Cryogenic Hydrogen Report from HII

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The Hydrogen Innovation Initiative has released an outstanding resource that can be accessed at the above caption link. Kudos to the individuals who created this well-done primer! Some quick notes on a few of the topics based on my experiences [1]:

3.1 Hazards. The high diffusivity of H2 combined with 20 m/s rise rate in air at ambient temperature makes leaks much less hazardous than many fuels in some regards. My three mantras for all H2 systems are: prevent leaks, provide ventilation, and eliminate ignition sources. It's worth noting that the H2 lower flammability range in air is not much different than methane (natural gas); and it's detonation lower limit range is more than 3 times greater than methane. LH2 pools should only occur in catastrophic accidents and do not last long in practice. Resulting cold vapor clouds are transient but a serious hazard until they warm and rise. For ambient temperature H2, there are no flammable clouds only flammable leak source jets. 

3.2 Ignition consequences. Infrared (IR) detectors and cameras should be used to detect and check for any ignited H2 leaks or flare stack operations (although, they are generally visible at night or in dark locations). The low thermal radiance compared to other fuel fires is due to the lack of soot particles and allows first responders to get closer to the flame if needed.

3.3 Pressure system hazards. Phase change from liquid to vapor at 1 bar results in a 53-fold increase in specific volume which can quickly cause overpressure in an improperly designed or operated LH2 system. The 1:848 expansion ratio is a bit misleading since it assumes the GH2 warms to ambient which would take quite a while to occur in a properly insulated vessel or pipeline. BLEVE is an interesting topic. I've run many thousands of LH2 tests over the years with significant flashing occurring in a receiving tank or vent line exit and never saw any evidence of it. The conditions where it may happen seem to be uncertain at this time.

3.4 Cryogenic hazards. In a properly designed and operated LH2 system, cold burns, hypothermia, and asphyxiation are extremely unlikely. But they must be guarded against like any other hazard. Proper piping and component design and insulation; no enclosed spaces where hydrogen can accumulate; and personal protective equipment (PPE) for any personnel who may be exposed to cryogenic surface during maintenance, etc. Also worth noting: although H2 is an asphyxiant if enough oxygen is displaced, it is not toxic. In fact, breathing gas mixtures for deep diving have used H2. RPT seems similar to BLEVE - a possible scenario but not proven for any specific conditions yet.

4.2 Component level design. Common insulation systems for LH2 include a vacuum jacket with insulation in the vacuum such as MLI, glass bubbles, perlite, or various aerogel formulations. Foam is only appropriate for launch vehicles or potentially other "load-and-go" high consumption applications that can tolerate the poor thermal performance (none currently outside of the space industry that I'm aware of). There is some recent R&D for non-vacuum LH2 insulation that has not been publicly tested or quantified yet. Until it is, vacuum jackets for any LH2 system vessel, transfer piping, and components in contact with the LH2 are a must unless you build rockets (or something with similar requirements). A common MLI construction is layers of double aluminized mylar with dacron netting between them. Approximately 30 layers with a thickness of 2.5 cm can get below 1 W/m^2 heat flux between 300 K and 20 K surfaces in a hard vacuum. Nothing provides near zero conductivity, unfortunately, but MLI in a hard vacuum is the best performing option.

5 Material considerations. While some materials become more brittle at LH2 temperatures (e.g., carbon steel, most plastics, most body-centered cubic metals), others retain their ductility (e.g., aluminum alloys, austenitic stainless with > 7% nickel, and most face-centered cubic metals). However, yield and ultimate strength actually increase generally for most solids; while elastic modulus and fatigue strength varies. Also worth noting is that many material and thermal properties of solids change in a highly nonlinear fashion as a function of temperature in the cryogenic range. This results in the need to integrate properties such as thermal conductivity and specific heat over the temperature range of interest when performing design calculations or modeling. A good deal of historical cryogenic materials testing was done and compiled by NASA, Purdue, NBS/NIST and other sources in addition to the ones mentioned. Coupon sample testing of any new materials, alloys, or processes is critical (especially any additively manufactured structures).

References

[1] Liquid Hydrogen Systems Course, 2025.

