Friction Layer Research Articles

Comparison Analysis on the Hydraulic Performance and Flow Characteristics on a Reactor Coolant Pump Under Rated Operating Condition Between Lead–Bismuth Eutectic and Water Mediums

Abstract Advanced Generation IV nuclear reactors aim to enhance the sustainability, passive safety, reliability, and economic efficiency of reactor operations. Within that, the reactor coolant pump is a critical component in the reactor's cooling system, due to the unique characteristics of the transported medium, posing challenges for engineering applications. This study focuses on a mixed-flow nuclear reactor coolant pump, indicating that significant differences in hydraulic performance and flow characteristics arise due to the varying flow Reynolds numbers under identical operating conditions for the two mediums. Research employing quantitative analysis of boundary layer friction losses and flow separation-induced flow blockage elucidates the origins of hydraulic performance differences. Subsequent studies focusing on the flow characteristics within the impeller reveal that, while the flow patterns inside the impeller show no fundamental differences, an increase in Reynolds number intensifies flow slippage phenomenon, partially diminishing the impeller's work capability. Analysis in static components indicates that the stronger centrifugal forces lead to increased nonuniformity in flow distribution within the guide vanes and an amplified wake phenomenon within the outlet pipe.

Atomic structures and electronic properties of different contact surfaces for C x F y -SiO2 triboelectric nanogenerator based on first-principles investigations.

Modification of the dielectric friction layer materials is an ideal way to enhance the output performance of a triboelectric nanogenerator (TENG), but current research mostly focuses on the metal-polymer or metal-SiO2 materials. In this work, we constructed different TENG models based on polymer C x F y -SiO2 electret materials, and the electronic properties of the different contact surfaces were investigated using first principles. We found that the charge transfer in C x F y -SiO2 materials occurred only at the contact interface, and it was partially affected by the terminal atoms near the SiO2 interface. The charge transfer of the polymer C x F y that was in contact with the O-terminated SiO2 achieved a more satisfactory effect. Among them, the II-C3F6-O model exhibited the highest amount of charge transfer because of the better hybridization of II-C3F6 with the O atoms of SiO2 layer. Our study showed that instead of adding different types of dielectric friction layers, varying the configurations of the same types of dielectric friction layers is an alternative way to regulate charge transfer. Furthermore, this strategy could provide new ideas for enhancing the performance of TENGs.

Effect of Ni–Bi Alloying on the Microstructure and Self‐Lubricating Properties of CoCrNi‐Based Coatings Across a Wide Temperature Range

This study investigates the use of bismuth (Bi) as a lubricating additive in laser cladding Co‐based composite coatings, addressing the issue of Bi segregation and agglomeration through Ni–Bi alloying. The microstructure, mechanical properties, and tribological properties of composite coatings with varying Ni–Bi contents are systematically evaluated at temperatures between 30 and 800 °C. Analysis reveals that Ni and Bi elemental powders are successfully alloyed to form BiNi and Bi3Ni intermetallic compounds following vacuum sintering. Incorporation of Ni–Bi alloying powder significantly enhances the friction coefficient and wear rates of the composite coating across the temperature range. Adhesive wear and abrasive wear are identified as primary wear mechanisms. Notably, the formation of BiNi, multiple oxides, and Bi16CrO27 compounds on the surface of the 85:15 (at%) Bi:Ni composite coating at 600 °C created a self‐lubricating friction layer, synergistically reducing friction. Consequently, compared to Co‐based alloy coatings without Ni–Bi alloying, the composite coating exhibited a three‐fold reduction in friction coefficient and a two‐order‐of‐magnitude improvement in wear rate, demonstrating exceptional tribological properties.

Synergistic effects of porous ferroelectric friction layer and intermediate layers for remarkable performance enhancement of triboelectric nanogenerator

Synergistic effects of porous ferroelectric friction layer and intermediate layers for remarkable performance enhancement of triboelectric nanogenerator

Luminescent Tactile Sensor System for Robots: Enhancing Human-Computer Interaction in Complex Dark Environments.

