Researchers at the FAMU-FSU College of Engineering have designed a liquid hydrogen storage and delivery system that could help make zero-emission aviation a reality. Their work outlines a scalable, integrated system that addresses several engineering challenges at once by enabling hydrogen to be used as a clean fuel and also as a built-in cooling medium for critical power systems aboard electric-powered aircraft.

The study, published in Applied Energy, introduces a design tailored for a 100-passenger hybrid-electric aircraft that draws power from both hydrogen fuel cells and hydrogen turbine-driven superconducting generators. It shows how liquid hydrogen can be efficiently stored, safely transferred and used to cool critical onboard systems — all while supporting power demands during various flight phases like takeoff, cruising, and landing.

“Our goal was to create a single system that handles multiple critical tasks: fuel storage, cooling and delivery control,” said Wei Guo, a professor in the Department of Mechanical Engineering and co-author of the study. “This design lays the foundation for real-world hydrogen aviation systems.”

WHAT THEY DID
Hydrogen is seen as a promising clean fuel for aviation because it packs more energy per kilogram than jet fuel and emits no carbon dioxide. But it’s also much less dense, meaning it takes up more space unless stored as a super-cold liquid at –253°C.

To address this challenge, the team conducted a comprehensive system-level optimization to design cryogenic tanks and their associated subsystems. Instead of focusing solely on the tank, they defined a new gravimetric index, which is the ratio of the fuel mass to the full fuel system. Their index includes the mass of the hydrogen fuel, tank structure, insulation, heat exchangers, circulatory devices and working fluids.

By repeatedly adjusting key design parameters, such as vent pressure and heat exchanger dimensions, they identified the configuration that yields the maximum fuel mass relative to total system mass. The resulting optimal configuration achieves a gravimetric index of 0.62, meaning 62% of the system’s total weight is usable hydrogen fuel, a significant improvement compared to conventional designs.

The system’s other key function is thermal management. Rather than installing a separate cooling system, the design routes the ultra-cold hydrogen through a series of heat exchangers that remove waste heat from onboard components like superconducting generators, motors, cables and power electronics. As hydrogen absorbs this heat, its temperature gradually rises, a necessary process since hydrogen must be preheated before entering the fuel cells and turbines.

HOW IT WORKS
Delivering liquid hydrogen throughout the aircraft presents its own challenges. Mechanical pumps add weight and complexity and can introduce unwanted heat or risk failure under cryogenic conditions. To avoid these issues, the team developed a pump-free system that uses tank pressure to control the flow of hydrogen fuel.

The pressure is regulated using two methods: injecting hydrogen gas from a standard high-pressure cylinder to increase pressure and venting hydrogen vapor to decrease it. A feedback loop links pressure sensors to the aircraft’s power demand profile, enabling real-time adjustment of tank pressure to ensure the correct hydrogen flow rate across all flight phases. Simulations show it can deliver hydrogen at rates up to 0.25 kilograms per second, sufficient to meet the 16.2-megawatt electrical demand during takeoff or an emergency go-around.

The heat exchangers are arranged in a staged sequence. As the hydrogen flows through the system, it first cools high-efficiency components operating at cryogenic temperatures, such as high-temperature superconducting generators and cables. It then absorbs heat from higher-temperature components, including electric motors, motor drives and power electronics. Finally, before reaching the fuel cells, the hydrogen is preheated to match the optimal fuel cell inlet conditions.

This staged thermal integration allows liquid hydrogen to serve as both a coolant and a fuel, maximizing system efficiency while minimizing hardware complexity.

“Previously, people were unsure about how to move liquid hydrogen effectively in an aircraft and whether you could also use it to cool down the power system component,” Guo said. “Not only did we show that it’s feasible, but we also demonstrated that you needed to do a system-level optimization for this type of design.”

FUTURE STEPS AND COLLABORATORS
While this study focused on design optimization and system simulation, the next phase will involve experimental validation. Guo and his team plan to build a prototype system and conduct tests at FSU’s Center for Advanced Power Systems.

The project is part of NASA’s Integrated Zero Emission Aviation program, which brings together institutions across the U.S. to develop a full suite of clean aviation technologies. Partner universities include Georgia Tech, Illinois Institute of Technology, University of Tennessee and University at Buffalo. FSU leads the effort in hydrogen storage, thermal management and power system design.

At FSU, key contributors include graduate student Parmit S. Virdi; professors Lance Cooley, Juan Ordóñez, Hui Li, Sastry Pamidi; and other faculty experts in cryogenics, superconductivity and power systems.

FUNDING
This project was supported by NASA as part of the organization’s University Leadership initiative, which provides an opportunity for U.S. universities to receive NASA funding and take the lead in building their own teams and setting their own research agenda with goals that support and complement the agency’s Aeronautics Research Mission Directorate and its Strategic Implementation Plan.

