Water, Toluene, Methanol, and Ethanol Under Microwave Irradiation: Numerical Simulations of the Effect of the Vessel's Size

In this article, we study numerically the effect of the variation of the vessel's radius on the distribution of flow velocity and temperature for four solvents with different dielectric properties, frequently used in organic chemistry: water, toluene, ethanol, and methanol, when they are irradiated with microwaves at 2.45 GHz. We use a multidimensional axisymmetric numerical model based on spectral element methods for solving heat and momentum equations coupled with Maxwell's equations. The varied dielectric behavior of the solvents results in a different behavior when the size of the vessel varies: from solvents for which the variation of the radius has little effect, as in the case of toluene due to its high penetration depth, to high absorbing solvents, with smaller penetration depth as ethanol, for which the effect of the radius is determinant for the distribution of the power absorption and, consequently, for the temperature and flow in the sample. Results are interesting as they provide a full description and understanding of the velocity and temperature distribution in the flow depending on the sample size and the dielectric properties of the solvents, becoming an important tool for prediction when parameters in the experiments are varied.