Volume Fraction Of Multi-walled Carbon Nanotubes Research Articles

Influence of agglomeration and waviness phenomena on torsional oscillation of MWCNTs-reinforced composite rods

There are some inevitable challenges during the manufacturing of reinforced composite structures. Agglomeration of reinforcement and wavy reinforcement are in this category. These phenomena possess remarkable effects on the mechanical behavior of reinforced composite structures. In the current research, the effect of agglomeration and waviness of reinforcements on torsional dynamic characteristics of multi-walled carbon nanotubes (MWCNTs) reinforced composite rods subjected to two various boundary conditions have been evaluated. Three dissimilar cross-section shapes have been considered to understand the effect of cross-section shapes on torsional behavior of MWCNTs-reinforced composite rods. A new form of Halpin-Tsai homogenization model has been exerted to estimate the material properties of composite structures. Additionally, Timoshenko-Gere theory in conjunction with the Hamilton’s principle has been employed to derive the partial differential governing equation of MWCNTs-reinforced composite rods. Afterward, the obtained equation was solved using an analytical approach. The precision of the methodology utilized has been evaluated against the results of previous studies documented in the literature. Ultimately, the effects of various significant parameters on the changes in natural torsional frequency have been analyzed and presented in a series of tables and figures. Based on the obtained results, the rectangular rod has the highest torsional frequency and also the effect of MWCNTs’ volume fraction depends on the consideration of waviness and agglomeration factors. At a greater volume fraction of MWCNTs, the agglomeration factor is more effective than the waviness factor and vice versa.

Numerical investigation of heat and mass transfer of SWCNT/MWCNT‐water suspension over a porous stretching sheet using Sisko fluid model

AbstractThis study presents a comprehensive numerical computation of heat‐mass transfer characteristics of single‐walled carbon nanotube (SWCNT)/multi‐walled carbon nanotube (MWCNT)‐water suspension flow over a porous stretching sheet with an inclined magnetic field. The governing equations for fluid flow characteristics are formulated using the Sisko fluid model to capture the Newtonian and non‐Newtonian behavior of the nanotube‐water mixture. The nonlinear coupled partial differential equations are converted into nonlinear dimensionless coupled ordinary differential equations using suitable similarity transformations. These equations are solved using MATLAB by implementing the four‐stage Lobatto IIIa formula. The comprehensive set of computations is performed to explore the influence of pertinent parameters, including Sisko fluid parameters, concentration of nanotubes, stretching sheet velocity, and porous medium characteristics on the flow, heat, and mass transfer profiles. From the graphs and statistical analysis, it is clear that the volume fraction of SWCNT and MWCNTs are strongly correlated. The investigation reveals that increasing the inclination angle affects the fluid velocity. The variation in all flow features is negligible for volume fractions of CNTs between 0% and 10% but a significant effect is observed only beyond 10%. Higher volume fractions of CNTs result in enhanced local heat transfer coefficient. This can be attributed due to the outstanding heat transfer capabilities of CNTs owing to their high thermal conductivity. However, Shear thickening fluids exhibit high heat transfer phenomena when compared to shear‐thinning and Newtonian fluids. This research provides valuable insights into the optimization of CNT‐based nanofluids for efficient heat and mass transfer applications in electronics cooling, heat exchangers, and solar energy systems, offering opportunities to enhance energy efficiency and device performance.

Amplifying thermal performance of solar flat plate collector by Al2O3/ Cu/MWCNT/SiO2 mono and hybrid nanofluid

