Thermodynamic Analysis of Wall Effects on Phase Stability and Homogeneous Nucleation in Nanotubes Containing Superheated Liquid

Rapid heating or sudden depressurization can create highly superheated liquid conditions in stationary or flowing liquid in nanochannels. In these situations, the phase stability of the liquid and the conditions for the onset of bubble nucleation are important factors in the fluid behavior in applications. In the investigation summarized here, a statistical thermodynamics analysis is used to derive a modified version of the Redlich-Kwong fluid property model that accounts for attractive forces between the solid wall surface atoms and liquid molecules in the fluid within a nanochannel. In this model, the wall-fluid attractive forces are quantified in terms of Hamaker constants, which makes it possible to assess the effect of wall-fluid force interactions on the spinodal conditions for a variety of fluid and surface material combinations. This investigation focuses on the application of the aforementioned model to high aspect ratio (parallel plate) channels where a second wall is placed parallel to the first at distances varying in scale from nanometers to micrometers. At large channel widths the fluid properties exhibit wall effects very near each wall with bulk fluid property values being predicted in the center of the channel. As the channel width decreases, the fluid in the center of the channel begins to feel the effects of both walls and the properties deviate from the bulk values throughout the channel; importantly, the spinodal temperature increases significantly above the bulk fluid value. Fluid property profiles are developed for common combinations of walls and fluids, and properties are investigated as a function of non-dimensionalized distance within the channel across various channel widths. The results of this analysis imply that in nano- and micro-passages and near walls with nano-to micro-scale roughness, fluid may experience a stabilizing effect due to its proximity to nearby walls.