Effects of inlet boundary conditions in an axial hydrocyclone

Abstract

Due to the reduced space in platform, compact oil–water separators are essential in offshore oil production. In this sense, a compact design is provided by the in-line axial segregator, taking advantage of the pipe geometry where oil–water mixture flows. Numerical simulation is conducted for laminar swirling flow in an axial hydrocyclone. To study the sensitivity of swirling flow inside the hydrocyclone to the inlet boundary condition, different inlet deflection angle and annular gap width are employed. Validation of the numerical results was achieved by comparing the numerical predictions of pressure drop in swirling flow with experimental values collected in 5 cm size 3 m long transparent pipe using a glycerine–water solution of 54 mPa s viscosity and 1210 kg/m3 density as working fluid, at several flow rates. The numerical results show that the centerline axial velocity, centerline pressure distribution, friction coefficient and swirl number are influenced by inlet boundary conditions. Variation in deflection angles and gap width brings about a considerable increase in friction factor coefficient and decaying of swirl. Vortex breakdown is analyzed too and occurs to inlet swirl numbers larger than 2.5. A correlation to predict the length of developed flow is proposed as a function of Reynolds number and swirl number at inlet.