Flat plate collectors (FPCs) have garnered widespread usage in applications such as water heating, space heating, and various thermal systems, presenting an eco-friendly and sustainable approach to harnessing solar energy. However, the thermal performance of FPCs has been adversely affected by the improper selection of Heat Transfer Fluids (HTFs). The purpose of the work is to explore and demonstrate the potential advancements in solar flat plate collector (FPC) technology through the use of nanofluids to Enhance Energy Conversion, Explore Synergistic Effects, Contribute to Sustainable Energy Solutions and Address Technological Challenges. That is to optimize the thermal performance of FPCs by incorporating standalone and hybrid nanoparticles into the base fluid to augment their thermal properties. This approach explores new possibilities for synergistic effects and enhanced thermal properties, offering a novel contribution to the field of nanofluid research. The standalone and hybrid nanofluids encompass nanoparticles such as Al2O3, Cu, multi-walled carbon nanotubes (MWCNT), and SiO2 at a concentration of 0.5 wt%. In the preparation of hybrid nanofluids, equal volume fractions (25 % each) of Al2O3, Cu, MWCNT, and SiO2 nanoparticles were employed. The investigation includes the evaluation of thermal performance parameters, namely heat gain, heat loss coefficients, and thermal efficiency of FPCs, comparing these values with those of water. Hybrid nanofluids exhibit significantly improved thermal performance compared to both plain water and monodisperse nanofluids. Employing hybrid nanofluids yields results that indicate a peak outlet temperature of approximately 83.2 °C, a higher heat gains of 2385 W, a reduced heat loss coefficient of 25.5 W/m2K, and a peak thermal efficiency of 70.4 %. The use of hybrid nanofluids, as opposed to monodisperse nanofluids, offers superior thermal performance for flat plate collector-based solar heating systems.

Using MWCNT and titanium oxide as boosters in passive heat transfer methods for clean and renewable energy applications

Passive heat transfer (PHT) methods provide an energy-efficient and environmentally friendly approach for transferring heat between systems, making them a promising solution for renewable and clean energy utilization across various applications. Changing the performance of heat transfer systems can be achieved by manipulating fluid flows. In this study, an investigation was conducted on the use of four blocks with different positions and sizes as obstacles embedded within a square enclosure, which affected the heat transfer through natural convection. Additionally, the study explored the effectiveness of a hybrid nanofluid created by injecting two types of nanoparticles, titanium oxide (TiO2) and Multi-walled Carbon Nanotube (MWCNT), into the cooling fluid. Computational fluid dynamics (CFD) simulations were employed to examine the impact of the blocks, nanoparticle concentration, and Rayleigh number on heat transfer parameters. The findings revealed that the addition of a 6 % volume fraction of titanium oxide and MWCNT to the base fluid resulted in a notable increase of over 5 % but less than 30 % in the average Nusselt number. In contrast to expectations, embedding obstacles drooped off average Nusselt number by 9 to 30 % in Rayleigh numbers of 10,000 and 100,000, and had no effect in Rayleigh numbers of 100 and 1000.

Experimental investigation and correlation development of flow condensation with R123/MWCNTs nanorefrigerant inside a horizontal tube

The current experimental study is focused on examining the behaviour of heat transfer of pure R123 and R123/multi-walled carbon nanotubes nanofluid condensing in a smooth horizontal pipe at a range of different working conditions, like the mass velocity of about 200–500 kg/m2s, multi-walled carbon nanotubes volume fraction of approximately 0.01, 0.05, and 0.1 %, vapour quality of approximately 0.05–0.9, and saturation temperature of about 35.3 and 40.9 °C. The heat transfer coefficient of pure R123 and nanorefrigerant is compared in this investigation. According to the results, employing multi-walled carbon nanotubes improves the heat transfer coefficient for all selected volume fractions. It is observed that the heat transfer coefficient for both pure and nanorefrigerant falls as the saturation temperature rises from 35.3 to 40.9 °C. For a mass velocity of about 400 kg/m2s, 0.1 % fraction of multi-walled carbon nanotubes results in the highest heat transfer coefficient increase of 29 % compared to the base refrigerant. The mean absolute error analysis is evaluated to forecast the accuracy of the experiments by comparing the experimentally captured condensation heat transfer data with available correlations, which shows good agreement. A new correlation for flow condensation heat transfer coefficient is suggested, with an acceptable mean absolute percentage error of about 9.6 %.

