Abstract

Understanding heat and mass transfer during microwave heating is essential for predicting evaporation, superheating, and temperature non-uniformity in liquid systems. Here, we present a systematic experimental–modeling investigation of microwave heating in water, sucrose, and NaCl solutions over a range of concentrations and input powers. Bulk and surface temperatures were monitored in real time using thermocouples and infrared pyrometry, enabling direct assessment of temperature non-uniformity. Evaporation- and superheating-induced mass loss was quantified using pixel-tracking image analysis (PTIA) and validated gravimetrically, with an average deviation of 6.91 ± 4.42%. Material property variations were minor for sucrose solutions but pronounced for NaCl solutions, which exhibited substantial increases in electrical conductivity and dielectric loss. Sub-boiling COMSOL simulations incorporating solution-dependent dielectric properties, microwave power dissipation, and natural convection reproduce nearly uniform heating in water and sucrose (ΔT<inf>uni</inf> = 0.37–0.51 °C) and pronounced surface-localized heating in NaCl solutions (ΔT<inf>uni</inf> = 4.0–4.9 °C), associated with reduced microwave penetration depth. All solutions exhibit superheating, reaching temperatures up to ∼112 °C with measurable mass loss. A simplified lumped and multi-domain heat–mass transfer model is used to interpret the transition from uniform to non-uniform heating and the associated evaporation behavior. Overall, this work provides an experimentally grounded framework for interpreting microwave heating in liquids and improving the reproducibility of microwave-assisted thermal processes.