Author Bio

Matt Moran is the Managing Member at Moran Innovation LLC, and previous Managing Partner at Isotherm Energy. He's been developing power and propulsion systems for more than 40 years; and first-of-a-kind gas, slush, and liquid hydrogen systems since the mid-1980s. Matt was also the Sector Manager for Energy & Materials in his final position at NASA where he worked for 31 years. He's been a cofounder in seven technology-based startups; and provided R&D, engineering, and innovation consulting to several hundred organizations. Matt has three patents and more than 50 publications including his online Cryogenic Fluid Management guide and Decarbonizing Mobility with Liquid Hydrogen SAE report. He has created and taught liquid hydrogen courses, webinars, and workshops to global audiences.

Cryogenic Hydrogen Thermal Design Options

A key storage consideration for liquid hydrogen is the vaporization rate caused by environmental heat loads, often referred to as boil-off. The above graphic shows some of the established methods for mitigating or eliminating boil-off categorized by the input power required [1].

Passive techniques require no input power and include design and material selection for insulation, structural supports, piping, and other tank interfaces that minimize heat transfer to the inner tank wall. Hybrid methods require some input power for valve actuation, mixers, pumps, or other components to reduce the boil-off rate. 

Finally, active techniques require power input for cryo-refrigeration or densification processes. Depending on the concept of operation for the system, application of the appropriate combination of these methods can minimize or eliminate boil-off losses [2].

UPDATE: Feedback Request on Cryogenic Fluid Management Report

I'm planning to write version 2 of this report to make it more accessible for readers with non-space applications (e.g., aviation, energy, transportation, marine, industrial, import/export, etc.). After reading it for free online or in paperback format, the following actions would be immensely helpful in preparing the next version:

1. Write a customer review on Amazon (if you read the online format of the report please indicate that in the review)
2. Email specific feedback on what you would like to see in version 2 that would be most helpful to your application(s) to: info@moraninnovation.com. Also, please note your Amazon review "name" so I can pair your inputs.

As a token of appreciation for anyone who takes the time and effort to complete 1 and 2 above, I'll email the full current pdf version as an attachment for your personal use. And if you purchased the paperback, will also provide a $10 USD rebate.

Thanks in advance for your feedback!

ORIGINAL POST:

My previous posts contained video clips of the NASA workshop short course I taught last year on this topic. All of these videos, an online version of the report, and a public GitHub repository of related interactive Python code and Jupyter notebooks are all available for free online. Links to these resources can be found at www.moraninnovation.com.

For those who would like a paperback version of the report, I've re-published it on Amazon for sale in all of its global markets. Whether you decide to purchase it, or simply use the online version for free, please consider leaving a review on Amazon. Feedback on topics of interest to include in subsequent reports in this series would be particularly appreciated. Here is a link: https://a.co/d/an7K0rd.

Matt Moran is the Managing Member at Moran Innovation LLC, and previous Managing Partner at Isotherm Energy. He's been developing power and propulsion systems for more than 40 years; and first-of-a-kind liquid, slush and gaseous hydrogen systems since the mid-1980s. Matt was also the Sector Manager for Energy & Materials in his last position at NASA where he worked for 31 years. He's been a cofounder in seven technology based start-ups; and provided R&D and engineering support to hundreds of organizations. Matt has three patents and more than 50 publications including the Cryogenic Fluid Management report series. He also leads the LH2 Era™ Webinar Series. More about Matt can be found on his LinkedIn page.

6.0 Other Topics in Cryogenic Fluid Management

This is the final post of video clips from the short course on cryogenic fluid management (CFM) I taught at NASA's Thermal and Fluid Analysis Workshop in September, 2022. The reference report used to present the course topics can be accessed on the Training page at www.moraninnovation.com.

Matt Moran is the Managing Member at Moran Innovation LLC, and previous Managing Partner at Isotherm Energy. He's been developing power and propulsion systems for more than 40 years; and first-of-a-kind liquid, slush and gaseous hydrogen systems since the mid-1980s. Matt was also the Sector Manager for Energy & Materials in his last position at NASA where he worked for 31 years. He's been a cofounder in seven technology based start-ups; and provided R&D and engineering support to hundreds of organizations. Matt has three patents and more than 50 publications including the Cryogenic Fluid Management report series. More about him can be found here.

5.0 Pressure Control in Cryogenic Systems

This post is a continuation of previous video clips from the short course on cryogenic fluid management (CFM) I taught at NASA's Thermal and Fluid Analysis Workshop in September, 2022. The reference report used to present the course topics can be accessed on the Training page at www.moraninnovation.com.

