Department of Mechanical Engineering, The University of New Mexico, Albuquerque, NM, 87131, USA.
Department of Nuclear Engineering, The University of New Mexico, Albuquerque, NM, 87131, USA.
Nat Commun. 2023 Jul 6;14(1):3983. doi: 10.1038/s41467-023-39211-z.
Our understanding of supercritical fluids has seen exciting advances over the last decades, often in direct contradiction to established textbook knowledge. Rather than being structureless, we now know that distinct supercritical liquid and gaseous states can be distinguished and that a higher order phase transition - pseudo boiling - occurs between supercritical liquid and gaseous states across the Widom line. Observed droplets and sharp interfaces at supercritical pressures are interpreted as evidence of surface tension due to phase equilibria in mixtures, given the lack of a supercritical liquid-vapor phase equilibrium in pure fluids. However, here we introduce an alternative physical mechanism that unexpectedly causes a sharpening of interfacial density gradients in absence of surface tension: thermal gradient induced interfaces (TGIIF). We show from first principles and simulations that, unlike in gases or liquids, stable droplets, bubbles, and planar interfaces can exist without surface tension. These results challenge and generalize our understanding of what droplets and phase interfaces are, and uncover yet another unexpected behavior of supercritical fluids. TGIIF provide a new physical mechanism that could be used to tailor and optimize fuel injection or heat transfer processes in high-pressure power systems.
在过去的几十年里，我们对超临界流体的理解取得了令人兴奋的进展，这些进展常常与既定的教科书知识直接矛盾。我们现在知道，超临界液体和气体状态可以区分开来，而且在 Widom 线处，超临界液体和气体状态之间会发生更高阶的相变——类沸腾相变。在超临界压力下观察到的液滴和锐利界面被解释为由于混合物中的相平衡而存在表面张力的证据，因为在纯流体中没有超临界液体-蒸气相平衡。然而，在这里，我们引入了一种替代的物理机制，它在没有表面张力的情况下出人意料地导致了界面密度梯度的锐化：热梯度诱导界面（TGIIF）。我们从第一性原理和模拟中表明，与气体或液体不同，稳定的液滴、气泡和平面界面可以在没有表面张力的情况下存在。这些结果挑战并概括了我们对液滴和相界面的理解，并揭示了超临界流体的另一种意外行为。TGIIF 提供了一种新的物理机制，可用于在高压动力系统中调整和优化燃料喷射或传热过程。
