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Nanofluid molecular dynamic model: CNT nanoparticle (red-colored) and surrounding water (bluecolored).
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The heat-transfer enhancement of nanofluids has made them attractive and the subject of many theoretical and experimental researches over the last decade. Of the theoretical approaches employed to investigate nanofluid properties, molecular dynamics (MD) simulation is a popular computational technique that is widely used to simulate and investigate...
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... effects of different factors on the shear viscosity of Al 2 O 3 nanofluids were studied by Lou and Yang [95], and they obtained similar results as in the case of previous studies related to the impact of the nanoparticle volume fraction on shear viscosity. In their simulations, periodic boundary conditions were applied in all the three directions and Nose- Hoover thermostat was used to set the temperature system. The TIP4P/2005 potential is used to describe the interactions among all water molecules and the CLAYFF force field [103] is applied for the particle-particle and water-particle interactions. For example, when the nanoparticle volume fraction increased from 1.24% to 3.72%, the shear viscosity increased from 1.21 mPa.s to 3.68 mPa.s at 300 K, and the viscosity increased to 3.59 mPa.s at 280 K. Therefore, the effect of the nanoparticle volume fraction was more significant at lower temperature. In order to have a good comparison between different studies, the viscosity of different nanofluid types versus the nanoparticle volume fraction is summarized in Fig. 11. It can be deduced that in all studies, the viscosity of the nanofluid is enhanced with an increasing solid volume fraction. The discrepancies between reports on Al 2 O 3 nanofluid may be due to the different nanoparticle diameters (100-450 Ǻ in [49] and 10.85 Ǻ in [95]). Fig. 11 Variation of the shear viscosity with the volume fraction based on different ...
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... effects of different factors on the shear viscosity of Al 2 O 3 nanofluids were studied by Lou and Yang [95], and they obtained similar results as in the case of previous studies related to the impact of the nanoparticle volume fraction on shear viscosity. In their simulations, periodic boundary conditions were applied in all the three directions and Nose- Hoover thermostat was used to set the temperature system. The TIP4P/2005 potential is used to describe the interactions among all water molecules and the CLAYFF force field [103] is applied for the particle-particle and water-particle interactions. For example, when the nanoparticle volume fraction increased from 1.24% to 3.72%, the shear viscosity increased from 1.21 mPa.s to 3.68 mPa.s at 300 K, and the viscosity increased to 3.59 mPa.s at 280 K. Therefore, the effect of the nanoparticle volume fraction was more significant at lower temperature. In order to have a good comparison between different studies, the viscosity of different nanofluid types versus the nanoparticle volume fraction is summarized in Fig. 11. It can be deduced that in all studies, the viscosity of the nanofluid is enhanced with an increasing solid volume fraction. The discrepancies between reports on Al 2 O 3 nanofluid may be due to the different nanoparticle diameters (100-450 Ǻ in [49] and 10.85 Ǻ in [95]). Fig. 11 Variation of the shear viscosity with the volume fraction based on different ...
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... this method, the Green-Kubo formula is used, which relates the ensemble mediocre of the autocorrelation of the stress function. :lJ J ) 12 ( Results presented by researchers show that at the beginning, the autocorrelation function of the stress rapidly decays with fluctuations, and it is then followed by a slower decay to zero (Fig. 10) [95], which is similar to that of the thermal conductivity [96]. Generally, there are fewer studies related to shear viscosity of nanofluids compared to studies on their thermal conductivity, especially in MD simulations [97]. In the following section, we classify the results of studies to calculate the shear viscosity of nanofluids. These results were also confirmed in another study [98] that is related to the shear viscosity of gold-water nanofluid. Liquid argon with aluminum and lithium nanoparticles was investigated by Rudyak and Krasnolutskii [99,100]. They used periodic boundary conditions and LJ potential to describe Interaction between the molecules of the base fluid while for modelling interaction between base fluid and nanoparticle atoms is used Rudyak- Krasnolutskii (RK) [101,102] potential. The results show that with an increase in the nanoparticle volume fraction, the viscosity of the nanofluid ...
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... material and shape of nanoparticles also affect the thermal conductivity of nanofluids, and by comparing nanoparticles with different shapes, we found that the thermal conductivity enhancement is higher if the surface-to-volume (S/V) value is higher. Fig. 1 Nanofluid molecular dynamic model: CNT nanoparticle (red-colored) and surrounding water (blue-colored). Variation of the shear viscosity with the volume fraction based on different studies. ...
