Is the fish-hook effect in hydrocyclones a real phenomenon?

Although the fish-hook effect has been reported by many for a very long time, scientists and practitioners alike share contradictory opinions about this phenomenon. While some believe that it is of physical origin, others opine that it is the result of measurement errors. This article investigates the possibility that the fish-hook effect could indeed be measurement error related. Since all the experimental errors are embedded in the raw size distribution measurements, the paper first lays down the steps that lead to estimation of the partition function and confidence bounds, which are seldom reported in hydrocyclone literature, from the errors associated with the experimental size distribution measurements. Using several data sets generated using a 100 mm diameter hydrocyclone operating under controlled dilute to dense regimes, careful analysis of the partition functions following the developed methodology yields unambiguous evidence that the fish-hook effect is a real physical phenomenon. An attempt is also made to reunite some of the major contradictory views behind the existence of the fish-hook based on sound statistical arguments

Velocity measurement in the hydrocyclone by oil droplet, doppler ultrasound velocimetry, and CFD modelling

International audienceTo develop the water treatment process, the hydrocyclone is now used as a unit to operate. Understanding hydrodynamics is a key step to improve the separation process efficiency. Recently, a new simple method called the oil droplet method was proposed by Bamrungsri et al. [Chem. Eng. Res. Design 86, 1263-1270 (2008)] and applied to velocity measurements in a hydrocyclone. The Doppler Velocimetry measurements and computational fluid dynamics (CFD) have been proposed by many researchers as effective for studying the flow field of a hydrocyclone. This work presents a comparison of the experimental results from these two methods along with those obtained from numerical simulations. The numerical calculations of the 3D flow field were performed with FLUENT using the k-epsilon model and the Reynolds stress model (RSM). Measurements and CFD simulations were performed for two hydrocyclone configurations (5 and 10cm diameter). Doppler ultrasound velocimetry data and CFD-RSM results are in close agreement. The oil droplet method is less accurate for the continuous phase velocity profiles but is promising for the validation of Lagrangian tracking simulations

Hydrocyclones

This chapter gives a brief synopsis of hydrocyclones in theory and in practice, including basic design, characterization of performance, models, scale-up and design, as well as monitoring and control of the equipment. The effect of various operational variables, such as pressure drop, cone angle, cyclone diameter, vortex finder and spigot diameters, and solids concentration in the feed on the throughput, cut size, and sharpness of classification of hydrocyclones, is summarized. Both fundamental and empirical models are considered. Numerical solution of first principles models is discussed, with different turbulence models, such as Reynolds averaged Navier-Stokes (RANS) models, large eddy simulation (LES) models, and direct numerical simulation (DNS) models. The Plitt model is considered as a widely used example of empirical models. As an example of the online monitoring of hydrocyclones, the analysis of videographic images of the underflow is discussed, as previously proposed in the literature. This includes the extraction of spray profile variables from image data and online mapping of the data to a process chart, where the normal operating region is delineated by contours following the density