Liquid hydrogen pipeline chill-down: Mathematical modelling and investigation

•An experimentally validated model for LH2 feed line chill-down investigation is presented.•Appropriate two-phase sound speed correlations for LH2 chill-down modelling is discussed.•Heat transfer characteristics during LH2 cool-down of long horizontal feed line is studied.•LH2 transfer line chill-down design recommendations and modelling strategy are proposed. Design and analysis of chill-down operation in LH2 feed lines used for refuelling stations, liquid propulsion tests etc. require an accurate prediction model to capture complex phase change flow and conjugate heat transfer. Although there are reports in the literature for chill down modelling, there is still scope for investigation of accurate constitutive relations for the velocity of sound, heat transfer, and pressure drop. In this work, an experimentally validated mathematical model is developed, that can address the above issues. The influence of two-phase sound speed correlations has been studied using six correlations in the literature, which revealed that sound speed does influence the model predictions and Picard and Bishnoi’s approach gave better results. The model is also employed to study the LH2 cool-down phenomenon in long horizontal transfer lines. Parametric investigations are performed to understand the influence of inlet sub-cooling, inlet pressure and axial distance from pipe inlet on cool-down heat transfer. The outcome of this article will provide useful insights into chill-down operation, its design recommendations and an accurate modelling strategy with a focus on LH2 transfer line.