Modelling Liquid Hydrogen Boil-Off Rate

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Discussion Overview

The discussion revolves around modeling the boil-off rate of liquid hydrogen in a specific tank configuration. Participants are exploring the parameters affecting the boil-off rate, including thermal conductivity, heat transfer coefficients, and tank geometry. The focus is on both theoretical modeling and practical simulation tools.

Discussion Character

  • Technical explanation
  • Experimental/applied
  • Debate/contested

Main Points Raised

  • One participant reports issues with the boilFAST simulation tool, noting an unrealistic negative spike in boil-off rate, which raises questions about the validity of the results.
  • Another participant requests additional data on heat transfer coefficients, thicknesses, thermal conductivities, and initial conditions to better understand the scenario.
  • A detailed description of the tank's geometry and initial conditions is provided, including dimensions, relief pressure, and thermal properties of the insulation.
  • Further inquiries are made regarding the material and wall thickness of the tank, indicating the importance of these factors in the modeling process.
  • Thermodynamic data is shared, including calculations for heat transfer rates and estimates of boil-off mass over time, which introduces specific numerical values into the discussion.

Areas of Agreement / Disagreement

Participants have not reached a consensus, as there are ongoing questions about the simulation results and the adequacy of the provided parameters. Multiple viewpoints regarding the modeling approach and the interpretation of results are present.

Contextual Notes

Limitations include the need for more specific data on tank materials and wall thickness, as well as potential discrepancies in simulation outputs that require further investigation.

Who May Find This Useful

This discussion may be useful for researchers and engineers involved in cryogenics, thermal management of cryogenic liquids, and those interested in simulation modeling of thermal processes.

JB312
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TL;DR
I am working on modelling the liquid hydrogen boil-off for a storage tank (30m3) over a period of 2.5 hours using three different insulation materials - polyurethane foam, aerogel, and MLI.
The relevant thermal conductivity, heat transfer coefficients, and thicknesses along with all other required parameters are known. I have attempted to use the online simulation tool boilFAST to simulate each scenario however, the results show a negative spike in boil-off rate which I don't see being possible as this would imply that there is an increase in the volume of liquid hydrogen. Does anyone have any experience in modelling similar scenarios or know another simulation tool that might be useful? Thanks in advance.
 
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Please provide the data on heat transfer coefficients, thicknesses, thermal conductivities, shape. Also, starting mass- or volume fraction of liquid and starting temperature or pressure.
 
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Certainly. Shape = horizontal cylinder with hemispherical end caps, volume = 30.02 m^3, initial liquid volume = 29.44 m^3, inner diameter = 2.93 m, length = 2.5 m (cylinder), relief pressure = 0.25 MPa, liquid temp = 20 K, pressure = 0.092 MPa, ambient temp = 293.15 K, insulation (MLI) thermal conductivity k = 0.00009 W m^-2 K^-1, thickness = 42.7 mm, corresponding heat transfer coefficient (k/thickness) = 0.0021 W m^-2 K^-1. Thank you very much for any help.
 
What is the tank made of, and what is its wall thickness?
 
Thermodynamic data on H2 are given in this reference: https://nvlpubs.nist.gov/nistpubs/Legacy/MONO/nbsmonograph168.pdf
The surface area for heat transfer is about 50 M^2, so the rate of heating is on the order of $$\dot{Q}=50(0.0021)(293-22)=28.5 W=102\ kJ/hr$$
The specific volume of liquid H2 at 20 K is 0.01412 m^3/kg, so the mass of liquid H2 originally in the tank is 29.44/0.01412 = 2085 kg.. At these temperatures, the heat of vaporization is about 450 kJ/kg, So, in 2.5 hours, roughly 0.6 kg would boil off.
 
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