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March 21, 2016

Turning Up the Heat Exchange

DropWise Technologies’ coatings promise major energy savings for power plants and other vital industrial uses.

Eric Bender

In a way, we’re still living in the Steam Age, and grappling with the limitations of steam power. More than 85% of the world’s electrical power comes from steam power plants, according to Adam Paxson, chief executive officer of DropWise Technologies. After driving the plant’s turbines, steam is condensed back to water in a heat exchanger, whose metal tubes are filled with running cold water. This condensation also creates a vacuum that helps to pull steam through the turbines. But condensation itself is not so efficient, because thick blankets of water build up on the condenser’s metal tubes and block the flow of heat.

Adam Paxson
DropWise Technologies CEO

DropWise Technologies, a startup based on research from two MIT labs, has developed ultra-thin, ultra-effective coatings to break down the blankets of water and bring major savings in energy and water use for these power plants. Just as crucially, the water-repellant coatings could fight climate change by cutting carbon dioxide production.

“Even a small incremental improvement across heat exchange efficiency can have enormous global impact, and with these coatings, we’re talking about heat exchanger coefficients going up by a factor of seven,” says Paxson. “Implementing this coating in a typical large-scale power plant would offset the amount of CO2 equivalent to a few thousand cars. And for the first time, retrofitting existing power plants can be done in a way that is economically and operationally viable, with just a truck outfitted with a small amount of chemicals and deposition equipment.”

Beyond power plants, almost every major industrial process makes heavy use of heat exchangers, he points out. DropWise also targets chemical processing, desalination, turbines, power components and other industrial applications that have not been addressed successfully by other coating technologies.

Coat dependent

Heat exchangers transfer heat from one fluid to another through a very thin sheet of metal, “which inevitably gets fouled or corroded by some form of material — whether it’s thick films of condensing steam that build up on these surfaces, or biofilms or corrosion,” Paxson explains. “Even a very thin layer, a micron thick, makes a significant impact on performance.”

Working on his PhD in the lab of Kripa Varanasi, associate professor of mechanical engineering, Paxson realized the need for a simple, highly manufacturable solution to the heat exchange problem, with coatings that were very thin, highly robust, and easily applied to large surfaces.

Paxson and Varanasi created advanced coating designs and collaborated with Karen Gleason, MIT associate provost and professor of chemical engineering. “We combined the coating processing and materials that Professor Gleason had been developing with the application expertise and testbeds in the Varanasi lab,” Paxson says. “Right away we started getting some incredible results in terms of both performance and durability.”

David Borrelli
DropWise Technologies CTO

The coatings are generated by an initiated chemical vapor deposition (iCVD) technique created by the Gleason lab, says David Borrelli, formerly a PhD student in the lab and now DropWise’s chief technology officer. The iCVD technique flows gases across hot filaments to graft ultra-thin polymers to metal surfaces, while maintaining the metal surfaces at room temperature.

This process creates an extremely thin film, about one two-thousandth the thickness of a piece of paper. “It’s very difficult by any finishing process to get a thin enough coating that the coating itself doesn’t inhibit your heat transfer,” says Borrelli. “That’s one of the key benefits in our processes.” Another is that the coating can be applied across large expanses of metal or other surfaces.

Two aspects of the technology impart durability, a crucial requirement. The polymers that are being deposited bond tightly with the metal oxides on the surface of the heat exchangers, and the polymers create a cross-linked overlying layer that protects against chemical reactions driven by the steam.

Paxson built a testbed in the Varanasi lab, essentially a miniature power plant that simulates the temperatures and pressures inside an actual operating power plant. Accelerated testing at higher temperatures has shown no degradation of coating performance over more than three years, and DropWise is running even longer-term durability tests.

“The coating is thick enough to impart a huge amount of durability but also thin enough that it doesn’t have any negative impact on the performance of the heat exchanger,” Paxson says. “This is the first coating technology that can meet all of those technical requirements and is economical enough that a plant can quickly recover the cost of applying the coating.”

Steaming ahead

Seeing a massive commercial opportunity for these coatings, as well as important environmental advantages, Paxson and Borrelli founded DropWise with their professors in 2014.

MIT’s entrepreneurial culture and resources have been particularly helpful in the difficult-to-enter market for advanced materials, Paxson says. With an office in north Cambridge, “we benefit from having the intense brainpower, both the professors and the potential employee pool in the MIT ecosystem, within a ten-minute walk,” he says. Additionally, many promising applications for the coatings have come in through the MIT community.

Annica Blake
DropWise Technologies COO

Sorting out the best early applications is a crucial business question for DropWise, because there are so many potential uses for the coatings. “You can increase heat transfer, or reduce fouling or corrosion of components, and the iCVD process is so flexible that it can be applied in large scales very economically or in small components that have very complex shapes,” notes Annica Blake, chief operating officer. “The choice is, what do we focus on?”

“The end goal for us has always been to get to power plants, because of the impact on the environment and the commercial viability of that market,” Blake says. “But we realize that will take a number of years, because it is a conservative industry and it operates at a large scale. So we’re looking for smaller stepping-stone applications that we can quickly address and bring to market.”

DropWise is running pilots for several such applications with commercial partners today and is optimistic that some uses for its coating technology will start to bring in revenue in the short term.

In September, the company announced a joint-development partnership with Henkel Corporation, a global supplier of coatings and related products. Henkel gives the company considerably more credibility with potential customers, Paxson points out, since the DropWise technology has been rigorously tested by the firm that invented many of the standard tests used by industry globally.

Environmental benefits remain a key driver for DropWise. “Applying this coating to power plant steam condensers can significantly increase the efficiency of the condensers, which increases the efficiency of the power generation cycle, which in turn lowers emissions and lowers water usage,” says Borrelli. “So applying this globally could have a huge impact on CO2 emissions.”

In fact, says Paxson, adopting the coatings in power plants could lower CO2 emissions more than all the solar energy equipment installed worldwide in a year. “The personal motivation behind this startup was the realization that with a handful of smart people, we can have more environmental impact than entire global energy industries,” he says.

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