Mystery solved: New coatings can make electric power more efficient while lowering emissions and cutting costs

Researchers at Texas A&M University have uncovered a solution to a decades-old mystery surrounding the failure of certain ultra-thin coatings during the phase-change heat transfer process.

A team from the J. Mike Walker ’66 Department of Mechanical Engineering has not only helped illuminate the previously elusive challenges facing silane self-assembled monolayers (SAMs) during the phase-change heat transfer but also developed enhanced versions of the coatings offering exponentially improved performance.

The research has the potential to provide significant improvements to the efficiency of electric power generation, resulting in lower carbon emissions for fossil fuel-based technology and lower energy production costs for renewable energy production methods.

Improved silane SAMs can affect the performance of heat exchanger components of refrigeration or air conditioning technology and devices, said team leader Dion Antao, assistant professor and J. Mike Walker ’66 Faculty Fellow II. Benefits could also extend to two-phase thermal management devices used to cool electronics or electrical devices in electric-based power generation or conversion technologies.

The concept of enhanced dropwise condensation came about in the 1930s and continued to be refined and further explored through the 1950s when researchers focused on ultra-thin silane SAM coatings. The silane SAMs, however, are known to degrade within minutes of operation during water vapor condensation — a failure that researchers have struggled to determine and improve upon for decades.

“To our knowledge, our work was the first in the field of thin coatings-assisted heat transfer enhancement to experimentally validate the coating failure mechanism and propose a corresponding method to mitigate coating degradation,” said Ruisong Wang, a former Texas A&M mechanical engineering doctoral student and a member of the research team.

Wang said the team first identified the bonding mechanism between the coating material and its underlying material, or substrate. After finding an explanation for why these silane SAMs fail during water vaper condensation heat transfer, the researchers then applied that knowledge to extend the lifetime of the coatings on silicon to at least 500 hours using oxygen plasma to enrich the surface. With that success, Antao and his team took those coating concepts and applied them to copper substrates.

“Copper as a substrate is much more widely used as a heat exchanger material than silicon, but it is also more challenging to create robust silane SAM coatings on copper or other metal substrates,” Antao said. “Our silane SAM coatings on copper that use our proposed coating integration and synthesis procedures were able to survive without failure for more than 350 hours, compared to coatings integrated on copper — or other metals — using the more common procedure, which fails within 30 minutes.”

The results of their testing showed the coatings on copper to have vastly improved condensation heat transfer characteristics, according to the team’s heat transfer measurements throughout the research process.

The research was published in the American Chemical Society’s Applied Materials & Interfaces journal and the International Journal of Heat and Mass Transfer, documenting their work to first determine why the coatings failed and how they successfully developed more robust silane SAM coatings.