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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 image of the BN nanoparticles. (a) 140 nm (b) 70 nm.
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Figure 7: HRTEM image of the BN nanoparticles. (a) 140 nm (b) 70 nm.

Mentions: Further observation on HRTEM image of these two kinds of BN nanoparticles indicates that the qualitative analysis about the phase component of 140-nm BN nanoparticles and 70-nm BN nanoparticles is correct, as shown in Figure 7a, b. The morphology of 140-nm BN nanoparticles is nearly all ellipsoid. However, the morphology of 70-nm BN nanoparticles is composed of cubic, ellipsoid, and spherical shape, as marked by arrows 1, 2, and 3 in Figure 7b. Moreover, the shape for most 70-nm BN nanoparticles is cubic and spherical, only few ellipsoid nanoparticles are observed. This difference in morphology indicate that nearly all 140-nm BN nanoparticles is composed of flake-like H-BN nanoparticles while 70-nm BN nanoparticles is composed of fewer flake-like H-BN and many cubic and spherical BN nanoparticles. For the specific surface area of flake-like nanoparticles is higher than that of cubic and spherical nanoparticles, the specific surface area of 140-nm BN nanoparticles is expected to be higher than that of 70-nm BN nanoparticles. Experiment showed that the specific surface area of 140-nm BN powder is 40.6098 m2/g while that of 70-nm BN powder is 35.71 m2/g. Besides, the aspect ratio of ellipsoid nanoparticles is higher than that of cubic and spherical nanoparticles. So the aspect ratio of 140-nm BN nanoparticles is higher than that of 70-nm BN nanoparticles. These differences in specific surface area and aspect ratio of 140-nm BN nanoparticles and 70-nm BN nanoparticles may be the main reasons for the abnormal different in thermal conductivity enhancement because heat transfer between the nanoparticle and the base fluid can be promoted for the larger specific surface area. Furthermore, rapid, longer heat flow paths are apt to the formation between higher aspect ratio nanoparticles and these heat flow paths can promote heat transfer also. The action of these two aspects leads to the enhancement of thermal conductivity for BN/EG nanofluids synthesis with 140-nm BN nanoparticles is higher than that synthesized with 70-nm BN nanoparticles.


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 image of the BN nanoparticles. (a) 140 nm (b) 70 nm.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 7: HRTEM image of the BN nanoparticles. (a) 140 nm (b) 70 nm.
Mentions: Further observation on HRTEM image of these two kinds of BN nanoparticles indicates that the qualitative analysis about the phase component of 140-nm BN nanoparticles and 70-nm BN nanoparticles is correct, as shown in Figure 7a, b. The morphology of 140-nm BN nanoparticles is nearly all ellipsoid. However, the morphology of 70-nm BN nanoparticles is composed of cubic, ellipsoid, and spherical shape, as marked by arrows 1, 2, and 3 in Figure 7b. Moreover, the shape for most 70-nm BN nanoparticles is cubic and spherical, only few ellipsoid nanoparticles are observed. This difference in morphology indicate that nearly all 140-nm BN nanoparticles is composed of flake-like H-BN nanoparticles while 70-nm BN nanoparticles is composed of fewer flake-like H-BN and many cubic and spherical BN nanoparticles. For the specific surface area of flake-like nanoparticles is higher than that of cubic and spherical nanoparticles, the specific surface area of 140-nm BN nanoparticles is expected to be higher than that of 70-nm BN nanoparticles. Experiment showed that the specific surface area of 140-nm BN powder is 40.6098 m2/g while that of 70-nm BN powder is 35.71 m2/g. Besides, the aspect ratio of ellipsoid nanoparticles is higher than that of cubic and spherical nanoparticles. So the aspect ratio of 140-nm BN nanoparticles is higher than that of 70-nm BN nanoparticles. These differences in specific surface area and aspect ratio of 140-nm BN nanoparticles and 70-nm BN nanoparticles may be the main reasons for the abnormal different in thermal conductivity enhancement because heat transfer between the nanoparticle and the base fluid can be promoted for the larger specific surface area. Furthermore, rapid, longer heat flow paths are apt to the formation between higher aspect ratio nanoparticles and these heat flow paths can promote heat transfer also. The action of these two aspects leads to the enhancement of thermal conductivity for BN/EG nanofluids synthesis with 140-nm BN nanoparticles is higher than that synthesized with 70-nm BN nanoparticles.

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.