In order to achieve interaction and collaboration with humans, robots need to have the ability for tactile perception of simulating human. Traditional methods use electrically connected sensors with complex arrays, leading to intricate wiring, high manufacturing costs, and demanding current environments. A flexible sensor with simple structure, easy preparation process, and low cost based on triboluminescence effect is proposed in this paper, which avoids the complex array and wiring of traditional sensors. The study discusses the relationship between luminescent intensity and factors such as luminescent particle content, luminescent layer thickness, encapsulation layer thickness, and friction layer thickness. It also analyzes the mechanism of luminescence. A micro charge-coupled device is configured for the luminescent unit to collect optical information and is integrated with the robot's manipulator for testing. A simple sensing system is constructed to demonstrate environmental perception, acquiring, and feeding back shape and size information of contact objects in the dark. The system successfully identifies and judges target objects in complex dark environments, offering insights for applications such as unmanned assembly lines. It overcomes the challenge of intricate electrical connections, paving new avenues for intelligent object recognition research in human-computer interaction.

Preparation and Mechanical Properties of (TiCrZrNb)C4-SiC Multiphase High-Entropy Ceramics.

Five carbide powders, TiC, Cr3C2, ZrC, NbC and SiC, were selected as raw materials and mixed by dry or wet milling. Then (TiCrZrNb)C4-SiC multiphase ceramics were successfully prepared by spark plasma sintering (SPS) at 1900 °C, using D-HECs-1900 (dry milling method) and W-HECs-1900 (wet milling method), respectively. In this study, the effects of the ball milling method on the microstructure and mechanical properties of the multiphase high-entropy ceramics were systematically investigated. Compared to D-HECs-1900, W-HECs-1900 has a more uniform elemental distribution and smaller grain size, with an average grain size of 1.8 μm, a higher Vickers hardness HV0.1 = 2178.41 kg/mm2 and a higher fracture toughness of KIC = 4.42 MPa·m1/2. W-HECs-1900 also shows better wear resistance with a wear rate 1.01 × 10-8 mm3·N-1·m-1. The oxide friction layer formed during friction is beneficial for reducing frictional wear, making W-HECs-1900 a potential wear-resistant material.

Liquid-Solid Triboelectric Nanogenerator-Based DNA Barcode Detection Biosensor for Species Identification.

DNA barcode detection method is widely applied for species identification, which is imperative to evaluate the effect of human economic activities on the biodiversity of ecosystem. However, the wide utilization of existing detection biosensors is limited by bulky and expensive instruments, such as Raman spectroscopy and electrochemical station. Herein, a liquid-solid triboelectric nanogenerator (TENG)-based DNA barcode detection biosensor is proposed, which consists of water flow, fluid channel, and PDMS film attached by specifically designed capture probe. Through sequentially combining capture probe, targeted DNA barcode, and signal probe with Au nanoparticles (NPs), the surface charge density of friction layer of TENG decreases under the effect of AuNPs, verified by the density functional theory (DFT) method. Consequently, the peak value of output current spike signal for targeted DNA is smaller than that for other DNA, which is the working mechanism of the present TENG-based biosensor. Such biosensor successfully recognizes Alvinocaris muricola among different types of Alvinocarididae shrimps, and its low limit detection can reach 1×10-12m. The present work provides a paradigm-shift way to develop an inexpensive and accurate technique to detect DNA barcode for species identification, and paves a novel way for the application of liquid-solid TENG.

Robust and ultra-thin nanocellulose/MXene composite film and its performance in efficient electricity-generation and sensing.

