Experimental Study on the Evaporation Process of Na₂SO₄ Aqueous Solution Droplets under Thermal Radiation Heating

To achieve the goal of deep desalination of saline wastewater driven by solar energy, the evaporation experiments of Na₂SO₄ aqueous solution droplets under thermal radiation heating condition have been carried out with the working conditions of 1450 and 1930 nm, heat flux varied from 1.1 × 10⁵ to 2.5 × 10⁵ W·m⁻², initial mass fraction in the range of 0.01~0.16 and droplet initial volume of 2.0~8.0 μL, respectively. The results indicate that absorption coefficient, initial mass fraction, heat flux and initial droplet volume have significantly influences on the evaporation characteristics. The main evaporation time can be shortened by 45.6% and 52% with the growth of the initial mass fraction from 0.01 to 0.16 and the decrease of the initial volume from 8 to 2 μL, respectively. The average evaporation can significantly increase by 55.7% and by 123% with the increase of the initial mass fraction from 0.01 to 0.16 and the heat flux varied from 1.1 × 10⁵ W·m⁻² to 2.5 × 10⁵ W·m⁻², respectively. Moreover, the average evaporation rate of the 1930 nm is 47.7% higher than that of the 1450 nm. Meanwhile, the experimental results have a good agreement with the theoretical values within the relative error in the range of ±30%. In summary, the above results can provide references for the design and engineering application of the desalination system and device of solar salty wastewater.