Critical Diameter for Continuous Evaporation is between 3 nm and 4 nm for Hydrophilic Nanopores

TL;DR

This study develops a machine learning-optimized coarse-grained water model to investigate evaporation in hydrophilic nanopores, identifying a critical diameter between 3 nm and 4 nm for continuous evaporation and revealing significantly higher heat fluxes than experimental reports.

Contribution

The paper introduces a multi-temperature Morse-D water model optimized via machine learning for nanoscale evaporation studies in hydrophilic nanopores.

Findings

Critical evaporation diameter between 3 nm and 4 nm.

Maximum heat flux of 21.3 kW/cm2 at 4.5 nm pore diameter.

Heat flux exceeds experimental values by an order of magnitude.

Abstract

Evaporation studies of water using classical molecular dynamics simulations are largely limited due to their high computational expense. This study addresses that issue by developing coarse-grained molecular dynamics models based on Morse potential. Models are optimized based on multi-temperature and at room temperature using machine learning techniques like genetic algorithm, Nelder-Mead algorithm, and Strength Pareto Evolutionary Algorithm. The multi-temperature based model named as Morse-D is found to be more accurate than single temperature model in representing the water properties at higher temperatures. Using this Morse-D water model, evaporation from hydrophilic nanopores with pore diameter varying from 2 nm to 5 nm is studied. Our results show that the critical diameter to initiate continuous evaporation at nanopores lies between 3 nm and 4 nm. A maximum heat flux of 21.3 kW/cm2 is observed for a pore diameter of 4.5 nm and a maximum mass flow rate of 16.2 ng/s for a pore diameter of 5 nm. The observed heat flux is an order of magnitude times larger than the currently reported values from experiments in the literature for water, which indicates that we need to focus on nanoscale evaporation to enhance the critical heat flux.