Origin of non-universal percolation/scaling and universal non-Debye relaxation in PVDF/MWCNT polymer nanocomposites

Polymer Nanocomposites (PNC) comprising polyvinylidene fluoride (PVDF)/Multi-walled Carbon Nanotubes (MWCNT) were studied. The structural composition and thermal stability were confirmed from XRD and DSC/TGA data, respectively. The extent of distribution of MWCNT in the PNC increases and the clustering of MWCNT also increases with an increase in the volume fraction of MWCNT ([Formula: see text], as confirmed by FESEM. The PNC shows an insulator-to-metal transition (IMT), with both non-universal percolation threshold [Formula: see text] of [Formula: see text] and scaling exponents [Formula: see text], respectively, attributed to adhesiveness/cold pressing and the higher aspect ratio/conductivity of MWCNT. Modulus spectroscopy confirms a non-Debye type universal relaxation behavior [Formula: see text] only for the percolative sample due to Maxwell–Wagner–Sillars/interfacial polarization, while only dipolar relaxation was probed or the samples below [Formula: see text]. The [Formula: see text] with static effective dielectric constant [Formula: see text] and low tan [Formula: see text] may be suitable for charge storage applications.

Investigating the effects of employing a cooling radiator on MHD natural convection by injecting MWCNTs into water

One of the best methods in thermal engineering for cooling a liquid is to use a radiator. Using the radiator mechanism in free convection systems is a successful and first idea to improve performance of natural convection systems, which have various applications in building, energy storage, and cooling systems. Therefore, a radiator with four constant temperature fins on each side was used to contribute to cool a hot plate in this study. The mechanism of this system was free convection of water with Multi-walled carbon nanotubes (MWCNTs), and a complex relationship was used for thermal conductivity nanofluid, respecting the thermal conductivity of MWCNT in radial and longitude directions. A deviated magnetic field also created a Lorentz force on the moving fluid to control natural convection mechanism. This system was modeled using the finite volume method to study the influences of Rayleigh number, volume fraction, and Hartmann number on the flow and heat transfer parameters. Evidences showed that injecting 3% volume fraction of MWCNT in Rayleigh numbers of 104 escalated the mean Nusselt number by 48% in all of the Hartmann numbers.

Study of the influence of nanoparticles on the behavior of composite materials

The objective of this work is to study the influence of additives of multi-walled carbon nanotubes (MWCNT) and silica nano-powder (SiO2) on the mechanical behavior of epoxy resin. Different volume fractions of MWCNT and SiO2were added. Mechanical characterization by tensile, three-point bending and Charpy tests were carried out. The experimental results show an increase in the mechanical performance of the mixtures (MWCNT ​+ ​epoxy), (SiO2 ​+ ​epoxy) up to 2% of additive. Beyond this value, a degradation of performance was observed. The addition of MWCNT gives better results when compared to the addition of SiO2. KIC-KCV correlations were made using empirical formulas to estimate the critical stress intensity factor KIC from the impact energy of the Charpy test.Unfortunately, this estimation does not provided a promising results, but other optimization methods were used to fit these empirical models to the behavior of our nanocomposites for which a good estimate was obtained after fitting these empirical models for SiO2.

A facile route to prepare high−performance dielectric nanocomposites of poly(methyl methacrylate)/poly(vinylidene fluoride)/carbon nanotubes

A facile route to prepare high−performance dielectric nanocomposites of poly(methyl methacrylate) (PMMA)/poly(vinylidene fluoride) (PVDF)/multi−walled carbon nanotubes (MWNTs) is systematically studied. A 30 wt % solution of PMMA/PVDF/MWNTs mixture in a solvent of N,N−dimethylformamide (DMF) is dried isothermally at ca. 20 °C below the upper critical solution temperature. Cocontinuous structure is formed through spinodal phase separation during the solvent evaporation and the MWNTs are found to be exclusively localized in the PVDF phase of the blends. The experiment results show that phase-separation and selection of CNTs occur quickly, while the conductive network needs more time to be formed. The domain size of such cocontinuous structure is in the sub−micrometer range, which is much lower than that produced by melt processing. When the volume fraction of MWNTs is 2 vol %, the dielectric constant of the composites is about 100 (at 100 Hz) and independent of frequency (102−105 Hz). The thermodynamics and kinetics of the polymer blends and composites are also studied by DSC and DMA. The composites have excellent ductility, their elongation at break is above 150%. Compared with the melt−mixing process, this approach provides a general pathway to prepare high−performance dielectric polymer materials containing cocontinuous microscale and nanoscale structures.