Matt Moran is the Managing Member at Moran Innovation LLC, and previous Managing Partner at Isotherm Energy. He's been developing power and propulsion systems for more than 40 years; and first-of-a-kind liquid, slush and gaseous hydrogen systems since the mid-1980s. Matt was also the Sector Manager for Energy & Materials in his last position at NASA where he worked for 31 years. He's been a cofounder in seven technology based start-ups; and provided R&D and engineering support to hundreds of organizations. Matt has three patents and more than 50 publications including the Cryogenic Fluid Management report series. More about him can be found here.

4.0 Venting of Cryogens

This post is a continuation of previous video clips from the short course on cryogenic fluid management (CFM) I taught at NASA's Thermal and Fluid Analysis Workshop in September, 2022. The reference report used to present the course topics can be accessed on the Training page at www.moraninnovation.com.

Matt Moran is the Managing Member at Moran Innovation LLC, and previous Managing Partner at Isotherm Energy. He's been developing power and propulsion systems for more than 40 years; and first-of-a-kind liquid, slush and gaseous hydrogen systems since the mid-1980s. Matt was also the Sector Manager for Energy & Materials in his last position at NASA where he worked for 31 years. He's been a cofounder in seven technology based start-ups; and provided R&D and engineering support to hundreds of organizations. Matt has three patents and more than 50 publications including the Cryogenic Fluid Management report series. More about him can be found here.

3.0 Cryogenic Tankage

This post is a continuation of previous video clips from the short course on cryogenic fluid management (CFM) I taught at NASA's Thermal and Fluid Analysis Workshop in September, 2022. The reference report used to present the course topics can be accessed on the Training page at www.moraninnovation.com.

Matt Moran is the Managing Member at Moran Innovation LLC, and previous Managing Partner at Isotherm Energy. He's been developing power and propulsion systems for more than 40 years; and first-of-a-kind liquid, slush and gaseous hydrogen systems since the mid-1980s. Matt was also the Sector Manager for Energy & Materials in his last position at NASA where he worked for 31 years. He's been a cofounder in seven technology based start-ups; and provided R&D and engineering support to hundreds of organizations. Matt has three patents and more than 50 publications including the Cryogenic Fluid Management report series. More about him can be found here.

2.0 Environments for Cryogenic Fluid Management

This post is a continuation of previous posts of video clips from the short course on cryogenic fluid management (CFM) I taught at NASA's Thermal and Fluid Analysis Workshop in September, 2022. The reference report used to present the course topics can be accessed on the Training page at www.moraninnovation.com.

Although this section on environments is tailored for the aerospace audience of the NASA short course, the approach can be applied to other applications with appropriate modifications. For example, stationary liquid hydrogen energy storage would need to address local transient solar flux (including day/night cycles), temperature, weather, and seasonal fluctuations (all in normal gravity). Likewise, mobile applications would have thermal and acceleration environments based on the the vehicle (e.g., aircraft, marine, train, truck, etc.) and associated operations.

Matt Moran is the Managing Member at Moran Innovation LLC, and previous Managing Partner at Isotherm Energy. He's been developing power and propulsion systems for more than 40 years; and first-of-a-kind liquid, slush and gaseous hydrogen systems since the mid-1980s. Matt was also the Sector Manager for Energy & Materials in his last position at NASA where he worked for 31 years. He's been a cofounder in seven technology based start-ups; and provided R&D and engineering support to hundreds of organizations. Matt has three patents and more than 50 publications including the Cryogenic Fluid Management report series. More about him can be found here.

Calculations for Introduction to Cryogenic Fluid Management

My previous post provided introductory video clips from the short course on cryogenic fluid management (CFM) I taught at NASA's Thermal and Fluid Analysis Workshop in September, 2022. The reference report used to present the course topics can be accessed on the Training page at www.moraninnovation.com.

The final section in the Introduction chapter contains example calculations to demonstrate how to use the tools and equations presented in the previous sections. As an additional resource, I've created a Jupyter notebook containing Python code with the key calculations and example exercises. It is available under a permissive open source license in my public GitHub repository at: https://github.com/moranmatthewe/CryoFM

I've attempted to include sufficient descriptive information and graphics to make the notebook useful as a standalone tool. The Python coding is intentionally straightforward to facilitate interpretation and make it easy to translate to other coding languages of interest to the user (e.g., VBA, C/C++, Matlab, Fortran, etc.).

