Decoupling thermal effects and possible non-thermal effects of microwaves in vacuum evaporation of glucose solutions

Abstract

Microwave vacuum evaporation (MVE) is a promising alternative to conventional methods. However, the mechanisms underlying its efficiency remain elusive. In this study, the effects of microwaves on glucose solutions were investigated via molecular dynamics (MD) simulations and experimental studies to elucidate possible microwave non-thermal and thermal effects, respectively. MD simulations on energy-related parameters, interfacial properties, and molecular migration indicated that a microwave electric field of 10 5 V/m could not influence water evaporation behavior at a constant temperature of 90 °C, validating the absence of non-thermal effects in the MVE of glucose solutions. Meanwhile, superheating was not observed in this study during microwave heating at atmospheric pressure or in vacuum. High-intensity microwaves enabled the solution to reach its boiling point rapidly and remarkably induced an intensified film boiling during MVE, thereby shortening the evaporation time. Therefore, the high efficiency of MVE may be attributed to the thermal effects of strong microwaves. • Thermal effects and possible non-thermal effects during MVE were studied. • Non-thermal effects were not observed during microwave evaporation at 10 5 V/m. • 10 9 V/m-z and 10 9 V/m-x microwaves accelerated and impeded evaporation, respectively. • Superheating did not occur during microwave heating with solution agitation.