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

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.

Boron nitride (BN) nanofluids as cooling agent in thermal management system (TMS)

“…4a and b show that the volume and number average particle size of BN nanoparticle are 87 and 80 nm, respectively, measured by dispersing small quantity of BN nanoparticle in deionized water, indicating no aggregation of particle at all. BET specific surface area of BN powder is found to be 127.48 m 2 /g after 4 month of milling which is higher than the reported value of 40.6098 m 2 /g [10]. This phenomena suggests that the proposed surface modification method successfully modifies BN powder into BN nanoparticle that allows dispersion in water for obtaining nanofluids.…”

“…They have claimed that nanofluids with larger sized nanoparticles provide higher increase in thermal conductivity compared to the ones prepared with smaller sized particles due to the different shapes of BN nanoparticles and their specific surface area. They also detected that BN/EG nanofluids with 0.025% particle volume concentration have greater thermal conductivity improvement compared to higher particle loadings [10]. In another study, high thermal conductivity of BN nanofluids is observed, which is synthesized using two-step method by maintaining different weight ratios of BN powder [11,12].…”

“…Recently, Boron nitride (BN) has attracted much more attention for excellent mechanical properties [7,8] and chemical inertness [9]. In recent times, attempts have also been made to synthesize BN nanofluids without surfactants via two-step method [10][11][12]. Influence of BN nanofluids particle size over the thermal conductivity is also reported.…”

Huge thermal conductivity enhancement in boron nitride – ethylene glycol nanofluids

“…Li et al [65] presented a paper in which they described two unusual phenomena in the thermal conductivity of this group of materials. Li et al showed that with low volume concentrations of nanoparticles thermal conductivity does not increase with concentration, but may decrease.…”

“…Li et al showed that with low volume concentrations of nanoparticles thermal conductivity does not increase with concentration, but may decrease. This is due to the aggregation of nanoparticles BN at higher concentrations and creates a, "cloud-like compact aggregations" [65]. Guo et al [66] investigated thermal conductivity of suspensions of BN nanoparticle in ethylene glycol with three types of dispersant.…”