Analysis of stability of two-phase flow mechanical seal with spiral groove under high speeds

Abstract

A thermo-hydrodynamic model was introduced by considering fluid film phase change to analyze the stability of a spiral groove mechanical seal under high speeds. The Reynolds equation, energy equation and heat conduction equation were solved using the finite difference method. Two kinds of phase state stability criteria and fluid film temperature or pressure distributions in each phase state were studied. Different phase states of fluid film and phase state stability of such a spiral groove mechanical seal under variable operating and geometry conditions were analyzed. The results show that vapor mass fraction volume ratio vs sealed fluid temperature (κ-Tf) curve and film pressure coefficient versus sealed fluid temperature (Km-Tf) curve can be used as phase state stability criteria which can predict the range of instability, stability and quasi-stability of a spiral groove mechanical seal. But the Km-Tf curve is more suitable for practical engineering applications. It is found that a significant change in pressure distribution will bring about instability of a spiral groove mechanical seal. The sudden change of film pressure distribution usually occurs when the leakage flow medium in the interface is in the transition phase from quasi-liquid to quasi-vapor where κλ=0 = κ0<λ<1 and κλ=1 = 0. Optimized design of a spiral groove mechanical seal will improve its stability during the phase change from liquid phase state to vapor phase state.