Theoretical modeling for leakage characteristics of two-phase flow in the cryogenic labyrinth seal

Labyrinth seals are widely used to seal cryogenic fluids in rocket engine turbopumps and cryogenic cooling machine tools. Cavitation is inevitably induced by pressure drop inside the cryogenic labyrinth seal. However, the occurrence and development of the cavitation as well as the leakage characteristics of two-phase flow are unclear yet. This research focuses on revealing cryogenic cavitation behavior and predicting variables of two-phase flow in the labyrinth seal. The method to determine the cavitation position is presented. Theoretical labyrinth seal leakage models of two-phase flow are proposed for the first time, and a mathematical calculation method is formed. A higher accuracy has been proved using the numerical method. The results indicate the starting position of cavitation is related to the inlet pressure, subcooling degree and seal geometry. The steady tooth clearance pressure drop of two-phase flow is extremely small, resulting in a lower leakage compared to the liquid without phase change. Also, the leakage of two-phase flow is dependent on the vapor volume fraction. This work provides a theoretical basis for further studies on the labyrinth sealing performance of cryogenic fluids. (C) 2020 Elsevier Ltd. All rights reserved.