A molecular dynamics study of thermal conductivity and viscosity in colloidal suspensions: From well-dispersed nanoparticles to nanoparticle aggregates

Somarathna, Chamara; Samaraweera, Nalaka; Jayasekara, Saliya; Perera, Kapila

doi:10.1016/j.applthermaleng.2023.120651

Cited by 5 publications

(4 citation statements)

References 71 publications

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“…A clear disagreement between the predictions by PHCM to the NEMD calculations can be seen in figure 3, where the PHCM overpredicts the NEMD calculations and, further fails to show any variation with the nanowire's length. In nanofluids with spherical particles as well, a similar disagreement was experienced by the present authors [37], whereas Maxwell's effective medium theory overpredicted the actual κ. The main reason for the deviation there was identified as the absence of interfacial thermal resistance (R b ) in Maxwell's formulation.…”

Section: Resultssupporting

confidence: 86%

“…Similarly, solid-like liquid layering around the nanoparticles is considered to be facilitating the κ enhancements of nanofluids by Loulijat et al [35] while Xue et al [36] argues oppositely as they have observed no difference in temperature gradients across the solid-like liquid layer and the general liquid. Following this, a recent discussion [37] by the present authors has revealed that the nanofluids containing spherical nanoparticles are unable to provide significant κ enhancements owing to the interface thermal resistance and clarifies that the previously proposed micromechanisms such as Brownian motion, Brownian motion induced micro-convection, and solid-like liquid layering do not effectively contribute to enhance the κ of such nanofluids. It also highlights the remarkable heat transfer potential of nanofluids based on extended nanostructures and demands further studies to uncover the underlying κ enhancement mechanisms of such nanofluids.…”

supporting

confidence: 79%

“…Green-Kubo formulation was previously experienced to deliver unrealistic κ enhancements in literature [55] as well as by the present authors [37]. Therefore, the Direct method κ evaluation is employed in the present study.…”

Section: Molecular Dynamics Methodsmentioning

confidence: 89%

“…However, an explanation beyond the simple parallel mode of heat transfer is indeed in need to grasp the complete picture of the heat transfer phenomenon in nanofluids based on extended nanostructures such as nanowires and nanotubes. Effects from the nanoscale dominant phenomena, including the ballistic nature of phonon transport in nanostructures, interfacial thermal resistance (R b ), and solid-like liquid layering, can be presented in the κ enhancements of this class of nanofluids [37] which are not accounted for in the simple parallel mode heat transfer analogy. New studies are being published where the κ enhancements in nanofluids based on extended nanostructures have been explained by new microscopic aspects such as improved dynamics of liquid atoms [33] and solid-like absorption layer [38] beyond the parallel mode of heat transfer.…”

mentioning

confidence: 99%

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Microscopic thermal characteristics of parallelly arranged nanowires in a liquid: the role of interface thermal resistance, solid-like liquid layer, and the restricted phonon transport

et al. 2023

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Nanofluids based on extended nanostructures, such as nanowires, have been demonstrated improved thermal conductivities (κ). However, the lack of a complete understanding at the microscopic level hinders the development of such nanofluids towards practical applications. We aim to provide it by investigating how the interface thermal resistance (Rb), ballistic phonon transport, and the solid-like liquid layer affect the heat conduction in nanowire based nanofluids. By employing Non-Equilibrium Molecular Dynamics (NEMD), it is found that the heat conduction in the parallelly arranged liquid and the nanowires exhibit a coupled thermal behavior owing to the Rb. This contradicts the predictions of the classical parallel heat conduction model, therefore, a novel model is proposed taking this coupled behavior into account. Using this model, it is shown that the high κ of the solid phase has a limited contribution to the effective κ of nanofluids having short nanowires due to the dominant Rb effect. For the case of long nanowires, however, the individual nanowire κ becomes a vital parameter defining the effective κ. Further, NEMD calculations reveal that the κ of suspended nanowires in a liquid is markedly reduced, questioning the validity of classical effective medium theories which use the bulk parameters. This reduction is attributed to surface atoms’ restricted vibrational freedom and the nanowire’s phonon-boundary scattering. By substituting this reduced κ of the solid phase into the new mathematical model, the theoretical predictions align closely with the NEMD calculations, exhibiting deviations below 10%. The sole contribution from the solid-like liquid layer to the κ enhancement lies between 20-30% in the nanofluids presently considered. Therefore, the findings of this study highlight the important roles played by the identified microscopic thermal characteristics in defining the effective κ for nanofluids based on nanowires.

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Section: Resultssupporting

confidence: 86%

supporting

confidence: 79%

Section: Molecular Dynamics Methodsmentioning

confidence: 89%

mentioning

confidence: 99%

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Microscopic thermal characteristics of parallelly arranged nanowires in a liquid: the role of interface thermal resistance, solid-like liquid layer, and the restricted phonon transport

et al. 2023

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Critical analysis of thermal conductivity enhancement of alumina–water nanofluids

Iqbal

Kouloulias

Sergis

et al. 2023

J Therm Anal Calorim

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Nanofluids are colloidal suspensions constituted of nanoparticles and typical heat transfer fluids which have shown potential in yielding enhanced heat transport for many applications. Significant attention has been paid to their thermal conductivity enhancement which has been alleged, in some cases, to exceed theoretical limits classifying the enhancement as “anomalous”. The present study aims to quantitatively investigate the nature of the enhancements reported in the literature and classify their alignment with theoretical predictions. To do so, a rigorous and objective mathematical analysis method has been employed. The novelty and value of the present work lies in the deeper characterisation and understanding of the anomalous observations reported. The present analytical study focuses on (spherical) Al2O3–water nanofluids. It was discovered that studies involving low nanoparticle concentrations ($$\phi $$ ϕ ≤ 0.2 vol%) and the use of electrostatic stabilisation (through pH control) as opposed to steric stabilisation (using surfactants) as suspension stability control methods are likely to report anomalous effects. An exceptional case was observed for d < 15 nm, where to achieve anomalous enhancement, surfactants and pH controllers should not be used to prevent significant interfacial resistance. The shared characteristics of these anomalous observations indicate that nanofluid preparation effects are linked to the underlying physical mechanisms of heat transfer involved and those should be further investigated. The failure of studies attempting to replicate anomalous thermal conductivity enhancement in the literature could hence be understood, as these did not satisfy the conditions required to lead to an anomalous enhancement. The role of measurement errors was also considered.

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Multi-objective optimization of thermophysical properties GO powders-DW/EG Nf by RSM, NSGA-II, ANN, MLP and ML

Kiannejad Amiri,

Ghorbanzade Zaferani,

Sarmasti Emami

et al. 2023

Energy

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A molecular dynamics study of thermal conductivity and viscosity in colloidal suspensions: From well-dispersed nanoparticles to nanoparticle aggregates

Cited by 5 publications

References 71 publications

Microscopic thermal characteristics of parallelly arranged nanowires in a liquid: the role of interface thermal resistance, solid-like liquid layer, and the restricted phonon transport

Microscopic thermal characteristics of parallelly arranged nanowires in a liquid: the role of interface thermal resistance, solid-like liquid layer, and the restricted phonon transport

Critical analysis of thermal conductivity enhancement of alumina–water nanofluids

Multi-objective optimization of thermophysical properties GO powders-DW/EG Nf by RSM, NSGA-II, ANN, MLP and ML

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