If you have Python and JupyterLab on your computer, the Introduction notebook and CryoFM™ functions library can be downloaded and used locally (subject to the Apache 2.0 license). If you don't have these applications loaded but would like to try them out, I suggest using the Anaconda distribution to set up your computer with these and other useful programming tools.

Alternatively, if you prefer not to load these programs onto your local machine (or are prohibited by your IT department from doing so), an interactive web browser instance can be invoked using Binder that requires no downloads nor software installation. To try this method, simply look at the readme file on my GitHub repository and click on the "launch binder" icon (see screenshot below).

Matt Moran is the Managing Member at Moran Innovation LLC, and previous Managing Partner at Isotherm Energy. He's been developing power and propulsion systems for more than 40 years; and first-of-a-kind liquid, slush and gaseous hydrogen systems since the mid-1980s. Matt was also the Sector Manager for Energy & Materials in his last position at NASA where he worked for 31 years. He's been a cofounder in seven technology based start-ups; and provided R&D and engineering support to hundreds of organizations. Matt has three patents and more than 50 publications including the Cryogenic Fluid Management report series. More about him can be found here.

1.0 Introduction to Cryogenic Fluid Management (CFM)

In September of 2022 I taught a short course on cryogenic fluid management (CFM) at NASA's Thermal and Fluid Analysis Workshop. The course covered analysis and design of liquid hydrogen systems as well as other cryogenic fluids used in power and propulsion applications.

Although the target audience was aerospace engineers and scientists, most of the topics are directly applicable to liquid hydrogen systems in general (e.g., energy, transportation, marine, etc.). As such, the course content can be used as a resource for the development of any liquid hydrogen system.

This first video is a short introduction. Subsequent videos posted over the coming weeks will cover the other topics presented during the course. My hope is that these edited clips will be easier to digest - and later revisit as needed - rather than posting the full ~3 hour video.

The reference report used to present the course topics can be accessed on the Training page at www.moraninnovation.com. Any feedback on this material, or future topics of interest, are appreciated and can be emailed to: info@moraninnovation.com.

The example calculations for these topics are discussed in the next post.

Matt Moran is the Managing Member at Moran Innovation LLC, and previous Managing Partner at Isotherm Energy. He's been developing power and propulsion systems for more than 40 years; and first-of-a-kind liquid, slush and gaseous hydrogen systems since the mid-1980s. Matt was also the Sector Manager for Energy & Materials in his last position at NASA where he worked for 31 years. He's been a cofounder in seven technology based start-ups; and provided R&D and engineering support to hundreds of organizations. Matt has three patents and more than 50 publications including the Cryogenic Fluid Management report series. More about him can be found here.

Moran Innovation 2022 Highlights

• Densified Propellant Testing: Moran Innovation was awarded a subcontract to provide subject matter expertise for densified propellant capabilities development at White Sands Test Facility.

• Short course, invited panelist, and presentation: Matt Moran taught a short course and was a panelist and presenter on the topic of cryogenic systems at NASA's 2022 Thermal and Fluids Analysis Workshop.

• NASA Cryogenic Systems Modeling: Moran Innovation is supporting additional new contract work for NASA related to validation of high fidelity modeling tools with experimental tests of liquid hydrogen, methane, oxygen, and other cryogens.

• Heavy-Lift Aircraft: Moran Innovation completed support of a design cycle for the liquid hydrogen propulsion and power system of a private sector heavy-lift cargo aircraft.

• NASA Support Contract Extensions: Moran Innovation has been awarded two contract extensions of 6 months and 18 months, respectively, related to the NASA Human Landing System program.

• Cryogenic Fluid Management: Part 1 of this report series has been published and is available online. In-house training based on the material is also available (see Training).
• Other news. See the Moran Innovation website and blog at LH2era.com for more in depth information and news on hydrogen, propulsion, and power systems.

