Investigating the solute concentration in capillary-fed vapor generators: A heat and mass transfer study

Abstract

Interfacial passive thermal evaporation is currently attracting considerable interest from the scientific community in light of its zero consumption of fossil fuels and its important implications in the field of sustainable water purification. However, very few works comprehensively address the crystalline solute deposition issue, which is the Achilles’ heel of this process. Here, we propose a numerical analysis of the solute concentration in the device to quantify the saturation times together with the operating condition ranges to act within to prevent crystallization. A simplified analytical approach is then proposed, which provides accurate information at the most critical and design-wise interesting point. The phenomenon of solute accumulation is revealed to exhibit an exponential trend over time, as determined by a time constant Γ. Interestingly, the saturation times can be easily estimated as 2.3 Γ. In detail, the saturation time evaluated with the analytical model is estimated as 2 h, in the case of a 2-meter length device, which is approximately 5% less than the numerically estimated value. In conclusion, this study aims at exploring, quantifying and discussing the limitations of wick-based media used to design solar/thermal interfacial passive evaporation devices, from the perspective of solute accumulation.