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The molecular dynamic simulation on impact and friction characters of nanofluids with many nanoparticles system.

Lv J, Bai M, Cui W, Li X - Nanoscale Res Lett (2011)

Bottom Line: The Cu-Ar nanofluid model consisted of eight spherical copper nanoparticles with each particle diameter of 4 nm and argon atoms as base liquid.The Lennard-Jones potential function was adopted to deal with the interactions between atoms.In this process, agglomeration of nanoparticles was very apparent, with the pressure increasing, the phenomenon became more prominent.

View Article: PubMed Central - HTML - PubMed

Affiliation: State Key Laboratory of Structural Analysis for Industrial Equipment, Department of Engineering Mechanics, Dalian University of Technology, Dalian 116024, China. lvjizu2002@yahoo.com.cn.

ABSTRACT
Impact and friction model of nanofluid for molecular dynamics simulation was built which consists of two Cu plates and Cu-Ar nanofluid. The Cu-Ar nanofluid model consisted of eight spherical copper nanoparticles with each particle diameter of 4 nm and argon atoms as base liquid. The Lennard-Jones potential function was adopted to deal with the interactions between atoms. Thus motion states and interaction of nanoparticles at different time through impact and friction process could be obtained and friction mechanism of nanofluids could be analyzed. In the friction process, nanoparticles showed motions of rotation and translation, but effected by the interactions of nanoparticles, the rotation of nanoparticles was trapped during the compression process. In this process, agglomeration of nanoparticles was very apparent, with the pressure increasing, the phenomenon became more prominent. The reunited nanoparticles would provide supporting efforts for the whole channel, and in the meantime reduced the contact between two friction surfaces, therefore, strengthened lubrication and decreased friction. In the condition of overlarge positive pressure, the nanoparticles would be crashed and formed particles on atomic level and strayed in base liquid.

No MeSH data available.


Related in: MedlinePlus

Comparison of impact processes of two cases. The screenshot times are at 600, 800, 1000, 1200, 1400, and 1600 ps.
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Figure 5: Comparison of impact processes of two cases. The screenshot times are at 600, 800, 1000, 1200, 1400, and 1600 ps.

Mentions: The motion states of nanoparticles between plates in the processes of impact and friction under two compressed modes are shown in Figure 5. Through comparative analysis, it could be clearly observed that influenced by the strong shear force nanoparticles make translation motions between plates, in case 1 the velocity of nanoparticles in upper layer during 800 to 1000 ps is statistically estimated as 65.5 m/s, those nanoparticles in lower layer is 25.5 m/s; in case 2 the translation velocity of nanoparticles in upper layer is 55 m/s and that of nanoparticles in lower layer is 32 m/s; the velocity of nanoparticles in lower layer is much lower than that of nanoparticles in upper layer, and the main reason might be the absorption force of plate for the nanoparticles. And under different compressed modes, the shear translation velocities are different, the more pressure, the more obvious the effects for nanoparticles in the lower layer is, which is influenced by the internal flow with the external compression. In the meantime, it could be found that accompanying with the translation motion, the nanoparticles have drastic rotation. But with the compression process penetrating deeply, the rotation of nanoparticles is inhibited, and the reason might be that the interactions between nanoparticles are much stronger that the shear force by the upper plate, and thus, as influenced by the upper plate, the rotation effect is further reduced. Especially as the nanoparticles are interacting, the selection effect of nanoparticles is completely inhibited. In the compression process, the distribution of nanoparticles is affected to some extent, and the internal structure of nanoparticle would change. Under the effect of positive pressure from the upper plate, nanoparticles would be first absorbed to the plate, and then separate from it for the effect of the strong shear force; however, some metallic atoms from nanoparticles would remain being absorbed to the plate and made some filling effect to the plate. Figure 6 shows the motion state distribution of nanoparticles between plates in the friction process. In which it could be found that the nanoparticles formed apparent agglomeration, and with the increase of pressure, the agglomeration effect of nanoparticles is different, which shows that with higher pressure, the more obvious the agglomeration effect is. And the nanoparticles after agglomeration would serve as a supporting effect for the channel, and therefore, reduce the interactions between plates, strengthen the lubrication action, and decrease the friction. In addition, when the pressure is too high, nanoparticles would be crushed and some individual metallic atoms would stray in base liquid which has certain pollution effect to the lubrication system. And in the friction process, the aggregation of nanoparticles would move between the plates and interact with the plates, therefore make some metallic nanoparticles be adsorbed to the plate which supports a filling effect for the plates. Particularly for a rough surface, this absorption effect would make the surface smoother and decrease the frictional resistance further.