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... are mixtures of two components, namely a base fluid and a small volume fraction (within the range of sub 1% up to 10%) of solid particles with sizes that are usually less than 100 nm [1]. Fig. 1 represents a molecular dynamics (MD) model of a nanofluid containing carbon nanotube (CNT) as the nanoparticle with water as the base fluid. The concept of nanofluids was first proposed by Choi [2] in the mid-nineties as a way of superseding micron-sized solids that were used inside conventional coolants to enhance their thermal conductivity. Researchers have devoted much effort to further understand the physics governing nanofluids, including calculating the thermal conductivity enhancement of various types of nanofluids using different methods, and to study mechanisms of heat transfer in nanofluids ...
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... 2,8 One of the main factors playing a predominant role in the nature of size effects in nanofluids is the adsorption of base fluid molecules on the surface of particles. 3,[9][10][11] The adsorbed layers have modified physical properties in comparison to the base fluid. Since the surface of nano-sized particles becomes extremely large, the influence of the adsorbed layers on the overall properties of nanofluids becomes significant. ...
... Since the surface of nano-sized particles becomes extremely large, the influence of the adsorbed layers on the overall properties of nanofluids becomes significant. In theoretical models, the structure of adsorbed layers can be directly studied within the molecular dynamics method, 3,10 or it can be introduced as the "third phase" between the particles and the base fluids in continuum models. 9,12,13 In the present study, we show that an alternative approach for the analysis of the size-dependent shear viscosity of nanofluids can be used considering micropolar effects in the base fluid. ...
The modified size-dependent Einstein's and Brinkman's solutions are established for the effective shear viscosity of rigid particle suspensions taking into account the micropolar effects in the base fluid. Solutions are obtained based on the homogenization approach and allow us to take into account the influence of the particle size. Two non-classical parameters arise in the considered micropolar solutions: the length scale parameter and the coupling (micropolarity) number of the base fluid. The solutions developed are validated using tests performed with polydimethylsiloxane based TiO2 nanofluids as well as other published data on the size-dependent shear viscosity of different nanofluids. Good agreement between the predictions and the experimental data is established across a wide range of volume fractions and size of nanoparticles. The possibility for unique identification (at given temperature) of the micropolar parameters of the base fluids is shown. Temperature-dependent values of non-classical rotational and spin viscosities of polydimethylsiloxane, ethylene glycol, and water are evaluated.
... Additionally, their findings demonstrated that argon gas exhibits a layered pattern at high pressures within nanochannels. Jabbari et al [9], have authored a comprehensive review paper on thermal conductivity and viscosity of nano-fluids, serving as an excellent and reliable reference for readers seeking in-depth insights into this subject. ...
In this work, we perform equilibrium molecular dynamics (EMD) simulation to study the thermal conductivity of hydrogen molecules (H2) under extreme confinement within graphene nanochannel. We analyze the structural behavior of H2 molecules inside the nanochannel and also examine the effect of nanochannel height, the number of H2 molecules, and temperature of the system on the thermal conductivity. Our results reveal that H2 molecules exhibit a strong propensity for absorption onto the nanochannel wall, consequently forming a dense packed layer in close to the wall. This phenomenon significantly impacts the thermal conductivity of the confined system. We made a significant discovery, revealing a strong correlation between the mass density near the nanochannel wall and the thermal conductivity. This finding highlights the crucial role played by the density near the wall in determining the thermal conductivity behavior. Surprisingly, the average thermal conductivity for nanochannels with a height (h) less than 27 Å exhibited an astonishing increase of over 18 times when compared to the bulk. Moreover, we observe that increasing the nanochannel height, while the number of H2 molecules fixed, leads to a notable decrease in thermal conductivity. Furthermore, we investigate the influence of temperature on thermal conductivity. Our simulations demonstrate that higher temperature enhance the thermal conductivity due to increased phonon activity and energy states, facilitating more efficient heat transfer and higher thermal conductivity. To gain deeper insights into the factors affecting thermal conductivity, we explored the phonon density of states (DOS). Studying the behavior of hydrogen in confined environments can offer valuable insights into its transport properties and its potential for industrial applications.
... In general, the MD method has been widely used to investigate the viscosity of nanofluids. The relevant bibliography for nanofluids with conventional spherical particles can be found in the reviews [20,21]. In addition to the fact that the use of the MD method has revealed new factors affecting the viscosity of nanofluids, it is absolutely indispensable when studying the corresponding mechanisms. ...
... The effect of NP-radii and Temp on the thermophysical properties of water/Ni NF was examined in NF systems with radii of 8, 10, and 12 Å and SVF=2% nickel. Based on the review article, the size of selected Ni in different studies was between 0.03 and 10 nm [69]. Three sizes of nickel NPs in this range were chosen for this research. ...
