A Continuous Boiling Model for Face Seals

Abstract

Mechanical face seals with phase change have extensive engineering applications, yet little theory exists to predict dynamic and thermodynamic behavior. At present, numerical solutions exist for two operating extremes—for low leakage laminar flow where boiling is assumed to occur discretely, and for high leakage, turbulent adiabatic flow. A model is presented herein which allows for continuous boiling, and considers thermal convection effects in laminar flow. Sample calculations and results are compared to the discrete boiling model, and as leakage increases and convection effects become more important boiling may occur over a large portion of the seal face. It is shown that contrary to the discrete boiling model, there may exist a narrow range of stable or bistable operation even when saturation conditions exist near the seal inlet. Instability will invariably occur however if the seal is sufficiently perturbed. This analysis is intended to explain some of the anomalous behavior observed in typical sealing applications, and to act as a guide for experimental verification.