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Investigation on two abnormal phenomena about thermal conductivity enhancement of BN/EG nanofluids.

Li Y, Zhou J, Luo Z, Tung S, Schneider E, Wu J, Li X - Nanoscale Res Lett (2011)

Bottom Line: The thermal conductivity of boron nitride/ethylene glycol (BN/EG) nanofluids was investigated by transient hot-wire method and two abnormal phenomena was reported.The chain-like loose aggregation of nanoparticles is responsible for the abnormal increment of thermal conductivity enhancement for the BN/EG nanofluids at very low particles volume fraction.And the difference in specific surface area and aspect ratio of BN nanoparticles may be the main reasons for the abnormal difference between thermal conductivity enhancements for BN/EG nanofluids prepared with 140- and 70-nm BN nanoparticles, respectively.

View Article: PubMed Central - HTML - PubMed

Affiliation: State Key Laboratory for Mechanical Behavior of Materials, School of Materials Science and Engineering, Xi'an Jiaotong University, Xi'an, Shanxi, 710049, China. lyj.xjtu@yahoo.com.cn.

ABSTRACT
The thermal conductivity of boron nitride/ethylene glycol (BN/EG) nanofluids was investigated by transient hot-wire method and two abnormal phenomena was reported. One is the abnormal higher thermal conductivity enhancement for BN/EG nanofluids at very low-volume fraction of particles, and the other is the thermal conductivity enhancement of BN/EG nanofluids synthesized with large BN nanoparticles (140 nm) which is higher than that synthesized with small BN nanoparticles (70 nm). The chain-like loose aggregation of nanoparticles is responsible for the abnormal increment of thermal conductivity enhancement for the BN/EG nanofluids at very low particles volume fraction. And the difference in specific surface area and aspect ratio of BN nanoparticles may be the main reasons for the abnormal difference between thermal conductivity enhancements for BN/EG nanofluids prepared with 140- and 70-nm BN nanoparticles, respectively.

No MeSH data available.


HRTEM micrographs of BN nanoparticles suspended in BN/EG nanofluids. (a) Chain-like loose aggregation of BN nanoparticles in 0.025vol% BN/EG nanofluids. (b) Cloud-like compact aggregation of BN nanoparticles in 0.2Vol% BN/EG nanofluids.
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Figure 4: HRTEM micrographs of BN nanoparticles suspended in BN/EG nanofluids. (a) Chain-like loose aggregation of BN nanoparticles in 0.025vol% BN/EG nanofluids. (b) Cloud-like compact aggregation of BN nanoparticles in 0.2Vol% BN/EG nanofluids.

Mentions: Figure 4a, b showed the morphology of nanoparticles suspended in 0.025 vol.% and 0.2 vol.% BN/EG nanofluids, respectively. It can be seen that the morphology of BN nanoparticles suspended in 0.025 vol.% BN/EG nanofluids is chain-like loose aggregation while in 0.2 vol.% BN/EG nanofluids is cloud-like compact aggregation. This discrepancy may be the main reason for the abnormal difference between the thermal conductivity enhancements of them. Generally, Brownian motion, by which particles move through liquid, thereby enabling direct solid-solid transport of heat from one to another, is considered as a key mechanism governing the thermal behavior of nanofluids [17-20]. In 0.025 vol.% BN/EG nanofluids, many uniform distributed chain-like loose aggregations of nanoparticles, acting as a three-dimensional dense network, can improve the heat transfer efficiency by providing many rapid, longer heat flow paths through Brownian motion of nanoparticles. While in 0.2 vol.% BN/EG nanofluids, high efficient heat transfer was limited in cloud-like compact aggregation. Heat transfer among cloud-like compact aggregations would be weakened for the large regions of particle-free liquid with high thermal resistance. It can be speculated that a more high thermal conductivity could be obtained when the volume fraction of these uniform distributed chain-like loose aggregations of nanoparticles in BN/EG nanofluid was increased because more efficient heat flow paths in the nanofluid could be provided.