The conversion of mechanical energy into electrical energy by triboelectric nanogenerators (TENG) has attracted attention in recent years, particularly in the field of wearable sensor. In this work, TEMPO-oxidized cellulose nanofibers (TOCNF) with carboxylate groups were compounded with MXene to serve as both the negative friction layer and the electrode in assembling a TENG with nylon. The synergistic effect between TOCNF and MXene was analyzed to disclose its influence on the performance of the as-prepared TENG. The MXene/TOCNF composite film, containing 50 wt% MXene, exhibited the best performance among all specimens, and the assembled TENG demonstrated excellent performance with an open-circuit voltage of 210 V, a short-circuit current of 0.84 μA, and a transferred charge of 8.6 nC. The excellent output performance might be attributed to the presence of carboxylate and F-containing groups in the composite film. This flexible TENG also functioned as a self-powered sensor, generating sensitive and stable signals in response to human motion and writing. This work verifies the simultaneous use of robust and flexible nanocellulose/MXene composite films as both the friction layer and electrode, which could spur the development of TENGs using sustainable and abundant cellulosic materials.

Friction and wear characteristics of acidic phosphate ester boundary layers analyzed by near-edge X-ray absorption fine structure

Friction and wear characteristics of acidic phosphate ester boundary layers analyzed by near-edge X-ray absorption fine structure

3-D woven triboelectric nanogenerators with integrated friction, spacer, and electrode layers for wearable energy harvesting and mechanical sensing

3-D woven triboelectric nanogenerators with integrated friction, spacer, and electrode layers for wearable energy harvesting and mechanical sensing

Micro water energy harvesting system based on tubular triboelectric nanogenerator

Abstract Constructing a micro-water energy-harvesting system for the power supply of micro-nano sensors in pipeline liquid transmission networks is of great significance. In this study, a micro water energy harvesting system based on a tubular triboelectric nanogenerator was designed, which achieves efficient energy harvesting and conversion by directly collecting the charge of the friction layer without the electrostatic induction effect. First, the working principle of the liquid–solid triboelectric nanogenerator is analyzed based on multi-physic coupling, and the potential distribution in the charge transfer process is analyzed. Second, the effects of liquid flow, pipe length, inner diameter, and material on the output characteristics of the triboelectric nanogenerator were investigated. Finally, the load power supply characteristics of the triboelectric nanogenerator were presented. The output characteristics of the liquid–solid triboelectric nanogenerator were proportional to the flow rate and inversely proportional to the inner diameter of the pipe. The output power of the liquid–solid triboelectric nanogenerator can be charged and stored by the capacitor through the rectifier bridge, and at least 30 LED lamp beads can be driven at a flow rate of 650 ml·min-1. This research has the potential to be applied to the construction of self-powered liquid-state monitoring intelligent sensors in pipeline networks.

Enhancing the Output Performance of Triboelectric Nanogenerators By Inserting CdS into Dielectric Layer

Triboelectric nanogenerators (TENGs) have emerged as promising devices for harvesting mechanical energy from various environmental sources. In this study, we focus on enhancing the performance of TENGs by inserting nano-sized cadmium sulfide (CdS) into a polydimethylsiloxane (PDMS) material. The synthesis of CdS nanomaterials was achieved through an ultrasonication method, resulting in a significant reduction in particle size compared to commercial CdS. The fabrication process of the TENG involved dispersing CdS nanoparticles into PDMS and depositing the composite thin film onto a polyethylene terephthalate (PET) substrate. Characterization studies using field emission scanning electron microscopy (FE-SEM) and UV-visible spectroscopy confirmed the successful transformation of micron-level CdS into nano-level CdS with improved optical and morphological properties.The TENG device was assembled employing a two-electrode configuration, comprising copper foils as electrodes and the CdS/PDMS composite thin film as the friction layer. Subsequent electrical measurements were conducted to assess the TENG's performance, encompassing evaluations of open circuit voltage, short circuit current, and charge transfer density. The findings revealed that the integration of CdS nanoparticles into PDMS significantly augmented the TENG's output, manifesting in notable increases in both voltage and current in comparison to PDMS-based TENGs. Moreover, a comparison between TENGs incorporating nano-scale CdS and those utilizing micro-scale CdS exhibited superior performance of the former, attributed to the enhanced charge transfer properties facilitated by the nanoparticles. Specifically, these findings indicate a threefold enhancement in output voltage and a 2.5-fold enhancement in current compared to the initial PDMS-based TENG.Additionally, a comprehensive study on the impact of external load resistance on the TENG's output energy density demonstrated its potential for practical applications, with the device capable of powering LEDs continuously. Rectification of the TENG's output voltage using a full bridge rectifier showcased efficient conversion of mechanical energy into electrical energy without a significant performance decline. Stability tests conducted over multiple days confirmed the reliability of the TENG based on CdS/PDMS, suggesting its suitability for long-term applications.In conclusion, the integration of nano-level CdS into PDMS material presents a promising approach to enhance the TENG performance for mechanical energy harvesting. Despite challenges such as CdS agglomeration in the polymer matrix, our findings highlight the potential of CdS-based TENGs for various energy harvesting applications and pave the way for future research in optimizing their performance and stability.

