Quenching, a powerful heat transfer mechanism, is remarkably effective at transporting heat away. But in extreme environments, like nuclear power plants and aboard spaceships, a lot rides on the efficiency and speed of the process.
It's why Marco Graffiedi, a fifth-year doctoral student at MIT's Department of Nuclear Science and Engineering (NSE), is researching the phenomenon to help develop the next generation of spaceships and nuclear plants.
Growing up in small-town Italy, Graffiedi's parents encouraged a sense of exploration, giving him responsibilities for family projects even at a young age. When they restored a countryside cabin in a small town near Palazzolo, in the hills between Florence and Bologna, the then-14-year-old Marco got a project of his own.
He had to ensure the animals on the property had enough accessible water without overfilling the storage tank. Marco designed and built a passive hydraulic system that effectively solved the problem and is still functional today.
His proclivity for science continued in high school in Lugo, where Graffiedi enjoyed recreating classical physics phenomena, through experiments. Incidentally, the high school is named after Gregorio Ricci-Curbastro, a mathematician who laid the foundation for the theory of relativity - history that is not lost on Graffiedi.
After high school, Graffiedi attended the International Physics Olympiad in Bangkok, a formative event that cemented his love for physics.
A passion for physics and basic sciences notwithstanding, Graffiedi wondered if he'd be a better fit for engineering, where he could use the study of physics, chemistry, and math as tools to build something. Following that path, he completed a bachelor's and master's in mechanical engineering - because an undergraduate degree in Italy takes only three years, pretty much everyone does a master's, Graffiedi laughs - at the Universita di Pisa and the Scuola Superiore Sant'Anna (School of Engineering).
The Sant'Anna is a highly selective institution that most students attend to complement their university studies. Graffiedi's university studies gradually moved him toward the field of environmental engineering. He researched concentrated solar power in order to reduce the cost of solar power by studying the associated thermal cycle and trying to improve solar power collection.
While the project was not very successful, it reinforced Graffiedi's impression of the necessity of alternative energies. Still firmly planted in energy studies, Graffiedi worked on fracture mechanics for his master's thesis, in collaboration with (what was then) GE Oil and Gas, researching how to improve the effectiveness of centrifugal compressors.
A summer internship at Fermilab had Graffiedi working on the thermal characterization of superconductive coatings. With his studies behind him, Graffiedi was still unsure about this professional path.
Through the Edison Program from GE Oil and Gas, where he worked shortly after graduation, Graffiedi got to test drive many fields - from mechanical and thermal engineering to exploring gas turbines and combustion. He eventually became a test engineer, coordinating a team of engineers to test a new upgrade to the company's gas turbines.
"I set up the test bench, understanding how to instrument the machine, collect data, and run the test," Graffiedi remembers, "there was a lot you need to think about, from a little turbine blade with sensors on it to the location of safety exits on the test bench."
As fun as the test engineering job was, Graffiedi started to crave more technical knowledge and wanted to pivot to science. As part of his exploration, he came across nuclear energy and, understanding it to be the future, decided to lean on his engineering background to apply to MIT NSE.
He found a fit in Professor Matteo Bucci's group and decided to explore boiling and quenching. The move from science to engineering, and back to science, was now complete.
NASA, the primary sponsor of the research, is interested in preventing boiling of cryogenic fuels, because boiling leads to loss of fuel and the resulting vapor will need to be vented to avoid overpressurizing a fuel tank. Graffiedi's primary focus is on quenching, which will play an important role in refueling in space - and in the cooling of nuclear cores.
When a cryogen is used to cool down a surface, it undergoes what is known as the Leidenfrost effect, which means it first forms a thin vapor film that acts as an insulator and prevents further cooling. To facilitate rapid cooling, it's important to accelerate the collapse of the vapor film. Graffiedi is exploring the mechanics of the quenching process on a microscopic level, studies that are important for land and space applications.
Boiling can be used for yet another modern application: to improve the efficiency of cooling systems for data centers. The growth of data centers and electric transportation systems needs effective heat transfer mechanisms to avoid overheating. Immersion cooling using dielectric fluids - fluids that do not conduct electricity - is one way to do so.
These fluids remove heat from a surface by leaning on the principle of boiling. For effective boiling, the fluid must overcome the Leidenfrost effect and break the vapor film that forms. The fluid must also have high critical heat flux (CHF), which is the maximum value of the heat flux at which boiling can effectively be used to transfer heat from a heated surface to a liquid.
Because dielectric fluids have lower CHF than water, Graffiedi is exploring solutions to enhance these limits. In particular, he is investigating how high electric fields can be used to enhance CHF and even to use boiling as a way to cool electronic components in the absence of gravity. Graffiedi's love of science and engineering shows in his commitment to teaching as well. He has been a teaching assistant for four classes at NSE, winning awards for his contributions.
His many additional achievements include winning the Manson Benedict Award presented to an NSE graduate student for excellence in academic performance and professional promise in nuclear science and engineering, and a service award for his role as past president of the MIT Division of the American Nuclear Society.
Boston has a fervent Italian community, Graffiedi says, and he enjoys being a part of it. Fittingly, the MIT Italian club is called MITaly. When he's not at work or otherwise engaged, Graffiedi loves Latin dancing, something he makes time for at least a couple of times a week. While he has his favorite Italian restaurants in the city, Graffiedi is grateful for another set of skills his parents gave him when was just 11: making perfect pizza and pasta.
He published this research in Applied Thermal Engineering in June.
Related Links
The Red Lab at MIT
Understanding Time and Space
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