Molecular dynamics simulations of energy accommodation between gases and polymers for ultra-low thermal conductivity insulation

Feng, Tianli; Rai, Amit; Hun, Diana; Shrestha, Som

doi:10.1016/j.ijheatmasstransfer.2020.120459

Cited by 16 publications

(8 citation statements)

References 40 publications

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“…An improved agreement is clearly obtained, compared to that of the classical Kaganer's model. The improvement can also endorse the calculation method of effective α proposed by Feng et al 33 Modified Kaganer's Model. The success in the above case can be extended to revise the classical Kaganer's model by considering the effect of gas−solid interaction (μ) on effective α.…”

Section: ■ Theoretical Modelingmentioning

confidence: 69%

“…The modification will be carried out by proposing an "effective thermal accommodation coefficient" (effective α). The effective α can be calculated from the gas−solid thermal conductance, according to a method recently proposed by Feng et al 33 The gas−solid thermal conductance (G ) can be expressed as where n is the collision rate of gas molecules per unit area calculated by π = n p mk T / 2 B with pressure p, molar mass of gas molecules m, and gas temperature T. Here, the effective α for the five cases are calculated and shown in Figure 3b. An averaged value can be obtained as 0.81, if we assume that the effective α is independent of Kn.…”

Section: ■ Theoretical Modelingmentioning

confidence: 99%

“…They then 32 analyzed the effect of surface properties on gas heat conduction. Recently, Feng et al 33 determined the accommodation coefficient of several types of gases on polymers. However, we still need some applicable knowledge for a practical solution of gas−solid interaction modeling.…”

Section: ■ Introductionmentioning

confidence: 99%

“…Obviously, the uncertainty in thermal accommodation can lead to more errors in heat conduction modellings. , So this issue has been explored theoretically, − numerically, − and experimentally. , Among these efforts, Molecular Dynamics (MD) simulation has delivered remarkable advances. ,− Rabani et al studied the influence of the temperature difference between two channel walls on gas molecular distribution and heat transfer. They then analyzed the effect of surface properties on gas heat conduction.…”

Section: Introductionmentioning

confidence: 99%

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How Gas–Solid Interaction Matters in Graphene-Doped Silica Aerogels

et al. 2022

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It was interesting to experimentally find that the thermal insulation of silica aerogels was improved by doping graphene sheets with high heat conductivity. The underlying mechanism is investigated in the present work from the perspective of gas−solid interaction using a comprehensive analysis of molecular dynamics (MD) simulations, theoretical modeling, and experimental data. The MD-modeled small pores are demonstrated to effectively represent big pores in silica aerogels because of similar heat conduction physics, because it is found that adsorption does not contribute to gas heat conduction. Meanwhile, based on the experimentally measured density, the porous structures are schematically re-engineered using molecular modeling for the first time. The evaluated pore size distributions numerically present a consistency with available experimental data. Inspired by the visualization of the 3D pore structure, we proposed a graphene/silica/nitrogen model to evaluate the role of graphene in heat conduction: it can not only reduce effective gas collision (impede heat transport) but also enhance the gas−solid coupling effect. The former is dominant because of the high porosity, leading to an improvement in thermal insulation. The competition between them can be the reason for the "trade-off" phenomenon in the graphene doping effect in the available experiment.

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Section: ■ Theoretical Modelingmentioning

confidence: 69%

Section: ■ Theoretical Modelingmentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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How Gas–Solid Interaction Matters in Graphene-Doped Silica Aerogels

et al. 2022

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“…This gives a first hint, in what range of values α could be expected, as the results of MD can be considered as the lower limit of the thermal accommodation coefficient on amorphous SiO 2 and CaSiO 3 . Using MD, many studies have been conducted previously to determine the accommodation coefficient values for different solid-gas molecule combinations (e. g. amorphous silica aerogels [7] or amorphous polystyrene [8], crystal [9]). However, the study of Zichunyang et al [7] neglects the influence of the attractive forces of the solid atoms between neighboring nanoparticle interfaces.…”

Section: Introductionmentioning

confidence: 99%

Determination of Thermal Accommodation Coefficients on CaSiO3 and SiO2 using Molecular Dynamics and Experiments

Bayer-Buhr,

Vimal,

Prakash

et al. 2021

Preprint

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The thermal accommodation coefficient α has been assumed, although lacking any experimental proof, to be near unity for most gases so far, which denotes no influence. However, it plays a contributing role in the field of the effective thermal conductivity of highly porous insulation materials based on SiO 2 or CaSiO 3 as it is shown in this work. Besides, this work investigates a possible influence on α for Ar, N 2 , He within parameters like temperature, roughness and contamination as this has not been examined on such materials so far. More importantly, it answers the question whether the assumption of α = 1 is valid.By using a parallel plates device, very similar to the guarded-hot-plate, following EN 12667 it was possible to determine α on a dense CaSiO 3 . It occured that the assumptions α = 1 (for Ar, N 2 ) and α = 0.3 (for He) are valid for measurements near room temperature. Further, physical adsorption was found to increase α. The determination of the influence of roughness has been started showing an interesting effect, but it still remains an open topic.In a collaborative study molecular dynamics (MD) simulations were performed showing a strong equivalence of α between SiO 2 and CaSiO 3 . These results can be considered a lower limit of α as neither roughness nor adsorption processes have been included in the simulation. Therefore, any deviations between experiments and MD could be considered as an apperance of physical adsorption.

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