Estimating the time needed to lower the temperature of a cryogenic propellant component through bulk boiling in tanks of launch vehicles and upper stages during pre-launch processing

The paper proposes a computational model for estimating the time needed to lower the temperature of liquid hydrogen used as a propellant component through bulk boiling as a particular case of thermostatting the tanks of launch vehicles and upper stages containing cryogenic propellants. The model includes three different methods of calculating the time of this process - an averaged estimate, equilibrium estimate and an estimate that takes into account the «swelling» applicable to the thermostatting on the ground. Based on the results of working according to all the methods included in the model a time estimate was made for the propellant temperature lowering during ground processing for the fuel tank of an advanced upper stage containing liquid hydrogen as a propellant component, while also obtaining the curve of internal tank parameters vs. time. As a specific case of the model considered in this paper, an estimate of the process was made taking into account the «swelling» of the propellant component, that is, the increase in the propellant component volume due to the volumes of the bubbles formed during bulk boiling of the component. Such an approach, besides providing an estimate of the time needed to lower the temperature through bulk boiling, also makes it possible to estimate the change in the height of propellant component in the tank during termostatting on the ground, and, accordingly, to evaluate the risks of the so-called «drop entrainment», that is, the loss of the propellant component through the vent line. Based on the results of this work, a piece of software was developed in the Visual Basic language, which enables, at the space hardware preliminary design phase, quick preliminary estimation of the time needed to lower the propellant component temperature through bulk boiling of liquid hydrogen in the tank.