In the previous post I provided some quick start guidelines for using the H2 Sage™ dewar sizing online app for creating a conceptual design of the inner vessel. The next step is to explore insulation options that will be installed around the inner vessel.
Insulation Options
A dropdown menu provides some of the most common insulation options used for liquid hydrogen dewars:
- Multilayer insulation (MLI) is the best performing type of insulation in a vacuum and is frequently used for mobile and stationary dewar tanks of small to moderate size (and vacuum-jacketed piping).
- Perlite has been historically used for large stationary liquid hydrogen dewar tanks.
- Glass bubbles are a newer option for stationary dewar tanks with better performance than perlite.
- Other insulation types can be specified for user-defined configurations, degraded vacuum conditions, or ambient pressure performance.
An annotated plot of the apparent thermal conductivity of various insulation types as a function of cold vacuum pressure is provided to aid in exploring other options. Note that this data is from calorimeter testing which results in better performance than tank-applied insulation systems.
Additional Inputs
Insulation thickness can be specified within a range dictated by the size of the inner vessel. Increasing thickness improves thermal performance but increases overall system mass (i.e., insulation system and outer vessel wall).
Degradation factor takes into account the reduced performance of tank-applied insulation with a value of 1.0 indicating no degradation. Seams, openings for piping and support structures, and other discontinuities in tank-applied MLI affect this factor. A value between 2.0 and 3.0 is recommended for MLI. Other insulation options have different characteristics that may warrant a lower degradation factor.
Warm boundary temperature is the condition at the outer surface of the insulation system (e.g., dewar tank outer vessel wall). This can generally be assumed to be ambient temperature in most scenarios. A lower warm boundary temperature would be used if a vapor-cooled shield, cold wall, or other method is being used to reduce heat leak into the cryogen.
Outputs (Figures of Merit)
Heat flux provides a comparative measure of the thermal performance of different insulation schemes. The total heat leak coming through the insulation for the given tank design will be estimated in a different tab that includes additional heat leak sources.
Areal density is a comparative measure of insulation mass that is particularly important for mobile applications. The insulation system mass will be estimated in a different tab that includes the masses of all the dewar tank structures and components.
Visit H2sage.com to access the online app and for more detailed information about insulation systems including pros and cons of each type.
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.
