Could tiny threads of carbon fiber do the same job as big metal industrial heating coils? A new breakthrough from researchers at Rice University says yes, and the finding could go a long way toward electrifying many manufacturing processes.
The heating of gas is used across multiple industries. For example, any manufacturing process that involves the melting, smelting, or heat-treatment of metals needs to heat gases to a very high temperature. Heated gas is also used to drive steam processes, sterilize products, create cement, dry grains and other food products, manufacture glass, and the list goes on.
Currently, industrial gas heating is largely achieved through the use of metal coils and the burning of other fuels. Not only does this increase the carbon output of many factories, but the most effective way to use coils is to place them directly in the gas stream, which can wreak havoc on the components.
"When you immerse a heater directly into a gas stream, you gain heat-transfer efficiency, but you also create a much harsher operating environment," said Rice assistant professor Daniel J. Preston, whose lab studies high-performance thermal management systems. "Geometry, stability and performance all become tightly coupled."
Seeking a better way forward, Preston and his colleagues turned to carbon nanotubes in a new study published in the journal Small.
Carbon nanotubes are incredibly small cylinders made from rolled graphene, a substance made entirely from carbon atoms. They've been studied and used for everything from safer football helmets, to headphone drivers, to smart bandages. The tubes, which can measure about 50,000 times thinner than a human hair, are extremely strong, excellent conveyors of heat, and can conduct electricity better than copper.
Because of their small yet robust makeup, the Rice researchers realized that they could be used to replace metal heater coils to improve efficiency and help the move to electrify the industrial heating process.
"Electrifying industrial heat is one of the most important, and most difficult, pieces of decarbonization," said first study author Monisha Vijay Kumar, a graduate student in applied physics. "We wanted to understand whether an entirely different class of materials could expand what’s possible in gas heating."
In tests, arrays of the threads were indeed able to achieve higher specific power loadings than similar metal-alloy elements. This means that for their size, they generated more power when electrified than traditional heating elements. They were also able to withstand the onslaught of moving gas. Plus, the team demonstrated that the threads could be woven into fabrics, which creates a high surface area through which gas could pass and get heated by the electric current running through the material.
"Textile techniques give us extraordinary freedom in creating three-dimensional architectures," said study co-author Vanessa Sanchez. "We can design heaters that are lightweight, porous and mechanically compliant while remaining electrically functional."
The carbon nanotubes also demonstrated their superiority at delivering more even heating with fewer hot spot formations – a problem that can plague traditional heating coils and lead to component failures.
Should the carbon nanotube materials continue to prove themselves, they could contribute significantly to electrifying industrial heating. In fact, according to a policy brief by ACEEE, if all industrial processes that heat under 300 °C were replaced with clean electricity by 2050, it could lead to a 30% reduction in total greenhouse gas emissions.
You can hear more about the research from Kumar in the following video.
Source: Rice University
