Solar thermal evaporation using bubbly nanofluids with recyclable magnetic particles

Abstract

Nanofluids have been extensively studied as light absorption and heat transfer medium for solar energy harvesting. In this work, we, for the first time, investigate the convective bubbly flow in recyclable Fe3O4 nanofluids for solar steam generation. The low-cost nanoparticles inherently exhibit broadband light harvesting properties and facile recyclability. The great amount of dispersed bubbles not only work as light transfer center to amplify solar flux, but also provide large areas for mass transport across the interfaces. Our experimental results show that the bubbly nanofluid can significantly enhance the solar thermal evaporation. The coupling effect from light harvesting nanoparticles and dispersed air bubbles finally results in 2.48 times enhancement of the evaporation rate compared to base water. Based on the experimental results, a fully discussion on heat transfer mechanisms around the coupling of nanoparticles and bubbles is additionally provided, in which the thermal boundary layers induced by the particle chain around bubbles played significant roles. This work opens an economic and efficient way for accelerating solar vapor generation, and such concept and methods can be translated into industrial applications such as solar desalination and wastewater treatment.