Matt Moran is the Managing Member at Moran Innovation LLC, and previous Managing Partner at Isotherm Energy. He's been developing power and propulsion systems for more than 40 years; and first-of-a-kind liquid, slush and gaseous hydrogen systems since the mid-1980s. Matt was also the Sector Manager for Energy & Materials in his last position at NASA where he worked for 31 years. He's been a cofounder in seven technology based start-ups; and provided R&D and engineering support to hundreds of organizations. Matt has three patents and more than 50 publications including the Cryogenic Fluid Management report series. He also leads the LH2 Era™ Webinar Series. More about Matt can be found on his LinkedIn page.

Cryogenic Systems Modeling and Analysis

Cryogenic Fluid Management (CryoFM™) Interactive Calculations Notebook

Last month I participated in NASA's annual Thermal and Fluids Analysis Workshop (TFAWS) as a short course instructor, panelist, and presenter on the topic of cryogenic fluid management. This is a critical topic for launch vehicles and spacecraft. It is also becoming a very important consideration for the rapid growth in production, energy storage, ground transportation, shipping, and aviation applications of liquid hydrogen systems.

What is Cryogenic Fluid Management?

Cryogenic fluid management deals with the systems, technologies, and operations associated with the liquefaction, storage, and transfer of cryogenic liquid propellants. Hydrogen, oxygen, and methane are the most commonly used fluids for this purpose.

Appropriate modeling and analysis is vital for development of high performing cryogenic systems. There are three broad categories of software tools typically used for this purpose:

1. Computational fluid dynamics (CFD): The highest fidelity option that also generally requires the highest level of resource commitment (i.e., computational, personnel, and licensing). CFD typically uses a very fine mesh of finite volumes to model the system. Setting up the model and the appropriate parameter adjustments requires experience with the particular CFD software being used and an understanding of how to best represent the actual system of interest.
2. Multi-nodal models: A moderate fidelity and resource option that divides a cryogenic system into discrete lumped nodes. The number of nodes can be few or many, and is a key determinant of the model resolution. Similar to CFD, the modeler's experience with the software and ability to accurately represent the actual system is critical.
3. System-level and first-order analysis: The lowest fidelity option with generally the lowest resource commitment. Reduced order system models and first order analyses can be used early in the development to narrow the trade space of feasible designs. Also useful as a check on the results obtained from higher fidelity tools.

System-Level and First-Order Analyses

Generally, the development of a new cryogenic system and assessment of key operations begins with system-level and first-order analyses. These activities can be performed faster and for lower resource expenditures compared to higher fidelity modeling. They enable assessment and modification of the early design and operational options.

Commercially available general purpose system simulation software options have limited cryogenic modeling capabilities. Conversely, while many cryogenic system specific software tools have been developed over the years, most are either proprietary or inconsistently maintained and documented. And validation of model results for all of the modeling options is an ongoing challenge for applying them to new cryogenic systems.

The short course I taught at the NASA TFAWS event was an attempt to address the documentation issue by presenting a publicly available report on passive cryogenic fluid management that can be accessed online by anyone at no cost. My subsequent technical presentation outlined the status and plans for a set of calculation software tools based on that report for quickly performing first-order analyses and building system-level models.

While both the training course and technical presentation were well received, several excellent questions from workshop participants have been on my mind:

• How can all of the planned cryogenic fluid management tools best be developed and maintained?
• What about users who don't have access to the tool platforms or aren't permitted by their organization to download them (e.g., Python)?
• If other platforms are of interest to specific users (e.g. Matlab), who will modify the tools for those users?

The Open Source Option

One potential approach to addressing these questions is to make the new cryogenic fluid management software tools open source. This approach would ensure that they are accessible; and would encourage  community development, maintenance, and expansion to other platforms and new capabilities.

The screenshot shown at the top of this post represents a small first step in that direction. It uses the Jupyter platform to integrate markdown outline, text, images, and equations with interactive calculations in the Python programming language. A fully functional instance of the notebook can be invoked in a web browser without downloading anything.

By hosting these tools in a public GitHub repository, full access is granted to anyone interested in using or modifying the tools subject to the open source license. Improvements and extension to other platforms can be likewise shared among the user community. If you have any feedback on this approach, or are interested in being part of a future beta test group for the software tools, send me a message at info@moraninnovation.com.

Matt Moran is the Managing Member at Moran Innovation LLC, and previous Managing Partner at Isotherm Energy. He's been developing power and propulsion systems for more than 40 years; and first-of-a-kind liquid, slush and gaseous hydrogen systems since the mid-1980s. Matt was also the Sector Manager for Energy & Materials in his last position at NASA where he worked for 31 years. He's been a cofounder in seven technology based start-ups; and provided R&D and engineering support to hundreds of organizations. Matt has three patents and more than 50 publications including the Cryogenic Fluid Management report series. More about him can be found here.

