Microwave Heating of Water, Ice and Saline Solution: Molecular Dynamics Study

TL;DR

This study uses molecular dynamics simulations to explore how microwaves heat water, ice, and saline solutions, revealing the effects of microwave frequency, water phase, and salt addition on heating efficiency.

Contribution

It introduces a molecular dynamics approach to analyze microwave heating mechanisms in water and saline solutions, highlighting the role of molecular motion and network defects.

Findings

Microwave energy is mainly stored as inter-molecular energy in liquid water.

Ice phase shows minimal heating due to strong hydrogen bonds.

Adding salt enhances heating by disrupting water's hydrogen-bond network.

Abstract

In order to study the heating process of water by the microwaves of 2.5-20GHz frequencies, we have performed molecular dynamics simulations by adopting a non-polarized water model that have fixed point charges on rigid-body molecules. All runs are started from the equilibrated states derived from the I$_{c}$ ice with given density and temperature. In the presence of microwaves, the molecules of liquid water exhibit rotational motion whose average phase is delayed from the microwave electric field. Microwave energy is transferred to the kinetic and inter-molecular energies of water, where one third of the absorbed microwave energy is stored as the latter energy. The water in ice phase is scarcely heated by microwaves because of the tight hydrogen-bonded network of water molecules. Addition of small amount of salt to pure water substantially increases the heating rate because of the weakening by defects in the water network due to sloshing large-size negative ions.