From heat pumps to dry cooling, Longtin’s aces are on it
When last we saw Mechanical Engineering Professor Jon Longtin, he was knee-deep in a multitude of U.S. Department of Energy projects – specifically, work involving the DOE’s Advanced Research Projects Agency-Energy (ARPA-E).
In addition to co-investigating an ARPA-E project led by SBU Mechanical Engineering Assistant Professor Sotrios Mamlis, Dr. Longtin leads his own ARPA-E adventure: ARID (Advanced Research in Dry Cooling), which looks to improve the efficiency of gas-fired power plants using football-field-sized heat exchangers suspended high in the air.
(Cliff’s Notes version: Water vapor from the combustion of natural gas is captured and converted to liquid water. This water is then evaporated into the air that is forced over those large heat exchangers above. Just like the fog coolers at an amusement park, the cooler air makes the plant run more efficiently.)
It’s a clever system, and an engineering feat requiring teams of big thinkers covering multiple disciplines. Dr. Longtin has relied heavily on graduate student researchers, including two PhD candidates who’ve made standout contributions.
Dr. Longtin sings the praises of several of his graduate students – Hanfei Chen has provided invaluable computer simulations for Advanced Energy Research and Technology Center (AERTC) client ThermoLift and its next-level Vuilleumier-cycle heat pump, for instance (more on this relationship later) – but without graduate students Wei Zhong and Tao He, ARID would be all wet.
“They’ve done a little bit of everything, which is kind of unique,” Dr. Longtin notes. “A lot of times, graduate students get stuck doing only one thing for their entire thesis.”
Not this dynamic duo. Both contributed basic theoretical modeling and high-fidelity computer simulations (involving computational fluid dynamics) to the ARID effort. They also rolled up their sleeves and helped construct experimental water-harvesting prototypes at both Stony Brook University (SBU) and Brookhaven National Laboratory (BNL).
“They physically constructed the things,” Dr. Longtin says. “They weren’t afraid to get their hands dirty and build stuff.
“I was really impressed how they picked up the experimental side of the project,” the professor adds. “They embraced it! They weren’t intimidated at all. A lot of people would be intimidated at the prospect of building a one-off testing facility that had never been done before.”
Each student also embarked on his own side adventure, starting with He, who completed a “technoeconomic analysis” – a key requirement of projects under the auspices of ARPA-E, where commercialization is always on the radar.
“You have to demonstrate that not only do you have a good idea, but that it makes sense financially.” Dr. Longtin notes. “Tao took care of that for our project. He had to model an entire power plant, in a very high-level software package, with our technology integrated into it, to prove it was viable economically.
“He helped us answer all of those technoeconomic analysis questions.”
Zhong, meanwhile, has dived into a potentially new technology based on some of ARID’s basic constructs. The exchanger collects and condenses water on what are, essentially, plastic tubes; the water runs along the inside tube surface in as a thin liquid film, with the film thickness varying depending on the amount of water that is flowing.
The basic thrust of Zhong’s side mission is to create a “pulsed flow” along the surface of a tube – essentially, to create a valve that turns waterflow on and off at highly controlled intervals, allowing the film to thin out but never break up. This helps, because thinner films work better for the water harvesting system.
Controlling the film thickness to this degree offers several engineering possibilities. Zhong has constructed some intriguing laboratoryexperiments involving lasers, clear tubes and food coloring to get the ball rolling -- or get the film flowing.
“Wei is developing measurement techniques and basic theoretical models to explain the physics of what’s going on, seeing if this is something we can continue to explore,” Dr. Longtin says. “It could be our next segue into something new.”
Both He and Zhong are candidates to receive their PhD degrees in May, as is Chen, the graduate student who’s worked alongside the ThermoLift team. Just as his classmates were to the ARID project, Chen has been a key contributor to the development of the highly advanced heat pump, according to Dr. Longtin.
“The ThermoLift heat pump is cutting edge in so many respects,” he says. “Our strength in academia is on the basic physics and operating principles. So Hanfei has done some thermodynamic modeling (exploring heat and pressure) and dynamic modeling (exploring motion and friction), and he is now working on an overall system optimization model for the entire machine.”
“You have to make key design decisions on a large number of parameters to make a machine like this operate effectively,” he adds. “They are using Hanfei’s work to help guide them through these important design decisions that will ultimately be used in the fabrication of their next-generation machine.”
While their paths went in decidedly different scientific directions, all three of these PhD candidates displayed similar traits, according to their professor: dedication, teamwork and some impressive laboratory chops.
“Wei and Tao had so many decisions to make – how big is this, how many fans over here, what size pump?” Dr. Longtin says. “But they worked hand-in-hand and made essential contributions.”
“And Hanfei has been a big part of what has been a remarkably successful partnership between industry and academia with ThermoLift,” he adds. “We get to contribute to this amazing technology, and they get students like Hanfei to help them with it.”