Wave dispersion analysis of embedded MWCNTs-reinforced nanocomposite beams by considering waviness and agglomeration factors

In the current investigation, the influences of waviness and agglomeration factor of nanofillers on wave dispersion of embedded nanocomposite beams reinforced with multi-walled carbon nanotubes (MWCNTs) is investigated for the first time. These beams are supported on Winkler–Pasternak elastic foundation. The effective mechanical properties of nanocomposite beam are estimated by employing a blend of a new form of Halpin–Tsai micromechanical model and rule of mixture. The kinematic and kinetic relations of nanocomposite beam are computed based upon refined higher-order shear deformation theory. Moreover, the governing equations are derived by utilizing the Hamiltonian approach. Afterward, an analytical method is used in order to solve the obtained governing equations. Effects of the wide range of variants such as volume fraction of MWCNTs, slenderness ratio, waviness factor, random orientation factor, agglomeration factor and elastic foundation coefficient on the variation of wave frequency and phase velocity have been illustrated comparatively. Furthermore, the results are thoroughly discussed to obtain the highlights of each figure.

Wave Dispersion Analysis of Fluid Conveying Nanocomposite Shell Reinforced by MWCNTs Considering the Effect of Waviness and Agglomeration Efficiency.

The current paper is aimed to investigate the effects of waviness, random orientation, and agglomeration factor of nanoreinforcements on wave propagation in fluid-conveying multi-walled carbon nanotubes (MWCNTs)-reinforced nanocomposite cylindrical shell based on first-order shear deformable theory (FSDT). The effective mechanical properties of the nanocomposite cylindrical shell are estimated employing a combination of a novel form of Halpin-Tsai homogenization model and rule of mixture. Utilized fluid flow obeys Newtonian fluid law and it is axially symmetric and laminar flow and it is considered to be fully developed. The effect of flow velocity is explored by implementing Navier-Stokes equation. The kinetic relations of nanocomposite shell are calculated via FSDT. Moreover, the governing equations are derived using the Hamiltonian approach. Afterward, a method which solves problems analytically is applied to solve the obtained governing equations. Effects of a wide range of variants such as volume fraction of MWCNTs, radius to thickness ratio, flow velocity, waviness factor, random orientation factor, and agglomeration factor on the phase velocity and wave frequency of a fluid conveying MWCNTs-reinforced nanocomposite cylindrical shell were comparatively illustrated and the results were discussed in detail.

3D Rayleigh‐Bénard‐type natural convection in MWCNT‐nanofluid‐filled L‐shaped enclosures with consideration of aggregation effect

Rayleigh‐Bénard type convective heat transfer in a 3D L‐shaped enclosure filled with multiwalled carbon nanotube (MWCNT)‐water nanofluids has been studied. The governing equations have been written using the vorticity‐vector potential formalism and solved based on the finite volume method (FVM). The simulations were performed for various values of Rayleigh number, aspect ratio, and MWCNT volume fraction. The aggregation effect was considered, and the viscosity and thermal cavity were evaluated accordingly to fit with the experimental properties. The heat transfer is enhanced by increasing MWCNT volume fraction. The aspect ratio is found to be an optimization parameter of heat transfer especially for low Ra values. The aspect ratio equal to 0.4 provides the highest heat transfer for fraction nanofluid less than 3% and Ra number less than 105. Increasing the aspect ratio and fraction nanofluid enhances of the 3D character.

Piezoresistivity of Cement Matrix Composites Incorporating Multiwalled Carbon Nanotubes due to Moisture Variation

Cementitious composites usually work under moisture condition. Presently, the piezoresistivity of cementitious composites incorporating multiwalled carbon nanotubes (MWCNTs) due to moisture variation was experimentally investigated. The variation of moisture content was controlled by drying specimens in an oven. In most cases of moisture content, the composites were observed to present positive piezoresistivity during the process of cyclic compression. While moisture content was in a specific range, the composites exhibited negative piezoresistivity. The whole transition from positive piezoresistivity to negative piezoresistivity and then positive piezoresistivity was obtained with moisture variation. Moreover, the amplitude of piezoresistivity changed in the process. These phenomena may be explained through the combination of ionic conduction and electronic conduction. A theoretical model of piezoresistivity, able to predict the effects of porosity, the volume fraction of MWCNTs, and the connectivity parameters, is proposed. Numerical results with the model show that the calculated piezoresistive responses of specimens agree reasonably well with testing data.