Entering the Cryo Zone with Hydrogen

Saturation temperature vs pressure for hydrogen, oxygen, and methane [1]

At ambient temperature and pressure (i.e., 298 K and 1.01 bar), hydrogen is a gas with approximately 7% the density of air. This results in an advantageous rise rate of nearly 20 m/s (or six times faster than natural gas) enabling rapid dispersion of any leaks. However, this low density is a challenge for storage.

The two most commonly used methods of increasing hydrogen density in order to store significant quantities are compression and liquefaction. Compressed storage up to 700 bar is commercially available and increases the density of hydrogen by a factor of 477 times greater than ambient pressure; whereas, liquefaction increases it by 866 times compared to ambient conditions (i.e., nearly double the density of compressed hydrogen at 700 bar).

Liquefying Hydrogen

In order to liquefy hydrogen it must be cooled to a very low temperature (e.g., 20 K at 1.01 bar). This is accomplished with a cryogenic liquefier or cryocooler. Various thermodynamic cycles and equipment are available for this purpose.

All liquefaction processes are limited by the ideal Carnot efficiency which is calculated as the ratio of the cold refrigeration temperature divided by the difference in cold refrigeration and warm rejection temperatures. The actual performance of hydrogen liquefiers are a fraction of the ideal efficiency, ranging from about 30-40% of Carnot for state-of-the-art systems.

Two-stage hydrogen liquefiers generally bring the hydrogen gas down to the 80-100 K range in the first stage (i.e., sensible cooling); and then cool and liquefy it in the 20 K range in the second stage (i.e. sensible and latent cooling). Efficiencies are much higher for the first stage due to the higher refrigeration temperature.

Hydrogen liquefaction must also address the conversion of ortho-to-para hydrogen that occurs at cryogenic temperature. This change in equilibrium electron spin state is an exothermic process that is generally accelerated with a catalyst during liquefaction.

Liquid Hydrogen Storage Behavior

Insight into the behavior of hydrogen and other fluids at cryogenic temperatures can be gleaned by examining their saturation temperature at the vapor pressure of interest (see above plot). In a container of liquid hydrogen, the interface between the liquid and vapor is always at the saturation temperature corresponding to the container vapor pressure.

However, the temperatures in the hydrogen vapor space of the container - also known as the ullage - are at or above the saturation temperature (i.e., superheated). For a stationary tank, the ullage thermally stratifies with the coolest temperature near the interface and warmest temperatures near the top of the container.

Conversely, the liquid hydrogen in such a container is at or below the saturation temperature (subcooled). A stationary container with subcooled liquid will also thermally stratify with the coldest temperatures near the bottom of the tank. If the subcooled liquid is circulated toward the interface by a mixer, or from momentum forces in a mobile application, the tank pressure will drop to a new saturation condition.

Over time, the liquid hydrogen in a container will warm toward the saturation temperature (but not above it) due to heat transfer from the environment. When all of the liquid reaches saturation temperature, it will begin to boil off and raise the tank pressure. This additional vapor must either be vented when the tank pressure reaches the maximum design limit; or reliquefied to maintain "zero boil-off" storage.

Cryogenic Material Properties

Most materials behave very differently at cryogenic temperatures compared to ambient conditions. These differences must be well understood by engineers, designers, and operators of cryogenic systems.

Thermal properties of materials such as conductivity and specific heat are highly nonlinear functions of temperature in the cryogenic range. As a result, heat transfer and energy balance calculations often require integrating the property of interest over the temperature range. Simply using an average value between the upper and lower temperature can result in significant calculation errors.

Mechanical properties that can vary significantly at low temperature include:

• Yield and ultimate strength: generally increases at lower temperatures for most solids
• Ductility: some materials remain ductile (e.g. aluminum alloys, austenitic stainless steel with > 7% nickel, most face-centered cubic metals); while some materials become brittle (carbon steel, most plastics, most body-centered cubic metals)
• Elastic modulus: varies
• Fatigue strength: varies

All of the above has implications for the selection of materials in liquid hydrogen system design. Storage tanks of 300 series stainless steel are common. Aluminum alloys are also used in some applications, and titanium alloys are suitable but rarely used outside of the aerospace industry.

