One storage concept for hydrogen-fueled vehicles is physical adsorption of hydrogen at cryogenic temperatures (nominally 80 K). During long idle periods, parasitic heat transfer from the environment induces desorption to the tank void volume. This desorption increases tank pressure such that it must be vented. To reduce the amount of fuel lost to venting, parasitic heating is minimized using multi-layer vacuum insulation and thermally isolating structures. A model is developed to predict the amount of conduction through structural supports and hydrogen lines, radiation through multi-layer insulation, and rarified gas conduction in the vacuum jacket of a tank sized for adsorption storage. The model reveals that conduction through structural supports is significant for cases of interest. Thus, two structural support architectures are compared: one utilizing G-10 CR composite and another involving Kevlar cable. The structural members are sized to support comparable inertial loadings; the overall parasitic heat transfer is found to be as much as 38 percent less for the Kevlar design. A lumped-parameter tank simulation is used to relate parasitic heat transfer to dormancy time and venting rate. The results of thermal testing of a sub-scale tank simulator are compared with model predictions.
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