Liquid Hydrogen Propellent Pipe Line Transient Chilldown Numerical Modeling and Simulation
For the future deep space exploration missions,the cryogenic propulsion engines are ex-pected to be restartable for many times.Prior to the restart,it is required to chill down the cryogenic propellent pipe lines.Besides,for the cryogenic upper stage,there are also demands for the pipe line chilldown.During the chilling down,there is a tradeoff between the propellent consumption and chilldown time.It is necessary to conduct studies on the chilldown characteristics for cryogenic propellent pipe lines and find efficient chilldown methods.However,due to pipe wall temperature variation and cryogenic fluid properties,the chilldown process involves some complicated two-phase flow heat transfer mechanisms such as nucleate boiling,inverted annular film boiling and so on.In addition,some abnormal phenomenons are also observed.For example,transition boiling occurs at around 120 K of wall temperature,which is much higher than steady state experimental results.In this study,a transient numerical model for the liquid hydrogen pipe line chilldown is established.Different heat transfer mechanisms during the chilldown are analyzed.The numerical model simu-lation results agree well with NASA's hydrogen experimental data.According to the model,during the chilldow,large amount of liquid hydrogen is entrained by the vapor,which results in the waste of liquid hydrogen.The wall heat flux comes to its local maximum valve when the wall temperature is around 115 K.This is due to the coexistence of nucleate boiling and film boiling.Thermal resistance of the pipe wall cannot be neglected.Using the multistep flow rate chilldown scheme can reduce the liquid hydrogen consumption of 27.5％without evident chilldown time extension.
propellentcryogenic fluidstwo-phase flowpipe line chilldownnumerical simulation
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