Background: In recent decades, using nanofluids (NFs) to improve the thermal properties of the NFs was widely considered. Methods: In the current study, molecular dynamics (MD) simulation was used to examine the effects of dispersion and morphology of nanoparticle aggregation (NA), solid volume fraction (SVF), temperature (Temp), nano-particle size (NS), and nanoparticle shape on the thermal properties of water/Nickel nanofluid (NF). The ther-mophysical properties of the NFs were simulated and studied using MD simulation, which was a common computational method because of the high cost and limitations of experimental approaches, particularly at molecular dimensions. LAMMPS software package, and the EAM potential function were used to simulate the structure. In the present simulation, three NF samples containing Ni with SVF of 1, 2, and 3% with two shape of spherical (SN) and cylindrical (CN) and in two different Temp of 313 to 358 K were considered. Also, the nanoparticles (NPs) with the radii of 8, 10, and 12 Å were considered in the simulation box. The results show that by increasing Temp and SVF, the diffusion coefficient (D nf) of NFs would increase and decrease, respectively. From a numerical point of view, by increasing Temp from 313 K to358 K in 1% SVF, thermal conductivity (k nf) and D nf increased from 0.25656 to 0.99688 W/mK and 0.34786075 to 0.68396948, respectively. Moreover, by increasing SVF and T, the viscosity (µ nf) of NF increased and decreased, respectively. Significant findings: As the radius of NPs increased, the D nf of the water-based NFs increased. This is because larger NPs can provide more surface area for water molecules to interact with, which can increase the overall mobility of water molecules and enhance the D nf. Also, the µ nf decreased. This is because larger NPs can reduce the overall µ nf of the NF by increasing the mobility of water molecules and reducing the degree of hydrogen bonding between water molecules. Besides, NFs containing CN had a lower D nf than NFs created by SN. On the other hand, suspensions containing CN had a greater µ nf and k nf .
... The work of Ghosh et al. [17] has shed light on the structural behavior of supercritical Lennard-Jones fluids under confinement, uncovering the presence of the Frenkel line and layered patterns in argon gas at high pressures within nanochannels. Jabbari et al. [18] have provided a comprehensive review on the thermal conductivity and viscosity of nanofluids, serving as an excellent resource for readers seeking in-depth knowledge on this subject. ...
... The rheology of benzene-based nanofluids with aluminum and copper particles of 3 and 6 nm in size is being studied, their volume concentration φ varied from 1 to 6%. The method of nonequilibrium molecular dynamics was used in the variant with modeling of the Couette flow between two plates [19,20]. The simulation cell was a rectangular parallelepiped. ...
This article discusses the rheology of nanofluids with ordinary spherical particles. It has been shown that about a quarter of nanofluids at not too low concentrations turn out to be pseudo- or viscoplastic. Their rheology is well described by power-law fluid or Herschel–Bulkley models. To study the mechanism of rheology change, the method of nonequilibrium molecular dynamics is used. It is established that the change in rheology has a threshold character. Critical values of the shear rates of rheology change and their dependence on the concentration of nanoparticles, their size and material are found. It is shown that the change in rheology is accompanied by a change in the structure of the studied fluids, which is illustrated by the corresponding radial distribution functions.
... In recent years, with the continuous improvement of computer computing speed and the development of molecular dynamics theory, molecular dynamics simulation has rapidly developed in fields such as biopharmaceuticals, chemical engineering, materials science, machinery, electronics, and physics [4][5][6][7][8][9]. MD simulation has unique advantages, not only as a supplement to experiments, but also due to its high reliability and low cost, and it is widely used to study the nanofabrication process of SiC [10]. ...
4H-SiC (silicon carbide) is widely used in semiconductor devices due to its superior characteristics. However, processing techniques such as cutting, grinding, and polishing generally have problems such as low processing efficiency, high cost, difficulties guaranteeing processing quality, and serious material waste. The in-depth research on the mechanical behavior, material removal, and damage mechanism of SiC single crystals at the micro/nano scale is the foundation for solving these problems. This paper establishes a molecular dynamics simulation model for 4H-SiC single-crystal nano scratches, using three different directions of a Berkovich indenter to scratch the surface of the workpiece, studying the surface morphology, scratching force, and material removal during the scratching process. The results indicate that scratching directions of the tool varies, and the surface morphology also varies. After the scratching depth exceeds 1.6 nm, complete dislocations with a Burges vector of 1/3<110> appear on the crystal subsurface, leading to the plastic removal of the material. During the process of material removal, a smaller tool rake angle removes a larger amount of material chips. By analyzing the damage layer of the workpiece, the difference in the damage layer is smaller when the scratching direction is different, but the damage layer generated by the smaller rake angle of the scratching tool is thinner. It shows that the scratching force and workpiece temperature are relatively small when the rake angle of the scratching tool is small. Therefore, when scratching 4H-SiC single crystals, choosing a tool with a smaller rake angle is more beneficial for the process.
