Research Terms
Mechanical Engineering Aerospace Engineering
This storage tank and propellant transfer apparatus conserves valuable cryogenic propellants in reduced gravity and microgravity environments. The extension of human space exploration is NASA’s primary challenge for the new millennium, and having an effective, sufficient, and reliable supply of cryogenic propellant fluids is integral to this mission. Storing and maintaining rocket propellant as a liquid at cryogenic temperatures enables lighter fuel tanks and denser energy storage. However, transfer of such propellant into empty fuel tanks, e.g., during refueling of a mission beyond Earth’s orbit, results in fuel losses as the propellant boils off in contact with the relatively hot tank walls. The losses can only end when the wall temperature equilibrates with the propellant, a process known as chill-down. However, chill-down is inefficient in low gravity, impeded by vapor film formation between the solid tank walls and the liquid propellant. The vapor film reduces heat transfer, resulting in “film boiling.”
Researchers at the University of Florida have developed a storage tank and propellant transfer line apparatus for quickly escaping the film boiling regime using a combination of a polymer coating on the tank wall and spray flow pulsing. This storage tank facilitates a shorter chill-down process and conserves rocket fuel.
Cryogenic propellant storage tank and transfer lines for efficient thermal management in microgravity and reduced gravity environments
In space, propellant transfer includes transfer line chill-down and storage tank chill-down. The processes cause the cryogenic propellant to boil off due to the high temperatures of the transfer line and receiver tank, making a more efficient chill-down process necessary. The primary reason for inefficient chill-down is the insulating vapor film that forms between the cold cryogenic propellant and the tank wall, drastically slowing the heat transfer. This redesigned storage tank combats the film boiling regime with two strategies. First, it contains a thin polymer coating on the tank wall that drives initial faster cooling of the wall surface at the cost of later slower interior cooling. However, surface cooling alone is enough to break out of the film boiling regime, so this strategy shortens the inefficiency period. Second, because heat transfer from the wall is strongest upon first contact with the wall, then decays, this apparatus deploys cryogenic propellant to the wall in repeated pulses, taking advantage of the most efficient moments of the heat transfer process repeatedly.
This steam gasification process converts solid-organic waste into syngas for power production. Solid-organic waste comes from ubiquitous sources such as municipal solid waste, biomass, wastewater sludge, municipal wastewater, and animal waste. The conversion of organic waste into products like electric power, green hydrogen, and syngas occurs via steam gasification, an efficient process for green energy production. The high-temperature steam converts carbon-containing materials into syngas, a mixture of H2 and CO, by reacting with steam only. However, reacting carbon-containing materials with steam requires very high temperatures, and achieving these high temperatures requires conventional fuels, like fossil fuels. The combustion of fossil fuels yields greenhouse gases, or the biomass itself, producing sulfur and nitrous oxides. A pathway to steam gasification of organic waste avoiding the harmful byproducts would allow clean, self-contained syngas production from everyday waste sources.
Researchers at the University of Florida have developed a steam gasification process that powers itself with biogas extracted via anaerobic digestion, opening a route to syngas production without fossil fuels and using only municipal solid waste as feedstock. The syngas outflow can produce power, synthetic fuels, or chemicals with subsequent processing.
Converts solid-organic waste into syngas fuel using clean steam gasification for energy production
This steam gasification system produces energy, such as syngas, green hydrogen, steam, or electricity, using solid-organic wastes as the only feedstock. It employs an anaerobic digester to break down biodegradable materials and produce biogas comprising CH4 and CO2. The system flexibly deploys this biogas as an internal heat source to dry the organic waste and increase the temperature of the steam.
The dried organic waste and high-temperature steam combine in the gasifier to produce an outflow of syngas and gasified components. The resulting product exits the gasifier through a moisture separator, yielding syngas pure enough for use as an energy source. This system also flexibly incorporates concentrated solar plants to supplement the biogas as a clean heat source for heating the steam.
This cryogenic heat transfer surface made of aluminum and an anodized aluminum oxide layer is capable of substantial heat transfer enhancement in all three boiling and quenching regimes. The surface layer features nanoscopic pores that effectively trap moisture to grant it substantial heat transfer enhancements. These enhancements can be applied effectively to a variety of engineering applications including power production, advance electronics, and cryogenic fluid systems. Cryogenic fluids are widely used in industrial applications, space explorations, and cryosurgery devices, and systems that use them require a "chilldown" process to adjust the system to low operating temperatures. Power production devices and advanced electronic systems rely on efficient heat transfer mechanisms to maintain an optimal temperature level to maximize power density for higher system efficiency. But as conventional convective heat transfer technologies reach their limits, researchers are looking for modern phase-change thermal energy transport mechanisms for solutions. Researchers at the University of Florida have developed a solution with this surface layer of anodized aluminum oxide nanopores that significantly enhances heat transfer.
Nanoporous aluminum oxide surface that enhances heat transfer efficiency to improve various industrial systems
The anodized aluminum oxide nanoporous texture of the surface layer creates a highly wettable and superhydrophilic property that drastically alters boiling and quenching properties. The pores are created by first electrically increasing the thickness of aluminum substrate, then using acid to create a pattern of nanopores on the aluminum surface. The nanoporous alumina substrates can be modified to have different pore sizes, distribution, and morphologies that in turn affect the heat exchange properties. For cryogenic applications, the nanoporous surface can shorten the chilldown time up to 20 percent, which can reduce cryogenic fluid consumption by nearly 30 percent and increase safely with reduced boil-off and venting points. This surface also significantly increases the Leidenfrost point, maintaining a higher level of heat transfer in a larger range of surface temperature.
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