Numerical and experimental investigation of floating wick solar still with a porous-media system

Abstract

Wick-based solar desalination and solar-driven interfacial evaporation have attracted significant attention for their high efficiency in evaporation and salt removal. This study presents both experimental and numerical models for wick solar desalination. Cotton fabric, coated with black carbon for enhanced radiation absorption, was used as the evaporation medium in experiments due to its superior desalination, capillary, and salt rejection properties. Experimental results showed an evaporation rate of 1.57 kg/m2·h and efficiency of 81 % with freshwater. For saltwater (3.6 % salinity), the evaporation rate and efficiency were 1.24 kg/m2·h and 71 %, under 1000 W/m2 radiation. After validating the numerical model, the effects of porosity, capillary pressure, wick thickness, and thickness of the fabric’s upper (solar absorber) layer were examined. Results showed that reducing the solar absorber fabric thickness (from 9 mm to 0.6 mm), lowering porosity (from 0.97 to 0.3), and increasing wick thickness (from 1.5 mm to 10.5 mm) improved evaporation rates by 58.6 %, 27 %, and 28.4 %, respectively. Capillary pressure and fabric submerged length had minimal effects on evaporation. The model estimates that in real conditions at Jask coastal port (Iran), a configuration with greater wick thickness (6 mm vs. 3 mm), reduced solar absorber fabric thickness (1 mm vs. 1.5 mm), and lower porosity (0.75 vs. 0.93) could increase annual freshwater output by 26.6 % (from 796.6 to 1008.4 kg/m2). The cost per liter of produced water in the best-case scenario is estimated to be $0.0045.