NASA has found that when transferring liquid hydrogen (LH2) from a delivery or storage tank to another tank, they lose 50–70% of the hydrogen to boil-off. Some of the biggest refueling challenges include the lengthy cool-down times needed to get LH2 to the fuel tank and wasted fuel due to hydrogen boil-off. Now, first-of-its-kind results from a NASA SBIR program show that GTL’s composite tubing can reduce chill-down time, hydrogen boil-off, and the dry mass of cryogenic fluid transfer lines.
GTL first developed BHL technology for cryo-tank applications, but it also works exceptionally well for transfer lines, tubes, and pipes, providing up to ten times lower thermal mass than metal tubing, according to the company. In a recent series of tests, GTL demonstrated the feasibility of these pipes in quickly reaching 20 degrees Kelvin and beginning the flow of liquid hydrogen within two seconds. This means that once integrated into operational systems, an aircraft could fill its LH2 tanks in minutes rather than hours and easily manage the small amount of hydrogen that boils off during fill operations, significantly reducing fuel costs and increasing operational safety.
“We are thrilled with our team’s efforts to test and validate our BHL technology and its demonstrated ability to outperform conventional metal transfer lines for both mass and boil-off characteristics,” said GTL President Paul Gloyer. “We first had strong results with our tank technology and now we have tubes that demonstrate fast fill and refill capabilities. The ultralight weight BHL technology being used/validated in this effort marks another key milestone in our efforts to advance hydrogen-powered innovation and vehicles.”
In the SBIR effort, a series of lightweight BHL composite tubes were tested alongside equivalent metal tubing. The tests confirmed and validated the enhanced thermal properties of BHL tubes, demonstrating that GTL’s BHL composite tubes chilled down approximately ten times faster than equivalent stainless-steel tubing. This improvement was achieved through a significant reduction in thermal mass and enhanced heat transfer properties. With this technology, LH2 boil-off during transfer can be significantly reduced, paving the way for practical no-vent filling of LH2 tanks for aircraft, trucks, and spacecraft.
The Phase II effort also verified the scalability of the BHL tubes, demonstrating the capability to build tubes with a range of diameters and lengths, as well as the ability to create tube bends and accommodate tube flexure. As part of the effort, GTL fabricated flight-capable BHL tubing for the main liquid oxygen and liquid methane propellant lines for GTL’s Disruptor suborbital rocket, which successfully underwent a cold-flow ground test.
GTL has multiple concurrent projects leveraging BHL technology. Currently, GTL is integrating BHL composite tubing into the flight prototype of its ultra-lightweight composite LH2 Dewar tank, scheduled for flight testing on a manned helicopter starting in Q4 2024. In the coming year, BHL tubes will be integrated into flight applications where their lightweight, high-performance capabilities will be further validated. GTL intends to integrate BHL tubes into future vehicle designs and cryogenic transfer line solutions. This BHL technology is applicable to nearly any cryogenic system, making it relevant for launch systems, Lunar, cislunar, and Mars applications, as well as satellite systems.
