Thermodynamics and Dynamics of Supercritical Water Pseudo‐Boiling

Abstract

Supercritical fluid pseudo‐boiling (PB), recently brought to the attention of the scientific community, is the phenomenon occurring when fluid changes its structure from liquid‐like (LL) to gas‐like (GL) states across the Widom line. This work provides the first quantitative analysis on the thermodynamics and the dynamics of water's PB, since the understanding of this phase transition is mandatory for the successful implementation of technologies using supercritical water (scH2O) for environmental, energy, and nanomaterial applications. The study combines computational techniques with in situ neutron imaging measurements. The results demonstrate that, during isobaric heating close to the critical point, while water density drops by a factor of three in the PB transitional region, the system needs >16 times less energy to increase its temperature by 1 K than to change its structure from LL to GL phase. Above the PB‐Widom line, the structure of LL water consists mainly of tetramers and trimers, while below the line mostly dimers and monomers form in the GL phase. At atomic level, the PB dynamics are similar to those of the subcritical water vaporization. This fundamental knowledge has great impact on water science, as it helps to establish the structure–properties relationship of scH2O.

Deciphering The Molecular Mechanism Of Water Boiling At Heterogeneous Interfaces

“…More speci cally, in respect to bulk properties, SPC/E water model reasonably predicts all the physical properties (density, compressibility, self-diffusion coe cient and dielectric constant). The Lorentz-Berthelot combining rule was used to determine the unlike Lennard-Jones parameters [54][55][56] .…”

“…The geometry of the SPC-water held xed using the rigid body approach 20,58 . An integration time step of 0.5 fs was used to ensure energy conservation and time-reversibility 56 , which is considered essential for the pathsampling scheme 21,22 . The temperature was controlled using a Nosé-Hoover thermostat with a relaxation time of 2.5 ps.…”

Functional Materials for Waste-to-Energy Processes in Supercritical Water

“…First, it is important to note that, when issues related to the fundamental research on supercritical water are discussed, the acronym used is scH 2 O [19,36], instead of the abbreviation SCW, which is mostly used when referring to the applications of water in supercritical conditions. For being consistent, the abbreviation SCW is used in this review.…”

“…With the knowledge delivered through the fundamental research in the field of supercritical fluids, it is now possible to finely tune the properties of water for the optimization of the operating parameters of SCW reactors. As an example, at 230 bar and in a temperature interval of about 6 K, the water density drops by a factor of three, the specific enthalpy increases ~500 J kg −1 [19], the self-diffusion coefficient doubles, and the dielectric constant drops to a half [20].…”

IR detection of the methane halides fluid-like state at ambient conditions

“…Therefore, the formation of supercritical fluids is generally limited to the simplest compoundswater and carbon dioxide. 3,4 One of the most perspective methods of fluid study seems to be IRspectroscopy since it clearly shows the transition of gaseous properties to liquid ones, with all accompanying transformations. However, IR study of fluids behavior and their liquid-like to gas-like state transitions are presented only in a few works to date.…”