Maximum Friction Research Articles

Efficiency analysis of thermosyphon solar flat plate collector with low mass concentrations of ND–Co3O4 hybrid nanofluids: an experimental study

In the present study, the thermal efficiency, convective heat transfer and friction factor analysis are investigated for a flat plate solar collector with thermosyphon (natural circulation) system using water and nanodiamond–cobalt oxide hybrid nanofluids as the working fluids. The nanodiamond–cobalt oxide hybrid nanoparticles were synthesized using in situ growth and chemical co-precipitation method and characterized using X-ray diffraction, transmission electron microscope and vibrating sample magnetometer. The investigations were performed at different volume flow rates 0.56–1.35 L min−1 and various mass concentrations of 0.05–0.15%. The thermal conductivity and viscosity of nanofluids were measured experimentally at various mass concentrations and temperatures. Due to the augmented thermo-physical properties of hybrid nanofluids, the collector reached higher coefficient of heat transfer as well as improved thermal efficiency than the water data. Maximum thermal conductivity and viscosity enhancements are found to be 15.71% and 45.83% at particle loadings of 0.15% mass concentration and at a temperature of 60 °C. Results show the Nusselt number enhancement of 0.15% mass concentration of hybrid nanofluid is 21.23% with maximum friction factor penalty of 1.13 times against water data. The collector thermal efficiency is found to 59% for the case of 0.15% mass concentration of hybrid nanofluid, where the thermal efficiency of water is 48%. The empirical correlations were developed for Nusselt number and friction factor for collector with hybrid nanofluids within the deviation of ± 3%.

Novel additive of PTFE@SiO2 core-shell nanoparticles with superior water lubricating properties

In order to solve the problems of poor dispersibility and wettability, as well as unsatisfactory wear resistance and load capacity of polytetrafluoroethylene (PTFE) as water lubricating additive, a new type of PTFE@silica (PTFE@SiO2) core-shell nanoparticles was prepared by encapsulating SiO2 layer on the surface of PTFE via chemical bonding. Electron microscope analysis showed that the synthesized particles had well-defined core-shell morphology. Special double/multi-core structure and a reduced thickness of the intermediate shell were found, and the formation mechanisms were also explored in detail. The water contact angle measurement proved that the wettability of PTFE could be greatly enhanced by coating SiO2 layer. The friction tests were performed to investigate the water lubrication properties of PTFE@SiO2 additive, the results indicated that the core-shell PTFE@SiO2 nanoparticles possessed the superior tribological properties, and the maximum friction coefficient and wear volume were respectively decreased by 75% and 99% when compared with pure water and water with PTFE/SiO2. Based on the analysis of worn surface, it was believed that the existence of core-shell structure and the formation of robust transfer film were the key to its excellent performance, and a possible lubrication mechanism was also proposed.

Synergistic effect of surface texturing and coating on the friction between piston ring and cylinder liner contact

It is well-established that the piston ring/cylinder liner (PRCL) contact is the major contributor to friction losses in the internal combustion engine. While numerous studies have evaluated the individual effect of surface engineering techniques like surface texturing, coating, on the PRCL system, however, its combined effect has not been thoroughly explored. In this work, the combined effect of surface coating and texturing on the frictional properties of piston ring/cylinder liner (PRCL) contact in different lubrication regimes has been simulated using a reciprocating tribometer rig. A cylinder liner of cast iron material and three different types of piston ring coatings, namely Diamond-like-carbon (DLC), chrome, and moly-chrome-ceramic (MCC) were used as samples. Under all lubrication regimes, the coated samples with texturing had better frictional performance compared to non-textured coated samples. The maximum friction reduction was observed for textured DLC coated samples under boundary lubrication regime. This behaviour was proposed to be a result of the synergistic effect of graphitisation and texturing.

