Weiming Peng

Neutrally buoyant tracer in gas cleaning equipment: a case study

A generic problem when studying the gas flow in gas cleaning equipment is that any conventional tracer, whether solid particles or liquid droplets, is separated out in accordance with the purpose of the equipment. This makes it impossible, for instance, to visualize the core of the vortex in centrifugal gas cleaning equipment. This paper explores the use of a neutrally buoyant tracer. The tracer is soap bubbles filled with helium. The smaller density of the helium relative to the surrounding air is precisely compensated by the mass of the bubble film to create a neutrally buoyant tracer. The method is used to study the flow in a swirl-tube gas–solid separator, highlighting flow features that cannot be shown with, for instance, LDA. Results are shown as controlled exposure time photographs, where pathlines of the tracer show the flow pattern. The results are further clarified by high-time-resolution pressure measurements at the walls. The work shows that the vortex core can be directly visualized using this technique. The vortex core is observed to, under some conditions, bend to—and spin around—the wall of the separator. Under other conditions, the vortex core coincides with the separator axis, and extends to the bottom of the hopper under the swirl tube. Also the flow in the downstream tubing is studied. The possibilities for obtaining quantitative data for the gas velocity field are discussed, and a promising method for doing this is identified.

Large Eddy Simulation of the Vortex End in Reverse‐Flow Centrifugal Separators

Different CFD models of reverse‐flow centrifugal separators, specifically swirl tubes, have been built in order to study and analyse in detail the phenomenon of the “end of the vortex.” The present numerical work is based on—and compared with—previous experimental studies of this phenomenon. The numerical models were built in complete agreement with the geometrical configurations and operating conditions used in these earlier experimental studies [1, 2]. Two different types of swirl tubes were analyzed. One type was an in principle long tube with variable length in which the dependence on the vessel length of the behavior of the vortex core in a simple, well‐defined geometry was studied. The other type was equipped with a wide “dust collection vessel” at the bottom, the depth of which was varied, to study the behaviour of the vortex core in a widely‐used geometry. 3‐D LES simulations were carried out using the commercial CFD package Star‐CD. The bending of the vortex core to the wall of the vessel and its...