... MD simulation a computer simulation is used to study molecular systems' physical basis and function. In MD simulation, the particles interact while obeying known physical laws for a period [21]. The MD simulation method was noted to study phase transition in different structures, such as fluids, nanofluids, and PCMs. ...
Using renewable energy sources is possible via thermal energy storage (TES) systems which use phase change materials (PCMs) to store energy. PCMs store and release a large amount of energy in terms of their high melting heat. This study considered paraffin as PCM within the porous carbon matrix and copper oxide (CuO) as the nanoparticles (NPs). The molecular dynamics (MD) simulation method studied the simulated structure's phase transition process. The effect of atomic porosity and the initial pressure (IP) was considered and used in the atomic samples to survey the studied structure's thermal performance (TP). For this purpose, the changes in the charge time, discharge time, heat flux (HF), and phase transition time (PTT) were studied. The temperature and the total energy (TE) converged to 300 K and − 1580 eV after 5 ns. It indicated that the defined matrix was physically stable. The increase in porosity from 1 % to 3 % increased HF from 1452 to 1642 W/m 2 and decreased PTT from 3.92 to 3.73 ns. But, a further increase in porosity reduced the TP of simulated samples. On the other hand, the results show that the simulated atomic structure's TP was reduced by increasing the IP. HF decreased from 1452 to 987 W/m 2 (1 to 5 % range), and the PTT increased from 3.92 to 4.05 ns (1 to 3 % range).
... Carbon nanostructures usually contain atomic-level defects that can significantly affect the transport properties of these structures, as indicated by Cui et al. [14] and Fthenakis et al. [15] using non-equilibrium MD simulations. For over a decade, nanofluids, which are fluids containing nanoparticles, have attracted the interest of the research community by their high thermal conductivities [16]. Topal et al. [17] studied thermal conductivity of a designed nanofluid with MD and presented the effect of nanoparticle volume fraction on thermal conductivity enhancement. ...
This paper is on determination of the thermal conductivities of several hydrocarbon base oils by means of non-equilibrium molecular dynamics simulations using two different force fields. It aims to explore a simulation-based method for lubricant molecular design and analysis concerning heat transfer in electrical vehicle lubrication. Argon was analyzed as a reference for method evaluation, and the results reveal that the calculated conductivity strongly depends on the size of the computational domain. However, for hydrocarbon base oils, the dependence on computation domain size is less prominent as the domain size increases. The method of direct calculation in a sufficiently large computation domain and that of reciprocal extrapolation with data calculated in a much smaller domain are both applicable, and each has a certain value in oil conductivity calculation. The calculated conductivities show certain overpredictions when compared with experimentally measured results, and the overprediction factor is related to number of carbon atoms of the liquid molecules. The results reveal that the thermal conductivity of a single-chain hydrocarbon liquid is linearly proportional to the number of carbon atoms. While each additional branch increases thermal conductivity slightly, the presence of multiple branches reduces it from the ideal linear relationship. A set of equations was formulated to correlate hydrocarbon liquid thermal conductivity with molecular characteristics in terms of number of carbon atoms and number of branches.
... Then, by calculating the temperature gradient between the heat source and heat sink using Fourier's law, the thermal conductivity is calculated from Eq.12. In this method, it is assumed that the system is isotropic [27,[30][31][32][33][34]. ...
Paying attention to transport phenomena in fluids has always been an integral part in designing chemical processes and water has always been a major part of scientific researches. In this study, the self-diffusion coefficient, shear viscosity and thermal conductivity of water at 298.15 K and 1 atm pressure were predicted and compared using four models of TIP3P-Ew, SPC, SPC/E and TIP4P-2005 by equilibrium and non-equilibrium molecular dynamics (NEMD) simulations. To predict the self-diffusion coefficient and shear viscosity, two equilibrium methods of Green-Kubo and Einstein were applied and there was approximately no difference between the results of these methods. Among the studied models, the results of TIP4P-2005 had the highest consistency with experimental data. To predict the thermal conductivity, Green-Kubo and NEMD methods were employed. The NEMD was a far more accurate and better method than Green-Kubo method and the results of TIP3P-Ew model had the highest agreement with the experimental data.
