A non-uniform pressure distribution model on the end face in screw expander and shaft seal leakage characteristics{fr}Etude des parame`tres de la Structure sur les fuites d'arbres dans un expandeur a` vis base sur un nouveau mode`le de distribution de pression non uniforme sur la face d'extremite

Pressure distribution on the end face of screw expanders is the primary premise for calculating shaft seal leakage and axial force. Different from other types of expanders, pressure distribution on the screw expander end face is not only affected by operating conditions but also closely related to rotor geometric parameters. To illustrate the leakage characteristics of shaft seal in screw expanders, a non-uniform pressure distribution model on the end face was proposed, and a thermodynamic leakage model in the shaft seal was established. Labyrinth seal, the most widely used sealing assembly, was taken as an example to study the effects of shaft seal parameters on leakage. The influence of four main parameters, namely tooth tip clearance, cavity depth, cavity width, and clearance on the rotor end face, on the leakage of the shaft seal was studied. The results show that pressure on the screw expander end face is non-uniformly distributed, and the average pressure is far less than the highest operating pressure. Moreover, the leakage through the shaft seal rises rapidly with the increase of end face clearance and tooth tip clearance, and a 0.1 mm increment of them can lead to increased leakage up to 108.6% and 52.5%, respectively. And the leakage drops with the increment of cavity width. There is an optimal depth-to width ratio of about 0.13 for minimum leakage. Clearance on the rotor end face has the most significant influence on the leakage of the seal, followed by the tooth tip clearance, cavity width, and cavity depth.