Thermal performance of a premixed impinging circular flame jet array with induced-swirl

An array of three identical premixed butane–air-fired impinging circular flames with induced-swirl operating at low-pressure and low-Reynolds-number was developed. A swirling motion was imparted successfully to the flame by forcing the butane/air mixture through a specially designed burner assembly before ignition. The burner assembly consisting of a conical base and a nozzle tube into which a cylindrical bar fabricated with three spiral channels was inserted. Its thermal performance was compared with that of a similar impinging flame jet system without induced-swirl. Effects of varying the Reynolds number and the equivalence ratio of the butane/air mixture and the nozzle-to-plate distance on the thermal performance of each of these two impinging flame jet systems were studied. Experiments were conducted with different combinations of Reynolds number, equivalence ratio and nozzle-to-plate distance. In the present investigation, the Reynolds number ranged from 500 to 2500, the equivalence ratio ranged from 1.0 to 1.8 and the nozzle-to-plate distance ranged from 20 mm to 30 mm. To facilitate comparison, flame shapes of both impinging flame jet systems were also visualized by a high speed digital camera system. The comparison showed that the array of three small-scale, low-pressure and low-Reynolds-number premixed butane–air-fired impinging circular flame jets could enhance its thermal performance, with respect to heat transfer characteristics and blow-out limits, by incorporating an induced-swirl. The performance enhancement increased with increasing Reynolds number or equivalence ratio, but decreased with increasing nozzle-to-plate distance.