Seals for fittings, gaskets, and valves must be comprised of compatible elastomers for cryogenic hydrogen service. Likewise, instrumentation and sensors designed for cryogenic temperatures are required for liquid hydrogen system monitoring and process control.

In the next post I'll touch on tank design options, insulation systems, and filling/draining operations.

References

[1] Cryogenic fluid management of liquid hydrogen, oxygen, and methane: Part 1 - passive technologies, systems, and operations. Moran Innovation LLC, 2022.

Matt Moran is the Managing Member at Moran Innovation LLC, and previous Managing Partner at Isotherm Energy. He's been developing power and propulsion systems for more than 40 years; and first-of-a-kind liquid, slush and gaseous hydrogen systems since the mid-1980s. Matt was also the Sector Manager for Energy & Materials in his last position at NASA where he worked for 31 years. He's been a cofounder in seven technology based start-ups; and provided R&D and engineering support to hundreds of organizations. Matt has three patents and more than 50 publications including the Cryogenic Fluid Management report series. More about him can be found here.

Hydrogen is Best Served Cold

Storage and Delivery Options

One of the key decisions in developing a hydrogen system is deciding how - and in what form - to store and deliver it. The most common approaches are ambient temperature compressed gas up to 700 bar, or low pressure cryogenic liquid near 20 K.

Other methods have been tried and are the subject of ongoing research and development. These include: materials that trap hydrogen by molecular or chemical means; cryo-compressed (transcritical); and hydrogen "carriers" that are converted prior to use (e.g. ammonia).

Any application should be evaluated to determine the best approach given the system objectives, requirements, constraints, and concept of operations. For large scale applications, and vehicles with onboard hydrogen storage (land, sea, air, or space), liquid hydrogen is often the best solution.

Liquefied Hydrogen

Liquid hydrogen has several critical advantages compared to other forms of hydrogen storage:

• Relatively high volumetric density at low operating pressures
• Long history of production, storage, transport, and usage
• Off-the-shelf subsystems and components available
• Many legacy stationary, over-the-road, train, barge, and launch systems
• Zero boil-off possible with proven cryo-refrigeration technology
• Low temperature provides ancillary system capabilities

The above advantages are partially offset by the unique design and operational considerations associated with liquid hydrogen. Some key considerations include: liquefaction (and re-liquefaction), material properties, fluid thermodynamics, phase change, and thermal management.

Although there are well established and validated methods to fully address these considerations, the requisite knowledge base is not widely disseminated yet. The primary motivation for this blog is to share that knowledge base with a wider audience to accelerate the safe and effective adoption of liquid hydrogen in new areas of application.

Below is a presentation I gave a few months ago at the Center for Hydrogen Safety Asia-Pacific Conference that addresses zero boil-off and densified liquid hydrogen systems. Future posts will provide more details on these and other related topics.

Matt Moran is the Managing Member at Moran Innovation LLC, and previous Managing Partner at Isotherm Energy. He's been developing power and propulsion systems for more than 40 years; and first-of-a-kind liquid, slush and gaseous hydrogen systems since the mid-1980s. Matt was also the Sector Manager for Energy & Materials in his last position at NASA where he worked for 31 years. He's been a cofounder in seven technology based start-ups; and provided R&D and engineering support to hundreds of organizations. Matt has three patents and more than 50 publications including the Cryogenic Fluid Management report series. More about him can be found here.

Cryogenic Fluid Management of Liquid Hydrogen...

Executive Summary

This report provides passive cryogenic fluid management (CFM) insights, methods, equations, and algorithms suitable for performing system designs and trades. The content is intended for engineers, designers, analysts, managers and others who are developing or operating passive CFM systems.

Topics covered are based on cryogenic systems subject matter expertise at Moran Innovation LLC that has been developed over the past 35 years. Each main section concludes with calculation examples to demonstrate how to use the equations presented and interpret the results.

