Capillary pumping-evaporation modeling and experimental characterization of saline water transport for passive solar desalination

Abstract

The scalability of passive solar desalination processes depends on capillary pumping capacity of hydrophilic porous structure, and their rational design requires reliable models of saline water uptake in wicking structures. Herein, we develop a new capillary pressure-saturation model for systematic characterization of the capillary-driven liquid uptake in synthetic porous stem to understand coupled physics of saline water transport and salt precipitation. Coupled with the non-dimensionalized momentum conservation equation for unsaturated passive liquid transport, the proposed model is able to predict the experimental wicking dynamics and saturation profile of water in micro/nano-structured wicks. The proposed capillary transport model can also be used to extract unknown macroscopic properties of the porous stem such as permeability, maximum wicking height and effective porosity. Moreover, for solar-driven interfacial evaporation of saline water, a physical model is proposed and experimentally validated to predict the locus of salt precipitation front and assess its effect on evaporation. The integrated evaporation-precipitation-transport model is employed to evaluate the capillary limits (e.g., dryout locus) and pumping capability of synthetic stem with salt precipitation. Our mechanistic modeling efforts offer in-depth understanding of the capillary-driven interfacial heat and mass transport in porous structures and valuable guidelines for rational design of scalable passive photothermal distillation systems.