A homogenous phase change model (HPCM) based on the mass conservation law is proposed to analyze the flow field of a two-phase mechanical seal with 3D face structures. The two-phase flow domain is governed by the simultaneous partial differential equation set containing a mass transfer governing equation for each phase with a source term derived from the Rayleigh–Plesset model and a Reynolds equation for the mixture, where the pressure and the liquid fraction are unknowns. A numerical solution is developed based on finite element method (FEM). The results from the present model are in good agreement with those from the previous two-phase mechanical seal models. A two-phase mechanical seal with wavy-tilt-dam face structure is calculated. The results indicate that the 3D face structure affects the phase distribution by altering the film pressure field. The present model is especially useful to analyze the two-phase film flow field bounded by the complex solid surfaces.

Seal failure is a common phenomenon that occurs when using a dry gas seal. Many seal failures occur during the start-up process of the seal. In this study, the state evolution of a dry gas seal during repeated start-stop operations was investigated using an acoustic emission (AE) method and a modified empirical mode decomposition using masking signals (MS-EMD). It was evident that the lift-off speed and root mean square (RMS) of the full-speed period changed in stages. According to the change of these parameters, the state evolution of the dry gas seal during the experiment occurred in four stages: the running-in stage, normal working stage, transition stage, and abnormal stage. During the normal working stage, the RMS curve of the late lift-off period oscillated, but its wave trough was flattened owing to the misalignment of the seal face. After entering the transition stage, the period flattened at the wave trough disappeared and was replaced by a period of slow decline, which is attributed to the existence of abrasive particles between the seal faces. The unsteady accumulation of abrasive particles caused the lift-off speed to fluctuate significantly. By monitoring the lift-off speed of the seal and the RMS of the full speed period, seal operators may assess the state of the seal and take intervention measures. This has great engineering value for the safe operation and life management of the seal.

The difficulty of knowing the real-time status of gas face seals is the main cause of common problems, including sudden failure, ineffective diagnosis, and unpredictability of service life. This study analyzed the acoustic emission signals generated from experiments, uncovering their features in terms of the frequency distribution, periodic fluctuations, and the behaviors during different operation phases. A new vectorization procedure was designed according to the knowledge of informative acoustic emission features. Based on the vectorization procedure, a support vector machine regression method was applied to develop models predicting the eccentric load on the stator of the seal. Cross-validation was conducted to evaluate the regression performance and search for a proper kernel scale. This study found the informative features of acoustic emissions at different timescales and during different seal operation phases, and particularly the great informative potential of certain segments of the starting and stopping phases. The vectorization and support vector machine regression were shown to be effective in estimating the loads in experiments with cross-validation. Thus, a method for estimating the status of gas face seals based on acoustic emission monitoring was established.