Growth of individual vapor bubbles in liquid hydrogen during boiling in microgravity

Understanding and modeling phase change inside a cryogenic hydrogen tank of a rocket upper stage or an envisioned fuel depot is essential to enable future exploration goals. Boiling under compensated gravity conditions is caused by local hot spots and influences the thermodynamic state of the fluid, the position of the liquid, and can cause a rise in system pressure. Modeling the boiling process which ranges from the micrometer scale of the cavity at the tank wall to the millimeter scale of the vapor bubbles is important in order to predict the full fluid behavior in the tank. Empirical data for individual hydrogen vapor bubbles under compensated gravity does not exist in literature and is a valuable baseline for analytical and numerical models. The lack of buoyancy increases the observation time and leads to larger bubbles which are better suited for evaluation. In the presented work, the growth of singular hydrogen vapor bubbles for a time of 3.6 s under isobaric conditions has been caused and observed. The growth was initiated at an artificial nucleation site with a diameter of 92.4 µm and a depth of 310 µm by dissipating a known heat flow. The bubble growth data is unique because the defined system conditions allow for a precise correlation of the applied stimuli to the growth behavior. • Isobaric boiling of individual bubbles in a cryogenic hydrogen system. • Cryogenic experiments under microgravity conditions. • Bubbles stays at nucleation site due to absence of buoyancy. • Artificial cavity was manufactured for cryogenic hydrogen fluid system. • Experimental data for liquid hydrogen is relevant for depots and upper stages.