Self-Powered, Flexible, Wireless and Intelligent Human Health Management System Based on Natural Recyclable Materials.

Combining wearable sensors with modern technologies such as internet of things and big data to monitor or intervene in obesity-induced chronic diseases, such as obstructive sleep apnea, type II diabetes, cardiovascular diseases, and Alzheimer's disease, is of great significance to the self-health management of human beings. This study designed a loofah-conducting graphite four friction layer enhanced triboelectric nanogenerator (LG-TENG) and developed a health management system for human motion recognition and early warning of sleep breathing abnormalities. By uniformly spraying and depositing conductive graphite on the surface of the loofah and the elastic film cross-interlocking bending structure design, the signal strength of the LG-TENG has been improved by 390%. The stable output signal is still maintained after 1500 s of continuous operation at a frequency of 2 Hz. LG-TENG can realize accurate motion analysis by muscle contraction state. Combining different deep learning models resulted in 98.1% accuracy in recognizing seven categories of displacement speeds for an individual and 96.46% accuracy in recognizing seven categories of displacement speeds for three individuals. In addition, the sleep breathing monitoring early warning system was developed by integrating Bluetooth wireless transmission and upper computer analysis technology. This system aims to analyze and provide real-time warnings for sleep-breathing abnormalities. This research promotes an innovation of TENG technology based on the advantages of natural materials, recyclability and low cost. It offers new ideas for self-health management and scientific exercise for obese people, showing a broad application prospect.

Natural convective heat transfer analysis of a vertical tapered inner annulus tube with dual inverted frusto-conical turbulator using CFD

Vertical tube heat exchangers play a pivotal role in various industrial processes, where efficient heat transfer is essential for optimal system performance. This research introduces a novel heat exchanger design, the Dual Inverted Frusto-Conical Turbulator Attached Tapered Inner Annulus Tube, aimed at enhancing natural convection in vertical annulus heat exchangers using nano-coolants. Traditional designs often suffer from non-uniform heat transfer due to varying boundary layer thicknesses along the height of the annulus. The proposed design mitigates this by incorporating a tapered inner annulus tube, which has a larger diameter at the bottom and gradually decreases towards the top. This taper reduces wall friction and boundary layer thickness, enhancing thermal diffusivity and improving the heat transfer rate. To further optimize heat transfer, Dual Inverted Frusto-Conical Turbulators are strategically placed around the tapered tube, generating controlled turbulence that minimizes drag and avoids unwanted flow reversals and recirculation. Simulation results show a Nusselt number of 321, a friction factor of 0.023, and a pressure drop of 154 Pa at a Reynolds number of 5000. The design also achieved a thermal conductivity of 0.3 kW/mK, thermal efficiency variation of 0.8658%, and a heat transfer coefficient of 26,000 W/m2K.