Analysis of boundary friction effect on the homogenization process of compacted bentonite/claystone mixture with technological voids upon hydration

Pre-compacted MX80 bentonite/Callovo-Oxfordian (COx) claystone mixture has been proposed to backfill and seal the underground galleries for radioactive waste disposal in France. While emplacing these pre-compacted blocks, technological voids are created between the blocks and the host rock and among the blocks themselves. It is expected that homogenization process will take place over time for the structure constructed with pre-compacted blocks upon hydration. This study investigated the boundary friction effect on such a process. Results showed that after the filling of technological voids, the soil far from the technological voids would swell further, while those near the voids would be compressed under the welling pressure generated by the soil behind, resulting in an increase in homogeneity in terms of dry density distribution. However, this homogenization process would stop after a certain time. Further examination showed that the homogenization process ended when the maximum boundary friction force became equal to or higher than the vector sum of swelling forces in the radial direction. Based on the force equilibrium and the mass conservation, the final dry density distribution was estimated. Comparison between the estimation and the measurement showed a good agreement, indicating the relevance of the identified mechanism related to boundary friction.

Corrosion and wear properties of micro-arc oxidation treated Ti6Al4V alloy prepared by selective electron beam melting

Abstract In order to analyze the effect of voltage during micro-arc oxidation (MAO) on corrosion and wear properties of Ti6Al4V (TC4), the MAO technology was employed to treat TC4 samples fabricated by selective electron beam melting (SEBM) at the voltages of 400, 420 and 450 V. The results show that the metastable anatase phase gradually transforms to rutile phase with oxidation time and temperature increasing. The surface morphology of coating contains numerous micropores with uniform size distribution. Cracks and pores over 10 μm are found on MAO-TC4 sample with applied voltage of 450 V. The thickness of MAO coating is positively correlated with the voltage. The corrosion resistance and wear resistance are related to phase composition, micropore size distribution on the surface and film thickness. When the voltage is 420 V, the coating shows the smallest corrosion current density (0.960×10−7 A/cm2) and the largest resistance (7.17×105 Ω·cm2). Under the same load condition, the coating exhibits larger friction coefficient and wear loss than the TC4 substrate. With the increase of voltage, the wear mechanism of the coating changes from abrasive wear to adhesive wear, and the adhesive wear is intensified at applied voltage of 450 V, with a maximum friction coefficient of 0.821.

Structural, morphological, optical and mechanical studies of annealed ZnO nano particles

The structural, morphological, optical and mechanical properties of Zinc oxide (ZnO) nanoparticles annealed at different temperatures from 500 °C to 1000 °C with a step size of 100 °C were synthesized from Sol-Gel method. The X-ray diffraction study revealed that ZnO has hexagonal Wurtzite structure. Scanning Electron Microscope(SEM) images of the studied materials possess spherical morphology with induced porosity due to change in annealing temperature. The computed size of nanoparticles from Transmission Electron Microscopy (TEM) was 21 nm. The UV–Visible Spectroscopy revealed that the band gap decreased with increase of the temperature from 3.05eV to 2.82eV. Photoluminescence (PL) spectrum of ZnO nanoparticles shows that oxygen vacancy related defects increased as the temperature increases from 500 °C to 800 °C and decreased beyond 800 °C. The wear resistance of ZnO nanoparticles is found to increase with increase of temperature owing to the generation of oxygen vacancies. The maximum friction coefficient was assigned to largest grain size.

Numerical Analysis of Energy Converter for Wave Energy Power Generation-Pendulum System

The wave energy power generation-pendulum system (WEPG-PS) is a four-wheeled instrument designed to convert wave power into electric energy. The first wheel is connected to the pendulum by a double freewheel, the second and third are ordinary wheels, while the fourth is a converter component that is axially connected to the electric generator. This design used the Euler-Lagrange formalism and Runge-Kutta method to examine an ideal dimension and determine the numerical solution of the equation of motion related to the rotation speed of the wheels. The result showed that the WEPG-PS' converter system rotated properly when its mass, length, and moment of inertia are 10 kg, 2.0 m, and 0.25 kgm2, respectively. This is in addition to when the radius of the first, second, third, and fourth wheels are 0.5, 0.4, 0.2, and 0.01 m, with inertia values of 0.005, 0.004, 0.003, and 0.1 kgm2. The converter system has the ability to rotate the fourth wheel, which acts as the handle of an electric generator at an angular frequency of approximately 500 - 600 rad/s. The converter system is optimally rotated when driven by a minimum force of 5 N and maximum friction of 0.05. Therefore, the system is used to generate electricity at an amplitude of 0.3 - 0.61 m, 220 V with 50 Hz. Besides, the lower rotation speed and frequency of the energy converter of the WEPG-PS (300 rad/s) and induction generator (50 Hz) were able to generate electric power of 7.5 kW.