Guo’s research was conducted at the FSU-headquartered National High Magnetic Field Laboratory, which is supported by the National Science Foundation and the State of Florida.

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Florida State University is partnering with the University of Florida (UF) to bring a flagship symposium in quantum materials to the state.

The 2024 International Symposium on Quantum Fluids and Solids will take place July 24-30 in Jacksonville, Fla. The event brings scientists and engineers whose work explores the workings of materials characterized by quantum mechanics, a branch of physics that describes the behavior of particles at very small scales, such as atoms, molecules and subatomic particles.

“Researchers in our state are making great strides in understanding quantum states and using that knowledge to develop groundbreaking tools,” said Wei Guo, a professor in the Department of Mechanical Engineering at the FAMU-FSU College of Engineering, who is a symposium co-chair with University of Florida Professor Yoonseok Lee.

More than 170 participants from 18 different countries have registered for the event.

Along with FSU and UF, sponsors include the National Science Foundation; Gordon and Betty Moore Foundation, which supports Guo’s research into superfluid helium; the International Union of Pure and Applied Physics; and the FSU-headquartered National High Magnetic Field Laboratory, which supports quantum research through resources such as its 32-tesla superconducting magnet and the laboratory’s quantum spin dynamics research group. Industry sponsors are Oxford Instruments PLC, Maybell Quantum and Bluefors.

The QFS conference has been a cornerstone in the exploration of quantum phenomena in materials since 1997. It focuses not only on conventional quantum fluid systems, such as helium and trapped cold atoms, but also extends to embrace interdisciplinary applications and recent developments.

“This is an exciting time to be researching quantum materials,” Guo said. “We are seeing some major developments in what we know and what is possible with these materials. Events like this symposium help to bring all that together, giving researchers the opportunity to hear firsthand from their colleagues about the latest breakthroughs.”

FSU is making major investments in quantum technology. At the university’s 2023 quantum symposium, President Richard McCullough announced $20 million in funding to support new faculty hiring, equipment and dedicated space in the university’s Interdisciplinary Research and Commercialization Building (IRCB), and seed money for new interdisciplinary collaborative efforts.

The new IRCB facility, which is expected to open in January 2025, will serve as the headquarters for FSU Quantum. With state-of-the-art equipment and remarkable faculty talent, FSU leadership envisions the IRCB as a regional focal point for quantum science and engineering, drawing researchers from around the Southeast who may use the equipment for their own projects.

Visit the symposium website for more information about the event and a full list of presentations.

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Quantum computers have the potential to be revolutionary tools for their ability to perform calculations that would take classical computers many years to resolve.

But to make an effective quantum computer, you need a reliable quantum bit, or qubit, that can exist in a simultaneous 0 or 1 state for a sufficiently long period, known as its coherence time.

One promising approach is trapping a single electron on a solid neon surface, called an electron-on-solid-neon qubit. A study led by FAMU-FSU College of Engineering Professor Wei Guo that was published in Physical Review Letters shows new insight into the quantum state that describes the condition of electrons on such a qubit, information that can help engineers build this innovative technology.

Guo’s team found that small bumps on the surface of solid neon in the qubit can naturally bind electrons, which creates ring-shaped quantum states of these electrons. The quantum state refers to the various properties of an electron, such as position, momentum and other characteristics, before they are measured. When the bumps are a certain size, the electron’s transition energy — the amount of energy required for an electron to move from one quantum ring state to another — aligns with the energy of microwave photons, another elementary particle.

This alignment allows for controlled manipulation of the electron, which is needed for quantum computing.

“This work significantly advances our understanding of the electron-trapping mechanism on a promising quantum computing platform,” Guo said. “It not only clarifies puzzling experimental observations but also delivers crucial insights for the design, optimization and control of electron-on-solid-neon qubits.”

Previous work by Guo and collaborators demonstrated the viability of a solid-state single-electron qubit platform using electrons trapped on solid neon. Recent research showed coherence times as great as 0.1 millisecond, or 100 times longer than typical coherence times of 1 microsecond for conventional semiconductor-based and superconductor-based charge qubits.

Coherence time determines how long a quantum system can maintain a superposition state — the ability of the system to be in multiple states at the same time until it is measured, which is one characteristic that gives quantum computers their unique abilities.

The extended coherence time of the electron-on-solid-neon qubit can be attributed to the inertness and purity of solid neon. This qubit system also addresses the issue of liquid surface vibrations, a problem inherent in the more extensively studied electron-on-liquid-helium qubit. The current research offers crucial insights into optimizing the electron-on-solid-neon qubit further.

