Hashimoto Shunsuke, Yamaguchi Satoshi, Harada Masashi, Nakajima Kenji, Kikuchi Tatsuya, Ohishi Kazuki
Energy Management Research-Domain, Emerging Technology Division, Toyota Central R&D Labs., Inc., 1-1, Yokomichi, Nagakute, Aichi 480-1192, Japan.
Analysis Research-Domain, Emerging Technology Division, Toyota Central R&D Labs., Inc., 1-1, Yokomichi, Nagakute, Aichi 480-1192, Japan.
J Colloid Interface Sci. 2023 May 15;638:475-486. doi: 10.1016/j.jcis.2023.01.101. Epub 2023 Feb 3.
Recently, it has been reported that anomalous improvement in the thermal conductivity of nanofluid composed of base liquids and dispersed solid nanoparticles, compared to the theoretically predicted value calculated from the particle fraction. Generally, the thermal conductivity values of gases and liquids are dominated by the mean free path of the molecules during translational motion. Herein, we present solid evidence showing the possible contribution of the vibrational behavior of liquid molecules around nanoparticles to increasing these thermal conductivities.
The behavior of liquid molecules in nanofluids containing SiO particles larger than 100 nm, which were dispersed in a 50 wt% aqueous solution of ethylene glycol, was investigated by means of small-angle neutron scattering, quasi-elastic neutron scattering, wide-angle X-ray scattering, and Raman spectroscopy.
The vibrational changes in the liquid molecules caused by the interactions between the nanoparticles and liquid molecules surrounding the nanoparticles contributed majorly to the increase in the thermal conductivity values of the SiO nanofluids. Because the vibration of liquid molecules is equivalent to phonon conduction in solids, the increase in thermal conductivity of the suspension due to the presence of nanoparticles was inferred to be derived from the limitation of the translational diffusion, which induces a solid-like behavior in the liquid.
最近有报道称，由基础液体和分散的固体纳米颗粒组成的纳米流体的热导率出现异常提高，相较于根据颗粒分数计算出的理论预测值。通常，气体和液体的热导率值由分子平移运动期间的平均自由程主导。在此，我们提供确凿证据，表明纳米颗粒周围液体分子的振动行为可能对提高这些热导率有贡献。
通过小角中子散射、准弹性中子散射、广角X射线散射和拉曼光谱，研究了分散在50 wt%乙二醇水溶液中的粒径大于100 nm的含SiO颗粒的纳米流体中液体分子的行为。
纳米颗粒与纳米颗粒周围液体分子之间的相互作用引起的液体分子振动变化，是SiO纳米流体热导率值增加的主要原因。由于液体分子的振动等同于固体中的声子传导，因此推断由于纳米颗粒的存在导致悬浮液热导率增加是由平移扩散的限制引起的，这在液体中诱导出类似固体的行为。
