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.