A crucial part of that optimization is creating qubits that are smooth through most of the solid neon surface but have bumps of the right size where they are needed. Designers want minimal naturally occurring bumps on the surface that attract disruptive background electrical charge. At the same time, intentionally fabricating bumps of the correct size within the microwave resonator on the qubit improves the ability to trap electrons.

“This research underscores the critical need for further study of how different conditions affect neon qubit manufacturing,” Guo said. “Neon injection temperatures and pressure influence the final qubit product. The more control we have over this process, the more precise we can build, and the closer we move to quantum computing that can solve currently unmanageable calculations.”

Co-authors on this paper were Toshiaki Kanai, a former graduate research student in the FSU Department of Physics, and Dafei Jin, an associate professor at the University of Notre Dame.

The research was supported by the National Science Foundation, the Gordon and Betty Moore Foundation, and the Air Force Office of Scientific Research.

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Wei Guo, a professor in the Department of Mechanical Engineering at the FAMU-FSU College of Engineering and a researcher at the National High Magnetic Field Laboratory, has been elected a Fellow of the American Physical Society (APS).

Guo received the honor for the development and advancement of flow visualization techniques using both molecular tracers and solidified particle tracers in liquid helium and their application to the study of quantum fluid dynamics in superfluid helium-4.

The APS Fellowship Program recognizes members who have made advances in physics through original research and publication or made innovative contributions applying physics to science and technology. He was recommended for the award by the American Physical Society Division of Condensed Matter Physics.

“It’s a genuine honor to be named an APS Fellow,” Guo said. “This distinction is a testament to the intriguing avenues this field has opened for me and the unwavering support from my colleagues and the institution I represent.”

Guo earned his doctoral degree in physics from Brown University in 2008, conducted postdoctoral work at Yale University from 2008 to 2012 and joined Florida State University in 2012. His research spans quantum fluid dynamics, dark matter detection, cryogenic accelerator physics, quantum-fluid-based qubits and liquid hydrogen aviation.

He has received support from federal funding agencies, including the National Science Foundation, the Department of Energy, NASA and the Army Research Office. He has been honored with several awards, including the Japan Society for the Promotion of Science Invitation Fellowship, funding from the Moore Foundation Experimental Physics Investigators Initiative, and the Outstanding Research Accomplishment Award from the FAMU-FSU College of Engineering.

Election to the APS is considered one of the most prestigious and exclusive honors bestowed on a physicist. The APS represents more than 50,000 members, including academia, national laboratories and industry in the United States and worldwide.

Each year, no more than one half of one percent of the society’s membership (excluding student members) is recognized by their peers for election to the status of Fellow of the American Physical Society.

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Superfluids are a fascinating topic in modern physics research. Governed by quantum mechanics and known for their frictionless flow, superfluids have intrigued scientists with their unusual properties and far-reaching applications.

Researchers from FAMU-FSU College of Engineering, led by Professor Wei Guo, have achieved a groundbreaking milestone in studying how vortices move in these quantum fluids. Their study of vortex ring motion in superfluid helium, published in Nature Communications, provides crucial evidence supporting a recently developed theoretical model of quantized vortices.

“Our findings resolve long-standing questions and enhance our understanding of vortex dynamics within the superfluid,” Guo said.

A key feature of superfluids is the presence of quantized vortices — thin, hollow tubes resembling miniature tornadoes. These play significant roles in phenomena such as turbulence in superfluid helium and glitches in neutron star rotation. However, accurately predicting the motion of vortices has proven challenging.

To address this, the research team used solidified deuterium tracer particles that were caught inside the vortex rings. By illuminating them with a sheet-shaped imaging laser, the team captured precise images and quantified their movement.

The researchers also conducted simulations using various theoretical models and demonstrated that only the recently proposed self-consistent two-way model, or S2W model, accurately reproduces the observed vortex ring motion. According to the S2W model, the ring should shrink as it interacts with the thermal environment, albeit at a slower rate than predicted by earlier theories.

“That was exactly what we saw,” said Yuan Tang, a postdoctoral researcher at the Florida State University-headquartered National High Magnetic Field Laboratory. “This research provides the first experimental evidence supporting the S2W model.”

The significance of this breakthrough extends beyond superfluid helium. The validated S2W model holds promise for applications in other quantum-fluid systems, such as atomic Bose-Einstein condensates and superfluid neutron stars.

“We are excited about the possibilities that the S2W model offers for future studies,” Guo said. “Now that we have confirmed its validity for superfluid helium, we aim to apply this model to other quantum-fluid systems and explore new scientific challenges.”

The research collaboration included co-authors Hiromichi Kobayashi from Keio University, Makoto Tsubota and Satoshi Yui from Osaka Metropolitan University and FSU graduate student Toshiaki Kanai.

This work was supported by the National Science Foundation, the Gordon and Betty Moore Foundation and the Japan Society for the Promotion of Science.

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