Nanofluids improve energy efficiency of membrane distillation

Thermal desalination of high salinity water resources is crucial for increasing freshwater supply, but efficiency enhancements are badly needed. Nanomaterial enhancements offer enormous potential for improving promising technologies like membrane distillation (MD). However, while many approaches have been tried, such as nanoparticle solar absorbers or nanomaterial membranes, there have not been studies to directly enhance the fluid properties in MD; via nanofluids. In this work, we examine nanofluids for gap-based MD systems, including the role of nanoscale physics and system-level energy efficiency enhancements. Our model includes the dominant micro-mixing from Brownian motion in fine particle nanofluids (copper oxide) and the unusually high axial conduction from phonon resonance through Van der Waals interaction in carbon nanotube nanofluids. Carbon nanotubes resulted in consistent, wide range of improvements; while copper oxide particles showcased diminishing returns after a concentration of 0.7%, where Brownian motion effects reduced. Nanofluid characterizations illustrated uniform dispersions after at least 75 min of sonication and using surfactants to stabilize the nanoparticles through micelle formations. However, the enhancements at higher concentrations from liquid layering around nanoparticles were impractical in gap-based MD configurations, since the related high surfactant levels compromised membrane hydrophobicity and promoted fouling. Dilute solutions of metallic nanofluids can be actively integrated to enhance the performance of gap-based MD systems, whereas stronger nanofluid solutions should be limited to heat exchangers that meet their thermal energy requirements.

Automated summary

The addition of carbon nanotubes in nanofluids results in consistent and wide-ranging improvements, while the addition of copper oxide particles shows diminishing returns after a concentration of 0.7%. Furthermore, it was discovered that enhancing the performance of MD systems can be achieved by uniformly dispersing nanoparticles in nanofluids and stabilizing them with surfactants.