of small diameter of transverse wire rib roughness on heat transfer and fluid flow have been investigated. The Reynolds number, relative roughness pitch (P/e) and relative roughness height (e/D) are chosen as design variables. A two-dimensional CFD simulation is performed using the ANSYS FLUENT 12.1 code. The Renormalization-group (RNG) k–ε model is selected as the most appropriate one. Results are validated by comparing with available experimental results. It is apparent that the turbulence created by small diameter of transverse wire ribs result in greater increase in heat transfer over the duct. However, the use of artificial roughness results in higher friction losses. The present CFD investigation clearly demonstrates that the average Nusselt number and average friction factor increase with increase in the relative roughness height while giving opposite trend with increase in relative roughness pitch. The condition for optimum performance has been determined in term of thermal enhancement factor. A maximum value of thermal enhancement factor has been found to be 1.65 for the range of parameters investigated.

C29 大負荷回転軸用の自成絞り非対称給気静圧ジャーナル軸受の特性(M-OS5-2 フルードパワーの基礎,M-OS5 フルードパワーの基礎と応用,「海を越え,国を越え,世代を超えて!」)

Rotating machineries have problems at bearings to support a rotor such as seismic ACROSS (Accurately Controlled Routinely Operated Signal System) transmitters. The rotor is supported by rolling contact bearings. The bearings in the transmitters, large heat generation occur caused by the high friction loss. In order to solve this problem, externally pressurized gas journal bearings with asymmetrically arranged inherent orifices has been developed for large load rotors. Numerical calculation of this bearing was carried out to obtain the characteristics using Divergence Formulation Method. Three types of bearing models have different placement of feed holes, respectively, i.e., Type A is the conventional symmetric type, which has eight feed holes in the bearing surface with equal distance. Type B is the proposed asymmetrical type, which has six feed holes at loading side of bearing surface and two feed holes at that of counter-loading side. Type C is also the proposed asymmetrical type, which has seven feed holes and one feed hole. The results showed that the proposed asymmetrical bearings have large load capacity and small flow rate compared with the conventional symmetric bearing.

Application of the constant rate of pressure change method to improve jet pump performance

This paper adopts a new method named the constant rate of pressure change (CRPC) to improve the jet pump performance. The main contribution of this method is that the diffuser generates uniform pressure gradient. The performance of the jet pump with new diffusers designed by the CRPC method, obtained by CFD methods, was compared with that of the jet pump with traditional conical diffusers. It is found that the CRPC diffuser produces a linear pressure increase indeed. The higher friction loss and the separation decrease the CRPC diffuser efficiency and then lower the pump efficiency. The pump with shorter throats has higher efficiency at small flow ratio while its efficiency is lower than the original pump at lager flow ratio and the peak efficiency of the pumps with the throat length of 5-6 Dt is higher than that of the pumps with other throat length. When the throat length is less than 4 Dt, the CRPC diffuser efficiency is higher than the conical diffuser. The CRPC method could also be used to design the nozzle and other situations needing the pressure change gradually.

Characteristics of turbulent flow distribution in branch piping system

Flow distribution in branch piping system is affected by flow characteristics and different geometric variations. Most of the flow distribution studies are performed with one-dimensional analysis to yield overall information only. However, detailed analysis is required to find effects of design parameters on the flow distribution. For this aspect, three-dimensional turbulent flow analysis was performed to assess turbulence model performance and effects of upstream pressure and branch pipe geometry. Three different turbulence models of standard k-ɛ model, realizable k-ɛ model and standard k-ω yield similar results, indicating small effects of turbulence models on flow characteristics analysis. Geometric variations include area ratio of main and branch pipes, branch pipe diameter, and connection shape of main and branch pipes. Among these parameters, area ratio and branch diameter and shape show strong effect on flow distribution due to high friction and minor loss. Uniform flow distribution is one of common requirements in the branch piping system and this can be achieved with rather high total loss design.

