Aerosol Science and Technology, 39:113–123, 2005CopyrightcAmerican Association for Aerosol ResearchISSN: 0278-6826 print / 1521-7388 onlineDOI: 10.1080/027868290907138Particle Collection and Concentration for CycloneConcentratorsK. S. Lim,1H. S. Kim,2Y. O. Park,1and K. W. Lee21Department of Clean Energy Research, Korea Institute of Energy Research, Daejeon, Korea2Department of Environmental Science and Engineering, Kwangju Institute of Science and Technology,Gwangju, KoreaFour cyclone concentrators were designed and fabricated tocompare their particle separation and concentration behavior, suchas the major, minor, outlet, and wall deposition fractions. Two ofthe cyclone concentrators were the conventional type, with the mi-nor flow tube connected to the particle outlet at the bottom of thecyclone. The others were modified cyclone concentrators with agap between the particle outlet at the bottom of the cyclone and theminor flow tube. The modified cyclone concentrators had differentparticle outlet and minor tube diameters, with variable minor tubeheights.The particle number fraction of the minor flow for the con-ventional cyclone concentrator increased and had wider U-shapedcurves, in the large particle size range, as the particle outlet di-ameter increased. In addition, the gap between the particle out-let and minor flow tube of modified cyclone concentrator had anadverse effect on the particle concentration ability of the cycloneconcentrator with a small minor tube diameter, in that the walldeposition and particle fraction of the minor flow were increasedand decreased, respectively. However, the modified cyclone concen-trator with a large minor flow was a better particle concentratorbecause the gap offered a space for the particles collected on thecyclone wall to gather, preventing the particles from going alongthe minor flow, especially with high particle concentrations in theinflow.INTRODUCTIONCyclones are widely used in the field of air pollution forambient and source sampling. They are also used for industrialparticulate control because of their simplicity of design, lowmaintenance costs, and adaptability to a wide range of operatingReceived 23 September 2003; accepted 4 November 2003.Address correspondence to K.W. Lee, Department of Environmen-tal Science and Engineering, Kwangju Institute of Science and Tech-nology 1 Oryong-dong, Buk-gu, Gwangju 500-712, Korea. E-mail:[email protected]. However, cyclones are incapable of collecting fineparticles because of their reliance on inertial forces to separateparticles from the gas stream. As a result, in industrial particlecontrol applications, they may well serve as a pre-cleaner forthe removal of the coarser particles of a heavily loaded stream,which will finally be cleaned by other types of equipment. Inaddition, in application for ambient and source sampling, cy-clones are used as samplers, with large cutoff diameters, dueto the flat collection efficiency curve for small particles. Thus,much interest has focused on the high collection efficienciesand sharp collection efficiency curves of cyclones in the smallparticle size range (DeOtte 1990; Dietz 1982; Dirgo and Leith1985; Iozia and Leith 1989; Kim and Lee 1990; Moore andMcFarland 1996; Smith et al. 1983; Sumner et al. 1987; Zhu et al.2001).In a cyclone, particle-laden air is introduced radially into theupper portion of a cylinder and accelerated outward to the cylin-der wall, where particles either stick and are retained or swirleddown to a collection port at the bottom of the cylinder. The over-all gas motion in the cyclone consists of an inner vortex movingtoward the cyclone exit, containing the smaller-sized particles,and an outer vortex moving in the opposite direction, carryingthe larger-sized particles. Thus, cyclones have been used onlyfor collecting large particles from a gas flow, by centrifugalforce, and removing them through the dust hopper. Recently,some studies (Galperin and Shapiro 1999; Kim et al. 2002) haveindicated that cyclones could possibly be used as particle con-centrators, which were referred to as cyclone concentrators byKim and colleagues (2002). Although the entire gas is carriedaway from conventional cyclones through the vortex finder, vir-tual cyclones have a small portion of the gas flow (minor flow)drawn out through the bottom of the cyclone, which concentratesthe particles, as shown in Figure 1. In a cyclone concentrator,the particles collected on the cyclone wall either are retained atthe wall or go down to the bottom of the cyclone, as in con-ventional cyclones, and a small portion of the gas flow (minor113Downloaded By: [University of North Carolina] At: 14:55 27 January 2009114 K. S. LIM ET AL.Figure 1. Conventional cyclone concentrator.flow) containing particles is pumped out at the bottom, wherethe particle concentration is much higher than that at the inlet.The large portion of the gas flow (major flow) that remains con-tains the small particles, which is carried away from the cyclonethrough the vortex finder.The virtual impactor is one of the most commonly used con-centrators, with typically S-shaped concentration factor curves,as it can concentrate particles larger than the 50% cut-off diam-eter. However, the concentration factor curves of cyclone con-centrators show reversed U-shaped curves with a maximum inthe region of the 50% cutoff diameter (Kim et al. 2002) becausemost particles larger than the 50% cutoff diameter are collectedand retained at the cyclone wall, with small particles followingthe major flow without being collecting. Galperin and Shapiro(1999) tested two multicyclones, operating as concentrators,by varying the ratios of the minor/major flow volumes. Theyfound that the collection efficiencies of the tested cyclones werehigher, and the 50% cut-off diameters lower, than that of conven-tional cyclones. Kim et al. (2002) also tested two cyclone con-centrators with different dimensions and described their highermajor flow efficiencies. In addition, they showed that the con-centration factor had reversed U-shaped curves, as mentionedabove, and that they had the greatest potential for concentratingparticles.This article evaluates the performance of cyclone concentra-tors, by varying the total flow rates and cyclone bottom diam-eters (particle exit diameter). The cyclone concentrators usedin this study have a gap between the particle exit tube, at theirbottoms, and the minor flow tube, as shown in Figure 2,