Behavior of single pile and pile groups in consolidating clay

As the pile group is commonly in use but the effect of consolidation times on the distribution of negative skin friction and drag force along the shaft of each pile in pile groups is still not well defined and studied. This paper presents the three-dimensional (3D) numerical analysis to study the behavior of a single pile and piles group consist of 3x3 piles embedded in a consolidated clay. Three-dimensional numerical simulation is carried out using Abaqus, a finite element software. Single circular piles and 3×3 circular piles in rectangular piles group with a spacing of 2.5D has chosen, where D is the diameter of circular pile. Based on the analyses, it is found that the location of the neutral plane is significantly influenced by the consolidation times. Results of this study showed that the maximum negative skin friction at 90 % degree of consolidations developed along the shaft of corner, side, and central pile compared with a single pile are 69%, 61%, and 45%, respectively.

Heat Transfer Improvement in a Double Backward-Facing Expanding Channel Using Different Working Fluids

This paper reports a numerical study on heat transfer improvement in a double backward-facing expanding channel using different convectional fluids. A finite volume method with the k-ε standard model is used to investigate the effects of step, Reynolds number and type of liquid on heat transfer enhancement. Three types of conventional fluids (water, ammonia liquid and ethylene glycol) with Reynolds numbers varying from 98.5 to 512 and three cases for different step heights at a constant heat flux (q = 2000 W/m2) are examined. The top wall of the passage and the bottom wall of the upstream section are adiabatic, while the walls of both the first and second steps downstream are heated. The results show that the local Nusselt number rises with the augmentation of the Reynolds number, and the critical effects are seen in the entrance area of the first and second steps. The maximum average Nusselt number, which represents the thermal performance, can be seen clearly in case 1 for EG in comparison to water and ammonia. Due to the expanding of the passage, separation flow is generated, which causes a rapid increment in the local skin friction coefficient, especially at the first and second steps of the downstream section for water, ammonia liquid and EG. The maximum skin friction coefficient is detected in case 1 for water with Re = 512. Trends of velocities for positions (X/H1 = 2.01, X/H2 = 2.51) at the first and second steps for all the studied cases with different types of convectional fluids are indicated in this paper. The presented findings also include the contour of velocity, which shows the recirculation zones at the first and second steps to demonstrate the improvement in the thermal performance.

Numerical study of ultimate bearing capacity of rectangular footing on layered sand

Purpose: The purpose of this study is to investigate the ultimate bearing capacity of the rectangular footing resting over layered sand using finite element method. Design/methodology/approach: Finite element analysis was used to investigate the dimensionless ultimate bearing capacity of the rectangular footing resting on a limited thickness of upper dense sand layer overlying limitless thickness of lower loose sand layer. The friction angle of the upper dense sand layer was varied from 41° to 46° whereas for the lower loose sand layer it was varied from 31° to 36°. Findings: The results reveal that the dimensionless ultimate bearing capacity was found to increase up to an H/W ratio of about 1.75 beyond which the increase was marginal. The results further reveal that the dimensionless ultimate bearing capacity was the maximum for the upper dense and lower loose sand friction angles of 46° and 36°, while it was the lowest for the upper dense and lower loose sands corresponding to the friction angle of 41° and 31°. For H/W = 0.5 and 2, the dimensionless bearing capacity decreases with the increase in the L/W ratio from 0.5 to 6 beyond which the dimensionless ultimate bearing capacity remains constant for all combinations of parameters. The results were presented in nondimensional manner and compared with the previous studies available in literature. Research limitations/implications: The analysis is performed using a ABAQUS 2017 software. The limitation of this study is that only finite element analysis is performed without conducting any experiments in the laboratory. Further the study is conducted only for the vertical loading. Practical implications: This proposed numerical study can be used to predict the ultimate bearing capacity of the rectangular footing resting on layered sand. Originality/value: The present study gives idea about the ultimate bearing capacity of rectangular footing when placed on layered sand (dense sand over loose sand) as well as the effect of thickness of top dense sand layer on the ultimate bearing capacity. The findings could be used to calculate the ultimate bearing capacity of the rectangular footing on layered sand.