Investigation on tribo‐properties of twaron pulp‐reinforced brake friction composites

AbstractDetermining the appropriate formulation in designing and developing brake friction materials is one of the most complex tasks. This study investigates the synergistic effect and optimization of twaron fiber on the fade and recovery performance of brake friction composites. For this purpose, a series of friction materials containing varying amounts of twaron between 1 and 9 wt% were developed, and their characterization and tribo evaluation were carried out. The tribo performance of the composites was evaluated in a Krauss‐type friction test machine in line with the ECE R90 procedure in terms of their fade and recovery behaviors. It was noted that the fade‐recovery friction response of composites was affected when fiber is added; that is, an increase in fiber content improved the fade performance, friction fluctuations decreased, and a higher recovery response was observed. The fade and average coefficient of friction were found to be the main determinants, while recovery was found to be the stabilizer. Analytical hierarchy process (AHP) was used to determine the priority of importance of criteria in the performance evaluation, and VIKOR (multi‐criteria optimization compromise solution) was used for ranking evaluation. The formulation with a concentration of twaron 7 wt% was found to have exhibited an optimal braking performance. The worn surfaces scanning electron microscope (SEM) study confirms the general friction and wear mechanisms of friction layers with fiber content.Highlights Development of twaron pulp‐reinforced eco‐friendly brake friction composites. Use of MCDM approach in the development of BFCs for braking applications. VIKOR optimization positioned 7 wt% twaron‐addition BFC as the optimal choice. It was observed that fiber amount is effective on the behaviors of composites.

Charge capturing effects of boron nitride nanosheets on enhanced triboelectric properties of polyimide nanocomposite films in a conductor-to-dielectric mode

Dielectric composite materials play a crucial role in the performance of triboelectric nanogenerators (TENGs) by influencing charge storage and transfer capabilities. In this study, we investigate the influence of boron nitride nanosheets (BNNS) on the triboelectric properties of polyimide (PI)-based dielectric nanocomposite films within a TENG setup employing a conductor-to-dielectric configuration and a contact-separation mode. To achieve this, we manufactured PI/BNNS nanocomposite films containing 1–10 wt% BNNS with a thickness of ∼14.67 nm via a solution casting method, followed by thermal imidization. Thermogravimetric characterization revealed that the thermal stability of the nanocomposites improved with increasing BNNS content. Additionally, the triboelectric performance of the PI/BNNS films, used as the negative friction layer, was enhanced due to the electron-trapping capabilities at the BNNS-PI interface. Among the samples, the nanocomposite film containing 5 wt% BNNS exhibited the most significant triboelectric output, generating a voltage of ∼4.0 V and a current of ∼426.4 nA. Moreover, the triboelectric AC output generated by the TENG using PI/BNNS nanocomposite films was successfully rectified into DC signals and subsequently stored in microcapacitors. This capability highlights the significant potential of PI/BNNS nanocomposite films for energy harvesting and storage applications, further supporting their suitability for integration into advanced flexible energy devices.

Magnetic PDMS@SiO2/Fe3O4 Composite Friction Layer Material for Enhanced Friction Nanogenerator Output Performance

Triboelectric nanogenerators (TENG) have exhibited remarkable potential in harnessing stochastic low-frequency mechanical energy from oceanic surfaces, attributed to their versatile architectures and capability for extensive deployment. Nonetheless, the relatively modest power output per unit area remains a critical limitation impeding the advancement of TENG technology. Consequently, the innovation of novel material systems and devices to augment the output performance and efficiency of TENG is paramount in achieving effective ocean energy exploitation. In our study, a vertical contact PC-TENG was utilized as an energy harvester, with the incorporation of magnetic nano-oxide particles to bolster the output efficiency of TENG. This investigation represents the inaugural application of SiO2 and Fe3O4 nanoparticles within PDMS negative friction layers. This strategy augments the specific surface area, thereby improving the contact between the friction materials and enhancing charge transfer efficiency. Moreover, the magnetic properties of Fe3O4 facilitate charge separation on the material's surface, culminating in an elevated voltage output. Comprehensive characterizations were conducted using SEM, FTIR, electrometer, and contact angle meter, while simulations were corroborated with COMSOL Multiphysics field simulation software. The output performance witnessed optimization through the incorporation of Fe3O4, culminating in a peak open-circuit voltage (VOC) of 85.1212 V, a maximum short-circuits current (ISC) of 8.4037 μA, and a maximum transferred charge (QSC) of 0.5638 nC, reflecting enhancements of 28%, 32%, and 27%, respectively, compared to conventional PDMS materials. The peak output power, achieved with an impedance match of 55 MΩ, was recorded at 19.03 mW, marking a 70.8% improvement in output performance. The findings revealed that the contact angle of PDMS@SiO2/Fe3O4 composites reached 100.092°, enhancing hydrophobicity by 8% relative to traditional PDMS materials, thereby rendering it more suitable for humid environments. COMSOL Multiphysics field simulation results further substantiated the viability of the PDMS@SiO2/Fe3O4 composite friction layer material for applications in oceanic wave environments. Ultimately, a rectifier bridge was introduced to convert the alternating current generated by the PC-TENG into direct current. This research offers a novel paradigm for the utilization of TENG in the realm of marine energy.

