Mini-hydrocyclones in water: state-of-the-art

A mini-hydrocyclone (MHC) is known for its higher separation efficiency, particularly for fine or ultra-fine particles. However, the exact mechanism for enhancing the separation efficiency of MHCs has not been fully elucidated. This literature review fills the existing gap by comprehensively reviewing characteristics of the flow field inside MHCs, metrics of separation performance, applicable research methods, influence of physical and operating parameters, and provides references for future design and applications. Among them, the metrics of separation performance include grade separation efficiency, total separation efficiency, cut size, pressure drop, separation sharpness, and the fish hook effect, etc. This is the first time to comprehensively review the differences between MHCs and conventional hydrocyclones (CHCs) based on the above characteristics and metrics and analyze the separation advantages of MHCs. The fluid in MHC exhibits larger centrifugal acceleration, poor symmetry of tangential velocity, higher proportion of the wall friction loss, more obvious amplitude of partial sway of the air core, and smaller ratio of the locus of zero vertical velocity height to the total length of MHC. Challenges and further work on MHCs are also discussed in terms of potential applications and needed improvements. • This is the first time to comprehensively compare the differences between MHC and CHC. • Differences between MHC and CHC have dramatic impacts on separation performance. • MHC possesses some unique characteristics that promote its separation efficiency. • This review may provide a basis for the design and precise application of MHCs.