Efficiency, energy and economic analysis of twisted tape inserts in a thermosyphon solar flat plate collector with Cu nanofluids

Heat transfer, friction factor and efficiency of a thermosyphon type flat plate collector with and without twisted tape inserts were analyzed experimentally. Water based Cu nanofluids were used as the absorber fluid to receive the heat from solar radiation into the flat plate collector. The experiments were conducted for volume concentrations of 0.1% and 0.3% and twist ratios of H/D = 5, 10 and 15. Results reveal that the heat transfer rate and efficiency of nanofluids increase with the increase of particle volume concentrations. The Nusselt number of 0.3% nanofluid is enhanced up to 20.46%, and it is further enhanced up to 46.90% with twisted tape insert of H/D = 5 with a maximum friction factor penalty of 1.477-times compared to plain collector. The efficiency of the solar collector with water is 52% and it is enhanced to 58% for 0.3% nanofluid, whereas it is further enhanced to 64% for 0.3% nanofluid with twisted tape insert of H/D = 5. Empirical correlations are proposed based on the experimental data for the friction factor and Nusselt number with a standard deviation of less than ±6.5%. The study indicates that for 100 units of solar flat plate collector the use of 0.1% and 0.3% Cu nanofluids leads to weight savings of 284 kg and 567 kg, respectively. The total weight of 100 units of solar flat plate collector is further saved by 767 kg, 1050 kg and 1250 kg for 0.3% nanofluid with twisted tape inserts of H/D = 15, H/D = 10 and H/D = 5, respectively. The collector cost is reduced by 5.66% and 11.33% for 0.1% and 0.3% nanofluids, and it is further reduced to 25% for 0.3% nanofluid with a twisted tape insert of H/D = 5.

Excellent lubrication properties of 3D printed ceramic bionic structures

Three-dimensional (3D) printed ceramic structures loaded with lubricating materials could exhibit excellent lubrication effect. In this paper, various bionic petal structures and tree frog toe end structure of 3D-printed alumina (Al2O3) ceramic are designed to study the effects of lubricating structures and tungsten disulfide (WS2) solid lubricant on the friction performance. Compared to the friction properties of various bionic lubricating structures loaded with WS2, the bionic small petal structure with hexagonal arrangement exhibits a lowest friction coefficient of 0.411 and moderate wear resistance due to more storage of lubricant and debris. The maximum friction coefficient of 1.177 and optimum anti-wear ability are offered by the bionic tree frog toe end structure. In particular, the friction coefficient of the bionic petal lubricating structures loaded with WS2 are lower than that of blank printed Al2O3 ceramic, indicating that the lubricating structures provide positive effect on improving friction performance. Therefore, the 3D printed ceramic lubricating structures provided a novel strategy for achieving lubrication in advanced applications.

Experimental and numerical studies of positive texture effect on friction reduction of sliding contact under mixed lubrication

Textured surfaces have been remarkable in improving the frictional performance of sliding contacts, particularly at instances such as boundary or mixed lubrication regimes. This article reports the results of an experimental and numerical study carried out by introducing surface textures in the form of protrusions to investigate its effects on friction performance under a mixed lubrication regime. The surface textures produced by the chemical etching process are tested on the pin on disc test rig by varying area density and height of the texture. In numerical simulation, the modified Reynolds equation (Patir–Cheng flow model) and asperity contact model (Greenwood–Tripp model) are solved for hydrodynamic and asperity pressures, respectively. The results indicate that the experimental measurements are qualitatively in good agreement with numerical predictions. Furthermore, the simulations are performed for different texture shapes by varying texture area density, height, and sliding velocity. The results depict that a maximum friction reduction of 87% with elliptical textures compared to the un-textured case.

