Evaporation Mass Flux: A Predictive Model and Experiments

Abstract

Evaporation is a fundamental and core phenomenon in a broad range of disciplines including power generation and refrigeration systems, desalination, electronic/photonic cooling, aviation systems, and even biosciences. Despite its importance, the current theories on evaporation suffer from fitting coefficients with reported values varying in a few orders of magnitude. Lack of a sound model impedes simulation and prediction of characteristics of many systems in these disciplines. Here, we studied evaporation at a planar liquid-vapor interface through a custom-designed, controlled, and automated experimental setup. This experimental setup provides the ability to accurately probe thermodynamic properties in vapor, liquid, and close to the liquid-vapor interface. Through analysis of these thermodynamic properties in a wide range of evaporation mass fluxes, we cast a predictive model of evaporation based on nonequilibrium thermodynamics with no fitting parameters. In this model, only the interfacial temperatures of liquid and vapor phases along with the vapor pressure are needed to predict evaporation mass flux. The model was validated by the reported study of an independent research group. The developed model provides a foundation for all liquid-vapor phase change studies including energy, water, and biological systems.

Thermo-osmotic pressure and resistance to mass transport in a vapor-gap membrane

“…27 It has been common to neglect this interaction of fluxes, but we know from other studies that the coupling between heat and mass transport at interfaces is significant. [28][29][30][31] This leads us to non-equilibrium thermodynamics theory, 30 which offers a precise description of what the thermal and chemical forces are, how they come into play, and how they interact. The theory enables us to define the maximum pressure difference that can arise from a temperature difference.…”

Kinetic simulation of the non-equilibrium effects at the liquid-vapor interface

“…Only recently, the new series of measurements [5], [6] have appeared, where the temperature jump was found of the same order as that predicted by the kinetic theory. However, still in recent papers [6], [7] the temperature in vapor near interface was measured higher compared to the interface temperature. The positive values of the temperature difference between liquid and vapor temperatures at interface (vapor temperature is lower than the interface temperature) were measured only by the authors of Ref.…”

Utilization of Nonequilibrium Phase Change Approach to Analyze the Nonisothermal Multiphase Flow in Shallow Subsurface Soils

“…In analogy, f c is the ratio of the number of molecules adsorbed by the liquid phase to the total number of molecules impinging on the liquid phase (Marek & Straub, 2001). Despite their physical meaning, evaporation and condensation coefficients are very hard to determine, and there is still ongoing theoretical and experimental research to obtain these values (Jafari et al, 2018). Both f e and f c values for water have been observed to vary from 10 −4 to 1, and also, they are not necessarily identical: f e ≠ f c (Marek & Straub, 2001).…”