Description of liquid–vapor transition behaviors in evaporative cooling technologies: A critical review

Abstract

Evaporative cooling technology benefits from the substantial latent heat released during the liquid–vapor phase transition process. A comprehensive understanding of the physical nature of phase transition is fundamental to this technology. This review provides an analysis of the theoretical foundations of the liquid–vapor transition, drawing on thermodynamics, kinetic theory, and relevant practical formulas. Additionally, the pertinent knowledge of hydrodynamics, particularly the description of vapor transport, is summarized. Subsequently, current models are reviewed from the perspective of the interplay between the liquid–vapor transition and vapor transport processes. The descriptions and limitations of phase transition processes in these models are then discussed. According to these analyses, a key distinction in the description of the liquid–vapor transition lies in the presence or absence of evaporative mass flux. Kirchhoff-type formulas describe a macroscopic steady-state liquid–vapor transition in equilibrium. The use of these formulas negates external environmental influences on the transition process, including boundary layer effects. Hertz-Knudsen-type formulas capture the essence of the process, although they make overly strict assumptions about surface geometry. It is, therefore, recommended that these accommodation coefficients be verified experimentally. The enthalpy difference models, also known as Merkel models, impose additional isobaric constraints on the isothermal process, making them suitable for working conditions where pressure remains relatively constant throughout the process.