Pressure surge during cryogenic feedline chilldown process

Cryogenic fluid entering a warm feedline absorbs heat and undergoes rapid flash evaporation leading to pressure surges, which can retard the flow inside the feedline. It may have serious repercussion in operation of the rocket engine during start up. Experimental and numerical studies are carried out to examine the effect of inlet pressure and initial feedline temperature on pressure surges. An analytical model using SINDA/FLUINT software is developed to investigate this complex two-phase flow phenomenon including the various boiling regimes that exist during line chilling. The numerical study is carried out considering 1D flow through a cryogenic feedline of 2.47m long and 0.01m inner diameter with liquid nitrogen at 77.3K as working fluid. Predictions are made for the inlet pressure in the range of 0.28-0.76 MPa and initial wall temperature of 200 K and 300 K. Subsequently, an experimental test rig is setup and the model is validated with the experimental data. The studies show that within the range of parameter considered, the magnitude of pressure surge increases exponentially with increase in inlet pressure and decreases with the prechilling of feedline.