Design and exergy analysis of solar roofs: A viable solution with esthetic appeal to collect solar heat

Application of a pipeline at the lower side of copper roofs to use them as solar collectors was investigated. An optimized module capable of converting a wide fraction of solar radiation into heat, and at the same time preserving the esthetic quality of the roof, was designed. Exergy analysis, which allowed quantification of the value of collected energy, including temperature effects and friction losses of the heated fluid, was applied. The results allowed suggestion of a rectangular module with four ducts having rectangular cross section. The basic proposed version was the Unglazed Solar Roof (USR), which showed interesting levels of efficiency (30–60%) over the entire working field. Even the glazed version (GSR) was introduced and analyzed, but its performance showed significant improvements only when extensively used during cold seasons. Compared with a commercial reference flat plate collector (FPC) model, the efficiency of USR is reduced by 20% over the whole operating field. The curves of exergy efficiency showed an optimization point at temperatures well above those in flat plate collectors. For this reason, exergy analysis applied to solar collectors is worth only (I) to evaluate the lower limits in cross sectional area of the ducts, to avoid too narrow height or width which may lead to very high friction losses and (II) to manage the flowrate to extract the highest amount of exergy during the variable environmental and fluid conditions. Integration with a domestic hot water system showed a potential achievement of a yearly solar fraction of 53% with USR and 60% with GSR. Considering that both systems are fully integrated within the roof cover, differently from standard collectors, the esthetic appeal of the building roof would not be affected.

Design Optimization of Cam & Follower Mechanism of an Internal Combustion Engine for Improving the Engine Efficiency

The current cam and follower mechanism in four stroke internal combustion engine employs a flat follower. In this work an attempt is made to change the flat face of follower to a curved face follower, so that the required point contact can be achieved. As line contact between existing cam and follower mechanism results in high frictional losses which results in low mechanical efficiency. It is observed that the frequency of vibration in the existing and modified cam and follower mechanism remains almost same. The finite element approach is used to perform the analysis.

Flow Pattern and Pressure Drop in Highly Concentrated Slurries Transportation Pipelines

Flow pattern and pressure drop in highly concentrated slurries transportation pipelines were discussed. The particles are settling, and tend to settle down to the bottom of pipes due to the action of gravity force forming different flow patterns which can be indicated by particle concentration profile. Three distinct flow patterns can be observed for different particle size distribution at different velocities: fully stratified, partially stratified and fully suspended flow patterns. As for pressure drop, it is well known that pressure drops in pipeline flows of slurries are strongly dependent on the flow pattern developed in a pipeline. Furthermore, fine particles suspended in water make the water more viscous, and increase the friction. In case of coarse particles, having larger volume, they have the tendency to contact with the pipe wall and with the other coarse particles more times, which increase the friction of flow. Meanwhile, coarse particles are lifted by the pressure difference generated as they rotate in the liquid preventing the coarse particles from settling down which results in less friction. The mixture of particles of different sizes is helpful to reduce pressure drop in pipeline flow slurries. Narrow grading particles tend to have high frictional losses, while broad grading particles have low frictional losses at high concentrations.

A novel revolving vane compressor with a fixed-vane

This paper presents design improvements of a Revolving Vane (RV) compressor which significantly reduce the frictional losses. The original RV compressor has a vane that swivels during the operation. Though in general, the frictional losses of the RV compressor are significantly lower than most currently available rotary compressors, this swivel vane design has a disadvantage of relatively high vane side friction loss. The latter is caused by a high vane-side and slot contact force due to a high gas pressure differential force across the vane. In this paper, a new design concept has been introduced to totally eliminate the vane side friction loss caused by the gas pressure differential force across the vane. This is achieved by rigidly fixes the vane onto the rotor or the cylinder. This new design yielded two possible variants, each reduces the frictional losses by 18% and 41% and improves the mechanical efficiency from 93% to 94% and 96% respectively. In this paper, details analysis on the new design that leads to the improvement in performance are presented and shown. The analysis also reveals that the design with the highest mechanical efficiency comes with a small price of a higher instantaneous peak torque requirement.

Blade optimization design and performance investigations of an ultra-low specific speed centrifugal blower

The ultra-low specific speed centrifugal blower is widely used in energy industries due to its features such as low flow rate, high pressure and low manufacturing cost. However, the width-to-diameter ratio of the above blower becomes relatively small to satisfy the needed operation condition and its performances are considerably degraded as a result of relatively high leakage, disc friction and passage friction loss consequently. The purpose of this paper is to improve its performance through the optimization design of the blade’s profile properly. Based on artificial neural networks (ANN) and hierarchical fair competition genetic algorithms with dynamic niche (HFCDN-GAs), the optimization design approach is established. By conjoining Bezier parameterization and FINE/TURBO solver, the optimized blade is designed by adjusting the profile gradually. An industrial ultra-low specific speed centrifugal blower with parallel hub and shroud has been selected as a reference case for optimization design. The performance investigations of the centrifugal blowers with different types of blades are conducted. The conclusions of the performance improvement of the optimized blade provide positive evidences in the application of the optimization design of the above blower blade.

