(311h) Influence of the Viscosity on the Velocity Propagation in Axial Direction in a Rietema Hydrocyclone

In the field of chemical or mineral industry hydrocyclones are widely used for solid-liquid separation [1]. In respect of geometrical similarity two well-known designs are dominating the field of hydrocyclones: The Rietema [2] and Bradley [3] hydrocyclones. For both types the geometric proportions are given. The main difference is the cone angle, which is 9° for Bradley hydrocyclones and 20° for Rietemahydrocyclones. Both designs mainly focus on water, which is the most common liquid media in hydrocyclone applications.

In the field of purification technology such as wastewater and sludge treatment, the rheological characteristics of the liquid media are significantly different from water [4]. As a result, the optimum geometrical proportions may not be sufficient for these applications. Therefore, the velocity propagation in the hydrocyclone is evaluated by PIV (Particle Image Velocimetry) measurements and CFD simulations in different axial positions.

For the rheological modelling of the sludge a mixture of water and glycerol with a viscosity of 6 mPas [5] is used. The results of measurements and simulations are compared with a water-only system. The hydrocyclone was designed and manufactured according to Rietemawith a diameter of 100 mm and 500 mm in length.

For the water-only system the averaged VelMag/VelMag_max is 0.86 at axial middle position of the cyclone while the velocity ratio is 0.53 for the system with higher viscosity. The viscosity has a strong influence on the axial propagation of the circumferential velocity which leads to a limited efficiency along the conical separation chamber of the hydrocyclone. In conclusion, both Rietema and Bradleygeometrical hydrocyclone proportions may not be the optimum solutions for sludge processing. Further parametric studies on the cone angle and the cyclone length shall lead to optimization potential in the separation process.

[1] Svarovsky, L., Thew, M.T., Hydrocyclones – Analysis and Applications, Kluwer Academic Publisher, Dordrecht, 1992.

[2] Bradley, D., The Hydrocyclone, Pergamon Press, London, 1965.

[3] Rietema, K., Performance and Design of Hydrocyclones, Chemical Engineering Science, 15, 298-325, 1961.

[4] Baudez, J.C., Markis, F., Eshtiaghi, N., Slatter, P., The rheological behaviour of anaerobic digested sludge, Water Research, 45, 2011.

[5] Haynes, W.M., CRC Handbook of Chemistry and Physics, 96^th edition, 2015.