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The performance of a gas–liquid cylindrical cyclone separator for the separation of air bubbles from hydraulic fluid has been analyzed numerically using the commercial computational fluid dynamics flow solver CFX. Two-phase flow behavior is modeled based on an Eulerian–Eulerian approach, representing both liquid and dispersed gas phase as interpenetrating media with interphase momentum transfer captured based on existing bubble drag models. Only a single bubble size is considered for the dispersed phase and bubble coalescence is ignored. At the tangential inlet, a homogeneous gas– liquid mixture is assumed with specified mass flow and air/liquid volume fractions. Pressure conditions were imposed at both the upper gas outlet and the lower liquid outlet boundaries. Effect of changes in turbulence model and bubble drag model on analysis predictions was analyzed for selected operating conditions, that is, bubble sizes, air/liquid volume fractions and flow rates. Separation efficiency was high only for larger bubble sizes (100 mm) and high flow rates (250 L/min). For bubble sizes below 35 mm, the cyclone was ineffective. At high flow rates, cyclone performance suffers due to liquid carry over in the form of a swirling liquid wall film carried with the gas (bubble) phase through the top outlet. The Explicit Algebraic Reynolds Stress Turbulence Model together with the Grace Drag Model was found to be effective in exploring changes to the cyclone geometry. Here, improvements in separation efficiency were only achieved with significantly increased tangential velocities as a consequences of a reduced inlet port cross section. Predicted bubble size separation limits as a function of Reynolds number and axial-to-tangential velocity ratios were found to compare favorably with existing literature.
bubbly flow, hydrocyclone, modeling, phase separation
[1] Swanbom, R.A., A new approach to the design of gas–liquid separators for the oil industry, Technical University Delft, Delft, The Netherlands, 1988.
[2] Slettebo, E.S., Separation of gas from liquids in viscous systems, NTNU Norwegian University of Sciences and Technology, Trondheim, Norway, 2009.
[3] Moore, J.Z.; Somoza, R.J.; Shih, A.J.; Filipi, Z.S; Moskalik, A.J.; Johnson, N.M., Characterization of the fluid deaeration device for a hydraulic hybrid vehicle system, SAE Technical Paper 2008-01-0308, 2008.
[4] Hoyt, N., et al., Cyclonic two-phase flow separator experimentation and simulation for use in a microgravity environment. Journal of Physics, 327, pp. 12–56, 2011. doi: http://dx.doi.org/10.1088/1742-6596/327/1/012056
[5] Kelsall, D.F., A study of the motion of solid particles in a hydraulic cyclone. Transactions of the Institution of Chemical Engineers, 30, p. 87, 1952.
[6] Bradley, D. & Pulling, D.J., Flow patterns in the hydraulic cyclone and their interpretation in terms of performance. Transactions of the Institution of Chemical Engineers, 37(1959), p. 34, 1959.
[7] Bradley, D., The Hydrocyclone, Pergamon Press Limited: Oxford, 1965.
[8] Svarovsky, L., Hydrocyclones, Holt Rinehart and Winston: London, 1984.
[9] Hoffman, A.C. & Stein, L.E., Gas Cyclones and Swirl Tubes: Principles, Design and Operation, Springer: Berlin, 2002.
[10] Cortes, C. & Gil, A., Modeling the gas and particle flow inside cyclone separators. Progress in Energy and Combustion Science, 33, pp. 409–452, 2007. doi: http://dx.doi.org/10.1016/j.pecs.2007.02.001
[11] Boysan, F.; Ayers, W.H.; Swithenbank, J.A., A fundamental mathematical modeling approach to cyclone design. Transactions of the Institution of Chemical Engineers, 60, pp. 222–230, 1982.
[12] Pericleous, K. & Rhodes, N., The hydrocyclone classifier – a numerical approach. International Journal of Mineral Processing, 17, pp. 23–43, 1986. doi: http://dx.doi.org/10.1016/0301-7516(86)90044-X
[13] Hsieh, K. & Rajamani, R., Mathematical model of the hydrocyclone based on physics of fluid flow. AIChE Journal, 37, pp. 735–746, 1991. doi: http://dx.doi.org/10.1002/aic.690370511
[14] Hsieh, K., Phenomenological model of the hydrocyclone, PhD Thesis, Department of Metallurgy and Metallurgical Engineering, University of Utah, 1988.
[15] Utikar, R.; Darmawan, N.; Tade, M.; Li, Q.; Evans, G.; Glenny, M.; Pareek, V., Hydrodynamic simulation of cyclone separator (Chapter 11). Computational Fluid Dynamics, ed. H.W. Oh, InTech: Croatia, pp. 241–266, 2010.
[16] Mantilla, I.; Shirazi, S.A.; Shoham, O., Flow field predictions and bubble trajectory model in gas-liquid cylindrical cyclone (GLCC) separators. ASME Journal, 121, pp. 9–15, 1999. doi: http://dx.doi.org/10.1115/1.2795063
[17] Menter, F., Two-equation eddy-viscosity turbulence models for engineering applications. AIAA Journal, 32(8), pp. 1598–1605, 1994. doi: http://dx.doi.org/10.2514/3.12149