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近年来，纳米技术的发展使得非球形纳米颗粒的工业化应用成为可能，形貌各向异性的非球形颗粒有利于改善纳米流体的传热性能。有研究表明，将Janus纳米颗粒引入到基液中可进一步增强纳米流体的导热特性。本文设计了一种具备亲水侧面和疏水底面的锥形Janus纳米颗粒，并将其引入到基液中形成锥形Janus纳米流体，采用分子动力学模拟计算了锥形和球形两种Janus纳米流体的热导率，对其导热机理进行了计算分析。结果表明，锥形颗粒表面的类固液体层效应更明显，其在基液中的扩散能力更强，因此锥形纳米流体具备比球形纳米流体更强的导热性能。对于Janus纳米流体，Janus颗粒独特的不对称结构使得其在基液中的布朗运动更为强烈，有效增强了纳米流体内部的传热效率。因此，非球形颗粒与Janus颗粒的结合可进一步提高纳米流体的导热性能，为开发新型传热工质提供了新的思路。It has been reported that the thermal conductivity of the nanofluids can be enhanced by adding Janus nanoparticles into the base fluid. Additionally, the non-spherical nanoparticles also affect the thermal characteristics of nanofluids. In this paper, conical nanoparticles are designed as Janus nanoparticles with hydrophilic side and hydrophobic bottom, which are suspended in the base fluid to form cone-shaped Janus nanofluids. By using molecular dynamics (MD) simulations, it is found that the thermal conductivity of conical Janus nanofluids can be enhanced by 43.4% compared to the base fluid, whereas the spherical Janus nanofluids demonstrate an increase of 33.7% under the same volume fraction. According to MD simulation results of the RDF and diffusion coefficients of solid particle and base fluid, the increased thermal conductivity observed in conical nanofluids can be attributed to the higher liquid layer density and the enhanced Brownian motion of the conical particles. For Janus nanofluids, the asymmetrical structure of Janus nanoparticles leads to higher diffusion coefficient compared to normal particles, which enhances the colliding possibility of Janus nanoparticles with surrounding liquid molecules and results in enhanced heat transfer in Janus nanofluids. This paper considered both fixed and unfixed particles to explore the impact of particle diffusion on nanofluids. Under the fixed condition, the Brownian motion of the nanoparticles is artificially excluded, while under the unfixed condition, the particle can diffuse in the base liquid. It is found that for both spherical and conical Janus nanofluids, the thermal conductivity of Janus nanofluids exhabits a gradual increase with rising asymmetry parameter δ under unfixed conditions. However, under fixed conditions, the thermal conductivity of Janus nanofluids is almost independent of the parameter δ. Therefore, the enhanced Brownian motion of the non-spherical particles is likely the cause of the increased thermal conductivity observed in conical Janus nanofluids. The combination of non-spherical particles and Janus particles provides a promising idea for the design of nanofluids with high thermal conductivity.
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Keywords:
- nanofluids /
- non-spherical particles /
- Janus particles /
- thermal conductivity /
- molecular dynamics simulation
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