Microwave driven atmospheric water harvesting with common sorbents

Abstract

Using sorbent materials to separate and concentrate ambient humidity is a promising option for atmospheric water harvesting in the face of impending worldwide freshwater scarcity. The method of cycled sorption and forced release can facilitate efficient condensation, but performance strongly depends on device-scale issues of heat and mass transfer. We examine the potential of using microwave radiation to liberate sorbed vapor, in proof-of-concept experiments with hygroscopic salt-infused paper towel as simple sorbents. We quantify performance as a function of tunable system parameters and ambient humidity. Our results demonstrate promising aspects: both rapid desorption and regeneration, owing to water-tuned dielectric heating and directing flow through fibrous sorbent, respectively; substantial efficiency of moisture separation toward very low (∼25%) relative humidity; and robust repeatability over many cycles, due to the targeted energy input and retention of hygroscopic salt within the paper scaffold.