Main sections and subsections include:

• Introduction to mission and vehicle drivers, thermophysical properties, thermodynamic behavior, fluid dynamics and heat transfer.
• Acceleration and thermal environments, and how these environments vary based on mission segment.
• Tankage for the storage of cryogenic propellants including: material properties; design and sizing; heat loads and insulation; and packaging and integration.
• Venting of cryogenic tanks and associated implications such as: cryogen losses; liquid level rise in low gravity; and utilization of vent gas for propulsive settling and/or structural cooling.
• Pressurization and pressure response of tanks including: active pressurization, interfacial heat and mass transfer, self-pressurization, and ullage collapse.
• Other passive CFM topics including: chilldown and tank filling; tank internal insulation and structures; tank external structures and components; mass and energy balance; and propellant tracking.
• References section with all sources cited in the footnotes; and an Appendix with instructions on how to access additional online content, and information on Moran Innovation LLC.

Online Access

The report is available online and can be accessed at: www.moraninnovation.com

The online version is a shared document in pdf format with viewer permission granted. Download and print functions are disabled. If you are having difficulty accessing the document, check with the IT department at your organization to ensure online access to shared Google Docs is permitted.

Matt Moran is the Managing Member at Moran Innovation LLC, and previous Managing Partner at Isotherm Energy. He's been developing power and propulsion systems for more than 40 years; and first-of-a-kind liquid, slush and gaseous hydrogen systems since the mid-1980s. Matt was also the Sector Manager for Energy & Materials in his last position at NASA where he worked for 31 years. He's been a cofounder in seven technology based start-ups; and provided R&D and engineering support to many industrial, government and research organizations. Matt has three patents and more than 50 publications including the Cryogenic Fluid Management report series. More about him can be found here.

Moran Innovation 2021 Highlights

NASA KSC LC39B New Liquid Hydrogen Dewar Tank (left: under construction in 2020, right: near completion in 2021)

• Hydrogen Systems Development: Past, Present and Future. Seminar presentation to LTA Research on the evolution of hydrogen systems in aerospace along with present day state-of-the-art technologies and future hydrogen systems. A publicly available abstract and version of the presentation package can be found here.
• Densified and No-Loss (Zero Boil-off) Liquid Hydrogen Systems. An overview of these systems along with safety considerations and proven mitigations presented at the Center for Hydrogen Safety Asia-Pacific Conference 2021. The abstract, video and presentations slides can be found here.
• Liquid Hydrogen Drones and Microgrids. US Air Force funded project to demonstrate extended duration drones and integrated hydrogen energy storage for base operations under subcontract to NEOEx Systems. A $10 million earmark from the 2022 US federal defense appropriation budget will support further development of liquid hydrogen refueling systems.
• Lunar Human Landing System (HLS). Support to NASA under subcontract to HX5 as a subject matter expert in cryogenic fluid management for the SpaceX HLS development of the first commercial human lander that will safely carry astronauts to the lunar surface.
• Long Term Liquid Hydrogen Storage. Support to NASA under subcontract to HX5 for the Lockheed Martin Tipping Point testing of more than a dozen cryogenic fluid management technologies, positioning them for infusion into future space systems.
• Orbital Cryogenic Propellant Transfer. Support to NASA under subcontract to HX5 for the SpaceX Tipping Point large-scale flight demonstration to transfer cryogenic propellant, specifically liquid oxygen, between tanks on a Starship vehicle.
• New design tools and training courses. Several new software tools for liquid hydrogen systems and cryogenic fluid management were created in 2021. Training courses on these topic areas are also under development and planned for rollout in 2022.
• Lunar ice mining concept. "Down Under Excavation and Transport (DUET) Lunar Mining System (LuMiS)", Free J., Cannard S., Sciortino J., Rhatigan J., Haberbusch M., Moran M. Submitted to the NASA Break the Ice Challenge and presented at the 2021 Lunar Surface Science Workshop.
• Other news. See the Moran Innovation website and blog at LH2era.com for more in depth information and news on hydrogen, propulsion, and power systems.

Matt Moran is the Managing Member at Moran Innovation LLC, and previous Managing Partner at Isotherm Energy. He's been developing power and propulsion systems for more than 40 years; and first-of-a-kind liquid, slush and gaseous hydrogen systems since the mid-1980s. Matt was also the Sector Manager for Energy & Materials in his last position at NASA where he worked for 31 years. He's been a cofounder in seven technology based start-ups; and provided R&D and engineering support to many industrial, government and research organizations. Matt has three patents and more than 50 publications including the Cryogenic Fluid Management report series. More about him can be found here.