Modeling the Electromagnetic Scattering Characteristics of Carbon Nanotube Composites Characterized by 3-D Tomographic Transmission Electron Microscopy

In all prior electromagnetic modeling studies of carbon nanotube (CNT) composites, the exact three-dimensional (3D) shape and spatial distribution of the CNTs in the composite were unknown. Therefore, simplifying assumptions had to be made regarding the CNT distributions. The effect of such assumptions on the electromagnetic response of CNT composites has not been quantified. Recent advances in electron-tomography and image analysis have allowed the generation of 3D maps of multi-walled carbon nanotube (MWCNT) distributions with sub-nanometer resolution. In this work, the electromagnetic responses of experimentally mapped 3D structures of aligned-CNT polymer nanocomposites were calculated using both full-wave electromagnetic solvers and dilute-limit Effective Medium Approximations (EMA). Our results show that the electromagnetic response calculated using the full-wave solver exhibits additional resonances that are absent in the response calculated using the dilute-limit EMA. This difference is due to the strong electromagnetic coupling between adjacent MWCNTs, within five CNT radii, of each other. Using the mapped 3D MWCNTs, we also studied the anisotropy in the electromagnetic response of the composites and showed that it increases with the MWCNT volume fraction. The full-wave analysis presented in this work provides a more accurate understanding of the electromagnetic reflection and anisotropy of CNT composites.

Thermo-Mechanical Post Buckling Analysis of Multiwall Carbon Nanotube-Reinforced Composite Laminated Beam under Elastic Foundation

Abstract In present paper, buckling analysis is performed over laminated composite beam incorporating multi walled carbon nanotube (MWCNT) polymer matrix and then reinforced with E-glass fiber in an orthotropic manner under inplane varying thermal and mechanical loads by finite element method (FEM). Aim of the study is to develop a model which accurately perform the buckling deterministic analysis of multi-walled carbon nanotube reinforced composite laminated beam (MWCNTRCLB) with the evaluation of material property by applying Halpin–Tsai model. Combined Higher order shear deformation theory and Pasternak elastic foundation based on von Karman nonlinear kinematics and Winkler cubic nonlinearity respectively, are successfully implemented. Through minimum potential energy principle, generalized static analysis is performed using FEM, based on interactive MATLAB coding. The critical buckling load and critical buckling temperature is presented under the action of inplane variable mechanical and thermal load, with different boundary conditions, beam thickness ratio and MWCNT aspect ratio, variation with MWCNT volume fraction and coefficient of thermal expansion, with and without foundation for linear and nonlinear cases.

Thermal behaviour of multi-walled carbon nanotube/polymer composites using lattice Boltzmann method

ABSTRACTA three-dimensional computational model was developed to study the thermal behaviour of multi-walled carbon nanotube (MWNT)-polymer composites. A lattice Boltzmann algorithm has been introduced to tackle the conjugate heat transfer among different phases. The model was validated by comparing with the theoretical solutions and simulation results. The effects of the orientation, volume fraction and diameter of MWNTs on the effective thermal conductivity (λe) of composites were quantified. It is found that the effective thermal conductivity of the composites weakens with the variation of MWNTs orientation angle, and the decrease extent deduces gradually. Moreover, with the same orientation angle, the λe of the composites increases with the volume fraction of MWNTs. It also indicates that MWNTs with a small diameter at a constant volume fraction can promote the thermal conductivity of the composites more efficiently than that with a larger diameter.

The effects of agglomerate on the piezoresistivity of conductive carbon nanotube/polyvinylidene fluoride composites

Conductive polymer composites are prepared with a polyvinylidene fluoride (PVDF) matrix and multiwalled carbon nanotube (MWCNT) as filler. The mechanical properties, electrical conductivity and piezoresistivity of the composites are investigated as a function of MWCNT volume fraction. An optimal combination of ductility and piezoresistivity is found in the composite slightly above the electrical percolation threshold, showing a maximum fracture strain ∼ 4 times higher than the pure PVDF samples, as well as an outstanding sensitivity of piezoresistive response. Increasing further the MWCNT volume fraction leads to deterioration of both ductility and piezoresistivity. The effects of MWCNT content on piezoresistivity and fracture strain can be understood based on the microstructure observations. In particular, by incorporating two characteristic microstructural features identified in the materials, i.e., the filler random distribution and the filler agglomerate, into a simple statistical network model, the experimental measurements of piezoresistivity can be successfully fitted and understood in a semi-quantitative manner.

