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Tobacco Virus Inspires Hot Coating

Wednesday, April 1, 2015

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Viruses that once plagued tobacco leaves are now the unlikely template for a coating that can triple the speed of boiling for industrial processes.

The discovery could reportedly save enormous amounts of energy in industrial power plants or large-scale electronic cooling systems.

Coating the heating element with the virus drastically reduces the size and number of bubbles that form around the element as it gets hotter, tripling the efficiency of boiling water, researchers say.

tobacco virus coating
Images, video: Drexel University

A Drexel University researcher is using a tobacco plant virus to create a coating that wicks moisture away from hot surfaces to increase the maximum heat transfer rate of numerous substrates.

"Even slight improvements to technologies that are used so widely can be quite impactful," says Drexel University researcher Matthew McCarthy, Ph.D., who is leading the research.

Nanostructured Coatings

The project focuses on creating nanostructured coatings for heat-transfer surfaces that can delay or prevent a vapor barrier from forming.

According to McCarthy, the ideal structure for high heat transfer during boiling is one that draws in the liquid and quickly re-wets once water transforms into vapor.

Improving that process could increase performance "in everything from power generation to water purification, HVAC and electronics cooling," he said.

Avoiding Burnout

In his Multiscale Thermofluidics Lab at Drexel, McCarthy and his team are focusing on the surface that links heat to water.

The goals are to control the formation and removal of vapor bubbles during the boiling process, while also delaying an undesirable condition called "critical heat flux." That occurs when the production of vapor cannot be balanced by replenishing liquid, allowing the surface to uncontrollably, dangerously overheat.

Such a failure, called "burnout," "can lead to the simple destruction of electronic components, or in power plant cooling applications, the catastrophic meltdown of a nuclear reactor," McCarthy said.

Scientists have found a way to harness viruses found on tobacco plants for a new coating for boiling surfaces.

The solution: Keep the surface wet, which the team does through wicking—the same technique behind athletic apparel that keeps sweat away from the body.

Grow Your Own

The trick to making a wicking, or hydrophilic, material is to increase its surface area to draw liquid toward a region of lower density, the team says.

That's where the tobacco virus comes in, allowing the coating of the surface with thousands of nanostructure tendrils.

McCarthy grows his own genetically modified strain of the virus on tobacco plants in his lab.

His version "introduces chemical binding sites—like molecular hooks—on the outer surface of the viruses that allow them to attach to nearly any substrate we want to use," McCarthy said.

The coating works with steel and a wide variety of other metals and polymers already in use in power plants and waste treatment facilities.

Bristly Enterprise

McCarthy's process involves pouring a solution with billions of viruses onto a substrate, where the rod-shaped viruses form a bristly layer. This layer is then thinly coated with a metal that rigidly attaches to the nanostructures.

This SEM image shows the micrometer-thick nanocoatings on a silicon substrate.

The viruses are inactive once coated and leave behind evenly spaced tendrils ("metallic grass," as McCarthy calls it). The grass wicks the liquids across the surface and—voila!—no burnout.

McCarthy calls the technique "quite efficient," with no need for electricity, power, heat or special equipment.

Testing Results

Preliminary results have shown boiling of the coated surface more than three times faster than the uncoated surface. The boiling process is also far more efficient, McCarthy says.

Now his team will look at the performance of dozens of surface configurations as part of his National Science Foundation CAREER award research. The tweaking will include the spacing and shape of nanostructures, as well as adjustments to the coating.

"Our lab has the unique ability to quickly design and build structured surfaces, thanks to our technique," McCarthy said.

"We can also create surfaces that are extremely difficult, if not impossible, to do using other methods,..." he added.

"Because we can do this cheaply and relatively quickly, we can test numerous surfaces and make scientific conclusions based on large data sets."


Tagged categories: Asia Pacific; Coating Materials; Colleges and Universities; EMEA (Europe, Middle East and Africa); High-heat coatings; Latin America; Nanotechnology; North America; Power Plants; Research; Temperature

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