The hydrocyclone for separating light dispersions

Abstract

Various new hydrocyclone designs developed by the author for separating light dispersions from heavier carrying fluids are demonstrated and their relative efficiencies compared using dispersions of plastic powders in water and suitable non-dimensional equivalence relations. Detailed measurements of the flow structure with in these hydrocyclones that have aided design work are also discussed.

The mixture entering the cylindrical hydrocyclone body tangentially generates a vortex and due to the centrifugal acceleration in this vortex the less dense particles migrate towards the axis forming a core. This is then removed through an axially placed outlet in the upstream end wall of the hydrocyclone with 5-10% of the total through flow while the remaining particle depleted stream passes out of the downstream end.

The work investigates the effects upon hydrocyclone performance of changes in total flow rate, mode of operation, and geometry by comparing particle concentrations in influent and effluent and the probability of separation of individual particles, which is calculated from input and output drop size spectra. From a flow of 60 L/min through an efficient hydrocyclone of diameter 30 mm with a total head loss of 3.2 bar, it is found that for particles with a relative differential density of 0.1 in water at 50°C, 99% at 50 µm are separated while 80% are separated at 17 µm and 50% separation occurs at less than 10 µm.

Measurements of the flow structure within the hydrocyclones have been made using a Laser Doppler Anemometer and from radial profiles of axial and tangential velocities particle trajectories have been calculated.

With the application of the hydrocyclone for use with other mixtures and dispersions in mind, an equivalence relation dependent upon hydrocyclone Reynolds number is employed by which hydrocyclone performance may be predicted from standard experimental results. The validity of this relationship is demonstrated by comparing results from similar geometry hydrocyclones over a range of sizes with different dispersions and changes in medium viscosity by using water at various temperatures.

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