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Show swirler designed specifically for use in the WSB. As the function of this swirler is to generate divergent flows for flame stabilization, a new fonnulation for the swirl number is developed to characterize swirl intensity and for potential future use as a design tool in scaling the WSB to other applications. Also reported are emission and efficiency results when the vane-swirled WSB is tested in a laboratory system that simulates the operation of a 60,00 BtuIhr. spa heater. CONVENTIONAL SWIRLER DESIGNS Swirling flows have been used for stabilizing nonpremixed and premixed combustion for decades in combustion systems such as turbines, industrial coal burners, and gas furnaces. Due to the impact of swirl in pollutant fonnation, combustion efficiency, combustion stability, fluid dynamics, and flowfield generation, swirling flows have been subjects of both basic and applied research that have been reported in many journals, review articles,3,4 and book chapters 5 • The majority of these articles focus on nonpremixed flames. This is reasonable, as commercial burners generally utilize a physical configuration where fuel (either gaseous, liquid droplets/spray, or solid particles) is injected into the chamber through a round orifice, with air being introduced to the system through an annular region surrounding the central fuel rod. ~wirl is imparted to the system by either swirling the coaxial air flow or by inj ecting the entire flow tangentially into a cylindrical chamber as in cyclone combustion chambers. In both cases, the function of the swirl is to create a toroidal recirculation zone (TRZ). The TRZ is fundamental to these burners as it quickly mixes the fuel and air to allow for complete combustion, lengthens the residence time of the products, stabilizes the combustion process, and dictates the physical shape and length of the flame. The non-dimensional swirl number, S, is a common parameter for characterizing swirl intensity. It is define as the ratio of axial flux of angular momentum to the axial flux of linear momentum divided by nozzle radius5 : S = Rf U Wrdr / R Rf U 2rdr o 0 (1) 3 |
