Intelligent Reliability of Ferrofluid Seals: A Review

Ferrofluid seals provide non-contact operation, low friction, and strong sealing performance in high-speed rotating equipment and liquid-sealing systems. However, high speed, liquid contact, thermal loading, vibration, and eccentricity can cause ferrofluid loss, performance degradation, leakage, and premature failure. Here, intelligent reliability denotes a reliability-centered framework that integrates condition monitoring, physically interpretable health assessment, fault diagnosis, uncertainty-aware prognosis, condition-based maintenance, and feedback-driven active control. This structured review synthesizes centrifugal, thermal, liquid-medium, eccentricity-related, and material-degradation mechanisms and evaluates pressure, leakage, temperature, torque, vibration, and acoustic-emission signals. It also assesses health indicators, diagnostic methods, remaining useful life (RUL) prediction, maintenance decisions, and health-management strategies. Its principal contribution is a framework linking degradation physics with observable evidence, health assessment, diagnosis, prognosis, and maintenance and design feedback. The framework also distinguishes direct ferrofluid-seal evidence from transferable methods and supports sensor selection, indicator design, validation planning, and intervention development. Key limitations include scarce public degradation datasets, inconsistent evaluation protocols, weak physical consistency of health indicators, and limited closed-loop implementation. Future work should prioritize public run-to-failure data, physics-informed multisource assessment, uncertainty-aware RUL prediction, and experimentally validated condition-based interventions and active-control strategies.