Effect of pristine multiwalled carbon nanotubes on tensile hysteresis in carboxylated nitrile rubber composites

This work deals with the study of effect of multiwalled carbon nanotubes (MWNT) on the tensile hysteresis behavior of carboxylated nitrile rubber composites under various cyclic strain levels (5, 25, and 300%). The presence of thermo‐labile ionic crosslinks as well as interfacial stick‐slip motion of filler in the matrix was found to enhance both Mullins effect and hysteretic damping. Hysteretic damping reached a maximum of 37% for 0.050 volume fraction of MWNT at medium strain (25%). The crosslink density measured through equilibrium swelling method revealed that the degree of ionic crosslinking decreased with increase in MWNT content, which was confirmed by infrared spectroscopy. Transmission electron microscopic images showed that agglomeration of nanotubes was prominent at higher volume fractions of MWNT. Acoustic absorption capability, as measured by the impulse method, decreased with increase in MWNT concentration. The high hysteretic damping and low acoustic absorption make the nanocomposites a superior choice for structural vibration damping in underwater acoustic sensor systems. POLYM. COMPOS., 39:E1269–E1279, 2018. © 2018 Society of Plastics Engineers

Development of large-movements and high-force electrothermal bimorph actuators based on aligned carbon nanotube reinforced epoxy composites

By using aligned multi-walled carbon nanotube (MWCNT) reinforced epoxy composites possessing a negative coefficient of thermal expansion (CTE) as well as high Young’s modulus and aluminum foils, novel electrothermal bimorph actuators are fabricated. U-shaped bimorph actuators are formed by cutting out the middle part of the composite/aluminum laminates, where the MWCNT-aligned direction is parallel to the length direction of the U-shaped bimorph actuators. We demonstrate that the bimorph actuators with a free length of 16mm show a large bending displacement and force output, and their values are 7.6–10.0mm and 0.8–7.8mN under a DC voltage of 5.2–6.0V. Based on these results, the bending displacement and force output of the bimorph actuator are modeled by combining strength-of-materials theories and rule of mixtures (Voigt model and Turner’s model). By using these models, we indicate contributions from two sources toward the increased bending displacement and force output in the bimorph actuator: (i) designing the Young’s modulus and negative CTE of the composite layer by controlling the MWCNT volume fraction and the dimensional parameters (especially thickness) of the bimorph actuator; (ii) selecting materials having a high Young’s modulus as well as a large CTE as the second layer.

Effect of far-field stresses and residual stresses incorporation in predicting fracture toughness of carbon nanotube reinforced yttria stabilized zirconia

Yttria-stabilized zirconia (YSZ) is a potential thermal insulating ceramic for high temperature applications (>1000 °C). YSZ reinforced with multi-walled carbon nanotubes (MWNTs) was processed via spark plasma sintering to produce dense, crack-free homogeneous sample and avoid any degradation of MWNTs when sintered using conventional routes. Despite porosity, the addition of MWNT has a profound effect in improving the damage tolerance of YSZ by allowing the retention of tetragonal phase. However, at some instances, the crack lengths in the MWNT reinforced YSZ matrices have been found to be longer than the standalone counterparts. Therefore, it becomes inappropriate to apply Anstis equation to calculate fracture toughness values. In this regard, a combined analytical cum numerical method is used to estimate the theoretical fracture toughness and quantitatively analyze the mechanics of matrix cracking in the reinforced composite matrices incorporating the effects of various factors (such as far-field stresses, volume fraction of MWNTs, change in the modulus and Poisson's ratio values along with the increase in porosity, and bridging and phase transformation mechanism) affecting the fracture toughness of YSZ-MWNT composites. The results suggest that the incorporation of far-field stresses cannot be ignored in estimating the theoretical fracture toughness of YSZ-MWNT composites.