Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussel, Belgium.
Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussel, Belgium.
J Chromatogr A. 2018 Nov 9;1575:26-33. doi: 10.1016/j.chroma.2018.08.056. Epub 2018 Sep 1.
We report on a numerical study of the thermal conductivity of core-shell particle packed bed columns. Covering a variety of packing structures and a broad range of mobile phase and porous zone conductivities, it was in all cases found that switching to particles with a highly conducting core (e.g., with a gold or copper core instead of a silica core) would produce a much smaller increase of the effective heat conductivity of the bed (k) than previously expected in literature. We found maximal increases on the order of some 20-70%, which is much lower than the potential increases up to 2000% assumed in literature. The overestimation in literature could be attributed to the fact that this literature was based on an incorrect extrapolation of the Zarichnyak-model which was the heat conductivity model predominantly used up till now. On the other hand, the computed relationships between k and the core conductivity obtained in the present study are in good agreement with an analytical solution derived from the effective medium theory, a theory which is physically much more relevant for the case at hand than the Zarichnyak-model. The results also show that the observed increase in effective bed conductivity between fully porous and core-shell particle beds frequently observed in literature is not only due to the presence of the core, but that differences in the shell layer conductivity can play an equally important role. In addition, it could also be demonstrated that, if ways could be found to increase the conductivity of the shell layer, this would produce a much stronger increase of the overall bed conductivity than will ever be possible by increasing the conductivity of the cores.
我们报告了一项关于核壳颗粒填充床柱热导率的数值研究。涵盖了各种填充结构和广泛的流动相和多孔区电导率，在所有情况下，我们都发现，将具有高导电性核（例如，用金或铜核代替硅核）的颗粒转换为颗粒会导致床有效热导率（k）的增加远小于文献中以前预期的增加。我们发现最大的增加幅度约为 20-70%，远低于文献中假设的高达 2000%的潜在增加。文献中的高估可以归因于这样一个事实，即该文献基于对 Zarichnyak 模型的不正确外推，该模型是迄今为止主要使用的热导率模型。另一方面，本研究中获得的 k 与核心电导率之间的计算关系与有效介质理论导出的解析解非常吻合，该理论对于当前情况比 Zarichnyak 模型更具物理相关性。结果还表明，文献中经常观察到的完全多孔和核壳颗粒床之间有效床电导率的增加不仅归因于核的存在，而且壳层电导率的差异也可以起到同样重要的作用。此外，还可以证明，如果能够找到增加壳层电导率的方法，那么与增加核的电导率相比，这将产生更强的整体床电导率的增加。