Study on a novel chemical slurry and the mechanical behavior of cemented sand

To enhance the strength and stability of the fine sandy soil in underground engineering construction, a novel chemical slurry was studied. Series of laboratory tests were performed to determine the effect of each component on the rheological properties of grout (e.g. viscosity, gel time and plastic strength). The relationship of the penetrability of grout in sand with different densities was explored by the falling-head permeability test. To assess the performance of cementation, the cemented sand specimens were prepared in the laboratory by hand mixing of grout and loose sand. A range of unconfined uniaxial compression tests, split tensile tests and direct shear tests were performed to determine the effect of several vital factors (e.g. the curing time, grout mix ratio and water content) on the mechanical properties of the cemented sand. As revealed from the results of the experiment, the slurry pertains to Newton fluid in the initial stage, which exhibits lower initial viscosity (2 mPa·s), controllable gel time (5–20 min) and higher plastic strength (35 kPa). In terms of the cemented sand, the maximal cohesion and friction angle is 403.8 kPa and 65°; the biggest compressive strength and tensile strength is 3.68 and 0.37 MPa. The slurry can enhance the strength and stiffness of the loose sand significantly, whereas the degree of improvement is dependent of the grout mix ratio and water content of cemented sand.

Effect of the matrix structure on vermicular graphite cast iron properties

Abstract Vermicular graphite cast iron (VGCI) prepared via the sandwich process was treated by annealing, and the microstructure and the mechanical and damping properties before and after the annealing treatment were studied. The graphite size, distribution and morphology did not change significantly after annealing. However, the matrix transformed from ferrite + pearlite to ferrite after annealing, the dislocation density decreased significantly, and the interfacial stacking faults between the matrix and graphite disappeared. The annealing treatment reduced the tensile strength by >12%, but increased the strain-to-fracture value to two times that of the as-cast sample. The damping properties varied with temperature with obvious S-K peaks and Ge peaks. The maximum internal friction changed from 0.023 (as-cast) to 0.011 (post-anneal).

The Influence of Convective Momentum Transport and Vertical Wind Shear on the Evolution of a Cold Air Outbreak

AbstractTo study the influence of convective momentum transport (CMT) on wind, boundary layer and cloud evolution in a marine cold air outbreak (CAO) we use large‐eddy simulations subject to different baroclinicity (wind shear) but similar surface forcing. The simulated domain is large enough, km2), to develop typical mesoscale cellular convective structures. We find that a maximum friction induced by momentum transport (MT) locates in the cloud layer for an increase of geostrophic wind with height (forward shear, FW) and near the surface for a decrease of wind with height (backward shear, BW). Although the total MT always acts as a friction, the interaction of friction‐induced cross‐isobaric flow with the Coriolis force can develop supergeostrophic winds near the surface (FW) or in the cloud layer (BW). The contribution of convection to MT is evaluated by decomposing the momentum flux by column water vapor and eddy size, revealing that CMT acts to accelerate subcloud layer winds under FW shear and that mesoscale circulations contribute significantly to MT for this horizontal resolution (250 m), even if small‐scale eddies are nonnegligible and likely more important as resolution increases. Under FW shear, a deeper boundary layer and faster cloud transition are simulated, because MT acts to increase surface fluxes and wind shear enhances turbulent mixing across cloud tops. Our results show that the coupling between winds and convection is crucial for a range of problems, from CAO lifetime and cloud transitions to ocean heat loss and near‐surface wind variability.