Investigation on two abnormal phenomena about thermal conductivity enhancement of BN/EG nanofluids.

Li Y, Zhou J, Luo Z, Tung S, Schneider E, Wu J, Li X - Nanoscale Res Lett (2011)

HRTEM micrographs of BN nanoparticles suspended in BN/EG nanofluids. (a) Chain-like loose aggregation of BN nanoparticles in 0.025vol% BN/EG nanofluids. (b) Cloud-like compact aggregation of BN nanoparticles in 0.2Vol% BN/EG nanofluids.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211862&req=5

Figure 4: HRTEM micrographs of BN nanoparticles suspended in BN/EG nanofluids. (a) Chain-like loose aggregation of BN nanoparticles in 0.025vol% BN/EG nanofluids. (b) Cloud-like compact aggregation of BN nanoparticles in 0.2Vol% BN/EG nanofluids.
Mentions: Figure 4a, b showed the morphology of nanoparticles suspended in 0.025 vol.% and 0.2 vol.% BN/EG nanofluids, respectively. It can be seen that the morphology of BN nanoparticles suspended in 0.025 vol.% BN/EG nanofluids is chain-like loose aggregation while in 0.2 vol.% BN/EG nanofluids is cloud-like compact aggregation. This discrepancy may be the main reason for the abnormal difference between the thermal conductivity enhancements of them. Generally, Brownian motion, by which particles move through liquid, thereby enabling direct solid-solid transport of heat from one to another, is considered as a key mechanism governing the thermal behavior of nanofluids [17-20]. In 0.025 vol.% BN/EG nanofluids, many uniform distributed chain-like loose aggregations of nanoparticles, acting as a three-dimensional dense network, can improve the heat transfer efficiency by providing many rapid, longer heat flow paths through Brownian motion of nanoparticles. While in 0.2 vol.% BN/EG nanofluids, high efficient heat transfer was limited in cloud-like compact aggregation. Heat transfer among cloud-like compact aggregations would be weakened for the large regions of particle-free liquid with high thermal resistance. It can be speculated that a more high thermal conductivity could be obtained when the volume fraction of these uniform distributed chain-like loose aggregations of nanoparticles in BN/EG nanofluid was increased because more efficient heat flow paths in the nanofluid could be provided.

Bottom Line: The thermal conductivity of boron nitride/ethylene glycol (BN/EG) nanofluids was investigated by transient hot-wire method and two abnormal phenomena was reported.The chain-like loose aggregation of nanoparticles is responsible for the abnormal increment of thermal conductivity enhancement for the BN/EG nanofluids at very low particles volume fraction.And the difference in specific surface area and aspect ratio of BN nanoparticles may be the main reasons for the abnormal difference between thermal conductivity enhancements for BN/EG nanofluids prepared with 140- and 70-nm BN nanoparticles, respectively.

View Article: PubMed Central - HTML - PubMed

Affiliation: State Key Laboratory for Mechanical Behavior of Materials, School of Materials Science and Engineering, Xi'an Jiaotong University, Xi'an, Shanxi, 710049, China. lyj.xjtu@yahoo.com.cn.

ABSTRACT
The thermal conductivity of boron nitride/ethylene glycol (BN/EG) nanofluids was investigated by transient hot-wire method and two abnormal phenomena was reported. One is the abnormal higher thermal conductivity enhancement for BN/EG nanofluids at very low-volume fraction of particles, and the other is the thermal conductivity enhancement of BN/EG nanofluids synthesized with large BN nanoparticles (140 nm) which is higher than that synthesized with small BN nanoparticles (70 nm). The chain-like loose aggregation of nanoparticles is responsible for the abnormal increment of thermal conductivity enhancement for the BN/EG nanofluids at very low particles volume fraction. And the difference in specific surface area and aspect ratio of BN nanoparticles may be the main reasons for the abnormal difference between thermal conductivity enhancements for BN/EG nanofluids prepared with 140- and 70-nm BN nanoparticles, respectively.

No MeSH data available.