Earthquake Faulting Effects on Buried Pipelines – Case History and Centrifuge Study

Permanent ground deformation (PGD) is one of the most damaging hazards for continuous buried lifelines. This hazard is especially severe when the PGD results in net compression in the pipe. In that case, buckling of pipe material can occur. If buckling is moderate, deformation of the pipe cross-section can lead to flow restriction and high friction losses, and eventually require line replacement. If buckling is severe, high localized strains can lead to pipe rupture, loss of contents, and possible pollution of surrounding soil. In this article, centrifuge tests of buried pipelines subject to abrupt ground failure in the form of surface faulting are presented. The fault movement results in mostly compression in the pipe. The test results are compared with a case history of pipe failure in the 1999 Izmit, Turkey earthquake and also with the results from the centrifuge tests which result in net tension in the pipe. The experimental setup, procedures, and instrumentation are described in detail. Suggestions for design practice are offered based on the analysis of results from both the 1999 Izmit case history and the centrifuge modeling.

Adsorption of methyl tertiary butyl ether on granular zeolites: Batch and column studies

Methyl tertiary butyl ether (MTBE) has been shown to be readily removed from water with powdered zeolites, but the passage of water through fixed-beds of very small powdered zeolites produces high friction losses not encountered in flow through larger sized granular materials. In this study, equilibrium and kinetic adsorption of MTBE onto granular zeolites, a coconut shell granular activated carbon (CS-1240), and a commercial carbon adsorbent (CCA) sample was evaluated. In addition, the effect of natural organic matter (NOM) on MTBE adsorption was evaluated. Batch adsorption experiments determined that ZSM-5 was the most effective granular zeolite for MTBE adsorption. Further equilibrium and kinetic experiments verified that granular ZSM-5 is superior to CS-1240 and CCA in removing MTBE from water. No competitive adsorption effects between NOM and MTBE were observed for adsorption to granular ZSM-5 or CS-1240, however there was competition between NOM and MTBE for adsorption onto the CCA granules. Fixed-bed adsorption experiments for longer run times were performed using granular ZSM-5. The bed depth service time model (BDST) was used to analyze the breakthrough data.

Single Channel Hybrid FES Gait Assist System

Loss of mobility due to lower limb paralysis is common consequence of thoracic level spinal cord injury (SCI). In the US there are approximately 253,000 persons with SCI. The wheelchair is the most common form of mobility for individuals with paraplegia but there remains a need for assistive technology that can enable paraplegics to walk and reach in the periphery of wheelchair. A new concept is presented that combines functional electrical stimulation (FES) with an energy storing orthosis (ESO) that contains a fluid power system to store and transfer energy during the gait cycle. Elastic energy storage elements on the orthosis hip and knee joints hold the leg in a flexed equilibrium position. Stimulation of the quadriceps extends the knee, placing excess energy in both the equilibrium spring and an energy transfer element. The stored energy is transferred to the hip where it is discharged and used to extend the hip against its equilibrium spring which also aids in forward progression. A new step is initiated by releasing the hip and knee joints from the straight leg position to the flexed position. The concept is realized using gas springs and pneumatic cylinders. Gas springs act as flexed energy storage elements. Lower air cylinder and the tubing acts as an accumulator and the upper cylinder acts as hip joint actuator. The system uses 2 way proportional solenoid actuated pneumatic valves for control during extension. The conceptual design of the ESO was completed and implemented in a dynamic simulation model (MSC ADAMS) and in a benchtop prototype for engineering measurements. Of the 14 joules of energy available from quadriceps, 8.9 joules of energy is utilized for doing work against springs and inertial forces; 5.4 joules is stored in pneumatic system; of which 1.4 joules is required for hip extensions and the remaining will be used for forward progression. No studies were conducted with human subjects. A hydraulic fluid power system was investigated for better control and braking possibilities but was not adopted because of difficulities in accumulator design and high fluid friction losses. A Matlab code was used to calculate the torques required at joints to support standing. Commerical braces are being used for improved user comfort. A wrap spring brake is being designed to maintain standing posture without FES or any active energy input. Technical feasibility of the ESO prototype will be evaluated using two subjects with paraplegia.