Experimental investigations on the influence of notch definition on the pullout performance of circumferentially notched z-pins

This paper presents the results of experimental investigations on the pullout properties of circumferentially notched z-pins in carbon-fiber/epoxy prepreg laminates with unidirectional (UD) and quasi-isotropic (QI) fiber orientation. Four different notch depths between 10 and 25 μm and three different notch distances between 100 and 300 μm were investigated to determine the influence of notches with rectangular shape incorporated at the pin surface on the characteristic z-pin bridging forces and the resulting pullout energies. At UD-laminates the highest increase of the maximum debonding force Pd and maximum friction force Pf could be determined with notched z-pins with a notch depth of 10 μm and a notch distance of 100 μm. This is also reflected in the specific pullout energy, which shows an increase of 40%, compared to samples with unnotched pins. For QI-laminates, the increases are higher and can be quantified with an increase in pullout energy of 55% at a notch depth of 15 μm. A variation of the notch distance at a constant notch depth of 20 μm shows linear dependencies of the pullout energy and achieves improvements of up to 29% for UD-laminates and 42% for QI-laminates at the highest notch distance of 300 μm.

Identifying dynamic equilibrium of an undeveloped alluvial stream by extremal hypotheses

The indeterminate channel problem arises from uncertainty in finding a closure relation for alluvial channels created by self-organizing erosional and depositional processes. Extremal hypotheses have been proposed as one potential approach to closing the system of governing equations for alluvial channels. Many different extremal hypotheses have been presented, but no substantive evidence has been developed to select which hypothesis may be most appropriate for natural alluvial river systems. This paper evaluates the ability of ten extremal hypotheses to identify dynamic equilibrium across a geomorphic gradient in the remote and undeveloped mid-latitude watershed of Rio Murta, Chile. This study (a) introduces extremal hypotheses, (b) describes the field site and geomorphic conditions, and (c) examines which extremal hypotheses are supported by the field data in identifying the evolutionary trend toward dynamic-equilibrium. The extremal hypotheses that identified dynamic equilibrium within the geomorphic gradient in the field are: (1) minimum kinetic energy, (2) minimum specific stream power, (3) maximum friction factor, and (4) maximum total friction factor, which collectively support minimizing kinetic energy of the system.

Reinforcement of the anchor balloon system in percutaneous coronary intervention: an in vitro assessment

We evaluated the factors that increase the maximum static friction force between the anchoring balloon and the vessel wall. The anchor technique in percutaneous coronary intervention (PCI) may be better supported by a guiding catheter. However, in some cases, the anchor balloon does not perform optimally due to slippage within the anchoring vessel. Furthermore, the optimal procedure for balloon anchoring remains unknown. We evaluated the maximum static friction force of the anchor balloon via in vitro assessments using a simulated vessel model and coronary balloons. The simulated vessel model was composed of polytetrafluoroethylene, and its inner diameter was 1.5mm. The various-sized balloons (diameter: 1.5mm, 1.75mm, and 2.0mm; length: 10mm and 15mm) were inflated within the simulated vessel at various atmospheres. The maximum static friction force was measured by pulling on the balloon catheter shaft using 10-g weights. We performed the same experiment with a jailing 0.014″ wire under the anchoring balloon. Evaluated wires included a silicon coating coil wire, hydrophilic coating coil wire, polymer-coated non-tapering wire, and polymer-coated tapered wire. The maximum static friction force between the anchoring balloon and the simulated vessel increased with an increase in inflation pressure and balloon length. However, increasing the balloon diameter was not effective. The jailing 0.014″ wire, particularly coil wire, was effective in increasing the maximum static friction force of the anchor balloon. A longer balloon, higher inflation pressure, and jailing coil wire could reinforce the anchor balloon system.

Effect of the matrix structure on vermicular graphite cast iron properties

Abstract Vermicular graphite cast iron (VGCI) prepared via the sandwich process was treated by annealing, and the microstructure and the mechanical and damping properties before and after the annealing treatment were studied. The graphite size, distribution and morphology did not change significantly after annealing. However, the matrix transformed from ferrite + pearlite to ferrite after annealing, the dislocation density decreased significantly, and the interfacial stacking faults between the matrix and graphite disappeared. The annealing treatment reduced the tensile strength by >12%, but increased the strain-to-fracture value to two times that of the as-cast sample. The damping properties varied with temperature with obvious S-K peaks and Ge peaks. The maximum internal friction changed from 0.023 (as-cast) to 0.011 (post-anneal).