The mini-hydrocyclone is being proposed as a micro-separator in complex micro-devices for in-line fine particle separation as it has a concise geometry and no moving parts,. In this work, we present a numerical study combined by experiments on a 5 mm minihydrocyclone to investigate the transitional flow and particle separation with the presence of a fishhook effect. The results showed that the simulation from the LES model gave good agreement with that from DNS at an inlet velocity of 0.4 m/s. The LES model was then used to study the higher inlet velocity cases of 1.0 and 1.8 m/s. The particle separation was predicted by a Lagrangian model with an added user defined function (UDF) in the Fluent code to account for the particle interaction. The modeling results for the three inlet velocities studied showed that small particle Reynolds number, ReP, resulted in a poorly developed wake behind the large particles, which did not entrain fine particles leading to a barely noticeable fishhook effect for the 0.4 m/s inlet velocity. In contrast, a large ReP gives rise to larger wakes, which are capable of entraining fine particles more efficiently causing the pronounced fishhook effect at higher inlet velocities. The results show the particle separation with the fishhook effect could be modeled based on the particle entrainment model, whereas the accurate simulation of the fishhook effect in future should include a correction coefficient that varies with Rep to improve the separation efficiency predictions.

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