The molecular dynamic simulation on impact and friction characters of nanofluids with many nanoparticles system.

Lv J, Bai M, Cui W, Li X - Nanoscale Res Lett (2011)

Comparison of impact processes of two cases. The screenshot times are at 600, 800, 1000, 1200, 1400, and 1600 ps.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211256&req=5

Figure 5: Comparison of impact processes of two cases. The screenshot times are at 600, 800, 1000, 1200, 1400, and 1600 ps.
Mentions: The motion states of nanoparticles between plates in the processes of impact and friction under two compressed modes are shown in Figure 5. Through comparative analysis, it could be clearly observed that influenced by the strong shear force nanoparticles make translation motions between plates, in case 1 the velocity of nanoparticles in upper layer during 800 to 1000 ps is statistically estimated as 65.5 m/s, those nanoparticles in lower layer is 25.5 m/s; in case 2 the translation velocity of nanoparticles in upper layer is 55 m/s and that of nanoparticles in lower layer is 32 m/s; the velocity of nanoparticles in lower layer is much lower than that of nanoparticles in upper layer, and the main reason might be the absorption force of plate for the nanoparticles. And under different compressed modes, the shear translation velocities are different, the more pressure, the more obvious the effects for nanoparticles in the lower layer is, which is influenced by the internal flow with the external compression. In the meantime, it could be found that accompanying with the translation motion, the nanoparticles have drastic rotation. But with the compression process penetrating deeply, the rotation of nanoparticles is inhibited, and the reason might be that the interactions between nanoparticles are much stronger that the shear force by the upper plate, and thus, as influenced by the upper plate, the rotation effect is further reduced. Especially as the nanoparticles are interacting, the selection effect of nanoparticles is completely inhibited. In the compression process, the distribution of nanoparticles is affected to some extent, and the internal structure of nanoparticle would change. Under the effect of positive pressure from the upper plate, nanoparticles would be first absorbed to the plate, and then separate from it for the effect of the strong shear force; however, some metallic atoms from nanoparticles would remain being absorbed to the plate and made some filling effect to the plate. Figure 6 shows the motion state distribution of nanoparticles between plates in the friction process. In which it could be found that the nanoparticles formed apparent agglomeration, and with the increase of pressure, the agglomeration effect of nanoparticles is different, which shows that with higher pressure, the more obvious the agglomeration effect is. And the nanoparticles after agglomeration would serve as a supporting effect for the channel, and therefore, reduce the interactions between plates, strengthen the lubrication action, and decrease the friction. In addition, when the pressure is too high, nanoparticles would be crushed and some individual metallic atoms would stray in base liquid which has certain pollution effect to the lubrication system. And in the friction process, the aggregation of nanoparticles would move between the plates and interact with the plates, therefore make some metallic nanoparticles be adsorbed to the plate which supports a filling effect for the plates. Particularly for a rough surface, this absorption effect would make the surface smoother and decrease the frictional resistance further.

Bottom Line: The Cu-Ar nanofluid model consisted of eight spherical copper nanoparticles with each particle diameter of 4 nm and argon atoms as base liquid.The Lennard-Jones potential function was adopted to deal with the interactions between atoms.In this process, agglomeration of nanoparticles was very apparent, with the pressure increasing, the phenomenon became more prominent.

View Article: PubMed Central - HTML - PubMed

Affiliation: State Key Laboratory of Structural Analysis for Industrial Equipment, Department of Engineering Mechanics, Dalian University of Technology, Dalian 116024, China. lvjizu2002@yahoo.com.cn.

ABSTRACT
Impact and friction model of nanofluid for molecular dynamics simulation was built which consists of two Cu plates and Cu-Ar nanofluid. The Cu-Ar nanofluid model consisted of eight spherical copper nanoparticles with each particle diameter of 4 nm and argon atoms as base liquid. The Lennard-Jones potential function was adopted to deal with the interactions between atoms. Thus motion states and interaction of nanoparticles at different time through impact and friction process could be obtained and friction mechanism of nanofluids could be analyzed. In the friction process, nanoparticles showed motions of rotation and translation, but effected by the interactions of nanoparticles, the rotation of nanoparticles was trapped during the compression process. In this process, agglomeration of nanoparticles was very apparent, with the pressure increasing, the phenomenon became more prominent. The reunited nanoparticles would provide supporting efforts for the whole channel, and in the meantime reduced the contact between two friction surfaces, therefore, strengthened lubrication and decreased friction. In the condition of overlarge positive pressure, the nanoparticles would be crashed and formed particles on atomic level and strayed in base liquid.

No MeSH data available.


Related in: MedlinePlus