Authors

D A Egarr, MG Faram, T O’Doherty

Abstract

A hydrodynamic vortex separator (HDVS) has been studied under laboratory conditions by using a specifically designed rig. Pressure tapping points placed at eight locations, six external and two internal, have revealed an even radial pressure distribution on the outer walls and central shaft. The ability of the HDVS to separate particulates has been studied. The particulates have been characterized by measurements of particle diameter and settling velocity, which have allowed efficiency cusps to be plotted against dimensionless groups used by other researchers. Owing to an unsatisfactory reduction of the data to a single curve by plotting the efficiency against dimensionless groups, an efficiency law has been determined based on the logistic equation and describes the separation efficiency in terms of the inlet flowrate, volume of the separator, and particle diameter and density.

Authors

K. Osei, R.Y.G. Andoh, J. MacKinnon and M.G.Faram

Abstract

Laboratory testing of stormwater separators can overcome many of the technical challenges associated with field testing. With laboratory testing, sediment characteristics and the flow rates at which a device is tested are known and measurable before, during, and after the test. This controlled environment ensures that test programmes can be set up to meet specific objectives, and data can be obtained in a repeatable and timely fashion. However there are differences in laboratory test protocols that can have a significant bearing on test results which, if overlooked, can result in invalid comparisons being made between different systems. This paper looks at two protocols for testing separators in the laboratory, normally referred to as the Direct Test Method and the Indirect Test Method. The test methodologies are described and the similarities and differences shown. Results from tests on a stormwater treatment separator using the two protocols are presented. The results show that for the same sediment gradation and flow rate, a difference of over 20% in measured removal efficiency is possible. They also show that the Direct Test Method produces outputs that are more consistent, conservative and representative of the removal efficiencies expected for stormwater treatment separators.

Authors

D.A. Phipps, R.M.Alkhaddar, E. Loffill, R.Y.G Andoh and M.G. Faram

Abstract

The factors affecting the overall efficiency for the removal of a solid from an influent stream of water by an HDVS (Hydrodynamic Vortex Separator) have been examined using a combination of solids capture/washout experiments and dye tracer studies. The overall solids removal efficiency of the device is a function of loading rate (overall flow). The efficiency can be considered in terms of the balance between initial capture of the sediment and any subsequent re-entrainment. Tracer studies have shown that a well-designed device offers almost complete separation into a mobile and quiescent zone, with slow exchange between the two. This enhances both sediment capture and its subsequent retention.