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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.


SEM image of the BN nanoparticles. (a) 140nm (b) 70nm.
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Figure 1: SEM image of the BN nanoparticles. (a) 140nm (b) 70nm.

Mentions: BN powder of 140 and 70 nm with purity more than 99% were used as additives, as shown in Figure 1a, b, and ethylene glycol in analytical grade was employed as basefluid to prepare BN/EG nanofluids. A two-step method was used to synthesize BN/EG nanofluids. Proper quantities of BN powder weighed by a mass balance with an accuracy of 0.1 mg were dispersed into the ethylene alcohol base fluid. No dispersant was added. In order to assure uniform dispersion of nanoparticles in the base fluid, magnetic force stirring and ultrasonic agitation for 30 min were then employed, respectively. The apparatus and parameters for preparing nanofluids are shown in Table 1. The morphology of the dry nanoparticles was observed by a JEOL JSM-7000F scanning electron microscope (JEOL Ltd., Tokyo, Japan) and the nanoparticles suspended in the nanofluid were observed by a JEM-200CX transmission electron microscope (TEM; JEOL Ltd). The specific surface area of the nanosized BN powders were measured by Brunnauer-Emmett-Teller methods using a micromeritics ASAP 2020 surface area and porosity analyzer (Micromeritics Instrument Corp., Norcross, GA, USA). The Crystalline structure of the BN nanoparticles was investigated by means of Rigaku D/MAX-2400 x-ray diffraction analysis (Rigaku Corp., Tokyo, Japan) (XRD) using Cu Ka radiation (λ = 0.15418nm) at room temperature. The thermal conductivity of the BN/EG nanofluids was measured by transient hot-wire apparatus [40]. The uncertainty of this apparatus is between ± 2.0%. To improve the accuracy of the data, the thermal conductivity of BN/EG nanofluids with lower nanoparticles volume fraction was measured by an improved transient hot-wire apparatus [41]. This improved transient hot-wire apparatus is simpler and more robust compared to previous ones besides the improvement on accuracy [42,43]. The uncertainty of the improved transient hot-wire apparatus is between ± 0.51%.


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)

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

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

Figure 1: SEM image of the BN nanoparticles. (a) 140nm (b) 70nm.
Mentions: BN powder of 140 and 70 nm with purity more than 99% were used as additives, as shown in Figure 1a, b, and ethylene glycol in analytical grade was employed as basefluid to prepare BN/EG nanofluids. A two-step method was used to synthesize BN/EG nanofluids. Proper quantities of BN powder weighed by a mass balance with an accuracy of 0.1 mg were dispersed into the ethylene alcohol base fluid. No dispersant was added. In order to assure uniform dispersion of nanoparticles in the base fluid, magnetic force stirring and ultrasonic agitation for 30 min were then employed, respectively. The apparatus and parameters for preparing nanofluids are shown in Table 1. The morphology of the dry nanoparticles was observed by a JEOL JSM-7000F scanning electron microscope (JEOL Ltd., Tokyo, Japan) and the nanoparticles suspended in the nanofluid were observed by a JEM-200CX transmission electron microscope (TEM; JEOL Ltd). The specific surface area of the nanosized BN powders were measured by Brunnauer-Emmett-Teller methods using a micromeritics ASAP 2020 surface area and porosity analyzer (Micromeritics Instrument Corp., Norcross, GA, USA). The Crystalline structure of the BN nanoparticles was investigated by means of Rigaku D/MAX-2400 x-ray diffraction analysis (Rigaku Corp., Tokyo, Japan) (XRD) using Cu Ka radiation (λ = 0.15418nm) at room temperature. The thermal conductivity of the BN/EG nanofluids was measured by transient hot-wire apparatus [40]. The uncertainty of this apparatus is between ± 2.0%. To improve the accuracy of the data, the thermal conductivity of BN/EG nanofluids with lower nanoparticles volume fraction was measured by an improved transient hot-wire apparatus [41]. This improved transient hot-wire apparatus is simpler and more robust compared to previous ones besides the improvement on accuracy [42,43]. The uncertainty of the improved transient hot-wire apparatus is between ± 0.51%.

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.