ЯВИЩЕ КОНЦЕНТРАЦІЙНОЇ ПОЛЯРИЗАЦІЇ: СТАН ПРОБЛЕМИІ АКТУАЛЬНІ НАПРЯМКИ ДОСЛІДЖЕНЬ

Concentration polarization is one of the key mass transfer phenomena occurring in membrane separation processes, electrochemical systems, heat and mass transfer equipment, and numerous technological processes in power engineering and industrial machinery. The phenomenon is associated with the formation of a concentration boundary layer near the phase interface, where the concentration of dissolved substances differs significantly from that in the bulk solution. This results in additional diffusion resistance, reduced process productivity, increased energy consumption, accelerated membrane fouling, and shortened equipment service life. As the requirements for energy efficiency, operational reliability, and environmental sustainability continue to increase, concentration polarization has become one of the major challenges limiting the performance of modern membrane and mass transfer systems. The aim of this study is to summarize the current state of research on concentration polarization in membrane-based water treatment and desalination processes, to analyze the physical mechanisms responsible for its formation, to review contemporary theoretical, numerical, and experimental approaches to its investigation, and to identify promising directions for minimizing its adverse effects. The study is based on a comprehensive analysis and systematization of recent scientific publications devoted to reverse osmosis, nanofiltration, ultrafiltration, microfiltration, and forward osmosis technologies. Particular attention is given to modern mathematical models describing concentration polarization, computational fluid dynamics (CFD) simulations, and advanced experimental techniques, including digital holographic interferometry and laser-induced fluorescence, which enable direct visualization of concentration boundary layers and local mass transfer phenomena. The influence of membrane structure, channel geometry, hydrodynamic conditions, flow turbulators, and membrane surface properties on the development of concentration polarization is analyzed. Special consideration is also given to internal concentration polarization in forward osmosis membranes and to recent advances in nanocomposite membrane materials designed to reduce concentration polarization and membrane fouling. The review demonstrates that integrating experimental observations with numerical simulations provides new opportunities for understanding and controlling concentration polarization in complex engineering systems. Furthermore, the rapid development of digital twins, artificial intelligence, and machine learning technologies creates new possibilities for predictive modeling, process optimization, and intelligent control of membrane systems. The practical significance of the study lies in the systematization of modern approaches aimed at mitigating concentration polarization and membrane fouling, the results of which can be applied in the design, optimization, and operation of membrane equipment for water treatment, desalination, and other industrial mass transfer processes.