Investigação numérica e experimental de sistemas de concentração solar com lentes de Fresnel para desinfecção de água

Abstract

Universal access to water is one of the United Nation’s 17 sustainable development goals and a fundamental human right. However, factors such as extreme poverty, geographical isolation, and climate change pose challenges to ensuring access to safe water for populations located mainly in rural communities in underdeveloped and developing countries. Among the existing technologies for water treatment in remote regions, solar water disinfection (SODIS) stands out, which can be intensified by solar concentrators that increase the intensity of sunlight, shortening the time required for exposure and increasing the rate of microorganism inactivation. This study evaluated the potential of alternative solar concentrators, such as point and linear Fresnel lenses, in photoactivated processes such as SODIS using computational fluid dynamics to solve the equations of momentum, radiation, and species transport. To this end, two experimental units and their respective computational models were developed and validated experimentally through actinometry with potassium ferrioxalate, and a simulation design was conducted to evaluate the effect of operational variables on the main responses that characterize the performance of these concentrators. A mechanistic model of E. coli disinfection based on the generation of reactive oxygen species (ROS) and inactivation of cell protection enzymes available in the literature was implemented in the computational models to enable the numerical evaluation of the performance of these Fresnel lens concentrator systems. The results obtained indicate that the computational models developed reproduced the radiation and velocity fields properly, and a high potential for radiation intensification in the reactors was observed using the lenses. In the linear Fresnel concentrator system, it was found that the recirculation flow rate has a small effect on the reaction rate within the range of 0.4 L·min-1 to 3.95 L·min-1, and the conversion depends mainly on the position of the reactor and solar irradiation. Disinfection kinetics results showed that for the point lens it is important to ensure adequate radiation distribution, while in the unit with a linear lens it is necessary to seek a balance between increasing the fluid’s residence time in the reactor and the fluid dynamics inside the tubular reactor. Both solar concentrator systems were able to substantially reduce the treatment time of conventional SODIS to just a few minutes of operation, based on the dimensions of the development of the experimental rigs.