Papers by Keyword: Thermotransport

Abstract: The influence of composition on thermotransport (coupling between mass and heat transport) in Ni-Al melts is investigated by making use of equilibrium molecular dynamics simulations in conjunction with the Green-Kubo formalism. To describe interatomic interactions in Ni-Al melt models, we employ the embedded-atom method potential developed in [G.P. Purja Pun, Y. Mishin, Phil. Mag., 2009, 89, 3245]. It is demonstrated that the employed interatomic potential gives good agreement with the recent experimental study [E. Sondermann, F. Kargl, A. Meyer, Presented at the 12th International Conference on Diffusion in Solids and Liquids (DSL-2016), 26-30 June 2016, Split, Croatia] regarding the direction of thermotransport in Al-rich liquid Ni-Al alloys. Moreover, the predicted values of the reduced heat of transport (the quantity which explicitly characterizes both the magnitude and direction of thermotransport) in Ni-Al melts, reveal fairly weak composition dependence while being practically independent of temperature at all. Accordingly, in the presence of a temperature gradient, our simulation results for the models of liquid Ni₂₅Al₇₅, Ni₅₀Al₅₀ and Ni₇₅Al₂₅ alloys predict consistently Ni and Al to migrate to the cold and hot ends, respectively. Meanwhile, the highest value, about eV, of the reduced heat of transport is observed for Ni₅₀Al₅₀ alloy model and it slightly decreases towards Al-rich and Ni-rich compositions.

Abstract: This article reviews the subject of the Soret effect and Thermodiffusion in solids more generally. In doing so it draws upon computer simulations made with a method (the Grout-Gillan method) derived from the Green-Kubo approach to transport coefficients in solids. The insights into the make-up of heats of transport parameters, Q*, so obtained are described and used to provide additional insight into measured heats of transport in situations where no reliable theories or simulations exist. These insights also point to the relations between heats of transport on the one hand and phonon thermal conductivity and focussed collision sequences on the other. These relations point to circumstances where the heat of transport may be small (e.g. low coordination in the lattice) or can be estimated from heats of activation for atom movements. In other cases the Grout-Gillan simulation method may offer the most reliable approach. These new insights are expected to be useful in materials modelling.

Abstract: We analyse the formalism of transport in a binary system especially focussing on a detailed consideration of the heat of transport parameter characterizing diffusion driven by a temperature gradient. We introduce the reduced heat of transport parameter Qc*' which characterizes part of the interdiffusion flux that is proportional to the temperature gradient. In an isothermal system Qc*' represents the reduced heat flow (pure heat conduction) consequent upon unit interdiffusion flux. We demonstrate that Qc*' is independent of reference frame and is practically useful for direct comparison of simulation and experimental data from different sources obtained in different reference frames. Then, we use equilibrium molecular dynamics simulations in conjunction with the Green-Kubo formalism to study the heat transport properties of a model of the liquid Ni₅₀Al₅₀ alloy at three state points within the temperature range 1500 – 4000 K. Our results predict that in the liquid Ni₅₀Al₅₀ alloy in the presence of a temperature gradient Ni tends to diffuse from the cold end to the hot end whilst Al tends to diffuse from the hot end to the cold end.

Abstract: Hydrogen redistribution caused by thermotransport in the Zr-1.0Nb-1.0Sn-0.1Fe alloy under the temperature gradient which is likely to be encountered between nuclear fuel cladding and primary cooling water (300-340
) was investigated. The heat of transport (Q*) of hydrogen was determined by using a steady state technique to evaluate the magnitude and direction of thermotransport of hydrogen in the alloy. The values of Q∗ were 23.1, 23.7 and 27.1 KJ/mol for the hydrogen concentration of 73.4, 75.8 and 94.3 ppm by weight respectively. In other words, hydrogen was transported from hot region to cold region and the value of Q∗ increased with increasing overall hydrogen concentration. The Zr-1.0Nb-1.0Sn-0.1Fe alloy had the smaller Q∗ value than that of Zircaloy-4 when compared with same overall hydrogen concentration. Thus, Zr-1.0Nb-1.0Sn-0.1Fe alloy has better resistance to the formation of hydride due to thermotransport than Zircaloy-4 does.