Enhanced braking performance of copper metal matrix composites incorporating fine mosaic pitch coke when mated with 30CrMnVA and C/C-SiC

By substituting 10 wt% of conventional graphite particles, pitch coke particles with fine mosaics demonstrate superior performance in enhancing the braking properties of copper metal matrix composites (CMMCs) operating at various conditions. When mated with C/C-SiC, the coefficient of friction increases by 18.6 % at low speeds and 38.8 % at high braking speeds, along with a significant enhancement in wear resistance across various counterparts. This improvement is attributed to the incorporation of pitch coke with fine mosaics and superior mechanical properties, which not only imparts high thermal capacity and mechanical strength to the CMMCs but also fosters a synergistic interaction between pitch coke and the iron oxide layer, stabilizing the friction layer.

Development of Turbocharging-Ability Hybrid Nanogenerators Comprising Bipolar PVDF-HFP/MXene Electrospun Composites.

Coupling piezo-active and triboelectric materials has recently emerged as an effective technique for developing high-performance hybrid nanogenerators (HNGs). This is the first paper to report the fabrication of piezo-active poly(vinylidene fluoride-hexafluoropropylene)(PVDF-HFP)/MXene-based hybrid composite fibers through conventional electrospinning. Here, the effect of MXene content (1-5%) on the surface potential and electrical performance of the as-synthesized composites is investigated and optimized. PVDF-HFP/3% MXene (PHM3)/Nylon 12+A-rGo (NY2)-HNG, which contains the best-performing composite (PMH3; containing 3% of MXene), exhibits turbocharging properties (charging a 10 µF capacitor with 16V within 100 s) and can continuously operate low-power electronics. Interestingly, PHM3 (with a negative surface potential) is transformed into PPHM3 (with a positive surface potential of +2190V) via corona poling. This study proposes a new class of HNGs containing frictional layers comprising bipolar PVDF-HFP/3% MXene composites (PHM3/PPHM3-HNG) with an excellent output performance of 297V and 5.1µA that exhibit broad application prospects in energy harvesting.

High-Performance Triboelectric Nanogenerator Based on Silk Fibroin-MXene Composite Film for Diagnosing Insomnia Symptoms.

In this study, we developed a flexible, biocompatible, and high-output electrical performance triboelectric nanogenerator (TENG) employing a silk fibroin (SF)-MXene composite film (SF-MXene-F) and a PDMS film as the friction layer. The inclusion of MXene in the SF film increased its surface charge density, presenting a practical approach to designing high-performance SF composite film-based TENGs. At a MXene content of 40%, our SF-MXene composite film-based TENG (SF-MXene-FTENG) achieved optimal output electrical performance, featuring a maximum open-circuit voltage (Voc) of 418 V, a maximum short-circuit current (Isc) of 11.6 μA, and a maximum output power density of 9.92 W/m2. The Voc and power densities of the SF-MXene-FTENG surpassed previously reported optimal values for SF-based TENGs by 1.6 and 3.8 times, respectively. Furthermore, leveraging the exceptional biocompatibility and light shading performance of TENGs, we designed a wearable smart TENG eye mask capable of diagnosing insomnia symptoms and monitoring sleep quality in real time. The SF-MXene-FTENG holds promising application potential as a wearable electronic device for diagnosing sleep-related diseases.