Thermal performance estimation for cryogenic storage tanks: Application to liquid hydrogen

The design of cryogenic liquid storage solutions requires accurate methods for estimating heat ingress, from the material level to the tank level. For insulation materials, thermal performance is usually measured using ambient conditions and liquid nitrogen at 77 K as boundary temperatures. A key question is how much heat ingress increases when storing liquid hydrogen (LH2) at 20 K. We address this by introducing the Concavity Hypothesis, namely that heat ingress is a concave function of the cold boundary temperature, and show that the increase in heat ingress is below 26 %. Additionally, we demonstrate that heat ingress is much more sensitive to the warm boundary temperature than the cold boundary temperature. At the tank level, we compare two methods for assessing the steady-state thermal performance of cryogenic tanks: thermal network models and the heat equation solved with the finite element method. The latter offers high accuracy and adaptability for complex geometries, while thermal network models benefit from simplicity, speed and robustness. We apply both approaches to a self-supported 40 000 m
LH2 tank concept for maritime transport that operates at constant pressure, and analyze sensitivity to structural support thickness, warm boundary temperature, and choice of insulation material. The thermal network model can estimate heat ingress with -1%
error and the cold-spot temperature with error less than 1 K.